Science.gov

Sample records for channel tidal delta

  1. Hydraulic Geometry of a tidally influenced delta channel network: the Mahakam Delta, East Kalimantan, Indonesia

    NASA Astrophysics Data System (ADS)

    Sassi, M.; Hoitink, A.; de Brye, B.; Deleersnijder, E.

    2011-12-01

    Hydraulic Geometry (HG) refers to relations between the characteristics of channels in a network, including mean depth, width, and bed slope, and the discharge conveyed by the channel during bank-full conditions. HG relations are of fundamental importance to water management in channel networks, and they bear an interesting relation with geomorphology. River delta channel networks typically scale according to HG relations such as log(A) ~ p*log(Q), where A is channel cross sectional area, Q water discharge, and the exponent p is in between 0.8 and 1.2. In tidal networks, the tidal prism or tidal discharge can be used, instead of a discharge with a constant frequency of occurrence. In the tidal case, the exponent often shows the same range of variation. Tidal rivers are intrinsically complex, as tidal propagation is influenced by river discharge and vice-versa. Consequently, channel geometry in tidally influenced river deltas may show a mixed scaling behavior of river and tidal channel networks, as the channel forming discharges may both be of river and tidal origin. In tidal regions, the tidal dynamics may lead to a cyclic variation in water discharge distribution at bifurcations, readily affecting HG relations. We present results from the Mahakam delta channel network in Indonesia, a tide-river dominated delta which has been prograding for 60 km over the last 5000 years. Bathymetric surveys were conducted over the distributary network and connected tidal channels. Based on a geomorphic analysis of the present distributary network, we show that channel geometry of the fluvial distributary network scales with bifurcation order. The bifurcation order does not feature a clear relation with bifurcate branch length or bifurcate width ratio, as in the case of river deltas. HG relations of the area of selected cross-sections are well represented by the tidal prism or by the river discharge, when scaled with the bifurcation order. Numerical simulations show that river

  2. Turning the tide: experimental creation of tidal channel networks and ebb deltas

    NASA Astrophysics Data System (ADS)

    Terwisscha van Scheltinga, R.; Kleinhans, M. G.; Baar, A.; Van Der Vegt, M.; Markies, H.

    2011-12-01

    Tidal channel networks, estuaries and ebb deltas usually formed over a period longer than observations cover. Much is known about their characteristics and formation from linear stability analyses, numerical modelling and field observations. However, experiments are rare whilst these provide data-rich descriptions of their evolution in fully controlled boundary and initial conditions. Our objective is to ascertain whether tidal basins can be formed in experiments, what possible scale effects are, and whether morphological equilibrium of such systems exist. We experimentally created tidal basins with simple channel networks and ebb deltas in a 1.5 m^2 square basin with a fixed tidal inlet and initially flat sediment bed in the basin raised above the bed of the sea. Rather than create tides by varying water level, we tilted the entire basin over the diagonal. The advantage of this novel method is that the bed surface slopes in downstream direction both during flood and ebb phase, resulting in significant transport and morphological change in the flood phase as well as the ebb phase. This overcomes the basic problem of earlier experiments which were entirely ebb-dominated, and reduces the experiment time from months to hours. Ebb deltas formed in sand were entirely bedload dominated whereas light-weight plastics showed much more suspension. Channels bifurcated during channel deepening and backward erosion to form a network of three orders. The tidal prism increased as more sediment was moved from basin to ebb delta, so that evolution accelerated initially. Given that most experiments were close to beginning of sediment motion, the rate of change, the size of the channels and the final length of channels and delta were very sensitive to the tidal amplitude, tidal period and water depth in the basin. The final situation was invariably below the threshold for sediment motion except in the inlet and first-order channels, suggesting that other forcings such as storm waves

  3. Multiscale heterogeneity characterization of tidal channel, tidal delta and foreshore facies, Almond Formation outcrops, Rock Springs uplift, Wyoming

    SciTech Connect

    Schatzinger, R.A.; Tomutsa, L.

    1997-08-01

    In order to accurately predict fluid flow within a reservoir, variability in the rock properties at all scales relevant to the specific depositional environment needs to be taken into account. The present work describes rock variability at scales from hundreds of meters (facies level) to millimeters (laminae) based on outcrop studies of the Almond Formation. Tidal channel, tidal delta and foreshore facies were sampled on the eastern flank of the Rock Springs uplift, southeast of Rock Springs, Wyoming. The Almond Fm. was deposited as part of a mesotidal Upper Cretaceous transgressive systems tract within the greater Green River Basin. Bedding style, lithology, lateral extent of beds of bedsets, bed thickness, amount and distribution of depositional clay matrix, bioturbation and grain sorting provide controls on sandstone properties that may vary more than an order of magnitude within and between depositional facies in outcrops of the Almond Formation. These features can be mapped on the scale of an outcrop. The products of diagenesis such as the relative timing of carbonate cement, scale of cemented zones, continuity of cemented zones, selectively leached framework grains, lateral variability of compaction of sedimentary rock fragments, and the resultant pore structure play an equally important, although less predictable role in determining rock property heterogeneity. A knowledge of the spatial distribution of the products of diagenesis such as calcite cement or compaction is critical to modeling variation even within a single facies in the Almond Fin. because diagenesis can enhance or reduce primary (depositional) rock property heterogeneity. Application of outcrop heterogeneity models to the subsurface is greatly hindered by differences in diagenesis between the two settings. The measurements upon which this study is based were performed both on drilled outcrop plugs and on blocks.

  4. Hydrodynamic Properties of a Large Tidal Channel on the Ganges-Brahmaputra Delta, Bangladesh, with Implications for Channel Morphology and Sediment Transport

    NASA Astrophysics Data System (ADS)

    Bain, R. L.; Goodbred, S. L., Jr.; Hale, R. P.; Reed, M. J.; Best, J.

    2015-12-01

    The Ganges-Brahmaputra Delta hosts a dense network of tidal channels extending inland as far as 100 kilometers from the coast. With semidiurnal tides up to 6.7 meters in amplitude, this setting is ideal for testing hypotheses related to tidal meander morphology, intertidal sediment transport, and channel-platform linkages. We present results from two field surveys in March and September 2015, corresponding to the dry and monsoon seasons, respectively. Comparing acoustic Doppler current profiler (ADCP) data and pressure sensor measurements from the Sibsa River in southwest Bangladesh reveals a phase lag of as much as 1 hour between maximum discharge and mean water level. Variations in this phase lag at different points along the channel allow us to test an existing conceptual model of cuspate tidal meander formation. To address a related but separate question, we observe that the ratio of cumulative discharges Qin/Qout is approximately equal during both spring and neap tides at a strategically-placed ADCP transect south of the study area. In contrast, ADCP data obtained north of the study area shows that Qin/Qout=1.4 during spring tides and 0.85 during neap tides. We examine the degree to which this phenomenon is controlled by the establishment of a hydraulic gradient between the Sibsa and a parallel tidal channel, the Pussur, versus the exchange of water between the channel and the tidal flats during the ebb-flood cycle. These results have implications for identifying loci of sediment erosion and deposition within the network.

  5. Tidal river dynamics: Implications for deltas

    NASA Astrophysics Data System (ADS)

    Hoitink, A. J. F.; Jay, D. A.

    2016-03-01

    Tidal rivers are a vital and little studied nexus between physical oceanography and hydrology. It is only in the last few decades that substantial research efforts have been focused on the interactions of river discharge with tidal waves and storm surges into regions beyond the limit of salinity intrusion, a realm that can extend inland hundreds of kilometers. One key phenomenon resulting from this interaction is the emergence of large fortnightly tides, which are forced long waves with amplitudes that may increase beyond the point where astronomical tides have become extinct. These can be larger than the linear tide itself at more landward locations, and they greatly influence tidal river water levels and wetland inundation. Exploration of the spectral redistribution and attenuation of tidal energy in rivers has led to new appreciation of a wide range of consequences for fluvial and coastal sedimentology, delta evolution, wetland conservation, and salinity intrusion under the influence of sea level rise and delta subsidence. Modern research aims at unifying traditional harmonic tidal analysis, nonparametric regression techniques, and the existing understanding of tidal hydrodynamics to better predict and model tidal river dynamics both in single-thread channels and in branching channel networks. In this context, this review summarizes results from field observations and modeling studies set in tidal river environments as diverse as the Amazon in Brazil, the Columbia, Fraser and Saint Lawrence in North America, the Yangtze and Pearl in China, and the Berau and Mahakam in Indonesia. A description of state-of-the-art methods for a comprehensive analysis of water levels, wave propagation, discharges, and inundation extent in tidal rivers is provided. Implications for lowland river deltas are also discussed in terms of sedimentary deposits, channel bifurcation, avulsion, and salinity intrusion, addressing contemporary research challenges.

  6. On funneling of tidal channels

    NASA Astrophysics Data System (ADS)

    Lanzoni, S.; D'Alpaos, A.

    2015-03-01

    Tidal channels dissect the tidal landscape and exert a crucial control on the morphodynamic evolution of these landscapes. Improving our understanding of channel equilibrium morphology is therefore an important issue for both theoretical and practical reasons. We analyze the case of a tidal channel dissecting a relatively short, unvegetated tidal flat characterized by microtidal conditions and a negligible external sediment supply. The three-dimensional equilibrium configuration of the channel is determined on the basis of a hydrodynamic model, describing the cross-sectional distribution of the longitudinal bed shear stresses, coupled with a morphodynamic model retaining the description of the main physical processes shaping the channel and the adjacent intertidal platform. Both channel bed and width are allowed to adapt to the flow field so that an equilibrium altimetric and planimetric configuration is eventually obtained, when erosion becomes negligibly small, and asymptotically constant elevations are reached everywhere within the domain. Model results reproduce several observed channel characteristics of geomorphic relevance, such as the relationship between channel cross-sectional area and the flowing tidal prism, the scaling of the width-to-depth ratio with channel width, and the longitudinal distributions of bed elevations and channel widths. In analogy with empirical evidence from estuaries, tidal channel funneling is usually assumed to be described by an exponential trend. Our theoretical analyses, modeling results, and observational evidence suggest that a linear relationship also provides a good approximation to describe longitudinal variations in channel width for short tidal channels. Longitudinal bed profiles characterized by a strong planform funneling tend to attain an upward concavity, whereas a low degree of convergence implies an almost linear profile. Finally, the model allows one to analyze the influence of environmental conditions (sediment

  7. Morphologic and stratigraphic evolution of muddy ebb-tidal deltas along a subsiding coast: Barataria Bay, Mississippi River delta

    USGS Publications Warehouse

    FitzGerald, D.M.; Kulp, M.; Penland, S.; Flocks, J.; Kindinger, J.

    2004-01-01

    The Barataria barrier coast formed between two major distributaries of the Mississippi River delta: the Plaquemines deltaic headland to the east and the Lafourche deltaic headland to the west. Rapid relative sea-level rise (1??03 cm year-1) and other erosional processes within Barataria Bay have led to substantial increases in the area of open water (> 775 km2 since 1956) and the attendant bay tidal prism. Historically, the increase in tidal discharge at inlets has produced larger channel cross-sections and prograding ebb-tidal deltas. For example, the ebb delta at Barataria Pass has built seaward > 2??2 km since the 1880s. Shoreline erosion and an increasing bay tidal prism also facilitated the formation of new inlets. Four major lithofacies characterize the Barataria coast ebb-tidal deltas and associated sedimentary environments. These include a proximal delta facies composed of massive to laminated, fine grey-brown to pale yellow sand and a distal delta facies consisting of thinly laminated, grey to pale yellow sand and silty sand with mud layers. The higher energy proximal delta deposits contain a greater percentage of sand (75-100%) compared with the distal delta sediments (60-80%). Associated sedimentary units include a nearshore facies consisting of horizontally laminated, fine to very fine grey sand with mud layers and an offshore facies that is composed of grey to dark grey, laminated sandy silt to silty clay. All facies coarsen upwards except the offshore facies, which fines upwards. An evolutionary model is presented for the stratigraphic development of the ebb-tidal deltas in a regime of increasing tidal energy resulting from coastal land loss and tidal prism growth. Ebb-tidal delta facies prograde over nearshore sediments, which interfinger with offshore facies. The seaward decrease in tidal current velocity of the ebb discharge produces a gradational contact between proximal and distal tidal delta facies. As the tidal discharge increases and the inlet

  8. Quantifying the effects of tidal amplitude on river delta network flow partitioning

    NASA Astrophysics Data System (ADS)

    Hiatt, M. R.; Sendrowski, A.; Passalacqua, P.

    2014-12-01

    Deltas are generally classified as river-, tide-, or wave-dominated systems, but the influences of all environmental forces cannot be ignored when fully addressing the dynamics of the system. For example, in river-dominated deltas, river flow from the feeder channel acts as the primary driver of dynamics within the system by delivering water, sediment, and nutrients through the distributary channels, but tides and waves may affect their allocation within the network. There has been work on the asymmetry of environmental fluxes at bifurcations, but relatively few studies exist on the water partitioning at the network scale. Understanding the network and environmental effects on the flux of water, sediment, and nutrients would benefit delta restoration projects and management practices. In this study, we investigate the allocation of water flow among the five major distributary channels at Wax Lake Delta (WLD), a micro-tidal river-dominated delta in coastal Louisiana, and the effects of tidal amplitude on distributary channel discharges. We collect and compare discharge results from acoustic Doppler current profiler (ADCP) velocity transects between spring and neap tide and between falling and rising tide. The results show that discharges increased from spring to neap tide and from rising to falling tide. We investigate the spatial gradients of tidal influence within the network and validate hydraulic geometry relations for tidally influenced channels. Our results give insight into the control of network structure on flow partitioning and show the degree of tidal influence on channel flow in the river-dominated WLD.

  9. On the Development of a Model for Flood-Tidal Deltas and the Hydraulic Efficiency of Associated Tidal Inlets

    NASA Astrophysics Data System (ADS)

    Borrelli, M.; Smith, T. L.; Giese, G. S.

    2014-12-01

    A highly energetic, rapidly changing system provides the opportunity to study the potential for linking flood-tidal deltas and tidal inlets in order to predict possible future inlet scenarios. These subtidal and intertidal sedimentary deposits are formed by flood-tidal currents and modified by ebb-tidal currents and as such can elucidate past and present hydraulic conditions. Further, within the proposed conceptual model the evolution of these features can lend insight into future system and inlet development. An ongoing study documented a feedback mechanism linking the primary flood-tidal delta with the migration of the tidal inlet in the study area on Cape Cod, Massachusetts USA. This was based on field surveys (n = 10) of intertidal bedforms, a tidal current velocity survey, and 2 dimensional analyses of aerial photographs from 1938 to the present (n = 32). Three-dimensional analysis of the flood-tidal delta and inlet was conducted using bathymetry from a 2014 vessel-based survey using Phase-Measuring Sidescan Sonar, coupled with bathymetric Lidar from 2007 and 2010. A conceptual model for this and similar systems is being developed. As seen in the study area material entrained in the longshore sediment transport system becomes incorporated into the swash platform. As a result more sediment is introduced into the harbor during flood tides increasing the size of the flood-tidal delta. If the increase in size reduces the hydraulic efficiency of the ebb-tidal flow a feedback mechanism can result. Ebb-tidal flow is restricted, channels become narrower and deeper, and this channelization leads to an increase in shallower areas in the harbor, which further increases sediment transport during flood-tidal flow. If the cycle continues the system becomes too hydraulically inefficient and a correction occurs, that can be gradual or rapid, either of which has implications for system evolution and/or management. This preliminary model was developed from field observations in

  10. The late-Holocene progradation of the Mahakam Delta, Indonesia - A case study of tidal, tropical deltas

    NASA Astrophysics Data System (ADS)

    Dalman, R.; Ranawijaya, D.; Missiaen, T.; Kroonenberg, S.; Storms, J.

    2011-12-01

    The Mahakam Delta is an oft-cited example of a mixed fluvial-tidally influenced delta. Yet the distinct separation of the tide-dominated delta plain and the fluvial distributaries make the delta unique amongst tidally influenced deltas. The delta prograded an average of 60 km over the last 5000 years. Most sediment transport is induced by tidal currents and fluvial discharge, which resulted in a distinct, dense network of distributary and tidal channels. In order to characterize the Holocene sedimentary architecture we describe a dataset of 10 new cores and a large survey of very high-resolution, shallow seismics. The seismics are recorded using an echosounder with a novel parametric source, allowing subsurface penetration in excess of 15 m while achieving a vertical resolution of 0.2 m. Distinct sedimentary facies are described in detail for delta plain, delta front, distributary and mouthbar deposits. A notable difference in stratal pattern has been observed between the inner and outer tide-dominated delta plain facies. The inner tidal channels cut deeply into the underlying deltafront deposits and form a distinct heterogenic laterally accreting and intercutting facies. Whereas the outer tide-dominated delta plain deposits accrete conformably on the marine deltafront facies and show a much more homogenous sedimentary architecture. The continual reworking of the inner tide-dominated delta plain results in a patchwork of deposits greatly varying in thickness and age albeit with a similar silty clay lithology. The area of the present-day delta was largely flooded after the early to mid-Holocene transgression, our data indicate that a small branch of fluvial distributaries was active on the current delta plain around 5 ka. Subsequently, the northernmost fluvial distributary built out rapidly over a period of 3 kyrs. The southern distributaries built out later, from 2 ka to the present. The mouthbar deposits in the south are significantly thicker than in the northern

  11. Foraging and growth potential of juvenile Chinook Salmon after tidal restoration of a large river delta

    USGS Publications Warehouse

    David, Aaron T.; Ellings, Christopher; Woo, Isa; Simenstad, Charles A.; Takekawa, John Y.; Turner, Kelley L.; Smith, Ashley L.; Takekawa, Jean E.

    2014-01-01

    We evaluated whether restoring tidal flow to previously diked estuarine wetlands also restores foraging and growth opportunities for juvenile Chinook Salmon Oncorhynchus tshawytscha. Several studies have assessed the value of restored tidal wetlands for juvenile Pacific salmon Oncorhynchus spp., but few have used integrative measures of salmon performance, such as habitat-specific growth potential, to evaluate restoration. Our study took place in the Nisqually River delta, Washington, where recent dike removals restored tidal flow to 364 ha of marsh—the largest tidal marsh restoration project in the northwestern contiguous United States. We sampled fish assemblages, water temperatures, and juvenile Chinook Salmon diet composition and consumption rates in two restored and two reference tidal channels during a 3-year period after restoration; these data were used as inputs to a bioenergetics model to compare Chinook Salmon foraging performance and growth potential between the restored and reference channels. We found that foraging performance and growth potential of juvenile Chinook Salmon were similar between restored and reference tidal channels. However, Chinook Salmon densities were significantly lower in the restored channels than in the reference channels, and growth potential was more variable in the restored channels due to their more variable and warmer (2°C) water temperatures. These results indicate that some—but not all—ecosystem attributes that are important for juvenile Pacific salmon can recover rapidly after large-scale tidal marsh restoration.

  12. Dispersion mechanisms of a tidal river junction in the Sacramento–San Joaquin Delta, California

    SciTech Connect

    Gleichauf, Karla T.; Wolfram, Philip J.; Monsen, Nancy E.; Fringer, Oliver B.; Monismith, Stephen G.

    2014-12-17

    In branching channel networks, such as in the Sacramento–San Joaquin River Delta, junction flow dynamics contribute to dispersion of ecologically important entities such as fish, pollutants, nutrients, salt, sediment, and phytoplankton. Flow transport through a junction largely arises from velocity phasing in the form of divergent flow between junction channels for a portion of the tidal cycle. Field observations in the Georgiana Slough junction, which is composed of the North and South Mokelumne rivers, Georgiana Slough, and the Mokelumne River, show that flow phasing differences between these rivers arise from operational, riverine, and tidal forcing. A combination of Acoustic Doppler Current Profile (ADCP) boat transecting and moored ADCPs over a spring–neap tidal cycle (May to June 2012) monitored the variability of spatial and temporal velocity, respectively. Two complementary drifter studies enabled assessment of local transport through the junction to identify small-scale intrajunction dynamics. We supplemented field results with numerical simulations using the SUNTANS model to demonstrate the importance of phasing offsets for junction transport and dispersion. Different phasing of inflows to the junction resulted in scalar patchiness that is characteristic of MacVean and Stacey’s (2011) advective tidal trapping. Furthermore, we observed small-scale junction flow features including a recirculation zone and shear layer, which play an important role in intra-junction mixing over time scales shorter than the tidal cycle (i.e., super-tidal time scales). Thus, the study period spanned open- and closed-gate operations at the Delta Cross Channel. Synthesis of field observations and modeling efforts suggest that management operations related to the Delta Cross Channel can strongly affect transport in the Delta by modifying the relative contributions of tidal and riverine flows, thereby changing the junction flow phasing.

  13. Dispersion mechanisms of a tidal river junction in the Sacramento–San Joaquin Delta, California

    DOE PAGES

    Gleichauf, Karla T.; Wolfram, Philip J.; Monsen, Nancy E.; ...

    2014-12-17

    In branching channel networks, such as in the Sacramento–San Joaquin River Delta, junction flow dynamics contribute to dispersion of ecologically important entities such as fish, pollutants, nutrients, salt, sediment, and phytoplankton. Flow transport through a junction largely arises from velocity phasing in the form of divergent flow between junction channels for a portion of the tidal cycle. Field observations in the Georgiana Slough junction, which is composed of the North and South Mokelumne rivers, Georgiana Slough, and the Mokelumne River, show that flow phasing differences between these rivers arise from operational, riverine, and tidal forcing. A combination of Acoustic Dopplermore » Current Profile (ADCP) boat transecting and moored ADCPs over a spring–neap tidal cycle (May to June 2012) monitored the variability of spatial and temporal velocity, respectively. Two complementary drifter studies enabled assessment of local transport through the junction to identify small-scale intrajunction dynamics. We supplemented field results with numerical simulations using the SUNTANS model to demonstrate the importance of phasing offsets for junction transport and dispersion. Different phasing of inflows to the junction resulted in scalar patchiness that is characteristic of MacVean and Stacey’s (2011) advective tidal trapping. Furthermore, we observed small-scale junction flow features including a recirculation zone and shear layer, which play an important role in intra-junction mixing over time scales shorter than the tidal cycle (i.e., super-tidal time scales). Thus, the study period spanned open- and closed-gate operations at the Delta Cross Channel. Synthesis of field observations and modeling efforts suggest that management operations related to the Delta Cross Channel can strongly affect transport in the Delta by modifying the relative contributions of tidal and riverine flows, thereby changing the junction flow phasing.« less

  14. Tidal intrusion within a mega delta: An unstructured grid modelling approach

    NASA Astrophysics Data System (ADS)

    Bricheno, Lucy M.; Wolf, Judith; Islam, Saiful

    2016-12-01

    The finite volume community ocean model (FVCOM) has been applied to the Ganges-Brahmaputra-Meghna (GBM) delta in the northern part of the Bay of Bengal in order to simulate tidal hydrodynamics and freshwater flow in a complex river system. The delta region is data-poor in observations of both bathymetry and water level; making it a challenge for accurate hydrodynamic models be configured for and validated in this area. This is the first 3D baroclinic model covering the whole GBM delta from deep water beyond the shelf break to 250 km inland, the limit of tidal penetration. This paper examines what controls tidal penetration from the open coast into an intricate system of river channels. A modelling approach is used to improve understanding of the hydrodynamics of the GBM delta system. Tidal penetration is controlled by a combination of bathymetry, channel geometry, bottom friction, and river flow. The simulated tides must be validated before this delta model is used further to investigate baroclinic processes, river salinity and future change in this area. The performance of FVCOM tidal model configuration is evaluated at a range of sites in order to assess its ability to capture water levels which vary over both a tidal and seasonal cycle. FVCOM is seen to capture the leading tidal constituents well at coastal tide gauge stations, with small root-mean-squared errors of 10 cm on average. Inland, the model compares favourably with twice daily observed water levels at thirteen stations where it is able to capture both tidal and annual timescales in the estuarine system. When the river discharge is particularly strong, the tidal range can be reduced as the tide and river are in direct competition. The bathymetry is found to be the most influential control on water levels within the delta, though tidal penetration can be significantly affected by the model's bottom roughness, and the inclusion of large river discharge. We discuss the generic problem of implementing a

  15. River discharge controlling a tidal delta: the interplay between monsoon input and tidal reworking in SW Bangladesh

    NASA Astrophysics Data System (ADS)

    Hale, R. P.; Goodbred, S. L., Jr.; Bain, R. L.; Wilson, C.; Best, J.; Reed, M. J.

    2015-12-01

    The Ganges-Brahmaputra-Meghna River system (GBM) is among the world's largest in terms of both annual water and sediment discharge. The subaerial delta (110,000 km2) is home to ~160 million people, in addition to the ecologically and economically critical Sundarbans National Forest (SNF). Recent sediment budgets suggest that ~15% of the 1 x 109 t yr-1 sediment load carried by the GBM is subsequently advected along shore and inland via tidal activity, to the otherwise-abandoned SW portion of the delta. A unit-scale estimate based on observed offshore suspended sediment concentrations (SSC) >1.0 g L-1 suggests that sufficient sediment is available in the system to maintain the elevation of the subaerial delta plain, even under current relative sea-level-rise rates. Recent work measuring sedimentation within SNF corroborates this finding, and understanding these sediment delivery dynamics will be critical for protecting the future of nearby regions that are heavily populated, but drastically altered by human activities. Cross-channel hydrodynamic surveys were conducted to estimate what fraction of the water (and sediment) is diverted from the major tidal channels toward the SNF interior. Measurements including profiles of velocity and SSC were collected on spring and neap tides during the dry and monsoon seasons, along transects bracketing major conduit channels into the SNF. During the dry season, we observe water flux at the southern end of the study area to be in approximate equilibrium regardless of tidal range, with SSC <0.3 g L-1 during neap tides, and <1.0 g L-1 during spring tides. North of the SNF conduit channels, we observe equilibrium water discharge and similarly low SSC during neap tides, but a modest ebb dominance and surface SSC >1.0 g L-1 during spring tides. This suggests the possibility of additional inputs of water and sediment from an adjacent tidal channel, as well as a potential source for the deposition observed on the Sundarbans platform

  16. Near-bed turbulence and sediment flux measurements in tidal channels

    USGS Publications Warehouse

    Wright, S.A.; Whealdon-Haught, D.R.

    2012-01-01

    Understanding the hydrodynamics and sediment transport dynamics in tidal channels is important for studies of estuary geomorphology, sediment supply to tidal wetlands, aquatic ecology and fish habitat, and dredging and navigation. Hydrodynamic and sediment transport data are essential for calibration and testing of numerical models that may be used to address management questions related to these topics. Herein we report preliminary analyses of near-bed turbulence and sediment flux measurements in the Sacramento-San Joaquin Delta, a large network of tidal channels and wetlands located at the confluence of the Sacramento and San Joaquin Rivers, California, USA (Figure 1). Measurements were made in 6 channels spanning a wide range of size and tidal conditions, from small channels that are primarily fluvial to large channels that are tidally dominated. The results of these measurements are summarized herein and the hydrodynamic and sediment transport characteristics of the channels are compared across this range of size and conditions.

  17. Tidal dynamics in channels: 2. Complex channel networks

    NASA Astrophysics Data System (ADS)

    Hill, A. E.; Souza, A. J.

    2006-11-01

    Intricate networks of tidal channels such as those found in fjordic, barrier island, and branching estuarine systems are often at risk from contaminant inputs and can be important as spawning grounds or migration pathways for marine organisms. These intricate systems are rarely spatially resolved in regional-scale numerical tidal models, and setting up a specific detailed numerical model for the purpose of rapidly assessing the likely tidal behavior of such geometrically complex systems carries a high overhead. Here we describe a straightforward algorithm (implemented in MATLAB) which permits rapid assessment of the linear tidal dynamics in an arbitrarily complex network of tidal channels. The method needs only a minimum of input data, namely, (1) the forcing tidal elevation amplitude and phase at the entrances of those channels directly exposed to the open sea and (2) the length, width, and depth of each channel. The performance of the method is tested against results from the finite element regional-scale numerical model of Foreman et al. (1993) in the fjordic region of western Canada.

  18. Residence Times of Juvenile Salmon and Steelhead in Off-Channel Tidal Freshwater Habitats, Columbia River, USA

    SciTech Connect

    Johnson, Gary E.; Ploskey, Gene R.; Sather, Nichole K.; Teel, D. J.

    2015-05-01

    We estimated seasonal residence times of acoustic-tagged juvenile salmonids in off-channel, tidal freshwater habitats of the Columbia River near the Sandy River delta (rkm 198; 2007, 2008, 2010, and 2011) and Cottonwood Island (rkm 112; 2012).

  19. Suspended sediment transport trough a large fluvial-tidal channel network

    USGS Publications Warehouse

    Wright, Scott A.; Morgan-King, Tara L.

    2015-01-01

    The confluence of the Sacramento and San Joaquin Rivers, CA, forms a large network of interconnected channels, referred to as the Sacramento-San Joaquin Delta (the Delta). The Delta comprises the transition zone from the fluvial influences of the upstream rivers and tidal influences of San Francisco Bay downstream. Formerly an extensive tidal marsh, the hydrodynamics and geomorphology of Delta have been substantially modified by humans to support agriculture, navigation, and water supply. These modifications, including construction of new channels, diking and draining of tidal wetlands, dredging of navigation channels, and the operation of large pumping facilities for distribution of freshwater from the Delta to other parts of the state, have had a dramatic impact on the physical and ecological processes within the Delta. To better understand the current physical processes, and their linkages to ecological processes, the USGS maintains an extensive network of flow, sediment, and water quality gages in the Delta. Flow gaging is accomplished through use of the index-velocity method, and sediment monitoring uses turbidity as a surrogate for suspended-sediment concentration. Herein, we present analyses of the transport and dispersal of suspended sediment through the complex network of channels in the Delta. The primary source of sediment to the Delta is the Sacramento River, which delivers pulses of sediment primarily during winter and spring runoff events. Upon reaching the Delta, the sediment pulses move through the fluvial-tidal transition while also encountering numerous channel junctions as the Sacramento River branches into several distributary channels. The monitoring network allows us to track these pulses through the network and document the dominant transport pathways for suspended sediment. Further, the flow gaging allows for an assessment of the relative effects of advection (the fluvial signal) and dispersion (from the tides) on the sediment pulses as they

  20. Long-term change in tidal dynamics and its cause in the Pearl River Delta, China

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Ruan, Xiaohong; Zheng, Jinhai; Zhu, Yuliang; Wu, Hongxu

    2010-08-01

    This paper focuses on identifying changes in the tidal range and the duration of the flood tide in the Pearl River Delta region, China. Mann-Kendall test and regression methods are employed to verify the existence of trends in the annual tidal range and duration series (from the 1950s to 2005) at 17 stations in the 3 major tributaries of the delta. The research results indicate that generally there is an increasing trend in the tidal range and flood tide duration at most of the stations in the channel network. Moreover, the more upstream the location of the station, the more obvious the change in trend is, and these increasing trends are all significant at the stations in the upper part of the delta. Specifically, the tidal range at Shilong station in the East River has increased abruptly since the middle of the 1980s such that the mean level of post-1990 data is approximately three times that for pre-1985. Most stations near the mouth of the estuary show significant downward trends in the tidal range and flood tide duration. Results of the intersection point of the Mann-Kendall test curves for these Pearl River Delta stations appear mostly in 1980s-1990s, indicating that a noticeable change point occurs during this period. Human activities in the Pearl River Delta reached their peak during the 1980s. Among these, large-scale and long-term sand excavation modified the hydrodynamic regime dramatically in a way that increased the water depth and lowered the level of the riverbed, leading to an increased tidal prism and upstream movement of the tidal limit. Land reclamation is also likely to have had a relatively large effect on the tidal range and flood tide duration at stations near to the estuary mouth. Changes in other factors, such as freshwater flow and sea-level rise, seem to be of relatively minor importance. It is noteworthy that in a dry season the tidal dynamics are greatly enhanced and has resulted in strong saltwater intrusion into the estuary in recent

  1. Abandoned Channel Fill Sequences in Tidal Estuaries

    NASA Astrophysics Data System (ADS)

    Gray, A. B.; Pasternack, G. B.; Goni, M. A.; Watson, E. B.

    2014-12-01

    This study proposes a modification of the current model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. Evidence supporting this concept came from a study of two consecutive channel abandonment sequences in Ropers Slough of the lower Eel River Estuary in northern California. Aerial photographs showed that Ropers Slough was abandoned around 1943, reoccupied after the 1964 flood, and abandoned again in 1974 with fill continuing to the present. Planform geomorphic characteristics derived from these images were used in conjunction with sub-cm resolution stratigraphic analyses to describe the depositional environment processes and their resultant sedimentary deposits. Results showed that both abandonment sequences recorded quasi-annual scale fluvial/tidal deposition couplets. In both cases tidal deposits contained very little sand, and were higher in organic and inorganic carbon content than the sandier fluvial through-flow deposits. However, the two abandonment fills differed significantly in terms of the temporal progression of channel narrowing and fluvial sediment deposition characteristics. The first abandonment sequence led to a more rapid narrowing of Ropers Slough and produced deposits with a positive relationship between grain size/deposit thickness and discharge. The second abandonment resulted in a much slower narrowing of Ropers Slough and generally thinner fluvial deposits with no clear relationship between grain size/deposit thickness and discharge. The δ13C values and organic nitrogen to organic carbon ratios of deposits from the first phase overlapped with Eel River suspended sediment characteristics found for low flows (1-5 times mean discharge), while those of the second phase were consistent suspended sediment from higher flows (7-10 times mean discharge). The abandoned channel fill sequences appeared to differ due to the topographic steering of bed sediment transport and

  2. Maintenance of large deltas through channelization

    NASA Astrophysics Data System (ADS)

    Giosan, L.; Constatinescu, S.; Filip, F.

    2013-12-01

    A new paradigm for delta restoration is currently taking shape using primarily Mississippi delta examples. Here we propose an alternative for delta maintenance primarily envisioned for wave-influenced deltas based on Danube delta experiences. Over the last half century, while the total sediment load of the Danube dramatically decreased due to dam construction on tributaries and its mainstem, a grand experiment was inadvertently run in the Danube delta: the construction of a dense network of canals, which almost tripled the water discharge toward the interior of the delta plain. We use core-based and chart-based sedimentation rates and patterns to explore the delta transition from the natural to an anthropogenic regime, to understand the effects of far-field damming and near-field channelization, and to construct a conceptual model for delta development as a function sediment partition between the delta plain and the delta coastal fringe. We show that sediment fluxes increased to the delta plain due to channelization, counteracting sea level rise. In turn, the delta coastal fringe was most impacted by the Danube's sediment load collapse. Furthermore, we show that morphodynamic feedbacks at the river mouth are crucial in trapping sediment near the coast and constructing wave-dominated deltas or lobes or delaying their destruction. As a general conclusion, we suggest that increased channelization that mimics and enhances natural processes may provide a simple solution for keeping delta plains above sea level and that abandonment of wave-dominated lobes may be the most long term efficient solution for protecting the internal fluvial regions of deltas and provide new coastal growth downcoast.

  3. Morphodynamics and Stratigraphy of Essex River EBB-Tidal Delta: Massachusetts

    DTIC Science & Technology

    1991-08-01

    AD-A241 424 TECHNICAL REPORT CERC-91 -11 --- "MORPHODYNAMICS AND STRATIGRAPHY OF ESSEX RIVER EBB-TIDAL DELTA: MASSACHUSETTS by J. Bailey Smith...COVERED I August 1991 Final report 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Morphodynamics and Stratigraphy of Essex River Ebb-Tidal Delta...12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited 13. ABSTRACT (Maximum 200 words) The Essex River Inlet ebb-tidal delta

  4. Sediment budgets, transport, and depositional trends in a large tidal delta

    USGS Publications Warehouse

    Morgan, Tara; Wright, Scott A.

    2016-01-01

    The Sacramento-San Joaquin Delta is the largest delta on the west coast of the United States. It is formed where the confluence of California’s two largest rivers (the Sacramento and San Joaquin) meet the ocean tides and has a significant physical gradient from fluvial to tidal. It is a semidiurnal system (two high and two low tides per day). Today, the Delta is one of the most manipulated in the United States. Once composed of many shallow, meandering and braided dendritic channels and dead-end sloughs and wetlands, it is now a network of leveed canals moving clear water around subsided islands. It historically has supported a biologically diverse tidal wetland complex, of which only 3% remains today (Whipple et al., 2012). It has also witnessed a collapse in the native fish populations. The Delta provides critical habitat for native species, however the hydrology and water quality are complicated by manipulations and diversions to satisfy multiple statewide objectives. Today water managers face co-equal goals of water supply to Californians and maintenance of ecosystem health and function. The Delta is a hub for both a multi-hundred-million dollar agricultural industry and a massive north-to-south water delivery system, supplying the primary source of freshwater to Central Valley farmers and drinking water for two-thirds of California’s population. Large pump facilities support the water demand and draw water from the Delta, further altering circulation patterns and redirecting the net flow toward the export facilities (Monsen et al., 2007). Fluvial sedimentation, along with organic accumulation, creates and sustains the Delta landscape. Hydraulic mining for gold in the watershed during the late 1800s delivered an especially large sediment pulse to the Delta. More recently, from 1955 to the present, a significant sediment decline has been observed that is thought to have been caused mostly by the construction of water storage reservoirs that trap the upstream

  5. Hydrodynamics and Morphodynamics of Shallow Tidal Channels and Intertidal Flats

    DTIC Science & Technology

    1993-02-01

    major controls on net sediment transport in shallow tidal systems : temporal and spatial asymmetries in maximum bottom shear stress (r). In the... asymmetries in tidally-induced bottom shear stress to patterns of net sediment transport along channelized tidal embayments (e.g., Wright et al. 1975; Allen et...motivated by long- standing models of morphologic equilibrium and net sediment transport in shallow tidal systems based on the spatial distribution of

  6. Riders on the storm: selective tidal movements facilitate the spawning migration of threatened delta smelt in the San Francisco Estuary

    USGS Publications Warehouse

    Bennett, W.A.; Burau, Jon R.

    2015-01-01

    Migration strategies in estuarine fishes typically include behavioral adaptations for reducing energetic costs and mortality during travel to optimize reproductive success. The influence of tidal currents and water turbidity on individual movement behavior were investigated during the spawning migration of the threatened delta smelt, Hypomesus transpacificus, in the northern San Francisco Estuary, California, USA. Water current velocities and turbidity levels were measured concurrently with delta smelt occurrence at sites in the lower Sacramento River and San Joaquin River as turbidity increased due to first-flush winter rainstorms in January and December 2010. The presence/absence of fish at the shoal-channel interface and near the shoreline was quantified hourly over complete tidal cycles. Delta smelt were caught consistently at the shoal-channel interface during flood tides and near the shoreline during ebb tides in the turbid Sacramento River, but were rare in the clearer San Joaquin River. The apparent selective tidal movements by delta smelt would facilitate either maintaining position or moving upriver on flood tides, and minimizing advection down-estuary on ebb tides. These movements also may reflect responses to lateral gradients in water turbidity created by temporal lags in tidal velocities between the near-shore and mid-channel habitats. This migration strategy can minimize the energy spent swimming against strong river and tidal currents, as well as predation risks by remaining in turbid water. Selection pressure on individuals to remain in turbid water may underlie population-level observations suggesting that turbidity is a key habitat feature and cue initiating the delta smelt spawning migration.

  7. Natural and anthropogenic change in the morphology and connectivity of tidal channels of southwest Bangladesh

    NASA Astrophysics Data System (ADS)

    Wilson, C.; Goodbred, S. L., Jr.; Wallace Auerbach, L.; Ahmed, K. R.; Small, C.; Sams, S. E.

    2014-12-01

    Over the last century, land use changes in the Ganges-Brahmaputra tidal delta have transformed >5000 km2 of intertidal mangrove forest to densely inhabited, agricultural islands that have been embanked to protect against tides and storm surges (i.e., polders). More recently, the conversion of rice paddies to profitable shrimp aquaculture has become increasingly widespread. Recent field studies documented that poldering in southwest Bangladesh has resulted in an elevation deficit relative to that of the natural mangrove forests and mean high water (MHW). The offset is a function of lost sedimentation, enhanced compaction, and an effective rise in MHW from tidal amplification. The morphologic adjustment of the tidal channel network to these perturbations, however, has gone largely undocumented. One effect has been the shoaling of many channels due to decreases in fluvial discharge and tidal prism. We document a previously unrecognized anthropogenic component: the widespread closure of large conduit tidal channels for land reclamation and shrimp farming. GIS analysis of historical Landsat and Google Earth imagery within six 1000 km2 study areas reveals that the tidal network in the natural Sundarbans mangrove forest has remained relatively constant since the 1970s, while significant changes are observed in human-modified areas. Construction of the original embankments removed >1000 km of primary tidal creeks, and >80 km2 of land has been reclaimed outside of polders through the closure of formerly active tidal channels (decrease in mean channel width from 256±91 m to 25±10 m). Tidal restriction by large sluice gates is prevalent, favoring local channel siltation. Furthermore, severing the intertidal platform and large conduit channels from the tidal network has had serious repercussions, such as increased lateral migration and straightening of the remaining channels. Where banklines have eroded, the adjacent embankments appear to be more vulnerable to failure, as

  8. Hydrodynamics and sediment suspension in shallow tidal channels intersecting a tidal flat

    NASA Astrophysics Data System (ADS)

    Pieterse, Aline; Puleo, Jack A.; McKenna, Thomas E.

    2016-05-01

    A field study was conducted on a tidal flat intersected by small tidal channels (depth <0.1 m, width <2 m) within a tidal marsh. Data were collected in the channels, and on the adjacent tidal flat that encompasses approximately 1600 m2 in planform area. Hydrodynamic processes and sediment suspension between the channels and adjacent flat were compared. Shear stress and turbulent kinetic energy were computed from high frequency velocity measurements. Maximum water depth at the field site varied from 0.11 m during the lowest neap high tide to 0.58 m during a storm event. In the channel intersecting the tidal flat, the shear stress, turbulence and along-channel velocity were ebb dominant; e.g. 0.33 m/s peak velocity for ebb compared to 0.19 m/s peak velocity for flood. Distinct pulses in velocity occurred when the water level was near the tidal flat level. The velocity pulse during flood tide occurred at a higher water level than during ebb tide. No corresponding velocity pulse on the tidal flat was observed. Sediment concentrations peaked at the beginning and end of each tidal cycle, and often had a secondary peak close to high tide, assumed to be related to sediment advection. The influence of wind waves on bed shear stress and sediment suspension was negligible. Water levels were elevated during a storm event such that the tidal flat remained inundated for 4 tidal cycles. The water did not drain from the tidal flat into the channels during the storm, and no velocity pulses occurred. Along-channel velocities, turbulent kinetic energy, and shear stresses were therefore smaller in the channels during storm conditions than during non-storm conditions.

  9. Ambient Noise in an Urbanized Tidal Channel

    NASA Astrophysics Data System (ADS)

    Bassett, Christopher

    levels that shows good agreement with 85% of the temporal data. Bed stresses associated with currents can produce propagating ambient noise by mobilizing sediments. The strength of the tidal currents in northern Admiralty Inlet produces bed stresses in excess of 20 Pa. Significant increases in noise levels at frequencies from 4-30 kHz, with more modest increases noted from 1-4 kHz, are attributed to mobilized sediments. Sediment-generated noise during strong currents masks background noise from other sources, including vessel traffic. Inversions of the acoustic spectra for equivalent grain sizes are consistent with qualitative observations of the seabed composition. Bed stress calculations using log layer, Reynolds stress, and inertial dissipation techniques generally agree well and are used to estimate the shear stresses at which noise levels increase for different grain sizes. Ambient noise levels in one-third octave bands with center frequencies from 1 kHz to 25 kHz are dominated by sediment-generated noise and can be accurately predicted using the near-bed current velocity above a critical threshold. When turbulence is advected over a pressure sensitive transducer, the turbulent pressure fluctuations can be measured as noise, though these pressure fluctuations are not propagating sound and should not be interpreted as ambient noise. Based on measurements in both Admiralty Inlet, Puget Sound and the Chacao Channel, Chile, two models are developed for flow-noise. The first model combined measurements of mean current velocities and turbulence and agrees well with data from both sites. The second model uses scaling arguments to model the flow-noise based solely on the mean current velocity. This model agrees well with the data from the Chacao Channel but performs poorly in Admiralty Inlet, a difference attributed to differences turbulence production mechanisms. At both sites, the spectral slope of flow noise follows a f-3.2 dependence, suggesting partial cancellation of

  10. Linking channel hydrology with riparian wetland accretion in tidal rivers

    USGS Publications Warehouse

    Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.

    2014-01-01

    The hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood, yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the non-tidal through oligohaline portion of two coastal plain rivers in Maryland, U.S.A., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a one year period using artificial marker horizons, channel hydrology was measured over a one month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the non-tidal sites (mean and standard deviation = 8 ± 8 mm yr-1), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr-1), low at the midstream TFFW (12 ± 9 mm yr-1), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr-1). Channel maximum flood and ebb velocity was 2-fold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: the oligohaline zone's SSC was more than double the tidal freshwater zone's, and was greater than historical SSC at the non-tidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. Overall sediment accretion was higher in the embayed river likely due to a single storm discharge and associated sedimentation.

  11. Tidal Energy Resource Assessment in Chacao Channel, Chile

    NASA Astrophysics Data System (ADS)

    Guerra, M.; Suarez, L.; Cienfuegos, R.; Thomson, J. M.

    2014-12-01

    The Chacao Channel, located in Los Lagos region in Chile (41º S; 73º W), is a highly energetic tidal channel, with a complex hydrodynamics resulting from the propagation of tidal waves through a narrow channel. The channel flow exhibits bi-directional tidal currents up to 4 to 5 m/s along with a high tidal range up to 6 m in its east end (Aiken, 2008: Cáceres et al., 2003). The channel has previously been identified as one of the most attractive sites in Chile for tidal energy extraction (Garrad Hassan and Partners, 2009); however this statement is based on global model predictions over coarse bathymetric information. In this investigation, the first hydrodynamic characterization of the Chacao channel is carried out in order to assess the hydrokinetic power available and to select the most interesting spots where the first tidal energy extraction devices might be installed in Chile. The Chacao channel hydrodynamic characterization and resource assessment is carried out in two stages: field measurements and numerical hydrodynamic modeling. The first stage involves a 10 m resolution multi-beam bathymetry of the channel, sea-level measurements using 6 tidal gauges distributed over the channel berms, tidal current measurements with 6 ADCPs distributed along the channel, and detailed measurements of turbulence in a specific spot in the channel using the Tidal Turbulence Mooring (TTM) developed by Thomson et al. (2013). In a second stage, numerical hydrodynamic modeling using FVCOM (Chen et al., 2003) was prepared for the entire Chacao channel region, using the field data collected in the first stage for calibration and validation of the model. The obtained results allow us to define suitable sites for marine energy extraction, finding large areas with 30 to 60 m depths where horizontal currents are above 1.5 m/s during 60% of the time of a 28 days tidal cycle, however the high levels of turbulence detected by the TTM indicate the need for more detailed studies on the

  12. Vegetation causes channel erosion in a tidal landscape

    NASA Astrophysics Data System (ADS)

    Temmerman, S.; Bouma, T. J.; van de Koppel, J.; van der Wal, D.; de Vries, M. B.; Herman, P. M. J.

    2007-07-01

    Vegetation is traditionally regarded to reduce the erosion of channels in both fluvial and tidal landscapes. We present a coupled hydrodynamic, morphodynamic, and plant growth model that simulates plant colonization and channel formation on an initially bare, flat substrate, and apply this model to a tidal landscape. The simulated landscape evolution is compared with aerial photos. Our results show that reduction of erosion by vegetation is only the local, on-site effect operating within static vegetation. Dynamic vegetation patches, which can expand or shrink, have a contrasting larger scale, off-site effect: they obstruct the flow, leading to flow concentration and channel erosion between laterally expanding vegetation patches. In contrast with traditional insights, our findings imply that in tidal landscapes, which are colonized by denser vegetation, channels are formed with a higher channel drainage density. Hence this study demonstrates that feedbacks between vegetation, flow, and landform have an important control on landscape evolution.

  13. Shear Stress, Turbulence Production and Dissipation in Small Tidal Channels Intersecting a Tidal Flat

    NASA Astrophysics Data System (ADS)

    Pieterse, A.; Puleo, J. A.; McKenna, T. E.

    2014-12-01

    A 16-day field experiment was conducted in March and April 2013 in a tidal wetland in Kent County, Delaware. The study area was a tidal flat fed by a second-order channel that flows into the Brockonbridge Gut, a small tributary of Delaware Bay. The goal of the field study was to investigate spatio-temporal variability in the hydrodynamics of the tidal flat and the small channels that intersect it, over the period of one spring-neap tidal cycle. The experiment combined remotely-sensed imagery with high-frequency in-situ measurements. A tower with imagers (RGB, NIR, TIR) was deployed to quantify the spatial variations of inundation of the channels, flat and marsh. In-situ sensors that measure flow velocity, sediment concentration and water depth were deployed at six locations on the tidal flat and in the channels. At three locations, a Nortek Vectrino II - profiling velocimeter was deployed that measures a 30 mm velocity profile at 1 mm vertical increments at 100 Hz. These velocity profiles are used to compute turbulent kinetic energy, turbulence dissipation and stress profiles close to the bed. Results show that peak velocities in the channels occur at the beginning and end of ebbing tide, when the water level is below the tidal flat level. At these instances, peaks in turbulence and bed stress also occur. The flow velocity and turbulence peaks are smaller when the water level does not fall below the tidal flat level. On the tidal flat, the flow velocities and turbulence are generally small compared to the intersecting tidal channel. Maximum flow velocities in the channels are around 0.4 m/s, while on the flat maximum velocities are under 0.1 m/s. A comparison is made between turbulence production and dissipation in both the channel and on the tidal flat to determine if advection and diffusion are important in this environment. In addition, the hydrodynamics at several locations in the channel are compared to investigate changes throughout the study area.

  14. Wind-driven modifications to the residual circulation in an ebb-tidal delta: Arcachon Lagoon, Southwestern France

    NASA Astrophysics Data System (ADS)

    Salles, Paulo; Valle-Levinson, Arnoldo; Sottolichio, Aldo; Senechal, Nadia

    2015-02-01

    A combination of observations and analytical solutions was used to determine the modifications caused by wind forcing on the residual or nontidal circulation in an ebb-tidal delta. Observations were obtained in the lower Arcachon Lagoon, southwestern France. The basic nontidal circulation was established with acoustic Doppler current profilers (ADCPs) that were (i) moored in the delta's two deepest channels, and (ii) towed along a cross-lagoon transect. The bathymetry of the lower lagoon, or ebb-tidal delta, featured two channels: North Pass (>9 m) and South Pass (>20 m). The basic nontidal circulation consisted of mostly inflow with weak surface outflow in the South Pass, and laterally sheared bidirectional flow, dominated by outflow, in the North Pass. Analytical solutions and comparison of observed dynamical terms suggested that, in addition to the conventionally accepted influence of tidal nonlinearities, density gradients contributed to the basic nontidal circulation in the lagoon. Observations also indicated that wind forcing altered the basic circulation by driving simultaneous upwind flows in both passes. This response was supported by an analytical solution to wind-driven flows over the bathymetry of the transect sampled. The response to seaward winds was to enhance inflow in South Pass and reduce outflow in North Pass. Landward winds caused diminished inflow in South Pass and increased outflow in North Pass.

  15. Salt marsh vegetation promotes efficient tidal channel networks.

    PubMed

    Kearney, William S; Fagherazzi, Sergio

    2016-07-19

    Tidal channel networks mediate the exchange of water, nutrients and sediment between an estuary and marshes. Biology feeds back into channel morphodynamics through the influence of vegetation on both flow and the cohesive strength of channel banks. Determining how vegetation affects channel networks is essential in understanding the biological functioning of intertidal ecosystems and their ecosystem services. However, the processes that control the formation of an efficient tidal channel network remain unclear. Here we compare the channel networks of vegetated salt marshes in Massachusetts and the Venice Lagoon to unvegetated systems in the arid environments of the Gulf of California and Yemen. We find that the unvegetated systems are dissected by less efficient channel networks than the vegetated salt marshes. These differences in network geometry reflect differences in the branching and meandering of the channels in the network, characteristics that are related to the density of vegetation on the marsh.

  16. Salt marsh vegetation promotes efficient tidal channel networks

    PubMed Central

    Kearney, William S.; Fagherazzi, Sergio

    2016-01-01

    Tidal channel networks mediate the exchange of water, nutrients and sediment between an estuary and marshes. Biology feeds back into channel morphodynamics through the influence of vegetation on both flow and the cohesive strength of channel banks. Determining how vegetation affects channel networks is essential in understanding the biological functioning of intertidal ecosystems and their ecosystem services. However, the processes that control the formation of an efficient tidal channel network remain unclear. Here we compare the channel networks of vegetated salt marshes in Massachusetts and the Venice Lagoon to unvegetated systems in the arid environments of the Gulf of California and Yemen. We find that the unvegetated systems are dissected by less efficient channel networks than the vegetated salt marshes. These differences in network geometry reflect differences in the branching and meandering of the channels in the network, characteristics that are related to the density of vegetation on the marsh. PMID:27430165

  17. Airborne radar imaging of subaqueous channel evolution in Wax Lake Delta, Louisiana, USA

    NASA Astrophysics Data System (ADS)

    Shaw, John B.; Ayoub, Francois; Jones, Cathleen E.; Lamb, Michael P.; Holt, Benjamin; Wagner, R. Wayne; Coffey, Thomas S.; Chadwick, J. Austin; Mohrig, David

    2016-05-01

    Shallow coastal regions are among the fastest evolving landscapes but are notoriously difficult to measure with high spatiotemporal resolution. Using Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data, we demonstrate that high signal-to-noise L band synthetic aperture radar (SAR) can reveal subaqueous channel networks at the distal ends of river deltas. Using 27 UAVSAR images collected between 2009 and 2015 from the Wax Lake Delta in coastal Louisiana, USA, we show that under normal tidal conditions, planform geometry of the distributary channel network is frequently resolved in the UAVSAR images, including ~700 m of seaward network extension over 5 years for one channel. UAVSAR also reveals regions of subaerial and subaqueous vegetation, streaklines of biogenic surfactants, and what appear to be small distributary channels aliased by the survey grid, all illustrating the value of fine resolution, low noise, L band SAR for mapping the nearshore subaqueous delta channel network.

  18. Recent scientific advances and their implications for sand management near San Francisco, California: the influences of the ebb tidal delta

    USGS Publications Warehouse

    Hanes, Daniel M.; Barnard, Patrick L.; Dallas, Kate; Elias, Edwin; Erikson, Li H.; Eshleman, Jodi; Hansen, Jeff; Hsu, Tian Jian; Shi, Fengyan

    2011-01-01

    Recent research in the San Francisco, California, U.S.A., coastal region has identified the importance of the ebb tidal delta to coastal processes. A process-based numerical model is found to qualitatively reproduce the equilibrium size and shape of the delta. The ebb tidal delta itself has been contracting over the past century, and the numerical model is applied to investigate the sensitivity of the delta to changes in forcing conditions. The large ebb tidal delta has a strong influence upon regional coastal processes. The prominent bathymetry of the ebb tidal delta protects some of the coast from extreme storm waves, but the delta also focuses wave energy toward the central and southern portions of Ocean Beach. Wave focusing likely contributes to a chronic erosion problem at the southern end of Ocean Beach. The ebb tidal delta in combination with non-linear waves provides a potential cross-shore sediment transport pathway that probably supplies sediment to Ocean Beach.

  19. Tidal truncation and barotropic convergence in a channel network tidally driven from opposing entrances

    USGS Publications Warehouse

    Warner, J.C.; Schoellhamer, D.; Schladow, G.

    2003-01-01

    Residual circulation patterns in a channel network that is tidally driven from entrances on opposite sides are controlled by the temporal phasing and spatial asymmetry of the two forcing tides. The Napa/Sonoma Marsh Complex in San Francisco Bay, CA, is such a system. A sill on the west entrance to the system prevents a complete tidal range at spring tides that results in tidal truncation of water levels. Tidal truncation does not occur on the east side but asymmetries develop due to friction and off-channel wetland storage. The east and west asymmetric tides meet in the middle to produce a barotropic convergence zone that controls the transport of water and sediment. During spring tides, tidally averaged water-surface elevations are higher on the truncated west side. This creates tidally averaged fluxes of water and sediment to the east. During neap tides, the water levels are not truncated and the propagation speed of the tides controls residual circulation, creating a tidally averaged flux in the opposite direction. ?? 2003 Elsevier Science B.V. All rights reserved.

  20. Linking channel hydrology with riparian wetland accretion in tidal rivers

    NASA Astrophysics Data System (ADS)

    Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.

    2014-01-01

    hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the nontidal through oligohaline portion of two coastal plain rivers in Maryland, U.S., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a 1 year period using artificial marker horizons, channel hydrology was measured over a 1 month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the nontidal sites (mean and standard deviation = 8 ± 8 mm yr-1), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr-1), low at the midstream TFFW (12 ± 9 mm yr-1), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr-1). Channel maximum flood and ebb velocity was twofold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: The oligohaline zone's SSC was more than double the tidal freshwater zone's and was greater than historical SSC at the nontidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. High sediment accretion at the upstream TFFW was likely due to high river discharge following a hurricane.

  1. Salt marsh vegetation promotes efficient tidal channel networks

    NASA Astrophysics Data System (ADS)

    Kearney, W. S.; Fagherazzi, S.

    2014-12-01

    Tidal channel networks mediate the exchange of water, nutrients and sediment between an estuary and marshes and mudflats. Biology feeds back into channel morphodynamics through vegetation's influence on the cohesive strength of channel banks. Understanding the morphology of a tidal channel network is thus essential to understanding both the biological functioning of intertidal ecosystems and the topographic signature of life. A critical measure of the morphology of a channel network is the unchanneled path length, which is characteristic of the efficiency with which a network dissects the marsh platform. However, the processes which control the formation and maintenance of an efficient tidal channel network remain unclear. Here we show that an unvegetated marsh platform (Estero La Ramada, Baja California, Mexico) is dissected by a less efficient channel network than a vegetated one (Barnstable, Massachusetts, United States). The difference in geometric efficiency reflects a difference in the branching and meandering characteristics of the network, characteristics controlled by the density of vegetation on the channel banks. Our results suggest a feedback between network geometry and vegetation, mediated by fluxes of nutrients and salinity through the channel network, maintains the observed network geometries. An efficient network can support a denser vegetation community which stabilizes channel banks, leading to an efficient meandering geometry.

  2. On the influence of vegetation on tidal channel network formation in sediment accretion contexts: preliminary results of an eco-geomorphic model

    NASA Astrophysics Data System (ADS)

    Belliard, Jean-Philippe; Toffolon, Marco

    2013-04-01

    Tidal channels represent a major morphological component in tidal wetlands as they transport tidal waters, suspended sediments and nutrients in and out of the marsh platform (e.g., Fagherazzi et al., 2012). Recent studies have helped to get further insights into tidal channel morphodynamics, yet a profound debate still prevails in the scientific community as regards the chief processes governing their formation and further elaboration. The dominant paradigm for tidal channel formation via headcutting of first order channels has been challenged by observations which suggest alternative mechanisms to explain tidal channel origination. Indeed, in view of the abundance and the high diversity of morphology tidal channels depict in worldwide estuarine landscapes, it comes to mind that other models different from the well-documented erosive-based model may be responsible for tidal channel ontogeny and further development. Therefore, models based on the presence of hummocks due to vegetation colonization, or via wind/wave erosion coupled with elongation of salt pans in the marsh surface, or linked to groundwater drainage mediated by crab burrowing activity have been successively proposed to explain origins of tidal channels. Moreover, based on observations of depositional channel network development in prograding deltas, Hood (2006) has suggested a model for tidal channel formation and evolution resulting from depositional processes of delta progradation, leading to the conversion of distributaries into blind tidal channels and creation of meanders occurring concurrently. Depositional channel development was also noticed in other marshes located in different estuarine landscapes. In fact, under conditions of high sediment supply and marsh progradation, depositional tidal channel development may prevail instead of erosional channel development. This diversity in tidal channel formation processes is not reflected in conceptual models of tidal channel evolution as they mostly

  3. Documenting Fine-Sediment Import and Export for Two Contrasting Mesotidal Flats Sediment Flux through the Mekong Tidal River, Delta and Mangrove Shoreline Instrumentation to Support Investigation of Large Tropical Deltas

    DTIC Science & Technology

    2013-09-30

    Contrasting Mesotidal Flats Sediment Flux through the Mekong Tidal River, Delta and Mangrove Shoreline Instrumentation to Support Investigation of Large...scales), and thereby validate localized measurements and numerical models of sediment transport for diverse tidal systems (tidal flats, mangrove forests...Sediment Flux through the Mekong Tidal River, Delta and Mangrove Shoreline Instrumentation to Support Investigation of Large Tropical Deltas 5a. CONTRACT

  4. Tidal regime deformation by sea level rise along the coast of the Mekong Delta

    NASA Astrophysics Data System (ADS)

    Nhan, Nguyen Huu

    2016-12-01

    The future of river deltas is believed to depend mainly on sea level rise (SLR) and on the processes controlling the adaptation of the substrate to human impacts. The deltas are increasingly deprived of riverine sediment by river diversion, dams, dykes and the destruction of wetlands, and they are often sinking due to mining for groundwater, gas and petroleum. The relative sea level rise is causing severe negative impacts in many river deltas worldwide. With continuously rising sea levels, this impact is expected to increase over time. The increased risk of delta flooding caused by tidal deformation associated with SLR in shallow coastal waters has received less attention. In this study, we demonstrate this effect for the case of the Mekong Delta where this study suggests that the maximum tidal water level and the tidal amplitude are increasing while the tidal phase at the coast is decreasing. In addition, the maximum water levels is rising faster than SLR because the tides themselves are modified by SLR. This effect is particularly pronounced for semi-diurnal tides and less so for diurnal tides. Similar effects may prevail for river deltas with extensive shallow coastal waters elsewhere in the world and deserve further investigation.

  5. Sediment Trapping Pathways and Mechanisms through the Mekong Tidal River and Subaqueous Delta

    DTIC Science & Technology

    2013-09-30

    strive to understand how the delicate balance of ebb and flood sediment fluxes is maintained to create tidal flat and mangrove complexes, and...subaqueous delta on the inner continental shelf, and sediment sinks within vegetated/ mangrove shoreline complexes. Our overall hypothesis is that sediment... Mangrove /Vegetated Intertidal Areas. Along the main stem tidal river and coastal banks may be shorelines lined with vegetation ( mangroves at the

  6. Scaling of equilibrium bed profiles in short tidal channels

    NASA Astrophysics Data System (ADS)

    Toffolon, M.; Lanzoni, S.

