Estimation of debris flow critical rainfall thresholds by a physically-based model

NASA Astrophysics Data System (ADS)

Papa, M. N.; Medina, V.; Ciervo, F.; Bateman, A.

2012-11-01

Real time assessment of debris flow hazard is fundamental for setting up warning systems that can mitigate its risk. A convenient method to assess the possible occurrence of a debris flow is the comparison of measured and forecasted rainfall with rainfall threshold curves (RTC). Empirical derivation of the RTC from the analysis of rainfall characteristics of past events is not possible when the database of observed debris flows is poor or when the environment changes with time. For landslides triggered debris flows, the above limitations may be overcome through the methodology here presented, based on the derivation of RTC from a physically based model. The critical RTC are derived from mathematical and numerical simulations based on the infinite-slope stability model in which land instability is governed by the increase in groundwater pressure due to rainfall. The effect of rainfall infiltration on landside occurrence is modelled trough a reduced form of the Richards equation. The simulations are performed in a virtual basin, representative of the studied basin, taking into account the uncertainties linked with the definition of the characteristics of the soil. A large number of calculations are performed combining different values of the rainfall characteristics (intensity and duration of event rainfall and intensity of antecedent rainfall). For each combination of rainfall characteristics, the percentage of the basin that is unstable is computed. The obtained database is opportunely elaborated to derive RTC curves. The methodology is implemented and tested on a small basin of the Amalfi Coast (South Italy).

Probability and volume of potential postwildfire debris flows in the 2012 High Park Burn Area near Fort Collins, Colorado

USGS Publications Warehouse

Verdin, Kristine L.; Dupree, Jean A.; Elliott, John G.

2012-01-01

This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2012 High Park fire near Fort Collins in Larimer County, Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and volume of debris flows along the burned area drainage network and to estimate the same for 44 selected drainage basins along State Highway 14 and the perimeter of the burned area. Input data for the models included topographic parameters, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall (25 millimeters); (2) 10-year-recurrence, 1-hour-duration rainfall (43 millimeters); and (3) 25-year-recurrence, 1-hour-duration rainfall (51 millimeters). Estimated debris-flow probabilities along the drainage network and throughout the drainage basins of interest ranged from 1 to 84 percent in response to the 2-year-recurrence, 1-hour-duration rainfall; from 2 to 95 percent in response to the 10-year-recurrence, 1-hour-duration rainfall; and from 3 to 97 in response to the 25-year-recurrence, 1-hour-duration rainfall. Basins and drainage networks with the highest probabilities tended to be those on the eastern edge of the burn area where soils have relatively high clay contents and gradients are steep. Estimated debris-flow volumes range from a low of 1,600 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages were also predicted to produce substantial volumes of material. The predicted probabilities and some of the volumes predicted for the modeled storms indicate a potential for substantial debris-flow impacts on structures, roads, bridges, and culverts located both within and immediately downstream from the burned area. Colorado State Highway 14 is also susceptible to impacts from debris flows.

Estimated probabilities and volumes of postwildfire debris flows—A prewildfire evaluation for the Pikes Peak area, El Paso and Teller Counties, Colorado

USGS Publications Warehouse

Elliott, John G.; Ruddy, Barbara C.; Verdin, Kristine L.; Schaffrath, Keelin R.

2012-01-01

Debris flows are fast-moving, high-density slurries of water, sediment, and debris that can have enormous destructive power. Although debris flows, triggered by intense rainfall or rapid snowmelt on steep hillsides covered with erodible material, are a common geomorphic process in some unburned areas, a wildfire can transform conditions in a watershed with no recent history of debris flows into conditions that pose a substantial hazard to residents, communities, infrastructure, aquatic habitats, and water supply. The location, extent, and severity of wildfire and the subsequent rainfall intensity and duration cannot be known in advance; however, hypothetical scenarios based on empirical debris-flow models are useful planning tools for conceptualizing potential postwildfire debris flows. A prewildfire study to determine the potential for postwildfire debris flows in the Pikes Peak area in El Paso and Teller Counties, Colorado, was initiated in 2010 by the U.S. Geological Survey, in cooperation with the City of Colorado Springs, Colorado Springs Utilities. The study was conducted to provide a relative measure of which subwatersheds might constitute the most serious potential debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall.

Rainfall control of debris-flow triggering in the Réal Torrent, Southern French Prealps

NASA Astrophysics Data System (ADS)

Bel, Coraline; Liébault, Frédéric; Navratil, Oldrich; Eckert, Nicolas; Bellot, Hervé; Fontaine, Firmin; Laigle, Dominique

2017-08-01

This paper investigates the occurrence of debris flow due to rainfall forcing in the Réal Torrent, a very active debris flow-prone catchment in the Southern French Prealps. The study is supported by a 4-year record of flow responses and rainfall events, from three high-frequency monitoring stations equipped with geophones, flow stage sensors, digital cameras, and rain gauges measuring rainfall at 5-min intervals. The classic method of rainfall intensity-duration (ID) threshold was used, and a specific emphasis was placed on the objective identification of rainfall events, as well as on the discrimination of flow responses observed above the ID threshold. The results show that parameters used to identify rainfall events significantly affect the ID threshold and are likely to explain part of the threshold variability reported in the literature. This is especially the case regarding the minimum duration of rain interruption (MDRI) between two distinct rainfall events. In the Réal Torrent, a 3-h MDRI appears to be representative of the local rainfall regime. A systematic increase in the ID threshold with drainage area was also observed from the comparison of the three stations, as well as from the compilation of data from experimental debris-flow catchments. A logistic regression used to separate flow responses above the ID threshold, revealed that the best predictors are the 5-min maximum rainfall intensity, the 48-h antecedent rainfall, the rainfall amount and the number of days elapsed since the end of winter (used as a proxy of sediment supply). This emphasizes the critical role played by short intense rainfall sequences that are only detectable using high time-resolution rainfall records. It also highlights the significant influence of antecedent conditions and the seasonal fluctuations of sediment supply.

Debris flow initiation by runoff in a recently burned basin: Is grain-by-grain sediment bulking or en masse failure to blame?

NASA Astrophysics Data System (ADS)

McGuire, Luke A.; Rengers, Francis K.; Kean, Jason W.; Staley, Dennis M.

2017-07-01

Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

Debris flow initiation by runoff in a recently burned basin: Is grain-by-grain sediment bulking or en masse failure to blame?

USGS Publications Warehouse

McGuire, Luke; Rengers, Francis K.; Kean, Jason W.; Staley, Dennis M.

2017-01-01

Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

Debris-flow generation from recently burned watersheds

USGS Publications Warehouse

Cannon, S.H.

2001-01-01

Evaluation of the erosional response of 95 recently burned drainage basins in Colorado, New Mexico and southern California to storm rainfall provides information on the conditions that result in fire-related debris flows. Debris flows were produced from only 37 of 95 (~40 percent) basins examined; the remaining basins produced either sediment-laden streamflow or no discernable response. Debris flows were thus not the prevalent response of the burned basins. The debris flows that did occur were most frequently the initial response to significant rainfall events. Although some hillslopes continued to erode and supply material to channels in response to subsequent rainfall events, debris flows were produced from only one burned basin following the initial erosive event. Within individual basins, debris flows initiated through both runoff and infiltration-triggered processes. The fact that not all burned basins produced debris flows suggests that specific geologic and geomorphic conditions may control the generation of fire-related debris flows. The factors that best distinguish between debris-flow producing drainages and those that produced sediment-laden streamflow are drainage-basin morphology and lithology, and the presence or absence of water-repellent soils. Basins underlain by sedimentary rocks were most likely to produce debris flows that contain large material, and sand- and gravel-dominated flows were generated primarily from terrain underlain by decomposed granite. Basin-area and relief thresholds define the morphologic conditions under which both types of debris flows occur. Debris flows containing large material are more likely to be produced from basins without water-repellent soils than from basins with water repellency. The occurrence of sand-and gravel-dominated debris flows depends on the presence of water-repellent soils.

Normalizing rainfall/debris-flow thresholds along the U.S. Pacific coast for long-term variations in precipitation climate

USGS Publications Warehouse

Wilson, Raymond C.

1997-01-01

Broad-scale variations in long-term precipitation climate may influence rainfall/debris-flow threshold values along the U.S. Pacific coast, where both the mean annual precipitation (MAP) and the number of rainfall days (#RDs) are controlled by topography, distance from the coastline, and geographic latitude. Previous authors have proposed that rainfall thresholds are directly proportional to MAP, but this appears to hold only within limited areas (< 1?? latitude), where rainfall frequency (#RDs) is nearly constant. MAP-normalized thresholds underestimate the critical rainfall when applied to areas to the south, where the #RDs decrease, and overestimate threshold rainfall when applied to areas to the north, where the #RDs increase. For normalization between climates where both MAP and #RDs vary significantly, thresholds may best be described as multiples of the rainy-day normal, RDN = MAP/#RDs. Using data from several storms that triggered significant debris-flow activity in southern California, the San Francisco Bay region, and the Pacific Northwest, peak 24-hour rainfalls were plotted against RDN values, displaying a linear relationship with a lower bound at about 14 RDN. RDN ratios in this range may provide a threshold for broad-scale regional forecasting of debris-flow activity.

Landscape aridity, fire severity and rainfall intensity as controls on debris flow frequency after the 2009 Black Saturday Wildfires in Victoria

NASA Astrophysics Data System (ADS)

Nyman, Petter; Sherwin, Christopher; Sheridan, Gary; Lane, Patrick

2015-04-01

This study uses aerial imagery and field surveys to develop a statistical model for determining debris flow susceptibility in a landscape with variable terrain, soil and vegetation properties. A measure of landscape scale debris flow response was obtained by recording all debris flow affected drainage lines in the first year after fire in a ~258 000 ha forested area that was burned by the 2009 Black Saturday Wildfire in Victoria. A total of 12 500 points along the drainage network were sampled from catchments ranging in size from 0.0001 km2to 75 km2. Local slope and the attributes of the drainage areas (including the spatially averaged peak intensity) were extracted for each sample point. A logistic regression was used to model how debris flow susceptibility varies with the normalised burn ratio (dNBR, from Landsat imagery), rainfall intensity (from rainfall radar), slope (from DEM) and aridity (from long-term radiation, temperature and rainfall data).The model of debris flow susceptibility produced a good fit with the observed debris flow response of drainage networks within the burned area and was reliable in distinguishing between drainage lines which produced debris flows and those which didn't. The performance of the models was tested through multiple iterations of fitting and testing using unseen data. The local channel slope captured the effect of scale on debris flow susceptibility with debris flow probability approaching zero as the channel slope decreased with increasing drainage area. Aridity emerged as an important predictor of debris flow susceptibility, with increased likelihood of debris flows in drier parts of the landscape, thus reinforcing previous research in the region showing that post-fire surface runoff from wet Eucalypt forests is insufficient for initiating debris flows. Fire severity, measured as dNBR, was also a very important predictor. The inclusion of local channel slope as a predictor of debris flow susceptibility proved to be an effective approach for implicitly incorporating scale and relief as parameters. When combined with models of debris flow magnitude the results from this study can be used obtain continuous probability-magnitude relations of sediment flux from debris flows for drainage networks across entire burned areas.

Geologic, geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachian Mountains of Macon County, North Carolina (southeastern USA)

USGS Publications Warehouse

Wooten, R.M.; Gillon, K.A.; Witt, A.C.; Latham, R.S.; Douglas, T.J.; Bauer, J.B.; Fuemmeler, S.J.; Lee, L.G.

2008-01-01

In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation model, remote imagery and field studies integrated in a geographic information system. Evidence of past debris flows was found at all recent debris flow sites. Orographic rainfall enhancement along topographic escarpments influenced debris flow frequency at higher elevations. A possible trigger for the Wayah and fatal Peeks Creek debris flows was a spiral rain band within Ivan that moved across the area with short duration rainfall rates of 150-230 mm/h. Intersecting bedrock structures in polydeformed metamorphic rock influence the formation of catchments within structural-geomorphic domains where debris flows originate. ?? 2007 Springer-Verlag.

Map of debris flows caused by rainfall during 1996 in parts of the Reedsport and Deer Head Point quadrangles, Douglas County, southern Coast Range, Oregon

USGS Publications Warehouse

Coe, Jeffrey A.; Michael, John A.; Burgos, Marianela Mercado

2011-01-01

This 1:12,000-scale map shows an inventory of debris flows caused by rainfall during 1996 in a 94.4 km2 area in the southern Coast Range of Oregon. This map and associated digital data are part of a larger U.S. Geological Survey study of debris flows in the southern Coast Range. Available evidence indicates that the flows were triggered by a rain storm that occurred between November 17 and 19. The closest rain gage in the Coast Range (Goodwin Peak) recorded 245 mm during the storm. Maximum rainfall intensity during the storm was 13.2 mm/hr on November 18. Debris flows were photogrammetrically mapped from 1:12,000-scale aerial photographs flown in May, 1997. The inventory is presented on imagery derived from LiDAR data acquired in 2008. We classified mapped debris flows into four categories based on the type of debris-flow activity: (1) discrete slide source areas, (2) predominantly erosion, (3) predominantly transport or mixed erosion and deposition, and (4) predominantly deposition. Locations of woody-debris jams are also shown on the map. The area encompassed by debris flows is 2.1 percent of the 94.4 km2 map area.

The Role of Fine Sediment Content on Soil Consolidation and Debris Flows Development after Earthquake

NASA Astrophysics Data System (ADS)

Lyu, L.; Xu, M., III; Wang, Z.

2017-12-01

Fine sediment has been identified as an important factor determining the critical runoff that initiates debris flows because its contribution to shear strength through consolidation. Especially, owing to the 2008 Wenchuan earthquake in China enormous of loose sediment with different fractions of fine particles was eroded and supplied as materials for debris flows. The loose materials are gradually consolidated along with time, and therefore stronger rainfall is required to overcome the shear strength and to initiate debris flows. In this study, flume experiments were performed to explore soil consolidation and shear strength on mass failure and debris flow initiation under the conditions that different fractions of fine sediment were contained in the materials. Under the low content of fine sediment conditions (mass percentages: 0-10%), the debris flows formed with large pores and low shear strength and thus fine particles were too few to fill up the pores among the coarse particles. The consolidation rate was mostly influenced by the content of the fine particles. Consolidation of fine particles caused an increase of the shear strength and decrease of the rainfall infiltration, and therefore, debris flow initiation required stronger rainfall as the consolidation of the fine particles developed.

Value of a dual-polarized gap-filling radar in support of southern California post-fire debris-flow warnings

USGS Publications Warehouse

Jorgensen, David P.; Hanshaw, Maiana N.; Schmidt, Kevin M.; Laber, Jayme L; Staley, Dennis M.; Kean, Jason W.; Restrepo, Pedro J.

2011-01-01

A portable truck-mounted C-band Doppler weather radar was deployed to observe rainfall over the Station Fire burn area near Los Angeles, California, during the winter of 2009/10 to assist with debris-flow warning decisions. The deployments were a component of a joint NOAA–U.S. Geological Survey (USGS) research effort to improve definition of the rainfall conditions that trigger debris flows from steep topography within recent wildfire burn areas. A procedure was implemented to blend various dual-polarized estimators of precipitation (for radar observations taken below the freezing level) using threshold values for differential reflectivity and specific differential phase shift that improves the accuracy of the rainfall estimates over a specific burn area sited with terrestrial tipping-bucket rain gauges. The portable radar outperformed local Weather Surveillance Radar-1988 Doppler (WSR-88D) National Weather Service network radars in detecting rainfall capable of initiating post-fire runoff-generated debris flows. The network radars underestimated hourly precipitation totals by about 50%. Consistent with intensity–duration threshold curves determined from past debris-flow events in burned areas in Southern California, the portable radar-derived rainfall rates exceeded the empirical thresholds over a wider range of storm durations with a higher spatial resolution than local National Weather Service operational radars. Moreover, the truck-mounted C-band radar dual-polarimetric-derived estimates of rainfall intensity provided a better guide to the expected severity of debris-flow events, based on criteria derived from previous events using rain gauge data, than traditional radar-derived rainfall approaches using reflectivity–rainfall relationships for either the portable or operational network WSR-88D radars. Part of the reason for the improvement was due to siting the radar closer to the burn zone than the WSR-88Ds, but use of the dual-polarimetric variables improved the rainfall estimation by ~12% over the use of traditional Z–R relationships.

Runoff-generated debris flows: observations and modeling of surge initiation, magnitude, and frequency

USGS Publications Warehouse

Kean, Jason W.; McCoy, Scott W.; Tucker, Gregory E.; Staley, Dennis M.; Coe, Jeffrey A.

2013-01-01

Runoff during intense rainstorms plays a major role in generating debris flows in many alpine areas and burned steeplands. Yet compared to debris flow initiation from shallow landslides, the mechanics by which runoff generates a debris flow are less understood. To better understand debris flow initiation by surface water runoff, we monitored flow stage and rainfall associated with debris flows in the headwaters of two small catchments: a bedrock-dominated alpine basin in central Colorado (0.06 km2) and a recently burned area in southern California (0.01 km2). We also obtained video footage of debris flow initiation and flow dynamics from three cameras at the Colorado site. Stage observations at both sites display distinct patterns in debris flow surge characteristics relative to rainfall intensity (I). We observe small, quasiperiodic surges at low I; large, quasiperiodic surges at intermediate I; and a single large surge followed by small-amplitude fluctuations about a more steady high flow at high I. Video observations of surge formation lead us to the hypothesis that these flow patterns are controlled by upstream variations in channel slope, in which low-gradient sections act as “sediment capacitors,” temporarily storing incoming bed load transported by water flow and periodically releasing the accumulated sediment as a debris flow surge. To explore this hypothesis, we develop a simple one-dimensional morphodynamic model of a sediment capacitor that consists of a system of coupled equations for water flow, bed load transport, slope stability, and mass flow. This model reproduces the essential patterns in surge magnitude and frequency with rainfall intensity observed at the two field sites and provides a new framework for predicting the runoff threshold for debris flow initiation in a burned or alpine setting.

A low-cost method to measure the timing of post-fire flash floods and debris flows relative to rainfall

USGS Publications Warehouse

Kean, Jason W.; Staley, Dennis M.; Leeper, Robert J.; Schmidt, Kevin Michael; Gartner, Joseph E.

2012-01-01

Data on the specific timing of post-fire flash floods and debris flows are very limited. We describe a method to measure the response times of small burned watersheds to rainfall using a low-cost pressure transducer, which can be installed quickly after a fire. Although the pressure transducer is not designed for sustained sampling at the fast rates ({less than or equal to}2 sec) used at more advanced debris-flow monitoring sites, comparisons with high-data rate stage data show that measured spikes in pressure sampled at 1-min intervals are sufficient to detect the passage of most debris flows and floods. Post-event site visits are used to measure the peak stage and identify flow type based on deposit characteristics. The basin response timescale (tb) to generate flow at each site was determined from an analysis of the cross correlation between time series of flow pressure and 5-min rainfall intensity. This timescale was found to be less than 30 minutes for 40 post-fire floods and 11 post-fire debris flows recorded in 15 southern California watersheds ({less than or equal to} 1.4 km2). Including data from 24 other debris flows recorded at 5 more instrumentally advanced monitoring stations, we find there is not a substantial difference in the median tb for floods and debris flows (11 and 9 minutes, respectively); however, there are slight, statistically significant differences in the trends of flood and debris-flow tb with basin area, which are presumably related to differences in flow speed between floods and debris flows.

Updated logistic regression equations for the calculation of post-fire debris-flow likelihood in the western United States

USGS Publications Warehouse

Staley, Dennis M.; Negri, Jacquelyn A.; Kean, Jason W.; Laber, Jayme L.; Tillery, Anne C.; Youberg, Ann M.

2016-06-30

Wildfire can significantly alter the hydrologic response of a watershed to the extent that even modest rainstorms can generate dangerous flash floods and debris flows. To reduce public exposure to hazard, the U.S. Geological Survey produces post-fire debris-flow hazard assessments for select fires in the western United States. We use publicly available geospatial data describing basin morphology, burn severity, soil properties, and rainfall characteristics to estimate the statistical likelihood that debris flows will occur in response to a storm of a given rainfall intensity. Using an empirical database and refined geospatial analysis methods, we defined new equations for the prediction of debris-flow likelihood using logistic regression methods. We showed that the new logistic regression model outperformed previous models used to predict debris-flow likelihood.

STEP-TRAMM - A modeling interface for simulating localized rainfall induced shallow landslides and debris flow runout pathways

NASA Astrophysics Data System (ADS)

von Ruette, Jonas; Lehmann, Peter; Fan, Linfeng; Bickel, Samuel; Or, Dani

2017-04-01

Landslides and subsequent debris-flows initiated by rainfall represent a ubiquitous natural hazard in steep mountainous regions. We integrated a landslide hydro-mechanical triggering model and associated debris flow runout pathways with a graphical user interface (GUI) to represent these natural hazards in a wide range of catchments over the globe. The STEP-TRAMM GUI provides process-based locations and sizes of landslides patterns using digital elevation models (DEM) from SRTM database (30 m resolution) linked with soil maps from global database SoilGrids (250 m resolution) and satellite based information on rainfall statistics for the selected region. In a preprocessing step STEP-TRAMM models soil depth distribution and complements soil information that jointly capture key hydrological and mechanical properties relevant to local soil failure representation. In the presentation we will discuss feature of this publicly available platform and compare landslide and debris flow patterns for different regions considering representative intense rainfall events. Model outcomes will be compared for different spatial and temporal resolutions to test applicability of web-based information on elevation and rainfall for hazard assessment.

Hydrologic conditions and terrestrial laser scanning of post-fire debris flows in the San Gabriel Mountains, CA, U.S.A.

USGS Publications Warehouse

Schmidt, Kevin M.; Hanshaw, M.N.; Howle, James F.; Kean, Jason W.; Staley, Dennis M.; Stock, Jonathan D.; Bawden, Gerald W.

2011-01-01

To investigate rainfall-runoff conditions that generate post-wildfire debris flows, we instrumented and surveyed steep, small watersheds along the tectonically active front of the San Gabriel Mountains, California. Fortuitously, we recorded runoff-generated debris-flows triggered by one spatially restricted convective event with 28 mm of rainfall falling over 62 minutes. Our rain gages, nested hillslope overland-flow sensors and soil-moisture probes, as well as a time series of terrestrial laser scanning (TLS) revealed the effects of the storm. Hillslope overland-flow response, along two ~10-m long flow lines perpendicular to and originating from a drainage divide, displayed only a 10 to 20 minute delay from the onset of rainfall with accumulated totals of merely 5-10 mm. Depth-stratified soil-moisture probes displayed a greater time delay, roughly 20- 30 minutes, indicating that initial overland flow was Hortonian. Furthermore, a downstream channel-monitoring array recorded a pronounced discharge peak generated by the passage of a debris flow after 18 minutes of rainfall. At this time, only four of the eleven hillslope overlandflow sensors confirmed the presence of surface-water flow. Repeat TLS and detailed field mapping using GPS document how patterns of rainsplash, overland-flow scour, and rilling contributed to the generation of meter-scale debris flows. In response to a single small storm, the debris flows deposited irregular levees and lobate terminal snouts on hillslopes and caused widespread erosion of the valley axis with ground surface lowering exceeding 1.5 m.

Coupling of rainfall-induced landslide triggering model with predictions of debris flow runout distances

NASA Astrophysics Data System (ADS)

Lehmann, Peter; von Ruette, Jonas; Fan, Linfeng; Or, Dani

2014-05-01

Rapid debris flows initiated by rainfall induced shallow landslides present a highly destructive natural hazard in steep terrain. The impact and run-out paths of debris flows depend on the volume, composition and initiation zone of released material and are requirements to make accurate debris flow predictions and hazard maps. For that purpose we couple the mechanistic 'Catchment-scale Hydro-mechanical Landslide Triggering (CHLT)' model to compute timing, location, and landslide volume with simple approaches to estimate debris flow runout distances. The runout models were tested using two landslide inventories obtained in the Swiss Alps following prolonged rainfall events. The predicted runout distances were in good agreement with observations, confirming the utility of such simple models for landscape scale estimates. In a next step debris flow paths were computed for landslides predicted with the CHLT model for a certain range of soil properties to explore its effect on runout distances. This combined approach offers a more complete spatial picture of shallow landslide and subsequent debris flow hazards. The additional information provided by CHLT model concerning location, shape, soil type and water content of the released mass may also be incorporated into more advanced models of runout to improve predictability and impact of such abruptly-released mass.

Recognizing the importance of tropical forests in limiting rainfall-induced debris flows

EPA Science Inventory

Worldwide concern for continuing loss of montane forest cover in the tropics usually focuses on adverse ecological consequences. Less recognized, but equally important to inhabitants of these affected regions, is an increasing susceptibility to rainfall-induced debris flows and t...

Postwildfire debris-flow hazard assessment of the area burned by the 2013 West Fork Fire Complex, southwestern Colorado

USGS Publications Warehouse

Verdin, Kristine L.; Dupree, Jean A.; Stevens, Michael R.

2013-01-01

This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2013 West Fork Fire Complex near South Fork in southwestern Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence, potential volume of debris flows, and the combined debris-flow hazard ranking along the drainage network within and just downstream from the burned area, and to estimate the same for 54 drainage basins of interest within the perimeter of the burned area. Input data for the debris-flow models included topographic variables, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall, referred to as a 2-year storm; (2) 10-year-recurrence, 1-hour-duration rainfall, referred to as a 10-year storm; and (3) 25-year-recurrence, 1-hour-duration rainfall, referred to as a 25-year storm. Estimated debris-flow probabilities at the pour points of the 54 drainage basins of interest ranged from less than 1 to 65 percent in response to the 2-year storm; from 1 to 77 percent in response to the 10-year storm; and from 1 to 83 percent in response to the 25-year storm. Twelve of the 54 drainage basins of interest have a 30-percent probability or greater of producing a debris flow in response to the 25-year storm. Estimated debris-flow volumes for all rainfalls modeled range from a low of 2,400 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages also were predicted to produce substantial debris flows. One of the 54 drainage basins of interest had the highest combined hazard ranking, while 9 other basins had the second highest combined hazard ranking. Of these 10 basins with the 2 highest combined hazard rankings, 7 basins had predicted debris-flow volumes exceeding 100,000 cubic meters, while 3 had predicted probabilities of debris flows exceeding 60 percent. The 10 basins with high combined hazard ranking include 3 tributaries in the headwaters of Trout Creek, four tributaries to the West Fork San Juan River, Hope Creek draining toward a county road on the eastern edge of the burn, Lake Fork draining to U.S. Highway 160, and Leopard Creek on the northern edge of the burn. The probabilities and volumes for the modeled storms indicate a potential for debris-flow impacts on structures, reservoirs, roads, bridges, and culverts located within and immediately downstream from the burned area. U.S. Highway 160, on the eastern edge of the burn area, also is susceptible to impacts from debris flows.

Analyzing the occurrence of debris flows and floods in a small watershed two years after a wildfire, San Gabriel Mountains, California

NASA Astrophysics Data System (ADS)

Leeper, R. J.; Barth, N. C.; Gray, A. B.

2016-12-01

The frontal range of the San Gabriel Mountains immediately abuts the Los Angeles basin for approximately 110 km. Along this wildland-urban interface and throughout the mountain range multiple overlapping natural hazards can occur, the most frequent of which are postfire debris flows and floods triggered by intense rainfall events. Recent studies in southern California of burned basins with steep slopes show that the timing of postfire debris flows and floods during the first winter following a wildfire is closely tied to high-intensity rainfall events. Here, we explore short-term (seasonal/annual) controls on sediment production and flux after the 2014 Colby Fire, which burned 8 km2 of the southern San Gabriel front directly above the city of Glendora, CA. To understand how sediment flux changes as a basin recovers following a wildfire, we installed and monitored a dense network of rain gages and pressure transducers within the Englewild watershed ( 1 km2) during the second winter following the Colby Fire. Site visits were made following each rainstorm to download pressure transducer and rainfall data and analyze the geomorphic response within the channel network. Preliminary results indicate that rainfall intensity-duration thresholds (5-min) previously identified as postfire debris flow triggers were exceeded multiple times throughout the winter. However, we only one documented one debris flow. Understanding changes in the rainfall intensity thresholds relative to debris flow timing and occurrence with system rebound after wildfire is important to help reduce risk and increase hazard resilience.

Uncertainties in predicting debris flow hazards following wildfire [Chapter 19

Treesearch

Kevin D. Hyde; Karin Riley; Cathelijne Stoof

2017-01-01

Wildfire increases the probability of debris flows posing hazardous conditions where values‐at‐risk exist downstream of burned areas. Conditions and processes leading to postfire debris flows usually follow a general sequence defined here as the postfire debris flow hazard cascade: biophysical setting, fire processes, fire effects, rainfall, debris flow, and values‐at‐...

Towards a debris-flow warning system based on hydrological measurements of the triggering conditions. A study of El Rebaixader catchment (Central Pyrenees, Spain)

NASA Astrophysics Data System (ADS)

Abancó, Clàudia; Hürlimann, Marcel; Moya, José

2014-05-01

Debris flows represent a risk to the society due to their high destructive power. Rainfall is the main debris-flow triggering factor. Rainfall thresholds are generally used for warning of debris flow occurrence in susceptible catchments. However, the efficiency of such thresholds for real time hazard assessment is often conditioned by many factors, such as: the location and number of the rain gauges used (both to define the thresholds, and for setting off warnings); the temporal and spatial evolution of rainfall's convective cells or the effect of snow cover melting. These factors affect the length of the warning time, which is of crucial importance for issuing alert messages or alarms to the people and infrastructures at risk. The Rebaixader catchment (Central Pyrenees, Spain) is being monitored since 2009 by six stations recording information on initiation (4 stations) and flow detection and cinematic behaviour (2 stations). Until December 2013, 7 debris flows, 17 debris floods and 4 rockfalls have been recorded. The objectives of this work were: a) the definition of rainfall thresholds at two different rain gauges; b) the analysis of the infiltration patterns in order to define their potential use for warning systems and c) preliminary testing of rainfall thresholds' efficiency in terms of warning time, in this catchment. This last goal consisted in the comparison of the time elapsed between the rainfall threshold was exceeded and the event occurrence was detected by the stations at the channel area. The results suggest that the intensity-duration rainfall thresholds sometimes provide warning times which would be too short for an adequate reaction in the Rebaixader catchment (less than 10 minutes). The combination of such rainfall thresholds with infiltration measurements is useful to increase the warning time. This occurs especially in the events triggered in spring, when the snowmelt plays an important role in the event's triggering conditions. However, the effects of infiltration associated to the summer convective rainfalls are almost imperceptible; therefore their importance in warning systems decreases.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Ammo Fire, San Diego County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Ammo Fire in San Diego County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 1.75 inches (44.45 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Ranch Fire, Ventura and Los Angeles Counties, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Ranch Fire in Ventura and Los Angeles Counties, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 2.25 inches (57.15 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency assessment of debris-flow hazards from basins burned by the 2007 Harris Fire, San Diego County, southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

IntroductionThe objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Harris Fire in San Diego County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 1.75 inches (44.45 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Rice Fire, San Diego County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Rice Fire in San Diego County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 1.75 inches (44.45 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Poomacha Fire, San Diego County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Poomacha Fire in San Diego County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 2.25 inches (57.15 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Witch Fire, San Diego County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Witch Fire in San Diego County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 2.25 inches (57.15 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Slide and Grass Valley Fires, San Bernardino County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Slide and Grass Valley Fires in San Bernardino County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 3.50 inches (88.90 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Buckweed Fire, Los Angeles County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Buckweed Fire in Los Angeles County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 2.25 inches (57.15 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Canyon Fire, Los Angeles County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Canyon Fire in Los Angeles County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 2.25 inches (57.15 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the 2007 Santiago Fire, Orange County, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Bauer, Mark A.; Stitt, Susan C.; Knifong, Donna L.; McNamara, Bernard J.; Roque, Yvonne M.

2007-01-01

INTRODUCTION The objective of this report is to present a preliminary emergency assessment of the potential for debris-flow generation from basins burned by the Santiago Fire in Orange County, southern California in 2007. Debris flows are among the most hazardous geologic phenomena; debris flows that followed wildfires in southern California in 2003 killed 16 people and caused tens of millions of dollars of property damage. A short period of even moderate rainfall on a burned watershed can lead to debris flows. Rainfall that is normally absorbed into hillslope soils can run off almost instantly after vegetation has been removed by wildfire. This causes much greater and more rapid runoff than is normal from creeks and drainage areas. Highly erodible soils in a burn scar allow flood waters to entrain large amounts of ash, mud, boulders, and unburned vegetation. Within the burned area and downstream, the force of rushing water, soil, and rock can destroy culverts, bridges, roadways, and buildings, potentially causing injury or death. This emergency debris-flow hazard assessment is presented as relative ranking of the predicted median volume of debris flows that can issue from basin outlets in response to 1.75 inches (44.45 mm) of rainfall over a 3-hour period. Such a storm has a 10-year return period. The calculation of debris flow volume is based on a multiple-regression statistical model that describes the median volume of material that can be expected from a recently burned basin as a function of the area burned at high and moderate severity, the basin area with slopes greater than or equal to 30 percent, and triggering storm rainfall. Cannon and others (2007) describe the methods used to generate the hazard maps. Identification of potential debris-flow hazards from burned drainage basins is necessary to issue warnings for specific basins, to make effective mitigation decisions, and to help plan evacuation timing and routes.

Predicting the occurrence of channelized debris flow by an integrated cascading model: A case study of a small debris flow-prone catchment in Zhejiang Province, China

NASA Astrophysics Data System (ADS)

Wei, Zhen-lei; Xu, Yue-Ping; Sun, Hong-yue; Xie, Wei; Wu, Gang

2018-05-01

Excessive water in a channel is an important factor that triggers channelized debris flows. Floods and debris flows often occur in a cascading manner, and thus, calculating the amount of runoff accurately is important for predicting the occurrence of debris flows. In order to explore the runoff-rainfall relationship, we placed two measuring facilities at the outlet of a small, debris flow-prone headwater catchment to explore the hydrological response of the catchment. The runoff responses generally consisted of a rapid increase in runoff followed by a slower decrease. The peak runoff often occurred after the rainfall ended. The runoff discharge data were simulated by two different modeling approaches, i.e., the NAM model and the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model. The results showed that the NAM model performed better than the HEC-HMS model. The NAM model provided acceptable simulations, while the HEC-HMS model did not. Then, we coupled the calculated results of the NAM model with an empirically based debris flow initiation model to obtain a new integrated cascading disaster modeling system to provide improved disaster preparedness and hazard management. In this case study, we found that the coupled model could correctly predict the occurrence of debris flows. Furthermore, we evaluated the effect of the range of input parameter values on the hydrographical shape of the runoff. We also used the grey relational analysis to conduct a sensitivity analysis of the parameters of the model. This study highlighted the important connections between rainfall, hydrological processes, and debris flow, and it provides a useful prototype model system for operational forecasting of debris flows.

Challenges in Modeling Debris-Flow Initiation during the Exceptional September 2013 Northern Colorado Front Range Rainstorm

NASA Astrophysics Data System (ADS)

Baum, R. L.; Coe, J. A.; Godt, J.; Kean, J. W.

2014-12-01

Heavy rainfall during 9 - 13 September 2013 induced about 1100 debris flows in the foothills and mountains of the northern Colorado Front Range. Eye-witness accounts and fire-department records put the times of greatest landslide activity during the times of heaviest rainfall on September 12 - 13. Antecedent soil moisture was relatively low, particularly at elevations below 2250 m where many of the debris flows occurred, based on 45 - 125 mm of summer precipitation and absence of rainfall for about 2 weeks before the storm. Mapping from post-event imagery and field observations indicated that most debris flows initiated as small, shallow landslides. These landslides typically formed in colluvium that consisted of angular clasts in a sandy or silty matrix, depending on the nature of the parent bedrock. Weathered bedrock was partially exposed in the basal surfaces of many of the shallow source areas at depths ranging from 0.2 to 5 m, and source areas commonly occupied less than 500 m2. Although 49% of the source areas occurred in swales and 3 % in channels, where convergent flow might have contributed to pore-pressure build up during the rainfall, 48% of the source areas occurred on open slopes. Upslope contributing areas of most landslides (58%) were small (< 1000 m2) and 78% of the slides occurred on south-facing slopes (90°≤ aspect ≤270°). These observations pose challenges for modeling initiation of the debris flows. Effects of variable soil depth and properties, vegetation, and rainfall must be examined to explain the dominance of debris flows on south-facing slopes. Accounting for the small sizes and mixed swale and open-slope settings of source areas demands new approaches for resolving soil-depth and physical-properties variability. The low-moisture initial conditions require consideration of unsaturated zone effects. Ongoing fieldwork and computational modeling are aimed at addressing these challenges related to initiation of the September 2013 debris flows.

Uncertainties on the definition of critical rainfall patterns for debris-flows triggering. Results from the Rebaixader monitoring site (Central Pyrenees)

NASA Astrophysics Data System (ADS)

Hürlimann, Marcel; Abancó, Clàudia; Moya, Jose; Berenguer, Marc

2015-04-01

Empirical rainfall thresholds are a widespread technique in debris-flow hazard assessment and can be established by statistical analysis of historic data. Typically, data from one or several rain gauges located nearby the affected catchment is used to define the triggering conditions. However, this procedure has been demonstrated not to be accurate enough due to the spatial variability of convective rainstorms. In 2009, a monitoring system was installed in the Rebaixader catchment, Central Pyrenees (Spain). Since then, 28 torrential flows (debris flows and debris floods) have occurred and rainfall data of 25 of them are available with a 5-minutes frequency of recording ("event rainfalls"). Other 142 rainfalls that did not trigger events ("no event rainfalls) were also collected and analysed. The goal of this work was threefold: a) characterize rainfall episodes in the Rebaixader catchment and compare rainfall data that triggered torrential events and others that did not; b) define and test Intensity-Duration (ID) thresholds using rainfall data measured inside the catchment; c) estimate the uncertainty derived from the use of rain gauges located outside the catchment based on the spatial correlation depicted by radar rainfall maps. The results of the statistical analysis showed that the parameters that more distinguish between the two populations of rainfalls are the rainfall intensities, the mean rainfall and the total precipitation. On the other side, the storm duration and the antecedent rainfall are not significantly different between "event rainfalls" and "no event rainfalls". Four different ID rainfall thresholds were derived based on the dataset of the first 5 years and tested using the 2014 dataset. The results of the test indicated that the threshold corresponding to the 90% percentile showed the best performance. Weather radar data was used to analyse the spatial variability of the triggering rainfalls. The analysis indicates that rain gauges outside the catchment may be considered useful or not to describe the rainfall depending on the type of rainfall. For widespread rainfalls, further rain gauges can give a reliable measurement, because the spatial correlation decreases slowly with the distance between the rain gauge and the debris-flow initiation area. Contrarily, local storm cells show higher space-time variability and, therefore, representative rainfall measurements are obtained only by the closest rain gauges. In conclusion, the definition of rainfall thresholds is a delicate task. When the rainfall records are coming from gauges that are outside the catchment under consideration, the data should be carefully analysed and crosschecked with radar data (especially for small convective cells).

Interaction between riverbed condition and characteristics of debris flow in Ichino-sawa subwatershed of Ohya-kuzure landslide, Japan

NASA Astrophysics Data System (ADS)

Tsunetaka, Haruka; Hotta, Norifumi; Imaizumi, Fumitoshi; Hayakawa, Yuichi S.; Yumen, Noriki

2015-04-01

Large-scale sediment movements, such as a deep-seated landslide, not only induce immediate sediment disasters but also produce a large amount of unstable sediment upstream. Most of the unstable sediment residing in the upstream area is discharged as debris flow. Hence, after the occurrence of large-scale sediment movement, debris flows have a long-term effect on the watershed regime. However, the characteristics of debris flow in upstream areas are not well understood, due to the topographic and grain-size conditions that are more complicated than the downstream area. This study was performed to reveal the relationship between such a riverbed condition and the characteristics of debris flow by field observations. The study site was Ichinosawa-subwatershed in the Ohya-kuzure basin, Shizuoka Prefecture, Japan. The basin experienced a deep-seated landslide about 300 years ago and is currently actively yielding sediment with a clear annual cycle. During the winter season, sediment is deposited on the valley bottom by freeze-thaw and weathering. In the summer season, the deposited sediment is discharged incrementally by debris flows related to storm events. Topographical survey and grain-size analysis were performed several times between November 2011 and November 2014. High-resolution digital elevation models (10 cm) were created from the results of a topographical survey using a terrestrial laser scanner. A grain-size analysis was conducted in the upper, middle, and lower parts of the study site. Debris flow occurrences were also monitored in the same period by a sensor-triggered video camera and interval camera. Rainfall was observed during the summer season for comparison with debris flow occurrence. Several debris flows of different magnitudes were observed during the study period. Although heavy rainfall events altered the bed inclination, the thickness of deposited sediment, and the grain-size distribution, more significant changes were detected after the debris flow. While the initial grain-size distribution in early spring was roughly identical across the study site, the subsequent changes in the grain-size distribution differed according to location. The source, transport and deposition areas of the debris flows differed among rainfall events, resulting in different transitions in topographic conditions at different locations. Furthermore, surges of debris flow not only induced erosion-deposited sediment but also suspended and deposited sediment in the same area during one typhoon event. A comparison of the results indicated that, in addition to the conditions of the triggering rainfall, topographic and grain-size conditions affected the debris flow occurrence and magnitude. These interactions also showed that the magnitude and form of the succeeding debris flow could be dominant, depending on changing riverbed condition by past debris flows in upstream areas.

Empirical models to predict the volumes of debris flows generated by recently burned basins in the western U.S.

USGS Publications Warehouse

Gartner, J.E.; Cannon, S.H.; Santi, P.M.; deWolfe, V.G.

2008-01-01

Recently burned basins frequently produce debris flows in response to moderate-to-severe rainfall. Post-fire hazard assessments of debris flows are most useful when they predict the volume of material that may flow out of a burned basin. This study develops a set of empirically-based models that predict potential volumes of wildfire-related debris flows in different regions and geologic settings. The models were developed using data from 53 recently burned basins in Colorado, Utah and California. The volumes of debris flows in these basins were determined by either measuring the volume of material eroded from the channels, or by estimating the amount of material removed from debris retention basins. For each basin, independent variables thought to affect the volume of the debris flow were determined. These variables include measures of basin morphology, basin areas burned at different severities, soil material properties, rock type, and rainfall amounts and intensities for storms triggering debris flows. Using these data, multiple regression analyses were used to create separate predictive models for volumes of debris flows generated by burned basins in six separate regions or settings, including the western U.S., southern California, the Rocky Mountain region, and basins underlain by sedimentary, metamorphic and granitic rocks. An evaluation of these models indicated that the best model (the Western U.S. model) explains 83% of the variability in the volumes of the debris flows, and includes variables that describe the basin area with slopes greater than or equal to 30%, the basin area burned at moderate and high severity, and total storm rainfall. This model was independently validated by comparing volumes of debris flows reported in the literature, to volumes estimated using the model. Eighty-seven percent of the reported volumes were within two residual standard errors of the volumes predicted using the model. This model is an improvement over previous models in that it includes a measure of burn severity and an estimate of modeling errors. The application of this model, in conjunction with models for the probability of debris flows, will enable more complete and rapid assessments of debris flow hazards following wildfire.

Mitigation of Debris Flow Damage--­ A Case Study of Debris Flow Damage

NASA Astrophysics Data System (ADS)

Lin, J. C.; Jen, C. H.

Typhoon Toraji caused more than 30 casualties in Central Taiwan on the 31st July 2001. It was the biggest Typhoon since the Chi-Chi earthquake of 1999 with huge amounts of rainfall. Because of the influence of the earthquake, loose debris falls and flows became major hazards in Central Taiwan. Analysis of rainfall data and sites of slope failure show that damage from these natural hazards were enhanced as a result of the Chi-Chi earthquake. Three main types of hazard occurred in Central Taiwan: land- slides, debris flows and gully erosion. Landslides occurred mainly along hill slopes and banks of channels. Many dams and houses were destroyed by flooding. Debris flows occurred during typhoon periods and re-activated ancient debris depositions. Many new gullies were therefore developed from deposits loosened and shaken by the earthquake. This paper demonstrates the geological/geomorphological background of the hazard area, and reviews methods of damage mitigation in central Taiwan. A good example is Hsi-Tou, which had experienced no gully erosion for more than 40 years. The area experienced much gully erosion as a result of the combined effects of earth- quake and typhoon. Although Typhoon Toraji produced only 30% of the rainfall of Typhoon Herb of 1996, it caused more damage in the Hsi-Tou area. The mitigation of debris flow hazards in Hsi-tou area is discussed in this paper.

A comparison between Bayes discriminant analysis and logistic regression for prediction of debris flow in southwest Sichuan, China

NASA Astrophysics Data System (ADS)

Xu, Wenbo; Jing, Shaocai; Yu, Wenjuan; Wang, Zhaoxian; Zhang, Guoping; Huang, Jianxi

2013-11-01

In this study, the high risk areas of Sichuan Province with debris flow, Panzhihua and Liangshan Yi Autonomous Prefecture, were taken as the studied areas. By using rainfall and environmental factors as the predictors and based on the different prior probability combinations of debris flows, the prediction of debris flows was compared in the areas with statistical methods: logistic regression (LR) and Bayes discriminant analysis (BDA). The results through the comprehensive analysis show that (a) with the mid-range scale prior probability, the overall predicting accuracy of BDA is higher than those of LR; (b) with equal and extreme prior probabilities, the overall predicting accuracy of LR is higher than those of BDA; (c) the regional predicting models of debris flows with rainfall factors only have worse performance than those introduced environmental factors, and the predicting accuracies of occurrence and nonoccurrence of debris flows have been changed in the opposite direction as the supplemented information.

Probability and volume of potential postwildfire debris flows in the 2012 Waldo Canyon Burn Area near Colorado Springs, Colorado

USGS Publications Warehouse

Verdin, Kristine L.; Dupree, Jean A.; Elliott, John G.

2012-01-01

This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the 2012 Waldo Canyon fire near Colorado Springs in El Paso County, Colorado. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and potential volume of debris flows along the drainage network of the burned area and to estimate the same for 22 selected drainage basins along U.S. Highway 24 and the perimeter of the burned area. Input data for the models included topographic parameters, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall, referred to as a 2-year storm (29 millimeters); (2) 10-year-recurrence, 1-hour-duration rainfall, referred to as a 10-year storm (42 millimeters); and (3) 25-year-recurrence, 1-hour-duration rainfall, referred to as a 25-year storm (48 millimeters). Estimated debris-flow probabilities at the pour points of the the drainage basins of interest ranged from less than 1 to 54 percent in response to the 2-year storm; from less than 1 to 74 percent in response to the 10-year storm; and from less than 1 to 82 percent in response to the 25-year storm. Basins and drainage networks with the highest probabilities tended to be those on the southern and southeastern edge of the burn area where soils have relatively high clay contents and gradients are steep. Nine of the 22 drainage basins of interest have greater than a 40-percent probability of producing a debris flow in response to the 10-year storm. Estimated debris-flow volumes for all rainfalls modeled range from a low of 1,500 cubic meters to a high of greater than 100,000 cubic meters. Estimated debris-flow volumes increase with basin size and distance along the drainage network, but some smaller drainages were also predicted to produce substantial volumes of material. The predicted probabilities and some of the volumes predicted for the modeled storms indicate a potential for substantial debris-flow impacts on structures, reservoirs, roads, bridges, and culverts located both within and immediately downstream from the burned area. U.S. Highway 24, on the southern edge of the burn area, is also susceptible to impacts from debris flows.

Slope stability in the critical zone: The relative influence of long vs. short-time scale soil and vegetation properties on debris-flow initiation during a catastrophic rainfall.

NASA Astrophysics Data System (ADS)

Rengers, F. K.; McGuire, L.; Coe, J. A.; Kean, J. W.; Baum, R. L.; Staley, D. M.; Godt, J.

2016-12-01

Within the critical zone there is a feedback between the state of soil and vegetation development, boundary conditions (e.g. topography, climate, hillslope aspect), and biogeochemical and geophysical process fluxes. Here we explore how one process—debris flows initiated by shallow landslides—is influenced by the critical zone development state and the imposed boundary conditions. In this study, we examine a rainstorm in September 2013 in the Colorado Front Range wherein 78% of 1138 debris flows were triggered on south-facing slopes. One hypothesis is that debris-flow initiation sites are controlled by long-term soil formation and bedrock weathering, which are aspect-dependent in the Front Range. A competing hypothesis is that debris flow initiation locations are controlled by present-day vegetation patterns within the critical zone. We tested these hypotheses with a regional investigation of the Green-Red Vegetation Index (GRVI), a metric used to identify the degree of vegetation cover. Although the majority of debris flows were observed on south-facing hillslopes, the GRVI analysis revealed that most debris-flow initiation locations had low tree density and high rainfall, regardless of hillslope aspect. We next numerically simulated soil pore pressure and slope stability using the September 2013 rainfall data at one site. Results suggest that spatial variations in soil depth and the relative extent of bedrock weathering on north- versus south-facing slopes are insufficient to explain the observed spatial variations in debris flow initiation. However, decreased debris flow initiation on north-facing slopes likely resulted from increased root reinforcement provided by trees on north-facing slopes. While the current vegetation regimes in the Colorado Front Range, and throughout much of the semi-arid southwestern U.S., are superimposed on a landscape where soil development and bedrock weathering (both of which affect slope stability) are responding to longer timescale processes, our analysis suggests landslide susceptibility was primarily governed by the local, geo-mechanical effects of vegetation during this extreme rainfall event.

The remarkable occurrence of large rainfall-induced debris flows at two different locations on July 12, 2008, Southern Sierra Nevada, CA, USA

USGS Publications Warehouse

DeGraff, J.V.; Wagner, D.L.; Gallegos, A.J.; DeRose, M.; Shannon, C.; Ellsworth, T.

2011-01-01

On July 12, 2008, two convective cells about 155 km apart produced a brief period of intense rainfall triggering large debris flows in the southern Sierra Nevada. The northernmost cell was centered over Oak Creek Canyon, an east-flowing drainage, and its tributaries near Independence, CA, USA. About 5:00 P.M., debris flows passed down the South Fork and North Fork of Oak Creek to merge into a large single feature whose passage affected the historic Mt. Whitney Fish hatchery and blocked California State Highway 395. At about the same time, the southernmost cell was largely centered over Erskine Creek, a main tributary of the west-flowing Kern River. Debris flows issued from several branches to coalesce into a large debris flow that passed along Erskine Creek, through the town of Lake Isabella, CA, USA and into the Kern River. It was observed reaching Lake Isabella about 6:30 P.M. Both debris flows caused significant disruption and damage to local communities. ?? 2011 Springer-Verlag.

Characterization of debris flows by rainstorm condition at a torrent on the Mount Yakedake volcano, Japan

NASA Astrophysics Data System (ADS)

Okano, Kazuyuki; Suwa, Hiroshi; Kanno, Tadahiro

2012-01-01

We analyzed rainstorm control on debris-flow magnitude and flow characteristics using the 14 sets of rainstorm and debris-flow data obtained from 1980 to 2005 at the Kamikamihorizawa Creek of Mount Yakedake. With the principal component analysis on five parameters of debris flows: frontal velocity, peak velocity, peak flow depth, peak discharge and total discharge, and with video-record of boulder-dams in motion, and the preceding rainfall intensities, we conclude that the 14 debris flows could be categorized into three groups. The flows in the first group have large hydraulic magnitude and massive and turbulent boulder-dams filled with slurry matrix. The flows in the second group have small hydraulic magnitude and boulder-dams scarcely filled with slurry matrix, and the dam is observed to alternate between stopping and starting. The flows in the third group have small hydraulic magnitude and boulder dams filled with slurry matrix. Analysis of hillslope hydrology and debris-flow data asserted that the antecedent rainfall conditions control not only the hydraulic magnitude of debris flows but also the boulder-dam features. Large rainstorms of high intensity and durations as short as 10 minutes induces fast and large storm runoff to the headwaters and the source reaches of debris flow, while rainstorms with durations as long as 24 h raises water content in the bottom deposits along the debris-flow growth reaches and generates substantial runoff from the tributaries. Classification of the three groups is done based on water availability to debris flows on the source and growth reaches at the occurrence of debris flow.

An Examination of Selected Historical Rainfall-Induced Debris-Flow Events within the Central and Southern Appalachian Mountains of the Eastern United States

USGS Publications Warehouse

Wieczorek, Gerald F.; Eaton, L. Scott; Morgan, Benjamin A.; Wooten, R.M.; Morrissey, M.

2009-01-01

Generally, every several years, heavy amounts of rainfall trigger a large number of debris flows within the central and southern Appalachian Mountains of the Eastern United States. These types of landslides damage buildings, disrupt infrastructure, and occasionally injure and kill people. One of the first large debris flows was described in Pennsylvania in August 1779. The most destructive event occurred during August 19-20, 1969, in Nelson County, Va. During a period of 8 hours, 710 to 800 milimeters of rain triggered more than 3,000 landslides, killing more than 150 people. As the population increases in this region, future storms will likely increase the risks of property damage and loss of life. We provide a general overview of debris flows in the Appalachians, using a compilation of 19 storm events for which rainfall, duration of the storm, and descriptions of the resulting landslides have been substantially documented.

Timing of susceptibility to post-fire debris flows in the western USA

USGS Publications Warehouse

DeGraff, Jerome V.; Cannon, Susan H.; Gartner, Joseph E.

2015-01-01

Watersheds recently burned by wildfires can have an increased susceptibility to debris flow, although little is known about how long this susceptibility persists, and how it changes over time. We here use a compilation of 75 debris-flow response and fire-ignition dates, vegetation and bedrock class, rainfall regime, and initiation process from throughout the western U.S. to address these issues. The great majority (85 percent) of debris flows occurred within the first 12 months following wildfire, with 71 percent within the first six months. Seven percent of the debris flows occurred between 1 and 1.5 years after a fire, or during the second rainy season to impact an area. Within the first 1.5 years following fires, all but one of the debris flows initiated through runoff-dominated processes, and debris flows occurred in similar proportions in forested and non-forested landscapes. Geologic materials affected how long debris-flow activity persisted, and the timing of debris flows varied within different rainfall regimes. A second, later period of increased debris flow susceptibility between 2.2 and 10 years after fires is indicated by the remaining 8 percent of events, which occurred primarily in forested terrains and initiated largely through landslide processes. The short time period between fire and debris-flow response within the first 1.5 years after ignition, and the longer-term response between 2.2 and 10 years after fire, demonstrate the necessity of both rapid and long-term reactions by land managers and emergency-response agencies to mitigate hazards from debris flows from recently burned areas in the western U.S.

Linking rainfall-induced landslides with debris flows runout patterns towards catchment scale hazard assessment

NASA Astrophysics Data System (ADS)

Fan, Linfeng; Lehmann, Peter; McArdell, Brian; Or, Dani

2017-03-01

Debris flows and landslides induced by heavy rainfall represent an ubiquitous and destructive natural hazard in steep mountainous regions. For debris flows initiated by shallow landslides, the prediction of the resulting pathways and associated hazard is often hindered by uncertainty in determining initiation locations, volumes and mechanical state of the mobilized debris (and by model parameterization). We propose a framework for linking a simplified physically-based debris flow runout model with a novel Landslide Hydro-mechanical Triggering (LHT) model to obtain a coupled landslide-debris flow susceptibility and hazard assessment. We first compared the simplified debris flow model of Perla (1980) with a state-of-the art continuum-based model (RAMMS) and with an empirical model of Rickenmann (1999) at the catchment scale. The results indicate that predicted runout distances by the Perla model are in reasonable agreement with inventory measurements and with the other models. Predictions of localized shallow landslides by LHT model provides information on water content of released mass. To incorporate effects of water content and flow viscosity as provided by LHT on debris flow runout, we adapted the Perla model. The proposed integral link between landslide triggering susceptibility quantified by LHT and subsequent debris flow runout hazard calculation using the adapted Perla model provides a spatially and temporally resolved framework for real-time hazard assessment at the catchment scale or along critical infrastructure (roads, railroad lines).

Operation of a real-time warning system for debris flows in the San Francisco bay area, California

USGS Publications Warehouse

Wilson, Raymond C.; Mark, Robert K.; Barbato, Gary; ,

1993-01-01

The United States Geological Survey (USGS) and the National Weather Service (NWS) have developed an operational warning system for debris flows during severe rainstorms in the San Francisco Bay region. The NWS makes quantitative forecasts of precipitation from storm systems approaching the Bay area and coordinates a regional network of radio-telemetered rain gages. The USGS has formulated thresholds for the intensity and duration of rainfall required to initiate debris flows. The first successful public warnings were issued during a severe storm sequence in February 1986. Continued operation of the warning system since 1986 has provided valuable working experience in rainfall forecasting and monitoring, refined rainfall thresholds, and streamlined procedures for issuing public warnings. Advisory statements issued since 1986 are summarized.

A combined triggering-propagation modeling approach for the assessment of rainfall induced debris flow susceptibility

NASA Astrophysics Data System (ADS)

Stancanelli, Laura Maria; Peres, David Johnny; Cancelliere, Antonino; Foti, Enrico

2017-07-01

Rainfall-induced shallow slides can evolve into debris flows that move rapidly downstream with devastating consequences. Mapping the susceptibility to debris flow is an important aid for risk mitigation. We propose a novel practical approach to derive debris flow inundation maps useful for susceptibility assessment, that is based on the integrated use of DEM-based spatially-distributed hydrological and slope stability models with debris flow propagation models. More specifically, the TRIGRS infiltration and infinite slope stability model and the FLO-2D model for the simulation of the related debris flow propagation and deposition are combined. An empirical instability-to-debris flow triggering threshold calibrated on the basis of observed events, is applied to link the two models and to accomplish the task of determining the amount of unstable mass that develops as a debris flow. Calibration of the proposed methodology is carried out based on real data of the debris flow event occurred on 1 October 2009, in the Peloritani mountains area (Italy). Model performance, assessed by receiver-operating-characteristics (ROC) indexes, evidences fairly good reproduction of the observed event. Comparison with the performance of the traditional debris flow modeling procedure, in which sediment and water hydrographs are inputed as lumped at selected points on top of the streams, is also performed, in order to assess quantitatively the limitations of such commonly applied approach. Results show that the proposed method, besides of being more process-consistent than the traditional hydrograph-based approach, can potentially provide a more accurate simulation of debris-flow phenomena, in terms of spatial patterns of erosion and deposition as well on the quantification of mobilized volumes and depths, avoiding overestimation of debris flow triggering volume and, thus, of maximum inundation flow depths.

Post-fire debris-flow hazard assessment of the area burned by the 2013 Beaver Creek Fire near Hailey, central Idaho

USGS Publications Warehouse

Skinner, Kenneth D.

2013-01-01

A preliminary hazard assessment was developed for debris-flow hazards in the 465 square-kilometer (115,000 acres) area burned by the 2013 Beaver Creek fire near Hailey in central Idaho. The burn area covers all or part of six watersheds and selected basins draining to the Big Wood River and is at risk of substantial post-fire erosion, such as that caused by debris flows. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the Intermountain Region in Western United States were used to estimate the probability of debris-flow occurrence, potential volume of debris flows, and the combined debris-flow hazard ranking along the drainage network within the burn area and to estimate the same for analyzed drainage basins within the burn area. Input data for the empirical models included topographic parameters, soil characteristics, burn severity, and rainfall totals and intensities for a (1) 2-year-recurrence, 1-hour-duration rainfall, referred to as a 2-year storm (13 mm); (2) 10-year-recurrence, 1-hour-duration rainfall, referred to as a 10-year storm (19 mm); and (3) 25-year-recurrence, 1-hour-duration rainfall, referred to as a 25-year storm (22 mm). Estimated debris-flow probabilities for drainage basins upstream of 130 selected basin outlets ranged from less than 1 to 78 percent with the probabilities increasing with each increase in storm magnitude. Probabilities were high in three of the six watersheds. For the 25-year storm, probabilities were greater than 60 percent for 11 basin outlets and ranged from 50 to 60 percent for an additional 12 basin outlets. Probability estimates for stream segments within the drainage network can vary within a basin. For the 25-year storm, probabilities for stream segments within 33 basins were higher than the basin outlet, emphasizing the importance of evaluating the drainage network as well as basin outlets. Estimated debris-flow volumes for the three modeled storms range from a minimal debris flow volume of 10 cubic meters [m3]) to greater than 100,000 m3. Estimated debris-flow volumes increased with basin size and distance downstream. For the 25-year storm, estimated debris-flow volumes were greater than 100,000 m3 for 4 basins and between 50,000 and 100,000 m3 for 10 basins. The debris-flow hazard rankings did not result in the highest hazard ranking of 5, indicating that none of the basins had a high probability of debris-flow occurrence and a high debris-flow volume estimate. The hazard ranking was 4 for one basin using the 10-year-recurrence storm model and for three basins using the 25-year-recurrence storm model. The maps presented herein may be used to prioritize areas where post-wildfire remediation efforts should take place within the 2- to 3-year period of increased erosional vulnerability.

Wildfire impacts on the processes that generate debris flows in burned watersheds

USGS Publications Warehouse

Parise, M.; Cannon, S.H.

2012-01-01

Every year, and in many countries worldwide, wildfires cause significant damage and economic losses due to both the direct effects of the fires and the subsequent accelerated runoff, erosion, and debris flow. Wildfires can have profound effects on the hydrologic response of watersheds by changing the infiltration characteristics and erodibility of the soil, which leads to decreased rainfall infiltration, significantly increased overland flow and runoff in channels, and movement of soil. Debris-flow activity is among the most destructive consequences of these changes, often causing extensive damage to human infrastructure. Data from the Mediterranean area and Western United States of America help identify the primary processes that result in debris flows in recently burned areas. Two primary processes for the initiation of fire-related debris flows have been so far identified: (1) runoff-dominated erosion by surface overland flow; and (2) infiltration-triggered failure and mobilization of a discrete landslide mass. The first process is frequently documented immediately post-fire and leads to the generation of debris flows through progressive bulking of storm runoff with sediment eroded from the hillslopes and channels. As sediment is incorporated into water, runoff can convert to debris flow. The conversion to debris flow may be observed at a position within a drainage network that appears to be controlled by threshold values of upslope contributing area and its gradient. At these locations, sufficient eroded material has been incorporated, relative to the volume of contributing surface runoff, to generate debris flows. Debris flows have also been generated from burned basins in response to increased runoff by water cascading over a steep, bedrock cliff, and incorporating material from readily erodible colluvium or channel bed. Post-fire debris flows have also been generated by infiltration-triggered landslide failures which then mobilize into debris flows. However, only 12% of documented cases exhibited this process. When they do occur, the landslide failures range in thickness from a few tens of centimeters to more than 6 m, and generally involve the soil and colluvium-mantled hillslopes. Surficial landslide failures in burned areas most frequently occur in response to prolonged periods of storm rainfall, or prolonged rainfall in combination with rapid snowmelt or rain-on-snow events. ?? 2011 Springer Science+Business Media B.V.

A numerical modeling investigation of erosion and debris flows following the 2016 Fish Fire in the San Gabriel Mountains, CA, USA

NASA Astrophysics Data System (ADS)

Tang, H.; McGuire, L.; Rengers, F. K.; Kean, J. W.; Staley, D. M.

2017-12-01

Wildfire significantly changes the hydrological characteristics of soil for a period of several years and increases the likelihood of flooding and debris flows during high-intensity rainfall in steep watersheds. Hazards related to post-fire flooding and debris flows increase as populations expand into mountainous areas that are susceptible to wildfire, post-wildfire flooding, and debris flows. However, our understanding of post-wildfire debris flows is limited due to a paucity of direct observations and measurements, partially due to the remote locations where debris flows tend to initiate. In these situations, numerical modeling becomes a very useful tool for studying post-wildfire debris flows. Research based on numerical modeling improves our understanding of the physical mechanisms responsible for the increase in erosion and consequent formation of debris flows in burned areas. In this contribution, we study changes in sediment transport efficiency with time since burning by combining terrestrial laser scanning (TLS) surveys of a hillslope burned during the 2016 Fish Fire with numerical modeling of overland flow and sediment transport. We also combine the numerical model with measurements of debris flow timing to explore relationships between post-wildfire rainfall characteristics, soil infiltration capacity, hillslope erosion, and debris flow initiation at the drainage basin scale. Field data show that an initial rill network developed on the hillslope, and became more efficient over time as the overall rill density decreased. Preliminary model results suggest that this can be achieved when flow driven detachment mechanisms dominate and raindrop-driven detachment is minimized. Results also provide insight into the hydrologic and geomorphic conditions that lead to debris flow initiation within recently burned areas.

Influence of topography on debris flow development in Ichino-sawa subwatershed of Ohya-kuzure landslide, Japan

NASA Astrophysics Data System (ADS)

Tsunetaka, H.; Hotta, N.; Imaizumi, F.; Hayakawa, Y. S.

2015-12-01

Large sediment movements, such as deep-seated landslides, produce unstable sediment over the long term. Most of the unstable sediment in a mountain torrent is discharged via the development of debris flows through entrainment. Consequently, after a large sediment movement, debris flows have long-term effects on the watershed regime. However, the development of debris flows in mountain torrents is poorly understood, since the topography is more complicated than downstream. We compared temporal changes in topography to examine how topography affects the development of flows. The study site was the Ichino-sawa subwatershed in the Ohya-kuzure landslide, Japan. Unstable sediment has been produced continuously since the landslide occurred in 1707. Several topographic surveys using a terrestrial laser scanner (TLS) and aerial shoots by an unmanned aerial vehicle (UAV) were performed between November 2011 (TLS) or November 2014 (UAV) and August 2015. High-resolution digital elevation models were created from the TLS and UAV results to detect temporal topographic changes. Debris flow occurrences and rainfall were also monitored using interval cameras and rain gauges. Downstream, the deposit depth decreased after the debris flows. Upstream, more complex changes were detected due to surges in the debris flows, which not only induced entrainment, but were also deposited in the valley floor. Furthermore, sediment was supplied from the stream bank during the debris flows. Consequently, several debris flows of different magnitudes were observed, although the rainfall conditions did not differ significantly. The results imply that the magnitude of the debris flows was affected by successive sediment movement resulting from the changing of the topographic conditions.

New insights into debris-flow hazards from an extraordinary event in the Colorado Front Range

USGS Publications Warehouse

Coe, Jeffrey A.; Kean, Jason W.; Godt, Jonathan W.; Baum, Rex L.; Jones, Eric S.; Gochis, David; Anderson, Gregory S

2016-01-01

Rainfall on 9–13 September 2013 triggered at least 1,138 debris flows in a 3430 km2 area of the Colorado Front Range. The historical record reveals that the occurrence of these flows over such a large area in the interior of North America is highly unusual. Rainfall that triggered the debris flows began after ~75 mm of antecedent rain had fallen, a relatively low amount compared to other parts of the United States. Most flows were triggered in response to two intense rainfall periods, one 12.5-hour-long period on 11–12 September, and one 8-hour-long period on 12 September. The maximum 10 min. intensities during these periods were 67 and 39 mm/hr. Ninety-five percent of flows initiated in canyons and on hogbacks at elevations lower than a widespread erosion surface of low slope and relief (25°), predominantly south- and east-facing slopes with upslope contributing areas 3300 m2. Areal concentrations of debris flows revealed that colluvial soils formed on sedimentary rocks were more susceptible to flows than soils on crystalline rocks. This event should serve as an alert to government authorities, emergency responders, and residents in the Front Range and other interior continental areas with steep slopes. Widespread debris flows in these areas occur infrequently but may pose a greater risk than in areas with shorter return periods, because the public is typically unprepared for them.

Debris flow study in Malaysia

NASA Astrophysics Data System (ADS)

Bahrin Jaafar, Kamal

2016-04-01

The phenomenon of debris flow occurs in Malaysia occasionally. The topography of Peningsular Malysia is characterized by the central mountain ranges running from south to north. Several parts of hilly areas with steep slopes, combined with high saturation of soil strata that deliberately increase the pore water pressure underneath the hill slope. As a tropical country Malaysia has very high intensity rainfall which is triggered the landslide. In the study area where the debris flow are bound to occur, there are a few factors that contribute to this phenomenon such as high rainfall intensity, very steep slope which an inclination more than 35 degree and sandy clay soil type which is easily change to liquidity soil. This paper will discuss the study of rainfall, mechanism, modeling and design of mitigation measure to avoid repeated failure in future in same area.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the Padua Fire of 2003, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Rupert, Michael G.; Michael, John A.

2004-01-01

Results of a present preliminary assessment of the probability of debris-flow activity and estimates of peak discharges that can potentially be generated by debris flows issuing from basins burned by the Padua Fire of October 2003 in southern California in response to 25-year, 10-year, and 2-year recurrence, 1-hour duration rain storms are presented. The resulting probability maps are based on the application of a logistic multiple-regression model (Cannon and others, 2004) that describes the percent chance of debris-flow production from an individual basin as a function of burned extent, soil properties, basin gradients, and storm rainfall. The resulting peak discharge maps are based on application of a multiple-regression model (Cannon and others, 2004) that can be used to estimate debris-flow peak discharge at a basin outlet as a function of basin gradient, burn extent, and storm rainfall. Probabilities of debris-flow occurrence for the Padua Fire range between 0 and 99% and estimates of debris-flow peak discharges range between 1211 and 6,096 ft3/s (34 to 173 m3/s). These maps are intended to identify those basins that are most prone to the largest debris-flow events and provide information for the preliminary design of mitigation measures and for the planning of evacuation timing and routes.

Meteorological Trigger Conditions for Different Geomorphic Processes in Steep Mountain Channels in the Austrian Alps

NASA Astrophysics Data System (ADS)

Kaitna, R.; Braun, M.

2016-12-01

Steep mountain channels episodically can experience very different geomorphic processes, ranging from flash floods, intensive bedload transport, debris floods, and debris flows. Rainfall-related trigger conditions and geomorphic disposition for each of these processes to occur, as well as conditions leading to one process and not to the other, are not well understood. In this contribution, we analyze triggering rainfalls for all documented events in the Eastern (Austrian) Alps on a daily and sub-daily basis. The analysis with daily rainfall data covers more than 6640 events between 1901 and 2014 and the analysis based on sub-daily (10 min interval) rainfall data includes around 950 events between 1992 and 2014. Of the four investigated event types, we find that debris flows are typically associated with the least cumulative rainfall, while intensive bedload transport as well as torrential floods occur when there is a substantial amount of cumulative rainfall. Debris floods are occurring on average with cumulative rainfall in a range between the aforementioned processes. Comparison of historical data shows, that about 90% of events are triggered with a combination of extreme rainfall and temperature. Bayesian analysis reveals that a high degree of geomorphic events is associated with very short rainfall durations that cannot be resolved with daily rainfall data. A comparison of both datasets shows that subdaily data gives more accurate results. Additionally, we find a high degree of regional differences, e.g. between regions north and south of the Alpine chain or high or low Alpine regions. There is indication that especially debris flows need less total rainfall amount when occurring in regions with a high relief energy than in less steep environments. The limitation of our analysis is mainly due to the distance between the locations of event triggering and rainfall measurement and the definition of rainfall events for the Bayesian analysis. In a next step, we will connect our results with the analyses of the hydrological as well as geomorphological disposition in selected study regions and with projections of changing climate conditions.

Mechanism of shallow disrupted slide induced by extreme rainfall

NASA Astrophysics Data System (ADS)

Igwe, O.; Fukuoka, H.

2010-12-01

On July 16, 2010, extreme rainfall attacked western Japan and it caused very intense rainfall in Shobara city, Hiroshima prefecture, Japan. This rainfall induced hundreds of shallow disrupted slides and many of those became debris flows. One of this debris flows attacked a house standing in front of the exit of a channel, and claimed a resident’s life. Western Japan had repeatedly similar disasters in the past. Last event took place from July 19 to 26, 2009, when western Japan had a severe rainstorms and caused floods and landslides. Most of the landslides are debris slide - debris flows. Most devastated case took place in Hofu city, Japan. On July 21, extremely intense rainstorm caused numerous debris flows and mud flows in the hillslopes. Some of the debris flows destroyed residential houses and home for elderly people, and finally killed 14 residents. One of the unusual feature of both disaster was that landslides are distributed in very narrow area. In the 2010 Shobara city disaster, all of the landslides were distributed in 5 km x 3 km, and in the 2009 Hofu city disaster, most devastated zone of landslides were 10 km x 5 km. Rain radars of Meteorological Agency of Government of Japan detected the intense rainfall, however, the spatial resolution is usually larger than 5 km and the disaster area is too small to predict landslides nor issue warning. Furthermore, it was found that the growth rate of baby clouds was very quick. The geology of both areas are rhyolite (Shobara) and granite (Hofu), so the areal assessment of landslide hazard should be prepared before those intense rainfall will come. As for the Hofu city case, it was proved that debris flows took place in the high precipitation area and covered by covered by weathered granite sands and silts which is called “masa". This sands has been proved susceptible against landslides under extreme rainfall conditions. However, the transition from slide - debris flow process is not well revealed, except authors past experiment on the similar masa samples in June 1999 Hiroshima debris flow case. Authors have embedded pore pressure control system for the undrained ring shear apparatus. Strongly weathered sandy soils were sampled just on the smooth and flat granitic sliding surface of one of the upstream small-scale landslides. Those contained finer grains and lower permeability rather than the one sampled in the Hiroshima case. Sample was consolidated by smaller stress corresponding to the site condition, and saturated by overnight circulating de-aired water. Normal stress and shear stress corresponding the slope condition was given, then, pore pressure (back pressure) was raised artificially at constant rate. When the effective stress reached the failure line, suddenly measured pore pressure monitored at about 2 mm above the shear plane, quickly increased. This sudden change abruptly accelerate the shear displacement. Stress condition soon reached the steady state and remained there thereafter. The reason of the excess pore pressure generation was the negative dilatancy, following a slight positive dilatancy. Most of the negative dilatancy could be explained by collapse of loose soil skelton as well as grain crushing during deformation and shearing.

Estimated probability of postwildfire debris flows in the 2012 Whitewater-Baldy Fire burn area, southwestern New Mexico

USGS Publications Warehouse

Tillery, Anne C.; Matherne, Anne Marie; Verdin, Kristine L.

2012-01-01

In May and June 2012, the Whitewater-Baldy Fire burned approximately 1,200 square kilometers (300,000 acres) of the Gila National Forest, in southwestern New Mexico. The burned landscape is now at risk of damage from postwildfire erosion, such as that caused by debris flows and flash floods. This report presents a preliminary hazard assessment of the debris-flow potential from 128 basins burned by the Whitewater-Baldy Fire. A pair of empirical hazard-assessment models developed by using data from recently burned basins throughout the intermountain Western United States was used to estimate the probability of debris-flow occurrence and volume of debris flows along the burned area drainage network and for selected drainage basins within the burned area. The models incorporate measures of areal burned extent and severity, topography, soils, and storm rainfall intensity to estimate the probability and volume of debris flows following the fire. In response to the 2-year-recurrence, 30-minute-duration rainfall, modeling indicated that four basins have high probabilities of debris-flow occurrence (greater than or equal to 80 percent). For the 10-year-recurrence, 30-minute-duration rainfall, an additional 14 basins are included, and for the 25-year-recurrence, 30-minute-duration rainfall, an additional eight basins, 20 percent of the total, have high probabilities of debris-flow occurrence. In addition, probability analysis along the stream segments can identify specific reaches of greatest concern for debris flows within a basin. Basins with a high probability of debris-flow occurrence were concentrated in the west and central parts of the burned area, including tributaries to Whitewater Creek, Mineral Creek, and Willow Creek. Estimated debris-flow volumes ranged from about 3,000-4,000 cubic meters (m3) to greater than 500,000 m3 for all design storms modeled. Drainage basins with estimated volumes greater than 500,000 m3 included tributaries to Whitewater Creek, Willow Creek, Iron Creek, and West Fork Mogollon Creek. Drainage basins with estimated debris-flow volumes greater than 100,000 m3 for the 25-year-recurrence event, 24 percent of the basins modeled, also include tributaries to Deep Creek, Mineral Creek, Gilita Creek, West Fork Gila River, Mogollon Creek, and Turkey Creek, among others. Basins with the highest combined probability and volume relative hazard rankings for the 25-year-recurrence rainfall include tributaries to Whitewater Creek, Mineral Creek, Willow Creek, West Fork Gila River, West Fork Mogollon Creek, and Turkey Creek. Debris flows from Whitewater, Mineral, and Willow Creeks could affect the southwestern New Mexico communities of Glenwood, Alma, and Willow Creek. The maps presented herein may be used to prioritize areas where emergency erosion mitigation or other protective measures may be necessary within a 2- to 3-year period of vulnerability following the Whitewater-Baldy Fire. This work is preliminary and is subject to revision. It is being provided because of the need for timely "best science" information. The assessment herein is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government may be held liable for any damages resulting from the authorized or unauthorized use of the assessment.

NOAA-USGS Debris-Flow Warning System - Final Report

USGS Publications Warehouse

,

2005-01-01

Landslides and debris flows cause loss of life and millions of dollars in property damage annually in the United States (National Research Council, 2004). In an effort to reduce loss of life by debris flows, the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS) and the U.S. Geological Survey (USGS) operated an experimental debris-flow prediction and warning system in the San Francisco Bay area from 1986 to 1995 that relied on forecasts and measurements of precipitation linked to empirical precipitation thresholds to predict the onset of rainfall-triggered debris flows. Since 1995, there have been substantial improvements in quantifying precipitation estimates and forecasts, development of better models for delineating landslide hazards, and advancements in geographic information technology that allow stronger spatial and temporal linkage between precipitation forecasts and hazard models. Unfortunately, there have also been several debris flows that have caused loss of life and property across the United States. Establishment of debris-flow warning systems in areas where linkages between rainfall amounts and debris-flow occurrence have been identified can help mitigate the hazards posed by these types of landslides. Development of a national warning system can help support the NOAA-USGS goal of issuing timely Warnings of potential debris flows to the affected populace and civil authorities on a broader scale. This document presents the findings and recommendations of a joint NOAA-USGS Task Force that assessed the current state-of-the-art in precipitation forecasting and debris-flow hazard-assessment techniques. This report includes an assessment of the science and resources needed to establish a demonstration debris-flow warning project in recently burned areas of southern California and the necessary scientific advancements and resources associated with expanding such a warning system to unburned areas and, possibly, to a national scope.

Debris flow monitoring in the Acquabona watershed on the Dolomites (Italian Alps)

USGS Publications Warehouse

Berti, M.; Genevois, R.; LaHusen, R.; Simoni, A.; Tecca, P.R.

2000-01-01

In 1997 a field monitoring system was installed in Acquabona Creek in the Dolomites (Eastern Italian Alps) to observe the hydrologic conditions for debris flow occurrence and some dynamic properties of debris flow. The monitoring system consists of three remote stations: an upper one located at the head of a deeply-incised channel and two others located downstream. The system is equipped with sensors for measuring rainfall, pore pressures in the mobile channel bottom, ground vibrations, debris flow depth, total normal stress and fluid pore-pressure at the base of the flow. Two video cameras record events at the upper channel station and one video is installed at the lowermost station. During summer 1998, three debris flows (volumes from less than 1000 m3 up to 9000 m3) occurred at Acquabona. The following results were obtained from a preliminary analysis of the data: 1) All of the flows were triggered by rainfalls of less than 1 hour duration, with peak rainfall intensities ranging from 4.8 to 14.7 mm / 10 minute. 2) Debris flows initiated in several reaches of the channel, including the head of the talus slope. 3) The initial surges of the mature flows had a higher solid concentration and a lower velocity (up to 4 m/s) than succeeding, more dilute surges (more than 7 m/s). 4) Total normal stress and pore fluid pressures measured at the base of the flow (mean depth about 1.1 m) were similar (about 15 kPa), indicating a completely liquefied flow. 5) Peak flows entrained debris at a rate of about 6 m3/m of channel length and channel bed scouring was proportional to the local slope gradient and was still evident in the lower channel where the slope was 7??. ?? 2000 Elsevier Science Ltd. All rights reserved.

Potential postwildfire debris-flow hazards - A prewildfire evaluation for the Jemez Mountains, north-central New Mexico

Treesearch

Anne C. Tillery; Jessica Haas

2016-01-01

Wildfire can substantially increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although the exact location, extent, and severity of wildfire or subsequent rainfall intensity and duration cannot be known, probabilities of fire and debris‑flow...

Limiting the immediate and subsequent hazards associated with wildfires

USGS Publications Warehouse

DeGraff, Jerome V.; Cannon, Susan H.; Parise, Mario

2013-01-01

Similarly, our capability to limit impacts from post-fire debris flows is improving. Empirical models for estimating the probability of debris-flow occurrence, the volume of such an event, and mapping the inundated area, linked with improved definitions of the rainfall conditions that trigger debris flows, can be used to provide critical information for post-fire hazard mitigation and emergency-response planning.

Impact of the 2008 Wenchuan earthquake in China on subsequent long-term debris flow activities in the epicentral area

NASA Astrophysics Data System (ADS)

Zhang, S.; Zhang, L. M.

2017-01-01

The 2008 Wenchuan earthquake triggered the largest number of landslides among the recent strong earthquake events around the world. The loose landslide materials were retained on steep terrains and deep gullies. In the period from 2008 to 2015, numerous debris flows occurred during rainstorms along the Provincial Road 303 (PR303) near the epicentre of the earthquake, causing serious damage to the reconstructed highway. Approximately 5.24 × 106 m3 of debris-flow sediment was deposited shortly after the earthquake. This paper evaluates the evolution of the debris flows that occurred after the Wenchuan earthquake, which helps understand long-term landscape evolution and cascading effects in regions impacted by mega earthquakes. With the aid of a GIS platform combined with field investigations, we continuously tracked movements of the loose deposit materials in all the debris flow gullies along an 18 km reach of PR303 and the characteristics of the regional debris flows during several storms in the past seven years. This paper presents five important aspects of the evolution of debris flows: (1) supply of debris flow materials; (2) triggering rainfall; (3) initiation mechanisms and types of debris flows; (4) runout characteristics; and (5) elevated riverbed due to the deposited materials from the debris flows. The hillslope soil deposits gradually evolved into channel deposits and the solid materials in the channels moved towards the ravine mouth. Accordingly, channelized debris flows became dominant gradually. Due to the decreasing source material volume and changes in debris flow characteristics, the triggering rainfall tends to increase from 30 mm h- 1 in 2008 to 64 mm h- 1 in 2013, and the runout distance tends to decrease over time. The runout materials blocked the river and elevated the riverbed by at least 30 m in parts of the study area. The changes in the post-seismic debris flow activity can be categorized into three stages, i.e., active, unstable, and recession.

A Warning System for Rainfall-Induced Debris Flows: A Integrated Remote Sensing and Data Mining Approach

NASA Astrophysics Data System (ADS)

Elkadiri, R.; Sultan, M.; Nurmemet, I.; Al Harbi, H.; Youssef, A.; Elbayoumi, T.; Zabramwi, Y.; Alzahrani, S.; Bahamil, A.

2014-12-01

We developed methodologies that heavily rely on observations extracted from a wide-range of remote sensing data sets (TRMM, Landsat ETM, ENVISAT, ERS, SPOT, Orbview, GeoEye) to develop a warning system for rainfall-induced debris flows in the Jazan province in the Red Sea Hills. The developed warning system integrates static controlling factors and dynamic triggering factors. The algorithm couples a susceptibility map with a rainfall I-D curve, both are developed using readily available remote sensing datasets. The static susceptibility map was constructed as follows: (1) an inventory was compiled for debris flows identified from high spatial resolution datasets and field verified; (2) 10 topographical and land cover predisposing factors (i.e. slope angle, slope aspect, normalized difference vegetation index, topographical position index, stream power index, flow accumulation, distance to drainage line, soil weathering index, elevation and topographic wetness index) were generated; (3) an artificial neural network model (ANN) was constructed, optimized and validated; (4) a debris-flow susceptibility map was generated using the ANN model and refined (using differential backscatter coefficient radar images). The rainfall threshold curve was derived as follows: (1) a spatial database was generated to host temporal co-registered and radiometrically and atmospherically corrected Landsat images; (2) temporal change detection images were generated for pairs of successively acquired Landsat images and criteria were established to identify "the change" related to debris flows, (3) the duration and intensity of the precipitation event that caused each of the identified debris flow events was assumed to be that of the most intense event within the investigated period; and (4) the I-D curve was extracted using data (intensity and duration of precipitation) for the inventoried events. Our findings include: (1) the spatial controlling factors with the highest predictive power of debris-flow locations are: topographic position index, slope, NDVI and distance to drainage line; (2) the ANN model showed an excellent prediction performance (area under receiver operating characteristic [ROC] curve: 0.961); 3) the preliminary I-D curve is I=39.797×D-0.7355 (I: Intensity and D: duration).

Debris flows in Grand Canyon National Park, Arizona: magnitude, frequency and effects on the Colorado River

USGS Publications Warehouse

Melis, Theodre S.; Webb, Robert H.; ,

1993-01-01

Debris flows are recurrent sediment-transport processes in 525 tributaries of the Colorado River in Grand Canyon. Arizona. Initiated by slope failures in bedrock and (or) colluvium during intense rainfall, Grand Canyon debris flows are high-magnitude, short-duration floods. Debris flows in these tributaries transport very large boulders into the river where they accumulate on debris fans and form rapids. The frequency of debris flows range from less than 1 per century to 10 or more per century in these tributaries. Before regulation by Glen Canyon Dam in 1963, high-magnitude floods on the Colorado River reworked debris fans by eroding all particles except large boulders. Because flow regulation has substantially decreased the river's competence, debris flows occurring after 1963 have increased accumulation of finer-grained sediments on debris fans and in rapids.

Frequency and magnitude of selected historical landslide events in the southern Appalachian Highlands of North Carolina and Virginia: relationships to rainfall, geological and ecohydrological controls, and effects

Treesearch

Richard M. Wooten; Anne C. Witt; Chelcy F. Miniat; Tristram C. Hales; Jennifer L. Aldred

2016-01-01

Landsliding is a recurring process in the southern Appalachian Highlands (SAH) region of the Central Hardwood Region. Debris flows, dominant among landslide processes in the SAH, are triggered when rainfall increases pore-water pressures in steep, soil-mantled slopes. Storms that trigger hundreds of debris flows occur about every 9 years and those that...

Radar-based quantitative precipitation estimation for the identification of debris flow occurrence over earthquake-affected regions in Sichuan, China

NASA Astrophysics Data System (ADS)

Shi, Zhao; Wei, Fangqiang; Chandrasekar, Venkatachalam

2018-03-01

Both Ms 8.0 Wenchuan earthquake on 12 May 2008 and Ms 7.0 Lushan earthquake on 20 April 2013 occurred in the province of Sichuan, China. In the earthquake-affected mountainous area, a large amount of loose material caused a high occurrence of debris flow during the rainy season. In order to evaluate the rainfall intensity-duration (I-D) threshold of the debris flow in the earthquake-affected area, and to fill up the observational gaps caused by the relatively scarce and low-altitude deployment of rain gauges in this area, raw data from two S-band China New Generation Doppler Weather Radar (CINRAD) were captured for six rainfall events that triggered 519 debris flows between 2012 and 2014. Due to the challenges of radar quantitative precipitation estimation (QPE) over mountainous areas, a series of improvement measures are considered: a hybrid scan mode, a vertical reflectivity profile (VPR) correction, a mosaic of reflectivity, a merged rainfall-reflectivity (R - Z) relationship for convective and stratiform rainfall, and rainfall bias adjustment with Kalman filter (KF). For validating rainfall accumulation over complex terrains, the study areas are divided into two kinds of regions by the height threshold of 1.5 km from the ground. Three kinds of radar rainfall estimates are compared with rain gauge measurements. It is observed that the normalized mean bias (NMB) is decreased by 39 % and the fitted linear ratio between radar and rain gauge observation reaches at 0.98. Furthermore, the radar-based I-D threshold derived by the frequentist method is I = 10.1D-0.52 and is underestimated by uncorrected raw radar data. In order to verify the impacts on observations due to spatial variation, I-D thresholds are identified from the nearest rain gauge observations and radar observations at the rain gauge locations. It is found that both kinds of observations have similar I-D thresholds and likewise underestimate I-D thresholds due to undershooting at the core of convective rainfall. It is indicated that improvement of spatial resolution and measuring accuracy of radar observation will lead to the improvement of identifying debris flow occurrence, especially for events triggered by the strong small-scale rainfall process in the study area.

Magnitude-Based Postfire Debris Flow Rainfall Accumulation-Duration Thresholds for Emergency-Response Planning

NASA Astrophysics Data System (ADS)

Cannon, S. H.; Boldt, E. M.; Laber, J. L.; Kean, J. W.; Staley, D. M.

2011-12-01

Following wildfires, emergency-response and public-safety agencies can be faced with evacuation and resource-deployment decisions well in advance of coming winter storms and during storms themselves. Information critical to these decisions is needed for recently burned areas in the San Gabriel Mountains of southern California. A compilation of information on the hydrologic response to winter storms from recently burned areas in southern California steeplands is used to develop a system for classifying magnitudes of hydrologic response in this setting. The four-class system describes combinations of reported volumes of individual debris flows, consequences of debris flows and floods in an urban setting, and spatial extents of the hydrologic response. Magnitude 0 events show a negligible response, while Magnitude I events are characterized by small (<1,000 m3) debris flows or low-discharge floods produced from one or two drainage basins. A few culverts and storm drains may be blocked, a few streets may be partially flooded or blocked by water and debris, and a few buildings near the mountain front may be damaged. Magnitude II events are characterized by two to five moderately-sized (1,000 to 10,000 m3) debris flows or one large (>10,000 m3) event. Several culverts or storm drains may be blocked or fail, several streets may be flooded or completely blocked by water and debris, and buildings, streets, and bridges may be damaged or destroyed. Magnitude III events consist of widespread and abundant debris flows of volumes >10,000 m3 and high discharge flooding causing significant impact to the built environment. Many streets, storm drains, and streets may be completely blocked by debris, making many streets unsafe for travel. Several large buildings, sections of infrastructure corridors and bridges may be damaged or destroyed. The range of rainfall conditions associated with different magnitude classes are defined by correlating local rainfall data with the response magnitude information. Magnitude 0 events can be expected when within-storm rainfall accumulations (A) of given durations (D) fall below the threshold A=0.4D0.5. Magnitude I events can be expected when storm rainfall conditions are above the threshold A=0.4D0.5 and below A=0.5D0.6 for durations greater than 1 hour. Magnitude II events will be generated in response to rainfall accumulations and durations between A=0.4D0.5 and A=0.9D0.5 for durations less than one hour, and between A=0.5D0.6 and A=0.9D0.5 for durations greater than one hour. Magnitude III events can be expected in response to rainfall conditions above the threshold A=0.9D 0.5. Rainfall threshold-magnitude relations are linked with potential emergency-response actions as an emergency-response decision chart, which leads a user through steps to determine potential event magnitudes and identify possible evacuation and resource-deployment levels. Use of this information in the planning and response decision-making process could result in increased safety for both the public and emergency responders.

Emergency Assessment of Debris-Flow Hazards from Basins Burned by the Piru, Simi, and Verdale Fires of 2003, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Rupert, Michael G.; Michael, John A.

2003-01-01

These maps present preliminary assessments of the probability of debris-flow activity and estimates of peak discharges that can potentially be generated by debris-flows issuing from basins burned by the Piru, Simi and Verdale Fires of October 2003 in southern California in response to the 25-year, 10-year, and 2-year 1-hour rain storms. The probability maps are based on the application of a logistic multiple regression model that describes the percent chance of debris-flow production from an individual basin as a function of burned extent, soil properties, basin gradients and storm rainfall. The peak discharge maps are based on application of a multiple-regression model that can be used to estimate debris-flow peak discharge at a basin outlet as a function of basin gradient, burn extent, and storm rainfall. Probabilities of debris-flow occurrence for the Piru Fire range between 2 and 94% and estimates of debris flow peak discharges range between 1,200 and 6,640 ft3/s (34 to 188 m3/s). Basins burned by the Simi Fire show probabilities for debris-flow occurrence between 1 and 98%, and peak discharge estimates between 1,130 and 6,180 ft3/s (32 and 175 m3/s). The probabilities for debris-flow activity calculated for the Verdale Fire range from negligible values to 13%. Peak discharges were not estimated for this fire because of these low probabilities. These maps are intended to identify those basins that are most prone to the largest debris-flow events and provide information for the preliminary design of mitigation measures and for the planning of evacuation timing and routes.

Natural hazards on alluvial fans: the debris flow and flash flood disaster of December 1999, Vargas state, Venezuela

USGS Publications Warehouse

Larsen, Matthew C.; Wieczorek, Gerald F.; Eaton, L.S.; Torres-Sierra, Heriberto; Sylva, Walter F.

2001-01-01

Large populations live on or near alluvial fans in locations such as Los Angeles, California, Salt Lake City, Utah, Denver, Colorado, and lesser known areas such as Sarno, Italy, and Vargas, Venezuela. Debris flows and flash floods occur episodically in these alluvial fan environments, and place many communities at high risk during intense and prolonged rainfall. In December 1999, rainstorms induced thousands of landslides along the Cordillera de la Costa, Vargas, Venezuela. Rainfall accumulation of 293 mm during the first 2 weeks of December was followed by an additional 911 mm of rainfall on December 14 through 16. Debris flows and floods inundated coastal communities resulting in a catastrophic death toll of as many as 30,000 people. Flash floods and debris flows caused severe property destruction on alluvial fans at the mouths of the coastal mountain drainage network. In time scales spanning thousands of years, the alluvial fans along this Caribbean coastline are dynamic zones of high geomorphic activity. Because most of the coastal zone in Vargas consists of steep mountain fronts that rise abruptly from the Caribbean Sea, the alluvial fans provide practically the only flat areas upon which to build. Rebuilding and reoccupation of these areas requires careful determination of hazard zones to avoid future loss of life and property. KEY TERMS: Debris flows, flash floods, alluvial fans, natural hazards, landslides, Venezuela

Transient hazard model using radar data for predicting debris flows in Madison County, Virginia

USGS Publications Warehouse

Morrissey, M.M.; Wieczorek, G.F.; Morgan, B.A.

2004-01-01

During the rainstorm of June 27, 1995, roughly 330-750 mm of rain fell within a 16-hour period, initiating floods and over 600 debris flows in a small area (130 km2) of Madison County, VA. We developed a distributed version of Iverson's transient response model for regional slope stability analysis for the Madison County debris flows. This version of the model evaluates pore-pressure head response and factor of safety on a regional scale in areas prone to rainfall-induced shallow (<2-3 m) landslides. These calculations used soil properties of shear strength and hydraulic conductivity from laboratory measurements of soil samples collected from field sites where debris flows initiated. Rainfall data collected by radar every 6 minutes provided a basis for calculating the temporal variation of slope stability during the storm. The results demonstrate that the spatial and temporal variation of the factor of safety correlates with the movement of the storm cell. When the rainstorm was treated as two separate rainfall events and a larger hydraulic conductivity and friction angle than the laboratory values were used, the timing and location of landslides predicted by the model were in closer agreement with eyewitness observations of debris flows. Application of spatially variable initial pre-storm water table depth and soil properties may improve both the spatial and temporal prediction of instability.

Using Logistic Regression to Predict the Probability of Debris Flows in Areas Burned by Wildfires, Southern California, 2003-2006

USGS Publications Warehouse

Rupert, Michael G.; Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.; Helsel, Dennis R.

2008-01-01

Logistic regression was used to develop statistical models that can be used to predict the probability of debris flows in areas recently burned by wildfires by using data from 14 wildfires that burned in southern California during 2003-2006. Twenty-eight independent variables describing the basin morphology, burn severity, rainfall, and soil properties of 306 drainage basins located within those burned areas were evaluated. The models were developed as follows: (1) Basins that did and did not produce debris flows soon after the 2003 to 2006 fires were delineated from data in the National Elevation Dataset using a geographic information system; (2) Data describing the basin morphology, burn severity, rainfall, and soil properties were compiled for each basin. These data were then input to a statistics software package for analysis using logistic regression; and (3) Relations between the occurrence or absence of debris flows and the basin morphology, burn severity, rainfall, and soil properties were evaluated, and five multivariate logistic regression models were constructed. All possible combinations of independent variables were evaluated to determine which combinations produced the most effective models, and the multivariate models that best predicted the occurrence of debris flows were identified. Percentage of high burn severity and 3-hour peak rainfall intensity were significant variables in all models. Soil organic matter content and soil clay content were significant variables in all models except Model 5. Soil slope was a significant variable in all models except Model 4. The most suitable model can be selected from these five models on the basis of the availability of independent variables in the particular area of interest and field checking of probability maps. The multivariate logistic regression models can be entered into a geographic information system, and maps showing the probability of debris flows can be constructed in recently burned areas of southern California. This study demonstrates that logistic regression is a valuable tool for developing models that predict the probability of debris flows occurring in recently burned landscapes.

Using Logistic Regression To Predict the Probability of Debris Flows Occurring in Areas Recently Burned By Wildland Fires

USGS Publications Warehouse

Rupert, Michael G.; Cannon, Susan H.; Gartner, Joseph E.

2003-01-01

Logistic regression was used to predict the probability of debris flows occurring in areas recently burned by wildland fires. Multiple logistic regression is conceptually similar to multiple linear regression because statistical relations between one dependent variable and several independent variables are evaluated. In logistic regression, however, the dependent variable is transformed to a binary variable (debris flow did or did not occur), and the actual probability of the debris flow occurring is statistically modeled. Data from 399 basins located within 15 wildland fires that burned during 2000-2002 in Colorado, Idaho, Montana, and New Mexico were evaluated. More than 35 independent variables describing the burn severity, geology, land surface gradient, rainfall, and soil properties were evaluated. The models were developed as follows: (1) Basins that did and did not produce debris flows were delineated from National Elevation Data using a Geographic Information System (GIS). (2) Data describing the burn severity, geology, land surface gradient, rainfall, and soil properties were determined for each basin. These data were then downloaded to a statistics software package for analysis using logistic regression. (3) Relations between the occurrence/non-occurrence of debris flows and burn severity, geology, land surface gradient, rainfall, and soil properties were evaluated and several preliminary multivariate logistic regression models were constructed. All possible combinations of independent variables were evaluated to determine which combination produced the most effective model. The multivariate model that best predicted the occurrence of debris flows was selected. (4) The multivariate logistic regression model was entered into a GIS, and a map showing the probability of debris flows was constructed. The most effective model incorporates the percentage of each basin with slope greater than 30 percent, percentage of land burned at medium and high burn severity in each basin, particle size sorting, average storm intensity (millimeters per hour), soil organic matter content, soil permeability, and soil drainage. The results of this study demonstrate that logistic regression is a valuable tool for predicting the probability of debris flows occurring in recently-burned landscapes.

Are erosion regimes in SE Australian forests responding to anthropogenic climate change?

NASA Astrophysics Data System (ADS)

Nyman, P.; Rutherfurd, I.; Lane, P. N. J.; Sheridan, G. J.

2017-12-01

In southeast Australia a series of exceptional climate events over the last decade have resulted in widespread debris flow activity across the region. The Millennium Drought (1996-2010), extreme fire-weather and record breaking rainfall in the La Nina year of 2011 have all contributed to an intensification of processes such as runoff production and mass failures that lead to debris flows. Debris flows in landmark locations such as the Grampians and Wilsons Promontory National Parks in 2011 were triggered by mass failure as a result of large volumes of intense summer rainfall. Runoff generated debris flows in burned areas have been occurring regularly and in large numbers along the East Coast Dividing Range from the Warrumbungle Mountains (New South Wales) in the north to Kinglake (Victoria) in the south. In northeast Victoria debris flows have been delivering sediment to the Ovens River following wildfires in 2003, 2007, 2009 and in 2013. The impact of these erosion events on infrastructure, water quality and aquatic ecosystems are considerable and important questions are emerging around i) how frequently events have occurred in the past, ii) the importance of fire as a geomorphic agent, and iii) the effects of climate change on erosion regimes. In this paper we investigate the conditions under which these debris flows occurred, and examine the underlying climatic events in context of historical records. Using data on rainfall distributions and fire history dating back to the 1960s we quantify the frequency with which catchments are primed for extreme erosion events. With these data we begin to speculate on whether or not current catchment conditions (e.g. soil depths, colluvial storage and accumulation rate) is consistent with the erosion regimes we observe. The broader aim of our research is to quantify debris flow thresholds using geophysical response models and use these models to determine the sensitivity of debris flow frequency to climatic forcing. In the presentation we outline a conceptual framework for combining such models with data on past debris flow activity to conduct an attribution study into the effect of anthropogenic climate change on erosion regimes in southeast Australian temperate forests.

Contrasting rainfall generated debris flows from adjacent watersheds at Forest Falls, southern California, USA

USGS Publications Warehouse

Morton, D.M.; Alvarez, R.M.; Ruppert, K.R.; Goforth, B.

2008-01-01

Debris flows are widespread and common in many steeply sloping areas of southern California. The San Bernardino Mountains community of Forest Falls is probably subject to the most frequently documented debris flows in southern California. Debris flows at Forest Falls are generated during short-duration high-intensity rains that mobilize surface material. Except for debris flows on two consecutive days in November 1965, all the documented historic debris flows have occurred during high-intensity summer rainfall, locally referred to as 'monsoon' or 'cloudburst' rains. Velocities of the moving debris range from about 5??km/h to about 90??km/h. Velocity of a moving flow appears to be essentially a function of the water content of the flow. Low velocity debris flows are characterized by steep snouts that, when stopped, have only small amounts of water draining from the flow. In marked contrast are high-velocity debris flows whose deposits more resemble fluvial deposits. In the Forest Falls area two adjacent drainage basins, Snow Creek and Rattlesnake Creek, have considerably different histories of debris flows. Snow Creek basin, with an area about three times as large as Rattlesnake Creek basin, has a well developed debris flow channel with broad levees. Most of the debris flows in Snow Creek have greater water content and attain higher velocities than those of Rattlesnake Creek. Most debris flows are in relative equilibrium with the geometry of the channel morphology. Exceptionally high-velocity flows, however, overshoot the channel walls at particularly tight channel curves. After overshooting the channel, the flows degrade the adjacent levee surface and remove trees and structures in the immediate path, before spreading out with decreasing velocity. As the velocity decreases the clasts in the debris flows pulverize the up-slope side of the trees and often imbed clasts in them. Debris flows in Rattlesnake Creek are relatively slow moving and commonly stop in the channel. After the channel is blocked, subsequent debris flows cut a new channel upstream from the blockage that results in the deposition of new debris-flow deposits on the lower part of the fan. Shifting the location of debris flows on the Rattlesnake Creek fan tends to prevent trees from becoming mature. Dense growths of conifer seedlings sprout in the spring on the late summer debris flow deposits. This repeated process results in stands of even-aged trees whose age records the age of the debris flows. ?? 2007.

Triggering conditions and mobility of debris flows associated to complex earthflows

NASA Astrophysics Data System (ADS)

Malet, J.-P.; Laigle, D.; Remaître, A.; Maquaire, O.

2005-03-01

Landslides on black marl slopes of the French Alps are, in most cases, complex catastrophic failures in which the initial structural slides transform into slow-moving earthflows. Under specific hydrological conditions, these earthflows can transform into debris flows. Due to their sediment volume and their high mobility, debris flow induced by landslides are far much dangerous than these resulting from continuous erosive processes. A fundamental point to correctly delineate the area exposed to debris flows on the alluvial fans is therefore to understand why and how some earthflows transform into debris flow while most of them stabilize. In this paper, a case of transformation from earthflow to debris flow is presented and analysed. An approach combining geomorphology, hydrology, geotechnics and rheology is adopted to model the debris flow initiation (failure stage) and its runout (postfailure stage). Using the Super-Sauze earthflow (Alpes-de-Haute-Provence, France) as a case study, the objective is to characterize the hydrological and mechanical conditions leading to debris flow initiation in such cohesive material. Results show a very good agreement between the observed runout distances and these calculated using the debris flow modeling code Cemagref 1-D. The deposit thickness in the depositional area and the velocities of the debris flows are also well reproduced. Furthermore, a dynamic slope stability analysis shows that conditions in the debris source area under average pore water pressures and moisture contents are close to failure. A small excess of water can therefore initiate failure. Seepage analysis is used to estimate the volume of debris that can be released for several hydroclimatic conditions. The failed volumes are then introduced in the Cemagref 1-D runout code to propose debris flow hazard scenarios. Results show that clayey earthflow can transform under 5-year return period rainfall conditions into 1-km runout debris flow of volumes ranging between 2000 to 5000 m 3. Slope failures induced by 25-year return period rainfall can trigger large debris flow events (30,000 to 50,000 m 3) that can reach the alluvial fan and cause damage.

Experimental Exploration on Rainfall-induced Mass Re-mobilization after Giant Earthquake: A case study in Wenchuan earthquake hit region, China

NASA Astrophysics Data System (ADS)

Yang, Zongji; Bogaard, Thom. A.; Qiao, Jianping; Jiang, Yuanjun

2015-04-01

Prevention and mitigation of rainfall induced geological hazards after the Ms=8 Wenchuan earthquake on May 12th, 2008 were gained more significance for the rebuild of earthquake hit regions in China. After the Wenchuan earthquake, there were thousands of slopes failure, which were much more susceptible to subsequent heavy rainfall and many even transformed into potential debris flows. An typical example can be found in the catastrophic disaster occurred in Zhongxing County, Chengdu City on 10th July, 2013 in which the unknown fractured slope up the mountain was triggered by a downpour and transformed into subsequent debris flow which wiped the community downstream, about 200 victims were reported in that tragic event. The transform patterns of rainfall-induced mass re-mobilization was categorized into three major type as the erosion of fractured slopes, initiate on loosen deposit and outbreak of landslide (debris flow) dams according to vast field investigation in the earthquake hit region. Despite the widespread and hidden characters,the complexity of the process also demonstrated in the transforms of the mass re-mobilized by the erosion of both gravity and streams in the small watersheds which have never been reported before the giant Wenchuan Earthquake in many regions. As a result, an increasing number of questions for disaster relief and mitigation were proposed including the threshold of early warning and measurement of the volume for the design of mitigation measures on rainfall-induced mass re-mobilization in debris flow gullies. This study is aimed for answer the essential questions about the threshold and amount of mass initiation triggered by the subsequent rainfall in post earthquake time. In this study, experimental tests were carried out for simulating the failure of the rainfall-induced mass re-mobilization in respectively in a natural co-seismic fractured slope outside and the debris flow simulation platform inside the laboratory. A natural fractured slope was selected to conduct the field experimental test,after the field experimental test, the correlation of rainfall parameters, deformation criterion and water content as well as the failure volume of gravity erosion was investigated. In addition, the loosen mass re-mobilized by the stream was also simulated by the model experiment by which the correlation of rainfall thresholds, and the initial volume of mass triggered by the flow was analyzed. Thus, the threshold and volume measurement model for the initiation of mass re-mobilization were proposed by means of this experimental research. Despite of the fact that the simplicity of the model derived from experimental and empirical method and some drawbacks connected with the uncertainty and complexity of the geological phenomenon, the proposed method have contributed a lot in application for the early warning and prevention of mass transformed debris flows in earthquake hit region, China.

Mitigating mass movement caused by earthquakes and typhoons: a case study of central Taiwan

NASA Astrophysics Data System (ADS)

Lin, Jiun-Chuan

2013-04-01

Typhoons caused huge damages to Taiwan at the average of 3.8 times a year in the last 100 years, according to Central Weather Bureau data. After the Chi-Chi earthquake of 1999 at the magnitude of Richard Scale 7.3, typhoons with huge rainfall would cause huge debris flow and deposits at river channels. As a result of earthquakes, loose debris falls and flows became significant hazards in central Taiwan. Analysis of rainfall data and data about the sites of slope failure show that damage from natural hazards was enhanced in the last 20 years, as a result of the Chi-Chi earthquake. There are three main types of mass movement in Central Taiwan: landslides, debris flows and gully erosion. Landslides occurred mainly along hill slopes and river channel banks. Many dams, check dams, housing structures and even river channels can be raised to as high as 60 meters as a result of stacking up floating materials of landslides. Debris flows occurred mainly through typhoon periods and activated ancient debris deposition. New gullies were thus developed from deposits loosened and shaken up by earthquakes. Extreme earthquakes and typhoon events occurred frequently in the last 20 years. This paper analyzes the geological and geomorphologic background for the precarious areas and typhoons in central Taiwan, to make a systematic understanding of mass movement harzards. The mechanism and relations of debris flows and rainfall data in central Taiwan are analyzed. Ways for mitigating mass movement threats are also proposed in this paper. Keywords: mass movement, earthquakes, typhoons, hazard mitigation, central Ta

Probability and volume of potential postwildfire debris flows in the 2010 Fourmile burn area, Boulder County, Colorado

USGS Publications Warehouse

Ruddy, Barbara C.; Stevens, Michael R.; Verdin, Kristine

2010-01-01

This report presents a preliminary emergency assessment of the debris-flow hazards from drainage basins burned by the Fourmile Creek fire in Boulder County, Colorado, in 2010. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and volumes of debris flows for selected drainage basins. Data for the models include burn severity, rainfall total and intensity for a 25-year-recurrence, 1-hour-duration rainstorm, and topographic and soil property characteristics. Several of the selected drainage basins in Fourmile Creek and Gold Run were identified as having probabilities of debris-flow occurrence greater than 60 percent, and many more with probabilities greater than 45 percent, in response to the 25-year recurrence, 1-hour rainfall. None of the Fourmile Canyon Creek drainage basins selected had probabilities greater than 45 percent. Throughout the Gold Run area and the Fourmile Creek area upstream from Gold Run, the higher probabilities tend to be in the basins with southerly aspects (southeast, south, and southwest slopes). Many basins along the perimeter of the fire area were identified as having low probability of occurrence of debris flow. Volume of debris flows predicted from drainage basins with probabilities of occurrence greater than 60 percent ranged from 1,200 to 9,400 m3. The predicted moderately high probabilities and some of the larger volumes responses predicted for the modeled storm indicate a potential for substantial debris-flow effects to buildings, roads, bridges, culverts, and reservoirs located both within these drainages and immediately downstream from the burned area. However, even small debris flows that affect structures at the basin outlets could cause considerable damage.

Rainfall thresholds for the initiation of debris flows at La Honda, California

USGS Publications Warehouse

Wilson, R.C.; Wieczorek, G.F.

1995-01-01

A simple numerical model, based on the physical analogy of a leaky barrel, can simulate significant features of the interaction between rainfall and shallow-hillslope pore pressures. The leaky-barrel-model threshold is consistent with, but slightly higher than, an earlier, purely empirical, threshold. The number of debris flows triggered by a storm can be related to the time and amount by which the leaky-barrel-model response exceeded the threshold during the storm. -from Authors

Model simulations of flood and debris flow timing in steep catchments after wildfire

NASA Astrophysics Data System (ADS)

Rengers, F. K.; McGuire, L. A.; Kean, J. W.; Staley, D. M.; Hobley, D. E. J.

2016-08-01

Debris flows are a typical hazard on steep slopes after wildfire, but unlike debris flows that mobilize from landslides, most postwildfire debris flows are generated from water runoff. The majority of existing debris flow modeling has focused on landslide-triggered debris flows. In this study we explore the potential for using process-based rainfall-runoff models to simulate the timing of water flow and runoff-generated debris flows in recently burned areas. Two different spatially distributed hydrologic models with differing levels of complexity were used: the full shallow water equations and the kinematic wave approximation. Model parameter values were calibrated in two different watersheds, spanning two orders of magnitude in drainage area. These watersheds were affected by the 2009 Station Fire in the San Gabriel Mountains, CA, USA. Input data for the numerical models were constrained by time series of soil moisture, flow stage, and rainfall collected at field sites, as well as high-resolution lidar-derived digital elevation models. The calibrated parameters were used to model a third watershed in the burn area, and the results show a good match with observed timing of flow peaks. The calibrated roughness parameter (Manning's n) was generally higher when using the kinematic wave approximation relative to the shallow water equations, and decreased with increasing spatial scale. The calibrated effective watershed hydraulic conductivity was low for both models, even for storms occurring several months after the fire, suggesting that wildfire-induced changes to soil-water infiltration were retained throughout that time. Overall, the two model simulations were quite similar suggesting that a kinematic wave model, which is simpler and more computationally efficient, is a suitable approach for predicting flood and debris flow timing in steep, burned watersheds.

Model simulations of flood and debris flow timing in steep catchments after wildfire

USGS Publications Warehouse

Rengers, Francis K.; McGuire, Luke; Kean, Jason W.; Staley, Dennis M.; Hobley, D.E.J

2016-01-01

Debris flows are a typical hazard on steep slopes after wildfire, but unlike debris flows that mobilize from landslides, most post-wildfire debris flows are generated from water runoff. The majority of existing debris-flow modeling has focused on landslide-triggered debris flows. In this study we explore the potential for using process-based rainfall-runoff models to simulate the timing of water flow and runoff-generated debris flows in recently burned areas. Two different spatially distributed hydrologic models with differing levels of complexity were used: the full shallow water equations and the kinematic wave approximation. Model parameter values were calibrated in two different watersheds, spanning two orders of magnitude in drainage area. These watersheds were affected by the 2009 Station Fire in the San Gabriel Mountains, CA, USA. Input data for the numerical models were constrained by time series of soil moisture, flow stage, and rainfall collected at field sites, as well as high-resolution lidar-derived digital elevation models. The calibrated parameters were used to model a third watershed in the burn area, and the results show a good match with observed timing of flow peaks. The calibrated roughness parameter (Manning's $n$) was generally higher when using the kinematic wave approximation relative to the shallow water equations, and decreased with increasing spatial scale. The calibrated effective watershed hydraulic conductivity was low for both models, even for storms occurring several months after the fire, suggesting that wildfire-induced changes to soil-water infiltration were retained throughout that time. Overall the two model simulations were quite similar suggesting that a kinematic wave model, which is simpler and more computationally efficient, is a suitable approach for predicting flood and debris flow timing in steep, burned watersheds.

Analysis of rainfall characteristics and its related disasters of slag disposal pit of a certain Gold-Copper Deposit in Fujian province

NASA Astrophysics Data System (ADS)

Pan, Huali; Hu, Mingjian; Ou, Guoqiang

2017-04-01

According to the geological investigation in Fujian province, the total number of geological disasters was 9513, in which the number of landslide, collapse, unstable slope and surface collapse was 5816, 1888, 1591, 103 and 115 respectively. The main geological disaster was the landslide with 61.1% of total geological disasters. Among all these geological disasters, only 6.0% was relative stable, 17.0% was basic stable, nearly 76.0% was unstable. The slope disaster was the main geological disaster, if the unstable slope was the potential landslide or collapse; the slope collapse was 98.0% of all geological disasters. The rainfall, in particular the heavy rain, was direct dynamic factor for geological disasters, but the occurrence probability of geological disasters was different because of the sensitivity of the geological environment though of the same intensity rainfall. To obtain the characteristics of soil erosion under the rainfall condition, the rainfall characteristics and its related disasters of slag disposal pit of a certain Gold-Copper Deposit in Fujian province was analyzed by the meteorological and rainfall data. According to the distribution of monitoring stations of hydrological and rainfall in Longyan city of Fujian province and the location of gold-copper deposit, the Shanghang monitoring station of hydrological and rainfall was chosen, which is the nearest one to the gold-copper deposit. Then main parameters of the prediction model, the antecedent precipitation, the rainfall on the day and the rainfall threshold, were calculated by using the rainfall data from 2002 to 2010. And the relationship between geological disasters and the rainfall characteristics were analyzed. The results indicated that there was high risk for the debris flow with landslide collapse when either the daily rainfall was more than 100.0 mm, or the total rainfall was more than 136.0mm in the gold-copper deposit and the Shanghang region. At the same time, although there was few risk for the debris flow when the daily rainfall was between 50.0-100.0mm, once the soil was saturated or nearly saturated because of the continuous antecedent precipitation, debris flow disaster would occur even the daily rainfall was only 50.0mm. In addition, it was prone to trigger debris flow disaster when the daily heavy rainfall was more than 100.0mm or the torrential rainfall in 3 days was between 250.0 -300.0mm.

STEP-TRAMM - A modeling interface for simulating localized rainfall induced shallow landslides and debris flow runout pathways

NASA Astrophysics Data System (ADS)

Or, D.; von Ruette, J.; Lehmann, P.

2017-12-01

Landslides and subsequent debris-flows initiated by rainfall represent a common natural hazard in mountainous regions. We integrated a landslide hydro-mechanical triggering model with a simple model for debris flow runout pathways and developed a graphical user interface (GUI) to represent these natural hazards at catchment scale at any location. The STEP-TRAMM GUI provides process-based estimates of the initiation locations and sizes of landslides patterns based on digital elevation models (SRTM) linked with high resolution global soil maps (SoilGrids 250 m resolution) and satellite based information on rainfall statistics for the selected region. In the preprocessing phase the STEP-TRAMM model estimates soil depth distribution to supplement other soil information for delineating key hydrological and mechanical properties relevant to representing local soil failure. We will illustrate this publicly available GUI and modeling platform to simulate effects of deforestation on landslide hazards in several regions and compare model outcome with satellite based information.

Systems and Sensors for Debris-flow Monitoring and Warning

PubMed Central

Arattano, Massimo; Marchi, Lorenzo

2008-01-01

Debris flows are a type of mass movement that occurs in mountain torrents. They consist of a high concentration of solid material in water that flows as a wave with a steep front. Debris flows can be considered a phenomenon intermediate between landslides and water floods. They are amongst the most hazardous natural processes in mountainous regions and may occur under different climatic conditions. Their destructiveness is due to different factors: their capability of transporting and depositing huge amounts of solid materials, which may also reach large sizes (boulders of several cubic meters are commonly transported by debris flows), their steep fronts, which may reach several meters of height and also their high velocities. The implementation of both structural and non-structural control measures is often required when debris flows endanger routes, urban areas and other infrastructures. Sensor networks for debris-flow monitoring and warning play an important role amongst non-structural measures intended to reduce debris-flow risk. In particular, debris flow warning systems can be subdivided into two main classes: advance warning and event warning systems. These two classes employ different types of sensors. Advance warning systems are based on monitoring causative hydrometeorological processes (typically rainfall) and aim to issue a warning before a possible debris flow is triggered. Event warning systems are based on detecting debris flows when these processes are in progress. They have a much smaller lead time than advance warning ones but are also less prone to false alarms. Advance warning for debris flows employs sensors and techniques typical of meteorology and hydrology, including measuring rainfall by means of rain gauges and weather radar and monitoring water discharge in headwater streams. Event warning systems use different types of sensors, encompassing ultrasonic or radar gauges, ground vibration sensors, videocameras, avalanche pendulums, photocells, trip wires etc. Event warning systems for debris flows have a strong linkage with debris-flow monitoring that is carried out for research purposes: the same sensors are often used for both monitoring and warning, although warning systems have higher requirements of robustness than monitoring systems. The paper presents a description of the sensors employed for debris-flow monitoring and event warning systems, with attention given to advantages and drawbacks of different types of sensors. PMID:27879828

Predicting sediment delivery from debris flows after wildfire

NASA Astrophysics Data System (ADS)

Nyman, Petter; Smith, Hugh G.; Sherwin, Christopher B.; Langhans, Christoph; Lane, Patrick N. J.; Sheridan, Gary J.

2015-12-01

Debris flows are an important erosion process in wildfire-prone landscapes. Predicting their frequency and magnitude can therefore be critical for quantifying risk to infrastructure, people and water resources. However, the factors contributing to the frequency and magnitude of events remain poorly understood, particularly in regions outside western USA. Against this background, the objectives of this study were to i) quantify sediment yields from post-fire debris flows in southeast Australian highlands and ii) model the effects of landscape attributes on debris flow susceptibility. Sediment yields from post-fire debris flows (113-294 t ha- 1) are 2-3 orders of magnitude higher than annual background erosion rates from undisturbed forests. Debris flow volumes ranged from 539 to 33,040 m3 with hillslope contributions of 18-62%. The distribution of erosion and deposition above the fan were related to a stream power index, which could be used to model changes in yield along the drainage network. Debris flow susceptibility was quantified with a logistic regression and an inventory of 315 debris flow fans deposited in the first year after two large wildfires (total burned area = 2919 km2). The differenced normalised burn ratio (dNBR or burn severity), local slope, radiative index of dryness (AI) and rainfall intensity (from rainfall radar) were significant predictors in a susceptibility model, which produced excellent results in terms identifying channels that were eroded by debris flows (Area Under Curve, AUC = 0.91). Burn severity was the strongest predictor in the model (AUC = 0.87 when dNBR is used as single predictor) suggesting that fire regimes are an important control on sediment delivery from these forests. The analysis showed a positive effect of AI on debris flow probability in landscapes where differences in moisture regimes due to climate are associated with large variation in soil hydraulic properties. Overall, the results from this study based in the southeast Australian highlands provide a novel basis upon which to model sediment delivery from post-fire debris flows. The modelling approach has wider relevance to post-fire debris flow prediction both from risk management and landscape evolution perspectives.

Development of the Assessment Items of Debris Flow Using the Delphi Method

NASA Astrophysics Data System (ADS)

Byun, Yosep; Seong, Joohyun; Kim, Mingi; Park, Kyunghan; Yoon, Hyungkoo

2016-04-01

In recent years in Korea, Typhoon and the localized extreme rainfall caused by the abnormal climate has increased. Accordingly, debris flow is becoming one of the most dangerous natural disaster. This study aimed to develop the assessment items which can be used for conducting damage investigation of debris flow. Delphi method was applied to classify the realms of assessment items. As a result, 29 assessment items which can be classified into 6 groups were determined.

Postwildfire debris-flow hazard assessment of the area burned by the 2012 Little Bear Fire, south-central New Mexico

USGS Publications Warehouse

Tillery, Anne C.; Matherne, Anne Marie

2013-01-01

A preliminary hazard assessment was developed of the debris-flow potential from 56 drainage basins burned by the Little Bear Fire in south-central New Mexico in June 2012. The Little Bear Fire burned approximately 179 square kilometers (km2) (44,330 acres), including about 143 km2 (35,300 acres) of National Forest System lands of the Lincoln National Forest. Within the Lincoln National Forest, about 72 km2 (17,664 acres) of the White Mountain Wilderness were burned. The burn area also included about 34 km2 (8,500 acres) of private lands. Burn severity was high or moderate on 53 percent of the burn area. The area burned is at risk of substantial postwildfire erosion, such as that caused by debris flows and flash floods. A postwildfire debris-flow hazard assessment of the area burned by the Little Bear Fire was performed by the U.S. Geological Survey in cooperation with the U.S. Department of Agriculture Forest Service, Lincoln National Forest. A set of two empirical hazard-assessment models developed by using data from recently burned drainage basins throughout the intermountain Western United States was used to estimate the probability of debris-flow occurrence and volume of debris flows along the burn area drainage network and for selected drainage basins within the burn area. The models incorporate measures of areal burn extent and severity, topography, soils, and storm rainfall intensity to estimate the probability and volume of debris flows following the fire. Relative hazard rankings of postwildfire debris flows were produced by summing the estimated probability and volume ranking to illustrate those areas with the highest potential occurrence of debris flows with the largest volumes. The probability that a drainage basin could produce debris flows and the volume of a possible debris flow at the basin outlet were estimated for three design storms: (1) a 2-year-recurrence, 30-minute-duration rainfall of 27 millimeters (mm) (a 50 percent chance of occurrence in any given year); (2) a 10-year-recurrence, 30-minute-duration rainfall of 42 mm (a 10 percent chance of occurrence in any given year); and (3) a 25-year-recurrence, 30-minute-duration rainfall of 51 mm (a 4 percent chance of occurrence in any given year). Thirty-nine percent of the 56 drainage basins modeled have a high (greater than 80 percent) probability of debris flows in response to the 2-year design storm; 80 percent of the modeled drainage basins have a high probability of debris flows in response to the 25-year design storm. For debris-flow volume, 7 percent of the modeled drainage basins have an estimated debris-flow volume greater than 100,000 cubic meters (m3) in response to the 2-year design storm; 9 percent of the drainage basins are included in the greater than 100,000 m3 category for both the 10-year and the 25-year design storms. Drainage basins in the greater than 100,000 m3 volume category also received the highest combined hazard ranking. The maps presented herein may be used to prioritize areas where emergency erosion mitigation or other protective measures may be needed prior to rainstorms within these drainage basins, their outlets, or areas downstream from these drainage basins within the 2- to 3-year period of vulnerability. This work is preliminary and is subject to revision. The assessment herein is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government may be held liable for any damages resulting from the authorized or unauthorized use of the assessment.

NOAA/National Weather Service Support in Response to the Threat of Debris Flows from the 2009 Station Fire in Los Angeles County: Lessons Learned in Hazard Communications and Public Response

NASA Astrophysics Data System (ADS)

Jackson, M.; Laber, J. L.; Boldt, E.

2010-12-01

The National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service (NWS) and the United States Geological Survey (USGS) have developed a prototype debris flow early warning system for Southern California. The system uses USGS-defined rainfall rate thresholds for debris flows and burn area hazard maps to protect interests in and near burn areas of damaging and potentially deadly debris flows. Although common throughout Southern California, as witnessed by the December 25, 2003 storm in which sixteen people were swept to their deaths by debris flows generated from a recent burn area near Devore, debris flows are commonly misunderstood by the public. They are often perceived as rare events, are difficult to warn for with sufficient lead time, and present unique challenges when communicating proper calls to action to best save lives and property. Many improvements to the system have been realized since the project’s inception in 2005, including using more refined rainfall rate thresholds, use of burn area hazard maps, and the establishment of a tiered system to categorize the potential severity of flash floods and debris flows. These efforts have collectively resulted in a reduction of warning false alarms. However, the massive 400,000 hectare 2009 Station burn area in the Angeles National Forest of Los Angeles County has created numerous challenges to the early warning system. The geology of the area burned is highly susceptible to debris flows, due in part to the burn severity, soil types and steep slopes. Most importantly, the burn area is adjacent to and uphill of the highly populated lower foothills of the San Fernando Valley. NOAA/NWS and the USGS have thus worked closely with local response and preparedness agencies to analyze and communicate the threat and assist in developing a unified command response plan in preparation for flash flood and debris flows from this burn area. The early warning system was put to the ultimate test on February 6, 2010 when intense rainfall over the burn area produced very damaging but fortunately nonfatal flash flooding and debris flows. Unfortunately public and local agency response to NWS forecasts, watches, and warnings issued for this event was minimal. Possible causes of, and actions needed to improve upon, this minimal response are examined, including 1) complacency due to previous watch and warning false alarms, 2) underestimating the hazard threat due to local residents having not personally experienced a severe debris flow event in recent history if ever, 3) misinterpretation of NWS point precipitation forecasts and current limits of predictability related to forecasting specific locations and amounts of intense rainfall beyond 12-24 hours, 4) the challenges of ensuring NWS information is consistently received and interpreted among the multiple agencies and jurisdictions of the unified command, and 5) the likelihood that most people did not hear NWS warnings due to the event taking place late at night. Also examined are proper calls to action to protect life and property at a time when evacuations may put people in harm's way.

Coupled prediction of flood response and debris flow initiation during warm and cold season events in the Southern Appalachians, USA

NASA Astrophysics Data System (ADS)

Tao, J.; Barros, A. P.

2013-07-01

Debris flows associated with rainstorms are a frequent and devastating hazard in the Southern Appalachians in the United States. Whereas warm season events are clearly associated with heavy rainfall intensity, the same cannot be said for the cold season events. Instead, there is a relationship between large (cumulative) rainfall events independently of season, and thus hydrometeorological regime, and debris flows. This suggests that the dynamics of subsurface hydrologic processes play an important role as a trigger mechanism, specifically through soil moisture redistribution by interflow. The first objective of this study is to investigate this hypothesis. The second objective is to assess the physical basis for a regional coupled flood prediction and debris flow warning system. For this purpose, uncalibrated model simulations of well-documented debris flows in headwater catchments of the Southern Appalachians using a 3-D surface-groundwater hydrologic model coupled with slope stability models are examined in detail. Specifically, we focus on two vulnerable headwater catchments that experience frequent debris flows, the Big Creek and the Jonathan Creek in the Upper Pigeon River Basin, North Carolina, and three distinct weather systems: an extremely heavy summertime convective storm in 2011; a persistent winter storm lasting several days; and a severe winter storm in 2009. These events were selected due to the optimal availability of rainfall observations, availability of detailed field surveys of the landslides shortly after they occurred, which can be used to evaluate model predictions, and because they are representative of events that cause major economic losses in the region. The model results substantiate that interflow is a useful prognostic of conditions necessary for the initiation of slope instability, and should therefore be considered explicitly in landslide hazard assessments. Moreover, the relationships between slope stability and interflow are strongly modulated by the topography and catchment specific geomorphologic features that determine subsurface flow convergence zones. The three case-studies demonstrate the value of coupled prediction of flood response and debris flow initiation potential in the context of developing a regional hazard warning system.

Coupled prediction of flood response and debris flow initiation during warm- and cold-season events in the Southern Appalachians, USA

NASA Astrophysics Data System (ADS)

Tao, J.; Barros, A. P.

2014-01-01

Debris flows associated with rainstorms are a frequent and devastating hazard in the Southern Appalachians in the United States. Whereas warm-season events are clearly associated with heavy rainfall intensity, the same cannot be said for the cold-season events. Instead, there is a relationship between large (cumulative) rainfall events independently of season, and thus hydrometeorological regime, and debris flows. This suggests that the dynamics of subsurface hydrologic processes play an important role as a trigger mechanism, specifically through soil moisture redistribution by interflow. We further hypothesize that the transient mass fluxes associated with the temporal-spatial dynamics of interflow govern the timing of shallow landslide initiation, and subsequent debris flow mobilization. The first objective of this study is to investigate this relationship. The second objective is to assess the physical basis for a regional coupled flood prediction and debris flow warning system. For this purpose, uncalibrated model simulations of well-documented debris flows in headwater catchments of the Southern Appalachians using a 3-D surface-groundwater hydrologic model coupled with slope stability models are examined in detail. Specifically, we focus on two vulnerable headwater catchments that experience frequent debris flows, the Big Creek and the Jonathan Creek in the Upper Pigeon River Basin, North Carolina, and three distinct weather systems: an extremely heavy summertime convective storm in 2011; a persistent winter storm lasting several days; and a severe winter storm in 2009. These events were selected due to the optimal availability of rainfall observations; availability of detailed field surveys of the landslides shortly after they occurred, which can be used to evaluate model predictions; and because they are representative of events that cause major economic losses in the region. The model results substantiate that interflow is a useful prognostic of conditions necessary for the initiation of slope instability, and should therefore be considered explicitly in landslide hazard assessments. Moreover, the relationships between slope stability and interflow are strongly modulated by the topography and catchment-specific geomorphologic features that determine subsurface flow convergence zones. The three case studies demonstrate the value of coupled prediction of flood response and debris flow initiation potential in the context of developing a regional hazard warning system.

Soil slip/debris flow localized by site attributes and wind-driven rain in the San Francisco Bay region storm of January 1982

USGS Publications Warehouse

Pike, R.J.; Sobieszczyk, S.

2008-01-01

GIS analysis at 30-m resolution reveals that effectiveness of slope-destabilizing processes in the San Francisco Bay area varies with compass direction. Nearly half the soil slip/debris flows mapped after the catastrophic rainstorm of 3-5 January 1982 occurred on slopes that face S to WSW, whereas fewer than one-quarter have a northerly aspect. Azimuthal analysis of hillside properties for susceptible terrain near the city of Oakland suggests that the skewed aspect of these landslides primarily reflects vegetation type, ridge and valley alignment, and storm-wind direction. Bedrock geology, soil expansivity, and terrain height and gradient also were influential but less so; the role of surface curvature is not wholly resolved. Normalising soil-slip aspect by that of the region's NNW-striking topography shifts the modal azimuth of soil-slip aspect from SW to SE, the direction of origin of winds during the 1982 storm-but opposite that of the prevailing WNW winds. Wind from a constant direction increases rainfall on windward slopes while diminishing it on leeward slopes, generating a modelled difference in hydrologically effective rainfall of up to 2:1 on steep hillsides in the Oakland area. This contrast is consistent with numerical simulations of wind-driven rain and with rainfall thresholds for debris-flow activity. We conclude that storm winds from the SE in January 1982 raised the vulnerability of the Bay region's many S-facing hillsides, most of which are covered in shallow-rooted shrub and grass that offer minimal resistance to soil slip. Wind-driven rainfall also appears to have controlled debris-flow location in a major 1998 storm and probably others. Incorporating this overlooked influence into GIS models of debris-flow likelihood would improve predictions of the hazard in central California and elsewhere.

Debris Flow Simulation using FLO-2D on the 2004 Landslide Area of Real, General Nakar, and Infanta, Philippines

NASA Astrophysics Data System (ADS)

Llanes, F.; dela Resma, M.; Ferrer, P.; Realino, V.; Aquino, D. T.; Eco, R. C.; Lagmay, A.

2013-12-01

From November 14 to December 3, 2004, Luzon Island was ravaged by 4 successive typhoons: Typhoon Mufia, Tropical Storm Merbok, Tropical Depression Winnie, and Super Typhoon Nanmadol. Tropical Depression Winnie was the most destructive of the four when it triggered landslides on November 29 that devastated the municipalities of Infanta, General Nakar, and Real in Quezon Province, southeast Luzon. Winnie formed east of Central Luzon on November 27 before it moved west-northwestward over southeastern Luzon on November 29. A total of 1,068 lives were lost and more than USD 170 million worth of damages to crops and infrastructure were incurred from the landslides triggered by Typhoon Winnie on November 29 and the flooding caused by the 4 typhoons. FLO-2D, a flood routing software for generating flood and debris flow hazard maps, was utilized to simulate the debris flows that could potentially affect the study area. Based from the rainfall intensity-duration-frequency analysis, the cumulative rainfall from typhoon Winnie on November 29 which was approximately 342 mm over a 9-hour period was classified within a 100-year return period. The Infanta station of the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) was no longer able to measure the amount of rainfall after this period because the rain gauge in that station was washed away by floods. Rainfall data with a 100-year return period was simulated over the watersheds delineated from a SAR-derived digital elevation model. The resulting debris flow hazard map was compared with results from field investigation and previous studies made on the landslide event. The simulation identified 22 barangays (villages) with a total of 45,155 people at risk of turbulent flow and flooding.

Proposal for a model to assess the effect of seismic activity on the triggering of debris flows

NASA Astrophysics Data System (ADS)

Vidar Vangelsten, Bjørn; Liu, Zhongqiang; Eidsvig, Unni; Luna, Byron Quan; Nadim, Farrokh

2013-04-01

Landslide triggered by earthquakes is a serious threat for many communities around the world, and in some cases is known to have caused 25-50% of the earthquake fatalities. Seismic shaking can contribute to the triggering of debris flows either during the seismic event or indirectly by increasing the susceptibility of the slope to debris flow during intense rainfall in a period after the seismic event. The paper proposes a model to quantify both these effects. The model is based on an infinite slope formulation where precipitation and earthquakes influence the slope stability as follows: (1) During the shaking, the factor of safety is reduced due to cyclic pore pressure build-up where the cyclic pore pressure is modelled as a function of earthquake duration and intensity (measured as number of equivalent shear stress cycles and cyclic shear stress magnitude) and in-situ soil conditions (measured as average normalised shear stress). The model is calibrated using cyclic triaxial and direct simple shear (DSS) test data on clay and sand. (2) After the shaking, the factor of safety is modified using a combined empirical and analytical model that links observed earthquake induced changes in rainfall thresholds for triggering of debris flow to an equivalent reduction in soil shear strength. The empirical part uses data from past earthquakes to propose a conceptual model linking a site-specific reduction factor for rainfall intensity threshold (needed to trigger debris flows) to earthquake magnitude, distance from the epicentre and time period after the earthquake. The analytical part is a hydrological model for transient rainfall infiltration into an infinite slope in order to translate the change in rainfall intensity threshold into an equivalent reduction in soil shear strength. This is generalised into a functional form giving a site-specific shear strength reduction factor as function of earthquake history and soil conditions. The model is suitable for hazard and risk assessment at local and regional scale for earthquake and rainfall induced landslide. The research leading to these results has received funding from the European Community's Seventh Framework Programme [FP7/2007-2013] under grant agreement No 265138 New Multi-HAzard and MulTi-RIsK Assessment MethodS for Europe (MATRIX).

Debris Flows and Floods in Southeastern Arizona from Extreme Precipitation in July 2006 - Magnitude, Frequency, and Sediment Delivery

USGS Publications Warehouse

Webb, Robert H.; Magirl, Christopher S.; Griffiths, Peter G.; Boyer, Diane E.

2008-01-01

From July 31 to August 1, 2006, an unusual set of atmospheric conditions aligned to produce record floods and an unprecedented number of slope failures and debris flows in southeastern Arizona. During the week leading up to the event, an upper-level low-pressure system centered over New Mexico generated widespread and locally heavy rainfall in southeastern Arizona, culminating in a series of strong, mesoscale convective systems that affected the region in the early morning hours of July 31 and August 1. Rainfall from July 27 through 30 provided sufficient antecedent moisture that the storms of July 31 through August 1 resulted in record streamflow flooding in northeastern Pima County and eastern Pinal County. The rainfall caused at least 623 slope failures in four mountain ranges, including more than 30 near Bowie Mountain in the northern Chiracahua Mountains, and 113 at the southern end of the Huachuca Mountains within and adjacent to Coronado National Memorial. In the Santa Catalina Mountains north of Tucson, 435 slope failures spawned debris flows on July 31 that, together with flood runoff, damaged structures and roads, affecting infrastructure within Tucson's urban boundary. Heavy, localized rainfall in the Galiuro Mountains on August 1, 2006, resulted in at least 45 slope failures and an unknown number of debris flows in Aravaipa Canyon. In the southern Santa Catalina Mountains, the maximum 3-day precipitation measured at a climate station for July 29-31 was 12.04 in., which has a 1,200-year recurrence interval. Other rainfall totals from late July to August 1 in southeastern Arizona also exceeded 1,000-year recurrence intervals. The storms produced floods of record along six watercourses, and these floods had recurrence intervals of 100-500 years. Repeat photography suggests that the spate of slope failures was historically unprecedented, and geologic mapping and cosmogenic dating of ancient debris-flow deposits indicate that debris flows reaching alluvial fans in the Tucson basin are extremely rare events. Although recent watershed changes - particularly the impacts of recent wildland fires - may be important locally, the record number of slope failures and debris flows were related predominantly to extreme precipitation, not other factors such as fire history. The large number of slope failures and debris flows in an area with few such occurrences historically underscores the rarity of this type of meteorological event in southeastern Arizona. Most slope failures appeared to be shallow-seated slope failures of colluvium on steep slopes that caused deep scour of chutes and substantial aggradation of channels downstream. In the southern Santa Catalina Mountains, we estimate that 1.5 million tons of sediment were released from slope failures into the channels of ten drainage basins. Thirty-six percent of this sediment (527,000 tons) is gravel-sized or smaller and is likely to be transported by streamflow out of the mountain drainages and into the drainage network of metropolitan Tucson. This sediment poses a potential flood hazard by reducing conveyance in fixed-section flood control structures along Rillito Creek and its major tributaries, although our estimates suggest that deposition may be small if it is distributed widely along the channel, which is expected. Using the stochastic debris-flow model LAHARZ, we simulated debris-flow transport from slope failures to the apices of alluvial fans flanking the southern Santa Catalina Mountains. Despite considerable uncertainty in applying coefficients developed from worldwide observations to conditions in the southern Santa Catalina Mountains, we predicted the approximate area of depositional zones for several 2006 debris flows, particularly for Soldier Canyon. Better results could be achieved in some canyons if sediment budgets could be developed to account for alternating transport and deposition zones in channels with abrupt expansions and contractions, such

Prediction of Rainfall-Induced Landslides

NASA Astrophysics Data System (ADS)

Nadim, F.; Sandersen, F.

2009-12-01

Rainfall-induced landslides can be triggered by two main mechanisms: shear failure due to build-up of pore water pressure and erosion by surface water runoff when flow velocity exceeds a critical value. Field measurements indicate that, in the initial phase, the slip surface of a landslide often occurs along the top of a relatively impermeable layer located at some depth within the soil profile, e.g. at the contact with a shallow underlying bedrock or parent rock. The shear strength along this surface and hence the stability of the slope is governed by the pore water pressure. The pore pressure is in turn controlled by water seepage through the slope, either from infiltrated rain, or from groundwater that follows bedrock joints and soil layers with high permeability. When the infiltration rate of the underlying layer is too low for further downward penetration of water or when a wetting front is produced, pore water pressure builds up, reducing the soil shear strength. During high intensity rainfall, surface water runoff will exert shear stresses on the bed material. De-pending on the grain size distribution and specific gravity of the material, erosion might occur when the flow velocity exceeds a critical value. As erosion progresses and sediment concentration increases, the flow regime may become unstable with heavy erosion at high flow velocity locations triggering a debris flow. In many cases, previous landslides along steep gully walls have fed an abundance of loose soil material into the gullies. Landslides along gully walls that obstruct the water transport may also trigger debris flows when the landslide-dam collapses, creating a surge downstream. Both the long-duration (1 or more days) and short-duration precipitation (of the order of 1 hour) are significant in the triggering of shallow landslides, since the critical short-duration rainfall intensity reduces as the antecedent accumulated rainfall increases. Experiences in Norway indicate that the maxi-mum intensity of rain within a short period of time (1-3 hours) during a storm is most critical for triggering of debris flows. Therefore empirical methods developed for prediction of initiation of debris flows include both long-duration and short-duration rain-fall. More recent research has focused on the spatial distribution of unstable areas and on better spatial resolution of the occurrence of landslide-triggering precipitation events. Spatial distribution can be assessed by analyzing the stability conditions for shallow landslides if reasonable estimates of strength parameters are available. In general, two different approaches may be adopted for the assessment of threshold values for rainfall-induced landslides: empirical methods that are based on past observations and statistical analyses, and numerical analyses that are based on geo-mechanical modelling. The former approach together with very short-term weather forecasting (now-casting) are commonly used in the design of early warning systems for debris flows.

Glacial-interglacial climate changes recorded by debris flow fan deposits, Owens Valley, California

NASA Astrophysics Data System (ADS)

D'Arcy, Mitch; Roda-Boluda, Duna C.; Whittaker, Alexander C.

2017-08-01

It is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy. Basin sediments produced by catchment-alluvial fan systems may record past climate over a variety of timescales, and could offer unique information about how climate controls sedimentation. Unfortunately, there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals. Here, we examine 35 debris flow fan surfaces in Owens Valley, California, that record deposition throughout the past 125,000 years, during which climate has varied significantly. We show that the last full glacial-interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits. These flows transported finer sediment during the cooler glacial climate, and became systematically coarser-grained as the climate warmed and dried. We explore the physical mechanisms that might explain this signal, and rule out changes in sediment supply through time. Instead, we propose that grain size records past changes in storm intensity, which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates. This is supported by an exponential Clausius-Clapeyron-style scaling between grain size and temperature, and also reconciles with climate dynamics and the initiation of debris flows. The fact that these alluvial fans exhibit a strong, sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing. Finally, our findings highlight the importance of threshold-controlled events, such as storms and debris flows, in driving erosion and sedimentation at the Earth's surface in response to climate change.

Post-failure characteristics of weathered soils in Korea: determination of rheological thresholds and debris flow mobility

NASA Astrophysics Data System (ADS)

Jeong, Sueng-Won; Fukuoka, Hiroshi; Im, Sang-June

2013-04-01

Landslides in Korea are mainly triggered by localized summer heavy rainfall. The water infiltration, wetting and fluidization process are the key roles in slope instability. Mechanically, a loss in soil strength of the soil at weakend layer takes place as a result of water infiltration. The transition from slides to flows can be defined by the variation in strength parameters. In the flowing stage with large volume of sediments, debris flow impact may be governed by the rheology of the failed mass. We performed the rheological tests using the ball-measuring and vane-inserted rheometer and examined a possible threshold of landslides on mudstone, weathered granitic and gneissic soils in the mountainous region of Korea. The materials examined exhibited the shear-thinning behavior, which is the viscosity decreases with increasing shear rates. There are positive relationships between liquidity index and rheological values (i.e., yield stress and viscosities). However, the difference in rheological properties is of significance for given shear rates. The effect of wall-slip in different geometries is emphasized. This work is also concerned with post-failure characteristics of rainfall-induced landslides that occur in Chuncheon, Miryang and Seoul debris flow occurrence in 2011. They are mainly composed of gneissic, sedimentary and gneissic weathered soils. The rheological properties is helpful to predict the mobilization of fine-laden debris flows. In the relationship between shear stress and shear rate, one of simplest rheological models, i.e., the ideal Bingham fluid model, is selected to examine the flow pattern and depositional features of debris flows. A comparison will be made for the debris flow occurence on weahtered soils in Korea.

Potential postwildfire debris-flow hazards—A prewildfire evaluation for the Jemez Mountains, north-central New Mexico

USGS Publications Warehouse

Tillery, Anne C.; Haas, Jessica R.

2016-08-11

Wildfire can substantially increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although the exact location, extent, and severity of wildfire or subsequent rainfall intensity and duration cannot be known, probabilities of fire and debris‑flow occurrence for given locations can be estimated with geospatial analysis and modeling. The purpose of this report is to provide information on which watersheds might constitute the most serious potential debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall in the Jemez Mountains. Potential probabilities and estimated volumes of postwildfire debris flows in both the unburned and previously burned areas of the Jemez Mountains and surrounding areas were estimated using empirical debris-flow models developed by the U.S. Geological Survey in combination with fire behavior and burn probability models developed by the U.S. Forest Service.Of the 4,998 subbasins modeled for this study, computed debris-flow probabilities in 671 subbasins were greater than 80 percent in response to the 100-year recurrence interval, 30-minute duration rainfall event. These subbasins ranged in size from 0.01 to 6.57 square kilometers (km2), with an average area of 0.29 km2, and were mostly steep, upstream tributaries to larger channels in the area. Modeled debris-flow volumes in 465 subbasins were greater than 10,000 cubic meters (m3), and 14 of those subbasins had modeled debris‑flow volumes greater than 100,000 m3.The rankings of integrated relative debris-flow hazard indexes for each subbasin were generated by multiplying the individual subbasin values for debris-flow volume, debris‑flow probability, and average burn probability. The subbasins with integrated hazard index values in the top 2 percent typically are large, upland tributaries to canyons and channels primarily in the Upper Rio Grande and Rio Grande-Santa Fe watershed areas. No subbasins in this group have basin areas less than 1.0 km2. Many of these areas already had significant mass‑wasting episodes following the Las Conchas Fire in 2011. Other subbasins with integrated hazard index values in the top 2 percent are scattered throughout the Jemez River watershed area, including some subbasins in the interior of the Valles Caldera. Only a few subbasins in the top integrated hazard index group are in the Rio Chama watershed area.This prewildfire assessment approach is valuable to resource managers because the analysis of the debris-flow threat is made before a wildfire occurs, which facilitates prewildfire management, planning, and mitigation. In north‑central New Mexico, widespread watershed restoration efforts are being done to safeguard vital watersheds against the threat of catastrophic wildfire. This study was designed to help select ideal locations for the restoration efforts that could have the best return on investment.

August 2014 Hiroshima landslide disaster and its societal impact

NASA Astrophysics Data System (ADS)

Fukuoka, Hiroshi; Sassa, Kyoji; Wang, Chunxiang

2015-04-01

In the early morning of August 20, 2014, Hiroshima city was hit by a number of debris flows along a linear rain band which caused extreme downpour. This disaster claimed 74 death, although this city experienced very similar disaster in 1999, claiming more than 30 residents lives. In the most severely affected debris flow torrent, more than 50 residents were killed. Most of the casualties arose in the wooden, vulnerable houses constructed in front of the exit of torrents. Points and lessons learnt from the disaster are as follows: 1. Extreme rainfall events : geology and geomorphology does not much affect the distribution of landslides initiation sites. 2. Area of causative extreme rainfall is localized in 2 km x 10 km along the rain band. 3. Authors collected two types of sands from the source scar of the initial debris slides which induced debris flows. Tested by the ring shear apparatus under pore-pressure control condition, clear "Sliding surface liquefaction" was confirmed for both samples even under small normal stress, representing the small thickness of the slides. These results shows even instant excess pore pressure could initiate the slides and trigger slide-induced debris flow by undrained loading onto the torrent deposits. 4. Apparently long-term land-use change affected the vulnerability of the community. Residential area had expanded into hill-slope (mountainous / semi-mountainous area) especially along the torrents. Those communities were developed on the past debris flow fan. 5. As the devastated area is very close to downtown of Hiroshima city, it gave gigantic societal impact to the Japanese citizens. After 1999 Hiroshima debris flow disaster, the Landslide disaster reduction law which intends to promote designation of landslide potential risk zones, was adopted in 2000. Immediately after 2014 disaster, national diet approved revision of the bill.

Relations Between Rainfall and Postfire Debris-Flow and Flood Magnitudes for Emergency-Response Planning, San Gabriel Mountains, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Boldt, Eric M.; Kean, Jason W.; Laber, Jayme; Staley, Dennis M.

2010-01-01

Following wildfires, emergency-response and public-safety agencies are faced often with making evacuation decisions and deploying resources both well in advance of each coming winter storm and during storms themselves. Information critical to this process is provided for recently burned areas in the San Gabriel Mountains of southern California. The National Weather Service (NWS) issues Quantitative Precipitation Forecasts (QPFs) for the San Gabriel Mountains twice a day, at approximately 4 a.m. and 4 p.m., along with unscheduled updates when conditions change. QPFs provide estimates of rainfall totals in 3-hour increments for the first 12-hour period and in 6-hour increments for the second 12-hour period. Estimates of one-hour rainfall intensities can be provided in the forecast narrative, along with probable peak intensities and timing, although with less confidence than rainfall totals. A compilation of information on the hydrologic response to winter storms from recently burned areas in southern California steeplands was used to develop a system for classifying the magnitude of the postfire hydrologic response. The four-class system is based on a combination of the reported volume of individual debris flows, the consequences of these events in an urban setting, and the spatial extent of the response to the triggering storm. Threshold rainfall conditions associated with debris flow and floods of different magnitude classes are defined by integrating local rainfall data with debris-flow and flood magnitude information. The within-storm rainfall accumulations (A) and durations (D) above which magnitude I events are expected are defined by A=0.3D0.6. The function A=0.5D0.6 defines the within-storm rainfall accumulations and durations above which a magnitude III event will occur in response to a regional-scale storm, and a magnitude II event will occur if the storm affects only a few drainage basins. The function A=1.0D0.5defines the rainfall conditions above which magnitude III events can be expected. Rainfall trigger-magnitude relations are linked with potential emergency-response actions in the form of an emergency-response decision chart. The chart leads a user through steps to determine potential event magnitudes, and identify possible evacuation and resource-deployment levels as a function of either individual storm forecasts or measured precipitation during storms. The ability to use this information in the planning and response decision-making process may result in significant financial savings and increased safety for both the public and emergency responders.

The increasing wildfire and post-fire debris-flow threat in western USA, and implications for consequences of climate change

USGS Publications Warehouse

Cannon, Susan H.; DeGraff, Jerry

2009-01-01

In southern California and the intermountain west of the USA, debris flows generated from recently-burned basins pose significant hazards. Increases in the frequency and size of wildfires throughout the western USA can be attributed to increases in the number of fire ignitions, fire suppression practices, and climatic influences. Increased urbanization throughout the western USA, combined with the increased wildfire magnitude and frequency, carries with it the increased threat of subsequent debris-flow occurrence. Differences between rainfall thresholds and empirical debris-flow susceptibility models for southern California and the intermountain west indicate a strong influence of climatic and geologic settings on post-fire debris-flow potential. The linkages between wildfires, debris-flow occurrence, and global warming suggests that the experiences in the western United States are highly likely to be duplicated in many other parts of the world, and necessitate hazard assessment tools that are specific to local climates and physiographies.

Set-up of debris-flow monitoring stations in the Eastern Pyrenees. Preliminary results and first experiences.

NASA Astrophysics Data System (ADS)

Hürlimann, Marcel; Abancó, Claudia; Moya, Jose; Chevalier, Guillaume; Raïmat, Carles; Luis-Fonseca, Roberto

2010-05-01

Direct observations of debris flows in the field by monitoring stations are of great importance to improve understandings of triggering, flow behaviour and accumulation of debris flows. Upon the knowledge of the authors, in Europe debris-flow monitoring stations are only situated in the Alps (Italy and Switzerland), while no test site is located in a catchment affected by Mediterranean climate. In 2005, the first monitoring system was set up by GEOBRUGG IBERICA SA in the Erill catchment, situated in the Axial Pyrenees. A flexible ring net VX160-H4 with load-cells was installed together with a video camera and four geophones. In addition, a meteorological station completed the instrumentation. During 2009, the monitoring of two additional catchments has been set up; Senet in the Axial Pyrenees and Ensija in the Pre-Pyrenees. Four geophones and one ultrasonic device are installed along the torrent in order to determine the flow velocity and flow depth/discharge of the events. As in Erill, a meteorological station completes the devices and measures rainfall and temperature. The main objective of the three monitoring stations is to get some insights on how the Mediterranean climate influences the critical rainfall for debris-flow initiation. The flow behaviour of debris flows is another major goal, while the Erill test site focuses basically on the effectiveness of flexible ring nets. In addition, the Erill installation also acts as protection for the village located on the fan. The calibration, installation and analysis during the testing phase showed that a correct implementation of the different sensors is not an easy task and needs knowledge in geophysics, electronics, telecommunications etc. Especially geophones and ultrasonic devices need special attentions. Geophone outputs are strongly affected by the type of underground and the distance to the torrent, while the measures of the ultrasonic sensor clearly depend on the temperature. To simplify the data storage and processing, geophone signals are converted into impulses. This involves definition of a threshold to filter seismic "noise" caused by other processes. An additional difficulty in our test sites is the remoteness, which needs an independent power supply by solar panels and GSM-transmission of the data gathered. In Senet and Ensija catchment, hyperconcentrated flows have been observed during summer 2009 by field surveys, although these events could not have been clearly detected by the geophones and the ultrasonic device. Thus, only the critical rainfall amount for generating such type of flows could be analysed. These data support the hypothesis that short-lasting and intensive summer storms are common triggering precipitations for hyperconcentrated flows and also for debris flows. In Erill, three small events with volumes of a few hundreds of cubic-meters have been occurred till now. All of them were stopped by the flexible ring barrier, while the barrier has been self-cleaned by the natural dynamics of the stream. Such events (hyperconcentrated flows) are allegedly exceptional; therefore the flows have been generated as consequence of high intensity rainfall, very common in this area. For this reason it's thought that the debris flow phenomenon and the trigger conditions should be studied in detail, to achieve the required knowledge to calculate the future impact loads and scenarios.

Generalised form of a power law threshold function for rainfall-induced landslides

NASA Astrophysics Data System (ADS)

Cepeda, Jose; Díaz, Manuel Roberto; Nadim, Farrokh; Høeg, Kaare; Elverhøi, Anders

2010-05-01

The following new function is proposed for estimating thresholds for rainfall-triggered landslides: I = α1Anα2Dβ, where I is rainfall intensity in mm/h, D is rainfall duration in h, An is the n-hours or n-days antecedent precipitation, and α1, α2, β and n are threshold parameters. A threshold model that combines two functions with different durations of antecedent precipitation is also introduced. A storm observation exceeds the threshold when the storm parameters are located at or above the two functions simultaneously. A novel optimisation procedure for estimating the threshold parameters is proposed using Receiver Operating Characteristics (ROC) analysis. The new threshold function and optimisation procedure are applied for estimating thresholds for triggering of debris flows in the Western Metropolitan Area of San Salvador (AMSS), El Salvador, where up to 500 casualties were produced by a single event. The resulting thresholds are I = 2322 A7d-1D-0.43 and I = 28534 A150d-1D-0.43 for debris flows having volumes greater than 3000 m3. Thresholds are also derived for debris flows greater than 200 000 m3 and for hyperconcentrated flows initiating in burned areas caused by forest fires. The new thresholds show an improved performance compared to the traditional formulations, indicated by a reduction in false alarms from 51 to 5 for the 3000 m3 thresholds and from 6 to 0 false alarms for the 200 000 m3 thresholds.

Debris flow-induced topographic changes: effects of recurrent debris flow initiation.

PubMed

Chen, Chien-Yuan; Wang, Qun

2017-08-12

Chushui Creek in Shengmu Village, Nantou County, Taiwan, was analyzed for recurrent debris flow using numerical modeling and geographic information system (GIS) spatial analysis. The two-dimensional water flood and mudflow simulation program FLO-2D were used to simulate debris flow induced by rainfall during typhoon Herb in 1996 and Mindulle in 2004. Changes in topographic characteristics after the debris flows were simulated for the initiation of hydrological characteristics, magnitude, and affected area. Changes in topographic characteristics included those in elevation, slope, aspect, stream power index (SPI), topographic wetness index (TWI), and hypsometric curve integral (HI), all of which were analyzed using GIS spatial analysis. The results show that the SPI and peak discharge in the basin increased after a recurrence of debris flow. The TWI was higher in 2003 than in 2004 and indicated higher potential of landslide initiation when the slope of the basin was steeper. The HI revealed that the basin was in its mature stage and was shifting toward the old stage. Numerical simulation demonstrated that the parameters' mean depth, maximum depth, affected area, mean flow rate, maximum flow rate, and peak flow discharge were increased after recurrent debris flow, and peak discharge occurred quickly.

Impact of recent extreme Arizona storms

USGS Publications Warehouse

Magirl, C.S.; Webb, R.H.; Schaffner, M.; Lyon, S.W.; Griffiths, P.G.; Shoemaker, C.; Unkrich, C.L.; Yatheendradas, S.; Troch, Peter A.; Pytlak, E.; Goodrich, D.C.; Desilets, S.L.E.; Youberg, A.; Pearthree, P.A.

2007-01-01

Heavy rainfall on 27–31 July 2006 led to record flooding and triggered an historically unprecedented number of debris flows in the Santa Catalina Mountains north of Tucson, Ariz. The U.S. Geological Survey (USGS) documented record floods along four watercourses in the Tucson basin, and at least 250 hillslope failures spawned damaging debris flows in an area where less than 10 small debris flows had been documented in the past 25 years. At least 18 debris flows destroyed infrastructure in the heavily used Sabino Canyon Recreation Area (http://wwwpaztcn.wr.usgs.gov/rsch_highlight/articles/20061 l.html). In four adjacent canyons, debris flows reached the heads of alluvial fans at the boundary of the Tucson metropolitan area. While landuse planners in southeastern Arizona evaluate the potential threat of this previously little recognized hazard to residents along the mountain front, an interdisciplinary group of scientists has collaborated to better understand this extreme event.

Methods for the Emergency Assessment of Debris-Flow Hazards from Basins Burned by the Fires of 2007, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Michael, John A.

2007-01-01

This report describes the approach used to assess potential debris-flow hazards from basins burned by the Buckweed, Santiago, Canyon, Poomacha, Ranch, Harris, Witch, Rice, Ammo, Slide, Grass Valley and Cajon Fires of 2007 in southern California. The assessments will be presented as a series of maps showing a relative ranking of the predicted volume of debris flows that can issue from basin outlets in response to a 3-hour duration rainstorm with a 10-year return period. Potential volumes of debris flows are calculated using a multiple-regression model that describes debris-flow volume at a basin outlet as a function of measures of basin gradient, burn extent, and storm rainfall. This assessment provides critical information for issuing basin-specific warnings, locating and designing mitigation measures, and planning of evacuation timing and routes.

Debris-Flow Hazards within the Appalachian Mountains of the Eastern United States

USGS Publications Warehouse

Wieczorek, Gerald F.; Morgan, Benjamin A.

2008-01-01

Tropical storms, including hurricanes, often inflict major damage to property and disrupt the lives of people living in coastal areas of the Eastern United States. These storms also are capable of generating catastrophic landslides within the steep slopes of the Appalachian Mountains. Heavy rainfall from hurricanes, cloudbursts, and thunderstorms can generate rapidly moving debris flows that are among the most dangerous and damaging type of landslides. This fact sheet explores the nature and occurrence of debris flows in the central and southern Appalachian Mountains, which extend from central Pennsylvania to northern Alabama.

Early warning of orographically induced floods and landslides in Western Norway

NASA Astrophysics Data System (ADS)

Leine, Ann-Live; Wang, Thea; Boje, Søren

2017-04-01

In Western Norway, landslides and debris flows are commonly initiated by short-term orographic rainfall or intensity peaks during a prolonged rainfall event. In recent years, the flood warning service in Norway has evolved from being solely a flood forecasting service to also integrating landslides into its early warning systems. As both floods and landslides are closely related to the same hydrometeorological processes, particularly in small catchments, there is a natural synergy between monitoring flood and landslide risk. The Norwegian Flood and Landslide Hazard Forecasting and Warning Service issues regional landslide hazard warnings based on hydrological models, threshold values, observations and weather forecasts. Intense rainfall events and/or orographic precipitation that, under certain topographic conditions, significantly increase the risk of debris avalanches and debris floods are lately receiving more research focus from the Norwegian warning service. Orographic precipitation is a common feature in W-Norway, when moist and relatively mild air arrives from the Atlantic. Steep mountain slopes covered by glacial till makes the region prone to landslides, as well as flooding. The operational early warning system in Norway requires constant improvement, especially with the enhanced number of intense rainfall events that occur in a warming climate. Here, we examine different cases of intense rainfall events which have lead to landslides and debris flows, as well as increased runoff in fast responding small catchments. The main objective is to increase the understanding of the hydrometeorological conditions related to these events, in order to make priorities for the future development of the warning service.

Potential postwildfire debris-flow hazards: a prewildfire evaluation for the Sandia and Manzano Mountains and surrounding areas, central New Mexico

USGS Publications Warehouse

Tillery, Anne C.; Haas, Jessica R.; Miller, Lara W.; Scott, Joe H.; Thompson, Matthew P.

2014-01-01

Wildfire can drastically increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although there is no way to know the exact location, extent, and severity of wildfire, or the subsequent rainfall intensity and duration before it happens, probabilities of fire and debris-flow occurrence for different locations can be estimated with geospatial analysis and modeling efforts. The purpose of this report is to provide information on which watersheds might constitute the most serious, potential, debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall in the Sandia and Manzano Mountains. Potential probabilities and estimated volumes of postwildfire debris flows in the unburned Sandia and Manzano Mountains and surrounding areas were estimated using empirical debris-flow models developed by the U.S. Geological Survey in combination with fire behavior and burn probability models developed by the U.S. Department of Agriculture Forest Service. The locations of the greatest debris-flow hazards correlate with the areas of steepest slopes and simulated crown-fire behavior. The four subbasins with the highest computed debris-flow probabilities (greater than 98 percent) were all in the Manzano Mountains, two flowing east and two flowing west. Volumes in sixteen subbasins were greater than 50,000 square meters and most of these were in the central Manzanos and the western facing slopes of the Sandias. Five subbasins on the west-facing slopes of the Sandia Mountains, four of which have downstream reaches that lead into the outskirts of the City of Albuquerque, are among subbasins in the 98th percentile of integrated relative debris-flow hazard rankings. The bulk of the remaining subbasins in the 98th percentile of integrated relative debris-flow hazard rankings are located along the highest and steepest slopes of the Manzano Mountains. One of the subbasins is several miles upstream from the community of Tajique and another is several miles upstream from the community of Manzano, both on the eastern slopes of the Manzano Mountains. This prewildfire assessment approach is valuable to resource managers because the analysis of the debris-flow threat is made before a wildfire occurs, which facilitates prewildfire management, planning, and mitigation. In northern New Mexico, widespread watershed restoration efforts are being carried out to safeguard vital watersheds against the threat of catastrophic wildfire. This study was initiated to help select ideal locations for the restoration efforts that could have the best return on investment.

Potential postwildfire debris-flow hazards - a prewildfire evaluation for the Sandia and Manzano Mountains and surrounding areas, central New Mexico

Treesearch

Anne C. Tillery; Jessica R. Haas; Lara W. Miller; Joe H. Scott; Matthew P. Thompson

2014-01-01

Wildfire can drastically increase the probability of debris flows, a potentially hazardous and destructive form of mass wasting, in landscapes that have otherwise been stable throughout recent history. Although there is no way to know the exact location, extent, and severity of wildfire, or the subsequent rainfall intensity and duration before it happens, probabilities...

Hydrological disposition of flash flood and debris flows events in an Alpine watershed in Austria

NASA Astrophysics Data System (ADS)

Prenner, David; Kaitna, Roland; Mostbauer, Karin; Hrachowitz, Markus

2017-04-01

Debris flows and flash floods including intensive bedload transport represent severe hazards in the Alpine environment of Austria. For neither of these processes, explicit rainfall thresholds - even for specific regions - are available. This may be due to insufficient data on the temporal and spatial variation of precipitation, but probably also due to variations of the geomorphic and hydrological disposition of a watershed to produce such processes in the course of a rainfall event. In this contribution we investigate the importance of the hydrological system state for triggering debris flows and flash floods in the Ill/Suggadin watershed (500 km2), Austria, by analyzing the effects of dynamics in system state variables such as soil moisture, snow pack, or ground water level. The analysis is based on a semi-distributed conceptual rainfall-runoff model, spatially discretizing the watershed according to the available precipitation observations, elevation, topographic considerations and land cover. Input data are available from six weather stations on a daily basis ranging back to 1947. A Thiessen polygon decomposition results in six individual precipitation zones with a maximum area of about 130 km2. Elevation specific behavior of the quantities temperature and precipitation is covered through an elevation-resolved computation every 200 m. Spatial heterogeneity is considered by distinct hydrological response units for bare rock, forest, grassland, and riparian zone. To reduce numerical smearing on the hydrological results, the Implicit Euler scheme was used to discretize the balance equations. For model calibration we utilized runoff hydrographs, snow cover data as well as prior parameter and process constraints. The obtained hydrological output variables are linked to documented observed flash flood and debris flow events by means of a multivariate logistic regression. We present a summary about the daily hydrological disposition of experiencing a flash flood or debris flow event in each precipitation zone of the Ill/Suggadin region over almost 65 years. Furthermore, we will provide an interpretation of the occurred hydrological trigger patterns and show a frequency ranking. The outcomes of this study shall lead to an improved forecasting and differentiation of trigger conditions leading to debris flows and flash floods.

Instrumental record of debris flow initiation during natural rainfall: Implications for modeling slope stability

USGS Publications Warehouse

Montgomery, D.R.; Schmidt, K.M.; Dietrich, W.E.; McKean, J.

2009-01-01

The middle of a hillslope hollow in the Oregon Coast Range failed and mobilized as a debris flow during heavy rainfall in November 1996. Automated pressure transducers recorded high spatial variability of pore water pressure within the area that mobilized as a debris flow, which initiated where local upward flow from bedrock developed into overlying colluvium. Postfailure observations of the bedrock surface exposed in the debris flow scar reveal a strong spatial correspondence between elevated piezometric response and water discharging from bedrock fractures. Measurements of apparent root cohesion on the basal (Cb) and lateral (Cl) scarp demonstrate substantial local variability, with areally weighted values of Cb = 0.1 and Cl = 4.6 kPa. Using measured soil properties and basal root strength, the widely used infinite slope model, employed assuming slope parallel groundwater flow, provides a poor prediction of hydrologie conditions at failure. In contrast, a model including lateral root strength (but neglecting lateral frictional strength) gave a predicted critical value of relative soil saturation that fell within the range defined by the arithmetic and geometric mean values at the time of failure. The 3-D slope stability model CLARA-W, used with locally observed pore water pressure, predicted small areas with lower factors of safety within the overall slide mass at sites consistent with field observations of where the failure initiated. This highly variable and localized nature of small areas of high pore pressure that can trigger slope failure means, however, that substantial uncertainty appears inevitable for estimating hydrologie conditions within incipient debris flows under natural conditions. Copyright 2009 by the American Geophysical Union.

A comparative analysis of simulated and observed landslide locations triggered by Hurricane Camille in Nelson County, Virginia

USGS Publications Warehouse

Morrissey, M.M.; Wieczorek, G.F.; Morgan, B.A.

2008-01-01

In 1969, Nelson County, Virginia received up to 71 cm of rain within 12 h starting at 7 p.m. on August 19. The total rainfall from the storm exceeded the 1000-year return period in the region. Several thousands of landslides were induced by rainfall associated with Hurricane Camille causing fatalities and destroying infrastructure. We apply a distributed transient response model for regional slope stability analysis to shallow landslides. Initiation points of over 3000 debris flows and effects of flooding from this storm are applied to the model. Geotechnical data used in the calculations are published data from samples of colluvium. Results from these calculations are compared with field observations such as landslide trigger location and timing of debris flows to assess how well the model predicts the spatial and temporal distribution. of landslide initiation locations. The model predicts many of the initiation locations in areas where debris flows are observed. Copyright ?? 2007 John Wiley & Sons, Ltd.

Using Google Earth To Interpret The Southern Taiwan Hsiaolin Village Catastrophe

NASA Astrophysics Data System (ADS)

Lin, Y. H.; Huang, C. M.; Keck, J.; Wei, L. W.; Pan, K. L.

2012-04-01

The August, 2009 Typhoon Morakot resulted in accumulated rainfalls exceeding 2000 mm and the triggering of a massive debris flow that buried Hsiaolin village. Hundreds of people were killed and both domestic and international natural disaster prevention agencies took note of this large scale disaster that was not prevented. Interpretation of Google Earth satellite images reveals that the Hsiaolin debris flow originated in a single location and then split into two parts. The northern debris flow, the smaller of the two parts, flowed within a ravine. The southern part of the debris flow, much larger than the northern part, was responsible for the burial of Hsiaolin village. The movement of the debris flow can be divided into three processes. First a slope failure and subsequent debris flow occurred within a curved ravine. Second, the debris flow eroded the bank of the ravine laterally, causing translational failure of the ravine walls. A massive debris flow, made up of a combination of materials from both the original debris flow and the ravine walls, jammed within the ravine. Finally, as a result of the jam, the debris flow was redirected towards Hsiaolin village. Overlaying locations of the post-Hsiaolin debris flow landforms on top of pre-failure satellite images reveals that characteristics of the post failure landforms match perfectly with characteristics observed in the pre-failure satellite images. This finding supports the thought that large scale geologic disasters are reoccurring. This finding also suggests that areas near villages can use simple satellite image analysis to rapidly identify ancient landslides and that such information may help early evacuation planning. With such planning, property and life losses due to natural disasters can be reduced. Key word: Hsiaolin Village, Debris Flow, Remote Sensing, Image Interpretation, Cause of Disaster, Disaster Recovery, Deep-Seated Landslide, Ancient Debris Flow

Mud Flow - Slow and Fast

NASA Astrophysics Data System (ADS)

Mei, C. C.; Liu, K.-F.; Yuhi, M.

Heavy and persistent rainfalls in mountainous areas can loosen the hillslope and induce mud flows which can move stones, boulders and even trees, with destructive power on their path. In China where 70% of the land surface is covered by mountains, debris flows due to landslides or rainfalls affect over 18.6% of the nation. Over 10,000 debris flow ravines have been identified; hundreds of lives are lost every year [1]. While accurate assessment is still pending, mud flows caused by Hurr icane Mitch in 1998 have incurred devastating floods in Central America. In Honduras alone more than 6000 people perished. Half of the nation's infrastructures were damaged. Mud flows can also be the result of volcanic eruption. Near the volcano, lava and pyroclastic flows dominate. Further downstream solid particles become smaller and can mix with river or lake water, rainfall, melting snow or ice, or eroded soil, resulting in hyperconcentrated mud mixed with rocks. The muddy debris can travel at high speeds over tens of miles down the hill slopes and devastate entire communities. In 1985 the catastrophic eruption of Nevado del Ruiz in Colombia resulted in mud flows which took the life of 23,000 inhabitants in the town of Amero [2]. During the eruption of Mt. Pinatubo in Phillipnes in 1991, one cubic mile of volcanic ash and rock fragments fell on the mountain slopes. Seasonal rain in the following months washed down much of the loose deposits, causing damage to 100,000 villages. These catastrophes have been vividly recorded in the film documentary by Lyons [3].

Positive feedback and momentum growth during debris-flow entrainment of wet bed sediment

USGS Publications Warehouse

Iverson, R.M.; Reid, M.E.; Logan, M.; LaHusen, R.G.; Godt, J.W.; Griswold, J.P.

2011-01-01

Debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep, debris-mantled slopes. The flows can then grow dramatically in size and speed as they entrain material from their beds and banks, but the mechanism of this growth is unclear. Indeed, momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged. Here we use data from large-scale experiments to assess the entrainment of bed material by debris flows. We find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows. The increased pore pressure facilitates progressive scour of the bed, reduces basal friction and instigates positive feedback that causes flow speed, mass and momentum to increase. If dryer bed sediment is entrained, however, the feedback becomes negative and flow momentum declines. We infer that analogous feedbacks could operate in other types of gravity-driven mass flow that interact with erodible beds. ?? 2011 Macmillan Publishers Limited. All rights reserved.

Debris Flows and Record Floods from Extreme Mesoscale Convective Thunderstorms over the Santa Catalina Mountains, Arizona

USGS Publications Warehouse

Magirl, Christopher S.; Shoemaker, Craig; Webb, Robert H.; Schaffner, Mike; Griffiths, Peter G.; Pytlak, Erik

2007-01-01

Ample geologic evidence indicates early Holocene and Pleistocene debris flows from the south side of the Santa Catalina Mountains north of Tucson, Arizona, but few records document historical events. On July 31, 2006, an unusual set of atmospheric conditions aligned to produce record floods and an unprecedented number of debris flows in the Santa Catalinas. During the week prior to the event, an upper-level area of low pressure centered near Albuquerque, New Mexico generated widespread heavy rainfall in southern Arizona. After midnight on July 31, a strong complex of thunderstorms developed over central Arizona in a deformation zone that formed on the back side of the upper-level low. High atmospheric moisture (2.00' of precipitable water) coupled with cooling aloft spawned a mesoscale thunderstorm complex that moved southeast into the Tucson basin. A 15-20 knot low-level southwesterly wind developed with a significant upslope component over the south face of the Santa Catalina Mountains advecting moist and unstable air into the merging storms. National Weather Service radar indicated that a swath of 3-6' of rainfall occurred over the lower and middle elevations of the southern Santa Catalina Mountains. This intense rain falling on saturated soil triggered over 250 hillslope failures and debris flows throughout the mountain range. Sabino Canyon, a heavily used recreation area administered by the U.S. Forest Service, was the epicenter of mass wasting, where at least 18 debris flows removed structures, destroyed the roadway in multiple locations, and closed public access for months. The debris flows were followed by streamflow floods which eclipsed the record discharge in the 75-year gaging record of Sabino Creek. In five canyons adjacent to Sabino Canyon, debris flows approached or excited the mountain front, compromising floow conveyance structures and flooding some homes.

Amplification of postwildfire peak flow by debris

NASA Astrophysics Data System (ADS)

Kean, J. W.; McGuire, L. A.; Rengers, F. K.; Smith, J. B.; Staley, D. M.

2016-08-01

In burned steeplands, the peak depth and discharge of postwildfire runoff can substantially increase from the addition of debris. Yet methods to estimate the increase over water flow are lacking. We quantified the potential amplification of peak stage and discharge using video observations of postwildfire runoff, compiled data on postwildfire peak flow (Qp), and a physically based model. Comparison of flood and debris flow data with similar distributions in drainage area (A) and rainfall intensity (I) showed that the median runoff coefficient (C = Qp/AI) of debris flows is 50 times greater than that of floods. The striking increase in Qp can be explained using a fully predictive model that describes the additional flow resistance caused by the emergence of coarse-grained surge fronts. The model provides estimates of the amplification of peak depth, discharge, and shear stress needed for assessing postwildfire hazards and constraining models of bedrock incision.

Amplification of postwildfire peak flow by debris

USGS Publications Warehouse

Kean, Jason W.; McGuire, Luke; Rengers, Francis K.; Smith, Joel B.; Staley, Dennis M.

2016-01-01

In burned steeplands, the peak depth and discharge of postwildfire runoff can substantially increase from the addition of debris. Yet methods to estimate the increase over water flow are lacking. We quantified the potential amplification of peak stage and discharge using video observations of postwildfire runoff, compiled data on postwildfire peak flow (Qp), and a physically based model. Comparison of flood and debris flow data with similar distributions in drainage area (A) and rainfall intensity (I) showed that the median runoff coefficient (C = Qp/AI) of debris flows is 50 times greater than that of floods. The striking increase in Qp can be explained using a fully predictive model that describes the additional flow resistance caused by the emergence of coarse-grained surge fronts. The model provides estimates of the amplification of peak depth, discharge, and shear stress needed for assessing postwildfire hazards and constraining models of bedrock incision.

Risk assessment of debris flow hazards in natural slope

NASA Astrophysics Data System (ADS)

Choi, Junghae; Chae, Byung-gon; Liu, Kofei; Wu, Yinghsin

2016-04-01

The study area is located at north-east part of South Korea. Referring to the map of landslide sus-ceptibility (KIGAM, 2009) from Korea Institute of Geoscience and Mineral Resources (KIGAM for short), there are large areas of potential landslide in high probability on slope land of mountain near the study area. Besides, recently some severe landslide-induced debris flow hazards occurred in this area. So this site is convinced to be prone to debris flow haz-ards. In order to mitigate the influence of hazards, the assessment of potential debris flow hazards is very important and essential. In this assessment, we use Debris-2D, debris flow numerical program, to assess the potential debris flow hazards. The worst scenario is considered for simulation. The input mass sources are determined using landslide susceptibility map. The water input is referred to the daily accumulative rainfall in the past debris flow event in study area. The only one input material property, i.e. yield stress, is obtained using calibration test. The simulation results show that the study area has po-tential to be impacted by debris flow. Therefore, based on simulation results, to mitigate debris flow hazards, we can propose countermeasures, including building check dams, constructing a protection wall in study area, and installing instruments for active monitoring of debris flow hazards. Acknowledgements:This research was supported by the Public Welfare & Safety Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2012M3A2A1050983)

Rainfall intensity-duration thresholds for postfire debris-flow emergency-response planning

USGS Publications Warehouse

Cannon, S.H.; Boldt, E.M.; Laber, J.L.; Kean, J.W.; Staley, D.M.

2011-01-01

Following wildfires, emergency-response and public-safety agencies can be faced with evacuation and resource-deployment decisions well in advance of coming winter storms and during storms themselves. Information critical to these decisions is provided for recently burned areas in the San Gabriel Mountains of southern California. A compilation of information on the hydrologic response to winter storms from recently burned areas in southern California steeplands is used to develop a system for classifying magnitudes of hydrologic response. The four-class system describes combinations of reported volumes of individual debris flows, consequences of debris flows and floods in an urban setting, and spatial extents of the hydrologic response. The range of rainfall conditions associated with different magnitude classes is defined by integrating local rainfall data with the response magnitude information. Magnitude I events can be expected when within-storm rainfall accumulations (A) of given durations (D) fall above the threshold A = 0.4D0.5 and below A = 0.5D0.6 for durations greater than 1 h. Magnitude II events will be generated in response to rainfall accumulations and durations between A = 0.4D0.5 and A = 0.9D0.5 for durations less than 1 h, and between A = 0.5D0.6 and A = 0.9D0.5 or durations greater than 1 h. Magnitude III events can be expected in response to rainfall conditions above the threshold A = 0.9D0.5. Rainfall threshold-magnitude relations are linked with potential emergency-response actions as an emergency-response decision chart, which leads a user through steps to determine potential event magnitudes and identify possible evacuation and resource-deployment levels. Use of this information in planning and response decision-making process could result in increased safety for both the public and emergency responders. ?? 2011 US Government.

High-Resolution Rainfall From Radar Reflectivity and Terrestrial Rain Gages for use in Estimating Debris-Flow Susceptibility in the Day Fire, California

NASA Astrophysics Data System (ADS)

Hanshaw, M. N.; Schmidt, K. M.; Jorgensen, D. P.; Stock, J. D.

2007-12-01

Constraining the distribution of rainfall is essential to evaluating the post-fire mass-wasting response of steep soil-mantled landscapes. As part of a pilot early-warning project for flash floods and debris flows, NOAA deployed a portable truck-mounted Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) to the 2006 Day fire in the Transverse Ranges of Southern California. In conjunction with a dense array of ground- based instruments, including 8 tipping-bucket rain gages located within an area of 170 km2, this C-band mobile Doppler radar provided 200-m grid cell estimates of precipitation data at fine temporal and spatial scales in burned steeplands at risk from hazardous flash floods and debris flows. To assess the utility of using this data in process models for flood and debris flow initiation, we converted grids of radar reflectivity to hourly time-steps of precipitation using an empirical relationship for convective storms, sampling the radar data at the locations of each rain gage as determined by GPS. The SMART-R was located 14 km from the farthest rain gage, but <10 km away from our intensive research area, where 5 gages are located within <1-2 km of each other. Analyses of the nine storms imaged by radar throughout the 2006/2007 winter produced similar cumulative rainfall totals between the gages and their SMART-R grid location over the entire season which correlate well on the high side, with gages recording the most precipitation agreeing to within 11% of the SMART-R. In contrast, on the low rainfall side, totals between the two recording systems are more variable, with a 62% variance between the minimums. In addition, at the scale of individual storms, a correlation between ground-based rainfall measurements and radar-based rainfall estimates is less evident, with storm totals between the gages and the SMART-R varying between 7 and 88%, a possible result of these being relatively small, fast-moving storms in an unusually dry winter. The SMART-R also recorded higher seasonal cumulative rainfall than the terrestrial gages, perhaps indicating that not all precipitation reached the ground. For one storm in particular, time-lapse photographs of the ground document snow. This could explain, in part, the discrepancy between storm-specific totals when the rain gages recorded significantly lower totals than the SMART-R. For example, during the storm where snow was observed, the SMART-R recorded a maximum of 66% higher rainfall than the maximum recorded by the gages. Unexpectedly, the highest elevation gage, located in a pre-fire coniferous vegetation community, consistently recorded the lowest precipitation, whereas gages in the lower elevation pre- fire chaparral community recorded the highest totals. The spatial locations of the maximum rainfall inferred by the SMART-R and the terrestrial gages are also offset by 1.6 km, with terrestrial values shifted easterly. The observation that the SMART-R images high rainfall intensities recorded by rain gages suggests that this technology has the ability to quantitatively estimate the spatial distribution over larger areas at a high resolution. Discrepancies on the storm scale, however, need to be investigated further, but we are optimistic that such high resolution data from the SMART-R and the terrestrial gages may lead to the effective application of a prototype debris-flow warning system where such processes put lives at risk.

Empirical models for predicting volumes of sediment deposited by debris flows and sediment-laden floods in the transverse ranges of southern California

USGS Publications Warehouse

Gartner, Joseph E.; Cannon, Susan H.; Santi, Paul M

2014-01-01

Debris flows and sediment-laden floods in the Transverse Ranges of southern California pose severe hazards to nearby communities and infrastructure. Frequent wildfires denude hillslopes and increase the likelihood of these hazardous events. Debris-retention basins protect communities and infrastructure from the impacts of debris flows and sediment-laden floods and also provide critical data for volumes of sediment deposited at watershed outlets. In this study, we supplement existing data for the volumes of sediment deposited at watershed outlets with newly acquired data to develop new empirical models for predicting volumes of sediment produced by watersheds located in the Transverse Ranges of southern California. The sediment volume data represent a broad sample of conditions found in Ventura, Los Angeles and San Bernardino Counties, California. The measured volumes of sediment, watershed morphology, distributions of burn severity within each watershed, the time since the most recent fire, triggering storm rainfall conditions, and engineering soil properties were analyzed using multiple linear regressions to develop two models. A “long-term model” was developed for predicting volumes of sediment deposited by both debris flows and floods at various times since the most recent fire from a database of volumes of sediment deposited by a combination of debris flows and sediment-laden floods with no time limit since the most recent fire (n = 344). A subset of this database was used to develop an “emergency assessment model” for predicting volumes of sediment deposited by debris flows within two years of a fire (n = 92). Prior to developing the models, 32 volumes of sediment, and related parameters for watershed morphology, burn severity and rainfall conditions were retained to independently validate the long-term model. Ten of these volumes of sediment were deposited by debris flows within two years of a fire and were used to validate the emergency assessment model. The models were validated by comparing predicted and measured volumes of sediment. These validations were also performed for previously developed models and identify that the models developed here best predict volumes of sediment for burned watersheds in comparison to previously developed models.

Vadose zone process that control landslide initiation and debris flow propagation

NASA Astrophysics Data System (ADS)

Sidle, Roy C.

2015-04-01

Advances in the areas of geotechnical engineering, hydrology, mineralogy, geomorphology, geology, and biology have individually advanced our understanding of factors affecting slope stability; however, the interactions among these processes and attributes as they affect the initiation and propagation of landslides and debris flows are not well understood. Here the importance of interactive vadose zone processes is emphasized related to the mechanisms, initiation, mode, and timing of rainfall-initiated landslides that are triggered by positive pore water accretion, loss of soil suction and increase in overburden weight, and long-term cumulative rain water infiltration. Both large- and small-scale preferential flow pathways can both contribute to and mitigate instability, by respectively concentrating and dispersing subsurface flow. These mechanisms are influenced by soil structure, lithology, landforms, and biota. Conditions conducive to landslide initiation by infiltration versus exfiltration are discussed relative to bedrock structure and joints. The effects of rhizosphere processes on slope stability are examined, including root reinforcement of soil mantles, evapotranspiration, and how root structures affect preferential flow paths. At a larger scale, the nexus between hillslope landslides and in-channel debris flows is examined with emphasis on understanding the timing of debris flows relative to chronic and episodic infilling processes, as well as the episodic nature of large rainfall and related stormflow generation in headwater streams. The hydrogeomorphic processes and conditions that determine whether or not landslides immediately mobilize into debris flows is important for predicting the timing and extent of devastating debris flow runout in steep terrain. Given the spatial footprint of individual landslides, it is necessary to assess vadose zone processes at appropriate scales to ascertain impacts on mass wasting phenomena. Articulating the appropriate level of detail of small-scale vadose zone processes into landslide models is a particular challenge. As such, understanding flow pathways in regoliths susceptible to mass movement is critical, including distinguishing between conditions conducive to vertical recharge of water through relatively homogeneous soil mantles and conditions where preferential flow dominates - either by rapid infiltration and lateral flow through interconnected preferential flow networks or via exfiltration through bedrock fractures. These different hydrologic scenarios have major implications for the occurrence, timing, and mode of slope failures.

Debris flow run-out simulation and analysis using a dynamic model

NASA Astrophysics Data System (ADS)

Melo, Raquel; van Asch, Theo; Zêzere, José L.

2018-02-01

Only two months after a huge forest fire occurred in the upper part of a valley located in central Portugal, several debris flows were triggered by intense rainfall. The event caused infrastructural and economic damage, although no lives were lost. The present research aims to simulate the run-out of two debris flows that occurred during the event as well as to calculate via back-analysis the rheological parameters and the excess rain involved. Thus, a dynamic model was used, which integrates surface runoff, concentrated erosion along the channels, propagation and deposition of flow material. Afterwards, the model was validated using 32 debris flows triggered during the same event that were not considered for calibration. The rheological and entrainment parameters obtained for the most accurate simulation were then used to perform three scenarios of debris flow run-out on the basin scale. The results were confronted with the existing buildings exposed in the study area and the worst-case scenario showed a potential inundation that may affect 345 buildings. In addition, six streams where debris flow occurred in the past and caused material damage and loss of lives were identified.

Coupled prediction of flash flood response and debris flow occurrence: Application on an alpine extreme flood event

NASA Astrophysics Data System (ADS)

Destro, Elisa; Amponsah, William; Nikolopoulos, Efthymios I.; Marchi, Lorenzo; Marra, Francesco; Zoccatelli, Davide; Borga, Marco

2018-03-01

The concurrence of flash floods and debris flows is of particular concern, because it may amplify the hazard corresponding to the individual generative processes. This paper presents a coupled modelling framework for the predictions of flash flood response and of the occurrence of debris flows initiated by channel bed mobilization. The framework combines a spatially distributed flash flood response model and a debris flow initiation model to define a threshold value for the peak flow which permits identification of channelized debris flow initiation. The threshold is defined over the channel network as a function of the upslope area and of the local channel bed slope, and it is based on assumptions concerning the properties of the channel bed material and of the morphology of the channel network. The model is validated using data from an extreme rainstorm that impacted the 140 km2 Vizze basin in the Eastern Italian Alps on August 4-5, 2012. The results show that the proposed methodology has improved skill in identifying the catchments where debris-flows are triggered, compared to the use of simpler thresholds based on rainfall properties.

Numerical simulation of failure behavior of granular debris flows based on flume model tests.

PubMed

Zhou, Jian; Li, Ye-xun; Jia, Min-cai; Li, Cui-na

2013-01-01

In this study, the failure behaviors of debris flows were studied by flume model tests with artificial rainfall and numerical simulations (PFC(3D)). Model tests revealed that grain sizes distribution had profound effects on failure mode, and the failure in slope of medium sand started with cracks at crest and took the form of retrogressive toe sliding failure. With the increase of fine particles in soil, the failure mode of the slopes changed to fluidized flow. The discrete element method PFC(3D) can overcome the hypothesis of the traditional continuous medium mechanic and consider the simple characteristics of particle. Thus, a numerical simulations model considering liquid-solid coupled method has been developed to simulate the debris flow. Comparing the experimental results, the numerical simulation result indicated that the failure mode of the failure of medium sand slope was retrogressive toe sliding, and the failure of fine sand slope was fluidized sliding. The simulation result is consistent with the model test and theoretical analysis, and grain sizes distribution caused different failure behavior of granular debris flows. This research should be a guide to explore the theory of debris flow and to improve the prevention and reduction of debris flow.

Differentiation of debris-flow and flash-flood deposits: implications for paleoflood investigations

USGS Publications Warehouse

Waythomas, Christopher F.; Jarrett, Robert D.; ,

1993-01-01

Debris flows and flash floods are common geomorphic processes in the Colorado Rocky Mountain Front Range and foothills. Usually, debris flows and flash floods are associated with excess summer rainfall or snowmelt, in areas were unconsolidated surficial deposits are relatively thick and slopes are steep. In the Front Range and foothills, flash flooding is limited to areas below about 2300m whereas, debris flow activity is common throughout the foothill and alpine zones and is not necessarily elevation limited. Because flash floods and debris flows transport large quantities of bouldery sediment, the resulting deposits appear somewhat similar even though such deposits were produced by different processes. Discharge estimates based on debris-flow deposits interpreted as flash-flood deposits have large errors because techniques for discharge retrodiction were developed for water floods with negligible sediment concentrations. Criteria for differentiating between debris-flow and flash-flood deposits are most useful for deposits that are fresh and well-exposed. However, with the passage of time, both debris-flow and flash-flood deposits become modified by the combined effects of weathering, colluviation, changes in surface morphology, and in some instances removal of interstitial sediment. As a result, some of the physical characteristics of the deposits become more alike. Criteria especially applicable to older deposits are needed. We differentiate flash-flood from debris-flow and other deposits using clast fabric measurements and other morphologic and sedimentologic techniques (e.g., deposit morphology, clast lithology, particle size and shape, geomorphic setting).

The Use 0f AVIRIS Imagery To Assess Clay Mineralogy And Debris-Flow Potential In Cataract Canyon, Utah: A Preliminary Report

NASA Technical Reports Server (NTRS)

Rudd, Lawrence; Merenyi, Erzsebet

2004-01-01

Worldwide debris flows destroy property and take human lives every year (Costa, 1984). As a result of extensive property damage and loss of life there is a pressing need to go beyond just describing the nature and extent of debris flows as they occur. Most of the research into debris-flow initiation has centered on rainfall, slope angle, and existing debris-flow deposits (Costa and Wieczorek, 1987). The factor of source lithology has been recently addressed by studies in the sedimentary terranes of Grand Canyon (Webb et al., 1996; Griffiths et al., 1996) and on the Colorado Plateau as a whole.3 On the Colorado Plateau shales dominated by kaolinite and illite clays are significantly more likely to be recent producers of debris-flows than are shales in which smectite clays dominate.3 Establishing the location of shales and colluvial deposits containing kaolinite and illite clays in sedimentary terranes on the Colorado Plateau is essential to predicting where debris flows are likely to occur. AVIRIS imagery can be used to distinguish between types of clay minerals (Chabrillat et al., 2001), providing the basis for surface-materials maps. The ultimate product of this study will be a model that can be used to estimate the debris-flow hazard in Cataract Canyon, Utah. This model will be based on GIS overlay analysis of debris-flow initiation factor maps, including surface-materials maps derived from AVIRIS data.

Debris flow susceptibility assessment after the 2008 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Fan, Xuanmei; van Westen, Cees; Tang, Chenxiao; Tang, Chuan

2014-05-01

Due to a tremendous amount of loose material from landslides that occurred during the Wenchuan earthquake, the frequency and magnitude of debris flows have been immensely increased, causing many casualties and economic losses. This study attempts to assess the post-earthquake debris flow susceptibility based on catchment units in the Wenchuan county, one of the most severely damaged county by the earthquake. The post earthquake debris flow inventory was created by RS image interpretation and field survey. According to our knowledge to the field, several relevant factors were determined as indicators for post-earthquake debris flow occurrence, including the distance to fault surface rupture, peak ground acceleration (PGA), coseismic landslide density, rainfall data, internal relief, slope, drainage density, stream steepness index, existing mitigation works etc. These indicators were then used as inputs in a heuristic model that was developed by adapting the Spatial Multi Criteria Evaluation (SMCE) method. The relative importance of the indicators was evaluated according to their contributions to the debris flow events that have occurred after the earthquake. The ultimate goal of this study is to estimate the relative likelihood of debris flow occurrence in each catchment, and use this result together with elements at risk and vulnerability information to assess the changing risk of the most susceptible catchment.