    2009-04-01

    We study the equilibrium bottom profile in short tidal channels using a simplified erosion/deposition relationship. The proposed approach, developed within the framework of a one-dimensional model and valid for the case of fine sediments, exploits some common assumptions: the inertial terms are neglected in the momentum equation, a purely sinusoidal tidal wave is considered; moreover the channel head is assumed to be always wet. The analytical solution is obtained for weakly dissipative channels in the limit of morphological long-term equilibrium by means of a perturbation analysis and is correct up to the second order of the perturbation of the frictional term. No assumption is made about the scale of the tidal amplitude with respect to the depth. The resulting bed profile is described by a single analytical relationship if expressed in terms of a modified longitudinal coordinate and tends to be flat in the landward part and linearly deepening seaward. The effect of channel convergence is included in the modified coordinate and tends to increase the upward concavity of the profile seaward when rewritten as a function of the physical variable; the possible presence of lateral tidal flats has a similar effect. The adoption of a suitably modified longitudinal coordinate, on the other hand, implies that the mouth of channels with different lengths is simply represented by points moving along the analytical curve describing the equilibrium profile. It is also possible to define a threshold between short flat channels and long linear channels, depending only on the critical velocity for erosion and the convergence length, so that convergent channels or sediment difficult to erode determine the tendency towards an almost horizontal bottom profile.

  7. Extraction of tidal channel networks from airborne scanning laser altimetry

    NASA Astrophysics Data System (ADS)

    Mason, David C.; Scott, Tania R.; Wang, Hai-Jing

    Tidal channel networks are important features of the inter-tidal zone, and play a key role in tidal propagation and in the evolution of salt marshes and tidal flats. The study of their morphology is currently an active area of research, and a number of theories related to networks have been developed which require validation using dense and extensive observations of network forms and cross-sections. The conventional method of measuring networks is cumbersome and subjective, involving manual digitisation of aerial photographs in conjunction with field measurement of channel depths and widths for selected parts of the network. This paper describes a semi-automatic technique developed to extract networks from high-resolution LiDAR data of the inter-tidal zone. A multi-level knowledge-based approach has been implemented, whereby low-level algorithms first extract channel fragments based mainly on image properties then a high-level processing stage improves the network using domain knowledge. The approach adopted at low level uses multi-scale edge detection to detect channel edges, then associates adjacent anti-parallel edges together to form channels. The higher level processing includes a channel repair mechanism. The algorithm may be extended to extract networks from aerial photographs as well as LiDAR data. Its performance is illustrated using LiDAR data of two study sites, the River Ems, Germany and the Venice Lagoon. For the River Ems data, the error of omission for the automatic channel extractor is 26%, partly because numerous small channels are lost because they fall below the edge threshold, though these are less than 10 cm deep and unlikely to be hydraulically significant. The error of commission is lower, at 11%. For the Venice Lagoon data, the error of omission is 14%, but the error of commission is 42%, due partly to the difficulty of interpreting channels in these natural scenes. As a benchmark, previous work has shown that this type of algorithm

  8. Quantifying Tidal Flat Areal Change of Yellow River (Huang He) Delta in China using SAR Intensity Data

    NASA Astrophysics Data System (ADS)

    Tanaka, A.

    2010-12-01

    Coast areas are highly dynamic units, and are ecologically and economically significant. However, particularly in Asia, delta systems, which characterize Asian coastal features, are increasingly being degraded and destroyed by human activities and by global warming. A variety of remote sensing systems can be used to monitor morphological changes in coastal areas as it has wide spatial coverage and high temporal repeatability. The Yellow River, Huang He, Delta in China is one of the fastest changing coasts on the Earth's surface. These drastic changes were caused by a number of factors, including heavy sediment loads, recent water demands, and frequent river course changes. In this paper, JERS-1 (Japanese Earth Resource Satellite-1) SAR (Synthetic Aperture Radar) data acquired during 1992 and 1997, a minimum temporal interval of 44 days, are used for monitoring of land cover changes in the Yellow River delta. Raw SAR data are processed, coregistered and geocoded, to make SAR backscatter intensity images. Radar backscatter intensity depends on various factors, including the physical properties of the surface, primarily its surface roughness and its dielectric constant. Dielectric constant of the soil, which depends primarily on the soil moisture content, and the target area are wet, boggy, and sometimes under water. Therefore, the image intensity mainly depends on the roughness of the surface. A binary image having only two intensity levels (black and white, where black represents smooth area, tidal flats in this case) was created from each SAR backscatter intensity image by choosing a threshold level using the Otsu method. A series of binary image of JERS-1 data demonstrates the ability to monitor tidal flat area quantitatively. Tidal flat area increased until 1995, and then eroded between 1995 and 1997. In May 1996, a new channel was cut near the tip of the delta, with the result that tidal flat area again increased. This area change is well correlated with annual

  9. Paleoenvironmental history of a drained tidal freshwater wetland in the Sacramento Delta, California

    NASA Astrophysics Data System (ADS)

    Brown, K. J.; Pasternack, G. B.

    2001-12-01

    The McCormack-Williamson Tract is a large island situated in the Sacramento Delta, California, USA. This leveed 1,600-acre parcel of land is slated for restoration by The Nature Conservancy, with the goal of reverting the island from intensive agricultur e to a historical tidal freshwater wetland and floodplain. To design a suitable restoration strategy, it is necessary to determine the past and present biogeomorphic processes that have operated at the study site using three cores that have been collected from the island. The length of the cores range from about 12-14 m depth and bottom out at a maximum radiocarbon age of 40,100 years before present. The lithostratigraphic facies that are identified in the cores include Holocene floodplain and channel d eposits, Scirpus marshes and associated mudflats. Pleistocene glaciofluvial outwash is recorded only in the southern section of island. Pollen and spore analyses reveal that Scirpus marshes occupied the northwest section of the site during the mid-late H olocene. Channels, riparian woodlands, and floodplain habitats occupied the remaining sections of the island throughout the Holocene. Charcoal data indicates that fire was not a significant type of disturbance, whereas the lack of pollen coupled with widespread inorganic sedimentation in many sections of the cores suggests that flooding was a frequent form of disturbance on the island throughout the Holocene. Elemental analysis, coupled with pollen data, clearly show the onset of agriculture as a land-use practice in more recent times. In combination, these data provide base-line studies that are suitable to assist in guiding restoration efforts on the island.A<â_¡ >http://lawr.ucdavis.edu/faculty/gpast/delta.html

  10. Changes of Soil Particle Size Distribution in Tidal Flats in the Yellow River Delta

    PubMed Central

    Lyu, Xiaofei; Yu, Junbao; Zhou, Mo; Ma, Bin; Wang, Guangmei; Zhan, Chao; Han, Guangxuan; Guan, Bo; Wu, Huifeng; Li, Yunzhao; Wang, De

    2015-01-01

    Background The tidal flat is one of the important components of coastal wetland systems in the Yellow River Delta (YRD). It can stabilize shorelines and protect coastal biodiversity. The erosion risk in tidal flats in coastal wetlands was seldom been studied. Characterizing changes of soil particle size distribution (PSD) is an important way to quantity soil erosion in tidal flats. Method/Principal findings Based on the fractal scale theory and network analysis, we determined the fractal characterizations (singular fractal dimension and multifractal dimension) soil PSD in a successional series of tidal flats in a coastal wetland in the YRD in eastern China. The results showed that the major soil texture was from silt loam to sandy loam. The values of fractal dimensions, ranging from 2.35 to 2.55, decreased from the low tidal flat to the high tidal flat. We also found that the percent of particles with size ranging between 0.4 and 126 μm was related with fractal dimensions. Tide played a great effort on soil PSD than vegetation by increasing soil organic matter (SOM) content and salinity in the coastal wetland in the YRD. Conclusions/Significance Tidal flats in coastal wetlands in the YRD, especially low tidal flats, are facing the risk of soil erosion. This study will be essential to provide a firm basis for the coast erosion control and assessment, as well as wetland ecosystem restoration. PMID:25816240

  11. Suspended sediment transport in distributary channel networks and its implication on the evolution of delta

    NASA Astrophysics Data System (ADS)

    Suying, Ou; hao, Yang

    2016-04-01

    Suspended sediment (SS) transport in distributary channels play an important role on the evolution of deltas and estuaries. Under the interactions between river discharge, tide, and bathymetry of Pearl River delta (PRD) in south China, the spatial and temporal characteristics of suspended sediment transport are investigated by using the field data of July 16 to 25, 1999 and February 7 to 15, 2001. The PRD, as one of the most complex tributary system in the world and composed of 324 transversal and longitudinal tributaries, with eight outlets to the three sub-estuaries, has higher suspended sediment load in middle delta including six outlets than in right and left tidal dominant channels of PRD, that is Humen channel and Yamen channel system. Under large river discharge of one flood in summer, the tidal averaged SS transport from channel to the estuaries, the SS concentration of middle delta is 10~20 times and the transport rate is 100~500 times of dry season. But the transport rate changes little between flood season and dry season in the upper channel system of Yamen and Humen, and in dry season the tidal averaged transport change direction from estuary to these channel systems. About 70~85% of total Pearl River SS load transport along the main channel of West River, then transport about 45~55% into the lower West river delta, about 30% of total SS load flushed into the Modaomen outlets. Under the bathymetry of branched channels, SS load which advected from the Pearl River and resuspended from bed, redistributed 4~8 times in the PRD and then cause the different changes of channels. It found that in flood season, the suspended sediment load from Pearl River including East, West, North River and Tanjiang, Liuxi River into the PRD is less than that discharged into the estuaries through eight outlets, which indicated the erosion in the channels of PRD especially in the lower part of PRD. Suspended sediment budget in dry season during neap-spring cycle indicated that

  12. Stratigraphy and Evolution of Delta Channel Deposits, Jezero Crater, Mars

    NASA Technical Reports Server (NTRS)

    Goudge, T. A.; Mohrig, D.; Cardenas, B. T.; Hughes, C. M.; Fassett, C. I.

    2017-01-01

    The Jezero impact crater hosted an open-basin lake that was active during the valley network forming era on early Mars. This basin contains a well exposed delta deposit at the mouth of the western inlet valley. The fluvial stratigraphy of this deposit provides a record of the channels that built the delta over time. Here we describe observations of the stratigraphy of the channel deposits of the Jezero western delta to help reconstruct its evolution.

  13. Tidal wetland conservation and restoration for flood mitigation in estuaries and deltas: examples and global potential

    NASA Astrophysics Data System (ADS)

    Temmerman, Stijn; Smolders, Sven; Stark, Jeroen; meire, patrick

    2014-05-01

    Low-lying and densely populated deltas and estuaries are world widely exposed to flood risks caused by storm surges. On the one hand, global change is increasing these flood risks through accelerating sea level rise and increasing storm intensity, but on the other hand, local-scale human impacts on deltas and estuaries are in many cases even more increasing the vulnerability to floods. Here we address the degradation and reclamation of tidal wetlands (i.e. salt marshes in the temperate zone and mangroves in the tropical zone) as a major source for increasing vulnerability to flooding of estuaries and deltas. Firstly, we present examples of flood mitigation by tidal wetland conservation and restoration, and secondly we explore the potentials and limitations for global application of this approach of ecosystem-based flood defense (see Temmerman et al. 2013). First, we use the Scheldt estuary (SW Netherlands and Belgium) as an example where historic wetland reclamation has importantly contributed to increasing flood risks, and where tidal marsh restoration on the previously reclaimed land is nowadays brought into large-scale practice as an essential part of the flood defense system. Based on data and hydrodynamic modelling, we show that large-scale historic marsh reclamation has largely reduced the water storage capacity of the estuary and has reduced the friction to propagating flood waves, resulting in an important landward increase of tidal and storm surge levels. Hydrodynamic model scenarios demonstrate how tidal and storm surge propagation through the estuary are affected by tidal marsh properties, including the surface area, elevation, vegetation and position of marshes along the estuary. We show that nowadays tidal wetland creation on previously reclaimed land is applied as an essential part of the flood defense system along the Scheldt estuary. Secondly, a global analysis is presented of the potential application of tidal wetlands in flood mitigation in

  14. Modeling the growth and migration of sandy shoals on ebb-tidal deltas

    NASA Astrophysics Data System (ADS)

    Ridderinkhof, W.; Swart, H. E.; Vegt, M.; Hoekstra, P.

    2016-07-01

    Coherent sandy shoals that migrate toward the downdrift coast are observed on many ebb-tidal deltas. In this study, processes that cause the growth and migration of shoals on ebb-tidal deltas are identified. Moreover, the effect of the incident wave energy and the tidal prism of an inlet on the migration speed of these shoals is investigated. For this, a numerical morphodynamic model with an idealized geometric setup is employed. The model computes the bed level evolution due to local erosion and deposition of sand driven by tides and waves. Analysis of model results shows that shoals grow when there is a local imbalance between the bathymetry and the wave conditions, which in this study was imposed by manually breaching the ebb-tidal delta or by adding storms to the wave forcing. There are thresholds for shoal formation that depend on the distribution of the sand and the incident wave energy. Wave refraction over the shoals leads to focusing of wave energy and increased wave energy dissipation around the location of the local minimum water depth. This generates residual currents over the shoal and increased skin friction toward the local minimum water depth, which together create a sand transport pattern that induces the growth and migration of the shoal. Sand transport due to asymmetric waves contributes to keeping the shoal a coherent structure. The shoal migration speed increases with increasing incident wave energy and decreasing tidal prism; this is because tidal residual currents oppose the wave-driven residual currents that cause shoal migration.

  15. COMMD1 regulates the delta epithelial sodium channel ({delta}ENaC) through trafficking and ubiquitination

    SciTech Connect

    Chang, Tina; Ke, Ying; Ly, Kevin; McDonald, Fiona J.

    2011-08-05

    Highlights: {yields} The COMM domain of COMMD1 mediates binding to {delta}ENaC. {yields} COMMD1 reduces the cell surface population of {delta}ENaC. {yields} COMMD1 increases the population of {delta}ENaC-ubiquitin. {yields} Both endogenous and transfected {delta}ENaC localize with COMMD1 and transferrin suggesting they are located in early/recycling endosomes. -- Abstract: The delta subunit of the epithelial sodium channel ({delta}ENaC) is a member of the ENaC/degenerin family of ion channels. {delta}ENaC is distinct from the related {alpha}-, {beta}- and {gamma}ENaC subunits, known for their role in sodium homeostasis and blood pressure control, as {delta}ENaC is expressed in brain neurons and activated by external protons. COMMD1 (copper metabolism Murr1 domain 1) was previously found to associate with and downregulate {delta}ENaC activity. Here, we show that COMMD1 interacts with {delta}ENaC through its COMM domain. Co-expression of {delta}ENaC with COMMD1 significantly reduced {delta}ENaC surface expression, and led to an increase in {delta}ENaC ubiquitination. Immunocytochemical and confocal microscopy studies show that COMMD1 promoted localization of {delta}ENaC to the early/recycling endosomal pool where the two proteins were localized together. These results suggest that COMMD1 downregulates {delta}ENaC activity by reducing {delta}ENaC surface expression through promoting internalization of surface {delta}ENaC to an intracellular recycling pool, possibly via enhanced ubiquitination.

  16. Decadal morphological response of an ebb-tidal delta and down-drift beach to artificial breaching and inlet stabilisation

    NASA Astrophysics Data System (ADS)

    Garel, E.; Sousa, C.; Ferreira, Ó.; Morales, J. A.

    2014-07-01

    The morphodynamic response of a mixed-energy ebb-tidal delta (Guadiana estuary, southern Portugal) and its down-drift barrier island (Canela Island) to channel relocation and stabilisation by jetties is examined using a series of sequential bathymetric maps and vertical aerial photographs spanning five decades. Morphological analysis indicates that the ebb delta is in an immature state, characterised by weak sediment bypassing. Landward-migrating shoals on the swash platform have been produced by the jetty-induced artificial bank-breaching and by the collapse of the eastern portion of the delta. The welding of these shoals has largely controlled the evolution of the coast, with local accretion and erosion lasting for years, and large amounts of regional accretion occurring over decades due to sand accumulation against jetties located further down-drift. These observations provide insights into the potential response of a coast to very large, locally concentrated sand nourishment in the form of shoals. The main effects of the jetties on the coast are observed at the centre of Canela Island, with the production of an erosion hot-spot associated with a temporally persistent and divergent longshore transport providing sand to the adjacent areas. Significant accretion is anticipated for the next decade along the entire island due to the ongoing attachment of the presently observed shoals. After the depletion of this sediment source, and in the context of weak sediment bypassing, the most severe down-drift erosion induced by the jetties is predicted to occur some decades after their construction. This study demonstrates that the geomorphic response of an ebb-tidal delta to jetty construction must be considered at multiple temporal and spatial scales when assessing the impacts of jetties on the down-drift coast.

  17. Modeling delta growth and channel geometry on Wax Lake Delta, Louisiana. Preliminary results

    NASA Astrophysics Data System (ADS)

    Viparelli, E.; Czapiga, M. J.; Li, C.; Shaw, J. B.; Parker, G.

    2013-12-01

    A numerical model of delta growth, in which the distributary channels are assumed to have self-constructed their cross sections, is validated on Wax Lake Delta, Louisiana. As in previous laterally averaged models of delta growth, the delta is divided in a low slope delta top, a steep delta front and a low slope basement. The flow on the delta top is assumed steady, and a backwater formulation is implemented. Since one or more channels can actively transport water and sediment on the delta top during floods, we simplify the problem by assuming that the bed material is transported in one rectangular channel, with width and depth roughly equal to the sum of the active channel widths, and to the average depth of the active channels. The problem is characterized by one equation (i.e. the backwater equation) in two unknowns, the channel width and depth. Another equation is thus needed to close the problem. Under the assumptions that 1) the system is at bankfull flow, and 2) the Shields number in the channels is equal to its channel formative value, our closure relation is a channel-formative criterion. In particular, a recently derived relation to estimate the formative (bankfull) Shields number as a function of the friction slope is implemented. Recent field work on Wax Lake Delta shows that the distributary channels are incising into a relatively stiff basement. In our model we do not attempt to directly model channel incision, but we implicitly account for it with a modified formulation to compute the shoreline migration rate. In this formulation the bed material at the shoreline is trapped in the non-channelized portion of the delta front only. Measured and numerical shoreline migration rates, longitudinal profiles of delta elevation, and channel geometry, i.e. width and depth, are compared. In the relatively near future we plan to 1) use our model to estimate land-building potential of engineered diversions of the Mississippi River, and 2) couple the present model

  18. Annotated Bibliography of Sediment Transport Occurring over Ebb-Tidal Deltas.

    DTIC Science & Technology

    1985-09-01

    on the South East Queensland coast, Australia. It has been found that the inlet entrance tidal prism-cross- sectional area relationship is controlled...coasts of: central South Carolina, Virginia, southern New Jersey, New England, the East Frisian Islands, and the Cooper River Delta in Alaska. Regardless... East Pass, Destin, Florida: Marine Geology , 12:43-58. Density contrasts between the water of Choctawhatchee Bay and the Gulf of Mexico result in sharp

  19. Temperature independent quantum well FET with delta channel doping

    NASA Technical Reports Server (NTRS)

    Young, P. G.; Mena, R. A.; Alterovitz, S. A.; Schacham, S. E.; Haugland, E. J.

    1992-01-01

    A temperature independent device is presented which uses a quantum well structure and delta doping within the channel. The device requires a high delta doping concentration within the channel to achieve a constant Hall mobility and carrier concentration across the temperature range 300-1.4 K. Transistors were RF tested using on-wafer probing and a constant G sub max and F sub max were measured over the temperature range 300-70 K.

  20. Assessing tidal marsh vulnerability to sea-level rise in the Skagit Delta

    USGS Publications Warehouse

    Hood, W. Gregory; Grossman, Eric; Curt Veldhuisen,

    2016-01-01

    Historical aerial photographs, from 1937 to the present, show Skagit Delta tidal marshes prograding into Skagit Bay for most of the record, but the progradation rates have been steadily declining and the marshes have begun to erode in recent decades despite the large suspended sediment load provided by the Skagit River. In an area of the delta isolated from direct riverine sediment supply by anthropogenic blockage of historical distributaries, 0.5-m tall marsh cliffs along with concave marsh profiles indicate wave erosion is contributing to marsh retreat. This is further supported by a “natural experiment” provided by rocky outcrops that shelter high marsh in their lee, while being bounded by 0.5-m lower eroded marsh to windward and on either side. Coastal wetlands with high sediment supply are thought to be resilient to sea level rise, but the case of the Skagit Delta shows this is not necessarily true. A combination of sea level rise and wave-generated erosion may overwhelm sediment supply. Additionally, anthropogenic obstruction of historical distributaries and levee construction along the remaining distributaries likely increase the jet momentum of river discharge, forcing much suspended sediment to bypass the tidal marshes and be exported from Skagit Bay. Adaptive response to the threat of climate change related sea level rise and increased wave frequency or intensity should consider the efficacy of restoring historical distributaries and managed retreat of constrictive river levees to maximize sediment delivery to delta marshes.

  1. Optical Estimation of Depth and Current in a Ebb Tidal Delta Environment

    NASA Astrophysics Data System (ADS)

    Holman, R. A.; Stanley, J.

    2012-12-01

    A key limitation to our ability to make nearshore environmental predictions is the difficulty of obtaining up-to-date bathymetry measurements at a reasonable cost and frequency. Due to the high cost and complex logistics of in-situ methods, research into remote sensing approaches has been steady and has finally yielded fairly robust methods like the cBathy algorithm for optical Argus data that show good performance on simple barred beach profiles and near immunity to noise and signal problems. In May, 2012, data were collected in a more complex ebb tidal delta environment during the RIVET field experiment at New River Inlet, NC. The presence of strong reversing tidal currents led to significant errors in cBathy depths that were phase-locked to the tide. In this paper we will test methods for the robust estimation of both depths and vector currents in a tidal delta domain. In contrast to previous Fourier methods, wavenumber estimation in cBathy can be done on small enough scales to resolve interesting nearshore features.

  2. Preliminary assessment of DOC and THM precursor loads from a freshwater restored wetland, an agricultural field, and a tidal wetland in the Sacramento-San Joaquin River Delta

    USGS Publications Warehouse

    Fujii, R.; Bergamaschi, B.A.; Ganju, N.K.; Fleck, J.A.; Burow-Fogg, K.R.; Schoellhamer, D.; Deverel, S.J.

    2003-01-01

    Water exported from the Sacramento-San Joaquin River Delta supplies drinking water to more than 22 million people in California. At certain times of the year, Delta waters contain relatively high concentrations of dissolved organic carbon (DOC) and bromide. During these times, chlorination of Delta water for drinking water disinfection will form disinfection byproducts, such as trihalomethanes (THMs), that can exceed the U.S. Environmental Protection Agency's maximum contaminant level for THMs of 80 mg/L. Important sources of DOC and THM precursors (types of DOC that form THMs when chlorinated) to the Delta include rivers, drainage water from peat islands, water from wetlands and areas with extensive riparian vegetation, and in-channel growth of algae and macrophytes. Due to proposed ecosystem restoration and creation of wetlands in the Delta, there is an urgent need for information on the relative loads of DOC and THM precursors produced from three different land uses: restored wetlands constructed for subsidence mitigation, tidal wetlands, and agricultural operations. We have been conducting research in the Delta to provide this information. A restored wetland and agricultural field located on Twitchell Island, and a tidal wetland on Browns Island have been monitored for flow, DOC, and THM precursors. Initial results indicate that the loads of DOC and THM precursors are similar for the restored wetland (surface water only) and the agricultural field. These land uses produce DOC loads of about 14 and 11 g C/m2/yr, respectively, and THM precursor loads of about 1.7 and 1.0 g THM/m2/yr, respectively. Estimates of DOC and THM precursor loads for the tidal wetland site on Browns Island and seepage associated with the restored wetland are being developed.

  3. Suspended sediment dynamics in a tidal channel network under peak river flow

    NASA Astrophysics Data System (ADS)

    Achete, Fernanda Minikowski; van der Wegen, Mick; Roelvink, Dano; Jaffe, Bruce

    2016-05-01

    Peak river flows transport fine sediment, nutrients, and contaminants that may deposit in the estuary. This study explores the importance of peak river flows on sediment dynamics with special emphasis on channel network configurations. The Sacramento-San Joaquin Delta, which is connected to San Francisco Bay (California, USA), motivates this study and is used as a validation case. Besides data analysis of observations, we applied a calibrated process-based model (D-Flow FM) to explore and analyze high-resolution (˜100 m, ˜1 h) dynamics. Peak river flows supply the vast majority of sediment into the system. Data analysis of six peak flows (between 2012 and 2014) shows that on average, 40 % of the input sediment in the system is trapped and that trapping efficiency depends on timing and magnitude of river flows. The model has 90 % accuracy reproducing these trapping efficiencies. Modeled deposition patterns develop as the result of peak river flows after which, during low river flow conditions, tidal currents are not able to significantly redistribute deposited sediment. Deposition is quite local and mainly takes place at a deep junction. Tidal movement is important for sediment resuspension, but river induced, tide residual currents are responsible for redistributing the sediment towards the river banks and to the bay. We applied the same forcing for four different channel configurations ranging from a full delta network to a schematization of the main river. A higher degree of network schematization leads to higher peak-sediment export downstream to the bay. However, the area of sedimentation is similar for all the configurations because it is mostly driven by geometry and bathymetry.

  4. ARRAY OPTIMIZATION FOR TIDAL ENERGY EXTRACTION IN A TIDAL CHANNEL – A NUMERICAL MODELING ANALYSIS

    SciTech Connect

    Yang, Zhaoqing; Wang, Taiping; Copping, Andrea

    2014-04-18

    This paper presents an application of a hydrodynamic model to simulate tidal energy extraction in a tidal dominated estuary in the Pacific Northwest coast. A series of numerical experiments were carried out to simulate tidal energy extraction with different turbine array configurations, including location, spacing and array size. Preliminary model results suggest that array optimization for tidal energy extraction in a real-world site is a very complex process that requires consideration of multiple factors. Numerical models can be used effectively to assist turbine siting and array arrangement in a tidal turbine farm for tidal energy extraction.

  5. Carbon Sequestration in Mediterranean Tidal Wetlands: San Francisco Bay and the Ebro River Delta (Invited)

    NASA Astrophysics Data System (ADS)

    Callaway, J.; Fennessy, S.; Ibanez, C.

    2013-12-01

    Tidal wetlands accumulate soil carbon at relatively rapid rates, in large part because they build soil to counteract increases in sea-level rise. Because of the rapid rates of carbon sequestration, there is growing interest in evaluating carbon dynamics in tidal wetlands around the world; however, few measurements have been completed for mediterranean-type tidal wetlands, which tend to have relatively high levels of soil salinity, likely affecting both plant productivity and decomposition rates. We measured sediment accretion and carbon sequestration rates at tidal wetlands in two mediterranean regions: the San Francisco Bay Estuary (California, USA) and the Ebro River Delta (Catalonia, Spain). Sampling sites within each region represented a range of conditions in terms of soil salinity and plant communities, and these sites serve as potential analogs for long-term carbon sequestration in restored wetlands, which could receive credits under emerging policies for carbon management. Within San Francisco Bay, we collected six sediment cores per site at four salt marshes and two brackish tidal wetlands (two transects with three stations per transect at each site) in order to identify spatial variation both within and among wetlands in the Estuary. At the Ebro Delta, individual sediment cores were collected across 14 tidal wetland sites, including salt and brackish marshes from impounded areas, river mouths, coastal lagoon, and open bay settings. Cores were collected to 50 cm, and cores were dated using 137Cs and 210Pb. Most sites within San Francisco accreted 0.3-0.5 cm/yr, with slightly higher rates of accretion at low marsh stations; accretions rates based on 137Cs were slightly higher than those based on 210Pb, likely because of the shorter time frame covered by 137Cs dating. Accretion rates from the Ebro Delta sites were similar although more variable, with rates based on 137Cs ranging from 0.1 to 0.9 cm/yr and reflecting the wide range of conditions and management

  6. Flow-noise and turbulence in two tidal channels.

    PubMed

    Bassett, Christopher; Thomson, Jim; Dahl, Peter H; Polagye, Brian

    2014-04-01

    Flow-noise resulting from oceanic turbulence and interactions with pressure-sensitive transducers can interfere with ambient noise measurements. This noise source is particularly important in low-frequency measurements (f < 100 Hz) and in highly turbulent environments such as tidal channels. This work presents measurements made in the Chacao Channel, Chile, and in Admiralty Inlet, Puget Sound, WA. In both environments, peak currents exceed 3 m/s and pressure spectral densities attributed to flow-noise are observed at frequencies up to 500 Hz. At 20 Hz, flow-noise exceeds mean slack noise levels by more than 50 dB. Two semi-empirical flow-noise models are developed and applied to predict flow-noise at frequencies from 20 to 500 Hz using measurements of current velocity and turbulence. The first model directly applies mean velocity and turbulence spectra while the second model relies on scaling arguments that relate turbulent dissipation to the mean velocity. Both models, based on prior formulations for infrasonic (f < 20 Hz) flow-noise, agree well with observations in Chacao Channel. In Admiralty Inlet, good agreement is shown only with the model that applies mean velocity and turbulence spectra, as the measured turbulence violates the scaling assumption in the second model.

  7. Sedimentary Facies Mapping Based on Tidal Channel Network and Topographic Features

    NASA Astrophysics Data System (ADS)

    Ryu, J. H.; Lee, Y. K.; Kim, K.; Kim, B.

    2015-12-01

    Tidal flats on the west coast of Korea suffer intensive changes in their surface sedimentary facies as a result of the influence of natural and artificial changes. Spatial relationships between surface sedimentary facies distribution and benthic environments were estimated for the open-type Ganghwa tidal flat and semi closed-type Hwangdo tidal flat, Korea. In this study, we standardized the surface sedimentary facies and tidal channel index of the channel density, distance, thickness and order. To extract tidal channel information, we used remotely sensed data, such as those from the Korea Multi-Purpose Satellite (KOMPSAT)-2, KOMPSAT-3, and aerial photographs. Surface sedimentary facies maps were generated based on field data using an interpolation method.The tidal channels in each sediment facies had relatively constant meandering patterns, but the density and complexity were distinguishable. The second fractal dimension was 1.7-1.8 in the mud flat, about 1.4 in the mixed flat, and about 1.3 in the sand flat. The channel density was 0.03-0.06 m/m2 in the mud flat and less than 0.02 m/m2 in the mixed and sand flat areas of the two test areas. Low values of the tidal channel index, which indicated a simple pattern of tidal channel distribution, were identified at areas having low elevation and coarse-grained sediments. By contrast, high values of the tidal channel index, which indicated a dendritic pattern of tidal channel distribution, were identified at areas having high elevation and fine-grained sediments. Surface sediment classification based on remotely sensed data must circumspectly consider an effective critical grain size, water content, local topography, and intertidal structures.

  8. Anthropogenic changes to the tidal channel network, sediment rerouting, and social implications in southwest Bangladesh

    NASA Astrophysics Data System (ADS)

    Wilson, C.; Goodbred, S. L., Jr.; Sams, S.; Small, C.

    2015-12-01

    The tidal channel network in southwest Bangladesh has been undergoing major adjustment in response to anthropogenic modification over the past few decades. Densely inhabited, agricultural islands that have been embanked to protect against inundation by tides, river flooding, and storm surges (i.e., polders) preclude tidal exchange and sedimentation. Studies reveal this results in elevation deficits relative to mean high water, endangering local communities when embankment failures occur (e.g., during storms, lateral channel erosion). In addition, many studies suggest that the decrease in tidal prism and associated change in hydrodynamics from poldering causes shoaling in remaining tidal channels, which can cause a disruption in transportation. The widespread closure and conversion of tidal channel areas to profitable shrimp aquaculture is also prevalent in this region. In this study, we quantify the direct closure of tidal channels due to poldering and shrimp aquaculture using historical Landsat and Google Earth imagery, and analyze the morphologic adjustment of the tidal channel network due to these perturbations. In the natural Sundarbans mangrove forest, the tidal channel network has remained relatively constant since the 1970s. In contrast, construction of polders removed >1000 km of primary tidal creeks and >90 km2 has been reclaimed outside of polders through infilling and closure of formerly-active, higher order conduit channels now used for shrimp aquaculture. Field validation confirm tidal restriction by large sluice gates is prevalent, favoring local channel siltation at rates up to 20cm/yr. With the impoundment of primary creeks and closure of 30-60% of conduit channels in the study area, an estimated 1,400 x 106 m3 of water has been removed from the tidal prism and potentially redirected within remaining channels. This has significant implications for tidal amplification in this region. Further, we estimate that 12.3 x 106 MT of sediment annually

  9. Linking human impacts within an estuary to ebb-tidal delta evolution

    USGS Publications Warehouse

    Dallas, Kate L.; Barnard, Patrick L.

    2009-01-01

    San Francisco Bay, California, USA is among the most anthropogenically altered estuaries in the entire United States, but the impact on sediment transport to the coastal ocean has not been quantified. Analysis of four historic bathymetric surveys has revealed large changes to the morphology of the San Francisco Bar, an ebb-tidal delta at the mouth of the San Francisco Bay. From 1873 to 2005 the bar eroded an average of 80 cm, which equates to a total volume loss of 100 + 65 x 106 m3 of sediment. Comparison of the surveys indicates the entire ebb delta has contracted radially while its crest has moved landward an average of 1 km. Compilation of historic records reveals that 130 x 106 m3 of sediment has been permanently removed from the San Francisco Bay and adjacent coastal ocean. Constriction of the bar is hypothesized to be from a decrease in sediment supply from San Francisco Bay, a reduction in the tidal prism of the estuary, and/or a reduction in the input of hydraulic mining debris. Changes to the morphology of the San Francisco Bar have likely altered wave refraction and focusing patterns on adjacent beaches and may be a factor in persistent beach erosion occurring in the area.

  10. Suspended sediment transport under estuarine tidal channel conditions

    USGS Publications Warehouse

    Sternberg, R.W.; Kranck, K.; Cacchione, D.A.; Drake, D.E.

    1988-01-01

    A modified version of the GEOPROBE tripod has been used to monitor flow conditions and suspended sediment distribution in the bottom boundary layer of a tidal channel within San Francisco Bay, California. Measurements were made every 15 minutes over three successive tidal cycles. They included mean velocity profiles from four electromagnetic current meters within 1 m of the seabed; mean suspended sediment concentration profiles from seven miniature nephelometers operated within 1 m of the seabed; near-bottom pressure fluctuations; vertical temperature gradient; and bottom photographs. Additionally, suspended sediment was sampled from four levels within 1 m of the seabed three times during each successive flood and ebb cycle. While the instrument was deployed, STD-nephelometer measurements were made throughout the water column, water samples were collected each 1-2 hours, and bottom sediment was sampled at the deployment site. From these measurements, estimates were made of particle settling velocity (ws) from size distributions of the suspended sediment, friction velocity (U*) from the velocity profiles, and reference concentration (Ca) was measured at z = 20 cm. These parameters were used in the suspended sediment distribution equations to evaluate their ability to predict the observed suspended sediment profiles. Three suspended sediment particle conditions were evaluated: (1) individual particle size in the 4-11 ?? (62.5-0.5 ??m) range with the reference concentration Ca at z = 20 cm (C??), (2) individual particle size in the 4-6 ?? size range, flocs representing the 7-11 ?? size range with the reference concentration Ca at z = 20 cm (Cf), and (3) individual particle size in the 4-6 ?? size range, flocs representing the 7-11 ?? size range with the reference concentration predicted as a function of the bed sediment size distribution and the square of the excess shear stress. In addition, computations of particle flux were made in order to show vertical variations

  11. Flood risk of natural and embanked landscapes on the Ganges-Brahmaputra tidal delta plain

    NASA Astrophysics Data System (ADS)

    Auerbach, L. W.; Goodbred, S. L., Jr.; Mondal, D. R.; Wilson, C. A.; Ahmed, K. R.; Roy, K.; Steckler, M. S.; Small, C.; Gilligan, J. M.; Ackerly, B. A.

    2015-02-01

    The Ganges-Brahmaputra river delta, with 170 million people and a vast, low-lying coastal plain, is perceived to be at great risk of increased flooding and submergence from sea-level rise. However, human alteration of the landscape can create similar risks to sea-level rise. Here, we report that islands in southwest Bangladesh, enclosed by embankments in the 1960s, have lost 1.0-1.5 m of elevation, whereas the neighbouring Sundarban mangrove forest has remained comparatively stable. We attribute this elevation loss to interruption of sedimentation inside the embankments, combined with accelerated compaction, removal of forest biomass, and a regionally increased tidal range. One major consequence of this elevation loss occurred in 2009 when the embankments of several large islands failed during Cyclone Aila, leaving large areas of land tidally inundated for up to two years until embankments were repaired. Despite sustained human suffering during this time, the newly reconnected landscape received tens of centimetres of tidally deposited sediment, equivalent to decades’ worth of normal sedimentation. Although many areas still lie well below mean high water and remain at risk of severe flooding, we conclude that elevation recovery may be possible through controlled embankment breaches.

  12. Relationships between sedimentation, plant species, and the proximity to tidal channels in coastal salt marshes

    NASA Astrophysics Data System (ADS)

    Mudd, S. M.; Howell, S. M.; Furbish, D. J.; Morris, J. T.

    2006-12-01

    Deposition of sediment on vegetated salt marshes enables these marshes to maintain their elevation relative to rising sea level. It has been found that deposition rates of suspended sediment on vegetated salt marshes are highest near tidal channels. This is due to the reduction in turbulence as flows from the tidal channel encounter the stems of the macrophytes that live on the marsh. Despite the presence of levees along some tidal channels, many marsh surfaces paradoxically slope gently upward away from tidal creeks, despite the reduction of deposition of suspended sediment distal from the salt marsh creek. We explore the effect of different marsh species on deposition rates in order to explain this apparent paradox. In the Beaufort Inlet, North Carolina, Spartina alterniflora tends to grow at low elevations near tidal channels, whereas Juncus roemerianus occupies higher elevations distal from the tidal channels. Juncus roemerianus tends to have greater biomass and stem density; this causes it to be more effective at trapping suspended sediment, and may lead Juncus roemerianus to have a higher rate of organogenic sedimentation compared to Spartina alterniflora. We explore how these two effects may allow the portion of the marsh populated by Juncus roemerianus to remain at a higher elevation than the portion of the marsh occupied by Spartina alterniflora, despite the greater rate of deposition due to the settling of suspended sediment in portions of the marsh near the tidal channels.

  13. Hydrodynamics and morphodynamics of shallow tidal channels and intertidal flats. Doctoral thesis

    SciTech Connect

    Friedrichs, C.T.

    1993-02-01

    In this thesis, mechanisms which control morphodynamics of shallow tidal embayments are investigated analytically. In the process of exploring these mechanisms (specifically asymmetries in bottom stress), Tau, basis momentum and mass balances which govern flow in these systems are clarified. Temporal asymmetries in Tau are investigated via a new perturbation scheme which quantifies nonlinear processes and combines geometric controls on asymmetry into a single non-dimensional parameter. Implications of spatial asymmetries in Tau are investigated through stability criteria based on a uniform distribution of Tau. Morphologic observations of both tidal channels and intertidal flats are consistent with a uniform distribution of Tau at equilibrium. Investigation of morphodynamic mechanisms leads to scalings of momentum and continuity which diverge from classical models. Scalings for prismatic channels with strong tidal asymmetries indicate friction often dominates acceleration in the momentum equation. The resulting zero-inertia balance gives a time-varying diffusion equation which requires along-channel amplitude to decay. Uniform Tau justifies a new scaling of continuity for exponentially-shaped channels. In such channels, along-channel gradients in tidal velocity are small and are often dominated by gradients in cross-sectional area. The resulting first-order wave equation allows only amplitude, forward propagating waveforms which are independent of channel length. Tidal channels Hydrodynamics, Tidal flats.

  14. Drivers of barotropic and baroclinic exchange through an estuarine navigation channel in the Mississippi River Delta Plain

    USGS Publications Warehouse

    Snedden, Gregg

    2016-01-01

    Estuarine navigation channels have long been recognized as conduits for saltwater intrusion into coastal wetlands. Salt flux decomposition and time series measurements of velocity and salinity were used to examine salt flux components and drivers of baroclinic and barotropic exchange in the Houma Navigation Channel, an estuarine channel located in the Mississippi River delta plain that receives substantial freshwater inputs from the Mississippi-Atchafalaya River system at its inland extent. Two modes of vertical current structure were identified from the time series data. The first mode, accounting for 90% of the total flow field variability, strongly resembled a barotropic current structure and was coherent with alongshelf wind stress over the coastal Gulf of Mexico. The second mode was indicative of gravitational circulation and was linked to variability in tidal stirring and the horizontal salinity gradient along the channel’s length. Tidal oscillatory salt flux was more important than gravitational circulation in transporting salt upestuary, except over equatorial phases of the fortnightly tidal cycle during times when river inflows were minimal. During all tidal cycles sampled, the advective flux, driven by a combination of freshwater discharge and wind-driven changes in storage, was the dominant transport term, and net flux of salt was always out of the estuary. These findings indicate that although human-made channels can effectively facilitate inland intrusion of saline water, this intrusion can be minimized or even reversed when they are subject to significant freshwater inputs.

  15. Changes in surfzone morphodynamics driven by multi-decadel contraction of a large ebb-tidal delta

    USGS Publications Warehouse

    Hansen, Jeff E.; Elias, Edwin; Barnard, Patrick L.; Barnard, P.L.; Jaffee, B.E.; Schoellhamer, D.H.

    2013-01-01

    The impact of multi-decadal, large-scale deflation (76 million m3 of sediment loss) and contraction (~ 1 km) of a 150 km2 ebb-tidal delta on hydrodynamics and sediment transport at adjacent Ocean Beach in San Francisco, CA (USA), is examined using a coupled wave and circulation model. The model is forced with representative wave and tidal conditions using recent (2005) and historic (1956) ebb-tidal delta bathymetry data sets. Comparison of the simulations indicates that along north/south trending Ocean Beach the contraction and deflation of the ebb-tidal delta have resulted in significant differences in the flow and sediment dynamics. Between 1956 and 2005 the transverse bar (the shallow attachment point of the ebb-tidal delta to the shoreline) migrated northward ~ 1 km toward the inlet while a persistent alongshore flow and transport divergence point migrated south by ~ 500 m such that these features now overlap. A reduction in tidal prism and sediment supply over the last century has resulted in a net decrease in offshore tidal current-generated sediment transport at the mouth of San Francisco Bay, and a relative increase in onshore-directed wave-driven transport toward the inlet, accounting for the observed contraction of the ebb-tidal delta. Alongshore migration of the transverse bar and alongshore flow divergence have resulted in an increasing proportion of onshore migrating sediment from the ebb-tidal delta to be transported north along the beach in 2005 versus south in 1956. The northerly migrating sediment is then trapped by Pt. Lobos, a rocky headland at the northern extreme of the beach, consistent with the observed shoreline accretion in this area. Conversely, alongshore migration of the transverse bar and divergence point has decreased the sediment supply to southern Ocean Beach, consistent with the observed erosion of the shoreline in this area. This study illustrates the utility of applying a high-resolution coupled circulation-wave model for

  16. Variability of tidal signals in the Brent Delta Front: New observations on the Rannoch Formation, northern North Sea

    NASA Astrophysics Data System (ADS)

    Wei, Xiaojie; Steel, Ronald J.; Ravnås, Rodmar; Jiang, Zaixing; Olariu, Cornel; Li, Zhiyang

    2016-04-01

    Detailed observations on the Rannoch Formation in several deep Viking Graben wells indicate that the 'classical' wave-dominated Brent delta-front shows coupled storm-tide processes. The tidal signals are of three types: I): alternations of thick cross-laminated sandstone and thin mud-draped sandstone, whereby double mud drapes are prominent but discretely distributed, II): a few tidal bundles within bottomsets and foresets of up to 10 cm-thick sets cross-strata, and III): dm-thick heterolithic lamination showing multiple, well-organized sand-mud couplets. During progradation of the Brent Delta, the Rannoch shoreline system passed upward from 1) a succession dominated by clean-water, storm-event sets and cosets frequently and preferentially interbedded with type I tidal beds, and occasional types II and III tidal deposits, toward 2) very clean storm-event beds less frequently separated by types II and III tidal beds, and then into 3) a thin interval showing muddier storm-event beds mainly alternating with type II tidal beds. It is likely that those variations in preservation bias of storm and tidal beds in each facies succession result from combined effects of 1) the frequency and duration of storms; 2) river discharge; and 3) the absolute and relative strength of tides. Tidal deposits are interpreted as inter-storm, fair-weather deposits, occurred preferentially in longer intermittent fair-weather condition and periods of lower river discharge, and well-pronounced in the distal-reach of delta-front. The formation and preservation of tidal signals between storm beds, indicate that the studied Rannoch Formation was most likely a storm-dominated, tide-influenced delta front 1) near the mouth of a large Brent river, where a significant tidal prism and high tidal range might be expected, and 2) in a setting where there were relatively high sedimentation rates associated with high local subsidence rates, so that the storm waves did not completely rework the inter

  17. The dynamics of an energetic tidal channel, the Pentland Firth, Scotland

    NASA Astrophysics Data System (ADS)

    Easton, Matthew C.; Woolf, David K.; Bowyer, Peter A.

    2012-10-01

    Shelf tidal stream velocities are accelerated by nearshore geographic features, such as headlands and islands. In the search for sustainable forms of electrical energy generation, such locations may become attractive for tidal stream power developments. For some prospective tidal stream energy sites, however, little is known about the intricacies of the local tidal dynamics: knowledge which is crucial to the understanding of the resource and the potential environmental consequences of its extraction. In this paper a two dimensional hydrodynamic model is used to investigate a complex tidal strait, the Pentland Firth (Scotland, UK). This channel, considered one of the most promising tidal stream energy sites in the world, is set for extensive development over the coming decade. We show that the tidal stream velocities that regularly occur within, and up to 20-km beyond the Pentland Firth, are accelerated above that of a free shallow-water wave. The primary mechanism for these accelerations is hydraulic in nature, associated with a large shift in tidal phase. Tidal streaming around headlands and islands further promotes conversion from potential to kinetic energy. We calculate a mean energy flux into the Pentland Firth from the North Atlantic Ocean of 8.97 GW. Changes in tidal amplitude and phase along the strait are associated with a reduction in energy flux, such that the majority (˜60%) of the incoming energy is lost within the Pentland Firth through bed friction. Localised geographical factors complicate the tidal dynamics of the Pentland Firth, therefore detailed modelling is the only means with which to accurately characterise the environmental conditions in this channel. Of more general oceanographic significance, this example shows that high levels of tidal energy dissipation are associated with energetic tidal straits. Energy losses in these straits may contribute significantly to balancing the energy flux onto the continental shelf from the deep seas.

  18. Tidal Channel Diatom Assemblages Reflect within Wetland Environmental Conditions and Land Use at Multiple Scales

    EPA Science Inventory

    We characterized regional patterns of the tidal channel benthic diatom community and examined the relative importance of local wetland and surrounding landscape level factors measured at multiple scales in structuring this assemblage. Surrounding land cover was characterized at ...

  19. Channel fill characteristics in submarine fans and deltas

    SciTech Connect

    Bouma, A.H.; Goddard, D. )

    1993-02-01

    Excellent data sources may not answer all pertinent questions and multifold seismic data usually cannot resolve internal characteristics of channel fills, even when it can detect the channel. Well log correlations can be wrong, especially when dealing with thin channel fills and outcrops are seldom sufficiently large to reveal a complete channel fill. In the final analysis, integration of all these types of data is necessary. Although not well understood, a lot of similarities exist between the channel fills from submarine fans and those from deltas. It is definitely beneficial to compare data from both environments. Channels and their fills can be: (1) primarily the result of major erosion forming an incisement that becomes gradually filled; (2) primarily the result of deposition, maintaining a channel, gradually filling it and simultaneously building its levees; (3) massive fill; (4) a bedded fill with or without an upward and/or lateral thinning or fining; or (5) a combination of thick bedded and thin bedded. Many channels alternate between erosional and depositional activities. Often an erosional cut is lined with shale, reducing fluid flow between channel sandstones and those of the levees. Also, a thorough knowledge of all of these varied processes is essential for the understanding of why [open quotes]massive[close quotes] channel fills can be wet and [open quotes]thin-bedded levees[close quotes] deposits oil prone.

  20. Tidal and meteorological forcing of sediment transport in tributary mudflat channels.

    PubMed

    Ralston, David K; Stacey, Mark T

    2007-06-01

    Field observations of flow and sediment transport in a tributary channel through intertidal mudflats indicate that suspended sediment was closely linked to advection and dispersion of a tidal salinity front. During calm weather when tidal forcing was dominant, high concentrations of suspended sediment advected up the mudflat channel in the narrow region between salty water from San Francisco Bay and much fresher runoff from the small local watershed. Salinity and suspended sediment dispersed at similar rates through each tidal inundation, such that during receding ebbs the sediment pulse had spread spatially and maximum concentrations had decreased. Net sediment transport was moderately onshore during the calm weather, as asymmetries in stratification due to tidal straining of the salinity front enhanced deposition, particularly during weaker neap tidal forcing. Sediment transport by tidal forcing was periodically altered by winter storms. During storms, strong winds from the south generated wind waves and temporarily increased suspended sediment concentrations. Increased discharge down the tributary channels due to precipitation had more lasting impact on sediment transport, supplying both buoyancy and fine sediment to the system. Net sediment transport depended on the balance between calm weather tidal forcing and perturbations by episodic storms. Net transport in the tributary channel was generally off-shore during storms and during calm weather spring tides, and on-shore during calm weather neap tides.

  1. Ecology of Juvenile Salmonids in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, Lower Columbia River, 2007 Annual Report.

    SciTech Connect

    Sobocinski, Kathryn; Johnson, Gary; Sather, Nichole

    2008-03-17

    community characteristics, including species composition, abundance, and temporal and spatial distributions. (1c) Estimate the stock of origin for the yearling and subyearling Chinook salmon captured at the sampling sites using genetic analysis. (1d) Statistically assess the relationship between salmonid abundance and habitat parameters, including ancillary variables such as temperature and river stage. (2) Acoustic Telemetry Monitoring-Assess feasibility of applying Juvenile Salmon Acoustic Telemetry System (JSATS) technology to determine migration characteristics from upriver of Bonneville Dam through the study area (vicinity of the Sandy River delta/Washougal River confluence). (2a) Determine species composition, release locations, and distributions of JSATS-tagged fish. (2b) Estimate run timing, residence times, and migration pathways for these fish. Additionally, both objectives serve the purpose of baseline research for a potential tidal rechannelization project on the Sandy River. The U.S. Forest Service, in partnership with the Bonneville Power Administration and the U.S. Army Corps of Engineers, is currently pursuing reconnection of the east (relict) Sandy River channel with the current channel to improve fish and wildlife habitat in the Sandy River delta. Our study design and the location of sampling sites in this reach provide baseline data to evaluate the potential restoration.

  2. Successive impact of tidal bores on sedimentary processes: Arcins channel, Garonne River

    NASA Astrophysics Data System (ADS)

    Reungoat, David; Leng, Xinqian; Chanson, Hubert

    2017-03-01

    A tidal bore is a hydrodynamic shock, propagating upstream as the tidal flow turns to rising, with macro-tidal conditions in a funnel shaped system with shallow waters. The tidal bore of the Garonne River was extensively investigated in the Arcins channel between 2010 and 2013, typically over one to two days. In 2015, new field measurements were repeated systematically at the same site on 29 August-1 September 2015 and on 27 October 2015. The nature of the observations was comprehensive, encompassing hydrodynamics and turbulence, as well as sediment properties and transport. The tidal bore occurrence had a marked effect on the velocity and suspended sediment field, including a rapid flow deceleration and flow reversal during the bore passage, with very large suspended sediment concentrations (SSCs) during the passage of the tidal bore front and early flood tide, as well as very large suspended sediment flux during the very early flood tide. The suspended sediment concentration (SSC) data indicated a gradual increase in initial mean SSC estimate prior to the bore from 29 August to 1 September 2015. A comparison between suspended sediment flux data showed very significant suspended sediment flux on the first day of tidal bore occurrence, with a decreasing magnitude over the next three days. The data suggested a two-stage bed scour process: at each tidal bore event, surface erosion occurred initially, in the form of stripping; the first stage was followed by delayed mass erosion, occurring about 5-15 min after the tidal bore.

  3. Morphological equilibrium of short channels dissecting the tidal flats of coastal lagoons

    NASA Astrophysics Data System (ADS)

    Toffolon, Marco; Lanzoni, Stefano

    2010-12-01

    The equilibrium bed profile of tidal channels dissecting the tidal flats of coastal lagoons is studied within a rational one-dimensional framework. A general analytical solution is obtained which expresses the bed profile in terms of a modified longitudinal coordinate, accounting implicitly for channel convergence and adjacent shoals. For values of the relevant parameters typical of costal lagoons, inertia and friction effects as well as overtides are shown to provide minor corrections to the equilibrium bed profile. The overall shape of the profile is also shown to be slightly affected by the equilibrium condition used in its derivation, consisting in a requirement on either residual erosion/deposition fluxes or maximum velocity. In particular, the asymptotic form of the analytical solution is common to both the equilibrium requirements, thus suggesting the existence of general morphological relationships relating the depth at the channel mouth or, alternatively, the length of the channel to the tidal amplitude, to the degree of channel convergence, to the critical velocity for erosion/deposition and to the extent of intertidal storage areas. The profile shape is affected as well; for instance, nearly constant-depth channels tend to form when convergence is strong. The equilibrium configuration also implies that a power law relationship of the type proposed by O'Brien-Jarret-Marchi for tidal inlets, relating the channel cross section to the tidal prism, holds throughout the entire channel. Finally, the theoretical profile is shown to reasonably reproduce the bed configurations observed in a number of tidal channels surveyed within the Lagoon of Venice (Italy).

  4. Impacts of salt marsh plants on tidal channel initiation and inheritance

    NASA Astrophysics Data System (ADS)

    Schwarz, Christian; Ye, Qinghua; van der Wal, Daphne; Zhang, Liquan; Ysebaert, Tom; Herman, Peter MJ

    2013-04-01

    Tidal channel networks are the most prominent and striking features visible in tidal wetlands. They serve as major pathways for the exchange of water, sediments, nutrients and contaminants between the wetland and the adjacent open water body. Previous studies identified topography guided sheet flows, as the predominate process for tidal channel initiation. Guided through differences in local topography, sheet flows are able to locally exceed bottom shear stress thresholds, initiating scouring and incision of tidal channels, which then further grow through head ward erosion. The fate of these channels after plant colonization is described in literature as being inherited into the salt marsh through vegetation induced bank stabilization (further referred to as vegetation stabilized channel inheritance). In this study we present a combination of flume experiments and modelling simulations elucidating the impact of vegetation on tidal channel initiation. We first studied the impact of plant properties (stiff: Spartina alterniflora versus flexible: Scirpus mariqueter) on local sediment transport utilizing a flume experiment. Then a coupled hydrodynamic morphodynamic plant growth model was set up to simulate plant colonization by these two different species in the pioneer zone at the mudflat - salt marsh transition. Based on the model we investigated the ramifications of interactions between vegetation, sediment and flow on tidal channel initiation. We specifically compared the effect of vegetation properties (such as stiffness, growth velocity and stress tolerance) on emerging channel patterns, hypothesizing that vegetation mediated channel incision (vegetation induced flow routing and differential sedimentation/erosion patterns leading to tidal channel incision) plays an active role in intertidal landscape evolution. We finally extended our model simulation by imposing pre-existing mudflat channels with different maximum depths, to investigate the impact of existing

  5. Impacts of salt marsh plants on tidal channel initiation and inheritance

    NASA Astrophysics Data System (ADS)

    Schwarz, C.; Ye, Q. H.; Wal, D.; Zhang, L. Q.; Bouma, T.; Ysebaert, T.; Herman, P. M. J.

    2014-02-01

    At the transition between mudflat and salt marsh, vegetation is traditionally regarded as a sustaining factor for previously incised mudflat channels, able to conserve the channel network via bank stabilization following plant colonization (i.e., vegetation-stabilized channel inheritance). This is in contrast to recent studies revealing vegetation as the main driver of tidal channel emergence through vegetation-induced channel erosion. We present a coupled hydrodynamic morphodynamic plant growth model to simulate plant expansion and channel formation by our model species (Spartina alterniflora) during a mudflat-salt marsh transition with various initial bathymetries (flat, shoal dense, shoal sparse, and deep dense channels). This simulated landscape development is then compared to remote sensing images of the Yangtze estuary, China, and the Scheldt estuary in Netherlands. Our results propose the existence of a threshold in preexisting mudflat channel depth, which favors either vegetation-stabilized channel inheritance or vegetation-induced channel erosion processes. The increase in depth of preexisting mudflat channels favors flow routing through them, consequently leaving less flow and momentum remaining for vegetation-induced channel erosion processes. This threshold channel depth will be influenced by field specific parameters such as hydrodynamics (tidal range and flow), sediment characteristics, and plant species. Hence, our study shows that the balance between vegetation-stabilized channel inheritance and vegetation-induced channel erosion depends on ecosystem properties.

  6. Rejuvenating Poldered Landscapes in a Tidally-Dominated, Sediment-Rich Delta: A Numerical Model and Analysis of the Effectiveness of Tidal River Management in Coastal Bangladesh

    NASA Astrophysics Data System (ADS)

    Tasich, C. M.; Goodbred, S. L., Jr.; Gilligan, J. M.; Wilson, C.

    2014-12-01

    The low-lying, coastal region of Bangladesh has relied on poldering (the creation of embanked islands) since the 1960s to mitigate the effects of tidal inundation and storm surge from tropical cyclones. The result has been an increase in total arable land and the ability to sustain food production for one of the most densely populated countries in the world. However, poldering has had the unintended consequences of starving embanked landscapes of sediment and increasing high water levels through tidal amplification. Thus, polder elevations have been declining while tidal channels have been aggrading. Recent small-scale engineering projects, locally referred to as tidal river management (TRM), have attempted to combat these effects by allowing water and sediment exchange between the polders and the tidal network. Anecdotal reports claim great success for TRM in some locations, but not in others. However, to date there has been almost no quantitative analysis. Here, we used measured sedimentation rates and water level data from Polder 32 (P32) and the adjacent pristine mangrove forest in southwest Bangladesh to parameterize a simple model of tidal inundation and resultant sediment accretion. P32 elevations are currently ~1 m lower than natural elevations resulting in ~105 cm of tidal inundation when embankments were breached versus only ~20 cm for the mangrove forest. We measured sedimentation rates of 20 cm/yr and 1 cm/yr, respectively. When normalized to the cumulative annual flooding depth, the resulting sediment extraction rates yield similar values of 300 mg/L and 230 mg/L. We employ these flooding depth and sediment extraction parameters in our model to quantify the amount of time and sediment needed to re-equilibrate the lowered polder elevation to that of the natural environment. Although relatively simple, results from this preliminary model corroborate anecdotes of TRM's effectiveness at restoring land-surface elevations in the polders of Bangladesh. Future

  7. Delta channel networks: 2. Metrics of topologic and dynamic complexity for delta comparison, physical inference, and vulnerability assessment

    NASA Astrophysics Data System (ADS)

    Tejedor, Alejandro; Longjas, Anthony; Zaliapin, Ilya; Foufoula-Georgiou, Efi

    2015-06-01

    Deltas are landforms that deliver water, sediment and nutrient fluxes from upstream rivers to the deltaic surface and eventually to oceans or inland water bodies via multiple pathways. Despite their importance, quantitative frameworks for their analysis lack behind those available for tributary networks. In a companion paper, delta channel networks were conceptualized as directed graphs and spectral graph theory was used to design a quantitative framework for exploring delta connectivity and flux dynamics. Here we use this framework to introduce a suite of graph-theoretic and entropy-based metrics, to quantify two components of a delta's complexity: (1) Topologic, imposed by the network connectivity and (2) Dynamic, dictated by the flux partitioning and distribution. The metrics are aimed to facilitate comparing, contrasting, and establishing connections between deltaic structure, process, and form. We illustrate the proposed analysis using seven deltas in diverse morphodynamic environments and of various degrees of channel complexity. By projecting deltas into a topo-dynamic space whose coordinates are given by topologic and dynamic delta complexity metrics, we show that this space provides a basis for delta comparison and physical insight into their dynamic behavior. The examined metrics are demonstrated to relate to the intuitive notion of vulnerability, measured by the impact of upstream flux changes to the shoreline flux, and reveal that complexity and vulnerability are inversely related. Finally, a spatially explicit metric, akin to a delta width function, is introduced to classify shapes of different delta types.

  8. Inferring tidal wetland stability from channel sediment fluxes: observations and a conceptual model

    USGS Publications Warehouse

    Ganju, Neil K.; Nidzieko, Nicholas J.; Kirwan, Matthew L.

    2013-01-01

    Anthropogenic and climatic forces have modified the geomorphology of tidal wetlands over a range of timescales. Changes in land use, sediment supply, river flow, storminess, and sea level alter the layout of tidal channels, intertidal flats, and marsh plains; these elements define wetland complexes. Diagnostically, measurements of net sediment fluxes through tidal channels are high-temporal resolution, spatially integrated quantities that indicate (1) whether a complex is stable over seasonal timescales and (2) what mechanisms are leading to that state. We estimated sediment fluxes through tidal channels draining wetland complexes on the Blackwater and Transquaking Rivers, Maryland, USA. While the Blackwater complex has experienced decades of degradation and been largely converted to open water, the Transquaking complex has persisted as an expansive, vegetated marsh. The measured net export at the Blackwater complex (1.0 kg/s or 0.56 kg/m2/yr over the landward marsh area) was caused by northwesterly winds, which exported water and sediment on the subtidal timescale; tidally forced net fluxes were weak and precluded landward transport of suspended sediment from potential seaward sources. Though wind forcing also exported sediment at the Transquaking complex, strong tidal forcing and proximity to a turbidity maximum led to an import of sediment (0.031 kg/s or 0.70 kg/m2/yr). This resulted in a spatially averaged accretion of 3.9 mm/yr, equaling the regional relative sea level rise. Our results suggest that in areas where seaward sediment supply is dominant, seaward wetlands may be more capable of withstanding sea level rise over the short term than landward wetlands. We propose a conceptual model to determine a complex's tendency toward stability or instability based on sediment source, wetland channel location, and transport mechanisms. Wetlands with a reliable portfolio of sources and transport mechanisms appear better suited to offset natural and

  9. A Modeling Study of In-stream Tidal Energy Extraction and Its Potential Environmental Impacts in a Tidal Channel and Bay System

    NASA Astrophysics Data System (ADS)

    Wang, T.; Yang, Z.; Copping, A. E.

    2012-12-01

    In recent years, there has been growing interest in harnessing in-stream tidal energy in response to concerns of increasing energy demand and to mitigate climate change impacts. While efforts have been made to assess and map available tidal energy resources using numerical models, little attention has been paid directly quantifying the associated potential environmental impacts as part of tidal energy generation. This paper presents the development of a tidal turbine module within a three-dimensional (3-D) unstructured grid coastal ocean model. The model is used to investigate in-stream tidal energy extraction and associated impacts on estuarine hydrodynamic and biological processes in a stratified estuarine system. A series of numerical experiments with varying numbers and configurations of turbines were carried out to assess the changes in the hydrodynamics and biological processes in the tidal channel and bay system due to tidal energy extraction. Model results show the maximum extractable energy depends strongly on the turbine hub height, and that the effects of energy extraction on the flow fields vary vertically. Preliminary model results also indicate that extraction of tidal energy increases vertical mixing and decreases flushing rate in the estuary. As one of the early modeling efforts aimed directly at examining the impacts of tidal energy extraction on estuarine circulation and biological processes, this study demonstrates that numerical models can serve as a very useful tool for this purpose. However, careful efforts are warranted to address system-specific environmental issues in real world, complex estuarine systems.

  10. Three-dimensional modeling of fecal coliform in the Tidal Basin and Washington Channel, Washington, DC.

    PubMed

    Bai, Sen; Lung, Wu-Seng

    2006-01-01

    Fecal coliform are widely used as bacterial indicator in the United States and around the world. Fecal coliform impaired water is highly possible to be polluted by pathogenic bacteria. The Tidal Basin and Washington Channel in Washington, DC are on the Total Maximum Daily Load (TMDL) list due to the high fecal coliform level. To support TMDL development, a three-dimensional numerical model of fecal coliform was developed using the EFDC framework. The model calculates the transport of fecal coliform under the influences of flap gate operations and tidal elevation. The original EFDC code was modified to calculate the die-off of fecal coliform under the impact of temperature and solar radiation intensity. The watershed contribution is expressed as storm water inflow and the load carried by the runoff. Model results show that fecal coliform vary strongly in space in both the Tidal Basin and Washington Channel. The storm water only impacts a small area around the storm water outfall in the Tidal Basin and the impacts are negligible in the Washington Channel due to dilution. The water from the Potomac River may affect the fecal coliform level in the area close to the flap gate in the Tidal Basin. The fecal coliform level in the Washington Channel is mainly controlled by the fecal coliform level in the Anacostia River, which is located at the open boundary of the Washington Channel. The potential sediment layer storage of fecal coliform was analyzed and it was found that the sediment layer fecal coliform level could be much higher than the water column fecal coliform level and becomes a secondary source under high bottom shear stress condition. The developed model built solid connection of fecal coliform source and concentration in the water column and has been used to develop TMDL.

  11. Conceptual framework for assessing the response of delta channel networks to Holocene sea level rise

    NASA Astrophysics Data System (ADS)

    Jerolmack, Douglas J.

    2009-08-01

    Recent research has identified two fundamental unit processes that build delta distributary channels. The first is mouth-bar deposition at the shoreline and subsequent channel bifurcation, which is driven by progradation of the shoreline; the second is avulsion to a new channel, a result of aggradation of the delta topset. The former creates relatively small, branching networks such as Wax Lake Delta; the latter generates relatively few, long distributaries such as the Mississippi and Atchafalaya channels on the Mississippi Delta. The relative rate of progradation to aggradation, and hence the creation of accommodation space, emerges as a controlling parameter on channel network form. Field and experimental research has identified sea level as the dominant control on Holocene delta growth worldwide, and has empirically linked channel network changes to changes in the rate of sea level rise. Here I outline a simple modeling framework for distributary network evolution, and use this to explore large-scale changes in Holocene channel pattern that have been observed in deltas such as the Rhine-Meuse and Mississippi. Rapid early- to mid-Holocene sea level rise forced many deltas into an aggradational mode, where I hypothesize that avulsion and the generation of large-scale branches should dominate. Slowing of sea level rise in the last ˜6000 yr allowed partitioning of sediment into progradation, facilitating the growth of smaller-scale distributary trees at the shorelines of some deltas, and a reduction in the number of large-scale branches. Significant antecedent topography modulates delta response; the filling of large incised valleys, for example, caused many deltas to bypass the aggradational phase. Human effects on deltas can be cast in terms of geologic controls affecting accommodation: constriction of channels forces rapid local progradation and mouth-bar bifurcation, while accelerated sea level rise increases aggradation and induces more frequent channel

  12. Ecology of Juvenile Salmon in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, Lower Columbia River, 2008 Annual Report.

    SciTech Connect

    Sather, NK; Johnson, GE; Storch, AJ

    2009-07-06

    delta. (2) Characterize the fish community and juvenile salmon migration, including species composition, length-frequency distribution, density (number/m{sup 2}), and temporal and spatial distributions in the vicinity of the Sandy River delta in the lower Columbia River and estuary (LCRE). (3) Determine the stock of origin for juvenile Chinook salmon (Oncorhynchus tshawytscha) captured at sampling sites through genetic identification. (4) Characterize the diets of juvenile Chinook and coho (O. kisutch) salmon captured within the study area. (5) Estimate run timing, residence times, and migration pathways for acoustic-tagged fish in the study area. (6) Conduct a baseline evaluation of the potential restoration to reconnect the old Sandy River channel with the delta. (7) Apply fish density data to initiate a design for a juvenile salmon monitoring program for beach habitats within the tidal freshwater segment of the LCRE (river kilometer 56-234).

  13. Modeling Tidal Stream Energy Extraction and its Effects on Transport Processes in a Tidal Channel and Bay System Using a Three-dimensional Coastal Ocean Model

    SciTech Connect

    Yang, Zhaoqing; Wang, Taiping; Copping, Andrea E.

    2013-02-28

    This paper presents a numerical modeling study for simulating in-stream tidal energy extraction and assessing its effects on the hydrodynamics and transport processes in a tidal channel and bay system connecting to coastal ocean. A marine and hydrokinetic (MHK) module was implemented in a three-dimensional (3-D) coastal ocean model using the momentum sink approach. The MHK model was validated with the analytical solutions for tidal channels under one-dimensional (1-D) conditions. Model simulations were further carried out to compare the momentum sink approach with the quadratic bottom friction approach. The effects of 3-D simulations on the vertical velocity profile, maximum extractable energy, and volume flux reduction across the channel were investigated through a series of numerical experiments. 3-D model results indicate that the volume flux reduction at the maximum extractable power predicted by the 1-D analytical model or two-dimensional (2-D) depth-averaged numerical model may be overestimated. Maximum extractable energy strongly depends on the turbine hub height in the water column, and which reaches a maximum when turbine hub height is located at mid-water depth. Far-field effects of tidal turbines on the flushing time of the tidal bay were also investigated. Model results demonstrate that tidal energy extraction has a greater effect on the flushing time than volume flux reduction, which could negatively affect the biogeochemical processes in estuarine and coastal waters that support primary productivity and higher forms of marine life.

  14. a Graph Based Model for the Detection of Tidal Channels Using Marked Point Processes

    NASA Astrophysics Data System (ADS)

    Schmidt, A.; Rottensteiner, F.; Soergel, U.; Heipke, C.

    2015-08-01

    In this paper we propose a new method for the automatic extraction of tidal channels in digital terrain models (DTM) using a sampling approach based on marked point processes. In our model, the tidal channel system is represented by an undirected, acyclic graph. The graph is iteratively generated and fitted to the data using stochastic optimization based on a Reversible Jump Markov Chain Monte Carlo (RJMCMC) sampler and simulated annealing. The nodes of the graph represent junction points of the channel system and the edges straight line segments with a certain width in between. In each sampling step, the current configuration of nodes and edges is modified. The changes are accepted or rejected depending on the probability density function for the configuration which evaluates the conformity of the current status with a pre-defined model for tidal channels. In this model we favour high DTM gradient magnitudes at the edge borders and penalize a graph configuration consisting of non-connected components, overlapping segments and edges with atypical intersection angles. We present the method of our graph based model and show results for lidar data, which serve of a proof of concept of our approach.

  15. Methods for accurate estimation of net discharge in a tidal channel

    USGS Publications Warehouse

    Simpson, M.R.; Bland, R.

    2000-01-01

    Accurate estimates of net residual discharge in tidally affected rivers and estuaries are possible because of recently developed ultrasonic discharge measurement techniques. Previous discharge estimates using conventional mechanical current meters and methods based on stage/discharge relations or water slope measurements often yielded errors that were as great as or greater than the computed residual discharge. Ultrasonic measurement methods consist of: 1) the use of ultrasonic instruments for the measurement of a representative 'index' velocity used for in situ estimation of mean water velocity and 2) the use of the acoustic Doppler current discharge measurement system to calibrate the index velocity measurement data. Methods used to calibrate (rate) the index velocity to the channel velocity measured using the Acoustic Doppler Current Profiler are the most critical factors affecting the accuracy of net discharge estimation. The index velocity first must be related to mean channel velocity and then used to calculate instantaneous channel discharge. Finally, discharge is low-pass filtered to remove the effects of the tides. An ultrasonic velocity meter discharge-measurement site in a tidally affected region of the Sacramento-San Joaquin Rivers was used to study the accuracy of the index velocity calibration procedure. Calibration data consisting of ultrasonic velocity meter index velocity and concurrent acoustic Doppler discharge measurement data were collected during three time periods. Two sets of data were collected during a spring tide (monthly maximum tidal current) and one of data collected during a neap tide (monthly minimum tidal current). The relative magnitude of instrumental errors, acoustic Doppler discharge measurement errors, and calibration errors were evaluated. Calibration error was found to be the most significant source of error in estimating net discharge. Using a comprehensive calibration method, net discharge estimates developed from the three

  16. Deltas as Ecomorphodynamic Systems: Effects of Vegetation Gradients on Sediment Trapping and Channel Dynamics

    NASA Astrophysics Data System (ADS)

    Piliouras, A.; Kim, W.; Goggin, H.

    2014-12-01

    Understanding the feedbacks between water, sediment, and vegetation in deltas is an important part of understanding deltas as ecomorphodynamic systems. We conducted a set of laboratory experiments using alfalfa (Medicago sativa) as a proxy for delta vegetation to determine (1) the effects of plants on delta growth and channel dynamics and (2) the influence of fine material on delta evolution. Vegetated experiments were compared to a control run without plants to isolate the effects of vegetation, and experiments with fine sediment were compared to a set of similar experiments with only sand. We found that alfalfa increased sediment trapping on the delta topset, and that the plants were especially effective at retaining fine material. Compared to the control run, the vegetated experiments showed an increased retention of fine sediment on the floodplain that resulted in increased delta relief and stronger pulses of shoreline progradation when channel avulsion and migration occurred. In other words, a higher amount of sediment storage with the addition of vegetation corresponded to a higher amount of sediment excavation during channelization events. In natural systems, dense bank vegetation is typically expected to help confine flow. We seeded our delta uniformly, which eliminated typical vegetation density gradients from riverbank to island center and therefore diminished the gradient in overbank sedimentation that best confines channels by creating levees. Dense clusters of alfalfa throughout the interior of the floodplain and delta islands were therefore able to induce flow splitting, where channels diverged around a stand of plants. This created several smaller channels that were then able to more widely distribute sediment at the delta front compared to unvegetated experiments. We conclude that plants are efficient sediment trappers that change the rate and amount of sediment storage in the delta topset, and that gradients in vegetation density are an important

  17. Modeling tidal freshwater marsh sustainability in the Sacramento-San Joaquin Delta under a broad suite of potential future scenarios

    USGS Publications Warehouse

    Swanson, Kathleen M.; Drexler, Judith Z.; Fuller, Christopher C.; Schoellhamer, David H.

    2015-01-01

    In this paper, we report on the adaptation and application of a one-dimensional marsh surface elevation model, the Wetland Accretion Rate Model of Ecosystem Resilience (WARMER), to explore the conditions that lead to sustainable tidal freshwater marshes in the Sacramento–San Joaquin Delta. We defined marsh accretion parameters to encapsulate the range of observed values over historic and modern time-scales based on measurements from four marshes in high and low energy fluvial environments as well as possible future trends in sediment supply and mean sea level. A sensitivity analysis of 450 simulations was conducted encompassing a range of eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. porosity values, initial elevations, organic and inorganic matter accumulation rates, and sea-level rise rates. For the range of inputs considered, the magnitude of SLR over the next century was the primary driver of marsh surface elevation change. Sediment supply was the secondary control. More than 84% of the scenarios resulted in sustainable marshes with 88 cm of SLR by 2100, but only 32% and 11% of the scenarios resulted in surviving marshes when SLR was increased to 133 cm and 179 cm, respectively. Marshes situated in high-energy zones were marginally more resilient than those in low-energy zones because of their higher inorganic sediment supply. Overall, the results from this modeling exercise suggest that marshes at the upstream reaches of the Delta—where SLR may be attenuated—and high energy marshes along major channels with high inorganic sediment accumulation rates will be more resilient to global SLR in excess of 88 cm over the next century than their downstream and low-energy counterparts. However, considerable uncertainties exist in the projected rates of sea-level rise and sediment avail-ability. In addition, more research is needed to constrain future

  18. Flow convergence caused by a salinity minimum in a tidal channel

    USGS Publications Warehouse

    Warner, John C.; Schoellhamer, David H.; Burau, Jon R.; Schladow, S. Geoffrey

    2006-01-01

    Residence times of dissolved substances and sedimentation rates in tidal channels are affected by residual (tidally averaged) circulation patterns. One influence on these circulation patterns is the longitudinal density gradient. In most estuaries the longitudinal density gradient typically maintains a constant direction. However, a junction of tidal channels can create a local reversal (change in sign) of the density gradient. This can occur due to a difference in the phase of tidal currents in each channel. In San Francisco Bay, the phasing of the currents at the junction of Mare Island Strait and Carquinez Strait produces a local salinity minimum in Mare Island Strait. At the location of a local salinity minimum the longitudinal density gradient reverses direction. This paper presents four numerical models that were used to investigate the circulation caused by the salinity minimum: (1) A simple one-dimensional (1D) finite difference model demonstrates that a local salinity minimum is advected into Mare Island Strait from the junction with Carquinez Strait during flood tide. (2) A three-dimensional (3D) hydrodynamic finite element model is used to compute the tidally averaged circulation in a channel that contains a salinity minimum (a change in the sign of the longitudinal density gradient) and compares that to a channel that contains a longitudinal density gradient in a constant direction. The tidally averaged circulation produced by the salinity minimum is characterized by converging flow at the bed and diverging flow at the surface, whereas the circulation produced by the constant direction gradient is characterized by converging flow at the bed and downstream surface currents. These velocity fields are used to drive both a particle tracking and a sediment transport model. (3) A particle tracking model demonstrates a 30 percent increase in the residence time of neutrally buoyant particles transported through the salinity minimum, as compared to transport

  19. Incised bifurcations and uneven radial distribution of channel incision in the Wax Lake Delta, USA

    NASA Astrophysics Data System (ADS)

    Shaw, J. B.; Mohrig, D. C.

    2009-12-01

    The Wax Lake Delta, southern Louisiana, has been found to possess distributary channels whose beds range from non-depositional to strongly erosional, cut into pre-delta muds. This discovery was unexpected given that the overall depositional setting has created greater than 100 square km of subareal land in less than 40 years. Furthermore, while map views of the system reveal an approximately radial symmetric depositional pattern and delta shape, the pattern of channel incision is unevenly distributed across the distributary network. The apex of Wax Lake delta is defined by an adverse ramp with a bed slope of 0.006 that connects the deep feeder channel (18m) to the shallower, first set of bifurcations. We find two distinct zones of channel bottom character within the distributary network. The first zone consists of substantially incised channels stemming from the bifurcation directly downstream of the Wax Lake Outlet and ramp described above. The maximum depth of incision into pre-delta mud decreases from roughly 3m to 1.5m nearer the delta front. This incision can make up greater than 1/3 of the total flow depth in these channels. The second zone is characterized by non-depositional channel bottoms that are located off to either side of the swath of incisional channels. These channels sit on top of the pre-delta substrate, showing no significant erosion or deposition. The occurrence of bed erosion and non-deposition throughout the observed channel network raises the previously unasked questions of whether these regimes extend to the very front of the delta located 10km from the delta apex, and whether incision plays an important role in the original development of bifurcations on this delta. The development of channel bifurcations under conditions with significant bed incision has yet to be discussed in the river bifurcation literature, and may play an important role in the observed constancy of channel network patterns. Using USACE bathymetry surveys as well as

  20. TIDALLY ENHANCED STELLAR WIND: A WAY TO MAKE THE SYMBIOTIC CHANNEL TO TYPE Ia SUPERNOVA VIABLE

    SciTech Connect

    Chen, X.; Han, Z.

    2011-07-10

    In the symbiotic (or WD+RG) channel of the single-degenerate scenario for type Ia supernovae (SNe Ia), the explosions occur a relatively long time after star formation. The birthrate from this channel would be too low to account for all observed SNe Ia were it not for some mechanism to enhance the rate of accretion on to the white dwarf. A tidally enhanced stellar wind, of the type which has been postulated to explain many phenomena related to giant star evolution in binary systems, can do this. Compared to mass stripping, this model extends the space of SNe Ia progenitors to longer orbital periods and hence increases the birthrate to about 0.0069 yr{sup -1} for the symbiotic channel. Two symbiotic stars, T CrB and RS Oph, considered to be the most likely progenitors of SNe Ia through the symbiotic channel, are well inside the period-companion mass space predicted by our models.

  1. Hydrological connectivity in river deltas: The first-order importance of channel-island exchange

    NASA Astrophysics Data System (ADS)

    Hiatt, Matthew; Passalacqua, Paola

    2015-04-01

    Deltaic systems are composed of distributary channels and interdistributary islands. While previous work has focused either on the channels or on the islands, here we study the hydrological exchange between channels and islands and point at its important role in delta morphology and ecology. We focus our analysis on Wax Lake Delta in coastal Louisiana (USA) and characterize the surface water component of hydrological connectivity through measurements of water discharge and hydraulic tracer propagation. We find that deltaic islands are zones of significant water flux as 23-54% of the incoming distributary channel flux enters the islands. A calculation of the travel times through a channel-island complex shows travel times through the islands to be at least 3 times their channel counterparts. A dye release experiment also indicates that travel times in islands are much longer that those within channels as dye remained in the island for the 3.8 day duration of the experiment. Additionally, islands are more sensitive than channels to environmental forces such as tides, which cause flow reversal and thus can increase travel times through the islands. Our work defines the "hydrological network" of a river delta to include not only the distributary channel network but also the interdistributary islands, quantifies the implications of channel-island hydrological connectivity to travel times through the system, and discusses the relevance of our findings to channel mouth dynamics at the delta front and the potential for denitrification in coastal systems.

  2. Pool spacing, channel morphology, and the restoration of tidal forested wetlands of the Columbia River, U.S.A.

    SciTech Connect

    Diefenderfer, Heida L.; Montgomery, David R.

    2008-10-09

    Tidal forested wetlands have sustained substantial areal losses, and restoration practitioners lack a description of many ecosystem structures associated with these late-successional systems in which surface water is a significant controlling factor on the flora and fauna. The roles of large woody debris in terrestrial and riverine ecosystems have been well described compared to functions in tidal areas. This study documents the role of large wood in forcing channel morphology in Picea-sitchensis (Sitka spruce) dominated freshwater tidal wetlands in the floodplain of the Columbia River, U.S.A. near the Pacific coast. The average pool spacing documented in channel surveys of three freshwater tidal forested wetlands near Grays Bay were 2.2 ± 1.3, 2.3 ± 1.2, and 2.5 ± 1.5. There were significantly greater numbers of pools on tidal forested wetland channels than on a nearby restoration site. On the basis of pool spacing and the observed sequences of log jams and pools, the tidal forested wetland channels were classified consistent with a forced step-pool class. Tidal systems, with bidirectional flow, have not previously been classified in this way. The classification provides a useful basis for restoration project design and planning in historically forested tidal freshwater areas, particularly in regard to the use of large wood in restoration actions and the development of pool habitats for aquatic species. Significant modifications by beaver on these sites warrant further investigation to explore the interactions between these animals and restoration actions affecting hydraulics and channel structure in tidal areas.

  3. Chromatium species: an emerging bioindicator of crude oil pollution of tidal mud flats in the Niger Delta mangrove ecosystem, Nigeria.

    PubMed

    Essien, J P; Antai, S P

    2009-06-01

    Establishing microbiological indices for the monitoring of environmental decay by crude oil pollution in the Niger Delta region has been a major concern of our current researches. Chromatium species, a purple, Gram positive pleomorphic, motile, microaerophlic sulfur bacterium offers a good potential for use in the assessment of the short term effects of oil pollution of tidal mud flats in the Niger Delta mangrove ecosystem. Its response to the November 22, 2003 spillage at the Qua Iboe Estuary and the adjoining Cross River Estuary was investigated. Our results have revealed that the sulphur bacterium is easily identified and widely distributed in the epipellic sediment of the mangrove ecosystem but very sensitive to hydrocarbon pollution. The bacterium was readily detected in the tidal mud flats containing as much as 2.0 mg kg(-1) but not detected in sediment with THC level of 3.65 mg kg(-1) and above. It is thus, suggestive that the threshold and lethal limits of effect of hydrocarbons against the sulfur bacterium lies between 2.04 and 3.65 mg kg(-1). These imply that in any case of crude oil pollution that Chromatium is not detected during monitoring the THC levels of the sediment may have been raised to a level close to or above 3.65 mg kg(-1). Statistical analysis of the relationship between THC level and density of Chromatium in sediment revealed a significant (p < 0.05) negative relationship (r = -0.85) in Qua Iboe mangrove ecosystem as against an insignificant (p > 0.05) relationship (r = -0.41) recorded for the Cross River mangrove ecosystem which served as the control. The result indicates that oil pollution affect the homeostatic status of Chromatium in tidal mud flats despite its even distribution (R2 = 71.4%). The finding though not definitive may contribute to the hierarchical process of oil pollution assessment in the Niger Delta region of Nigeria. However, its effective utilization will require not only the development of a selective medium for

  4. Can tide dominance be inferred from the point bar pattern of tidal meandering channels?

    NASA Astrophysics Data System (ADS)

    Tambroni, N.; Luchi, R.; Seminara, G.

    2017-02-01

    We performed 2-D numerical simulations of flow and bed topography in a channel consisting of a sequence of tidal meanders connected to a tidal sea at one end and closed at the other end. Our main goal was to investigate whether the location of point bars relative to the bend apex is correlated with the character of the local flow field, i.e., its flood or ebb dominance. Validation of the model was achieved performing a comparison with results of laboratory observations. Simulations did reproduce the observed evolution of the laterally averaged bed profile toward an equilibrium configuration characterized by the classical landward aggrading trend typical of straight tidal channels with the formation of a shore at the landward end. The presence of meanders led to small amplitude spatial oscillations of the profile on the meander scale. The bar pattern developed when the morphology was far from equilibrium, such that the sediment transport was sufficiently intense to drive significant morphodynamic perturbations. Numerical results did show conclusively that the key factor controlling the phase of the point bar pattern relative to curvature is the flood- or ebb-dominant character of the basic flow field. More precisely, ebb/flood dominance led to point bars located seaward/landward relative to the bend apex. Moreover, two almost symmetrical long lobes that trailed away from the meander apex in both the ebb and flood directions formed in the transition region where the flow field shifts from flood into ebb dominant.

  5. First documentation of tidal-channel sponge biostromes (upper Pleistocene, southeastern Florida)

    NASA Astrophysics Data System (ADS)

    Cunningham, Kevin J.; Rigby, J. Keith; Wacker, Michael A.; Curran, H. Allen

    2007-05-01

    Sponges are not a common principal component of Cenozoic reefs and are more typically dominant in deep-water and/or cold-water localities. Here we report the discovery of extensive upper Pleistocene shallow-marine, tropical sponge biostromes from the Miami Limestone of southeastern Florida built by a new ceractinomorph demosponge. These upright, barrel- to vase-shaped sponges occur in monospecific aggregations constructed within the tidal channels of an oolitic tidal-bar belt similar to modern examples on the Great Bahama Bank. The biostromes appear to have a ribbon-like geometry, with densely spaced sponges populating a paleochannel along a 3.5 km extent in the most lengthy biostrome. These are very large (as high as 2 m and 1.8 m in diameter), particularly well-preserved calcified sponges with walls as hard as concrete. Quartz grains are the most common particles agglutinated in the structure of the sponge walls. Where exposed, sediment fill between the sponges is commonly a highly burrowed or cross-bedded ooid-bearing grainstone and, locally, quartz sand. It is postulated that the dense, localized distribution of these particular sponges was due to a slight edge over competitors for food or energy supply and space in a stressed environment of tidal-influenced salinity and nutrient changes, strong currents, and frequently shifting submarine sand dunes. To our knowledge, this represents the first documentation of sponge biostromes composed of very large upright sponges within high-energy tidal channels between ooid shoals. The remarkably well-preserved accumulations provide an alternative example of sponge reefs for comparative paleoenvironmental studies.

  6. First documentation of tidal-channel sponge biostromes (upper Pleistocene, southeastern Florida)

    USGS Publications Warehouse

    Cunningham, K.J.; Rigby, J.K.; Wacker, M.A.; Curran, H.A.

    2007-01-01

    Sponges are not a common principal component of Cenozoic reefs and are more typically dominant in deep-water and/or cold-water localities. Here we report the discovery of extensive upper Pleistocene shallow-marine, tropical sponge biostromes from the Mami Limestone of southeastern Florida built by a new ceractinomorph demosponge. These upright, barrel- to vase-shaped sponges occur in monospecific aggregations constructed within the tidal channels of an oolitic tidal-bar belt similar to modern examples on the Great Bahama Bank. The biostromes appear to have a ribbon-like geometry, with densely spaced sponges populating a paleochannel along a 3.5 km extent in the most lengthy biostrome. These are very large (as high as 2 m and 1.8 m in diameter), particularly well-preserved calcified sponges with walls as hard as concrete. Quartz grains are the most common particles agglutinated in the structure of the sponge walls. Where exposed, sediment fill between the sponges is commonly a highly burrowed or cross-bedded ooid-bearing grainstone and, locally, quartz sand. It is postulated that the dense, localized distribution of these particular sponges was due to a slight edge over competitors for food or energy supply and space in a stressed environment of tidal-influenced salinity and nutrient changes, strong currents, and frequently shifting submarine sand dunes. To our knowledge, this represents the first documentation of sponge biostromes composed of very large upright sponges within high-energy tidal channels between ooid shoals. The remarkably well-preserved accumulations provide an alternative example of sponge reefs for comparative paleoenvironmental studies. ?? 2007 The Geological Society of America.

  7. Turbine Siting Metrics for Simulated Tidal Flow in a Double-Silled Channel

    NASA Astrophysics Data System (ADS)

    Thyng, K. M.; Kawase, M.; Riley, J. J.; Northwest National Marine Renewable Energy Center

    2010-12-01

    An important component of site and resource characterization for marine renewable energy projects is to identify areas with large potential resource but also with easy extractability of the available resource for commercial develop- ment. Metrics that characterize potential resource include mean kinetic power density and speed over a tidal cycle, while important metrics for extractability include measures of the bidirectionality of the tidal flow (asymmetry, directional deviation, and power bias of ebb versus flood tide) as well as percentage of time spent by the device producing power at the particular site. This study examines the character of a tidal flow over an idealized two- dimensional (x-z) double sill in a rectangular channel in terms of these resource characterization metrics. This domain is meant to capture the bulk features of Admiralty Inlet, the main entrance to the Puget Sound, a fjord-like estuary in western Washington State. Admiralty Inlet is an area of interest for build- ing a commercial-scale tidal turbine array, and is currently the location of two potential pilot-scale tidal hydrokinetic projects. Initial results point to the speed up of the incoming flow due to the shallowest sill as an area of strong resource. The presence of the deeper sill affects the character of this strong resource in a way that the metrics can help quantify in terms of extractability of the resource and vertical structure. Together, these metrics will give a clear understanding of the tidal turbine siting characteristics of the domain. In the case of the idealized double sill simulation, the mean speed is increased by a factor of more than 2 over the mean incoming speed at the entrance of the channel due to the shallower, more prominent sill, while the deeper sill sees a multiplication factor of close to 1.5. This is a modest increase in mean speed, but translates to a multiplication factor of over 8 from the nominal far field value near the shallow sill in the mean

  8. The Role of Backwater Hydraulics in Mediating Avulsion Location, Channel Migration Rate, and Delta Shoreline Rugosity

    NASA Astrophysics Data System (ADS)

    Chadwick, A. J.; Lamb, M. P.; Ganti, V.; Hassenruck-Gudipati, H. J.

    2015-12-01

    River deltas earn their name from a characteristic planform-triangular shape, but in reality demonstrate a wide range of morphologies. The sinuosity of delta shorelines, i.e. shoreline rugosity, is particularly variable worldwide even among deltas where waves and tides are not dominant processes. We hypothesize that river-dominated deltas built through construction of depositional lobes develop a characteristic shoreline rugosity that is determined by long-term patterns in avulsion location, avulsion timing, and channel migration, all of which can be strongly influenced by backwater hydrodynamics. Scaling arguments predict that shoreline rugosity should increase linearly with avulsion timescale, inversely with avulsion lengthscale, and inversely with channel lateral migration rate. We present results from two scaled flume experiments that confirm this hypothesis, and furthermore illustrate the importance of backwater hydrodynamics in controlling the dominant rates and scales in a growing delta. Under the case of variable discharge floods that maintain a dynamic backwater zone, avulsions occur at a fixed distance from the shoreline, resulting in the construction of lobes of constant size even during shoreline progradation. In addition, erosion caused by drawdown hydrodynamics during floods eliminates alternating bars, which slows lateral migration of the channel and allows for more elongate delta lobes. Based on these results, and a compilation of modern river-dominated deltas, we propose a new dimensionless phase space for the occurrence backwater-mediated deltas with rugose shorelines.

  9. Peat formation processes through the millennia in tidal marshes of the Sacramento-San Joaquin Delta, California, USA

    USGS Publications Warehouse

    Drexler, Judith Z.

    2011-01-01

    The purpose of this study was to determine peat formation processes throughout the millennia in four tidal marshes in the Sacramento-San Joaquin Delta. Peat cores collected at each site were analyzed for bulk density, loss on ignition, and percent organic carbon. Core data and spline fit age-depth models were used to estimate inorganic sedimentation, organic accumulation, and carbon sequestration rates in the marshes. Bulk density and percent organic matter content of peat fluctuated through time at all sites, suggesting that peat formation processes are dynamic and responsive to watershed conditions. The balance between inorganic sedimentation and organic accumulation at the sites also varied through time, indicating that marshes may rely more strongly on either norganic or organic matter for peat formation at particular times in their existence. Mean carbon sequestration rates found in this study (0.38-0.79 Mg C ha-1 year-1) were similar to other long-term estimates for temperate peatlands.

  10. Sedimentological characterization of flood-tidal delta deposits in the Sego Sandstone, subsidence analysis in the Piceance Creek Basin, and uranium-lead geochronology (NW Colorado, USA)

    NASA Astrophysics Data System (ADS)

    York, Carly C.

    The Sego Sandstone located in western Colorado is a member of the Upper Cretaceous Mesaverde Group and is considered an analogue of the Canadian heavy oil sands. Deposition of the Sego Sandstone occurred during the Upper Campanian (~78 Ma) at the end of the Sevier Orogeny and the beginning of the Laramide Orogeny on the western edge of the Cretaceous Interior Seaway. Although regional studies have detailed time equivalent deposits in the Book Cliffs, UT, the tidally influenced and marginal marine lithofacies observed north of Rangely, CO are distinctly different from the dominately fluvial and tidally-influenced delta facies of Book Cliff outcrops to the southwest. This study characterized flood-tidal delta deposits within the Sego Sandstone, the subsidence history of the Upper Cretaceous sedimentary rocks within the present day Piceance Creek Basin in NW Colorado, and the detrital zircon signal and oldest depositional age of the Sego Sandstone. The goals of this study are to (i) identify relative controls on reservoir characteristics of marginal marine deposits, specifically in flood-tidal delta deposits; (ii) identify the possible mechanisms responsible for subsidence within the present day Piceance Creek Basin during the Late Cretaceous; and (iii) better constrain the provenance and maximum depositional age of the Sego Sandstone. In this study I compared grain size diameter, grain and cement composition, and the ratio of pore space/cement from thin sections collected in tidal, shoreface, and flood-tidal delta facies recognized along detailed measured stratigraphic sections. This analysis provides a detailed comparison between different depositional environments and resultant data showed that grain size diameter is different between tidal, shoreface, and flood-tidal delta facies. Identifying the subsidence mechanisms affecting the Piceance Creek Basin and sediment source of the Late Cretaceous sediments, on the other hand, is important for evaluation of controls

  11. Identification of natural coumarin compounds that rescue defective DeltaF508-CFTR chloride channel gating.

    PubMed

    Xu, Li-Na; Na, Wan-Li; Liu, Xin; Hou, Shu-Guang; Lin, Sen; Yang, Hong; Ma, Tong-Hui

    2008-08-01

    1. Deletion of phenylalanine at position 508 (DeltaF508) of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is the most common mutation causing cystic fibrosis (CF). Effective pharmacological therapy of CF caused by the DeltaF508-CFTR mutation requires the rescue of both intracellular processing and channel gating defects. 2. We identified a class of natural coumarin compounds that can correct the defective DeltaF508-CFTR chloride channel gating by screening a collection of 386 single natural compounds from Chinese medicinal herbs. Screening was performed with an iodide influx assay in Fischer rat thyroid epithelial cells coexpressing DeltaF508-CFTR and an iodide-sensitive fluorescent indicator (YFP-H148Q/I152L). 3. Dose-dependent potentiation of defective DeltaF508-CFTR chloride channel gating by five coumarin compounds was demonstrated by the fluorescent iodide influx assay and confirmed by an Ussing chamber short-circuit current assay. Activation was fully abolished by the specific CFTR inhibitor CFTR(inh)-172. Two potent compounds, namely imperatorin and osthole, have activation K(d) values of approximately 10 micromol/L, as determined by the short-circuit current assay. The active coumarin compounds do not elevate intracellular cAMP levels. Activation of DeltaF508-CFTR by the coumarin compounds requires cAMP agonist, suggesting direct interaction with the mutant CFTR molecule. Kinetics analysis indicated rapid activation of DeltaF508-CFTR by the coumarin compounds, with half-maximal activation of < 5 min. The activating effect was fully reversed for all five active compounds 45 min after washout. 4. In conclusion, the natural coumarin DeltaF508-CFTR activators may represent a new class of natural lead compounds for the development of pharmacological therapies for CF caused by the DeltaF508 mutation.

  12. Tidal Fluctuations in a Deep Fault Extending Under the Santa Barbara Channel, California

    NASA Astrophysics Data System (ADS)

    Garven, G.; Stone, J.; Boles, J. R.

    2013-12-01

    Faults are known to strongly affect deep groundwater flow, and exert a profound control on petroleum accumulation, migration, and natural seafloor seepage from coastal reservoirs within the young sedimentary basins of southern California. In this paper we focus on major fault structure permeability and compressibility in the Santa Barbara Basin, where unique submarine and subsurface instrumentation provide the hydraulic characterization of faults in a structurally complex system. Subsurface geologic logs, geophysical logs, fluid P-T-X data, seafloor seep discharge patterns, fault mineralization petrology, isotopic data, fluid inclusions, and structural models help characterize the hydrogeological nature of faults in this seismically-active and young geologic terrain. Unique submarine gas flow data from a natural submarine seep area of the Santa Barbara Channel help constrain fault permeability k ~ 30 millidarcys for large-scale upward migration of methane-bearing formation fluids along one of the major fault zones. At another offshore site near Platform Holly, pressure-transducer time-series data from a 1.5 km deep exploration well in the South Ellwood Field demonstrate a strong ocean tidal component, due to vertical fault connectivity to the seafloor. Analytical models from classic hydrologic papers by Jacob-Ferris-Bredehoeft-van der Kamp-Wang can be used to extract large-scale fault permeability and compressibility parameters, based on tidal signal amplitude attenuation and phase shift at depth. For the South Ellwood Fault, we estimate k ~ 38 millidarcys (hydraulic conductivity K~ 3.6E-07 m/s) and specific storage coefficient Ss ~ 5.5E-08 m-1. The tidal-derived hydraulic properties also suggest a low effective porosity for the fault zone, n ~ 1 to 3%. Results of forward modeling with 2-D finite element models illustrate significant lateral propagation of the tidal signal into highly-permeable Monterey Formation. The results have important practical implications

  13. Moving beyond the Galloway diagrams for delta classification: Connecting morphodynamic and sediment-mechanistic properties with metrics of delta channel network topology and dynamics

    NASA Astrophysics Data System (ADS)

    Tejedor, A.; Longjas, A.; Caldwell, R. L.; Edmonds, D. A.; Zaliapin, I. V.; Foufoula-Georgiou, E.

    2015-12-01

    Delta channel networks self-organize to a variety of stunning and complex patterns that carry the signature of their climatic and hydro-morphodynamic forcings (e.g., river, tides and waves) and the mechanistic properties of their sediment (e.g., particle size, cohesiveness). Recently, we presented a rigorous framework based on spectral graph theory to study delta channel networks from a topologic (channel connectivity) and dynamic (flux exchange) perspective for advancing our understanding of deltas as complex systems [Tejedor et al., 2015a,b]. The framework enhances the quantitative comparison of deltas and seeks to replace the still qualitative diagrams [Galloway, 1975; Orton and Reading, 1993] by relating the controlling physical mechanisms of delta formation to the spatial patterns they create. Here we examine one controlling factor of river dominated delta evolution, namely the sediment cohesiveness. To explore the dependence of the delta channel network topo-dynamic complexity on sediment composition, we have simulated delta channel networks using a hydro-dynamic model (Delft3D) with varying sediment parameters. The results of our analysis show how complexity metrics are able not only to capture the variability in the delta network structure, but also to quantify the increase of complexity when the sediment composition transitions to coarser grains.

  14. Process-Based Evidence of Coastal Accretion Adjacent to a Natural Inlet and Ebb-Tidal Delta on the North Florida Atlantic Coast

    NASA Astrophysics Data System (ADS)

    Adams, P. N.; Olabarrieta, M.; Keough, K. M.

    2015-12-01

    Physical mechanisms of tidal inlet accretion are difficult to document because of the episodic nature of sediment delivery to the coast from fluvial sources and the complex patterns of current magnitudes and directions arising from the interaction of nearshore waves with ebb-tidal delta bathymetry. Using monthly RTK-GPS field measurements of beach topography adjacent to a natural inlet, we document a shoreline change time series that illustrates a bi-directional, alongshore spreading pattern of accretion following an exceptionally high rainfall-discharge event in May 2009. Numerical modeling of wave set-up and nearshore currents in the vicinity of the inlet and ebb tidal delta produces depth-averaged flow velocity patterns consistent with our field observations of coastal accretion. Our results are in agreement with an accretion mechanism, proposed by other researchers, that involves sediment delivery to the margins of the ebb tidal delta during high velocity ebb flows that accompany large rainfall-discharge events, followed by onshore migration of swash bars during subsequent days to months, at a rate dependent upon the timing of nearshore wave energy delivery to the site.

  15. On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting.

    PubMed

    van Maanen, B; Coco, G; Bryan, K R

    2015-08-08

    An ecomorphodynamic model was developed to study how Avicennia marina mangroves influence channel network evolution in sandy tidal embayments. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. The presence of mangroves was found to enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The enhanced branching of channels is also the result of a vegetation-induced increase in erosion threshold. On the other hand, this reduction in bed erodibility, together with the soil expansion driven by organic matter production, reduces the landward expansion of channels. The ongoing accretion in mangrove forests ultimately drives a reduction in tidal prism and an overall retreat of the channel network. During sea-level rise, mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone, while hindering both the branching and headward erosion of the landward expanding channels. The modelling results presented here indicate the critical control exerted by ecogeomorphological interactions in driving landscape evolution.

  16. On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting

    PubMed Central

    van Maanen, B.; Coco, G.; Bryan, K. R.

    2015-01-01

    An ecomorphodynamic model was developed to study how Avicennia marina mangroves influence channel network evolution in sandy tidal embayments. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. The presence of mangroves was found to enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The enhanced branching of channels is also the result of a vegetation-induced increase in erosion threshold. On the other hand, this reduction in bed erodibility, together with the soil expansion driven by organic matter production, reduces the landward expansion of channels. The ongoing accretion in mangrove forests ultimately drives a reduction in tidal prism and an overall retreat of the channel network. During sea-level rise, mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone, while hindering both the branching and headward erosion of the landward expanding channels. The modelling results presented here indicate the critical control exerted by ecogeomorphological interactions in driving landscape evolution. PMID:26339195

  17. Differentiation of delta-front and barrier lithofacies of the Upper Cretaceous Pictured Cliffs Sandstone, southwest San Juan Basin, New Mexico.

    USGS Publications Warehouse

    Flores, R.M.; Erpenbeck, Michael F.

    1981-01-01

    This Sandstone represents a regressive littoral marine unit deposited during the final retreat of the Cretaceous epeiric sea. Differences in rock type, internal and penecontemporaneous deformation structures, textural sequences, mineral composition and trace fossil content permit recognition of laterally contemporaneous delta-front and barrier lithofacies. The delta-front lithofacies consists of distal bar, distributary mouth bar, and distributary channel deposits. The barrier lithofacies consists of shoreface, beach, washover channel, tidal inlet, tidal channel, and ebb-tidal delta deposits; these lithofacies are coarsening-upward sequences of shale, siltstone and sandstone, locally scoured in the upper part by fining-upward channel deposits.-from Authors

  18. Turbulence Measurements from a Moored Platform at Mid-Depth in a Swift Tidal Channel

    NASA Astrophysics Data System (ADS)

    Hay, Alex; Lueck, Rolf; Wolk, Fabian; McMillan, Justine

    2014-05-01

    Results are presented from a turbulence experiment with a 3-m long streamlined floatation body, instrumented with velocity shear probes, fast-response thermistors, a 1 MHz Acoustic Doppler Current Profiler (AD2CP), and an Acoustic Doppler Velocimeter (ADV). The system was deployed over seven tidal cycles at mid-depth in a 30-m deep tidal channel in the lower Bay of Fundy, Canada. Peak flow speeds exceeded 2 m s-1, and while 10-min time scale average speeds were similar between ebb and flood, the variances were markedly higher during flood. Turbulent kinetic energy (TKE) dissipation rates measured with the shear probes exhibit a pronounced flood/ebb contrast: O(10-4) W kg-1 peak values during flood, but lower by an order of magnitude during ebb. Dissipation rates follow u3 scaling over a wide range of flow speeds between 0.5 and 2.5 m s-1. Below 0.5 m s-1 an asymmetry in the mounting arrangement caused the floatation body to pitch upward, biasing the measured dissipation values high. The ADV on the platform registered mean speed - used to implement Taylor's hypothesis - which was corroborated with the platform-mounted ADCP. Additional ADCPs were also deployed on a nearby bottom pod, sampling at turbulence resolving rates - up to 8 Hz. Comparisons between the shear probe and acoustic estimates of the TKE spectrum and dissipation rate - at comparable depths - are presented.

  19. Soil phosphorus forms and profile distributions in the tidal river network region in the Yellow River Delta estuary.

    PubMed

    Yu, Junbao; Qu, Fanzhu; Wu, Huifeng; Meng, Ling; Du, Siyao; Xie, Baohua

    2014-01-01

    Modified Hedley fraction method was used to study the forms and profile distribution in the tidal river network region subjected to rapid deposition and hydrologic disturbance in the Yellow River Delta (YRD) estuary, eastern China. The results showed that the total P (Pt) ranged from 612.1 to 657.8 mg kg(-1). Dilute HCl extractable inorganic P (Pi) was the predominant form in all profiles, both as absolute values and as a percentage of total extracted Pi. The NaOH extractable organic P (Po) was the predominant form of total extracted Po, while Bicarb-Pi and C.HCl-Po were the lowest fractions of total extracted Pi and Po in all the P forms. The Resin-P concentrations were high in the top soil layer and decreased with depth. The Pearson correlation matrix indicated that Resin-P, Bicarb-Pi, NaOH-Pi, and C.HCl-Pi were strongly positively correlated with salinity, TOC, Ca, Al, and Fe but negatively correlated with pH. The significant correlation of any studied form of organic P (Bicarb-Po, NaOH-Po, and C.HCl-Po) with geochemical properties were not observed in the study. Duncan multiple-range test indicated that the P forms and distribution heterogeneity in the profiles could be attributed to the influences of vegetation cover and hydrologic disturbance.

  20. Peat Formation Processes Through the Millennia in Tidal Marshes of the Sacramento-San Joaquin Delta, California, USA

    USGS Publications Warehouse

    Drexler, J.Z.

    2011-01-01

    The purpose of this study was to determine peat formation processes throughout the millennia in four tidal marshes in the Sacramento-San Joaquin Delta. Peat cores collected at each site were analyzed for bulk density, loss on ignition, and percent organic carbon. Core data and spline fit age-depth models were used to estimate inorganic sedimentation, organic accumulation, and carbon sequestration rates in the marshes. Bulk density and percent organic matter content of peat fluctuated through time at all sites, suggesting that peat formation processes are dynamic and responsive to watershed conditions. The balance between inorganic sedimentation and organic accumulation at the sites also varied through time, indicating that marshes may rely more strongly on either inorganic or organic matter for peat formation at particular times in their existence. Mean carbon sequestration rates found in this study (0. 38-0. 79 Mg C ha-1 year-1) were similar to other long-term estimates for temperate peatlands. ?? 2011 Coastal and Estuarine Research Federation (outside the USA).

  1. Structural requirement of the calcium-channel subunit alpha2delta for gabapentin binding.

    PubMed Central

    Wang, M; Offord, J; Oxender, D L; Su, T Z

    1999-01-01

    Gabapentin [Neurontin, 1-(aminomethyl)cyclohexaneacetic acid] is a novel anticonvulsant drug with a high binding affinity for the Ca(2+)-channel subunit alpha(2)delta. In this study, the gabapentin-binding properties of wild-type and mutated porcine brain alpha(2)delta proteins were investigated. Removal of the disulphide bonds between the alpha(2) and the delta subunits did not result in a significant loss of gabapentin binding, suggesting that the disulphide linkage between the two subunits is not required for binding. Singly expressed alpha(2) protein remained membrane associated. However, alpha(2) alone was unable to bind gabapentin, unless the cells were concurrently transfected with the expression vector for delta, suggesting that both alpha(2) and delta are required for gabapentin binding. Using internal deletion mutagenesis, we mapped two regions [amino acid residues 339-365 (DeltaF) and 875-905 (DeltaJ)] within the alpha(2) subunit that are not required for gabapentin binding. Further, deletion of three other individual regions [amino acid residues 206-222 (DeltaD), 516-537 (DeltaH) and 583-603 (DeltaI)] within the alpha(2) subunit disrupted gabapentin binding, suggesting the structural importance of these regions. Using alanine to replace four to six amino acid residues in each of these regions abolished gabapentin binding. These results demonstrate that region D, between the N-terminal end and the first putative transmembrane domain of alpha(2), and regions H and I, between the putative splicing acceptor sites (Gln(511) and Ser(601)), may play important roles in maintaining the structural integrity for gabapentin binding. Further single amino acid replacement mutagenesis within these regions identified Arg(217) as critical for gabapentin binding. PMID:10455017

  2. Long-term morphological response to dredging including cut-across-shoal in a tidal channel-shoal system

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Hai; Wang, Chong-Hao; Tang, Li-Qun; Liu, Da-Bin; Guo, Chuan-Sheng; Liu, Chun-Jing; Zhao, Hui-Ming

    2014-12-01

    This study examines long-term channel-shoal stability in the Tieshan Bay, which is located on the southwest coast of China. A large-scale channel-shoal system has historically existed in the outer Tieshan Bay. A navigation waterway is initiated by cutting and dredging a mid-channel shoal to supply coal to a power plant on the middle coast of the Tieshan Bay. Dredging of the access channel to the Tieshan Port was conducted in two stages followed by land reclamation. It is thus of practical meaning to explore how the channel-shoal system will evolve in long term afterwards. This study uses the process-based finite-volume coastal ocean model (FVCOM) to investigate long-term (centennial) morphological evolution of the channel-shoal system. After well calibration of hydrodynamics and sediment transport, the model forecasts morphodynamic evolution in hundred years. The simulations show that continuous erosion in tidal channels and accretion over shoals and intertidal flats occur. However, the cutting and access channels will be subjected to long-term siltation. A secondary channel indicating the reorientation of the access channel will emerge, and a localized channel-ridge system at the junction of the major channels will be formed. The overall erosion/accretion pattern demonstrates the combined effect of bottom friction and advective sediment transport processes to be responsible for the channel-shoal formation. Dredging of the tidal channels will stimulate the stability of the channel-shoal pattern. It suggests that the navigation waterway should be set up following the long-term morphological evolution of the channel-shoal system at a design stage and maintenance dredging volume might thus be minimized.

  3. Tide-driven variations of sediment suspension over large bedforms in a tidal inlet channel

    NASA Astrophysics Data System (ADS)

    Kwoll, E. K.; Becker, M.; Ernstsen, V. B.; Winter, C.

    2012-12-01

    In the presence of bedforms, erosion and vertical mixing of suspended sediment is governed by the bedform-induced turbulent flow field. Subject to strong velocity gradients and regular reversion of the flow, analysis of suspended-load patterns in tidal inlets requires high-resolution in-situ observations of bedform morphology, turbulent flow field and suspended sediment variability on short time scales such as a tidal cycle. Aim of this study is to quantify the relative contribution of suspended load to the sedimentary budget of a bedform field in the high-energy environment of a tidal channel. Serving as a major transport pathway to and from the inlet, suspension processes within the channel are of vital importance for the overall inlet morphology. In the Danish Wadden Sea, ship-based in-situ measurements of combined acoustic Doppler current profiling (1200 and 300 kHz ADCP) and multibeam echosounding (MBES) were carried out along a longitudinal bedform transect and stationary above the bedform stoss-side and crest. Simultaneously, a multi-sensor probe equipped with laser in-situ scattering transmissometry (LISST) and conductivity, temperature, depth sensor (CTD) was lowered into the water column and coupled online with the ADCPs in the ViSea Plume Detection Toolbox (©Aquavison). Combining the acoustic and optical backscatter signals of these instruments enabled real-time detection of suspended sediment structures. Water samples were taken from within the structures by means of a water pump located on the multi-sensor probe. Surveyed ebb-directed bedforms were on average 6.5 m high and 200 m long (lee-side angles of 12-18 °) and located in approximately 15 m water depth. The tidal range comprised 1.8 m with asymmetric currents (max. ebb flow: 1.5 m/s and max. flood flow: 1.1 m/s) following a plateau-shaped signature of strong velocity gradients during acceleration and deceleration. The topographic forcing of the flow was consistently evident: flow acceleration

  4. Optimization of multiple turbine arrays in a channel with tidally reversing flow by numerical modelling with adaptive mesh.

    PubMed

    Divett, T; Vennell, R; Stevens, C

    2013-02-28

    At tidal energy sites, large arrays of hundreds of turbines will be required to generate economically significant amounts of energy. Owing to wake effects within the array, the placement of turbines within will be vital to capturing the maximum energy from the resource. This study presents preliminary results using Gerris, an adaptive mesh flow solver, to investigate the flow through four different arrays of 15 turbines each. The goal is to optimize the position of turbines within an array in an idealized channel. The turbines are represented as areas of increased bottom friction in an adaptive mesh model so that the flow and power capture in tidally reversing flow through large arrays can be studied. The effect of oscillating tides is studied, with interesting dynamics generated as the tidal current reverses direction, forcing turbulent flow through the array. The energy removed from the flow by each of the four arrays is compared over a tidal cycle. A staggered array is found to extract 54 per cent more energy than a non-staggered array. Furthermore, an array positioned to one side of the channel is found to remove a similar amount of energy compared with an array in the centre of the channel.

  5. Delta channel networks: 1. A graph-theoretic approach for studying connectivity and steady state transport on deltaic surfaces

    NASA Astrophysics Data System (ADS)

    Tejedor, Alejandro; Longjas, Anthony; Zaliapin, Ilya; Foufoula-Georgiou, Efi

    2015-06-01

    River deltas are intricate landscapes with complex channel networks that self-organize to deliver water, sediment, and nutrients from the apex to the delta top and eventually to the coastal zone. The natural balance of material and energy fluxes, which maintains a stable hydrologic, geomorphologic, and ecological state of a river delta, is often disrupted by external perturbations causing topological and dynamical changes in the delta structure and function. A formal quantitative framework for studying delta channel network connectivity and transport dynamics and their response to change is lacking. Here we present such a framework based on spectral graph theory and demonstrate its value in computing delta's steady state fluxes and identifying upstream (contributing) and downstream (nourishment) areas and fluxes from any point in the network. We use this framework to construct vulnerability maps that quantify the relative change of sediment and water delivery to the shoreline outlets in response to possible perturbations in hundreds of upstream links. The framework is applied to the Wax Lake delta in the Louisiana coast of the U.S. and the Niger delta in West Africa. In a companion paper, we present a comprehensive suite of metrics that quantify topologic and dynamic complexity of delta channel networks and, via application to seven deltas in diverse environments, demonstrate their potential to reveal delta morphodynamics and relate to notions of vulnerability and robustness.

  6. Altered mangrove wetlands as habitat for estuarine nekton: are dredged channels and tidal creeks equivalent?

    USGS Publications Warehouse

    Krebs, Justin M.; Brame, Adam B.; McIvor, Carole C.

    2007-01-01

    Hasty decisions are often made regarding the restoration of "altered" habitats, when in fact the ecological value of these habitats may be comparable to natural ones. To assess the "value" of altered mangrove-lined habitats for nekton, we sampled for 1 yr within three Tampa Bay wetlands. Species composition, abundance, and spatial distribution of nekton assemblages in permanent subtidal portions of natural tidal creeks and wetlands altered by construction of mosquito-control ditches and stormwater-drainage ditches were quantified through seasonal seine sampling. Results of repeated-measures analysis of variance and ordination of nekton community data suggested differences in species composition and abundance between natural and altered habitat, though not consistently among the three wetlands. In many cases, mosquito ditches were more similar in assemblage structure to tidal creeks than to stormwater ditches. In general, mosquito ditches and stormwater ditches were the most dissimilar in terms of nekton community structure. These dissimilarities were likely due to differences in design between the two types of ditches. Mosquito ditches tend to fill in over time and are thus more ephemeral features in the landscape. In contrast, stormwater ditches are a more permanent altered habitat that remain open due to periodic flushing from heavy runoff. Results indicate that environmental conditions (e.g., salinity, current velocity, vegetative structure) may provide a more useful indication of potential habitat "value" for nekton than whether the habitat has been altered. The type of ditching is therefore more important than ditching per se when judging the habitat quality of these altered channels for fishes, shrimps and crabs. Planning should entail careful consideration of environmental conditions rather than simply restoring for restoration's sake.

  7. Toward a Reduced Complexity Channel Resolving Model for Sedimentary Delta Formation

    NASA Astrophysics Data System (ADS)

    Liang, M.; Voller, V. R.; Edmonds, D. A.; Paola, C.

    2010-12-01

    Predicting styles of delta growth in restoration areas is a challenge as we try to restore impacted coastlines. Cellular and rule-based reduced complexity models offer a worthwhile means of uncovering key dynamics in delta morphodynamics without the need to fully solve the governing transport equations. In terms of modeling sedimentary delta building processes a critical ingredients is accounting for the formation and bifurcation of channels; phenomena that can be related to the formation of levees and mouth-bars. To that end, we have developed a reduced complexity model that uses a simplified shallow-water solver to study channel formation, mouth bar deposition, and delta development under different forcings. Under the assumption that the flow has a very low Froude Number (Fr2<<1), the inertia term is dropped out and only the gravitational term and friction term remain in the momentum equation. The coupled mass conservation equation becomes a non-linear diffusive equation, which is linearized by a Kirchhoff transformation. Directional diffusivity is added to this system to compensate the loss of inertia and promote spreading of the turbulent jet. We test the reduced model against flow over Gaussian-shaped bumps of various heights. Comparison of results from this model with results from a full scale commercial code (Delft3D) show a satisfactory agreement on the critical mouth bar height needed to divert flow around the bar. Based on the same diffusive equation, we develop a low-Froude water-routing method for reduced complexity morphodynamics models. The preliminary results show that the method is capable of producing reasonable channel forms and mouth bar formation, and provides a good starting point for development of a channel resolving delta building model.

  8. Ecology of Juvenile Salmonids in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, Lower Columbia River, 2007

    SciTech Connect

    Sobocinski, Kathryn L.; Johnson, Gary E.; Sather, Nichole K.; Storch, Adam; Jones, Tucker A.; Mallette, Christine; Dawley, Earl M.; Skalski, John R.; Teel, David; Moran, Paul

    2008-03-18

    This document is the first annual report for the study titled “Ecology of Juvenile Salmonids in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta in the Lower Columbia River.” Hereafter, we refer to this research as the Tidal Freshwater Monitoring (TFM) Study. The study is part of the research, monitoring, and evaluation effort developed by the Action Agencies (Bonneville Power Administration, U.S. Army Corps of Engineers, U.S. Bureau of Reclamation) in response to obligations arising from the Endangered Species Act as a result of operation of the Federal Columbia River Power System (FCRPS). The project is performed under the auspices of the Northwest Power and Conservation Council’s Columbia Basin Fish and Wildlife Program.

  9. Eocene tidal deposits, northern San Diego County, California

    SciTech Connect

    Eisenberg, L.I.; Abbott, P.L.

    1985-02-01

    A transgressive-regressive sedimentation sequence is recorded in a band of middle Eocene strata a few miles wide. An abundance of primary sedimentary structures, along with interfingering relationships and paleontology, define 12 lithofacies representing depositional environments including nearshore shelf, outer and inner barrier island, tidal flats and channels, lagoon and lagoonal delta. Tide-influenced sedimentary features are well defined and include meandering and abandoned tidal channels, oppositely inclined superimposed cross-strata, interlaminated mud and sand along the basal and lateral accretion surfaces of migrating tidal channels, flaser and wavy bedding, and storm-deposited strata. The first sedimentary half cycle was transgressive and documents the compression of dominantly tidal-flat and lagoonal environments against a steep, hilly coastline by the overall rising sea level of early and medial middle Eocene time. The inboard tidal-flat and lagoonal mudstones (Delmar and Friars Formations) and outboard tidal flat, channel and bar sandstones (Torrey Sandstone and Scripps Formation) interfinger in a landward-climbing, 3-dimensional sedimentary mass that parallels and meets the basement with a pronounced unconformity. The second half cycle was regressive and occurred in the medial and late middle Eocene. It formed due to the influx of coarser, more angular sediment from the adjacent basement into the narrowed paralic zone. This westward (seaward) progradation of lagoonal delta and inner tidal-flat sandy sediments occurred despite the still-rising sea level.

  10. Adjustment of Submarine Channel Architecture to Changes in Sediment Supply, Western Niger Delta Slope

    NASA Astrophysics Data System (ADS)

    Jobe, Z. R.; Sylvester, Z.; Parker, A. O.; Pirmez, C.; Slowey, N. C.

    2013-12-01

    Three-dimensional seismic, piston cores, and autonomous underwater vehicle data (chirp sub-bottom profiles, multibeam bathymetry, and sidescan sonar) provide a multi-scale dataset used to examine the evolution of a submarine channel system on the western Niger Delta continental slope. Four phases of channel evolution are documented that are interpreted to relate to changes in the sediment routing system. The first phase is incisional and creates a large valley within which the subsequent phases evolve. The second phase records the development of sinuosity through lateral accretion of the meander bends. Meander cutoffs and channel-bank mass wasting result in terraced and scalloped channel margins. This phase is volumetrically most significant in terms of channel fill. The third phase is characterized by thalweg aggradation with slight channel narrowing; preferential deposition towards the outer banks results in a reduction of sinuosity. This phase likely reflects the updip abandonment of the channel system. The fourth phase is characterized by inner levee deposition that occurs primarily on outer banks, causing a reduction in channel width and sinuosity. These changes are caused by the capture of a small slope channel that is the source for underfit flows that attempt to adjust the channel cross section and thalweg gradient through inner levee deposition. Chirp sub-bottom profiles and piston core data reveal that these sigmoidal inner levees consist of thin-bedded, ripple-laminated turbidites interbedded with mudstones. The channel thalweg consists of amalgamated, sand-rich turbidites with dune-scale bedforms and occasional mass transport deposits. Core transects taken across the channel demonstrate that sand bed thickness decreases with height above the channel thalweg. Laser particle size analyzer data indicate a progressive decrease in grain size with height above the channel thalweg. These vertical trends in grain size and bed thickness distribution are used to

  11. Dune convergence/divergence controlled by residual current vortices in the Jade tidal channel, south-eastern North Sea

    NASA Astrophysics Data System (ADS)

    Kubicki, Adam; Kösters, Frank; Bartholomä, Alexander

    2017-02-01

    A field of large to very large subaqueous dunes was investigated in the Jade tidal channel, south-eastern North Sea, between January 2006 and October 2011. A ground-truthed sidescan sonar sediment map shows that the dunes, which are located on top of a consolidated clay surface, are composed of medium to coarse sand. A series of 35 consecutive high-resolution bathymetric surfaces collected by multibeam echosounder revealed a complex migration pattern induced by the reversing tidal currents. Various parts of the dune field are under the influence of either ebb- or flood-dominated currents, as indicated by dune asymmetries. Although some dunes migrate at a pace exceeding 100 m/year, the majority are displaced by 30 m/year in the direction of the locally dominant current. In the deepest part of the channel, however, dunes were observed to converge head-on, resulting in practically zero net transport with minor oscillations of symmetrical dunes at the apex. Applying the numerical UnTRIM model for the simulation of the fair-weather hydrology, a simplified map of residual current vectors over the dune field was generated. The residual flow vectors are found to perfectly match the derived dune migration vectors, suggesting that dune convergence is controlled by two counter-rotating residual current vortices caused by the local shape of the tidal channel. As no sediment build-up is observed, a mechanism of sediment bypassing with potential recirculation must exist, but has not yet been identified.