Channel geometry change of a first-order stream after a small debris flow in Ashio Mountains of central Japan

NASA Astrophysics Data System (ADS)

Hattanji, T.; Wasklewicz, T.

2006-12-01

We examined geometry change of a steep first-order channel with a laserscanner before and after a small debris flow. The study site is located in chert area, Ashio Mountains, Japan. On August 12, 2005, a 20-year storm event with maximum 1-hour rainfall of 75.4 mm/h triggered a small landslide at a steep channel head. The sliding material moved as a debris flow along the first-order channel (C3) to the mouth. We successfully measured high-resolution channel topography with the Leica Geosystems High-Definition Surveying Laser Scanner before (April 30) and after the debris-flow event (October 9-11). Width, depth and other related parameters were measured for 30 selected cross sections. Bankfull stage of this first-order channel after the debris-flow event is much higher than two-year flood stage. The magnitude of channel geometry change varies non-linearly in downstream direction. The non-linear variability is attributed to differences in stream bed and bank characteristics. Bedrock-channel reach is less impacted by the debris flow. The largest magnitude changes in the channel geometry parameters occur along colluvially confined channel reaches.

Landslides induced by heavy rainfall in July 2012 in Northern Kyushu District, Japan and the influence of long term rainfall increase comparing with the slope destabilization due to strong seismic shaking

NASA Astrophysics Data System (ADS)

Kubota, Tetsuya; Shinohara, Yoshinori; Aditian, Aril

2013-04-01

1. Objective We had a deluge in July 2012 in the northern Kyushu district with intense rainfall of 800mm and 108mm/hr. This intensity yielded countless traces of debris flow and landslides, slope failures that induced tremendous damage and causalities in the area. Hence, several field investigations and reconnaissance tasks were conducted to delve into this sediment-related disaster. The various results and the information obtained through this investigation were reported, mentioning the damage, the meteorological condition, geologic-geomorphologic features and hydraulic characteristics of the debris flows, vegetation effects, and the influence of the climate change. Increase in rainfall that may be induced by the global climate change is obvious in Kyushu district, Japan, according to the analysis of rain data observed in various locations including mountainside points that are not influenced by local warming due to urbanization. On this point of view, we are intrigued to elucidate the response of landslide to this increase in rainfall. Hence, its long term impact on this landslide disaster is also analyzed comparing with the slope destabilization due to strong seismic shaking. 2. Method and target areas Field investigation on landslides slopes, slope failures and torrents where debris flows occurred are conducted to obtain the geologic data, geo-structure, vegetation feature, soil samples and topographic data i.e. cross sections, then soil shear tests and soil permeability tests are also conducted. The rainfall data at the nearest rain observatory were obtained from the database of Japan meteorological agency. The long term impact on the slope stability at some slopes in the area is analyzed by the finite element method (FEM) combined with rain infiltration and seepage analysis with the long term rainfall fluctuation data, obtaining factor of safety ( Fs) on real landslide slopes. The results are compared with the destabilized influence on the slopes due to the soil strength reduction by seismic shaking. The target areas are located in northern Kyushu district, western Japan where they often have severe landslide disasters. The geology in research areas consists of Paleozoic and Mesozoic rocks (mainly schist, slate) and Quaternary volcanic sediment such as Aso volcano body. The vegetation consists of mainly Japanese cypress, cedar or bamboo. 3. Result and consideration Consequently, the long term rainfall increase in the region such as increment of approximately 20 mm/hr for rain intensity Ri in 36 years is confirmed statistically using Kendall's rank correlation, and it is found that its impact on slope stability is considerable and critical in other cases. In the sample landslide slopes, even the increase in rain of duration for only 10 years has impact to a certain extent on their stabilities in terms of Fs. The Fs calculated with rains in previous decade is higher than 1.0 that corresponds to stable state, whereas the Fs with present rains is lower than 1.0 such as 0.99 which means unstable state. Extremely heavy rainfall with this impact is generally cause extreme ground water pressure in the slope. It is also obvious that the extreme ground water content rendered even small landslides liquefied to be source of destructive debris flows. In this disaster, especially in the Aso volcanic region, tremendous number of debris flow occurred and even the talus cone slopes which are usually stable collapsed to flow down. However, the influence of the long term rainfall increase on the slopes (such as 1% decrease in Fs) is not relatively small compared with the destabilization of the slopes due to the reduction of soil strength by seismic shaking (8~9 % reduction in Fs after seismic shaking of even 490gal). 4. Conclusion In the disaster in July 2012, many landslides and debris flows originated from landslides induced by concentrated underground water supplied by the heavy rainfall occurred. The increase of rainfall due to climate change with the increasing rate such as 20 mm/hr surely has impact on almost landslide slopes in aspects of slope stability, although the influence of the long term rainfall increase on the slopes is relatively small compared with the destabilization of the slopes due to the reduction of soil strength by seismic shakings. Therefore, with this rain increase rate, it is possible for many forest slopes or natural slopes to become unstable and cause landslide disasters especially after potential strong earthquake in the near future.

Influence of The Rise of 0c Isotherm On Debris Flow Magnitude During Autumn 2000 Bad Weather In Wallis, Switzerland

NASA Astrophysics Data System (ADS)

Bardou, E.

The triggering of debris flows is a complex phenomenon in which rainfall amount and intensity, antecedent moisture, temperature, etc., play a part. Some interesting observations were made during the October 2000 bad weather, particularly about the effects of the 0C isotherm's rise. First, a map showing the differential rise of the 0C isotherm was drawn. The com- puter performed interpolation was manually corrected to reflect as well as possible the effects of the topography. In parallel, the major part of the territory of the canton of Valais was surveyed, and relative intensities of debris flows were estimated. This means that we took even into account debris flows which didn't cause damages. In concrete terms, the magnitude of the October 2000 events were compared to the size of the older ones (or to the tracks of the past events). Assuming that the climatic situ- ation was an extreme one, we divided the debris flows in 3 classes: debris flows with an abnormal high magnitude, debris flows with an abnormal low magnitude, and de- bris flows with a normal magnitude. Then we compared the relative magnitude of the debris flows with the intensity of the 0C isotherm's rise on the same area. The results show a good agreement between these two parameters. Thus, the 0C isotherm's rise is a new parameter to be taken into account for the assessment of the debris flow's hazard. The present study gives new possibilities for watershed's monitoring.

Comparing two models for post-wildfire debris flow susceptibility mapping

NASA Astrophysics Data System (ADS)

Cramer, J.; Bursik, M. I.; Legorreta Paulin, G.

2017-12-01

Traditionally, probabilistic post-fire debris flow susceptibility mapping has been performed based on the typical method of failure for debris flows/landslides, where slip occurs along a basal shear zone as a result of rainfall infiltration. Recent studies have argued that post-fire debris flows are fundamentally different in their method of initiation, which is not infiltration-driven, but surface runoff-driven. We test these competing models by comparing the accuracy of the susceptibility maps produced by each initiation method. Debris flow susceptibility maps are generated according to each initiation method for a mountainous region of Southern California that recently experienced wildfire and subsequent debris flows. A multiple logistic regression (MLR), which uses the occurrence of past debris flows and the values of environmental parameters, was used to determine the probability of future debris flow occurrence. The independent variables used in the MLR are dependent on the initiation method; for example, depth to slip plane, and shear strength of soil are relevant to the infiltration initiation, but not surface runoff. A post-fire debris flow inventory serves as the standard to compare the two susceptibility maps, and was generated by LiDAR analysis and field based ground-truthing. The amount of overlap between the true locations where debris flow erosion can be documented, and where the MLR predicts high probability of debris flow initiation was statistically quantified. The Figure of Merit in Space (FMS) was used to compare the two models, and the results of the FMS comparison suggest that surface runoff-driven initiation better explains debris flow occurrence. Wildfire can breed conditions that induce debris flows in areas that normally would not be prone to them. Because of this, nearby communities at risk may not be equipped to protect themselves against debris flows. In California, there are just a few months between wildland fire season and the wet season to assess a community's risk and prepare. It is important, therefore, that researchers have a way to quickly and accurately assess the susceptibility for debris flows in recently burned areas.

Stability analysis and hazard assessment of the northern slopes of San Vicente Volcano in central El Salvador

NASA Astrophysics Data System (ADS)

Smith, Daniel M.

Geologic hazards affect the lives of millions of people worldwide every year. El Salvador is a country that is regularly affected by natural disasters, including earthquakes, volcanic eruptions and tropical storms. Additionally, rainfall-induced landslides and debris flows are a major threat to the livelihood of thousands. The San Vicente Volcano in central El Salvador has a recurring and destructive pattern of landslides and debris flows occurring on the northern slopes of the volcano. In recent memory there have been at least seven major destructive debris flows on San Vicente volcano. Despite this problem, there has been no known attempt to study the inherent stability of these volcanic slopes and to determine the thresholds of rainfall that might lead to slope instability. This thesis explores this issue and outlines a suggested method for predicting the likelihood of slope instability during intense rainfall events. The material properties obtained from a field campaign and laboratory testing were used for a 2-D slope stability analysis on a recent landslide on San Vicente volcano. This analysis confirmed that the surface materials of the volcano are highly permeable and have very low shear strength and provided insight into the groundwater table behavior during a rainstorm. The biggest factors on the stability of the slopes were found to be slope geometry, rainfall totals and initial groundwater table location. Using the results from this analysis a stability chart was created that took into account these main factors and provided an estimate of the stability of a slope in various rainfall scenarios. This chart could be used by local authorities in the event of a known extreme rainfall event to help make decisions regarding possible evacuation. Recommendations are given to improve the methodology for future application in other areas as well as in central El Salvador.

Observations of debris flows at Chalk Cliffs, Colorado, USA: Part 1, in-situ measurements of flow dynamics, tracer particle movement and video imagery from the summer of 2009

USGS Publications Warehouse

McCoy, Scott W.; Coe, Jeffrey A.; Kean, Jason W.; Tucker, Greg E.; Staley, Dennis M.; Wasklewicz, Thad A.

2011-01-01

Debris flows initiated by surface-water runoff during short duration, moderate- to high-intensity rainfall are common in steep, rocky, and sparsely vegetated terrain. Yet large uncertainties remain about the potential for a flow to grow through entrainment of loose debris, which make formulation of accurate mechanical models of debris-flow routing difficult. Using a combination of in situ measurements of debris flow dynamics, video imagery, tracer rocks implanted with passive integrated transponders (PIT) and pre- and post-flow 2-cm resolution digital terrain models (terrain data presented in a companion paper by STALEY et alii, 2011), we investigated the entrainment and transport response of debris flows at Chalk Cliffs, CO, USA. Four monitored events during the summer of 2009 all initiated from surface-water runoff, generally less than an hour after the first measurable rain. Despite reach-scale morphology that remained relatively constant, the four flow events displayed a range of responses, from long-runout flows that entrained significant amounts of channel sediment and dammed the main-stem river, to smaller, short-runout flows that were primarily depositional in the upper basin. Tracer-rock travel-distance distributions for these events were bimodal; particles either remained immobile or they travelled the entire length of the catchment. The long-runout, large-entrainment flow differed from the other smaller flows by the following controlling factors: peak 10-minute rain intensity; duration of significant flow in the channel; and to a lesser extent, peak surge depth and velocity. Our growing database of natural debris-flow events can be used to develop linkages between observed debris-flow transport and entrainment responses and the controlling rainstorm characteristics and flow properties.

Analysis and mapping of post-fire hydrologic hazards for the 2002 Hayman, Coal Seam, and Missionary Ridge wildfires, Colorado

USGS Publications Warehouse

Elliott, J.G.; Smith, M.E.; Friedel, M.J.; Stevens, M.R.; Bossong, C.R.; Litke, D.W.; Parker, R.S.; Costello, C.; Wagner, J.; Char, S.J.; Bauer, M.A.; Wilds, S.R.

2005-01-01

Wildfires caused extreme changes in the hydrologic, hydraulic, and geomorphologic characteristics of many Colorado drainage basins in the summer of 2002. Detailed assessments were made of the short-term effects of three wildfires on burned and adjacent unburned parts of drainage basins. These were the Hayman, Coal Seam, and Missionary Ridge wildfires. Longer term runoff characteristics that reflect post-fire drainage basin recovery expected to develop over a period of several years also were analyzed for two affected stream reaches: the South Platte River between Deckers and Trumbull, and Mitchell Creek in Glenwood Springs. The 10-, 50-, 100-, and 500-year flood-plain boundaries and water-surface profiles were computed in a detailed hydraulic study of the Deckers-to-Trumbull reach. The Hayman wildfire burned approximately 138,000 acres (216 square miles) in granitic terrain near Denver, and the predominant potential hazard in this area is flooding by sediment-laden water along the large tributaries to and the main stem of the South Platte River. The Coal Seam wildfire burned approximately 12,200 acres (19.1 square miles) near Glenwood Springs, and the Missionary Ridge wildfire burned approximately 70,500 acres (110 square miles) near Durango, both in areas underlain by marine shales where the predominant potential hazard is debris-flow inundation of low-lying areas. Hydrographs and peak discharges for pre-burn and post-burn scenarios were computed for each drainage basin and tributary subbasin by using rainfall-runoff models because streamflow data for most tributary subbasins were not available. An objective rainfall-runoff model calibration method based on nonlinear regression and referred to as the ?objective calibration method? was developed and applied to rainfall-runoff models for three burned areas. The HEC-1 rainfall-runoff model was used to simulate the pre-burn rainfall-runoff processes in response to the 100-year storm, and HEC-HMS was used for runoff hydrograph generation. Post-burn rainfall-runoff parameters were determined by adjusting the runoff-curve numbers on the basis of a weighting procedure derived from the U.S. Soil Conservation Service (now the National Resources Conservation Service) equation for precipitation excess and the effect of burn severity. This weighting procedure was determined to be more appropriate than simple area weighting because of the potentially marked effect of even small burned areas on the runoff hydrograph in individual drainage basins. Computed water-peak discharges from HEC-HMS models were increased volumetrically to account for increased sediment concentrations that are expected as a result of accelerated erosion after burning. Peak discharge estimates for potential floods in the South Platte River were increased by a factor that assumed a volumetric sediment concentration (Cv) of 20 percent. Flood hydrographs for the South Platte River and Mitchell Creek were routed down main-stem channels using watershed-routing algorithms included in the HEC-HMS rainfall-runoff model. In areas subject to debris flows in the Coal Seam and Missionary Ridge burned areas, debris-flow discharges were simulated by 100-year rainfall events, and the inflow hydrographs at tributary mouths were simulated by using the objective calibration method. Sediment concentrations (Cv) used in debris-flow simulations were varied through the event, and were initial Cv 20 percent, mean Cv approximately 31 percent, maximum Cv 48 percent, Cv 43 percent at the time of the water hydrograph peak, and Cv 20 percent for the duration of the event. The FLO-2D flood- and debris-flow routing model was used to delineate the area of unconfined debris-flow inundation on selected alluvial fan and valley floor areas. A method was developed to objectively determine the post-fire recovery period for the Hayman and Coal Seam burned areas using runoff-curve numbers (RCN) for all drainage basins for a 50-year period. A

Climate change impacts on mass movements--case studies from the European Alps.

PubMed

Stoffel, M; Tiranti, D; Huggel, C

2014-09-15

This paper addresses the current knowledge on climate change impacts on mass movement activity in mountain environments by illustrating characteristic cases of debris flows, rock slope failures and landslides from the French, Italian, and Swiss Alps. It is expected that events are likely to occur less frequently during summer, whereas the anticipated increase of rainfall in spring and fall could likely alter debris-flow activity during the shoulder seasons (March, April, November, and December). The magnitude of debris flows could become larger due to larger amounts of sediment delivered to the channels and as a result of the predicted increase in heavy precipitation events. At the same time, however, debris-flow volumes in high-mountain areas will depend chiefly on the stability and/or movement rates of permafrost bodies, and destabilized rock glaciers could lead to debris flows without historic precedents in the future. The frequency of rock slope failures is likely to increase, as excessively warm air temperatures, glacier shrinkage, as well as permafrost warming and thawing will affect and reduce rock slope stability in the direction that adversely affects rock slope stability. Changes in landslide activity in the French and Western Italian Alps will likely depend on differences in elevation. Above 1500 m asl, the projected decrease in snow season duration in future winters and springs will likely affect the frequency, number and seasonality of landslide reactivations. In Piemonte, for instance, 21st century landslides have been demonstrated to occur more frequently in early spring and to be triggered by moderate rainfalls, but also to occur in smaller numbers. On the contrary, and in line with recent observations, events in autumn, characterized by a large spatial density of landslide occurrences might become more scarce in the Piemonte region. Copyright © 2014 Elsevier B.V. All rights reserved.

THRESH—Software for tracking rainfall thresholds for landslide and debris-flow occurrence, user manual

USGS Publications Warehouse

Baum, Rex L.; Fischer, Sarah J.; Vigil, Jacob C.

2018-02-28

Precipitation thresholds are used in many areas to provide early warning of precipitation-induced landslides and debris flows, and the software distribution THRESH is designed for automated tracking of precipitation, including precipitation forecasts, relative to thresholds for landslide occurrence. This software is also useful for analyzing multiyear precipitation records to compare timing of threshold exceedance with dates and times of historical landslides. This distribution includes the main program THRESH for comparing precipitation to several kinds of thresholds, two utility programs, and a small collection of Python and shell scripts to aid the automated collection and formatting of input data and the graphing and further analysis of output results. The software programs can be deployed on computing platforms that support Fortran 95, Python 2, and certain Unix commands. The software handles rainfall intensity-duration thresholds, cumulative recent-antecedent precipitation thresholds, and peak intensity thresholds as well as various measures of antecedent precipitation. Users should have predefined rainfall thresholds before running THRESH.

Fires, storms, and water supplies: a case of compound extremes?

NASA Astrophysics Data System (ADS)

Sheridan, G. J.; Nyman, P.; Langhans, C.; Jones, O.; Lane, P. N.

2013-12-01

Intense rainfall events following fire can wash sediment and ash into streams and reservoirs, contaminating water supplies for cities and towns. Post fire flooding and debris flows damage infrastructure and endanger life. These kinds of risks which are associated with a combination of two or more events (which may or may not be extreme when occurring independently) are an example of what the IPCC recently referred to as ';compound extremes'. Detailed models exist for modeling fire and erosion events separately, however there have been few attempts to integrate these models so as to estimate the water quality and infrastructure risks associated with combined fire and rainfall regimes. This presentation will articulate the issues associated with modeling the compound effects of fire and subsequent rainfall events on erosion, debris flows and water quality, and will describe and contrast several new approaches to modeling this problem developed and applied to SE Australian fire prone landscapes under the influence of climate change.

Debris flow susceptibility assessment based on an empirical approach in the central region of South Korea

NASA Astrophysics Data System (ADS)

Kang, Sinhang; Lee, Seung-Rae

2018-05-01

Many debris flow spreading analyses have been conducted during recent decades to prevent damage from debris flows. An empirical approach that has been used in various studies on debris flow spreading has advantages such as simple data acquisition and good applicability for large areas. In this study, a GIS-based empirical model that was developed at the University of Lausanne (Switzerland) is used to assess the debris flow susceptibility. Study sites are classified based on the types of soil texture or geological conditions, which can indirectly consider geotechnical or rheological properties, to supplement the weaknesses of Flow-R which neglects local controlling factors. The mean travel angle for each classification is calculated from a debris flow inventory map. The debris flow susceptibility is assessed based on changes in the flow-direction algorithm, an inertial function with a 5-m DEM resolution. A simplified friction-limited model was applied to the runout distance analysis by using the appropriate travel angle for the corresponding classification with a velocity limit of 28 m/s. The most appropriate algorithm combinations that derived the highest average of efficiency and sensitivity for each classification are finally determined by applying a confusion matrix with the efficiency and the sensitivity to the results of the susceptibility assessment. The proposed schemes can be useful for debris flow susceptibility assessment in both the study area and the central region of Korea, which has similar environmental factors such as geological conditions, topography and rainfall characteristics to the study area.

Analysis of Geomorphic and Hydrologic Characteristics of Mount Jefferson Debris Flow, Oregon, November 6, 2006

USGS Publications Warehouse

Sobieszczyk, Steven; Uhrich, Mark A.; Piatt, David R.; Bragg, Heather M.

2008-01-01

On November 6, 2006, a rocky debris flow surged off the western slopes of Mount Jefferson into the drainage basins of Milk and Pamelia Creeks in Oregon. This debris flow was not a singular event, but rather a series of surges of both debris and flooding throughout the day. The event began during a severe storm that brought warm temperatures and heavy rainfall to the Pacific Northwest. Precipitation measurements near Mount Jefferson at Marion Forks and Santiam Junction showed that more than 16.1 centimeters of precipitation fell the week leading up to the event, including an additional 20.1 centimeters falling during the 2 days afterward. The flooding associated with the debris flow sent an estimated 15,500 to 21,000 metric tons, or 9,800 to 13,000 cubic meters, of suspended sediment downstream, increasing turbidity in the North Santiam River above Detroit Lake to an estimated 35,000 to 55,000 Formazin Nephelometric Units. The debris flow started small as rock and ice calved off an upper valley snowfield, but added volume as it eroded weakly consolidated deposits from previous debris flows, pyroclastic flows, and glacial moraines. Mud run-up markings on trees indicated that the flood stage of this event reached depths of at least 2.4 meters. Velocity calculations indicate that different surges of debris flow and flooding reached 3.9 meters per second. The debris flow reworked and deposited material ranging in size from sand to coarse boulders over a 0.1 square kilometer area, while flooding and scouring as much as 0.45 square kilometer. Based on cross-sectional transect measurements recreating pre-event topography and other field measurements, the total volume of the deposit ranged from 100,000 to 240,000 cubic meters.

Evolution of a giant debris flow in the transitional mountainous region between the Tibetan Plateau and the Qinling Mountain range, Western China: Constraints from broadband seismic records

NASA Astrophysics Data System (ADS)

Huang, Xinghui; Li, Zhengyuan; Yu, Dan; Xu, Qiang; Fan, Junyi; Hao, Zhen; Niu, Yanping

2017-10-01

The catastrophic Sanyanyu and Luojiayu debris flows, which were induced by heavy rainfall, occurred at approximately midnight, August 7th, 2010 (Beijing time, UTC + 8) and claimed 1,765 lives. Most seismic stations located within 150 km did not detect the debris flows except for the closest seismic station, ZHQ, indicating that the seismic signals generated by the debris flows decayed rapidly. We analyzed broadband seismic signals from the ZHQ seismic station, beginning approximately 20 min before the outbreak of the Sanyanyu debris flow, to rebuild its evolution processes. Seismic signals can detect development of the Sanyanyu debris flow approximately 20 min after a heavy rain started falling in its initiation area; this time was characterized by a gradual increase in seismic amplitude accompanied by a series of spike signals that were probably generated by rock collapses within the catchment. The frequency contents and the characteristics of seismic signals before and after 23:33:15 (T1) are distinctively different, which we interpret as being generated by a large quantity of flowing material entering the main channel, marking the formation of the Sanyanyu debris flow. We attribute seismic amplitude increases between 23:33:15 (T1) and 23:34:26 (T2) and between 23:35:40 (T3) and 23:36:49 (T4) to entrainment of the deposit material after initiation of the debris flow and to its flow through a colluvial deposit area, respectively. The main frequency band broadening of seismic signals after 23:37:30 (T5) is believed to have been induced by impacts between the flowing material and check dams.

Map showing recent (1997-98 El Nino) and historical landslides, Crow Creek and vicinity, Alameda and Contra Costa Counties, California

USGS Publications Warehouse

Coe, Jeffrey A.; Godt, Jonathan; Tachker, Pierre

2004-01-01

This report documents the spatial distribution of 3,800 landslides caused by 1997-98 El Ni?o winter rainfall in the vicinity of Crow Creek in Alameda and Contra Costa Counties, California. The report also documents 558 historical (pre-1997-98) landslides. Landslides were mapped from 1:12,000-scale aerial photographs and classified as either debris flows or slides. Slides include rotational and translational slides, earth flows, and complex slope movements. Debris flows and slides from the 1997-98 winter modified 1 percent of the surface of the 148.6 km2 study area. Debris flows were scattered throughout the area, regardless of the type of underlying bedrock geology. Slides, however, were concentrated in a soft sandstone, conglomerate, and clayey group of rock units. Digital map files accompany the report.

Hydrologic monitoring of a landslide-prone hillslope in the Elliott State Forest, Southern Coast Range, Oregon, 2009-2012

USGS Publications Warehouse

Smith, Joel B.; Godt, Jonathan W.; Baum, Rex L.; Coe, Jeffrey A.; Burns, William J.; Morse, Michael M.; Sener-Kaya, Basak; Kaya, Murat

2014-01-01

The Oregon Coast Range is dissected by numerous unchanneled headwater basins, which can generate shallow landslides and debris flows during heavy or prolonged rainfall. An automated monitoring system was installed in an unchanneled headwater basin to measure rainfall, volumetric water content, groundwater temperature, and pore pressures at 15-minute intervals. The purpose of this report is to describe and present the methods used for the monitoring as well as the preliminary data collected during the period from 2009 to 2012. Observations show a pronounced seasonal variation in volumetric water content and pore pressures. Increases in pore pressures and volumetric water content from dry-season values begin with the onset of the rainy season in the fall (typically early to mid October). High water contents and pore pressures tend to persist throughout the rainy season, which typically ends in May. Heavy or prolonged rainfall during the wet season that falls on already moist soils often generates positive pore pressures that are observed in the deeper instruments. These data provide a record of the basin’s hydrologic response to rainfall and provide a foundation for understanding the conditions that lead to landslide and debris-flow occurrence.

A debris avalanche at Forest Falls, San Bernardino County, California, July 11, 1999

USGS Publications Warehouse

Morton, Douglas M.; Hauser, Rachel M.

2001-01-01

This publication consists of the online version of a CD-ROM publication, U.S. Geological Survey Open-File Report 01-146. The data for this publication total 557 MB on the CD-ROM. For speed of transfer, the main PDF document has been compressed (with a subsequent loss of image quality) from 145 to 18.1 MB. The community of Forest Falls, California, is frequently subject to relatively slow moving debris flows. Some 11 debris flow events that were destructive to property have been recorded between 1955 and 1998. On July 11 and 13, 1999, debris flows again occurred, produced by high-intensity, short-duration monsoon rains. Unlike previous debris flow events, the July 11 rainfall generated a high-velocity debris avalanche in Snow Creek, one of the several creeks crossing the composite, debris flow dominated, alluvial fan on which Forest Falls is located. This debris avalanche overshot the bank of the active debris flow channel of Snow Creek, destroying property in the near vicinity and taking a life. The minimum velocity of this avalanche is calculated to have been in the range of 40 to 55 miles per hour. Impact from high-velocity boulders removed trees where the avalanche overshot the channel bank. Further down the fan, the rapidly moving debris fragmented the outer parts of the upslope side of large pine trees and embedded rock fragments into the tree trunks. Unlike the characteristic deposits formed by debris flows, the avalanche spread out down-slope and left no deposit suggestive of a debris avalanche. This summer monsoon-generated debris avalanche is apparently the first recorded for Forest Falls. The best indications of past debris avalanches may be the degree of permanent scars produced by extensive abrasion and splintering of the outer parts of pine trees that were in the path of an avalanche.

The use of remote sensing for rapid post-disaster assessment - an example from Kedarnath, Uttarakhand, north India (Invited)

NASA Astrophysics Data System (ADS)

Petley, D. N.

2013-12-01

Kedarnath is small town built around in important Hindu temple in the Rudraprayag district, Uttarakhand in northern India. Located at an elevation of 3,583 m, it is situated in a remote valley with no vehicular access. In summer, the temple is an important pilgrimage destination, with thousands of visitors per day, all of whom have to access the location via a 14 km trek or horse ride along a paved pathway, or via a helicopter ride. Between 14th and 17th June 2013, Uttarakhand was affected by unusually heavy early monsoonal rainfall. Whilst the rainfall totals did not reach record levels, the precipitation fell onto thawing snow, inducing very large debris flows. Kedarnath was affected by two major debris flows. According to eyewitness reports the first struck without warning in the evening of 16th June at about 7 pm local time. The second, larger, event occurred the following morning at about 6 am. The two debris flows destroyed most of the buildings in Kedarnath, although the temple survived with some damage. Across Uttarakhand it is estimated that about 5700 people died in the debris flows; the majority of these losses were at Kedarnath and in the immediate downstream communities. In the aftermath of the disaster there was considerable uncertainty as to the cause of the debris flows, with much speculation about the possibility that either a rock avalanche had developed on the flanks of the adjacent mountains or that there had been a catastrophic glacial collapse event upstream of the town. On 18th June the Indian Remote Sensing Organisation (IRSO) captured and released a RISAT-1 image of Kedarnath. Although the resolution was insufficient to determine what had occurred to trigger the disaster, it served to highlight two potential sources of the debris flows. One of these was an area of disturbance at the snout of the Charobari Glacier upslope from the town; the other was a possible landslide scar on an adjacent slope. On 23rd June 2013 NASA captured a Landsat 8 image of the site, which suggested that both of these sources might have been responsible for the debris flows. Finally, on 27th June IRSO released a high resolution RISAT-1 image of the Kedarnath region. This showed clearly that the first (16th June) debris flow originated from a landslide event upstream and to the east of the town. This took the form of an initially small, superficial landslide that entrained large volumes of debris before striking the town as a highly mobile debris flow. The second debris flow (on 17th June) was caused when an ephemeral lake, trapped behind a lateral moraine from the Charobari glacier upstream and to the east of the town, overtopped and catastrophically breached its barrier. The resultant flood scoured a large volume of sediment from the steep channel above the town, generating a very dense debris flow that was exceptionally destructive. Subsequent analyses by ground-based teams has suggested that this initial interpretation from remotely-sensed data was correct. Both of the sources of the debris flows were clearly evident on images captured before the event, and it is also clear that temple and the adjacent town were built on a terrace constructed in an earlier debris event. Thus, remotely sensed images could have played a role in the management of the hazard prior to the disaster.

Critical rainfall conditions for the initiation of torrential flows. Results from the Rebaixader catchment (Central Pyrenees)

NASA Astrophysics Data System (ADS)

Abancó, Clàudia; Hürlimann, Marcel; Moya, José; Berenguer, Marc

2016-10-01

Torrential flows like debris flows or debris floods are fast movements formed by a mix of water and different amounts of unsorted solid material. They generally occur in steep torrents and pose high risk in mountainous areas. Rainfall is their most common triggering factor and the analysis of the critical rainfall conditions is a fundamental research task. Due to their wide use in warning systems, rainfall thresholds for the triggering of torrential flows are an important outcome of such analysis and are empirically derived using data from past events. In 2009, a monitoring system was installed in the Rebaixader catchment, Central Pyrenees (Spain). Since then, rainfall data of 25 torrential flows (;TRIG rainfalls;) were recorded, with a 5-min sampling frequency. Other 142 rainfalls that did not trigger torrential flows (;NonTRIG rainfalls;) were also collected and analyzed. The goal of this work was threefold: (i) characterize rainfall episodes in the Rebaixader catchment and compare rainfall data that triggered torrential flows and others that did not; (ii) define and test Intensity-Duration (ID) thresholds using rainfall data measured inside the catchment by with different techniques; (iii) analyze how the criterion used for defining the rainfall duration and the spatial variability of rainfall influences the value obtained for the thresholds. The statistical analysis of the rainfall characteristics showed that the parameters that discriminate better the TRIG and NonTRIG rainfalls are the rainfall intensities, the mean rainfall and the total rainfall amount. The antecedent rainfall was not significantly different between TRIG and NonTRIG rainfalls, as it can be expected when the source material is very pervious (a sandy glacial soil in the study site). Thresholds were derived from data collected at one rain gauge located inside the catchment. Two different methods were applied to calculate the duration and intensity of rainfall: (i) using total duration, Dtot, and mean intensity, Imean, of the rainfall event, and (ii) using floating durations, D, and intensities, Ifl, based on the maximum values over floating periods of different duration. The resulting thresholds are considerably different (Imean = 6.20 Dtot-0.36 and Ifl_90% = 5.49 D-0.75, respectively) showing a strong dependence on the applied methodology. On the other hand, the definition of the thresholds is affected by several types of uncertainties. Data from both rain gauges and weather radar were used to analyze the uncertainty associated with the spatial variability of the triggering rainfalls. The analysis indicates that the precipitation recorded by the nearby rain gauges can introduce major uncertainties, especially for convective summer storms. Thus, incorporating radar rainfall can significantly improve the accuracy of the measured triggering rainfall. Finally, thresholds were also derived according to three different criteria for the definition of the duration of the triggering rainfall: (i) the duration until the peak intensity, (ii) the duration until the end of the rainfall; and, (iii) the duration until the trigger of the torrential flow. An important contribution of this work is the assessment of the threshold relationships obtained using the third definition of duration. Moreover, important differences are observed in the obtained thresholds, showing that ID relationships are significantly dependent on the applied methodology.

Effect of antecedent-hydrological conditions on rainfall triggering of debris flows in ash-fall pyroclastic mantled slopes of Campania (southern Italy)

USGS Publications Warehouse

Napolitano, E.; Fusco, F; Baum, Rex L.; Godt, Jonathan W.; De Vita, P.

2016-01-01

Mountainous areas surrounding the Campanian Plain and the Somma-Vesuvius volcano (southern Italy) are among the most risky areas of Italy due to the repeated occurrence of rainfallinduced debris flows along ash-fall pyroclastic soil-mantled slopes. In this geomorphological framework, rainfall patterns, hydrological processes taking place within multi-layered ash-fall pyroclastic deposits and soil antecedent moisture status are the principal factors to be taken into account to assess triggering rainfall conditions and the related hazard. This paper presents the outcomes of an experimental study based on integrated analyses consisting of the reconstruction of physical models of landslides, in situ hydrological monitoring, and hydrological and slope stability modeling, carried out on four representative source areas of debris flows that occurred in May 1998 in the Sarno Mountain Range. The hydrological monitoring was carried out during 2011 using nests of tensiometers and Watermark pressure head sensors and also through a rainfall and air temperature recording station. Time series of measured pressure head were used to calibrate a hydrological numerical model of the pyroclastic soil mantle for 2011, which was re-run for a 12-year period beginning in 2000, given the availability of rainfall and air temperature monitoring data. Such an approach allowed us to reconstruct the regime of pressure head at a daily time scale for a long period, which is representative of about 11 hydrologic years with different meteorological conditions. Based on this simulated time series, average winter and summer hydrological conditions were chosen to carry out hydrological and stability modeling of sample slopes and to identify Intensity- Duration rainfall thresholds by a deterministic approach. Among principal results, the opposing winter and summer antecedent pressure head (soil moisture) conditions were found to exert a significant control on intensity and duration of rainfall triggering events. Going from winter to summer conditions requires a strong increase of intensity and/or duration to induce landslides. The results identify an approach to account for different hazard conditions related to seasonality of hydrological processes inside the ash-fall pyroclastic soil mantle. Moreover, they highlight another important factor of uncertainty that potentially affects rainfall thresholds triggering shallow landslides reconstructed by empirical approaches.

Landslide database dominated by rainfall triggered events

NASA Astrophysics Data System (ADS)

Devoli, G.; Strauch, W.; Álvarez, A.

2009-04-01

A digital landslide database has been created for Nicaragua to provide the scientific community and national authorities with a tool for landslide hazard assessment. Valuable information on landslide events has been obtained from a great variety of sources. On the basis of the data stored in the database, preliminary analyses performed at national scale aimed to characterize landslides in terms of spatial and temporal distribution, types of slope movements, triggering mechanisms, number of casualties and damage to infrastructure. A total of about 17000 events spatially distributed in mountainous and volcanic terrains have been collected in the database. The events are temporally distributed between 1826 and 2003, but a large number of the records (62% of the total number) occurred during the disastrous Hurricane Mitch in October 1998. The results showed that debris flows are the most common types of landslides recorded in the database (66% of the total amount), but other types, including rockfalls and slides, have also been identified. Rainfall, also associated with tropical cyclones, is the most frequent triggering mechanism of landslides in Nicaragua, but also seismic and volcanic activities are important triggers or, especially, the combination of one of them with rainfall. Rainfall has caused all types of failures, but debris flows and translational shallow slides are more frequent types. Earthquakes have most frequently triggered rockfalls and slides, while volcanic eruptions rockfalls and debris flows. Landslides triggered by rainfall were limited in time to the wet season that lasts from May to October and an increase in the number of events is observed during the months of September and October, which is in accord with the period of the rainy season in the Pacific and Northern and Central regions and when the country has the highest probability of being impacted by hurricanes. Both Atlantic and Pacific tropical cyclones have triggered landslides. At the medium scale, the influence of topographic and lithologic parameters on the occurrence of landslides was also analyzed and the physical characterization of landslides was done to better understand the landslide dynamics and run-out distances in both volcanic and non-volcanic areas. Data from fairly well documented events in Nicaragua were compared with other similar events in Central America and elsewhere and treated statistically to search for possible correlations and empirical relationships to predict run-out distances for different types of landslides, knowing the height of fall or the volume. The empirical relationships showed that debris flows and debris avalanches at volcanoes have the highest mobility and reach longer distances compared to other types of landslides. Because of their characteristics and downstream behaviour (long run-out distances and large volumes) both types of landslides have produced the highest number of victims in the country being the most dangerous to life and property.

Information Needs While A Disaster Is Occurring

NASA Astrophysics Data System (ADS)

Perry, S. C.

2010-12-01

Evidence from recent earthquakes, wildfires, and debris flows in southern California indicates that many people - local officials as well as residents and visitors - lack important understanding during the time that a disaster is unfolding, a time of uncertainty and confusion. While some of the uncertainty is inherent, some could be alleviated. Physical scientists and engineers know what to expect as the event unfolds. Social scientists know how humans will react during a disaster, and how to effectively communicate the warnings or evacuation orders that may precede it. Such knowledge can improve public safety. As just a few of many examples: - Based on questions posed at numerous public talks, many individuals who practice "Drop Cover and Hold" during earthquake drills do not understand what they are protecting themselves against, and thus cannot determine what to do when an earthquake strikes and they have no cover available. Similarly, they do not know how to act during the aftershocks that follow. - The 2009 Station Fire in the San Gabriel Mountains put foothills communities at risk, first from the wildfire and then from debris flows. Some neighborhoods received multiple evacuation notices during a few days or months. Local officials have expressed frustration and concern about an evacuation compliance rate that is steadily dropping and is now below 50%. The debris flow danger will persist over the next 2-4 winters yet evacuation compliance may drop lower still. - On February 6, 2010, a significant rainstorm brought the threat of imminent debris flows to areas burned by the Station Fire. In one neighborhood, residents loaded their cars with important belongings then waited for indications that they should evacuate. Powerful debris flows suddenly appeared, sweeping the cars downhill and destroying both cars and belongings. Some residents did understand that rainfall intensity would control the generation of debris flows in that storm. But they didn't understand that rainfall intensity at their homes might be less than the intensity up in the mountains where the debris flows would start. Nor did they know that debris flows travel too quickly to be outrun. These and many other examples indicate need for social and natural scientists to increase awareness of what to expect when the disaster strikes. This information must be solidly understood before the event occurs - while a disaster is unfolding there are no teachable moments. Case studies indicate that even those who come into a disaster well educated about the phenomenon can struggle to apply what they know when the real situation is at hand. In addition, psychological studies confirm diminished ability to comprehend information at times of stress.

Evidence for enhanced debris-flow activity in the Northern Calcareous Alps since the 1980s (Plansee, Austria)

NASA Astrophysics Data System (ADS)

Dietrich, A.; Krautblatter, M.

2017-06-01

Debris flows are among the most important natural hazards. The Northern Calcareous Alps with their susceptible lithology are especially affected by a double digit number of major hazard events per year. It is hypothesised that debris-flow intensity has increased significantly in the last decades in the Northern Calcareous Alps coincident to increased rainstorm frequencies, but yet there is only limited evidence. The Plansee catchment exposes extreme debris-flow activity due to the intensely jointed Upper Triassic Hauptdolomit lithology, being responsible for most of the debris-flow activity in the Northern Calcareous Alps. The debris flows feed into a closed sediment system, the Plansee Lake, where Holocene/Lateglacial sedimentation rates, rates since the late 1940s and recent rates can be inferred accurately. Using aerial photos and field mapping, the temporal and spatial development of eight active debris-flow fans is reconstructed in six time intervals from 1947, 1952, 1971, 1979, 1987, 2000 and 2010 and mean annual debris-flow volumes are calculated. These are compared with mean Holocene/Lateglacial debris-flow volumes derived from the most prominent cone whose contact with the underlying till is revealed by electrical resistivity tomography (ERT). Debris-flow activity there increased by a factor of 10 from 1947-1952 (0.23 ± 0.07 · 103 m3/yr) to 1987-2000 (2.41 ± 0.66 · 103 m3/yr). Mean post-1980 rates from all eight fans exceed pre-1980 rates by a factor of more than three coinciding with enhanced rainstorm activity recorded at meteorological stations in the Northern Calcareous Alps. The frequency of rain storms (def. 35 mm/d) has increased in the study area on average by 10% per decade and has nearly doubled since 1921. Recent debris-flow activity is also 2-3 times higher than mean Holocene/Lateglacial rates. The strong correlation between the non-vegetated catchment area and the annual debris-flow volume might indicate a decadal positive feedback between enhanced rainstorm activity and debris flows. Here we investigate the temporal and spatial development of debris-flow fans to better understand the sensitivity of alpine catchments to heavy rainfall events in the context of climate change. n.m. = not measurable.

Debris flows as geomorphic agents in the Huachuca Mountains of southeastern Arizona

USGS Publications Warehouse

Wohl, E.E.; Pearthree, P.P.

1991-01-01

Numerous debris flows occurred in the Huachuca Mountains of southeastern Arizona during the summer rainy season of 1988 in areas that were burned by a forest fire earlier in the summer. Debris flows occurred following a major forest fire in 1977 as well, suggesting a causal link between fires and debris flows. Abundant evidence of older debris flows preserved along channels and in mountain front fans indicates that debris flows have occurred repeteadly during the late Quaternary in this environment. Soil development in sequences of debris-flow deposits indicates that debris flows probably recur over time intervals of several hundred to a thousand years in individual drainage basins in the study area. Surface runoff in the steep drainage basins of the Huachuca Mountains is greatly enhanced following forest fires, as the hillslopes are denuded of their vegetative cover. Water and sediment eroded from the hillslope regolith are rapidly introduced into the upper reaches of tributary channels by widespread rilling and slope wash during rainfall events. This influx of water and sediment destabilizes regolith previously accumulated in the channel, triggering debris flows that scour the channel to bedrock in the upper reaches. Following a debris flow, the scoured, trapezoidally-shaped channel gradually assumes a swale shape and the percentage of exposed bedrock declines, as material is introduced from the slopes. Debris flows do a tremendous amount of work in a very short time, however, and are the major channel-forming events. Where the tributary channels enter larger, trunk channels, the debris flows serve as the main source of very coarse sediment. The local slope and coarse particle distribution of the trunk channel depend on the competence of water flows in the channel to transport the material introduced by debris flows. Where the smaller channels drain directly to the mountain front, debris flows create extensive alluvial fans which dominate the morphology of the basin-range boundary. Time intervals between debris flows in the drainage basins of the Huachuca Mountains are probably controlled by complex interactions among climate, forest fires and slope processes. Fires destroy the protective vegetation that stabilizes the upper catchment slopes and inhibits erosion. However, not every fire that burns a catchment causes debris flows, because sufficient weathered material must accumulate in the upper channel reaches to initiate a large debris flow. If such accumulation has not occurred, the material introduced to a channel following a forest fire will move only a short distance down the channel. Thus, the episodic nature of debris flows probably depends on rates of slope weathering and erosion, which are in turn controlled by climate, both directly and through vegetation and forest fires. ?? 1991.

Elucidating the role of vegetation in the initiation of rainfall-induced shallow landslides: Insights from an extreme rainfall event in the Colorado Front Range

USGS Publications Warehouse

McGuire, Luke; Rengers, Francis K.; Kean, Jason W.; Coe, Jeffrey A.; Mirus, Benjamin B.; Baum, Rex L.; Godt, Jonathan W.

2016-01-01

More than 1100 debris flows were mobilized from shallow landslides during a rainstorm from 9 to 13 September 2013 in the Colorado Front Range, with the vast majority initiating on sparsely vegetated, south facing terrain. To investigate the physical processes responsible for the observed aspect control, we made measurements of soil properties on a densely forested north facing hillslope and a grassland-dominated south facing hillslope in the Colorado Front Range and performed numerical modeling of transient changes in soil pore water pressure throughout the rainstorm. Using the numerical model, we quantitatively assessed interactions among vegetation, rainfall interception, subsurface hydrology, and slope stability. Results suggest that apparent cohesion supplied by roots was responsible for the observed connection between debris flow initiation and slope aspect. Results suggest that future climate-driven modifications to forest structure could substantially influence landslide hazards throughout the Front Range and similar water-limited environments where vegetation communities may be more susceptible to small variations in climate.

Initiation of Recent Debris Flows on Mount Rainier, Washington: A Climate Warming Signal?

NASA Astrophysics Data System (ADS)

Copeland, E. A.; Kennard, P.; Nolin, A. W.; Lancaster, S. T.; Grant, G. E.

2008-12-01

The first week of November 2006 an intense rainstorm inundated the Pacific Northwest and triggered debris flows on many large volcanoes in the Cascade Range of Washington and Oregon. At Mount Rainier, Washington, 45.7 cm of rain was recorded in 36 hours; the storm was preceded by a week of light precipitation and moderate temperatures, so that rain fell on nearly-saturated ground with minimal snow cover. The November 2006 storm was exceptional in that it resulted in a 100-year flood and caused an unprecedented six-month closure of Mount Rainier National Park. It also focused inquiry as to whether debris flows from Cascade volcanoes are likely to occur more frequently in the future as glaciers recede due to climate warming, leaving unstable moraines and sediment that can act as initiation sites. We examined the recent history of debris flows from Mount Rainier using aerial photographs and field surveyed debris flow tracks. Prior to 2001, debris flows were recorded in association with rainfall or glacial outburst floods in 4 drainages, but 3 additional drainages were first impacted by debris flows in 2001, 2005, and 2006, respectively. We discovered that most of the recent debris flows initiated as small gullies in unconsolidated material at the edge of fragmented glaciers or areas of permanent snow and ice. Other initiation sites occur on steep-sided un-vegetated moraines. Of the 28 named glaciers on Mount Rainier, debris flows initiated near five glaciers in the exceptional storm of 2006 (Winthrop, Inter, Kautz-Success, Van Trump, Pyramid, and South Tahoma). Less exceptional storms, however, have also produced wide-spread debris flows: in September 2005, 15.3 cm of rain fell in 48 hours on minimal snow cover and caused debris flows in all except 2 of the glacier drainages that initiated in 2006. Debris flows from both storms initiated at elevations of 1980 to 2400 m, traveled 5 to 10 kilometers, and caused significant streambed aggradation. These results suggest a complex view of debris flow initiation. Retreat and fragmentation of glaciers create debris-covered stagnant ice masses in the steep-sided, tiered channels and expose steep edifices of unstable glacial material, both of which may promote debris flow initiation. Possible reduced snow cover and higher freezing levels during autumn storms due to climate warming may further influence debris flow initiation on the glaciated stratovolcanoes of Washington and Oregon.

Alpine debris flows triggered by a 28 July 1999 thunderstorm in the central Front Range, Colorado

NASA Astrophysics Data System (ADS)

Godt, Jonathan W.; Coe, Jeffrey A.

2007-02-01

On 28 July 1999, about 480 alpine debris flows were triggered by an afternoon thunderstorm along the Continental Divide in Clear Creek and Summit counties in the central Front Range of Colorado. The thunderstorm produced about 43 mm of rain in 4 h, 35 mm of which fell in the first 2 h. Several debris flows triggered by the storm impacted Interstate Highway 70, U.S. Highway 6, and the Arapahoe Basin ski area. We mapped the debris flows from color aerial photography and inspected many of them in the field. Three processes initiated debris flows. The first process initiated 11% of the debris flows and involved the mobilization of shallow landslides in thick, often well vegetated, colluvium. The second process, which was responsible for 79% of the flows, was the transport of material eroded from steep unvegetated hillslopes via a system of coalescing rills. The third, which has been termed the "firehose effect," initiated 10% of the debris flows and occurred where overland flow became concentrated in steep bedrock channels and scoured debris from talus deposits and the heads of debris fans. These three processes initiated high on steep hillsides (> 30°) in catchments with small contributing areas (< 8000 m 2), however, shallow landslides occurred on slopes that were significantly less steep than either overland flow process. Based on field observations and examination of soils mapping of the northern part of the study area, we identified a relation between the degree of soil development and the process type that generated debris flows. In general, areas with greater soil development were less likely to generate runoff and therefore less likely to generate debris flows by the firehose effect or by rilling. The character of the surficial cover and the spatially variable hydrologic response to intense rainfall, rather than a threshold of contributing area and topographic slope, appears to control the initiation process in the high alpine of the Front Range. Because debris flows initiated by rilling and the firehose effect tend to increase in volume as they travel downslope, these debris flows are potentially more hazardous than those initiated by shallow landslides, which tend to deposit material along their paths.

Alpine debris flows triggered by a 28 July 1999 thunderstorm in the central Front Range, Colorado

USGS Publications Warehouse

Godt, J.W.; Coe, J.A.

2007-01-01

On 28 July 1999, about 480 alpine debris flows were triggered by an afternoon thunderstorm along the Continental Divide in Clear Creek and Summit counties in the central Front Range of Colorado. The thunderstorm produced about 43??mm of rain in 4??h, 35??mm of which fell in the first 2??h. Several debris flows triggered by the storm impacted Interstate Highway 70, U.S. Highway 6, and the Arapahoe Basin ski area. We mapped the debris flows from color aerial photography and inspected many of them in the field. Three processes initiated debris flows. The first process initiated 11% of the debris flows and involved the mobilization of shallow landslides in thick, often well vegetated, colluvium. The second process, which was responsible for 79% of the flows, was the transport of material eroded from steep unvegetated hillslopes via a system of coalescing rills. The third, which has been termed the "firehose effect," initiated 10% of the debris flows and occurred where overland flow became concentrated in steep bedrock channels and scoured debris from talus deposits and the heads of debris fans. These three processes initiated high on steep hillsides (> 30??) in catchments with small contributing areas (< 8000??m2), however, shallow landslides occurred on slopes that were significantly less steep than either overland flow process. Based on field observations and examination of soils mapping of the northern part of the study area, we identified a relation between the degree of soil development and the process type that generated debris flows. In general, areas with greater soil development were less likely to generate runoff and therefore less likely to generate debris flows by the firehose effect or by rilling. The character of the surficial cover and the spatially variable hydrologic response to intense rainfall, rather than a threshold of contributing area and topographic slope, appears to control the initiation process in the high alpine of the Front Range. Because debris flows initiated by rilling and the firehose effect tend to increase in volume as they travel downslope, these debris flows are potentially more hazardous than those initiated by shallow landslides, which tend to deposit material along their paths. ?? 2006 Elsevier B.V. All rights reserved.

Assessment of Debris Flow Potential Hazardous Zones Using Numerical Models in the Mountain Foothills of Santiago, Chile

NASA Astrophysics Data System (ADS)

Celis, C.; Sepulveda, S. A.; Castruccio, A.; Lara, M.

2017-12-01

Debris and mudflows are some of the main geological hazards in the mountain foothills of Central Chile. The risk of flows triggered in the basins of ravines that drain the Andean frontal range into the capital city, Santiago, increases with time due to accelerated urban expansion. Susceptibility assessments were made by several authors to detect the main active ravines in the area. Macul and San Ramon ravines have a high to medium debris flow susceptibility, whereas Lo Cañas, Apoquindo and Las Vizcachas ravines have a medium to low debris flow susceptibility. This study emphasizes in delimiting the potential hazardous zones using the numerical simulation program RAMMS-Debris Flows with the Voellmy model approach, and the debris-flow model LAHARZ. This is carried out by back-calculating the frictional parameters in the depositional zone with a known event as the debris and mudflows in Macul and San Ramon ravines, on May 3rd, 1993, for the RAMMS approach. In the same scenario, we calibrate the coefficients to match conditions of the mountain foothills of Santiago for the LAHARZ model. We use the information obtained for every main ravine in the study area, mainly for the similarity in slopes and material transported. Simulations were made for the worst-case scenario, caused by the combination of intense rainfall storms, a high 0°C isotherm level and material availability in the basins where the flows are triggered. The results show that the runout distances are well simulated, therefore a debris-flow hazard map could be developed with these models. Correlation issues concerning the run-up, deposit thickness and transversal areas are reported. Hence, the models do not represent entirely the complexity of the phenomenon, but they are a reliable approximation for preliminary hazard maps.

Debris-flow and flooding deposits in coastal Venezuela associated with the storm of December 14-16, 1999

USGS Publications Warehouse

Wieczorek, Gerald F.; Larsen, Matthew C.; Eaton, L. Scott; Morgan, Benjamin A.; Blair, J. Luke

2002-01-01

Heavy rainfall from the storm of December 14?16, 1999, triggered thousands of shallow landslides on steep slopes of the Sierra de Avila north of Caracas, Venezuela, and caused flooding and massive debris flows in the channels of major drainages that severely damaged coastal communities along the Caribbean Sea. Within this region we characterized geologic conditions where landslides initiated on hillsides and examined the texture of debris-flow deposits in the channels of nine drainages. In one of the most severely damaged areas on a highly developed alluvial fan at Caraballeda, we measured debris-flow deposits that ranged up to 5 meters (m) in thickness, inundating structures and roads over a large portion of the fan. Boulders up to 5 m long were carried along by the flows, impacted structures causing serious damage, and were deposited on the fan. Using field measurements and comparing pre-event and post-event topography from aerial photographs, we determined the volume of debris-flow and flood deposition on the fan to be about 2 million cubic meters. The total volume of material transported and deposited by landslides throughout the Vargas region ranks this as one of the most severe historical erosional events worldwide.

A database on post-fire erosion rates and debris flows in Mediterranean-Basin watersheds

NASA Astrophysics Data System (ADS)

Parise, M.; Cannon, S. H.

2009-04-01

Wildfires can affect many Mediterranean countries on a yearly bases, producing damage and economic losses, both as direct effect of the fires and as consequent events, including erosion and sedimentation in the recently burned areas. Even though most of the wildfires occur in Spain, Portugal, southern France, Italy and Greece, it can be stated that no one of the Mediterranean countries is completely immune by such hazards. In addition to destruction of the vegetation, and in addition to direct losses to the built-up environment, further effects may also be registered as a consequence of the fire, even weeks or months after its occurrence. Wildfire can have, in fact, profound effects on the hydrologic response of watersheds, and debris-flow activity is among the most destructive consequences of these effects, often causing extensive damage to human infrastructure. Wildfires are today continuously monitored by several European institutions, and forecasting of the conditions (weather, temperature, wind, etc.) more likely conducive to their occurrence is often available in real time. On the other hand, not much is known about the processes that occur as a consequence of the fire, including erosion and debris flows. These are often underestimated, and become object of study only after some catastrophic event has occurred. This is in strong contrast with all the established techniques of risk mitigation; as a result, no prevention action is generally considered, and the society relies only on the emergency phase following a disaster. Aimed at contributing to gather information about the occurrence of erosional and debris-flow activity in recently burned Mediterranean areas, and at making available these information to land planners and scientists, a specific database has been compiled and presented in this contribution. To date, scientific literature on the topic in Europe has never been catalogued, and was dispersed in a number of different journals and in conference proceedings. The database derives from critical analysis of the existing literature, integrated by case studies directly studied by the authors. Studies on recently burned areas in the Mediterranean basin are most frequently carried out on small experimental plots, often with simulated rainfall A problem of scale therefore exists when trying to extrapolate the erosion rates (also reported as sediment yields or as sediment losses) from these studies to a watershed scale. Very few articles, on the other hand, were found that document the watershed-scale response of basins to rainfall-induced erosion and debris flows following wildfires. The few reported cases of debris flows in the Mediterranean Basin describe erosion of sediment from the hillslopes and the channels (sometimes down to bedrock), and, for a limited number of sites, failure of discrete landslides. This information indicates that debris-flow generation from recently burned areas in the Mediterranean basin appears to occur primarily through sediment bulking processes. Nevertheless, the database so far compiled shows a distribution of post-fire erosion and debris flows in the western Mediterranean basin (Spain, essentially, but also Portugal), followed by the eastern Mediterranean area (Israel), and then by France, Italy and Greece. Even though still in a preliminary version, that needs to be integrated and updated from further sources, our data compilation allows for the unique opportunity to examine issues related to the generation of post-wildfire debris flows across a variety of environments and under a variety of conditions, and to move from a qualitative conception of the controls on post-fire debris-flow generation to the definition of specific conditions that result in their occurrence. Future activities of the project will include: i) updating and integration of the preliminary version of the database; ii) development of models that can be used to identify the probability of debris-flow occurrence and the magnitude of the event for pre- and post-fire hazard assessment in Mediterranean climates; iii) definition of rainfall thresholds for post-fire debris-flow events in Mediterranean climates, as a tool to provide guidance for preliminary warning systems.

DEFORESTATION AND LANDSLIDES IN YUNNAN, CHINA.

USGS Publications Warehouse

Wieczorek, Gerald F.; Wu, Jishan; Li, Tianchi

1987-01-01

Landslides historically have caused severe erosion problems in the Xiao River drainage region of northeastern Yunnan Province, China, that hence resulted in serious economic and social consequences. Owing to monsoonal storms of high rainfall intensity, the erosion potential is high in this mountainous, seismically active region. Landslides transported large quantities of materials into the ravines. During intense storms, high runoff from the deforested areas has mobilized this material into debris flows. Where these flows emerged onto flatter slopes in the lower parts of the watersheds, the channels were too small to hold them, so farmland and villages were inundated. Debris flows in this region during June-August 1985 killed 12 people, damaged roads and the main rail line to Kunming, the capital of Yunnan Province, inundated farmland, and overflowed debris-retention structures. To mitigate these severe erosion problems, several different methods have been used.

Forewarning of Debris flows using Intelligent Geophones

NASA Astrophysics Data System (ADS)

PK, I.; Ramesh, M. V.

2017-12-01

Landslides are one of the major catastrophic disasters that cause significant damage to human life and civil structures. Heavy rainfall on landslide prone areas can lead to most dangerous debris flow, where the materials such as mud, sand, soil, rock, water and air will move with greater velocity down the mountain. This sudden slope instability can lead to loss of human life and infrastructure. According to our knowledge, till now no one could identify the minutest factors that lead to initiation of the landslide. In this work, we aim to study the landslide phenomena deeply, using the landslide laboratory set up in our university. This unique mechanical simulator for landslide initiation is equipped with the capability to generate rainfall, seepage, etc., in the laboratory setup. Using this setup, we aim to study several landslide initiation scenarios generated by varying different parameters. The complete setup will be equipped with heterogeneous sensors such as rain gauge, moisture sensor, pore pressure sensor, strain gauges, tiltmeter, inclinometer, extensometer, and geophones. Our work will focus on the signals received from the intelligent geophone system for identifying the underground vibrations during a debris flow. Using the large amount of signals derived from the laboratory set up, we have performed detailed signal processing and data analysis to determine the fore warning signals captured by these heterogeneous sensors. Detailed study of these heterogeneous signals has provided the insights to forewarning the community based on the signals generated during the laboratory tests. In this work we will describe the details of the design, development, methodology, results, inferences and the suggestion for the next step to detect and forewarn the students. The response of intelligent geophone sensors at the time of failure, failure style and subsequent debris flow for heterogeneous soil layers were studied, thus helping in the development of fore warning systems for debris flows.

A data-driven approach for modeling post-fire debris-flow volumes and their uncertainty

USGS Publications Warehouse

Friedel, Michael J.

2011-01-01

This study demonstrates the novel application of genetic programming to evolve nonlinear post-fire debris-flow volume equations from variables associated with a data-driven conceptual model of the western United States. The search space is constrained using a multi-component objective function that simultaneously minimizes root-mean squared and unit errors for the evolution of fittest equations. An optimization technique is then used to estimate the limits of nonlinear prediction uncertainty associated with the debris-flow equations. In contrast to a published multiple linear regression three-variable equation, linking basin area with slopes greater or equal to 30 percent, burn severity characterized as area burned moderate plus high, and total storm rainfall, the data-driven approach discovers many nonlinear and several dimensionally consistent equations that are unbiased and have less prediction uncertainty. Of the nonlinear equations, the best performance (lowest prediction uncertainty) is achieved when using three variables: average basin slope, total burned area, and total storm rainfall. Further reduction in uncertainty is possible for the nonlinear equations when dimensional consistency is not a priority and by subsequently applying a gradient solver to the fittest solutions. The data-driven modeling approach can be applied to nonlinear multivariate problems in all fields of study.

A Detailed Study of Debris Flow Source Areas in the Northern Colorado Front Range.

NASA Astrophysics Data System (ADS)

Arana-Morales, A.; Baum, R. L.; Godt, J.

2014-12-01

Nearly continuous, heavy rainfall occurred during 9-13 September 2013 causing flooding and widespread landslides and debris flows in the northern Colorado Front Range. Whereas many recent studies have identified erosion as the most common process leading to debris flows in the mountains of Colorado, nearly all of the debris flows mapped in this event began as small, shallow landslides. We mapped the boundaries of 415 September 2013 debris flows in the Eldorado Springs and Boulder 7.5-minute quadrangles using 0.5-m-resolution satellite imagery. We characterized the landslide source areas of six debris flows in the field as part of an effort to identify what factors controlled their locations. Four were on a dip slope in sedimentary rocks in the Pinebrook Hills area, near Boulder, and the other two were in granitic rocks near Gross Reservoir. Although we observed no obvious geomorphic differences between the source areas and surrounding non-landslide areas, we noted several characteristics that the source areas all had in common. Slopes of the source areas ranged from 28° to 35° and most occurred on planar or slightly concave slopes that were vegetated with grass, small shrubs, and sparse trees. The source areas were shallow, irregularly shaped, and elongated downslope: widths ranged from 4 to 9 m, lengths from 6 to 40 m and depths ranged from 0.7 to 1.2 m. Colluvium was the source material for all of the debris flows and bedrock was exposed in the basal surface of all of the source areas. We observed no evidence for concentrated surface runoff upslope from the sources. Local curvature and roughness of bedrock and surface topography, and depth distribution and heterogeneity of the colluvium appear to have controlled the specific locations of these shallow debris-flow source areas. The observed distribution and characteristics of the source areas help guide ongoing efforts to model initiation of the debris flows.

Soil slips and debris flows on terraced slopes

NASA Astrophysics Data System (ADS)

Crosta, G. B.; Dal Negro, P.; Frattini, P.

Terraces cover large areas along the flanks of many alpine and prealpine valleys. Soil slips and soil slips-debris flows are recurrent phenomena along terraced slopes. These landslides cause damages to people, settlements and cultivations. This study investigates the processes related to the triggering of soil slip-debris flows in these settings, analysing those occurred in Valtellina (Central Alps, Italy) on November 2000 after heavy prolonged rainfalls. 260 landslides have been recognised, mostly along the northern valley flank. About 200 soil slips and slumps occurred in terraced areas and a third of them evolved into debris flows. Field work allowed to recognise the settings at soil slip-debris flow source areas. Landslides affected up to 2.5 m of glacial, fluvioglacial and anthropically reworked deposits overlying metamorphic basement. Laboratory and in situ tests allowed to characterise the geotechnical and hydraulic properties of the terrains involved in the initial failure. Several stratigraphic and hydrogeologic factors have been individuated as significant in determining instabilities on terraced slopes. They are the vertical changes of physical soil properties, the presence of buried hollows where groundwater convergence occurs, the rising up of perched groundwater tables, the overflow and lateral infiltration from superficial drainage network, the runoff concentration by means of pathways and the insufficient drainage of retaining walls.

Coupled prediction of flash flood response and debris flow occurrence in an alpine basin

NASA Astrophysics Data System (ADS)

Amponsah, William

2015-04-01

Coupled prediction of flash flood response and debris flow occurrence in an alpine basin Author(s): William Amponsah1, E.I. Nikolopoulos2, Lorenzo Marchi1, Roberto Dinale4, Francesco Marra3,Davide Zoccatelli2 , Marco Borga2 Affiliation(s): 1CNR - IRPI, Corso Stati Uniti 4, 35127, Padova, ITALY, 2Department of Land, Environment, Agriculture and Forestry, University of Padova,VialeDell'Università 16, 35020, Legnaro PD, ITALY 3Department of Geography, Hebrew University of Jerusalem, ISRAEL 4Ufficio Idrografico, Provincia Autonoma di Bolzano, Bolzano, Italy This contribution examines the main hydrologic and morphologic metrics responsible for widespread triggering of debris-flows associated with flash flood occurrences in headwater alpine catchments.To achieve this objective, we investigate the precipitation forcing, hydrologic responses and landslides and debris-flow occurrences that prevailed during the August 4-5, 2012 extreme flash flood on the 140 km2 Vizze basin in the Eastern Alps of Italy. An intensive post-event survey was carried out a few days after the flood. This included the surveys of cross-sectional geometry and flood marks for the estimation of the peak discharges at multiple river sections and of the initiation and deposition areas of several debris flows. Rainfall estimates are based on careful analysis of weather radar observations and raingauge data. These data and observations permitted the implementation and calibration of a spatially distributed hydrological model, which was used to derive simulated flood hydrographs in 58 tributaries of the Vizze basin. Of these, 33 generated debris-flows, with area ranging from 0.02 km2 to 10 km2, with an average of 1.5 km2. With 130 mm peak event rainfall and a duration of 4 hours (with a max intensity of 90 mm h-1 for 10 min), model-simulated unit peak discharges range from 4 m3 s-1 km-2for elementary catchments up to 10 km2 to 2 m3 s-1 km-2 for catchments in the range of 50 - 100 km2. These are very high values when considering the local runoff regime. We used a threshold criterion based on past works (Tognaccaet al., 2000; Berti and Simoni, 2005; Gregoretti and Dalla Fontana, 2008) to identify tributaries associated to debris flow events. The threshold is defined for each channel grid as a function of the simulated unit width peak flow, of the local channel bed slope and of the mean grain size. Based on assumptions concerning the mean grain size and given the distribution of the threshold values over the river network, we derive a catchment scale threshold index for the tributaries. The results show that the index has considerable skill in identifying the catchments where the studied rainstorm caused debris-flows. Berti, M. andA.Simoni, 2005: Experimental evidences and numerical modelling of debris flow initiated by channel runoff. Landslides, 2 (3), 171-182. Gregoretti, C. and G. Dalla Fontana, 2008:The triggering of debris flow due to channel-bed failure in some alpine headwater basins of the Dolomites: analyses of critical runoff. Hydrol. Process. 22, 2248-2263. Tognacca C., G.R. Bezzola andH.E.Minor, 2000: Threshold criterion fodebrisflow initiation due to channel bed failure. In Proceedings of the Second International Conference on Debris Flow Hazards Mitigation Taipei,August, Wiezczorek, Naeser (eds): 89-97.

Eddy covariance and lysimeter measurements of moisture fluxes over supraglacial debris

NASA Astrophysics Data System (ADS)

Brock, Benjamin

2015-04-01

Supraglacial debris covers have the potential to evaporate large quantities of water derived from either sub-debris ice melt or precipitation. Currently, knowledge of evaporation and condensation rates in supraglacial debris is limited due to the difficulty of making direct measurements. This paper presents eddy covariance and lysimeter measurements of moisture fluxes made over a 0.2 m debris layer at Miage debris covered glacier, Italian Alps, during the 2013 ablation season. The meteorological data are complimented by reflectometer measurements of volumetric water fraction in the saturated and vadose zones of the debris layer. The lysimeters were designed specifically to mimic the debris cover and were embedded within the debris matrix, level with the surface. Over the ablation season, the latent heat flux is dominated by evaporation, and the flux magnitude closely follows the daily cycle of daytime solar heating and night time radiative cooling of debris. Mean flux values are of the order of 1 kg m-2 day-1, but often higher for short periods following rainfall. Condensation rates are relatively small and restricted to night time and humid conditions when the debris-atmosphere vapour pressure gradient reverses due to relatively warm air overlying cold debris. The reflectometer measurements provide evidence of vertical water movement through capillary rise in the upper part of the fine-grained debris layer, just above the saturated horizon, and demonstrate how debris bulk water content increases after rainfall. The latent heat flux responds directly to changes in wind speed, indicating that atmospheric turbulence can penetrate porous upper debris layers to the saturated horizon. Hence, vertical sorting of debris sediments and antecedent rainfall are important in determining evaporation rates, in addition to current meteorological conditions. Comparison of lysimeter measurements with rainfall data provides an estimate that between 45% and 89% of rainfall is evaporated directly back to the atmosphere. Rainfall evaporation rates increase with debris impermeability and temperature, with highest rates occurring when a shower falls on hot debris. If these point measurements are representative of larger scales, evaporation rates of the order of 1000 tonnes km-2 day-1 are implied, with higher rates following rainfall. This has important implications for downstream runoff, sub-debris ice melt rates (due to consumption of evaporative latent heat energy) and, possibly, convective atmospheric processes.

Geomorphological Controls and Land-use Effects on Rainfall Triggered Debris Flows in Brazil

NASA Astrophysics Data System (ADS)

Fernandes, N. F.; Amaral, C. P.; Mota, M.; Gomes, R. A. T.; Guimarães, R. F.; Carvalho, O., Jr.; Vieira, B. C.; Vargas, E. A., Jr.; de Campos, T. M.

2009-04-01

Debris flows are major processes controlling landscape evolution, especially in tropical environments, where thick talus and colluvial deposits are observed filling bedrock topographic hollows and larger valleys. Besides their geomorphological meaning, they also represent an enormous danger to man when soil-mantled steep hillslopes are densely occupied in urban areas. In Brazil, especially in southern and southeastern portions, due to the steep hilly topography, the high precipitation values and the expansion of the urbanization towards the hillslopes, debris flows are becoming more frequent. This has been the case of the catastrophic debris flows observed in Rio de Janeiro (e.g., 1967, 1988, 1996, 2002) and São Paulo (e.g., 1967, 1975). In these states, due to the dense occupation, debris flows tend to frequently achieve catastrophic proportions. However, more recently, even in areas with sparse occupation and with no previous records of catastrophic landslides, like the ones in the southern states of Paraná and Santa Catarina, debris flows are taking place. This is the case of the recent rainfall triggered catastrophic debris flows that occurred last November in the area Morro do Baú, Santa Catarina state, by far, the most important event that took place in this region. In this location, besides the striking pluviometric records and the geological/geomorphological aspects, land-use changes (huge banana plantations and Pines forested areas) seems to have played a major role in amplifying the magnitude of the processes. However, the scientific community in Brazil seems to be still more concerned with small shallow landslides. Although a lot of effort has already been made towards a better understanding of the conditioning factors controlling landslide initiation at a specific site (hillslope scale), it is urgent to improve our ability in predicting landslide instability in larger areas (drainage basin scale), where positive and negative feedbacks between the hillslope and the channel segments play a major role. Modeling hillslope stability, of course, is not an easy task, especially when dealing with large drainage basin. Consequently, different approaches should be combined in order to attain success in prediction landslide hazards. In this study, based on detailed field mapping and modeling, we compare the role played by the geomorphological and geological factors in defining the location of major debris flows in Brazil. Besides, we discuss the effects of land-use changes, especially the introduction of huge banana plantations on steep slopes, on soil hydrology and landsliding. At last, we show some modeling results obtained in combining the models SHALSTAB and FLO-2D to simulate the catastrophic debris flows that took place in Rio de Janeiro city in 1996. Although our ability to predict where landslides might occur in a certain landscape has greatly improved in the last decades, we still have a long way towards being able to define when they will take place.

Magnitude and frequency data for historic debris flows in Grand Canyon National Park and vicinity, Arizona

USGS Publications Warehouse

Melis, T.S.; Webb, R.H.; Griffiths, P.G.; Wise, T.J.

1995-01-01

Debris flows occur in 529 tributaries of the Colorado River in Grand Canyon between Lees Ferry and Diamond Creek, Arizona (river miles 0 to 225). An episodic type of flash flood, debris flows transport poorly-sorted sediment ranging in size from clay to boulders into the Colorado River. Debris flows create and maintain debris fans and the hundreds of associated riffles and rapids that control the geomorphic framework of the Colorado River downstream from Glen Canyon Dam. Between 1984 and 1994, debris flows created 4 new rapids and enlarged 17 existing rapids and riffles. Debris flows in Grand Canyon are initiated by slope failures that occur during intense rainfall. Three of these mechanisms of slope failure are documented. Failures in weathered bedrock, particularly in the Hermit Shale and Supai Group, have initiated many historic debris flows in Grand Canyon. A second mechanism, termed the fire-hose effect, occurs when runoff pours over cliffs onto unconsolidated colluvial wedges, triggering a failure. A third initiation mechanism occurs when intense precipitation causes failures in colluvium overlying bedrock. Multiple source areas and extreme topographic relief in Grand Canyon commonly result in combinations of these three initiation mechanisms. Interpretation of 1,107 historical photographs spanning 120 years, supplemented with aerial photography made between 1935 and 1994, yielded information on the frequency of debris flows in 168 of the 529 tributaries (32 percent) of the Colorado River in Grand Canyon. Of the 168 tributaries, 96 contain evidence of debris flows that have occurred since 1872, whereas 72 tributaries have not had a debris flow during the last century. The oldest debris flow we have documented in Grand Canyon occurred 5,400 years ago in an unnamed tributary at river mile 63.3-R. Our results indicate that the frequency of debris flows ranges from one every 10 to 15 years in certain eastern tributaries, to less than one per century in other drainage basins. On average, debris flows may recur approximately every 30 to 50 years in individual tributaries, although adjacent tributaries may have considerably different histories. Peak discharges were estimated in 18 drainages for debris flows that occurred between 1939 and 1994. Typically, discharges range from about 100 to 300 cubic meters per second (m3/s). The largest debris flow in Grand Canyon during the last century, which occurred in Prospect Canyon in 1939, had a peak discharge of about 1,000 m3/s. Debris-flow deposits generally contain 15 to 30 percent sand-and-finer sediment; however, the variability of sand-and-finer sediment contained by recent debris flows is large. Reconstitution of debris-flow samples indicates a range in water content of 10 to 25 percent by weight;. Before flow regulation of the Colorado River began, debris fans aggraded by debris flows were periodically reworked by large river floods that may have been as large as 11,000 m3/s. Impoundment of the river by Glen Canyon Dam in 1963, and subsequent operation of the reservoir have reduced the magnitude of these floods. Flow releases from the dam since 1963 have only partly reworked recently-aggraded debris fans. Significant reworking of new debris-flow deposits now occurs only during river discharges higher than typical power plant releases, which currently range between 142 and 510 m3/s.

Rainfall Generated Debris flows on Mount Shasta: July 21, 2015

NASA Astrophysics Data System (ADS)

Mikulovsky, R. P.; De La Fuente, J. A.; Courtney, A.; Bachmann, S.; Rodriguez, H.; Rust, B.; Schneider, F.; Veich, D.

2015-12-01

Convective storms on the evening of July 21, 2015 generated a number of debris flows on the SE flank of Mount Shasta Volcano, Shasta-Trinity National Forest. Widespread rilling, gullying and sheet erosion occurred throughout the affected area. These storms damaged roads by scouring drainage ditches, blocking culverts, eroding road prisms, and depositing debris where streams emerged from their incised channels and flowed over their alluvial fans. Effects were limited geographically to a narrow band about 6 miles wide trending in a northeasterly direction. Debris flows were identified at Pilgrim Creek and nearby channels, and Mud Creek appears to have experienced sediment laden flows rather than debris flows. Doppler radar data reveal that the storm cells remained nearly stationary for two hours before moving in a northeasterly direction. Debris flows triggered by convective storms occur often at Mount Shasta, with a similar event recorded in 2003 and a larger one in 1935, which also involved glacial melt. The 1935 debris flow at Whitney Creek buried Highway 97 north of Weed, CA, and took out the railroad above the highway. In September, 2014, a large debris flow occurred in Mud Creek, but it was associated solely with glacial melt and was not accompanied by rain. The 2014 event at Mud Creek filled the channel and parts of the floodplain with debris. This debris was in turn reworked and eroded by sediment laden flows on July 21, 2015. This study was initiated in August, 2015, and began with field inventories to identify storm effects. Lidar data will be used to identify possible avulsion points that could result in unexpected flash flooding outside of the main Mud Creek channel and on adjacent streams. The results of this study will provide critical information that can be used to assess flash flood risk and better understand how to manage those risks. Finally, some conclusions may be drawn on the kinds of warning systems that may be appropriate for possible flash flood events and possible effective road designs for stream crossings and road surface drainage.

Hydro-mechanical mechanism and thresholds of rainfall-induced unsaturated landslides

NASA Astrophysics Data System (ADS)

Yang, Zongji; Lei, Xiaoqin; Huang, Dong; Qiao, Jianping

2017-04-01

The devastating Ms 8 Wenchuan earthquake in 2008 created the greatest number of co-seismic mountain hazards ever recorded in China. However, the dynamics of rainfall induced mass remobilization and transport deposits after giant earthquake are not fully understood. Moreover, rainfall intensity and duration (I-D) methods are the predominant early warning indicators of rainfall-induced landslides in post-earthquake region, which are a convenient and straight-forward way to predict the hazards. However, the rainfall-based criteria and thresholds are generally empirical and based on statistical analysis,consequently, they ignore the failure mechanisms of the landslides. This study examines the mechanism and hydro-mechanical behavior and thresholds of these unsaturated deposits under the influence of rainfall. To accomplish this, in situ experiments were performed in an instrumented landslide deposit, The field experimental tests were conducted on a natural co-seismic fractured slope to 1) simulate rainfall-induced shallow failures in the depression channels of a debris flow catchment in an earthquake-affected region, 2)explore the mechanisms and transient processes associated with hydro-mechanical parameter variations in response to the infiltration of rainfall, and 3) identify the hydrologic parameter thresholds and critical criteria of gravitational erosion in areas prone to mass remobilization as a source of debris flows. These experiments provided instrumental evidence and directly proved that post-earthquake rainfall-induced mass remobilization occurred under unsaturated conditions in response to transient rainfall infiltration, and revealed the presence of transient processes and the dominance of preferential flow paths during rainfall infiltration. A hydro-mechanical method was adopted for the transient hydrologic process modelling and unsaturated slope stability analysis. and the slope failures during the experimental test were reproduced by the model, indicating that the decrease in matrix suction and increase in moisture content in response to rainfall infiltration contributed greatly to post-earthquake shallow mass movement. Thus, a threshold model for the initiation of mass remobilization is proposed based on correlations between slope stability and volumetric water content and matrix suction As a complement to rainfall-based early warning strategies, the water content and suction threshold models based on the water infiltration induced slope failure mechanism. the proposed method are expected to improve the accuracy of prediction and early warnings of post-earthquake mountain hazards

Increased precipitation drives mega slump development and destabilization of ice-rich permafrost terrain, northwestern Canada

NASA Astrophysics Data System (ADS)

Kokelj, S. V.; Tunnicliffe, J.; Lacelle, D.; Lantz, T. C.; Chin, K. S.; Fraser, R.

2015-06-01

It is anticipated that an increase in rainfall will have significant impacts on the geomorphology of permafrost landscapes. Field observations, remote sensing and historical climate data were used to investigate the drivers, processes and feedbacks that perpetuate the growth of large retrogressive thaw slumps. These "mega slumps" (5-40 ha) are now common in formerly glaciated, fluvially incised, ice-cored terrain of the Peel Plateau, NW Canada. Individual thaw slumps can persist for decades and their enlargement due to ground ice thaw can displace up to 106 m3 of materials from slopes to valley bottoms reconfiguring slope morphology and drainage networks. Analysis of Landsat images (1985-2011) indicate that the number and size of active slumps and debris tongue deposits has increased significantly with the recent intensification of rainfall. The analyses of high resolution climatic and photographic time-series for summers 2010 and 2012 shows strong linkages amongst temperature, precipitation and the downslope sediment flux from active slumps. Ground ice thaw supplies meltwater and sediments to the slump scar zone and drives diurnal pulses of surficial flow. Coherence in the timing of down valley debris tongue deposition and fine-scaled observations of sediment flux indicate that heavy rainfall stimulates major mass flow events. Evacuation of sediments from the slump scar zone can help to maintain a headwall of exposed ground ice, perpetuating slump growth and leading to larger disturbances. The development of debris tongue deposits divert streams and increase thermoerosion to initiate adjacent slumps. We conclude that higher rainfall can intensify thaw slump activity and rapidly alter the slope-sediment cascade in regions of ice-cored glaciogenic deposits.

A GIS-based numerical simulation of the March 2014 Oso landslide fluidized motion

NASA Astrophysics Data System (ADS)

Fukuoka, H.; Ogbonnaya, I.; Wang, C.

2014-12-01

Sliding and flowing are the major movement type after slope failures. Landslides occur when slope-froming material moves downhill after failing along a sliding surface. Most debris flows originally occur in the form of rainfall-induced landslides before they move into valley channel. Landslides that mobilize into debris flows usually are characterized by high-speed movement and long run-out distance and may present the greatest risk to human life. The 22 March 2014 Oso landslide is a typical case of landside transformint to debris flow. The landslide was triggered on the edge of a plateau about 200 m high composed of glacial sediments after excessive prolonged rainfall of 348 in March 2014. After its initiation, portions of the landslide materials transitioned into a rapidly moving debris flow which traveled long distances across the downslope floodplain. U.S. Geological Survey estimated the volume of the slide to be about 7 million m3, and it traveled about 1 km from the toe of the slope. The apparent friction angle measured by the energy line drawn from the crown of the head scarp to the toe of the deposits which reached largest distance, was only 5~6 degrees. we performed two numerical modeling to predicting the runout distance and to get insight into the behaviour of the landslide movement. One is GIS-based revised Hovland's 3D limit equilibrium model which is used to simulate the movement and stoppage of a landslide. In this research, sliding is defined by a slip surface which cuts through the slope, causing the mass of earth to move above it. The factor of safety will be calculated step by step during the sliding process simulation. Stoppage is defined by the factor of safety much greater than one and the velocity equal zero. The other is GIS-based depth-averaged 2D numerical model using a coupled viscous and Coulomb type law to simulate a debris flow from initiation to deposition. We compared our simulaiton results with the results of preliminary computer simulation of the Oso landslide movement which was produced by David L. George and Richard M. Iverson on April 10, 2014.　

Flood Simulation Using WMS Model in Small Watershed after Strong Earthquake -A Case Study of Longxihe Watershed, Sichuan province, China

NASA Astrophysics Data System (ADS)

Guo, B.

2017-12-01

Mountain watershed in Western China is prone to flash floods. The Wenchuan earthquake on May 12, 2008 led to the destruction of surface, and frequent landslides and debris flow, which further exacerbated the flash flood hazards. Two giant torrent and debris flows occurred due to heavy rainfall after the earthquake, one was on August 13 2010, and the other on August 18 2010. Flash floods reduction and risk assessment are the key issues in post-disaster reconstruction. Hydrological prediction models are important and cost-efficient mitigation tools being widely applied. In this paper, hydrological observations and simulation using remote sensing data and the WMS model are carried out in the typical flood-hit area, Longxihe watershed, Dujiangyan City, Sichuan Province, China. The hydrological response of rainfall runoff is discussed. The results show that: the WMS HEC-1 model can well simulate the runoff process of small watershed in mountainous area. This methodology can be used in other earthquake-affected areas for risk assessment and to predict the magnitude of flash floods. Key Words: Rainfall-runoff modeling. Remote Sensing. Earthquake. WMS.

Mapping debris flow susceptibility using analytical network process in Kodaikkanal Hills, Tamil Nadu (India)

NASA Astrophysics Data System (ADS)

Sujatha, Evangelin Ramani; Sridhar, Venkataramana

2017-12-01

Rapid debris flows, a mixture of unconsolidated sediments and water travelling at speeds > 10 m/s are the most destructive water related mass movements that affect hill and mountain regions. The predisposing factors setting the stage for the event are the availability of materials, type of materials, stream power, slope gradient, aspect and curvature, lithology, land use and land cover, lineament density, and drainage. Rainfall is the most common triggering factor that causes debris flow in the Palar subwatershed and seismicity is not considered as it is a stable continental region and moderate seismic zone. Also, there are no records of major seismic activities in the past. In this study, one of the less explored heuristic methods known as the analytical network process (ANP) is used to map the spatial propensity of debris flow. This method is based on top-down decision model and is a multi-criteria, decision-making tool that translates subjective assessment of relative importance to weights or scores and is implemented in the Palar subwatershed which is part of the Western Ghats in southern India. The results suggest that the factors influencing debris flow susceptibility in this region are the availability of material on the slope, peak flow, gradient of the slope, land use and land cover, and proximity to streams. Among all, peak discharge is identified as the chief factor causing debris flow. The use of micro-scale watersheds demonstrated in this study to develop the susceptibility map can be very effective for local level planning and land management.

The application of numerical debris flow modelling for the generation of physical vulnerability curves

NASA Astrophysics Data System (ADS)

Luna, B. Quan; Blahut, J.; van Westen, C. J.; Sterlacchini, S.; van Asch, T. W. J.; Akbas, S. O.

2011-07-01

For a quantitative assessment of debris flow risk, it is essential to consider not only the hazardous process itself but also to perform an analysis of its consequences. This should include the estimation of the expected monetary losses as the product of the hazard with a given magnitude and the vulnerability of the elements exposed. A quantifiable integrated approach of both hazard and vulnerability is becoming a required practice in risk reduction management. This study aims at developing physical vulnerability curves for debris flows through the use of a dynamic run-out model. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results can then be applied to consequence analyses and risk calculations. On 13 July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of the Valtellina Valley (Lombardy Region, Northern Italy). One of the largest debris flows events occurred in a village called Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. The Selvetta event was modelled with the FLO-2D program, an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The behaviour and run-out of the flow was reconstructed. The significance of calculated values of the flow depth, velocity, and pressure were investigated in terms of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which was calculated as the ratio between the monetary loss and the reconstruction value. Three different empirical vulnerability curves were obtained, which are functions of debris flow depth, impact pressure, and kinematic viscosity, respectively. A quantitative approach to estimate the vulnerability of an exposed element to a debris flow which can be independent of the temporal occurrence of the hazard event is presented.

Reconstruction of glacial lake outburst floods in northern Tien Shan: Implications for hazard assessment

NASA Astrophysics Data System (ADS)

Zaginaev, V.; Ballesteros-Cánovas, J. A.; Erokhin, S.; Matov, E.; Petrakov, D.; Stoffel, M.

2016-09-01

Glacier lake outburst floods (GLOFs) and related debris flows are among the most significant natural threats in the Tien Shan Mountains of Kyrgyzstan and have even caused the loss of life and damage to infrastructure in its capital Bishkek. An improved understanding of the occurrence of this process is essential so as to be able to design reliable disaster risk reduction strategies, even more so in view of ongoing climate change and scenarios of future evolutions. Here, we apply a dendrogeomorphic approach to reconstruct past debris-flow activity on the Aksay cone (Ala-Archa valley, Kyrgyz range), where outbursting glacier lakes and intense rainfalls have triggered huge debris flows over the past decades. A total of 96 Picea abies (L.) Karst. trees growing on the cone and along the main channel have been selected based on the evidence of past debris-flow damage in their trunks; these trees were then sampled using increment borers. The dating of past events was based on the assessment of growth disturbances (GD) in the tree-ring records and included the detection of injuries, tangential rows of traumatic resin ducts, reaction wood, and abrupt growth changes. In total, 320 GD were identified in the tree-ring samples. In combination with aerial imagery and geomorphic recognition in the field, reactions in trees and their position on the cone have allowed reconstruction of the main spatial patterns of past events on the Aksay cone. Our findings suggest that at least 27 debris flows have occurred on the site between 1877 and 2015 and point to the occurrence of at least 17 events that were not documented prior to this study. We also observe high process activity during the 1950s and 1960s, with major events on the cone in 1950, 1966, and 1968, coinciding with phases of slight glacier advance. The spatial analyses of events also point to two different spatial patterns, suggesting that quite dissimilar magnitudes probably occurred during glacier lake outburst floods and rainfall-induced debris-flow events. The results presented here represent the longest, annually resolved GLOF series in the region, which in turn has key implications on risk assessment, not just in the Ala-Archa valley, but also in the entire Kyrgyz range (northern Tien Shan).

Feasibility Study on the Satellite Rainfall Data for Prediction of Sediment- Related Disaster by the Japanese Prediction Methodology

NASA Astrophysics Data System (ADS)

Shimizu, Y.; Ishizuka, T.; Osanai, N.; Okazumi, T.

2014-12-01

In this study, the sediment-related disaster prediction method which based ground gauged rainfall-data, currently practiced in Japan was coupled with satellite rainfall data and applied to domestic large-scale sediment-related disasters. The study confirmed the feasibility of this integrated method. In Asia, large-scale sediment-related disasters which can sweep away an entire settlement occur frequently. Leyte Island suffered from a huge landslide in 2004, and Typhoon Molakot in 2009 caused huge landslides in Taiwan. In the event of these sediment-related disasters, immediate responses by central and local governments are crucial in crisis management. In general, there are not enough rainfall gauge stations in developing countries. Therefore national and local governments have little information to determine the risk level of water induced disasters in their service areas. In the Japanese methodology, a criterion is set by combining two indices: the short-term rainfall index and long-term rainfall index. The short-term rainfall index is defined as the 60-minute total rainfall; the long-term rainfall index as the soil-water index, which is an estimation of the retention status of fallen rainfall in soil. In July 2009, a high-density sediment related disaster, or a debris flow, occurred in Hofu City of Yamaguchi Prefecture, in the western region of Japan. This event was calculated by the Japanese standard methodology, and then analyzed for its feasibility. Hourly satellite based rainfall has underestimates compared with ground based rainfall data. Long-term index correlates with each other. Therefore, this study confirmed that it is possible to deliver information on the risk level of sediment-related disasters such as shallow landslides and debris flows. The prediction method tested in this study is expected to assist for timely emergency responses to rainfall-induced natural disasters in sparsely gauged areas. As the Global Precipitation Measurement (GPM) Plan progresses, spatial resolution, time resolution and accuracy of rainfall data should be further improved and will be more effective in practical use.

How predictable is the behaviour of torrential processes: two case studies of the summer 2012

NASA Astrophysics Data System (ADS)

Huebl, Johannes; Eisl, Julia; Janu, Stefan; Hanspeter, Pussnig

2013-04-01

Debris flow hazards play an important role in the Austrian Alps since many villages are located on alluvial fans. Most of the mitigation Measures as well as Hazard Zone Maps are designed by engineers of previous generations, who know quite a lot about the torrential behaviour from their experience. But speaking in terms of recurrence intervals of 100 years or even more, human memory is restricted. On the other hand numerical modelling is a fast growing task in dealing with natural hazards. Scenarios of torrential hazards can be defined and accordant deposition pattern, flow depths and velocities are calculated. But of course, errors in the input data must lead to fatal errors in the results, consequently threaten human life in possible affected areas. Thus the need for data collection of exceptional events can help to reproduce the reality in a quite high grade, indeed, but unexpected events are still an issue and pose a challenge to engineers. In summer 2012 two debris flow events occurred in Austria with quite different behaviours, from triggering mechanism and flow behaviour through to deposition: Thunderstorms or long lasting rainfall, slope failures with subsequent channel blockage and dike breaching or linear erosion, one or more debris flows, one huge debris flow surge or a series of debris flow surges, sediments without clay or cohesive material, near channel deposition or outspread deposits. Both debris flows have been unexpected in their dimension, although mitigation measures and hazard maps exist. Both events were documented accurately, first to try to understand the torrential process occurred, second to identify the most fitting mitigation measures, ranging from permanent structures to temporary warning systems.

Debris-flow hazards caused by hydrologic events at Mount Rainier, Washington

USGS Publications Warehouse

Vallance, James W.; Cunico, Michelle L.; Schilling, Steve P.

2003-01-01

At 4393 m, ice-clad Mount Rainier has great potential for debris flows owing to its precipitous slopes and incised steep valleys, the large volume of water stored in its glaciers, and a mantle of loose debris on its slopes. In the past 10,000 years, more than sixty Holocene lahars have occurred at Mount Rainier (Scott et al., 1985), and, in addition more than thirty debris flows not related to volcanism have occurred in historical time (Walder and Driedger, 1984). Lahars at Mount Rainier can be classed in 3 groups according to their genesis: (1) flank collapse of hydrothermally altered, water-saturated rock; (2) eruption-related release of water and loose debris; and (3) hydrologic release of water and debris (Scott et al., 1985). Lahars in the first two categories are commonly voluminous and are generally related to unrest and explosions that occur during eruptive episodes. Lahars in the third category, distinguished here as debris flows, are less voluminous than the others but occur frequently at Mount Rainier, often with little or no warning. Historically at Mount Rainier, glacial outburst floods, torrential rains, and stream capture have caused small- to moderate-size debris flows (Walder and Driedger, 1984). Such debris flows are most likely to occur in drainages that have large glaciers in them. Less commonly, a drainage diversion has triggered a debris flow in an unglaciated drainage basin. For example, the diversion of Kautz Glacier meltwater into Van Trump basin triggered debris flows on the south side of Rainier in August 2001. On the basis of historical accounts, debris flows having hydrologic origins are likely to be unheralded, and have occurred as seldom as once in 8 years and as often as four times per year at Mount Rainier (Walder and Driedger, 1984). Such debris flows are most likely to occur during periods of hot dry weather or during periods of intense rainfall, and therefore must occur during the summer and fall. They are likely to begin at or above the elevations of glacier termini and extend down valley. This report discusses potential hazards from debris flows induced by hydrologic events such as glacial outburst floods and torrential rain at Mount Rainier and the surrounding area bounded by Mount Rainier National Park. The report also shows, in the accompanying hazard-zonation maps, which areas are likely to be at risk from future such debris flows at Mount Rainier. Lahar hazards related to avalanches of altered rock and to the interactions of hot rock and ice during eruptions are discussed in Scott and Vallance (1995) and Hoblitt et al. (1998) and are not addressed in this report.

Cosesimic landslides and their post-quake effects (Invited)

NASA Astrophysics Data System (ADS)

Huang, R.; Fan, X.

2013-12-01

On May 12, 2008, a devastating earthquake of magnitude Mw 7.9 hit China's Sichuan province. The quake, originating in the Longmen Shan fault zone at the eastern margin of Tibetan Plateau, was the country's largest seismic event in more than 50 years. It triggered more than 60,000 destructive landslides and 828 landslide dams over an area of 35,000 square kilometers, that caused about one third of the total fatalities. The combination of strong and long-lasting ground shaking, steep, rugged topography and a fragile and densely jointed lithology probably controlled the occurrence of landslides during the earthquake, but we found that other two factors (fault type and slip rate during the earthquake), may also have played a role. Landslides were clustered in a much wider corridor along the thrusting part of the Yingxiu-Beichuan fault than the strike-slip part. Large-scale landslides with an area of more than 50,000 m2 were concentrated where fault slip-rates were highest, near the intersections and junctures of individual segments of the fault. After the earthquake, debris flow hazard has become a significant concern. A tremendous amount of loose material from landslides that occurred during the earthquake is suspended on the hillslopes, ready to be eroded and transported by rain. More than 2000 occurrences of debris flow have been recorded by the Land and Resources Department of Sichuan Province following the 2008 quake till 2012. The threshold in hourly rainfall intensity for triggering debris flows was found to be around 60% lower after the earthquake than it had been before, according to the record in Beichuan. How long it will take for the debris flow frequency to return to pre-earthquake levels depends on a large number of factors, including rainfall intensity, natural re-vegetation and self-stabilization processes on slopes. We anticipate that - despite large uncertainties - debris flows that directly result from sediment movement during the 2008 earthquake may remain active for another two decades. Presumably, their frequency will decline over time, which may draw out the effect even longer. Heightened landslide frequency after a quake, with potential secondary effects like river damming and subsequent floods, need more focused attention.

Rainfall characteristics associated to the triggering of fast- and slow-moving landslides - a comparison between the South French Alps and Lower Austria

NASA Astrophysics Data System (ADS)

Remaitre, Alexandre; Wallner, Stefan; Promper, Catrin; Glade, Thomas; Malet, Jean-Philippe

2013-04-01

Rainfall is worldwide a recognized trigger of landslides. Numerous studies were conducted in order to define the relationships between the precipitations and the triggering or the reactivation of landslides. Hydrological triggering of landslides can be divided in three general types: (1) development of local perched water tables in the subsoil leading to shallow slope instabilities and possible gravitational flows, (2) long-lasting rise in permanent water tables leading to more deep-seated slope instabilities, and (3) intense runoff causing channel-bed erosion and debris flows. Types (1) and (3) are usually observed during high rainfall intensities (hourly and daily rainfall) associated to heavy storms; type (2) is usually observed through increasing water content in the subsoil due to antecedent rainfalls (weekly or monthly rainfall) and/or massive snowmelt. Many investigations have been carried out to determine the amount of precipitation needed to trigger slopes failures. For rainfall-induced landslides a threshold may be define the rainfall, soil moisture or hydrological conditions that, when reached or exceeded, are likely to trigger landslides. Usually rainfall thresholds can be defined on physical process-based or conceptual models or empirical, historical and statistical bases. Nevertheless, both the large variety of landslides and to the extreme variety of climatic conditions leading to the triggering or the reactivation of a landslide lead to a regional definition of relationships between landslide occurrence and associated climatic conditions. The purpose of this case study is to analyze the relationships between the triggering of three types of landslides, debris flows, shallow landslides and deep-seated mudslides, and different patterns of rainfall in two study sites with different physiographic and climatic characteristics: the Barcelonnette basin in the South French Alps and the Waidhofen an der Ybbs area in Lower Austria. For this purpose, we exploit for the two test sites a landslide catalogue and rainfall data series to define a typology of rainfall induced-landslides for the relevant landslide types. Results from an analysis of the rainfall conditions associated to these events at different time scale (yearly, monthly, daily and hourly) show a clear distinction between these landslides. Slow-moving landslides are often associated to persistent rainstorms with low intensities during long periods causing the saturation of the soils while fast-moving landslides are usually triggered by short rainfall events with high intensities that occur in summer.

An important erosion process on steep burnt hillslopes

NASA Astrophysics Data System (ADS)

Langhans, Christoph; Nyman, Petter; Noske, Philip; Lane, Patrick; Sheridan, Gary

2016-04-01

Steep forested hillslopes often display a high degree of armouring where diffusive erosion processes preferentially remove the fine fraction of the surface soil. High infiltration capacities, hydraulic resistance to overland flow and physical anchoring by cover plants and litter mean that even the most extreme rainfall events usually do not erode the armouring substantially. We argue that fire (wild or planned) is essential to the mobilization and transport of the armouring by increasing the rates of overland flow and decreasing trapping opportunities. We present evidence of the types of erosion that lead to the stripping of the surface armouring using post-event surveys and high-rate overland flow experiments. The type of erosion depends on the relative abundance of non-cohesive surface material to overland flow, but we found that a particular type of transport dominates that has no representation in current erosion models: On steep slopes overland flow can lead to incipient motion of individual stones that transfer their momentum to other stones leading to a rapid mobilization of the whole non-cohesive, armoured surface layer. Once in motion, the layer quickly separates out into a granular flow front and liquefied body, akin to debris flows in channels. Depending on the size of the event, these hillslope debris flows (HDF) either get trapped or enter into the channel, stripping the hillslope of most armouring on their way. They provide channels with the material and shear stress needed to erode into the channel bed, increasing the risk of channel debris flows. We present a simple physical model of HDF initiation, movement, and possible re-mobilization on hillslopes that was derived from debris flow theory. Understanding this process, its frequency, and magnitude are important for assessing the role of fire in landscape evolution and risk to humans through debris flow impacts.

Hydrologic behavior of a steep forested slope prone to shallow landsliding

NASA Astrophysics Data System (ADS)

Berti, Matteo; Simoni, Alessandro

2015-04-01

Over the past ten years, the frequency of debris flows in the Northern Apennines of Italy has significantly increased. Gravitational movements in the area are dominated by slow-moving landslides involving fine-grained soils and, to a lesser extent, by shallow slips in weathered arenaceous rocks. During the past 5 years, at least 20 debris flow events were triggered by exceptional rainfall events. Although no fatalities of injuries resulted from these landslides, the appearance of this new danger generated great concern among local communities. The Civil Protection Agency of the Emilia-Romagna region therefore decided to produce a debris flow susceptibility map to target high-risk zones and to help local authorities in emergency planning. This task, however, is particularly difficult due to the lack of historical data required to apply heuristic or statistical methods. In this context we installed a monitoring system on a representative slope in order to investigate the hydrologic response to rainfall and to support the choice of a suitable deterministic model. The selected slope is close to the village of Porretta Terme (Province of Bologna, Italy) at an elevation of 510 m asl. The slope has an inclination of about 30° and consists of a thin soil cover (0.5-1 thickness) lying over a fractured arenaceous bedrock. The soil is a well-graded sand with silt, gravel, cobbles, and weathered rock blocks. The slope is densely vegetated with grass, shrubs and mature trees. Part of the slope failed on the 30th November 2008 after a rainfall of 140 mm in 24 hours. A shallow slide of the soil mantle rapidly mobilized into debris flow leaving the bedrock exposed in the source area. The monitoring system is located on an unfailed slope close to the initiation area. The system consists of three stations aligned along the maximum slope at a distance of 15-20 m. Each station is equipped with: i) an open-standpipe piezometer installed near the soil-rock interface (1 m deep); ii) three tensiometers installed in the soil cover at different depths (0.2, 0.5 and 0.8 m); iii) three soil moisture capacitance sensors installed beside the tensiometer probes. The uphill station also includes an ultrasonic sensor for measuring snow depth and a barometric/temperature sensor. A tipping-bucket rain gage is installed in an area free of tree vegetation located 50 m further uphill. All the data are recorded every 10 minutes and stored on site. The monitoring system was installed in September 2012 and the first two years of data provide a consistent picture of slope hydrology. During all the dry season (from June to September) the sandy soil is essentially dry with strong negative pore pressures (less than -80 kPa). Occasional summer rainfall causes the infiltration of water into the unsaturated soil but the soil never approaches the saturation, nor groundwater is accumulated at the soil-rock interface. With the start of the wet season (around October) the soil water content progressively increases and the pore pressure rises to values detectable by the tensiometers (higher than 80 kPa). The soil, however, remains generally unsaturated with negative pore pressures in the order of -20/-30 kPa. Full saturation is temporarily reached in response to intense rainfall events. Rainfall water induce fast, transient pore pressure increases in the soil mantle and moves vertically toward the soil-rock interface, eventually leading to the development of a transient perched water table during the heaviest rainfall events. The thickness of the perched water table is clearly related to rainfall intensity (very intense rainfall may saturate up to 80% of the soil profile) while the contribution of lateral flow is less evident probably because it is dominated by macropores or because because bedrock fractures favour deeper circulation.

Controls on debris flow bulking in proglacial gully networks on Mount Rainier, WA

NASA Astrophysics Data System (ADS)

Legg, N. T.; Meigs, A.; Grant, G. E.; Kennard, P.

2012-12-01

Conversion of floodwaters to debris flows due to sediment bulking continues to be a poorly understood phenomenon. This study examines the initiation zone of a series of six debris flows that originated in proglacial areas of catchments on the flank of Mount Rainier during one storm in 2006. One-meter spatial resolution aerial photographs and LiDAR DEMs acquired before and after the storm reveal the lack of a single mass failure to explain the debris flow deposits. Rather, the imagery show appreciable gully widening along reaches up to approximately 1.5 km in length. Based on gully discharges estimated from rainfall rates and estimates of sediment contribution from gully wall width change, we find that the sediment volumes contributed from gully walls are sufficient to bulk floodwaters up to debris flow concentrations. Points in gullies where width change began (upstream limit) in 2006 have a power law trend (R2 = 0.58) in terms of slope-drainage area. Reaches with noticeable width change, which we refer to as bulking reaches (BR), plot along a similar trend with greater drainage areas and gentler slopes. We then extracted slope and drainage area of all proglacial drainage networks to examine differences in morphology between debris flow basins (DFB) and non-debris flow basins (NDFB), hypothesizing that DFB would have a greater portion of their drainage networks with similar morphology to BR than NDFB. A comparison of total network length with greater slope and area than BR reveals that the two basins types are not statistically different. Lengths of the longest reaches with greater slope and drainage area than the BR trend, however, are statistically longer in DFB than in the NDFBs (p<0.05). These results suggest that debris flow initiation by sediment bulking does not operate as a simple threshold phenomenon in slope-area space. Instead debris flow initiation via bulking depends upon slope, drainage area, and gully length. We suspect the dependence on length relates to the poorly understood bulking process where feedback mechanisms working to progressively increase sediment concentrations likely operate. The apparent length dependence revealed in this study requires a shift in thought about the conditions leading to debris flow generation in catchments dominated by unconsolidated and transportable material.

Regional danger assessment of Debris flow and its engineering mitigation practice in Sichuan-Tibet highway

NASA Astrophysics Data System (ADS)

Su, Pengcheng; Sun, Zhengchao; li, Yong

2017-04-01

Luding-Kangding highway cross the eastern edge of Qinghai-Tibet Plateau where belong to the most deep canyon area of plateau and mountains in western Sichuan with high mountain and steep slope. This area belongs to the intersection among Xianshuihe, Longmenshan and Anninghe fault zones which are best known in Sichuan province. In the region, seismic intensity is with high frequency and strength, new tectonic movement is strong, rock is cracked, there are much loose solid materials. Debris flow disaster is well developed under the multiple effects of the earthquake, strong rainfall and human activity which poses a great threat to the local people's life and property security. So this paper chooses Kangding and LuDing as the study area to do the debris flow hazard assessment through the in-depth analysis of development characteristics and formation mechanism of debris flow. Which can provide important evidence for local disaster assessment and early warning forecast. It also has the important scientific significance and practical value to safeguard the people's life and property safety and the security implementation of the national major project. In this article, occurrence mechanism of debris flow disasters in the study area is explored, factor of evaluation with high impact to debris flow hazards is identified, the database of initial evaluation factors is made by the evaluation unit of basin. The factors with high impact to hazards occurrence are selected by using the stepwise regression method of logistic regression model, at the same time the factors with low impact are eliminated, then the hazard evaluation factor system of debris flow is determined in the study area. Then every factors of evaluation factor system are quantified, and the weights of all evaluation factors are determined by using the analysis of stepwise regression. The debris flows hazard assessment and regionalization of all the whole study area are achieved eventually after establishing the hazard assessment model. In this paper, regional debris flows hazard assessment method with strong universality and reliable evaluation result is presented. The whole study area is divided into 1674 units by automatically extracting and artificial identification, and then 11 factors are selected as the initial assessment factors of debris flow hazard assessment in the study area. The factors of the evaluation index system are quantified using the method of standardized watershed unit amount ratio. The relationship between debris flow occurrence and each evaluation factor is simulated using logistic regression model. The weights of evaluation factors are determined, and the model of debris flows hazard assessment is established in the study area. Danger assessment result of debris flow was applied in line optimization and engineering disaster reduction of Sichuan-Tibet highway (section of Luding-Kangding).

Debris flow reconstruction - geomorphologic and numerical approach. A case study from the Selvetta event in Valtellina, Italy, July 2008

NASA Astrophysics Data System (ADS)

Blahut, J.; Luna, B. Quan; Akbas, S. O.; van Westen, C. J.

2009-04-01

On Sunday morning of 13th July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of Valtellina valley between Morbegno and Berbenno. One of the largest debris flows occurred in Selvetta, a fraction of Colorina municipality. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. At first several rock blocks about 2 m3 in size fell down from the direction of the torrent. The blocks were followed by a wave of debris and mud that immediately destroyed one building and caused damage to other nine houses. A stream flow following the debris flow consisting of fine mud with high water content that partially washed away the accumulation of deposits from the debris phase could also be distinguished. Geomorphologic investigations allowed identification of five main sections of the flow: 1) the proper scarp; 2) path in the forested area; 3) path on the alpine meadows; 4) accelerating section; 5) accumulation area. The initiation area of the flow is situated at 1760 m. a.s.l. (1480 m above the deposition zone) in a coniferous forest. The proper scarp consisted of an area of approximately 20 m2 in size, and a height of about 0.8 m. The final volume of the debris was estimated by field mapping to be between 12 000 and 15 000 m3. It was observed that erosion and entrainment played an important role in the development of the debris flow. The Selvetta event was modelled with the FLO2D program. FLO2D is an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. Entrainment was modeled at each section of the flow, and different hydrographs were produced in agreement with the behavior of the debris flow during its course. The significance of calculated values of pressure and velocity were investigated in terms of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which is defined as the ratio between the monetary loss and the reconstruction value. Two different empirical vulnerability curves were obtained, which are functions of debris flow velocity and pressure, respectively.

Seismological Aspects of the August 7th Zhouqu Debris Flows

NASA Astrophysics Data System (ADS)

Dan, Y.; Huang, X.

2016-12-01

Broadband seismic records have been proven to be a sufficient tool in extracting movement characteristics of debris flows in the last decades. The catastrophic Sanyanyu and Luojiayu debris flows, which were induced by a heavy rainfall, occurred at approximately the midnight of August 7th, 2010 (Beijing time, UTC+8) and claimed 1,765 lives. Broadband seismic signals recorded by the Zhouqu seismic station positioned only 150 meters away from the exit are acquired and analyzed in this study. Seismic signals reveal that the Sanyanyu debris flow started developing after a major rock collapse at approximately 23:23:50. The formation time of the Sanyanyu debris flow to separate its development stage and maturity stage was determined at 23:33:15 using spectrograms and amplitude variation patterns of seismic signals. Seismic signals, before and after the formation time, have distinctively different frequency characteristics. The frequency content of seismic signals generated by the maturity stage is more regular than that generated by the development stage. The maturity stage was further divided into five sub stages according to its amplitude variation patterns, including three increase sub stages and two stable sub stages alternately distributed. These five sub stages belong to two processes of the Sanyanyu debris flow which generate seismic signals with different frequency contents. The main frequency band of the first four sub stages continuously varies from approximately 2 - 8.5 Hz at start to approximately 3 - 9.5 Hz in the end. For the last sub stage, the upper boundary of the main frequency increases in a near linear way and reaches approximately 13 - 16 Hz in the end. Two sub stages are recognized from the satellite image of the Sanyanyu flow path, and the mean movement velocities of the Sanyanyu debris flow during these two sub stages are estimated to be 9.2 m/s and 9.7 m/s respectively.

Monitoring of debris flows and landslides by wired and wireless systems. Experiences from the Catalan Pyrenees.

NASA Astrophysics Data System (ADS)

Hürlimann, Marcel; Abancó, Clàudia; Moya, José; Vilajosana, Ignasi; Llosa, Jordi

2013-04-01

Sophisticated monitoring of landslides for research purpose has started in the 1990thies in the Catalan Pyrenees. Since then several types of mass movements (large landslides, debris flows, shallow landslides and rock falls) and multiples techniques have been applied. In this contribution, special attention will be given to the debris-flow monitoring system installed since summer 2009 in the Rebaixader catchment, Central Pyrenees. The monitoring system has continuously been improved during the last years and nowadays includes devices studying the three major aspects: 1) initiation, 2) flow dynamics, and 3) accumulation. While some parts of the monitoring network include a traditional wired system, the newer parts were installed using low-power wireless devices. Two major aspects will be discussed. First, results of the Rebaixader monitoring site will be presented. Second, experience regarding the monitoring will be evaluated focussing on technical aspects and the comparison between wired and wireless techniques. In the Rebaixader catchment, 6 debris flows and 11 debris floods were observed between August 2009 and October 2012. Surprisingly, also 4 major rock falls were recorded. The rainfall analysis shows that the debris flows were triggered by short, high-intensity rainstorms with a preliminary threshold of about 15 mm during 1 hour. In addition, there was observed a positive trend between event volume and rainfall amount or intensity. The analysis of the ground vibration signals shows significant differences between the time series recorded at the different geophones. These differences are associated with the geophone location in the channel (distance and material), the mounting or the data acquisition system. For instance, the most downstream geophone, installed in bedrock, shows the clearest debris-flows vibration time series, while the uppermost is the most reliable regarding the detection of rockfalls. An evaluation of wired versus wireless monitoring systems shows that wireless techniques have several advantages. They are generally smaller and due to the wireless condition the selection of the sensor location is not restricted like in the standard wired systems. Additionally, they are simple to install and consume much less power. Importantly, they are also more competitive in terms of pricing versus traditional wired solutions. Nevertheless, the adoption of this new technology has not been straightforward due to the harsh conditions where sensors are usually deployed. The later delayed and complicated the installation of some sensors in the Rebaixader site but allowed us to improve the monitoring solution. Finally, some very recent experiences on the wireless sensor network installed in a shallow landslide in the Pre-Pyrenees confirmed that this technique is a perfect solution not only for monitoring, but also for warning systems.

Flash floods and debris flow in the city area of Messina, North-East part of Sicily, Italy in October 2009: the case of the Giampilieri catchment

NASA Astrophysics Data System (ADS)

Aronica, G. T.; Brigandi, G.; Morey, N.

2010-09-01

Flash floods are phenomena in which the important hydrologic processes are occurring on the same spatial and temporal scales as the intense precipitation. Most of the catchment in the North-East part of Sicily (Italy) are small, with a steep slope, and characterized by short concentration times. These characteristics make those catchment prone to flash flood formation, as demonstrated by events that occurred in the area around Messina in the North-East part of Sicily, Italy in the last recent years. The events occurred on 25th October 2007 in the Mastroguglielmo torrent on the ionic sea coast, on 11th December 2008 in the Elicona catchment on the Tyrrhenian sea coast and on 1st October 2009 in Racinazzi and Giampilieri torrents on the ionic sea coast are an example of flash floods and debris flow events that caused not only significant economic damages to property, buildings, roads and bridges but also, for this that concern the 1st October 2009 flash flood event, loss of human life. This work is aimed by the 1st October 2009 flash flood and debris flow event where a devastating flooding was caused by a very intense rainfall concentrated over the Messina area. The storm caused severe flash floods in many villages around the city of Messina, such as Giampilieri, Scaletta Zanclea, Altolia Superiore and Molino with forty casualties and significant damage to property, buildings, roads and bridges estimated close to 200 million Euro. Main focus of this work is to perform a post event analysis of the 2009 flash flood event, putting together available meteorological and hydrological data in order to get better insight into temporal and spatial variability of the rain storm, the soil moisture condition and the consequent flash floods in the catchment of the Giampilieri catchment. Starting from these information another objective has been, then, to document the post-failure stage of event concerning slid materials. With the help of GIS technology and particularly spatial analysis, volume of debris gone down for the Giampilieri catchment has been calculated. The event was investigated using observed data from a raingauge network and hydraulic evidences. Statistical analysis using GEV distribution was performed and rainfall return period (storm severity) was estimated. Further, measured rainfall data and rainfall-runoff modeling were used to analyze the hydrological behaviour and to reconstruct flood and debris hydrographs. The study confirmed that post-flood investigation should focus on discharges and hydrological response of the catchment rather than simply analyzing statistical characteristics of rainfall. Thanks to LIDAR data produced immediately after the event, issued one meter precision DEM has been compared with a two meter precision one provided two years before. GIS maps with landslide and material deposit areas have been produced and analyzed.

Landslides triggered by the winter 1996-97 storms in the Puget Lowland, Washington

USGS Publications Warehouse

Baum, Rex L.; Chleborad, Alan F.; Schuster, Robert L.

1998-01-01

Snowmelt and rainfall events triggered many landslides and debris flows in the Seattle, Washington, area during late December 1996 and January and March 1997. Landslides caused the deaths of at least four people, millions of dollars in damage to public and private property, lost revenues, traffic diversions, and other direct and indirect losses. Although shallow slides and debris flows were the most common slope failures, many deep-seated slides also occurred. Comparing maps that show distribution of historic landslides with reports of landslides compiled by city and county governments for the winter of 1996-97 and our field reconnaissance of recent landslide deposits and scars indicates that many bluffs and steep hillsides are sites of recurring failures. Investigation of the 1996-97 landslides indicates that houses and other structures built downslope from steep bluffs are in particular danger of impact by debris flows, while those on the benches, slopes, or rim of bluffs are subject to severe damage by deep slides.

Evidence for enhanced debris flow activity in the Northern Calcareous Alps since the 1980s (Plansee, Austria)

NASA Astrophysics Data System (ADS)

Dietrich, Andreas; Krautblatter, Michael

2016-04-01

From 1950 to 2011 almost 80.000 people lost their lives through the occurrence of debris flow events (Dowling and Santi, 2014). Debris flows occur in all alpine regions due to intensive rainstorms and mobilisable loose debris. Due to their susceptible lithology, the Northern Calcareous Alps are affected by a double digit number of major hazard events per year. Some authors hypothesised a relation between an increasing frequency of heavy rainstorms and an increasing occurrence of landslides in general (Beniston and Douglas, 1996) and debris flows in special (Pelfini and Santilli, 2008), but yet there is only limited evidence. The Plansee catchment in the Ammergauer Alps consists of intensely jointed Upper Triassic Hauptdolomit lithology and therefore shows extreme debris flow activity. To investigate this activity in the last decades, the temporal and spatial development of eight active debris flow fans is examined with GIS and field mapping. The annual rates since the late 1940s are inferred accurately by using aerial photos from 1947, 1952, 1971, 1979, 1987, 2000 and 2010. These rates are compared to the mean Holocene/Lateglacial debris flow volume derived from the most prominent cone. The contact with the underlying till is revealed by electrical resistivity tomography (ERT). It shows that the mean annual debris flow volume has increased there by a factor of 10 from 1947-1952 (0.23 ± 0.07 10³m³/yr) to 1987-2000 (2.41 ± 0.66 10³m³/yr). A similar trend can be seen on all eight fans: mean post-1980 rates exceed pre-1980 rates by a factor of more than three. This increasing debris flow activity coincides with an enhanced rainstorm (def. 35 mm/d) frequency recorded at the nearest meteorological station. Since 1921 the frequency of heavy rainstorms has increased there on average by 10% per decade. Recent debris flow rates are also 2-3 times higher compared to mean Holocene/Lateglacial rates. Furthermore, we state a strong correlation between the non-vegetated catchment area and the annual debris flow volume. This might indicate a decadal positive feedback between enhanced rainstorm frequency and the occurrence of debris flows. The study contributes to a better understanding of the sensitivity of alpine catchments to heavy rainfall events in the context of climate change. Beniston, M., Douglas, G.F., 1996. Impacts of climate change on mountain regions. In: Watson, R.T., Zinyowera, M.C., Moss, R.H., Dokken, D.J. (Eds.), Climate Change 1995. Impacts, Adaptations and Mitigation of Climate Change: Scientific-Technical Analysis. Cambridge Univ. Press, Cambridge, pp. 191-213. Dowling, C.A., Santi, P.M., 2014. Debris flows and their toll on human life: a global analysis of debris-flow fatalities from 1950 to 2011. Nat. Hazards 71, 203-227. doi: 10.1007/s11069-013-0907-4 Pelfini, M., Santilli, M., 2008. Frequency of debris flows and their relation with precipitation: A case study in the Central Alps, Italy. Geomorphology 101, 721-730. doi:10.1016/j.geomorph.2008.04.002

Propagation of a channelized debris-flow: experimental investigation and parameters identification for numerical modelling

NASA Astrophysics Data System (ADS)

Termini, Donatella

2013-04-01

Recent catastrophic events due to intense rainfalls have mobilized large amount of sediments causing extensive damages in vast areas. These events have highlighted how debris-flows runout estimations are of crucial importance to delineate the potentially hazardous areas and to make reliable assessment of the level of risk of the territory. Especially in recent years, several researches have been conducted in order to define predicitive models. But, existing runout estimation methods need input parameters that can be difficult to estimate. Recent experimental researches have also allowed the assessment of the physics of the debris flows. But, the major part of the experimental studies analyze the basic kinematic conditions which determine the phenomenon evolution. Experimental program has been recently conducted at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Materials (DICAM) - University of Palermo (Italy). The experiments, carried out in a laboratory flume appositely constructed, were planned in order to evaluate the influence of different geometrical parameters (such as the slope and the geometrical characteristics of the confluences to the main channel) on the propagation phenomenon of the debris flow and its deposition. Thus, the aim of the present work is to give a contribution to defining input parameters in runout estimation by numerical modeling. The propagation phenomenon is analyzed for different concentrations of solid materials. Particular attention is devoted to the identification of the stopping distance of the debris flow and of the involved parameters (volume, angle of depositions, type of material) in the empirical predictive equations available in literature (Rickenmanm, 1999; Bethurst et al. 1997). Bethurst J.C., Burton A., Ward T.J. 1997. Debris flow run-out and landslide sediment delivery model tests. Journal of hydraulic Engineering, ASCE, 123(5), 419-429 Rickenmann D. 1999. Empirical relationships fro debris flow. Natural hazards, 19, pp. 47-77

A 38,000-year record of floods and debris flows in the Ilo region of southern Peru and its relation to El Niño events and great earthquakes

USGS Publications Warehouse

Keefer, David K.; Moseley, Michael E.; DeFrance, Susan D.

2003-01-01

Previous work throughout the Ilo region of south coastal Peru has documented the existence of flood and debris-flow deposits produced by two El Niño events evidently much more severe than any in recent history. These two events have been dated to ca. AD 1300–1400 and AD 1607–08. The Late Pleistocene to Holocene record of older sedimentary deposits in this region is dominated by flood and debris-flow deposits of similar scale. These older deposits have been described and dated from three coastal, alluvial-fan sites. These deposits, which are as old as 38 200 years, are dominated by massive debris-flow deposits, several tens of cm thick, typically composed of cobble- and boulder-sized clasts in a matrix of silty sand, with characteristics indicating generation by heavy rainfall in an arid environment. Twenty-two radiocarbon dates and a single infrared-stimulated luminescence date show that particularly severe El Niño events occurred throughout the Late Pleistocene and two of three divisions of the Holocene with significantly different frequencies. The period of greatest activity was during the Early Holocene when at least six such events took place during a period of ca. 3600 years, beginning near the end of the Younger Dryas ca. 12 000 years ago. One of these events produced a debris flow that may have caused abandonment of the Paleo-Indian site at Quebrada Tacahuay, one of the oldest on the Andean coast. No severe events took place during the Middle Holocene between ca. 8400 and 5300 years ago, when a wide variety of other paleoclimate proxy records indicate that the El Niño–Southern Oscillation regime was particularly weak. Since ca. 5300 years ago, four of these severe events have taken place. The Late Pleistocene sequence is constrained by only two dates, which indicate that at least ten severe events took place between ca. 38 200 and 12 900 years ago. Mechanisms probably responsible for generating these large-scale deposits include: (1) ‘Mega-Niños’ that produced anomalously heavy rainfall along most or all of the central Andean coast; (2) El Niños that occurred shortly after great earthquakes that produced large amounts of sediment; or (3) El Niños that produced anomalously heavy local rainfall. The existence of these large-scale deposits in the Ilo region implies a level of hazard much higher than indicated by the historical record alone

Tree ring-based chronology of hydro-geomorphic processes as a fundament for identification of hydro-meteorological triggers in the Hrubý Jeseník Mountains (Central Europe).

PubMed

Tichavský, Radek; Šilhán, Karel; Tolasz, Radim

2017-02-01

Hydro-geomorphic processes have significantly influenced the recent development of valley floors, river banks and depositional forms in mountain environments, have caused considerable damage to manmade developments and have disrupted forest management. Trees growing along streams are affected by the transported debris mass and provide valuable records of debris flow/flood histories in their tree-ring series. Dendrogeomorphic approaches are currently the most accurate methods for creating a chronology of the debris flow/flood events in forested catchments without any field-monitoring or a stream-gauging station. Comprehensive studies focusing on the detailed chronology of hydro-geomorphic events and analysis of meteorological triggers and weather circulation patterns are still lacking for the studied area. We provide a spatio-temporal reconstruction of hydro-geomorphic events in four catchments of the Hrubý Jeseník Mountains, Czech Republic, with an analysis of their triggering factors using meteorological data from four nearby rain gauges. Increment cores from 794 coniferous trees (Picea abies [L.] Karst.) allowed the identification of 40 hydro-geomorphic events during the period of 1889-2013. Most of the events can be explained by extreme daily rainfalls (≥50mm) occurring in at least one rain gauge. However, in several cases, there was no record of extreme precipitation at rain gauges during the debris flow/flood event year, suggesting extremely localised rainstorms at the mountain summits. We concluded that the localisation, intensity and duration of rainstorms; antecedent moisture conditions; and amount of available sediments all influenced the initiation, spatial distribution and characteristics of hydro-geomorphic events. The most frequent synoptic situations responsible for the extreme rainfalls (1946-2015) were related to the meridional atmospheric circulation pattern. Our results enhance current knowledge of the occurrences and triggers of debris flows/floods in the Central European mountains in transition between temperate oceanic and continental climatic conditions and may prompt further research of these phenomena in the Eastern Sudetes in general. Copyright © 2016 Elsevier B.V. All rights reserved.

Water Induced Hazard Mapping in Nepal: A Case Study of East Rapti River Basin

NASA Astrophysics Data System (ADS)

Neupane, N.

2010-12-01

This paper presents illustration on typical water induced hazard mapping of East Rapti River Basin under the DWIDP, GON. The basin covers an area of 2398 sq km. The methodology includes making of base map of water induced disaster in the basin. Landslide hazard maps were prepared by SINMAP approach. Debris flow hazard maps were prepared by considering geology, slope, and saturation. Flood hazard maps were prepared by using two approaches: HEC-RAS and Satellite Imagery Interpretation. The composite water-induced hazard maps were produced by compiling the hazards rendered by landslide, debris flow, and flood. The monsoon average rainfall in the basin is 1907 mm whereas maximum 24 hours precipitation is 456.8 mm. The peak discharge of the Rapati River in the year of 1993 at station was 1220 cu m/sec. This discharge nearly corresponds to the discharge of 100-year return period. The landslides, floods, and debris flows triggered by the heavy rain of July 1993 claimed 265 lives, affected 148516 people, and damaged 1500 houses in the basin. The field investigation and integrated GIS interpretation showed that the very high and high landslide hazard zones collectively cover 38.38% and debris flow hazard zone constitutes 6.58%. High flood hazard zone occupies 4.28% area of the watershed. Mitigation measures are recommendated according to Integrated Watershed Management Approach under which the non-structural and structural measures are proposed. The non-structural measures includes: disaster management training, formulation of evacuation system (arrangement of information plan about disaster), agriculture management practices, protection of water sources, slope protections and removal of excessive bed load from the river channel. Similarly, structural measures such as dike, spur, rehabilitation of existing preventive measures and river training at some locations are recommendated. The major factors that have contributed to induce high incidences of various types of mass movements and inundation in the basin are rock and soil properties, prolonged and high-intensity rainfall, steep topography and various anthropogenic factors.

Postwildfire debris flows hazard assessment for the area burned by the 2011 Track Fire, northeastern New Mexico and southeastern Colorado

USGS Publications Warehouse

Tillery, Anne C.; Darr, Michael J.; Cannon, Susan H.; Michael, John A.

2011-01-01

In June 2011, the Track Fire burned 113 square kilometers in Colfax County, northeastern New Mexico, and Las Animas County, southeastern Colorado, including the upper watersheds of Chicorica and Raton Creeks. The burned landscape is now at risk of damage from postwildfire erosion, such as that caused by debris flows and flash floods. This report presents a preliminary hazard assessment of the debris-flow potential from basins burned by the Track Fire. A pair of empirical hazard-assessment models developed using data from recently burned basins throughout the intermountain western United States were used to estimate the probability of debris-flow occurrence and volume of debris flows at the outlets of selected drainage basins within the burned area. The models incorporate measures of burn severity, topography, soils, and storm rainfall to estimate the probability and volume of post-fire debris flows following the fire. In response to a design storm of 38 millimeters of rain in 30 minutes (10-year recurrence-interval), the probability of debris flow estimated for basins burned by the Track fire ranged between 2 and 97 percent, with probabilities greater than 80 percent identified for the majority of the tributary basins to Raton Creek in Railroad Canyon; six basins that flow into Lake Maloya, including the Segerstrom Creek and Swachheim Creek basins; two tributary basins to Sugarite Canyon, and an unnamed basin on the eastern flank of the burned area. Estimated debris-flow volumes ranged from 30 cubic meters to greater than 100,000 cubic meters. The largest volumes (greater than 100,000 cubic meters) were estimated for Segerstrom Creek and Swachheim Creek basins, which drain into Lake Maloya. The Combined Relative Debris-Flow Hazard Ranking identifies the Segerstrom Creek and Swachheim Creek basins as having the highest probability of producing the largest debris flows. This finding indicates the greatest post-fire debris-flow impacts may be expected to Lake Maloya. In addition, Interstate Highway 25, Raton Creek and the rail line in Railroad Canyon, County road A-27, and State Highway 526 in Sugarite Canyon may also be affected where they cross drainages downstream from recently burned basins. Although this assessment indicates that a rather large debris flow (approximately 42,000 cubic meters) may be generated from the basin above the City of Raton (basin 9) in response to the design storm, the probability of such an event is relatively low (approximately 10 percent). Additional assessment is necessary to determine if the estimated volume of material is sufficient to travel into the City of Raton. In addition, even small debris flows may affect structures at or downstream from basin outlets and increase the threat of flooding downstream by damaging or blocking flood mitigation structures. The maps presented here may be used to prioritize areas where erosion mitigation or other protective measures may be necessary within a 2- to 3-year window of vulnerability following the Track Fire.

"The Great Cataract" - Effects of Late Holocene Debris Flows on Lava Falls Rapid, Grand Canyon National National Park, Arizona

USGS Publications Warehouse

Webb, Robert H.; Melis, Theodore S.; Wise, Thomas W.; Elliott, John G.

1996-01-01

Lava Falls Rapid is the most formidable reach of whitewater on the Colorado River in Grand Canyon and is one of the most famous rapids in the world. Although the rapid was once thought to be controlled by the remnants of lava dams of Pleistocene age, Lava Falls was created and is maintained by frequent debris flows from Prospect Canyon. We used 232 historical photographs, of which 121 were replicated, and 14C and 3He dating methods to reconstruct the ages and, in some cases, the magnitudes of late Holocene debris flows. We quantified the interaction between Prospect Canyon debris flows and the Colorado River using image processing of the historical photographs. The highest and oldest debris-flow deposits on the debris fan yielded a 3He date of 2.9?0.6 ka (950 BC), which indicates predominately late Holocene aggradation of one of the largest debris fans in Grand Canyon. The deposit, which has a 25-m escarpment caused by river reworking, crossed the Colorado River and raised its base level by 30 m for an indeterminate, although probably short, period. We mapped depositional surfaces of 6 debris flows that occurred after 950 BC. The most recent prehistoric debris flow occurred no more than 500 years ago (AD 1434). From April 1872 to July 1939, no debris flows occurred in Prospect Canyon. Debris flows in 1939, 1954, 1955, 1963, 1966, and 1995 constricted the Colorado River between 35 and 80 percent and completely changed the pattern of flow through the rapid. The debris flows had discharges estimated between about 290 and 1,000 m3/s and transported boulders as heavy as 30 Mg. The recurrence interval of these debris flows, calculated from the volume of the aggraded debris fan, ranged from 35 to 200 yrs. The 1939 debris flow in Prospect Canyon appears to have been the largest debris flow in Grand Canyon during the last 125 years. Debris flows in Prospect Canyon are initiated by streamflow pouring over a 325-m waterfall onto unconsolidated colluvium, a process called the firehose effect. Floods in Prospect Valley above the waterfall are generated during regional winter storms, localized summer thunderstorms, and occasional tropical cyclones. Winter precipitation has increased in the Grand Canyon region since the early 1960s, and the most recent debris flows have occurred during winter storms. Summer rainfall has declined in the same period, decreasing the potential for debris flows in the summer months. The history of river reworking of the Prospect Canyon debris fan illustrates the interrelation between tributary debris fans and mainstem floods in bedrock canyons. Lava Falls Rapid did not change despite Colorado River floods of 8,500 m3/s in 1884 and 6,230 m3/s in 1921. Floods up to 3,540 m3/s that occurred after the historical, pre-dam debris flows removed most of the deposits within 3 years. Releases in 1965 from Glen Canyon Dam that were above powerplant capacity but less than 1,640 m3/s removed most of the debris fan deposited in 1963, and the combination of dam releases and a 1973 flood on the Little Colorado River removed the 1966 aggradation. About 4,800 m3 of the 1995 deposit was reworked on the day of the 1995 debris flow, dam releases of less than 570 m3/s had not reworked the remainder of the aggraded debris fan. Lava Falls Rapid has been the most unstable reach of whitewater in Grand Canyon during the late Holocene and particularly during the last 120 years. Rapids in bedrock canyons controlled by tributary deposition in the main channel are aggradational features that reflect the net effect of tributary-mainstem interactions. Boulders that form the core of rapids in Grand Canyon are essentially immobile by both regulated and unregulated Colorado River flows. Historical operation of Glen Canyon Dam, which was completed in 1963, has reduced the potential for reworking of debris fans, and has accelerated the rate of net aggradation at the mouths of tributary canyons. Because debris fans that formed after 196

Sediment Transportation Induced by Deep-Seated Landslides in a Debris Flow Basin in Taiwan

NASA Astrophysics Data System (ADS)

Lin, Meei Ling; Chen, Te Wei; Chen, Yong Sheng; Sin Jhuang, Han

2016-04-01

Typhoon Morakot brought huge amount of rainfall to the southern Taiwan in 2009 and caused severe landslides and debris flow hazard. After Typhoon Morakot, it was found that the volume of sediment transported by the debris flow and its effects on the affected area were much more significant compared to previous case history, which may due to the huge amount of rainfall causing significant deep-seated landslides in the basin. In this study, the effects and tendency of the sediment transportation in a river basin following deep-seated landslides caused by typhoon Morakot were evaluated. We used LiDAR, DEM, and aerial photo to identify characteristics of deep-seated landslides in a debris flow river basin, KSDF079 in Liuoguey District, Kaohsiung City, Taiwan. Eight deep-seated landslides were identified in the basin. To estimate the potential landslide volume associated with the deep-seated landslides, the stability analysis was conducted to locate the critical sliding surface, and the potential landside volume was estimated based on the estimation equation proposed by the International Geotechnical Societies' UNESCO Working Party on World Landslide Inventory (WP/WLI, 1990). The total potential landslide volume of the eight deep-seated landslides in KSDF079 basin was about 28,906,856 m3. Topographic analysis was performed by using DEM before and LiDAR derived DEM after typhoon Morakot to calculate the landslide volume transported. The result of erosion volume and deposition volume lead to a run out volume of 5,832,433 m3. The results appeared to consist well with the field condition and aerial photo. Comparing the potential landslide volume and run out volume of eight deep-seated landslides, it was found that the remaining potential landslide volume was about 80%. Field investigation and topographic analysis of the KSDF079 debris flow revealed that a significant amount of sediment deposition remained in the river channel ranging from the middle to the downstream section of the channel, and the channel has been widen. Such large proportion of landslide volume remained in the basin on deep-seated landslide scars and debris flow river channel would likely to cause further debris transportation in the future events. The stability analysis used in this study provided a feasible method and satisfactory results for estimating sediment volume transportation associated with the deep-seated landslides in the study area. Combination of the stability analysis results and the topographic analysis provided estimation of sediment transportation caused by the deep-seated landslides, and trend variation of further sediment transport of the basin, which could provide vital information for hazard mitigation. Keyword: deep-seated landslide, sediment transport, DEM, LiDAR, stability analysis

Multi-scale quantitative vulnerability assessment of buildings towards debris-flows: an application to Fella River Basin, Italy

NASA Astrophysics Data System (ADS)

Liliana Ciurean, Roxana; Hussin, Haydar; Glade, Thomas; van Westen, Cees; Papathoma-Köhle, Maria

2015-04-01

In physical vulnerability assessments, selection of working tools and methods is dependent not only on practical applications or decision question and data availability, but also on the scale of investigation. The aim of this study is to implement and compare two methodologies for assessing vulnerability of buildings in Fella River Basin (Friuli-Venezia Giulia, Italy). In this region, a major rainfall event in August 2003 triggered more than a thousand debris flows and floods resulting in two casualties. Damages to buildings, communication and transport infrastructure exceeded 400 million euros of monetary losses. The approaches considered are developed based on two methods of estimating debris-flow intensities: (1) for the regional and local scale, the behavior and run-out of the flow event was reconstructed using numerical debris flow modeling (Flow-R and Flow2D, respectively) to generate physical outputs (extension, depth, impact pressure, velocities) and determine the areas where elements at risk can be impacted; (2) for the local scale, a second method uses orthophoto documentation acquired shortly after the 2003 event for determining the location of the debris deposition and its depth at each impacted building. An extensive building inventory comprising information about the material of construction, occupancy type and use was compiled by desktop mapping and field work. The significance of the calculated intensity values were investigated in terms of resulting physical damages which were quantified for each affected structure as the ratio between the monetary loss and the reconstruction value. Different empirical vulnerability curves were obtained as functions of debris flow depth and impact pressure, respectively. The obtained curves were lastly compared with existing ones from the literature and sources of uncertainty from data input and the models employed were studied and discussed. The results of this study can be applied to further local consequence analysis and risk calculations, but can also been applied in other regions worldwide where respective data are available.

Effective mitigation of debris flows at Lemon Dam, La Plata County, Colorado

NASA Astrophysics Data System (ADS)

deWolfe, Victor G.; Santi, Paul M.; Ey, J.; Gartner, Joseph E.

2008-04-01

To reduce the hazards from debris flows in drainage basins burned by wildfire, erosion control measures such as construction of check dams, installation of log erosion barriers (LEBs), and spreading of straw mulch and seed are common practice. After the 2002 Missionary Ridge Fire in southwest Colorado, these measures were implemented at Knight Canyon above Lemon Dam to protect the intake structures of the dam from being filled with sediment. Hillslope erosion protection measures included LEBs at concentrations of 220-620/ha (200-600% of typical densities), straw mulch was hand spread at concentrations up to 5.6 metric tons/hectare (125% of typical densities), and seeds were hand spread at 67-84 kg/ha (150% of typical values). The mulch was carefully crimped into the soil to keep it in place. In addition, 13 check dams and 3 debris racks were installed in the main drainage channel of the basin. The technical literature shows that each mitigation method working alone, or improperly constructed or applied, was inconsistent in its ability to reduce erosion and sedimentation. At Lemon Dam, however, these methods were effective in virtually eliminating sedimentation into the reservoir, which can be attributed to a number of factors: the density of application of each mitigation method, the enhancement of methods working in concert, the quality of installation, and rehabilitation of mitigation features to extend their useful life. The check dams effectively trapped the sediment mobilized during rainstorms, and only a few cubic meters of debris traveled downchannel, where it was intercepted by debris racks. Using a debris volume-prediction model developed for use in burned basins in the Western U.S., recorded rainfall events following the Missionary Ridge Fire should have produced a debris flow of approximately 10,000 m 3 at Knight Canyon. The mitigation measures, therefore, reduced the debris volume by several orders of magnitude. For comparison, rainstorm-induced debris flows occurred in two adjacent canyons at volumes within the range predicted by the model.

Swarm slide - debris flow disaster induced by extreme rainfall in Hiroshima, August 2014 and lessons learnt in urban designing

NASA Astrophysics Data System (ADS)

Fukuoka, H.; Wang, C.

2015-12-01

Hiroshima city was hit by swarm debris flows along a narrow, and linear-shaped rain band of 2 km x 10 km which appeared in the early morning of August 20, 2014. Most of the flows were induced by shallow slide in the upstream. This disaster claimed 74 death, although this city experienced very similar disaster in 1999, claiming more than 30 residents lives. In the most severely affected debris flow torrent, more than 50 residents were killed. Most of the casualties arose in the wooden, vulnerable houses constructed in front of the exit of torrents. Points and lessons learnt from the disaster are as follows:1. Authors collected two types of sands from the source scar of the initial debris slides which induced debris flows. Tested by the ring shear apparatus under pore-pressure control condition, clear "Sliding surface liquefaction" was confirmed for both samples even under small normal stress, representing the small thickness of the slides. These results shows even instant excess pore pressure could initiate the slides and trigger slide-induced debris flow byundrained loading onto the torrent deposits.2. Apparently long-term land-use change since 1945 affected and raised the vulnerability of the community. Residential area had expanded into hill-slope (mountainous / semi-mountainous area) especially along the torrents. Those communities were developed on the past debris flow fan.3. As the devastated area is very close to downtown of Hiroshima city, it gave large societal impact to the Japanese citizens. After 1999 Hiroshima debris flow disaster, the Landslide disaster reduction law which intends to promote designation of landslide potential risk zones, was adopted in 2000. Immediately after 2014 disaster, national diet approved revision of the bill to promote rapid completion of the designation over the national territory. MLIT (Ministry of Land, Infrastructure, Tranportation and Tourism) decided to install X-band rain radars at more sites to cover whole city zones of the country. However, narrow extreme rain bands or spots which can not be detected effectively, often appear these years. It means more rain gauges conncted to the net should be implemented at upstreams of the communities facing torrent exits and on debris fan.

Rainfall Induced Landslides in Brazil: Geomorphological Controls and Land-use Effects

NASA Astrophysics Data System (ADS)

Fernandes, N. F.; Guimarães, R. F.; Gomes, R. A.; Carvalho, O. A., Jr.; Vieira, B. C.; Amaral, C. P.; Vargas, E. A., Jr.; Campos, T. M.

2009-12-01

Landslides are major processes controlling landscape evolution, especially in tropical environments, where thick talus and colluvial deposits are observed filling bedrock topographic hollows and larger valleys. Besides their geomorphological meaning, they also represent an enormous danger to man when soil-mantled steep hillslopes are densely occupied in urban areas. In Brazil, especially in southern and southeastern portions, due to the steep hilly topography, the high precipitation values and the expansion of the urbanization towards the hillslopes, debris flows are becoming more frequent. However, more recently, even in areas with sparse occupation and with no previous records of catastrophic landslides, like the ones in the southern states of Paraná and Santa Catarina, debris flows are taking place. This is the case of the recent rainfall triggered catastrophic debris flows that occurred last November in the area Morro do Baú, Santa Catarina state, by far, the most important event that took place in this region. In this location, besides the striking pluviometric records and the geological/geomorphological aspects, land-use changes (huge banana plantations and Pines forested areas) seems to have played a major role in amplifying the magnitude of the processes. However, the scientific community in Brazil seems to be still more concerned with small shallow landslides. Although a lot of effort has already been made towards a better understanding of the conditioning factors controlling landslide initiation at a specific site (hillslope scale), it is urgent to improve our ability in predicting landslide instability in larger areas (drainage basin scale), where positive and negative feedbacks between the hillslope and the channel segments play a major role. Modeling hillslope stability, of course, is not an easy task, especially when dealing with large drainage basin. Consequently, different approaches should be combined in order to attain success in prediction landslide hazards. In this study, based on detailed field mapping and modeling, we compare the role played by the geomorphological and geological factors in defining the location of major debris flows in Brazil. Besides, we discuss the effects of land-use changes, especially the introduction of huge banana plantations on steep slopes, on soil hydrology and landsliding. At last, we show some modeling results obtained in combining the models SHALSTAB and FLO-2D to simulate the catastrophic debris flows that took place in Rio de Janeiro city in 1996.

Physical modelling of rainfall-induced flow failures in loose granular soils

NASA Astrophysics Data System (ADS)

Take, W. A.; Beddoe, R. A.

2015-09-01

The tragic consequences of the March 2014 Oso landslide in Washington, USA were particularly high due to the mobility of the landslide debris. Confusingly, a landslide occurred at that exact same location a number of years earlier, but simply slumped into the river at the toe of the slope. Why did these two events differ so drastically in their mobility? Considerable questions remain regarding the conditions required to generate flow failures in loose soils. Geotechnical centrifuge testing, in combination with high-speed cameras and advanced image analysis has now provided the landslides research community with a powerful new tool to experimentally investigate the complex mechanics leading to high mobility landslides. This paper highlights recent advances in our understanding of the process of static liquefaction in loose granular soil slopes achieved through observations of highly-instrumented physical models. In particular, the paper summarises experimental results aimed to identify the point of initiation of the chain-reaction required to trigger liquefaction flow failures, to assess the effect of slope inclination on the likelihood of a flowslide being triggered, and to quantify the effect of antecedent groundwater levels on the distal reach of landslide debris with the objective of beginning to explain why neighbouring slopes can exhibit such a wide variation in landslide travel distance upon rainfall-triggering.

Landslides triggered by Hurricane Mitch in Guatemala -- inventory and discussion

USGS Publications Warehouse

Bucknam, Robert C.; Coe, Jeffrey A.; Chavarria, Manuel Mota; Godt, Jonathan W.; Tarr, Arthur C.; Bradley, Lee-Ann; Rafferty, Sharon A.; Hancock, Dean; Dart, Richard L.; Johnson, Margo L.

2001-01-01

The torrential rains that accompanied Hurricane Mitch in October and November of 1998 triggered thousands of landslides in the moderate to steep terrain bordering the Motagua and Polochic Rivers in eastern Guatemala. Using aerial photographs taken between January and March 2000 we mapped all visible landslides larger than about 15 m in minimum dimension in a study area of 10,000 km2 encompassing twenty 1:50,000-scale topographic map quadrangles. Rainfall from Hurricane Mitch was exceptional because it was geographically widespread, prolonged over a period of about a week, moderate to heavy in intensity, and occurred at the end of the rainy season when the ground already had a high moisture content. As documented in this report, this type of rainfall, on saturated or nearly saturated ground, has the capability to trigger both shallow and deep-seated landslides over a large area. We mapped about 11,500 landslides in the study area. The mapped landslides were of two general types: relatively small, translational and rotational landslides that commonly mobilized into debris flows and covered less than several hectares in area (not including flow paths), and large, commonly translational, landslides that sometimes generated debris flows and covered between 15 ha and 25 ha (not including flow paths). The main concentrations of landslides are on moderate-to-steep hillslopes underlain by diverse geologic units. For the purpose of describing the mapped landslides, we divided the study area into five distinct regions based on differing geologic and geomorphic characteristics. These regions include the upper Polochic valley and surrounding highlands, the central Sierra de las Minas, the hills surrounding La Union and Zacapa, the eastern Sierra de las Minas, and the border region with Honduras. All of these areas received between 200 mm and 600 mm of rain over a 13-day period between October 25 and November 6. The highest rainfall amounts (400 mm to 600 mm) occurred in the Upper Polochic valley and surrounding highlands and in the central Sierra de las Minas. The lower rainfall amounts (200 mm to 400 mm) occurred in the hills surrounding La Union, the eastern Sierra de las Minas, and in the border region with Honduras. In general, the rainfall received in these areas is roughly equivalent to the average precipitation received in a 1-year period. We used 10-m digital elevation models (DEMs) generated from contours on two quadrangles in the central Sierra de las Minas to create a map showing areas that were susceptible to landslides during Hurricane Mitch. To create the Hurricane Mitch susceptibility map, we developed a susceptibility threshold equation based on elevation and gradient. The analysis indicates that, at least on two quadrangles, gradients less than 9? were not susceptible to landslides during Hurricane Mitch. The slope of the line defined by the threshold equation indicates that less rainfall was required to initiate landslides on steep gradients than on shallow gradients. Ninety percent of the mapped landslides that were triggered by Hurricane Mitch are within the susceptible zone shown on the map. Eightysix percent of landslides that were mapped as predating Hurricane Mitch, and all landslides mapped as postdating Hurricane Mitch, are within the susceptible zone. We used LAHARZ software to model the potential downstream area affected by debris if a large landslide dam on the Rio La Lima were to fail. The model shows that the area affected would be similar to the area that was affected by a debris flow that mobilized from a large landslide along the Rio La Lima during Hurricane Mitch. The characteristics of rainfall-triggered landslides described in this report can be used as a partial guide to future landslide activity triggered by rainstorms. On the basis of existing data, hazardous areas include: moderate to steep hillslopes and

Predictive susceptibility analysis of typhoon induced landslides in Central Taiwan

NASA Astrophysics Data System (ADS)

Shou, Keh-Jian; Lin, Zora

2017-04-01

Climate change caused by global warming affects Taiwan significantly for the past decade. The increasing frequency of extreme rainfall events, in which concentrated and intensive rainfalls generally cause geohazards including landslides and debris flows. The extraordinary, such as 2004 Mindulle and 2009 Morakot, hit Taiwan and induced serious flooding and landslides. This study employs rainfall frequency analysis together with the atmospheric general circulation model (AGCM) downscaling estimation to understand the temporal rainfall trends, distributions, and intensities in the adopted Wu River watershed in Central Taiwan. To assess the spatial hazard of the landslides, landslide susceptibility analysis was also applied. Different types of rainfall factors were tested in the susceptibility models for a better accuracy. In addition, the routes of typhoons were also considered in the predictive analysis. The results of predictive analysis can be applied for risk prevention and management in the study area.

Quantitative risk assessment using empirical vulnerability functions from debris flow event reconstruction

NASA Astrophysics Data System (ADS)

Luna, Byron Quan; Blahut, Jan; Camera, Corrado; van Westen, Cees; Sterlacchini, Simone; Apuani, Tiziana; Akbas, Sami

2010-05-01

For a quantitative risk assessment framework it is essential to assess not only the hazardous process itself but to perform an analysis of their consequences. This quantitative assessment should include the expected monetary losses as the product of the probability of occurrence of a hazard with a given magnitude and its vulnerability. A quantifiable integrated approach of both hazard and risk is becoming a required practice in risk reduction management. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results are then applied for vulnerability and risk calculations. The risk assessment has been conducted in the Valtellina Valley, a typical Italian alpine valley lying in northern Italy (Lombardy Region). On 13th July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of valley between Morbegno and Berbenno. One of the largest debris flows occurred in Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. Also inside the Valtellina valley, between the 22nd and the 23rd of May 1983, two debris flows happened in Tresenda (Teglio municipality), causing casualties and considerable economic damages. On the same location, during the 26th of November 2002, another debris flow occurred that caused significant damage. For the quantification of a new scenario, the outcome results obtained from the event of Selvetta were applied in Tresenda. The Selvetta and Tresenda event were modelled with the FLO2D program. FLO2D is an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The significance of calculated values of pressure and velocity were investigated in terms of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which is defined as the ratio between the monetary loss and the reconstruction value. Two different empirical vulnerability curves were obtained, which are functions of debris flow velocity and pressure, respectively. Prospective economic direct losses were estimated.

Improving transferability strategies for debris flow susceptibility assessment: Application to the Saponara and Itala catchments (Messina, Italy)

NASA Astrophysics Data System (ADS)

Cama, M.; Lombardo, L.; Conoscenti, C.; Rotigliano, E.

2017-07-01

Debris flows can be described as rapid gravity-induced mass movements controlled by topography that are usually triggered as a consequence of storm rainfalls. One of the problems when dealing with debris flow recognition is that the eroded surface is usually very shallow and it can be masked by vegetation or fast weathering as early as one-two years after a landslide has occurred. For this reason, even areas that are highly susceptible to debris flow might suffer of a lack of reliable landslide inventories. However, these inventories are necessary for susceptibility assessment. Model transferability, which is based on calibrating a susceptibility model in a training area in order to predict the distribution of debris flows in a target area, might provide an efficient solution to dealing with this limit. However, when applying a transferability procedure, a key point is the optimal selection of the predictors to be included for calibrating the model in the source area. In this paper, the issue of optimal factor selection is analysed by comparing the predictive performances obtained following three different factor selection criteria. The study includes: i) a test of the similarity between the source and the target areas; ii) the calibration of the susceptibility model in the (training) source area, using different criteria for the selection of the predictors; iii) the validation of the models, both at the source (self-validation, through random partition) and at the target (transferring, through spatial partition) areas. The debris flow susceptibility is evaluated here using binary logistic regression through a R-scripted based procedure. Two separate study areas were selected in the Messina province (southern Italy) in its Ionian (Itala catchment) and Tyrrhenian sides (Saponara catchment), each hit by a severe debris flow event (in 2009 and 2011, respectively). The investigation attested that the best fitting model in the calibration areas resulted poorly performing in predicting the landslides of the test target area. At the same time, the susceptibility models calibrated with an optimal set of covariates in the source area allowed us to produce a robust and accurate prediction image for the debris flows activated in the Saponara catchment in 2011, exploiting only the data known after the Itala-2009 event.

Landslide overview map of the conterminous United States

USGS Publications Warehouse

Radbruch-Hall, Dorothy H.; Colton, Roger B.; Davies, William E.; Lucchitta, Ivo; Skipp, Betty A.; Varnes, David J.

1982-01-01

The accompanying landslide overview map of the conterminous United States is one of a series of National Environmental Overview Maps that summarize geologic, hydrogeologic, and topographic data essential to the assessment of national environmental problems. The map delineates areas where large numbers of landslides exist and areas which are susceptible to landsliding. It was prepared by evaluating the geologic map of the United States and classifying the geologic units according to high, medium, or low landslide incidence (number) and high, medium, or low susceptibility to landsliding. Rock types, structures, topography, precipitation, landslide type, and landslide incidence are mentioned for each physical subdivision of the United States. The differences in slope stability between the Colorado Plateau, the Appalachian Highlands, the Coast Ranges of California, and the Southern Rocky Mountains are compared in detail, to illustrate the influence of various natural factors on the types of landsliding that occur in regions having different physical conditions. These four mountainous regions are among the most landslide-prone areas in the United States. The Colorado Plateau is a deformed platform where interbedded sedimentary rocks of varied lithologic properties have been gently warped and deeply eroded. The rocks are extensively fractured. Regional fracture systems, joints associated with individual geologic structures, and joints parallel to topographic surfaces, such as cliff faces, greatly influence slope stability. Detached blocks at the edges of mesas, as well as columns, arched recesses, and many natural arches on the Colorado Plateau, were formed wholly or in part by mass movement. In the Appalachian Highlands, earth flows, debris flows, and debris avalanches predominate in weathered bedrock and colluvium. Damaging debris avalanches result when persistent steady rainfall is followed by a sudden heavy downpour. Landsliding in unweathered bedrock is controlled locally by joint systems similar to those on the Colorado Plateau. In some places, outward gravitational movement of valley walls due to stress release has formed anticlines and caused thrusting in the center of valleys. In the Coast Ranges of California, slopes are steep, and rocks are varied and extensively deformed. One of the most slide-prone terrains of the Coast Ranges is the tectonic melange of the Franciscan assemblage, on which huge masses of debris are moving slowly downslope. In southern California, debris flows generated by soil slips are particularly damaging. Similar flows are common in poorly consolidated Tertiary rocks of the central part of the State. Like the debris avalanches of the Appalachian Highlands, the flows form during intense rainfall after previous steady rain. The Southern Rocky Mountains are complex in rock type and climate, so that the landslides there are also complex. Slides range from rock-falls at one extreme to slumps and debris flows at the other. They include ?sackungen,? which are distinguished by ridgetop grabens associated with uphill-facing scarps on ridge sides, both features of gravitational origin. Extensive regional joint patterns have not been recognized, and shallow soil slips are only a minor hazard.

Debris Flows and Water Tracks in Continental Antarctica: Water as a geomorphic agent in a hyperarid polar desert

NASA Astrophysics Data System (ADS)

Hauber, E.; Sassenroth, C.; De Vera, J.-P.; Schmitz, N.; Reiss, D.; Hiesinger, H.; Johnsson, A.

2017-09-01

Most studies using Antarctica as a Mars analogue have focused on the McMurdo Dry Valleys, which are among the coldest and driest places on Earth. However, other ice-free areas in continental Antarctica also display landforms that can inform the study of the possible geomorphic impact of water in a polar desert. Here we present a new analogue site in the interior of the Transantarctic Mountains in Northern Victoria Land. Gullies show unambiguous evidence for debris flows, and water tracks act as shallow subsurface pathways of water on top of the permafrost tale. Both processes are driven by meltwater from glacier ice and snow in an environ-ment which never experiences rainfall and in which the air temperatures probably never exceed 0°C.

Risk assessment of debris flow in Yushu seismic area in China: a perspective for the reconstruction

NASA Astrophysics Data System (ADS)

Lan, H. X.; Li, L. P.; Zhang, Y. S.; Gao, X.; Liu, H. J.

2013-11-01

The 14 April 2010 Ms = 7.1 Yushu Earthquake (YE) had caused severe damage in the Jiegu township, the residential centre of Yushu Tibetan Autonomous Prefecture, Qinghai Province, China. In view of the fragile geological conditions after YE, risk assessment of secondary geohazards becomes an important concern for the reconstruction. A quantitative methodology was developed to assess the risk of debris flow by taking into account important intensity information. Debris flow scenarios were simulated with respect to rainfall events with 10, 50 and 100 yr returning period, respectively. The possible economic loss and fatalities caused by damage to buildings were assessed both in the settlement area and in the low hazard settlement area regarding the simulated debris flow events. Three modelled building types were adopted, i.e. hollow brick wood (HBW), hollow brick concrete (HBC) and reinforced concrete (RC) buildings. The results suggest that HBC structure achieves a good balance for the cost-benefit relationship compared with HBW and RC structures and thus could be an optimal choice for most of the new residential buildings in the Jiegu township. The low hazard boundary presents significant risk reduction efficiency in the 100 yr returning debris flow event. In addition, the societal risk for the settlement area is unacceptable when the 100 yr returning event occurs but reduces to ALARP (as low as reasonably practicable) level as the low hazard area is considered. Therefore, the low hazard area was highly recommended to be taken into account in the reconstruction. Yet, the societal risk might indeed approach an unacceptable level if one considers that YE has inevitably increased the occurrence frequency of debris flow. The quantitative results should be treated as a perspective for the reconstruction rather than precise numbers of future losses, owing to the complexity of the problem and the deficiency of data.

Hazard assessment of landslide and debris flow in the Rjeina river valley, Croatia

NASA Astrophysics Data System (ADS)

Wang, Chunxiang; Watanabe, Naoki; Marui, Hideaki

2013-04-01

The Rječina River extends approximately 18.7km long and flows into the Adriatic Sea at the center of Rijeka City, Croatia. Landslide, debris flow and rockfall are main geohazards in the middle part of the Rječina river basin. The zone between the Valići reservoir dam and the Pasac Bridge is particularly the most unstable and hazardous area in the river basin. The Grohovo landslide in the middle part of the river basin is located on the valley's slope facing southwest and situated at just downstream of the Valići dam. This landslide is the largest active landslide along the Adriatic Sea coast in Croatia. Assuming that serious heavy rainfall or earthquake occurs, it is most likely to occur two types of geohazard event. One scenario is that the debris deposited on the Grohovo landslide will move down to the channel of the Rječina River and dam up the river course. Another scenario is that the slope deposits on the landslide will be mixed with water and subsequently turn into a debris flow reaching to Rijeka City. We simulate both two cases of the formation of landslide-dam and the occurrence of debris-flow by two integrated models using GIS to represent the dynamic process across 3D terrains. In the case of the formation of landslide-dam, it is assumed that slope deposits will move downhill after failing along a shear zone. GIS-based revised Hovland's 3D limit equilibrium model is used to simulate the movement and stoppage of the slope deposits to form landslide-dam. The 3D factor of safety will be calculated step by step during the sliding process simulation. Stoppage is defined by the factor of safety much greater than one and the velocity equal to zero. The simulation result shows that the height of the landslide-dam will be nine meters. In case of debris flow, the mixture of slope deposits and water will be differentiated from landslide by fluid-like deformation of the mobilized material. GIS-based depth-averaged 2D numerical model is used to predict the runout distance and inundated area of the debris flow. The simulation result displays the propagation and deposition of the debris flow across the complex topography and shows that the debris flow takes about 16 minutes to travel about 6 km along the Rječina River and consequently reaches to Rijeka City.

The comparison between two airborne LiDAR datasets to analyse debris flow initiation in north-western Iceland

NASA Astrophysics Data System (ADS)

Morino, Costanza; Conway, Susan J.; Balme, Matthew R.; Jordan, Colm; Hillier, John; Sæmundsson, Þorsteinn; Argles, Tom

2015-04-01

A debris flow is a very rapid to extremely rapid flow (e.g., 0.8-28 ms-1) [1], that occurs when coarse and poorly-sorted debris, mixed with water and/or air, move down hill slopes in response to gravity [2]. Both the fluid and the solid have a strong influence on the movement of debris flows. They can be extremely destructive, due to their capability of transporting metre-size boulders [e.g., 3, 4]. There are two main ways in which a debris flow can be initiated: by slope failure or by the "fire hose" effect. The slope failure type is particularly common in alpine regions, where landslides can evolve into debris flows [5], triggered by the coalescence of different slope failures. Steep slope gradients, high pore-water pressures, heavy rainfall and/or snowmelt favour this process. The "fire hose" effect occurs when there is a high concentration of debris accumulated within a pre-existing channel; a surge of water through the channel can then develop into a debris flow by incorporating this debris [e.g. 5-7]. In this study, we examine the triggering style of debris flows above the town of Ísafjörður in the Westfjords of Iceland. The slope above the town is characterised by a large topographic bench upon which 20-35 m of glacial till is perched. The sediments are unstable at the bench margin and thus generate frequent, large, hillslope debris flows [8, 9]. In our new analysis, we report on the comparison between the two airborne LiDAR elevation models (collected in 2007 and 2013 by the UK Natural Environment Research Council Airborne Research and Survey Facility), which display several new debris flows and also related mass movements. From these analyses, we find that debris flows in the region are triggered by simple failure of the glacial till, as recognised before [8, 9]. However, debris flows may also be regenerated by the "fire hose" effect, when debris that has collapsed into chutes is remobilised by a later snowmelt or precipitation event. Comparing different airborne LiDAR datasets has proven to be a powerful tool, not just in the topographic analysis of landscape, but also in the discrimination of the causes of potentially disastrous phenomena. This suggests new possibilities for using remote sensing analysis to mitigate the effects of natural hazards. References: [1] Rickenmann, D., 1999. Natural Hazards, 19 (1), 47-77. [2] Iverson, R.M., 1997. Reviews of Geophysics, 35 (3), 245-296. [3] Clague, J.J., Evans, S.G., Blown, I.G., 1985. Journal of Earth Sciences, 22 (10), 1492-1502. [4] Kanji, M.A., Cruz, P.T., Massad, F., 2008. Landslides, 5 (1), 71-82. [5] Johnson, A.M. and Rodine, J. R. 1984. Slope Instability. Wiley, New York, 257-361. [6] Coe, J.A., Glancy, P.A., Whitney, J.W., 1997. Geomorphology, 20, 11-28. [7] Griffiths, P.G., Webb, R.H., Melis, T.S., 2004. Journal of Geophysical Research, 109, 321-336. [8] Conway, S. J., Decaulne, A., Balme, M. R., Murray, J. B., Towner, M. C., 2010. Geomorphology, 114 (4), 556-572. [9] Decaulne, A., Sæmundsson, Þ., Pétursson, O., 2005. Geografiska Annaler: Series A, Physical Geography, 87A, 487-500.

Multivariate Statistical Models for Predicting Sediment Yields from Southern California Watersheds

USGS Publications Warehouse

Gartner, Joseph E.; Cannon, Susan H.; Helsel, Dennis R.; Bandurraga, Mark

2009-01-01

Debris-retention basins in Southern California are frequently used to protect communities and infrastructure from the hazards of flooding and debris flow. Empirical models that predict sediment yields are used to determine the size of the basins. Such models have been developed using analyses of records of the amount of material removed from debris retention basins, associated rainfall amounts, measures of watershed characteristics, and wildfire extent and history. In this study we used multiple linear regression methods to develop two updated empirical models to predict sediment yields for watersheds located in Southern California. The models are based on both new and existing measures of volume of sediment removed from debris retention basins, measures of watershed morphology, and characterization of burn severity distributions for watersheds located in Ventura, Los Angeles, and San Bernardino Counties. The first model presented reflects conditions in watersheds located throughout the Transverse Ranges of Southern California and is based on volumes of sediment measured following single storm events with known rainfall conditions. The second model presented is specific to conditions in Ventura County watersheds and was developed using volumes of sediment measured following multiple storm events. To relate sediment volumes to triggering storm rainfall, a rainfall threshold was developed to identify storms likely to have caused sediment deposition. A measured volume of sediment deposited by numerous storms was parsed among the threshold-exceeding storms based on relative storm rainfall totals. The predictive strength of the two models developed here, and of previously-published models, was evaluated using a test dataset consisting of 65 volumes of sediment yields measured in Southern California. The evaluation indicated that the model developed using information from single storm events in the Transverse Ranges best predicted sediment yields for watersheds in San Bernardino, Los Angeles, and Ventura Counties. This model predicts sediment yield as a function of the peak 1-hour rainfall, the watershed area burned by the most recent fire (at all severities), the time since the most recent fire, watershed area, average gradient, and relief ratio. The model that reflects conditions specific to Ventura County watersheds consistently under-predicted sediment yields and is not recommended for application. Some previously-published models performed reasonably well, while others either under-predicted sediment yields or had a larger range of errors in the predicted sediment yields.

Landslides in the northern Colorado Front Range caused by rainfall, September 11-13, 2013

USGS Publications Warehouse

Godt, Jonathan W.; Coe, Jeffrey A.; Kean, Jason W.; Baum, Rex L.; Jones, Eric S.; Harp, Edwin L.; Staley, Dennis M.; Barnhart, William D.

2014-01-01

During the second week of September 2013, nearly continuous rainfall caused widespread landslides and flooding in the northern Colorado Front Range. The combination of landslides and flooding was responsible for eight fatalities and caused extensive damage to buildings, highways, and infrastructure. Three fatalities were attributed to a fast moving type of landslide called debris flow. One fatality occurred in Jamestown, and two occurred in the community of Pinebrook Hills immediately west of the City of Boulder. All major canyon roads in the northern Front Range were periodically closed between September 11 and 13, 2013. Some canyon closures were caused by undercutting of roads by landslides and flooding, and some were caused by debris flows and rock slides that deposited material on road surfaces. Most of the canyon roads, with the exceptions of U.S. Highway 6 (Clear Creek Canyon), State Highway 46/Jefferson Co. Rd. 70 (Golden Gate Canyon), and Sunshine Canyon in Boulder County, remained closed at the end of September 2013. A review of historical records in Colorado indicates that this type of event, with widespread landslides and flooding occurring over a very large region, in such a short period of time, is rare.

A model for assessing water quality risk in catchments prone to wildfire

NASA Astrophysics Data System (ADS)

Langhans, Christoph; Smith, Hugh; Chong, Derek; Nyman, Petter; Lane, Patrick; Sheridan, Gary

2017-04-01

Post-fire debris flows can have erosion rates up to three orders of magnitude higher than background rates. They are major sources of fine suspended sediment, which is critical to the safety of water supply from forested catchments. Fire can cover parts or all of these large catchments and burn severity is often heterogeneous. The probability of spatial and temporal overlap of fire disturbance and rainfall events, and the susceptibility of hillslopes to severe erosion determine the risk to water quality. Here we present a model to calculate recurrence intervals of high magnitude sediment delivery from runoff-generated debris flows to a reservoir in a large catchment (>100 km2) accounting for heterogeneous burn conditions. Debris flow initiation was modelled with indicators of surface runoff and soil surface erodibility. Debris flow volume was calculated with an empirical model, and fine sediment delivery was calculated using simple, expert-based assumptions. In a Monte-Carlo simulation, wildfire was modelled with a fire spread model using historic data on weather and ignition probabilities for a forested catchment in central Victoria, Australia. Multiple high intensity storms covering the study catchment were simulated using Intensity-Frequency-Duration relationships, and the runoff indicator calculated with a runoff model for hillslopes. A sensitivity analysis showed that fine sediment is most sensitive to variables related to the texture of the source material, debris flow volume estimation, and the proportion of fine sediment transported to the reservoir. As a measure of indirect validation, denudation rates of 4.6 - 28.5 mm ka-1 were estimated and compared well to other studies in the region. From the results it was extrapolated that in the absence of fire management intervention the critical sediment concentrations in the studied reservoir could be exceeded in intervals of 18 - 124 years.

Postwildfire preliminary debris flow hazard assessment for the area burned by the 2011 Las Conchas Fire in north-central New Mexico

USGS Publications Warehouse

Tillery, Anne C.; Darr, Michael J.; Cannon, Susan H.; Michael, John A.

2011-01-01

The Las Conchas Fire during the summer of 2011 was the largest in recorded history for the state of New Mexico, burning 634 square kilometers in the Jemez Mountains of north-central New Mexico. The burned landscape is now at risk of damage from postwildfire erosion, such as that caused by debris flows and flash floods. This report presents a preliminary hazard assessment of the debris-flow potential from 321 basins burned by the Las Conchas Fire. A pair of empirical hazard-assessment models developed using data from recently burned basins throughout the intermountain western United States was used to estimate the probability of debris-flow occurrence and volume of debris flows at the outlets of selected drainage basins within the burned area. The models incorporate measures of burn severity, topography, soils, and storm rainfall to estimate the probability and volume of debris flows following the fire. In response to a design storm of 28.0 millimeters of rain in 30 minutes (10-year recurrence interval), the probabilities of debris flows estimated for basins burned by the Las Conchas Fire were greater than 80 percent for two-thirds (67 percent) of the modeled basins. Basins with a high (greater than 80 percent) probability of debris-flow occurrence were concentrated in tributaries to Santa Clara and Rio del Oso Canyons in the northeastern part of the burned area; some steep areas in the Valles Caldera National Preserve, Los Alamos, and Guaje Canyons in the east-central part of the burned area; tributaries to Peralta, Colle, Bland, and Cochiti canyons in the southwestern part of the burned area; and tributaries to Frijoles, Alamo, and Capulin Canyons in the southeastern part of the burned area (within Bandelier National Monument). Estimated debris-flow volumes ranged from 400 cubic meters to greater than 72,000 cubic meters. The largest volumes (greater than 40,000 cubic meters) were estimated for basins in Santa Clara, Los Alamos, and Water Canyons, and for two basins at the northeast edge of the burned area tributary to Rio del Oso and Vallecitos Creek. The Combined Relative Debris-Flow Hazard Rankings identify the areas of highest probability of the largest debris flows. Basins with high Combined Relative Debris-Flow Hazard Rankings include upper Santa Clara Canyon in the northern section of the burn scar, and portions of Peralta, Colle, Bland, Cochiti, Capulin, Alamo, and Frijoles Canyons in the southern section of the burn scar. Three basins with high Combined Relative Debris-Flow Hazard Rankings also occur in areas upstream from the city of Los Alamos—the city is home to and surrounded by numerous technical sites for the Los Alamos National Laboratory. Potential debris flows in the burned area could affect the water supply for Santa Clara Pueblo and several recreational lakes, as well as recreational and archeological resources in Bandelier National Monument. Debris flows could damage bridges and culverts along State Highway 501 and other roadways. Additional assessment is necessary to determine if the estimated volume of material is sufficient to travel into areas downstream from the modeled basins along the valley floors, where they could affect human life, property, agriculture, and infrastructure in those areas. Additionally, further investigation is needed to assess the potential for debris flows to affect structures at or downstream from basin outlets and to increase the threat of flooding downstream by damaging or blocking flood mitigation structures. The maps presented here may be used to prioritize areas where erosion mitigation or other protective measures may be necessary within a 2- to 3-year window of vulnerability following the Las Conchas Fire.

Record of Plio-Pleistocene extreme event in the Lesser Antilles fore-arc basin. Example of Grande-Terre (Guadeloupe, French West Indies).

NASA Astrophysics Data System (ADS)

Jeanlèn, L.; Philippon, M. M.; Randrianasolo, A.; Jean-Frederic, L.; Cornée, J. J.; Münch, P.

2015-12-01

Guadeloupe archipelago is part of the Lesser Antilles active volcanic arc and is therefore subjected to both enhanced seismic and volcanic activity related to the Lesser Antilles subduction zone, along which the Atlantic plate is subducted westward bellow the Caribbean plate. The volcanic arc is composed of several immerged volcanic islands (St Kitts, Nevis Montserrat, Basse Terre, Dominica, Martinique, St Lucia, Grenada) and submerged volcanoes (Kick em'Jenny). These volcanoes are known to be explosives and when they are entering in an eruptive cycle, debris flow could potentially initiate a tsunami and generate peculiar deposits within the sedimentary record recognized as tsunami deposits (or tsunamite). Subduction- related earthquakes might also initiate slope instabilities and trigger debris flow. Another controlling factor of slope (in-)-stabilities and debris flow is massive rainfalls. During cyclonic season (June to December), massive rainfalls are recorded in the area, which moreover is located on the trajectory of Atlantic Hurricanes that are responsible for numerous landslides. As a consequence, tsunami deposit are described and well studied in the Lesser Antilles arc as the islands shoreline and coastal plain are perpetually re-shaped by hurricanes responsible for tempestite deposits. However, the report of these deposit concern recent to actual events, for example present-day deposits consisting of large (metric) boulders, more or less aligned, located in the supralittoral fringe can be observed along Guadeloupe shore. In this study, we investigate the Plio-pleistocene sedimentary sequence of Grande Terre carbonate platform (Guadeloupe), and track the presence of such extreme-event related deposits and discuss our findings in the frame of the Lesser Antilles geological context.

Nonstationary Intensity-Duration-Frequency Curves for Drainge Infrastructure Coping with Climate Change

NASA Astrophysics Data System (ADS)

Kim, Byung Sik; Jeung, Se Jin; Lee, Dong Seop; Han, Woo Suk

2015-04-01

As the abnormal rainfall condition has been more and more frequently happen and serious by climate change and variabilities, the question whether the design of drainage system could be prepared with abnormal rainfall condition or not has been on the rise. Usually, the drainage system has been designed by rainfall I-D-F (Intensity-Duration-Frequency) curve with assumption that I-D-F curve is stationary. The design approach of the drainage system has limitation not to consider the extreme rainfall condition of which I-D-F curve is non-stationary by climate change and variabilities. Therefore, the assumption that the I-D-F curve is stationary to design drainage system maybe not available in the climate change period, because climate change has changed the characteristics of extremes rainfall event to be non-stationary. In this paper, design rainfall by rainfall duration and non-stationary I-D-F curve are derived by the conditional GEV distribution considering non-stationary of rainfall characteristics. Furthermore, the effect of designed peak flow with increase of rainfall intensity was analyzed by distributed rainfall-runoff model, S-RAT(Spatial Runoff Assessment Tool). Although there are some difference by rainfall duration, the traditional I-D-F curves underestimates the extreme rainfall events for high-frequency rainfall condition. As a result, this paper suggest that traditional I-D-F curves could not be suitable for the design of drainage system under climate change condition. Keywords : Drainage system, Climate Change, non-stationary, I-D-F curves This research was supported by a grant 'Development of multi-function debris flow control technique considering extreme rainfall event' [NEMA-Natural-2014-74] from the Natural Hazard Mitigation Research Group, National Emergency Management Agency of KOREA

Effective mitigation of debris flows at Lemon Dam, La Plata County, Colorado

USGS Publications Warehouse

deWolfe, V.G.; Santi, P.M.; Ey, J.; Gartner, J.E.

2008-01-01

To reduce the hazards from debris flows in drainage basins burned by wildfire, erosion control measures such as construction of check dams, installation of log erosion barriers (LEBs), and spreading of straw mulch and seed are common practice. After the 2002 Missionary Ridge Fire in southwest Colorado, these measures were implemented at Knight Canyon above Lemon Dam to protect the intake structures of the dam from being filled with sediment. Hillslope erosion protection measures included LEBs at concentrations of 220-620/ha (200-600% of typical densities), straw mulch was hand spread at concentrations up to 5.6??metric tons/hectare (125% of typical densities), and seeds were hand spread at 67-84??kg/ha (150% of typical values). The mulch was carefully crimped into the soil to keep it in place. In addition, 13 check dams and 3 debris racks were installed in the main drainage channel of the basin. The technical literature shows that each mitigation method working alone, or improperly constructed or applied, was inconsistent in its ability to reduce erosion and sedimentation. At Lemon Dam, however, these methods were effective in virtually eliminating sedimentation into the reservoir, which can be attributed to a number of factors: the density of application of each mitigation method, the enhancement of methods working in concert, the quality of installation, and rehabilitation of mitigation features to extend their useful life. The check dams effectively trapped the sediment mobilized during rainstorms, and only a few cubic meters of debris traveled downchannel, where it was intercepted by debris racks. Using a debris volume-prediction model developed for use in burned basins in the Western U.S., recorded rainfall events following the Missionary Ridge Fire should have produced a debris flow of approximately 10,000??m3 at Knight Canyon. The mitigation measures, therefore, reduced the debris volume by several orders of magnitude. For comparison, rainstorm-induced debris flows occurred in two adjacent canyons at volumes within the range predicted by the model. ?? 2007 Elsevier B.V. All rights reserved.

Occurrence of Landslides during the Approach of Tropical Cyclone Juliette (2001) to Baja California Sur, Mexico

NASA Astrophysics Data System (ADS)

Antinao, J.; Farfan, L.

2012-12-01

The approach of Tropical Cyclone Juliette to the Baja California Peninsula in September 2001 triggered at least 419 landslides. Most of the landslides were shallow slips and debris slides, of limited areal extent, which were converted rapidly into debris flows to be exported quickly out of the mountain areas towards the lowlands. Main factors affecting landslide occurrence were total storm rainfall and intensity, aspect, geology and vegetation association. Two processes can be distinguished as initiating slope failure. The first process is linked to failures in concave topography, where accumulation of rainfall from exposed bedrock slopes generated excess overland flow that aggregated to generate a 'fire hose' effect on the base of slopes, mobilizing regolith. A second process involved a combination of wind and excess overland flow developed in the more convex or planar upper slopes, where heterogeneous regolith has formed in time following successional changes in vegetation associations along the oak-dry tropical forest ecotone. In this area, wind uprooted trees that dislodged large regolith and bedrock blocks, priming hillslopes for further runoff concentration. From the analysis of historical information, an estimative threshold curve for triggering landslides in this region is sketched. It was also determined that storms like Juliette approach the southern peninsula on average once every 100 years. Denudation estimates are in the higher end of the spectrum for a tectonically passive margin. These estimates should be considered when taking decisions regarding management of water resources in this area through damming of streams. The results emphasize the need for a more detailed representation of the spatial distribution of the rainfall and winds for this mountainous region frequently affected by the passage of tropical cyclones.

Field and laboratory analysis of hillslope debris flows in Switzerland

NASA Astrophysics Data System (ADS)

Hürlimann, Marcel; McArdell, Brian W.; Rickli, Christian

2014-05-01

Hillslope or open-slope debris flows are unconfined flows that originate by shallow failures in colluvium or other unconsolidated material. The most common triggering factor is rainfall, sometimes combined with snowmelt. Hillslope debris flows can reach high velocity and runout distances up to several hundreds of meters. Although these facts confirm the important hazard of hillslope debris flows, little research has been performed on this type of mass movement. Thus, the present study intends to improve the knowledge on the characteristics of the initial failure as well as on the runout mechanisms. Two major tasks were carried out to achieve this major goal. First, detailed inventories of hill-slope debris flows in Switzerland during the last two decades were analysed. The datasets include field observations and measurements on morphometrics, hydrology and geology of more than 500 events. Second, laboratory tests were carried out to study the effect of the water content, the clay amount and the volume on the post-failure behaviour of the flow. The investigation of the inventories show that hill-slope debris flows mostly starts as translational slides of up to 400 - 500 m3 at a terrain slope angle between 25 to 45º. The initial failure has normally a mean thickness from 0.2 to 1.5m, a width between a few meters and 30 m and a length of 5 to 50 m. The maximum runout distance of the event is mostly less than 200 m, but there are also some events with distances of up to 500 m. These data were used to dimension the experimental set-up, with a scale factor of 20 and represented by a 7.5m long and 30º inclined laboratory slope. Flow velocity and flow depth were measured using point lasers installed at different positions along the slope and a high-speed camera, while the final deposit was documented using laser scanning techniques. First results with mixtures of 4 and 10 dm3, using clay amounts between 5 and 20% and water contents ranging from 22 to 32% show that even small changes of the clay amount and the water content strongly alters the behaviour of the flow and directly influence the maximum runout. The relationship between total runout distance and water content is best fit by a power law, which is consistent with previous studies. The results of this on-going study improve the understanding of the initiation and kinematics of hill-slope debris flows and provides useful inputs for a correct hazard assessment of this type of mass movements.

The RHYTMME system: an operational real-time warning and mapping system for flash floods, debris flows, landslide and rock falls in Southeastern France.

NASA Astrophysics Data System (ADS)

Fouchier, Catherine; Mériaux, Patrice; Atger, Frédéric; Ecrepont, Stéphane; Liébault, Frédéric; Bertrand, Mélanie; Bel, Coraline; Batista, Dominique; Azemard, Pierre; Saint-Martin, Clotilde; Javelle, Pierre

2016-04-01

Almost all municipalities of Southeastern France are concerned by natural hazards triggered by heavy rainfalls such as floods, debris flows, landslides and rock falls. Although some tools exist to forecast and monitor heavy rains and floods in France, their spatial resolution sometimes does not meet the needs of local risk managers who have to monitor events at a small spatial scale. In order to improve the risk management in the mountainous and Mediterranean areas of Southeastern France, Irstea and Météo-France have led the RHYTMME project. The goal of this project is to improve the ability to forecast and localize high-risk rainfall-induced hazards in the Provence-Alpes-Côte d'Azur administrative area. This goal is currently under achievement thanks to the implementation of a real-time warning and mapping system for rainfall induced natural hazards, fed by radar data and whose outputs are made available via the Internet to operators in charge of risk management (local and regional authorities, emergency and rescue services, road and rail networks managers, ...). This system provides maps which display in real-time: - the radar estimations of rainfall for different rain durations and at the spatial resolution of 1 km² (Westrelin et al., 2013), - the estimation of the scarcity of these rainfall estimations, also at the spatial resolution of 1 km², thanks to a comparison with threshold values provided by a regionalized stochastic hourly point rainfall generator (Arnaud et al., 2007), - an anticipation of the rivers discharges, computed at the outlet of 1700 watersheds of Southeastern France thanks to the AIGA warning system which combines a rainfall runoff model and an estimation of the scarcity of the discharges thanks to a comparison with threshold values (Javelle et al., 2014). Maps of susceptibility to debris flow, landslide and rock falls can also be displayed in the RHYTMME warning system along with the real time maps of rainfall hazard (Batista, 2013a, 2013b; Bertrand, 2014). It enables to identify, during intense events, the reaches the more likely to generate and/or to spread debris flow and the areas the more likely to generate landslide and/or rock falls. The RHYTMME warning and mapping system is now fully operational. It is currently being provided to local authorities (City councils, River boards, …) as well as State authorities in charge of risk managements in the Provence-Alpes-Côte d'Azur administrative area. Training sessions are organized in order to help these end-users to handle the system. References Arnaud P., Fine J.-A. and Lavabre J. (2007). An hourly rainfall generation model applicable to all types of climate. Atmospheric Research 85(2): 230-242. Batista D., Azémard P., Boutry M. (2013). Prévision de l'aléa glissement de terrain et analyse statistique des facteurs de prédisposition par l'outil SIG, sur la région Provence-Alpes-Côte d'Azur. Journées Aléas Gravitaires, 17 et 18/9/2013 - Grenoble, 11 p. Batista D., Azémard P., Rougé A.C., Dumalin M., Rault C. (2013). Prévision de l'aléa chute de blocs, analyse statistique des facteurs de prédisposition et des critères de déclenchement sur la région Provence-Alpes-Côte d'Azur. Journées Aléas Gravitaires, 17 et 18/9/2013 - Grenoble, 11 p. Bertrand M. (2014). Approches régionales de la susceptibilité torrentielle dans les Alpes du Sud. Thèse de Doctorat, École Normale Supérieure de Lyon, 162 pp. Javelle P., Demargne J., Defrance D., Pansu J., Arnaud P. (2014). Evaluating flash-flood warnings at ungauged locations using post-event surveys: A case study with the AIGA warning system. Hydrological Sciences Journal 59 (7): 1390-1402. Westrelin S., Mériaux P., Dalle S., Fradon B., Jamet G. (2013). Déploiement d'un réseau de radars pour anticiper les risques hydro-météorologiques, La Météorologie 8 (83): 69-79.

Floods, landslides and erosion from severe meteorological events in the Benevento Province, southern Italy.

NASA Astrophysics Data System (ADS)

Mascellaro, Neri; Guerriero, Luigi; Revellino, Paola; Grelle, Gerardo; Guadagno, Francesco M.

2017-04-01

As effect of the ongoing climate change, heavy meteorological events are increasing in frequency all over the world. The Campania Region in southern Italy is among the areas mostly affected by severe rainstorms and is periodically hit by their effect like floods and landslides. In October 2015, two intense rainfall events hit the central and southern regions of Italy but the most destructive effects occurred in the Benevento province (Campania region). The first storm, a self-healing V-shaped storm, began around at 7 p.m. of 14th October and stopped around at 3:00 a.m. of 15th October and was originated by the development of a cyclogenesis. The rain gages recorded a maximum cumulative value of 415.6 mm of rain in Paupisi (BN) and a strong increase in temperature; the maxima for the Benevento province was 24°C. The second storm began around at 12 a.m. of 19th October and stopped around at 7 p.m. of 20th October with a maximum cumulative value of 146.8 mm of rain in Colle Sannita(BN). These storms triggered a set of different effects that devastated more than 60 municipalities of the Sannio Province and were responsible for two casualties, €700 million of damage to infrastructures (estimates from Campania region) and about €1 billion damages to agriculture (Italian farmer Confederation). The the Calore river of the Benevento province and some of its tributaries overflowed destroying the surrounding area; major damages were recorded in the industrial area of the Benevento town. In the central and in the eastern sectors of the Benevento Province characterized by the outcropping of flyschoid units, the heavy rain triggered shallow earth flows, debris flows induced by rilling and soil slides. Debris avalanches and runoff-initiated debris flows reshaped the creeks of the Taburno-Camposauro massif and damaged a lot of infrastructure of the surrounding area. Flood events from the Calore river in the Benevento district have significant historical precedents. The most important events recorded in the past are: 1) the flood of the 2nd of October, 1949, that caused 20 fatalities, and 2) the flooding of May 1729. As first step of our study we reconstructed the spatial pattern and the temporal evolution of the storms affecting the Sannio area using the rainfall data recorded by the meteorological stations distributed across the Benevento Province. Subsequently we mapped all the effects to the landscape caused by the storms as: earth flows, soil slides, flooded area, runoff initiated debris flows and debris avalanches, debris flows initiated by rilling and soil erosion (using mainly Google earth images and field survey). We compered the location of these phenomena with the geological and topographic characteristics to understand likely controls in promote the triggering and the development of this unusual combination of different hazardous effects.

Estimation of Vulnerability Functions for Debris Flows Using Different Intensity Parameters

NASA Astrophysics Data System (ADS)

Akbas, S. O.; Blahut, J.; Luna, B. Q.; Sterlacchini, S.

2009-04-01

In landslide risk research, the majority of past studies have focused on hazard analysis, with only few targeting the concept of vulnerability. When debris flows are considered, there is no consensus or even modest agreement on a generalized methodology to estimate physical vulnerability of the affected buildings. Very few quantitative relationships have been proposed between intensities and vulnerability values. More importantly, in most of the existing relationships, information on process intensity is often missing or only described semi-quantitatively. However, robust assessment of vulnerabilities along with the associated uncertainties is of utmost importance from a quantitative risk analysis point of view. On the morning of 13th July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of Valtellina, an Italian alpine valley in Lombardy Region. One of the largest muddy-debris flows occurred in Selvetta, a fraction of Colorina municipality. The result was the complete destruction of two buildings, and damage at varying severity levels to eight others. The authors had the chance to gather detailed information about the event, by conducting extensive field work and interviews with local inhabitants, civil protection teams, and officials. In addition to the data gathered from the field studies, the main characteristics of the debris flow have been estimated using numerical and empirical approaches. The extensive data obtained from Selvetta event gave an opportunity to develop three separate empirical vulnerability curves, which are functions of deposition height, debris flow velocity, and pressure, respectively. Deposition heights were directly obtained from field surveys, whereas the velocity and pressure values were back-calculated using the finite difference program FLO2D. The vulnerability was defined as the ratio between the monetary loss and the reconstruction value. The monetary losses were obtained from official RASDA documents, which were compiled for claim purposes. For each building, the approximate reconstruction value was calculated according to the building type and size, using the official data given in the Housing Prices Index prepared by the Engineers and Architects of Milan. The resulting vulnerability curves were compared to those in the literature, and among themselves. Specific recommendations were given regarding the most suitable parameter to be used for characterizing the intensity of debris flows within the context of physical vulnerability.

A combined morphometric, sedimentary, GIS and modelling analysis of flooding and debris flow hazard on a composite alluvial fan, Caveside, Tasmania

NASA Astrophysics Data System (ADS)

Kain, Claire L.; Rigby, Edward H.; Mazengarb, Colin

2018-02-01

Two episodes of intense flooding and sediment movement occurred in the Westmorland Stream alluvial system near Caveside, Australia in January 2011 and June 2016. The events were investigated in order to better understand the drivers and functioning of this composite alluvial system on a larger scale, so as to provide awareness of the potential hazard from future flood and debris flow events. A novel combination of methods was employed, including field surveys, catchment morphometry, GIS mapping from LiDAR and aerial imagery, and hydraulic modelling using RiverFlow-2D software. Both events were initiated by extreme rainfall events (< 1% Annual Exceedance Probability for durations exceeding 6 h) and resulted in flooding and sediment deposition across the alluvial fan. The impacts of the 2011 and 2016 events on the farmland appeared similar; however, there were differences in sediment source and transport processes that have implications for understanding recurrence probabilities. A debris flow was a key driver in the 2011 event, by eroding the stream channel in the forested watershed and delivering a large volume of sediment downstream to the alluvial fan. In contrast, modelled flooding velocities suggest the impacts of the 2016 event were the result of an extended period of extreme stream flooding and consequent erosion of alluvium directly above the current fan apex. The morphometry of the catchment is better aligned with values from fluvially dominated fans found elsewhere, which suggests that flooding represents a more frequent future risk than debris flows. These findings have wider implications for the estimation of debris flow and flood hazard on alluvial fans in Tasmania and elsewhere, as well as further demonstrating the capacity of combined hydraulic modelling and geomorphologic investigation as a predictive tool to inform hazard management practices in environments affected by flooding and sediment movement.

Numerical ages of Holocene tributary debris fans inferred from dissolution pitting on carbonate boulders in the Grand Canyon of Arizona

USGS Publications Warehouse

Hereford, R.; Thompson, K.S.; Burke, K.J.

1998-01-01

Carbonate boulders transported down steep tributary channels by debris flow came to rest on Holocene debris fans beside the Colorado River in Grand Canyon National Park. Weakly acidic rainfall and the metabolic activity of blue-green algae have produced roughly hemispheric dissolution pits as much as 2-cm deep on the initially smooth surfaces of the boulders. The average depth of dissolution pits increases with relative age of fan surfaces. The deepening rate averages 2.4 mm/1000 yr (standard error = 0.2 mm/1000 yr), as calculated from several radiometrically dated surfaces and an archeological structure. This linear rate, which appears constant over at least the past 3000 yr, is consistent with field relations limiting the maximum age of the fans and with the physical chemistry of limestone dissolution. Dissolution-pit measurements (n = 6973) were made on 617 boulders on 71 fan surfaces at the 26 largest debris fans in Grand Canyon. Among these fan surfaces, the average pit depth ranges from 1.2 to 17.4 mm, and the resulting pit dissolution ages range from 500 to 7300 cal yr B.P. Most (75%) surfaces are younger than 3000 yr, probably because of removal of older debris fans by the Colorado River. Many of the ages are close to 800, 1600, 2300, 3100, or 4300 cal yr B.P. If not the result of differential preservation of fan surfaces, this clustering implies periods of heightened debris-flow activity and increased precipitation.

Analysis with SfM on-motion method of July 2015 extreme rainfall impacts on the S-charl valley road in the Canton of Graubünden, Switzerland

NASA Astrophysics Data System (ADS)

Voumard, Jérémie; Jaboyedoff, Michel

2016-04-01

The 22-23th July 2015, two severe storms at one day interval have caused in Scuol, lower Engadine (Canton of Graubünden, Switzerland). The static storm cells produced up to 150 mm rain precipitations in three hours generating several debris flow. On 22 July 2015, three buildings in the Pradella hamlet near Scuol were damaged by a debris flow. People of two holiday camps, 100 children and 40 adults, were evacuated. Nobody was injured but the buildings damages are important. A day after, about 200 mm rain in a short time were measured in the same area. A car was been swept away by a debris flow in the Scuol village and its driver could escape at the last moment. The S-charl valley was isolated during more than one week by seven big debris flows and several little ones. About 100 people, in majority holidaymakers, were blocked in the S-charl hamlet without power supply during few days. Until the swiss army built a provisional emergency bridge to open the valley access, the only way to access the S-charl valley was by helicopter. Overall damages -roads infrastructures, buildings, drinking water supply, power supply and other- are estimated to one million Swiss Francs and the debris flow volume is estimated to 100'00 cubic meters. The S-charl valley roadsides were photographed fifteen days before the extreme storm event from an on-motion vehicle. The same roadsides were photographed twenty days after the event with the same acquisition methodology. 3D point clouds from Structure of Motion (SfM) from the -before and after event- pictures have been produced and compared. Thus, is was possible to evaluate the number of debris flows that occurred in the S-charl valley and estimate their volume in the roadsides. This study case allows to evaluate the low-cost SfM on-motion methodology and to give theirs main advantages and disadvantages when it is used to estimate changes roadsides due to a natural hazard event.