  12. Recent morphological changes in the Mekong and Bassac river channels, Mekong delta: The marked impact of river-bed mining and implications for delta destabilisation

    NASA Astrophysics Data System (ADS)

    Brunier, Guillaume; Anthony, Edward J.; Goichot, Marc; Provansal, Mireille; Dussouillez, Philippe

    2014-11-01

    The Mekong delta, in Vietnam, is the world's third largest delta. Densely populated, the delta has been significantly armoured with engineering works and dykes to protect populations and infrastructure from storms, and shrimp farms from saltwater intrusion. Considerable development pressures in Vietnam and in the upstream countries have resulted in the construction of several dams in China and in important channel-bed aggregate extractions especially in Cambodia. The effects of these developments impact the delta dynamics in various ways. In this study, changes in the channel morphology of the Mekong proper and the Bassac, the two main distributaries in the 250 km-long deltaic reach from the Cambodian border to the coast, were analysed using channel depth data for 1998 and 2008. The channels display important and irregular bed changes over the 10-year comparison period, including significant incision and expansion and deepening of numerous pools. The mean depth of both channels increased by more than 1.3 m. Both channels also showed correlative significant bed material losses: respectively 90 million m3 in the Mekong and 110 million m3 in the Bassac over the 10-year period. These important losses over a relatively short period, and weak correlations between bed incision and hydraulic parameters suggest that the marked morphological changes are not in equilibrium with flow and sediment entrainment conditions, and are therefore not related to changes in river hydrology. We claim that aggregate extraction, currently practised on a very large scale in the Mekong delta channels and upstream of the delta, is the main cause of these recent morphological changes. These changes are deemed to contribute actively to rampant bank erosion in the delta as well as to erosion of the Mekong delta shoreline. Other contributory activities include the numerous dykes and embankments. The role of existing dams in bed losses remains unclear in the absence of reliable data on the Mekong

  13. Modelling of the flow field surrounding tidal turbine arrays for varying positions in a channel.

    PubMed

    Daly, T; Myers, L E; Bahaj, A S

    2013-02-28

    The modelling of tidal turbines and the hydrodynamic effects of tidal power extraction represents a relatively new challenge in the field of computational fluid dynamics. Many different methods of defining flow and boundary conditions have been postulated and examined to determine how accurately they replicate the many parameters associated with tidal power extraction. This paper outlines the results of numerical modelling analysis carried out to investigate different methods of defining the inflow velocity boundary condition. This work is part of a wider research programme investigating flow effects in tidal turbine arrays. Results of this numerical analysis were benchmarked against previous experimental work conducted at the University of Southampton Chilworth hydraulics laboratory. Results show significant differences between certain methods of defining inflow velocities. However, certain methods do show good correlation with experimental results. This correlation would appear to justify the use of these velocity inflow definition methods in future numerical modelling of the far-field flow effects of tidal turbine arrays.

  14. A Comparison of Peat Formation Processes over Recent and Millennial Time Scales in Tidal Marshes of the Sacramento-San Joaquin Delta, California

    NASA Astrophysics Data System (ADS)

    Drexler, J. Z.

    2012-12-01

    The Sacramento-San Joaquin Delta, which is found at the landward edge of the San Francisco Estuary, was once a vast temperate peatland with 1400 km2 of tidal marshes and waterways. Subsequent to reclamation for farming, only a few remnant marshes remain today. The peat formation processes of four of these marshes were examined over recent (the past 40-50 years) and millennial time scales (the entire lifetime of each marsh: 2500-6300 years). Two marshes, Browns Island and the Tip of Mandeville Tip, are located in high energy hydrogeomorphic zones and two other marshes, Franks Wetland and Bacon Channel Island, are located in low energy hydrogeomorphic zones. Peat cores were collected at these island marshes between 2005-2010. Cores were sectioned and analyzed for bulk density, percent organic matter, percent organic carbon, 210Pb, 137Cs, and 14C. Mean vertical accretion rates ranged from 0.19 to 0.73 cm yr-1 during the past 40-50 years and 0.12 to 0.18 cm yr-1 over the lifetime of the marshes. Both recent and millennial vertical accretion rates bracket sea-level rise estimates for their prospective time periods. Millennial accretion rates are 25-84% of the recent rates. Mass accumulation rates were 0.05 to 0.27 g cm-2 yr-1 during the past 40-50 years and 0.01 to 0.04 g cm-2 yr-1 over the lifetime of the marshes. The millennial mass accumulation rates are 15-81% of the recent mass accumulation rates. Recent carbon sequestration rates were a fraction of millennial rates, which spanned from 40-80 g organic carbon m-2 yr-1. Rates of vertical accretion, mass accumulation, and carbon sequestration were generally greater in the high energy hydrogeomorphic zones than the low energy hydrogeomorphic zones. Peat formation processes are strongly linked to watershed processes as well as anthropogenic disturbance including land-use change, urbanization, and hydraulic gold mining during the past 150 years.

  15. Processes governing decadal-scale depositional narrowing of the major tidal channel in San Pablo Bay, California, USA

    NASA Astrophysics Data System (ADS)

    Wegen, M.; Jaffe, B. E.

    2014-05-01

    Bathymetric measurements show that a deep, subtidal channel in San Pablo Bay, California, has consistently narrowed during the past 150 years. This raises general questions on the seasonal and intertidal morphodynamic processes acting at the subtidal channel-shoal interface. The current work addresses these questions using a process-based morphodynamic model (Delft3D). Model results reveal considerable morphodynamic activity during a tidal cycle. Deposition on the channel margin is largest during flooding of the shoals. Erosion rates (mainly occuring during ebb) remain relatively small, so that net accretion occurs on much of the channel margin. A remarkable finding is that locally generated wind waves are responsible for shoal extension and depositional channel narrowing. High suspended sediment concentration (SSC) in the channel is a critical factor. Apart from sediment supply during high river flow, wind waves suspending sediment on the shoals cause high SSC levels in the channel at ebb. Sensitivity analysis shows that wind direction even determines the location of channel margin accretion. Fluvial sediment supply is another cause of high SSC in the channel. Density currents, 3-D circulation flows, sea level rise, or varied sediment characteristics only have a limited effect on the erosion and sedimentation patterns. A 30 year forecast shows that deeper shoals and decreasing fluvial sediment supply lower SSC levels in the channel, limit channel margin accretion, and even lead to net channel margin erosion in some areas. Channel shape thus remains subject to dynamic processes related to local variations in sediment supply, albeit to a more limited extent than in earlier decades.

  16. Inhibition of recombinant human T-type calcium channels by Delta9-tetrahydrocannabinol and cannabidiol.

    PubMed

    Ross, Hamish Redmond; Napier, Ian; Connor, Mark

    2008-06-06

    Delta(9)-Tetrahydrocannabinol (THC) and cannabidiol (CBD) are the most prevalent biologically active constituents of Cannabis sativa. THC is the prototypic cannabinoid CB1 receptor agonist and is psychoactive and analgesic. CBD is also analgesic, but it is not a CB1 receptor agonist. Low voltage-activated T-type calcium channels, encoded by the Ca(V)3 gene family, regulate the excitability of many cells, including neurons involved in nociceptive processing. We examined the effects of THC and CBD on human Ca(V)3 channels stably expressed in human embryonic kidney 293 cells and T-type channels in mouse sensory neurons using whole-cell, patch clamp recordings. At moderately hyperpolarized potentials, THC and CBD inhibited peak Ca(V)3.1 and Ca(V)3.2 currents with IC(50) values of approximately 1 mum but were less potent on Ca(V)3.3 channels. THC and CBD inhibited sensory neuron T-type channels by about 45% at 1 mum. However, in recordings made from a holding potential of -70 mV, 100 nm THC or CBD inhibited more than 50% of the peak Ca(V)3.1 current. THC and CBD produced a significant hyperpolarizing shift in the steady state inactivation potentials for each of the Ca(V)3 channels, which accounts for inhibition of channel currents. Additionally, THC caused a modest hyperpolarizing shift in the activation of Ca(V)3.1 and Ca(V)3.2. THC but not CBD slowed Ca(V)3.1 and Ca(V)3.2 deactivation and inactivation kinetics. Thus, THC and CBD inhibit Ca(V)3 channels at pharmacologically relevant concentrations. However, THC, but not CBD, may also increase the amount of calcium entry following T-type channel activation by stabilizing open states of the channel.

  17. Effects of the El Mayor Cucapah April 4, 2010 earthquake and water management decisions on the Colorado River Delta tidal inundation patterns: implications for shorebirds habitat availability

    NASA Astrophysics Data System (ADS)

    Gomez-Sapiens, M.; Flessa, K. W.; Glenn, E. P.; Nelson, S. M.

    2010-12-01

    The Upper Gulf of California and Colorado River Delta (CRD) provide feeding and resting areas for migratory and resident shorebirds. Coastal and inland wetlands create a variety of habitats that support 31 shorebird species. Total shorebirds during the winter and spring migration ranges from 56,156 to 195,073. The Cienega de Santa Clara is an artificial wetland that receives saline water inflows from the United States, and the southeastern portion (the Santa Clara Slough) receives a mix of brackish effluent from the Cienega and occasional tidal inundation during extreme high tides. This transitional wetland between the sea and the land is one of the main shorebird aggregation areas within the CRD, supporting 29 to 75% of the individuals using the entire Upper Gulf and CRD. The Cienega de Santa Clara is currently experiencing a 30% reduction in inflows due to operation of the Yuma Desalting Plant in the United States. The 2010 Baja California earthquake caused changes in the tidal water inflows patterns in the delta. Time sequence Landsat images and aerial observations showed that a new wetland area has been created since tidal water inflows are now diverted from the southeast edge of the Cienega to the southwest areas due to subsidence effects. The aim of this study was to document the changes in the shorebird inland habitats to predict shifts in shorebird habitat use by using aerial and ground surveys before and after the earthquake. Preliminary results shows that some of the areas with a high density of shorebird use has dried out mainly as a consequence of the reduction in water inflows to the Cienega from the United States and diversion of water from the Santa Clara Slough to the new tidal basins northwest of the Slough. Aerial surveys suggest that shorebirds were not yet visiting the new wetland area during the past spring migration and were more abundant over the San Felipe coastline and Montague Island. Shorebird habitat has been influenced by a combination

  18. Using Hydrological Modeling to Explain Patterns of Habitat Use by Fishes and Crustaceans in Channelized Tidal Wetlands

    NASA Astrophysics Data System (ADS)

    Krebs, J. M.; Hearn, C. J.; McIvor, C. C.; Brame, A. B.

    2006-12-01

    Wetland ditching for mosquito control and stormwater drainage has undoubtedly affected patterns of water flow in tidal wetlands throughout the United States. Ditches alter the hydrological regime by diverting water from natural channels and by concentrating discharge thereby reducing sheet flow from the marsh surface. Hydrological instruments can be used to measure parameters like water level, current velocity, and salinity for comparison of flow regime between natural and altered tidal channels. Surveys of fish habitat use can be used to quantify differences in species composition and abundance between natural and altered wetlands. By integrating both hydrology and ecology, models can be developed to better explain the processes that underlie physical and biological differences between natural and hydrologically altered tidal wetlands. Here we present some of our early work to describe hydrology and fish habitat use in a hydrologically altered mangrove wetland in Tampa Bay. We hope that the results of this study will provide a useful contrast to data collected following hydrological restoration of the wetland.

  19. Solution structure of delta-Am2766: a highly hydrophobic delta-conotoxin from Conus amadis that inhibits inactivation of neuronal voltage-gated sodium channels.

    PubMed

    Sarma, Siddhartha P; Kumar, G Senthil; Sudarslal, S; Iengar, Prathima; Ramasamy, P; Sikdar, Sujit K; Krishnan, K S; Balaram, Padmanabhan

    2005-04-01

    The three-dimensional (3D) NMR solution structure (MeOH) of the highly hydrophobic delta-conotoxin delta-Am2766 from the molluscivorous snail Conus amadis has been determined. Fifteen converged structures were obtained on the basis of 262 distance constraints, 25 torsion-angle constraints, and ten constraints based on disulfide linkages and H-bonds. The root-mean-square deviations (rmsd) about the averaged coordinates of the backbone (N, C(alpha), C) and (all) heavy atoms were 0.62+/-0.20 and 1.12+/-0.23 A, respectively. The structures determined are of good stereochemical quality, as evidenced by the high percentage (100%) of backbone dihedral angles that occupy favorable and additionally allowed regions of the Ramachandran map. The structure of delta-Am2766 consists of a triple-stranded antiparallel beta-sheet, and of four turns. The three disulfides form the classical 'inhibitory cysteine knot' motif. So far, only one tertiary structure of a delta-conotoxin has been reported; thus, the tertiary structure of delta-Am2766 is the second such example. Another Conus peptide, Am2735 from C. amadis, has also been purified and sequenced. Am2735 shares 96% sequence identity with delta-Am2766. Unlike delta-Am2766, Am2735 does not inhibit the fast inactivation of Na+ currents in rat brain Na(v)1.2 Na+ channels at concentrations up to 200 nM.

  20. DELTAE

    SciTech Connect

    Ward, W.C. ); Swift, G.W. )

    1993-11-01

    In thermoacoustic engines and refrigerators, and in many simple acoustic systems, a one dimensional wave equation determines the spatial dependence of the acoustic pressure and velocity. DELTAE numerically integrates such wave equations in the acoustic approximation, in gases or liquids, in user-defined geometries. Boundary conditions can include conventional acoustic boundary conditions of geometry and impedance, as well as temperature and thermal power in thermoacoustic systems. DELTAE can be used easily for apparatus ranging from simple duct networks and resonators to thermoacoustic engines refrigerators and combinations thereof. It can predict how a given apparatus will perform, or can allow the user to design an apparatus to achieve desired performance. DELTAE views systems as a series of segments; twenty segment types are supported. The purely acoustic segments include ducts and cones, and lumped impedances including compliances, series impedances, and endcaps. Electroacoustics tranducer segments can be defined using either frequency-independent coefficients or the conventional parameters of loudspeaker-style drivers: mass, spring constant, magnetic field strength, etc. Tranducers can be current driven, voltage driven, or connected to an electrical load impedance. Thermoacoustic segment geometries include parallel plates, circular and rectangular pores, and pin arrays. Side branches can be defined with fixed impedances, frequency-dependent radiation impedances, or as an auxiliary series of segments of any types. The user can select working fluids from among air, helium, neon, argon, hydrogen, deuterium, carbon dioxide, nitrogen, helium-argon mixtures, helium-xenon mixtures, liquid sodium, and eutectic sodium-potassium. Additional fluids and solids can be defined by the user.

  1. Bacterial community structure and function shift along a successional series of tidal flats in the Yellow River Delta

    NASA Astrophysics Data System (ADS)

    Lv, Xiaofei; Ma, Bin; Yu, Junbao; Chang, Scott X.; Xu, Jianming; Li, Yunzhao; Wang, Guangmei; Han, Guangxuan; Bo, Guan; Chu, Xiaojing

    2016-11-01

    Coastal ecosystems play significant ecological and economic roles but are threatened and facing decline. Microbes drive various biogeochemical processes in coastal ecosystems. Tidal flats are critical components of coastal ecosystems; however, the structure and function of microbial communities in tidal flats are poorly understood. Here we investigated the seasonal variations of bacterial communities along a tidal flat series (subtidal, intertidal and supratidal flats) and the factors affecting the variations. Bacterial community composition and diversity were analyzed over four seasons by 16S rRNA genes using the Ion Torrent PGM platform. Bacterial community composition differed significantly along the tidal flat series. Bacterial phylogenetic diversity increased while phylogenetic turnover decreased from subtidal to supratidal flats. Moreover, the bacterial community structure differed seasonally. Canonical correspondence analysis identified salinity as a major environmental factor structuring the microbial community in the sediment along the successional series. Meanwhile, temperature and nitrite concentration were major drivers of seasonal microbial changes. Despite major compositional shifts, nitrogen, methane and energy metabolisms predicted by PICRUSt were inhibited in the winter. Taken together, this study indicates that bacterial community structure changed along the successional tidal flat series and provides new insights on the characteristics of bacterial communities in coastal ecosystems.

  2. Bacterial community structure and function shift along a successional series of tidal flats in the Yellow River Delta

    PubMed Central

    Lv, Xiaofei; Ma, Bin; Yu, Junbao; Chang, Scott X.; Xu, Jianming; Li, Yunzhao; Wang, Guangmei; Han, Guangxuan; Bo, Guan; Chu, Xiaojing

    2016-01-01

    Coastal ecosystems play significant ecological and economic roles but are threatened and facing decline. Microbes drive various biogeochemical processes in coastal ecosystems. Tidal flats are critical components of coastal ecosystems; however, the structure and function of microbial communities in tidal flats are poorly understood. Here we investigated the seasonal variations of bacterial communities along a tidal flat series (subtidal, intertidal and supratidal flats) and the factors affecting the variations. Bacterial community composition and diversity were analyzed over four seasons by 16S rRNA genes using the Ion Torrent PGM platform. Bacterial community composition differed significantly along the tidal flat series. Bacterial phylogenetic diversity increased while phylogenetic turnover decreased from subtidal to supratidal flats. Moreover, the bacterial community structure differed seasonally. Canonical correspondence analysis identified salinity as a major environmental factor structuring the microbial community in the sediment along the successional series. Meanwhile, temperature and nitrite concentration were major drivers of seasonal microbial changes. Despite major compositional shifts, nitrogen, methane and energy metabolisms predicted by PICRUSt were inhibited in the winter. Taken together, this study indicates that bacterial community structure changed along the successional tidal flat series and provides new insights on the characteristics of bacterial communities in coastal ecosystems. PMID:27824160

  3. A potential vorticity theory for the formation of elongate channels in river deltas and lakes

    NASA Astrophysics Data System (ADS)

    Falcini, Federico; Jerolmack, Douglas J.

    2010-12-01

    Rivers empty into oceans and lakes as turbulent sediment-laden jets, which can be characterized by a Gaussian horizontal velocity profile that spreads and decays downstream because of shearing and lateral mixing at the jet margins. Recent experiments demonstrate that this velocity field controls river-mouth sedimentation patterns. In nature, diffuse jets are associated with mouth bar deposition forming bifurcating distributary networks, while focused jets are associated with levee deposition and the growth of elongate channels that do not bifurcate. River outflows from elongate channels are similar in structure to cold filaments observed in ocean currents, where high potential vorticity helps to preserve coherent structure over large distances. Motivated by these observations, we propose a hydrodynamic theory that seeks to predict the conditions under which elongate channels form. Our approach models jet velocity patterns using the flow vorticity. Both shearing and lateral spreading are directly related to the vertical component of vorticity. We introduce a new kind of potential vorticity that incorporates sediment concentration and thus allows study of jet sedimentation patterns. The potential vorticity equation reduces the number of fluid momentum equations to one without losing generality. This results in a compact analytical solution capable of describing the streamwise evolution of the potential vorticity of a sediment-laden jet from initial conditions at the river mouth. Our theory predicts that high potential vorticity is a necessary condition for focused levee deposition and the creation of elongate channels. Comparison to numerical, laboratory, and field studies indicates that potential vorticity is a primary control on channel morphology. Our results may be useful for designing river delta restoration schemes such as the proposed Mississippi Delta diversion.

  4. Suspended-sediment trapping in the tidal reach of an estuarine tributary channel

    USGS Publications Warehouse

    Downing-Kunz, Maureen; Schoellhamer, David H.

    2015-01-01

    Evidence of decreasing sediment supply to estuaries and coastal oceans worldwide illustrates the need for accurate and updated estimates. In the San Francisco Estuary (Estuary), recent research suggests a decrease in supply from its largest tributaries, implying the increasing role of smaller, local tributaries in sediment supply to this estuary. Common techniques for estimating supply from tributaries are based on gages located above head of tide, which do not account for trapping processes within the tidal reach. We investigated the effect of a tidal reach on suspended-sediment discharge for Corte Madera Creek, a small tributary of the Estuary. Discharge of water (Q) and suspended-sediment (SSD) were observed for 3 years at two locations along the creek: upstream of tidal influence and at the mouth. Comparison of upstream and mouth gages showed nearly 50 % trapping of upstream SSD input within the tidal reach over this period. At the storm time scale, suspended-sediment trapping efficiency varied greatly (range −31 to 93 %); storms were classified as low- or high-yield based on upstream SSD. As upstream peak Q increased, high-yield storms exhibited significantly decreased trapping. Tidal conditions at the mouth—ebb duration and peak ebb velocity—during storms had a minor effect on sediment trapping, suggesting fluvial processes dominate. Comparison of characteristic fluvial and tidal discharges at the storm time scale demonstrated longitudinal differences in the regulating process for SSD. These results suggest that SSD from gages situated above head of tide overestimate sediment supply to the open waters beyond tributary mouths and thus trapping processes within the tidal reach should be considered.

  5. A New Channel for the Formation of Binary Black Holes - Chemically Homogeneous Evolution in Tidally Distorted Binaries

    NASA Astrophysics Data System (ADS)

    Mandel, Ilya; De Mink, Selma

    2016-07-01

    We explore a new channel to create binary black holes of stellar origin. This scenario applies to massive, tidally distorted binaries where mixing slowly enriches the entire star with helium produced by nuclear bruning. The stars evolve nearly chemically homogeneously and remain compact, eventually forming to two black holes. We find that this channel preferentially creates binary black holes, with comparable masses (m2/m1>0.65) and total masses between 50 and 110 solar masses. These typically merge 4-11 Gyr after formation implying local binary black hole merger rate of about 10 Gpc-3 yr-1 at redshift z = 0, peaking at twice this rate at z = 0.5 (Mandel & de Mink 2016). The channel is competitive, in terms of expected rates, with the conventional formation scenarios that involve a common envelope phase during isolated binary evolution or dynamical interaction in a dense cluster. The parameters for GW150914 and the rate inferred during the first 16 days O1 run are consistent with the predictions from this channel. While GW150914 may have originated from this channel, we can not distinguish at present between this and the two classical formation channels. However, the near future perspective of probing the black hole demographics is extremely promising.

  6. Sediment Transport and Infilling of a Borrow Pit on an Energetic Sandy Ebb Tidal Delta Offshore of Hilton Head Island, South Carolina

    NASA Astrophysics Data System (ADS)

    Wren, A.; Xu, K.; Ma, Y.; Sanger, D.; Van Dolah, R.

    2014-12-01

    Bottom-mounted instrumentation was deployed at two sites on an ebb tidal delta to measure hydrodynamics, sediment transport, and seabed elevation. One site ('borrow site') was 2 km offshore and used as a dredging site for beach nourishment of nearby Hilton Head Island in South Carolina, and the other site ('reference site') was 10 km offshore and not directly impacted by the dredging. In-situ time-series data were collected during two periods after the dredging: March 15 - June 12, 2012('spring') and August 18 - November 18, 2012 ('fall'). At the reference site directional wave spectra and upper water column current velocities were measured, as well as high-resolution current velocity profiles and suspended sediment concentration profiles in the Bottom Boundary Layer (BBL). Seabed elevation and small-scale seabed changes were also measured. At the borrow site seabed elevation and near-bed wave and current velocities were collected using an Acoustic Doppler Velocimeter. Throughout both deployments bottom wave orbital velocities ranged from 0 - 110 m/s at the reference site. Wave orbital velocities were much lower at the borrow site ranging from 10-20 cm/s, as wave energy was dissipated on the extensive and rough sand banks before reaching the borrow site. Suspended sediment concentrations increased throughout the BBL when orbital velocities increased to approximately 20 cm/s. Sediment grain size and critical shear stresses were similar at both sites, therefore, re-suspension due to waves was less frequent at the borrow site. However, sediment concentrations were highly correlated with the tidal cycle at both sites. Semidiurnal tidal currents were similar at the two sites, typically ranging from 0 - 50 cm/s in the BBL. Maximum currents exceeded the critical shear stress and measured suspended sediment concentrations increased during the first hours of the tidal cycle when the tide switched to flood tide. Results indicate waves contributed more to sediment mobility at

  7. A project summary: Water and energy budget assessment for a non-tidal wetland in the Sacramento-San Joaquin delta

    USGS Publications Warehouse

    Anderson, F.E.; Snyder, R.L.; Paw, U.K.T.; Drexler, J.Z.

    2004-01-01

    The methods used to obtain universal cover coefficient (Kc) values for a non-tidal restored wetland in the Sacramento-San Joaquin river delta, US, during the summer of the year 2002 and to investigate possible differences during changing wind patterns are described. A micrometeorological tower over the wetland was established to quantify actual evapotranspiration (ETa) rates and surface energy fluxes for water and energy budget analysis. The eddy-covariance (EC) system was used to measure the surface energy budget data in the period from May 23 to November 6, 2002. The results show that K c values should be lower during westerly than northerly wind events during the midseason period due to the reduced vapor pressure deficit.

  8. An experimental study of voice communication over a bandlimited channel using variable bit width delta modulation

    NASA Astrophysics Data System (ADS)

    Tumok, N. Nur

    1989-12-01

    A variable bit width delta modulator (VBWDM) demodulator was designed, built and tested to achieve voice and music communication using a bandlimited channel. Only baseband modulation is applied to the input signal. Since there is no clock used during the digitizing process at the modulator, no bit synchronization is required for signal recovery in the receiver. The modulator is a hybrid design using 7 linear and 3 digital integrated circuits (IC), and the demodulator uses 2 linear ICs. A lowpass filter (LPF) is used to simulate the channel. The average number of bits sent over the channel is measured with a frequency counter at the output of the modulator. The minimum bandwidth required for the LPF is determined according to the intelligibility of the recovered message. Measurements indicate an average bit rate required for intelligible voice transmission is in the range of 2 to 4 kilobits per seconds (kbps) and between 2 to 5 kbps for music. The channel 3 dB bandwidth required is determined to be 1.5 kilohertzs. Besides the hardware simplicity, VBWDM provides an option for intelligible digitized voice transmission at very low bit rates without requiring synchronization. Another important feature of the modulator design is that no bits are sent when no signal is present at the input which saves transmitter power (important for mobile stations) and reduces probability of intercept and jamming in military applications.

  9. Expression of the alpha(2)delta subunit interferes with prepulse facilitation in cardiac L-type calcium channels.

    PubMed Central

    Platano, D; Qin, N; Noceti, F; Birnbaumer, L; Stefani, E; Olcese, R

    2000-01-01

    We investigated the role of the accessory alpha(2)delta subunit on the voltage-dependent facilitation of cardiac L-type Ca(2+) channels (alpha(1C)). alpha(1C) Channels were coexpressed in Xenopus oocytes with beta(3) and alpha(2)delta calcium channel subunits. In alpha(1C) + beta(3), the amplitude of the ionic current (measured during pulses to 10 mV) was in average approximately 1.9-fold larger after the application of a 200-ms prepulse to +80 mV. This phenomenon, commonly referred to as voltage-dependent facilitation, was not observed when alpha(2)delta was coexpressed with alpha(1C) + beta(3). In alpha(1C) + beta(3), the prepulse produced a left shift ( approximately 40 mV) of the activation curve. Instead, the activation curve for alpha(1C) + beta(3) + alpha(2)delta was minimally affected by the prepulse and had a voltage dependence very similar to the G-V curve of the alpha(1C) + beta(3) channel facilitated by the prepulse. Coexpression of alpha(2)delta with alpha(1C) + beta(3) seems to mimic the prepulse effect by shifting the activation curve toward more negative potentials, leaving little room for facilitation. The facilitation of alpha(1C) + beta(3) was associated with an increase of the charge movement. In the presence of alpha(2)delta, the charge remained unaffected after the prepulse. Coexpression of alpha(2)delta seems to set all the channels in a conformational state from where the open state can be easily reached, even without prepulse. PMID:10827975

  10. Turbulent stresses and secondary currents in a tidal-forced channel with significant curvature and asymmetric bed forms

    USGS Publications Warehouse

    Fong, D.A.; Monismith, Stephen G.; Stacey, M.T.; Burau, J.R.

    2009-01-01

    Acoustic Doppler current profilers are deployed to measure both the mean flow and turbulent properties in a channel with significant curvature. Direct measurements of the Reynolds stress show a significant asymmetry over the tidal cycle where stresses are enhanced during the flood tide and less prominent over the ebb tide. This asymmetry is corroborated by logarithmic fits using 10 min averaged velocity data. A smaller yet similar tendency asymmetry in drag coefficient is inferred by fitting the velocity and estimated large-scale pressure gradient to a one-dimensional along-channel momentum balance. This smaller asymmetry is consistent with recent modeling work simulating regional flows in the vicinity of the study site. The asymmetry in drag suggests the importance of previously reported bed forms for this channel and demonstrates spatial and temporarily variations in bed stress. Secondary circulation patterns observed in a relatively straight section of channel appear driven by local curvature rather than being remotely forced by the regions of significant curvature only a few hundred meters from the measurement site. ?? 2009 ASCE.

  11. Piping coarse-grained sediment to a deep water fan through a shelf-edge delta bypass channel: Tank experiments

    NASA Astrophysics Data System (ADS)

    Kim, Yuri; Kim, Wonsuck; Cheong, Daekyo; Muto, Tetsuji; Pyles, David R.

    2013-12-01

    is now generally accepted that deltas that prograde to the shelf edge are able to transport coarse sediment to deep water either with or without sea level changes. However, it is still unclear how feeder rivers behave differently in the shelf-edge delta case to rivers found in a delta that progrades over the shelf. A series of nine shelf-edge delta experiments are presented to investigate the lateral mobility of the feeder channel at the shelf edge and the associated deep water depositional system under a range of sediment supply rates and shelf-front depths. In the experiments, constant sediment supply from an upstream point source under static sea level led the fluviodeltaic system to prograde over the shallow shelf surface and advance beyond the shelf edge into deep water. The feeder river of the fluviodeltaic system became a bypass system once the toe of the delta front reached the shelf edge. After the delta front was perched at the shelf edge, a submarine fan developed in deep water although remaining disconnected from the delta. In this bypass stage, no regional avulsion or lateral migration of the feeder river occurred and all sediment from the upstream source bypassed the river, delta front, and shelf-front slope. The duration of the bypass stage is proportional to shelf-front depth and inversely proportional to sediment discharge. The combined duration of the shelf-transit phase of the fluviodeltaic system and the bypass phase is the characteristic time scale for the continental margin to "anneal" transgression-inducing perturbation due to high-frequency and/or high-amplitude relative sea level rise. The sequential evolution in the experiment compares favorably to the Eocene Sobrarbe Formation, a shelf-edge delta in Spain, although natural variations are noted. This comparison justifies the application of concepts proposed herein to natural systems and provides insight into interpreting processes from ancient shelf-edge delta systems.

  12. Monitoring Water Quality at Lake Merritt, Oakland, CA Following Improvements to the Tidal Channel to the San Francisco Bay

    NASA Astrophysics Data System (ADS)

    Bracho, H.; Martinez, J.; Johnson, M.; Turrey, A.; Avila, M.; Medina, S.; Rubio, E.; Ahumada, E.; Nguyen, S.; Guzman, Y.

    2014-12-01

    Elliot Ahumada, Esosa Oghogho, Samantha Nguyen, Humberto Bracho, Diego Quintero, Ashanti Johnson and Kevin Cuff Lake Merritt is a tidal lagoon in the center of Oakland, California, just east of Downtown. Water quality at Lake Merritt has been a major concern for community members and researchers for many years (Pham 200X). Results of past research lead to recommendations to lengthen a channel that connects Lake Merritt with the San Francisco Bay to improve water flow and quality. In 2012 the City of Oakland responded to these recommendations by initiating the creation of a 230-meter long channel. In conducting our research we use a water quality index that takes into account measurements of pH, temperature, water hardness (dissolved solids), ammonia, salinity, dissolved oxygen, and nitrate. Newly collected data is then compared with that collected by Pham using comparable parameters to assess the impact of recent changes at the Lake on its overall water quality. In addition, we measured the abundance of aquatic species at four different sites within the Lake. Preliminary results suggest that an increase in the abundance of fish and improved overall water quality have resulted from channel extension at Lake Merritt.

  13. Tidal marsh accretion processes in the San Francisco Bay-Delta - are our models underestimating the historic and future importance of plant-mediated organic accretion?

    NASA Astrophysics Data System (ADS)

    Windham-Myers, L.; Drexler, J. Z.; Byrd, K. B.; Schile, L. M.

    2012-12-01

    Peat-accreting coastal wetlands have the potential to keep elevational pace with sea-level rise, thus providing both adaptation and mitigation for expected rises in atmospheric concentrations of greenhouse gases (GHGs). Due to oxidation and sedimentation processes, marsh elevations are generally constrained by sea level rise (1-2 mm yr-1). However, the relative importance of mineral vs. organic accretion remain poorly understood. At least four lines of evidence from the brackish-fresh region of California's SFBay-Delta suggest that potential rates of organic accretion may be underestimated in calibration datasets of the last century. First, tidal marsh elevations have been maintained with changing rates of SLR over the past 6700 years even during periods of low sediment availability. Second, the presence of fibric remnants in historic peat cores suggests that millennial preservation of autochtonous material may be greater in the absence of mineral inputs. Third, an experimental restoration of emergent marsh on subsided peat soil has generated new "proto-peat" at average rates of 4 cm y-1, nearly 40-times mean sea level rise, storing an average of 1 kg C m-2 yr-1 since 1997. Fourth, annual measurements of root production of the dominant fresh-brackish marsh species tule (Schoenoplectus acutus) show high productivity and minimal sensitivity to variable tidal range elevations and fresh-brackish salinities. Separating the relative importance of belowground productivity from decomposition in driving rates of organic accretion may be possible by assessment of fibric remnants, as an index of organic "preservation". Using three distinct peat cores from a larger study with calibrated dating and geochemistry data, fibric remnants (particles >2mm) were assessed at 10 cm intervals and compared with physical and associated geochemical down-core variability (n=230 segments). The presence of fibric remnants was reduced in the presence of sediment, as indicated by mineral content

  14. Erosion Between Two Delta Fronts, the Mekong Delta Case

    NASA Astrophysics Data System (ADS)

    Unverricht, D.; Heinrich, C.; Nguyen, T. C.; Szczucinski, W.; Schwarzer, K.; Stattegger, K.

    2013-12-01

    ridges are situated on top of older delta foresets that are incised by the channels between the ridges. We conclude that both wind and tidal driven longshore currents maintain the sand ridges. However, erosion in the channel region is amplified due to increased current velocities. Thereby, the sand-ridge-channel-system serves as sediment conveyor between the two delta fronts. The age of the sand-ridge-channel-system is unknown, but its initiation is referred to the last century in relation to coastal erosion caused by mangrove deforestation and to less sediment supply due to damming and sand mining along the Mekong River.

  15. Spatiotemporal Dynamics of River Channel Migration on the Ganges-Brahmaputra Delta: 2000-2013

    NASA Astrophysics Data System (ADS)

    Small, C.; Chiu, S.; Sousa, D.; Mondal, D. R.; Steckler, M. S.; Akhter, S. H.; Mia, B.; Goodbred, S. L., Jr.; Wilson, C.; Seeber, L.

    2014-12-01

    We use multitemporal multiscale satellite remote sensing to complement field observations and subsurface measurements to better understand the relationship between recent and historic fluvial dynamics on the Ganges-Brahmaputra (GB) delta. To provide regional context for the interannual changes in river channel geometry we conduct spatiotemporal (ST) analyses of MODIS Enhanced Vegetation Index (EVI) imagery for 2000-2013 using a new method of Empirical Orthogonal Function (EOF) analysis. We use EVI because it distinguishes water from wet and dry sediment on the basis of the spectral slope at VNIR wavelengths. Water has a negative slope while dry sediment has a small positive slope and vegetation has a large positive slope. To characterize the ST patterns associated with river channel migration we use iterative EOF analysis (iEOF). In iEOF we first conduct a single year EOF analysis for each year in the time series to identify the primary spatial principal component (PC1) for each year and separate this from the spatial structure of the subannual temporal patterns associated with vegetation phenology. We then construct a decadal time series of PC 1 for each single year and conduct a second EOF analysis of the time series of 13 individual year PCs. The standard EOFs of the full (312 images x 16 day) time series only resolve a decadal trend (EOF 8), but the iEOF clearly distinguishs the progressive decadal trend (EOF 2) from the cyclic component (EOF 3) of decadal changes in sediment reflectance. The temporal feature space constructed from PC 2 and PC 3 (corresponding to temporal EOFs 2 and 3) distinguishes pixels with progressive decadal increases and decreases in reflectance from pixels with cyclic changes. Evolution of the annual structure is animated at www.youtube.com/watch?v=UM1UYvdnYXk Despite significant differences in the 2 rivers'morphologies, and the considerable magnitude of flooding every year, we observe year-to-year continuity in the progressive

  16. Tidal Meanders

    NASA Astrophysics Data System (ADS)

    Marani, M.; Lanzoni, S.; Zandolin, D.; Seminara, S.; Rinaldo, A.

    Observational evidence is presented on the geometry of meandering tidal channels evolved within coastal wetlands characterized by different tidal, hydrodynamic, to- pographic, vegetational and ecological features. New insight is provided on the ge- ometrical properties of tidal meanders, with possible dynamic implications on their evolution. In particular, it is shown that large spatial gradients of leading flow rates induce important spatial variabilities of meander wavelengths and widths, while their ratio remains remarkably constant in the range of scales of observation. This holds regardless of changes in width and wavelength up to two orders of magnitude. This suggests a locally adapted evolution, involving the morphological adjustment to the chief landforming events driven by local hydrodynamics. The spectral analysis of lo- cal curvatures reveals that Kinoshita's model curve does not fit tidal meanders due to the presence of even harmonics, in particular the second mode. Geometric parameters are constructed that are suitable to detect possible geomorphic signatures of the tran- sitions from ebb- to flood-dominated hydrodynamics, here related to the skewness of the tidal meander. Trends in skewness, however, prove elusive to measure and fail to show detectable patterns. We also study comparatively the spatial patterns of evolu- tion of the ratios of channel width to depth, and the ratio of width to local radius of curvature. Interestingly, the latter ratio exhibits consistency despite sharp differences in channel incision. Since the degree of incision, epitomized by the width-to-depth ratio, responds to the relevant erosion and migrations mechanisms and is much sen- sitive to vegetation and sediment properties, it is noticeable that we observe a great variety of landscape carving modes and yet recurrent planar features like constant width/curvature and wavelength/width ratios.

  17. Pregabalin action at a model synapse: binding to presynaptic calcium channel alpha2-delta subunit reduces neurotransmission in mice.

    PubMed

    Joshi, Indu; Taylor, Charles P

    2006-12-28

    Pregabalin, ((S)-3-(aminomethyl)-5-methylhexanoic acid, also known as (S)-3-isobutyl GABA, Lyricatrade mark) is approved for treatment of certain types of peripheral neuropathic pain and as an adjunctive therapy for partial seizures of epilepsy both the EU and the USA and also for generalized anxiety disorder in the EU. Though pregabalin binds selectively to the alpha(2)-delta (alpha(2)-delta) auxiliary subunit of voltage-gated calcium channels, the cellular details of pregabalin action are unclear. The high density of alpha(2)-delta in skeletal muscle fibers raises the question of whether pregabalin alters excitation-contraction coupling. We used the mouse soleus neuromuscular junction from mice containing an artificially mutated alpha(2)-delta Type 1 protein (R217A) as a model to examine the effect of pregabalin. Pregabalin reduced nerve-evoked muscle contractions by 16% at a clinically relevant concentration of 10 muM in wildtype mice. When acetylcholine receptors were blocked with curare, pregabalin had no effect on contraction from direct stimulation of muscle, suggesting a lack of drug effects on contraction coupling. Our data are consistent with pregabalin having no effect on striated muscle L-type calcium channel function. However, in mice expressing mutant (R217A) alpha(2)-delta Type 1, there was no significant effect of pregabalin on nerve-evoked muscle contraction. We propose that pregabalin reduces presynaptic neurotransmitter release without altering postsynaptic receptors or contraction coupling and that these effects require high affinity binding to alpha(2)-delta Type 1 auxiliary subunit of presynaptic voltage-gated calcium channels.

  18. Techniques for accurate estimation of net discharge in a tidal channel

    USGS Publications Warehouse

    Simpson, Michael R.; Bland, Roger

    1999-01-01

    An ultrasonic velocity meter discharge-measurement site in a tidally affected region of the Sacramento-San Joaquin rivers was used to study the accuracy of the index velocity calibration procedure. Calibration data consisting of ultrasonic velocity meter index velocity and concurrent acoustic Doppler discharge measurement data were collected during three time periods. The relative magnitude of equipment errors, acoustic Doppler discharge measurement errors, and calibration errors were evaluated. Calibration error was the most significant source of error in estimating net discharge. Using a comprehensive calibration method, net discharge estimates developed from the three sets of calibration data differed by less than an average of 4 cubic meters per second. Typical maximum flow rates during the data-collection period averaged 750 cubic meters per second.

  19. Evolution and stratigraphy of a sandy tidal-flat complex within a Mesotidal embayment

    SciTech Connect

    McCants, C.Y.; Zarillo, G.A.

    1985-02-01

    Sand-dominated intertidal environments in St. Helena Sound, South Carolina, a mesotidal estuarine system, can be divided into a continuum of barlike deposits dominated by tidal flows and sheetlike deposits of sandy tidal flats that are influenced by both waves and currents. A large sand flat attached to a marsh-island complex in the central interior of St. Helena Sound resembles a large flood-tidal delta and has been reworked by waves and migrating ebb-dominated tidal channels. The lower tidal flat (flood ramp) is composed of coarse to medium sand mixed with shell material. Large-scale planar cross-beds are formed by flood-oriented sand waves. Middle tidal-flat deposits consist of fine to very fine sand where burrowing by intertidal fauna disrupts structures of intermediate to small-scale bed forms generated by both waves and tidal currents. The muddy, fine-grained sands of the upper tidal flat are reworked by wave-generated small-scale ripples and are partially bioturbated. A salt marsh-chenier complex, landward of the upper tidal flat, has prograded over older portions of the sand flat during earlier regressive phases. Evolution of the St. Helena Sound sand flats began with a transgressive phase marked by a transgressive lag deposit dated at 4200 yr B.P., overlying Pleistocene estuarine, mud-flat, and salt-marsh deposits. Sediment for buildup of the sand flats was derived from reworking of surrounding barrier-island sands by migrating tidal channels. Sand was introduced into the lower tidal flat by swash-bar accumulation or strong flood-tidal currents. Building of the sand-flat sequence and development of the overlying salt marsh-chenier complex occurred episodically due to minor fluctuations in sea level. At present, the sand-flat sequence is in a transgressive phase and is being reworked by migrating tidal channels and the seawardmost chenier is subject to frequent overwashing.

  20. On the dynamics of compound bedforms in high-energy tidal channels: field observations in the German Bight and the Danish Wadden Sea

    NASA Astrophysics Data System (ADS)

    Ernstsen, Verner B.; Winter, Christian; Becker, Marius; Bartholdy, Jesper

    2010-05-01

    Tidal inlets are a common feature along much of the world's coastlines. They interrupt the alongshore continuity of shoreline processes, and by being exposed to both wave and current forcing, tidal inlets belong to the morphologically most dynamic and complex coastal systems on Earth. The tidal channels in these inlets are characterized by high flow velocities and, accordingly, the channel beds are typically sandy and covered with bedforms. The bedform fields in nature are often complex systems with larger primary-bedforms superimposed by smaller secondary-bedforms (cf. Bartholdy et al., 2002). There is a considerable amount of detailed field investigations on the dynamics of primary-bedforms at various temporal scales, ranging from short- to long-term tide-related cycles to flood hydrographs to seasonality. However, Julien et al. (2002) stated that a composite analysis of primary- and secondary-bedforms is recommended for future studies on resistance to flow. Such knowledge on the behaviour of compound bedforms is still deficient. In this study, we combine the findings on the dynamics of primary- and secondary-bedform height from detailed field investigations carried out in two high-energy tidal channels during 2007 and 2008: the Knudedyb tidal inlet channel in the Danish Wadden Sea and the Innenjade tidal channel in the Jade Bay, German Bight (both survey areas being ebb-dominated). We provide process-based explanations of the bedform behaviour and present a conceptual model of compound bedform dynamics. The conducted field investigations comprised repetitive, simultaneous measurements of high-resolution swath bathymetry (using a multibeam echosounder system) and flow velocity (using an acoustic Doppler current profiler) in combination with detailed spatial mapping of bed material characteristics (from grab sampling of bed material). For an objective and discrete analysis of primary- and secondary-bedforms a modified version of the bedform tracking tool

  1. Rescue of functional DeltaF508-CFTR channels by co-expression with truncated CFTR constructs in COS-1 cells.

    PubMed

    Owsianik, Grzegorz; Cao, Lishuang; Nilius, Bernd

    2003-11-06

    The most frequent mutant variant of the cystic fibrosis transmembrane conductance regulator (CFTR), DeltaF508-CFTR, is misprocessed and subsequently degraded in the endoplasmic reticulum. Using the patch-clamp technique, we showed that co-expressions of DeltaF508-CFTR with the N-terminal CFTR truncates containing bi-arginine (RXR) retention/retrieval motifs result in a functional rescue of the DeltaF508-CFTR mutant channel in COS-1 cells. This DeltaF508-CFTR rescue process was strongly impaired when truncated CFTR constructs possessed either the DeltaF508 mutation or arginine-to-lysine mutations in RXRs. In conclusions, our data demonstrated that expression of truncated CFTR constructs could be a novel promising approach to improve maturation of DeltaF508-CFTR channels.

  2. Sub-tidal Circulation in a deep-silled fjord: Douglas Channel, British Columbia (Canada)

    NASA Astrophysics Data System (ADS)

    Wan, Di; Hannah, Charles; Foreman, Mike

    2016-04-01

    Douglas Channel, a deep fjord on the west coast of British Columbia, Canada, is the main waterway in Kitimat fjord system that opens to Queen Charlotte Sound and Hecate Strait. The fjord is separated from the open shelf by a broad sill that is about 150 m deep, and there is another sill (200 m) that separates the fjord into an outer and an inner basin. This study examines the low-frequency (from seasonal to meteorological bands) circulation in Douglas Channel from data collected from three moorings deployed during 2013-2015, and the water property observations collected during six cruises (2014 and 2015). Estuarine flow dominates the circulation above the sill-depth. The deep flows are dominated by a yearly renewal that takes place from early June to September, and this dense water renews both basins in the form of gravity currents at 0.1 - 0.2 m/s with a thickness of 100 m. At other times of the year, the deep flow structures and water properties suggest horizontal and vertical processes and support the re-circulation idea in the inner and the outer basins. The near surface current velocity fluctuations are dominated by the along-channel wind. Overall, the circulation in the meteorological band is a mix of the estuarine flow, direct wind driven flow, and the baroclinic response to changes to the surface pressure gradient caused by the wind driven currents.

  3. Monitoring the exchanges of water, solids, and solutes between channels and islands of Wax Lake Delta, Louisiana: Key to defining the resiliency of this coastal environment

    NASA Astrophysics Data System (ADS)

    Mohrig, D. C.; Hiatt, M. R.; Piliouras, A.; Shaw, J. B.; Wagner, R. W.; Passalacqua, P.; Kim, W.

    2014-12-01

    Deltas are typically treated as binary systems composed of a channel network and the land separating adjacent channels. Field studies of these systems have tended to focus on collecting data either from the channels or from the land, and by doing so have missed a central characteristic of deltas, the connectedness between the land and channels. We propose that the resiliency of any delta can only be accurately assessed if the naturally occurring exchanges of fluid, solids and solutes between the channels and islands (neighboring land) are understood. These exchanges control the growth of land via the deposition of sediment and accumulation of plant biomass, and also affect delta ecology by mediating water temperature and solute concentrations. The deposition of sediment and organic material in turn influences future growth and pattern development for the deltaic channel network. Exchanges between channelized flow in the delta network and the more distributed flow over submerged island tops is currently being monitored and studied at an NSF-funded observatory under development at Wax Lake Delta, Louisiana. Characterization of flow in distributary channels and on island tops reveals that a considerable fraction of water originally travelling in the large channels is transferred onto island tops either through focused entry points (tie channels) or via distributed flow through island-bounding levees. These volume transfer fractions range between 10 and 60 percent, and are sensitive to location within the delta, as well as river discharge, tides, and winds. Island tops develop tributary-like networks through which the fluid, solids, and solutes drain back into adjacent channels or drain out of the system at the front of the delta, in between the mouths of primary distributary channels. Characteristic fluid velocities vary over roughly two orders of magnitude (centimeter- to meter-per-second) depending on whether a fluid parcel is located in shallow laterally unconfined

  4. Medium timescale stability of tidal mudflats in Bridgwater Bay, Bristol Channel, UK: Influence of tides, waves and climate

    NASA Astrophysics Data System (ADS)

    Kirby, Jason R.; Kirby, Robert

    2008-11-01

    This paper presents the results of an 11-year study into mudflat elevation changes within the intertidal zone at Stert Flats in Bridgwater Bay, Somerset. This site is located in the outer Severn Estuary/inner Bristol Channel which is a macro-hypertidal regime dominated by physical processes, characterized by strong tidal currents, high turbidity and a significant degree of exposure to wind generated waves. Two transects of stakes were installed perpendicular to the coast, extending seawards 300 m from the edge of the saltmarsh onto the mudflats, against which variations in accretion or erosion could be measured. The mudflats themselves consisted of an underlying consolidated clay of Holocene age and a surface veneer of fluid mud and/or mobile sand patches which varied both spatially and temporally. Mudflat development was recorded over both short-term (monthly/seasonal) and medium-term (inter-annual) timescales. The results display a significant degree of scatter over all timescales. Such variability in response may be expected in such a dynamic system where noise can be attributed to a combination of factors such as the mobility of surface fluid mud and sand patches and the migration of the underlying ridge-runnel drainage network. Despite this, the expected short-term variations related to neap-spring tidal conditions and seasonal influences were observed at a number of locations on the transects although these were weakly expressed. The over-riding feature of the profiles is a consistent long-term trend of erosion which appears to be masking shorter term trends within the dataset. Viewed over the 11-year period, the changes in mudflat elevation closely match the pattern of the index of the North Atlantic Oscillation (NAO) during the 1990s, suggesting a strong climatic control over mudflat development on a medium-term/decadal scale. Most profiles display a strong erosional trend during the early 1990s when the NAO index was positive. The erosional trend peaked in

  5. Lime-mud layers in high-energy tidal channels: a record of hurricane deposition

    USGS Publications Warehouse

    Shinn, E.A.; Steinen, R.P.; Dill, R.F.; Major, R.

    1993-01-01

    During or immediately following the transit of Hurricane Andrew (August 23-24, 1992) across the northern part of the Great Bahama Bank, thin laminated beds of carbonate mud were deposited in high-energy subtidal channels (4 m depth) through the ooid shoals of south Cat Cay and Joulters Cays. Thicker, more cohesive (and therefore older) mud beds and angular mud fragments associated with ooids from Joulters Cays have similar characteristics but lack fresh plant fragments. We infer that these older beds were similarly deposited and thus record the passage of previous hurricanes or tropical storms. -from Authors

  6. Coastline changes and sedimentation related with the opening of an artificial channel: the Valo Grande Delta, SE Brazil.

    PubMed

    De Mahiques, Michel M; Figueira, Rubens C L; Alves, Daniel P V; Italiani, Diana M; Martins, Cristina C; Dias, João M A

    2014-12-01

    The role played by human activity in coastline changes indicates a general tendency of retreating coasts, especially deltaic environments, as a result of the recent trend of sea level rise as well as the blockage of the transfer of sediments towards the coast, especially due to the construction of dams. This is particularly important in deltaic environments which have been suffering a dramatic loss of area in the last decades. In contrast, in this paper, we report the origin and evolution of an anthropogenic delta, the Valo Grande delta, on the south-eastern Brazilian coast, whose origin is related to the opening of an artificial channel and the diversion of the main flow of the Ribeira de Iguape River. The methodology included the analysis of coastline changes, bathymetry and coring, which were used to determine the sedimentation rates and grain-size changes over time. The results allowed us to recognize the different facies of the anthropogenic delta and establish its lateral and vertical depositional trends. Despite not being very frequent, anthropogenic deltas represent a favorable environment for the record of natural and anthropogenic changes in historical times and, thus, deserve more attention from researchers of different subjects.

  7. Suspended sediment transport in the Deepwater Navigation Channel, Yangtze River Estuary, China, in the dry season 2009: 1. Observations over spring and neap tidal cycles

    NASA Astrophysics Data System (ADS)

    Song, Dehai; Wang, Xiao Hua; Cao, Zhenyi; Guan, Weibing

    2013-10-01

    The in situ data in the Deepwater Navigation Channel (DNC), Yangtze River Estuary (YRE), China, in the dry season 2009, shows spring tides associated with greater maximum velocities, more mixing, less stratification, and diffused fluid mud; whereas neap tides are associated with smaller maximum velocities, greater stratification, inhibited mixing, and stratified fluid muds. The balance of salt flux indicates the seaward salt transport is dominated by fluvial flows, and the landward salt transport is generated by compensation flows during spring tides, but shear effects during neap tidal cycles. The balance of suspended sediment flux illustrates the offshore sediment transport is dominated by fluvial flows as well, but the onshore transport is induced by tidal-pumping effects on spring tides, and shear effects on neaps. The suspended sediment transport is strongly affected by the salinity distribution and salinity-gradient-induced stratification in the DNC. The spring-neap asymmetry is generated by the estuarine gravitational circulation during low-flow conditions; while the flood-ebb asymmetric stratification within a tidal cycle is due to the semidiurnal tidally movement of the salt front.

  8. Tidal-Fluvial and Estuarine Processes in the Lower Columbia River: I. Along-channel Water Level Variations, Pacific Ocean to Bonneville Dam

    SciTech Connect

    Jay, D. A.; Leffler, K.; Diefenderfer, Heida L.; Borde, Amy B.

    2015-03-01

    This two-part paper provides comprehensive time and frequency domain analyses and models of along-channel water level variations in the 234km-long Lower Columbia River and Estuary (LCRE) and documents the response of floodplain wetlands thereto. In Part I, power spectra, continuous wavelet transforms, and harmonic analyses are used to understand the influences of tides, river flow, upwelling and downwelling, and hydropower operations ("power-peaking") on the water level regime. Estuarine water levels are influenced primarily by astronomical tides and coastal processes, and secondarily by river flow. The importance of coastal and tidal influences decreases in the landward direction, and water levels are increasingly controlled by river flow variations at periods from ≤1 day to years. Water level records are only slightly non-stationary near the ocean, but become increasingly irregular upriver. Although astronomically forced tidal constituents decrease above the estuary, tidal fortnightly and overtide variations increase for 80-200km landward, both relative to major tidal constituents and in absolute terms.

  9. Linking process, morphology, and stratigraphy in the Ganges-Brahmaputra-Meghna delta

    NASA Astrophysics Data System (ADS)

    Wilson, C.; Goodbred, S. L., Jr.; Sincavage, R.; Steckler, M. S.; Pickering, J.

    2015-12-01

    The Ganges-Brahmaputra-Meghna delta (GBMD) is characterized as a composite system with an upland fluvial fan delta, a lowland, backwater-reach delta, a downdrift tidal delta plain, and an offshore subaqueous-delta, reflecting the respective dominance of fluvial, tidal, and marine processes. Topographic transitions, coupled with surface morphology and underlying stratigraphy define the temporally and spatially integrated patterns of river behavior and sediment dispersal that characterize the delta system. These play important roles in the scale of natural hazards, such as flooding and storm surges, affecting the 150 million inhabitants of the GBMD. Within the upland fan delta, aggradation of mobile braided channels within the active rivers support the wide-scale distribution of bed- and suspended-load sands that constitute nearly the entire underlying architecture of upper GBMD stratigraphy. Finer silt-dominated facies form on the floodplain from overbank deposition during waning stages of flow; however preservation is very low and localized because of the persistent lateral migration of braided channels. A differentiation in stream morphology and channel behavior is associated with a sharp decrease in stream gradient, channel avulsion and abandonment, and the transition across the backwater. Deposition and preservation of fine-grained mud and organic-rich successions are concentrated within broad interdistributary basins of the lowland fluvial plain or within tectonically subsiding Sylhet Basin. While ~15% of the 1 x 109 t yr-1 sediment load carried by the rivers is advected along shore and inland via tidal activity, a rapidly prograding subaqueous clinoform and the adjacent Swatch of No Ground canyon system offshore receive ~50% of the modern sediment load. The overall stability of the GBMD landform, relative to many deltas, reflects the efficient, widespread dispersal of sediment by the large monsoon discharge and high-energy tides that affect this region

  10. A 110-nW in-channel sigma-delta converter for large-scale neural recording implants.

    PubMed

    Rezaei, M; Maghsoudloo, E; Sawan, M; Gosselin, B

    2016-08-01

    Advancement in wireless and microsystems technology have ushered in new devices that can directly interface with the central nervous system for stimulating and/or monitoring neural circuitry. In this paper, we present an ultra low-power sigma-delta analog-to-digital converter (ADC) intended for utilization into large-scale multi-channel neural recording implants. This proposed design, which provides a resolution of 9 bits using a one-bit oversampled ADC, presents several desirable features that allow for an in-channel ADC scheme, where one sigma-delta converter is provided for each channel, enabling development of scalable systems that can interface with different types of high-density neural microprobes. The proposed circuit, which have been fabricated in a TSMC 180-nm CMOS process, employs a first order noise shaping topology with a passive integrator and a low-supply voltage of 0.6 V to achieve ultra low-power consumption and small size. The proposed ADC clearly outperforms other designs with a power consumption as low as 110 nW for a precision of 9 bits (11-fJ per conversion), a silicon area of only 82 μm × 84 μm and one of the best reported figure of merit among recently published data converters utilized in similar applications.

  11. Tidal wetland fluxes of dissolved organic carbon and sediment at Browns Island, California: initial evaluation

    USGS Publications Warehouse

    Ganju, N.K.; Bergamaschi, B.; Schoellhamer, D.H.

    2003-01-01

    Carbon and sediment fluxes from tidal wetlands are of increasing concern in the Sacramento-San Joaquin River Delta (Delta), because of drinking water issues and habitat restoration efforts. Certain forms of dissolved organic carbon (DOC) react with disinfecting chemicals used to treat drinking water, to form disinfection byproducts (DBPs), some of which are potential carcinogens. The contribution of DBP precursors by tidal wetlands is unknown. Sediment transport to and from tidal wetlands determines the potential for marsh accretion, thereby affecting habitat formation.Water, carbon, and sediment flux were measured in the main channel of Browns Island, a tidal wetland located at the confluence of Suisun Bay and the Delta. In-situ instrumentation were deployed between May 3 and May 21, 2002. Water flux was measured using acoustic Doppler current profilers and the index-velocity method. DOC concentrations were measured using calibrated ultraviolet absorbance and fluorescence instruments. Suspended-sediment concentrations were measured using a calibrated nephelometric turbidity sensor. Tidally averaged water flux through the channel was dependent on water surface elevations in Suisun Bay. Strong westerly winds resulted in higher water surface elevations in the area east of Browns Island, causing seaward flow, while subsiding winds reversed this effect. Peak ebb flow transported 36% more water than peak flood flow, indicating an ebb-dominant system. DOC concentrations were affected strongly by porewater drainage from the banks of the channel. Peak DOC concentrations were observed during slack after ebb, when the most porewater drained into the channel. Suspended-sediment concentrations were controlled by tidal currents that mobilized sediment from the channel bed, and stronger tides mobilized more sediment than the weaker tides. Sediment was transported mainly to the island during the 2-week monitoring period, though short periods of export occurred during the spring

  12. Characterization and Absolute QE Measurements of Delta-Doped N-Channel and P-Channel CCDs

    NASA Technical Reports Server (NTRS)

    Jacquot, Blake C.; Monacos, Steve P.; Jones, Todd J.; Blacksberg, Jordana; Hoenk, Michael E.; Nikzad, Shouleh

    2010-01-01

    In this paper we present the methodology for making absolute quantum efficiency (QE) measurements from the vacuum ultraviolet (VUV) through the near infrared (NIR) on delta-doped silicon CCDs. Delta-doped detectors provide an excellent platform to validate measurements through the VUV due to their enhanced UV response. The requirements for measuring QE through the VUV are more strenuous than measurements in the near UV and necessitate, among other things, the use of a vacuum monochromator, and good camera vacuum to prevent chip condensation, and more stringent handling requirements. The system used for these measurements was originally designed for deep UV characterization of CCDs for the WF/PC instrument on Hubble and later for Cassini CCDs.

  13. Observations of tidal flux between a submersed aquatic plant stand and the adjacent channel in the Potomac River near Washington, D.C.

    USGS Publications Warehouse

    Rybicki, N.B.; Jenter, H.L.; Carter, V.; Baltzer, R.A.; Turtora, M.

    1997-01-01

    Dye injection studies and direct velocity and water-level measurements were made in macrophyte stands and adjacent channels in order to observe the effects of the macrophyte stand on flow and mass exchange in the tidal Potomac River. During the summer, dense stands of submersed aquatic plants cover most shoals <2 m deep. Continuous summertime water-level records within a submersed aquatic plant stand and in the adjacent channel revealed time-varying gradients in water-surface elevation between the two areas. Water-level gradients are created by differing rates of tidal water-level change in vegetated and unvegetated areas. Results were consistent with the idea that on a rising tide the water was slower to enter a macrophyte stand, and on a falling tide it was slower to leave it. Differences in water elevation between the stand and the open channel generated components of velocity in the stand that were at right angles to the line of flow in the channel. Seasonal differences in flow speed and direction over the shoals indicate substantial differences in resistance to flow as a result of the vegetation.

  14. Arsenic and heavy metal pollution in wetland soils from tidal freshwater and salt marshes before and after the flow-sediment regulation regime in the Yellow River Delta, China

    NASA Astrophysics Data System (ADS)

    Bai, Junhong; Xiao, Rong; Zhang, Kejiang; Gao, Haifeng

    2012-07-01

    SummarySoil samples were collected in tidal freshwater and salt marshes in the Yellow River Delta (YRD), northern China, before and after the flow-sediment regulation. Total concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) were determined using inductively coupled plasma atomic absorption spectrometry to investigate the characteristics of heavy metal pollution in tidal wetlands before and after the regulation regime. The results demonstrated that marsh soils in both marshes had higher silt and total P contents, higher bulk density and lower sand contents after the flow-sediment regulation; moreover, soil salinity was significantly decreased in the tidal salt marsh. As and Cd concentrations were significantly higher in both marsh soils after the regulation than before, and there were no significant differences in the concentrations of Cu, Pb and Zn measured before and after the regulation. No significant differences in heavy metal concentrations were observed between freshwater and salt marsh soils, either before or after the regulation. Before the regulation regime, soil organic matter, pH and sulfer (S) were the main factors influencing heavy metal distribution in tidal freshwater marshes, whereas for tidal salt marshes, the main factors are soil salinity and moisture, pH and S. However, bulk density and total P became the main influencing factors after the regulation. The sediment quality guidelines and geoaccumulation indices showed moderately or strongly polluted levels of As and Cd and unpolluted or moderately polluted levels of Cu, Pb and Zn; As and Cd pollution became more serious after the regulation. Factor analysis indicated thatthese heavy metals including As were closely correlated and orginated from common pollution sources before the flow-sediment regulation; however, the sources of As and Cd separated from the sources of Cu, Pb and Zn after the regulation regime, implying that the flow-sediment regulation regime

  15. The interaction between deepwater channel systems and growing thrusts and folds, toe-thrust region of the deepwater Niger Delta

    NASA Astrophysics Data System (ADS)

    Jolly, B.; Lonergan, L.; Whittaker, A.