Sedimentary gravity flows from subaerial fan-deltas in Loreto Bay, Baja California Sur, Mexico

NASA Astrophysics Data System (ADS)

Navarro-Lozano, José O.; Nava-Sánchez, Enrique H.; Godínez-Orta, Lucio

2010-05-01

Fan-deltas from Loreto Bay show recent evidences of sedimentary gravity flows as a result from catastrophic events during hurricane rainfalls. The knowledge of hydrological characteristics of these flows is important for understanding the effects of storms on fan-deltas geomorphology in this region, as well as for the urban developing planning of the city of Loreto in order to avoid hazardous zones. The analysis of precipitation and hurricane tracks data for the period 1945 to 2009 indicates that hurricanes have caused catastrophic floods every 20 years. Stratigraphy from the channel incision shows a sequence of stream flow and debris flow controlled by changes in the competence and capacity of the stream, which are associated to the gentle slope (<2 °) of the fan-deltas. However fans from the north of the bay (Arce and Gúa) show deposits of debris flows associated to catastrophic floods, which have caused the incision channel to drift towards the southern part of the fans, while flows from Las Parras fan-delta, from the middle of the bay, are dominated by stream flows. These differences in the type of the flows are controlled by lithology, shape and size of the drainage basin, and slope of the transit zone in the feeder channel.

Coupled surface and subsurface flow modeling of natural hillslopes in the Aburrá Valley (Medellín, Colombia)

NASA Astrophysics Data System (ADS)

Blessent, Daniela; Barco, Janet; Temgoua, André Guy Tranquille; Echeverrri-Ramirez, Oscar

2017-03-01

Numerical results are presented of surface-subsurface water modeling of a natural hillslope located in the Aburrá Valley, in the city of Medellín (Antioquia, Colombia). The integrated finite-element hydrogeological simulator HydroGeoSphere is used to conduct transient variably saturated simulations. The objective is to analyze pore-water pressure and saturation variation at shallow depths, as well as volumes of water infiltrated in the porous medium. These aspects are important in the region of study, which is highly affected by soil movements, especially during the high-rain seasons that occur twice a year. The modeling exercise considers rainfall events that occurred between October and December 2014 and a hillslope that is currently monitored because of soil instability problems. Simulation results show that rainfall temporal variability, mesh resolution, coupling length, and the conceptual model chosen to represent the heterogeneous soil, have a noticeable influence on results, particularly for high rainfall intensities. Results also indicate that surface-subsurface coupled modeling is required to avoid unrealistic increase in hydraulic heads when high rainfall intensities cause top-down saturation of soil. This work is a first effort towards fostering hydrogeological modeling expertise that may support the development of monitoring systems and early landslide warning in a country where the rainy season is often the cause of hydrogeological tragedies associated with landslides, mud flow or debris flow.

Digital inventory of landslides and related deposits in Honduras triggered by Hurricane Mitch

USGS Publications Warehouse

Harp, Edwin L.; Hagaman, Kirk W.; Held, Matthew D.; McKenna, Jonathan P.

2002-01-01

Intense rainfall from Hurricane Mitch from October 27-31, 1998, exceeded 900 mm in places in Honduras and triggered in excess of 500,000 landslides throughout the country. Landslides damaged an estimated 70% of the road network in Honduras based on estimates by the U. S Army Corps of Engineers. Numbers of fatalities due to landslides are not accurately known due to the fact that numerous small villages throughout Honduras lost residents to landslides without an official count being recorded. A conservative estimate would place the number at near 1,000. Debris flows accounted for over 95% of the landslides and ranged in thickness from 1 to 15 m. Flow path lengths of these failures ranged from several meters to 7.5 km. The highest concentrations of debris flows occurred in the mountains near the town of Choluteca where over 900 mm of rain fell in three days. Although landslides other than debris flows were few, several deep-seated landslides in the city of Tegucigalpa severely impacted people and property. The 'El Berrinche' rotational slump/earth flow of approximately six million cubic meters volume destroyed the entire neighborhood of Colonia Soto near the center of the city. The landslide also dammed the Rio Choluteca and created a lagoon behind the landslide dam, which immediately posed a health problem for the city, because raw, untreated sewage was emptying into the Rio Choluteca. Several areas of highly concentrated landslides have been responsible for much of the flooding problem as well. Huge sediment influxes from landslide source areas near La Ceiba, La Libertad, Marale, and in several arms of El Cajon Reservoir have reduced stream capacities to practically nothing and have exacerbated flooding conditions in even the moderate rainfall seasons since Hurricane Mitch. The ongoing hazard to communities from landslides triggered during Hurricane Mitch are being analyzed using aerial photography taken by the U.S. Air Force and by supplemental photography taken by local contractors. Through the use of digital elevation models derived from 1:50,000-scale topographic maps and geologic maps, landslide susceptibility maps will be derived to aid land-use planning and relocation efforts.

Time-series analysis on bed morphology affected by debris flows along a headwater steep channel in Ohya-kuzure landslide, central Japan

NASA Astrophysics Data System (ADS)

Hayakawa, Y. S.; Imaizumi, F.; Hotta, N.; Tsunetaka, H.

2013-12-01

Deformation of steep terrain has been occurring since the formation of Ohyakuzure landslide in 1707. Although erosion controls in recent decades have resulted in vegetation recovery in downstream portions of the landslide terrain, hillslope erosion and debris flows frequently occur in uppermost steep subwatersheds in the landslide area to yield vast amount of sediment downstream. Ichino-sawa subwatershed in the landslide terrain, where detailed monitoring of debris flows and related topographic changes have previously been performed, has particularly steep slopes, and geomorphic processes therein have been quite active. Freeze-thaw weathering of fractured bedrock on hillslopes made of shale and sandstone frequently occurs in winter to spring season, and resultant sediment particles are provided into channel beds, which act as a source of debris flows that frequently occurs in summer season with heavy or accumulated rainfalls. High-resolution assessment of erosion/deposition patterns in channel bed of the Ichinosawa catchment was performed using multi-temporal terrestrial laser scanning data covering 3 seasons for 2 years. Seasonal changes in spatial distribution of erosion and deposition in the channel bed is quantified using a 0.1-m DEM converted from the original point cloud by TLS. The multi-temporal datasets provides an estimate of annual sediment storage and yield on the order of 1,000 - 5,000 m3. Analysis of changes in elevation by transverse and longitudinal profiles shows contrasting patterns of erosion and deposition along the studied reach: in particular, changes in bed elevation is found to be less in a 50-m long reach, whose downstream part seems bounded by valley narrowing and a knickpoint. Several topographic metrics, including stream gradient, surface roughness and topographic openness, were examined to estimate the characteristics of differing transport processes induced by debris flows along the reaches.

Geomorphic change caused by outburst floods and debris flows at Mount Rainier, Washington, with emphasis on Tahoma Creek valley

USGS Publications Warehouse

Walder, J.S.; Driedger, C.L.

1994-01-01

Debris flows have caused rapid geomorphic change in several glacierized drainages on Mount Rainier, Washington. Nearly all of these flows began as glacial outburst floods, then transformed to debris flows by incorporating large masses of sediment in channel reaches where streams have incised proglacial sediments and stagnant glacier ice. This stagnant ice is a relic of advanced glacier positions achieved during the mid-nineteenth century Little Ice Age maximum and the readvance of the 1960's and 1970's. Debris flows have been especially important agents of geomorphic change along Tahoma Creek, which drains South Tahoma Glacier. Debris flows in Tahoma Creek valley have transported downstream about 107 m3 Of sediment since 1967, causing substantial aggradation and damage to roads and facilities in Mount Rainier National Park. The average denudation rate in the upper part of the Tahoma Creek drainage basin in the same period has been extraordinarily high: more than 20 millimeters per year, a value exceeded only rarely in basins affected by debris flows. However, little or none of this sediment has yet passed out of the Tahoma Creek drainage basin. Outburst floods from South Tahoma Glacier form by release of subglacially stored water. The volume of stored water discharged during a typical outburst flood would form a layer several tens of millimeters thick over the bed of the entire glacier, though it is more likely that large linked cavities account for most of the storage. Statistical analysis shows that outburst floods usually occur during periods of atypically hot or rainy weather in summer or early autumn, and that the probability of an outburst increases with temperature (a proxy measure of ablation rate) or rainfall rate. On the basis of these results, we suggest that outburst floods are triggered when rapid input of water to the glacier bed causes transient increase in water pressure, thereby destabilizing the linked-cavity system. The probabilistic nature of the relation between water-input rate and outburst-flood occurrence suggests that the connections between englacial conduits, basal cavities and main meltwater channels may vary temporally. The correlation between outburst floods and meteorological factors casts doubt on an earlier hypothesis that melting around geothermal vents triggers outburst floods from South Tahoma Glacier. The likelihood that outburst floods from South Tahoma Glacier will trigger debris flows should decrease with time, as the deeply incised reach of Tahoma Creek widens by normal slope processes and stagnant ice decays. Drawing analogies to the geomorphic evolution of a reach of Tahoma Creek first incised by an outburst flood in 1967, we suggest the present period of debris-flow activity along Tahoma Creek will last about 25 years, that is, until about the year 2010. Comparison of geomorphic change at Tahoma Creek to that in two other glacierized alphine basins indicates that debris-rich stagnant ice can be an importantsource of sediment to debris flows as long as floods are frequent or channel slope is great.

Can earthquake fissures predispose hillslopes to landslides? - Evidence from Central and East Asia

NASA Astrophysics Data System (ADS)

Sidle, Roy C.; Gomi, Takashi; Rajapbaev, Muslim; Chyngozhoev, Nurstan

2017-04-01

Factors affecting earthquake-initiated landslides include earthquake magnitude, focal depth, and seismic wave propagation and attenuation. In contrast to rainfall-initiated landslides, earthquake-induced landslides often occur on convex slopes and near ridgelines. Here we present evidence from Fergana Basin, Kyrgyzstan and Kumamoto, Japan on how fissures developed during earthquakes may promote subsequent initiation of rainfall-triggered landslides. More than 1800 recent major landslides in hilly terrain and soft sediments of the Fergana Basin have been largely attributed to accumulation of heavy rainfall and snowmelt. While no large earthquakes have occurred in the Fergana Basin, smaller earthquakes have generated fissures near ridgelines and on convex slopes. The connection of fissures, developed years or decades before slope failure, with preferential transport of rainwater and runoff into the soil has not been previously investigated. Fissures have been observed to expand with time, particularly during subsequent minor earthquakes, further promoting preferential infiltration. Because the soil mantle does not have large contrasts in permeability that would define a slip plane for landslides, it appears that the position and depth of these fissures may control the location and depth of failures. Zones in the soil where surficial inputs of water are preferentially transported, augment natural subsurface accumulation of antecedent rainfall. Many landslides in the eastern Fergana Basin occur after several months of accumulated precipitation and groundwater has been observed emerging on critical hillside locations (near ridgelines and on convex slopes) prior to slope failure. During the 2016 Kumamoto Earthquake (M 7.3), many landslides were triggered in forest and grassland hillslopes near Mount Aso. All of these earthquakes were shallow (focal depths about 10 km), causing high shaking intensity and ground rupturing. Because soils were relatively dry during these earthquakes, occurrence of debris flows was limited. Instead, most landslides travelled limited distances and consisted of ruptured soil blocks. Large, parallel fissures developed along ridgelines and convex slopes, providing opportunities for preferential flow to initiate mass wasting during later heavy rainfalls. The progressive deterioration of ridgelines could change future catchment drainage patterns. Additionally, sediment accumulated in headwater channels from the initial earthquake-triggered landslides may mobilize as devastating debris flows after additional sediment loading during a large storm. As such, cascading effects of prior earthquakes on later mass wasting appear evident in both regions.

Debris flow early warning systems in Norway: organization and tools

NASA Astrophysics Data System (ADS)

Kleivane, I.; Colleuille, H.; Haugen, L. E.; Alve Glad, P.; Devoli, G.

2012-04-01

In Norway, shallow slides and debris flows occur as a combination of high-intensity precipitation, snowmelt, high groundwater level and saturated soil. Many events have occurred in the last decades and are often associated with (or related to) floods events, especially in the Southern of Norway, causing significant damages to roads, railway lines, buildings, and other infrastructures (i.e November 2000; August 2003; September 2005; November 2005; Mai 2008; June and Desember 2011). Since 1989 the Norwegian Water Resources and Energy Directorate (NVE) has had an operational 24 hour flood forecasting system for the entire country. From 2009 NVE is also responsible to assist regions and municipalities in the prevention of disasters posed by landslides and snow avalanches. Besides assisting the municipalities through implementation of digital landslides inventories, susceptibility and hazard mapping, areal planning, preparation of guidelines, realization of mitigation measures and helping during emergencies, NVE is developing a regional scale debris flow warning system that use hydrological models that are already available in the flood warning systems. It is well known that the application of rainfall thresholds is not sufficient to evaluate the hazard for debris flows and shallow slides, and soil moisture conditions play a crucial role in the triggering conditions. The information on simulated soil and groundwater conditions and water supply (rain and snowmelt) based on weather forecast, have proved to be useful variables that indicate the potential occurrence of debris flows and shallow slides. Forecasts of runoff and freezing-thawing are also valuable information. The early warning system is using real-time measurements (Discharge; Groundwater level; Soil water content and soil temperature; Snow water equivalent; Meteorological data) and model simulations (a spatially distributed version of the HBV-model and an adapted version of 1-D soil water and energy balance model COUP). The data are presented in a web- and GIS-based system with daily nationwide maps showing the meteorological and hydrological conditions for the present and the near future from quantitative weather prognosis. In addition a division of the country in homogenous debris flow-prone regions is also under progress based on geomorfological, topographic parameters and loose quaternary deposits distribution. Threshold-levels are being investigated by using statistical analyses of historical debris flows events and measured hydro-meteorological parameters. The debris flow early warning system is currently being tested and is expected to be operational in 2013. Final products will be warning messages and a map showing the different hazard levels, from low to high, indicating the landslide probability and the type of expected damages in a certain area. Many activities are realized in strong collaboration with the road and railway authorities, the geological survey and private consultant companies.

Preliminary soil-slip susceptibility maps, southwestern California

USGS Publications Warehouse

Morton, Douglas M.; Alvarez, Rachel M.; Campbell, Russell H.; Digital preparation by Bovard, Kelly R.; Brown, D.T.; Corriea, K.M.; Lesser, J.N.

2003-01-01

This group of maps shows relative susceptibility of hill slopes to the initiation sites of rainfall-triggered soil slip-debris flows in southwestern California. As such, the maps offer a partial answer to one part of the three parts necessary to predict the soil-slip/debris-flow process. A complete prediction of the process would include assessments of “where”, “when”, and “how big”. These maps empirically show part of the “where” of prediction (i.e., relative susceptibility to sites of initiation of the soil slips) but do not attempt to show the extent of run out of the resultant debris flows. Some information pertinent to “when” the process might begin is developed. “When” is determined mostly by dynamic factors such as rainfall rate and duration, for which local variations are not amenable to long-term prediction. “When” information is not provided on the maps but is described later in this narrative. The prediction of “how big” is addressed indirectly by restricting the maps to a single type of landslide process—soil slip-debris flows. The susceptibility maps were created through an iterative process from two kinds of information. First, locations of sites of past soil slips were obtained from inventory maps of past events. Aerial photographs, taken during six rainy seasons that produced abundant soil slips, were used as the basis for soil slip-debris flow inventory. Second, digital elevation models (DEM) of the areas that were inventoried were used to analyze the spatial characteristics of soil slip locations. These data were supplemented by observations made on the ground. Certain physical attributes of the locations of the soil-slip debris flows were found to be important and others were not. The most important attribute was the mapped bedrock formation at the site of initiation of the soil slip. However, because the soil slips occur in surficial materials overlying the bedrocks units, the bedrock formation can only serve as a surrogate for the susceptibility of the overlying surficial materials. The maps of susceptibility were created from those physical attributes learned to be important from the inventories. The multiple inventories allow a model to be created from one set of inventory data and evaluated with others. The resultant maps of relative susceptibility represent the best estimate generated from available inventory and DEM data. Slope and aspect values used in the susceptibility analysis were 10-meter DEM cells at a scale of 1:24,000. For most of the area 10-meter DEMs were available; for those quadrangles that have only 30-meter DEMs, the 30-meter DEMS were resampled to 10-meters to maintain resolution of 10-meter cells. Geologic unit values used in the susceptibility analysis were five-meter cells. For convenience, the soil slip susceptibility values are assembled on 1:100,000-scale bases. Any area of the 1:100,000-scale maps can be transferred to 1:24,000-scale base without any loss of accuracy. Figure 32 is an example of part of a 1:100,000-scale susceptibility map transferred back to a 1:24,000-scale quadrangle.

A multi-sensor approach to landslide monitoring of rainfall-induced failures in Scotland.

NASA Astrophysics Data System (ADS)

Gilles, Charlie; Hoey, Trevor; Williams, Richard

2017-04-01

Landslides are of significant interest in upland areas of the United Kingdom due to their: complex mechanics, potential to channelize into hazardous debris flows and their costly potential impacts on infrastructure. The British Geological Survey National Landslide Database contains an average of 367 landslides per year (from 1970). Slope failures in the UK are typically triggered by extended periods of intense rainfall, and can occur at any time of year. In any given rainfall event that triggers landslides, most potentially vulnerable slopes remain stable. Accurate warning systems would be facilitated by identifying landslide precursors prior to failure events. This project tests whether such precursors can be identified in the valley of Glen Ogle, Scotland (87 km north-west of Edinburgh), where in summer 2004 two debris flows blocked the main road (A85), trapping fifty-seven people. Two adjacent sites have been selected on a west facing slope in Glen Ogle, one of which (the control) has been stable since at least 2004 and the other failed in 2004 and remains unstable. Understanding the immediate causes and antecedent conditions responsible for landslides requires a multi-scale approach. This project uses multiple sensors to assess failure mechanisms of landslides in Glen Ogle: (1) 3-monthly, high (1.8 arcsec) resolution terrestrial laser scanning of topography to detect changes and identify patterns of movement prior to major failure, using the Riegl VZ-1000 (NERC Geophysical Equipment Fund); (2) rainfall and soil moisture data to monitor pore pressure of landslide failure prior to and after hydrologically triggered events; (3) monitoring ground motion using grain-scale sensors which are becoming lower cost, more efficient in terms of power, and can be wirelessly networked these will be used to detect small scale movement of the landslide. Comparative data from the control and test sites will be presented, from which patterns of surface deformation between failure events will be derived.

Integration of rainfall/runoff and geomorphological analyses flood hazard in small catchments: case studies from the southern Apennines (Italy)

NASA Astrophysics Data System (ADS)

Palumbo, Manuela; Ascione, Alessandra; Santangelo, Nicoletta; Santo, Antonio

2017-04-01

We present the first results of an analysis of flood hazard in ungauged mountain catchments that are associated with intensely urbanized alluvial fans. Assessment of hydrological hazard has been based on the integration of rainfall/runoff modelling of drainage basins with geomorphological analysis and mapping. Some small and steep, ungauged mountain catchments located in various areas of the southern Apennines, in southern Italy, have been chosen as test sites. In the last centuries, the selected basins have been subject to heavy and intense precipitation events, which have caused flash floods with serious damages in the correlated alluvial fan areas. Available spatial information (regional technical maps, DEMs, land use maps, geological/lithological maps, orthophotos) and an automated GIS-based procedure (ArcGis tools and ArcHydro tools) have been used to extract morphological, hydrological and hydraulic parameters. Such parameters have been used to run the HEC (Hydrologic Engineering Center of the US Army Corps of Engineers) software (GeoHMS, GeoRAS, HMS and RAS) based on rainfall-runoff models, which have allowed the hydrological and hydraulic simulations. As the floods occurred in the studied catchments have been debris flows dominated, the solid load simulation has been also performed. In order to validate the simulations, we have compared results of the modelling with the effects produced by past floods. Such effects have been quantified through estimations of both the sediment volumes within each catchment that have the potential to be mobilised (pre-event) during a sediment transfer event, and the volume of sediments delivered by the debris flows at basins' outlets (post-event). The post-event sediment volume has been quantified through post-event surveys and Lidar data. Evaluation of the pre-event sediment volumes in single catchments has been based on mapping of sediment storages that may constitute source zones of bed load transport and debris flows. For such an approach has been used a methodology that consists of the application of a process-based geomorphological mapping, based on data derived from GIS analysis using high-resolution DEMs, field measurements and aerial photograph interpretations. Our integrated approach, which allows quantification of the flow rate and a semi-quantitative assessment of sediment that can be mobilized during hydro-meteorological events, is applied for the first time to torrential catchmenmts of the southern Apennines and may significantly contribute to previsional studies aimed at risk mitigation in the study region.

Assessing the Potential Impact of the 2015-2016 El Niño on the California Rim Fire Burn Scar Through Debris Flow Hazard Mapping

NASA Astrophysics Data System (ADS)

Larcom, S.; Grigsby, S.; Ustin, S.

2015-12-01

Wildfires are a perennial issue for California, and the current record-breaking drought is exacerbating the potential problems for the state. Fires leave behind burn scars characterized by diminished vegetative cover and abundant bare soil, and these areas are especially susceptible to storm events that pose an elevated risk of debris flows and sediment-rich sheet wash. This study focused on the 2013 Rim Fire that devastated significant portions of Stanislaus National Forest and Yosemite National Park, and utilized readily available NASA JPL SRTM elevation data and AVIRIS spectral imaging data to construct a debris flow hazard map that assesses mass wasting risk for the Rim Fire burn scar. This study consisted entirely of remotely sensed data, which was processed in software programs such as ENVI, GRASS GIS, ArcMap, and Google Earth. Parameters that were taken into consideration when constructing this map include hill slope (greater than 30 percent rise), burn severity (assessed by calculating NDVI), and erodibility of the soil (by comparing spectral reflectance of AVIRIS images with the reference spectra of illite). By calculating percent of total burn area, 6% was classified as low risk, 55% as medium risk, and 39% as high risk. In addition, this study assessed the importance of the 2015-2016 El Niño, which is projected to be one of the strongest on record, by studying historic rainfall records and storm events of past El Niño's. Hydrological and infrastructural problems that could be caused by short-term convective or long-term synoptic storms and subsequent debris flows were explored as well.

The 22 March 2014 Oso landslide, Washington, USA

NASA Astrophysics Data System (ADS)

Wartman, Joseph; Montgomery, David R.; Anderson, Scott A.; Keaton, Jeffrey R.; Benoît, Jean; dela Chapelle, John; Gilbert, Robert

2016-01-01

The Oso, Washington, USA, landslide occurred on the morning of Saturday, 22 March 2014 and claimed the lives of 43 people. The landslide began within an 200-m-high hillslope comprised of unconsolidated glacial and previous landslide/colluvial deposits; it continued as a debris avalanche/debris flow that rapidly inundated a neighborhood of 35 single-family residences. An intense three-week rainfall that immediately preceded the event most likely played a role in triggering the landslide; and other factors that likely contributed to destabilization of the landslide mass include alteration of the local groundwater recharge and hydrogeological regime from previous landsliding, weakening and alteration of the landslide mass caused by previous landsliding, and changes in stress distribution resulting from removal and deposition of material from earlier landsliding. Field reconnaissance following the event revealed six distinctive zones and several subzones that are characterized on the basis of geomorphic expression, styles of deformation, geologic materials, and the types, size, and orientation of vegetation. Seismic recording of the landslide indicate that the event was marked by several vibration-generating episodes of mass movement. We hypothesize that the landslide occurred in two stages, with the first being a sequential remobilization of existing slide masses from the most recent (2006) landslide and from an ancient slide that triggered a devastating debris avalanche/debris flow. The second stage involved headward extension into previously unfailed material that occurred in response to unloading and redirection of stresses.

Extreme events assessment methodology coupling rainfall and tidal levels in the coastal floodplain of the São Paulo North Coast (Brazil) for drainage purposes

NASA Astrophysics Data System (ADS)

Alfredini, P.; Cartacho, D. L.; Arasaki, E.; Rosso, M.; Sousa, W. C., Jr.; Lanzieri, D. R.; Ferreira, J. P. M.

2012-04-01

The Caraguatatuba Coastal Plain is the wider in São Paulo State (Brazil) North Coastline. The Santo Antônio Torrent Catchmenth drains that region with high urban concentration (around 100,000 permanent inhabitants), which may quintuplicate with the turists in the summer period. In the last decade important oil and gas sea reserves were discovered and the facilities for their treatment were located in that region. For that great economic growth scenario it is mandatory to design mitigation risk measures to have the fluvial forcing processes well known, considering the natural hazards. The Santo Antônio catchment has a surface area of 40 km2, heavy rainfall rates (around 3000 mm/year), concentrated mainly in the summer period, producing high fluvial sediment transport capacity, floods and debris-flows. Due to the steep slopes and the altitude (~ 1000 m) of the mountains near the coast, the hydrological orographic effect rapidly condensates the sea humidity and recurrent and intense flood events cause extensive risks and damages to population and infrastructures. Strong debris-flows occur in that region, because rains higher than 300-400 mm per day occur in multi decadal periods. Due to the wind blowing landward the humidity from the sea, also meteorological tides occur in correspondence of high rainfall rates. The aim of this project is to present an extreme hydrological assessment methodology, coupling rainfall rates and tidal levels, to show the impact of climate changes during the last decades. It is also presented the magnitude of the rising meteorological tide coupled with the extreme rainfall events. The data base analysed comprised long term data of rainfall and tidal measurements from 1954 to 2003. The correlations of the two data were divided in five classes of rainfall in mm per day (> 0, > 25, > 50, > 75 and > 100) and estimated the tidal levels for different return periods in years (2, 5, 10, 20, 50, 75 and 100). The comparison of two distint periods (1954 to 1980 and 1981 to 2000) for extreme events typically used for drainage projects (rains higher than 50 mm/day) clearly showed an increasing in tidal levels for the same return period. That trend indicates the importance to mantain a monitoring network in order to avoid the interruption of long term data series. According to that conclusions were evaluated the number of constructions and inhabitants affected in the are prone of that flooding in the next decades.

Video monitoring in the Gadria debris flow catchment: preliminary results of large scale particle image velocimetry (LSPIV)

NASA Astrophysics Data System (ADS)

Theule, Joshua; Crema, Stefano; Comiti, Francesco; Cavalli, Marco; Marchi, Lorenzo

2015-04-01

Large scale particle image velocimetry (LSPIV) is a technique mostly used in rivers to measure two dimensional velocities from high resolution images at high frame rates. This technique still needs to be thoroughly explored in the field of debris flow studies. The Gadria debris flow monitoring catchment in Val Venosta (Italian Alps) has been equipped with four MOBOTIX M12 video cameras. Two cameras are located in a sediment trap located close to the alluvial fan apex, one looking upstream and the other looking down and more perpendicular to the flow. The third camera is in the next reach upstream from the sediment trap at a closer proximity to the flow. These three cameras are connected to a field shelter equipped with power supply and a server collecting all the monitoring data. The fourth camera is located in an active gully, the camera is activated by a rain gauge when there is one minute of rainfall. Before LSPIV can be used, the highly distorted images need to be corrected and accurate reference points need to be made. We decided to use IMGRAFT (an opensource image georectification toolbox) which can correct distorted images using reference points and camera location, and then finally rectifies the batch of images onto a DEM grid (or the DEM grid onto the image coordinates). With the orthorectified images, we used the freeware Fudaa-LSPIV (developed by EDF, IRSTEA, and DeltaCAD Company) to generate the LSPIV calculations of the flow events. Calculated velocities can easily be checked manually because of the already orthorectified images. During the monitoring program (since 2011) we recorded three debris flow events at the sediment trap area (each with very different surge dynamics). The camera in the gully was in operation in 2014 which managed to record granular flows and rockfalls, which particle tracking may be more appropriate for velocity measurements. The four cameras allows us to explore the limitations of camera distance, angle, frame rate, and image quality.

Lahars at Cotopaxi and Tungurahua Volcanoes, Ecuador: Highlights from stratigraphy and observational records and related downstream hazards: Chapter 6

USGS Publications Warehouse

Mothes, Patricia A; Vallance, James W.

2015-01-01

Lahars are volcanic debris flows that are dubbed primary when triggered by eruptive activity or secondary when triggered by other factors such as heavy rainfall after eruptive activity has waned. Variation in time and space of the proportion of sediment to water within a lahar dictates lahar flow phase and the resultant sedimentary character of deposits. Characteristics of source material and of debris eroded and incorporated during flow downstream may strongly affect the grain-size composition of flowing lahars and their deposits. Lahars borne on the flanks of two steep-sided stratocones in Ecuador exemplify two important lahar types. Glacier-clad Cotopaxi volcano has been a producer of primary lahars that flow great distances downstream. Such primary lahars include those of both clast-rich and matrix-rich composition—some of which have flowed as far as 325 km to the Pacific Ocean. Cotopaxi's last important eruption in 1877 generated formidable syneruptive lahars comparable in size to those that buried Armero, Colombia, following the 1985 eruption of Nevado del Ruiz volcano. In contrast, ash-producing eruptive activity during the past 15 years at Tungurahua volcano has generated a continual supply of fresh volcaniclastic debris that is regularly remobilized by precipitation. Between 2000 and 2011, 886 rain-generated lahars were registered at Tungurahua. These two volcanoes pose dramatically different hazards to nearby populations. At Tungurahua, the frequency and small sizes of lahars have resulted in effective mitigation measures. At Cotopaxi 137 years have passed since the last important lahar-producing eruption, and there is now a high-risk situation for more than 100,000 people living in downstream valleys.

Slope movements triggered by heavy rainfall, November 3–5, 1985, in Virginia and West Virginia, U.S.A.

USGS Publications Warehouse

Jacobson, Robert B.; Cron, Elizabeth D.; McGeehin, John P.

1989-01-01

Study of slope movements triggered by the storm of November 3–5, 1985, in the central Appalachian Mountains, U.S.A., has helped to define the meteorologic conditions leading to slope movements and the relative importance of land cover, bedrock, surficial geology, and geomorphology in slope movement location. This long-duration rainfall at moderate intensities triggered more than 1,000 slope movements in a 1,040-km2 study area. Most were shallow slips and slip-flows in thin colluvium and residuum on shale slopes. Locations of these failures were sensitive to land cover and slope aspect but were relatively insensitive to topographic setting. A few shallow slope movements were triggered by the same rainfall on interbedded limestone, shale, and sandstone. Several large debris slide-avalanches were triggered in sandstone regolith high on ridges in areas of the highest measured rainfall. Most of these sites were on slopes that dip 30 to 35° and lie parallel to bedding planes, presumably the sites of least stability.

Attribution of extreme precipitation in the lower reaches of the Yangtze River during May 2016

NASA Astrophysics Data System (ADS)

Li, Chunxiang; Tian, Qinhua; Yu, Rong; Zhou, Baiquan; Xia, Jiangjiang; Burke, Claire; Dong, Buwen; Tett, Simon F. B.; Freychet, Nicolas; Lott, Fraser; Ciavarella, Andrew

2018-01-01

May 2016 was the third wettest May on record since 1961 over central eastern China based on station observations, with total monthly rainfall 40% more than the climatological mean for 1961-2013. Accompanying disasters such as waterlogging, landslides and debris flow struck part of the lower reaches of the Yangtze River. Causal influence of anthropogenic forcings on this event is investigated using the newly updated Met Office Hadley Centre system for attribution of extreme weather and climate events. Results indicate that there is a significant increase in May 2016 rainfall in model simulations relative to the climatological period, but this increase is largely attributable to natural variability. El Niño years have been found to be correlated with extreme rainfall in the Yangtze River region in previous studies—the strong El Niño of 2015-2016 may account for the extreme precipitation event in 2016. However, on smaller spatial scales we find that anthropogenic forcing has likely played a role in increasing the risk of extreme rainfall to the north of the Yangtze and decreasing it to the south.

Assessment of Vulnerability to Extreme Flash Floods in Design Storms

PubMed Central

Kim, Eung Seok; Choi, Hyun Il

2011-01-01

There has been an increase in the occurrence of sudden local flooding of great volume and short duration caused by heavy or excessive rainfall intensity over a small area, which presents the greatest potential danger threat to the natural environment, human life, public health and property, etc. Such flash floods have rapid runoff and debris flow that rises quickly with little or no advance warning to prevent flood damage. This study develops a flash flood index through the average of the same scale relative severity factors quantifying characteristics of hydrographs generated from a rainfall-runoff model for the long-term observed rainfall data in a small ungauged study basin, and presents regression equations between rainfall characteristics and the flash flood index. The aim of this study is to develop flash flood index-duration-frequency relation curves by combining the rainfall intensity-duration-frequency relation and the flash flood index from probability rainfall data in order to evaluate vulnerability to extreme flash floods in design storms. This study is an initial effort to quantify the flash flood severity of design storms for both existing and planned flood control facilities to cope with residual flood risks due to extreme flash floods that have ocurred frequently in recent years. PMID:21845165

Assessment of vulnerability to extreme flash floods in design storms.

PubMed

Kim, Eung Seok; Choi, Hyun Il

2011-07-01

There has been an increase in the occurrence of sudden local flooding of great volume and short duration caused by heavy or excessive rainfall intensity over a small area, which presents the greatest potential danger threat to the natural environment, human life, public health and property, etc. Such flash floods have rapid runoff and debris flow that rises quickly with little or no advance warning to prevent flood damage. This study develops a flash flood index through the average of the same scale relative severity factors quantifying characteristics of hydrographs generated from a rainfall-runoff model for the long-term observed rainfall data in a small ungauged study basin, and presents regression equations between rainfall characteristics and the flash flood index. The aim of this study is to develop flash flood index-duration-frequency relation curves by combining the rainfall intensity-duration-frequency relation and the flash flood index from probability rainfall data in order to evaluate vulnerability to extreme flash floods in design storms. This study is an initial effort to quantify the flash flood severity of design storms for both existing and planned flood control facilities to cope with residual flood risks due to extreme flash floods that have ocurred frequently in recent years.

Meteorological tools in support to the railway security system on the Calabria region

NASA Astrophysics Data System (ADS)

Laviola, Sante; Gabriele, Salvatore; Iovine, Giulio; Baldini, Luca; Chiravalloti, Francesco; Federico, Stefano; Miglietta, Marcello Mario; Milani, Lisa; Procopio, Antonio; Roberto, Nicoletta; Tiesi, Alessandro; Agostino, Mario; Niccoli, Raffaele; Stassi, Sergio; Rago, Valeria

2017-04-01

RAMSES (RAilway Meteorological SEcurity System) is a pilot project co-funded by the Italian Railway Company - RFI S.p.A. and conceived for the mitigation of the hydrological risk along the Calabria railways. RAMSES aims at improving the forecast of very short life-cycle convection systems, responsible of intense and localized rainfalls affecting small catchment areas, which are often underestimated by the numerical weather models and even non-adequately detected by the network of sparse raingauges. The RAMSES operational design is based on a synergistic and integrated architecture, providing a series of information able to identify the most active convective cells and monitoring their evolution in terms of vertical structure, rain intensity and geo-hydrological effects at ground (debris flow, landslides, collapses of bridges, erosion of the ballast). The RAMSES meteorological component is designed to identify and track the short-term evolution (15-60 min) of convective cells, by means of imaging techniques based on dual-polarization weather radar and Meteosat data. In support of this quasi-real time analysis, the numerical model WRF provides the weather forecast at 3-6 hours range by ingesting, through the assimilation system LAPS, the observational data (rain gauges, ground weather stations, radar, satellites) in order to improve the initial condition. Finally, the hydraulic flow modeling is used to assess the ground effects in terms of landslide susceptibility, rainfall-runoff intensity, debris impact on the drainage network and evaluate of risk along the railway track.

Simulation of debris flow events in Sicily by cellular automata model SCIDDICA_SS3

NASA Astrophysics Data System (ADS)

Cancelliere, A.; Lupiano, V.; Peres, D. J.; Stancanelli, L.; Avolio, M.; Foti, E.; Di Gregorio, S.

2013-12-01

Debris flow models are widely used for hazard mapping or for evaluating the effectiveness of risk mitigation measures. Several models analyze the dynamics of debris flow runout solving Partial Differential Equations. In use of such models, difficulties arise in estimating kinematic geotechnical soil parameters for real phenomena. In order to overcome such difficulties, alternative semi-empirical approaches can be employed, such as macroscopic Cellular Automata (CA). In particular, for CA simulation purposes, the runout of debris flows emerges from local interactions in a dynamical system, subdivided into elementary parts, whose state evolves within a spatial and temporal discretum. The attributes of each cell (substates) describe physical characteristics. For computational reasons, the natural phenomenon is splitted into a number of elementary processes, whose proper composition makes up the CA transition function. By simultaneously applying this function to all the cells, the evolution of the phenomenon can be simulated in terms of modifications of the substates. In this study, we present an application of the macroscopic CA semi-empirical model SCIDDICA_SS3 to the Peloritani Mountains area in Sicily island, Italy. The model was applied using detailed data from the 1 October 2009 debris flow event, which was triggered by a rainfall event of about 250 mm falling in 9 hours, that caused the death of 37 persons. This region is characterized by river valleys with large hillslope angles (30°-60°), catchment basins of small extensions (0.5-12 km2) and soil composed by metamorphic material, which is easy to be eroded. CA usage implies a calibration phase, that identifies an optimal set of parameters capable of adequately play back the considered case, and a validation phase, that tests the model on a sufficient (and different) number of cases similar in terms of physical and geomorphological properties. The performance of the model can be measured in terms of a fitness function that compares the observed landslide with the simulated one. This function returns values from 0 (completely wrong simulation) to 1 (perfect match); values greater than 0.7 are considered acceptable. The adopted version SCIDDICA_SS3 was calibrated on debris-flows occurred in Torrente Sopra Urno, that have caused most of the damage in Giampilieri town. Other 5 events, occurred in the same day and on the same area, were used for validation with fitness function ranging from 0.72 to 0.78. Simulations show a good capability of the model to describe the runout of debris in such highly-urbanized area, according to several performance indices. The calibrated parameters may be reasonably used to simulate debris flow runout in the nearby catchments for predictive purposes, aimed at risk assessment. Acknowledgements: This research was funded by the Italian Education, University and Research Ministry (MIUR), PON Project No. 01_01503 'Integrated Systems for Hydrogeological Risk Monitoring, Early Warning and Mitigation Along the Main Lifelines', CUP B31H11000370005

Capturing the Initiation and Spatial Variability of Runoff on Soils Affected by Wildfire

NASA Astrophysics Data System (ADS)

Martin, D. A.; Wickert, A. D.; Moody, J. A.

2011-12-01

Rainfall after wildfire often leads to intense runoff and erosion, since fire removes ground cover that impedes overland flow and water is unable to efficiently infiltrate into the fire-affected soils. In order to understand the relation between rainfall, infiltration, and runoff, we modified a camera to be triggered by a rain gage to take time-lapse photographs of the ground surface every 10 seconds until the rain stops. This camera allows us to observe directly the patterns of ground surface ponding, the initiation of overland flow, and erosion/deposition during single rainfall events. The camera was deployed on a hillslope (average slope = 23 degrees) that was severely burned by the 2010 Fourmile Canyon Fire near Boulder, Colorado. The camera's field of view is approximately 3 m2. We integrate the photographs with rainfall and overland flow measurements to determine thresholds for the initiation of overland flow and erosion. We have recorded the spatial variability of wetted patches of ground and the connection of these patches together to initiate overland flow. To date we have recorded images for rain storms with 30-minute maximum intensities ranging from 5 mm/h (our threshold to trigger continuous photographs) to 32 mm/h. In the near future we will update the camera's control system to 1) include a clock to enable time-lapse photographs at a lower frequency in addition to the event-triggered images, and 2) to add a radio to allow the camera to be triggered remotely. Radio communication will provide a means of starting the camera in response to non-local events, allowing us to capture images or video of flash flood surge fronts and debris flows, and to synchronize the operations of multiple cameras in the field. Schematics and instructions to build this camera station, which can be used to take either photos or video, are open-source licensed and are available online at http://instaar.colorado.edu/~wickert/atvis. It is our hope that this tool can be used by other researchers to better understand processes in burned watersheds and other sensitive areas that are likely to respond rapidly to rainfall.

Debris flow hazards mitigation--Mechanics, prediction, and assessment

USGS Publications Warehouse

Chen, C.-L.; Major, J.J.

2007-01-01

These proceedings contain papers presented at the Fourth International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment held in Chengdu, China, September 10-13, 2007. The papers cover a wide range of topics on debris-flow science and engineering, including the factors triggering debris flows, geomorphic effects, mechanics of debris flows (e.g., rheology, fluvial mechanisms, erosion and deposition processes), numerical modeling, various debris-flow experiments, landslide-induced debris flows, assessment of debris-flow hazards and risk, field observations and measurements, monitoring and alert systems, structural and non-structural countermeasures against debris-flow hazards and case studies. The papers reflect the latest devel-opments and advances in debris-flow research. Several studies discuss the development and appli-cation of Geographic Information System (GIS) and Remote Sensing (RS) technologies in debris-flow hazard/risk assessment. Timely topics presented in a few papers also include the development of new or innovative techniques for debris-flow monitoring and alert systems, especially an infra-sound acoustic sensor for detecting debris flows. Many case studies illustrate a wide variety of debris-flow hazards and related phenomena as well as their hazardous effects on human activities and settlements.

The use of land- and satellite-based precipitation radar to forecast debris flows and high water discharge: case study from June 2nd, 2016 in southern Norway.

NASA Astrophysics Data System (ADS)

Devoli, Graziella; Mengistu, Zelalem T.; Elo, Christoffer A.; Boje, Søren; Rønning, Snorre S.; Engeland, Kolbjørn; Lussana, Cristian

2017-04-01

The Norwegian flood- and landslide forecasting service at the Norwegian Water Resources and Energy Directorate (NVE) (www.varsom.no), has issued flood forecasts since 1989, and since 2013 the occurrence of many landslides events at regional level, due either to severe storms or intense snow melting, has been predicted. High intensity and short duration (less than 1 hour) rainfalls may cause sudden and abundant runoff that can entrain large quantities of loose sediments and originate debris flows. Intense convective rainstorms often develop quickly, especially during summer, and they are difficult to forecast and even to observe with a standard (synoptic) network of precipitation gauges. In those cases, the forecaster on duty can send warning messages for a very large area (encompassing many counties and many municipalities), because of the large spatial uncertainty of the prognoses and amount of rain. A standard sentence in the warning message is always included, recommending to the population to monitor the evolution of the rainstorm with weather radar products, which are available on institutional websites. In other cases, especially when the convective rainstorm is spatially confined in a small area and highly uncertain, the forecaster may choose to not issue any warning. The first situation yields false alarms for some areas, while the second situation could result in a missing event, if a landslide actually occurs. The Norwegian Meteorological Institute (MET) and NVE are working on a project to further promote the use of radar-derived products in landslides and flood forecasting. In this study, we focus on the description of a case study to present the potential of MET-NVE collaboration on the topic. As a case study, we have chosen a short-lived rainstorm occurred on June 2nd, 2016 in Motland (Rogaland county, Southern Norway), which had triggered 2 debris flows that were not forecasted. Land- and satellite-based weather radar and lighting data were used to analyse and recreate the triggering conditions for these events. The closest rain gauges in the area show very low rain intensity that cannot explain the initiation of the landslides. This is in disagreement with the eye-witness that observed intense and very local showers. The analysis of rainfall intensity estimated by both land-based and satellite-based (IMERG) radar data confirms the eye-witness observations, and it results in significantly higher values for the areas where the debris flows were triggered, if compared to precipitation interpolated from gauge observations. This was also supported by discharge responses from three small catchments in the area. Our results indicates that weather radar and lighting data are useful complements to the traditional analysis of landslide events made only by means of gauges, moreover they can be used: a) in back analyses on rainfall and landslide events in order to improve landslide thresholds; b) has a potential to assist in now-casting operations as supporting tool of a regional warning, especially in summer season, and radar prediction can be used in the proximate hour to see the storm development.

Deterministic estimation of hydrological thresholds for shallow landslide initiation and slope stability models: case study from the Somma-Vesuvius area of southern Italy

USGS Publications Warehouse

Baum, Rex L.; Godt, Jonathan W.; De Vita, P.; Napolitano, E.

2012-01-01

Rainfall-induced debris flows involving ash-fall pyroclastic deposits that cover steep mountain slopes surrounding the Somma-Vesuvius volcano are natural events and a source of risk for urban settlements located at footslopes in the area. This paper describes experimental methods and modelling results of shallow landslides that occurred on 5–6 May 1998 in selected areas of the Sarno Mountain Range. Stratigraphical surveys carried out in initiation areas show that ash-fall pyroclastic deposits are discontinuously distributed along slopes, with total thicknesses that vary from a maximum value on slopes inclined less than 30° to near zero thickness on slopes inclined greater than 50°. This distribution of cover thickness influences the stratigraphical setting and leads to downward thinning and the pinching out of pyroclastic horizons. Three engineering geological settings were identified, in which most of the initial landslides that triggered debris flows occurred in May 1998 can be classified as (1) knickpoints, characterised by a downward progressive thinning of the pyroclastic mantle; (2) rocky scarps that abruptly interrupt the pyroclastic mantle; and (3) road cuts in the pyroclastic mantle that occur in a critical range of slope angle. Detailed topographic and stratigraphical surveys coupled with field and laboratory tests were conducted to define geometric, hydraulic and mechanical features of pyroclastic soil horizons in the source areas and to carry out hydrological numerical modelling of hillslopes under different rainfall conditions. The slope stability for three representative cases was calculated considering the real sliding surface of the initial landslides and the pore pressures during the infiltration process. The hydrological modelling of hillslopes demonstrated localised increase of pore pressure, up to saturation, where pyroclastic horizons with higher hydraulic conductivity pinch out and the thickness of pyroclastic mantle reduces or is interrupted. These results lead to the identification of a comprehensive hydrogeomorphological model of susceptibility to initial landslides that links morphological, stratigraphical and hydrological conditions. The calculation of intensities and durations of rainfall necessary for slope instability allowed the identification of deterministic hydrological thresholds that account for uncertainty in properties and observed rainfall intensities.

Effects of Recent Debris Flows on Stream Ecosystems and Food Webs in Small Watersheds in the Central Klamath Mountains, NW California

NASA Astrophysics Data System (ADS)

Cover, M. R.; de La Fuente, J.

2008-12-01

Debris flows are common erosional processes in steep mountain areas throughout the world, but little is known about the long-term ecological effects of debris flows on stream ecosystems. Based on debris flow histories that were developed for each of ten tributary basins, we classified channels as having experienced recent (1997) or older (pre-1997) debris flows. Of the streams classified as older debris flow streams, three streams experienced debris flows during floods in 1964 or 1974, while two streams showed little or no evidence of debris flow activity in the 20th century. White alder (Alnus rhombifolia) was the dominant pioneer tree species in recent debris flow streams, forming localized dense patches of canopy cover. Maximum temperatures and daily temperature ranges were significantly higher in recent debris flow streams than in older debris flow streams. Debris flows resulted in a shift in food webs from allochthonous to autochthonous energy sources. Primary productivity, as measured by oxygen change during the day, was greater in recent debris flow streams, resulting in increased abundances of grazers such as the armored caddisfly Glossosoma spp. Detritivorous stoneflies were virtually absent in recent debris flow streams because of the lack of year-round, diverse sources of leaf litter. Rainbow trout (Oncorhynchus mykiss) were abundant in four of the recent debris flow streams. Poor recolonizers, such as the Pacific giant salamander (Dicamptodon tenebrosus), coastal tailed frog (Ascaphus truei), and signal crayfish (Pacifistacus leniusculus), were virtually absent in recent debris flow streams. Forest and watershed managers should consider the role of forest disturbances, such as road networks, on debris flow frequency and intensity, and the resulting ecological effects on stream ecosystems.

Sediment trapping efficiency of adjustable check dam in laboratory and field experiment

NASA Astrophysics Data System (ADS)

Wang, Chiang; Chen, Su-Chin; Lu, Sheng-Jui

2014-05-01

Check dam has been constructed at mountain area to block debris flow, but has been filled after several events and lose its function of trapping. For the reason, the main facilities of our research is the adjustable steel slit check dam, which with the advantages of fast building, easy to remove or adjust it function. When we can remove transverse beams to drain sediments off and keep the channel continuity. We constructed adjustable steel slit check dam on the Landow torrent, Huisun Experiment Forest station as the prototype to compare with model in laboratory. In laboratory experiments, the Froude number similarity was used to design the dam model. The main comparisons focused on types of sediment trapping and removing, sediment discharge, and trapping rate of slit check dam. In different types of removing transverse beam showed different kind of sediment removal and differences on rate of sediment removing, removing rate, and particle size distribution. The sediment discharge in check dam with beams is about 40%~80% of check dam without beams. Furthermore, the spacing of beams is considerable factor to the sediment discharge. In field experiment, this research uses time-lapse photography to record the adjustable steel slit check dam on the Landow torrent. The typhoon Soulik made rainfall amounts of 600 mm in eight hours and induced debris flow in Landow torrent. Image data of time-lapse photography demonstrated that after several sediment transport event the adjustable steel slit check dam was buried by debris flow. The result of lab and field experiments: (1)Adjustable check dam could trap boulders and stop woody debris flow and flush out fine sediment to supply the need of downstream river. (2)The efficiency of sediment trapping in adjustable check dam with transverse beams was significantly improved. (3)The check dam without transverse beams can remove the sediment and keep the ecosystem continuity.

Sediment budget analysis from Landslide debris and river channel change during the extreme event - example of Typhoon Morakot at Laonong river, Taiwan

NASA Astrophysics Data System (ADS)

Chang, Kuo-Jen; Huang, Yu-Ting; Huang, Mei-Jen; Chiang, Yi-Lin; Yeh, En-Chao; Chao, Yu-Jui

2014-05-01

Taiwan, due to the high seismicity and high annual rainfall, numerous landslides triggered every year and severe impacts affect the island. Typhoon Morakot brought extreme and long-time rainfall for Taiwan in August 2009. It further caused huge loss of life and property in central and southern Taiwan. Laonong River is the largest tributary of Gaoping River. It's length is 137 km, and the basin area is 1373 km2. More than 2000mm rainfall brought and maximum rainfall exceeded 100mm/hr in the region by Typhoon Morakot in Aug, 2009. Its heavy rains made many landslides and debris flew into the river and further brought out accumulation and erosion on river banks of different areas. It caused severe disasters within the Laonong River drainage. In the past, the study of sediment blockage of river channel usually relies on field investigation, but due to inconvenient transportation, topographical barriers, or located in remote areas, etc. the survey is hardly to be completed sometimes. In recent years, the rapid development of remote sensing technology improves image resolution and quality significantly. Remote sensing technology can provide a wide range of image data, and provide essential and precious information. Furthermore, although the amount of sediment transportation can be estimated by using data such as rainfall, river flux, and suspended loads, the situation of large debris migration cannot be studied via those data. However, landslides, debris flow and river sediment transportation model in catchment area can be evaluated easily through analyzing the digital terrain model (DTM) . The purpose of this study is to investigate the phenomenon of river migration and to evaluate the amount of migration along Laonong River by analyzing the DEM before and after the typhoon Morakot. The DEMs are built by using the aerial images taken by digital mapping camera (DMC) and by airborne digital scanner 40 (ADS 40) before and after typhoon event. The results show that lateral erosion of the Laonong River caused by the typhoon seriously, especially in Yushan National Park, and midstream region. However, lateral erosion in downstream region is not so obvious. Meanwhile the siltation depth resulted from the Typhoon Morakot is larger in upstream region than in midstream and downstream regions. The amount of landslide debris created by Typhoon Morakot was too excessive to be transported. Materials just siltated in the upstream in place, same as in the middle stream area. Because of the amount of river slope erosion and sediment collapse in the downstream region is less than in upstream and midstream region, the amount of river erosion slightly larger than the amount of river siltation. The goals of this project are trying to decipher the sliding process and morphologic changes of large landslide areas, sediment transport and budgets, and to investigate the phenomenon of river migration. The results of this study provides not only geomatics and GIS dataset of the hazards, but also for essential geomorphologic information for other study, and for hazard mitigation and planning, as well.

Deciphering landslide behavior using large-scale flume experiments

USGS Publications Warehouse

Reid, Mark E.; Iverson, Richard M.; Iverson, Neal R.; LaHusen, Richard G.; Brien, Dianne L.; Logan, Matthew

2008-01-01

Landslides can be triggered by a variety of hydrologic events and they can exhibit a wide range of movement dynamics. Effective prediction requires understanding these diverse behaviors. Precise evaluation in the field is difficult; as an alternative we performed a series of landslide initiation experiments in the large-scale, USGS debris-flow flume. We systematically investigated the effects of three different hydrologic triggering mechanisms, including groundwater exfiltration from bedrock, prolonged rainfall infiltration, and intense bursts of rain. We also examined the effects of initial soil porosity (loose or dense) relative to the soil’s critical-state porosity. Results show that all three hydrologic mechanisms can instigate landsliding, but water pathways, sensor response patterns, and times to failure differ. Initial soil porosity has a profound influence on landslide movement behavior. Experiments using loose soil show rapid soil contraction during failure, with elevated pore pressures liquefying the sediment and creating fast-moving debris flows. In contrast, dense soil dilated upon shearing, resulting in slow, gradual, and episodic motion. These results have fundamental implications for forecasting landslide behavior and developing effective warning systems.

EDDA 1.0: integrated simulation of debris flow erosion, deposition and property changes

NASA Astrophysics Data System (ADS)

Chen, H. X.; Zhang, L. M.

2015-03-01

Debris flow material properties change during the initiation, transportation and deposition processes, which influences the runout characteristics of the debris flow. A quasi-three-dimensional depth-integrated numerical model, EDDA (Erosion-Deposition Debris flow Analysis), is presented in this paper to simulate debris flow erosion, deposition and induced material property changes. The model considers changes in debris flow density, yield stress and dynamic viscosity during the flow process. The yield stress of the debris flow mixture determined at limit equilibrium using the Mohr-Coulomb equation is applicable to clear water flow, hyper-concentrated flow and fully developed debris flow. To assure numerical stability and computational efficiency at the same time, an adaptive time stepping algorithm is developed to solve the governing differential equations. Four numerical tests are conducted to validate the model. The first two tests involve a one-dimensional debris flow with constant properties and a two-dimensional dam-break water flow. The last two tests involve erosion and deposition, and the movement of multi-directional debris flows. The changes in debris flow mass and properties due to either erosion or deposition are shown to affect the runout characteristics significantly. The model is also applied to simulate a large-scale debris flow in Xiaojiagou Ravine to test the performance of the model in catchment-scale simulations. The results suggest that the model estimates well the volume, inundated area, and runout distance of the debris flow. The model is intended for use as a module in a real-time debris flow warning system.

Understanding three decades of land use changes and a cloudburst in Phewa Lake Watershed, Western Nepal

NASA Astrophysics Data System (ADS)

Sudmeier-Rieux, Karen; Tonini, Marj; Vulliez, Cindy; Sanjaya, Devkota; Derron, Marc-Henri; Jaboyedoff, Michel

2017-04-01

This paper details an extreme rainfall event, or cloudburst (315 mm/ 24 hours) which occurred on July 29-30, 2015 in the Phewa Lake Watershed, Western Nepal, three months after the April 25, 2015 Gorkha Earthquake. The event triggered over 170 landslides and debris flows, caused 8 deaths and considerable damage to livelihoods. The fatal debris flow started from one of the numerous rural roads, which have proliferated exponentially over the past decades. In addition to mapping landslides due to this extreme rainfall event, our study sought to document and analyze underlying natural and human land use factors that may have impacted the occurrence of landsliding (Vulliez et al submitted). To do so, our study analyzed land cover/ land use changes for the period 1979-2016 based on an interpretation of aerial photos and satellite images, combined with ground truthing. We studied how land use / land cover changes have resulted in a shift of active erosion zones from overgrazing around streams and forests to an exponential number of small failures along unplanned earthen rural roads, or "bulldozer roads". With several hundred small failures documented along roadsides (Leibundgut et al., 2016) as compared to only 14 landslides prior to 2015 extreme rainfall event - and none triggered by the 2015 earthquake - roads are thus a major driver of active erosion zones and small failures in the watershed. More effective management of the current unsustainable mode of rural road construction is required to reduce further environmental and economic impacts on vulnerable populations in Nepal. Leibundgut, G., Sudmeier-Rieux, K. Devkota, S., Jaboyedoff, M., Derron, M-H., Penna, I. Nguyen, L. (2016). Rural earthen roads impact assessment in Phewa watershed, Western region, Nepal. Geoenvironmental Disasters (2016) 3:13. DOI 10.1186/s40677-016-0047-8 Vulliez, C, Tonini, M., Sudmeier-Rieux, K. Devkota, S., Derron, M-H, Jaboyedoff, M. (submitted) Land use changes, landslides and roads in the Phewa Watershed, Western Nepal from 1979 to 2016. Applied Geography

EDDA: integrated simulation of debris flow erosion, deposition and property changes

NASA Astrophysics Data System (ADS)

Chen, H. X.; Zhang, L. M.

2014-11-01

Debris flow material properties change during the initiation, transportation and deposition processes, which influences the runout characteristics of the debris flow. A quasi-three-dimensional depth-integrated numerical model, EDDA, is presented in this paper to simulate debris flow erosion, deposition and induced material property changes. The model considers changes in debris flow density, yield stress and dynamic viscosity during the flow process. The yield stress of debris flow mixture is determined at limit equilibrium using the Mohr-Coulomb equation, which is applicable to clear water flow, hyper-concentrated flow and fully developed debris flow. To assure numerical stability and computational efficiency at the same time, a variable time stepping algorithm is developed to solve the governing differential equations. Four numerical tests are conducted to validate the model. The first two tests involve a one-dimensional dam-break water flow and a one-dimensional debris flow with constant properties. The last two tests involve erosion and deposition, and the movement of multi-directional debris flows. The changes in debris flow mass and properties due to either erosion or deposition are shown to affect the runout characteristics significantly. The model is also applied to simulate a large-scale debris flow in Xiaojiagou Ravine to test the performance of the model in catchment-scale simulations. The results suggest that the model estimates well the volume, inundated area, and runout distance of the debris flow. The model is intended for use as a module in a real-time debris flow warning system.

[Research progress in post-fire debris flow].

PubMed

Di, Xue-ying; Tao, Yu-zhu

2013-08-01

The occurrence of the secondary disasters of forest fire has significant impacts on the environment quality and human health and safety. Post-fire debris flow is one of the most hazardous secondary disasters of forest fire. To understand the occurrence conditions of post-fire debris flow and to master its occurrence situation are the critical elements in post-fire hazard assessment. From the viewpoints of vegetation, precipitation threshold and debris flow material sources, this paper elaborated the impacts of forest fire on the debris flow, analyzed the geologic and geomorphic conditions, precipitation and slope condition that caused the post-fire debris flow as well as the primary mechanisms of debris-flow initiation caused by shallow landslide or surface runoff, and reviewed the research progress in the prediction and forecast of post-fire debris flow and the related control measures. In the future research, four aspects to be focused on were proposed, i. e., the quantification of the relationships between the fire behaviors and environmental factors and the post-fire debris flow, the quantitative research on the post-fire debris flow initiation and movement processes, the mechanistic model of post-fire debris flow, and the rapid and efficient control countermeasures of post-fire debris flow.

Dendrogeomorphic evidence of debris flow frequency and magnitude at Mount Shasta, California

USGS Publications Warehouse

Hupp, C.R.

1984-01-01

Debris-flow deposits and woody vegetation adjacent to and growing within the channels of Whitney, Bolam, Mud, Ash, and Panthe creeks provide a 300-year record of debris-flow frequency at Mount Shasta Dendrochronologic (tree-ring) dating methods for the debris flows proved consistent with available documented records of debris flows Nine debris flows not reported in the historic record were documented and dated dendrochronologically. The oldest tree-ring date for a mudflow was about 1670 Combined geomorphic and botanical evidence shows that debris flows are a common occurrence at Mount Shasta Debris flows traveling at least 2 km have occurred at the rate of about 8 3 per century Smaller debris flows occur substantially more frequently and usually do not proceed as far downslope as larger debris flows. Cyclic scouring and filling by debris flows, in and adjacent to the stream channels, is suggested by dendrogeomorphic evidence and appears to be related to their magnitude and frequency Debris flows, small and large, may be the major surficial geomorphic agent in the vicinity of mount Shasta, sculpturing the channels and developing large alluvial fans ?? 1984 Springer-Verlag New York Inc.

Simulation of Sediment Transport Caused by Landslide at Nanhua Reservoir Watershed in Southern Taiwan

NASA Astrophysics Data System (ADS)

Lee, Ming-Hsi; Huang, Cong-Gi; Lin, Huan-Hsuan

2016-04-01

As a result of heavy rainfall, steep topography, young and weak geological formations, earthquakes, loose soils, slope land cultivation and other human disturbance, much area in Taiwan are prone to the occurrence of disastrous mass movements such as landslides and sediment disasters. During recent years, the extreme rainfall events brought huge amounts of rainfall and triggered severe changes in watershed environments. Typhoon Morakot in August 2009 caused severe landslides, debris flow, flooding and sediment disasters induced by record-break rainfall. The maximum rainfall of mountain area in Chiayi, Tainan, Kaohsiung and Pingtung County were over 2,900 mm. The study area is located at Nanhua reservoir watershed in southern Taiwan. The numerical model (HEC-RAS 4.1 and FLO-2D) will be used to simulate the sediment transport caused by landslide and the study will find out the separating location of erosion and deposition in the river, the danger area of riverbank, and the safety of the river terrace village under the return period of 50-year, 100-year and 200-year (such as Typhoon Morakot). The results of this study can provide for the disaster risk management of administrative decisions to lessen the impacts of natural hazards and may also be useful for time-space variation of sediment disasters caused by Climate Change.

Extreme rainfalls in Eastern Himalaya and southern slope of Meghalaya Plateau and their geomorphologic impacts

NASA Astrophysics Data System (ADS)

Soja, Roman; Starkel, Leszek

2007-02-01

This paper presents the detailed rainfall characteristics of 3 key areas located in the eastern monsoon India: the margin of Darjeeling Himalaya, the margin of Bhutanese Himalaya and the Cherrapunji region at the southern slope of Meghalaya Upland. All these areas are sensitive to changes but differ in annual rainfall totals (2000-4000 mm, 4000-6000 m and 6000-23,000 mm respectively) and in the frequency of extreme rainfalls. Therefore the response of geomorphic processes is different, also due to various human impact. In the Darjeeling Himalaya the thresholds may be passed 2-3 times in one century and the system may return to the former equilibrium. At the margin of western Bhutanese Himalaya in 1990s, the clustering of three events caused an acceleration in the transformation and formation of a new trend of evolution, especially in the piedmont zone. In the Cherrapunji of Meghalaya region in the natural conditions the effects of dozens of extreme rainfalls every year were checked by the dense vegetation cover. After deforestation and extensive land use the fertile soil was removed and either the exposed bedrock or armoured debris top layer protect the surface against degradation and facilitate only rapid overland flow. A new "sterile" system has been formed.

Rainfall and snow-melt triggered glacial lake outbursts: a systematic analysis of the Kedarnath (Uttarakhand, India), June 2013 disaster

NASA Astrophysics Data System (ADS)

Allen, Simon; Rastner, Philipp; Arora, Manohar; Huggel, Christian; Stoffel, Markus

2015-04-01

Heavy rainfall in early June 2013 triggered flash flooding and landslides throughout the Indian Himalayan state of Uttarakhand, killing more than 6000 people. The destruction of roads and trekking routes left around 100,000 pilgrims and tourists stranded. Most fatalities and damages resulted directly from a lake outburst and debris flow disaster originating from above the village of Kedarnath on June 16 and 17. Here we provide a first systematic analysis of the contributing factors leading to the Kedarnath disaster, both in terms of hydro-meteorological triggering (rainfall, snowmelt, and temperature) and topographic predisposition. Specifically, the topographic characteristics of the Charobari lake watershed above Kedarnath are compared with other glacial lakes across the northwestern Indian Himalayan states of Uttarakhand and Himachal Pradesh, and implications for glacier lake outburst hazard assessment in a changing climate are discussed. Our analysis suggests that the early onset of heavy monsoon rainfall (390 mm, June 10 - 17) immediately following a prolonged four week period of unusually rapid snow cover depletion and elevated streamflow is the crucial hydro-meteorological factor, resulting in slope saturation and significant runoff into the small seasonal glacial lake. Over a four week period the MODIS-derived snow covered area above Kedarnath decreased nearly 50%, from above average coverage in mid-May to well below average coverage by the second week of June. Such a rapid decrease has not been observed in the previous 13-year record, where the average decrease in snow covered area over the same four week window is only 15%. The unusual situation of the lake being dammed in a steep, unstable paraglacial environment, but fed entirely from snow-melt and rainfall within a fluvial dominated watershed is important in the context of this disaster. A simple scheme enabling large-scale recognition of such an unfavorable topographic setting is presented, and on the basis of all assessed watershed parameters, the situation at Charobari lake indicates an anomalous predisposition towards rapid runoff and infilling during enhanced snowmelt or heavy rainfall. In view of projected 21st century changes in monsoon timing and heavy precipitation in South Asia, more emphasis should be given to potential hydro-meteorological triggering of lake outburst and related debris flow disasters in the Himalayas. The potential for Kedarnath-type lake breaching may further increase as glaciers recede or ultimately disappear, and watersheds become increasingly rainfall dominated. Hence, a long-term perspective to glacier lake outburst hazard assessment and management is required, as the greatest threat from hydro-meteorological triggering of related disasters may only be realized in an ice-free environment.

Debris flow initiation in proglacial gullies on Mount Rainier, Washington

NASA Astrophysics Data System (ADS)

Legg, Nicholas T.; Meigs, Andrew J.; Grant, Gordon E.; Kennard, Paul

2014-12-01

Effects of climate change, retreating glaciers, and changing storm patterns on debris flow hazards concern managers in the Cascade Range (USA) and mountainous areas worldwide. During an intense rainstorm in November 2006, seven debris flows initiated from proglacial gullies of separate basins on the flanks of Mount Rainier. Gully heads at glacier termini and widespread failure of gully walls imply that overland flow was transformed into debris flow along gullies. We characterized gully change and morphology, and assessed spatial distributions of debris flows to infer the processes and conditions for debris flow initiation. Slopes at gully heads were greater than ~ 0.35 m m- 1 (19°) and exhibited a significant negative relationship with drainage area. A break in slope-drainage area trends among debris flow gullies also occurs at ~ 0.35 m m- 1, representing a possible transition to fluvial sediment transport and erosion. An interpreted hybrid model of debris flow initiation involves bed failure near gully heads followed by sediment recruitment from gully walls along gully lengths. Estimates of sediment volume loss from gully walls demonstrate the importance of sediment inputs along gullies for increasing debris flow volumes. Basin comparisons revealed significantly steeper drainage networks and higher elevations in debris flow-producing than non-debris flow-producing proglacial areas. The high slopes and elevations of debris flow-producing proglacial areas reflect positive slope-elevation trends for the Mount Rainier volcano. Glacier extent therefore controls the slope distribution in proglacial areas, and thus potential for debris flow generation. As a result, debris flow activity may increase as glacier termini retreat onto slopes inclined at angles above debris flow initiation thresholds.

Modeling regional initiation of rainfall-induced shallow landslides in the eastern Umbria Region of central Italy

USGS Publications Warehouse

Salciarini, D.; Godt, J.W.; Savage, W.Z.; Conversini, P.; Baum, R.L.; Michael, J.A.

2006-01-01

We model the rainfall-induced initiation of shallow landslides over a broad region using a deterministic approach, the Transient Rainfall Infiltration and Grid-based Slope-stability (TRIGRS) model that couples an infinite-slope stability analysis with a one-dimensional analytical solution for transient pore pressure response to rainfall infiltration. This model permits the evaluation of regional shallow landslide susceptibility in a Geographic Information System framework, and we use it to analyze susceptibility to shallow landslides in an area in the eastern Umbria Region of central Italy. As shown on a landslide inventory map produced by the Italian National Research Council, the area has been affected in the past by shallow landslides, many of which have transformed into debris flows. Input data for the TRIGRS model include time-varying rainfall, topographic slope, colluvial thickness, initial water table depth, and material strength and hydraulic properties. Because of a paucity of input data, we focus on parametric analyses to calibrate and test the model and show the effect of variation in material properties and initial water table conditions on the distribution of simulated instability in the study area in response to realistic rainfall. Comparing the results with the shallow landslide inventory map, we find more than 80% agreement between predicted shallow landslide susceptibility and the inventory, despite the paucity of input data.

Assessment of Debris Flow Hazards, North Mountain, Phoenix, AZ

NASA Astrophysics Data System (ADS)

Reavis, K. J.; Wasklewicz, T. A.

2014-12-01

Urban sprawl in many western U.S. cities has expanded development onto alluvial fans. In the case of metropolitan Phoenix, AZ (MPA), urban sprawl has led to an exponential outward growth into surrounding mountainous areas and onto alluvial fans. Building on alluvial fans places humans at greater risk to flooding and debris flow hazards. Recent research has shown debris flows often supply large quantities of material to many alluvial fans in MPA. However, the risk of debris flows to built environments is relatively unknown. We use a 2D debris flow modeling approach, aided by high-resolution airborne LiDAR and terrestrial laser scanning (TLS) topographic data, to examine debris flow behavior in a densely populated portion of the MPA to assess the risk and vulnerability of debris flow damage to the built infrastructure. A calibrated 2D debris flow model is developed for a "known" recent debris flow at an undeveloped site in MPA. The calibrated model and two other model scenarios are applied to a populated area with historical evidence of debris flow activity. Results from the modeled scenarios show evidence of debris flow damage to houses built on the alluvial fan. Debris flow inundation is also evident on streets on the fan. We use housing values and building damage to estimate the costs assocaited with various modeled debris flow scenarios.

Aspect-dependent soil saturation and insight into debris-flow initiation during extreme rainfall in the Colorado Front Range

USGS Publications Warehouse

Ebel, Brian A.; Rengers, Francis K.; Tucker, Gregory E.

2015-01-01

Hydrologic processes during extreme rainfall events are poorly characterized because of the rarity of measurements. Improved understanding of hydrologic controls on natural hazards is needed because of the potential for substantial risk during extreme precipitation events. We present field measurements of the degree of soil saturation and estimates of available soil-water storage during the September 2013 Colorado extreme rainfall event at burned (wildfire in 2010) and unburned hillslopes with north- and south-facing slope aspects. Soil saturation was more strongly correlated with slope aspect than with recent fire history; south-facing hillslopes became fully saturated while north-facing hillslopes did not. Our results suggest multiple explanations for why aspect-dependent hydrologic controls favor saturation development on south-facing slopes, causing reductions in effective stress and triggering of slope failures during extreme rainfall. Aspect-dependent hydrologic behavior may result from (1) a larger gravel and stone fraction, and hence lower soil-water storage capacity, on south-facing slopes, and (2) lower weathered-bedrock permeability on south-facing slopes, because of lower tree density and associated deep roots penetrating bedrock as well as less intense weathering, inhibiting soil drainage.

The Effect of Debris-Flow Composition on Runout Distance

NASA Astrophysics Data System (ADS)

Haas, T. D.; Braat, L.; Leuven, J.; Lokhorst, I.; Kleinhans, M. G.

2014-12-01

Estimating runout distance is of major importance for the assessment and mitigation of debris-flow hazards. Debris-flow runout distance depends on debris-flow composition and topography, but state-of-the-art runout prediction methods are mainly based on topographical parameters and debris-flow volume, while composition is generally neglected or incorporated in empirical constants. Here we experimentally investigated the effect of debris-flow composition and topography on runout distance. We created the first small-scale experimental debris flows with self-formed levees, distinct lobes and morphology and texture accurately resembling natural debris flows. In general, debris-flow composition had a larger effect on runout distance than topography. Enhancing channel slope and width, outflow plain slope, debris-flow size and water fraction leads to an increase in runout distance. However, runout distance shows an optimum relation with coarse-material and clay fraction. An increase in coarse-material fraction leads to larger runout distances by increased grain collisional forces and more effective levee formation, but too much coarse debris causes a large accumulation of coarse debris at the flow front, enhancing friction and decreasing runout. An increase in clay fraction initially enlarges the volume and viscosity of the interstitial fluid, liquefying the flow and enhancing runout, while a further increase leads to very viscous flows with high yield strength, reducing runout. These results highlight the importance and further need of research on the relation between debris-flow composition and runout distance. Our experiments further provide valuable insight on the effects of debris-flow composition on depositional mechanisms and deposit morphology.

The effect of debris-flow composition on runout distance

NASA Astrophysics Data System (ADS)

de Haas, Tjalling; Braat, Lisanne; Leuven, Jasper; Lokhorst, Ivar; Kleinhans, Maarten

2015-04-01

Estimating runout distance is of major importance for the assessment and mitigation of debris-flow hazards. Debris-flow runout distance depends on debris-flow composition and topography, but state-of-the-art runout prediction methods are mainly based on topographical parameters and debris-flow volume, while composition is generally neglected or incorporated in empirical constants. Here we experimentally investigated the effect of debris-flow composition and topography on runout distance. We created the first small-scale experimental debris flows with self-formed levees, distinct lobes and morphology and texture accurately resembling natural debris flows. In general, the effect of debris-flow composition on runout distance was larger than the effect of topography. Enhancing channel slope and width, outflow plain slope, debris-flow size and water fraction leads to an increase in runout distance. However, runout distance shows an optimum relation with coarse-material and clay fraction. An increase in coarse-material fraction leads to larger runout distances by increased grain collisional forces and more effective levee formation, but too much coarse debris causes a large accumulation of coarse debris at the flow front, enhancing friction and decreasing runout. An increase in clay fraction initially enlarges the volume and viscosity of the interstitial fluid, liquefying the flow and enhancing runout, while a further increase leads to very viscous flows with high yield strength, reducing runout. These results highlight the importance and further need of research on the relation between debris-flow composition and runout distance. Our experiments further provide valuable insight on the effects of debris-flow composition on depositional mechanisms and deposit morphology.

Rainfall thresholds and susceptibility mapping for shallow landslides and debris flows in Scotland

NASA Astrophysics Data System (ADS)

Postance, Benjamin; Hillier, John; Dijkstra, Tom; Dixon, Neil

2017-04-01

Shallow translational slides and debris flows (hereafter 'landslides') pose a significant threat to life and cause significant annual economic impacts (e.g. by damage and disruption of infrastructure). The focus of this research is on the definition of objective rainfall thresholds using a weather radar system and landslide susceptibility mapping. In the study area Scotland, an inventory of 75 known landslides was used for the period 2003 to 2016. First, the effect of using different rain records (i.e. time series length) on two threshold selection techniques in receiver operating characteristic (ROC) analysis was evaluated. The results show that thresholds selected by 'Threat Score' (minimising false alarms) are sensitive to rain record length and which is not routinely considered, whereas thresholds selected using 'Optimal Point' (minimising failed alarms) are not; therefore these may be suited to establishing lower limit thresholds and be of interest to those developing early warning systems. Robust thresholds are found for combinations of normalised rain duration and accumulation at 1 and 12 day's antecedence respectively; these are normalised using the rainy-day normal and an equivalent measure for rain intensity. This research indicates that, in Scotland, rain accumulation provides a better indicator than rain intensity and that landslides may be generated by threshold conditions lower than previously thought. Second, a landslide susceptibility map is constructed using a cross-validated logistic regression model. A novel element of the approach is that landslide susceptibility is calculated for individual hillslope sections. The developed thresholds and susceptibility map are combined to assess potential hazards and impacts posed to the national highway network in Scotland.

Volcano hazards in the San Salvador region, El Salvador

USGS Publications Warehouse

Major, J.J.; Schilling, S.P.; Sofield, D.J.; Escobar, C.D.; Pullinger, C.R.

2001-01-01

San Salvador volcano is one of many volcanoes along the volcanic arc in El Salvador (figure 1). This volcano, having a volume of about 110 cubic kilometers, towers above San Salvador, the country’s capital and largest city. The city has a population of approximately 2 million, and a population density of about 2100 people per square kilometer. The city of San Salvador and other communities have gradually encroached onto the lower flanks of the volcano, increasing the risk that even small events may have serious societal consequences. San Salvador volcano has not erupted for more than 80 years, but it has a long history of repeated, and sometimes violent, eruptions. The volcano is composed of remnants of multiple eruptive centers, and these remnants are commonly referred to by several names. The central part of the volcano, which contains a large circular crater, is known as El Boquerón, and it rises to an altitude of about 1890 meters. El Picacho, the prominent peak of highest elevation (1960 meters altitude) to the northeast of the crater, and El Jabali, the peak to the northwest of the crater, represent remnants of an older, larger edifice. The volcano has erupted several times during the past 70,000 years from vents central to the volcano as well as from smaller vents and fissures on its flanks [1] (numerals in brackets refer to end notes in the report). In addition, several small cinder cones and explosion craters are located within 10 kilometers of the volcano. Since about 1200 A.D., eruptions have occurred almost exclusively along, or a few kilometers beyond, the northwest flank of the volcano, and have consisted primarily of small explosions and emplacement of lava flows. However, San Salvador volcano has erupted violently and explosively in the past, even as recently as 800 years ago. When such eruptions occur again, substantial population and infrastructure will be at risk. Volcanic eruptions are not the only events that present a risk to local communities. Another concern is a landslide and an associated debris flow (a watery flow of mud, rock, and debris--also known as a lahar) that could occur during periods of no volcanic activity. An event of this type occurred in 1998 at Casita volcano in Nicaragua when extremely heavy rainfall from Hurricane Mitch triggered a landslide that moved down slope and transformed into a rapidly moving debris flow that destroyed two villages and killed more than 2000 people. Historical landslides up to a few hundred thousand cubic meters in volume have been triggered on San Salvador volcano by torrential rainstorms and earthquakes, and some have transformed into debris flows that have inundated populated areas down stream. Destructive rainfall- and earthquake-triggered landslides and debris flows on or near San Salvador volcano in September 1982 and January 2001 demonstrate that such mass movements in El Salvador have also been lethal. This report describes the kinds of hazardous events that occur at volcanoes in general and the kinds of hazardous geologic events that have occurred at San Salvador volcano in the past. The accompanying volcano-hazards-zonation maps show areas that are likely to be at risk when hazardous events occur again.

A Passive Nuclear Debris Collector.

ERIC Educational Resources Information Center

Griffin, John J.; And Others

1979-01-01

Describes a nuclear debris collector which removes trace substances from the lower atmosphere during rainfall. Suggests that the collector could be implemented into courses at various educational levels and could result in developing a network for monitoring the geographical extent of nuclear contamination. (Author/SA)

Rheological characteristics of waste rock materials in abandoned mine deposit and debris flow hazards

NASA Astrophysics Data System (ADS)

Jeong, Sueng-Won; Lee, Choonoh; Cho, Yong-Chan; Wu, Ying-Hsin

2015-04-01

In Korea, approximately 5,000 metal mines are spread, but 50% of them are still abandoned without any proper remediation and cleanup. Summer heavy rainfall can result in the physicochemical modification of waste rock materials in the mountainous. From the geotechnical monitoring and field investigation, there are visible traces of mass movements every year. Soil erosion is one of severe phenomena in the study area. In particular, study area is located in the upper part of the Busan Metropolitan City and near the city's water supply. With respect to the supply of drinking water and maintenance of ecological balance, proper disposal of waste rock materials is required. For this reason, we examine the rheological properties of waste rock materials as a function of solid content using a ball- and vane-penetrated rheometer. In the flow curves, which are the relationship between the shear stress and shear rate of waste rock materials, we found that the soil samples exhibited a shear thinning beahivor regardless of solid content. The Bingham, Herschel-Bulkley, Power-law, and Papanastasiou models are used to determine the rheological properties. Assuming that the soil samples behaved as the viscoplastic behavior, the yield stress and viscosity are determined for different water contents. As a result, there are clear relationships between the solid content and rheological values (i.e., Bingham yield stress and plastic viscosity). From these relationships, the maximum and minimum of Bingham yield stresses are ranged from 100 to 2000 Pa. The debris flow mobilization is analysed using a 1D BING and 2D Debris flow models. In addition, the effect of wall slip and test apparatus are discussed.

Autogenic dynamics of debris-flow fans

NASA Astrophysics Data System (ADS)

van den Berg, Wilco; de Haas, Tjalling; Braat, Lisanne; Kleinhans, Maarten

2015-04-01

Alluvial fans develop their semi-conical shape by cyclic avulsion of their geomorphologically active sector from a fixed fan apex. These cyclic avulsions have been attributed to both allogenic and autogenic forcings and processes. Autogenic dynamics have been extensively studied on fluvial fans through physical scale experiments, and are governed by cyclic alternations of aggradation by unconfined sheet flow, fanhead incision leading to channelized flow, channel backfilling and avulsion. On debris-flow fans, however, autogenic dynamics have not yet been directly observed. We experimentally created debris-flow fans under constant extrinsic forcings, and show that autogenic dynamics are a fundamental intrinsic process on debris-flow fans. We found that autogenic cycles on debris-flow fans are driven by sequences of backfilling, avulsion and channelization, similar to the cycles on fluvial fans. However, the processes that govern these sequences are unique for debris-flow fans, and differ fundamentally from the processes that govern autogenic dynamics on fluvial fans. We experimentally observed that backfilling commenced after the debris flows reached their maximum possible extent. The next debris flows then progressively became shorter, driven by feedbacks on fan morphology and flow-dynamics. The progressively decreasing debris-flow length caused in-channel sedimentation, which led to increasing channel overflow and wider debris flows. This reduced the impulse of the liquefied flow body to the flow front, which then further reduced flow velocity and runout length, and induced further in-channel sedimentation. This commenced a positive feedback wherein debris flows became increasingly short and wide, until the channel was completely filled and the apex cross-profile was plano-convex. At this point, there was no preferential transport direction by channelization, and the debris flows progressively avulsed towards the steepest, preferential, flow path. Simultaneously, the debris flows started to channelize, forced by increasingly effective concentration of the flow impulse to the flow front, which caused more effective lateral levee formation and an increasingly well-defined channel. This process continued until the debris flows reached their maximum possible extent and the cycle was reverted. Channelization occurred in the absence of erosion, in contrast with fluvial fans. Backfilling and channelization cycles were gradual and symmetric, requiring multiple debris flows to be completed. These results add debris-flow fans to the spectrum of fan-shaped aqueous systems that are affected by autogenic dynamics, now ranging from low-gradient rivers systems to steep-gradient mass-flow fans.

Debris flows from tributaries of the Colorado River, Grand Canyon National Park, Arizona

USGS Publications Warehouse

Webb, R.H.; Pringle, P.T.; Rink, G.R.

1987-01-01

A reconnaissance of 36 tributaries of the Colorado River indicates that debris flows are a major process by which sediment is transported to the Colorado River in Grand Canyon National Park. Debris flows are slurries of sediment and water that have a water content < 40% by volume. Debris flows occur frequently in arid and semiarid regions. Slope failures commonly trigger debris flows, which can originate from any rock formation in the Grand Canyon. The largest and most frequent flows originate from the Permian Hermit Shale, the underlying Esplanade Sandstone of the Supai Group, and other formations of the Permian and Pennsylvanian Supai Group. Debris flows have reached the Colorado River on an average of once every 20 to 30 yr in the Lava-Chuar Creek drainage since about 1916. Two debris flows have reached the Colorado River in the last 25 yr in Monument Creek. The Crystal Creek drainage has had an average of one debris flow reaching the Colorado River every 50 yr, although the debris flow of 1966 has been the only flow that reached the Colorado River since 1900. Debris flows may actually reach the Colorado River more frequently in these drainages because evidence for all debris flows may not have been preserved in the channel-margin stratigraphy. Discharges were estimated for the peak flow of three debris flows that reached the Colorado River. The debris flow of 1966 in the Lava-Chuar Creek drainage had an estimated discharge of 4,000 cu ft/sec. The debris flow of 1984 in the Monument Creek drainage had a discharge estimated between 3,600 and 4,200 cu ft/sec. The debris flow of 1966 in the Crystal Creek drainage had a discharge estimated between 9,200 and 14,000 cu ft/sec. Debris flows in the Grand Canyon generally are composed of 10 to 40% sand by weight and may represent a significant source of beach-building sand along the Colorado River. The particle size distributions are very poorly sorted and the largest transported boulders were in the Crystal Creek drainage. Reworking of debris fans by the Colorado River creates debris bars that constrain the size of eddy systems and forms secondary rapids and riffles below tributary mouths. (See also W89-09239) (Lantz-PTT)

Sediment yield during typhoon events in relation to landslides, rainfall, and catchment areas in Taiwan

NASA Astrophysics Data System (ADS)

Chen, Chi-Wen; Oguchi, Takashi; Hayakawa, Yuichi S.; Saito, Hitoshi; Chen, Hongey; Lin, Guan-Wei; Wei, Lun-Wei; Chao, Yi-Chiung

2018-02-01

Debris sourced from landslides will result in environmental problems such as increased sediment discharge in rivers. This study analyzed the sediment discharge of 17 main rivers in Taiwan during 14 typhoon events, selected from the catchment area and river length, that caused landslides according to government reports. The measured suspended sediment and water discharge, collected from hydrometric stations of the Water Resources Agency of Taiwan, were used to establish rating-curve relationships, a power-law relation between them. Then sediment discharge during typhoon events was estimated using the rating-curve method and the measured data of daily water discharge. Positive correlations between sediment discharge and rainfall conditions for each river indicate that sediment discharge increases when a greater amount of rainfall or a higher intensity of rainfall falls during a typhoon event. In addition, the amount of sediment discharge during a typhoon event is mainly controlled by the total amount of rainfall, not by peak rainfall. Differences in correlation equations among the rivers suggest that catchments with larger areas produce more sediment. Catchments with relatively low sediment discharge show more distinct increases in sediment discharge in response to increases in rainfall, owing to the little opportunity for deposition in small catchments with high connectivity to rivers and the transportation of the majority of landslide debris to rivers during typhoon events. Also, differences in geomorphic and geologic conditions among catchments around Taiwan lead to a variety of suspended sediment dynamics and the sediment budget. Positive correlation between average sediment discharge and average area of landslides during typhoon events indicates that when larger landslides are caused by heavier rainfall during a typhoon event, more loose materials from the most recent landslide debris are flushed into rivers, resulting in higher sediment discharge. The high proportion of large landslides in Taiwan contributes significantly to the high annual sediment yield, which is among the world's highest despite the small area of Taiwan.

Extreme erosion response after wildfire in the Upper Ovens, south-east Australia: Assessment of catchment scale connectivity by an intensive field survey

NASA Astrophysics Data System (ADS)

Box, Walter; Keestra, Saskia; Nyman, Petter; Langhans, Christoph; Sheridan, Gary

2015-04-01

South-eastern Australia is generally regarded as one of the world's most fire-prone environments because of its high temperatures, low rainfall and flammable native Eucalyptus forests. Modifications to the landscape by fire can lead to significant changes to erosion rates and hydrological processes. Debris flows in particular have been recognised as a process which increases in frequency as a result of fire. This study used a debris flow event in the east Upper Ovens occurred on the 28th of February 2013 as a case study for analysing sediment transport processes and connectivity of sediment sources and sinks. Source areas were identified using a 15 cm resolution areal imagery and a logistic regression model was made based on fire severity, aridity index and slope to predict locations of source areas. Deposits were measured by making cross-sections using a combination of a differential GPS and a total station. In total 77 cross-sections were made in a 14.1 km2 sub-catchment and distributed based on channel gradient and width. A more detailed estimation was obtained by making more cross-sections where the volume per area is higher. Particle size distribution between sources and sink areas were obtained by combination of field assessment, photography imagery analyses and sieve and laser diffraction. Sediment was locally eroded, transported and deposited depending on factors such as longitude gradient, stream power and the composition of bed and bank material. The role of headwaters as sediment sinks changed dramatically as a result of the extreme erosion event in the wildfire affected areas. Disconnected headwaters became connected to low order streams due to debris flow processes in the contributing catchment. However this redistribution of sediment from headwaters to the drainage network was confined to upper reaches of the Ovens. Below this upper part of the catchment the event resulted in redistribution of sediment already existing in the channel through a combination of debris flows and hyperconcentrated flows. These results indicate that there is a stepwise outflow of sediment influencing long-term erosion rates and landform development.

Effects of debris-flow composition on runout and erosion

NASA Astrophysics Data System (ADS)

Haas, T. D.; Kleinhans, M. G.

2016-12-01

Predicting debris-flow runout is of major importance for hazard mitigation. Apart from topography and volume, runout depends on debris-flow composition (i.e., particle-size distribution and water content), but how is poorly understood. Moreover, debris flows can grow greatly in size by entrainment of bed material, enhancing their volume and thereby runout and hazardous impact. Debris-flow erosion rates also depend on debris-flow composition, but the relation between the two is largely unexplored. Composition thus strongly affects the dynamics of debris flows. We experimentally investigate the effects of composition on debris-flow runout and erosion. We find a clear optimum in the relations of runout with coarse-material fraction and clay fraction. Increasing coarse material concentration leads to larger runout. However, excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity, increasing frontal friction and decreasing runout. Increasing clay content initially enhances runout, but too much clay leads to very viscous flows, reducing runout. We further find that debris-flow runout depends at least as much on composition as on topography. In general, erosion depth increases with basal shear stress in our experiments, while there is no correlation with grain collisional stress. There are substantial differences in the scour caused by different types of debris flows. Mean and maximum erosion depths generally become larger with increasing water fraction and grain size and decrease with increasing clay content. However, the erodibility of the very coarse-grained experimental debris flows is unrelated to basal shear stress. This relates to the relatively large influence of grain-collisional stress to the total bed stress in these flows (30-50%). The relative effect of grain-collisional stress is low in the other experimental debris flows (<5%) causing erosion to be largely controlled by basal shear stress. These results show that the erosive behaviour of debris flows may change from basal-shear stress dominated to grain-collisional stress dominated in increasingly coarse-grained debris flows. In short, this study improves our understanding of the effects of debris-flow composition on runout and erosion.

Analysis of rainfall-induced shallow landslides and debris flows in the Eastern Pyrenees

NASA Astrophysics Data System (ADS)

Portilla Gamboa, M.; Hürlimann, M.; Corominas, J.

2009-09-01

The inventory of rainfall-induced mass movements, rainfall data, and slope characteristics are considered the basis of the analysis determining appropriate rainfall thresholds for mass movements in a specific region. The rainfall-induced landslide thresholds established in the literature for the Catalan Pyrenees have been formulated referring to the rainfall events of November 1982, September 1992, December 1997, and others occurred after 1999. It has been shown that a rainfall intensity greater than 190 mm in 24 hours without antecedent rainfall would be necessary to produce mass movements (Corominas and Moya, 1999; Corominas et al, 2002) or 51mm in 24h with 61 mm of accumulated rainfall (Marco, 2007). Short duration-high intensity rainfalls have brought about several mass movements in some Catalonian regions throughout the course of twenty-first century (Berga, Bonaigua, Saldes, Montserrat, Port-Ainé, Riu Runer, and Sant Nicolau). Preliminary analysis of these events shows that it is necessary to review the thresholds defined so far and redo the existing inventory of mass movements for the Catalan Pyrenees. The present work shows the usefulness of aerial photographs in the reconstruction of the inventory of historic mass movements (Molló-Queralbs, 1940; Arties-Vielha, 1963; Barruera-Senet, 1940 and 1963, and Berga-Cercs, 1982, 1997 and 2008). Also, it highlights the treatment given to scarce and scattered rainfall data available inside these Catalonia’s regions, and the application of Geographic Information Systems (ArcGIS) in the management of the gathered information. The results acquired until now show that the historic rainfall events occurred in the Eastern Pyrenees have yielded many more mass movements than those reported in the literature. Besides, it can be said that the thresholds formulated for the Pyrenees are valid for longstanding regional rainfalls, and not for local downpours. In the latter cases it should be necessary to take into account the rainfall intensity of short duration (mm/h, mm/min.) and maybe the role played by the antecedent rainfall.

GB-InSAR monitoring of slope deformations in a mountainous area affected by debris flow events

NASA Astrophysics Data System (ADS)

Frodella, William; Salvatici, Teresa; Pazzi, Veronica; Morelli, Stefano; Fanti, Riccardo

2017-10-01

Diffuse and severe slope instabilities affected the whole Veneto region (north-eastern Italy) between 31 October and 2 November 2010, following a period of heavy and persistent rainfall. In this context, on 4 November 2010 a large detrital mass detached from the cover of the Mt. Rotolon deep-seated gravitational slope deformation (DSGSD), located in the upper Agno River valley, channelizing within the Rotolon Creek riverbed and evolving into a highly mobile debris flow. The latter phenomena damaged many hydraulic works, also threatening bridges, local roads, and the residents of the Maltaure, Turcati, and Parlati villages located along the creek banks and the town of Recoaro Terme. From the beginning of the emergency phase, the civil protection system was activated, involving the National Civil Protection Department, Veneto Region, and local administrations' personnel and technicians, as well as scientific institutions. On 8 December 2010 a local-scale monitoring system, based on a ground-based interferometric synthetic aperture radar (GB-InSAR), was implemented in order to evaluate the slope deformation pattern evolution in correspondence of the debris flow detachment sector, with the final aim of assessing the landslide residual risk and managing the emergency phase. This paper describes the results of a 2-year GB-InSAR monitoring campaign (December 2010-December 2012) and its application for monitoring, mapping, and emergency management activities in order to provide a rapid and easy communication of the results to the involved technicians and civil protection personnel, for a better understanding of the landslide phenomena and the decision-making process in a critical landslide scenario.

Effects of debris flow composition on runout, depositional mechanisms, and deposit morphology in laboratory experiments

NASA Astrophysics Data System (ADS)

Haas, Tjalling; Braat, Lisanne; Leuven, Jasper R. F. W.; Lokhorst, Ivar R.; Kleinhans, Maarten G.

2015-09-01

Predicting debris flow runout is of major importance for hazard mitigation. Apart from topography and volume, runout distance and area depends on debris flow composition and rheology, but how is poorly understood. We experimentally investigated effects of composition on debris flow runout, depositional mechanisms, and deposit geometry. The small-scale experimental debris flows were largely similar to natural debris flows in terms of flow behavior, deposit morphology, grain size sorting, channel width-depth ratio, and runout. Deposit geometry (lobe thickness and width) in our experimental debris flows is largely determined by composition, while the effects of initial conditions of topography (i.e., outflow plain slope and channel slope and width) and volume are negligible. We find a clear optimum in the relations of runout with coarse-material fraction and clay fraction. Increasing coarse-material concentration leads to larger runout. However, excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity, increasing frontal friction and decreasing runout. Increasing clay content initially enhances runout, but too much clay leads to very viscous flows, reducing runout. Runout increases with channel slope and width, outflow plain slope, debris flow volume, and water fraction. These results imply that debris flow runout depends at least as much on composition as on topography. This study improves understanding of the effects of debris flow composition on runout and may aid future debris flow hazard assessments.

Erosion of steepland valleys by debris flows

USGS Publications Warehouse

Stock, J.D.; Dietrich, W.E.

2006-01-01

Episodic debris flows scour the rock beds of many steepland valleys. Along recent debris-flow runout paths in the western United States, we have observed evidence for bedrock lowering, primarily by the impact of large particles entrained in debris flows. This evidence may persist to the point at which debris-flow deposition occurs, commonly at slopes of less than ???0.03-0.10. We find that debris-flow-scoured valleys have a topographic signature that is fundamentally different from that predicted by bedrock river-incision models. Much of this difference results from the fact that local valley slope shows a tendency to decrease abruptly downstream of tributaries that contribute throughgoing debris flows. The degree of weathering of valley floor bedrock may also decrease abruptly downstream of such junctions. On the basis of these observations, we hypothesize that valley slope is adjusted to the long-term frequency of debris flows, and that valleys scoured by debris flows should not be modeled using conventional bedrock river-incision laws. We use field observations to justify one possible debris-flow incision model, whose lowering rate is proportional to the integral of solid inertial normal stresses from particle impacts along the flow and the number of upvalley debris-flow sources. The model predicts that increases in incision rate caused by increases in flow event frequency and length (as flows gain material) downvalley are balanced by rate reductions from reduced inertial normal stress at lower slopes, and stronger, less weathered bedrock. These adjustments lead to a spatially uniform lowering rate. Although the proposed expression leads to equilibrium long-profiles with the correct topographic signature, the crudeness with which the debris-flow dynamics are parameterized reveals that we are far from a validated debris-flow incision law. However, the vast extent of steepland valley networks above slopes of ???0.03-0.10 illustrates the need to understand debris-flow incision if we hope to understand the evolution of steep topography around the world. ?? 2006 Geological Society of America.