    2012-04-01

    Gravity-driven seaward-verging thrusts, landward-verging back-thrusts and associated folds often characterize the slope and deepwater settings of passive margins. These structures, found in the "toe-thrust" region of the system, exert a significant control on sediment gravity flows because they create and determine the location and configuration of sediment depocentres and transport systems. However, to fully understand the interaction between sediment gravity flows and seabed topography we need to evaluate and quantify the geomorphic response of sub-marine channels to faulting in an area where the degree of tectonic shortening can be well constrained. This study exploits 3D seismic data in the outer toe-thrust region of the deepwater Niger Delta to analyze the interaction between Plio-Pleistocene channel systems and actively growing folds and thrusts. We first mapped folds and thrusts from the seismic data and we used this data to reconstruct the history of fold growth. We then used the sea-bed seismic horizon to build a 50 m resolution Digital Elevation Model (DEM) of the sea floor in Arc-GIS. From the DEM, we extracted channel long profiles across growing structures for both the current channel thalwegs and for the associated channel cut-and-fill sequences identified from the seismic data. We measured channel geometry at regular intervals along the channel length to evaluate system response to tectonic perturbation, and we used this data to help us approximate the down-system distribution of bed shear stress, and hence incision capacity. Initial results show that changes in submarine channel longitudinal profiles are directly correlated to underlying seabed thrusts and folds. Channels gradients are typically linear to slightly concave, and have an average gradient of 0.90. Actively growing thrusts are associated with a local steepening in channel gradient (up to 200% change), which typically extends 0.5 to 2 km upstream of the fault. Within these "knickzones

  16. The structure and functioning of the benthic macrofauna of the Bristol Channel and Severn Estuary, with predicted effects of a tidal barrage.

    PubMed

    Warwick, R M; Somerfield, P J

    2010-01-01

    The severity of the physical regime in the hypertidal Severn Estuary and Bristol Channel decreases in intensity in the seaward direction. As a result, the diversity of benthic macrofaunal species is very low in the Estuary and Inner Channel, but is still relatively low in the Outer Channel compared with more benign conditions elsewhere in the UK. Nevertheless, the taxonomic spread of species (taxonomic distinctness) throughout the area is no lower than expected. Barrage construction would result in an increase in the area of soft sediment relative to hard bottom benthic assemblages and the disappearance of reduced communities seaward of the barrage, although the time-scale of such a change is not known. Above the barrage the overall species richness, density and biomass of the benthos are likely to increase, factors that will ameliorate the loss of inter-tidal area.

  17. Constraining the erosional response of deep-water channel systems to growing folds and thrusts, Niger Delta.

    NASA Astrophysics Data System (ADS)

    Whittaker, A. C.; Lonergan, L.; Jolly, B. A.

    2015-12-01

    Gravity-driven folds and thrusts often characterize the slope and deep-water settings of passive margins. These structures exert a significant control on sediment gravity flows because they determine the location and configuration of sediment depo-centres and transport systems. Here we exploit 3D seismic data in the outer toe-thrust region of the deep-water Niger Delta to analyse the interaction between Plio-Pleistocene channel systems and actively-growing folds and thrusts. We first map folds and thrusts from the seismic data and we use this data to reconstruct the history of fold growth in detail. We then make quantitative measurements of the geomorphic response of submarine channels to growing tectonic structures in order to provide new constraints on their long-term erosional dynamics. This information is used to infer morphodyanamic processes that sculpted the channel systems through time, and to estimate the bed shear stresses and fluid velocities of typical flow events. The bathymetric long profiles of these channels have concavities that range from -0.08 to -0.34, and an average gradient of ~1o. Thrusts are associated with a local steepening in channel gradient of up to 3 times, and this effect extends 0.5 - 2 km upstream of the thrust. Within these knickzones, channel incision increases by approximately by a factor of 2, with a corresponding width decrease of approximately 25%. Channel incision across growing structures is achieved through enhanced bed-shear stress driven incision (up to 200 Pa) and flow velocity (up to 5 ms-1) assuming typical bulk sediment concentrations of 0.6%. Comparison of structural uplift since 1.7 Ma, and channel incision over an equivalent period, shows that many of these channels are able to keep pace with the time-integrated uplift since 1.7 Ma, and may have reached a bathymetric steady-state. Generally, bed-shear stresses of ~150 Pa are sufficient to keep pace with structural strain rates of 10-15 s-1. More widely, our data

  18. Characterization of the transport properties of channel delta-doped structures by light-modulated Shubnikov-de Haas measurements

    NASA Technical Reports Server (NTRS)

    Mena, R. A.; Schacham, S. E.; Haugland, E. J.; Alterovitz, S. A.; Young, P. G.; Bibyk, S. B.; Ringel, S. A.

    1995-01-01

    The transport properties of channel delta-doped quantum well structures were characterized by conventional Hall effect and light-modulated Shubnikov-de Haas (SdH) effect measurements. The large number of carriers that become available due to the delta-doping of the channel, leads to an apparent degeneracy in the well. As a result of this degeneracy, the carrier mobility remains constant as a function of temperature from 300 K down to 1.4 K. The large amount of impurity scattering, associated with the overlap of the charge carriers and the dopants, resulted in low carrier mobilities and restricted the observation of the oscillatory magneto-resistance used to characterize the two-dimensional electron gas (2DEG) by conventional SdH measurements. By light-modulating the carriers, we were able to observe the SdH oscillation at low magnetic fields, below 1.4 tesla, and derive a value for the quantum scattering time. Our results for the ratio of the transport and quantum scattering times are lower than those previously measured for similar structures using much higher magnetic fields.

  19. The interaction between deepwater channel systems and growing thrusts and folds, toe-thrust region of the deepwater Niger Delta

    NASA Astrophysics Data System (ADS)

    Jolly, Byami; Whittaker, Alex; Lonergan, Lidia

    2015-04-01

    Gravity-driven seaward-verging thrusts, landward-verging back-thrusts and associated folds often characterize the slope and deepwater settings of passive margins. These structures, found in the 'toe-thrust' region of the system, exert a significant control on sediment gravity flows because they create and determine the location and configuration of sediment depocentres and transport systems. Consequently, a quantitative understanding of the interaction between sediment gravity flows and seabed topography is required to understand these systems effectively. Here we make quantitative measurements of the geomorphic response of submarine channels to growing tectonic structures with the aim of providing new constraints on the long-term erosional dynamics of submarine channel systems. This study exploits 3D seismic data in the outer toe-thrust region of the deepwater Niger Delta to analyze the interaction between Plio-Pleistocene channel systems and actively growing folds and thrusts. We mapped folds and thrusts from the seismic data and we used this data to reconstruct the history of fold growth. We then used the sea-bed seismic horizon to build a 50 m resolution Digital Elevation Model (DEM) of the sea floor in Arc-GIS. We extracted channel long- profiles across growing structures from the DEM, and made measurements of channel geometries at regular intervals along the channel length. This information was used to infer morphodyanamic processes that sculpted the channel systems through time, and to estimate the bed shear stresses and fluid velocities of typical flow events. The bathymetric long profiles of these channels are relatively linear with concavity that range from -0.08 to -0.34, and an average gradient of ~1o. Actively growing thrusts are typically associated with a local steepening in channel gradient by a factor of up to 3, and this effect extends 0.5 - 2 km upstream of the thrust. Within these knickzones, channel incision increases by approximately by a

  20. Why do a precision measurement of delta m(atm)**2 in the electron-neutrino and anti-electron-neutrino disappearance channel?

    SciTech Connect

    Nunokawa, H; Parke, Stephen J; Zukanovich Funchal, R

    2005-07-01

    We discuss why high precision measurements of {delta}m{sub atm}{sup 2} in the {nu}{sub e}/{bar {nu}}{sub e} disappearance channels would be desirable in conjunction with the {delta}m{sub atms}{sup 2} high precision measurements that will be performed in the {nu}{sub {mu}} and {bar {nu}}{sub {mu}} disappearance channels by long baseline experiments such as T2K and NOvA. We show that if these measurements can achieve the challenging precision of about 0.5%, it will be possible to determine the mass hierarchy of the neutrino sector without the need of matter effects.

  1. Spatial variation of bed material grain size over a large dune in the Jade Bay tidal channel, German Wadden Sea (preliminary results)

    NASA Astrophysics Data System (ADS)

    Thompson, J. A.; Ernstsen, V. B.

    2007-12-01

    High-resolution bathymetry of a large dune with a height of ~4 m, a length of ~70 m and a cross- channel width of ~400 m was measured in the Jade Bay tidal channel, German Wadden Sea, using a multibeam echosounder (MBES) system. A total of 34 bed material samples were collected along 5 transects (trough-crest-trough) across the dune using a ShipekTM grab sampler. High-resolution flow velocity measurements, by means of an acoustic Doppler current profiler (ADCP), were conducted along 3 of these transects during a tidal cycle. Along the channel, mean grain sizes increase from trough to crest along all 5 transects. This increase is most pronounced in the center of the channel (trough ~340 μm, crest ~610 μm) compared to near the channel sides (trough ~425 μm, crest ~500 μm). Across the channel, mean grain sizes decrease along the crest (center ~610 μm, sides ~500 μm), but increase along the trough (center ~340 μm, sides ~425 μm) from the channel center toward the channel sides. The along-channel increase in mean grain size from trough to crest is coherent with an increase in the maximum near-bed flow velocity (calculated as the average flow velocity in the interval from 1 to 2 m above the bed). Moreover, this increase in near-bed flow velocity from trough to crest is more pronounced in the center of the channel (trough ~0.7 m/s, crest ~1.1 m/s) than near the channel sides (trough ~0.9 m/s, crest ~1.1 m/s), which is in line with the larger gradients in mean grain size in the center than along the sides. The higher flow velocities recorded at the crest relative to the trough is due to flow continuity. The across-track increase in mean grain size in the trough from the channel center toward the channel sides is consistent with an increase in the maximum near-bed flow velocity (center ~0.7 m/s, sides ~0.9 m/s). The decrease in mean grain size on the crest from the channel center toward the channel sides cannot simply be explained by lower near-bed flow velocities

  2. MAPPING AND MONITORING OF SALT MARSH VEGETATION AND TIDAL CHANNEL NETWORK FROM HIGH RESOLUTION IMAGERY (1975-2006). EXAMPLE OF THE MONT-SAINT-MICHEL BAY (FRANCE)

    NASA Astrophysics Data System (ADS)

    Puissant, A. P.; Kellerer, D.; Gluard, L.; Levoy, F.

    2009-12-01

    Coastal landscapes are severely affected by environmental and social pressures. Their long term development is controlled by both physical and anthropogenic factors, which spatial dynamics and interactions may be analysed by Earth Observation data. The Mont-Saint-Michel Bay (Normandy, France) is one of the European coastal systems with a very high tidal range (approximately 15m during spring tides) because of its geological, geomorphological and hydrodynamical contexts at the estuary of the Couesnon, Sée and Sélune rivers. It is also an important touristic place with the location of the Mont-Saint-Michel Abbey, and an invaluable ecosystem of wetlands forming a transition between the sea and the land. Since 2006, engineering works are performed with the objective of restoring the maritime character of the Bay. These works will lead to many changes in the spatial dynamics of the Bay which can be monitored with two indicators: the sediment budget and the wetland vegetation surfaces. In this context, the aim of this paper is to map and monitor the tidal channel network and the extension of the salt marsh vegetation formation in the tidal zone of the Mont-Saint-Michel Bay by using satellite images. The spatial correlation between the network location of the three main rivers and the development of salt marsh is analysed with multitemporal medium (60m) to high spatial resolution (from 10 to 30 m) satellite images over the period 1975-2006. The method uses a classical supervised algorithm based on a maximum likelihood classification of eleven satellites images. The salt-marsh surfaces and the tidal channel network are then integrated in a GIS. Results of extraction are assessed by qualitative (visual interpretation) and quantitative indicators (confusion matrix). The multi-temporal analysis between 1975 and 2006 highlights that in 1975 when the study area is 26000 ha, salt marshes cover 16% (3000ha), the sandflat (slikke) and the water represent respectively 59% and 25

  3. Quantifying the Effects of Combined Waves and Tides on Deltas: An Experimental Study

    NASA Astrophysics Data System (ADS)

    Paola, C.; Baumgardner, S. E.

    2015-12-01

    The classical Galloway diagram captures qualitatively the dramatic effect waves and tides have on reshaping river deltas. Here we investigate these controls in a series of laboratory experiments in which the relative energetics of river, wave, and tidal forcing could be controlled and systematically varied. The delta is fed from a single source of water and low-density, sand-size sediment in one corner of a 5m x 5m basin. Experimental tides are produced by transferring water back and forth between the main experimental basin and an auxiliary holding basin. The tidal period is 60 s and a typical tidal range is 30 mm. Waves are produced using a floating, oscillating paddle placed opposite the sediment feed location. They typically have a period of 1 s and an amplitude of 10 mm. The total energy flux associated with waves and tides is controlled by varying the temporal intermittency of each process, while river energy and sediment fluxes are held steady. The experiments show a variation in delta morphology as a function of wave and tidal forcing that parallels that observed in the field: increasing wave strength redistributes sediment and flattens the shoreline; increasing tidal strength creates well defined tidal channels as well as inlets through the wave-worked shoreline. Both waves and tides reduce the mobility of the main fluvial channel. Quantitative morphologic measures of these effects vary systematically as a function of dimensionless relative wave and tidal strength. The image below shows typical experimental delta morphology associated with mixed wave-tide forcing.

  4. Structural controls on channel-related seismic facies distribution in the toe-thrust of deepwater Niger Delta

    NASA Astrophysics Data System (ADS)

    Jolly, Byami A.; Anyiam, Okwudiri A.; Omeru, Tuviere

    2017-01-01

    Deepwater gravitational settings are often characterised by active structures at, or near the seabed. Consequently, these structures exert significant control on sediment distribution especially on the distribution of reservoir-grade sediments often transported to deepwater by turbidity flows. This study investigates structural controls on the spatial and temporal facies distribution in the deepwater Niger Delta using 3D seismic reflection data. The study shows that the main seismic facies include: (a) channel-axis sands and channel levees; (b) sheet sands deposited immediately outboard of channel levees; (c) pelagic deposits; and (d) slump deposits. The distribution and overall geometry/architecture of these facies vary from the west of the study area (dominated by growing fault-propagation folds) to the east where a piggyback basin had developed, and bounded by a broad detachment fold. Reservoir grade sheet sands (splays) are common, and their deposition is triggered by a sudden increase in seabed gradient (between 0.8° and 4°) at fold locations. The spatial distribution of the splays is controlled by the distribution of seabed scarps - located on the forelimbs of growing folds. Splays deposited in sub-basins in the west of the study area are lobate-shaped (up to 10 × 15 km). In contrast, splays deposited within the piggyback basin have shapes that are elongated parallel to a growing detachment fold that is causing channels to divert. This study has provided great insight into the distribution of seismic facies in a complex deepwater setting, and in particular, into the temporal evolution of reservoir facies and their potential organization into hydrocarbon traps as they interact with growing structures through time.

  5. Wetlands: Tidal

    USGS Publications Warehouse

    Conner, William H.; Krauss, Ken W.; Baldwin, Andrew H.; Hutchinson, Stephen

    2014-01-01

    Tidal wetlands are some of the most dynamic areas of the Earth and are found at the interface between the land and sea. Salinity, regular tidal flooding, and infrequent catastrophic flooding due to storm events result in complex interactions among biotic and abiotic factors. The complexity of these interactions, along with the uncertainty of where one draws the line between tidal and nontidal, makes characterizing tidal wetlands a difficult task. The three primary types of tidal wetlands are tidal marshes, mangroves, and freshwater forested wetlands. Tidal marshes are dominated by herbaceous plants and are generally found at middle to high latitudes of both hemispheres. Mangrove forests dominate tropical coastlines around the world while tidal freshwater forests are global in distribution. All three wetland types are highly productive ecosystems, supporting abundant and diverse faunal communities. Unfortunately, these wetlands are subject to alteration and loss from both natural and anthropogenic causes.

  6. Experimental studies of vertical mixing patterns in open channel flow generated by two delta wings side-by-side

    NASA Astrophysics Data System (ADS)

    Vaughan, Garrett

    Open channel raceway bioreactors are a low-cost system used to grow algae for biofuel production. Microalgae have many promises when it comes to renewable energy applications, but many economic hurdles must be overcome to achieve an economic fuel source that is competitive with petroleum-based fuels. One way to make algae more competitive is to improve vertical mixing in algae raceway bioreactors. Previous studies show that mixing may be increased by the addition of mechanisms such as airfoils. The circulation created helps move the algae from the bottom to top surface for necessary photosynthetic exchange. This improvement in light utilization allowed a certain study to achieve 2.2-2.4 times the amount of biomass relative to bioreactors without airfoils. This idea of increasing mixing in open channel raceways has been the focus of the Utah State University (USU) raceway hydraulics group. Computational Fluid Dynamics (CFD), Acoustic Doppler Velocimetry (ADV), and Particle Image Velocimetry (PIV) are all methods used at USU to computationally and experimentally quantify mixing in an open channel raceway. They have also been used to observe the effects of using delta wings (DW) in increasing vertical mixing in the raceway. These efforts showed great potential in the DW in increasing vertical mixing in the open channel bioreactor. However, this research begged the question, does the DW help increase algae growth? Three algae growth experiments comparing growth in a raceway with and without DW were completed. These experiments were successful, yielding an average 27.1% increase in the biomass. The DW appears to be a promising method of increasing algae biomass production. The next important step was to quantify vertical mixing and understand flow patterns due to two DWs side-by-side. Raceway channels are wider as they increase in size; and arrays of DWs will need to be installed to achieve quality mixing throughout the bioreactor. Quality mixing was attained for

  7. Principal components granulometric analysis of tidally dominated depositional environments

    SciTech Connect

    Mitchell, S.W. ); Long, W.T. ); Friedrich, N.E. )

    1991-02-01

    Sediments often are investigated by using mechanical sieve analysis (at 1/4 or 1/2{phi} intervals) to identify differences in weight-percent distributions between related samples, and thereby, to deduce variations in sediment sources and depositional processes. Similar granulometric data from groups of surface samples from two siliciclastic estuaries and one carbonate tidal creek have been clustered using principal components analysis. Subtle geographic trends in tidally dominated depositional processes and in sediment sources can be inferred from the clusters. In Barnstable Harbor, Cape Cod, Massachusetts, the estuary can be subdivided into five major subenvironments, with tidal current intensities/directions and sediment sources (longshore transport or sediments weathering from the Sandwich Moraine) as controls. In Morro Bay, San Luis Obispo county, California, all major environments (beach, dune, bay, delta, and fluvial) can be easily distinguished; a wide variety of subenvironments can be recognized. On Pigeon Creek, San Salvador Island, Bahamas, twelve subenvironments can be recognized. Biogenic (Halimeda, Peneroplios, mixed skeletal), chemogenic (pelopids, aggregates), and detrital (lithoclastis skeletal), chemogenic (pelopids, aggregates), and detrital (lithoclastis of eroding Pleistocene limestone) are grain types which dominate. When combined with tidal current intensities/directions, grain sources produce subenvironments distributed parallel to tidal channels. The investigation of the three modern environments indicates that principal components granulometric analysis is potentially a useful tool in recognizing subtle changes in transport processes and sediment sources preserved in ancient depositional sequences.

  8. Understanding how gravity flows shape deep-water channels. The Rhone delta canyon (Lake Geneva, Switzerland/France)

    NASA Astrophysics Data System (ADS)

    Corella, Juan Pablo; Loizeau, Jean Luc; Hilbe, Michael; le Dantec, Nicolas; Sastre, Vincent; Girardclos, Stéphanie

    2014-05-01

    Deep-water marine channels are highly dynamic environments due to the erosive power of sediment-laden currents that are continuously reshaping the morphology of these major sediment conduits. Proximal levees are prone to scarp failures generating gravity flows that can be transported thousands of kilometres from the original landslide. Nevertheless, the evolution of these underflows is still poorly understood because of the spatial scale of the processes and their difficult monitoring. For this reason, the smaller size, well-known boundary conditions and detailed bathymetric data makes Lake Geneva's sub-aquatic canyon in the Rhone delta an excellent analogue to understand these types of sedimentary processes that usually occur in deep-water channels in the marine realm. A multidisciplinary research strategy including innovative coring via MIR submersibles, in-situ geotechnical tests, geophysical and sedimentological analyses, as well as acquisition of different multibeam bathymetric data sets, were applied to understand the triggering processes, transport mechanisms and deposit features of gravity flows throughout the Rhone delta active canyon. The difference between two bathymetric surveys in 1986 and 2000 revealed an inversion in the topography of the distal active canyon, as a former distal canyon was transformed into a mound-like structure. A 12 m-thick layer was deposited in the canyon and modified the sediment transfer conduit. Sediment cores from this deposit were retrieved in-situ in 2002 and 2011 via the "F.-A. Forel" and Russian MIR submersibles, respectively. These cores contained a homogeneous, sandy material. Its sediment texture, grain-size, high density and shear strength, and low water content suggests that it corresponds to a debris-flow deposit that possibly took place after the initiation of a mass movement due to a scarp failure in proximal areas of the canyon. In addition, in-situ geotechnical tests on the modern canyon floor have shown a soft

  9. The San Juan Delta, Colombia: tides, circulations, and salt dispersion

    NASA Astrophysics Data System (ADS)

    Restrepo, Juan D.; Kjerfve, Björn

    2002-05-01

    The San Juan River delta (Colombia) with an area of 800 km 2 is the largest delta environment on the Pacific coast of South America. It consists of active distributaries maintained by an average discharge of 2500 m 3 s -1, is tide dominated, and has relatively narrow estuarine mixing zones <17 km wide and typically ˜7 km wide. Water level and current time series in two distributary mouths indicate that the tide is semidiurnal with a form number 0.1-0.2 and a mean range of 3 m. Processes at tidal frequencies explain 75-95% of the water level variability with the remaining low-frequency variability attributed to meteorological forcing and river processes. The tidal phase for the main diurnal and semidiurnal constituents progress from north to south along the coast. Only the southernmost distributary experiences significant tidal asymmetry as a result of strong river discharge and shallow depths. In the northernmost distributary, shallow water constituents are insignificant. Tidal currents were more semidiurnal than the water level, with form number 0.09-0.13. Tidal ellipses indicated that currents were aligned with the channels and mean amplitudes <1 m s -1. In the delta distributaries, circulation modes varied from seaward flow at all depths during intermediate runoff conditions to gravitational circulation during rising and high discharge periods. In San Juan and Chavica distributaries, the currents were ebb-directed, while in Charambirá they were flood-directed. The circulation appears to be controlled by the morphology of the distributaries, which were weakly stratified and only sometimes moderately stratified. The net salt transport was directed seaward in San Juan and Charambirá, and landward at Chavica, indicating an imbalance in the salt budget, and signifying non-steady state behavior. The net longitudinal salt flux in the San Juan delta is largely a balance between ebb-directed advective flux, and flood-directed tidal sloshing. Along the distributary

  10. Tidal inlet processes and deposits along a low energy coastline: easter Barataria Bight, Louisiana

    SciTech Connect

    Moslow, T.F.; Levin, D.R.

    1985-01-01

    Historical, seismic and vibracore data were used to determine the geologic framework of sand deposits along the predominantly muddy coastline of eastern Barataria Bight, Louisiana. Three inlet types with distinct sand body geometries and morphologies were identified and are found 1) at flanking barrier island systems spread laterally across the front of interdistributary bays; 2) in old distributary channels; 3) at overwash breaches; or 4) combination of these. Barataria Bight, a sheltered barrier island shoreline embayment with limited sand supply, minimal tidal range (36 cm) and low wave energies (30 cm) can be used to show examples of each inlet type. Barataria Pass and Quatre Bayou Pass are inlets located in old distributary channels. However, Barataria Pass has also been affected by construction between barrier islands. Pass Ronquille is located where the coastline has transgressed a low area in the delta plain. This breach is situated in a hydraulically efficient avenue between the Gulf and Bay Long behind it. Pass Abel is a combination of a low-profile barrier breach and the reoccupation of an old distributary channel. Shelf and shoreline sands are reworked from abandoned deltaic distributaries and headlands. Inner shelf sands are concentrated in thick (10 m) shore-normal relict distributary channels with fine grained cross-bedded and ripple laminated sand overlain by burrowed shelf muds. Shoreface sand deposits occur as 2-3 m thick, fine-grained, coarsening upward and burrowed ebb-tidal delta sequences and shore-parallel relict tidal inlet channels filled through lateral accretion.

  11. Ecosystem level methane fluxes from tidal freshwater and brackish marshes of the Mississippi River Delta: Implications for coastal wetland carbon projects

    USGS Publications Warehouse

    Holm, Guerry O.; Perez, Brian C.; McWhorter, David E.; Krauss, Ken W.; Johnson, Darren J.; Raynie, Richard C.; Killebrew, Charles J.

    2016-01-01

    Sulfate from seawater inhibits methane production in tidal wetlands, and by extension, salinity has been used as a general predictor of methane emissions. With the need to reduce methane flux uncertainties from tidal wetlands, eddy covariance (EC) techniques provide an integrated methane budget. The goals of this study were to: 1) establish methane emissions from natural, freshwater and brackish wetlands in Louisiana based on EC; and 2) determine if EC estimates conform to a methane-salinity relationship derived from temperate tidal wetlands with chamber sampling. Annual estimates of methane emissions from this study were 62.3 g CH4/m2/yr and 13.8 g CH4/m2/yr for the freshwater and brackish (8–10 psu) sites, respectively. If it is assumed that long-term, annual soil carbon sequestration rates of natural marshes are ~200 g C/m2/yr (7.3 tCO2e/ha/yr), healthy brackish marshes could be expected to act as a net radiative sink, equivalent to less than one-half the soil carbon accumulation rate after subtracting methane emissions (4.1 tCO2e/ha/yr). Carbon sequestration rates would need case-by-case assessment, but the EC methane emissions estimates in this study conformed well to an existing salinity-methane model that should serve as a basis for establishing emission factors for wetland carbon offset projects.

  12. Development of tidal inlet on Mississippi River deltaic plain

    SciTech Connect

    Howard, P.C.

    1983-09-01

    Surface sampling and bathymetric surveying in 1981 and charts from 1853 to 1934 are used to formulate the history of Quatre Bayou Pass, a major inlet within the transgressive environment of the Mississippi River deltaic plain. Over this period, land loss processes caused marsh to give way to lakes and bays; therefore, tidal exchange intensified through a break in the coastal barrier. Beach sand was reworked into small tidal deltas. As lakes and bays enlarged further, the tidal prism increased; consequently, both the pass and the sandy tidal deltas increased in size. Over the last century, the increased tidal flow caused Quatre Bayou Pass to have an eight-fold cross-sectional area enlargement and a three-fold ebb-tidal delta volume increase. At present, the throat is 15 m (49 ft) deep and 1.2 km (0.7 mi) wide, while the ebb-tidal delta is comprised of 14.9 by 10/sup 6/ +/- 10% m/sup 3/ of sediment. Concurrent with these developments, recession of the barrier and much of the shoreface proceeded at a rapid rate. Because the ebb-tidal delta had a simultaneous increase in volume, the shoreface in front of the pass remained relatively stable. In other words, bathymetric expression of the ebb-tidal delta did not develop solely through progradation, but was also formed through erosion of the surrounding Gulf bottom. Accordingly, the shoal is termed ebb-tidal delta retreat body.

  13. TIDAL AND TIDALLY AVERAGED CIRCULATION CHARACTERISTICS OF SUISUN BAY, CALIFORNIA.

    USGS Publications Warehouse

    Smith, Lawrence H.; Cheng, Ralph T.

    1987-01-01

    Availability of extensive field data permitted realistic calibration and validation of a hydrodynamic model of tidal circulation and salt transport for Suisun Bay, California. Suisun Bay is a partially mixed embayment of northern San Francisco Bay located just seaward of the Sacramento-San Joaquin Delta. The model employs a variant of an alternating direction implicit finite-difference method to solve the hydrodynamic equations and an Eulerian-Lagrangian method to solve the salt transport equation. An upwind formulation of the advective acceleration terms of the momentum equations was employed to avoid oscillations in the tidally averaged velocity field produced by central spatial differencing of these terms. Simulation results of tidal circulation and salt transport demonstrate that tides and the complex bathymetry determine the patterns of tidal velocities and that net changes in the salinity distribution over a few tidal cycles are small despite large changes during each cycle.

  14. Delineation of tidal scour through marine geophysical techniques at Sloop Channel and Goose Creek bridges, Jones Beach State Park, Long Island, New York

    USGS Publications Warehouse

    Stumm, Frederick; Chu, Anthony; Reynolds, Richard J.

    2001-01-01

    Inspection of the Goose Creek Bridge in southeastern Nassau County in April 1998 by the New York State Department of Transportation (NYSDOT) indicated a separation of bridge piers from the road bed as a result of pier instability due to apparent seabed scouring by tidal currents. This prompted a cooperative study by the U.S. Geological Survey with the NYSDOT to delineate the extent of tidal scour at this bridge and at the Sloop Channel Bridge, about 0.5 mile to the south, through several marine- geophysical techniques. These techniques included use of a narrow-beam, 200-kilohertz, research-grade fathometer, a global positioning system accurate to within 3 feet, a 3.5 to 7-kilohertz seismic-reflection profiler, and an acoustic Doppler current profiler (ADCP). The ADCP was used only at the Sloop Channel Bridge; the other techniques were used at both bridges.Results indicate extensive tidal scour at both bridges. The fathometer data indicate two major scour holes nearly parallel to the Sloop Channel Bridge—one along the east side, and one along the west side (bridge is oriented north-south). The scour-hole depths are as much as 47 feet below sea level and average more than 40 feet below sea level; these scour holes also appear to have begun to connect beneath the bridge. The deepest scour is at the north end of the bridge beneath the westernmost piers. The east-west symmetry of scour at Sloop Channel Bridge suggests that flood and ebb tides produce extensive scour.The thickness of sediment that has settled within scour holes could not be interpreted from fathometer data alone because fathometer frequencies cannot penetrate beneath the sea-floor surface. The lower frequencies used in seismic-reflection profiling can penetrate the sea floor and underlying sediments, and indicate the amount of infilling of scour holes, the extent of riprap under the bridge, and the assemblages of clay, sand, and silt beneath the sea floor. The seismic- reflection surveys detected 2 to

  15. Delineation of tidal scour through marine geophysical techniques at Sloop Channel and Goose Creek bridges, Jones Beach State Park, Long Island, New York

    USGS Publications Warehouse

    Stumm, Frederick; Chu, Anthony; Reynolds, Richard J.

    2001-01-01

    Inspection of the Goose Creek Bridge in southeastern Nassau County in April 1998 by the New York State Department of Transportation (NYSDOT) indicated a separation of bridge piers from the road bed as a result of pier instability due to apparent seabed scouring by tidal currents. This prompted a cooperative study by the U.S. Geological Survey with the NYSDOT to delineate the extent of tidal scour at this bridge and at the Sloop Channel Bridge, about 0.5 mile to the south, through several marine- geophysical techniques. These techniques included use of a narrow-beam, 200-kilohertz, research-grade fathometer, a global positioning system accurate to within 3 feet, a 3.5 to 7-kilohertz seismic-reflection profiler, and an acoustic Doppler current profiler (ADCP). The ADCP was used only at the Sloop Channel Bridge; the other techniques were used at both bridges. Results indicate extensive tidal scour at both bridges. The fathometer data indicate two major scour holes nearly parallel to the Sloop Channel Bridge -- one along the east side, and one along the west side (bridge is oriented north-south). The scour-hole depths are as much as 47 feet below sea level and average more than 40 feet below sea level; these scour holes also appear to have begun to connect beneath the bridge. The deepest scour is at the north end of the bridge beneath the westernmost piers. The east-west symmetry of scour at Sloop Channel Bridge suggests that flood and ebb tides produce extensive scour. The thickness of sediment that has settled within scour holes could not be interpreted from fathometer data alone because fathometer frequencies cannot penetrate beneath the sea-floor surface. The lower frequencies used in seismic-reflection profiling can penetrate the sea floor and underlying sediments, and indicate the amount of infilling of scour holes, the extent of riprap under the bridge, and the assemblages of clay, sand, and silt beneath the sea floor. The seismic- reflection surveys detected 2

  16. Role of sediment supply and relative sea-level on sediment delivery to submarine deltas and fans of the Laurentian Channel (Lower St. Lawrence Estuary, Eastern Canada)

    NASA Astrophysics Data System (ADS)

    Normandeau, Alexandre; Lajeunesse, Patrick; St-Onge, Guillaume; Francus, Pierre

    2016-04-01

    Series of submarine canyons and channels observed in the Lower St. Lawrence Estuary (LSLE; Eastern Canada) provide an opportunity to analyze in great detail their morphology, spatial distribution and Holocene activity in a relatively shallow (≤300 m) semi-enclosed basin. Four categories of canyons and channels were identified according to their feeding sources: glacially-fed, river-fed, longshore drift-fed and sediment-starved systems. This presentation will focus on the interaction between glacially-fed, river-fed (deltas) and longshore drift-fed systems. Three main types of deposits were identified in sediment core samples and seismic stratigraphy: turbidites, debrites and hyperpycnites. The analysis of high-resolution multibeam data, seismic profiles and sediment cores reveals the differences in timing of these gravity flow deposits related to submarine fan deposition. Submarine fans related to glacial meltwaters were formed during deglaciation, near 11 ka cal BP. Following the retreat of the Laurentide Ice Sheet margin in the LSLE, delta progradation allowed the formation of submarine channels by debris and hyperpycnal flows. A reduction of sediment supply from the rivers and a relative sea-level stabilization by 7 ka cal BP then limited the occurrence of these debris and hyperpycnal flows and favoured erosion of the delta fronts. During delta progradation, longshore drift-fed submarine fans were also formed due to high sediment supply, but continued transferring terrigenous material throughout the Holocene. This continued activity was possible because delta fronts eroded and longshore drift transported sediments to the canyons located at the end of a littoral cell. This study highlights that the variability and timing of sediment deposition in submarine deltas and fans is controlled primarily by variations in sediment supply in a formerly glaciated environment.

  17. Increased gamma- and decreased delta-oscillations in a mouse deficient for a potassium channel expressed in fast-spiking interneurons.

    PubMed

    Joho, R H; Ho, C S; Marks, G A

    1999-10-01

    Kv3.1 is a voltage-gated, fast activating/deactivating potassium (K(+)) channel with a high-threshold of activation and a large unit conductance. Kv3.1 K(+) channels are expressed in fast-spiking, parvalbumin-containing interneurons in cortex, hippocampus, striatum, the thalamic reticular nucleus (TRN), and in several nuclei of the brain stem. A high density of Kv3.1 channels contributes to short-duration action potentials, fast afterhyperpolarizations, and brief refractory periods enhancing the capability in these neurons for high-frequency firing. Kv3.1 K(+) channel expression in the TRN and cortex also suggests a role in thalamocortical and cortical function. Here we show that fast gamma and slow delta oscillations recorded from the somatomotor cortex are altered in the freely behaving Kv3.1 mutant mouse. Electroencephalographic (EEG) recordings from homozygous Kv3.1(-/-) mice show a three- to fourfold increase in both absolute and relative spectral power in the gamma frequency range (20-60 Hz). In contrast, Kv3.1-deficient mice have a 20-50% reduction of power in the slow delta range (2-3 Hz). The increase in gamma power is most prominent during waking in the 40- to 55-Hz range, whereas the decrease in delta power occurs equally across all states of arousal. Our findings suggest that Kv3. 1-expressing neurons are involved in the generation and maintenance of cortical fast gamma and slow delta oscillations. Hence the Kv3. 1-mutant mouse could serve as a model to study the generation and maintenance of fast gamma and slow delta rhythms and their involvement in behavior and cognition.

  18. Room-temperature field effect transistors with metallic ultrathin TiN-based channel prepared by atomic layer delta doping and deposition.

    PubMed

    Cheng, Po-Hsien; Wang, Chun-Yuan; Chang, Teng-Jan; Shen, Tsung-Han; Cai, Yu-Syuan; Chen, Miin-Jang

    2017-04-13

    Metallic channel transistors have been proposed as the candidate for sub-10 nm technology node. However, the conductivity modulation in metallic channels can only be observed at low temperatures usually below 100 K. In this study, room-temperature field effect and modulation of the channel resistance was achieved in the metallic channel transistors, in which the oxygen-doped TiN ultrathin-body channels were prepared by the atomic layer delta doping and deposition (AL3D) with precise control of the channel thickness and electron concentration. The decrease of channel thickness leads to the reduction in electron concentration and the blue shift of absorption spectrum, which can be explained by the onset of quantum confinement effect. The increase of oxygen incorporation results in the increase of interband gap energy, also giving rise to the decrease in electron concentration and the blue shift of absorption spectrum. Because of the significant decrease in electron concentration, the screening effect was greatly suppressed in the metallic channel. Therefore, the channel modulation by the gate electric field was achieved at room temperature due to the quantum confinement and suppressed screening effect with the thickness down to 4.8 nm and the oxygen content up to 35% in the oxygen-doped TiN ultrathin-body channel.

  19. Morphology and sedimentation on open-coast intertidal flats of the Changjiang Delta, China

    USGS Publications Warehouse

    Fan, D.; Li, C.; Wang, D.; Wang, P.; Archer, A.W.; Greb, S.F.

    2004-01-01

    On many intertidal flats, lateral aggradation and reworking by large tidal channels is the dominant sedimentary process. On the open-coast intertidal flats of the Changjiang Delta large laterally migrating tidal channels are absent. Instead, numerous shallow tidal creeks cut across the intertidal flats. On these flats, vertical rather than lateral migration dominates sedimentation. Observations over semidiurnal tidal cycles show that both flood and ebb tides have the potential to deposit their own mud-sand couplets, but four couplets per day are rarely preserved. Reworking by tidal currents and/or weak waves results in loss of tidal couplets or amalgamation of two or more thin couplets into a single thick couplet. Measurements of preserved couplets show that they can represent a single flooding or ebbing event (half day) to a period of several neap-spring cycles. Diastems within amalgamated couplets are generally not distinguishable. The key agent for reworking open-coast intertidal flat deposits is not tidal creek migration but seasonal storm waves. Seasonal storm deposits consist of a basal scour and sand-dominant laminae with mud pebbles, grading upward to mud-dominated layers of fair-weather deposits. Sand-dominated layers are also reworked.

  20. Ecology of Juvenile Salmon in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, Lower Columbia River, 2008

    SciTech Connect

    Sather, Nichole K.; Johnson, Gary E.; Storch, Adam; Teel, David; Skalski, John R.; Jones, Tucker A.; Dawley, Earl M.; Zimmerman, Shon A.; Borde, Amy B.; Mallette, Christine; Farr, R.

    2009-05-29

    The tidal freshwater monitoring (TFM) project reported herein is part of the research, monitoring, and evaluation effort developed by the Action Agencies (Bonneville Power Administration, the U.S. Army Corps of Engineers [USACE], and the U.S. Bureau of Reclamation) in response to obligations arising from the Endangered Species Act (ESA) as a result of operation of the Federal Columbia River Power System. The project is being performed under the auspices of the Northwest Power and Conservation Council’s Columbia Basin Fish and Wildlife Program (Project No. 2005-001-00). The research is a collaborative effort among the Pacific Northwest National Laboratory, the Oregon Department of Fish and Wildlife, the National Marine Fisheries Service, and the University of Washington.

  1. Sediment fluxes and delta evolution at Tuapaat, Disko Island, Greenland

    NASA Astrophysics Data System (ADS)

    Kroon, A.; Andersen, T. J.; Bendixen, M.

    2013-12-01

    Ice and snow and freezing temperatures have an important influence on the coastal morphodynamics in arctic polar coastal environments. Global climate changes induce many changes along the arctic coasts. Sea-levels are rising due to thermal expansion and due to an increased fresh water flux from the glaciers and land ice masses while ice coverage of the coastal waters decreases and the open water periods in summer extend. On a yearly basis, there is a strong variation over the seasons with open waters and active rivers in summer and ice-covered coastal waters and inactive rivers in winter. The coastal processes by waves and tides are thus often limited to the summer and early fall. On a daily basis, there is also a strong variation in fluvial discharges due to the daily variations in glacier melt with maximum melt in the afternoon and minimum values at night. At the same time, the actual flux of the river to the coastal bay is also influenced by the tidal phase: low tides in the afternoon will probably give the maximum plumes in the coastal waters and high tides in the early morning will reduce the input of sediments to the coastal waters to zero. The southern shore of Disko Island in western Greenland has four deltas: Igpik, Signiffik, Tuappat and Skansen. The sediments of these deltas are a mixture of sand and gravel and they are fed by melting glaciers. The Tuapaat delta is located at the end of a pro-glacial and fluvial valley at about 16 km from the glacier. The shores of the delta are reworked by waves, predominantly from southwestern (largest fetch, over 50 km), southern, and southeastern directions. The environment has a micro- to meso- tidal range with a spring tidal range of 2.7m. The morphologic changes on the delta over the last decades clearly showed an eastward migration of the main delta channel, probably due to wave-driven alongshore processes in the ice-free periods. In this presentation, we focus on quantification of sediment fluxes on the Tuapaat

  2. Submarine sedimentary features on a fjord delta front, Queen Inlet, Glacier Bay, Alaska

    USGS Publications Warehouse

    Carlson, Paul R.; Powell, Ross D.; Phillips, Andrew C.

    1992-01-01

    Side-scan sonar images provide a view of an actively changing delta front in a marine outwash fjord in Glacier Bay, Alaska. Numerous interconnected gullies and chute-like small channels form paths for the transport of sand and coarse silt from the braided glacial outwash streams on the delta plain to the sinuous turbidity-current channels incised into the fjord floor. These turbidity-current channels carry coarse sediment through the fjord and into the adjoining glacial trunk valley. Several sedimentary processes affect the development of this delta front: overflow plumes deposit fine sediment; sediment gravity flows result from episodic delivery of large loads of coarse sediment; and mass movement may be triggered by earthquakes and, more regularly, by spring-tidal drawdown or hydraulic loading.

  3. Morphodynamics of the Pacific and Caribbean deltas of Colombia, South America

    NASA Astrophysics Data System (ADS)

    Restrepo, Juan D.; López, Sergio A.

    2008-02-01

    , respectively, and the lowest attenuation index of deep-water waves, is the most wave-influenced delta of Colombia. Statistical relationships show that the area of Colombian deltas is best predicted from average discharge and bank-full width of river entering the delta. The number of distributary channels is explained by the marine power index and the gradient of the delta plain. The average and total width of distributary channels are largely controlled by the tidal range. Further analysis of shoreline changes indicate that the retreating behavior of the western part of the Magdalena delta has been due to anthropogenic causes, including the construction of jetties in 1936. By contrast, processes of rapid erosion in the San Juan delta have been the result of 2.6 mm yr -1 long-term relative sea level rise due to tectonic induced subsidence coupled with a eustatic rise of sea level. Overall, the other deltas are experiencing prograding phases with rates of accretion of 100 m yr -1 in the artificial delta of the Canal del Dique.

  4. Overland Tidal Power Generation Using Modular Tidal Prism

    SciTech Connect

    Khangaonkar, Tarang; Yang, Zhaoqing; Geerlofs, Simon H.; Copping, Andrea

    2010-03-01

    Naturally occurring sites with sufficient kinetic energy suitable for tidal power generation with sustained currents > 1 to 2 m/s are relatively rare. Yet sites with greater than 3 to 4 m of tidal range are relatively common around the U.S. coastline. Tidal potential does exist along the shoreline but is mostly distributed, and requires an approach which allows trapping and collection to also be conducted in a distributed manner. In this paper we examine the feasibility of generating sustainable tidal power using multiple nearshore tidal energy collection units and present the Modular Tidal Prism (MTP) basin concept. The proposed approach utilizes available tidal potential by conversion into tidal kinetic energy through cyclic expansion and drainage from shallow modular manufactured overland tidal prisms. A preliminary design and configuration of the modular tidal prism basin including inlet channel configuration and basin dimensions was developed. The unique design was shown to sustain momentum in the penstocks during flooding as well as ebbing tidal cycles. The unstructured-grid finite volume coastal ocean model (FVCOM) was used to subject the proposed design to a number of sensitivity tests and to optimize the size, shape and configuration of MTP basin for peak power generation capacity. The results show that an artificial modular basin with a reasonable footprint (≈ 300 acres) has the potential to generate 10 to 20 kw average energy through the operation of a small turbine located near the basin outlet. The potential of generating a total of 500 kw to 1 MW of power through a 20 to 40 MTP basin tidal power farms distributed along the coastline of Puget Sound, Washington, is explored.

  5. Tidal currents in the Adriatic as measured by surface drifters

    NASA Astrophysics Data System (ADS)

    Poulain, Pierre-Marie

    2013-03-01

    Velocities of surface drifters are analyzed to study tidal currents throughout the Adriatic Sea. Spectral and harmonic analyses indicate that the M2, S2, and K1 constituents dominate. Maps of tidal characteristics show that M2 and S2 are rectilinear currents (reversing tides) aligned with the main axis of the Adriatic basin with maximum amplitude (~7 cm/s for M2 and ~4 cm/s for S2) in the northern area off the Istrian Peninsula. Near the northern coast, semidiurnal tidal currents decrease in amplitude and rotate in the counterclockwise sense. Near the Po River delta, M2 (S2) motions rotate in the counterclockwise (clockwise) sense. S2 rotation is also counterclockwise near the northeastern coast. M2 phases increase from about 130° on the eastern Croatian coast to 190° on the western Italian side. S2 phases range from 150° to 200°. In the middle and southern Adriatic, the semidiurnal tides are small (~1 cm/s). The diurnal tidal currents (K1) are strong across the basin at the levels of Monte Conero and the Gargano Peninsula with speed larger than 5 cm/s and mainly clockwise rotation, and also in coastal areas (e.g., on the Albanian shelf and close to the Otranto Channel). Phases increase from the east to the west coasts (by as much as 150°). These new results compare satisfactorily with previous observations and numerical simulations, although tidal amplitudes are under-estimated with respect to mooring measurements. They extend for the first time the description of the Adriatic tidal currents to the entire basin based on direct velocity observations.

  6. Identification of the alternative spliced form of the alpha 2/delta subunit of voltage sensitive Ca2+ channels expressed in PC12 cells.

    PubMed

    Gilad, B; Shenkar, N; Halevi, S; Trus, M; Atlas, D

    1995-07-07

    The alpha 2/delta subunit of voltage sensitive Ca2+ channels expressed in PC12 has been cloned and partially sequenced. The message observed in Northern blot analysis displays a 7.5 kb transcript, identical in size to mRNA of rabbit skeletal muscle and rat brain. The nucleotide sequence of the cloned alpha 2 subunit of the PC12 specific cDNA is > 99% identical to rat brain sequence and 85% to skeletal muscle. Reverse-transcriptase-polymerase chain reaction (RT-PCR) of the alternative splicing region identifies two deleted regions of 57 bp and 21 bp in PC12 expressed alpha 2/delta transcript. The alternative variant alpha 2e of alpha 2/delta subunit which is expressed in PC12 cells was previously identified in human embryonic kidney (HEK293) cells. RT-PCR analysis show two different sized alternative PCR fragments in rat lung and none in rat spleen, kidney and intestine. Antibodies prepared against a 19 amino acid peptide within the alternative spliced region effectively inhibits [3H]dopamine release in PC12 cells. This implies that the alternatively spliced region is positioned extracellularly and is involved in regulation of the L-type Ca2+ channel-mediated transmitter release.

  7. Tidal Energy.

    ERIC Educational Resources Information Center

    Impact of Science on Society, 1987

    1987-01-01

    States that tidal power projects are feasible in a relatively limited number of locations around the world. Claims that together they could theoretically produce the energy equivalent to more than one million barrels of oil per year. (TW)

  8. Tidal dunes versus tidal bars: The sedimentological and architectural characteristics of compound dunes in a tidal seaway, the lower Baronia Sandstone (Lower Eocene), Ager Basin, Spain

    NASA Astrophysics Data System (ADS)

    Olariu, Cornel; Steel, Ronald J.; Dalrymple, Robert W.; Gingras, Murray K.

    2012-11-01

    The Lower Eocene Baronia Formation in the Ager Basin is interpreted as a series of stacked compound dunes confined within a tectonically generated embayment or tidal seaway. This differs from the previous interpretation of lower Baronia sand bodies as tidal bars in the front of a delta. The key architectural building block of the succession, the deposit of a single compound dune, forms a 1-3 m-thick, upward coarsening succession that begins with highly bioturbated, muddy, very fine to fine grained sandstone that contains an open-marine Cruziana ichnofacies. This is overlain gradationally by ripple-laminated sandstone that is commonly bioturbated and contains mud drapes. The succession is capped by fine- to coarse-grained sandstones that contain both planar and trough cross-strata with unidirectional or bi-directional paleocurrent directions and occasional thin mud drapes on the foresets. The base of a compound dune is gradational where it migrated over muddy sandstone deposited between adjacent dunes, but is sharp and erosional where it migrated over the stoss side of a previous compound dune. The cross strata that formed by simple superimposed dunes dip in the same direction as the inclined master bedding planes within the compound dune, forming a forward-accretion architecture. This configuration is the fundamental reason why these sandbodies are interpreted as compound tidal dunes rather than as tidal bars, which, in contrast, generate lateral-accretion architecture. In the Baronia, fields of compound dunes generated tabular sandbodies 100s to 1000s of meters in extent parallel to the paleocurrent direction and up to 6 m thick that alternate vertically with highly bioturbated muddy sandstones (up to 10 m thick) that represent the low-energy fringes of the dune fields or periods of high sea level when current speeds decreased. Each cross-stratified sandstone sheet (compound-dune complexes) contains overlapping lenticular "shingles" formed by individual compound

  9. Tidal Power Exploitation in Korea

    NASA Astrophysics Data System (ADS)

    Choi, Byung Ho; Kim, Kyeong Ok; Choi, Jae Cheon

    The highest tides in South Korea are found along the northwest coast between latitudes 36-38 degrees and the number of possible sites for tidal range power barrages to create tidal basins is great due to irregular coastlines with numerous bays. At present Lake Sihwa tidal power plant is completed. The plant is consisted of 10 bulb type turbines with 8 sluice gates. The installed capacity of turbines and generators is 254MW and annual energy output expected is about 552.7 GWh taking flood flow generation scheme. Three other TPP projects are being progressed at Garolim Bay (20 turbines with 25.4MW capacity), Kangwha (28 turbines with 25.4MW capacity), Incheon (44 or 48 turbines with 30 MW capacity) and project features will be outlined here. The introduction of tidal barrages into four major TPP projects along the Kyeonggi bay will render wide range of potential impacts. Preliminary attempts were performed to quantify these impacts using 2 D hydrodynamic model demonstrating the changes in tidal amplitude and phase under mean tidal condition, associated changes in residual circulation (indicator for SPM and pollutant dispersion), bottom stress (indicator for bedload movement), and tidal front (positional indicator for bio-productivity) in both shelf scale and local context. Tidal regime modeling system for ocean tides in the seas bordering the Korean Peninsula is designed to cover an area that is broad in scope and size, yet provide a high degree of resolution in strong tidal current region including off southwestern tip of the Peninsula (Uldolmok , Jangjuk, Wando-Hoenggan), Daebang Sudo (Channel) and Kyeonggi Bay. With this simulation system, real tidal time simulation of extended springneap cycles was performed to estimate spatial distribution of tidal current power potentials in terms of power density, energy density and then extrapolated annual energy density.

  10. River salinity on a mega-delta, an unstructured grid model approach.

    NASA Astrophysics Data System (ADS)

    Bricheno, Lucy; Saiful Islam, Akm; Wolf, Judith

    2014-05-01

    With an average freshwater discharge of around 40,000 m3/s the BGM (Brahmaputra Ganges and Meghna) river system has the third largest discharge worldwide. The BGM river delta is a low-lying fertile area covering over 100,000 km2 mainly in India and Bangladesh. Approximately two-thirds of the Bangladesh people work in agriculture and these local livelihoods depend on freshwater sources directly linked to river salinity. The finite volume coastal ocean model (FVCOM) has been applied to the BGM delta in order to simulate river salinity under present and future climate conditions. Forced by a combination of regional climate model predictions, and a basin-wide river catchment model, the 3D baroclinic delta model can determine river salinity under the current climate, and make predictions for future wet and dry years. The river salinity demonstrates a strong seasonal and tidal cycle, making it important for the model to be able to capture a wide range of timescales. The unstructured mesh approach used in FVCOM is required to properly represent the delta's structure; a complex network of interconnected river channels. The model extends 250 km inland in order to capture the full extent of the tidal influence and grid resolutions of 10s of metres are required to represent narrow inland river channels. The use of FVCOM to simulate flows so far inland is a novel challenge, which also requires knowledge of the shape and cross-section of the river channels.

  11. Role of spinal voltage-dependent calcium channel alpha 2 delta-1 subunit in the expression of a neuropathic pain-like state in mice.

    PubMed

    Narita, Minoru; Nakajima, Mayumi; Miyoshi, Kan; Narita, Michiko; Nagumo, Yasuyuki; Miyatake, Mayumi; Yajima, Yoshinori; Yanagida, Kiyomi; Yamazaki, Mitsuaki; Suzuki, Tsutomu

    2007-05-08

    The present study was undertaken to investigate the role of spinal voltage-dependent calcium channel alpha(2)delta-1 subunit in the expression of a neuropathic pain-like state induced by partial sciatic nerve ligation in mice. In cultured spinal neurons, gabapentin (GBP), which displays the inhibitory effect of alpha(2)delta-1 subunit, suppressed the extracellular Ca(2+) influx induced by KCl, whereas it failed to inhibit the intracellular Ca(2+) release induced by inositol-1,4,5-triphosphate. Seven days after sciatic nerve ligation, the protein level of alpha(2)delta-1 subunit in the ipsilateral spinal cord was clearly increased compared to that observed in sham-operated mice. In addition, the mRNA level of alpha(2)delta-1 subunit was significantly increased in the dorsal root ganglion, but not in the spinal cord, of nerve-ligated mice. Under these conditions, a marked decrease in the latency of paw-withdrawal against a thermal stimulation and tactile stimulation, induced by sciatic nerve ligation was abolished by repeated intrathecal (i.t.) treatment with GBP. Additionally, the persistent reduction in the nociceptive threshold by i.t. treatment with GBP at the early stage of the neuropathic pain-like state was maintained for 7 days even after GBP withdrawal. It is of interest to note that a single i.t. post-injection of GBP showed a marked and transient inhibitory effect on the developed neuropathic pain-like state, whereas repeated i.t. post-treatment with GBP produced a persistent inhibitory effect during the treatment. In conclusion, we propose here that the neuropathic pain-like state with sciatic nerve ligation is associated with the increased level of the alpha(2)delta-1 subunit of Ca(2+) channels at the sensory nerve terminal in the spinal dorsal horn of mice. Furthermore, the present data provide evidence that the neuropathic pain may be effectively controlled by repeated treatment with GBP at the early stage.

  12. Facies architecture of submarine channel deposits on the western Niger Delta slope: Implications for grain-size and density stratification in turbidity currents

    NASA Astrophysics Data System (ADS)

    Jobe, Zane; Sylvester, Zoltán.; Pittaluga, Michele Bolla; Frascati, Alessandro; Pirmez, Carlos; Minisini, Daniel; Howes, Nick; Cantelli, Alessandro

    2017-02-01

    High-resolution bathymetry, seismic reflection, and piston core data from a submarine channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above channel thalweg and/or distance from channel centerline. A 5 times decrease in bed thickness and 1-2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for submarine channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.

  13. Modeling Tidal and Floodplain Inundation for Restoration on the McCormack-Williamson Tract

    NASA Astrophysics Data System (ADS)

    Hammersmark, C. T.; Schladow, S. G.; Fleenor, W. E.; Blake, S. H.

    2001-12-01

    To support management decisions regarding the proposed McCormack-Williamson Tract restoration program, a dynamic hydraulic numerical model of the lower Cosumnes River, lower Mokelumne River, and the northern portion of the Sacramento San Joaquin Delta Region is employed. Goals of the restoration program include the development of diverse aquatic and terrestrial habitats and agricultural land uses, which are seasonally attractive to migratory bird species. In addition to utilization of the McCormack-Williamson Tract for continued agricultural use and restoration of functional and sustainable tidal fresh water marsh habitat, enhanced flood management and water conveyance objectives are sought. The complex nature of surface water flow resulting from a regulated watershed (Mokelumne River), an unregulated watershed (Cosumnes River), and the tidally influenced North Delta is simulated with a one-dimensional unsteady hydraulic model using MIKE 11. The model includes all relevant river channels and sloughs within the study area, and extends from the San Joaquin River to the south, the Sacramento River to the west, and east to Woodbridge on the Mokelumne River, Galt on Dry Creek, and Michigan Bar on the Cosumnes River. Gage data from the flood periods (January to April) of the years 1996, 1998, 1999, and 2000 are used as boundary conditions to drive the model. The model is used to examine several proposed management scenarios, with design alternatives varying with regard to the extent and location of the restored region, configuration of water control structures and/or levee breaches, and operations scenarios of the existing Delta Cross Channel and the proposed Through Delta Facility. The model output is used to analyze effects to the regional hydraulics, with an emphasis placed on upstream and downstream stage, and the magnitude, duration and frequency of tidal and flood flows within different zones of the proposed project.

  14. Effect of tides, river flow, and gate operations on entrainment of juvenile salmon into the interior Sacramento–San Joaquin River Delta

    USGS Publications Warehouse

    Perry, Russell W.; Brandes, Patricia L.; Burau, Jon R.; Sandstrom, Philip T.; Skalski, John R.

    2015-01-01

    Juvenile Chinook Salmon Oncorhynchus tshawytscha emigrating from natal tributaries of the Sacramento River, California, must negotiate the Sacramento-San Joaquin River Delta (hereafter, the Delta), a complex network of natural and man-made channels linking the Sacramento River with San Francisco Bay. Fish that enter the interior and southern Delta—the region to the south of the Sacramento River where water pumping stations are located—survive at a lower rate than fish that use alternative migration routes. Consequently, total survival decreases as the fraction of the population entering the interior Delta increases, thus spurring management actions to reduce the proportion of fish that are entrained into the interior Delta. To better inform management actions, we modeled entrainment probability as a function of hydrodynamic variables. We fitted alternative entrainment models to telemetry data that identified when tagged fish in the Sacramento River entered two river channels leading to the interior Delta (Georgiana Slough and the gated Delta Cross Channel). We found that the probability of entrainment into the interior Delta through both channels depended strongly on the river flow and tidal stage at the time of fish arrival at the river junction. Fish that arrived during ebb tides had a low entrainment probability, whereas fish that arrived during flood tides (i.e., when the river's flow was reversed) had a high probability of entering the interior Delta. We coupled our entrainment model with a flow simulation model to evaluate the effect of nighttime closures of the Delta Cross Channel gates on the daily probability of fish entrainment into the interior Delta. Relative to 24-h gate closures, nighttime closures increased daily entrainment probability by 3 percentage points on average if fish arrived at the river junction uniformly throughout the day and by only 1.3 percentage points if 85% of fish arrived at night. We illustrate how our model can be used to

  15. Holocene evolution of the western Orinoco Delta, Venezuela

    USGS Publications Warehouse

    Aslan, A.; White, W.A.; Warne, A.G.; Guevara, E.H.

    2003-01-01

    The pristine nature of the Orinoco Delta of eastern Venezuela provides unique opportunities to study the geologic processes and environments of a major tropical delta. Remote-sensing images, shallow cores, and radiocarbon-dating of organic remains form the basis for describing deltaic environments and interpreting the Holocene history of the delta. The Orinoco Delta can be subdivided into two major sectors. The southeast sector is dominated by the Rio Grande-the principal distributary-and complex networks of anastomosing fluvial and tidal channels. The abundance of siliciclastic deposits suggests that fluvial processes such as over-bank flooding strongly influence this part of the delta. In contrast, the northwest sector is represented by few major distributaries, and overbank sedimentation is less widespread relative to the southeast sector. Peat is abundant and occurs in herbaceous and forested swamps that are individually up to 200 km2 in area. Northwest-directed littoral currents transport large volumes of suspended sediment and produce prominent mudcapes along the northwest coast. Mapping of surface sediments, vegetation, and major landforms identified four principal geomorphic systems within the western delta plain: (1) distributary channels, (2) interdistributary flood basins, (3) fluvial-marine transitional environments, and (4) marine-influenced coastal environments. Coring and radiocarbon dating of deltaic deposits show that the northern delta shoreline has prograded 20-30 km during the late Holocene sea-level highstand. Progradation has been accomplished by a combination of distributary avulsion and mudcape progradation. This style of deltaic progradation differs markedly from other deltas such as the Mississippi where distributary avulsion leads to coastal land loss, rather than shoreline progradation. The key difference is that the Orinoco Delta coastal zone receives prodigious amounts of sediment from northwest-moving littoral currents that transport

  16. Turning the tide: effects of river inflow and tidal amplitude on sandy estuaries in laboratory landscape experiments

    NASA Astrophysics Data System (ADS)

    Kleinhans, Maarten; Braat, Lisanne; Leuven, Jasper; Baar, Anne; van der Vegt, Maarten; van Maarseveen, Marcel; Markies, Henk; Roosendaal, Chris; van Eijk, Arjan

    2016-04-01

    Many estuaries formed over the Holocene through a combination of fluvial and coastal influxes, but how estuary planform shape and size depend on tides, wave climate and river influxes remains unclear. Here we use a novel tidal flume setup of 20 m length by 3 m width, the Metronome (http://www.uu.nl/metronome), to create estuaries and explore a parameter space for the simple initial condition of a straight river in sandy substrate. Tidal currents capable of transporting sediment in both the ebb and flood phase because they are caused by periodic tilting of the flume rather than the classic method of water level fluctuation. Particle imaging velocimetry and a 1D shallow flow model demonstrate that this principle leads to similar sediment mobility as in nature. Ten landscape experiments recorded by timelapse overhead imaging and AGIsoft DEMs of the final bed elevation show that absence of river inflow leads to short tidal basins whereas even a minor discharge leads to long convergent estuaries. Estuary width and length as well as morphological time scale over thousands of tidal cycles strongly depend on tidal current amplitude. Paddle-generated waves subdue the ebb delta causing stronger tidal currents in the basin. Bar length-width ratios in estuaries are slightly larger to those in braided rivers in experiments and nature. Mutually evasive ebb- and flood-dominated channels are ubiquitous and appear to be formed by an instability mechanism with growing bar and bifurcation asymmetry. Future experiments will include mud flats and live vegetation.

  17. Impact of river-tide dynamics on the residual water level slope and residual sediment transport in the Pearl River channel networks

    NASA Astrophysics Data System (ADS)

    Cai, Huayang; Zhang, Zihao; Yang, Qingshu; Ou, Suying

    2016-04-01

    Large-scale delta systems, such as the Rhine-Meuse delta, the Mississippi River delta, the Mekong delta, the Yangtze delta and the Pearl River delta etc., usually feature a typical channel networks, where individual channels are interrelated through a networks system, resulting in both longitudinal and transverse variations of residual water level slope (averaged over a lunar day) caused by the river-tide interplay. Enhancing our insight of river-tide dynamics in these channel networks has vital importance for the protection and management of estuarine environment since river-tide interplay is closely related to sediment transport, water quality, water utilization and estuarine ecosystem. In this study, we investigate the impact of river-tide dynamics on the temporal-spatial changes of flow and suspended sediment load in terms of residual water level slope and residual sediment transport in the Pearl River channel networks, which is one of the complex channel networks in the world. Making use of a nonstationary harmonic analysis (NS_TIDE), the continuous time series observations of velocity covering a spring-neap cycle in 1999 (representing flood season) and 2001 (representing dry season) collected from around 60 stations in the Pearl River channel networks have been used to extract the temporal-spatial changes in residual velocity and tidal properties (including amplitudes and phases) as a function of variable river flow debouching into the delta. On the basis of harmonic analysis, the tidally averaged friction is decomposed into contributions made by riverine forcing alone, river-tide interaction and tidal asymmetry using Chebyshev polynomials approach. It is shown that river flow enhances friction via river-tide interaction, which increases the residual water level slope that influences the distribution of suspended sediment load in the Pearl River channel networks.

  18. Sand Waves in Tidal Channels

    DTIC Science & Technology

    2007-01-01

    example, in the Bahia Blanca Estuary (Argentina), the sand wave field terminated when the surficial sand sheet became too thin (Aliotta and Perillo... Rosa Island partially breached near the present-day location of the inlet mouth, but soon closed. It was reopened in March 1929 when the local...and Perillo, 1987) Bahia Blanca Estuary mean 11˚ max 30˚ mean 4˚ (Anthony and Leth, 2002) North Sea 2-4˚ 66 Figure 24. Sand wave

  19. Depositional controls on tidally influenced fluvial successions, Neslen Formation, Utah, USA

    NASA Astrophysics Data System (ADS)

    Shiers, M. N.; Mountney, N. P.; Hodgson, D. M.; Cobain, S. L.

    2014-08-01

    The stratigraphic architecture of marginal marine successions records the interplay of autogenic and allogenic processes, and discerning their relative role in governing the morphology of the palaeoenvironment and the architecture of the preserved sedimentary succession is not straightforward. The Campanian Neslen Formation, Mesaverde Group, Utah, is a tidally influenced fluvial succession sourced from the Sevier Orogen, which prograded eastwards into the Western Interior Seaway. Detailed mapping in three dimensions of architectural relationships between sandstone bodies has enabled documentation of lateral and vertical changes in the style of channel-body stacking and analysis of the distribution of sedimentary evidence for tidal influence. Upwards, through the succession, sandstone channel bodies become larger and more amalgamated. Laterally, the dominant style of channel bodies changes such that ribbon channel-fills are restricted to the east of the study area whereas lateral accretion deposits dominate to the west. Combined allogenic and autogenic controls gave rise to the observed stratigraphy. A temporal decrease in the rate of accommodation generation resulted in an upward increase in amalgamation of sand-bodies. Autogenic processes likely played a significant role in moderating the preserved succession: up-succession changes in the style of stacking of channelized bodies could have arisen either from progradation of a distributive fluvial system or from an upstream nodal avulsion of a major trunk channel; accumulation of tide influenced, wave dominated units likely record episodes of delta-lobe abandonment, subsidence and submergence to allow accumulation of near shore sand bars with associated washover complexes.

  20. Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta

    USGS Publications Warehouse

    Sobczak, W.V.; Cloern, J.E.; Jassby, A.D.; Cole, B.E.; Schraga, T.S.; Arnsberg, A.

    2005-01-01

    Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that detritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production. ?? 2005 Estuarine Research Federation.

  1. Tidal Energy Research

    SciTech Connect

    Stelzenmuller, Nickolas; Aliseda, Alberto; Palodichuk, Michael; Polagye, Brian; Thomson, James; Chime, Arshiya; Malte, Philip

    2014-03-31

    This technical report contains results on the following topics: 1) Testing and analysis of sub-scale hydro-kinetic turbines in a flume, including the design and fabrication of the instrumented turbines. 2) Field measurements and analysis of the tidal energy resource and at a site in northern Puget Sound, that is being examined for turbine installation. 3) Conceptual design and performance analysis of hydro-kinetic turbines operating at high blockage ratio, for use for power generation and flow control in open channel flows.

  2. Continuous delta opioid receptor activation reduces neuronal voltage gated sodium channel (NaV1.7) levels through activation of protein kinase C in painful diabetic neuropathy

    PubMed Central

    Chattopadhyay, Munmun; Mata, Marina; Fink, David J.

    2012-01-01

    The NaV1.7 tetrodotoxin-sensitive voltage-gated sodium channel isoform plays a critical role in nociception. In rodent models of diabetic neuropathy, increased NaV1.7 in dorsal root ganglion (DRG) neurons correlates with the emergence of pain-related behaviors characteristic of painful diabetic neuropathy (PDN). We examined the effect of transgene-mediated expression of enkephalin on pain-related behaviors and their biochemical correlates in DRG neurons. Transfection of DRG neurons by subcutaneous inoculation of a herpes simplex virus (HSV)-based vector expressing proenkephalin (PE) reversed nocisponsive behavioral responses to heat, cold, and mechanical pressure characteristic of PDN. Vector-mediated enkephalin production in vivo prevented the increase in DRG NaV1.7 observed in PDN, an effect that correlated with inhibition of phosphorylation of p38 MAP kinase and protein kinase C (PKC). Primary DRG neurons in vitro exposed to 45 mM glucose for 18 hrs also demonstrated an increase in NaV1.7 and increased phosphorylation of p38 and PKC; these changes were prevented by transfection in vitro with the enkephalin-expressing vector. The effect of hyperglycemia on NaV1.7 production in vitro was mimicked by exposure to PMA, and blocked by the myristolated PKC inhibitor 20–28 or the p38 inhibitor SB202190; the effect of vector-mediated enkephalin on NaV1.7 levels was prevented by naltrindole. The results of these studies suggest that activation of the presynaptic delta opioid receptor by enkephalin prevents the increase in neuronal NaV1.7 in DRG through inhibition of PKC and p38. These results establish a novel interaction between the delta opioid receptor and voltage gated sodium channels. PMID:18579738

  3. Effects of flow diversions on water and habitat quality: Examples from California's highly manipulated Sacramento–San Joaquin Delta

    USGS Publications Warehouse

    Monsen, Nancy E.; Cloern, James E.; Burau, Jon R.

    2007-01-01

    We use selected monitoring data to illustrate how localized water diversions from seasonal barriers, gate operations, and export pumps alter water quality across the Sacramento-San Joaquin Delta (California). Dynamics of water-quality variability are complex because the Delta is a mixing zone of water from the Sacramento and San Joaquin Rivers, agricultural return water, and the San Francisco Estuary. Each source has distinct water-quality characteristics, and the contribution of each source varies in response to natural hydrologic variability and water diversions. We use simulations with a tidal hydrodynamic model to reveal how three diversion events, as case studies, influence water quality through their alteration of Delta-wide water circulation patterns and flushing time. Reduction of export pumping decreases the proportion of Sacramento- to San Joaquin-derived fresh water in the central Delta, leading to rapid increases in salinity. Delta Cross Channel gate operations control salinity in the western Delta and alter the freshwater source distribution in the central Delta. Removal of the head of Old River barrier, in autumn, increases the flushing time of the Stockton Ship Channel from days to weeks, contributing to a depletion of dissolved oxygen. Each shift in water quality has implications either for habitat quality or municipal drinking water, illustrating the importance of a systems view to anticipate the suite of changes induced by flow manipulations, and to minimize the conflicts inherent in allocations of scarce resources to meet multiple objectives.

  4. Localization of the gene encoding the [alpha][sub 2]/[delta] subunit (CACNL2A) of the human skeletal muscle voltage-dependent Ca[sup 2+] channel to chromosome 7q21-q22 by somatic cell hybrid analysis

    SciTech Connect

    Powers, P.A.; Hogan, K.; Gregg, R.G. ); Scherer, S.W.; Tsui, L.C. Hospital for Sick Children, Ontario )

    1994-01-01

    Activation of voltage-dependent calcium channels (VDCCs) by membrane depolarization triggers key cellular responses such as contraction, secretion, excitation, and electrical signaling. The skeletal muscle L-type VDCC is a heteromultimer complex containing four subunits, [alpha][sub 1],[alpha][sub 2]/[delta],[beta][sub 1], and [gamma]. The [alpha][sub 2]/[delta] subunit, an integral component of the VDCC, appears to modulate the channel kinetics. The [alpha][sub 2]/[delta] gene is expressed in many tissues, including skeletal muscle, brain, heart, and lung, and cDNAs representing the skeletal muscle and brain isoforms have been isolated. DNA sequence comparisons indicate that these cDNAs are encoding by a single gene. 15 refs., 1 fig.

  5. 2008 NWFSC Tidal Freshwater Genetics Results

    SciTech Connect

    David Teel

    2009-05-01

    Genetic Analysis of Juvenile Chinook Salmon for inclusion in 'Ecology of Juvenile Salmon in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, Lower Columbia River, 2008. Annual Report to Bonneville Power Administration, Contract DE-AC05-76RL01830.'

  6. Geomorphology and Landscape Evolution Model for the natural and human-impacted regions of the Ganges-Brahmaputra-Meghna Delta

    NASA Astrophysics Data System (ADS)

    Wilson, C.; Goodbred, S. L.; Wallace Auerbach, L.; Ahmed, K.; Paola, C.; Reitz, M. D.; Pickering, J.

    2013-12-01

    The Ganges-Brahmaputra-Meghna delta (GBMD) in south Asia is generally considered a tide-dominated system, but much of the subaerial delta plain is geomorphically similar to river-dominated systems such as the Mississippi River delta, with a well-developed distributary network separated by low-lying, organic-rich interdistributary basins. By contrast, the lower GBMD is dominated by tidal processes and comprises a 100-km wide coastal plain with dense, interconnected tidal channels that are amalgamated to the seaward edge of the river-dominated portion of the delta. These distinct river- and tide-dominated geomorphic regions are simultaneously sustained by the enormous sediment load of the GBM rivers and its efficient dispersal via the distributary channel network and onshore advection by tides. Together these processes have resulted in the ability of the GBMD to keep pace with sea-level rise throughout the Holocene, with comparatively little shoreline transgression. However, topographic data from the Shuttle Radar Topography Mission (SRTM) highlight low-lying regions of the delta that are located at the interface of the river- and tide-dominated portions of the delta, where the transport energy of small distributaries and the upper tidal zone go to zero. As a result, these are the most sediment-starved regions of the delta and those most at risk to flooding by the summer monsoon and storm surges. Compounding the slow rates of sedimentation and high local organic content, these regions have been strongly affected by the construction of embankments (polders) that artificially de-water the soils and accelerate organic decomposition during the dry season, and further starve the land surface of sediment. Here, we present an integrated conceptual model for the geomorphic evolution of the GBMD that incorporates river- and tide-dominated regions in conjunction with channel-avulsion processes and delta-lobe construction. Each of these is also overprinted by tectonic

  7. Modern sedimentation and morphology of the subaqueous Mekong Delta, Southern Vietnam

    NASA Astrophysics Data System (ADS)

    Unverricht, Daniel; Szczuciński, Witold; Stattegger, Karl; Jagodziński, Robert; Le, Xuan Thuyen; Kwong, Laval Liong Wee

    2013-11-01

    The Mekong River Delta is among the Asian mega-deltas and is influenced by various factors including tides (meso-tidal system), waves, coastal currents, monsoon-driven river discharge and human impact (agriculture, fishing, sand dredging, tourism). The present study aims to document the seafloor relief, sediment distribution and sediment accumulation rates to interpret modern sediment transport directions and main sedimentation processes in the subaqueous Mekong Delta. The major results of this investigation include the detection of two delta fronts 200 km apart, one at the mouth of the Bassac River (the biggest branch of the Mekong Delta) and the other around Cape Ca Mau (most south-western end of the Mekong Delta). Additionally, a large channel system runs in the subaqueous delta platform parallel to the shore and between the two fronts. The sediment accumulation rates vary greatly according to the location in the subaqueous delta and have reached up to 10 cm/yr for the last century. A cluster analysis of surface sediment samples revealed two different sediment types within the delta including a well-sorted sandy sediment and a poorly sorted, silty sediment. In addition, a third end member with medium to coarse sand characterised the distant parts of the delta at the transition to the open shelf. The increase of organic matter and carbonate content to the bottom set area and other sedimentary features such as shell fragments, foraminiferas and concretions of palaeo-soils that do not occur in delta sediments, supported grain size-based classification. Beginning in front of the Bassac River mouth, sedimentary pattern indicates clockwise sediment transport alongshore in the western direction to a broad topset area and the delta front around Cape Ca Mau. Our results clearly show the large lateral variability of the subaqueous Mekong Delta that is further complicated by strong monsoon-driven seasonality. River, tidal and wave forcing vary at local and seasonal scales

  8. Martian deltas: Morphology and distribution

    NASA Technical Reports Server (NTRS)

    Rice, J. W., Jr.; Scott, D. H.

    1993-01-01

    Recent detailed mapping has revealed numerous examples of Martian deltas. The location and morphology of these deltas are described. Factors that contribute to delta morphology are river regime, coastal processes, structural stability, and climate. The largest delta systems on Mars are located near the mouths of Maja, Maumee, Vedra, Ma'adim, Kasei, and Brazos Valles. There are also several smaller-scale deltas emplaced near channel mouths situated in Ismenius Lacus, Memnonia, and Arabia. Delta morphology was used to reconstruct type, quantity, and sediment load size transported by the debouching channel systems. Methods initially developed for terrestrial systems were used to gain information on the relationships between Martian delta morphology, river regime, and coastal processes.

  9. Dealing with the safety paradox of delta-branches closure; a geomorphology study

    NASA Astrophysics Data System (ADS)

    Sloff, C.; Tromp, R.; Sieben, A.

    2013-12-01

    Closing off estuaries by dams is a conventional solution to reduce flood risks and salt intrusion in river deltas. However, if not all branches are closed, residual tidal currents develop or increase in connecting channels between the closed and open branches. These channels start to erode, causing bank instability and possible failure of levees. Hence, paradoxically, the intended increase in safety by this closure creates a new threat with increased flood risks. We illustrate this for existing channel erosion and dike stability problems in the Dutch Rhine River delta in the Netherlands, as well as for proposed future closure works in the Mekong River in Vietnam. Crucial for assessing and dealing with the erosion problems, is a proper prediction of flow conditions and of bed erodibility. The channels incise ancient deltaic deposits, consisting of diverse sections and layers of sand, clay and peat with diverse states of compaction. In the presented studies we show how we applied Delft3D to model the full delta, with all relevant dynamics and complex interactions between tidal flow and river discharges. For the Dutch situation, we simulated the long-term fate of the eroding interconnecting channels, applying a detailed description of subsurface heterogeneous erodibility (space and depth varying). Since these rivers are incising slowly in clay and peat beds covering highly-erodible sand layers, alternate sections occur of undersupplied ';fixed' beds, and of very deep scour holes. For the Vietnam case, we show how the location of a barrier and operation of gates, can be used to control both the salinity intrusion and channel erosion for the Mekong delta. Although the morphology studies for the Dutch delta with high-density data availability obviously justify a detailed Delft3D approach, it is shown that even in the Mekong delta with poor data quality, a coarse-grid large-scale Delft3D model can provide the answers necessary for planning the closure works and potential

  10. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The streamers of clouds draped over the Gulf of Mexico in this true-color MODIS image from February 27, 2002, suggest that a cold, dry wind was blowing southward over the United States and began to pick up moisture over the Gulf, causing these strips of clouds. That the clouds didn't pick up until some distance from the coastline allowed MODIS to get a perfect view of the dynamic Gulf Coast environment spanning (left to right) Texas, Louisiana, Mississippi, Alabama, and Florida's Western Panhandle. The Mississippi River runs roughly down the center of the image, and is joined in Louisiana by the Red River coming in from the northwest. Over the past 7000 years, the actual delta, where the main river channel empties into the Gulf, has wandered around what we now think of as the Louisiana coast. Considering all the sediment visible in this image, it's not hard to imagine that the river carries about 2.4 billion kilograms of sediment into the Gulf each year. Deposition of some of this sediment has been building up the current delta, called the Birdfoot Delta, for obvious reasons, for about 700 years. The coastal waters are alive with microscopic organisms called phytoplankton, which contain colorful pigments, including chlorophyll, for harvesting sunlight. Beyond the sediment plume off Louisiana, the waters are very dark, which could indicate that a large amount of chlorophyll is present, absorbing lots of sunlight and causing the water to appear dark. Farther south, the waters appear bright blue, which could be a signature of coccolithophores, which use highly reflective calcium carbonate to build scaly coverings for themselves. The brighter offshore waters could also be caused by a blue-green algae called Trichodesmium, an organism that can not only harness carbon dioxide for photosynthesis, but can also take nitrogen from the air and turn it into a form that can be used by living organisms. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  11. Tidal asymmetry in a funnel-shaped estuary with mixed semidiurnal tides

    NASA Astrophysics Data System (ADS)

    Gong, Wenping; Schuttelaars, Henk; Zhang, Heng

    2016-05-01

    Different types of tidal asymmetry (see review of de Swart and Zimmerman Annu Rev Fluid Mech 41: 203-229, 2009) are examined in this study. We distinguish three types of tidal asymmetry: duration and magnitude differences between flood and ebb tidal flow, duration difference between the rising and falling tides. For waterborne substance transport, the first two asymmetries are important while the last one is not. In this study, we take the Huangmaohai Estuary (HE), Pearl River Delta, China as an example to examine the spatio-temporal variations of the tidal asymmetry in a mixed semidiurnal tidal regime and to explain them by investigating the associated mechanisms. The methodology defining the tidal duration asymmetry and velocity skewness, proposed by Nidzieko (J Geophys Res 115: C08006. doi: 10.1029/2009JC005864 , 2010) and synthesized by Song et al. (J Geophys Res 116: C12007. doi: 10.1029/2011JC007270 , 2011), is utilized here and referred to as tidal duration asymmetry (TDA) and flow velocity asymmetry (FVA), respectively. The methodology is further used to quantify the flow duration asymmetry (FDA). A positive asymmetry means a shorter duration of low water slack for FDA, a shorter duration of the rising tide for TDA, and a flood dominance for FVA and vice versa. The Regional Ocean Modeling System (ROMS) model is used to provide relatively long-term water elevation and velocity data and to conduct diagnostic experiments. In the HE, the main tidal constituents are diurnal tides K 1, O 1 and semidiurnal tides M 2 and S 2. The interaction among the diurnal and semidiurnal tides generates a negative tidal asymmetry, while the interactions among semidiurnal tides and their overtides or compound tides result in a positive tidal asymmetry. The

  12. A possible formation channel for blue hook stars in globular cluster - II. Effects of metallicity, mass ratio, tidal enhancement efficiency and helium abundance

    NASA Astrophysics Data System (ADS)

    Lei, Zhenxin; Zhao, Gang; Zeng, Aihua; Shen, Lihua; Lan, Zhongjian; Jiang, Dengkai; Han, Zhanwen

    2016-12-01

    Employing tidally enhanced stellar wind, we studied in binaries the effects of metallicity, mass ratio of primary to secondary, tidal enhancement efficiency and helium abundance on the formation of blue hook (BHk) stars in globular clusters (GCs). A total of 28 sets of binary models combined with different input parameters are studied. For each set of binary model, we presented a range of initial orbital periods that is needed to produce BHk stars in binaries. All the binary models could produce BHk stars within different range of initial orbital periods. We also compared our results with the observation in the Teff-logg diagram of GC NGC 2808 and ω Cen. Most of the BHk stars in these two GCs locate well in the region predicted by our theoretical models, especially when C/N-enhanced model atmospheres are considered. We found that mass ratio of primary to secondary and tidal enhancement efficiency have little effects on the formation of BHk stars in binaries, while metallicity and helium abundance would play important roles, especially for helium abundance. Specifically, with helium abundance increasing in binary models, the space range of initial orbital periods needed to produce BHk stars becomes obviously wider, regardless of other input parameters adopted. Our results were discussed with recent observations and other theoretical models.

  13. Effects of human alterations on the hydrodynamics and sediment transport in the Sacramento-San Joaquin Delta, California

    USGS Publications Warehouse

    Marineau, Mathieu D.; Wright, Scott A.

    2015-01-01

    The Sacramento-San Joaquin Delta, California, (Delta) has been significantly altered since the mid-nineteenth century. Many existing channels have been widened or deepened and new channels have been created for navigation and water conveyance. Tidal marshes have been drained and leveed to form islands that have subsided, some of which have permanently flooded. To understand how these alterations have affected hydrodynamics and sediment transport in the Delta, we analysed measurements from 27 sites, along with other spatial data, and previous literature. Results show that: (a) the permanent flooding of islands results in an increase in the shear velocity of channels downstream, (b) artificial widening and deepening of channels generally results in a decrease in shear velocity except when the channel is also located downstream of a flooded island, (c) 1.5 Mt/year of sediment was deposited in the Delta (1997–2010), and of this deposited sediment, 0.31 Mt/year (21%) was removed through dredging.

  14. Role of river bends for the formation and evolution of channel bedforms: Combined field studies and numerical modeling from the tidally influenced zones of the Yellow River, China, and Mississippi River, USA.

    NASA Astrophysics Data System (ADS)

    Ma, H.; Nittrouer, J. A.; Moodie, A.; Calson, B.; Parker, G.

    2015-12-01

    River bedforms represent the unstable interface between fluid flow and the granular channel bed, and these features play an important role for modifying flow resistance and sediment transport rates, and thus influencing river morphology. Although widely observed in natural rivers, bedforms are difficult to measure quantitatively and are rarely connected to other fluvial morphological processes. This study presents high-resolution channel bathymetric data from the tidally influenced, lowermost Yellow River, China, collected using a multibeam swath profiler. Repeat surveys were conducted over rising and flood discharge conditions, which is the first such kind of survey in Yellow River. The bathymetry data show that for all water discharges, a flat bed, devoid of a thalweg or dunes, persists within straight-reach segments near the bends of the Yellow River, despite the bed consisting of fine sand. Interestingly, in bend segments, the channel deepens, and linear dunes develop. Moreover, as the water discharge increases over time, the edge of dune field contained in the bend segments propagates into the adjacent upstream and downstream straight-reach segments. In contrasting case study, Nittrouer et al. (2008) reported persistent dune field in the straight reaches of the tidally influenced Mississippi River; however these dunes disappear in neighboring river bends. Based on the two cases of the Yellow and Mississippi Rivers, which have fundamentally different conditions of water-to-sediment discharge ratios, the threshold condition of bedform formation and stability are evaluated, and connected to local conditions of river bend morphology. This work improves the understanding of the co-evolution of bedforms and flow conditions in river bends, which are intertwined and important morphological processes that affect fluvial-deltaic sediment transport dynamics. In addition, the straight-bend structure is a basic element of river morphology, and so the results of this study

  15. Characterization of Organic Carbon Released from Different Wetland Habitats in the Sacramento-San Joaquin Delta

    NASA Astrophysics Data System (ADS)

    Kraus, T. E.; Bergamaschi, B. A.; Stepanauskas, R.; Fram, M. S.; Doctor, D. H.; Kendall, C.; Losee, R. F.; Eckard, R. S.; Hollibaugh, J. T.; Hernes, P. J.

    2005-05-01

    The Sacramento-San Joaquin Delta is a source of drinking water for over 22 million people in California as well as a source of carbon for the aquatic foodweb in San Francisco Bay. To improve the ecological health of the Bay-Delta system, large areas of the Delta may be restored to wetlands. We investigated the potential impact of these changes on the compositional quality of dissolved organic material (DOM) in the Delta by examining alterations of DOM concentration and composition through interactions with tidal and non-tidal wetlands, and agricultural water use. Fourteen sites were sampled for two years and analyses were conducted on both whole water and XAD isolated material. Our comprehensive chemical characterization of DOM included measurement of drinking water disinfection byproduct formation potential, bioavailability, optical properties, isotopic ratios (C, N, S), carbohydrate content and lignin-phenolic content. The isotopic and molecular tracer data can help us elucidate if the DOM is derived from wetland plants, peat soils, or in-channel algal productivity, which vary seasonally and by site. The impact of restored wetlands on drinking water quality and the aquatic foodweb will depend on DOM loads as well as composition.

  16. Tidal power in Argentina

    SciTech Connect

    Aisiks, E.G.

    1993-03-01

    This presentation describes the tidal power potential of Argentina and the current status of its utilization. The topics of the presentation include tidal power potential, electric production of the region and the Argentine share of production and consumption, conventional hydroelectric potential, economic feasibility of tidal power production, and the general design and feasibility of a tidal power plant planned for the San Jose Gulf.

  17. Shallow stratigraphy of the Skagit River Delta, Washington, derived from sediment cores

    USGS Publications Warehouse

    Grossman, Eric E.; George, Douglas A.; Lam, Angela

    2011-01-01

    Sedimentologic analyses of 21 sediment cores, ranging from 0.4 to 9.6 m in length, reveal that the shallow geologic framework of the Skagit River Delta, western Washington, United States, has changed significantly since 1850. The cores collected from elevations of 3.94 to -2.41 m (relative to mean lower low water) along four cross-shore transects between the emergent marsh and delta front show relatively similar environmental changes across an area spanning ~75 km2. Offshore of the present North Fork Skagit River and South Fork Skagit River mouths where river discharge is focused by diked channels through the delta, the entire 5–7-km-wide tidal flats are covered with 1–2 m of cross-bedded medium-to-coarse sands. The bottoms of cores, collected in these areas are composed of mud. A sharp transition from mud to a cross-bedded sand unit indicates that the tidal flats changed abruptly from a calm environment to an energetic one. This is in stark contrast to the Martha's Bay tidal flats north of the Skagit Bay jetty that was completed in the 1940s to protect the newly constructed Swinomish Channel from flooding and sedimentation. North of the jetty, mud ranging from 1 to 2 m thick drapes a previously silt- and sand-rich tidal flat. The silty sand is a sediment facies that would be expected there where North Fork Skagit River sedimentation occurred prior to jetty emplacement. This report describes the compositional and textural properties of the sediment cores by using geophysical, photographic, x-radiography, and standard sediment grain-size and carbon-analytical methods. The findings help to characterize benthic habitat structure and sediment transport processes and the environmental changes that have occurred across the nearshore of the Skagit River Delta. The findings will be useful for quantifying changes to nearshore marine resources, including impacts resulting from diking, river-delta channelization, shoreline development, and natural variations in fluvial

  18. Tidally influenced alongshore circulation at an inlet-adjacent shoreline

    USGS Publications Warehouse

    Hansen, Jeff E.; Elias, Edwin P.L.; List, Jeffrey H.; Erikson, Li H.; Barnard, Patrick L.

    2013-01-01

    The contribution of tidal forcing to alongshore circulation inside the surfzone is investigated at a 7 km long sandy beach adjacent to a large tidal inlet. Ocean Beach in San Francisco, CA (USA) is onshore of a ∼150 km2 ebb-tidal delta and directly south of the Golden Gate, the sole entrance to San Francisco Bay. Using a coupled flow-wave numerical model, we find that the tides modulate, and in some cases can reverse the direction of, surfzone alongshore flows through two separate mechanisms. First, tidal flow through the inlet results in a barotropic tidal pressure gradient that, when integrated across the surfzone, represents an important contribution to the surfzone alongshore force balance. Even during energetic wave conditions, the tidal pressure gradient can account for more than 30% of the total alongshore pressure gradient (wave and tidal components) and up to 55% during small waves. The wave driven component of the alongshore pressure gradient results from alongshore wave height and corresponding setup gradients induced by refraction over the ebb-tidal delta. Second, wave refraction patterns over the inner shelf are tidally modulated as a result of both tidal water depth changes and strong tidal flows (∼1 m/s), with the effect from currents being larger. These tidally induced changes in wave refraction result in corresponding variability of the alongshore radiation stress and pressure gradients within the surfzone. Our results indicate that tidal contributions to the surfzone force balance can be significant and important in determining the direction and magnitude of alongshore flow.

  19. Modeling the tidal and sub-tidal hydrodynamics in a shallow, micro-tidal estuary

    NASA Astrophysics Data System (ADS)

    Rayson, Matthew D.; Gross, Edward S.; Fringer, Oliver B.

    2015-05-01

    The three-dimensional hydrodynamics of Galveston Bay were simulated in two periods of several month duration. The physical setting of Galveston Bay is described by synthesis of long-term observations. Several processes in addition to tidal hydrodynamics and baroclinic circulation processes contribute substantially to the observed variability of currents, water level and salinity. The model was therefore forced with realistic water levels, river discharges, winds, coastal buoyancy currents (due to the Mississippi River plume) and surface heat fluxes. Quantitative metrics were used to evaluate model performance against observations and both spatial and temporal variability in tidal and sub-tidal hydrodynamics were generally well represented by the model. Three different unstructured meshes were tested, a triangular mesh that under-resolved the shipping channel, a triangular mesh that resolved it, and a mixed quadrilateral-triangular grid with approximately equivalent resolution. It is shown that salinity and sub-tidal velocity are better predicted when the important topographic features, such as the shipping channel, are resolved. It was necessary to increase the seabed drag roughness in the mixed quadrilateral-triangular grid simulation to attain similar performance to the equivalent triangular mesh.

  20. Tidal Asteroseismology

    NASA Astrophysics Data System (ADS)

    Burkart, Joshua

    2012-01-01

    The recently discovered Kepler system KOI-54 is a face-on eccentric binary consisting of two similar A stars. Its lightcurve exhibits 20 tidally excited pulsations at perfect harmonics of the orbital frequency, and another 10 nonharmonic pulsations. Analysis of such data is a new form of asteroseismology in which oscillation amplitudes and phases rather than frequencies contain information that can be mined to constrain stellar properties. I will discuss the physics of mode excitation and the range of harmonics expected to be observed. I will then show the results of numerical modeling of the pulsation spectrum, using a nonadiabatic stellar oscillation code including rotation in the "traditional approximation", which qualitatively reproduce the observations. I will discuss the evolutionary history of the KOI-54 system, and will show that the system is likely in a state of stochastic dynamical pseudosynchronization with stellar spin periods of 1.5 days, significantly faster than the classical theoretical prediction of 2.5 days. Time permitting, I will also address the nonharmonic pulsations observed in KOI-54, and show that they can be produced by nonlinear three-mode coupling.

  1. Natural processes in delta restoration: application to the Mississippi Delta.

    PubMed

    Paola, Chris; Twilley, Robert R; Edmonds, Douglas A; Kim, Wonsuck; Mohrig, David; Parker, Gary; Viparelli, Enrica; Voller, Vaughan R

    2011-01-01

    Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local engineered structures at the points of diversion, restoration mainly relies on natural delta-building processes. Present understanding of such processes is sufficient to provide a basis for determining the feasibility of restoration projects through quantitative estimates of land-building rates and sustainable wetland area under different scenarios of sediment supply, subsidence, and sea-level rise. We are not yet to the point of being able to predict the evolution of a restored delta in detail. Predictions of delta evolution are based on field studies of active deltas, deltas in mine-tailings ponds, experimental deltas, and countless natural experiments contained in the stratigraphic record. These studies provide input for a variety of mechanistic delta models, ranging from radially averaged formulations to more detailed models that can resolve channels, topography, and ecosystem processes. Especially exciting areas for future research include understanding the mechanisms by which deltaic channel networks self-organize, grow, and distribute sediment and nutrients over the delta surface and coupling these to ecosystem processes, especially the interplay of topography, network geometry, and ecosystem dynamics.

  2. Changing tidal hydrodynamics during different stages of eco-geomorphological development of a tidal marsh: A numerical modeling study

    NASA Astrophysics Data System (ADS)

    Stark, J.; Meire, P.; Temmerman, S.

    2017-03-01

    The eco-geomorphological development of tidal marshes, from initially low-elevated bare tidal flats up to a high-elevated marsh and its typical network of channels and creeks, induces long-term changes in tidal hydrodynamics in a marsh, which will have feedback effects on the marsh development. We use a two-dimensional hydrodynamic model of the Saeftinghe marsh (Netherlands) to study tidal hydrodynamics, and tidal asymmetry in particular, for model scenarios with different input bathymetries and vegetation coverages that represent different stages of eco-geomorphological marsh development, from a low elevation stage with low vegetation coverage to a high and fully vegetated marsh platform. Tidal asymmetry is quantified along a 4 km marsh channel by (1) the difference in peak flood and peak ebb velocities, (2) the ratio between duration of the rising tide and the falling tide and (3) the time-integrated dimensionless bed shear stress during flood and ebb. Although spatial variations in tidal asymmetry are large and the different indicators for tidal asymmetry do not always respond similarly to eco-geomorphological changes, some general trends can be obtained. Flood-dominance prevails during the initial bare stage of a low-lying tidal flat. Vegetation establishment and platform expansion lead to marsh-scale flow concentration to the bare channels, causing an increase in tidal prism in the channels along with a less flood-dominant asymmetry of the horizontal tide. The decrease in flood-dominance continues as the platform grows vertically and the sediment-demand of the platform decreases. However, when the platform elevation gets sufficiently high in the tidal frame and part of the spring-neap cycle is confined to the channels, the discharge in the channels decreases and tidal asymmetry becomes more flood-dominant again, indicating an infilling of the marsh channels. Furthermore, model results suggest that hydro-morphodynamic feedbacks based on tidal prism to channel

  3. Consolidation of geologic studies of geopressured-geothermal resources in Texas: Barrier-bar tidal-channel reservoir facies architecture, Jackson Group, Prado Field, South Texas

    SciTech Connect

    Seni, S.J.; Choh, S.J.

    1993-09-01

    Sandstone reservoirs in the Jackson barrier/strandplain play are characterized by low recovery efficiencies and thus contain a large hydrocarbon resource target potentially amenable to advanced recovery techniques. Prado field, Jim Hogg County, South Texas, has produced over 23 million bbl of oil and over 32 million mcf gas from combination structural-stratigraphic traps in the Eocene lower Jackson Group. Hydrocarbon entrapment at Prado field is a result of anticlinal nosing by differential compaction and updip pinch-out of barrier bar sandstone. Relative base-level lowering resulted in forced regression that established lower Jackson shoreline sandstones in a relatively distal location in central Jim Hogg County. Reservoir sand bodies at Prado field comprise complex assemblages of barrier-bar, tidal-inlet fill, back-barrier bar, and shoreface environments. Subsequent progradation built the barrier-bar system seaward 1 to 2 mi. With the barrier-bar system, favorable targets for hydrocarbon reexploration are concentrated in tidal-inlet facies because they possess the greatest degree of depositional heterogeneity.

  4. Consolidation of geologic studies of geopressured-geothermal resources in Texas: Barrier-bar tidal-channel reservoir facies architecture, Jackson Group, Prado field, South Texas; Final report

    SciTech Connect

    Seni, S.J.; Choh, S.J.

    1994-01-01

    Sandstone reservoirs in the Jackson barrier/strandplain play are characterized by low recovery efficiencies and thus contain a large hydrocarbon resource target potentially amenable to advanced recovery techniques. Prado field, Jim Hogg County, South Texas, has produced over 23 million bbl of oil and over 32 million mcf gas from combination structural-stratigraphic traps in the Eocene lower Jackson Group. Hydrocarbon entrapment at Prado field is a result of anticlinal nosing by differential compaction and updip pinch-out of barrier bar sandstone. Relative base-level lowering resulted in forced regression that established lower Jackson shoreline sandstones in a relatively distal location in central Jim Hogg County. Reservoir sand bodies at Prado field comprise complex assemblages of barrier-bar, tidal-inlet fill, back-barrier bar, and shoreface environments. Subsequent progradation built the barrier-bar system seaward 1 to 2 mi. Within the barrier-bar system, favorable targets for hydrocarbon reexploration are concentrated in tidal-inlet facies because they possess the greatest degree of depositional heterogeneity. The purpose of this report is (1) to describe and analyze the sand-body architecture, depositional facies variations, and structure of Prado field, (2) to determine controls on distribution of hydrocarbons pertinent to reexploration for bypassed hydrocarbons, (3) to describe reservoir models at Prado field, and (4) to develop new data affecting the suitability of Jackson oil fields as possible candidates for thermally enhanced recovery of medium to heavy oil.

  5. Understanding pesticides in California's Delta

    USGS Publications Warehouse

    Kuivila, Kathryn; Orlando, James L.

    2012-01-01

    The Sacramento-San Joaquin River Delta (Delta) is the hub of California’s water system and also an important habitat for imperiled fish and wildlife. Aquatic organisms are exposed to mixtures of pesticides that flow through the maze of Delta water channels from sources including agricultural, landscape, and urban pest-control applications. While we do not know all of the effects pesticides have on the ecosystem, there is evidence that they cause some damage to organisms in the Delta. Decades of USGS research have provided a good understanding of when, where, and how pesticides enter the Delta. However, pesticide use is continually changing. New field studies and methods are needed so that scientists can analyze which pesticides are present in the Delta, and at what concentrations, enabling them to estimate exposure and ultimate effects on organisms. Continuing research will provide resource managers and stakeholders with crucial information to manage the Delta wisely.

  6. Tidal wave transformations in the German Bight

    NASA Astrophysics Data System (ADS)

    Stanev, Emil V.; Al-Nadhairi, Rahma; Staneva, Joanna; Schulz-Stellenfleth, Johannes; Valle-Levinson, Arnoldo

    2014-07-01

    Mesoscale and submesoscale dynamics associated with tidal wave transformations were addressed in the German Bight using numerical simulations. Tidal gauge and velocity observations in several locations were used to validate the numerical model. A downscaling approach included analysis of simulations with horizontal resolutions of 1, 0.4, and 0.2 km. It was shown that the modified tidal wave lost most of its energy after reflection or refraction over the eastern part of the German Bight. Energy loss resulted in a pronounced change of the wave's spectral composition and generation of overtides. Tidal oscillations were modified by mesoscale processes associated with bathymetric channels. Semidiurnal and quarterdiurnal tides revealed very different spatial patterns. The former were aligned with the bathymetric channels, while the latter were rather "patchy" and had about half the spatial scales. In numerous areas around the bathymetric channels, the major axis of the M4 ellipses was normal or at some angle with the major axis of the M2 ellipses. Thus, higher harmonics developed "orthogonal" patterns that drove secondary circulations. Moreover, the ratio between spring and neap tidal amplitudes was relatively low in the Wadden Sea, showing reduced sensitivity of this very shallow area to fortnightly tidal variations. It was demonstrated that simulated hydrodynamics patterns help explain the physical mechanism shaping the median grain size distribution in the German Bight.

  7. Organic matter sources and rehabilitation of the Sacramento-San Joaquin Delta (California, USA)

    USGS Publications Warehouse

    Jassby, A.D.; Cloern, J.E.

    2000-01-01

    1. The Sacramento San Joaquin River Delta, a complex mosaic of tidal freshwater habitats in California, is the focus of a major ecosystem rehabilitation effort because of significant long-term changes in critical ecosystem functions. One of these functions is the production, transport and transformation of organic matter that constitutes the primary food supply, which may be sub-optimal at trophic levels supporting fish recruitment. A long historical data set is used to define the most important organic matter sources, the factors underlying their variability, and the implications of ecosystem rehabilitation actions for these sources. 2. Tributary-borne loading is the largest organic carbon source on an average annual Delta-wide basis; phytoplankton production and agricultural drainage are secondary; wastewater treatment plant discharge, tidal marsh drainage and possibly aquatic macrophyte production are tertiary; and benthic microalgal production, urban run-off and other sources are negligible. 3. Allochthonous dissolved organic carbon must be converted to particulate form - with losses due to hydraulic flushing and to heterotroph growth inefficiency - before it becomes available to the metazoan food web. When these losses are accounted for, phytoplankton production plays a much larger role than is evident from a simple accounting of bulk organic carbon sources, especially in seasons critical for larval development and recruitment success. Phytoplankton-derived organic matter is also an important component of particulate loading to the Delta. 4. The Delta is a net producer of organic matter in critically dry years but, because of water diversion from the Delta, transport of organic matter from the Delta to important, downstream nursery areas in San Francisco Bay is always less than transport into the Delta from upstream sources. 5. Of proposed rehabilitation measures, increased use of floodplains probably offers the biggest increase in organic matter sources. 6

  8. Nile Delta

    Atmospheric Science Data Center

    2013-04-15

    article title:  The Nile River Delta     View Larger Image ... of eastern Africa. At the apex of the fertile Nile River Delta is the Egyptian capital city of Cairo. To the west are the Great Pyramids ...

  9. Volga Delta

    Atmospheric Science Data Center

    2013-04-17

    article title:  Volga Delta and the Caspian Sea     View ... appear reddish. A small cloud near the center of the delta separates into red, green, and blue components due to geometric parallax ... include several linear features located near the Volga Delta shoreline. These long, thin lines are artificially maintained shipping ...

  10. Process regime variability across growth faults in the Paleogene Lower Wilcox Guadalupe Delta, South Texas Gulf Coast

    NASA Astrophysics Data System (ADS)

    Olariu, Mariana I.; Ambrose, William A.

    2016-07-01

    The Wilcox Group in Texas is a 3000 m thick unit of clastic sediments deposited along the Gulf of Mexico coast during early Paleogene. This study integrates core facies analysis with subsurface well-log correlation to document the sedimentology and stratigraphy of the Lower Wilcox Guadalupe Delta. Core descriptions indicate a transition from wave- and tidally-influenced to wave-dominated deposition. Upward-coarsening facies successions contain current ripples, organic matter, low trace fossil abundance and low diversity, which suggest deposition in a fluvial prodelta to delta front environment. Heterolithic stratification with lenticular, wavy and flaser bedding indicate tidal influence. Pervasively bioturbated sandy mudstones and muddy sandstones with Cruziana ichnofacies and structureless sandstones with Ophiomorpha record deposition in wave-influenced deltas. Tidal channels truncate delta front deposits and display gradational upward-fining facies successions with basal lags and sandy tabular cross-beds passing into heterolithic tidal flats and biologically homogenized mudstones. Growth faults within the lower Wilcox control expanded thickness of sedimentary units (up to 4 times) on the downdip sides of faults. Increased local accommodation due to fault subsidence favors a stronger wave regime on the outer shelf due to unrestricted fetch and water depth. As the shoreline advances during deltaic progradation, successively more sediment is deposited in the downthrown depocenters and reworked along shore by wave processes, resulting in a thick sedimentary unit characterized by repeated stacking of shoreface sequences. Thick and laterally continuous clean sandstone successions in the downthrown compartments represent attractive hydrocarbon reservoirs. As a consequence of the wave dominance and increased accommodation, thick (tens of meters) sandstone-bodies with increased homogeneity and vertical permeability within the stacked shoreface successions are created.

  11. Fine sediment transport by tidal asymmetry in the high-concentrated Ems River: indications for a regime shift in response to channel deepening

    NASA Astrophysics Data System (ADS)

    Winterwerp, Johan C.

    2011-03-01

    This paper describes an analysis of the observed up-river transport of fine sediments in the Ems River, Germany/Netherlands, using a 1DV POINT MODEL, accounting for turbulence-induced flocculation and sediment-induced buoyancy destruction. From this analysis, it is inferred that the net up-river transport is mainly due to an asymmetry in vertical mixing, often referred to as internal tidal asymmetry. It is argued that the large stratification observed during ebb should be attributed to a profound interaction between turbulence-induced flocculation and sediment-induced buoyancy destruction, as a result of which the river became an efficient trap for fine suspended sediment. Moreover, an asymmetry in flocculation processes was found, such that during flood relative large flocs are transported at relative large flow velocity high in the water column, whereas during ebb, the larger flocs are transported at smaller velocities close to the bed—this asymmetry contributes to the large trapping mentioned above. The internal tidal asymmetry and asymmetry in flocculation processes are both driven by the pronounced asymmetry in flow velocities, with flood velocities almost twice the ebb values. It is further argued that this efficient trapping is the result of a continuous deepening of the river, and occurs when concentrations in the river become typically a few hundred mg/l; this was the case during the 1990 survey analyzed in this paper. We also speculate that a second regime shift did occur in the river when fluid mud layers become so thick that net transport rates are directly related to the asymmetry in flow velocity itself, probably still in conjunction with internal asymmetry as well. This would yield an efficient mechanism to transport large amounts of fine sediment far up-river, as currently observed.

  12. Repeated surveys by acoustic Doppler current profiler for flow and sediment dynamics in a tidal river

    USGS Publications Warehouse

    Dinehart, R.L.; Burau, J.R.

    2005-01-01

    A strategy of repeated surveys by acoustic Doppler current profiler (ADCP) was applied in a tidal river to map velocity vectors and suspended-sediment indicators. The Sacramento River at the junction with the Delta Cross Channel at Walnut Grove, California, was surveyed over several tidal cycles in the Fall of 2000 and 2001 with a vessel-mounted ADCP. Velocity profiles were recorded along flow-defining survey paths, with surveys repeated every 27 min through a diurnal tidal cycle. Velocity vectors along each survey path were interpolated to a three-dimensional Cartesian grid that conformed to local bathymetry. A separate array of vectors was interpolated onto a grid from each survey. By displaying interpolated vector grids sequentially with computer animation, flow dynamics of the reach could be studied in three-dimensions as flow responded to the tidal cycle. Velocity streamtraces in the grid showed the upwelling of flow from the bottom of the Sacramento River channel into the Delta Cross Channel. The sequential display of vector grids showed that water in the canal briefly returned into the Sacramento River after peak flood tides, which had not been known previously. In addition to velocity vectors, ADCP data were processed to derive channel bathymetry and a spatial indicator for suspended-sediment concentration. Individual beam distances to bed, recorded by the ADCP, were transformed to yield bathymetry accurate enough to resolve small bedforms within the study reach. While recording velocity, ADCPs also record the intensity of acoustic backscatter from particles suspended in the flow. Sequential surveys of backscatter intensity were interpolated to grids and animated to indicate the spatial movement of suspended sediment through the study reach. Calculation of backscatter flux through cross-sectional grids provided a first step for computation of suspended-sediment discharge, the second step being a calibrated relation between backscatter intensity and sediment

  13. A Tale of Two Deltas: Contrasting Perspectives on the State of Natural and Human-modified Regions of the Ganges-Brahmaputra River Delta (Invited)

    NASA Astrophysics Data System (ADS)

    Goodbred, S. L.; Wallace Auerbach, L.; Wilson, C.; Gilligan, J. M.; Roy, K.; Ahmed, K.; Steckler, M. S.; Seeber, L.; Akhter, S. H.; Hossain, S.

    2013-12-01

    Effective risk analysis and the management of complex coastal systems require that the scale of interest be well defined. Here we present recent research from the Ganges-Brahmaputra river delta (GBD) that highlights different, if not divergent, perspectives on the current status of this system and its potential response to future environmental change. The contrasts emerge from viewing the GBD at different temporal and spatial scales, raising the question of how scientists, stakeholders, and decision makers might most effectively develop a shared understanding of large, at-risk delta systems. Among the world's deltas, the GBD is often cited as being highly vulnerable to future sea-level rise and environmental change, owing to its vast low-lying landscape and large human population. Taking a broad perspective, however, it is not coincident that the GBD, the world's largest delta system, is fed by immense water and sediment discharge from the Asian monsoon and Himalayan orogen - simply, the size of the GBD reflects the robust processes that have constructed and maintained it. At the regional scale, the deltaplain itself is interconnected by a labyrinth of fluvial and tidal channels that effectively convey sediment to most areas of the landscape, through overbank flooding, distributaries, and tidal transport. Together, the sediment supply, water discharge, and dense channel network bless the GBD with potential basinwide accretion rates >5 mm/yr. More locally, modern sedimentation rates >10 mm/yr are observed in many areas of the tidal delta plain, which are sufficient to maintain land-surface elevations under a variety of sea-level rise scenarios, or at least to mitigate whatever effects do occur. The long-term stratigraphic record of the GBD also reflects a system in dynamic equilibrium, with major landforms persisting through changes in sea level, sediment loading, river avulsion, and delta lobe switching - together providing an encouraging outlook in the face of

  14. Trapping of sediment along the Amazon tidal river in diverse floodplain environments

    NASA Astrophysics Data System (ADS)

    Fricke, A. T.; Nittrouer, C. A.; Ogston, A. S.; Nowacki, D. J.; Souza Filho, P. W.; Silveira, O.; Asp, N. E.

    2013-12-01

    The Amazon tidal river, the freshwater reach that is influenced by tides, extends roughly 800 kilometers upstream of the river mouth. Previous studies suggest that up to one third of the sediment measured at the upstream limit of tides does not reach the ocean, and is likely trapped along the tidal river. Here we present data from a variety of depositional environments along this reach, including intertidal vegetated floodplains, floodplain lakes, and drowned tributary confluences. Sediment delivery to each of these environments is temporally variable as a result of changing tides and river stage, and spatially variable along the continuum from the purely fluvial upstream condition to the strongly tidal downstream environment. Short-term instrument records and direct observations are paired with sedimentological and radiochemical techniques to identify mechanisms of sediment exchange between river and floodplain and associated patterns of sediment accumulation. Sediments in vegetated intertidal floodplains exhibit tidal laminations and incised channel networks similar to muddy marine intertidal areas. Floodplain lakes experience dramatic seasonal changes in size, and during high flows of the river skim water and sediment from the Amazon River by providing a shortcut relative to the meandering mainstem. Amazon sediment is fluxed into the drowned tributary confluences (rías) of the Xingu and Tapajos Rivers by density-driven underflows. In the Tapajos Ría, sediment from the Amazon River has built a 25-km long birdfoot delta, suggesting these tributaries may be net sinks of sediment, rather than sources. These findings help define the importance of each tidal environment in trapping Amazon sediment before it reaches the marine environment.

  15. A Tidally Averaged Sediment-Transport Model for San Francisco Bay, California

    USGS Publications Warehouse

    Lionberger, Megan A.; Schoellhamer, David H.

    2009-01-01

    A tidally averaged sediment-transport model of San Francisco Bay was incorporated into a tidally averaged salinity box model previously developed and calibrated using salinity, a conservative tracer (Uncles and Peterson, 1995; Knowles, 1996). The Bay is represented in the model by 50 segments composed of two layers: one representing the channel (>5-meter depth) and the other the shallows (0- to 5-meter depth). Calculations are made using a daily time step and simulations can be made on the decadal time scale. The sediment-transport model includes an erosion-deposition algorithm, a bed-sediment algorithm, and sediment boundary conditions. Erosion and deposition of bed sediments are calculated explicitly, and suspended sediment is transported by implicitly solving the advection-dispersion equation. The bed-sediment model simulates the increase in bed strength with depth, owing to consolidation of fine sediments that make up San Francisco Bay mud. The model is calibrated to either net sedimentation calculated from bathymetric-change data or measured suspended-sediment concentration. Specified boundary conditions are the tributary fluxes of suspended sediment and suspended-sediment concentration in the Pacific Ocean. Results of model calibration and validation show that the model simulates the trends in suspended-sediment concentration associated with tidal fluctuations, residual velocity, and wind stress well, although the spring neap tidal suspended-sediment concentration variability was consistently underestimated. Model validation also showed poor simulation of seasonal sediment pulses from the Sacramento-San Joaquin River Delta at Point San Pablo because the pulses enter the Bay over only a few days and the fate of the pulses is determined by intra-tidal deposition and resuspension that are not included in this tidally averaged model. The model was calibrated to net-basin sedimentation to calculate budgets of sediment and sediment-associated contaminants. While

  16. Environmental and eelgrass response to dike removal: Nisqually River Delta (2010–14)

    USGS Publications Warehouse

    Takesue, Renee K.

    2016-10-03

    Restoration of tidal flows to formerly diked marshland can alter land-to-sea fluxes and patterns of accumulation of terrestrial sediment and organic matter, and these tidal flows can also affect existing nearshore habitats. Dikes were removed from 308 hectares (ha) of the Nisqually National Wildlife Refuge on the Nisqually River Delta in south Puget Sound, Washington, in fall 2009 to improve habitat for wildlife, such as juvenile salmon. Ecologically important intertidal and subtidal eelgrass (Zostera marina) beds grow on the north and west margins of the delta. The goal of this study was to understand long-term changes in eelgrass habitat and their relation to dike removal. Sediment and eelgrass properties were monitored annually in May from 2010 to 2014 at two sites on the west side of the Nisqually River Delta along McAllister Creek, a spring-fed creek near two restored tidal channels. In May 2014, the mean canopy height of eelgrass was the same as in previous years in an 8-ha bed extending to the Nisqually River Delta front, but mean canopy height was 20 percent lower in a 0.3-ha eelgrass bed closer to the restored marsh when compared to mean canopy height of eelgrass in May 2010, 6 months after dike removal was completed. Over 5 years, the amount of eelgrass leaf area per square meter (m2) in the 8-ha bed increased slightly, and surface-sediment grain size became finer. In contrast, in the 0.3-ha bed, eelgrass leaf area per m2 decreased by 45 percent, and surface sediment coarsened. Other potential stressors, including sediment pore water reduction-oxidation potential (redox) and hydrogen sulfide (H2S) concentration in the eelgrass rhizosphere, or root zone, were below levels that negatively affect eelgrass growth and therefore did not appear to be environmental stressors on plants. Eelgrass biomass partitioning, though less favorable in the 8-ha eelgrass bed compared to the 0.3-ha one, was well above the critical above-ground to below-ground biomass ratio of

  17. 234U/238U and δ87Sr in peat as tracers of paleosalinity in the Sacramento-San Joaquin Delta of California, USA

    USGS Publications Warehouse

    Drexler, Judith Z.; Paces, James B.; Alpers, Charles N.; Windham-Myers, Lisamarie; Neymark, Leonid; Bullen, Thomas D.; Taylor, Howard E.

    2013-01-01

    The purpose of this study was to determine the history of paleosalinity over the past 6000+ years in the Sacramento-San Joaquin Delta (the Delta), which is the innermost part of the San Francisco Estuary. We used a combination of Sr and U concentrations, d87Sr values, and 234U/238U activity ratios (AR) in peat as proxies for tracking paleosalinity. Peat cores were collected in marshes on Browns Island, Franks Wetland, and Bacon Channel Island in the Delta. Cores were dated using 137Cs, the onset of Pb and Hg contamination from hydraulic gold mining, and 14C. A proof of concept study showed that the dominant emergent macrophyte and major component of peat in the Delta, Schoenoplectus spp., incorporates Sr and U and that the isotopic composition of these elements tracks the ambient water salinity across the Estuary. Concentrations and isotopic compositions of Sr and U in the three main water sources contributing to the Delta (seawater, Sacramento River water, and San Joaquin River water) were used to construct a three-end-member mixing model. Delta paleosalinity was determined by examining variations in the distribution of peat samples through time within the area delineated by the mixing model. The Delta has long been considered a tidal freshwater marsh region, but only peat samples from Franks Wetland and Bacon Channel Island have shown a consistently fresh signal (<0.5 ppt) through time. Therefore, the eastern Delta, which occurs upstream from Bacon Channel Island along the San Joaquin River and its tributaries, has also been fresh for this time period. Over the past 6000+ years, the salinity regime at the western boundary of the Delta (Browns Island) has alternated between fresh and oligohaline (0.5-5 ppt).

  18. Delta Subsidence in California: The Sinking Heart of the State

    USGS Publications Warehouse

    Ingebritsen, S.E.; Ikehara, M.E.; Galloway, D.L.; Jones, D.R.

    2000-01-01

    The Sacramento-San Joaquin River Delta of California once was a great tidal freshwater marsh blanketed by peat and peaty alluvium. Beginning in the late 1800s, levees were built along the stream channels, and the land thus protected from flooding was drained, cleared, and planted. Although the Delta is now an exceptionally rich agricultural area (over a $500 million crop value in 1993), its unique value is as a source of freshwater for the rest of the State. It is the heart of a massive north-to-south waterdelivery system. Much of this water is pumped southward for use in the San Joaquin Valley and elsewhere in central and southern California. The leveed tracts and islands help to protect water-export facilities in the southern Delta from saltwater intrusion by displacing water and maintaining favorable freshwater gradients. However, ongoing subsidence behind the levees reduces levee stability and, thus, threatens to degrade water quality in the massive north-to-south water-transfer system.

  19. Tidal Inlet Morphology Classification and Empirical Determination of Seaward and Down-Drift Extents of Tidal Inlets

    DTIC Science & Technology

    2012-05-01

    original Hayes (1979) diagram were not typical barrier island inlets. Some of them were fjords, and Bristol Bay and the Copper River Delta in Alaska included...shore that allows exchange of water between the ocean and bays , lagoons, and marsh and tidal creek systems, and for which the tidal current maintains...wave- dominated (Plum Island Sound, Essex Bay Inlet, and Newbury Port Harbor, all in Massachusetts) but lying close to the original line demarking tide

  20. Delta-doping of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schubert, E. F.

    2005-08-01

    Part I: 1. Introduction E. F. Schubert; Part II: 2. Electronic structure of delta-doped semiconductors C. R. Proetto; Part III: 3. Recent progress in delta-like confinement of impurities in GaAs K. H. Ploog; 4. Flow-rate modulation epitaxy (FME) of III-V semiconductors T. Makimoto and Y. Horikoshi; 5. Gas source molecular beam epitaxy (MBE) of delta-doped III-V semiconductors D. Ritter; 6. Solid phase epitaxy for delta-doping in silicon I. Eisele; 7. Low temperature MBE of silicon H.-J. Gossmann; Part IV: 8. Secondary ion mass spectrometry of delta-doped semiconductors H. S. Luftmann; 9. Capacitance-voltage profiling E. F. Schubert; 10. Redistribution of impurities in III-V semiconductors E. F. Schubert; 11. Dopant diffusion and segregation in delta-doped silicon films H.-J. Gossmann; 12. Characterisation of silicon and delta-doped structures in GaAs R. C. Newman; 13. The DX-center in silicon delta-doped GaAs and AlxGa1-xAs P. M. Koenraad; Part V: 14. Luminescence and ellipsometry spectroscopy H. Yao and E. F. Schubert; 15. Photoluminescence and Raman spectroscopy of single delta-doped III-V semiconductor heterostructures J. Wagner and D. Richards; 16. Electron transport in delta-doped quantum wells W. T. Masselink; 17. Electron mobility in delta-doped layers P. M. Koenraad; 18. Hot electrons in delta-doped GaAs M. Asche; 19. Ordered delta-doping R. L. Headrick, L. C. Feldman and B. E. Weir; Part IV: 20. Delta-doped channel III-V field effect transistors (FETs) W.-P. Hong; 21. Selectively doped heterostructure devices E. F. Schubert; 22. Silicon atomic layer doping FET K. Nakagawa and K. Yamaguchi; 23. Planar doped barrier devices R. J. Malik; 24. Silicon interband and intersubband photodetectors I. Eisele; 25. Doping superlattice devices E. F. Schubert.

  1. Simulating hydrodynamics on tidal mudflats

    NASA Astrophysics Data System (ADS)

    Cook, S.; Lippmann, T. C.

    2014-12-01

    Biogeochemical cycling in estuaries is governed by fluxes from both riverine sources and through estuarine sediment deposits. Although estimates from river sources are relatively common and easily sampled, estimates of nutrient fluxes through the fluid-sediment interface are less common and limited to deeper portions of the bays away from intertidal areas. Lack of quantifiable shear stress estimates over intertidal areas limits our overall understanding of nutrient budgets in estuaries. Unfortunately, observation of intertidal hydrodynamics and nutrient fluxes over tidal flats and near the water's edge is difficult owing to the temporally varying and spatially extensive region where the tides inundate, and thus numerical modeling is often employed. In this work, the Regional Ocean Modeling System (ROMS), a three dimensional numerical hydrodynamic model was used to investigate the shear stresses over intertidal mudflats in the Great Bay, a tidally-dominated New England estuary cut by several tidal channels and with over 50% of the estuary exposed at low tide. The ROMS wetting and drying scheme was used to simulate the rising and falling tide on the flats, a successful approach adapted in other regions of the world but not always inclusive of tidal channels. Bathymetric data obtained in 2009 and 2013 was used to define the model grid. Predicted tides are forced at Adam's Pt., a natural constriction in the estuary about 20 km upstream of the mouth and at the entrance to the Great Bay. Of particular interest are fluxes of material on-to and off-of the tidal flats which contribute to water quality conditions in the estuary, and are largely governed by shear stresses that drive nutrient fluxes at the fluid-sediment interface. Basin wide estimates of near-bottom shear stresses can be used to estimate first order nutrient fluxes over a tidal cycle and hence describe general biogeochemical dynamics of the estuary. Future work will include enhanced forcing of currents by

  2. Modern Pearl River Delta and Permian Huainan coalfield, China: A comparative sedimentary facies study

    USGS Publications Warehouse

    Suping, P.; Flores, R.M.

    1996-01-01

    Sedimentary facies types of the Pleistocene deposits of the Modern Pearl River Delta in Guangdong Province, China and Permian Member D deposits in Huainan coalfield in Anhui Province are exemplified by depositional facies of anastomosing fluvial systems. In both study areas, sand/sandstone and mud/mudstone-dominated facies types formed in diverging and converging, coeval fluvial channels laterally juxtaposed with floodplains containing ponds, lakes, and topogenous mires. The mires accumulated thin to thick peat/coal deposits that vary in vertical and lateral distribution between the two study areas. This difference is probably due to attendant sedimentary processes that affected the floodplain environments. The ancestral floodplains of the Modern Pearl River Delta were reworked by combined fluvial and tidal and estuarine processes. In contrast, the floodplains of the Permian Member D were mainly influenced by freshwater fluvial processes. In addition, the thick, laterally extensive coal zones of the Permian Member D may have formed in topogenous mires that developed on abandoned courses of anastomosing fluvial systems. This is typified by Seam 13-1, which is a blanket-like body that thickens to as much as 8 in but also splits into thinner beds. This seam overlies deposits of diverging and converging, coeval fluvial channels of the Sandstone D, and associated overbank-floodplain deposits. The limited areal extent of lenticular Pleistocene peat deposits of the Modern Pearl River Delta is due to their primary accumulation in topogenous mires in the central floodplains that were restricted by contemporaneous anastomosing channels.