Time-dependent landslide probability mapping

USGS Publications Warehouse

Campbell, Russell H.; Bernknopf, Richard L.; ,

1993-01-01

Case studies where time of failure is known for rainfall-triggered debris flows can be used to estimate the parameters of a hazard model in which the probability of failure is a function of time. As an example, a time-dependent function for the conditional probability of a soil slip is estimated from independent variables representing hillside morphology, approximations of material properties, and the duration and rate of rainfall. If probabilities are calculated in a GIS (geomorphic information system ) environment, the spatial distribution of the result for any given hour can be displayed on a map. Although the probability levels in this example are uncalibrated, the method offers a potential for evaluating different physical models and different earth-science variables by comparing the map distribution of predicted probabilities with inventory maps for different areas and different storms. If linked with spatial and temporal socio-economic variables, this method could be used for short-term risk assessment.

The Braunsbach Flashflood of May 29, 2016: A forensic analysis of the meteorological origin and the hydrological development an extreme hydro-meteorological event

NASA Astrophysics Data System (ADS)

Bronstert, Axel; Ankit, Agarwal; Berry, Boessenkool; Madlen, Fischer; Maik, Heistermann; Lisei, Köhn-Reich; Thomas, Moran; Dadiyorto, Wendi

2017-04-01

The flash-flood at 29th May 2016 in the vicinity of the village of Braunsbach in Southwestern Germany, State of Baden-Wuerttemberg, has been a particularly concise event of the floods occurring in southern Germany at the end of May / early June 2016. This extreme event was triggered by a convective high intensity rain storm, causing extreme discharge rates and subsequent debris flow in the local creek. This led to severe flooding of the village with immense damages. Besides its extreme nature, the event is characterized by very local and short term scales, i.e. the catchment of the creek covers an area of only six km2 and the whole event lasted only two hours. This contribution presents a retrospective analysis with regard to meteorology and hydrology to obtain a quantitative assessment of the governing processes and their development. We term this a "forensic analysis" because due to the very local and sudden feature of this flashflood event, the processes cannot be directly measured during the event and/or at the site. Instead, they need to be reconstructed and estimated after the event from a variety of rather different information sources and "soft" data. Using these types of post event observations and analysis, we aim at obtaining a rather comprehensive picture of the event and its consequences. Regarding rainfall, both station data from the surroundings of the catchment and radar data from the German Weather Service were analyzed, including the analysis of different errors types and dynamic features of the convective system. The flood hydrograph, including the maximum discharge rate during the event, was estimated by three different approaches, which were compared to obtain an idea of the associated uncertainty. The overall results of this forensic analysis show that it was a very rare rainfall event with extreme rainfall intensities, e.g. return period exceeding 100 years. Catalyzed by catchment properties, this lead to extreme runoff, severe soil erosion, and subsequent debris flow processes. Due to the complex and interacting processes, the hazard must not be attributed to a single cause, since only the interplay of the different processes and catchment conditions can lead to such an event. The people in the region say that such an event "has never happened before". However, from some first geomorphological analysis we got some indications that such events, including debris flow, might have happened before during previous times (time scale of millennia). Therefore, it would be more appropriate to state that "nobody can remember of such an event".

Enhanced Orographic Tropical Rainfall: An Study of the Colombia's rainfall

NASA Astrophysics Data System (ADS)

Peñaranda, V. M.; Hoyos Ortiz, C. D.; Mesa, O. J.

2015-12-01

Convection in tropical regions may be enhanced by orographic barriers. The orographic enhancement is an intensification of rain rates caused by the forced lifting of air over a mountainous structure. Orographic heavy rainfall events, occasionally, comes along by flooding, debris flow and substantial amount of looses, either economics or human lives. Most of the heavy convective rainfall events, occurred in Colombia, have left a lot of victims and material damages by flash flooding. An urgent action is required by either scientific communities or society, helping to find preventive solutions against these kind of events. Various scientific literature reports address the feedback process between the convection and the local orographic structures. The orographic enhancement could arise by several physical mechanism: precipitation transport on leeward side, convection triggered by the forcing of air over topography, the seeder-feeder mechanism, among others. The identification of the physical mechanisms for orographic enhancement of rainfall has not been studied over Colombia. As far as we know, orographic convective tropical rainfall is just the main factor for the altitudinal belt of maximum precipitation, but the lack of detailed hydro-meteorological measurements have precluded a complete understanding of the tropical rainfall in Colombia and its complex terrain. The emergence of the multifractal theory for rainfall has opened a field of research which builds a framework for parsimonious modeling of physical process. Studies about the scaling behavior of orographic rainfall have found some modulating functions between the rainfall intensity probability distribution and the terrain elevation. The overall objective is to advance in the understanding of the orographic influence over the Colombian tropical rainfall based on observations and scaling-analysis techniques. We use rainfall maps, weather radars scans and ground-based rainfall data. The research strategy is the analysis of rainfall fields via first-order statistical properties, scaling functions, structure functions and spectral analysis, taking into account cloud-motion directions over mountainous slopes (windward/leeward side) and timing of the diurnal cycle. The analysis is developed for some Colombia's locations.

Debris flows from tributaries of the Colorado River, Grand Canyon National Park, Arizona

USGS Publications Warehouse

Webb, Robert H.; Pringle, Patrick T.; Rink, Glenn R.

1989-01-01

A reconnaissance of 36 tributaries of the Colorado River indicates that debris flows are a major process by which sediment is transported to the Colorado River in Grand Canyon National Park. Debris flows are slurries of sediment and water that have a water content of less than about 40 percent by volume. Debris flows occur frequently in arid and semiarid regions. Slope failures commonly trigger debris flows, which can originate from any rock formation in the Grand Canyon. The largest and most frequent flows originate from the Permian Hermit Shale, the underlying Esplanade Sandstone of the Supai Group, and other formations of the Permian and Pennsylvanian Supai Group. Debris flows also occur in the Cambrian Muav Limestone and underlying Bright Angel Shale and the Quaternary basalts in the western Grand Canyon. Debris-flow frequency and magnitude were studied in detail in the Lava-Chuar Creek drainage at Colorado River mile 65.5; in the Monument Creek drainage at mile 93.5; and in the Crystal Creek drainage at mile 98.2. Debris flows have reached the Colorado River on an average of once every 20 to 30 years in the Lava-Chuar Creek drainage since about 1916. Two debris flows have reached the Colorado River in the last 25 years in Monument Creek. The Crystal Creek drainage has had an average of one debris flow reaching the Colorado River every 50 years, although the debris flow of 1966 has been the only flow that reached the Colorado River since 1900. Debris flows may actually reach the Colorado River more frequently in these drainages because evidence for all debris flows may not have been preserved in the channel-margin stratigraphy. Discharges were estimated for the peak flow of three debris flows that reached the Colorado River. The debris flow of 1966 in the Lava-Chuar Creek drainage had an estimated discharge of 4,000 cubic feet per second. The debris flow of 1984 in the Monument Creek drainage had a discharge estimated between 3,600 and 4,200 cubic feet per second. The debris flow of 1966 in the Crystal Creek drainage had a discharge estimated between 9,200 and 14,000 cubic feet per second. Determination of the effective cross-sectional area was a problem in all calculations involving superelevations on bends because areas near superelevation marks were 1.5 to 3.5 times larger than areas of upstream or downstream cross sections. Debris flows in the Grand Canyon generally are composed of 10 to 40 percent sand by weight and may represent a significant source of beach-building sand along the Colorado River. The particle-size distributions are very poorly sorted and the largest transported boulders were in the Crystal Creek drainage. The large boulders transported into the Colorado River by debris flows create or change hydraulic controls (rapids); these controls appear to be governed by the magnitude and frequency of tributary-flow events and the history of discharges on the Colorado River. Reworking of debris fans by the Colorado River creates debris bars that constrain the size of eddy systems and forms secondary rapids and riffles below tributary mouths.

The issues of current rainfall estimation techniques in mountain natural multi-hazard investigation

NASA Astrophysics Data System (ADS)

Zhuo, Lu; Han, Dawei; Chen, Ningsheng; Wang, Tao

2017-04-01

Mountain hazards (e.g., landslides, debris flows, and floods) induced by rainfall are complex phenomena that require good knowledge of rainfall representation at different spatiotemporal scales. This study reveals rainfall estimation from gauges is rather unrepresentative over a large spatial area in mountain regions. As a result, the conventional practice of adopting the triggering threshold for hazard early warning purposes is insufficient. The main reason is because of the huge orographic influence on rainfall distribution. Modern rainfall estimation methods such as numerical weather prediction modelling and remote sensing utilising radar from the space or on land are able to provide spatially more representative rainfall information in mountain areas. But unlike rain gauges, they only indirectly provide rainfall measurements. Remote sensing suffers from many sources of errors such as weather conditions, attenuation and sampling methods, while numerical weather prediction models suffer from spatiotemporal and amplitude errors depending on the model physics, dynamics, and model configuration. A case study based on Sichuan, China is used to illustrate the significant difference among the three aforementioned rainfall estimation methods. We argue none of those methods can be relied on individually, and the challenge is on how to make the full utilisation of the three methods conjunctively because each of them only provides partial information. We propose that a data fusion approach should be adopted based on the Bayesian inference method. However such an approach requires the uncertainty information from all those estimation techniques which still need extensive research. We hope this study will raise the awareness of this important issue and highlight the knowledge gap that should be filled in so that such a challenging problem could be tackled collectively by the community.

Assessment and prediction of debris-flow hazards

USGS Publications Warehouse

Wieczorek, Gerald F.; ,

1993-01-01

Study of debris-flow geomorphology and initiation mechanism has led to better understanding of debris-flow processes. This paper reviews how this understanding is used in current techniques for assessment and prediction of debris-flow hazards.

Volcanic debris flows in developing countries - The extreme need for public education and awareness of debris-flow hazards

USGS Publications Warehouse

Major, J.J.; Schilling, S.P.; Pullinger, C.R.; ,

2003-01-01

In many developing countries, volcanic debris flows pose a significant societal risk owing to the distribution of dense populations that commonly live on or near a volcano. At many volcanoes, modest volume (up to 500,000 m 3) debris flows are relatively common (multiple times per century) and typically flow at least 5 km along established drainages. Owing to typical debris-flow velocities there is little time for authorities to provide effective warning of the occurrence of a debris flow to populations within 10 km of a source area. Therefore, people living, working, or recreating along channels that drain volcanoes must learn to recognize potentially hazardous conditions, be aware of the extent of debris-flow hazard zones, and be prepared to evacuate to safer ground when hazardous conditions develop rather than await official warnings or intervention. Debris-flow-modeling and hazard-assessment studies must be augmented with public education programs that emphasize recognizing conditions favorable for triggering landslides and debris flows if effective hazard mitigation is to succeed. ?? 2003 Millpress,.

Debris flow deposition and reworking by the Colorado River in Grand Canyon, Arizona

USGS Publications Warehouse

Yanites, Brian J.; Webb, Robert H.; Griffiths, Peter G.; Magirl, Christopher S.

2006-01-01

Flow regulation by large dams affects downstream flow competence and channel maintenance. Debris flows from 740 tributaries in Grand Canyon, Arizona, transport coarse‐grained sediment onto debris fans adjacent to the Colorado River. These debris fans constrict the river to form rapids and are reworked during river flows that entrain particles and transport them downstream. Beginning in 1963, flood control operations of Glen Canyon Dam limited the potential for reworking of aggraded debris fans. We analyzed change in debris fans at the mouths of 75‐Mile and Monument Creeks using photogrammetry of aerial photography taken from 1965 to 2000 and supplemented with ground surveys performed from 1987 to 2005. Our results quantify the debris fan aggradation that resulted from debris flows from 1984 to 2003. Volume, area, and river constriction increased at both debris fans. Profiles of the two debris fans show that net aggradation occurred in the middle of debris fans at stages above maximum dam releases, and surface shape shifted from concave to convex. Dam releases above power plant capacity partially reworked both debris fans, although reworking removed much less sediment than what was added by debris flow deposition. Large dam releases would be required to create additional reworking to limit the rate of debris fan aggradation in Grand Canyon.

Detecting debris flows using ground vibrations

USGS Publications Warehouse

LaHusen, Richard G.

1998-01-01

Debris flows are rapidly flowing mixtures of rock debris, mud, and water that originate on steep slopes. During and following volcanic eruptions, debris flows are among the most destructive and persistent hazards. Debris flows threaten lives and property not only on volcanoes but far downstream in valleys that drain volcanoes where they arrive suddenly and inundate entire valley bottoms. Debris flows can destroy vegetation and structures in their path, including bridges and buildings. Their deposits can cover roads and railways, smother crops, and fill stream channels, thereby reducing their flood-carrying capacity and navigability.

Empirical model for the volume-change behavior of debris flows

USGS Publications Warehouse

Cannon, S.H.; ,

1993-01-01

The potential travel down hillsides; movement stops where the volume-change behavior of flows as they travel down hillsides ; movement stops where the volume of actively flowing debris becomes negligible. The average change in volume over distance for 26 recent debris flows in the Honolulu area was assumed to be a function of the slope over which the debris flow traveled, the degree of flow confinement by the channel, and an assigned value for the type of vegetation through which the debris flow traveled. Analysis of the data yielded a relation that can be incorporated into digital elevation models to characterize debris-flow travel on Oahu.

Debris flows associated with the 2015 Gorkha Earthquake in Nepal

NASA Astrophysics Data System (ADS)

Dahlquist, M. P.; West, A. J.; Martinez, J.

2017-12-01

Debris flows are a primary driver of erosion and a major geologic hazard in many steep landscapes, particularly near the headwaters of rivers, and are generated in large numbers by extreme events. The 2015 Mw 7.8 Gorkha Earthquake triggered 25,000 coseismic landslides in central Nepal. During the ensuing monsoon, sediment delivered to channels by landslides was mobilized in the heavy rains, and new postseismic landslides were triggered in rock weakened by the shaking. These coseismic and postseismic landslide-generated debris flows form a useful dataset for studying the impact and behavior of debris flows on one of the most active landscapes on Earth. Debris flow-dominated channel reaches are generally understood to have a topographic signature recognizable in slope-area plots and distinct from fluvial channels, but in examining debris flows associated with the Gorkha earthquake we find they frequently extend into reaches with geometry typically associated with fluvial systems. We examine a dataset of these debris flows, considering whether they are generated by coseismic or postseismic landslides, whether they are likely to be driving active incision into bedrock, and whether their channels correspond with those typically associated with debris flows. Preliminary analysis of debris flow channels in Nepal suggests there may be systematic differences in the geometry of channels containing debris flows triggered by coseismic versus postseismic landslides, which potentially holds implications for hazard analyses and the mechanics behind the different debris flow types.

On the connection of permafrost and debris flow activity in Austria

NASA Astrophysics Data System (ADS)

Huber, Thomas; Kaitna, Roland

2016-04-01

Debris flows represent a severe hazard in alpine regions and typically result from a critical combination of relief energy, water, and sediment. Hence, besides water-related trigger conditions, the availability of abundant sediment is a major control on debris flows activity in alpine regions. Increasing temperatures due to global warming are expected to affect periglacial regions and by that the distribution of alpine permafrost and the depth of the active layer, which in turn might lead to increased debris flow activity and increased interference with human interests. In this contribution we assess the importance of permafrost on documented debris flows in the past by connecting the modeled permafrost distribution with a large database of historic debris flows in Austria. The permafrost distribution is estimated based on a published model approach and mainly depends of altitude, relief, and exposition. The database of debris flows includes more than 4000 debris flow events in around 1900 watersheds. We find that 27 % of watersheds experiencing debris flow activity have a modeled permafrost area smaller than 5 % of total area. Around 7 % of the debris flow prone watersheds have an area larger than 5 %. Interestingly, our first results indicate that watersheds without permafrost experience significantly less, but more intense debris flow events than watersheds with modeled permafrost occurrence. Our study aims to contribute to a better understanding of geomorphic activity and the impact of climate change in alpine environments.

Landslides and Mudslides

MedlinePlus

... from landslides and debris flows In the United States, landslides and debris flows result in 25 to 50 deaths each year. ... and debris flows. Learn whether landslides or debris flows have ... department, state geological surveys or departments of natural resources, or ...

Application of geotechnical and geophysical field measurements in an active alpine environment

NASA Astrophysics Data System (ADS)

Lucas, D. R.; Fankhauser, K.; Springman, S. M.

2015-09-01

Rainfall can trigger landslides, rockfalls and debris flow events. When rainfall infiltrates into the soil, the suction (if there is any) is reduced, until positive water pressure can be developed, decreasing the effective stresses and leading to a potential failure. A challenging site for the study of mass movement is the Meretschibach catchment, a location in the Swiss Alps in the vicinity of Agarn, Canton of Valais. To study the effect of rainfall on slope stabilities, the soil characterization provides valuable insight on soil properties, necessary to establish a realistic ground model. This model, together with an effective long term-field monitoring, deliver the essential information and boundary conditions for predicting and validating rainfall- induced slope instabilities using numerical and physical modelling. Geotechnical monitoring, including soil temperature and volumetric water content measurements, has been performed on the study site together with geophysical measurements (ERT) to study the effect of rainfall on the (potential) triggering of landslides on a scree slope composed of a surficial layer of gravelly soil. These techniques were combined to provide information on the soil characteristics and depth to the bedrock. Seasonal changes of precipitation and temperature were reflected in corresponding trends in all measurements. A comparison of volumetric water content records was obtained from decagons, time domain reflectometry (TDR) and electrical resistivity tomography (ERT) conducted throughout the spring and summer months of 2014, yielding a reasonable agreement.

Sources of debris flow material in burned areas

USGS Publications Warehouse

Santi, P.M.; deWolfe, V.G.; Higgins, J.D.; Cannon, S.H.; Gartner, J.E.

2008-01-01

The vulnerability of recently burned areas to debris flows has been well established. Likewise, it has been shown that many, if not most, post-fire debris flows are initiated by runoff and erosion and grow in size through erosion and scour by the moving debris flow, as opposed to landslide-initiated flows with little growth. To better understand the development and character of these flows, a study has been completed encompassing 46 debris flows in California, Utah, and Colorado, in nine different recently burned areas. For each debris flow, progressive debris production was measured at intervals along the length of the channel, and from these measurements graphs were developed showing cumulative volume of debris as a function of channel length. All 46 debris flows showed significant bulking by scour and erosion, with average yield rates for each channel ranging from 0.3 to 9.9??m3 of debris produced for every meter of channel length, with an overall average value of 2.5??m3/m. Significant increases in yield rate partway down the channel were identified in 87% of the channels, with an average of a three-fold increase in yield rate. Yield rates for short reaches of channels (up to several hundred meters) ranged as high as 22.3??m3/m. Debris was contributed from side channels into the main channels for 54% of the flows, with an average of 23% of the total debris coming from those side channels. Rill erosion was identified for 30% of the flows, with rills contributing between 0.1 and 10.5% of the total debris, with an average of 3%. Debris was deposited as levees in 87% of the flows, with most of the deposition occurring in the lower part of the basin. A median value of 10% of the total debris flow was deposited as levees for these cases, with a range from near zero to nearly 100%. These results show that channel erosion and scour are the dominant sources of debris in burned areas, with yield rates increasing significantly partway down the channel. Side channels are much more important sources of debris than rills. Levees are very common, but the size and effect on the amount of debris that reaches a canyon mouth is highly variable. ?? 2007 Elsevier B.V. All rights reserved.

Prediction of the run out extents of the Slano Blato landslide for future debris flow events

NASA Astrophysics Data System (ADS)

Askarinejad, Amin; Leu, Pascal; Macek, Matej; Petkovsek, Ana; Springman, Sarah

2013-04-01

The Slano Blato landslide has a volume of about 1 mio m3 and is located in the western part of Slovenia. It has been considered to be a potential natural hazard for the village of Lokavec for more than 200 years. Several mud flows, exhibiting a range of volumes and velocities, have originated from the landslide body since the year 2000, when the landslide was reactivated due to an intense rainfall event. A series of obstacles, including safety dams and deposition ponds, have been constructed for the remediation of the landslide. These obstacles are designed to absorb and contain future debris flow hazard. A prerequisite to any risk analysis is to establish the vulnerability to the hazard event. The aim of this work is to simulate possible future debris flow scenarios in order to predict the run out distances, flow heights, impact pressures and potential effects on the downstream village buildings and infrastructure. The simulations were carried out using the RAMMS program (RApid Mass MovementS, www.ramms.slf.ch). A three dimensional terrain model of the landslide area and the downstream zones, with or without the inclusion of the obstacles, was made for the simulations and different scenarios concerning the released volume, the internal friction and viscosity of the sliding mass were studied. The results indicate that low viscosity mudflows with a volume of 5,000 m3 endanger some parts of Lokavec village. However, the simulations with volumes of 15,000 and 50,000 m3 predict catastrophic effects in terms of either impact pressures or deposition heights for the majority of houses. Moreover, the simulations confirmed that the choice of the material properties (internal friction and viscosity), the characteristics of the release hydrograph, event location, and natural or man-made obstacles play major roles in the run out distances and impact pressures.

Identification of debris-flow hazards in warm deserts through analyzing past occurrences: Case study in South Mountain, Sonoran Desert, USA

NASA Astrophysics Data System (ADS)

Dorn, Ronald I.

2016-11-01

After recognition that debris flows co-occur with human activities, the next step in a hazards analysis involves estimating debris-flow probability. Prior research published in this journal in 2010 used varnish microlamination (VML) dating to determine a minimum occurrence of 5 flows per century over the last 8100 years in a small mountain range of South Mountain adjacent to neighborhoods of Phoenix, Arizona. This analysis led to the conclusion that debris flows originating in small mountain ranges in arid regions like the Sonoran Desert could pose a hazard. Two major precipitation events in the summer of 2014 generated 35 debris flows in the same study area of South Mountain-providing support for the importance of probability analysis as a key step in a hazards analysis in warm desert settings. Two distinct mechanisms generated the 2014 debris flows: intense precipitation on steep slopes in the first storm; and a firehose effect whereby runoff from the second storm was funneled rapidly by cleaned-out debris-flow chutes to remobilize Pleistocene debris-flow deposits. When compared to a global database on debris flows, the 2014 storms were among the most intense to generate desert debris flows - indicating that storms of lesser intensity are capable of generating debris flows in warm desert settings. The 87Sr/86Sr analyses of fines and clasts in South Mountain debris flows of different ages reveal that desert dust supplies the fines. Thus, wetter climatic periods of intense rock decay are not needed to resupply desert slopes with fines; instead, a combination of dust deposition supplying fines and dirt cracking generating coarse clasts can re-arm chutes in a warm desert setting with abundant dust.

A hacker's guide to catching a debris flow: Lessons learned from four years of chasing mud in Colorado and southern California

NASA Astrophysics Data System (ADS)

Kean, J. W.; McCoy, S. W.; Staley, D. M.; Coe, J.; Leeper, R.; Tucker, G. E.

2012-12-01

Direct measurements of natural debris flows provide valuable insights into debris-flow processes and hazards. Yet debris flows are difficult to "catch" because they live in rugged terrain, appear infrequently, and have an appetite for destroying monitoring equipment. We present an overview of some successful (and failed) techniques we have used over the past four years to obtain direct measurements of 40+ debris flows in Colorado and southern California. Following the "MacGyver" theme of the session, we focus on the improvised equipment and methods we use in our hunt for quality data. These include an inexpensive erosion sensor to measure rates of debris-flow entrainment, a custom load cell enclosure for measuring debris-flow normal force, tracer rocks implanted with passive integrated transponders, basic pressure transducers to measure debris-flow timing, and standard digital cameras adapted to obtain high-resolution (1936 x 1288 pixels) video footage of debris flows. These techniques are also suitable for catching data on elusive flash floods. In addition, we also share some practical solutions to the logistical problems associated with installing monitoring equipment in rugged debris-flow terrain, such as suspension of non-contact stage gages high above channels.

Emergency Assessment of Postfire Debris-Flow Hazards for the 2009 Station Fire, San Gabriel Mountains, Southern California

USGS Publications Warehouse

Cannon, Susan H.; Gartner, Joseph E.; Rupert, Michael G.; Michael, John A.; Staley, Dennis M.; Worstell, Bruce B.

2009-01-01

This report presents an emergency assessment of potential debris-flow hazards from basins burned by the 2009 Station fire in Los Angeles County, southern California. Statistical-empirical models developed for postfire debris flows are used to estimate the probability and volume of debris-flow production from 678 drainage basins within the burned area and to generate maps of areas that may be inundated along the San Gabriel mountain front by the estimated volume of material. Debris-flow probabilities and volumes are estimated as combined functions of different measures of basin burned extent, gradient, and material properties in response to both a 3-hour-duration, 1-year-recurrence thunderstorm and to a 12-hour-duration, 2-year recurrence storm. Debris-flow inundation areas are mapped for scenarios where all sediment-retention basins are empty and where the basins are all completely full. This assessment provides critical information for issuing warnings, locating and designing mitigation measures, and planning evacuation timing and routes within the first two winters following the fire. Tributary basins that drain into Pacoima Canyon, Big Tujunga Canyon, Arroyo Seco, West Fork of the San Gabriel River, and Devils Canyon were identified as having probabilities of debris-flow occurrence greater than 80 percent, the potential to produce debris flows with volumes greater than 100,000 m3, and the highest Combined Relative Debris-Flow Hazard Ranking in response to both storms. The predicted high probability and large magnitude of the response to such short-recurrence storms indicates the potential for significant debris-flow impacts to any buildings, roads, bridges, culverts, and reservoirs located both within these drainages and downstream from the burned area. These areas will require appropriate debris-flow mitigation and warning efforts. Probabilities of debris-flow occurrence greater than 80 percent, debris-flow volumes between 10,000 and 100,000 m3, and high Combined Relative Debris-Flow Hazard Rankings were estimated in response to both short recurrence-interval (1- and 2-year) storms for all but the smallest basins along the San Gabriel mountain front between Big Tujunga Canyon and Arroyo Seco. The combination of high probabilities and large magnitudes determined for these basins indicates significant debris-flow hazards for neighborhoods along the mountain front. When the capacity of sediment-retention basins is exceeded, debris flows may be deposited in neighborhoods and streets and impact infrastructure between the mountain front and Foothill Boulevard. In addition, debris flows may be deposited in neighborhoods immediately below unprotected basins. Hazards to neighborhoods and structures at risk from these events will require appropriate debris-flow mitigation and warning efforts.

Numerical investigation of debris materials prior to debris flow hazards using satellite images

NASA Astrophysics Data System (ADS)

Zhang, N.; Matsushima, T.

2018-05-01

The volume of debris flows occurred in mountainous areas is mainly affected by the volume of debris materials deposited at the valley bottom. Quantitative evaluation of debris materials prior to debris flow hazards is important to predict and prevent hazards. At midnight on 7th August 2010, two catastrophic debris flows were triggered by the torrential rain from two valleys in the northern part of Zhouqu City, NW China, resulting in 1765 fatalities and huge economic losses. In the present study, a depth-integrated particle method is adopted to simulate the debris materials, based on 2.5 m resolution satellite images. In the simulation scheme, the materials are modeled as dry granular solids, and they travel down from the slopes and are deposited at the valley bottom. The spatial distributions of the debris materials are investigated in terms of location, volume and thickness. Simulation results show good agreement with post-disaster satellite images and field observation data. Additionally, the effect of the spatial distributions of the debris materials on subsequent debris flows is also evaluated. It is found that the spatial distributions of the debris materials strongly influence affected area, runout distance and flow discharge. This study might be useful in hazard assessments prior to debris flow hazards by investigating diverse scenarios in which the debris materials are unknown.

Debris dams and the relief of headwater streams.

Treesearch

S.T. Lancaster; G.E. Grant

2005-01-01

In forested, mountain landscapes where debris flows are common, valley-spanning debris dams formed by debris-flow deposition are a common feature of headwater valleys. In this paper, we examine how wood and boulder steps, i.e., debris dams, affect longitudinal profile relief and gradient at the debris-flow-fluvial transition in three sites in the Oregon Coast Range,...

Monitoring and modelling of landslide and debris flow impact on transport and building infrasructure in the Carpathians

NASA Astrophysics Data System (ADS)

Ivanik, Olena; Shevchuk, Viktor; Yahno, Evgen

2016-04-01

Mechanisms and factors of formation of landslide and debris flow processes are examined in terms of model objects in the Carpathians. The study area is within Eastern Carpathians and Transcarpathian depression (Tisa river basin). There were investigated more than 220 stabilized and active landslides. The analysis of water-gravitational processes in this region with complex heterogeneous geological structure confirmed the priority nature of occurrence of structural landslides in rheologically different geological environments, and made it possible to create a new classification of structural landslides and conditions of their formation with the decisive influence of destructive zones. This classification is the basis for constructing geological, physical and mathematical models of landslide slopes, and subsequent modeling of the landslide hazard based on the determination of the stress-strain state of slopes. Under the proposed mathematical model, the examined phenomenon is described as thermoelastic-plastic equilibrium of the isotropic matrix under effect of applied mass (gravitational field of the Earth) and surface efforts, inhomogeneous stationary temperature field. In addition, it is assumed that the Young modulus at each point of the matrix depends on the water saturation. Debris and mudflows in the Carpathians have a stage character, non-stationary and avalanche movements. The territory is prone to be affected by debris and mudflows, due to the geological, geomorphological and climatic conditions. Therefore the main conditions of the mudflow formation are as follows: the presence of the rock destruction products which could be a solid phase of debris mudflow; presence of the enough quantity of the rainfall runoff for the unconsolidated material removal; ruggedness of relief that provides simultaneous movement of the big values of the water-soil mass with the big velocities. The algorithm calculating the mudflow impact on infrastructure objects in Carpathians has been developed. It based on the empiric data and fundamental hydrodynamic lows, on formula Bernoulli in particular. Using this formula we obtain the expression for the impingement hydrodynamic pressure:

The hydrological response of a rocky head water basin to convective rainfalls

NASA Astrophysics Data System (ADS)

Gregoretti, Carlo; Bernard, Martino; Degetto, Massimo; Matteo, Berti; Alessandro, Simoni; Stefano, Lanzoni

2015-04-01

A sharp-crested weir is installed at the outlet (altitude 1770 m a.s.l) of a rocky channel incised on the walls of Dimai Peak in the area of Fiames (Cortina d'Ampezzo, Dolomites-North Eastern Italian Alps) at the purpose of measuring runoff discharges. The area of the headwater basin is just 0.032 km2 but sub-vertical cliffs are capable to generate notable discharge during severe rainstorms. Due to the severe environment only five runoff events were measured (two times the facility was destroyed by rock falls and avalanches; other times failure of sensors stopped the measurements). Hydrological response is characterized by peaked hydrographs with very high rising limb. A kinematic distributed hydrological model was used to simulate the response of the basin to the convective rainfalls with the help of two rain gauges placed upstream the basin head and downstream the outlet respectively. The hydrological model uses an hortonian simplified law for determining excess rainfall and satisfactorily simulates the measured hydrographs. Such measurements are important for the understanding the hydrological response of a rocky basin to a convective rainfall. Their modeling are important as well when focused on predicting both flash floods in mountain torrents and the triggering conditions and magnitude of runoff generated debris flows.

Holocene debris flows on the Colorado Plateau: The influence of clay mineralogy and chemistry

USGS Publications Warehouse

Webb, R.H.; Griffiths, P.G.; Rudd, L.P.

2008-01-01

Holocene debris flows do not occur uniformly on the Colorado Plateau province of North America. Debris flows occur in specific areas of the plateau, resulting in general from the combination of steep topography, intense convective precipitation, abundant poorly sorted material not stabilized by vegetation, and the exposure of certain fine-grained bedrock units in cliffs or in colluvium beneath those cliffs. In Grand and Cataract Canyons, fine-grained bedrock that produces debris flows contains primarily single-layer clays - notably illite and kaolinite - and has low multilayer clay content. This clay-mineral suite also occurs in the colluvium that produces debris flows as well as in debris-flow deposits, although unconsolidated deposits have less illite than the source bedrock. We investigate the relation between the clay mineralogy and major-cation chemistry of fine-grained bedrock units and the occurrence of debris flows on the entire Colorado Plateau. We determined that 85 mapped fine-grained bedrock units potentially could produce debris flows, and we analyzed clay mineralogy and major-cation concentration of 52 of the most widely distributed units, particularly those exposed in steep topography. Fine-grained bedrock units that produce debris flows contained an average of 71% kaolinite and illite and 5% montmorillonite and have a higher concentration of potassium and magnesium than nonproducing units, which have an average of 51% montmorillonite and a higher concentration of sodium. We used multivariate statistics to discriminate fine-grained bedrock units with the potential to produce debris flows, and we used digital-elevation models and mapped distribution of debris-flow producing units to derive a map that predicts potential occurrence of Holocene debris flows on the Colorado Plateau. ?? 2008 Geological Society of America.

Public perception and stakeholder involvement in the crisis management of sediment-related disasters and their mitigation: the case of the Stože debris flow in NW Slovenia.

PubMed

Mikoš, Matjaz

2011-04-01

Sediments can pose a threat to humans not only when these deposits are polluted but also due to their large quantities. This physical aspect of sediments as a risk will be shown on a case study of a sediment-related disaster that occurred in the mountainous part of Slovenia, Central Europe in 2000. In November 2000, after a long wet period a large debris landslide had been triggered on the Stože slope and stopped in the channel of the Mangart creek. Such an event took the majority of local inhabitants and emergency staff by surprise. Nevertheless, they had just organized the first mitigation measures when, after 35 hours, they were surprised by an even larger debrisflowinitiated as the second phase of the same mass movement event. Within a few minutes, the wet debris flow had devastated the alpine valley of the Koritnica River and killed 7 people in the village of Log pod Mangartom. This paper deals with crisis management and first mitigation measures under this very tense situation of searching for dead bodies. The uncertainty about possible new debris flows drove all inhabitants out of the village by a decision of the civil protection unit, and also other activities of the emergency relief units were overshadowed by the 7 victims. One of the main problems and challenges at the same time was the over 700,000 m³ of wet debris flow deposits in the area of the village of Log pod Mangartom within the Triglav National park, which posed a direct threat of flooding during the first heavy rainfalls in spring 2001, and which were about to be removed to make place for future debris flows. The understanding about what really happened or about the immediate triggering factors was different among the professionals in charge for relief action and for preparing a final remediation plan. The first phase during and immediately after the disaster (relief intervention of emergency units especially those for civil protection) can be described as Concern-Driven Crisis Management or as Judgment-Based Crisis Management, respectively. The Quantitative Risk Assessment came into play in the second remediation phase through special law enforcement. Even after 10 years since the disaster, general public perception speaks in favor of judgment-based risk management rather than quantitative risk assessment, a situation that can be explained by the poor understanding of the system by local inhabitants, by low public involvement in the preparation of the final remediation plan undertaken by the state agencies, and by the fact that the final remediation is still not finished. Copyright © 2010 SETAC.

Analysis of post-earthquake landslide activity and geo-environmental effects

NASA Astrophysics Data System (ADS)

Tang, Chenxiao; van Westen, Cees; Jetten, Victor

2014-05-01

Large earthquakes can cause huge losses to human society, due to ground shaking, fault rupture and due to the high density of co-seismic landslides that can be triggered in mountainous areas. In areas that have been affected by such large earthquakes, the threat of landslides continues also after the earthquake, as the co-seismic landslides may be reactivated by high intensity rainfall events. Earthquakes create Huge amount of landslide materials remain on the slopes, leading to a high frequency of landslides and debris flows after earthquakes which threaten lives and create great difficulties in post-seismic reconstruction in the earthquake-hit regions. Without critical information such as the frequency and magnitude of landslides after a major earthquake, reconstruction planning and hazard mitigation works appear to be difficult. The area hit by Mw 7.9 Wenchuan earthquake in 2008, Sichuan province, China, shows some typical examples of bad reconstruction planning due to lack of information: huge debris flows destroyed several re-constructed settlements. This research aim to analyze the decay in post-seismic landslide activity in areas that have been hit by a major earthquake. The areas hit by the 2008 Wenchuan earthquake will be taken a study area. The study will analyze the factors that control post-earthquake landslide activity through the quantification of the landslide volume changes well as through numerical simulation of their initiation process, to obtain a better understanding of the potential threat of post-earthquake landslide as a basis for mitigation planning. The research will make use of high-resolution stereo satellite images, UAV and Terrestrial Laser Scanning(TLS) to obtain multi-temporal DEM to monitor the change of loose sediments and post-seismic landslide activities. A debris flow initiation model that incorporates the volume of source materials, vegetation re-growth, and intensity-duration of the triggering precipitation, and that evaluates different initiation mechanisms such as erosion and landslide reactivation will be developed. The developed initiation model will be integrated with run-out model to simulate the dynamic process of post-earthquake debris flows in the study area for a future period and make a prediction about the decay of landslide activity in future.

Performance evaluation of the national early warning system for shallow landslides in Norway

NASA Astrophysics Data System (ADS)

Dahl, Mads-Peter; Piciullo, Luca; Devoli, Graziella; Colleuille, Hervé; Calvello, Michele

2017-04-01

As a consequence of the increased number of rainfall-and snowmelt-induced landslides (debris flows, debris slides, debris avalanches and slush flows) occurring in Norway, a national landslide early warning system (EWS) has been developed for monitoring and forecasting the hydro-meteorological conditions potentially necessary of triggering slope failures. The system, operational since 2013, is managed by the Norwegian Water Resources and Energy Directorate (NVE) and has been designed in cooperation with the Norwegian Public Road Administration (SVV), the Norwegian National Rail Administration (JBV) and the Norwegian Meteorological Institute (MET). Decision-making in the EWS is based upon hazard threshold levels, hydro-meteorological and real-time landslide observations as well as landslide inventory and susceptibility maps. Hazard threshold levels have been obtained through statistical analyses of historical landslides and modelled hydro-meteorological parameters. Daily hydro-meteorological conditions such as rainfall, snowmelt, runoff, soil saturation, groundwater level and frost depth have been derived from a distributed version of the hydrological HBV-model. Two different landslide susceptibility maps are used as supportive data in deciding daily warning levels. Daily alerts are issued throughout the country considering variable warning zones. Warnings are issued once per day for the following 3 days with an update possibility later during the day according to the information gathered by the monitoring variables. The performance of the EWS has been evaluated applying the EDuMaP method. In particular, the performance of warnings issued in Western Norway, in the period 2013-2014 has been evaluated using two different landslide datasets. The best performance is obtained for the smallest and more accurate dataset. Different performance results may be observed as a function of changing the landslide density criterion, Lden(k), (i.e., thresholds considered to differentiate among classes of landslide events) used as an input parameter within the EDuMaP method. To investigate this issue, a parametric analysis has been conducted; the results of the analysis show clear differences among computed performances when absolute or relative landslide density criteria are considered.

Application of Radar-Based Accumulated Rainfall Products for Early Detection of Heavy Rainfall Occurrence

NASA Astrophysics Data System (ADS)

Nishiyama, K.; Wakimizu, K.; Yokota, I.; Tsukahara, K.; Moriyama, T.

2016-12-01

In Japan, river and debris flow disasters have been frequently caused by heavy rainfall occurrence under the influence of the activity of a stationary front and associated inflow of a large amount of moisture into the front. However, it is very difficult to predict numerically-based heavy rainfall and associated landslide accurately. Therefore, the use of meteorological radar information is required for enhancing decision-making ability to urge the evacuation of local residents by local government staffs prior to the occurrence of the heavy rainfall disaster. It is also desirable that the local residents acquire the ability to determine the evacuation immediately after confirming radar information by themselves. Actually, it is difficult for untrained local residents and local government staffs to easily recognize where heavy rainfall occurs locally for a couple of hours. This reason is that the image of radar echoes is equivalent to instant electromagnetic distribution measured per a couple of minutes, and the distribution of the radar echoes moves together with the movement of a synoptic system. Therefore, in this study, considering that the movement of radar echoes also may stop in a specific area if stationary front system becomes dominant, radar-based accumulated rainfall information is defined here. The rainfall product is derived by the integration of radar intensity measured every ten minutes during previous 1 hours. Using this product, it was investigated whether and how the radar-based accumulated rainfall displayed at an interval of ten minutes can be applied for early detection of heavy rainfall occurrence. The results are summarized as follows. 1) Radar-based accumulated rainfall products could confirm that some of stationary heavy rainfall systems had already appeared prior to disaster occurrence, and clearly identify the movement of heavy rainfall area. 2) Moreover, accumulated area of rainfall could be visually and easily identified, compared with time-series (movie) of real-time radar-based rainfall intensity. Therefore, the accumulated rainfall distribution provides effective information for early detection of heavy rainfall causing disasters through the training of local residents and local government staffs who have no meteorologically-technical knowledge.

Assessing the debris flow run-out frequency of a catchment in the French Alps using a parameterization analysis with the RAMMS numerical run-out model

NASA Astrophysics Data System (ADS)

Hussin, H. Y.; Luna, B. Quan; van Westen, C. J.; Christen, M.; Malet, J.-P.; van Asch, Th. W. J.

2012-04-01

Debris flows occurring in the European Alps frequently cause significant damage to settlements, power-lines and transportation infrastructure which has led to traffic disruptions, economic loss and even death. Estimating the debris flow run-out extent and the parameter uncertainty related to run-out modeling are some of the difficulties found in the Quantitative Risk Assessment (QRA) of debris flows. Also, the process of the entrainment of material into a debris flow is until now not completely understood. Debris flows observed in the French Alps entrain 5 - 50 times the amount of volume compared to the initially mobilized source volume. In this study we analyze a debris flow that occurred in 2003 at the Faucon catchment in the Barcelonnette Basin (Southern French Alps). The analysis was carried out using the Voellmy rheology and an entrainment model imbedded in the RAMMS 2D numerical modeling software. The historic event was back calibrated based on source, entrainment and deposit volumes, including the run-out distance, velocities and deposit heights of the debris flow. This was then followed by a sensitivity analysis of the rheological and entrainment parameters to produce 120 debris flow scenarios leading to a frequency assessment of the run-out distance and deposit height at the debris fan. The study shows that the Voellmy frictional parameters mainly influence the run-out distance and velocity of the flow, while the entrainment parameter has a major impact on the debris flow height. The frequency assessment of the 120 simulated scenarios further gives an indication on the most likely debris flow run-out extents and heights for this catchment. Such an assessment can be an important link between the rheological model parameters and the spatial probability of the run-out for the Quantitative Risk Assessment (QRA) of debris flows.

Towards a Quasi-global precipitation-induced Landslide Detection System using Remote Sensing Information

NASA Astrophysics Data System (ADS)

Adler, B.; Hong, Y.; Huffman, G.; Negri, A.; Pando, M.

2006-05-01

Landslides and debris flows are one of the most widespread natural hazards on Earth, responsible for thousands of deaths and billions of dollars in property damage per year. Currently, no system exists at either a national or a global scale to monitor or detect rainfall conditions that may trigger landslides. In this study, global landslide susceptibility is mapped using USGS GTOPO30 Digital Elevation, hydrological derivatives (slopes and wetness index etc.) from HYDRO1k data, soil type information downscaled from Digital Soil Map of the World (Sand, Loam, Silt, or Clay etc.), and MODIS land cover/use classification data. These variables are then combined with empirical landslide inventory data, if available, to derive a global landslide susceptibility map at elemental resolution of 1 x 1 km. This map can then be overlain with the driving force, namely rainfall estimates from the TRMM-based Multiple-satellite Precipitation Analysis to identify when areas with significant landslide potential receive heavy rainfall. The relations between rainfall intensity and rainstorm duration are regionally specific and often take the form of a power-law relation. Several empirical landslide-triggering Rainfall Intensity-Duration thresholds are implemented regionally using the 8-year TRMM-based precipitation with or without the global landslide susceptibility map at continuous space and time domain. Finally, the effectiveness of this system is validated by studying several recent deadly landslide/mudslide events. This study aims to build up a prototype quasi-global potential landslide warning system. Spatially-distributed landslide susceptibility maps and regional empirical rainfall intensity-duration thresholds, in combination with real-time rainfall measurements from space and rainfall forecasts from models, will be the basis for this experimental system.

Entrainment of bed sediment by debris flows: results from large-scale experiments

USGS Publications Warehouse

Reid, Mark E.; Iverson, Richard M.; Logan, Matthew; LaHusen, Richard G.; Godt, Jonathan W.; Griswold, Julie P.

2011-01-01

When debris flows grow by entraining sediment, they can become especially hazardous owing to increased volume, speed, and runout. To investigate the entrainment process, we conducted eight largescale experiments in the USGS debris-flow flume. In each experiment, we released a 6 m3 water-saturated debris flow across a 47-m long, ~12-cm thick bed of partially saturated sediment lining the 31º flume. Prior to release, we used low-intensity overhead sprinkling and real-time monitoring to control the bed-sediment wetness. As each debris flow descended the flume, we measured the evolution of flow thickness, basal total normal stress, basal pore-fluid pressure, and sediment scour depth. When debris flows traveled over relatively dry sediment, net scour was minimal, but when debris flows traveled over wetter sediment (volumetric water content > 0.22), debris-flow volume grew rapidly and flow speed and runout were enhanced. Data from scour sensors showed that entrainment occurred by rapid (5-10 cm/s), progressive scour rather than by mass failure at depth. Overriding debris flows rapidly generated high basal pore-fluid pressures when they loaded and deformed bed sediment, and in wetter beds these pressures approached lithostatic levels. Reduction of intergranular friction within the bed sediment thereby enhanced scour efficiency, entrainment, and runout.

Landslide monitoring and early warning systems in Lower Austria - current situation and new developments

NASA Astrophysics Data System (ADS)

Thiebes, Benni; Glade, Thomas; Schweigl, Joachim; Jäger, Stefan; Canli, Ekrem

2014-05-01

Landslides represent significant hazards in the mountainous areas of Austria. The Regional Geological Surveys are responsible to inform and protect the population, and to mitigate damage to infrastructure. Efforts of the Regional Geological Survey of Lower Austria include detailed site investigations, the planning and installation of protective structures (e.g. rock fall nets) as well as preventive measures such as regional scale landslide susceptibility assessments. For potentially endangered areas, where protection works are not feasible or would simply be too costly, monitoring systems have been installed. However, these systems are dominantly not automatic and require regular field visits to take measurements. Therefore, it is difficult to establish any relation between initiating and controlling factors, thus to fully understand the underlying process mechanism which is essential for any early warning system. Consequently, the implementation of new state-of-the-art monitoring and early warning systems has been started. In this presentation, the design of four landslide monitoring and early warning systems is introduced. The investigated landslide process types include a deep-seated landslide, a rock fall site, a complex earth flow, and a debris flow catchment. The monitoring equipment was chosen depending on the landslide processes and their activity. It aims to allow for a detailed investigation of process mechanisms in relation to its triggers and for reliable prediction of future landslide activities. The deep-seated landslide will be investigated by manual and automatic inclinometers to get detailed insights into subsurface displacements. In addition, TDR sensors and a weather station will be employed to get a better understanding on the influence of rainfall on sub-surface hydrology. For the rockfall site, a wireless sensor network will be installed to get real-time information on acceleration and inclination of potentially unstable blocks. The movement of the earth flow site will be monitored by differential GPS to get high precision information on displacements of marked points. Photogrammtetry based on octocopter surveys will provide spatial information on movement patterns. A similar approach will be followed for the debris flow catchment. Here, the focus lies on a monitoring of the landslide failures in the source area which prepares the material for subsequent debris flow transport. In addition to the methods already mentioned, repeated terrestrial laserscanning campaigns will be used to monitor geomorphological changes at all sites. All important data, which can be single measurements, episodic or continuous monitoring data for a given point (e.g. rainfall, inclination) or of spatial character (e.g. LiDAR measurements), are collected and analysed on an external server. Automatic data analysis methods, such as progressive failure analysis, are carried out automatically based on field measurements. The data and results from all monitoring sites are visualised on a web-based platform which enables registered users to analyse the respective information in near-real-time. Moreover, thresholds can be determined which trigger automated warning messages to the involved scientists if thresholds are exceeded by field measurements. The described system will enable scientists and decision-makers to access the latest data from the monitoring systems. Automatic alarms are raised when thresholds are exceeded to inform them about potentially hazardous changes. Thereby, a more efficient hazard management and early warning can be achieved. Keywords: landslide, rockfall, debris flow, earth flow, monitoring, early warning system.

Effects of composition of grains of debris flow on its impact force

NASA Astrophysics Data System (ADS)

Tang, jinbo; Hu, Kaiheng; Cui, Peng

2017-04-01

Debris flows compose of solid material with broad size distribution from fine sand to boulders. Impact force imposed by debris flows is a very important issue for protection engineering design and strongly influenced by their grain composition. However, this issue has not been studied in depth and the effects of grain composition not been considered in the calculation of the impact force. In this present study, the small-scale flume experiments with five kinds of compositions of grains for debris flow were carried out to study the effect of the composition of grains of debris flow on its impact force. The results show that the impact force of debris flow increases with the grain size, the hydrodynamic pressure of debris flow is calibrated based on the normalization parameter dmax/d50, in which dmax is the maximum size and d50 is the median size. Furthermore, a log-logistic statistic distribution could be used to describe the distribution of magnitude of impact force of debris flow, where the mean and the variance of the present distribution increase with grain size. This distribution proposed in the present study could be used to the reliability analysis of structures impacted by debris flow.

Emergency assessment of post-fire debris-flow hazards for the 2013 Powerhouse fire, southern California

USGS Publications Warehouse

Staley, Dennis M.; Smoczyk, Gregory M.; Reeves, Ryan R.

2013-01-01

Wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce dangerous flash floods and debris flows. Existing empirical models were used to predict the probability and magnitude of debris-flow occurrence in response to a 10-year recurrence interval rainstorm for the 2013 Powerhouse fire near Lancaster, California. Overall, the models predict a relatively low probability for debris-flow occurrence in response to the design storm. However, volumetric predictions suggest that debris flows that occur may entrain a significant volume of material, with 44 of the 73 basins identified as having potential debris-flow volumes between 10,000 and 100,000 cubic meters. These results suggest that even though the likelihood of debris flow is relatively low, the consequences of post-fire debris-flow initiation within the burn area may be significant for downstream populations, infrastructure, and wildlife and water resources. Given these findings, we recommend that residents, emergency managers, and public works departments pay close attention to weather forecasts and National-Weather-Service-issued Debris Flow and Flash Flood Outlooks, Watches, and Warnings and that residents adhere to any evacuation orders.

Climatological and meteorological conditions associated with rain-induced periglacial debris flows in the Cascade Range, USA

NASA Astrophysics Data System (ADS)

Parker, L.; Nolin, A. W.

2009-04-01

Title: Climatological and meteorological conditions associated with rain-induced periglacial debris flows in the Cascade Range, USA Authors: L. Parker, A.W. Nolin Affiliation: Department of Geosciences, Oregon State University, Corvallis, Oregon, USA In November of 2006 an intense rainstorm of tropical origin, known colloquially as "Pineapple Express," inundated the Pacific Northwest region of the United States, initiating numerous periglacial debris flows on several of the stratovolcanoes in the Cascade Range of Oregon and Washington. Rain-induced periglacial debris flows are the result of the over-saturation and subsequent collapse of steep moraine in formerly glaciated valleys. These debris flows rapidly aggrade channels, deposit thick sediments in their path, and severely damage infrastructure. Here we focus on Mount Hood, Oregon and Mount Rainier, Washington in the investigation of meteorological and climatological conditions surrounding rain-induced periglacial debris flow events and their variability over time. Both anecdotal and observational evidence suggest that the Pineapple Express storms are a likely triggering mechanism for these rain-induced debris flows on the stratovolcanoes. Dates for the debris flow events for each mountain were linked with corresponding Pineapple Express storm events. Preliminary analysis suggests that one or more particular climatological or meteorological conditions may be central to the initiation of debris flows, though these conditions may not always be present during Pineapple Express storms. Antecedent snowpack conditions are also hypothesized to play an important role in periglacial rain-induced debris flow initiation as the presence of snow cover on the moraines and glaciers is thought to reduce the likelihood of a debris flow. Radiosonde and precipitation data from Salem, Oregon (KSLE) and Quillayute, Washington (KUIL) data are used to determine if freezing levels and precipitation amounts have changed over time for all documented Pineapple Express events. Particular focus is placed on those events associated with debris flows. Additionally, Snowpack Telemetry (SNOTEL) data are used to examine the antecedent snowpack conditions for each debris flow event. These results will ultimately be coupled with research concerning the geomorphological mechanisms behind debris flows on stratovolcanoes in the Cascades, and may lead to improved understanding and future projections concerning the timing, frequency and intensity of rain-induced periglacial debris flow events.

Mathematical modelling of the transport of a poorly sorted granular mixture as a debris-flow. The case of Madeira Island torrential floods in 2010

NASA Astrophysics Data System (ADS)

Ferreira, Rui M. L.; Oliveira, Rodrigo P.; Conde, Daniel

2016-04-01

On the 20th February 2010, heavy rainfall was registered at Madeira Island, North Atlantic. Stony debris flows, mudflows and mudslides ensued causing severe property loss, 1.5 m thick sediment deposits at downtown Funchal including 16th century monuments, and a death toll of 47 lives. Debris-flow fronts propagated downstream while carrying very high concentrations of solid material. These two-phase solid-fluid flows were responsible for most of the infrastructural damage across the island, due to their significantly increased mass and momentum. The objective of the present modelling work is to validate a 2DH model for torrential flows featuring the transport and interaction of several size fractions of a poorly-sorted granular mixture typical of stony debris flow in Madeira. The module for the transport of poorly-sorted material was included in STAV-2D (CERIS-IST), a shallow-water and morphology solver based on a finite-volume method using a flux-splitting technique featuring a reviewed Roe-Riemann solver, with appropriate source-term formulations to ensure full conservativeness. STAV-2D also includes formulations of flow resistance and bedload transport adequate for debris-flows with natural mobile beds (Ferreira et al., 2009) and has been validated with both theoretical solutions and laboratory data (Soares-Frazão et al., 2012; Canelas et al., 2013). The modelling of the existing natural and built environment is fully explicit. All buildings, streets and channels are accurately represented within the mesh geometry. Such detail is relevant for the reliability of the validation using field data, since the major sedimentary deposits within the urban meshwork of Funchal were identified and characterized in terms of volume and grain size distribution during the aftermath of the 20th February of 2010 event. Indeed, the measure of the quality of the numerical results is the agreement between simulated and estimated volume of deposited sediment and between estimated and modelled grain-size distribution of the deposits. The formulations expressing closures for size fraction interaction and active layer dynamics are discussed. The simulation tool resulting from this modelling effort is expected to help the establishment of new methodologies and parameters for hydraulic design and hazard assessment in the Island of Madeira. Acknowledgements This work was partially funded by FEDER, program COMPETE, and by national funds through Portuguese Foundation for Science and Technology (FCT) project RECI/ECM-HID/0371/2012. References Canelas, R.; Murillo, J. & Ferreira, R.M.L. (2013). Two-dimensional depth-averaged modelling of dambreak flows over mobile beds. Journal of Hydraulic Research, 51(4), 392-407. Ferreira, R. M. L., Franca, M. J., Leal, J. G., & Cardoso, A. H. (2009). Mathematical modelling of shallow flows: Closure models drawn from grain-scale mechanics of sediment transport and flow hydrodynamics. Canadian Journal of Civil Engineering, 36(10), 1605-1621. Soares-Frazão and IAHR Working group for Dam-break flows over mobile beds (2012) Dam-break flows over mobile beds: Experiments and benchmark tests for numerical models. Journal of Hydraulic Research, 50(4), 364-375. DOI: 10.1080/00221686.2012.689682

Evaluating tsunami hazards from debris flows

USGS Publications Warehouse

Watts, P.; Walder, J.S.; ,

2003-01-01

Debris flows that enter water bodies may have significant kinetic energy, some of which is transferred to water motion or waves that can impact shorelines and structures. The associated hazards depend on the location of the affected area relative to the point at which the debris flow enters the water. Three distinct regions (splash zone, near field, and far field) may be identified. Experiments demonstrate that characteristics of the near field water wave, which is the only coherent wave to emerge from the splash zone, depend primarily on debris flow volume, debris flow submerged time of motion, and water depth at the point where debris flow motion stops. Near field wave characteristics commonly may be used as & proxy source for computational tsunami propagation. This result is used to assess hazards associated with potential debris flows entering a reservoir in the northwestern USA. ?? 2003 Millpress,.

Debris flow occurrence and sediment persistence, Upper Colorado River Valley, CO

USGS Publications Warehouse

Grimsley, Kyle J; Rathburn, Sara L.; Friedman, Jonathan M.; Mangano, Joseph F.

2016-01-01

Debris flow magnitudes and frequencies are compared across the Upper Colorado River valley to assess influences on debris flow occurrence and to evaluate valley geometry effects on sediment persistence. Dendrochronology, field mapping, and aerial photographic analysis are used to evaluate whether a 19th century earthen, water-conveyance ditch has altered the regime of debris flow occurrence in the Colorado River headwaters. Identifying any shifts in disturbance processes or changes in magnitudes and frequencies of occurrence is fundamental to establishing the historical range of variability (HRV) at the site. We found no substantial difference in frequency of debris flows cataloged at eleven sites of deposition between the east (8) and west (11) sides of the Colorado River valley over the last century, but four of the five largest debris flows originated on the west side of the valley in association with the earthen ditch, while the fifth is on a steep hillslope of hydrothermally altered rock on the east side. These results suggest that the ditch has altered the regime of debris flow activity in the Colorado River headwaters as compared to HRV by increasing the frequency of debris flows large enough to reach the Colorado River valley. Valley confinement is a dominant control on response to debris flows, influencing volumes of aggradation and persistence of debris flow deposits. Large, frequent debris flows, exceeding HRV, create persistent effects due to valley geometry and geomorphic setting conducive to sediment storage that are easily delineated by valley confinement ratios which are useful to land managers.

Debris Flow Occurrence and Sediment Persistence, Upper Colorado River Valley, CO

NASA Astrophysics Data System (ADS)

Grimsley, K. J.; Rathburn, S. L.; Friedman, J. M.; Mangano, J. F.

2016-07-01

Debris flow magnitudes and frequencies are compared across the Upper Colorado River valley to assess influences on debris flow occurrence and to evaluate valley geometry effects on sediment persistence. Dendrochronology, field mapping, and aerial photographic analysis are used to evaluate whether a 19th century earthen, water-conveyance ditch has altered the regime of debris flow occurrence in the Colorado River headwaters. Identifying any shifts in disturbance processes or changes in magnitudes and frequencies of occurrence is fundamental to establishing the historical range of variability (HRV) at the site. We found no substantial difference in frequency of debris flows cataloged at eleven sites of deposition between the east (8) and west (11) sides of the Colorado River valley over the last century, but four of the five largest debris flows originated on the west side of the valley in association with the earthen ditch, while the fifth is on a steep hillslope of hydrothermally altered rock on the east side. These results suggest that the ditch has altered the regime of debris flow activity in the Colorado River headwaters as compared to HRV by increasing the frequency of debris flows large enough to reach the Colorado River valley. Valley confinement is a dominant control on response to debris flows, influencing volumes of aggradation and persistence of debris flow deposits. Large, frequent debris flows, exceeding HRV, create persistent effects due to valley geometry and geomorphic setting conducive to sediment storage that are easily delineated by valley confinement ratios which are useful to land managers.

Debris Flow Occurrence and Sediment Persistence, Upper Colorado River Valley, CO.

PubMed

Grimsley, K J; Rathburn, S L; Friedman, J M; Mangano, J F

2016-07-01

Debris flow magnitudes and frequencies are compared across the Upper Colorado River valley to assess influences on debris flow occurrence and to evaluate valley geometry effects on sediment persistence. Dendrochronology, field mapping, and aerial photographic analysis are used to evaluate whether a 19th century earthen, water-conveyance ditch has altered the regime of debris flow occurrence in the Colorado River headwaters. Identifying any shifts in disturbance processes or changes in magnitudes and frequencies of occurrence is fundamental to establishing the historical range of variability (HRV) at the site. We found no substantial difference in frequency of debris flows cataloged at eleven sites of deposition between the east (8) and west (11) sides of the Colorado River valley over the last century, but four of the five largest debris flows originated on the west side of the valley in association with the earthen ditch, while the fifth is on a steep hillslope of hydrothermally altered rock on the east side. These results suggest that the ditch has altered the regime of debris flow activity in the Colorado River headwaters as compared to HRV by increasing the frequency of debris flows large enough to reach the Colorado River valley. Valley confinement is a dominant control on response to debris flows, influencing volumes of aggradation and persistence of debris flow deposits. Large, frequent debris flows, exceeding HRV, create persistent effects due to valley geometry and geomorphic setting conducive to sediment storage that are easily delineated by valley confinement ratios which are useful to land managers.

Effect of excess pore pressure on the long runout of debris flows over low gradient channels: A case study of the Dongyuege debris flow in Nu River, China

NASA Astrophysics Data System (ADS)

Zhou, Zhen-Hua; Ren, Zhe; Wang, Kun; Yang, Kui; Tang, Yong-Jun; Tian, Lin; Xu, Ze-Min

2018-05-01

Debris flows with long reaches are one of the major natural hazards to human life and property on alluvial fans, as shown by the debris flow that occurred in the Dongyuege (DYG) Gully in August 18, 2010, and caused 96 deaths. The travel distance and the runout distance of the DYG large-scale tragic debris flow were 11 km and 9 km, respectively. In particular, the runout distance over the low gradient channel (channel slope < 5°) upstream of the depositional fan apex reached up to 3.3 km. The build-up and maintenance of excess pore pressure in the debris-flow mass might have played a crucial role in the persistence and long runout of the bouldery viscous debris flow. Experiments to measure pore pressure and pore water escape have been carried out by reconstituting the debris flow bodies with the DYG debris flow deposit. The slurrying of the debris is governed by solid volumetric concentration (SVC), and the difference between the lower SVC limit and the upper SVC limit can be defined as debris flow index (Id). Peak value (Kp) and rate of dissipation (R) of relative excess pore pressure are dependent on SVC. Further, the SVC that gives the lowest rate of dissipation is regarded as the optimum SVC (Cvo). The dissipation response of excess pore pressure can be characterized by the R value under Cvo at a given moment (i.e., 0.5 h, 1 h or 2 h later after peak time). The results reveal that a relatively high level of excess pore pressure developed within the DYG debris-flow mass and had a strong persistence capability. Further research shows that the development, peak value and dissipation of excess pore pressure in a mixture of sediment and water are related to the maximum grain size (MGS), gradation and mineralogy of clay-size particles of the sediment. The layer-lattice silicates in clay particles can be the typical clay minerals, including kaolinite, montmorillonite and illite, and also the unrepresentative clay minerals such as muscovite and chlorite. Moreover, small woody debris can also contribute to the slurrying of sediments and maintenance of debris flows in well vegetated mountainous areas and the boulders suspended in debris flows can elevate excess pore pressure and extend debris-flow mobility. The parameters, including Id, Kp, R and etc., are affected by the intrinsic properties of debris. They, therefore, can reflect the slurrying susceptibility of sediments, and can also be applied to the research on the occurrence mechanisms and risk assessment of other debris flows.

Identification of independent storm events: Seasonal and spatial variability of times between storms in Alpine area

NASA Astrophysics Data System (ADS)

Iadanzaa, Carla; Rianna, Maura; Orlando, Dario; Ubertini, Lucio; Napolitano, Francesco

2013-10-01

The aim of the paper is the identification of rain events that trigger landslides through the use of an exponential method to separate stochastic independent events. This activity is carried out within the definition of empirical rainfall thresholds for debris flows and shallow landslides. The study area is the Trento district, which is located in the northeast zone of an Alpine area. The work evaluates the factors that affect the variability in space and time of the critical duration of each rain gauge, defined as the minimum dry period duration that separates two rainy periods that are stochastically independent.

Experimental studies of deposition at a debris-flow flume

USGS Publications Warehouse

Major, Jon J.

1995-01-01

Geologists commonly infer the flow conditions and the physical properties of debris flows from the sedimentologic, stratigraphic, and morphologic characteristics of their deposits. However, such inferences commonly lack corroboration by direct observation because the capricious nature of debris flows makes systematic observation and measurement of natural events both difficult and dangerous. Furthermore, in contrast to the numerous experimental studies of water flow and related fluvial deposition, few real-time observations and measurements of sediment deposition by large-scale mass flow of debris under controlled conditions have been made. Recent experiments at the U.S. Geological Survey debris-flow flume in the H. J. Andrews Experimental Forest, Oregon (Iverson and others, 1992) are shedding new insight on sediment deposition by debris flows and on the veracity of methods commonly used to reconstruct flow character from deposit characteristics.

Response of steelhead/rainbow trout (Oncorhynchus mykiss) populations to debris flows

Treesearch

Jason L. White; Bret C. Harvey

2017-01-01

To better understand the effects of debris flows on salmonid populations, we studied juvenile steelhead/rainbow trout (Oncorhynchus mykiss) populations in six streams in the Klamath Mountains of northern California: three affected by debris flows on 01 January 1997 and three that experienced elevated streamflows but no debris flows. We surveyed...

Unsaturated flow processes in structurally-variable pathways in wildfire-affected soils and ash

NASA Astrophysics Data System (ADS)

Ebel, B. A.

2016-12-01

Prediction of flash flood and debris flow generation in wildfire-affected soils and ash hinges on understanding unsaturated flow processes. Water resources issues, such as groundwater recharge, also rely on our ability to quantify subsurface flow. Soil-hydraulic property data provide insight into unsaturated flow processes and timescales. A literature review and synthesis of existing data from the literature for wildfire-affected soils, including ash and unburned soils, facilitated calculating metrics and timescales of hydrologic response related to infiltration and surface runoff generation. Sorptivity (S) and the Green-Ampt wetting front parameter (Ψf) were significantly lower in burned soils compared to unburned soils, while field-saturated hydraulic conductivity (Kfs) was not significantly different. The magnitude and duration of the influence of capillarity was substantially reduced in burned soils, leading to faster ponding times in response to rainfall. Ash had large values of S and Kfs compared to unburned and burned soils but intermediate values of Ψf, suggesting that ash has long ponding times in response to rainfall. The ratio of S2/Kfs was nearly constant ( 100 mm) for unburned soils, but was more variable in burned soils. Post-wildfire changes in this ratio suggested that unburned soils had a balance between gravity and capillarity contributions to infiltration, which may depend on soil organic matter, while burning shifted infiltration more towards gravity contributions by reducing S. Taken together, the changes in post-wildfire soil-hydraulic properties increased the propensity for surface runoff generation and may have enhanced subsurface preferential flow through pathways altered by wildfire.

The physics of debris flows

NASA Astrophysics Data System (ADS)

Iverson, Richard M.

1997-08-01

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ˜10 m³ of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

The physics of debris flows

USGS Publications Warehouse

Iverson, R.M.

1997-01-01

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ???10 m3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

Emergency assessment of post-fire debris-flow hazards for the 2013 Springs Fire, Ventura County, California

USGS Publications Warehouse

Staley, Dennis M.

2014-01-01

Wildfire can significantly alter the hydrologic response of a watershed to the extent that even modest rainstorms can produce dangerous flash floods and debris flows. In this report, empirical models are used to predict the probability and magnitude of debris-flow occurrence in response to a 10-year rainstorm for the 2013 Springs fire in Ventura County, California. Overall, the models predict a relatively high probability (60–80 percent) of debris flow for 9 of the 99 drainage basins in the burn area in response to a 10-year recurrence interval design storm. Predictions of debris-flow volume suggest that debris flows may entrain a significant volume of material, with 28 of the 99 basins identified as having potential debris-flow volumes greater than 10,000 cubic meters. These results of the relative combined hazard analysis suggest there is a moderate likelihood of significant debris-flow hazard within and downstream of the burn area for nearby populations, infrastructure, wildlife, and water resources. Given these findings, we recommend that residents, emergency managers, and public works departments pay close attention to weather forecasts and National Weather Service-issued Debris Flow and Flash Flood Outlooks, Watches, and Warnings, and that residents adhere to any evacuation orders.

Resistance formulas in hydraulics-based models for routing debris flows

USGS Publications Warehouse

Chen, Cheng-lung; Ling, Chi-Hai

1997-01-01

The one-dimensional, cross-section-averaged flow equations formulated for routing debris flows down a narrow valley are identical to those for clear-water flow, except for the differences in the values of the flow parameters, such as the momentum (or energy) correction factor, resistance coefficient, and friction slope. Though these flow parameters for debris flow in channels with cross-sections of arbitrary geometric shape can only be determined empirically, the theoretical values of such parameters for debris flow in wide channels exist. This paper aims to derive the theoretical resistance coefficient and friction slope for debris flow in wide channels using a rheological model for highly-concentrated, rapidly-sheared granular flows, such as the generalized viscoplastic fluid (GVF) model. Formulating such resistance coefficient or friction slope is equivalent to developing a generally applicable resistance formula for routing debris flows. Inclusion of a nonuniform term in the expression of the resistance formula proves useful in removing the customary assumption that the spatially varied resistance at any section is equal to what would take place with the same rate of flow passing the same section under conditions of uniformity. This in effect implies an improvement in the accuracy of unsteady debris-flow computation.

Numerical modelling study of gully recharge and debris flows in Haida Gwaii, British Columbia

NASA Astrophysics Data System (ADS)

Martin, Yvonne; Johnson, Edward; Chaikina, Olga

2015-04-01

In high mountains, debris flows are a major process responsible for transferring sediment to more downstream fluvial reaches. This sediment transfer begins on mountain hillslopes where various mass wasting processes move sediment from hillslopes to uppermost reaches of the channel system (these reaches are herein referred to as gullies and only experience water flow during high intensity precipitation events). Sediment recharge into gullies, which has received minimal attention in the scientific literature, refers to the transfer of sediment and other debris from surrounding hillslopes into gullies (Jakob and Oden, 2005). Debris flow occurrence and debris flow volumes depend on some precipitation threshold as well as volumes of material contained in the particular gully. For example, if one debris flow has removed all of the accumulated material from the gully, then any subsequent debris flow will be smaller if enough time has not yet passed for notable sediment recharge. Herein, we utilize the numerical model of landscape development, LandMod (Martin, 1998; Dadson and Church, 2005; Martin, 2007), to explore connections between hillslope processes, gully recharge rates, and transfer of sediment to downstream channel reaches in the Haida Gwaii, British Columbia. Hillslope processes in the model include shallow landsliding, bedrock failures and weathering. The updated debris flow algorithm is based on extensive field data available for debris flows in Haida Gwaii (e.g., Rood, 1984; Oden, 1994; Jakob and Oden, 2005), as well as theoretical considerations based on debris flow studies. The most significant model extension is the calculation of gully recharge rates; for each gully, the total accumulated sediment in gullies at each time step is determined using a power-law relation for area-normalized recharge rate versus elapsed time since the last debris flow. Thus, when the stochastic driver for debris flow occurrence triggers an event, the amount of stored material is known and can be transferred and deposited along the channel system. Results show that the size distribution of debris flows and sediment transfers from gullies to downstream reaches are modified by the inclusion of a module that accounts for sediment recharge when compared to model runs that do not consider gully recharge.

The morphometric and stratigraphic framework for estimates of debris flow incidence in the North Cascades foothills, Washington State, USA

NASA Astrophysics Data System (ADS)

Kovanen, Dori J.; Slaymaker, Olav

2008-07-01

Active debris flow fans in the North Cascade Foothills of Washington State constitute a natural hazard of importance to land managers, private property owners and personal security. In the absence of measurements of the sediment fluxes involved in debris flow events, a morphological-evolutionary systems approach, emphasizing stratigraphy, dating, fan morphology and debris flow basin morphometry, was used. Using the stratigraphic framework and 47 radiocarbon dates, frequency of occurrence and relative magnitudes of debris flow events have been estimated for three spatial scales of debris flow systems: the within-fan site scale (84 observations); the fan meso-scale (six observations) and the lumped fan, regional or macro-scale (one fan average and adjacent lake sediments). In order to characterize the morphometric framework, plots of basin area v. fan area, basin area v. fan gradient and the Melton ruggedness number v. fan gradient for the 12 debris flow basins were compared with those documented for semi-arid and paraglacial fans. Basin area to fan area ratios were generally consistent with the estimated level of debris flow activity during the Holocene as reported below. Terrain analysis of three of the most active debris flow basins revealed the variety of modes of slope failure and sediment production in the region. Micro-scale debris flow event systems indicated a range of recurrence intervals for large debris flows from 106-3645 years. The spatial variation of these rates across the fans was generally consistent with previously mapped hazard zones. At the fan meso-scale, the range of recurrence intervals for large debris flows was 273-1566 years and at the regional scale, the estimated recurrence interval of large debris flows was 874 years (with undetermined error bands) during the past 7290 years. Dated lake sediments from the adjacent Lake Whatcom gave recurrence intervals for large sediment producing events ranging from 481-557 years over the past 3900 years and clearly discernible sedimentation events in the lacustrine sediments had a recurrence interval of 67-78 years over that same period.

Sedimentology, Behavior, and Hazards of Debris Flows at Mount Rainier, Washington

USGS Publications Warehouse

Scott, K.M.; Vallance, J.W.; Pringle, P.T.

1995-01-01

Mount Rainier is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle. Many debris flows and their distal phases have inundated areas far from the volcano during postglacial time. Two types of debris flows, cohesive and noncohesive, have radically different origins and behavior that relate empirically to clay content. The two types are the major subpopulations of debris flows at Mount Rainier. The behavior of cohesive flows is affected by the cohesion and adhesion of particles; noncohesive flows are dominated by particle collisions to the extent that particle cataclasis becomes common during near-boundary shear. Cohesive debris flows contain more than 3 to 5 percent of clay-size sediment. The composition of these flows changed little as they traveled more than 100 kilometers from Mount Rainier to inundate parts of the now-populated Puget Sound lowland. They originate as deep-seated failures of sectors of the volcanic edifice, and such failures are sufficiently frequent that they are the major destructional process of Mount Rainier's morphologic evolution. In several deposits of large cohesive flows, a lateral, megaclast-bearing facies (with a mounded or hummocky surface) contrasts with a more clay-rich facies in the center of valleys and downstream. Cohesive flows at Mount Rainier do not correlate strongly with volcanic activity and thus can recur without warning, possibly triggered by non-magmatic earthquakes or by changes in the hydrothermal system. Noncohesive debris flows contain less than 3 to 5 percent clay-size sediment. They form most commonly by bulking of sediment in water surges, but some originate directly or indirectly from shallow slope failures that do not penetrate the hydrothermally altered core of the volcano. In contrast with cohesive flows, most noncohesive flows transform both from and to other flow types and are, therefore, the middle segments of flow waves that begin and end as flood surges. Proximally, through the bulking of poorly sorted volcaniclastic debris on the flanks of the volcano, flow waves expand rapidly in volume by transforming from water surges through hyperconcentrated stream flow (20 to 60 percent sediment by volume) to debris flow. Distally, the transformations occur more slowly in reverse order - from debris flow, to hyperconcentrated flow, and finally to normal streamflow with less than 20 percent sediment by volume. During runout of the largest noncohesive flows, hyperconcentrated flow has continued for as much as 40 to 70 kilometers. Lahars (volcanic debris flows and their deposits) have occurred frequently at Mount Rainier over the past several thousand years, and generally they have not clustered within discrete eruptive periods as at Mount St. Helens. An exception is a period of large noncohesive flows during and after construction of the modern summit cone. Deposits from lahar-runout flows, the hyperconcentrated distal phases of lahars, document the frequency and extent of noncohesive lahars. These deposits also record the following transformations of debris flows: (1) the direct, progressive dilution of debris flow to hyperconcentrated flow, (2) deposition of successively finer grained lobes of debris until only the hyperconcentrated tail of the flow remains to continue downstream, and (3) dewatering of coarse debris flow deposits to yield fine-grained debris flow or hyperconcentrated flow. Three planning or design case histories represent different lengths of postglacial time. Case I is representative of large, infrequent (500 to 1,000 years on average) cohesive debris flows. These flows need to be considered in long-term planning in valleys around the volcano. Case II generalizes the noncohesive debris flows of intermediate size and recurrence (100 to 500 years). This case is appropriate for consideration in some structural design. Case III flows are

Headwater sediment dynamics in a debris flow catchment constrained by high-resolution topographic surveys

NASA Astrophysics Data System (ADS)

Loye, Alexandre; Jaboyedoff, Michel; Theule, Joshua Isaac; Liébault, Frédéric

2016-06-01

Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter-early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope-channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.

Hydraulic modeling of unsteady debris-flow surges with solid-fluid interactions

USGS Publications Warehouse

Iverson, Richard M.

1997-01-01

Interactions of solid and fluid constituents produce the unique style of motion that typifies debris flows. To simulate this motion, a new hydraulic model represents debris flows as deforming masses of granular solids variably liquefied by viscous pore fluid. The momentum equation of the model describes how internal and boundary forces change as coarse-grained surge heads dominated by grain-contact friction grade into muddy debris-flow bodies more strongly influenced by fluid viscosity and pressure. Scaling analysis reveals that pore-pressure variations can cause flow resistance in surge heads to surpass that in debris-flow bodies by orders of magnitude. Numerical solutions of the coupled momentum and continuity equations provide good predictions of unsteady, nonuniform motion of experimental debris flows from initiation through deposition.

Modeling sediment concentration in debris flow by Tsallis entropy

NASA Astrophysics Data System (ADS)

Singh, Vijay P.; Cui, Huijuan

2015-02-01

Debris flow is a natural hazard that occurs in landscapes having high slopes, such as mountainous areas. It can be so powerful that it destroys whatever comes in its way, that is, it can kill people and animals; decimate roads, bridges, railway tracks, homes and other property; and fill reservoirs. Owing to its frequent occurrence, it is receiving considerable attention these days. Of fundamental importance in debris flow modeling is the determination of concentration of debris (or sediment) in the flow. The usual approach to determining debris flow concentration is either empirical or hydraulic. Both approaches are deterministic and therefore say nothing about the uncertainty associated with the sediment concentration in the flow. This paper proposes to model debris flow concentration using the Tsallis entropy theory. Verification of the entropy-based distribution of debris flow concentration using the data and equations reported in the literature shows that the Tsallis entropy-proposed model is capable of mimicking the field observed concentration and has potential for practical application.

Landslide monitoring in the Atlantic Highlands area, New Jersey

USGS Publications Warehouse

Reilly, Pamela A.; Ashland, Francis X.; Fiore, Alex R.

2017-08-25

Shallow and deep-seated landslides have occurred episodically on the steep coastal bluffs of the Atlantic Highlands area (Boroughs of Atlantic Highlands and Highlands) in New Jersey. The oldest documented deep-seated landslide occurred in April 1782 and significantly changed the morphology of the bluff. However, recent landslides have been mostly shallow in nature and have occurred during large storms with exceptionally heavy rainfall. These shallow landslides have resulted in considerable damage to residential property and local infrastructure and threatened human safety.The recent shallow landslides in the area (locations modified from New Jersey Department of Environmental Protection) consist primarily of slumps and flows of earth and debris within areas of historical landslides or on slopes modified by human activities. Such landslides are typically triggered by increases in shallow soil moisture and pore-water pressure caused by sustained and intense rainfall associated with spring nor’easters and late summer–fall tropical cyclones. However, the critical relation between rainfall, soil-moisture conditions, and landslide movement has not been fully defined. The U.S. Geological Survey is currently monitoring hillslopes within the Atlantic Highlands area to better understand the hydrologic and meteorological conditions associated with shallow landslide initiation.

Hyper-dry conditions provide new insights into the cause of extreme floods after wildfire

USGS Publications Warehouse

Moody, John A.; Ebel, Brian A.

2012-01-01

A catastrophic wildfire in the foothills of the Rocky Mountains near Boulder, Colorado provided a unique opportunity to investigate soil conditions immediately after a wildfire and before alteration by rainfall. Measurements of near-surface (θ; and matric suction, ψ), rainfall, and wind velocity were started 8 days after the wildfire began. These measurements established that hyper-dryconditions (θ 3 cm-3; ψ > ~ 3 x 105 cm) existed and provided an in-situ retention curve for these conditions. These conditions exacerbate the effects of water repellency (natural and fire-induced) and limit the effectiveness of capillarity and gravity driven infiltration into fire-affected soils. The important consequence is that given hyper-dryconditions, the critical rewetting process before the first rain is restricted to the diffusion–adsorption of water-vapor. This process typically has a time scale of days to weeks (especially when the hydrologic effects of the ash layer are included) that is longer than the typical time scale (minutes to hours) of some rainstorms, such that under hyper-dryconditions essentially no rain infiltrates. The existence of hyper-dryconditions provides insight into why, frequently during the first rain storm after a wildfire, nearly all rainfall becomes runoff causing extremefloods and debris flows.

Topographic changes and their driving factors after 2008 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Li, Congrong; Wang, Ming; Liu, Kai; Xie, Jun

2018-06-01

The 2008 Wenchuan Earthquake caused topographic change in the stricken areas because of the occurrence of numerous coseismic landslides. The emergence of new landslides and debris flows and movement of loose materials under the driving force of high rainfall could further shape the local topography. Currently, little attention has been paid to continuously monitoring and assessing topographic changes after the major earthquake. In this research, we obtained an elevation dataset (2002, 2010, 2013 and 2015) based on digital elevation model (DEM) data and a DEM extracted from ZY-3 stereo paired images with validation by field measurement. We quantitatively assessed elevation changes in different years and qualitatively analyzed spatiotemporal variation of the terrain and mass movement across the study area. The results show that the earthquake affected area experienced substantial elevation changes caused by seismic forces and subsequent rainfalls. High rainfall after the earthquake have become the biggest driver of elevation reduction, which overwhelmed elevation increase caused by the major earthquake. Increased post-earthquake erosion intensity has caused large amounts of loose materials to accumulate in river channels, and gullies and on upper-middle mountain slopes, which increases the risk of flooding and geo-hazards in the area.

A database on flood and debris-flow processes in alluvial fans: a preliminary analysis aimed at evaluation of the damage

NASA Astrophysics Data System (ADS)

Vennari, Carmela; Santangelo, Nicoletta; Santo, Antonio; Parise, Mario

2015-04-01

Debris-flow and flood events cause yearly wide damages to buildings and infrastructures, and produce many casualties and fatalities. These processes are very common in Italy, affecting mainly torrential stream basins with different geological and morphological settings: in the Alpine mountain areas they are quite well analysed, whilst much less attention is generally paid in contexts such as those of the Apennines mostly due to the minor frequency of the events. Nevertheless, debris-flows and flood processes occur along many alluvial fans, have greatly contributed to their building up, and are therefore worth to be studied. Along many areas of the Southern Apennines, coalescent alluvial fans are a widespread geomorphic unit, typically located at the foot of steep slopes. In most cases these areas correspond to the more highly urbanised sectors, generally considered to be safer than the bottom valley, as concerns the direct effects from flooding. During intense storms, villages and towns built on alluvial fans may be affected by flooding and/or debris flow processes originated in the above catchment, and rapidly transferred downslope due to the steep slopes and the torrential character of the streams. This creates a very high hazard to the population and is at the origin of the severe and recurrent damage to urban settlements. Starting from the above considerations, we compiled a catalogue of flood and debris-flow events occurred in Campania Region, southern Italy, by consulting very different information sources: national and local newspapers and journals, regional historical archives, scientific literature, internet blogs. More than 350 events, occurred in Campania from 1700 to present, were collected. Information on time of occurrence and location are available for each event, with different level of accuracy, that is typically lower going back to the oldest events for which only the year or the month of occurrence of the event was identified; nevertheless, for more than 75 % of the collected data, the complete date of occurrence is known. All the provinces of Campania are affected by debris-flow and flood processes, but the most interested appear to be Naples and Salerno. Debris flows and flood produced in the Region more than 2400 fatalities, about 200 injured people, and about 100 missing people, with more than 6000 homeless. Very harmful were the events occurred in 1581, 1841, 1910,1924, 1954, 1998; each of these caused more than 100 fatalities. With regard to homeless, the most damaging event took place in the area of Salerno, causing more than 5000 homeless. Buildings and infrastructures were also involved by the events dealt with here. A third of the processes included in the catalogue caused the total destruction of private buildings, and serious damage to communication routes (roads and railways), pipelines, factories and architectonical structures. The most disastrous season, as concerns the damage to infrastructures and humans, is the autumn. The catalogue is still in progress, being continually updated for new events, but, at the same time, continuing to perform archive and literature scrutiny as regards the past events. Further, another important part of the research is the investigation of the link with the triggering events (rainfall): at this aim, daily (or hourly, when available) pluviometric data are being analysed. Our final goal is to provide a method to estimate hazard assessment in alluvial basins torrents, that might be exportable in similar geological-geomorphological contexts. In such an effort, the first and mandatory step is the collection of historical data.

Geomorphological characteristics of increased landslide activity in the Gudbrandsdalen valley, Norway

NASA Astrophysics Data System (ADS)

Heyerdahl, Håkon; Høydal, Øyvind

2016-04-01

The Gudbrandsdalen valley in Eastern Norway lies in a region where annual precipitation is generally low (down to 300 mm/year). The landslide activity has consequently historically been low, although the lower part of the valley sides generally is draped with thick layers of Quaternary deposits, primarily of glacial or glaciofluvial origin. The perception of natural hazards in the valley was previously primarily connected to flooding in the main river in the valley bottom during early summer, due to large discharges resulting from snowmelt in the mountainous regions west and east of the valley. However, several high-intensity events have changed the image of the region. Starting with a localized, but intense, landslide event in the Northern part of the valley in year 2008, two larger events covering almost the entire valley occurred in the years 2011 and 2013. A high number of landslides was triggered in all these events, including many flash floods and debris flows/debris slides in small and steep tributary rivers along the valley slopes. Landslide triggering covers different release mechanisms: In 2008, landslides were triggered without precipitation in not-frozen soil deposits without snow cover in the lower part of the valley. Groundwater flow through the permeable bedrock ("Otta schist") resulting from snow-melt in the elevated mountainous areas caused landslide triggering due to positive pore-water pressures forming at the bedrock surface below soil deposits, or at depressions in the terrain. Subsequent rainfall resulted in even more landslides being released. In later events (years 2011 and 2013) many landslides were caused by surface water taking new paths downslope, often due to man-made changes in existing waterways (typically poorly planned drainage solutions or new roads). Relatively small discharges in slopes with unconsolidated and easily erodible glacial deposits (typically lateral moraine) in many cases lead to small initial slides that down-slope developed into large erosional debris slides/floods of considerable size. Also along existing tributary rivers, the intense rainfall events resulted in flash-floods with heavy erosion and entrainment of deposits from the riverbed, including massive transport of trees. Also on open slopes a number of landslides were observed, assumedly triggered primarily by direct infiltration of rainfall, and possibly assisted by groundwater flow in underlying bedrock. Considerable damage to infrastructure and also dwellings has resulted from the events. A new approach has proved necessary to capture the risk elements connect to landslide and flood for this valley region when it comes to planning purposes. Among others, there is a need to consider the potential damage resulting from under-dimensioned culverts leading to complete failure of railroad or road embankments). Work is underway in order to improve the understanding of release mechanisms for typical landslides in the valley, which also will be highly relevant for other areas in Norway were similar natural hazards are encountered, and where climatic change may change the regional landslide activity.

Debris flows of the mountain massif of Hjorthfjellet and Adventtoppen, Svalbard: Implications for gullies on mountains in the Argyre basin, Mars

NASA Astrophysics Data System (ADS)

Reiss, D.; Hiesinger, H.; Zanetti, M.; Hauber, E.; Johnsson, A.; Carlsson, E.; Raack, J.; Olvmo, M.; Johansson, H. A. B.; Johansson, L.; Fredriksson, S.; Schmidt, H. T.; McDaniel, S.; Heldmann, J. L.; McKay, C. P.

2008-09-01

Martian gullies resemble terrestrial features formed by mass-wasting processes of a flowing mixture of clastic debris and water (debris flows). Their existence on Mars is interpreted to indicate liquid water in the recent past because of their pristine appearance, their stratigraphic relationships to young surface features, their lack of superimposed impact craters, and their distinct albedo relative to the surroundings, indicating limited dust cover [1]. The global distribution of gullies is limited to midand high-latitudes poleward of 30° in both hemispheres, with the highest frequency in the 30°- 50° latitude bands [1, 2]. Gullies occur preferentially on poleward-facing slopes [1, 2, 3, 4]. The most likely and physically most plausible medium to explain the gully morphology is liquid water [e.g., 1, 5]. Two main theories exist for the water source. One holds that water was released from the subsurface [1]. The other proposes that water is deposited as nearsurface ice or snow from the atmosphere and is subsequently melted by insolation [6, 7]. Debris flows found in Arctic climates on Earth could be an equitable analog for the Martian gullies. A comparative analysis might help to understand their formation mechanisms and the latitude-dependent, but clustered distribution as well as their specific orientations. The comparative analysis in the Arctic environment of Svalbard will be carried out in July/August of 2008. First results of the analog study of gullies will be presented at the conference. Debris flows on Svalbard Svalbard is located at 76°-81°N and 10°-35°E (Fig. 1), in the discontinuous zone of permafrost. Because the landscape of Svalbard is under the influence of the polar desert climate, it is a good analog for comparative Martian studies. These were performed in the last two years in the valley of Longyearbyen and on costal slopes of Isfjorden [8]. This study is complementary to the one described by Carlsson et al., 2008, this issue). Here we will focus on the regional distribution of gullies on the Hjorthfjellet and Adventtoppen mountain massif (Fig. 1, inset and Fig. 2), and detailed local studies of individual gullies on the same mountain massif are carried out as described by [8] and [9]. The Hjorthfjellet and Adventtoppen mountain massif consists of four stratigraphic units of sandstone and shales from the Tertiary and Mesozoic [10]. Several studies concerning talus slopes and debris flows on Svalbard have been performed in the last decades [e.g., 11, 12, 13, 14]. Regional studies of [14] using airborne imagery revealed that there are differences in the frequency and activity of debris flows on Svalbard between east- and west-facing slopes. Åkerman [14] suggested that differences in the solar radiation, the depth of the active layer and the amount of precipitation cause variances in the morphology and morphometry of the debris slopes as well as variances in the frequency and age of debris flows between east- and west-facing slopes. Studies and direct observations imply that debris flows on Svalbard are triggered by high intensity rainfall [e.g., 14, 15]. Gullies on mountains in Argyre basin, Mars For a comparative study on Mars we chose the Argyre region. Several isolated mountain massifs occur in the Nereidum and Charitum Montes (Fig. 3) with similar morphologies as the studied massif in Svalbard. A first data analysis with High Resolution Stereo Camera (HRSC) data revealed that gullies occur on the mountain slopes only at specific orientations. Fig. 4 shows an example of an isolated mountain, on which gullies only occur on west-facing slopes. Project Description The formation of gullies on Earth depends on several parameters, including rainfall and/or melting of snow, the presence of steep slopes, and sufficient amounts of fines/debris [e.g., 16]. As on Earth, the differences of slope angles and variabilities in bedrock and grain sizes influence the regional occurrence of gullies [17]. The main goals in both study regions on Earth and Mars are to classify different gully morphologies, map their distribution and orientations, gather information about bedrock, grain sizes and slopes and assess how all these parameters might influence the different gully morphologies, orientations, geological settings and their frequency. Airborne imagery from 1999 and a new, planned campaign in 2008 will be used to track the recent activity of debris flows in the last decade. In addition, a planned flight campaign with the High Resolution Stereo Camera (HRSC-AX) at the same time as the field trip might acquire high resolution image (10 cm/pxl) and topographic data (25 cm/pxl), if weather conditions are good. References [1] Malin, M.C. and Edgett K. S. (2000) Science, 288, 2330-2335. [2] Balme, M. et al. (2006) J. Geophys. Res. 111, E05001, doi:10.1029/2005JE002607. [3] Dickson, J.L. (2007) Icarus 188, 315-323. [4] Heldmann, J.L. and Mellon, M.T. (2004) Icarus, 168, 285-304. [5] Stewart, S.T. and Nimmo, F. (2002) J. Geophys. Res. 107, 5069, doi:10.1029/2000JE001465. [6] Costard, F. et al. (2002) Science 295, 110-113. [7] Christensen, P.R. (2003) Nature 422, 45-48. [8] Carlsson, E. et al. (2008) LPSC XXXIX, abstract 1852. [9] Carlsson, E. et al. (2008), this issue. [10] Dallmann et al. (2002) Norsk Polarinstitutt Temakart No. 33. [11] Rapp, A. (1957) Zeitschrift für Geomorphologie 1, 179-200. [12] Rapp, A. (1960) Norsk Polarinst. Skrifter 119, 1-96. [13] Larsson, S. (1982) Geografiska Annaler A64, 105-125. [14] Åkerman, J. (1984) Geografiska Annaler A66, 267-284. [15] Thiedig, F. and Kreling, A. (1973) Polarforschung 43, 40-49. [16] Costa, J.E. (1984) In: Developments and Applications of Geomorphology, Springer-Verlag, Berlin, 268-317. [17] Reiss et al. [2008] submitted to Planet. Space Sci.

Global hotspots of river erosion under global warming

NASA Astrophysics Data System (ADS)

Plink-Bjorklund, P.; Reichler, T.

2017-12-01

Extreme precipitation plays a significant role for river hydrology, flood hazards and landscape response. For example, the September 2013 rainstorm in the Colorado Front Range evacuated the equivalent of hundreds to thousands of years of hillslope weathering products. Although promoted by steep topography, the Colorado event is clearly linked to rainfall intensity, since most of the 1100 debris flows occurred within the highest rainfall contour. Additional evidence for a strong link between extreme precipitation and river erosion comes from the sedimentary record, and especially from that of past greenhouse climates. The existence of such a link suggests that information about global rainfall patterns can be used to define regions of increased erosion potential. However, the question arises what rainfall criteria to use and how well the method works. A related question is how ongoing climate change and the corresponding shifts in rainfall might impact the results. Here, we use atmospheric reanalysis and output from a climate model to identify regions that are particularly susceptible to landscape change in response to extreme precipitation. In order to define the regions, we combine several hydroclimatological and geomorphological criteria into a single index of erosion potential. We show that for current climate, our criteria applied to atmospheric reanalysis or to climate model data successfully localize known areas of increased erosion potential, such as the Colorado region. We then apply our criteria to climate model data for future climate to document how the location, extent, and intensity of erosion hotspots are likely to change under global warming.

Calibration of numerical models for small debris flows in Yosemite Valley, California, USA

USGS Publications Warehouse

Bertolo, P.; Wieczorek, G.F.

2005-01-01

This study compares documented debris flow runout distances with numerical simulations in the Yosemite Valley of California, USA, where about 15% of historical events of slope instability can be classified as debris flows and debris slides (Wieczorek and Snyder, 2004). To model debris flows in the Yosemite Valley, we selected six streams with evidence of historical debris flows; three of the debris flow deposits have single channels, and the other three split their pattern in the fan area into two or more channels. From field observations all of the debris flows involved coarse material, with only very small clay content. We applied the one dimensional DAN (Dynamic ANalysis) model (Hungr, 1995) and the two-dimensional FLO2D model (O'Brien et al., 1993) to predict and compare the runout distance and the velocity of the debris flows observed in the study area. As a first step, we calibrated the parameters for the two softwares through the back analysis of three debris- flows channels using a trial-and-error procedure starting with values suggested in the literature. In the second step we applied the selected values to the other channels, in order to evaluate their predictive capabilities. After parameter calibration using three debris flows we obtained results similar to field observations We also obtained a good agreement between the two models for velocities. Both models are strongly influenced by topography: we used the 30 m cell size DTM available for the study area, that is probably not accurate enough for a highly detailed analysis, but it can be sufficient for a first screening. European Geosciences Union ?? 2005 Author(s). This work is licensed under a Creative Commons License.

Volumetric analysis and hydrologic characterization of a modern debris flow near Yucca Mountain, Nevada

USGS Publications Warehouse

Coe, J.A.; Glancy, P.A.; Whitney, J.W.

1997-01-01

On July 21 or 22, 1984, debris flows triggered by rainfall occurred on the southern hillslope of Jake Ridge, about 6 km east of the crest of Yucca Mountain, Nevada. Rain gages near Jake Ridge recorded 65 mm and 69 mm on July 21, and 20 mm and 17 mm on July 22. Rates of rainfall intensity ranged up to 73 mm/h on the twenty-first, and 15 mm/h on the twenty-second. Digital elevation models with 2.0 m grid-node spacing, measured from pre-storm and post-storm aerial stereo-photographs, were used to map hillslope erosion and the downslope distribution of debris. Volumetric calculations indicate that about 7040 m3 of debris was redistributed on the 49,132 m2 hillslope study area during the two-day storm period. About 4580 m3 (65%) of the eroded sediment was deposited within the study area and the remaining 35% was deposited outside the study area in a short tributary to Fortymile Wash and in the wash itself. The maximum and mean depths of erosion in the study area were about 1.8 m and 5 cm, respectively. The mean depths of erosion on the upper and middle hillslope were 27 cm and 4 cm, respectively. The mean depth of deposition on the lower hillslope was 16 cm. Analysis of the values of cumulative precipitation in the context of the precipitation-frequency atlas of the National Oceanic and Atmospheric Administration indicates that precipitation from the main storm on July 21 was more than double that expected, on average, once during a 100-year period. The relations of precipitation intensity/duration, developed from data recorded at a nearby precipitation gage, indicate a storm interval of 500 years or greater. The amount of erosion caused by such a storm is primarily dependent on three variables: storm intensity, development of the drainage network on the hillslope, and the amount of available colluvium. Additionally, the erosive ability of successive storms of equal intensity will decrease because such storms would tend to progressively isolate and reduce the amount of colluvium available. The preservation of Pleistocene deposits on hillslopes of Yucca Mountain, in general, indicates that erosional events that strip 5% of the available hillslope colluvium must be quite rare. We conclude that the recurrence interval of an erosional event comparable to the July, 1984 event is probably much longer than 500 years.