  3. Tidal creek changes at the Sonoma Baylands restoration site

    USGS Publications Warehouse

    Dingler, John R.; Cacchione, David A.; ,

    1998-01-01

    Over the past 150 years, human activity has had a major impact on tidal wetlands adjoining the San Francisco Bay-Delta estuary Growing concern about the effect of this change on the ecology of the estuary has prompted Bay area managers to attempt to reclaim tidal wetlands. The Sonoma Baylands Restoration Project is designed to use dredge material to convert 348 acres from farmland to wetland. This paper describes changes to a tidal creek that flows from that restoration site to San Pablo Bay (north San Francisco Bay) through an existing tidal wetland during different phases of the project. Hydrologic measurements near the bottom of the creek and cross-creek profiles show how the creek responded to non-tidal flow conditions introduced by filling the site with dredge materials. At the time of this study, the creek had deepened by approximately 40 cm but had not widened.

  4. Quaternary geology and geomorphology of the Sacramento-San Joaquin Delta, California: evolution and processes

    NASA Astrophysics Data System (ADS)

    Gatti, E.; Maier, K. L.; Holzer, T. L.; Knudsen, K. L.; Olson, H.; Pagenknopp, M.; Ponti, D. J.; Rosa, C.; Tinsley, J. C.; Wan, E.

    2013-12-01

    The Sacramento-San Joaquin Delta (~1,400 km2) is a combination of tidal marsh, islands and agricultural lands at the confluence of the Sacramento and the San Joaquin Rivers, in northern California. Most of the Delta islands are now 3 to 8 m below sea-level and must be protected by levees from inundation. Because of the Delta's crucial role in conveying fresh water to the State, levee failures can cause substantial economic loss by disrupting this supply. Understanding the evolution of the Delta is fundamental to assess the vulnerability of the Delta islands to seismically-induced levee failure. The modern Delta is a young geological feature that began forming during the middle Holocene. Preceding versions of the Delta hosted a variety of depositional environments as sea level fluctuated, responding to climatically-controlled changes. The rising sea reached the Delta about 8,000 years ago, and modern deltaic evolution continued into Holocene time until present. More accurate stratigraphic studies incorporating depositional ages are required to i) better understand the late Quaternary evolution of the Delta, ii) trace the base of Holocene deposits, iii) identify potentially active faults, and iv) evaluate liquefaction hazard for the Delta . This study uses the large amount of data available on the Delta (collected by the California Department of Water Resources and others during the past 30 years) and merges them into a unified dataset. We have produced a database that includes historic and surficial maps, aerial photographs, boreholes, and CPT data, for the purpose of clarifying the nature of the Quaternary deposits and the evolution of the Late Quaternary Delta. Additionally, we have identified recently discovered Pleistocene tephra as the Rockland ash, ~0.575 Ma, and the Loleta ash, ~0.40-0.37 Ma, which have improved stratigraphic correlations and assessment of subsidence rates. Delta sediments include sequences of glacial and interglacial deposits. Borehole logs

  5. Mechanics and rates of tidal inlet migration: Modeling and application to natural examples

    NASA Astrophysics Data System (ADS)

    Nienhuis, Jaap H.; Ashton, Andrew D.

    2016-11-01

    Tidal inlets on barrier coasts can migrate alongshore hundreds of meters per year, often presenting great management and engineering challenges. Here we perform model experiments with migrating tidal inlets in Delft3D-SWAN to investigate the mechanics and rates of inlet migration. Model experiments with obliquely approaching waves suggest that tidal inlet migration occurs due to three mechanisms: (1) littoral sediment deposition along the updrift inlet bank, (2) wave-driven sediment transport preferentially eroding the downdrift bank of the inlet, and (3) flood-tide-driven flow preferentially cutting along the downdrift inlet bank because it is less obstructed by flood-tidal delta deposits. To quantify tidal inlet migration, we propose and apply a simple mass balance framework of sediment fluxes around inlets that includes alongshore sediment bypassing and flood-tidal delta deposition. In model experiments, both updrift littoral sediment and the eroded downdrift inlet bank are sediment sources to the growing updrift barrier and the flood-tidal delta, such that tidal inlets can be net sink of up to 150% of the littoral sediment flux. Our mass balance framework demonstrates how, with flood-tidal deltas acting as a littoral sediment sink, migrating tidal inlets can drive erosion of the downdrift barrier beach. Parameterizing model experiments, we propose a predictive model of tidal inlet migration rates based upon the relative momentum flux of the inlet jet and the alongshore radiation stress; we then compare these predicted migration rates to 22 natural tidal inlets along the U.S. East Coast and find good agreement.

  6. Zircons traced from the 700-500 Ma Transgondwanan Supermountains and the Gamburtsev Subglacial Mountains to the Ordovician Lachlan Orogen, Cretaceous Ceduna Delta, and modern Channel Country, central-southern Australia

    NASA Astrophysics Data System (ADS)

    Veevers, J. J.; Belousova, E. A.; Saeed, A.

    2016-04-01

    We test the hypothesis that the Transgondwanan Supermountains at the collision of East and West Gondwanaland were the provenance of a vast turbiditic fan that stretched alongside the East Gondwanaland margin to eastern Australia which, in turn, became the provenance of sediment shed into interior Australia to the Cretaceous Ceduna Delta in central-southern Australia and the modern Channel Country of central Australia. We employ an integrated analysis (U-Pb, Lu-Hf isotopes and trace elements) of detrital zircons in the Ceduna Delta and Channel Country. The main properties of the detrital zircons are U-Pb ages of 700-500 Ma (model ages TDMC 2.5-1.0 Ga; εHf +10 to -20) and 1300-1000 Ma ages (TDMC 2.7-1.3 Ga; εHf +4 to -17), in hosts of mafic granitoids with alkaline affinity. Zircons with these properties can be traced back through the drainage/paleo-slope to the intermediate provenances of the Ordovician turbidites and S-type granitoids of the Lachlan Orogen, then up-paleoslope to the primary or secondary provenance of the ancestral Gamburtsev Subglacial Mountains, and finally to the primary provenance of the Transgondwanan Supermountains atop the 700-500 Ma East African-Antarctic Orogen. Another primary provenance, the 140-95 Ma Whitsunday Volcanic Province/New Caledonia arc in northeastern Australia, also shed sediment across Australia to the Ceduna Delta. We suggest that the primary sediment from the 700-500 Ma East African-Antarctic Orogen and the ancestral Gamburtsev Subglacial Mountains was shed into a deep-sea super-fan to (1) Ordovician turbidites in southeast Australia, recycled by melting of the turbidites to (2) 450 Ma S-type granites in the Lachlan Orogen, and (3) finally deposited, together with volcanogenic sediment from northeast Australia, in the Ceduna Delta. Zircons in the Channel Country and the Ceduna Delta have essentially the same properties, and indicate that the northeastern Australian provenance was largely unchanged over the past 100 Ma.

  7. Identification and synthesis of [1,2,4]triazolo[3,4-a]phthalazine derivatives as high-affinity ligands to the alpha 2 delta-1 subunit of voltage gated calcium channel.

    PubMed

    Lebsack, Alec D; Gunzner, Janet; Wang, Bowei; Pracitto, Richard; Schaffhauser, Hervé; Santini, Angelina; Aiyar, Jayashree; Bezverkov, Robert; Munoz, Benito; Liu, Wensheng; Venkatraman, Shankar

    2004-05-17

    We have identified and synthesized a series of [1,2,4]triazolo[3,4-a]phthalazine derivatives as high-affinity ligands to alpha 2 delta-1 subunit of voltage gated calcium channels. Structure-activity relationship studies directed toward improving the potency and physical properties of 2 lead to the discovery of 20 (IC(50)=15 nM) and (S)-22 (IC(50)=30 nM). A potent and selective radioligand, [(3)H]-(S)-22 was also synthesized to demonstrate that this ligand binds to the same site as gabapentin.

  8. Potent stimulation of large-conductance Ca2+-activated K+ channels by rottlerin, an inhibitor of protein kinase C-delta, in pituitary tumor (GH3) cells and in cortical neuronal (HCN-1A) cells.

    PubMed

    Wu, Sheng-Nan; Wang, Ya-Jean; Lin, Ming-Wei

    2007-03-01

    The effects of rottlerin, a known inhibitor of protein kinase C-delta activation, on ion currents were investigated in pituitary tumor (GH3) cells. Rottlerin (0.3-100 microM) increased the amplitude of Ca2+-activated K+ current (I K(Ca)) in a concentration-dependent manner with an EC50 value of 1.7 microM. In intracellular perfusion with rottlerin (1 microM) or staurosporine (10 microM), phorbol 12-myristate 13-acetate-induced inhibition of I K(Ca) in these cells was abolished. In cell-attached mode, rottlerin applied on the extracellular side of the membrane caused activation of large-conductance Ca2+-activated K+ (BK(Ca)) channels, and a further application of BAPTA-AM (10 microM) to the bath had no effect on rottlerin-stimulated channel activity. When cells were exposed to rottlerin, the activation curve of these channels was shifted to less positive potential with no change in the slope factor. Rottlerin increased BK(Ca)-channel activity in outside-out patches. Its change in kinetic behavior of BK(Ca) channels is primarily due to an increase in mean open time. With the aid of minimal kinetic scheme, a quantitative description of rottlerin stimulation on BK(Ca) channels in GH3 cells was also provided. Under current-clamp configuration, rottlerin (1 microM) decreased the firing of action potentials. I K(Ca) elicited by simulated action potential waveforms was enhanced by this compound. In human cortical HCN-1A cells, rottlerin (1 microM) could also interact with the BK(Ca) channel to stimulate I K(Ca). Therefore, rottlerin may directly activate BK(Ca) channels in neurons or endocrine cells.

  9. Channels, reservoir orientation, and paleocurrents - Theory and exploitation

    SciTech Connect

    Grace, L.M.; Pirie, R.G. ); Potter, P.E. )

    1990-05-01

    Channels, from a few up to hundreds of meters thick, occur in virtually all the major sandy and carbonate environments. The fill of channels varies greatly and includes stream deposits, delta distributaries, tidal deposits, debris flows, marine detritus washed both longitudinally and laterally into shelf channels, deep-water turbidites, glacial deposits, and volcanic rocks. Landslide blocks from collapsing channel margins can also be incorporated in the fill. Most of these occur in combinations, although a few combinations are very common and some are rare. Reservoirs in channels are increasingly significant in mature basins. The authors propose a general set of rules for predicting reservoir orientation in channels. The rules are independent of depositional environment and scale, and depend only on the physical processes of channel filling. This set of rules is based on studies of outcrop and electrical images from well bores and includes channel sinuosity, type of accretion, and the orientation of paleocurrent structures. A key concept is compactional dip, which mirrors the channel's bottom morphology. These rules are illustrated with case histories of successful offset wells from basins of all ages throughout the world.

  10. Human induced discharge diversion in a tropical delta and its environmental implications: The Patía River, Colombia

    NASA Astrophysics Data System (ADS)

    Restrepo, Juan D.; Kettner, Albert

    2012-03-01

    SummaryThe Patía River, the number one in terms of sediment yield ˜1500 t km-2 yr-1 draining the western South America, has the most extensive and well developed delta on the Pacific coast, measuring 1700 km2. During the Holocene, nature forced the Patía delta to the south; however, a major water diversion, starting in 1972, diverted the Patía flow to the Sanguianga River, the latter, a small stream draining internal lakes from the Pacific lowlands. This human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain. Overall, major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels, are evidenced by: (1) coastal retreat along the abandoned delta lobe; 63% of the southern shoreline is retreating at maximum rates of 7 m yr-1, with a corresponding coastal land loss of 106 m yr-1; (2) transgressive barrier islands with exposed peat soils in the surf zone; (3) abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas; (4) breaching events on barrier islands; and (5) distributary channel accretion in the northern delta plain by morphological processes such as sedimentation (also in crevasses), overbank flow, increasing width of levees, interdistributary channel fill, and colonization of pioneer mangrove. The Sanguianga Mangrove National Park (SMNP), the largest mangrove reserve in Colombia, measuring 800 km2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Observed environmental changes in the SMNP, include (1) seaward advance of the sub-aqueous delta front at the Sanquianga inlet evidenced by an increase in tidal flat area from 5.4 Mm2 in 1986 to 14 Mm2 in 2001; (2) freshening conditions in the Sanguianga distributary channel, a hydrologic change that has shifted the

  11. TIDEV: Tidal Evolution package

    NASA Astrophysics Data System (ADS)

    Cuartas-Restrepo, P.; Melita, M.; Zuluaga, J.; Portilla, B.; Sucerquia, M.; Miloni, O.

    2016-09-01

    TIDEV (Tidal Evolution package) calculates the evolution of rotation for tidally interacting bodies using Efroimsky-Makarov-Williams (EMW) formalism. The package integrates tidal evolution equations and computes the rotational and dynamical evolution of a planet under tidal and triaxial torques. TIDEV accounts for the perturbative effects due to the presence of the other planets in the system, especially the secular variations of the eccentricity. Bulk parameters include the mass and radius of the planet (and those of the other planets involved in the integration), the size and mass of the host star, the Maxwell time and Andrade's parameter. TIDEV also calculates the time scale that a planet takes to be tidally locked as well as the periods of rotation reached at the end of the spin-orbit evolution.

  12. Suspended sediment fluxes in a tidal wetland: Measurement, controlling factors, and error analysis

    USGS Publications Warehouse

    Ganju, N.K.; Schoellhamer, D.H.; Bergamaschi, B.A.

    2005-01-01

    Suspended sediment fluxes to and from tidal wetlands are of increasing concern because of habitat restoration efforts, wetland sustainability as sea level rises, and potential contaminant accumulation. We measured water and sediment fluxes through two channels on Browns Island, at the landward end of San Francisco Bay, United States, to determine the factors that control sediment fluxes on and off the island. In situ instrumentation was deployed between October 10 and November 13, 2003. Acoustic Doppler current profilers and the index velocity method were employed to calculate water fluxes. Suspended sediment concentrations (SSC) were determined with optical sensors and cross-sectional water sampling. All procedures were analyzed for their contribution to total error in the flux measurement. The inability to close the water balance and determination of constituent concentration were identified as the main sources of error; total error was 27% for net sediment flux. The water budget for the island was computed with an unaccounted input of 0.20 m 3 s-1 (22% of mean inflow), after considering channel flow, change in water storage, evapotranspiration, and precipitation. The net imbalance may be a combination of groundwater seepage, overland flow, and flow through minor channels. Change of island water storage, caused by local variations in water surface elevation, dominated the tidalty averaged water flux. These variations were mainly caused by wind and barometric pressure change, which alter regional water levels throughout the Sacramento-San Joaquin River Delta. Peak instantaneous ebb flow was 35% greater than peak flood flow, indicating an ebb-dominant system, though dominance varied with the spring-neap cycle. SSC were controlled by wind-wave resuspension adjacent to the island and local tidal currents that mobilized sediment from the channel bed. During neap tides sediment was imported onto the island but during spring tides sediment was exported because the main

  13. Tidal and subtidal hydrodynamics and energetics in a constricted estuary

    NASA Astrophysics Data System (ADS)

    Zarzuelo, Carmen; López-Ruiz, Alejandro; Díez-Minguito, Manuel; Ortega-Sánchez, Miguel

    2017-02-01

    The dynamics of coastal plain estuaries are mainly associated with variable tidal forcing and local winds in combination with bathymetric complexity and coastline irregularity. Specific features, such as constricted areas, can potentially affect and energize the hydrodynamics of these types of systems. Particularly, tidal range and tidal currents can be significantly amplified where the incoming tidal wave becomes constricted. In this work, the impact of a narrow constriction on a mesotidal estuary was analysed at tidal and subtidal time scales. Tidal hydrodynamics, energy fluxes and energy dissipation were determined for the entire Cádiz Bay (southwestern Spain) using the Delft3D numerical model. Field observations were used to analyse tidal propagation and energy dissipation along the bay constriction and to calibrate and test the numerical model. The results indicate that the presence of the constriction transformed and distorted the tide and increased the tidal range and flow velocities along the channel, with implications on energy dissipation. The tidal currents were oriented along-channel at the central part of the constriction, although abrupt bathymetric changes at the channel inner boundary provoked a sudden rotation of the flow. Although the energy fluxes were higher for spring tides and were strongly influenced by winds, the energy dissipation was controlled by bed shear stresses and vertical dispersion. The significance of this energy dissipation was that it destabilized the water column, which resulted in a weakly stratified system with implications on water quality. At a subtidal scale, the residual water volume exchange was the result of the combined effects of the neap/spring tides, wind and waves, whereas tides were dominant at the tidal scale.

  14. Wave-driven tidal inlet migration: mechanics and effects on barrier morphology

    NASA Astrophysics Data System (ADS)

    Nienhuis, J.; Ashton, A. D.

    2015-12-01

    Littoral sediment transport on barrier island coasts can cause tidal inlets to migrate alongshore up to hundreds of meters per year and pose significant hazards and challenges to coastal communities, infrastructure, and ecosystems. Surprisingly little is known about either the mechanisms or the expected rates of tidal inlet migration. Here we propose and test a simple framework of inlet migration that allows us to investigate the movement of sediment around tidal inlets and predict the corresponding migration rates. We test this framework using a combination of observed migration rates and idealized inlet simulations from the coupled hydrodynamic and morphodynamic model Delft3D-SWAN. In the Delft3D experiments, the tidal inlets quickly reach a dynamic state where the inlet cross-sectional area, the tidal prism and the migration rate, all of which are emergent characteristics of the experiment, remain constant through time. Tracking the sources of sediments deposited around the tidal inlet, we find that the eroded downdrift barrier is a significant source of sediment to both the flood tidal delta and the newly constructed barrier updrift of the inlet. The alongshore sediment bypassing volumes and pathways affecting inlet migration depend strongly on wave and tidal conditions. Furthermore, we find that migrating flood tidal deltas can act as a net sink of up to 80% of the littoral sediment flux. This sink reduces alongshore sediment bypassing of tidal inlets and thins the barrier downdrift. These modeled tidal inlets can therefore act as a migrating "buzzsaw" across barrier coasts that leave a zone of flood tidal delta deposits in their wake, an efficacious sediment mover that contributes significantly to the long-term landward migration of barrier islands with or without sea level rise.

  15. Rapid evolution of a marsh tidal creek network in response to sea level rise.

    NASA Astrophysics Data System (ADS)

    Hughes, Z. J.; Fitzgerald, D. M.; Mahadevan, A.; Wilson, C. A.; Pennings, S. C.

    2008-12-01

    In the Santee River Delta (SRD), South Carolina, tidal creeks are extending rapidly onto the marsh platform. A time-series of aerial photographs establishes that these channels were initiated in the 1950's and are headward eroding at a rate of 1.9 m /yr. Short-term trends in sea level show an average relative sea level rise (RSLR) of 4.6 mm/yr over a 20-year tide gauge record from nearby Winyah Bay and Charleston Harbor (1975-1995). Longer-term (85-year) records in Charleston suggest a rate of 3.2 mm/yr. RSLR in the SRD is likely even higher as sediment cores reveal that the marsh is predominantly composed of fine-grained sediment, making it highly susceptible to compaction and subsidence. Furthermore, loss in elevation will have been exacerbated by the decrease in sediment supply due to the damming of the Santee River in 1939. The rapid rate of headward erosion indicates that the marsh platform is in disequilibrium; unable to keep pace with RSLR through accretionary processes and responding to an increased volume and frequency of inundation through the extension of the drainage network. The observed tidal creeks show no sinuosity and a distinctive morphology associated with their young age and biological mediation during their evolution. Feedbacks between tidal flow, vegetation and infauna play a strong role in the morphological development of the creeks. The creek heads are characterized by a region denuded of vegetation, the edges of which are densely populated and burrowed by Uca Pugnax (fiddler crab). Crab burrowing destabilizes sediment, destroys rooting and impacts drainage. Measured infiltration rates are three orders of magnitude higher in the burrowed regions than in a control area (1000 ml/min and 0.6 ml/min respectively). Infiltration of oxygenated water enhances decomposition of organic matter and root biomass is reduced within the creek head (marsh=4.3 kg/m3, head=0.6 kg/m3). These processes lead to the removal and collapse of the soils, producing

  16. Developing a Truly Global Delta Database to Assess Delta Morphology and Morphodynamics

    NASA Astrophysics Data System (ADS)

    Caldwell, R. L.; Edmonds, D. A.; Baumgardner, S. E.; Whaling, A.

    2015-12-01

    Delta morphology reflects the interplay of various environmental parameters, though these relationships have only been tested on small datasets with 30-50 deltas. These datasets are biased toward the largest deltas, which typically have compound morphologies, form on passive margins, and may not be representative of the full breadth in delta morphology. With the goal of building more robust predictions of delta morphology to enhance hazard mitigation and resiliency planning, we have developed a truly global delta database including every delta on the world's marine coastlines. Using Google Earth imagery, we first identified all fluvial river mouths (≥ 50 m wide) connected to an upstream catchment. Deltas are defined geomorphically as river mouths that split into two or more active or relict distributary channels, end in a depositional protrusion from the shoreline, or do both. In our database we identified 5,801 river mouths, and 1,426 of those coastal rivers (~25%) have a geomorphic delta. ~75% of deltas exhibit an active or relict distributary network, while the remaining ~25% are single channel deltas with a basinward protrusion. Preliminary morphometric analysis (ratio of shore-parallel width, W, to shore-perpendicular length, L) on a subset of 159 deltas suggests W:L values range from 0.52 (elongate) to 23.6 (broad/cuspate). The median W:L value is 2.68, suggesting the majority of deltas are roughly semi-circular (W:L = 2), and the distribution is heavily skewed to the broad/cuspate deltas (~28% are >4 times wider than they are long). Preliminary comparison to downstream significant wave height data shows that the 'wider' deltas relate to higher wave heights (R2 = 0.42), though the data are scattered. Ultimately, the database will include additional measured morphometrics, including number of channel mouths and delta area, and morphodynamic data derived from serial Landsat imagery.

  17. A modeling study of tidal energy extraction and the associated impact on tidal circulation in a multi-inlet bay system of Puget Sound

    DOE PAGES

    Wang, Taiping; Yang, Zhaoqing

    2017-03-25

    Previously, a major focus of tidal energy studies in Puget Sound were the deep channels such as Admiralty Inlet that have a larger power potential. Our paper focuses on the possibility of extracting tidal energy from minor tidal channels of Puget Sound by using a hydrodynamic model to quantify the power potential and the associated impact on tidal circulation. The study site is a multi-inlet bay system connected by two narrow inlets, Agate Pass and Rich Passage, to the Main Basin of Puget Sound. A three-dimensional hydrodynamic model was applied to the study site and validated for tidal elevations andmore » currents. Here, we examined three energy extraction scenarios in which turbines were deployed in each of the two passages and concurrently in both. Extracted power rates and associated changes in tidal elevation, current, tidal flux, and residence time were examined. Maximum instantaneous power rates reached 250 kW, 1550 kW, and 1800 kW, respectively, for the three energy extraction scenarios. Model results suggest that with the level of energy extraction in the three energy extraction scenarios, the impact on tidal circulation is very small. It is worth investigating the feasibility of harnessing tidal energy from minor tidal channels of Puget Sound.« less

  18. Laboratory Observations on Tidal Network Growth and Development

    NASA Astrophysics Data System (ADS)

    Stefanon, L.; Carniello, L.; D'Alpaos, A.

    2011-12-01

    We present the results of laboratory experiments carried out in a large experimental apparatus aimed at reproducing a typical lagoonal environment subject to tidal forcings. The experiments were designed in order to improve our understanding of the main processes governing tidal network initiation and its progressive morphodynamic evolution. In particular, the experiments summarized herein aimed at understanding the physical processes, as well as boundary and initial conditions, which lead to the initiation and subsequent development of a tidal channel network, starting from a plane horizontal tidal flat located behind a barrier island and connected through the sea by a single inlet. During the experiments we observed the growth and development of tidal networks and analyzed their most relevant geomorphic features, taking into account the role played by the characteristics of the tidal forcing in driving the development of channelled patterns. The experimental evidence suggests that general network evolution is substantially characterized by three processes: (1) channel elongation via headward growth, driven by the exceedance of a critical bottom shear stress; (2) incision and sinuosity gradually increasing with channels age; (3) formation of new lateral creeks and tributaries. The lack of external sediment supply, the absence of vegetation, and the prevalence of bedload transport prevented any deposition processes and lateral surface accretion, attributing a purely erosive character to the experimental lagoon. Nevertheless, the morphodynamic feedbacks occurring in the erosional case are essentially the same that occur under depositional conditions. In fact, in both cases, channel excavation is closely connected to concentration of tidal fluxes within the channel network during maximum ebb phase when maximum velocities and shear stresses are reached. In this experimental lagoon the main morphodynamic process responsible for tidal network initiation and development

  19. An optimal tuning strategy for tidal turbines

    NASA Astrophysics Data System (ADS)

    Vennell, Ross

    2016-11-01

    Tuning wind and tidal turbines is critical to maximizing their power output. Adopting a wind turbine tuning strategy of maximizing the output at any given time is shown to be an extremely poor strategy for large arrays of tidal turbines in channels. This `impatient-tuning strategy' results in far lower power output, much higher structural loads and greater environmental impacts due to flow reduction than an existing `patient-tuning strategy' which maximizes the power output averaged over the tidal cycle. This paper presents a `smart patient tuning strategy', which can increase array output by up to 35% over the existing strategy. This smart strategy forgoes some power generation early in the half tidal cycle in order to allow stronger flows to develop later in the cycle. It extracts enough power from these stronger flows to produce more power from the cycle as a whole than the existing strategy. Surprisingly, the smart strategy can often extract more power without increasing maximum structural loads on the turbines, while also maintaining stronger flows along the channel. This paper also shows that, counterintuitively, for some tuning strategies imposing a cap on turbine power output to limit loads can increase a turbine's average power output.

  20. An optimal tuning strategy for tidal turbines.

    PubMed

    Vennell, Ross

    2016-11-01

    Tuning wind and tidal turbines is critical to maximizing their power output. Adopting a wind turbine tuning strategy of maximizing the output at any given time is shown to be an extremely poor strategy for large arrays of tidal turbines in channels. This 'impatient-tuning strategy' results in far lower power output, much higher structural loads and greater environmental impacts due to flow reduction than an existing 'patient-tuning strategy' which maximizes the power output averaged over the tidal cycle. This paper presents a 'smart patient tuning strategy', which can increase array output by up to 35% over the existing strategy. This smart strategy forgoes some power generation early in the half tidal cycle in order to allow stronger flows to develop later in the cycle. It extracts enough power from these stronger flows to produce more power from the cycle as a whole than the existing strategy. Surprisingly, the smart strategy can often extract more power without increasing maximum structural loads on the turbines, while also maintaining stronger flows along the channel. This paper also shows that, counterintuitively, for some tuning strategies imposing a cap on turbine power output to limit loads can increase a turbine's average power output.

  1. Analysis of Meander Migration Rates in Tidal Landscapes

    NASA Astrophysics Data System (ADS)

    Finotello, Alvise; D'Alpaos, Andrea; Ghinassi, Massimiliano; Lanzoni, Stefano; Marani, Marco; Rinaldo, Andrea

    2015-04-01

    Meandering patterns are universal features of tidal landscapes, which exert a great influence on the dynamics of tidal channel networks and on the stratigraphy of intertidal platforms. Despite their importance in landscape evolution and their ubiquity, tidal meanders have received less attention when compared to their fluvial counterparts. Quite a few studies, in fact, have focused on the morphodynamic evolution of tidal meanders, together with their planimetric shape and morphometric characteristics. To improve current understanding of tidal meander migration, a key step to address tidal meander evolution, we have analyzed a sequence of aerial photographs (from 1938 to present day) for about 400 meander bends, over 40 salt-marsh channels in the Northern part of the Venice Lagoon (Italy). Tidal meanders display similarities with fluvial meanders, although important differences emerge. Meanders cutting through the San Felice marsh follow the relationship between cartesian length and channel width, typical of meanders developed within different landscapes. However, meander migration rates, which were determined on the basis of three different methods, proved to be smaller than those characterizing fluvial meanders. Our analysis suggests mean migration rates of about 0.10 m/year, which is consistent with migration rates determined by previous studies on tidal meanders. The relationship between erosion (migration) rate and bend radius (R), both made dimensionless with channel width (W), displays a bell-shaped envelope pattern, in analogy with fluvial meanders although with smaller migration rates. In the tidal case, in fact, the largest migration rate is about 0.10 channel widths per year, which is smaller than the largest migration rate (0.20 channel widths per year) characterizing fluvial meanders that we found in the literature. Interestingly, in the case of tidal meanders the peak of the bell-shaped curve corresponds to a R/W ratio between 4 and 5, whereas the same

  2. Propagation of tidal waves up in Yangtze Estuary during the dry season

    NASA Astrophysics Data System (ADS)

    Lu, Sheng; Tong, Chaofeng; Lee, Dong-Young; Zheng, Jinhai; Shen, Jian; Zhang, Wei; Yan, Yixin

    2015-09-01

    Tide is one of the most important hydrodynamic driving forces and has unique features in the Yangtze Estuary (YE) due to the complex geometry of third-order bifurcations and four outlets. This paper characterizes the tidal oscillations, tidal dampening, tidal asymmetry, and tidal wave propagation, which provides insights into the response of the estuary to tides during the dry season. The structural components of tidal oscillations are initially attained by tidal analysis. The increasingly richer spectrum inside the estuary shows an energy transfer corresponding to the generation and development of nonlinear overtides and compound tides. A 2-D numerical model is further set up to reproduce tidal dynamics in the estuary. The results show that the estuary is a strongly dissipative estuary with a strong nonlinear phenomenon. Three amplifications are presented in the evolution process of tidal ranges due to the channel convergence. Tidal asymmetry is spatiotemporally characterized by the M4/M2 amplitude ratio, the 2M2-M4 phase difference, and the flood-ebb duration-asymmetry parameter, and the estuary tends to be flood-dominant. There exists mimic standing waves with the phase difference of the horizontal and vertical tide close to 90° when tidal wave propagates into the estuary, especially during the neap tide. In addition, the differences in tidal distortion, tidal ranges, and tidal waves along the two routes in the South Branch (S-B) suggest the branched system behaves differently from a single system.

  3. Tidal alignment of galaxies

    SciTech Connect

    Blazek, Jonathan; Vlah, Zvonimir; Seljak, Uroš

    2015-08-01

    We develop an analytic model for galaxy intrinsic alignments (IA) based on the theory of tidal alignment. We calculate all relevant nonlinear corrections at one-loop order, including effects from nonlinear density evolution, galaxy biasing, and source density weighting. Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales. This effect may be responsible for much of the luminosity dependence in IA observations. The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields. We also consider the impact of smoothing the tidal field on halo scales. We compare the performance of this consistent nonlinear model in describing the observed alignment of luminous red galaxies with the linear model as well as the frequently used "nonlinear alignment model," finding a significant improvement on small and intermediate scales. We also show that the cross-correlation between density and IA (the "GI" term) can be effectively separated into source alignment and source clustering, and we accurately model the observed alignment down to the one-halo regime using the tidal field from the fully nonlinear halo-matter cross correlation. Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting nonlinear processes that must be considered when modeling IA on these scales. Finally, we discuss tidal alignment in the context of cosmic shear measurements.

  4. Tidal alignment of galaxies

    SciTech Connect

    Blazek, Jonathan; Vlah, Zvonimir; Seljak, Uroš E-mail: zvlah@stanford.edu

    2015-08-01

    We develop an analytic model for galaxy intrinsic alignments (IA) based on the theory of tidal alignment. We calculate all relevant nonlinear corrections at one-loop order, including effects from nonlinear density evolution, galaxy biasing, and source density weighting. Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales. This effect may be responsible for much of the luminosity dependence in IA observations. The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields. We also consider the impact of smoothing the tidal field on halo scales. We compare the performance of this consistent nonlinear model in describing the observed alignment of luminous red galaxies with the linear model as well as the frequently used 'nonlinear alignment model,' finding a significant improvement on small and intermediate scales. We also show that the cross-correlation between density and IA (the 'GI' term) can be effectively separated into source alignment and source clustering, and we accurately model the observed alignment down to the one-halo regime using the tidal field from the fully nonlinear halo-matter cross correlation. Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting nonlinear processes that must be considered when modeling IA on these scales. Finally, we discuss tidal alignment in the context of cosmic shear measurements.

  5. Delta in Eberswalde

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This HiRISE image covers a portion of a delta that partially fills Eberswalde crater in Margaritifer Sinus. The delta was first recognized and mapped using MOC images that revealed various features whose presence required sustained flow and deposition into a lake that once occupied the crater. The HiRISE image resolves meter-scale features that record the migration of channels and delta distributaries as the delta grew over time. Differences in grain-size of sediments within the environments on the delta enable differential erosion of the deposits. As a result, coarser channel deposits are slightly more resistant and stand in relief relative to finer-grained over-bank and more easily eroded distal delta deposits. Close examination of the relict channel deposits confirms the presence of some meter-size blocks that were likely too coarse to have been transported by water flowing within the channels. These blocks may be formed of the sand and gravel that more likely moved along the channels that was lithified and eroded. Numerous meter-scale polygonal structures are common on many surfaces, but mostly those associated with more quiescent depositional environments removed from the channels. The polygons could be the result of deposition of fine-grained sediments that were either exposed and desiccated (dried out), rich in clays that shrunk when the water was removed, turned into rock and then fractured and eroded, or some combination of these processes.

    Image PSP_001336_1560 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 8, 2006. The complete image is centered at -23.8 degrees latitude, 326.4 degrees East longitude. The range to the target site was 256.3 km (160.2 miles). At this distance the image scale is 25.6 cm/pixel (with 1 x 1 binning) so objects 77 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel and north is up. The image was

  6. Stellar dynamics and tidal disruption events in galactic nuclei

    NASA Astrophysics Data System (ADS)

    Alexander, T.

    2012-12-01

    The disruption of a star by the tidal field of a massive black hole is the final outcome of a chain of complex dynamical processes in the host galaxy. I introduce the "loss cone problem", and describe the many theoretical and numerical challenges on the path of solving it. I review various dynamical channels by which stars can be supplied to a massive black hole, and the relevant dynamical relaxation/randomization mechanisms. I briefly mention some "exotic" tidal disruption scenarios, and conclude by discussing new dynamical results that are changing our understanding of dynamics near a massive black hole, and may well be relevant for tidal disruption dynamics.

  7. The role of tidal marsh restoration in fish management in the San Francisco Estuary

    USGS Publications Warehouse

    Herbold, Bruce; Baltz, Donald; Brown, Larry R.; Grossinger, Robin; Kimmerer, Wim J.; Lehman, Peggy W.; Moyle, Peter B.; Nobriga, Matthew L.; Simenstad, Charles A.

    2015-01-01

    Tidal marsh restoration is an important management issue in the San Francisco Estuary (estuary). Restoration of large areas of tidal marsh is ongoing or planned in the lower estuary (up to 6,000 ha, Callaway et al. 2011). Large areas are proposed for restoration in the upper estuary under the Endangered Species Act biological opinions (3,237 ha) and the Bay Delta Conservation Plan (26,305 ha). In the lower estuary, tidal marsh has proven its value to a wide array of species that live within it (Palaima 2012). In the Sacramento–San Joaquin Delta (Delta), one important function ascribed to restoration of freshwater tidal marshes is that they make large contributions to the food web of fish in open waters (BDCP 2013). The Ecosystem Restoration Program ascribed a suite of ecological functions to tidal marsh restoration, including habitat and food web benefits to native fish (CDFW 2010). This background was the basis for a symposium, Tidal Marshes and Native Fishes in the Delta: Will Restoration Make a Difference? held at the University of California, Davis, on June 10, 2013. This paper summarizes conclusions the authors drew from the symposium.

  8. Catalog of worldwide tidal bore occurrences and characteristics

    USGS Publications Warehouse

    Bartsch-Winkler, S.; Lynch, David K.

    1988-01-01

    Documentation of tidal bore phenomena occurring throughout the world aids in defining the typical geographical setting of tidal bores and enables prediction of their occurrence in remote areas. Tidal bores are naturally occurring, tidally generated, solitary, moving water waves up to 6 meters in height that form upstream in estuaries with semidiurnal or nearly semidiurnal tide ranges exceeding 4 meters. Estuarine settings that have tidal bores typically include meandering fluvial systems with shallow gradients. Bores are well defined, having amplitudes greater than wind- or turbulence-caused waves, and may be undular or breaking. Formation of a bore is dependent on depth and velocity of the incoming tide and river outflow. Bores may occur in series (in several channels) or in succession (marking each tidal pulse). Tidal bores propagate up tidal estuaries a greater distance than the width of the estuary and most occur within 100 kilometers upstream of the estuary mouth. Because they are dynamic, bores cause difficulties in some shipping ports and are targets for eradication. Tidal bores are known to occur, or to have occurred in the recent past, in at least 67 localities in 16 countries at all latitudes, including every continent except Antarctica. Parts of Argentina, Canada, Central America, China, Mozambique, Madagascar, Northern Europe, North and South Korea, the United Kingdom, and the U.S.S.R. probably have additional undiscovered or unreported tidal bores. In Turnagain Arm estuary in Alaska, bores cause an abrupt increase in salinity, suspended sediment, surface character, and bottom pressure, a decrease in illumination of the water column, and a change in water temperature. Tidal bores occurring in Turnagain Arm, Alaska, have the

  9. Nearshore circulation and water-column properties in the Skagit River Delta, northern Puget Sound, Washington: juvenile Chinook Salmon habitat availability in the Swinomish Channel

    USGS Publications Warehouse

    Grossman, Eric E.; Stevens, Andrew W.; Gelfenbaum, Guy; Curran, Christopher

    2007-01-01

    Time-series and spatial measurements of nearshore hydrodynamic processes and water properties were made in the Swinomish Channel to quantify the net direction and rates of surface water transport that influence habitat for juvenile Chinook salmon along their primary migratory corridor between the Skagit River and Padilla Bay in northern Puget Sound, Washington. During the spring outmigration of Skagit River Chinook between March and June 2007, currents measured with fixed acoustic doppler current profilers (ADCP) at the south and north end of the Swinomish Channel and with roving ADCP revealed that the currents are highly asymmetric with a dominant flow to the north (toward Padilla Bay). Maximum surface current velocities reached 1.5 m/s and were generally uniform across the channel near McGlinn Island Causeway. Transport times for surface water to travel the 11 km from the southern end of Swinomish Channel at McGlinn Island to Padilla Bay ranged from 2.1 hours to 5.5 days. The mean travel time was ~1 day, while 17 percent of the time, transport of water and passive particles occurred within 3.75 hours. Surface water in the Swinomish Channel during this time was generally very saline 20-27 psu, except south of the Rainbow Bridge in the town of La Conner where it ranged 0-15 psu depending on tide and Skagit River discharge. This salinity regime restricts suitable low salinity (

  10. {Delta} isobars and (p,p') reactions

    SciTech Connect

    Sammarruca, F.; Stephenson, E. J.

    2001-09-01

    We explore the role of coupling to {Delta} isobars (in both the N{Delta} and {Delta}{Delta} channels) in medium modifications of the effective NN interaction that drives 200-MeV proton inelastic scattering. A comparison of the predictions to natural-parity (p,p') cross section and analyzing power data show that isobar degrees of freedom in the medium generate overly repulsive effective interactions. Furthermore, this model extension is unable to resolve difficulties observed earlier describing polarization transfer measurements in some high-spin, unnatural-parity (p,p') transitions.

  11. Source, transport, and evolution of saline groundwater in a shallow Holocene aquifer on the tidal deltaplain of southwest Bangladesh

    NASA Astrophysics Data System (ADS)

    Worland, Scott C.; Hornberger, George M.; Goodbred, Steven L.

    2015-07-01

    Deltaic groundwater resources are often vulnerable to degradation from seawater intrusion or through interaction with saline paleowaters. The Ganges-Brahmaputra-Meghna River delta, in Bangladesh and West Bengal, India, is a particularly vulnerable area with an estimated 20 million coastal inhabitants directly affected by saline drinking water. The shallow groundwater of the coastal regions is primarily brackish with pockets of fresher water. A small-scale hydrologic investigation of groundwater salinity beneath an embanked tidal channel island was undertaken to explore possible hydrogeological explanations of the distribution of water salinities in the shallow aquifer. This study employs a combination of 3H and 14C dating, electromagnetic subsurface mapping, and a 2-D solute transport model. The authors conclude that the shallow groundwater salinity can best be explained by the slow infiltration of meteoric water into paleo-brackish estuarine water that was deposited during the early-mid Holocene.

  12. AN APPROACH FOR CLASSIFYING TIDAL REGIMES BASED ON TIDAL CONSTITUENTS

    EPA Science Inventory

    Tidal fluctuations can be one of the dominant physical processes in estuaries. This paper presents a numerical classification of tidal regimes that can be used to summarize local conditions and facilitate comparisons among locations. Tide predictions are customarily calculated ...

  13. Sediment facies, depositional environments, and distribution of phytoclasts in the recent Mahakam River delta, Kalimantan, Indonesia

    SciTech Connect

    Gastaldo, R.A. ); Huc, A.Y. )

    1992-12-01

    The Mahakam River delta is a tide- and wave-dominated delta located on the edge of the Kutei basin, eastern Kalimantan, Borneo. It is a coastal deltaic sequence, Neogene to Holocene in age, from which all recoverable hydrocarbons (crude oil and natural gas) are considered to be derived from kerogen III predecessors. However, a complete understanding of the types of sediments sourcing the hydrocarbons has not yet been achieved. A vibracoring program sampled the principal fine-grained depositional environments in two transects; one within the fluvially-dominated regime, one within the tidally-dominated regime. Ten sedimentary facies are distinguished and phytoclasts have been recovered from all environments of deposition. Canopy parts from the mixed tropical forest community are preserved throughout the delta, whereas dicotyledonous angiosperm mangroves are restricted to the subtidal zone and delta front. Nypa parts are preserved in most depositional environments. In sites where there appears to be an absence of macrodetritus, dispersed cuticle is recoverable. Identifiable plant parts include wood and fibrous tissues, Nypa petioles and leaf laminae, dicotyledonous angiosperm leaves and isolated cuticles, fruits and seeds, roots and rootlets, and moss. Dammar is found either as dispersed resin ducts or amorphous clasts. Additional biotic components found in bedded plant litters include insects, gastropods, bivalves, sand dollars, ostracods, and crabs. Fluvial channels and depositional sites associated with these systems in the delta front can be differentiated from Nypa swamps and mixed tropical hardwood-palm swamps based on their phytological components and accessory biotic elements. 39 refs., 10 figs., 3 tabs.

  14. Modeling wind waves and tidal flows in shallow micro-tidal basins

    NASA Astrophysics Data System (ADS)

    Carniello, L.; D'Alpaos, A.; Defina, A.

    2011-04-01

    Observational evidence and mathematical modeling have demonstrated the crucial role of wind waves on sediment resuspension in shallow micro-tidal basins, where tidal fluxes alone are unable to mobilize tidal flat sediments. Carniello et al. (2005) presented a numerical model which combines wind waves with tidal fluxes in a shallow micro-tidal basin. The highly irregular bathymetry typical of these environments characterized by the presence of deep channels, emergent salt marshes and extensive tidal flats suggested the introduction of specific hypotheses while solving the wave action conservation equation to describe wind-wave generation and propagation. In particular, as suggested by field measurements, the wave spectrum in this type of environment is quite often very narrow. Thus Carniello et al. (2005) originally followed a monochromatic approach, further assuming that the direction of wave propagation instantaneously adjusts to the wind direction and a constant wave period both in space and time. In the present contribution, we relax the latter assumption by introducing a variable wave period through a suitable empirical power law which relates wave period to wind speed and flow depth, based on wind-wave data collected in the Venice Lagoon. The same relationship came out to fit quite well also data collected in Lake George (AU) and, more recently, data collected in a system of lagoons at the Virginia Coast Reserve, USA ( Mariotti et al., 2010). The noteworthy improvement in the estimation of wave height obtained by considering the local wave period is shown on the basis of the results of a number of simulations carried out for different storm events. The improvement obtained in the wind-wave field description reflects also on the estimation of the bottom shear stress and, therefore, on the description of the processes responsible for the morphological evolution of shallow tidal environments.

  15. Towards global scale coastal flood hazard in Delta Cities with 30-meter SRTM and 3D_i

    NASA Astrophysics Data System (ADS)

    Winsemius, Hessel; Verhoeven, Govert; Van Leeuwen, Elgard; Van der Klis, Hanneke; Van Wesenbeeck, Bregje; Cumiskey, Lydia; Verlaan, Martin; Muis, Sanne; Ward, Philip; Kwadijk, Jaap

    2015-04-01

    Most attempts to globally simulate inundation at the land-coast interface rely on maximum flood level GIS-based flood spreading models. These are generally not mass conservative, do not account for the genesis of tidal and surges in time, and do not include channel geometry and surface roughness. Furthermore, these methods cannot be used to study the impact of hazard reducing intervention measures that increase roughness at the land-coast interface. These measures include breakwaters and coastal ecosystems, such as mangrove forests and shell fish and coral reefs. Recently, new datasets and models are becoming available that allow us to greatly improve simulation of inundation in global deltas in a rapid and computationally feasible way. In this poster we demonstrate the feasibility of modelling all global deltas with strongly urbanised areas explicitly using these datasets and models. This will allow initiatives such as the 100 resilient cities (Rockefeller foundation) and the 'making cities resilient' campaign (UNISDR) to tackle the issue of coastal flood risk efficiently. We propose to use the following materials: A subgrid enabling 1D-2D model code Outputs from a global tidal and storm surge model Open topographical data We demonstrate the feasibility of this approach by modelling the Mississippi delta with: a) a lidar derived topography dataset (www.gis.ms.gov/); and b) the recently released 30 meter elevation dataset from the Shuttle Radar Topography Mission. We use the new 3Di subgrid code to rapidly schematise the vast delta area with a quadtree mesh. We force the model at the boundaries with water level estimates during the Katrina cyclone. We invite scientists working on global scale inundation modelling to visit our poster in order to discuss possibilities and limitations of the proposed methods related to model codes, data quality and calibration.

  16. Preliminary simulated tidal flow and circulation patterns in Hillsborough Bay, Florida

    USGS Publications Warehouse

    Goodwin, Carl R.

    1980-01-01

    The effect of channel dredging and island construction on tidal flow and circulation in Hillsborough Bay, Fla., due to the Tampa Harbor Deepening Project is being investigated using a two-dimensional, finite-difference numerical model. Preliminary model results are presented as a series of maps showing tidal flood, tidal ebb, and circulation patterns in the bay for predredging and postdredging conditions. Complex circulation patterns occur near the bay mouth in an area where there is (1) a change in thalweg alinement of the bay, (2) an intersection of three major ship channels, and (3) submergent and emergent dredged material located adjacent to each of the channels. (USGS)

  17. High-resolution analysis of the deposition pattern on the Amazon sub-aquatic delta and outer continental shelf

    NASA Astrophysics Data System (ADS)

    Hübscher, C.; Figueiredo, A. G., Jr.; Kruse, L.; Spieß, V.

    Continental shelves off major river deltas or estuaries act as an interface between terrestrial environments and marine depo centers like the Amazon Fan. In order to understand sedimentary processes on the Amazon sub-aquatic delta and outer shelf, Late-Quaternary erosional and depositional structures have been investigated with an ultra high-resolution seismic survey system (4 kHz). The wavy morphology of the outer shelf implies the presence of tidal sand ridges or meandering channels. In the latter case, the local presence of channel fill deposits suggests several cut-off loops (ox bows). The inter-channel areas are consequently interpreted as levees, which reach their maximum height of 10 m in the area between the Amazon river mouth and the Amazon canyon. The morphology of terraces in front of the sub-aquatic delta reflect erosional processes which presumably occurred during accelerated sea level rise at the beginning and the end of the Younger Dryas. A carbonate platform is present in the northwestern survey area close to the shelf break. Its water depth of 120-130 m implies an evolution during the last glacial maximum. The asymmetric shape of the Cabo Norte Shoal on the topset of the sub-aquatic delta is typical of bottom current produced shoals. The steeper northwestern flank lies in the lee position of the northwest flowing coastal current. Southeast of the shoal the <10 m thick uppermost sequence of presumably Holocene age consists of lobes that dip with the same apparent angle as the foreset towards the offlap break. Within the area 20 km northwest of the shoal the uppermost sequence forms a smooth depression and may be erosionally truncated at the seafloor. Here, the prograding direction includes a northwest component. A shale diapir, which rises from a transparent underlying sequence, marks the transition to an area where the upper sequence is not resolved in the data.

  18. Hard breakup of the deuteron into two {Delta} isobars

    SciTech Connect

    Granados, Carlos G.; Sargsian, Misak M.

    2011-05-15

    We study high-energy photodisintegration of the deuteron into two {Delta} isobars at large center of mass angles within the QCD hard rescattering model (HRM). According to the HRM, the process develops in three main steps: the photon knocks a quark from one of the nucleons in the deuteron; the struck quark rescatters off a quark from the other nucleon sharing the high energy of the photon; then the energetic quarks recombine into two outgoing baryons which have large transverse momenta. Within the HRM, the cross section is expressed through the amplitude of pn{yields}{Delta}{Delta} scattering which we evaluated based on the quark-interchange model of hard hadronic scattering. Calculations show that the angular distribution and the strength of the photodisintegration is mainly determined by the properties of the pn{yields}{Delta}{Delta} scattering. We predict that the cross section of the deuteron breakup to {Delta}{sup ++}{Delta}{sup -} is 4-5 times larger than that of the breakup to the {Delta}{sup +}{Delta}{sup 0} channel. Also, the angular distributions for these two channels are markedly different. These can be compared with the predictions based on the assumption that two hard {Delta} isobars are the result of the disintegration of the preexisting {Delta}{Delta} components of the deuteron wave function. In this case, one expects the angular distributions and cross sections of the breakup in both {Delta}{sup ++}{Delta}{sup -} and {Delta}{sup +}{Delta}{sup 0} channels to be similar.

  19. Mississippi Delta

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Mississippi River delta teems with sediment deposited by the river as it flows into the Gulf of Mexico in this true-color image captured by MODIS on October 15, 2001. The sediment, which is marked by brown swirls in the Gulf, provides nutrients for the bloom of phytoplankton visible as blue-green swirls off the coastline. In the high-resolution image the city of Memphis can be seen in the southwest corner of Tennessee, which is just to left of center at the top of the image. The brown coloration that encompasses Memphis and either side of the river, as flows north to south along the left side of the image, is the river's flood plain. Also visible, in the upper-right hand corner of the image is the southern end of the Appalachian Mountains.

  20. The Effect of Tidal Exchange on Residence Time

    NASA Astrophysics Data System (ADS)

    Rynne, P.; Reniers, A.; Van De Kreeke, J.; MacMahan, J. H.

    2014-12-01

    As the conduit between the ocean and an inland body of water such as a lagoon, estuary or harbor, tidal inlets serve an important role in the hydrodynamics of the nearshore environment. As the global population grows in a world where 13% of the coastline is composed of barrier islands, an understanding of the physical processes that influence the transport of inland waters offshore is increasingly paramount. Water renewal, or the replacement of old lagoon water with new seawater has been well studied and is controlled by the tides through the process of tidal exchange or 'tidal pumping'. The magnitude of tidal exchange is influenced by the inlet hydraulics and geometry of the inlet and various physical processes driven by the tide, wind, and waves. To examine the correlation between tidal exchange and the renewal of lagoon water with seawater, a new method to quantify lagoon residence time is explored. Modeling experiments in Delft3D of idealized inlet systems are used to quantify the effect that tidal exchange has on residence time. Tidal exchange is decomposed into two fractions, an ocean exchange fraction and a lagoon exchange fraction. A simple transport model that utilizes both these fractions is compared to both a tidal prism model that neglects the lagoon exchange fraction and Delft3D. The tidal prism model over predicts the seaward transport of lagoon water as compared to Delft3D for all inlet channel geometries studied. The transport model shows good agreement with Delft3D for narrower inlets that support high ocean exchange fractions, but less agreement for wider inlets that support low ocean exchange fractions. Residence time distributions for each geometry are calculated using a new virtual tracer method in Delft3D. The spatially averaged residence time in the lagoon is found to be inversely proportional to the product of the two exchange fractions of each inlet system. Funded by ONR and NDSEG

  1. Discharge Asymmetry in Delta Bifurcations

    NASA Astrophysics Data System (ADS)

    Salter, G.; Paola, C.; Voller, V. R.

    2015-12-01

    Distributary networks are formed by channels which bifurcate downstream in a river delta. Sediment and water fluxes are often split unequally in delta bifurcations. Understanding flux asymmetry in distributary networks is important for predicting how a delta will respond to sea-level rise. We present results of a quasi-1D model of a delta bifurcation. Consistent with previous results, in the absence of deposition, stable bifurcations may be either symmetric or asymmetric, depending on flow conditions. However, in a depositional setting, a stable asymmetric flow partitioning is no longer possible, as the dominant branch becomes less and less steep relative to the other branch. This feedback eventually causes the second branch to become favored. For the depositional case, we identify three regimes of bifurcation behavior: 1) stable symmetric bifurcation, 2) "soft" avulsions where the dominant branch switches without complete abandonment of the previous channel, and 3) complete avulsions where one branch is completely abandoned. In each case, the bifurcation is symmetric in the long-term average, but the latter two allow for short-term asymmetry. We find that keeping upstream sediment and water discharges fixed, as downstream channel length increases the regime shifts from symmetric to soft avulsions to complete avulsions. In the two avulsion regimes we examine the effect of upstream sediment and water discharges and downstream channel length on avulsion period and maximum discharge ratio. Finally, we compare numerical modeling results to a fixed-wall bifurcation experiment. As in the numerical model, the presence or absence of a downstream sink exerts a strong control on system behavior. If a sink is present, a bifurcation may be asymmetric indefinitely. Conversely, without a sink the system is depositional, and the feedback between sediment discharge asymmetry and slope causes the bifurcation to remain symmetric in the long-term average.

  2. Field and remote sensing for findings on the functions and evolutions of deltas

    NASA Astrophysics Data System (ADS)

    Taramelli, A.; Valentini, E.

    2013-12-01

    In a rapidly changing environment we realise that traditional knowledge of physical processes (both biotic and a-biotic) is insufficient to adequately deal with societal threats and opportunities particularly in low laying deltas, such changes to environments as a result of urbanization or changes to ecosystems as a result of climate change. Pattern formation and strong bio-morphological interactions are a striking features in deltas: vegetation distribution has been observed to be related with tidal channel network, with wind/wave forces as well as with the urbanization and natural built, but the relationship between the relevant biological, physical and anthropogenic processes are fairly unexplored. Through the combination of spaceborne optical and SAR imagery, we derived both ecological and morphological parameters, to be integrated for a multi-temporal analysis of the dominant processes and trends in a specific delta. Based on inter annual and intra annual time series of fractional abundance from multispectral imagery, the vegetation phenology in urbanized, non urbanized and buffer zones of the Po delta and adjoin wetlands were calculated and the relationship between them and the major physical drivers was studied. The results highlight that over time, the dynamics of different subsystems represents a balance between inputs (forcing agents like climate) and natural responses (related responses like the vegetation evolution) relevant to urbanization. Basically the urbanization is strongly linked with the phenology and spatial patterns of vegetation cover and not with the channel distribution. Agricultural and farmers uses are in fact the urban edges and they didn't changed obviously if seasonal trends are subtracted from the inter-annual ones. Changes in buffer zones if they were closer to urban or agricultural areas were observed different from the adjoining coastal areas. Finally the uncertainties calculation of the Delta system (i.e. subsidence rates or

  3. Large-scale suspended sediment transport and sediment deposition in the Mekong Delta

    NASA Astrophysics Data System (ADS)

    Manh, N. V.; Dung, N. V.; Hung, N. N.; Merz, B.; Apel, H.

    2014-08-01

    Sediment dynamics play a major role in the agricultural and fishery productivity of the Mekong Delta. However, the understanding of sediment dynamics in the delta, one of the most complex river deltas in the world, is very limited. This is a consequence of its large extent, the intricate system of rivers, channels and floodplains, and the scarcity of observations. This study quantifies, for the first time, the suspended sediment transport and sediment deposition in the whole Mekong Delta. To this end, a quasi-2D hydrodynamic model is combined with a cohesive sediment transport model. The combined model is calibrated using six objective functions to represent the different aspects of the hydraulic and sediment transport components. The model is calibrated for the extreme flood season in 2011 and shows good performance for 2 validation years with very different flood characteristics. It is shown how sediment transport and sediment deposition is differentiated from Kratie at the entrance of the delta on its way to the coast. The main factors influencing the spatial sediment dynamics are the river and channel system, dike rings, sluice gate operations, the magnitude of the floods, and tidal influences. The superposition of these factors leads to high spatial variability of sediment transport, in particular in the Vietnamese floodplains. Depending on the flood magnitude, annual sediment loads reaching the coast vary from 48 to 60% of the sediment load at Kratie. Deposited sediment varies from 19 to 23% of the annual load at Kratie in Cambodian floodplains, and from 1 to 6% in the compartmented and diked floodplains in Vietnam. Annual deposited nutrients (N, P, K), which are associated with the sediment deposition, provide on average more than 50% of mineral fertilizers typically applied for rice crops in non-flooded ring dike floodplains in Vietnam. Through the quantification of sediment and related nutrient input, the presented study provides a quantitative basis for

  4. Developments in tidal power

    NASA Astrophysics Data System (ADS)

    Charlier, R. H.

    Successful, planned, and potential tidal power plants and sites are discussed. Units are in operation in France and Russia, with the French plant using reversible blade turbines being used as a design guide for plants in Argentina and Australia. The U.S. is studying the feasibility of a plant in Passamaquaddy Bay, and Canada is pursuing construction of a plant in the Bay of Fundy. The Severn River in Great Britain is receiving a site study, and over a hundred plants have been built as local power systems in China. Bulb-type turbines, which enhance the volume emptying and filling the retaining basin, are considered as the highest performing power unit. Simpler one-way flow turbines have been suggested as more economical to install. Governmental, institutional, and investor impediments to tidal power plant are explored.

  5. Tidal Heating in Enceladus

    NASA Astrophysics Data System (ADS)

    Meyer, Jennifer; Wisdom, J.

    2007-07-01

    The heating in Enceladus in an equilibrium resonant configuration with other saturnian satellites can be estimated independently of the physical properties of Enceladus. Our results update the values obtained for the equilibrium tidal heating found by Lissauer et al. (1984) and Peale (2003). We find that equilibrium tidal heating cannot account for the heat that is observed to be coming from Enceladus, and current heating rates are even less for conventional estimates of the Love number for Enceladus. Even allowing for a much larger dynamic Love number, as can occur in viscoelastic models (Ross and Schubert, 1989), the equilibrium tidal heating is less than the heat observed to be coming from Enceladus. One resolution is that the tidal equilibrium is unstable and that the system oscillates about equilibrium. Yoder (1981) suggested that Enceladus might oscillate about equilibrium if the Q of Enceladus is stress dependent. An alternate suggestion was made by Ojakangas and Stevenson (1986), who emphasized the possible temperature dependence of Q. In these models Enceladus would now be releasing heat stored during a recent high eccentricity phase. However, we have shown that the Ojakangas and Stevenson model does not produce oscillations for parameters appropriate for Enceladus. Other low-order resonance configurations are possible for the saturnian satellites in the past. These include the 3:2 Mimas-Enceladus and the 3:4 Enceladus-Tethys resonances. The latter resonance has no equilibrium because the orbits are diverging, and the former has an equilibrium heating rate of only 0.48 GW. So equilibrium heating at past resonances is no more successful at explaining past resurfacing events than equilibrium heating is at explaining the present activity.

  6. Relativistic tidal disruption events

    NASA Astrophysics Data System (ADS)

    Levan, A.

    2012-12-01

    In March 2011 Swift detected an extremely luminous and long-lived outburst from the nucleus of an otherwise quiescent, low luminosity (LMC-like) galaxy. Named Swift J1644+57, its combination of high-energy luminosity (1048 ergs s-1 at peak), rapid X-ray variability (factors of >100 on timescales of 100 seconds) and luminous, rising radio emission suggested that we were witnessing the birth of a moderately relativistic jet (Γ ˜ 2 - 5), created when a star is tidally disrupted by the supermassive black hole in the centre of the galaxy. A second event, Swift J2058+0516, detected two months later, with broadly similar properties lends further weight to this interpretation. Taken together this suggests that a fraction of tidal disruption events do indeed create relativistic outflows, demonstrates their detectability, and also implies that low mass galaxies can host massive black holes. Here, I briefly outline the observational properties of these relativistic tidal flares observed last year, and their evolution over the first year since their discovery.

  7. Does centennial morphodynamic evolution lead to higher channel efficiency in San Pablo Bay, California?

    USGS Publications Warehouse

    van der Wegen, M.; Jaffe, B.E.; Barnard, P.L.; Jaffee, B.E.; Schoellhamer, D.H.

    2013-01-01

    Measured bathymetries on 30 year interval over the past 150 years show that San Pablo Bay experienced periods of considerable deposition followed by periods of net erosion. However, the main channel in San Pablo Bay has continuously narrowed. The underlying mechanisms and consequences of this tidal channel evolution are not well understood. The central question of this study is whether tidal channels evolve towards a geometry that leads to more efficient hydraulic conveyance and sediment throughput. We applied a hydrodynamic process-based, numerical model (Delft3D), which was run on 5 San Pablo Bay bathymetries measured between 1856 and 1983. Model results shows increasing energy dissipation levels for lower water flows leading to an approximately 15% lower efficiency in 1983 compared to 1856. During the same period the relative seaward sediment throughput through the San Pablo Bay main channel increased by 10%. A probable explanation is that San Pablo Bay is still affected by the excessive historic sediment supply. Sea level rise and Delta surface water area variations over 150 years have limited effect on the model results. With expected lower sediment concentrations in the watershed and less impact of wind waves due to erosion of the shallow flats, it is possible that energy dissipations levels will decrease again in future decades. Our study suggests that the morphodynamic adaptation time scale to excessive variations in sediment supply to estuaries may be on the order of centuries.