Forecasting inundation from debris flows that grow during travel, with application to the Oregon Coast Range, USA

USGS Publications Warehouse

Reid, Mark E.; Coe, Jeffrey A.; Brien, Dianne

2016-01-01

Many debris flows increase in volume as they travel downstream, enhancing their mobility and hazard. Volumetric growth can result from diverse physical processes, such as channel sediment entrainment, stream bank collapse, adjacent landsliding, hillslope erosion and rilling, and coalescence of multiple debris flows; incorporating these varied phenomena into physics-based debris-flow models is challenging. As an alternative, we embedded effects of debris-flow growth into an empirical/statistical approach to forecast potential inundation areas within digital landscapes in a GIS framework. Our approach used an empirical debris-growth function to account for the effects of growth phenomena. We applied this methodology to a debris-flow-prone area in the Oregon Coast Range, USA, where detailed mapping revealed areas of erosion and deposition along paths of debris flows that occurred during a large storm in 1996. Erosion was predominant in stream channels with slopes > 5°. Using pre- and post-event aerial photography, we derived upslope contributing area and channel-length growth factors. Our method reproduced the observed inundation patterns produced by individual debris flows; it also generated reproducible, objective potential inundation maps for entire drainage networks. These maps better matched observations than those using previous methods that focus on proximal or distal regions of a drainage network.

A two-phase debris-flow model that includes coupled evolution of volume fractions, granular dilatancy, and pore-fluid pressure

USGS Publications Warehouse

George, David L.; Iverson, Richard M.

2011-01-01

Pore-fluid pressure plays a crucial role in debris flows because it counteracts normal stresses at grain contacts and thereby reduces intergranular friction. Pore-pressure feedback accompanying debris deformation is particularly important during the onset of debrisflow motion, when it can dramatically influence the balance of forces governing downslope acceleration. We consider further effects of this feedback by formulating a new, depth-averaged mathematical model that simulates coupled evolution of granular dilatancy, solid and fluid volume fractions, pore-fluid pressure, and flow depth and velocity during all stages of debris-flow motion. To illustrate implications of the model, we use a finite-volume method to compute one-dimensional motion of a debris flow descending a rigid, uniformly inclined slope, and we compare model predictions with data obtained in large-scale experiments at the USGS debris-flow flume. Predictions for the first 1 s of motion show that increasing pore pressures (due to debris contraction) cause liquefaction that enhances flow acceleration. As acceleration continues, however, debris dilation causes dissipation of pore pressures, and this dissipation helps stabilize debris-flow motion. Our numerical predictions of this process match experimental data reasonably well, but predictions might be improved by accounting for the effects of grain-size segregation.

Mapping debris-flow hazard in Honolulu using a DEM

USGS Publications Warehouse

Ellen, Stephen D.; Mark, Robert K.; ,

1993-01-01

A method for mapping hazard posed by debris flows has been developed and applied to an area near Honolulu, Hawaii. The method uses studies of past debris flows to characterize sites of initiation, volume at initiation, and volume-change behavior during flow. Digital simulations of debris flows based on these characteristics are then routed through a digital elevation model (DEM) to estimate degree of hazard over the area.

Depositional processes in large-scale debris-flow experiments

USGS Publications Warehouse

Major, J.J.

1997-01-01

This study examines the depositional process and characteristics of deposits of large-scale experimental debris flows (to 15 m3) composed of mixtures of gravel (to 32 mm), sand, and mud. The experiments were performed using a 95-m-long, 2-m-wide debris-flow flume that slopes 31??. Following release, experimental debris flows invariably developed numerous shallow (???10 cm deep) surges. Sediment transported by surges accumulated abruptly on a 3?? runout slope at the mouth of the flume. Deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion. Progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows. Despite progressive sediment emplacement, deposits were composed of unstratified accumulations of generally unsorted debris; hence massively textured, poorly sorted debris-flow deposits are not emplaced uniquely en masse. The depositional process was recorded mainly by deposit morphology and surface texture and was not faithfully registered by interior sedimentary texture; homogeneous internal textures could be misinterpreted as the result of en masse emplacement by a single surge. Deposition of sediment by similar, yet separate, debris flows produced a homogenous, massively textured composite deposit having little stratigraphic distinction. Similar deposit characteristics and textures are observed in natural debris-flow deposits. Experimental production of massively textured deposits by progressive sediment accretion limits interpretations that can be drawn from deposit characteristics and casts doubt on methods of estimating flow properties from deposit thickness or from relations between particle size and bed thickness.

Emergency assessment of post-fire debris-flow hazards for the 2013 Rim Fire, Stanislaus National Forest and Yosemite National Park, California

USGS Publications Warehouse

Staley, Dennis M.

2013-01-01

Wildfire can significantly alter the hydrologic response of a watershed to the extent that even modest rainstorms can produce dangerous flash floods and debris flows. In this report, empirical models are used to predict the probability and magnitude of debris-flow occurrence in response to a 10-year rainstorm for the 2013 Rim fire in Yosemite National Park and the Stanislaus National Forest, California. Overall, the models predict a relatively high probability (60–80 percent) of debris flow for 28 of the 1,238 drainage basins in the burn area in response to a 10-year recurrence interval design storm. Predictions of debris-flow volume suggest that debris flows may entrain a significant volume of material, with 901 of the 1,238 basins identified as having potential debris-flow volumes greater than 10,000 cubic meters. These results of the relative combined hazard analysis suggest there is a moderate likelihood of significant debris-flow hazard within and downstream of the burn area for nearby populations, infrastructure, wildlife, and water resources. Given these findings, we recommend that residents, emergency managers, and public works departments pay close attention to weather forecasts and National-Weather-Service-issued Debris Flow and Flash Flood Outlooks, Watches and Warnings and that residents adhere to any evacuation orders.

Debris-flow origin for the Simud/Tiu deposit on Mars

USGS Publications Warehouse

Tanaka, K.L.

1999-01-01

A late Hesperian smooth plains deposit on Mars interpreted as a debris flow extends more than 2000 km from Hydraotes Chaos, through Simud and Tiu Valles, and into Chryse Planitia. The Simud/Tiu deposit widens out to >1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity. Morphologic features of the Simud/Tiu deposit observed in Viking and Pathfinder images are generally consistent with a debris-flow origin, but some of the deposit's salient features are not readily explained by catastrophic flooding or ice flow. Internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow. Possible flow lobes within the deposit may have formed by successive flow surges within the flow unit. The Pathfinder landing site is on the Simud/Tiu deposit, and the observations there are consistent with debris flow. The low, longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt. Imbricated, planar rocks on the ridges, such as in the Rock Garden, also may have been emplaced by debris or ice flow. However, stream energy calculations at Ares Vallis and channel geology indicate that flooding probably was incapable of emplacing the meter-size boulders observed at the Pathfinder site. Dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long. Local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material. The debris-flow unit apparently coalesced from outflows of water-fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of Simud and Tiu Valles. The deposit is onlapped from the north by another flow deposit originating from Acidalia Planitia. If the Simud/Tiu debris flow had entered a standing body of water, a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the Acidalia deposit.

Debris flows through different forest age classes in the central Oregon Coast Range

Treesearch

C. L. May

2002-01-01

Abstract - Debris flows in the Pacific Northwest can play a major role in routing sediment and wood stored on hillslopes and in first- through third-order channels and delivering it to higher-order channels. Field surveys following a large regional storm event investigated 53 debris flows in the central Oregon Coast Range to determine relationships among debris flow...

Emergency assessment of post-fire debris-flow hazards for the 2013 Mountain fire, southern California

USGS Publications Warehouse

Staley, Dennis M.; Gartner, Joseph E.; Smoczyk, Greg M.; Reeves, Ryan R.

2013-01-01

Wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce dangerous flash floods and debris flows. We use empirical models to predict the probability and magnitude of debris flow occurrence in response to a 10-year rainstorm for the 2013 Mountain fire near Palm Springs, California. Overall, the models predict a relatively high probability (60–100 percent) of debris flow for six of the drainage basins in the burn area in response to a 10-year recurrence interval design storm. Volumetric predictions suggest that debris flows that occur may entrain a significant volume of material, with 8 of the 14 basins identified as having potential debris-flow volumes greater than 100,000 cubic meters. These results suggest there is a high likelihood of significant debris-flow hazard within and downstream of the burn area for nearby populations, infrastructure, and wildlife and water resources. Given these findings, we recommend that residents, emergency managers, and public works departments pay close attention to weather forecasts and National Weather Service–issued Debris Flow and Flash Flood Outlooks, Watches and Warnings and that residents adhere to any evacuation orders.

Debris flows resulting from glacial-lake outburst floods in tibet, China

USGS Publications Warehouse

Cui, P.; Dang, C.; Cheng, Z.; Scott, K.

2010-01-01

During the last 70 years of general climatic amelioration, 18 glacial-lake outburst floods (GLOFs) and related debris flows have occurred from 15 moraine-dammed lakes in Tibet, China. Catastrophic loss of life and property has occurred because of the following factors: the large volumes of water discharged, the steep gradients of the U-shaped channels, and the amount and texture of the downstream channel bed and bank material. The peak discharge of each GLOF exceeded 1000 m3/s. These flood discharges transformed to non-cohesive debris flows if the channels contained sufficient loose sediment for entrainment (bulking) and if their gradients were >1%. We focus on this key element, transformation, and suggest that it be included in evaluating future GLOF-related risk, the probability of transformation to debris flow and hyperconcentrated flow. The general, sequential evolution of the flows can be described as from proximal GLOFs, to sedimentladen streamflow, to hyperconcentrated flow, to non-cohesive debris flow (viscous or cohesive debris flow only if sufficient fine sediment is present), and then, distally, back to hyperconcentrated flow and sediment-laden streamflow as sediment is progressively deposited. Most of the Tibet examples transformed only to non-cohesive debris flows. The important lesson for future hazard assessment and mitigation planning is that, as a GLOF entrains (bulks) enough sediment to become a debris flow, the flow volume must increase by at least three times (the "bulking factor"). In fact, the transforming flow waves overrun and mix with downstream streamflow, in addition to adding the entrained sediment (and thus enabling addition of yet more sediment and a bulking factor in excess of three times). To effectively reduce the risk of GLOF debris flows, reducing the level of a potentially dangerous lake with a siphon or excavated spillway or installing gabions in combination with a downstream debris dam are the primary approaches.

Quantifying sources of fine sediment supplied to post-fire debris flows using fallout radionuclide tracers

NASA Astrophysics Data System (ADS)

Smith, Hugh G.; Sheridan, Gary J.; Nyman, Petter; Child, David P.; Lane, Patrick N. J.; Hotchkis, Michael A. C.; Jacobsen, Geraldine E.

2012-02-01

Fine sediment supply has been identified as an important factor contributing to the initiation of runoff-generated debris flows after fire. However, despite the significance of fines for post-fire debris flow generation, no investigations have sought to quantify sources of this material in debris flow affected catchments. In this study, we employ fallout radionuclides ( 137Cs, 210Pb ex and 239,240Pu) as tracers to measure proportional contributions of fine sediment (< 10 μm) from hillslope surface and channel bank sources to levee and terminal fan deposits formed by post-fire debris flows in two forest catchments in southeastern Australia. While 137Cs and 210Pb ex have been widely used in sediment tracing studies, application of Pu as a tracer represents a recent development and was limited to only one catchment. The ranges in estimated proportional hillslope surface contributions of fine sediment to individual debris flow deposits in each catchment were 22-69% and 32-74%. The greater susceptibility of 210Pb ex to apparent reductions in the ash content of channel deposits relative to hillslope sources resulted in its exclusion from the final analysis. No systematic change in the proportional source contributions to debris flow deposits was observed with distance downstream from channel initiation points. Instead, spatial variability in source contributions was largely influenced by the pattern of debris flow surges forming the deposits. Linking the tracing analysis with interpretation of depositional evidence allowed reconstruction of temporal sequences in sediment source contributions to debris flow surges. Hillslope source inputs dominated most elevated channel deposits such as marginal levees that were formed under peak flow conditions. This indicated the importance of hillslope runoff and fine sediment supply for debris flow generation in both catchments. In contrast, material stored within channels that was deposited during subsequent surges was predominantly channel-derived. The results demonstrate that fallout radionuclide tracers may provide unique information on changing source contributions of fine sediment during debris flow events.

Quantifying sources of fine sediment supplied to post-fire debris flows using fallout radionuclide tracers

NASA Astrophysics Data System (ADS)

Smith, Hugh; Sheridan, Gary; Nyman, Petter; Child, David; Lane, Patrick; Hotchkis, Michael

2013-04-01

The supply of fine sediment and ash has been identified as an important factor contributing to the initiation of runoff-generated debris flows after fire. However, despite the significance of fines for post-fire debris flow generation, no investigations have sought to quantify sources of this material in debris flow affected catchments. In this study, we employ fallout radionuclides (Cs-137, excess Pb-210 and Pu-239,240) as tracers to measure proportional contributions of fine sediment (<10 μm) from hillslope surface and channel bank sources to levee and terminal fan deposits formed by post-fire debris flows in two forest catchments in southeastern Australia. While Cs-137 and excess Pb-210 have been widely used in sediment tracing studies, application of Pu as a tracer represents a recent development and was limited to only one catchment. The estimated range in hillslope surface contributions of fine sediment to individual debris flow deposits in each catchment was 22-69% and 32-74%, respectively. No systematic change in the source contributions to debris flow deposits was observed with distance downstream from channel initiation points. Instead, spatial variability in source contributions was largely influenced by the pattern of debris flow surges forming the deposits. Linking the sediment tracing with interpretation of depositional evidence allowed reconstruction of temporal sequences in sediment source contributions to debris flow surges. Hillslope source inputs dominated most elevated channel deposits such as marginal levees that were formed under peak flow conditions. This indicated the importance of hillslope runoff and sediment supply for debris flow generation in both catchments. In contrast, material stored within channels that was deposited during subsequent surges was predominantly channel-derived. The results demonstrate that fallout radionuclide tracers may provide unique information on the changing source contributions of fine sediment during debris flow events.

Hydrological sensitivity of volcanically disturbed watersheds—a lesson reinforced at Pinatubo

NASA Astrophysics Data System (ADS)

Major, J. J.; Janda, R. J.

2016-12-01

The climactic June 1991 eruption of Mount Pinatubo devastated many surrounding catchments with thick pyroclastic fall and flow deposits, and subsequent hydrogeomorphic responses were dramatic and persisted for years. But in the 24 hours preceding the climactic eruption there was less devastating eruptive activity that had more subtle, yet significant, impact on catchment hydrology. Stratigraphic relations show damaging lahars swept all major channels east of the volcano, starting late on June 14 and continuing through (and in some instances after) midday on June 15, before the climactic phase of the eruption began and before Typhoon Yunya struck the region. These early lahars were preceded by relatively small explosions and pyroclastic surges that emplaced fine-grained ash in the upper catchments, locally damaged or destroyed vegetation, reduced hillside infiltration capacity, and smoothed surface roughness. Thus the lahars, likely triggered by typical afternoon monsoon storms perhaps enhanced by local thermal influences of fresh volcanic deposits, did not result from extraordinary tropical rainfall or exceptional volcaniclastic deposition. Instead, direct rainfall-runoff volume increased substantially as a consequence of vegetation damage and moderate deposition of fine ash. Rapid runoff from hillsides to channels initiated hillside and bank erosion as well as channel scour, producing debris flows and hyperconcentrated flows. Timing of some lahars varied across catchments as well as downstream within catchments with respect to climactic pumice fall, demonstrating complex interplay among volcanic processes, variations in catchment disturbance, and rainfall timing and intensity. Occurrence of these early lahars supports the hypothesis that eruptions that deposit fine ash in volcanic catchments can instigate major hydrogeomorphic responses even when volcanic disturbances are modest—an effect that can be masked by later eruption impacts.

Development and maintenance of a telescoping debris flow fan in response to human-induced fan surface channelization, Chalk Creek Valley Natural Debris Flow Laboratory, Colorado, USA

NASA Astrophysics Data System (ADS)

Wasklewicz, T.; Scheinert, C.

2016-01-01

Channel change has been a constant theme throughout William L. Graf's research career. Graf's work has examined channel changes in the context of natural environmental fluctuations, but more often has focused on quantifying channel change in the context of anthropogenic modifications. Here, we consider how channelization of a debris flows along a bajada has perpetuated and sustained the development of 'telescoping' alluvial fan. Two-dimensional debris-flow modeling shows the importance of the deeply entrenched channelized flow in the development of a telescoping alluvial fan. GIS analyses of repeat (five different debris flows), high-resolution (5 cm) digital elevation models (DEMs) generated from repeat terrestrial laser scanning (TLS) data elucidate sediment and topographic dynamics of the new telescoping portion of the alluvial fan (the embryonic fan). Flow constriction from channelization helps to perpetuate debris-flow runout and to maintain the embryonic fan and telescoping nature of the alluvial fan complex. Embryonic fan development, in response to five debris flows, proceeds with a major portion of the flows depositing on the southern portion of the embryonic fan. The third through the fifth debris flows also begin to shift some deposition to the northern portion of the embryonic. The transfer of sediment from a higher portion of the embryonic fan to a lower portion continues currently on the embryonic fan. While channelized flow has been shown to be critical to the maintenance of the telescoping fan, the flow constriction has led to higher than background levels of sediment deposition in Chalk Creek, a tributary of the Arkansas River. A majority of the sediment from each debris flow is incorporated into Chalk Creek as opposed to being stored on the embryonic fan.

Transformation of dilative and contractive landslide debris into debris flows-An example from marin County, California

USGS Publications Warehouse

Fleming, R.W.; Ellen, S.D.; Algus, M.A.

1989-01-01

The severe rainstorm of January 3, 4 and 5, 1982, in the San Francisco Bay area, California, produced numerous landslides, many of which transformed into damaging debris flows. The process of transformation was studied in detail at one site where only part of a landslide mobilized into several episodes of debris flow. The focus of our investigation was to learn whether the landslide debris dilated or contracted during the transformation from slide to flow. The landslide debris consisted of sandy colluvium that was separable into three soil horizons that occupied the axis of a small topographic swale. Failure involved the entire thickness of colluvium; however, over parts of the landslide, the soil A-horizon failed separately from the remainder of the colluvium. Undisturbed samples were taken for density measurements from outside the landslide, from the failure zone and overlying material from the part of the landslide that did not mobilize into debris flows, and from the debris-flow deposits. The soil A-horizon was contractive and mobilized to flows in a process analogous to liquefaction of loose, granular soils during earthquakes. The soil B- and C-horizons were dilative and underwent 2 to 5% volumetric expansion during landslide movement that permitted mobilization of debris-flow episodes. Several criteria can be used in the field to differentiate between contractive and dilative behavior including lag time between landsliding and mobilization of flow, episodic mobilization of flows, and partial or complete transformation of the landslide. ?? 1989.

Effects of Debris Flows on Stream Ecosystems of the Klamath Mountains, Northern California

NASA Astrophysics Data System (ADS)

Cover, M. R.; Delafuente, J. A.; Resh, V. H.

2006-12-01

We examined the long-term effects of debris flows on channel characteristics and aquatic food webs in steep (0.04-0.06 slope), small (4-6 m wide) streams. A large rain-on-snow storm event in January 1997 resulted in numerous landslides and debris flows throughout many basins in the Klamath Mountains of northern California. Debris floods resulted in extensive impacts throughout entire drainage networks, including mobilization of valley floor deposits and removal of vegetation. Comparing 5 streams scoured by debris flows in 1997 and 5 streams that had not been scoured as recently, we determined that debris-flows decreased channel complexity by reducing alluvial step frequency and large woody debris volumes. Unscoured streams had more diverse riparian vegetation, whereas scoured streams were dominated by dense, even-aged stands of white alder (Alnus rhombiflia). Benthic invertebrate shredders, especially nemourid and peltoperlid stoneflies, were more abundant and diverse in unscoured streams, reflecting the more diverse allochthonous resources. Debris flows resulted in increased variability in canopy cover, depending on degree of alder recolonization. Periphyton biomass was higher in unscoured streams, but primary production was greater in the recently scoured streams, suggesting that invertebrate grazers kept algal assemblages in an early successional state. Glossosomatid caddisflies were predominant scrapers in scoured streams; heptageniid mayflies were abundant in unscoured streams. Rainbow trout (Oncorhynchus mykiss) were of similar abundance in scoured and unscoured streams, but scoured streams were dominated by young-of-the-year fish while older juveniles were more abundant in unscoured streams. Differences in the presence of cold-water (Doroneuria) versus warm-water (Calineuria) perlid stoneflies suggest that debris flows have altered stream temperatures. Debris flows have long-lasting impacts on stream communities, primarily through the cascading effects of removal of riparian vegetation. Because debris flow frequency increases following road construction and timber harvest, the long-term biological effects of debris flows on stream ecosystems, including anadromous fish populations, needs to be considered in forest management decisions.

Surge dynamics coupled to pore-pressure evolution in debris flows

USGS Publications Warehouse

Savage, S.B.; Iverson, R.M.; ,

2003-01-01

Temporally and spatially varying pore-fluid pressures exert strong controls on debris-flow motion by mediating internal and basal friction at grain contacts. We analyze these effects by deriving a one-dimensional model of pore-pressure diffusion explicitly coupled to changes in debris-flow thickness. The new pore-pressure equation is combined with Iverson's (1997) extension of the depth-averaged Savage-Hutter (1989, 1991) granular avalanche equations to predict motion of unsteady debris-flow surges with evolving pore-pressure distributions. Computational results illustrate the profound effects of pore-pressure diffusivities on debris-flow surge depths and velocities. ?? 2003 Millpress,.

Assessment of topographic and drainage network controls on debris-flow travel distance along the west coast of the United States

USGS Publications Warehouse

Coe, Jeffrey A.; Reid, Mark E.; Brien, Dainne L.; Michael, John A.

2011-01-01

To better understand controls on debris-flow entrainment and travel distance, we examined topographic and drainage network characteristics of initiation locations in two separate debris-flow prone areas located 700 km apart along the west coast of the U.S. One area was located in northern California, the other in southern Oregon. In both areas, debris flows mobilized from slides during large storms, but, when stratified by number of contributing initiation locations, median debris-flow travel distances in Oregon were 5 to 8 times longer than median distances in California. Debris flows in Oregon readily entrained channel material; entrainment in California was minimal. To elucidate this difference, we registered initiation locations to high-resolution airborne LiDAR, and then examined travel distances with respect to values of slope, upslope contributing area, planform curvature, distance from initiation locations to the drainage network, and number of initiation areas that contributed to flows. Results show distinct differences in the topographic and drainage network characteristics of debris-flow initiation locations between the two study areas. Slope and planform curvature of initiation locations (landslide headscarps), commonly used to predict landslide-prone areas, were not useful for predicting debris-flow travel distances. However, a positive, power-law relation exists between median debris-flow travel distance and the number of contributing debris-flow initiation locations. Moreover, contributing area and the proximity of the initiation locations to the drainage network both influenced travel distances, but proximity to the drainage network was the better predictor of travel distance. In both study areas, flows that interacted with the drainage network flowed significantly farther than those that did not. In California, initiation sites within 60 m of the network were likely to reach the network and generate longtraveled flows; in Oregon, the threshold was 80 m.

Different kernel functions due to rainfall response from borehole strainmeter in Taiwan

NASA Astrophysics Data System (ADS)

Yen Chen, Chih; Hu, Jyr Ching; LIu, Chi Ching

2014-05-01

In order to realize reasons inducing earthquakes, project of monitoring of the fault activity using 3-component Gladwin Tensor Strainmeter (GTSM) has been initiated since 2003 in Taiwan, which is one of the most active seismic regions in the world. Observed strain contains several different effects within including barometric, tidal, groundwater, precipitation, tectonics, seismic and other irregular noise. After removing the response of tides and air pressure on strain, we still can find some anomalies highly related to the rainfall in short time in days. The strain response induced by rainfall can be separated into two parts as observation in groundwater, slow response and quick response, respectively. Quick response reflects the strain responding to the load of falling water drops on the ground surface. A kernel function shows the continual response induced by unit precipitation water in time domain. We split the quick response from data removing tidal and barometric response, and then calculate the kernel function by use of deconvolution method. More, an average kernel function was calculated to reduce the noise level. There are five of the sites installed by CGS Taiwan were selected to calculate kernel functions for individual sites. The results show there may be different on rainfall response in different environmental settings. In the case of stations site on gentle terrain, kernel function for each site shows the similar trend, it rises quickly to maximum in 1 to 2 hrs, and then goes down near to zero gently in period of 2-3 days. But in the case of sites settled side by the rivers, there will be 2nd peak of function when collected water in the catchment flows along by the sites related to the hydrograph of creeks. More, landslides will occur in some sites in hazard of landslide with more rainfall stored on, just like DARB in ChiaYi. The curve of kernel function will be controlled by landslides and debris flows.

Wildfire-related debris-flow initiation processes, Storm King Mountain, Colorado

USGS Publications Warehouse

Cannon, S.H.; Kirkham, R.M.; Parise, M.

2001-01-01

A torrential rainstorm on September 1, 1994 at the recently burned hillslopes of Storm King Mountain, CO, resulted in the generation of debris flows from every burned drainage basin. Maps (1:5000 scale) of bedrock and surficial materials and of the debris-flow paths, coupled with a 10-m Digital Elevation Model (DEM) of topography, are used to evaluate the processes that generated fire-related debris flows in this setting. These evaluations form the basis for a descriptive model for fire-related debris-flow initiation. The prominent paths left by the debris flows originated in 0- and 1st-order hollows or channels. Discrete soil-slip scars do not occur at the heads of these paths. Although 58 soil-slip scars were mapped on hillslopes in the burned basins, material derived from these soil slips accounted for only about 7% of the total volume of material deposited at canyon mouths. This fact, combined with observations of significant erosion of hillslope materials, suggests that a runoff-dominated process of progressive sediment entrainment by surface runoff, rather than infiltration-triggered failure of discrete soil slips, was the primary mechanism of debris-flow initiation. A paucity of channel incision, along with observations of extensive hillslope erosion, indicates that a significant proportion of material in the debris flows was derived from the hillslopes, with a smaller contribution from the channels. Because of the importance of runoff-dominated rather than infiltration-dominated processes in the generation of these fire-related debris flows, the runoff-contributing area that extends upslope from the point of debris-flow initiation to the drainage divide, and its gradient, becomes a critical constraint in debris-flow initiation. Slope-area thresholds for fire-related debris-flow initiation from Storm King Mountain are defined by functions of the form Acr(tan ??)3 = S, where Acr is the critical area extending upslope from the initiation location to the drainage divide, and tan ?? is its gradient. The thresholds vary with different materials. ?? 2001 Elsevier Science B.V. All rights reserved.

Debris Flow Process and Climate Controls on Steepland Valley Form and Evolution

NASA Astrophysics Data System (ADS)

Struble, W.; Roering, J. J.

2017-12-01

In unglaciated mountain ranges, steepland bedrock valleys often dominate relief structure and dictate landscape response to perturbations in tectonics or climate; drainage divides have been shown to be dynamic and drainage capture is common. Landscape evolution models often use the stream power model to simulate morphologic changes, but steepland valley networks exhibit trends that deviate from predictions of this model. The prevalence of debris flows in steep channels has motivated approaches that account for commonly observed curvature of slope-area data at small drainage areas. Debris flow deposits correspond with observed curvature in slope-area data, wherein slope increases slowly as drainage area decreases; debris flow incision is implied upstream of deposits. In addition, shallow landslides and in-channel sediment entrainment in humid and arid regions, respectively, have been identified as likely debris flow triggering mechanisms, but the extent to which they set the slope of steep channels is unclear. While an untested model exists for humid landscape debris flows, field observations and models are lacking for regions with lower mean annual precipitation. The Oregon Coastal Ranges are an ideal humid setting for observing how shallow landslide-initiated debris flows abrade channel beds and/or drive exposure-driven weathering. Preliminary field observations in the Lost River Range and the eastern Sierra Nevada - semi-arid and unglaciated environments - suggest that debris flows are pervasive in steep reaches. Evidence for fluvial incision is lacking and the presence of downstream debris flow deposits and a curved morphologic signature in slope-area space suggests stream power models are insufficient for predicting and interpreting landscape dynamics. Investigation of debris flow processes in both humid and arid sites such as these seeks to identify the linkage between sediment transport and the characteristic form of steepland valleys. Bedrock weathering, fracture density, recurrence interval, bulking, and grain size may determine process-form linkages in humid and arid settings. Evaluation of debris flow processes in sites of varying climate presents the opportunity to quantify the role of debris flow incision in the evolution of steepland valleys and improve landscape evolution models.

Debris flows: behavior and hazard assessment

USGS Publications Warehouse

Iverson, Richard M.

2014-01-01

Debris flows are water-laden masses of soil and fragmented rock that rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form lobate deposits when they spill onto valley floors. Because they have volumetric sediment concentrations that exceed 40 percent, maximum speeds that surpass 10 m/s, and sizes that can range up to ~109 m3, debris flows can denude slopes, bury floodplains, and devastate people and property. Computational models can accurately represent the physics of debris-flow initiation, motion and deposition by simulating evolution of flow mass and momentum while accounting for interactions of debris' solid and fluid constituents. The use of physically based models for hazard forecasting can be limited by imprecise knowledge of initial and boundary conditions and material properties, however. Therefore, empirical methods continue to play an important role in debris-flow hazard assessment.

GIS-based modeling of debris flow processes in an Alpine catchment, Antholz valley, Italy

NASA Astrophysics Data System (ADS)

Sandmeier, Christine; Damm, Bodo; Terhorst, Birgit

2010-05-01

Debris flows are frequent natural hazards in mountain regions, which seriously can threat human lives and economic values. In the European Alps the occurrence of debris flows might even increase with respect to climate change, including permafrost degradation, glacier retreat and variable precipitation patterns. Thus, detailed understanding of process parameters and spatial distribution of debris flows is necessary to take appropriate protection measures for risk assessment. In this context, numerical models have been developed and applied successfully for simulation and prediction of debris-flow hazards and related process areas. In our study a GIS-based model is applied in an alpine catchment to address the following questions: Where are potential initiating areas of debris flows? How much material can be mobilized? What is the influence of topography and precipitation? The study area is located in the Antholz valley in the eastern Alps of Northern Italy. The investigated catchment of the Klammbach creek comprises 6.5 km² and is divided into two sub-catchments. Geologically it is dominated by metamorphic rock and altitudes range between 1310 and 3270 m. In summer 2005 a debris flow of more than 100000 m³ took place, originating from a steep, sparsely vegetated debris cone in the western part of the catchment. According to a regional study, the lower permafrost boundary in this area has risen by 250 m. In a first step, during a field survey, geomorphological mapping was performed, several channel cross-sections were measured and sediment samples were taken. Using mapping results and aerial images, a geomorphological map was created. In further steps, results from the field work, the geomorphological map and existing digital data sets, including a digital elevation model with 2.5 m resolution, are used to derive input data for the modeling of debris flow processes. The model framework ‘r.debrisflow' based on GRASS GIS is applied (Mergili, 2008*), as it is capable of simulating the potential spatial patterns of debris flow deposition, as well as their initiation and movement. Furthermore it is a freely available and opensource software and can thus be improved and extended. ‘r.debrisflow' couples a hydraulic, a slope stability, a sediment transport and a debris flow runout model, which are combined differently in 6 simulation modes. In a first step, model parameters are calibrated using the runout only mode with known parameters of the 2005 debris flow. Finally, the full mode will be used to evaluate the debris-flow potential of the whole catchment. First results from the geomorphological mapping reveal numerous surface forms, like levees, debris flow lobes or scars that indicate past and recent debris flow activity in the area. In both sub-catchments, there are large areas of unconsolidated, sparsely or unvegetated sediments, surrounded by high rock walls, which conduct precipitation rapidly into the debris. The two sub-catchments, however, have different topographic characteristics, which can be analyzed with the model in more detail. In a next step, the potential starting areas of future debris flows shall be identified and the potential amount of mobilized material shall be estimated by the model. *Mergili, M. (2008): Integrated modelling of debris flows with Open Source GIS. Ph.D. thesis. University of Innsbruck. http://www.uibk.ac.at/geographie/personal/mergili/dissertation.pdf

The early warning system of landslides and sediment runoffs using meteorological condition including rainfall-soil moisture index (Invited)

NASA Astrophysics Data System (ADS)

Kubota, T.; Silva, I. C.; Hasnawir, H.

2009-12-01

The research including observation of rain, soil moisture content and sediment discharge is conducted on a torrent in northern Kyushu whose geology consists of Paleozoic metamorphic rocks (mainly schist) and whose vegetation consists of mainly Japanese cypress and cedar. Soil depth is approximately 50cm in average and permeability k is 0.1~0.01 order. With data obtained by the observation for more than 4 years, standard rainfalls of warning and evacuation against the sudden sediment runoffs are analyzed. Then, the result was compared with the ones in Nuevo Leon Mexico (geology of schist, slate, k=0.01~0.001 order) and in southern Sulawesi Island Indonesia (volcanic geology, k=0.001~0.0001 order). Hitherto, various methods were proposed to analyze the warning critical standard for landslide disaster or large sediment discharge. In this study, we employed Hirano's element slope runoff theory, the Self Organized Criticality Assumption (SOC), and the Elementary Catastrophe Theory (ETC) to analyze the data, although the soil moisture fluctuation, meteorological condition such as upper air wind and dew point depression, the rainfall-soil moisture index provided by Japan Meteorological Agency was considered. The last one is a cutting edge technology based on the tank model calculation of soil moisture content combined with short term rainfall prediction which is a product of numerical simulation using radar image advection analysis compensated with surface rain data and with orographic rain effect. In Hirano's theory, we can describe the critical rain Rc and rain intensity Ric as following equation. Q/A/M/ cosθ = Ri ∫(r*cosθ)dt = Ri*R (1) ∴ Ric*Rc = C (2) Here, Q: sediment runoff or debris flow discharge, A: watershed area, M: function concerning with sediment deposit features on the upstream torrents or slopes (porosity, torrent bed slope gradient, sediment accumulation length and depth, cohesion), t: time, θ: torrent bed or hillside slope gradient, r: instant precipitation. C: constant, given as 8000 in Fukuoka (Kyushu, Japan), as 3750 in Sierra Madere Oriental (Nuevo Leon, Mexico), as 9000 in southern Sulawesi(Indonesia). Consequently, the forecast-warning system which has enough accuracy of 80% against sediment runoffs or debris flows for both wide range region with meteorological conditions and narrow region with the critical rain standard are established. However, in the region with lower soil permeability we may revise the standard rain by the compensation with the soil moisture content response such as increasing rate.

Effects of rainfall patterns and land cover on the subsurface flow generation of sloping Ferralsols in southern China

PubMed Central

Yang, Jie; Tang, Chongjun; Chen, Lihua; Liu, Yaojun; Wang, Lingyun

2017-01-01

Rainfall patterns and land cover are two important factors that affect the runoff generation process. To determine the surface and subsurface flows associated with different rainfall patterns on sloping Ferralsols under different land cover types, observational data related to surface and subsurface flows from 5 m × 15 m plots were collected from 2010 to 2012. The experiment was conducted to assess three land cover types (grass, litter cover and bare land) in the Jiangxi Provincial Soil and Water Conservation Ecological Park. During the study period, 114 natural rainfall events produced subsurface flow and were divided into four groups using k-means clustering according to rainfall duration, rainfall depth and maximum 30-min rainfall intensity. The results showed that the total runoff and surface flow values were highest for bare land under all four rainfall patterns and lowest for the covered plots. However, covered plots generated higher subsurface flow values than bare land. Moreover, the surface and subsurface flows associated with the three land cover types differed significantly under different rainfall patterns. Rainfall patterns with low intensities and long durations created more subsurface flow in the grass and litter cover types, whereas rainfall patterns with high intensities and short durations resulted in greater surface flow over bare land. Rainfall pattern I had the highest surface and subsurface flow values for the grass cover and litter cover types. The highest surface flow value and lowest subsurface flow value for bare land occurred under rainfall pattern IV. Rainfall pattern II generated the highest subsurface flow value for bare land. Therefore, grass or litter cover are able to convert more surface flow into subsurface flow under different rainfall patterns. The rainfall patterns studied had greater effects on subsurface flow than on total runoff and surface flow for covered surfaces, as well as a greater effect on surface flows associated with bare land. PMID:28792507

The rain-triggered Atenquique volcaniclastic debris flow of October 16, 1955 at Nevado de Colima Volcano, Mexico

NASA Astrophysics Data System (ADS)

Saucedo, R.; Macías, J. L.; Sarocchi, D.; Bursik, M.; Rupp, B.

2008-06-01

On October 16, 1955, at 10:45 a.m. (local time), after three days of intense rain (140 mm) that was twice the monthly average precipitation, a devastating flood surge formed a volcaniclastic debris flow on the eastern slopes of Nevado de Colima Volcano. Nearly simultaneous flood surges formed in the Arroyo Seco, Los Platanos, and Dos Volcanes ravines that coalesced with the larger flow in the Atenquique ravine. At each confluence with a tributary, the flow was diluted. The texture and structure of the preserved 1955 deposits near high water marks indicate that the downstream flow was mainly in the lower range of debris flow concentration (60% sediment concentration by weight). Downstream the tributaries, the flood encountered a ˜ 0.06 × 10 6 m 3 water reservoir that failed, significantly increasing the surge volume. Additional entrained sediment also increased the flow volume. Downstream, the flood wave reached the town of Atenquique as an 8-9 m catastrophic wave causing the death of more than 23 people, the partial destruction of the town, and losses of ˜ 13,000,000 pesos (˜ 1 million US dollars today) to a paper mill and company facilities. According to eyewitness accounts the flood wave had a peak discharge that lasted ca. 10 to 15 minutes at Atenquique. Deposits at the site and the high-water marks observed from photographs of the town's church indicate that sediment concentration was ca. 60 wt.%. The flood continued for about 1 km to its junction with the Tuxpan River where it was diluted by mixing with normal flood flow. The deposits covered an area of ˜ 1.2 km 2 and had a minimum volume of ˜ 3.2 × 10 6 m 3. The main deposit consists of a single unit, averaging 4 m in thickness, with weak textural variations that suggest surging within the flood wave. The deposit is heterolithologic and consists of boulders set in a matrix of sand-size sediment, with polymodal or bimodal distributions and normal grading varying with distance from source. The town of Atenquique has been reconstructed largely within the area inundated by the 1955 flood wave, thus creating the conditions for a future disaster. A rainfall-intensity warning system and an educational program for inhabitants are strategies to mitigate this risk.

The perfect debris flow? Aggregated results from 28 large-scale experiments

USGS Publications Warehouse

Iverson, Richard M.; Logan, Matthew; LaHusen, Richard G.; Berti, Matteo

2010-01-01

Aggregation of data collected in 28 controlled experiments reveals reproducible debris-flow behavior that provides a clear target for model tests. In each experiment ∼10 m3 of unsorted, water-saturated sediment composed mostly of sand and gravel discharged from behind a gate, descended a steep, 95-m flume, and formed a deposit on a nearly horizontal runout surface. Experiment subsets were distinguished by differing basal boundary conditions (1 versus 16 mm roughness heights) and sediment mud contents (1 versus 7 percent dry weight). Sensor measurements of evolving flow thicknesses, basal normal stresses, and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated, coarse-grained, high-friction snouts, followed by bodies of nearly liquefied, finer-grained debris. Mud enhanced flow mobility by maintaining high pore pressures in flow bodies, and bed roughness reduced flow speeds but not distances of flow runout. Roughness had these effects because it promoted debris agitation and grain-size segregation, and thereby aided growth of lateral levees that channelized flow. Grain-size segregation also contributed to development of ubiquitous roll waves, which had diverse amplitudes exhibiting fractal number-size distributions. Despite the influence of these waves and other sources of dispersion, the aggregated data have well-defined patterns that help constrain individual terms in a depth-averaged debris-flow model. The patterns imply that local flow resistance evolved together with global flow dynamics, contradicting the hypothesis that any consistent rheology applied. We infer that new evolution equations, not new rheologies, are needed to explain how characteristic debris-flow behavior emerges from the interactions of debris constituents.

Debris flows from failures Neoglacial-age moraine dams in the Three Sisters and Mount Jefferson wilderness areas, Oregon

USGS Publications Warehouse

O'Connor, J. E.; Hardison, J.H.; Costa, J.E.

2001-01-01

The highest concentration of lakes dammed by Neoglacial moraines in the conterminous United States is in the Mount Jefferson and Three Sisters Wilderness Areas in central Oregon. Between 1930 and 1980, breakouts of these lakes have resulted in 11 debris flows. The settings and sequences of events leading to breaching and the downstream flow behavior of the resulting debris flows provide guidance on the likelihood and magnitude of future lake breakouts and debris flows.

Probabilistic forecasts of debris-flow hazard at the regional scale with a combination of models.

NASA Astrophysics Data System (ADS)

Malet, Jean-Philippe; Remaître, Alexandre

2015-04-01

Debris flows are one of the many active slope-forming processes in the French Alps, where rugged and steep slopes mantled by various slope deposits offer a great potential for triggering hazardous events. A quantitative assessment of debris-flow hazard requires the estimation, in a probabilistic framework, of the spatial probability of occurrence of source areas, the spatial probability of runout areas, the temporal frequency of events, and their intensity. The main objective of this research is to propose a pipeline for the estimation of these quantities at the region scale using a chain of debris-flow models. The work uses the experimental site of the Barcelonnette Basin (South French Alps), where 26 active torrents have produced more than 150 debris-flow events since 1850 to develop and validate the methodology. First, a susceptibility assessment is performed to identify the debris-flow prone source areas. The most frequently used approach is the combination of environmental factors with GIS procedures and statistical techniques, integrating or not, detailed event inventories. Based on a 5m-DEM and derivatives, and information on slope lithology, engineering soils and landcover, the possible source areas are identified with a statistical logistic regression model. The performance of the statistical model is evaluated with the observed distribution of debris-flow events recorded after 1850 in the study area. The source areas in the three most active torrents (Riou-Bourdoux, Faucon, Sanières) are well identified by the model. Results are less convincing for three other active torrents (Bourget, La Valette and Riou-Chanal); this could be related to the type of debris-flow triggering mechanism as the model seems to better spot the open slope debris-flow source areas (e.g. scree slopes), but appears to be less efficient for the identification of landslide-induced debris flows. Second, a susceptibility assessment is performed to estimate the possible runout distance with a process-based model. The MassMov-2D code is a two-dimensional model of mud and debris flow dynamics over complex topography, based on a numerical integration of the depth-averaged motion equations using shallow water approximation. The run-out simulations are performed for the most active torrents. The performance of the model has been evaluated by comparing modelling results with the observed spreading areas of several recent debris flows. Existing data on the debris flow volume, input discharge and deposits were used to back-analyze those events and estimate the values of the model parameters. Third, hazard is estimated on the basis of scenarios computed in a probabilistic way, for volumes in the range 20'000 to 350'000 m3, and for several combinations of rheological parameters. In most cases, the simulations indicate that the debris flows cause significant overflowing on the alluvial fans for volumes exceeding 100'000 m3 (height of deposits > 2 m, velocities > 5 m.s-1). Probabilities of debris flow runout and debris flow intensities are then computed for each terrain units.

Predicting spatial distribution of postfire debris flows and potential consequences for native trout in headwater streams

USGS Publications Warehouse

Sedell, Edwin R; Gresswell, Bob; McMahon, Thomas E.

2015-01-01

Habitat fragmentation and degradation and invasion of nonnative species have restricted the distribution of native trout. Many trout populations are limited to headwater streams where negative effects of predicted climate change, including reduced stream flow and increased risk of catastrophic fires, may further jeopardize their persistence. Headwater streams in steep terrain are especially susceptible to disturbance associated with postfire debris flows, which have led to local extirpation of trout populations in some systems. We conducted a reach-scale spatial analysis of debris-flow risk among 11 high-elevation watersheds of the Colorado Rocky Mountains occupied by isolated populations of Colorado River Cutthroat Trout (Oncorhynchus clarkii pleuriticus). Stream reaches at high risk of disturbance by postfire debris flow were identified with the aid of a qualitative model based on 4 primary initiating and transport factors (hillslope gradient, flow accumulation pathways, channel gradient, and valley confinement). This model was coupled with a spatially continuous survey of trout distributions in these stream networks to assess the predicted extent of trout population disturbances related to debris flows. In the study systems, debris-flow potential was highest in the lower and middle reaches of most watersheds. Colorado River Cutthroat Trout occurred in areas of high postfire debris-flow risk, but they were never restricted to those areas. Postfire debris flows could extirpate trout from local reaches in these watersheds, but trout populations occupy refugia that should allow recolonization of interconnected, downstream reaches. Specific results of our study may not be universally applicable, but our risk assessment approach can be applied to assess postfire debris-flow risk for stream reaches in other watersheds.

Debris flow susceptibility mapping using a qualitative heuristic method and Flow-R along the Yukon Alaska Highway Corridor, Canada

NASA Astrophysics Data System (ADS)

Blais-Stevens, A.; Behnia, P.

2016-02-01

This research activity aimed at reducing risk to infrastructure, such as a proposed pipeline route roughly parallel to the Yukon Alaska Highway Corridor (YAHC), by filling geoscience knowledge gaps in geohazards. Hence, the Geological Survey of Canada compiled an inventory of landslides including debris flow deposits, which were subsequently used to validate two different debris flow susceptibility models. A qualitative heuristic debris flow susceptibility model was produced for the northern region of the YAHC, from Kluane Lake to the Alaska border, by integrating data layers with assigned weights and class ratings. These were slope angle, slope aspect, surficial geology, plan curvature, and proximity to drainage system. Validation of the model was carried out by calculating a success rate curve which revealed a good correlation with the susceptibility model and the debris flow deposit inventory compiled from air photos, high-resolution satellite imagery, and field verification. In addition, the quantitative Flow-R method was tested in order to define the potential source and debris flow susceptibility for the southern region of Kluane Lake, an area where documented debris flow events have blocked the highway in the past (e.g. 1988). Trial and error calculations were required for this method because there was not detailed information on the debris flows for the YAHC to allow us to define threshold values for some parameters when calculating source areas, spreading, and runout distance. Nevertheless, correlation with known documented events helped define these parameters and produce a map that captures most of the known events and displays debris flow susceptibility in other, usually smaller, steep channels that had not been previously documented.

Debris flow susceptibility mapping using a qualitative heuristic method and Flow-R along the Yukon Alaska Highway Corridor, Canada

NASA Astrophysics Data System (ADS)

Blais-Stevens, A.; Behnia, P.

2015-05-01

This research activity aimed at reducing risk to infrastructure, such as a proposed pipeline route roughly parallel to the Yukon Alaska Highway Corridor (YAHC) by filling geoscience knowledge gaps in geohazards. Hence, the Geological Survey of Canada compiled an inventory of landslides including debris flow deposits, which were subsequently used to validate two different debris flow susceptibility models. A qualitative heuristic debris flow susceptibility model was produced for the northern region of the YAHC, from Kluane Lake to the Alaska border, by integrating data layers with assigned weights and class ratings. These were slope angle, slope aspect (derived from a 5 m × 5 m DEM), surficial geology, permafrost distribution, and proximity to drainage system. Validation of the model was carried out by calculating a success rate curve which revealed a good correlation with the susceptibility model and the debris flow deposit inventory compiled from air photos, high resolution satellite imagery, and field verification. In addition, the quantitative Flow-R method was tested in order to define the potential source and debris flow susceptibility for the southern region of Kluane Lake, an area where documented debris flow events have blocked the highway in the past (e.g., 1988). Trial and error calculations were required for this method because there was not detailed information on the debris flows for the YAHC to allow us to define threshold values for some parameters when calculating source areas, spreading, and runout distance. Nevertheless, correlation with known documented events helped define these parameters and produce a map that captures most of the known events and displays debris flow susceptibility in other, usually smaller, steep channels that had not been previously documented.

Influential factors on debris flow events and hillslope-channel connectivity in Alpine regions: case studies from two Alpine regions in Styria, Austria

NASA Astrophysics Data System (ADS)

Traper, Sandra; Pöppl, Ronald; Rascher, Eric; Sass, Oliver

2016-04-01

In recent times different types of natural disasters like debris flow events have attracted increasing attention worldwide, since they can cause great damage and loss of infrastructure or even lives is not unusual when it comes to such an event. The engagement with debris flows is especially important in mountainous areas like Austria, since Alpine regions have proved to be particularly prone to the often harmful consequences of such events because of increasing settlement of previously uninhabited regions. Due to those frequently damaging effects of debris flows, research on this kind of natural disaster often focuses on mitigation and recovery measures after an event and on how to restore the initial situation. However, a view on the situation of an area, where severe debris flows recently occurred and are well documented, before the actual event can aid in discovering important preparatory factors that contribute to initiating debris flows and hillslope-channel connectivity in the first place. Valuable insights into the functioning and preconditions of debris flows and their potential connectivity to the main channel can be gained. The study focuses on two geologically different areas in the Austrian Alps, which are both prone to debris flows and have experienced rather severe events recently. Based on data from debris flow events in two regions in Styria (Austria), the Kleinsölk and the Johnsbach valleys, the aim of the study is to identify factors which influence the development of debris flows and the potential of such debris flows to reach the main channel potentially clogging up the river (hillslope-channel connectivity). The degree of hillslope-channel coupling was verified in extensive TLS and ALS surveys, resulting in DEMs of different resolution and spatial extension. Those factors are obtained, analyzed and evaluated with DEM-based GIS- and statistical analyses. These include factors that are attributed to catchment topography, such as slope angle, curvature, size, shape as well as topographic channel parameters. Together with factors of land cover/use and lithology those features provide the independent variables for further statistical analyses. With the help of several logistic regressions the likelihoods of influencing topographical and lithological factors and factors of land cover/use leading to debris flow events and those for debris flows to reach the main channel (hillslope-channel connectivity) are computed. First results will be presented at the EGU General Assembly 2016.

Sediment Budget Analysis and Hazard Assessment in the Peynin, a Small Alpine Catchment (Upper Guil River, Southern Alps, France)

NASA Astrophysics Data System (ADS)

Carlier, Benoit; Arnaud-Fassetta, Gilles; Fort, Monique; Bouccara, Fanny; Sourdot, Grégoire; Tassel, Adrien; Lissak, Candide; Betard, François; Cossart, Etienne; Madelin, Malika; Viel, Vincent; Charnay, Bérengère; Bletterie, Xavier

2014-05-01

The upper Guil catchment (Southern Alps) is prone to hydro-geomorphic hazards. Major hazards are related to catastrophic floods, with an amplification of their impacts due to strong hillslope-channel connectivity as observed in 1957 and 2000. In both cases, the rainfall intensity, aggravated by the pre-existing saturated soils, explained the instantaneous response of the fluvial system, such as destabilisation of slopes, high sediment discharge, and subsequent damages to exposed structures and settlements present in the floodplain and at confluence sites. The Peynin junction with the Guil River is one of these sites, where significant land-use change during the last decades in relation to the development of handicraft and tourism economy has increased debris flow threat to population. Here, we adopt a sediment budget analysis aimed at better understanding the functioning of this small subcatchment. This latter offers a combination of factors that favour torrential and gravitational activity. It receives abundant and intense rainfall during "Lombarde" events (moist air mass from Mediterranean Sea). Its elongated shape and small surface area (15 km²) together with asymmetric slopes (counter dip slope on the left bank) accelerate runoff on a short response time. In addition highly tectonised shaly schists supply a large volume of debris (mostly platy clasts and fine, micaceous sediment). The objectives of this study, carried out in the frame of SAMCO (ANR) project, are threefold: Identify the different sediment storages; Characterise the processes that put sediment into motion; Quantify volumes of sediment storages. We produced a geomorphic map using topographic surveys and aerial photos in order to locate the different sediment storage types and associated processes. This analysis was made with respect to geomorphic coupling and sediment flux activity. In terms of surface area, the dominant landforms in the valley were found to be mass wasting, talus slopes and alluvial fans and plains. Most of these forms are relict landforms, decoupled from the present geomorphic system. Notable sediment transport is limited to avalanche tracks, debris flows, and along floodplains. Sediment volumes were calculated using a combination of polynomial functions of cross sections and GIS modelling. We calculated the overall sediment volume of the valley fill deposits to be 1.05 km3. This corresponds to a mean sediment thickness of 90.2 m. Landslides appear as the major sediment storage, representing more than 35% of the sediment volume stored in the Peynin subcatchment. For some locations, the polynomial-generated cross sections resulted in overestimations of sediment thickness, therefore, these results have to be considered as an order of magnitude. Future investigations will include seismic refraction profiles that may provide bedrock depth, hence a better control on sediment thickness (estimates generated thanks to GIS). Eventually, we expect our results to be used to better model, hence prevent future debris-flow events at the confluence of Peynin stream with the Guil River.

The Time-Frequency Signatures of Advanced Seismic Signals Generated by Debris Flows

NASA Astrophysics Data System (ADS)

Chu, C. R.; Huang, C. J.; Lin, C. R.; Wang, C. C.; Kuo, B. Y.; Yin, H. Y.

2014-12-01

The seismic monitoring is expected to reveal the process of debris flow from the initial area to alluvial fan, because other field monitoring techniques, such as the video camera and the ultrasonic sensor, are limited by detection range. For this reason, seismic approaches have been used as the detection system of debris flows over the past few decades. The analysis of the signatures of the seismic signals in time and frequency domain can be used to identify the different phases of debris flow. This study dedicates to investigate the different stages of seismic signals due to debris flow, including the advanced signal, the main front, and the decaying tail. Moreover, the characteristics of the advanced signals forward to the approach of main front were discussed for the warning purpose. This study presents a permanent system, composed by two seismometers, deployed along the bank of Ai-Yu-Zi Creek in Nantou County, which is one of the active streams with debris flow in Taiwan. The three axes seismometer with frequency response of 7 sec - 200 Hz was developed by the Institute of Earth Sciences (IES), Academia Sinica for the purpose to detect debris flow. The original idea of replacing the geophone system with the seismometer technique was for catching the advanced signals propagating from the upper reach of the stream before debris flow arrival because of the high sensitivity. Besides, the low frequency seismic waves could be also early detected because of the low attenuation. However, for avoiding other unnecessary ambient vibrations, the sensitivity of seismometer should be lower than the general seismometer for detecting teleseism. Three debris flows with different mean velocities were detected in 2013 and 2014. The typical triangular shape was obviously demonstrated in time series data and the spectrograms of the seismic signals from three events. The frequency analysis showed that enormous debris flow bearing huge boulders would induce low frequency seismic waves. Owing to the less attenuation of low frequency waves, advanced signals mainly ranged between 2 and 10 Hz were detected in several minutes prior to the arrival of the main surge of a debris flow. As the results, the prior time of the advanced signals could be used not only to extend the warning time, but also to identify the initial location of a developing debris flow.

The Characteristics and triggering Factors of the October 2013 Obudu International Tourist Centre catastrophic Landslide South-East Nigeria

NASA Astrophysics Data System (ADS)

Fukuoka, Hiroshi; Igwe, Ogbonnaya

2015-04-01

The October 2013 catastrophic landslides at the Obudu international tourist zone south-east Nigeria destroyed resources worth several millions of dollars and trapped international tourist who were later rescued by a helicopter. Intense rainfall caused several slope failures on the steep slopes of the hills. These landslides occurred after several days of heavy rain (> 600 mm) and were the first reported slope failures in this region. The failures were on a predominantly metamorphic terrain and only on slopes adjacent to the main road. They occurred as slides, not debris flow, but produced a wide range of casualties. The failures were of residual materials (about 1 m thick) obtained from weathering of schist. One of the landslides involved the movement of about 70,000 m3 debris for 8.6 m with depth of slip surface of 6 m. Another, which produced the most fatality initiated on a slope greater than 40o and displaced about 77, 000 m3. It had a runout length of 60 m, width of 98 m, depth to slip surface of 8 m and depositional area of about 2,500 m2. Had the opposite slope bounding the other side of the road not hindered the movement of debris, the runout distance could have been larger. The research found that all the landslides occurred on slope-portions composed of schist rather than gneiss or granite. Slip surfaces developed within the regolith and the shear zone was characterized by the presence of silty materials supported by clayey matrix. Field observations indicated that the failures generally developed as localized translational slides within the semi-consolidated, cohesive soil units (with high plasticity and low strength) within the upper to middle weathered zone of the schist. The increase in pore pressure arising from elevated water table during rainfall created instability by weakening the shear strength along the failure plane. However, differences in permeability favored the formation of perched water table which eventually triggered sliding.

Generation of Martian chaos and channels by debris flows

NASA Technical Reports Server (NTRS)

Nummedal, D.; Prior, D. B.

1981-01-01

A debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into Crysae Planitia from the adjacent southern uplands of Mars. Based on considerations of the juxtaposition of individual channel environments, the morphological assemblages within each environment and flow dynamics, it is suggested that the debris flows were triggered by the large-scale failure of subsurface sediments, possibly initiated by a seismic event. During the initial, slow-moving phase of the flow, the debris would have formed gently sinuous channels with multiple side-wall slumps, grooves and ridges, and elongate erosional remnants. The flow would have gained mobility as the debris moved downslope, producing travel distances greatly in excess of those characteristic of terrestrial examples, and eroded, streamlined remnants at the distal reaches of the channel. Finally, due to internal and boundary friction, the flow would have been slowed down once it entered the Chryse plains, resulting in a thin debris blanket with no depositional relief.

On debris flows, river networks, and the spatial structure of channel morphology.

Treesearch

P.E. Bigelow; L.E. Benda; D.J. Miller; K.M. Burnett

2007-01-01

In this paper, we examine the influence of debris-flow deposits and fans on channels and habitat characteristics in small to intermediate-size watersheds in the Oregon Coast Range. We evaluate: (1) the proportion of stream length bordered by debris fans and the spacing between fans, (2) the recurrence interval of debris flows in unmanaged watersheds, (3) the proportion...

A probabilistic model of debris-flow delivery to stream channels, demonstrated for the Coast Range of Oregon, USA

Treesearch

Daniel J. Miller; Kelly M. Burnett

2008-01-01

Debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance. Identification of channels susceptible to debris-flow inputs of sediment and organic debris, and quantification of the likelihood and magnitude of those inputs, are key tasks for characterizing...

Predicting debris-flow initiation and run-out with a depth-averaged two-phase model and adaptive numerical methods

NASA Astrophysics Data System (ADS)

George, D. L.; Iverson, R. M.

2012-12-01

Numerically simulating debris-flow motion presents many challenges due to the complicated physics of flowing granular-fluid mixtures, the diversity of spatial scales (ranging from a characteristic particle size to the extent of the debris flow deposit), and the unpredictability of the flow domain prior to a simulation. Accurately predicting debris-flows requires models that are complex enough to represent the dominant effects of granular-fluid interaction, while remaining mathematically and computationally tractable. We have developed a two-phase depth-averaged mathematical model for debris-flow initiation and subsequent motion. Additionally, we have developed software that numerically solves the model equations efficiently on large domains. A unique feature of the mathematical model is that it includes the feedback between pore-fluid pressure and the evolution of the solid grain volume fraction, a process that regulates flow resistance. This feature endows the model with the ability to represent the transition from a stationary mass to a dynamic flow. With traditional approaches, slope stability analysis and flow simulation are treated separately, and the latter models are often initialized with force balances that are unrealistically far from equilibrium. Additionally, our new model relies on relatively few dimensionless parameters that are functions of well-known material properties constrained by physical data (eg. hydraulic permeability, pore-fluid viscosity, debris compressibility, Coulomb friction coefficient, etc.). We have developed numerical methods and software for accurately solving the model equations. By employing adaptive mesh refinement (AMR), the software can efficiently resolve an evolving debris flow as it advances through irregular topography, without needing terrain-fit computational meshes. The AMR algorithms utilize multiple levels of grid resolutions, so that computationally inexpensive coarse grids can be used where the flow is absent, and much higher resolution grids evolve with the flow. The reduction in computational cost, due to AMR, makes very large-scale problems tractable on personal computers. Model accuracy can be tested by comparison of numerical predictions and empirical data. These comparisons utilize controlled experiments conducted at the USGS debris-flow flume, which provide detailed data about flow mobilization and dynamics. Additionally, we have simulated historical large-scale debris flows, such as the (≈50 million m^3) debris flow that originated on Mt. Meager, British Columbia in 2010. This flow took a very complex route through highly variable topography and provides a valuable benchmark for testing. Maps of the debris flow deposit and data from seismic stations provide evidence regarding flow initiation, transit times and deposition. Our simulations reproduce many of the complex patterns of the event, such as run-out geometry and extent, and the large-scale nature of the flow and the complex topographical features demonstrate the utility of AMR in flow simulations.

Evaluation of the potential for debris and hyperconcentrated flows in Capulin Canyon as a result of the 1996 Dome fire, Bandelier National Monument, New Mexico

USGS Publications Warehouse

Cannon, Susan H.

1997-01-01

The Dome fire of April 1996 burned 6684 ha in Bandelier National Monument and the adjacent Sante Fe National Forest. The potential for significant debris- and hyperconcentrated-flow activity in Capulin Canyon is evaluated through 1) a systematic consideration of geologic and geomorphic factors that characterize the condition of the hillslope materials and channels following the fire, 2) examination of sedimentologic evidence for past debris-flow activity in the canyon, and 3) evaluation of the response of the watershed through the 1996 summer monsoon season. The lack of accumulations of dry-ravel material on the hillslopes or in channels, the absence of a continuous hydrophobic layer, the relatively intact condition of the riparian vegetation and of the fibrous root mat on the hillslopes, and the lack of evidence of widespread past debris- and hyperconcentrated-flow activity, even with evidence of past fires, indicate a low potential for debris-flow activity in Capulin Canyon. In addition, thunderstorms during the summer monsoon of 1996 resulted in abundant surface overland flow on the hillslopes which transported low-density pumice, charcoal, ash and some mineral soil downslope as small-scale and non-erosive debris flows. In some places cobble- and boulder-sized material was moved short distances. A moderate potential for debris- and hyperconcentrated-flow activity is identified for the two major tributary canyons to Capulin Canyon based on evidence of both summer of 1996 and possible historic significant debris-flow activity.

[Relations of landslide and debris flow hazards to environmental factors].

PubMed

Zhang, Guo-ping; Xu, Jing; Bi, Bao-gui

2009-03-01

To clarify the relations of landslide and debris flow hazards to environmental factors is of significance to the prediction and evaluation of landslide and debris flow hazards. Base on the latitudinal and longitudinal information of 18431 landslide and debris flow hazards in China, and the 1 km x 1 km grid data of elevation, elevation difference, slope, slope aspect, vegetation type, and vegetation coverage, this paper analyzed the relations of landslide and debris flow hazards in this country to above-mentioned environmental factors by the analysis method of frequency ratio. The results showed that the landslide and debris flow hazards in China more occurred in lower elevation areas of the first and second transitional zones. When the elevation difference within a 1 km x 1 km grid cell was about 300 m and the slope was around 30 degree, there was the greatest possibility of the occurrence of landslide and debris hazards. Mountain forest land and slope cropland were the two land types the hazards most easily occurred. The occurrence frequency of the hazards was the highest when the vegetation coverage was about 80%-90%.

Effects of wood on debris flow runout in small mountain watersheds.

Treesearch

Stephen T. Lancaster; Shannon K. Hayes

2003-01-01

Debris flows have typically been viewed as two-phase mixtures of sediment and water, but in forested mountain landscapes, wood can represent a sizable fraction of total flow volume. The effects of this third phase on flow behavior are poorly understood. To evaluate whether wood can have a significant effect on debris flow runout in small mountainous watersheds, we used...

Estimation of Rheological Properties of Viscous Debris Flow Using a Belt Conveyor

NASA Astrophysics Data System (ADS)

Hübl, J.; Steinwendtner, H.

2000-09-01

Rheological parameters of viscous debris flows are influenced by a great amount of factors and are therefore extremely difficult to estimate. Because of this uncertainties a belt conveyor (conveyor channel) was constructed to measure flow behaviour and rheological properties of natural debris flow material. The upward movement of the smooth rubberised belt between fixed lateral plastic walls causes a stationary wave relative to these bends. This special experimental design enables to study behaviour of viscous ebris flow material with maximum grain diameters up to 20 mm within several minutes and to hold measuring equipment very simple. The conveyor channel was calibrated first with Xanthan, a natural polysaccharide used as thickener in food technology, whose rheological properties are similar to viscous debris flow material. In a second step natural debris flow material was investigated. Velocities and rheological parameters were measured with varying solid concentration and slope of the channel. In cases where concentration of coarse particles exceed around 15% by volume the conveyor channel obtains an alternative to expensive commercial viscometers for determination of rheological parameters of viscous debris flows.

Development of a debris flow model in a geotechnical centrifuge

NASA Astrophysics Data System (ADS)

Cabrera, Miguel Angel; Wu, Wei

2013-04-01

Debris flows occur in three main stages. At first the initial soil mass, which rests in a rigid configuration, reaches a critic state releasing a finite mass over a failure surface. In the second stage the released mass starts being transported downhill in a dynamic motion. Segregation, erosion, entrainment, and variable channel geometry are among the more common characteristics of this stage. Finally, at the third stage the transported mass plus the mass gained or loosed during the transportation stage reach a flat and/or a wide area and its deposition starts, going back to a rigid configuration. The lack of understanding and predictability of debris flow from the traditional theoretical approaches has lead that in the last two decades the mechanics of debris flows started to be analysed around the world. Nevertheless, the validation of recent numerical advances with experimental data is required. Centrifuge modelling is an experimental tool that allows the test of natural processes under defined boundary conditions in a small scale configuration, with a good level of accuracy in comparison with a full scale test. This paper presents the development of a debris flow model in a geotechnical centrifuge focused on the second stage of the debris flow process explained before. A small scale model of an inclined flume will be developed, with laboratory instrumentation able to measure the pore pressure, normal stress, and velocity path, developed in a scaled debris flow in motion. The model aims to reproduce in a controlled environment the main parameters of debris flow motion. This work is carried under the EC 7th Framework Programme as part of the MUMOLADE project. The dataset and data-analysis obtained from the tests will provide a qualitative description of debris flow motion-mechanics and be of valuable information for MUMOLADE co-researchers and for the debris flow research community in general.

Grain size indicators of sedimentary coupling between hillslopes and channels in a dryland basin

NASA Astrophysics Data System (ADS)

Hollings, Rory; Michealides, Katerina; Bliss Singer, Michael

2017-04-01

In dryland landscapes, heterogeneous and short-lived rainstorms generate runoff on slopes and streamflow in channels, which drive sediment movement from hillslope surfaces to channels and the transport of bed material sediment within channels. Long-term topographic evolution of drainage basins is partly determined by the relative balance of hillslope sediment supply to channels and the evacuation of channel sediment. However, it is not clear whether supply or evacuation is dominant over longer timescales (>>100 y) within dryland basins. One important indicator of local cumulative sediment transport is grain size (GS). On dryland hillslopes, grain size is governed over long timescales by weathering, but on short time scales (events to decades), is controlled by event-driven transport of the debris mantle. In the channel, GS reflects the input of hillslope sediment and the selective transport of particles along the bed. It is currently unknown how these two processes are expressed systematically within GS distributions on slopes and in channels within drylands, but this information could be useful to explain the history of the relative balance between hillslope sediment supply to channels and net sediment transport in the channel. We investigate this problem by combining field measurements of surface sediment grain size distributions in channels and on hillslopes with 1m LiDAR topography, >60 years of rainfall and channel discharge data from the Walnut Gulch Experimental Watershed (WGEW) in Arizona, and simple calculations of grain-sized based local stress distributions for various rainfall and discharge events. Hydrological scenarios of overland flow on hillslopes and channel flow conditions were derived from distributions of historic data at WGEW and were selected to reflect the wide range of storm intensities and durations, and channel discharges. 1) We used three quartiles of the entire distribution of measured discharge values for 80 locations throughout the channel network to represent low, medium and high flows. 2) For rainfall we used three quartiles of the entire distribution of measured rainfall intensity and duration from 85 rain gauges spanning the basin, to derive low, medium and high rainfall durations. We then calculated the corresponding rainfall intensities based on four intensity-duration curves that were characteristic of different parts of the phase space of the measured data-points. 3) The derived rainfall intensities and durations were converted into hillslope overland flow using Coup2D (a hillslope rainfall-runoff model) for 44 hillslopes within WGEW for which we have GS and topographic data. We employ the median grain size (D50) to compare stress metrics on hillslopes and in channel for each location. Typically, low-order streams experience greater influxes of hillslope derived sediment than is evacuated by the channel. However, the main channel stem is characterised by sediment removal in most scenarios including low discharge, long duration rainfall, suggesting most hillslope supplied sediment is balanced by channel evacuation. Near tributary junctions, and close to the mouth of the basin there are fluctuations in net balance of sediment transport from evacuation- to supply-dominance for different scenarios. These fluctuations could influence channel bed GS distribution and longitudinal profile development.

Rainfall influence on styles of mass movement

NASA Astrophysics Data System (ADS)

Anderson, S. P.; Rengers, F. K.; Foster, M. A.; Winchell, E. W.; Anderson, R. S.

2017-12-01

Precipitation characteristics influence whether hillslope materials move in rain-splash driven hops, shallow landslides, or in deep-seated failures. While one might expect a particular style of slope failure to dominate in a region, we report on multiple distinctive mass movements on a single ridge, each associated with different weather events. This suggests that understanding climate regulation of denudation rates and hillslope morphology requires quantifying both triggering hydro-climates, and the corresponding hillslope response to the full spectrum of events. We explore these connections on Dakota Ridge, a hogback at the eastern margin of the Colorado Front Range. The dipslope of Dakota Ridge has generated slumps, debris flows, and an earthflow over the last 4 years; Pleistocene-era deep-seated landslides are also evident. We document mass-movements along a 1 km long segment of Dakota Ridge. Weeklong precipitation and flooding in September 2013 produced slumps, each of which displaced 50-100 m3 of mobile regolith several meters downslope, and some of which triggered shallow, relatively non-erosive debris flows. By contrast, a similar precipitation total over the month of May 2015 mobilized an earthflow. The 10 m wide earthflow displaced mobile regolith downslope as much as 10 m over its 150 m length. These recent landslides are dwarfed by a 400 m wide deep-seated landslide that controls slope morphology from ridge crest to toe. Exposure ages (10Be) suggest a late-Pleistocene age for this feature. Although the September 2013 storm produced record-setting rainfall totals at daily, monthly and annual timescales (e.g., annual exceedance probability of <1/1000 for daily totals), the failures from that event, while numerous, were the smallest of all the landslides in the study area. These observations raise the question: what hydro-climatic conditions produce deep-seated, bedrock involved slope failures? Recent storms suggest that within mobile regolith, individual failure size increases with duration of the triggering weather event. Ridge-scale bedrock-involved failures presumably reflect a more persistently wet climate.

Evolving Hazard Monitoring and Communication at San Vicente Volcano, El Salvador

NASA Astrophysics Data System (ADS)

Bowman, L. J.; Gierke, J. S.

2014-12-01

El Salvador has 20 potentially active volcanoes, four of which have erupted in the last 100 years. Since San Vicente Volcano has had no historic eruptions, monitoring is not a high priority; especially given the current eruptive crisis at San Miguel Volcano. Though probability of eruptive hazards remains low at San Vicente, it is arguably one of the most hazardous volcanoes in the country due to rainfall-induced landslides and debris-flow risk. At least 250 deaths occurred in November 2009 from landslides and debris flows triggered by Hurricane Ida. This disaster caused the Universidad de El Salvador - Facultad Multidisciplinaria Paracentral (UES-FMP, San Vicente, El Salvador) to partner with governmental and nongovernmental organizations (including the U.S. Peace Corps, U.S. Fulbright Program, Korean International Cooperation Agency, Protección Civil and the Centro de Protección para Desastres (CEPRODE)) to focus its faculty and student research toward hazard monitoring and risk studies. Newly established monitoring efforts include: measurement of surface cracks and localized rainfall by Protección Civil and local residents using crude extensometers and rain gauges; installation of six weather stations that operate within the most at-risk municipalities; seismic refraction surveys to better characterize stratigraphy and seasonal water table changes; and most recently, a USAID/NSF-funded initiative partnered with the UES-FMP to monitor seasonal hydrologic conditions related to flooding and groundwater recharge. The information from these initiatives is now used to communicate current conditions and warnings through a network of two-way radios established by CEPRODE and Protección Civil. Representatives from the multi-institutional team also communicate the data to authorities who make better-informed decisions regarding warnings and evacuations, as well as determine suitable areas for population relocation in the event of a crisis. Data will eventually be used to model and forecast potential hazard events.

VISCOPLASTIC FLUID MODEL FOR DEBRIS FLOW ROUTING.

USGS Publications Warehouse

Chen, Cheng-lung

1986-01-01

This paper describes how a generalized viscoplastic fluid model, which was developed based on non-Newtonian fluid mechanics, can be successfully applied to routing a debris flow down a channel. The one-dimensional dynamic equations developed for unsteady clear-water flow can be used for debris flow routing if the flow parameters, such as the momentum (or energy) correction factor and the resistance coefficient, can be accurately evaluated. The writer's generalized viscoplastic fluid model can be used to express such flow parameters in terms of the rheological parameters for debris flow in wide channels. A preliminary analysis of the theoretical solutions reveals the importance of the flow behavior index and the so-called modified Froude number for uniformly progressive flow in snout profile modeling.

Influence of deposition of fine plant debris in river floodplain shrubs on flood flow conditions - The Warta River case study

NASA Astrophysics Data System (ADS)

Mazur, Robert; Kałuża, Tomasz; Chmist, Joanna; Walczak, Natalia; Laks, Ireneusz; Strzeliński, Paweł

2016-08-01

This paper presents problems caused by organic material transported by flowing water. This material is usually referred to as plant debris or organic debris. Its composition depends on the characteristic of the watercourse. For lowland rivers, the share of the so-called small organic matter in plant debris is considerable. This includes both various parts of water plants and floodplain vegetation (leaves, stems, blades of grass, twigs, etc.). During floods, larger woody debris poses a significant risk to bridges or other water engineering structures. It may cause river jams and may lead to damming of the flowing water. This, in turn, affects flood safety and increases flood risk in river valleys, both directly and indirectly. The importance of fine plant debris for the phenomenon being studied comes down to the hydrodynamic aspect (plant elements carried by water end up on trees and shrubs, increase hydraulic flow resistance and contribute to the nature of flow through vegetated areas changed from micro-to macro-structural). The key part of the research problem under analysis was to determine qualitative and quantitative debris parameters and to establish the relationship between the type of debris and the type of land use of river valleys (crop fields, meadows and forested river sections). Another problem was to identify parameters of plant debris for various flow conditions (e.g. for low, medium and flood flows). The research also included an analysis of the materials deposited on the structure of shrubs under flood flow conditions during the 2010 flood on the Warta River.

Evidence for debris flow gully formation initiated by shallow subsurface water on Mars

USGS Publications Warehouse

Lanza, N.L.; Meyer, G.A.; Okubo, C.H.; Newsom, Horton E.; Wiens, R.C.

2010-01-01

The morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation, erosion, and deposition. On Earth, debris flows are often triggered by shallow subsurface throughflow of liquid water in slope-mantling colluvium. This flow causes increased levels of pore pressure and thus decreased shear strength, which can lead to slide failure of slope materials and subsequent debris flow. The threshold for pore pressure-induced failure creates a distinct relationship between the contributing area supplying the subsurface flow and the slope gradient. To provide initial tests of a similar debris flow initiation hypothesis for martian gullies, measurements of the contributing areas and slope gradients were made at the channel heads of martian gullies seen in three HiRISE stereo pairs. These gullies exhibit morphologies suggestive of debris flows such as leveed channels and lobate debris fans, and have well-defined channel heads and limited evidence for multiple flows. Our results show an area-slope relationship for these martian gullies that is consistent with that observed for terrestrial gullies formed by debris flow, supporting the hypothesis that these gullies formed as the result of saturation of near-surface regolith by a liquid. This model favors a source of liquid that is broadly distributed within the source area and shallow; we suggest that such liquid could be generated by melting of broadly distributed icy materials such as snow or permafrost. This interpretation is strengthened by observations of polygonal and mantled terrain in the study areas, which are both suggestive of near-surface ice. ?? 2009 Elsevier Inc.

Estimation of the Relative Severity of Floods in Small Ungauged Catchments for Preliminary Observations on Flash Flood Preparedness: A Case Study in Korea

PubMed Central

Kim, Eung Seok; Choi, Hyun Il

2012-01-01

An increase in the occurrence of sudden local flooding of great volume and short duration has caused significant danger and loss of life and property in Korea as well as many other parts of the World. Since such floods usually accompanied by rapid runoff and debris flow rise quite quickly with little or no advance warning to prevent flood damage, this study presents a new flash flood indexing methodology to promptly provide preliminary observations regarding emergency preparedness and response to flash flood disasters in small ungauged catchments. Flood runoff hydrographs are generated from a rainfall-runoff model for the annual maximum rainfall series of long-term observed data in the two selected small ungauged catchments. The relative flood severity factors quantifying characteristics of flood runoff hydrographs are standardized by the highest recorded maximum value, and then averaged to obtain the flash flood index only for flash flood events in each study catchment. It is expected that the regression equations between the proposed flash flood index and rainfall characteristics can provide the basis database of the preliminary information for forecasting the local flood severity in order to facilitate flash flood preparedness in small ungauged catchments. PMID:22690208

Development of potential map for landslides by comparing instability indices of various time periods

NASA Astrophysics Data System (ADS)

Chiang, Jie-Lun; Tian, Yu-Qing; Chen, Yie-Ruey; Tsai, Kuang-Jung

2017-04-01

In recent years, extreme rainfall events occur frequently and induced serious landslides and debris flow disasters in Taiwan. The instability indices will differ when using landslide maps of different time periods. We analyzed the landslide records during the period year, 2008 2012, the landslide area contributed 0.42% 2.94% of the total watershed area, the 2.94% was caused by the typhoon Morakot in August, 2009, which brought massive rainfall in which the cumulative maximum rainfall was up to 2900 mm. We analyzed the instability factors including elevation, slope, aspect, soil, and geology. And comparing the instability indices by using individual landslide map of 2008 2012, the landslide maps of the union of the five years, and interaction of the five years. The landslide area from union of the five years contributed 3.71%,the landslide area from interaction of the five years contributed 0.14%. In this study, Kriging was used to establish the susceptibility map in selected watershed. From interaction of the five years, we found the instability index above 4.3 can correspond to those landslide records. The potential landslide area of the selected watershed, where collapses occur more likely, belongs to high level and medium-high level; the area is 13.43% and 3.04% respectively.

Typical Geo-Hazards and Countermeasures of Mines in Yunnan Province, Southwest China

NASA Astrophysics Data System (ADS)

Cheng, Xianfeng; Qi, Wufu; Huang, Qianrui; Zhao, Xueqiong; Fang, Rong; Xu, Jun

2016-10-01

Mining-induced geo-hazards have caused enormous destruction and threat to mines. Known as the "kingdom of nonferrous metals" and located in Southwest China, Yunnan Province developed mining-induced geo-hazards well with characteristics of multiple types, widespread distribution and serious damage. Landslides and debris flows are two common sub-types of geohazards causing most serious damage in Yunnan, and some of them were very representative in the world. Two landslides and two debris flows were chosen to analyze deeply. Both Laojinshan Landslide and Sunjiaqing Landslide possess the characteristic of rock avalanches. The high sliding speed and long distance made the landslides translate into clastic flows with impact force and caused enormous destruction. Rainstorm and mining waste rock were two main factors to induce debris flows in Yunnan mines. Heishan valley debris flow of Dongchuan copper mine was a super large rainstorm type viscose debris flow with very low frequency, which brought a good caution to utilize valleys which looked an unlikely debris flow. Nandagou Valley of Jinding lead-zinc mine in Lanping County was a rainstorm stimulating, gully-type, high frequency and large scale debris flow, which was induced by mining activities. Many countermeasures have been used for Yunnan mines, including engineering treatment technology and ecological remediation, monitoring and forecasting, relocation and public administration.

Parameterization of a numerical 2-D debris flow model with entrainment: a case study of the Faucon catchment, Southern French Alps

NASA Astrophysics Data System (ADS)

Hussin, H. Y.; Luna, B. Quan; van Westen, C. J.; Christen, M.; Malet, J.-P.; van Asch, Th. W. J.

2012-10-01

The occurrence of debris flows has been recorded for more than a century in the European Alps, accounting for the risk to settlements and other human infrastructure that have led to death, building damage and traffic disruptions. One of the difficulties in the quantitative hazard assessment of debris flows is estimating the run-out behavior, which includes the run-out distance and the related hazard intensities like the height and velocity of a debris flow. In addition, as observed in the French Alps, the process of entrainment of material during the run-out can be 10-50 times in volume with respect to the initially mobilized mass triggered at the source area. The entrainment process is evidently an important factor that can further determine the magnitude and intensity of debris flows. Research on numerical modeling of debris flow entrainment is still ongoing and involves some difficulties. This is partly due to our lack of knowledge of the actual process of the uptake and incorporation of material and due the effect of entrainment on the final behavior of a debris flow. Therefore, it is important to model the effects of this key erosional process on the formation of run-outs and related intensities. In this study we analyzed a debris flow with high entrainment rates that occurred in 2003 at the Faucon catchment in the Barcelonnette Basin (Southern French Alps). The historic event was back-analyzed using the Voellmy rheology and an entrainment model imbedded in the RAMMS 2-D numerical modeling software. A sensitivity analysis of the rheological and entrainment parameters was carried out and the effects of modeling with entrainment on the debris flow run-out, height and velocity were assessed.

Scaling and design of landslide and debris-flow experiments

USGS Publications Warehouse

Iverson, Richard M.

2015-01-01

Scaling plays a crucial role in designing experiments aimed at understanding the behavior of landslides, debris flows, and other geomorphic phenomena involving grain-fluid mixtures. Scaling can be addressed by using dimensional analysis or – more rigorously – by normalizing differential equations that describe the evolving dynamics of the system. Both of these approaches show that, relative to full-scale natural events, miniaturized landslides and debris flows exhibit disproportionately large effects of viscous shear resistance and cohesion as well as disproportionately small effects of excess pore-fluid pressure that is generated by debris dilation or contraction. This behavioral divergence grows in proportion to H3, where H is the thickness of a moving mass. Therefore, to maximize geomorphological relevance, experiments with wet landslides and debris flows must be conducted at the largest feasible scales. Another important consideration is that, unlike stream flows, landslides and debris flows accelerate from statically balanced initial states. Thus, no characteristic macroscopic velocity exists to guide experiment scaling and design. On the other hand, macroscopic gravity-driven motion of landslides and debris flows evolves over a characteristic time scale (L/g)1/2, where g is the magnitude of gravitational acceleration and L is the characteristic length of the moving mass. Grain-scale stress generation within the mass occurs on a shorter time scale, H/(gL)1/2, which is inversely proportional to the depth-averaged material shear rate. A separation of these two time scales exists if the criterion H/L < < 1 is satisfied, as is commonly the case. This time scale separation indicates that steady-state experiments can be used to study some details of landslide and debris-flow behavior but cannot be used to study macroscopic landslide or debris-flow dynamics.

Distinguishing between debris flows and floods from field evidence in small watersheds

USGS Publications Warehouse

Pierson, Thomas C.

2005-01-01

Post-flood indirect measurement techniques to back-calculate flood magnitude are not valid for debris flows, which commonly occur in small steep watersheds during intense rainstorms. This is because debris flows can move much faster than floods in steep channel reaches and much slower than floods in low-gradient reaches. In addition, debris-flow deposition may drastically alter channel geometry in reaches where slope-area surveys are applied. Because high-discharge flows are seldom witnessed and automated samplers are commonly plugged or destroyed, determination of flow type often must be made on the basis of field evidence preserved at the site.

A water balance approach to enhance national (GB) Daily Landslide Hazard Assessments

NASA Astrophysics Data System (ADS)

Dijkstra, Tom; Reeves, Helen; Freeborough, Katy; Dashwood, Claire; Pennington, Catherine; Jordan, Hannah; Hobbs, Peter; Richardson, Jennifer; Banks, Vanessa; Cole, Steven; Wells, Steven; Moore, Robert

2017-04-01

The British Geological Survey (BGS) is a member of the Natural Hazards Partnership (NHP) and delivers a national (GB) daily landslide hazard assessment (DLHA). The DLHA is based largely on 'expert' driven evaluations of the likelihood of landslides in response to antecedent ground conditions, adverse weather and reported landslide events. It concentrates on shallow translational slides and debris flows - events that most frequently have societal consequences by disrupting transport infrastructure and affecting buildings. Considerable experience with the issuing of DLHAs has been gained since 2012. However, it remains very difficult to appropriately assess changing ground conditions throughout GB even when good quality precipitation forecasts are available. Soil moisture sensors are available, but the network is sparse and not yet capable of covering GB to the detail required to underpin the forecasts. Therefore, we developed an approach where temporal and spatial variations in soil moisture can be obtained from a water balance model, representing processes in the near-surface and configured on a relatively coarse grid of 1 km2. Model outputs are not intended to be relevant to the slope scale. The assumption is that the likelihood of landslides being triggered by rainfall is dependent upon the soil moisture conditions of the near-surface, in combination with how much rain is forecast to occur for the following day. These variables form the basis for establishing thresholds to guide the issuing of DLHA and early warnings. The main aim is to obtain an insight into regional patterns of change and threshold exceedance. The BGS water balance model is still in its infancy and it requires substantial work to fine-tune and validate it. To test the performance of the BGS model we focused on an analysis of Scottish landslides (2004-2015) comprising translational slides and debris flows where the BGS model is conditionally evaluated against the Grid-to-Grid (G2G) Model. G2G is a physical-conceptual distributed hydrological model developed by the Centre for Ecology & Hydrology, also an NHP member. G2G is especially suited to simulate river flows over ungauged areas and has the capability to forecast fluvial river flows at any location across a gridded model domain. This is achieved by using spatial datasets on landscape properties - terrain, land-cover, soil and geology - in combination with gridded time-series of rainfall to shape a rainfall pattern into a river flow response over the model domain. G2G is operational on a 1 km2 grid over the GB and outputs soil moisture estimates that take some account of terrain slope in its water balance calculation. This research is part of an evolutionary process where capabilities of establishing the likelihood of landslides will develop as datasets are becoming increasingly detailed (and accessible) and the representation of hydrogeological and geotechnical processes continues to develop.

Mobility statistics and automated hazard mapping for debris flows and rock avalanches

USGS Publications Warehouse

Griswold, Julia P.; Iverson, Richard M.

2008-01-01

Power-law equations that are physically motivated and statistically tested and calibrated provide a basis for forecasting areas likely to be inundated by debris flows, rock avalanches, and lahars with diverse volumes. The equations A=α1V2/3 and B=α2V2/3 are based on the postulate that the maximum valley cross-sectional area (A) and total valley planimetric area (B) likely to be inundated by a flow depend only on its volume (V) and the topography of the flow path. Testing of these equations involves determining whether or not they fit data for documented flows satisfactorily, and calibration entails determining best-fit values of the coefficients α1 and α2 for debris flows, rock avalanches, and lahars. This report describes statistical testing and calibration of the equations by using field data compiled from many sources, and it describes application of the equations to delineation of debris-flow hazard zones. Statistical results show that for each type of flow (debris flows, rock avalanches, and lahars), the dependence of A and B on V is described well by power laws with exponents equal to 2/3. This value of the exponent produces fits that are effectively indistinguishable from the best fits obtained by using adjustable power-law exponents. Statistically calibrated values of the coefficients α1 and α2 provide scale-invariant indices of the relative mobilities of rock avalanches (α1 = 0.2, α2 = 20), nonvolcanic debris flows (α1 = 0.1, α2 = 20), and lahars (α1 = 0.05, α2 = 200). These values show, for example, that a lahar of specified volume can be expected to inundate a planimetric area ten times larger than that inundated by a rock avalanche or nonvolcanic debris flow of the same volume. The utility of the calibrated debris-flow inundation equations A=0.1V2/3 and B=20V2/3 is demonstrated by using them within the GIS program LAHARZ to delineate nested hazard zones for future debris flows in an area bordering the Umpqua River in the south-central Oregon Coast Range. This application requires use of high-resolution topographic data derived form LIDAR surveys, knowledge of local geology to specify a suitable range of prospective debris-flow volumes, and development and use of a new algorithm for identification of prospective debris-flow source areas in finely dissected terrain.

Monitoring and modeling conditions for regional shallow landslide initiation in the San Francisco Bay area, California

NASA Astrophysics Data System (ADS)

Collins, B. D.; Stock, J. D.; Godt, J. W.

2012-12-01

Intense winter storms in the San Francisco Bay area (SFBA) of California often trigger widespread landsliding, including debris flows that originate as shallow (<3 m) landslides. The strongest storms result in the loss of lives and millions of dollars in damage. Whereas precipitation-based rainfall intensity-duration landslide initiation thresholds are available for the SFBA, antecedent soil moisture conditions also play a major role in determining the likelihood for landslide generation from a given storm. Previous research has demonstrated that antecedent triggering conditions can be obtained using pre-storm precipitation thresholds (e.g., 250-400 mm of seasonal pre-storm rainfall). However, these types of thresholds do not account for the often cyclic pattern of wetting and drying that can occur early in the winter storm season (i.e. October - December), and which may skew the applicability of precipitation-only based thresholds. To account for these cyclic and constantly evolving soil moisture conditions, we have pursued methods to measure soil moisture directly and integrate these measurements into predictive analyses. During the past three years, the USGS installed a series of four subsurface hydrology monitoring stations in shallow landslide-prone locations of the SFBA to establish a soil-moisture-based antecedent threshold. In addition to soil moisture sensors, the monitoring stations are each equipped with piezometers to record positive pore water pressure that is likely required for shallow landslide initiation and a rain gauge to compare storm intensities with existing precipitation-based thresholds. Each monitoring station is located on a natural, grassy hillslope typically composed of silty sands, underlain by sandstone, sloping at approximately 30°, and with a depth to bedrock of approximately 1 meter - conditions typical of debris flow generation in the SFBA. Our observations reveal that various locations respond differently to seasonal precipitation, with some areas (e.g., Marin County) remaining at higher levels of saturation for longer periods of time during the winter compared to other areas (e.g., the East Bay Hills). In general, this coincides directly with relative precipitation totals in each region (i.e., Marin county typically receives more rainfall over a longer period of time than the East Bay). In those areas that are saturated for longer periods, the shallow landslide hazard is prolonged because these conditions are first needed for storm-related precipitation to subsequently generate positive pore pressure on the failure plane. Both piezometric field measurements and limit equilibrium slope stability analyses indicate that positive pore pressure is required for most shallow landslide failures to occur in the study regions. Based on measurements from two of the sites, our analyses further indicate that at least 2 kPa of pressure is required to trigger shallow landsliding. We measured this pressure at one of our sites in 2011, where more than 30 landslides, including several that mobilized into debris flows, occurred. Additional monitoring at these sites will be used to further constrain and refine antecedent moisture-based thresholds for shallow landslide initiation.

Grain size controls on sediment supply from debris-mantled dryland hillslopes

NASA Astrophysics Data System (ADS)

Michaelides, K.

2011-12-01

Debris-mantled hillslopes are common in arid and semiarid environments where low rates of chemical weathering give rise to thin, non-cohesive soils mantled with a layer of coarse rock fragments derived from weathered bedrock that can reach boulder size. The grain size distributions (GSDs) on the surface of these hillslopes interact with different magnitudes and frequencies of runoff-producing rainfall events that selectively transport grain sizes of different classes depending on flow, grain position on the slope, and hillslope attributes. Sediment transport over many runoff events determines sediment delivery to the slope base, which ultimately modifies the GSD of valley floors. The relationship between hillslope attributes and sediment flux forms the basis of geomorphic transport laws used to model the topographic evolution of drainage basins over >104 y timescales, but the specific responses of sediment flux across the hillslope and the corresponding changes in GSDs to individual storm events are poorly understood. Sheetwash erosion of coarse fragments presents a particular set of conditions for sediment transport that is poorly resolved in current models. A particle-based model for sheetwash sediment transport on debris-mantled hillslopes was developed within a rainfall-runoff model. The rainfall-runoff model produces spatial values of flow depth and velocity which are used to drive a particle-by-particle force-balance model derived from first principles for grain sizes > 1 mm. Particles on the hillslope surface are represented explicitly and can be composed of mixed grain sizes of any distribution or of uniform sizes of any diameter. The model resolves all the forces on each particle at each time and space step based on the flow hydraulics acting on them, so no assumptions are made about incipient motion using Shield's criterion. This research examines how the interplay between hillslope GSD, hillslope attributes (gradient and length) and runoff characteristics, determine sediment transport dynamics and net flux, GSD supplied to the slope base and the changes in GSD on the hillslope. The results show a strong control of initial hillslope GSD on flux characteristics: (1) GSD controls the degree of non-linearity in the relationship between sediment flux and hillslope gradient. (2) Grain size uniformity controls the degree and form of non-linearity in the relationship between sediment flux and gradient. (3) Over multiple runoff events, slopes coarsen - steeper slopes become coarser than shallow slopes. For individual events, changes in GSD on the slope depend on the magnitude and duration of the runoff event and can result in variable coarsening and fining on different parts of the slope. (4) The GSD of sediment delivered to the slope base is dependent on the hillslope GSD and the hillslope attributes and runoff characteristics. For most runoff events, the GSD of fluxed sediment is finer than the hillslope GSD except for extreme runoff events on very steep slopes with intermediate GSD (not extremely coarse). These findings provide insights into hillslope responses to climatic forcing and have theoretical implications for modeling hillslope evolution in drylands.

A comparative analysis of hazard models for predicting debris flows in Madison County, VA

USGS Publications Warehouse

Morrissey, Meghan M.; Wieczorek, Gerald F.; Morgan, Benjamin A.

2001-01-01

During the rainstorm of June 27, 1995, roughly 330-750 mm of rain fell within a sixteen-hour period, initiating floods and over 600 debris flows in a small area (130 km2) of Madison County, Virginia. Field studies showed that the majority (70%) of these debris flows initiated with a thickness of 0.5 to 3.0 m in colluvium on slopes from 17 o to 41 o (Wieczorek et al., 2000). This paper evaluated and compared the approaches of SINMAP, LISA, and Iverson's (2000) transient response model for slope stability analysis by applying each model to the landslide data from Madison County. Of these three stability models, only Iverson's transient response model evaluated stability conditions as a function of time and depth. Iverson?s model would be the preferred method of the three models to evaluate landslide hazards on a regional scale in areas prone to rain-induced landslides as it considers both the transient and spatial response of pore pressure in its calculation of slope stability. The stability calculation used in SINMAP and LISA is similar and utilizes probability distribution functions for certain parameters. Unlike SINMAP that only considers soil cohesion, internal friction angle and rainfall-rate distributions, LISA allows the use of distributed data for all parameters, so it is the preferred model to evaluate slope stability over SINMAP. Results from all three models suggested similar soil and hydrologic properties for triggering the landslides that occurred during the 1995 storm in Madison County, Virginia. The colluvium probably had cohesion of less than 2KPa. The root-soil system is above the failure plane and consequently root strength and tree surcharge had negligible effect on slope stability. The result that the final location of the water table was near the ground surface is supported by the water budget analysis of the rainstorm conducted by Smith et al. (1996).

Hydrologic Triggering of Shallow Landslides in a Field-scale Flume

NASA Astrophysics Data System (ADS)

Reid, M. E.; Iverson, R. M.; Iverson, N. R.; Brien, D. L.; Lahusen, R. G.; Logan, M.

2006-12-01

Hydrologic Triggering of Shallow Landslides in a Field-scale Flume Mark E. Reid, Richard M. Iverson, Neal R. Iverson, Dianne L. Brien, Richard G. LaHusen, and Mathew Logan Shallow landslides are often triggered by pore-water pressure increases driven by 1) groundwater inflow from underlying bedrock or soil, 2) prolonged moderate-intensity rainfall or snowmelt, or 3) bursts of high-intensity rainfall. These shallow failures are difficult to capture in the field, limiting our understanding of how different water pathways control failure style or timing. We used the field-scale, USGS debris-flow flume for 7 controlled landslide initiation experiments designed to examine the influence of different hydrologic triggers and the role of soil density, relative to critical state, on failure style and timing. Using sprinklers and/or groundwater injectors, we induced failure in a 0.65m thick, 2m wide, 6m3 prism of loamy sand on a 31° slope, placed behind a retaining wall. We monitored ~50 sensors to measure soil deformation (tiltmeters & extensometers), pore pressure (tensiometers and transducers), and soil moisture (TDR probes). We also extracted soil samples for laboratory estimates of porosity, shear strength, saturated hydraulic conductivity at differing porosities, unsaturated moisture retention characteristics, and compressibility. Experiments with loose soil all resulted in abrupt failure along the concrete flume bed with rapid mobilization into a debris flow. Each of the 3 water pathways, however, resulted in slightly different pore-pressure fields at failure and different times to failure. For example, groundwater injection at the flume bed led to a saturated zone that advanced upward, wetting over half the soil prism before pressures at the bed were sufficient to provoke collapse. With moderate-intensity surface sprinkling, an unsaturated wetting front propagated downward until reaching the bed, then a saturated zone built upward, with the highest pressures at the bed. With the third trigger, soils were initially wetted (but not saturated) with moderate-intensity sprinkling and then subjected to a high-intensity burst, causing failure without widespread positive pressures. It appears that a small pressure perturbation from the burst traveled rapidly downward through tension-saturated soil and led to positive pressure development at the flume bed resulting in failure. In contrast, failures in experiments with stronger, denser soil were gradual and episodic, requiring both sprinkling and groundwater injection. Numerical simulations of variably saturated groundwater flow mimic the behaviors described above. Simulated rainfall with an intensity greater than soil hydraulic conductivity generates rapid pressure perturbations, whereas lower intensity rainfall leads to wetting front propagation and water table buildup. Our results suggest that transient responses induced by high intensity bursts require relatively high frequency monitoring of unsaturated zone changes; in this case conventional piezometers would be unlikely to detect failure-inducing pore pressure changes. These experiments also indicate that although different water pathways control the timing of failure, initial soil density controls the style of failure.

Spatial and temporal patterns of debris flow deposition in the Oregon Coast Range, USA

USGS Publications Warehouse

May, Christine L.; Gresswell, Robert E.

2004-01-01

Patterns of debris-flow occurrence were investigated in 125 headwater basins in the Oregon Coast Range. Time since the previous debris-flows was established using dendrochronology, and recurrence interval estimates ranged from 98 to 357 years. Tributary basins with larger drainage areas had a greater abundance of potential landslide source areas and a greater frequency of scouring events compared to smaller basins. The flux rate of material delivered to the confluence with a larger river influenced the development of small-scale debris-flow fans. Fans at the mouths of tributary basins with smaller drainage areas had a higher likelihood of being eroded by the mainstem river in the interval between debris-flows, compared to bigger basins that had larger, more persistent fans. Valley floor width of the receiving channel also influenced fan development because it limited the space available to accommodate fan formation. Of 63 recent debris-flows, 52% delivered sediment and wood directly to the mainstem river, 30% were deposited on an existing fan before reaching the mainstem, and 18% were deposited within the confines of the tributary valley before reaching the confluence. Spatial variation in the location of past and present depositional surfaces indicated that sequential debris-flow deposits did not consistently form in the same place. Instead of being spatially deterministic, results of this study suggest that temporally variable and stochastic factors may be important for predicting the runout length of debris-flows.

Three occurred debris flows in North-Eastern Italian Alps: documentation and modeling

NASA Astrophysics Data System (ADS)

Boreggio, Mauro; Gregoretti, Carlo; Degetto, Massimo; Bernard, Martino

2015-04-01

Three occurred events of debris flows are documented and modeled by back-analysis. The three debris flows events are those occurred at Rio Lazer on the 4th of November 1966, at Fiames on the 5th of July 2006 and at Rovina di Cancia on the 18th of July 2009. All the three sites are located in the North-Eastern Italian Alps. In all the events, runoff entrained sediments present on natural channels and formed a solid-liquid wave that routed downstream. The first event concerns the routing of debris flow on an inhabited fan. Map of deposition pattern of sediments are built by using post-events photos through stereoscopy techniques. The second event concerns the routing of debris flow along the main channel descending from Pomagagnon Fork. Due to the obstruction of the cross-section debris flow deviated from the original path on the left side and routed downstream by cutting a new channel on the fan. It dispersed in multiple paths when met the wooden area. Map of erosion and deposition depths are built after using a combination of Lidar and GPS data. The third event concerns the routing of debris flow in the Rovina di Cancia channel that filled the reservoir built at the end of the channel and locally overtopped the retaining wall on the left side. A wave of mud and debris inundated the area downstream the overtopping point. Map of erosion and deposition depths are obtained by subtracting two GPS surveys, pre and post event. All the three occurred debris flows are simulated by modeling runoff that entrained debris flow for determining the solid-liquid hydrograph downstream the triggering areas. The routing of the solid-liquid hydrograph was simulated by a bi-phase cell model based on the kinematic approach. The comparison between simulated and measured erosion and deposition depths is satisfactory. The same parameters for computing erosion and deposition were used for the three occurred events.

Effects of episodic sediment supply on bedload transport rate in mountain rivers. Detecting debris flow activity using continuous monitoring

NASA Astrophysics Data System (ADS)

Uchida, Taro; Sakurai, Wataru; Iuchi, Takuma; Izumiyama, Hiroaki; Borgatti, Lisa; Marcato, Gianluca; Pasuto, Alessandro

2018-04-01

Monitoring of sediment transport from hillslopes to channel networks as a consequence of floods with suspended and bedload transport, hyperconcentrated flows, debris and mud flows is essential not only for scientific issues, but also for prevention and mitigation of natural disasters, i.e. for hazard assessment, land use planning and design of torrent control interventions. In steep, potentially unstable terrains, ground-based continuous monitoring of hillslope and hydrological processes is still highly localized and expensive, especially in terms of manpower. In recent years, new seismic and acoustic methods have been developed for continuous bedload monitoring in mountain rivers. Since downstream bedload transport rate is controlled by upstream sediment supply from tributary channels and bed-external sources, continuous bedload monitoring might be an effective tool for detecting the sediments mobilized by debris flow processes in the upper catchment and thus represent an indirect method to monitor slope instability processes at the catchment scale. However, there is poor information about the effects of episodic sediment supply from upstream bed-external sources on downstream bedload transport rate at a single flood time scale. We have examined the effects of sediment supply due to upstream debris flow events on downstream bedload transport rate along the Yotagiri River, central Japan. To do this, we have conducted continuous bedload observations using a hydrophone (Japanese pipe microphone) located 6.4 km downstream the lower end of a tributary affected by debris flows. Two debris flows occurred during the two-years-long observation period. As expected, bedload transport rate for a given flow depth showed to be larger after storms triggering debris flows. That is, although the magnitude of sediment supply from debris flows is not large, their effect on bedload is propagating >6 km downstream at a single flood time scale. This indicates that continuous bedload observations could be effective for detecting sediment supply as a consequence of debris flow events.

An experimental operative system for shallow landslide and flash flood warning based on rainfall thresholds and soil moisture modelling

NASA Astrophysics Data System (ADS)

Brigandı, G.; Aronica, G. T.; Basile, G.; Pasotti, L.; Panebianco, M.

2012-04-01

On November 2011 a thunderstorms became almost exceptional over the North-East part of the Sicily Region (Italy) producing local heavy rainfall, mud-debris flow and flash flooding. The storm was concentrated on the Tyrrhenian sea coast near the city of Barcellona within the Longano catchment. Main focus of the paper is to present an experimental operative system for alerting extreme hydrometeorological events by using a methodology based on the combined use of rainfall thresholds, soil moisture indexes and quantitative precipitation forecasting. As matter of fact, shallow landslide and flash flood warning is a key element to improve the Civil Protection achievements to mitigate damages and safeguard the security of people. It is a rather complicated task, particularly in those catchments with flashy response where even brief anticipations are important and welcomed. It is well known how the triggering of shallow landslides is strongly influenced by the initial soil moisture conditions of catchments. Therefore, the early warning system here applied is based on the combined use of rainfall thresholds, derived both for flash flood and for landslide, and soil moisture conditions; the system is composed of several basic component related to antecedent soil moisture conditions, real-time rainfall monitoring and antecedent rainfall. Soil moisture conditions were estimated using an Antecedent Precipitation Index (API), similar to this widely used for defining soil moisture conditions via Antecedent Moisture conditions index AMC. Rainfall threshold for landslides were derived using historical and statistical analysis. Finally, rainfall thresholds for flash flooding were derived using an Instantaneous Unit Hydrograph based lumped rainfall-runoff model with the SCS-CN routine for net rainfall. After the implementation and calibration of the model, a testing phase was carried out by using real data collected for the November 2001 event in the Longano catchment. Moreover, in order to test the capability of the system to forecast thise event, Quantitative Precipitation Forecasting provided by the SILAM (Sicily Limited Area Model), a meteorological model run by SIAS (Sicilian Agrometeorological Service) with a forecast horizon up to 144 hours, have been used to run the system.

Catastrophic debris flows transformed from landslides in volcanic terrains : mobility, hazard assessment and mitigation strategies

USGS Publications Warehouse

Scott, Kevin M.; Macias, Jose Luis; Naranjo, Jose Antonio; Rodriguez, Sergio; McGeehin, John P.

2001-01-01

Communities in lowlands near volcanoes are vulnerable to significant volcanic flow hazards in addition to those associated directly with eruptions. The largest such risk is from debris flows beginning as volcanic landslides, with the potential to travel over 100 kilometers. Stratovolcanic edifices commonly are hydrothermal aquifers composed of unstable, altered rock forming steep slopes at high altitudes, and the terrain surrounding them is commonly mantled by readily mobilized, weathered airfall and ashflow deposits. We propose that volcano hazard assessments integrate the potential for unanticipated debris flows with, at active volcanoes, the greater but more predictable potential of magmatically triggered flows. This proposal reinforces the already powerful arguments for minimizing populations in potential flow pathways below both active and selected inactive volcanoes. It also addresses the potential for volcano flank collapse to occur with instability early in a magmatic episode, as well as the 'false-alarm problem'-the difficulty in evacuating the potential paths of these large mobile flows. Debris flows that transform from volcanic landslides, characterized by cohesive (muddy) deposits, create risk comparable to that of their syneruptive counterparts of snow and ice-melt origin, which yield noncohesive (granular) deposits, because: (1) Volcano collapses and the failures of airfall- and ashflow-mantled slopes commonly yield highly mobile debris flows as well as debris avalanches with limited runout potential. Runout potential of debris flows may increase several fold as their volumes enlarge beyond volcanoes through bulking (entrainment) of sediment. Through this mechanism, the runouts of even relatively small collapses at Cascade Range volcanoes, in the range of 0.1 to 0.2 cubic kilometers, can extend to populated lowlands. (2) Collapse is caused by a variety of triggers: tectonic and volcanic earthquakes, gravitational failure, hydrovolcanism, and precipitation, as well as magmatic activity and eruptions. (3) Risk of collapse begins with initial magmatic activity and increases as intrusion proceeds. An archetypal debris flow from volcanic terrain occurred in Colombia with a tectonic earthquake (M 6.4) in 1994. The Rio Piez conveyed a catastrophic wave of debris flow over 100 kilometers, coalesced from multiple slides of surflcial material weakened both by weathering and by hydrothermal alteration in a large strato- volcano. Similar seismogenic flows occurred in Mexico in 1920 (M -6.5), Chile in 1960 (M 9.2), and Ecuador in 1987 (M 6.1 and 6.9). Velocities of wave fronts in two examples were 60 to 90 km/hr (17-25 meters per second) over the initial 30 kilometers. Volcano flank and sector collapses may produce untransformed debris avalanches, as occurred initially at Mount St. Helens in 1980. However, at least as common is direct transformation of the failed mass to a debris flow. At two other volcanoes in the Cascade Range-- Mount Rainier and Mount Baker--rapid transformation and high mobility were typical of most of at least 15 Holocene flows. This danger exists downstream from many stratovolcanoes worldwide; the population at risk is near 150,000 and increasing at Mount Rainier. The first step in preventing future catastrophes is documenting past flows. Deposits of some debris flows, however, can be mistaken for those of less-mobile debris avalanches on the basis of mounds formed by buoyed megaclasts. Megaclasts may record only the proximal phase of a debris flow that began as a debris avalanche. Runout may have extended much farther, and thus furore flow mobility may be underestimated. Processes and behaviors of megaclast-bearing paleoflows are best inferred from the intermegaclast matrix. Mitigation strategy can respond to volcanic flows regardless of type and trigger by: (1) Avoidance: Limit settlement in flow pathways to numbers that can be evacuated after event warnings (flow is occurring). (2) Instrumental even

Map showing inventory and regional susceptibility for Holocene debris flows, and related fast-moving landslides in the conterminous United States

USGS Publications Warehouse

Brabb, Earl E.; Colgan, Joseph P.; Best, Timothy C.

2000-01-01

Introduction Debris flows, debris avalanches, mud flows and lahars are fast-moving landslides that occur in a wide variety of environments throughout the world. They are particularly dangerous to life and property because they move quickly, destroy objects in their paths, and often strike without warning. This map represents a significant effort to compile the locations of known debris flows in United Stated and predict where future flows might occur. The files 'dfipoint.e00' and 'dfipoly.e00' contain the locations of over 6600 debris flows from published and unpublished sources. The locations are referenced by numbers that correspond to entries in a bibliography, which is part of the pamphlet 'mf2329pamphlet.pdf'. The areas of possible future debris flows are shown in the file 'susceptibility.tif', which is a georeferenced TIFF file that can be opened in an image editing program or imported into a GIS system like ARC/INFO. All other databases are in ARC/INFO export (.e00) format.

Monitoring subsurface hydrologic response for precipitation-induced shallow landsliding in the San Francisco Bay area, California, USA

USGS Publications Warehouse

Collins, Brian D.; Stock, Jonathan; Weber, Lisa C.; Whitman, K.; Knepprath, N.

2012-01-01

Intense winter storms in the San Francisco Bay area (SFBA) of California, USA often trigger shallow landslides. Some of these landslides mobilize into potentially hazardous debris flows. A growing body of research indicates that rainfall intensity-duration thresholds are insufficient for accurate prediction of landslide occurrence. In response, we have begun long-term monitoring of the hydrologic response of land-slide-prone hillslopes to rainfall in several areas of the SFBA. Each monitoring site is equipped with sensors for measuring soil moisture content and piezometric pressure at several soil depths along with a rain gauge connected to a cell phone or satellite telemetered data logger. The data are transmitted in near-real-time, providing the ability to monitor hydrologic conditions before, during, and after storms. Results are guiding the establishment of both antecedent and storm-specific rainfall and moisture content thresholds which must be achieved before landslide-causative positive pore water pressures are generated. Although widespread shallow landsliding has not yet occurred since the deployment of the monitoring sites, several isolated land-slides have been observed in the area of monitoring. The landslides occurred during a period when positive pore water pressures were measured as a result of intense rainfall that followed higher-than-average season precipitation totals. Continued monitoring and analysis will further guide the establishment of more general-ized thresholds for different regions of the SFBA and contribute to the development and calibration of physi-cally-based predictive models.

Experimental Investigation of Rainfall Impact on Overland Flow Driven Erosion Processes and Flow Hydrodynamics on a Steep Hillslope

NASA Astrophysics Data System (ADS)

Tian, P.; Xu, X.; Pan, C.; Hsu, K. L.; Yang, T.

2016-12-01

Few attempts have been made to investigate the quantitative effects of rainfall on overland flow driven erosion processes and flow hydrodynamics on steep hillslopes under field conditions. Field experiments were performed in flows for six inflow rates (q: 6-36 Lmin-1m-1) with and without rainfall (60 mm h-1) on a steep slope (26°) to investigate: (1) the quantitative effects of rainfall on runoff and sediment yield processes, and flow hydrodynamics; (2) the effect of interaction between rainfall and overland flow on soil loss. Results showed that the rainfall increased runoff coefficients and the fluctuation of temporal variations in runoff. The rainfall significantly increased soil loss (10.6-68.0%), but this increment declined as q increased. When the interrill erosion dominated (q=6 Lmin-1m-1), the increment in the rill erosion was 1.5 times that in the interrill erosion, and the effect of the interaction on soil loss was negative. When the rill erosion dominated (q=6-36 Lmin-1m-1), the increment in the interrill erosion was 1.7-8.8 times that in the rill erosion, and the effect of the interaction on soil loss became positive. The rainfall was conducive to the development of rills especially for low inflow rates. The rainfall always decreased interrill flow velocity, decreased rill flow velocity (q=6-24 Lmin-1m-1), and enhanced the spatial uniformity of the velocity distribution. Under rainfall disturbance, flow depth, Reynolds number (Re) and resistance were increased but Froude number was reduced, and lower Re was needed to transform a laminar flow to turbulent flow. The rainfall significantly increased flow shear stress (τ) and stream power (φ), with the most sensitive parameters to sediment yield being τ (R2=0.994) and φ (R2=0.993), respectively, for non-rainfall and rainfall conditions. Compared to non-rainfall conditions, there was a reduction in the critical hydrodynamic parameters of mean flow velocity, τ, and φ by the rainfall. These findings provide a better understanding on the influence mechanism of rainfall impact on hillslope erosion processes.

Morphometric Analysis and Delineation of Debris Flow Susceptible Alluvial Fans in the Philippines after the 2015 Koppu and Melor Typhoon Events

NASA Astrophysics Data System (ADS)

Llanes, F.; Rodolfo, K. S.; Lagmay, A. M. A.

2017-12-01

On 17 October 2015, Typhoon Koppu brought heavy rains that generated debris flows in the municipalities of Bongabon, Laur, and Gabaldon in Nueva Ecija province. Roughly two months later on 15 December, Typhoon Melor made landfall in the province of Oriental Mindoro, bringing heavy rains that also generated debris flows in multiple watersheds in the municipality of Baco. Despite not being in the direct path of the typhoon, debris flows were triggered in Bongabon, Gabaldon, and Laur, whereas old debris-flow deposits were remobilized in Dingalan, a coastal town in Aurora province adjacent to Gabaldon. During the onslaught of Typhoons Koppu and Melor, landslides of rock, soil, and debris converged in the mountain stream networks where they were remobilized into debris flows that destroyed numerous houses and structures situated on alluvial fans. Satellite images before and after the two typhoons were compared to calculate the deposit extents on the fans and to determine the number and extent of landslides on each watershed. The affected alluvial fans were investigated in the field to determine whether they are debris flow or flood-prone, using a set of established geomorphic and sedimentary characteristics that differentiate deposits of the two processes. Melton ratio, watershed length, and other significant morphometric indices were calculated and analyzed for the affected watersheds using geographic information system (GIS) and high-resolution digital terrain models. A GIS model that can delineate debris flow susceptible alluvial fans in the Philippines was derived and developed from the analysis. Limitations of the model are discussed, as well as recommendations to improve and refine it.

Flow behavior and mobility of contaminated waste rock materials in the abandoned Imgi mine in Korea

NASA Astrophysics Data System (ADS)

Jeong, S. W.; Wu, Y.-H.; Cho, Y. C.; Ji, S. W.

2018-01-01

Incomplete mine reclamation can cause ecological and environmental impacts. This paper focuses on the geotechnical and rheological characteristics of waste rock materials, which are mainly composed of sand-size particles, potentially resulting in mass movement (e.g., slide or flow) and extensive acid mine drainage. To examine the potential for contaminant mobilization resulting from physicochemical processes in abandoned mines, a series of scenario-based debris flow simulations was conducted using Debris-2D to identify different hazard scenarios and volumes. The flow behavior of waste rock materials was examined using a ball-measuring rheometric apparatus, which can be adapted for large particle samples, such as debris flow. Bingham yield stresses determined in controlled shear rate mode were used as an input parameter in the debris flow modeling. The yield stresses ranged from 100 to 1000 Pa for shear rates ranging from 10- 5 to 102 s- 1. The results demonstrated that the lowest yield stress could result in high mobility of debris flow (e.g., runout distance > 700 m from the source area for 60 s); consequently, the material contaminants may easily reach the confluence of the Suyoung River through a mountain stream. When a fast slide or debris flow occurs at or near an abandoned mine area, it may result in extremely dynamic and destructive geomorphological changes. Even for the highest yield stress of debris flow simulation (i.e., τy = 2000 Pa), the released debris could flow into the mountain stream; therefore, people living near abandoned mines may become exposed to water pollution throughout the day. To maintain safety at and near abandoned mines, the physicochemical properties of waste materials should be monitored, and proper mitigation measures post-mining should be considered in terms of both their physical damage and chemical pollution potential.

Estimating ice albedo from fine debris cover quantified by a semi-automatic method: the case study of Forni Glacier, Italian Alps

NASA Astrophysics Data System (ADS)

Azzoni, Roberto Sergio; Senese, Antonella; Zerboni, Andrea; Maugeri, Maurizio; Smiraglia, Claudio; Diolaiuti, Guglielmina Adele

2016-03-01

In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface. Accordingly, we proposed a novel method based on semi-automatic image analysis to estimate ice albedo from fine debris coverage (d). Our procedure was tested on the surface of a wide Alpine valley glacier (the Forni Glacier, Italy), in summer 2011, 2012 and 2013, acquiring parallel data sets of in situ measurements of ice albedo and high-resolution surface images. Analysis of 51 images yielded d values ranging from 0.01 to 0.63 and albedo was found to vary from 0.06 to 0.32. The estimated d values are in a linear relation with the natural logarithm of measured ice albedo (R = -0.84). The robustness of our approach in evaluating d was analyzed through five sensitivity tests, and we found that it is largely replicable. On the Forni Glacier, we also quantified a mean debris coverage rate (Cr) equal to 6 g m-2 per day during the ablation season of 2013, thus supporting previous studies that describe ongoing darkening phenomena at Alpine debris-free glaciers surface. In addition to debris coverage, we also considered the impact of water (both from melt and rainfall) as a factor that tunes albedo: meltwater occurs during the central hours of the day, decreasing the albedo due to its lower reflectivity; instead, rainfall causes a subsequent mean daily albedo increase slightly higher than 20 %, although it is short-lasting (from 1 to 4 days).

Relative tectonics and debris flow hazards in the Beijing mountain area from DEM-derived geomorphic indices and drainage analysis

NASA Astrophysics Data System (ADS)

Cheng, Weiming; Wang, Nan; Zhao, Min; Zhao, Shangmin

2016-03-01

The geomorphic setting of the tectonically active area around Beijing is a result of complex interactions involving Yanshan neotectonic movements and processes of erosion and deposition. The Beijing Mountain study area contains the junction of two mountain ranges (the Yanshan Mountains and the Taihang Mountains). Tectonic activity has significantly influenced the drainage system and the geomorphic situation in the area, leading to a high probability of the development of debris flows, which is one of the major abrupt geological disasters in the region. Based on 30-m-resolution ASTER GDEM data, a total of 752 drainage basins were extracted using ArcGIS software. A total of 705 debris flow valleys were visually interpreted from ALOS satellite images and published documents. Seven geomorphic indices were calculated for each basin including the relief amplitude, the hypsometric integral, the stream length gradient, the basin shape indices, the fractal dimension, the asymmetry factor, and the ratio of the valley floor width to the height. These geomorphic indices were divided into five classes and the ratio of the number of the debris flow valleys to the number of the drainage basins for each geomorphic index was computed and analyzed for every class. Average class values of the seven indices were used to derive an index of relative active tectonics (IRAT). The ratio of the number of the debris flow valleys to the number of the drainage basins was computed for every class of IRAT. The degree of probable risk level was then defined from the IRAT classes. Finally, the debris flow hazard was evaluated for each drainage basin based on the combined effect of probable risk level and occurrence frequency of the debris flows. The result showed a good correspondence between IRAT classes and the ratio of the number of the debris flow valleys to the number of the drainage basins. Approximately 65% of the drainage basins with occurred debris flow valleys are at a high risk level, while 43% of the drainage basins without occurred debris flow valleys are at a high risk level. A comparison with results from past studies demonstrated that the accuracy of these findings is greater than 85%, indicating that the basin topography created by rapid tectonic deformations is more favorable for debris flows.

Wildfire-induced initiation of debris flows in a steep bedrock landscape, San Gabriel Mountains, California

NASA Astrophysics Data System (ADS)

Ulizio, T. P.; Palucis, M. C.; Fuller, B. M.; Lamb, M. P.

2017-12-01

Steep, rocky landscapes often produce large sediment yields and increased debris flow activity following wildfire. There are two main hypotheses for debris flow initiation in burned regions during rain storms: (1) debris flows initiate from failure of the soil mantle on hillslopes where fire has destroyed root systems resulting in loss of soil strength, and (2) debris flows initiate in river channels that have been loaded by dry ravel following incineration of vegetation dams on hillslopes. To evaluate these hypotheses, we monitored a steep first-order catchment that burned in the 2016 Fish Canyon fire within the front range of the San Gabriel Mountains, CA. Following each post-fire storm, we measured the hillslope and channel topography using UAV imaging and structure-from-motion, and monitored activity during storm events with field cameras. Following the fire, but prior to the first storm event, most of the hillslopes were stripped to bedrock and 0.5 m of dry ravel had accumulated along the length of the channel. By using measurements of sediment storage behind vegetation in a nearby unburned catchment, but with a similar burn history, we found that much of the loose sediment in the channel can be attributed to dry ravel following incineration of vegetation dams. Throughout the rainy season, the catchment produced a series of debris flows that evacuated the accumulated dry ravel in the channel, exposed bedrock in the channel, and built a debris flow fan across a terrace that abuts the downstream end of the channel. Although later storms were larger, most sediment transport occurred during the first few storms, indicating that sediment supply can limit debris flow activity, and that larger storms do not necessarily produce larger debris flows. Our measurements of the volume of the newly formed debris flow fan approximately matches the volume of evacuated ravel from the channel, and we did not observe landslide scars on hillslopes. Together, these observations and mass-balance constraints support the model by which limited hillslope soil in steep rocky landscapes is destabilized as dry ravel following wildfire, leading to infilling of channels with relatively fine and loose sediment that subsequently fails, producing debris flows during rain storms.

Debris exhaust system

DOEpatents

McBride, Donald D.; Bua, Dominic; Domankevitz, Yacov; Nishioka, Norman

1998-01-01

A debris removal system removes debris from a work site by flowing fluid away from the work site toward the periphery of a structure. The fluid flow can be kept constant around the periphery so that debris is removed evenly. The structure can have a reduced cross section between the fluid inlet and the work site so that the resulting increased fluid velocity works to prevent debris from escaping.

Debris exhaust system

DOEpatents

McBride, D.D.; Bua, D.; Domankevitz, Y.; Nishioka, N.

1998-06-23

A debris removal system removes debris from a work site by flowing fluid away from the work site toward the periphery of a structure. The fluid flow can be kept constant around the periphery so that debris is removed evenly. The structure can have a reduced cross section between the fluid inlet and the work site so that the resulting increased fluid velocity works to prevent debris from escaping. 9 figs.

Lessons From the Largest Historic Floods Documented by the U.S. Geological Survey

NASA Astrophysics Data System (ADS)

Costa, J. E.

2003-12-01

A recent controversy over the flood risk downstream from a USGS streamgaging station in southern California that recorded a large debris flow led to the decision to closely examine a sample of the largest floods documented in the US. Twenty-nine floods that define the envelope curve of the largest rainfall-runoff floods were examined in detail, including field visits. These floods have a profound impact on local, regional, and national interpretations of potential peak discharges and flood risk. These 29 floods occured throughout the US from the northern Chesapeake Bay in Maryland to Kauai, Hawaii, and over time from 1935-1978. Methods used to compute peak discharges were slope-area (21/29), culvert computations (2/29), measurements lost or not available for study (2/29), bridge contraction, culvert flow, and flow over road (1/29), rating curve extension (1/29), current meter measurement (1/29), and rating curve and current meter measurement (1/29). While field methods and tools have improved significantly over the last 70 years (e.g. total stations, GPS, GIS, hydroacoustics, digital plotters and computer programs like SAC and CAP), the primary methods of hydraulic analysis for indirect measurements of outstanding floods has not changed: today flow is still assumed to be 1-D and gradually varied. Unsteady or multi-dimensional flow models are rarely if ever used to determine peak discharges. Problems identified in this sample of 29 floods include debris flows misidentified as water floods, small drainage areas determined from small-scale maps and mislocated sites, high-water marks set by transient hydraulic phenomena, possibility of disconnected flow surfaces, scour assumptions in sand channels, poor site selection, incorrect approach angle for road overflow, and missing or lost records. Each published flood magnitude was checked by applying modern computer models with original field data, or by re-calculating computations. Four of 29 floods in this sample were found to have errors resulting in a change of the peak discharge of more than 10%.

Skiff-based Sonar/LiDAR Survey to Calibrate Reservoir Volumes for Watershed Sediment Yield Studies: Carmel River Example

NASA Astrophysics Data System (ADS)

Smith, D. P.; Kvitek, R.; Quan, S.; Iampietro, P.; Paddock, E.; Richmond, S. F.; Gomez, K.; Aiello, I. W.; Consulo, P.

2009-12-01

Models of watershed sediment yield are complicated by spatial and temporal variability of geologic substrate, land cover, and precipitation parameters. Episodic events such as ENSO cycles and severe wildfire are frequent enough to matter in the long-term average yield, and they can produce short-lived, extreme geomorphic responses. The sediment yield from extreme events is difficult to accurately capture because of the obvious dangers associated with field measurements during flood conditions, but it is critical to include extreme values for developing realistic models of rainfall-sediment yield relations, and for calculating long term average denudation rates. Dammed rivers provide a time-honored natural laboratory for quantifying average annual sediment yield and extreme-event sediment yield. While lead-line surveys of the past provided crude estimates of reservoir sediment trapping, recent advances in geospatial technology now provide unprecedented opportunities to improve volume change measurements. High-precision digital elevation models surveyed on an annual basis, or before-and-after specific rainfall-runoff events can be used to quantify relations between rainfall and sediment yield as a function of landscape parameters, including spatially explicit fire intensity. The Basin-Complex Fire of June and July 2008 resulted in moderate to severe burns in the 114 km^2 portion of the Carmel River watershed above Los Padres Dam. The US Geological Survey produced a debris flow probability/volume model for the region indicating that the reservoir could lose considerable capacity if intense enough precipitation occurred in the 2009-10 winter. Loss of Los Padres reservoir capacity has implications for endangered steelhead and red-legged frogs, and groundwater on municipal water supply. In anticipation of potentially catastrophic erosion, we produced an accurate volume calculation of the Los Padres reservoir in fall 2009, and locally monitored hillslope and fluvial processes during winter months. The pre-runoff reservoir volume was developed by collecting and merging sonar and LiDAR data from a small research skiff equipped with a high-precision positioning and attitude-correcting system. The terrestrial LiDAR data were augmented with shore-based total station positioning. Watershed monitoring included benchmarked serial stream surveys and semi-quantitative assessment of a variety of near-channel colluvial processes. Rainfall in the 2009-10 water year was not intense enough to trigger widespread debris flows of slope failure in the burned watershed, but dry ravel was apparently accelerated. The geomorphic analysis showed that sediment yield was not significantly higher during this low-rainfall year, despite the wide-spread presence of very steep, fire-impacted slopes. Because there was little to no increase in sediment yield this year, we have postponed our second reservoir survey. A predicted ENSO event that might bring very intense rains to the watershed is currently predicted for winter 2009-10.

Mid-Holocene Climate and Culture Change in the Atacama Desert, Northern Chile

NASA Astrophysics Data System (ADS)

Grosjean, Martin; Núñez, Lautaro; Cartajena, Isabel; Messerli, Bruno

1997-09-01

Twenty archaeological campsites intercalated between more than 30 debris flows caused by heavy rainfall events between 6200 and 3100 14C yr B.P. have recently been discovered at Quebrada Puripica in the Atacama Desert of northern Chile. This record provides detailed information about extreme, short-lived climatic events during the hyperarid mid-Holocene period. For the first time, we found evidence of continuous human occupation in this area, filling the regional hiatus in the Atacama basin ("Silencio Arqueologico") between 8000 and 4800 14C yr B.P. The transformation of Early Archaic hunters into the complex Late Archaic cultural tradition was an adaptive process. During this time, the site was a local ecological refuge with abundant resources in a generally hostile environment.

The debris-flow rheology myth

USGS Publications Warehouse

Iverson, R.M.; ,

2003-01-01

Models that employ a fixed rheology cannot yield accurate interpretations or predictions of debris-flow motion, because the evolving behavior of debris flows is too complex to be represented by any rheological equation that uniquely relates stress and strain rate. Field observations and experimental data indicate that debris behavior can vary from nearly rigid to highly fluid as a consequence of temporal and spatial variations in pore-fluid pressure and mixture agitation. Moreover, behavior can vary if debris composition changes as a result of grain-size segregation and gain or loss of solid and fluid constituents in transit. An alternative to fixed-rheology models is provided by a Coulomb mixture theory model, which can represent variable interactions of solid and fluid constituents in heterogeneous debris-flow surges with high-friction, coarse-grained heads and low-friction, liquefied tails. ?? 2003 Millpress.

Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

NASA Astrophysics Data System (ADS)

Walter, Fabian; Burtin, Arnaud; McArdell, Brian W.; Hovius, Niels; Weder, Bianca; Turowski, Jens M.

2017-06-01

Heavy precipitation can mobilize tens to hundreds of thousands of cubic meters of sediment in steep Alpine torrents in a short time. The resulting debris flows (mixtures of water, sediment and boulders) move downstream with velocities of several meters per second and have a high destruction potential. Warning protocols for affected communities rely on raising awareness about the debris-flow threat, precipitation monitoring and rapid detection methods. The latter, in particular, is a challenge because debris-flow-prone torrents have their catchments in steep and inaccessible terrain, where instrumentation is difficult to install and maintain. Here we test amplitude source location (ASL) as a processing scheme for seismic network data for early warning purposes. We use debris-flow and noise seismograms from the Illgraben catchment, Switzerland, a torrent system which produces several debris-flow events per year. Automatic in situ detection is currently based on geophones mounted on concrete check dams and radar stage sensors suspended above the channel. The ASL approach has the advantage that it uses seismometers, which can be installed at more accessible locations where a stable connection to mobile phone networks is available for data communication. Our ASL processing uses time-averaged ground vibration amplitudes to estimate the location of the debris-flow front. Applied to continuous data streams, inversion of the seismic amplitude decay throughout the network is robust and efficient, requires no manual identification of seismic phase arrivals and eliminates the need for a local seismic velocity model. We apply the ASL technique to a small debris-flow event on 19 July 2011, which was captured with a temporary seismic monitoring network. The processing rapidly detects the debris-flow event half an hour before arrival at the outlet of the torrent and several minutes before detection by the in situ alarm system. An analysis of continuous seismic records furthermore indicates that detectability of Illgraben debris flows of this size is unaffected by changing environmental and anthropogenic seismic noise and that false detections can be greatly reduced with simple processing steps.

A Study on the Priority Selection of Sediment-related Desaster Evacuation Using Debris Flow Combination Degree of Risk

NASA Astrophysics Data System (ADS)

Woo, C.; Kang, M.; Seo, J.; Kim, D.; Lee, C.

2017-12-01

As the mountainous urbanization has increased the concern about landslides in the living area, it is essential to develop the technology to minimize the damage through quick identification and sharing of the disaster occurrence information. In this study, to establish an effective system of alert evacuation that has influence on the residents, we used the debris flow combination degree of risk to predict the risk of the disaster and the level of damage and to select evacuation priorities. Based on the GIS information, the physical strength and social vulnerability were determined by following the debris flow combination of the risk formula. The results classify the physical strength hazard rating of the debris flow combination of the through the normalization process. Debris flow the estimated residential population included in the damage range of the damage prediction map is based on the area and the unit size data. Prediction of occupant formula was calculated by applying different weighting to the resident population and users, and the result was classified into 5 classes as the debris flow physical strength. The debris flow occurrence physical strength and social and psychological vulnerability were classified into the classifications to be reflected in the debris flow integrated risk map using the matrix technique. In addition, to supplement the risk of incorporation of debris flow, we added weight to disaster vulnerable facilities that require a lot of time and manpower to evacuate. The basic model of welfare facilities was supplemented by using basic data, population density, employment density and GDP. First, evacuate areas with high integrated degree of risk level, and evacuate with consideration of physical class differences if classification difficult because of the same or similar grade among the management areas. When the physical hazard class difference is similar, the population difference of the area including the welfare facility is considered first, and the priority is decided in order of age distribution, population density by period, and class difference of residential facility. The results of this study are expected be used as basic data for establishing a safety net for landslide by evacuation systems for disasters. Keyword: Landslide, Debris flow, Early warning system, evacuation

Volcano fact sheet; glacier-generated debris flows at Mount Rainier

USGS Publications Warehouse

Walder, J.S.; Driedger, C.L.

1993-01-01

Mount Rainier is a young volcano whose slopes are undergoing rapid change by a variety of geologic processes, including debris flows. Debris flows are churning masses of water, rock and mud that travel rapidly down the volcano's steep, glacially carved valleys, leaving in their wake splintered trees, picnic sites buried in mud, and damaged roads. Debris flows typically contain as much as 65 to 70 percent rock and soil by volume and have the appearance of wet concrete. At Mount Rainier National Park, these flows invariably begin in remote areas nearly inaccessible to people, but may move rapidly downstream into areas frequented by visitors.

An integrated study to evaluate debris flow hazard in alpine environment

NASA Astrophysics Data System (ADS)

Tiranti, Davide; Crema, Stefano; Cavalli, Marco; Deangeli, Chiara

2018-05-01

Debris flows are among the most dangerous natural processes affecting the alpine environment due to their magnitude (volume of transported material) and the long runout. The presence of structures and infrastructures on alluvial fans can lead to severe problems in terms of interactions between debris flows and human activities. Risk mitigation in these areas requires identifying the magnitude, triggers, and propagation of debris flows. Here, we propose an integrated methodology to characterize these phenomena. The methodology consists of three complementary procedures. Firstly, we adopt a classification method based on the propensity of the catchment bedrocks to produce clayey-grained material. The classification allows us to identify the most likely rheology of the process. Secondly, we calculate a sediment connectivity index to estimate the topographic control on the possible coupling between the sediment source areas and the catchment channel network. This step allows for the assessment of the debris supply, which is most likely available for the channelized processes. Finally, with the data obtained in the previous steps, we modelled the propagation and depositional pattern of debris flows with a 3D code based on Cellular Automata. The results of the numerical runs allow us to identify the depositional patterns and the areas potentially involved in the flow processes. This integrated methodology is applied to a test-bed catchment located in Northwestern Alps. The results indicate that this approach can be regarded as a useful tool to estimate debris flow related potential hazard scenarios in an alpine environment in an expeditious way without possessing an exhaustive knowledge of the investigated catchment, including data on historical debris flow events.

Geologic, geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachian Mountains of Macon County, North Carolina (southeastern USA)

Treesearch

R. M. Wooten; K. A. Gillon; A. C. Witt; R. S. Latham; T. J. Douglas; J. B. Bauer; S. J. Fuemmeler; L. G. Lee

2008-01-01

In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation...

Post-wildfire landscape change and erosional processes from repeat terrestrial lidar in a steep headwater catchment, Chiricahua Mountains, Arizona, USA

NASA Astrophysics Data System (ADS)

DeLong, Stephen B.; Youberg, Ann M.; DeLong, Whitney M.; Murphy, Brendan P.

2018-01-01

Flooding and erosion after wildfires present increasing hazard as climate warms, semi-arid lands become drier, population increases, and the urban interface encroaches farther into wildlands. We quantify post-wildfire erosion in a steep, initially unchannelized, 7.5 ha headwater catchment following the 2011 Horseshoe 2 Fire in the Chiricahua Mountains of southeastern Arizona. Using time-lapse cameras, rain gauges, and repeat surveys by terrestrial laser scanner, we quantify the response of a burned landscape to subsequent precipitation events. Repeat surveys provide detailed pre-and post-rainfall measurements of landscape form associated with a range of weather events. The first post-fire precipitation led to sediment delivery equivalent to 0.017 m of erosion from hillslopes and 0.12 m of erosion from colluvial hollows. Volumetrically, 69% of sediment yield was generated from hillslope erosion and 31% was generated from gully channel establishment in colluvial hollows. Processes on hillslopes included erosion by extensive shallow overland flow, formation of rills and gullies, and generation of sediment-laden flows and possibly debris flows. Subsequent smaller rain events caused ongoing hillslope erosion and local deposition and erosion in gullies. Winter freeze-thaw led to soil expansion, likely related to frost-heaving, causing a net centimeter-scale elevation increase across soil-mantled slopes. By characterizing landscape form, the properties of near-surface materials, and measuring both precipitation and landscape change, we can improve our empirical understanding of landscape response to environmental forcing. This detailed approach to studying landscape response to wildfires may be useful in the improvement of predictive models of flood, debris flow and sedimentation hazards used in post-wildfire response assessments and land management, and may help improve process-based models of landscape evolution.

Post-wildfire landscape change and erosional processes from repeat terrestrial lidar in a steep headwater catchment, Chiricahua Mountains, Arizona, USA

USGS Publications Warehouse

DeLong, Stephen B.; Youberg, Ann M.; DeLong, Whitney M.; Murphy, Brendan P.

2018-01-01

Flooding and erosion after wildfires present increasing hazard as climate warms, semi-arid lands become drier, population increases, and the urban interface encroaches farther into wildlands. We quantify post-wildfire erosion in a steep, initially unchannelized, 7.5 ha headwater catchment following the 2011 Horseshoe 2 Fire in the Chiricahua Mountains of southeastern Arizona. Using time-lapse cameras, rain gauges, and repeat surveys by terrestrial laser scanner, we quantify the response of a burned landscape to subsequent precipitation events. Repeat surveys provide detailed pre-and post-rainfall measurements of landscape form associated with a range of weather events. The first post-fire precipitation led to sediment delivery equivalent to 0.017 m of erosion from hillslopes and 0.12 m of erosion from colluvial hollows. Volumetrically, 69% of sediment yield was generated from hillslope erosion and 31% was generated from gully channel establishment in colluvial hollows. Processes on hillslopes included erosion by extensive shallow overland flow, formation of rills and gullies, and generation of sediment-laden flows and possibly debris flows. Subsequent smaller rain events caused ongoing hillslope erosion and local deposition and erosion in gullies. Winter freeze-thaw led to soil expansion, likely related to frost-heaving, causing a net centimeter-scale elevation increase across soil-mantled slopes. By characterizing landscape form, the properties of near-surface materials, and measuring both precipitation and landscape change, we can improve our empirical understanding of landscape response to environmental forcing. This detailed approach to studying landscape response to wildfires may be useful in the improvement of predictive models of flood, debris flow and sedimentation hazards used in post-wildfire response assessments and land management, and may help improve process-based models of landscape evolution.

Distribution of Amphipods (Gammarus nipponensis Ueno) Among Mountain Headwater Streams with Different Legacies of Debris Flow Occurrence

EPA Science Inventory

To understand the impacts of debris flows on the distribution of an amphipod with limited dispersal ability in the context of stream networks, we surveyed the presence of Gammarus nipponensis in 87 headwater streams with different legacies of debris flow occurrence within an 8.5-...

Debris-flow initiation from large, slow-moving landslides

USGS Publications Warehouse

Reid, M.E.; Brien, D.L.; LaHusen, R.G.; Roering, J.J.; de la Fuente, J.; Ellen, S.D.; ,

2003-01-01

In some mountainous terrain, debris flows preferentially initiate from the toes and margins of larger, deeper, slower-moving landslides. During the wet winter of 1997, we began real-time monitoring of the large, active Cleveland Corral landslide complex in California, USA. When the main slide is actively moving, small, shallow, first-time slides on the toe and margins mobilize into debris flows and travel down adjacent gullies. We monitored the acceleration of one such failure; changes in velocity provided precursory indications of rapid failure. Three factors appear to aid the initiation of debris flows at this site: 1) locally steepened ground created by dynamic landslide movement, 2) elevated pore-water pressures and abundant soil moisture, and 3) locally cracked and dilated materials. This association between debris flows and large landslides can be widespread in some terrain. Detailed photographic mapping in two watersheds of northwestern California illustrates that the areal density of debris-flow source landsliding is about 3 to 7 times greater in steep geomorphically fresher landslide deposits than in steep ground outside landslide deposits. ?? 2003 Millpress.

Mount Baker lahars and debris flows, ancient, modern, and future

USGS Publications Warehouse

Tucker, David S; Scott, Kevin M.; Grossman, Eric E.; Linneman, Scott

2014-01-01

Holocene lahars and large debris flows (>106 m3) have left recognizable deposits in the Middle Fork Nooksack valley. A debris flow in 2013 resulting from a landslide in a Little Ice Age moraine had an estimated volume of 100,000 m3, yet affected turbidity for the entire length of the river, and produced a slug of sediment that is currently being reworked and remobilized in the river system. Deposits of smaller-volume debris flows, deposited as terraces in the upper valley, may be entirely eroded within a few years. Consequently, the geologic record of small debris flows such as those that occurred in 2013 is probably very fragmentary. Small debris flows may still have significant impacts on hydrology, biology, and human uses of rivers downstream. Impacts include the addition of waves of fine sediment to stream loads, scouring or burying salmon-spawning gravels, forcing unplanned and sudden closure of municipal water intakes, damaging or destroying trail crossings, extending river deltas into estuaries, and adding to silting of harbors near river mouths.

Centrifuge Modeling of Rainfall Induced Slope Failure

NASA Astrophysics Data System (ADS)

Ling, H.; Wu, M.

2006-12-01

Rainfall induces slope failure and debris flow which are considered as one of the major natural disasters. The scope of such failure is very large and it cannot be studied easily in the laboratory. Traditionally, small scale model tests are used to study such problem. Knowing that the behavior of soil is affected by the stress level, centrifuge modeling technique has been used to simulate more realistically full scale earth structures. In this study, two series of tests were conducted on slopes under the centrifugal field with and without the presence of rainfall. The soil used was a mixture of sand and 15 percent fines. The slopes of angle 60 degrees were prepared at optimum water content in order to achieve the maximum density. In the first series of tests, three different slope heights of 10 cm, 15 cm and 20 cm were used. The gravity was increased gradually until slope failure in order to obtain the prototype failure height. The slope model was cut after the test in order to obtain the configuration of failure surface. It was found that the slope geometry normalized by the height at failure provided unique results. Knowing the slope height or gravity at failure, the second series of tests with rainfall were conducted slightly below the critical height. That is, after attaining the desired gravity, the rainfall was induced in the centrifuge. Special nozzles were used and calibrated against different levels of gravity in order to obtain desired rainfall intensity. Five different rainfall intensities were used on the 15-cm slopes at 80g and 60g, which corresponded to 12 m and 9 m slope height, respectively. The duration until failure for different rainfall intensities was obtained. Similar to the first series of tests, the slope model was cut and investigated after the test. The results showed that the failure surface was not significantly affected by the rainfall. That is, the excess pore pressure induced by rainfall generated slope failure. The prediction curves of rainfall intensity versus duration were obtained from the test results. Such curves are extremely useful for disaster management. This study indicated feasibilities of using centrifuge modeling technique in simulating rainfall induced slope failure. The results obtained may also be used for validating numerical tools.

Modeling four occurred debris flow events in the Dolomites area (North-Eastern Italian Alps)

NASA Astrophysics Data System (ADS)

Boreggio, Mauro; Gregoretti, Carlo; Degetto, Massimo; Bernard, Martino

2016-04-01

Four occurred debris flows in the Dolomites area (North-Eastern Italian Alps) are modeled by back-analysis. The four debris flows events are those occurred at Rio Lazer (Trento) on the 4th of November 1966, at Fiames (Belluno) on the 5th of July 2006, at Rovina di Cancia (Belluno) on the 18th of July 2009 and at Rio Val Molinara (Trento) on the 15th of August 2010. In all the events, runoff entrained sediments present on natural channels and formed a solid-liquid wave that routed downstream. The first event concerns the routing of debris flow on an inhabited fan. The second event the deviation of debris flow from the usual path due to an obstruction with the excavation of a channel in the scree and the downstream spreading in a wood. The third event concerns the routing of debris flow in a channel with an ending the reservoir, its overtopping and final spreading in the inhabited area. The fourth event concerns the routing of debris flow along the main channel downstream the initiation area until spreading just upstream a village. All the four occurred debris flows are simulated by modeling runoff that entrained debris flow for determining the solid-liquid hydrograph. The routing of the solid-liquid hydrograph is simulated by a bi-phase cell model based on the kinematic approach. The comparison between simulated and measured erosion and deposition depths is satisfactory. Nearly the same parameters for computing erosion and deposition were used for all the four occurred events. The maps of erosion and deposition depths are obtained by comparing the results of post-event surveys with the pre-event DEM. The post-event surveys were conducted by using different instruments (LiDAR and GPS) or the combination photos-single points depth measurements (in this last case it is possible obtaining the deposition/erosion depths by means of stereoscopy techniques).

Joint NOAA/NWS/USGS prototype debris flow warning system for recently burned areas in Southern California

USGS Publications Warehouse

Restrepo, P.; Jorgensen, D.P.; Cannon, S.H.; Costa, J.; Laber, J.; Major, J.; Martner, B.; Purpura, J.; Werner, K.

2008-01-01

Debris flows, also known as mudslides, are composed gravity-driven mixtures of sediment and water that travel through steep channels, over open hillslopes, and the like. Addressing this issue, US Geological Survey (USGS) and NOAA have established a debris-flow warning system that has the ability to monitor and forecast precipitation and issue timely weather hazard warning. In 2005, this joint NOAA-USGS prototype debris-flow warning system was issued in Southern California and as a result, it has provided valuable information to emergency managers in affected communities.

Evolution of a natural debris flow: In situ measurements of flow dynamics, video imagery, and terrestrial laser scanning

USGS Publications Warehouse

McCoy, S.W.; Kean, J.W.; Coe, J.A.; Staley, D.M.; Wasklewicz, T.A.; Tucker, G.E.

2010-01-01

Many theoretical and laboratory studies have been undertaken to understand debris-flow processes and their associated hazards. However, complete and quantitative data sets from natural debris flows needed for confirmation of these results are limited. We used a novel combination of in situ measurements of debris-flow dynamics, video imagery, and pre- and postflow 2-cm-resolution digital terrain models to study a natural debris-flow event. Our field data constrain the initial and final reach morphology and key flow dynamics. The observed event consisted of multiple surges, each with clear variation of flow properties along the length of the surge. Steep, highly resistant, surge fronts of coarse-grained material without measurable pore-fluid pressure were pushed along by relatively fine-grained and water-rich tails that had a wide range of pore-fluid pressures (some two times greater than hydrostatic). Surges with larger nonequilibrium pore-fluid pressures had longer travel distances. A wide range of travel distances from different surges of similar size indicates that dynamic flow properties are of equal or greater importance than channel properties in determining where a particular surge will stop. Progressive vertical accretion of multiple surges generated the total thickness of mapped debris-flow deposits; nevertheless, deposits had massive, vertically unstratified sedimentological textures. ?? 2010 Geological Society of America.

Onset of submarine debris flow deposition far from original giant landslide.

PubMed

Talling, P J; Wynn, R B; Masson, D G; Frenz, M; Cronin, B T; Schiebel, R; Akhmetzhanov, A M; Dallmeier-Tiessen, S; Benetti, S; Weaver, P P E; Georgiopoulou, A; Zühlsdorff, C; Amy, L A

2007-11-22

Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the world's rivers. Understanding how this type of submarine flow evolves is a significant problem, because they are extremely difficult to monitor directly. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, the deposit of which extends downslope from the original landslide. We provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a more dilute flow type called turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor, where the flow was locally very erosive. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05 degrees to 0.01 degrees. This debris flow was probably generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelized debris flow left almost no trace of its passage across one hundred kilometres of flat (0.2 degrees to 0.05 degrees) sea floor. Our work shows that initially well-mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean.

Analysis of the Mobilization of Debris Flows

DTIC Science & Technology

1974-10-01

31 17 . Debris-flow source area at Roofing Granule Quarry, San Bernardino County, California 39 18. Debris-flow source area at Roofing Granule...down a channel about 12 to 16 cm wide with a 35 degree slope. Water, oozing out of the landslide mass into 17 wmmaaaamam’j ■ma the debris channel...marble used as roofing granules (Fig. 17 ) 2 1/2 km north of the town of Wrightwood, about 65 km north- * east of Los Angeles, California (Fig. 1

The role of large woody debris in modulating the dispersal of a post-fire sediment pulse

NASA Astrophysics Data System (ADS)

Short, Lauren E.; Gabet, Emmanuel J.; Hoffman, Daniel F.

2015-10-01

In 2001, a series of post-fire debris flows brought 30,000 m3 of sediment, deposited as fans, to the narrow valley floor of Sleeping Child Creek in western Montana (USA). In 2005, pebble-counts and surveys of the channel in proximity to six of the debris flow fans documented a regular sequence of fine-grained aggradation upstream of the fans, incision through the fans, and coarse-grained aggradation downstream of the fans. These measurements were repeated in 2012. We found that the delivery of large woody debris (LWD) over the intervening 7 years has been a dominant factor in the disposition of the debris-flow material. The amount of LWD in the study reach has increased by as much as 50% in the areas with a high burn severity, leading to the formation of large logjams that interrupt the flow of sediment along the streambed. Nearly all of the surveyed reaches have aggraded since 2005, including those that had initially begun incising through the debris flow deposits, and the streambed has become generally finer. We hypothesize that, over the next few decades, debris flow sediment not colonized and anchored by riparian vegetation will trickle out of the affected reaches as the logjams slowly degrade.

Four-way coupling of a three-dimensional debris flow solver to a Lagrangian Particle Simulation: method and first results

NASA Astrophysics Data System (ADS)

von Boetticher, Albrecht; Rickenmann, Dieter; McArdell, Brian; Kirchner, James W.

2017-04-01

Debris flows are dense flowing mixtures of water, clay, silt, sand and coarser particles. They are a common natural hazard in mountain regions and frequently cause severe damage. Modeling debris flows to design protection measures is still challenging due to the complex interactions within the inhomogeneous material mixture, and the sensitivity of the flow process to the channel geometry. The open-source, OpenFOAM-based finite-volume debris flow model debrisInterMixing (von Boetticher et al, 2016) defines rheology parameters based on the material properties of the debris flow mixture to reduce the number of free model parameters. As a simplification in this first model version, gravel was treated as a Coulomb-viscoplastic fluid, neglecting grain-to-grain collisions and the coupling between the coarser gravel grains and the interstitial fluid. Here we present an extension of that solver, accounting for the particle-to-particle and particle-to-boundary contacts with a Lagrangian Particle Simulation composed of spherical grains and a user-defined grain size distribution. The grain collisions of the Lagrangian particles add granular flow behavior to the finite-volume simulation of the continuous phases. The two-way coupling exchanges momentum between the phase-averaged flow in a finite volume cell, and among all individual particles contained in that cell, allowing the user to choose from a number of different drag models. The momentum exchange is implemented in the momentum equation and in the pressure equation (ensuring continuity) of the so-called PISO-loop, resulting in a stable 4-way coupling (particle-to-particle, particle-to-boundary, particle-to-fluid and fluid-to-particle) that represents the granular and viscous flow behavior of debris flow material. We will present simulations that illustrate the relative benefits and drawbacks of explicitly representing grain collisions, compared to the original debrisInterMixing solver.

Runoff of small rocky headwater catchments: Field observations and hydrological modeling

NASA Astrophysics Data System (ADS)

Gregoretti, C.; Degetto, M.; Bernard, M.; Crucil, G.; Pimazzoni, A.; De Vido, G.; Berti, M.; Simoni, A.; Lanzoni, S.

2016-10-01

In dolomitic headwater catchments, intense rainstorms of short duration produce runoff discharges that often trigger debris flows on the scree slopes at the base of rock cliffs. In order to measure these discharges, we placed a measuring facility at the outlet (elevation 1770 m a.s.l.) of a small, rocky headwater catchment (area ˜0.032 km2, average slope ˜320%) located in the Venetian Dolomites (North Eastern Italian Alps). The facility consists of an approximately rectangular basin, ending with a sharp-crested weir. Six runoff events were recorded in the period 2011-2014, providing a unique opportunity for characterizing the hydrological response of the catchment. The measured hydrographs display impulsive shapes, with an abrupt raise up to the peak, followed by a rapidly decreasing tail, until a nearly constant plateau is eventually reached. This behavior can be simulated by means of a distributed hydrological model if the excess rainfall is determined accurately. We show that using the Soil Conservation Service Curve-Number (SCS-CN) method and assuming a constant routing velocity invariably results in an underestimated peak flow and a delayed peak time. A satisfactory prediction of the impulsive hydrograph shape, including peak value and timing, is obtained only by combining the SCS-CN procedure with a simplified version of the Horton equation, and simulating runoff routing along the channel network through a matched diffusivity kinematic wave model. The robustness of the proposed methodology is tested through a comparison between simulated and observed timings of runoff or debris flow occurrence in two neighboring alpine basins.

Assessing the effects of check dams on sediment dynamics in a debris-flow catchment through SfM technique

NASA Astrophysics Data System (ADS)

Cucchiaro, Sara; Beinat, Alberto; Calsamiglia, Aleix; Cavalli, Marco; Cazorzi, Federico; Crema, Stefano; Marchi, Lorenzo

2017-04-01

The Moscardo Torrent (eastern Italian Alps) is a small rugged catchment (drainage area 4.1 km2, range in elevation between 890 and 2043 m) frequently affected by debris flows that deliver large amounts of sediment to the receiving stream, and cause concerns for infrastructures located on the alluvial fan and near the confluence. Over the last decades, hydraulic control works were implemented in the main channel to limit bed erosion and to stabilize channel banks. Although the objectives of training works have been only partly achieved, check dams and hillslope stabilization works have affected the sediment transfer from hillslopes to the channels and along the main channel. The effects of hydraulic control works were investigated by means of multi-temporal Structure from Motion (SfM) surveys based on images taken from the ground and UAV. The ground and air based surveys were carried out over a channel reach in which two check dams have recently been built. SfM surveys were taken before and after three debris-flow events (occurred between June and July 2016), allowing the generation of four high-resolution Digital Elevation Models (DEMs). Geomorphic changes caused by the debris-flow events have been assessed in order to produce the DEM of Differences (DoDs with a 0.2 m spatial resolution) that allowed estimating erosion and deposition volumes in the study area. Furthermore a debris-flow monitoring system has been in operation in the Moscardo Torrent; the analysis of the videos and of the hydrographs recorded by ultrasonic sensors permitted to assess the debris-flow volumes. These estimates were used to characterize the magnitude of events in support of the topographic analysis. By examining the changing pattern of erosion and deposition over time it was possible to understand the check dams' effects on sediment dynamics. The results show that the new check dams effectively stored sediment transported by the three debris flows. However, once the check dams have been completely filled, they lost their functionality, letting sediment flow downstream along paths drawn accidentally by the torrent control works and by the morphology of debris-flow deposits. Moreover, debris-flow lobes deposited upstream of the check dams could act as sediment sources further increasing downstream debris-flow magnitude.

Physical Limits on the Predictability of Erosion and Sediment Transport by Landslides and Debris Flows

NASA Astrophysics Data System (ADS)

Iverson, R. M.

2015-12-01

Episodic landslides and debris flows play a key role in sculpting many steep landscapes, and they also pose significant natural hazards. Field evidence, laboratory experiments, and theoretical analyses show that variations in the quantity, speed, and distance of sediment transport by landslides and debris flows can depend strongly on nuanced differences in initial conditions. Moreover, initial conditions themselves can be strongly dependent on the geological legacy of prior events. The scope of these dependencies is revealed by the results of landslide dynamics experiments [Iverson et al., Science, 2000], debris-flow erosion experiments [Iverson et al., Nature Geosci., 2011], and numerical simulations of the highly destructive 2014 Oso, Washington, landslide [Iverson et al., Earth Planet. Sci. Let., 2015]. In each of these cases, feedbacks between basal sediment deformation and pore-pressure generation cause the speed and distance of sediment transport to be very sensitive to subtle differences in the ambient sediment porosity and water content. On the other hand, the onset of most landslides and debris flows depends largely on pore-water pressure distributions and only indirectly on sediment porosity and water content. Thus, even if perfect predictions of the locations and timing of landslides and debris flows were available, the dynamics of the events - and their consequent hazards and sediment transport - would be difficult to predict. This difficulty is a manifestation of the nonlinear physics involved, rather than of poor understanding of those physics. Consequently, physically based models for assessing the hazards and sediment transport due to landslides and debris flows must take into account both evolving nonlinear dynamics and inherent uncertainties about initial conditions. By contrast, landscape evolution models that use prescribed algebraic formulas to represent sediment transport by landslides and debris flows lack a sound physical basis.

Spatial and temporal patterns of stranded intertidal marine debris: is there a picture of global change?

PubMed

Browne, Mark Anthony; Chapman, M Gee; Thompson, Richard C; Amaral Zettler, Linda A; Jambeck, Jenna; Mallos, Nicholas J

2015-06-16

Floating and stranded marine debris is widespread. Increasing sea levels and altered rainfall, solar radiation, wind speed, waves, and oceanic currents associated with climatic change are likely to transfer more debris from coastal cities into marine and coastal habitats. Marine debris causes economic and ecological impacts, but understanding the scope of these requires quantitative information on spatial patterns and trends in the amounts and types of debris at a global scale. There are very few large-scale programs to measure debris, but many peer-reviewed and published scientific studies of marine debris describe local patterns. Unfortunately, methods of defining debris, sampling, and interpreting patterns in space or time vary considerably among studies, yet if data could be synthesized across studies, a global picture of the problem may be avaliable. We analyzed 104 published scientific papers on marine debris in order to determine how to evaluate this. Although many studies were well designed to answer specific questions, definitions of what constitutes marine debris, the methods used to measure, and the scale of the scope of the studies means that no general picture can emerge from this wealth of data. These problems are detailed to guide future studies and guidelines provided to enable the collection of more comparable data to better manage this growing problem.

Capturing spatiotemporal variation in wildfires for improving postwildfire debris-flow hazard assessments: Chapter 20

USGS Publications Warehouse

Haas, Jessica R.; Thompson, Matthew P.; Tillery, Anne C.; Scott, Joe H.

2017-01-01

Wildfires can increase the frequency and magnitude of catastrophic debris flows. Integrated, proactive natural hazard assessment would therefore characterize landscapes based on the potential for the occurrence and interactions of wildfires and postwildfire debris flows. This chapter presents a new modeling effort that can quantify the variability surrounding a key input to postwildfire debris-flow modeling, the amount of watershed burned at moderate to high severity, in a prewildfire context. The use of stochastic wildfire simulation captures variability surrounding the timing and location of ignitions, fire weather patterns, and ultimately the spatial patterns of watershed area burned. Model results provide for enhanced estimates of postwildfire debris-flow hazard in a prewildfire context, and multiple hazard metrics are generated to characterize and contrast hazards across watersheds. Results can guide mitigation efforts by allowing planners to identify which factors may be contributing the most to the hazard rankings of watersheds.

Rapid geomorphic change caused by glacial outburst floods and debris flows along Tahoma Creek, Mount Rainier, Washington, USA

USGS Publications Warehouse

Walder, J.S.; Driedger, C.L.

1994-01-01

As part of a hazards-assessment study, we examined the nature and rate of geomorphic change caused by outburst floods and debris flows along Tahoma Creek. Mount Rainier, since 1967. Archival aerial photographs of the area proved to be a rich source of qualitative geomorphic information. On the basis of limited direct evidence and considerations of stream hydrology, we conclude that nearly all of these debris flows began as outburst floods from South Tahoma Glacier. The water floods transformed to debris flows by incorporating large masses of sediment in a 2-km-long channel reach where the stream has incised proglacial sediments and debris-rich, stagnant glacier ice. Comparison of topographic maps for 1970 and 1991 shows that the average sediment flux out of the incised reach has been about 2 to 4 × 105 m3 a-1 corresponding to an average denudation rate in the upper part of the Tahoma Creek drainage basin of about 20 to 40 mm a-1, a value exceeded only rarely in basins affected by debris flows. However, little of this sediment has yet passed out of the Tahoma Creek basin. Comparison of geomorphic change at Tahoma Creek to that in two other alpine basins affected by outburst floods suggests that debris-rich stagnant ice can be an important source of sediment for debris flows as long as floods are frequent or channel slope is great.

Contrasting origin of two clay-rich debris flows at Cayambe Volcanic Complex, Ecuador

NASA Astrophysics Data System (ADS)

Detienne, M.; Delmelle, P.; Guevara, A.; Samaniego, P.; Opfergelt, S.; Mothes, P. A.

2017-04-01

We investigate the sedimentological and mineralogical properties of a debris flow deposit west of Cayambe Volcanic Complex, an ice-clad edifice in Ecuador. The deposit exhibits a matrix facies containing up to 16 wt% of clays. However, the stratigraphic relationship of the deposit with respect to the Canguahua Formation, a widespread indurated volcaniclastic material in the Ecuadorian inter-Andean Valley, and the deposit alteration mineralogy differ depending on location. Thus, two different deposits are identified. The Río Granobles debris flow deposit ( 1 km3) is characterised by the alteration mineral assemblage smectite + jarosite, and sulphur isotopic analyses point to a supergene hydrothermal alteration environment. This deposit probably derives from a debris avalanche initiated before 14-21 ka by collapse of a hydrothermally altered rock mass from the volcano summit. In contrast, the alteration mineralogy of the second debris flow deposit, which may itself comprise more than one unit, is dominated by halloysite + smectite and relates to a shallower and more recent (<13 ky) mass movement of high-altitude (>3200 m) volcanic soils. Our study reinforces the significance of hydrothermal alteration in weakening volcano flanks and in favouring rapid transformation of a volcanic debris avalanche into a clay-rich debris flow. It also demonstrates that mineralogical analysis provides crucial information for resolving the origin of a debris flow deposit in volcanic terrains. Finally, we posit that slope instability, promoted by ongoing subglacial hydrothermal alteration, remains a significant hazard at Cayambe Volcanic Complex.

Geological mechanism of hazardous debris flows in central Taiwan

NASA Astrophysics Data System (ADS)

Chen, H.; Chen, R. H.; Lin, M. L.; Su, D. Y.

2003-04-01

GEOLOGICAL MECHANISM OF HAZARDOUS DEBRIS FLOWS IN CENTRAL PART OF TAIWAN H. Chen (1), R. H. Chen (2), M. L. Lin (2), D.Y. Su (3) (1) Department of Geosciences, National Taiwan University, (2) Department of Civil Engineering, National Taiwan University, (3) MAA Ltd., Taiwan hche02@esc.cam.ac.uk/Fax:+44-01223-333450 This study revealed that the distribution of rock discontinuities, geomaterial characteristics and water pressure were the major hazardous factors of the triggering mechanism in the debris flows. Attention is drawn to the discontinuities pattern within the sidewalls of the gullies, which emphasized the significance of material slumping and forming the accumulated deposits in the gullies. The accumulated deposits are the main source of the debris flow once the disaster is triggered and produced large quantities of debris. A modified channel box test was used to comprehend the effect of water sources in this study. The results of this experimental test displayed that water supplied from the bottom or the top will both cause large material movement. But water supplied from the bottom tends to cause a larger and faster flow than water from the top. The visual evidence of a flushed network of discontinuities exposed after the debris flow provided in situ indications of increased pore water pressure. This rapidly increasing water pressure evidently contributed a sizable dynamic force to initiate movement of the debris flow. The heavy slurry became an effective cutting device to erode the sidewalls and move large quantities of the debris materials to the end of the gullies. Based on field investigations and laboratory tests, the precipitation could increase the water content and water pressure, and decrease the shear strength of the gullies material. It also can add confirmation to this research that debris flows are triggered by accumulated deposits from sidewalls and moved by high intensity precipitation.

Dynamics of Unusual Debris Flows on Martian Sand Dunes

NASA Technical Reports Server (NTRS)

Miyamoto, Hideaki; Dohm, James M.; Baker, Victor R.; Beyer, Ross A.; Bourke, Mary

2004-01-01

Gullies that dissect sand dunes in Russell impact crater often display debris flow-like deposits in their distal reaches. The possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a Bingham plastic flow to help explain the formation of these features. Our simulated results are best explained by a rapid debris flow. For example, a debris flow with the viscosity of 10(exp 2) Pa s and the yield strength of 10(exp 2) Pa can form the observed deposits with a flow rate of 0.5 cu m/s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters, which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth.

Instrumental lahar monitoring at Merapi Volcano, Central Java, Indonesia

USGS Publications Warehouse

Lavigne, Franck; Thouret, J.-C.; Voight, B.; Young, K.; LaHusen, R.; Marso, J.; Suwa, H.; Sumaryono, A.; Sayudi, D.S.; Dejean, M.

2000-01-01

More than 50 volcanic debris flows or lahars were generated around Mt Merapi during the first rainy season following the nuees ardentes of 22 November 1994. The rainfalls that triggered the lahars were analyzed, using such instruments as weather radar and telemetered rain gauges. Lahar dynamics were also monitored, using new non-contact detection instrumentation installed on the slopes of the volcano. These devices include real-time seismic amplitude measurement (RSAM), seismic spectral amplitude measurement (SSAM) and acoustic flow monitoring (AFM) systems. Calibration of the various systems was accomplished by field measurements of flow velocities and discharge, contemporaneously with instrumental monitoring. The 1994–1995 lahars were relatively short events, their duration in the Boyong river commonly ranging between 30 min and 1 h 30 min. The great majority (90%) of the lahars was recognized at Kaliurang village between 13:00 and 17:30 h, due to the predominance of afternoon rainfalls. The observed mean velocity of lahar fronts ranged between 1.1 and 3.4 m/s, whereas the peak velocity of the flows varied from 11 to 15 m/s, under the Gardu Pandang viewpoint location at Kaliurang, to 8–10 m/s at a section 500 m downstream from this site. River slopes vary from 28 to 22 m/km at the two sites. Peak discharges recorded in various events ranged from 33 to 360 m3/s, with the maximum value of peak discharge 360 m3/s, on 20 May 1995. To improve the lahar warning system along Boyong river, some instrumental thresholds were proposed: large and potentially hazardous lahars may be detected by RSAM units exceeding 400, SSAM units exceeding 80 on the highest frequency band, or AFM values greater than 1500 mV on the low-gain, broad-band setting.

Mechanics of debris flows and rock avalanches: Chapter 43

USGS Publications Warehouse

Iverson, Richard M.; Fernando, Harindra Joseph

2012-01-01

Debris flows are geophysical phenomena intermediate in character between rock avalanches and flash floods. They commonly originate as water-laden landslides on steep slopes and transform into liquefied masses of fragmented rock, muddy water, and entrained organic matter that disgorge from canyons onto valley floors. Typically including 50%–70% solid grains by volume, attaining speeds >10 m/s, and ranging in size up to ∼109 m3, debris flows can denude mountainsides, inundate floodplains, and devastate people and property (Figure 43.1). Notable recent debris-flow disasters resulted in more than 20,000 fatalities in Armero, Colombia, in 1985 and in Vargas state, Venezuela, in 1999.

Experiment study of mud to the moving process influent about viscous debris flow along slope

NASA Astrophysics Data System (ADS)

Jun, JiXian; Ying, Liang; Li, Pan Hua; Qiang, OuGuo

2018-01-01

Mud is the main component of viscous debris flow. The physical model experiments of viscous debris flow were carried out through the mixing mud with different density and fixed components of coarse particles. The width, longitudinal movement distance and motion velocity were recorded by video cameras during experiment. Through viscous debris flow physical model experiments, the influence of mud to transverse width, longitudinal movement distance and motion velocity was discussed. The physical model experiment results show that the motion forms change from inviscid particle flow to viscous debris flow and to the whole mass sliding with the increase of mud density; the width and the length along the slope decrease with mud density increasing; the movement process has classified phenomena about viscous debris flow composed by different mud densities: the velocity increases rapidly with time and the change gradient is steady when the density of mud is lower than 1.413g/cm3; the movement process can be divided into two stages when the density of mud is higher than 1.413g/cm3: the movement velocity is lower and the gradient change is small in the initial stage; but in the second stage, the movement velocity increases quickly, and the gradient is higher than the first stage, and with steady value.

Exploiting LSPIV to assess debris-flow velocities in the field

NASA Astrophysics Data System (ADS)

Theule, Joshua I.; Crema, Stefano; Marchi, Lorenzo; Cavalli, Marco; Comiti, Francesco

2018-01-01

The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

Flow Patterns of Lobate Debris Aprons and Lineated Valley Fill North of Ismeniae Fossae, Mars

NASA Astrophysics Data System (ADS)

Baker, D. M.; Head, J. W.; Marchant, D. R.

2009-03-01

Flow patterns are mapped within lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars. Flowlines are sourced in plateau alcoves and form large, well-integrated systems, consistent with a debris-covered glacier interpretation.

The rainfall-triggered landslide and flash-flood disaster in northern Venezuela, December 1999

USGS Publications Warehouse

Larsen, Matthew C.; Wieczorek, Gerald F.; Eaton, L.S.; Heriberto Torres-Sierra,

2001-01-01

Rainstorms in December 1999 induced thousands of landslides along the northern slopes of the Cordillera de la Costa mountain range principally in the state of Vargas, Venezuela. Rainfall accumulation of 293 millimeters during the first 2 weeks ofDecember was followed by an additional 911 millimeters of rainfall on December 14 through 16. The landslides and floods inundated coastal communities resulting in a catastrophic death toll estimated at between 15,000 and 30,000 people. Debris flow damage to houses, buildings, and infrastructure in the narrow coastal zone was severe. Flash floods on alluvial fans at the mouths of rivers draining the coastal mountain range also contributed to the general destruction. In time scales spanning decades to centuries, the alluvial fans along this Caribbean coastline are areas of high geomorphic activity. Because most of the coastal zone in Vargas consists of steep mountain fronts that rise directly from the Caribbean Sea, the alluvial fans provide the only relatively flat areas upon which to build. Rebuilding and reoccupation of these areas requires careful determination of hazard zones to avoid future loss of life and property. A limited assessment of the distribution and character of landslides is currently in progress by the U.S. Geological Survey in cooperation with the Venezuelan Ministry of Environment and Natural Resources.

Apparatus for controlling nuclear core debris

DOEpatents

Jones, Robert D.

1978-01-01

Nuclear reactor apparatus for containing, cooling, and dispersing reactor debris assumed to flow from the core area in the unlikely event of an accident causing core meltdown. The apparatus includes a plurality of horizontally disposed vertically spaced plates, having depressions to contain debris in controlled amounts, and a plurality of holes therein which provide natural circulation cooling and a path for debris to continue flowing downward to the plate beneath. The uppermost plates may also include generally vertical sections which form annular-like flow areas which assist the natural circulation cooling.

Processes and rates of sediment and wood accumulation in headwater streams of the Oregon Coast Range, USA

USGS Publications Warehouse

May, Christine L.; Gresswell, Robert E.

2003-01-01

Channels that have been scoured to bedrock by debris flows provide unique opportunities to calculate the rate of sediment and wood accumulation in low-order streams, to understand the temporal succession of channel morphology following disturbance, and to make inferences about processes associated with input and transport of sediment. Dendrochronology was used to estimate the time since the previous debris flow and the time since the last stand-replacement fire in unlogged basins in the central Coast Range of Oregon. Debris flow activity increased 42 per cent above the background rate in the decades immediately following the last wildfire. Changes in wood and sediment storage were quantified for 13 streams that ranged from 4 to 144 years since the previous debris flow. The volume of wood and sediment in the channel, and the length of channel with exposed bedrock, were strongly correlated with the time since the previous debris flow. Wood increased the storage capacity of the channel and trapped the majority of the sediment in these steep headwater streams. In the absence of wood, channels that have been scoured to bedrock by a debris flow may lack the capacity to store sediment and could persist in a bedrock state for an extended period of time. With an adequate supply of wood, low-order channels have the potential of storing large volumes of sediment in the interval between debris flows and can function as one of the dominant storage reservoirs for sediment in mountainous terrain.

Debris Flows and Related Phenomena

NASA Astrophysics Data System (ADS)

Ancey, C.

Torrential floods are a major natural hazard, claiming thousands of lives and millions of dollars in lost property each year in almost all mountain areas on the Earth. After a catastrophic eruption of Mount St. Helen in the USA in May 1980, water from melting snow, torrential rains from the eruption cloud, and water displaced from Spirit Lake mixed with deposited ash and debris to produce very large debris flows and cause extensive damage and loss of life [1]. During the 1985 eruption of Nevado del Ruiz in Colombia, more than 20,000 people perished when a large debris flow triggered by the rapid melting of snow and ice at the volcano summit, swept through the town of Armero [2]. In 1991, the eruption of Pinatubo volcano in the Philippines disperses more than 5 cubic kilometres of volcanic ash into surrounding valleys. Much of that sediment has subsequently been mobilised as debris flows by typhoon rains and has devastated more than 300 square kilometres of agricultural land. Even, in Eur opean countries, recent events that torrential floods may have very destructive effects (Sarno and Quindici in southern Italy in May 1998, where approximately 200 people were killed). The catastrophic character of these floods in mountainous watersheds is a consequence of significant transport of materials associated with water flows. Two limiting flow regimes can be distinguished. Bed load and suspension refer to dilute transport of sediments within water. This means that water is the main agent in the flow dynamics and that the particle concentration does not exceed a few percent. Such flows are typically two-phase flows. In contrast, debris flows are mas s movements of concentrated slurries of water, fine solids, rocks and boulders. As a first approximation, debris flows can be treated as one-phase flows and their flow properties can be studied using classical rheological methods. The study of debris flows is a very exciting albeit immature science, made up of disparate elements borrowed from geomorphology, geology, hydrology, soil mechanics, and fluid mechanics. The purpose of this chapter is to provide an introduction to physical aspects of debris flows, with specific attention directed to their rheological features. Despite attempts to provide a coherent view on the topic, coverage is incomplete and the reader is referred to a series of papers and books. Three books are particularly commendable [3-5]. Some review papers provide interesting overviews, introducing the newcomers to the field to the main concepts [6-8]. The background material in rheology can be found in Chaps. 2 and 3.

Debris flows susceptibility mapping under tropical rain conditions in Rwanda.

NASA Astrophysics Data System (ADS)

Nduwayezu, Emmanuel; Nsengiyumva, Jean-Baptiste; BUgnon, Pierre-Charles; Jaboyedoff, Michel; Derron, Marc-Henri

2017-04-01

Rwanda is a densely populated country. It means that all the space is exploited, including sometimes areas with very steep slopes. This has as for consequences that during the rainy season slopes with human activities are affected by gravitational processes, mostly debris and mud flows and shallow landslides. The events of early May 2016 (May 8 and 9), with more than 50 deaths, are an illustration of these frequents landslides and inundations. The goal of this work is to produce a susceptibility map for debris/mud flows at regional/national scale. Main available pieces of data are a national digital terrain model at 10m resolution, bedrock and soil maps, and information collected during field visits on some specific localities. The first step is the characterization of the slope angle distribution for the different types of bedrock or soils (decomposition in Gaussian populations). Then, the combination of this information with other geomorphic and hydrologic parameters is used to define potential source areas of debris flows. Finally, propagation maps of debris flows are produced using FLOW-R (Horton et al. 2013). Horton, P., Jaboyedoff, M., Rudaz, B., and Zimmermann, M.: Flow-R, a model for susceptibility mapping of debris flows and other gravitational hazards at a regional scale, Nat. Hazards Earth Syst. Sci., 13, 869-885, doi:10.5194/nhess-13-869-2013, 2013. The paper is in open access.

Slope stability problems associated with timber harvesting in mountainous regions of the western United States.

Treesearch

D.N. Swanston

1974-01-01

Natural soil-mass-movements on forested slopes in the Western United States can be divided into two major groups of closely related landslide types. These include, in order of decreasing importance and regional frequency of occurrence: (1) debris slides, debris avalanches, debris flows, and debris torrents; and (2) creep, slumps, and earth flows. Each type requires the...

Rainstorms able to induce flash floods in a Mediterranean-climate region (Calabria, southern Italy)

NASA Astrophysics Data System (ADS)

Terranova, O. G.; Gariano, S. L.

2014-03-01

Heavy rainstorms often induce flash flooding, one of the natural disasters most responsible for damage to man-made infrastructure and loss of lives, adversely affecting also the opportunities for socio-economic development of Mediterranean Countries. The frequently dramatic damage of flash floods are often detected with sufficient accuracy by post-event surveys, but rainfall causing them are still only roughly characterized. With the aim of improving the understanding of the temporal structure and spatial distribution of heavy rainstorms in the Mediterranean context, a statistical analysis was carried out in Calabria (southern Italy) concerning rainstorms that mainly induced flash floods, but also shallow landslides and debris-flows. Thus a method is proposed - based on the overcoming of heuristically predetermined threshold values of cumulated rainfall, maximum intensity, and kinetic energy of the rainfall event - to select and characterize the rainstorms able to induce flash floods in the Mediterranean-climate Countries. Therefore the obtained (heavy) rainstorms were automatically classified and studied according to their structure in time, localization and extension. Rainfall-runoff watershed models can consequently benefit from the enhanced identification of design storms, with a realistic time structure integrated with the results of the spatial analysis. A survey of flash flood events recorded in the last decades provides a preliminary validation of the method proposed to identify the heavy rainstorms and synthetically describe their characteristics. The notable size of the employed sample, including data with a very detailed resolution in time, that relate to several rain gauges well-distributed throughout the region, give robustness to the obtained results.

Rainstorms able to induce flash floods in a Mediterranean-climate region (Calabria, southern Italy)

NASA Astrophysics Data System (ADS)

Terranova, O. G.; Gariano, S. L.

2014-09-01

Heavy rainstorms often induce flash flooding, one of the natural disasters most responsible for damage to man-made infrastructures and loss of lives, also adversely affecting the opportunities for socio-economic development of Mediterranean countries. The frequently dramatic damage of flash floods are often detected, with sufficient accuracy, by post-event surveys, but rainfall causing them are still only roughly characterized. With the aim of improving the understanding of the temporal structure and spatial distribution of heavy rainstorms in the Mediterranean context, a statistical analysis was carried out in Calabria (southern Italy) concerning rainstorms that mainly induced flash floods, but also shallow landslides and debris flows. Thus, a method is proposed - based on the overcoming of heuristically predetermined threshold values of cumulated rainfall, maximum intensity, and kinetic energy of the rainfall event - to select and characterize the rainstorms able to induce flash floods in the Mediterranean-climate countries. Therefore, the obtained (heavy) rainstorms were automatically classified and studied according to their structure in time, localization, and extension. Rainfall-runoff watershed models can consequently benefit from the enhanced identification of design storms, with a realistic time structure integrated with the results of the spatial analysis. A survey of flash flood events recorded in the last decades provides a preliminary validation of the method proposed to identify the heavy rainstorms and synthetically describe their characteristics. The notable size of the employed sample, including data with a very detailed resolution in time that relate to several rain gauges well-distributed throughout the region, gives robustness to the obtained results.

Experimental testing of flexible barriers for containment of debris flows

USGS Publications Warehouse

DeNatale, Jay S.; Iverson, Richard M.; Major, Jon J.; LaHusen, Richard G.; Fliegel, Gregg L.; Duffy, John D.

1999-01-01

In June 1996, six experiments conducted at the U.S. Geological Survey Debris Flow Flume demonstrated that flexible, vertical barriers constructed of wire rope netting can stop small debris flows. All experimental debris flows consisted of water-saturated gravelly sand with less than two percent finer sediment by weight. All debris flows had volumes of about 10 cubic meters, masses of about 20 metre tons, and impact velocities of 5 to 9 meters per second. In four experiments, the debris flow impacted pristine, unreformed barriers of varying design; in the other two experiments, the debris flow impacted barriers already loaded with sediment from a previous flow. Differences in barrier design led to differences in barrier performance. Experiments were conducted with barriers constructed of square-mesh wire-rope netting with 30centimeter, 20centimeter, and 15 centimeter mesh openings as well as 30centimeter diameter interlocking steel rings. In all cases, sediment cascading downslope at the leading edge of the debris flows tended to spray through the nets. Nets fitted with finer-mesh chain link or chicken wire liners contained more sediment than did unlined nets, and a ring net fitted with a synthetic silt screen liner contained nearly 100 percent of the sediment. Irreversible net displacements of up to 2 meters and friction brake engagement on the support and anchor cables dissipated some of the impact energy. However, substantial forces developed in the steel support columns and the lateral and tie-back anchor cables attached to these columns. As predicted by elementary mechanics, the anchor cables experienced larger tensile forces when the support columns were hinged at the base rather than bolted rigidly to the foundation. Measured loads in the lateral anchor cables exceeded those in the tie-back anchor cables and the load cell capacity of 45 kilo-Newtons. Measurements also indicated that the peak loads in the tie- back anchors were highly transient and occurred at the points of maximum momentum impulse to the net.

Gravity flows associated with flood events and carbon burial: Taiwan as instructional source area.

PubMed

Liu, James T; Kao, Shuh-Ji; Huh, Chih-An; Hung, Chin-Chang

2013-01-01

Taiwan's unique setting allows it to release disproportionately large quantities of fluvial sediment into diverse dispersal systems around the island. Earthquakes, lithology, topography, cyclone-induced rainfall, and human disturbance play major roles in the catchment dynamics. Deep landslides dominate the sediment-removal process on land, giving fluvial sediment distinct geochemical signals. Extreme conditions in river runoff, sediment load, nearshore waves and currents, and the formation of gravity flows during typhoon events can be observed within short distances. Segregation of fresh biomass and clastic sediment occurs during the marine transport process, yet turbidity currents in the Gaoping Submarine Canyon carry woody debris. Strong currents in the slope and back-arc basin of the Okinawa Trough disperse fine-grained sediments rapidly and widely. Temporal deposition and remobilization may occur when the shallow Taiwan Strait acts as a receptacle. Taiwan can therefore serve as a demonstration of the episodic aspect of the source-to-sink pathway to both the coastal and deep-ocean environments.

Structural characteristics of cohesive flow deposits, and a sedimentological approach on their flow mechanisms.

NASA Astrophysics Data System (ADS)

Tripsanas, E. K.; Bryant, W. R.; Prior, D. B.

2003-04-01

A large number of Jumbo Piston cores (up to 20 m long), acquired from the continental slope and rise of the Northwest Gulf of Mexico (Bryant Canyon area and eastern Sigsbee Escarpment), have recovered various mass-transport deposits. The main cause of slope instabilities over these areas is oversteepening of the slopes due to the seaward mobilization of the underlying allochthonous salt masses. Cohesive flow deposits were the most common recoveries in the sediment cores. Four types of cohesive flow deposits have been recognized: a) fluid debris flow, b) mud flow, c) mud-matrix dominated debris flow, and d) clast-dominated debris flow deposits. The first type is characterized by its relatively small thickness (less than 1 m), a mud matrix with small (less than 0.5 cm) and soft mud-clasts, and a faint layering. The mud-clasts reveal a normal grading and become more abundant towards the base of each layer. That reveals that their deposition resulted by several successive surges/pulses, developed in the main flow, than the sudden “freezing” of the whole flow. The main difference between mud flow and mud-matrix dominated debris flow deposits is the presence of small to large mud-clasts in the later. Both deposits consist of a chaotic mud-matrix, and a basal shear laminated zone, where the strongest shearing of the flow was exhibited. Convolute laminations, fault-like surfaces, thrust faults, and microfaults are interpreted as occurring during the “freezing” of the flows and/or by adjustments of the rested deposits. Clast-dominated debris flow deposits consist of three zones: a) an upper plug-zone, characterized by large interlocked clasts, b) a mid-zone, of higher reworked, inversely graded clasts, floating in a mud-matrix, and c) a lower shear laminated zone. The structure of the last three cohesive flow deposits indicate that they represent deposition of typical Bingham flows, consisting of an upper plug-zone in which the yield stress is not exceeded and an underlain shearing zone, where the shear stress exceeded the yield strength of the sediments. Mud-matrix, and clast-dominated debris flow deposits are the pervasive ones. Intensely sheared thin layers (5- to 20 cm) with sharp bases, displayed as successive layers at the base of mud/debris flow deposits, or as isolated depositional units interbedded in hemipelagic sediments, are as interesting, as enigmatic. They are interpreted as basal self-lubricating layers, of having high shear stress and pore pressures, over which the mud/debris flows were able to travel for very long distances.

Water saturation of hydrothermal smectite-rich clay might have promoted slope instability prior to the 1998 debris avalanche at Casita volcano, Nicaragua

NASA Astrophysics Data System (ADS)

Delmelle, P.; Opfergelt, S.; Boivin, P.; Delvaux, B.

2006-12-01

In October 1998, a relatively small collapse (1 600 000 cubic meters) of a pre-existing scarp occurred on the southern flank of the dormant Casita volcano, Nicaragua. It resulted in a debris avalanche, which quickly transformed into a disastrous debris flow that destroyed two towns and killed more than 2500 people. The failure was shown to be triggered by an excess pore water pressure within highly fractured rocks, following prolonged seasonal rains and precipitations from Hurricane Mitch. This pressure was linked to the water saturation of a hydrothermally-altered clay bedrock impeding in-depth infiltration. Yet, the nature and amounts of the clay material involved in the slope failure were still unknown. Here we report on physical, chemical and mineralogical investigations aimed at quantifying the clay content, and identifying the layer silicates of the hydrothermally-altered clays uncovered by the 1998 debris avalanche. The fine clay material was exceptionally rich in smectite (up to 50 wt. percent), which swells upon wetting and shrinks during dry conditions (Opfergelt et al., 2006, Geophys. Res. Lett., 33 (15), L15305). The smectite belonged to the beidellite-montmorillonite series. The pervasive presence of water-saturated smectitic clay strongly reduced the permeability in depth, and also altered the rheological and mechanical properties of both the pre-failure rock mass and flow materials. The shrink-swell behavior progressively decreased the rock's shear strength, and gradually destabilized the overlying rock mass in the decades and centuries before the landslide, thereby contributing to slope instability. Prolonged intense rainfall led to the formation of incipient weak failure surfaces in the superficial rock mass. As provoked by water saturation, this process was likely favored by the rapid change of the mechanical properties of smectite-rich clays deposited in fracture, joint and gouge interfaces. We suggest that hazard assessments associated with unstable volcanic slopes, especially on volcanoes hosting a long-lived hydrothermal system, should include the potential long and short-term impacts of swelling clays.

Flank collapse at Mount Wrangell, Alaska, recorded by volcanic mass-flow deposits in the Copper River lowland

USGS Publications Warehouse

Waythomas, C.F.; Wallace, K.L.

2002-01-01

An areally extensive volcanic mass-flow deposit of Pleistocene age, known as the Chetaslina volcanic mass-flow deposit, is a prominent and visually striking deposit in the southeastern Copper River lowland of south-central Alaska. The mass-flow deposit consists of a diverse mixture of colorful, variably altered volcanic rocks, lahar deposits, glaciolacustrine diamicton, and till that record a major flank collapse on the southwest flank of Mount Wrangell. The deposit is well exposed near its presumed source, and thick, continuous, stratigraphic exposures have permitted us to study its sedimentary characteristics as a means of better understanding the origin, significance, and evolution of the deposit. Deposits of the Chetaslina volcanic mass flow in the Chetaslina River drainage are primary debris-avalanche deposits and consist of two principal facies types, a near-source block facies and a distal mixed facies. The block facies is composed entirely of block-supported, shattered and fractured blocks with individual blocks up to 40 m in diameter. The mixed facies consists of block-sized particles in a matrix of poorly sorted rock rubble, sand, and silt generated by the comminution of larger blocks. Deposits of the Chetaslina volcanic mass flow exposed along the Copper, Tonsina, and Chitina rivers are debris-flow deposits that evolved from the debris-avalanche component of the flow and from erosion and entrainment of local glacial and glaciolacustrine diamicton in the Copper River lowland. The debris-flow deposits were probably generated through mixing of the distal debris avalanche with the ancestral Copper River, or through breaching of a debris-avalanche dam across the ancestral river. The distribution of facies types and major-element chemistry of clasts in the deposit indicate that its source was an ancestral volcanic edifice, informally known as the Chetaslina vent, on the southwest side of Mount Wrangell. A major sector collapse of the Chetaslina vent initiated the Chetaslina volcanic mass flow forming a debris avalanche of about 4 km3 that subsequently transformed to a debris flow of unknown volume.

Applying genetic algorithms for calibrating a hexagonal cellular automata model for the simulation of debris flows characterised by strong inertial effects

NASA Astrophysics Data System (ADS)

Iovine, G.; D'Ambrosio, D.; Di Gregorio, S.

2005-03-01

In modelling complex a-centric phenomena which evolve through local interactions within a discrete time-space, cellular automata (CA) represent a valid alternative to standard solution methods based on differential equations. Flow-type phenomena (such as lava flows, pyroclastic flows, earth flows, and debris flows) can be viewed as a-centric dynamical systems, and they can therefore be properly investigated in CA terms. SCIDDICA S 4a is the last release of a two-dimensional hexagonal CA model for simulating debris flows characterised by strong inertial effects. S 4a has been obtained by progressively enriching an initial simplified model, originally derived for simulating very simple cases of slow-moving flow-type landslides. Using an empirical strategy, in S 4a, the inertial character of the flowing mass is translated into CA terms by means of local rules. In particular, in the transition function of the model, the distribution of landslide debris among the cells is obtained through a double cycle of computation. In the first phase, the inertial character of the landslide debris is taken into account by considering indicators of momentum. In the second phase, any remaining debris in the central cell is distributed among the adjacent cells, according to the principle of maximum possible equilibrium. The complexities of the model and of the phenomena to be simulated suggested the need for an automated technique of evaluation for the determination of the best set of global parameters. Accordingly, the model is calibrated using a genetic algorithm and by considering the May 1998 Curti-Sarno (Southern Italy) debris flow. The boundaries of the area affected by the debris flow are simulated well with the model. Errors computed by comparing the simulations with the mapped areal extent of the actual landslide are smaller than those previously obtained without genetic algorithms. As the experiments have been realised in a sequential computing environment, they could be improved by adopting a parallel environment, which allows the performance of a great number of tests in reasonable times.

Agricultural terraces and slope instability at Cinque Terre (NW Italy)

NASA Astrophysics Data System (ADS)

Brandolini, Pierluigi; Cevasco, Andrea

2015-04-01

Cinque Terre, located in the eastern Liguria, are one of the most representative examples of terraced coastal landscape within the Mediterranean region. They are the result of a century-old agricultural practice and constitute an outstanding example of human integration with the natural landscape. For this highly unusual man-made coastal landscape, the Cinque Terre have been recognized as a World Heritage Site by UNESCO since 1997 and became National Park in 1999. The complex network of retaining dry stone walls and drainage networks ensured through times the control of shallow water erosion and therefore, indirectly, favoured debris cover stability. The lack of maintenance of terracing due to farmer abandonment since the 1950s led to widespread slope erosion phenomena. The effects of such phenomena culminated during the 25 October 2011 storm rainfall event, when slope debris materials charged by streams gave rise to debris floods affecting both Monterosso and Vernazza villages. As the analysis of the relationships between geo-hydrological processes and land use in the Vernazza catchment highlighted, abandoned and not well maintained terraces were the most susceptible areas to shallow landsliding and erosion triggered by intense rainfall. As a consequence, the thousands of kilometres of dry stone walls retaining millions of cubic metres of debris cover at Cinque Terre currently constitute a potential menace for both villages, that are mainly located at the floor of deep cut valleys, and tourists. Given the increasing human pressure due to tourist activities, geo-hydrological risk mitigation measures are urgently needed. At the same time, restoration policies are necessary to preserve this extraordinary example of terraced coastal landscape. In this framework, the detailed knowledge of the response of terraced areas to intense rainfall in terms of slope instability is a topic issue in order to identify adequate land planning strategies as well as the areas where interventions should be focused primarily. In this study, with the aim to contribute to a better understanding of geo-hydrological hazards at basin scale, the main types of slope instability phenomena that occurred on agricultural terraces at Cinque Terre following the 25 October 2011 rainfall event are presented in relation to different geological and geomorphological conditions. In particular, selected examples of shallow landslides and erosive slope processes due to running water affecting abandoned or cultivated terraces for vineyards and olive grooves will be shown.

KENNEDY SPACE CENTER, FLA. - In the Columbia Debris Hangar, Scott Thurston, NASA vehicle flow manager, addresses the media about efforts to pack the debris stored in the Columbia Debris Hangar. More than 83,000 pieces of debris were shipped to KSC during search and recovery efforts in East Texas. That represents about 38 percent of the dry weight of Columbia, equaling almost 85,000 pounds. An area of the Vehicle Assembly Building is being prepared to store the debris permanently.

NASA Image and Video Library

2003-09-11

KENNEDY SPACE CENTER, FLA. - In the Columbia Debris Hangar, Scott Thurston, NASA vehicle flow manager, addresses the media about efforts to pack the debris stored in the Columbia Debris Hangar. More than 83,000 pieces of debris were shipped to KSC during search and recovery efforts in East Texas. That represents about 38 percent of the dry weight of Columbia, equaling almost 85,000 pounds. An area of the Vehicle Assembly Building is being prepared to store the debris permanently.