  8. Tidal Venuses: triggering a climate catastrophe via tidal heating.

    PubMed

    Barnes, Rory; Mullins, Kristina; Goldblatt, Colin; Meadows, Victoria S; Kasting, James F; Heller, René

    2013-03-01

    Traditionally, stellar radiation has been the only heat source considered capable of determining global climate on long timescales. Here, we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high-enough levels to induce a runaway greenhouse for a long-enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets "Tidal Venuses" and the phenomenon a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits (i.e., with negligible tidal heating) in the habitable zone (HZ). However, these planets are not habitable, as past tidal heating desiccated them, and hence should not be ranked highly for detailed follow-up observations aimed at detecting biosignatures. We simulated the evolution of hypothetical planetary systems in a quasi-continuous parameter distribution and found that we could constrain the history of the system by statistical arguments. Planets orbiting stars with masses<0.3 MSun may be in danger of desiccation via tidal heating. We have applied these concepts to Gl 667C c, a ∼4.5 MEarth planet orbiting a 0.3 MSun star at 0.12 AU. We found that it probably did not lose its water via tidal heating, as orbital stability is unlikely for the high eccentricities required for the tidal greenhouse. As the inner edge of the HZ is defined by the onset of a runaway or moist greenhouse powered by radiation, our results represent a fundamental revision to the HZ for noncircular orbits. In the appendices we review (a) the moist and runaway greenhouses, (b) hydrogen escape, (c) stellar mass-radius and mass-luminosity relations, (d) terrestrial planet mass-radius relations, and (e) linear tidal theories.

  9. Estuarine circulation versus tidal pumping: Sediment transport in a well-mixed tidal inlet

    NASA Astrophysics Data System (ADS)

    Becherer, Johannes; Flöser, Götz; Umlauf, Lars; Burchard, Hans

    2016-08-01

    High-resolution water column observations have been carried out in the Wadden Sea to understand suspended particulate matter (SPM) transport in well-mixed tidal channels. These observations include more than 4000 consecutive CTD, microstructure shear and turbidity profiles from a free-falling microstructure probe, as well as velocity data from an ADCP and SPM samples for calibration. A horizontal density gradient was established by a landward temperature gradient built up during an extraordinarily warm and calm spring season. Tidal averaging along σ-layers (relative depth) provides the first direct observations of along-channel estuarine circulation in the Wadden Sea, with net inflow near the bottom and outflow near the surface. Increased westerly (up-estuary) winds during the second part of the campaign weakened and eventually even reversed estuarine circulation and yielded a net barotropic eastward transport. SPM concentrations showed a strong quarter-diurnal signal with maxima near full flood and full ebb and were generally lower during the calm period and increased during the windy period, mainly due to wave-related resuspension over nearby intertidal flats. The sediment flux analysis was based on a decomposition of the vertically integrated SPM flux into a barotropic advective component, an estuarine circulation component and a tidal pumping component. As a result, tidal pumping (due to ebb-dominance weakly seaward) dominated the SPM flux during calm conditions, whereas barotropic advection dominated the strong landward SPM flux during the windy period. Along-channel estuarine circulation is found to be of minor importance for the net SPM transport in such well-mixed systems.

  10. Recognition of synodic and tropical tidal periodicities in tidal rhythmites

    SciTech Connect

    Archer, A.W. ); Kvale, E.P. ); Johnson, H.P. )

    1990-05-01

    Tidal processes are capable of producing bedding that records individual tidal events; however, only within the last decade have tidal cycles, such as neap-spring periodicities become widely recognized. Such cycles have been documented within thinly laminated, vertically accreted siltstones. The laminae exhibit systematic patterns of thickening and thinning that have been equated to the lunar orbital period (synodic month). However, modem tides are subject to periodicities other than the synodic month and such additional periods can be the causative mechanism for neap-spring tidal periods. Gravitational interactions of the earth, moon, and sun generate tides that fluctuate with periods that correspond to the phases of the moon (synodic month), declination of the moon (tropical month), and distance of the moon from the earth (anomalistic month). Although harmonic analyses of semidiurnal tidal data indicate that such systems are controlled by synodic factors, there are also indications that diurnal systems can be controlled by tropical factors. Thus neap-spring periods are not only related to lunar phase (synodic month), but can be related to tropical month (lunar declination) in diurnal systems. Analysis of laminae-thickness periodicities in a variety of Pennsylvanian tidal rhythmites, which include apparent examples of diurnal as well as semidiurnal tidal patterns, indicates similarities to modern tidal systems. For example, semidiurnal tidal rhythmites exhibit not only synodic periodicities but also exhibit a weaker, tropical periodicity. Conversely, within rhythmites that exhibit a diurnal pattern, it is not completely clear whether tropical or synodic periodicities are being expressed.

  11. Morphodynamics and Sedimentology of a Falling Stage Sandy Fjord Delta, Goose River, Labrador

    NASA Astrophysics Data System (ADS)

    Slingerland, R.; Edmonds, D. A.; Parsons, D. R.; Best, J. L.; Royce, J.; Burpee, A.; Cederberg, J.; Caldwell, R.; Nijhuis, A.; McGuffin, A.

    2012-12-01

    Sediment size and degree of cohesion are thought to exert a strong control on the morphodynamic processes, planform shape and clinoform stratigraphy of deltas. To test model predictions concerning these two parameters, we present a morphometric and stratigraphic analysis of a sandy delta formed where the Goose River flows into Goose Bay at the western end of Lake Melville, Labrador. Goose River delta sediments consist of arkosic, heavy-mineral-rich sand (D50 = 225 to 600 microns) with very little silt and clay, placing this delta at the coarser-grained, non-cohesive end of the spectrum. The delta started to form approx. 7000 years ago as the Laurentide ice sheet retreated and post-glacial rebound created a relative base level fall of approximately 4 mm/yr. The current tidal range in Goose Bay averages 0.5 m, and the average wave height is negligible. Results from our 2012 field season show that the delta planform consists of two moribund lobes at elevations of ~ 5 m and ~ 2 m and a presently active delta at sea level. Aerial photography from 1951 to 2012 show there has been surprisingly little progradation despite active channel change at the six-month timescale and an assumed base level fall of 244 mm during that period. A topographic section along a dipline consists of three treads and two clinoform risers. The bottomset tread is a virtually featureless fjord bottom at ~35 m from which a first clinoform rises to a second tread at ~-15 m. The second tread is a sandy platform onto which an upper clinoform downlaps. This upper sandy clinoform ranges in dip from 9 to 17 dg. and passes into the topset at an elevation of ~ -1 m. The topset consists of braid-like trapezoidal unit bars that in GPR show little evidence of wave, alongshore current, or ice reworking, even though they are submerged at higher high tides. The planform, bar geometries and facies, and clinoform dips and dip-directions are remarkably consistent with model predictions from Delft3d.

  12. Landscape scale controls on the vascular plant component of dissolved organic carbon across a freshwater delta

    NASA Astrophysics Data System (ADS)

    Eckard, Robert S.; Hernes, Peter J.; Bergamaschi, Brian A.; Stepanauskas, Ramunas; Kendall, Carol

    2007-12-01

    Lignin phenol concentrations and compositions were determined on dissolved organic carbon (DOC) extracts (XAD resins) within the Sacramento-San Joaquin River Delta (the Delta), the tidal freshwater portion of the San Francisco Bay Estuary, located in central California, USA. Fourteen stations were sampled, including the following habitats and land-use types: wetland, riverine, channelized waterway, open water, and island drains. Stations were sampled approximately seasonally from December, 1999 through May, 2001. DOC concentrations ranged from 1.3 mg L -1 within the Sacramento River to 39.9 mg L -1 at the outfall from an island drain (median 3.0 mg L -1), while lignin concentrations ranged from 3.0 μg L -1 within the Sacramento River to 111 μg L -1 at the outfall from an island drain (median 11.6 μg L -1). Both DOC and lignin concentrations varied significantly among habitat/land-use types and among sampling stations. Carbon-normalized lignin yields ranged from 0.07 mg (100 mg OC) -1 at an island drain to 0.84 mg (100 mg OC) -1 for a wetland (median 0.36 mg (100 mg OC) -1), and also varied significantly among habitat/land-use types. A simple mass balance model indicated that the Delta acted as a source of lignin during late autumn through spring (10-83% increase) and a sink for lignin during summer and autumn (13-39% decrease). Endmember mixing models using S:V and C:V signatures of landscape scale features indicated strong temporal variation in sources of DOC export from the Delta, with riverine source signatures responsible for 50% of DOC in summer and winter, wetland signatures responsible for 40% of DOC in summer, winter, and late autumn, and island drains responsible for 40% of exported DOC in late autumn. A significant negative correlation was observed between carbon-normalized lignin yields and DOC bioavailability in two of the 14 sampling stations. This study is, to our knowledge, the first to describe organic vascular plant DOC sources at the level of

  13. Reconstructing paleosalinity in the Sacramento-San Joaquin Delta of California using major elements in peat

    NASA Astrophysics Data System (ADS)

    Drexler, J. Z.; Alpers, C. N.; Taylor, H. E.; Windham-Myers, L.; Neymark, L. A.; Paces, J. B.

    2010-12-01

    Marshes in the Sacramento-San Joaquin Delta, the most landward extent of the San Francisco Estuary, started forming around ~6,700 years ago. Currently, Delta marshes are classified as tidal freshwater, however it is unknown to what degree the salinity regime has varied between brackish and fresh conditions since marsh development. This information is important to managers considering major changes to the flow regime in the Delta, because such changes could impact the future sustainability of endangered species such as the Delta smelt (Hypomesus transpacificus), which live in or just upstream of the mixing zone between fresh and brackish water. The main goal of the Rates and Evolution of PEat Accretion through Time project (REPEAT II) is to reconstruct paleosalinity regimes in the Delta. We are using elemental concentrations of Na, Ca, K, and Mg (the major cations in ocean water) in peat profiles to develop a quantitative index of salinity for the past 6000+ years. We are normalizing the elemental concentrations to Ti (a proxy for inorganic sediment content because it is inversely correlated with loss on ignition, a measure of peat organic content) to correct for bias in elemental concentrations caused by variations in the inorganic sediment content of peat through time. Plots of Ti-normalized element concentration vs. peat depth (or age) indicate that Browns Island, a brackish marsh on the western edge of the Delta, has experienced significant variations in salinity through the millennia. Vertical peat profiles show a spatial trend of decreasing salinity from west (bay-side) to east (landward) (i.e., Browns Island > Sherman Island > Franks Wetland ≧ Bacon Channel Island). During the period from 2300 to 500 calibrated years before present, Na concentrations in peat at Browns Island indicate a particularly saline period, with peat containing up to 3 wt. % Na. In the last 100 years or so, salinity at Browns Island has apparently decreased and the Na content of peat

  14. Landscape scale controls on the vascular plant component of dissolved organic carbon across a freshwater delta

    USGS Publications Warehouse

    Eckard, Robert S.; Hernes, Peter J.; Bergamaschi, Brian A.; Stepanauskas, Ramunas; Kendall, Carol

    2007-01-01

    Lignin phenol concentrations and compositions were determined on dissolved organic carbon (DOC) extracts (XAD resins) within the Sacramento-San Joaquin River Delta (the Delta), the tidal freshwater portion of the San Francisco Bay Estuary, located in central California, USA. Fourteen stations were sampled, including the following habitats and land-use types: wetland, riverine, channelized waterway, open water, and island drains. Stations were sampled approximately seasonally from December, 1999 through May, 2001. DOC concentrations ranged from 1.3 mg L-1 within the Sacramento River to 39.9 mg L-1 at the outfall from an island drain (median 3.0 mg L-1), while lignin concentrations ranged from 3.0 μL-1 within the Sacramento River to 111 μL-1 at the outfall from an island drain (median 11.6 μL-1). Both DOC and lignin concentrations varied significantly among habitat/land-use types and among sampling stations. Carbon-normalized lignin yields ranged from 0.07 mg (100 mg OC)-1 at an island drain to 0.84 mg (100 mg OC)-1 for a wetland (median 0.36 mg (100 mg OC)-1), and also varied significantly among habitat/land-use types. A simple mass balance model indicated that the Delta acted as a source of lignin during late autumn through spring (10-83% increase) and a sink for lignin during summer and autumn (13-39% decrease). Endmember mixing models using S:V and C:V signatures of landscape scale features indicated strong temporal variation in sources of DOC export from the Delta, with riverine source signatures responsible for 50% of DOC in summer and winter, wetland signatures responsible for 40% of DOC in summer, winter, and late autumn, and island drains responsible for 40% of exported DOC in late autumn. A significant negative correlation was observed between carbon-normalized lignin yields and DOC bioavailability in two of the 14 sampling stations. This study is, to our knowledge, the first to describe organic vascular plant DOC sources at the level of localized

  15. Dissipation of Tidal Energy

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The moon's gravity imparts tremendous energy to the Earth, raising tides throughout the global oceans. What happens to all this energy? This question has been pondered by scientists for over 200 years, and has consequences ranging from the history of the moon to the mixing of the oceans. Richard Ray at NASA's Goddard Space Flight Center, Greenbelt, Md. and Gary Egbert of the College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Ore. studied six years of altimeter data from the TOPEX/Poseidon satellite to address this question. According to their report in the June 15 issue of Nature, about 1 terawatt, or 25 to 30 percent of the total tidal energy dissipation, occurs in the deep ocean. The remainder occurs in shallow seas, such as on the Patagonian Shelf. 'By measuring sea level with the TOPEX/Poseidon satellite altimeter, our knowledge of the tides in the global ocean has been remarkably improved,' said Richard Ray, a geophysicist at Goddard. The accuracies are now so high that this data can be used to map empirically the tidal energy dissipation. (Red areas, above) The deep-water tidal dissipation occurs generally near rugged bottom topography (seamounts and mid-ocean ridges). 'The observed pattern of deep-ocean dissipation is consistent with topographic scattering of tidal energy into internal motions within the water column, resulting in localized turbulence and mixing', said Gary Egbert an associate professor at OSU. One important implication of this finding concerns the possible energy sources needed to maintain the ocean's large-scale 'conveyor-belt' circulation and to mix upper ocean heat into the abyssal depths. It is thought that 2 terawatts are required for this process. The winds supply about 1 terawatt, and there has been speculation that the tides, by pumping energy into vertical water motions, supply the remainder. However, all current general circulation models of the oceans ignore the tides. 'It is possible that properly

  16. Modern sedimentary environments in a large tidal estuary, Delaware Bay

    USGS Publications Warehouse

    Knebel, H. J.

    1989-01-01

    Data from an extensive grid of sidescan-sonar records reveal the distribution of sedimentary environments in the large, tidally dominated Delaware Bay estuary. Bathymetric features of the estuary include large tidal channels under the relatively deep (> 10 m water depth) central part of the bay, linear sand shoals (2-8 m relief) that parallel the sides of the tidal channels, and broad, low-relief plains that form the shallow bay margins. The two sedimentary environments that were identified are characterized by either (1) bedload transport and/or erosion or (2) sediment reworking and/or deposition. Sand waves and sand ribbons, composed of medium to coarse sands, define sites of active bedload transport within the tidal channels and in gaps between the linear shoals. The sand waves have spacings that vary from 1 to 70 m, amplitudes of 2 m or less, and crestlines that are usually straight. The orientations of the sand waves and ribbons indicate that bottom sediment movement may be toward either the northwest or southeast along the trends of the tidal channels, although sand-wave asymmetry indicates that the net bottom transport is directed northwestward toward the head of the bay. Gravelly, coarse-grained sediments, which appear as strongly reflective patterns on the sonographs, are also present along the axes and flanks of the tidal channels. These coarse sediments are lag deposits that have developed primarily where older strata were eroded at the bay floor. Conversely, fine sands that compose the linear shoals and muddy sands that cover the shallow bay margins appear mainly on the sonographs either as smooth featureless beds that have uniform light to moderate shading or as mosaics of light and dark patches produced by variations in grain size. These acoustic and textural characteristics are the result of sediment deposition and reworking. Data from this study (1) support the hypothesis that bed configurations under deep tidal flows are functions of current

  17. Migration Rate Of Tidal Meanders: Inferences From The Venice Lagoon

    NASA Astrophysics Data System (ADS)

    Finotello, A.; D'Alpaos, A.; Ghinassi, M.; Lanzoni, S.; Marani, M.; Rinaldo, A.

    2015-12-01

    Meandering channels are ubiquitous features of tidal landscapes. However, despite their fundamental role on the eco-morphodynamic evolution of these landscapes, tidal meanders have received less attention when compared to their fluvial counterparts. Improving current understanding of tidal meander migration, a largely-examined topic in fluvial landscapes, is a key step to highlight analogies and differences between tidal and fluvial cases. The migration of about 400 meander bends, belonging to 40 salt-marsh channels in the Northern Venice Lagoon (Italy), from 1968 to nowadays, has been investigated by means of both a classical method in fluvial frameworks and new procedure. Similarities with fluvial meanders occur, although important difference also emerge. Meanders cutting through the San Felice marsh follow the relationship between cartesian length and channel width, typical of meanders developed within different settings. However, meander migration rates proved to be smaller than those characterizing fluvial meanders. Indeed, the analysis of meander migration suggests a mean migration rate of about 0.10 m/year, consistent with the few data available in the literature. As for the fluvial case, the maximum-potential migration rate (i.e. the envelope curve of the relationship between migration rate and bend radius, both divided by channel width) reaches a maximum for radius-over-width ratio included between 2 and 3, regardless of the considered method. Nevertheless, the new-proposed method allows us to provide a more objective and continuous characterization. By using this new procedure, the channel curvature has finally been Fourier-analyzed, confirming the importance of even harmonics along the curvature spectrum. A correlation between migration rates and dominant harmonics seems to drive the evolution of tidal meanders and might represent a key-feature to distinguish them from their fluvial counterparts.

  18. Tidal Meander Migration: a Case Study from the Venice Lagoon

    NASA Astrophysics Data System (ADS)

    D'Alpaos, A.; Ghinassi, M.; Bellucci, L. G.; Marani, M.

    2014-12-01

    Meandering patterns are universal features of tidal landscapes which exert a great influence on the dynamics of tidal channel networks and on the stratigraphy of intertidal platforms. Despite their importance in landscape evolution and their ubiquity, tidal meanders have received less attention when compared to their fluvial counterparts. Quite a few studies, in fact, have focused on the morphodynamic evolution of tidal meanders, together with their planimetric shape and morphometric characteristics. To improve current understanding of tidal meander migration and its possible stratigraphic implications, we have analyzed a sequence of aerial photographs (from 1938 to present day) for a 20 m in diameter, abandoned tidal meander in the Venice Lagoon, and have carried out high-resolution sedimentological and chronostratigraphical analyses of channel deposits. Aerial photographs before and after the cutoff event have been used to infer a minimum velocity of migration. Well-cores have also been collected along a transect crossing through the neck zone in order to evaluate changes in grain size, sedimentation rates across the cutoff event, and gain further insight into the velocity of migration of meander bends. Spatial distribution of sedimentary facies (pointbar sand, oxbowlake and saltmarsh mud), grain size analyses, and 210 Pb and 137Cs chronometers highlighted that meander cutoff occurred progressively around 60 years ago with a velocity of migration of about 0.5m/year. The effectiveness of the methods and the high spatial and temporal resolution of the data call for further investigations and analyses of the type proposed herein, furthermore highlighting the potentiality of the study area as modern analogue for ancient tidal deposits.

  19. The Delta 2 launcher

    NASA Astrophysics Data System (ADS)

    Ousley, Gilbert W., Sr.

    1991-12-01

    The utilization of the Delta 2 as the vehicle for launching Aristoteles into its near Sun synchronous orbit is addressed. Delta is NASA's most reliable launch vehicle and is well suited for placing the present Aristoteles spacecraft into a 400 m circular orbit. A summary of some of the Delta 2 flight parameters is presented. Diagrams of a typical Delta 2 two stage separation are included along with statistics on delta reliability and launch plans.

  20. Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA

    USGS Publications Warehouse

    Barnhardt, W.A.; Sherrod, B.L.

    2006-01-01

    Episodic, large-volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late Holocene delta at southern Puget Sound. Multibeam bathymetry, ground-penetrating radar (GPR) and vibracores were used to investigate the morphologic and stratigraphic evolution of the Nisqually River delta. Two fluvial–deltaic facies are recognized on the basis of GPR data and sedimentary characteristics in cores, which suggest partial emplacement from sediment-rich floods that originated on Mount Rainier. Facies S consists of stacked, sheet-like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta. Flat-lying, highly reflective surfaces separate the sand sheets and comprise important facies boundaries. Beds of massive, pumice- and charcoal-rich sand overlie one of the buried surfaces. Organic-rich material from that surface, beneath the massive sand, yielded a radiocarbon age that is time-correlative with a series of known eruptive events that generated lahars in the upper Nisqually River valley. Facies CF consists of linear sandbodies or palaeochannels incised into facies S on the lower delta plain. Radiocarbon ages of wood fragments in the sandy channel-fill deposits also correlate in time to lahar deposits in upstream areas. Intrusive, sand-filled dikes and sills indicate liquefaction caused by post-depositional ground shaking related to earthquakes. Continued progradation of the delta into Puget Sound is currently balanced by tidal-current reworking, which redistributes sediment into large fields of ebb- and flood-oriented bedforms.

  1. Wave-angle control of delta evolution

    NASA Astrophysics Data System (ADS)

    Ashton, Andrew D.; Giosan, Liviu

    2011-07-01

    Wave-influenced deltas, with large-scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first-order influence upon its plan-view morphologic evolution and sedimentary architecture. The directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan-view form. This plan-form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self-organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand waves—features observed on natural deltas. Somewhat surprisingly, waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan-form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth.

  2. Conservation of tidal marshes

    SciTech Connect

    Daiber, F.C.

    1986-01-01

    This book is the first attempt to examine collectively the various uses and the consequences of marsh conservation efforts. Author Franklin Daiber emphasizes tidal marsh conservation from a holistic perspective rather than from the perspective of a single purpose or special economic interest. He addresses a topic receiving increasing attention, namely the concept of open marsh management as a means of controlling mosquito production without harmful effects on other marsh organisms. Topics considered include: water management; dikes, impoundments, ponds and ditches; reclaimed land and impoundments; ditching and ponding for mosquito control; sewage disposal and waste treatment; dredge material for wetland restoration; insecticides; oil pollution; and petroleum hydrocarbon interactions.

  3. Tidal heating of Ariel

    NASA Astrophysics Data System (ADS)

    Tittemore, William C.

    1990-09-01

    During evolution through the 4:1 commensurability early in the history of the Uranian system, over 3.8 billion years ago, tidal heating may have raised the internal temperature of Ariel by up to about 20 K; the internal temperature of Ariel may already have been high in virtue of both accretional and radiogenic heating. The additional increase in Ariel's temperature could then have triggered the geological activity that led to a late resurfacing, by decreasing lithospheric thickness and exacerbating thermal stresses on it to the point where observed cracks and faults formed.

  4. Tidal heating of Ariel

    NASA Technical Reports Server (NTRS)

    Tittemore, William C.

    1990-01-01

    During evolution through the 4:1 commensurability early in the history of the Uranian system, over 3.8 billion years ago, tidal heating may have raised the internal temperature of Ariel by up to about 20 K; the internal temperature of Ariel may already have been high in virtue of both accretional and radiogenic heating. The additional increase in Ariel's temperature could then have triggered the geological activity that led to a late resurfacing, by decreasing lithospheric thickness and exacerbating thermal stresses on it to the point where observed cracks and faults formed.

  5. Diel activity patterns of juvenile late fall-run Chinook salmon with implications for operation of a gated water diversion in the Sacramento–San Joaquin River Delta

    USGS Publications Warehouse

    Plumb, John M.; Adams, Noah S.; Perry, Russell W.; Holbrook, Christopher; Romine, Jason G.; Blake, Aaron R.; Burau, Jon R.

    2016-01-01

    In the Sacramento-San Joaquin River Delta, California, tidal forces that reverse river flows increase the proportion of water and juvenile late fall-run Chinook salmon diverted into a network of channels that were constructed to support agriculture and human consumption. This area is known as the interior delta, and it has been associated with poor fish survival. Under the rationale that the fish will be diverted in proportion to the amount of water that is diverted, the Delta Cross Channel (DCC) has been prescriptively closed during the winter out-migration to reduce fish entrainment and mortality into the interior delta. The fish are thought to migrate mostly at night, and so daytime operation of the DCC may allow for water diversion that minimizes fish entrainment and mortality. To assess this, the DCC gate was experimentally opened and closed while we released 2983 of the fish with acoustic transmitters upstream of the DCC to monitor their arrival and entrainment into the DCC. We used logistic regression to model night-time arrival and entrainment probabilities with covariates that included the proportion of each diel period with upstream flow, flow, rate of change in flow and water temperature. The proportion of time with upstream flow was the most important driver of night-time arrival probability, yet river flow had the largest effect on fish entrainment into the DCC. Modelling results suggest opening the DCC during daytime while keeping the DCC closed during night-time may allow for water diversion that minimizes fish entrainment into the interior delta.

  6. Ancient Martian Deltas: Evidence for Shallow and Deep Standing Bodies of Water

    NASA Astrophysics Data System (ADS)

    Jew, C. L.; Kim, W.; Lim, Y.; Piliouras, A.

    2015-12-01

    Ancient deltas on Mars are indicative of a geologic history composed of complex fluvio-deltaic deposits. We focus on two morphologically different deltas preserved on Mars, one located in the Jezero crater and the other in the Shalbatana Valles canyon. The Jezero delta, formed during the Noachian age, is a large fluvial delta with strong channelization and a rigid shoreline resembling a terrestrial delta. In contrast, the Shalbatana Delta is a smaller scaled more briefly lived delta system, developed during the Hesperian, that is characterized by its smooth and simple planform. Evidence from previous studies on these Martian deltas such as the base level, mechanism to build sediment cohesion, estimated discharge, and time of formation offer support to ultimately discover why one delta drastically differs from the other. Based upon the observations from these two locations, we investigate through our physical experiments the conditions required to create these prograding deltas. We use carbonate precipitation in our experiments as a mechanism to increase bank stability, an alternative for any chemically driven precipitated deposits that potentially improve cohesion as vegetation does for terrestrial deltas. We found that there are differences in floodplain thickness, channelization, shoreline rugosity, and delta shape in the carbonate verse non-carbonate runs. Additionally, we conducted runs for isolating the influence that shallow and deep standing bodies of water have on prograding deltas. The experimental results suggested that the highly channelized delta (e.g., Jezero delta) rapidly prograded into a shallow body of water, covering a broader surface area and is dependent on a cohesive force for channel organization. On the contrary, Gilbert-type delta (e.g., Shalbatana delta) was best replicated when prograding into a deep standing body of water. Investigation using the experimental carbonate deltas suggests that cohesion results in better channelization (more

  7. Energy storage inherent in large tidal turbine farms

    PubMed Central

    Vennell, Ross; Adcock, Thomas A. A.

    2014-01-01

    While wind farms have no inherent storage to supply power in calm conditions, this paper demonstrates that large tidal turbine farms in channels have short-term energy storage. This storage lies in the inertia of the oscillating flow and can be used to exceed the previously published upper limit for power production by currents in a tidal channel, while simultaneously maintaining stronger currents. Inertial storage exploits the ability of large farms to manipulate the phase of the oscillating currents by varying the farm's drag coefficient. This work shows that by optimizing how a large farm's drag coefficient varies during the tidal cycle it is possible to have some flexibility about when power is produced. This flexibility can be used in many ways, e.g. producing more power, or to better meet short predictable peaks in demand. This flexibility also allows trading total power production off against meeting peak demand, or mitigating the flow speed reduction owing to power extraction. The effectiveness of inertial storage is governed by the frictional time scale relative to either the duration of a half tidal cycle or the duration of a peak in power demand, thus has greater benefits in larger channels. PMID:24910516

  8. Energy storage inherent in large tidal turbine farms.

    PubMed

    Vennell, Ross; Adcock, Thomas A A

    2014-06-08

    While wind farms have no inherent storage to supply power in calm conditions, this paper demonstrates that large tidal turbine farms in channels have short-term energy storage. This storage lies in the inertia of the oscillating flow and can be used to exceed the previously published upper limit for power production by currents in a tidal channel, while simultaneously maintaining stronger currents. Inertial storage exploits the ability of large farms to manipulate the phase of the oscillating currents by varying the farm's drag coefficient. This work shows that by optimizing how a large farm's drag coefficient varies during the tidal cycle it is possible to have some flexibility about when power is produced. This flexibility can be used in many ways, e.g. producing more power, or to better meet short predictable peaks in demand. This flexibility also allows trading total power production off against meeting peak demand, or mitigating the flow speed reduction owing to power extraction. The effectiveness of inertial storage is governed by the frictional time scale relative to either the duration of a half tidal cycle or the duration of a peak in power demand, thus has greater benefits in larger channels.

  9. Tidal Pools--Miniature Oceans

    ERIC Educational Resources Information Center

    Plake, Linda Perry

    1977-01-01

    A comprehensive discussion of the biological activity in tidal pools is provided. The importance of environmental factors such as oxygen supply, temperature, salinity, and light is detailed. Plants and animals that might be found in a tidal pool are identified and described. (BT)

  10. Fan-delta and interdeltaic shoreline sediments of Middle Devonian Granite Wash and Keg River clastics, Red Earth field, north Alberta basin, Canada

    SciTech Connect

    Sabry, H.

    1989-03-01

    A detailed sedimentological investigation of over 4000 ft of core and 500 well logs of the Middle Devonian granite wash and Keg River clastics in the Red Earth field, North Alberta basin, Canada, has led to the recognition of a granite wash subaerial fan-delta system that is laterally continuous with a Keg River subaqueous delta component along an eastern shoreline of the ancestral Peace River arch. The subaerial fan delta includes alluvial fan facies, sheet wash and mud flows, and playa lakes. The subaqueous delta component includes lower shoreface, upper shoreface, beach-foreshore, eolian sand dunes, lagoon, washover sands, tidal channels and flats, and supratidal carbonates and anhydrites. Within this system, six mappable units are defined. A conceptual depositional model for the sequence depicts four main events. (1) Erosion of Peach River arch uplifted fault blocks, which produced coarse-grained fan-delta sediments in an adjacent fault-bounded margin. Subsequent fluvial reworking resulted in the deposition of thick, lenticular, wedge-shaped alluvial fans of granite wash. (2) Progradation of alluvial fans seaward into the Keg River Sea. (3) Transgression by Middle Devonian seas from the east, which reworked alluvial fans and led to deposition of discontinuous linear sand bodies represented by the Keg River regressive shoreline sediments. (4) Restriction of the sea by the Presqu'ile barrier reef to the north, which deposited evaporites of the Muskeg Formation over the whole sequence. Modern analog to this fan-delta system is the coastal fans of the Gulf of Aqaba, Red Sea. Red Earth field contains over 27 million bbl of recoverable oil, related to a combination structural-stratigraphic trap.

  11. DTP: a Tidal Power Revolution

    NASA Astrophysics Data System (ADS)

    Steijn, Robbert; Hulsbergen, Kees; van Banning, Gijs

    2013-04-01

    Tidal power can significantly contribute to the global mix of sustainable energy resources. It is climate-independent, fully predictable, and if designed properly it is environmentally friendly and socio-economically feasible. The two traditional methods of exploiting tidal power are Tidal Barrage and Tidal Stream. This study deals with an alternative Third Method, named Dynamic Tidal Power (DTP), which contrary to the other methods, utilises the oscillating character of tides, or more precisely: the acceleration inherent to unsteady flow. DTP uses a long dam (order of tens of km's), attached and perpendicular to a coast with shore-parallel tidal currents, to generate a local hydraulic head. This time-varying head is used to generate electricity in a more or less standard way with turbines and generators placed in (many) dam openings. For a first impression only: typical installed power for one DTP is more than 10 GW with electricity output > 2.1010 kWh/y and construction costs of ca. 1 EUR/W. The physical mechanism behind the creation of the head has been described by Hulsbergen e.a., (2012). Following a heuristic approach based on analytical work done by Kolkman (unpubl.), and output from numerical tidal models, Hulsbergen (2012) concluded that the maximum head (near the coast), is: hmax = 6,8*?*D*Vmax/(g*T), with Vmax the maximum alongshore flow velocity during the tidal cycle, T the tidal period and D the length of dam. Such simple relationship was also found by Mei (2012) who made a rigorous analysis of a process-based model. After a thorough reflection on DTP, this study will first check the above formula for hmax , by comparing its predictions with the output from various numerical tidal models. Any differences will be analysed in the study through an evaluation of the dominant physical processes and the schematisations inherent to both the analytical and the numerical models. The study will also address the effect of the openings in the dam, as well as the

  12. Temporal variation of velocity and turbulence characteristics at a tidal energy site

    NASA Astrophysics Data System (ADS)

    Gunawan, B.; Neary, V. S.; Colby, J.

    2013-12-01

    This study examines the temporal variability, frequency, direction and magnitude of the mean current, turbulence, hydrodynamic force and tidal power availability at a proposed tidal energy site in a tidal channel located in East River, NY, USA. The channel has a width of 190 m, a mean water level of 9.8 m and a mean tidal range of 1.3 m. A two-month velocity measurement was conducted at the design hub-height of a tidal turbine using an acoustic Doppler velocimeter (ADV). The site has semi-diurnal tidal characteristics with tidal current pattern resembles that of sinusoidal function. The five-minute mean currents at the site varied between 0 and 2.4 m s-1. Flood current magnitudes were typically higher that the ebb current magnitudes, which skewed the tidal energy production towards the flood period. The effect of small-scale turbulence on the computed velocity, hydrodynamic load and power densities timeseries were investigated. Excluding the small-scale turbulence may lead to a significant underestimation of the mean and the maximum values of the analyzed variable. Comparison of hydrodynamic conditions with other tidal energy sites indicates that the key parameters for tidal energy site development are likely to be site-specific, which highlight the need to develop a classification system for tidal energy sites. Such a classification system would enable a direct comparison of key parameters between potential project locations and ultimately help investors in the decision making process. Turbulence intensity vs. mean current magnitude

  13. Processes Controlling Transfer of Fine-Grained Sediment in Tidal Systems Spanning a Range of Fluvial Influence

    DTIC Science & Technology

    2012-09-30

    understand how the delicate balance of ebb and flood sediment fluxes is maintained to create tidal flat and mangrove complexes, and distributary shoals and...and the subaqueous delta on the inner continental shelf, and sediment sinks within vegetated/ mangrove shoreline complexes. Our overall hypothesis...on Mangrove /Vegetated Intertidal Areas. Along the main stem tidal river and in the offshore banks may be shorelines lined with vegetation ( mangroves

  14. Hydro-environmental status and soil management of the River Nile Delta, Egypt

    NASA Astrophysics Data System (ADS)

    Elewa, H. H.; El Nahry, A. H.

    2009-04-01

    The sea level rise has its own-bearing on the coastal recession and hydro-environmental degradation of the River Nile Delta. Attempts are made here to use remote sensing to detect the coastal recession in some selected parts and delineating the chemistry of groundwater aquifers and surface water, which lie along south-mid-northern and coastal zone of the Nile Delta. Eight water samples from groundwater monitoring wells and 13 water samples from surface water were collected and analyzed for various hydrochemical parameters. The groundwater samples are classified into five hydrochemical facies on Hill-Piper trilinear diagram based on the dominance of different cations and anions: facies 1: Ca-Mg-Na-HCO3-Cl-SO4 type I; facies 2: Na-Cl-HCO3 type II; facies 3: Na-Ca-Mg-Cl type III, facies 4: Ca-Na-Mg-Cl-HCO3 type IV and facies 5: Na-Mg-Cl type V. The hydrochemical facies showed that the majority of samples were enriched in sodium, bicarbonate and chloride types and, which reflected that the sea water and tidal channel play a major role in controlling the groundwater chemical composition in the Quaternary shallow aquifers, with a severe degradation going north of Nile Delta. Also, the relationship between the dissolved chloride (Cl, mmol/l), as a variable, and other major ion combinations (in mmol/l) were considered as another criterion for chemical classification system. The low and medium chloride groundwater occurs in southern and mid Nile Delta (Classes A and B), whereas the high and very high chloride (classes D and C) almost covers the northern parts of the Nile Delta indicating the severe effect of sea water intrusion. Other facets of hydro-environmental degradation are reflected through monitoring the soil degradation process within the last two decades in the northern part of Nile Delta. Land degradation was assessed by adopting new approach through the integration of GLASOD/FAO approach and Remote Sensing/GIS techniques. The main types of human induced soil

  15. delta-Hexachlorocyclohexane (delta-HCH)

    Integrated Risk Information System (IRIS)

    delta - Hexachlorocyclohexane ( delta - HCH ) ; CASRN 319 - 86 - 8 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Ass

  16. Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating

    PubMed Central

    Mullins, Kristina; Goldblatt, Colin; Meadows, Victoria S.; Kasting, James F.; Heller, René

    2013-01-01

    Abstract Traditionally, stellar radiation has been the only heat source considered capable of determining global climate on long timescales. Here, we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high-enough levels to induce a runaway greenhouse for a long-enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets “Tidal Venuses” and the phenomenon a “tidal greenhouse.” Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits (i.e., with negligible tidal heating) in the habitable zone (HZ). However, these planets are not habitable, as past tidal heating desiccated them, and hence should not be ranked highly for detailed follow-up observations aimed at detecting biosignatures. We simulated the evolution of hypothetical planetary systems in a quasi-continuous parameter distribution and found that we could constrain the history of the system by statistical arguments. Planets orbiting stars with masses<0.3 MSun may be in danger of desiccation via tidal heating. We have applied these concepts to Gl 667C c, a ∼4.5 MEarth planet orbiting a 0.3 MSun star at 0.12 AU. We found that it probably did not lose its water via tidal heating, as orbital stability is unlikely for the high eccentricities required for the tidal greenhouse. As the inner edge of the HZ is defined by the onset of a runaway or moist greenhouse powered by radiation, our results represent a fundamental revision to the HZ for noncircular orbits. In the appendices we review (a) the moist and runaway greenhouses, (b) hydrogen escape, (c) stellar mass-radius and mass-luminosity relations, (d) terrestrial planet mass-radius relations, and (e) linear tidal theories. Key Words: Extrasolar terrestrial

  17. Delta agent (Hepatitis D)

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/000216.htm Delta agent (Hepatitis D) To use the sharing features on this page, please enable JavaScript. Delta agent is a type of virus called hepatitis ...

  18. Modeling the Effects of Tidal Energy Extraction on Estuarine Hydrodynamics in a Stratified Estuary

    SciTech Connect

    Yang, Zhaoqing; Wang, Taiping

    2013-08-15

    A three-dimensional coastal ocean model with a tidal turbine module was used in this paper to study the effects of tidal energy extraction on temperature and salinity stratification and density driven two-layer estuarine circulation. Numerical experiments with various turbine array configurations were carried out to investigate the changes in tidally mean temperature, salinity and velocity profiles in an idealized stratified estuary that connects to coastal water through a narrow tidal channel. The model was driven by tides, river inflow and sea surface heat flux. To represent the realistic size of commercial tidal farms, model simulations were conducted based on a small percentage of the total number of turbines that would generate the maximum extractable energy in the system. Model results indicated that extraction of tidal energy will increase the vertical mixing and decrease the stratification in the estuary. Extraction of tidal energy has stronger impact on the tidally-averaged salinity, temperature and velocity in the surface layer than the bottom. Energy extraction also weakens the two-layer estuarine circulation, especially during neap tides when tidal mixing the weakest and energy extraction is the smallest. Model results also show that energy generation can be much more efficient with higher hub height with relatively small changes in stratification and two-layer estuarine circulation.

  19. Galileo's tidal theory.

    PubMed

    Naylor, Ron

    2007-03-01

    The aim of Galileo's tidal theory was to show that the tides were produced entirely by the earth's motion and thereby to demonstrate the physical truth of Copernicanism. However, in the Dialogue Concerning the Two Chief World Systems Galileo did not explain some of the most significant aspects of the theory completely. As a consequence, the way the theory works has long been disputed. Though there exist a number of interpretations in the literature, the most widely accepted are based on ideas that are not explicitly articulated by Galileo in the Dialogue. This essay attempts to understand the way the theory functions in terms of Galilean physics. It is an interpretation of the theory based solely on Galileo's arguments--and one that reveals it to have had some unrecognized consequences. This interpretation indicates that Galileo's theory would not have worked in the manner he described in the Dialogue.

  20. Intertidal benthic resources of the Copper River Delta, Alaska, USA

    NASA Astrophysics Data System (ADS)

    Powers, Sean P.; Bishop, Mary Anne; Grabowski, Jonathan H.; Peterson, Charles H.

    2002-02-01

    The Copper River Delta, Alaska is the largest contiguous coastal wetland system along the West Coast of North America. Vast expanses of tidal mud flats formed by sediments carried by the suspended load of the Copper River serve as a connection between the Gulf of Alaska and the extensive network of wetlands, rivers and sloughs of the delta system. In addition to providing habitat for resident fish, shrimp and crabs, these tidal flats serve as critical feeding grounds for up to 5 million migratory shorebirds as well as an entry and exit corridor for three species of commercially fished salmonids. Here we report the first description of the benthic community of these intertidal flats. Between April and September 2000, we conducted three samplings on the Copper River Delta in which we quantified benthic macro-invertebrates inhabiting silt-clay sediments, the dominant substrate in the system, over a range of tidal inundation. Specifically, sampling was performed in two areas on the delta: near the outflows of the Eyak River and Pete Dahl Slough. Pore-water salinity of surficial sediment ranged from 4 psu during peak summer flow of the Copper River to 14 psu in April prior to increased riverine input. Sediment temperatures corresponded to ambient air temperatures with lowest temperatures during the April-September observation period recorded in April (4°C) and warmest in August (16°C). The benthic community of the delta's tidal flats was characterised by low species diversity and was dominated by the tellinid bivalve Macoma balthica, which reached densities greater than 4000 m -2. Age-length relationship of M. balthica indicated slow growth and longevity of up to 8 years. Polychaete densities, primarily the phyllodocid Eteone longa, were low throughout the study period, reaching a maximum of only 700 m -2 in August. Amphipod densities, primarily the corophid amphipod Corophium salmonis, were high (up to 7000 m -2) only during the August sampling. Spatial patterns of

  1. Tidal Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Houck, James R.; Higdon, Sarah

    2004-09-01

    Tidal Dwarf Galaxies (TDG's) are formed from material stripped from the disks of spiral galaxies, which are undergoing tidal interactions with a nearby companion. These galaxies provide important clues to our understanding of galaxy formation, evolution and cosmic recycling. Using the IRS we will measure the star formation activity in 6 TDG candidates. We will measure the ionization state ( [NeII] 12.8 um, [NeIII] 15.6 um and [NeV] 14.3um and [OIV] 25.9 um), the density in the ionized gas ([SIII] 18.7um/33.5um), the PAH fractions at 5.5-9um and 11-12.2um and possibly (optimistic here!) molecular hydrogen emission form PDRs at H2 (S0) 28um and H2 (S1) at 17um. In addition to the IRS observations we will map both the Guitar and Stephan's Quintet with IRAC. This will enable us to compare the PAH fraction in the dwarf galaxy to that of its parent. Similarly we will compare our observation of the proposed TDG at the southern tip of NGC 4038 with the GT observations of the central region of the Antennae. This program compliments two existing GT programmes: 1) the high-Z program - these observations enable us to observe in fine detail the nearby/present day analogs of galaxy formation in the early universe. 2) Blue Compact Dwarf programme - On first inpsection BCD's and TDG's appear the same: BCDs are similar in size to TDG's, but TDG's may not have a large dark matter halo component (affecting the long term stability of an object) and BCD's typically have a much lower metallicity. We will be able to compare the star formation activity in terms of the ionization state and PAH fraction in the two galaxy types.

  2. Observations and modeling of a tidal inlet dye tracer plume

    NASA Astrophysics Data System (ADS)

    Feddersen, Falk; Olabarrieta, Maitane; Guza, R. T.; Winters, D.; Raubenheimer, Britt; Elgar, Steve

    2016-10-01

    A 9 km long tracer plume was created by continuously releasing Rhodamine WT dye for 2.2 h during ebb tide within the southern edge of the main tidal channel at New River Inlet, NC on 7 May 2012, with highly obliquely incident waves and alongshore winds. Over 6 h from release, COAWST (coupled ROMS and SWAN, including wave, wind, and tidal forcing) modeled dye compares well with (aerial hyperspectral and in situ) observed dye concentration. Dye first was transported rapidly seaward along the main channel and partially advected across the ebb-tidal shoal until reaching the offshore edge of the shoal. Dye did not eject offshore in an ebb-tidal jet because the obliquely incident breaking waves retarded the inlet-mouth ebb-tidal flow and forced currents along the ebb shoal. The dye plume largely was confined to <4 m depth. Dye was then transported downcoast in the narrow (few 100 m wide) surfzone of the beach bordering the inlet at 0.3 m s-1 driven by wave breaking. Over 6 h, the dye plume is not significantly affected by buoyancy. Observed dye mass balances close indicating all released dye is accounted for. Modeled and observed dye behaviors are qualitatively similar. The model simulates well the evolution of the dye center of mass, lateral spreading, surface area, and maximum concentration, as well as regional ("inlet" and "ocean") dye mass balances. This indicates that the model represents well the dynamics of the ebb-tidal dye plume. Details of the dye transport pathways across the ebb shoal are modeled poorly perhaps owing to low-resolution and smoothed model bathymetry. Wave forcing effects have a large impact on the dye transport.

  3. Water-level controls on macro-tidal rip currents

    NASA Astrophysics Data System (ADS)

    Austin, Martin J.; Masselink, Gerd; Scott, Tim M.; Russell, Paul E.

    2014-03-01

    Field measurements and numerical modelling have been used to investigate the water-level control of rip current dynamics on a macro-tidal beach. Field data collected over 32 complete tidal cycles, spanning a range of wave and tide conditions, demonstrate that rip current strength and behaviour is modulated at the semi-diurnal frequency by tide-induced changes in the water-level over bar/rip morphology. Peak flow speeds in the rip neck correspond to the time of maximum wave breaking 1.5 h before and after low water. Alongshore-directed water surface gradients ∂η/∂y were measured along the feeder channel and around the ends of the inter-tidal bar, with head differences O(0.1 m). The numerical model reproduced ∂η/∂y with a good level of skill and showed that ∂η/∂y and increase with the proportion of breaking waves Qb over the inter-tidal bar; but was maximised during peak Qb, maximum ∂η/∂y occurred when wave breaking moved offshore to the sub-tidal bar and Qb was reduced. Around low water, the forcing of the rip current by the alongshore pressure-driven feeder current was reduced by the decrease in Qb over the bar and feeder regions, but an offshore flow through the rip channel was maintained by a localised intensification of ∂η/∂y around the ends of the inter-tidal bar.

  4. 100 years of mapping the Holocene Rhine-Meuse delta plain: combining research and teaching

    NASA Astrophysics Data System (ADS)

    Cohen, K. M.; Stouthamer, E.; Hoek, W. Z.; Middelkoop, H.

    2012-04-01

    The history of modern soil, geomorphological and shallow geological mapping in the Holocene Rhine-Meuse delta plain goes back about 100 years. The delta plain is of very heterogeneous build up, with clayey and peaty flood basins, dissected by sandy fluvial distributary channel belts with fine textured levees grading into tidal-influenced rivers and estuaries. Several generations of precursor rivers occur as alluvial ridges and buried ribbon sands. They form an intricate network originating from repeated avulsions, back to 8000 years ago. Present rivers have been embanked since ca. 1250 AD and the delta plain (~ 3000 km2) has been reclaimed for agriculture. Soils are young and subject to oxidation and compaction. The first detailed field map of channel belts and floodbasins was made in 1926 by Vink, a geography teacher from Amsterdam. Soil mapping and Holocene geology gained interest after WW-II, with Wageningen soil scientists Edelman, Hoeksema and Pons taking lead. Utrecht University started teaching and research on the subject in 1959, launching an undergraduate mapping field course based on hand augering and field observation. An archive of borehole logs and local maps started to build up. Initially focused on soil mapping, from 1973 the course shifted to a geomorphological-geological focus. Berendsen took over supervision, introduced standard description protocols and legends and increased coring depth. This resulted in 1982 in his influential PhD thesis on the Rhine delta's genesis. New coring and sampling methods came and extensive 14C dating campaigns began. With steadily increasing numbers of students, accumulation of data speeded up, and increasingly larger parts of the delta were mapped. The academic mapping ran in parallel with soil survey and geological survey mapping campaigns. The computer was introduced in the field course and digital data archiving began in 1989. A series of PhD studies on thematic aspects of delta evolution and an increasing number

  5. Modelling the impacts of sea level rise on tidal basin ecomorphodynamics and mangrove habitat evolution

    NASA Astrophysics Data System (ADS)

    van Maanen, Barend; Coco, Giovanni; Bryan, Karin

    2016-04-01

    The evolution of tidal basins and estuaries in tropical and subtropical regions is often influenced by the presence of mangrove forests. These forests are amongst the most productive environments in the world and provide important ecosystem services. However, these intertidal habitats are also extremely vulnerable and are threatened by climate change impacts such as sea level rise. It is therefore of key importance to improve our understanding of how tidal systems occupied by mangrove vegetation respond to rising water levels. An ecomorphodynamic model was developed that simulates morphological change and mangrove forest evolution as a result of mutual feedbacks between physical and biological processes. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. Under stable water levels, model results indicate that mangrove trees enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The landward expansion of the channels, on the other hand, is reduced. Model simulations including sea level rise suggest that mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone. While the sea level is rising, mangroves are migrating landward and the channel network tends to expand landward too. The presence of mangrove trees, however, was found to hinder both the branching and headward erosion of the landward expanding channels. Simulations are performed according to different sea level rise scenarios and with different tidal range conditions to assess which tidal environments are most vulnerable. Changes in the properties of the tidal channel networks are being examined as well. Overall, model results highlight the role of mangroves in driving the

  6. A coupled geomorphic and ecological model of tidal marsh evolution.

    PubMed

    Kirwan, Matthew L; Murray, A Brad

    2007-04-10

    The evolution of tidal marsh platforms and interwoven channel networks cannot be addressed without treating the two-way interactions that link biological and physical processes. We have developed a 3D model of tidal marsh accretion and channel network development that couples physical sediment transport processes with vegetation biomass productivity. Tidal flow tends to cause erosion, whereas vegetation biomass, a function of bed surface depth below high tide, influences the rate of sediment deposition and slope-driven transport processes such as creek bank slumping. With a steady, moderate rise in sea level, the model builds a marsh platform and channel network with accretion rates everywhere equal to the rate of sea-level rise, meaning water depths and biological productivity remain temporally constant. An increase in the rate of sea-level rise, or a reduction in sediment supply, causes marsh-surface depths, biomass productivity, and deposition rates to increase while simultaneously causing the channel network to expand. Vegetation on the marsh platform can promote a metastable equilibrium where the platform maintains elevation relative to a rapidly rising sea level, although disturbance to vegetation could cause irreversible loss of marsh habitat.

  7. A coupled geomorphic and ecological model of tidal marsh evolution

    PubMed Central

    Kirwan, Matthew L.; Murray, A. Brad

    2007-01-01

    The evolution of tidal marsh platforms and interwoven channel networks cannot be addressed without treating the two-way interactions that link biological and physical processes. We have developed a 3D model of tidal marsh accretion and channel network development that couples physical sediment transport processes with vegetation biomass productivity. Tidal flow tends to cause erosion, whereas vegetation biomass, a function of bed surface depth below high tide, influences the rate of sediment deposition and slope-driven transport processes such as creek bank slumping. With a steady, moderate rise in sea level, the model builds a marsh platform and channel network with accretion rates everywhere equal to the rate of sea-level rise, meaning water depths and biological productivity remain temporally constant. An increase in the rate of sea-level rise, or a reduction in sediment supply, causes marsh-surface depths, biomass productivity, and deposition rates to increase while simultaneously causing the channel network to expand. Vegetation on the marsh platform can promote a metastable equilibrium where the platform maintains elevation relative to a rapidly rising sea level, although disturbance to vegetation could cause irreversible loss of marsh habitat. PMID:17389384

  8. Laboratory Modeling of Self-Formed Leveed Channels From Sediment-Laden Flows Entering Still Water

    NASA Astrophysics Data System (ADS)

    Rowland, J. C.; Dietrich, W. E.

    2004-12-01

    Self-formed leveed channels constructed by deposition of suspended sediment from sediment-laden flows entering still water are common features in nature. Such channels drive delta progradation, develop at tidal inlets and occur where mainstem river flows empty into oxbows and blocked valley lakes. Presently there is no theory for the formation of such channels. This lack of theory is partly due to a lack of field or laboratory studies that provide insight about the mechanism controlling these self-formed, propagating channels. The creation of such features in the laboratory, have proved illusive to date. Our ongoing experiments aimed at modeling the formation of floodplain tie channels provide insight into the necessary conditions for levee formation and channel growth. Under conditions of steady water discharge, constant sediment feed rate, unimodal sediment distribution and invariant basin stage we are able to create subaqueous lateral bars (submerged levees) along the margins of a sediment laden jet. Our results highlight the sensitivity of channel formation to issues of scaling and experimental design. In the laboratory, levee formation has only been possible with the use of plastic particles (specific gravity ~1.5); complete bed alluviation and dune formation results from the use of particles with specific gravities of ~ 2.65 across a range grain diameters and shapes. We hypothesize this effect is related to high entrainment thresholds relative to suspension thresholds of small (< 100 mm) natural particles under conditions of reduced turbulence in laboratory scaled flows. Additionally, both the width to depth ratio and the form of the outlet channel introducing the sediment laden flow into the experimental basin exert a strong control on sedimentation pattern and levee growth. Continuing experiments are focused on generating emergent channel levees and a basin ward propagation of the channel by adjusting the form of the feed channel, varying basin stage, and

  9. Bathymetric influences on tidal currents at the entrance to a highly stratified, shallow estuary

    NASA Astrophysics Data System (ADS)

    Lee, Jungwoo; Webb, Bret M.; Dzwonkowski, Brian; Park, Kyeong; Valle-Levinson, Arnoldo

    2013-04-01

    Bathymetric effects on tidal currents are investigated at Main Pass, which is the primary inlet of Mobile Bay, Alabama. A 12-h ship-mounted ADCP survey, which covered nearly one-half of the diurnal tide during flood conditions, included 24 repetitions. The resulting velocity data demonstrate significant tidal variability in the horizontal and vertical current structure between the ship channel and the shoals. The diurnal tidal flows, the dominant tidal forcing, are 72° (4.8 h) ahead of the water level throughout shallower areas of Main Pass, indicating near-standing wave conditions. Moving across the mouth, a phase lag (5.37° or 20 min) develops with the deep channel tidal currents lagging the shoal region. The vertical tidal structure is also modified across the mouth where near-bottom flows change their direction first in the ship channel, while near-surface flows change their direction first over the western shoal. This may be related to the seaward pressure gradient associated with the relatively large (~1715 m3/s) freshwater discharge or the discharge interaction with a nearby opening, Pass-aux-Herons. Current magnitudes over the shoals and in the ship channel vary by as much as 1 m/s. Flows at the east side of Main Pass, close to Mobile Point, behave oppositely to those in the rest of the transect during the survey. This inconsistent flow pattern is caused by an anticyclonic eddy that is triggered by flow separation at Mobile Point.

  10. Sedimentation processes in tidal marshes of the Delaware Bay

    SciTech Connect

    Fonjweng, G.T. . Dept. of Geology)

    1993-03-01

    A study of sedimentation processes in the tidal marshes of the Delaware Bay was done in order to enhance out understanding of the effects of storms, tidal fluctuations, microtopography and distance from channel on the accumulation of sediments. Sedimentation plates were placed along transects perpendicular to tidal channels in the Woodland Beach and Bombay Hook wildlife areas, Bowers and South Bowers marshes. The thickness of sediments on the plates was measured approximately two days after every lunar phase, first and last quarters, full and new moons. Thus far, the results of this study show that the largest single act of deposition occurred during the tropical storm Danielle. Danielle deposited an average of 7.3 mm of sediments as compared to an average of only 1.8 mm deposited during the six weeks prior to the storm. Pre- and post-storm sedimentation showed a pattern that corresponded with the different lunar phases. Highest sedimentation rates coincided with the new moon, whereas the lowest sedimentation and highest erosion rates coincided with the last quarter of the moon. Sedimentation rates were lowest close to the banks of channels and highest away from the channels. On humocky marsh surfaces, sedimentation was greatest in the depressions and lowest on the tops of mounds. It appears that sedimentation in Delaware Bay tidal marshes is episodic and varies laterally. Different parts of the marsh undergo sedimentation and erosion simultaneously. Any meaningful long-term sedimentation rate measurement has to take into account storm intensity, frequency, microtopography and distance from the channel.

  11. Paleoecological Perspectives on Tidal Marsh Degradation at Elkhorn Slough, California

    NASA Astrophysics Data System (ADS)

    Watson, E. B.; Wasson, K.; Woolfolk, A.; van Dyke, E.

    2007-05-01

    Elkhorn Slough is the second largest area of estuarine tidal wetlands in California, and one of the first U.S. estuarine sanctuaries. Region-wide, 90% of historic tidal wetlands have been lost or restricted from tidal flow due to diking for agricultural use, salt pond construction, and development. However, wetland loss at Elkhorn Slough is currently being driven largely by tidal erosion, and the subsequent expansion of tidal channels and shoreline recession. This study reports on the use of paleoecological analyses to support and inform current restoration and conservation activities at Elkhorn Slough. Analyses of three sediment cores for fossil pollen, organic content, accretion rates, and the removal and stratigraphic description of twelve additional cores have established the timing of marsh establishment, current and prehistoric estuarine salinity, wetland plant abundance and distributions, and the relative contributions of mineral and organic sediment to wetland sediment accumulation. By understanding prehistoric processes and conditions and past variability more thoroughly, managers will be able to evaluate conservation, restoration, and management alternatives in a more informed fashion.

  12. Recent progress in tidal modeling

    NASA Technical Reports Server (NTRS)

    Vial, F.; Forbes, J. M.

    1989-01-01

    Recent contributions to tidal theory during the last five years are reviewed. Specific areas where recent progress has occurred include: the action of mean wind and dissipation on tides, interactions of other waves with tides, the use of TGCM in tidal studies. Furthermore, attention is put on the nonlinear interaction between semidiurnal and diurnal tides. Finally, more realistic thermal excitation and background wind and temperature models have been developed in the past few years. This has led to new month-to-month numerical simulations of the semidiurnal tide. Some results using these models are presented and compared with ATMAP tidal climatologies.

  13. Construction and maintenance of the Ganges-Brahmaputra-Meghna delta: linking process, morphology, and stratigraphy.

    PubMed

    Wilson, Carol A; Goodbred, Steven L

    2015-01-01

    We present a review of the processes, morphology, and stratigraphy of the Ganges-Brahmaputra-Meghna delta (GBMD), including insights gained from detailed elevation data. The review shows that the GBMD is best characterized as a composite system, with different regions having morphologic and stratigraphic attributes of an upland fluvial fan delta; a lowland, backwater-reach delta; a downdrift tidal delta plain; and an offshore subaqueous-delta clinoform. These distinct areas of upland and lowland fluvial reaches and tidal dominance vary in time and space, and we distinguish late-Holocene phases of delta construction, maintenance, and decline similar to delta-lobe cycling in other systems. The overall stability of the GBMD landform, relative to many deltas, reflects the efficient, widespread dispersal of sediment by the large monsoon discharge and high-energy tides that affect this region. However, we do identify portions of the delta that are in decline and losing elevation relative to sea level owing to insufficient sediment delivery. These areas, some of which are well inland of the coast, represent those most at risk to the continued effect of sea-level rise.

  14. Multiscale simulations of a horizontal axis tidal turbine in a tidal site

    NASA Astrophysics Data System (ADS)

    Fernandez, Arturo; Tejada-Martinez, Andres; Juha, Mario

    2016-11-01

    We present multiscale simulations of a three-bladed horizontal axis tidal turbine (HATT) in a tidal site. The power and wake generated by the HATT are computed using an Overset Large Eddy Simulation (OLES) technique, where the velocity field is split into a background and a perturbation field. The background flow is a tidal boundary layer with a depth of 10 m, which exhibits a logarithmic distribution for the averaged streamwise velocity. This flow is computed via Large Eddy Simulation for an open channel flow with a time varying pressure gradient. The interaction between this background flow and the HATT is captured using a line actuator model, which generates the perturbation flow representing the turbulent wake. These simulations assume the turbine to have a diameter of 2.5 m and the hub to be located 7.5 m from the bottom floor. The results show the power coefficient to exhibit a cyclical behavior and the power spectral density to have peaks at multiples of one third of the rotational frequency. The turbulent wake exhibits the classical behavior with the near wake dominated by helicoidal vortical structures, and the far wake characterized by diffusion phenomena.

  15. Sedimentary Processes on Tidal Flats: Recent Studies of Mesotidal Settings in the US Pacific Northwest (Invited)

    NASA Astrophysics Data System (ADS)

    Nittrouer, C.; Ogston, A. S.; Lee, K. M.; Boldt, K. V.; Research Team

    2010-12-01

    Tidal flats are coastal environments that are very sensitive to environmental change, especially sea level. The sedimentary processes operating on flats control the deposits that accumulate there, and preserve a high-resolution record of coastal history - with impacts from both land and ocean. Over the past century, many studies have examined tidal flats around the world. Recent investigations of mesotidal flats in Washington state have provided much new insight to the hydrodynamics of water and sediment transport, biological influences on sediment entrapment, resulting morphology of tidal-flat and channel surfaces, and the dynamics of sediment accumulation. This research has been done in northern Puget Sound near the mouth of the Skagit River, and at the south end of Willapa Bay removed from significant fluvial discharge. The physical processes (winds, waves, tides, river discharge) operating on the Skagit tidal flat are sufficient to rework the flat on most tidal cycles, and cause regular resuspension of the upper 1-3 cm of sediment. This causes effective removal of fine sediment discharged by the river, and tidal currents transport this material to distant subtidal areas for accumulation. The resulting sand flat is non-cohesive, and tidal channels are able to migrate easily. During periods of significant sediment discharge (winter floods, summer snowmelt) some fine-grained material (mud) can be buried on the flanks of the migrating channels. These processes are distinctly different than in southern Willapa Bay, where fine-grained sediment (mud) dominates accumulation and is supplied from distant river sources during winter floods. The mud moves between tidal flats and channels, but primarily resides in tidal channels during winter. Sea grasses and benthic algae become more prevalent during summer, and the mud is trapped on the flats as these biological components cause shear stresses to decrease and shear strengths to increase. The net result is a mudflat

  16. Sedimentology and ichnology of Neogene Coastal Swamp deposits in the Niger Delta Basin, Nigeria

    NASA Astrophysics Data System (ADS)

    Ezeh, Sunny C.; Mode, Wilfred A.; Ozumba, Berti M.; Yelwa, Nura A.

    2016-09-01

    Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mudstones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamma ray logs, described sedimentological cores showing sedimentary features and ichnological characteristics; these were integrated to define the depositional settings. Some portions from one of the well sections reveal a blocky gamma ray well log signature instead of a coarsening-upward trend that characterises a shoreface setting while in other wells the signatures for heteroliths at some sections are bell blocky in shaped rather than serrated. Besides, heteroliths and mudstones within the proximal facies and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on sedimentology and ichnology of cores from these facies was used to correct these inconsistencies. It follows that depositional environment interpretation (especially in multifarious depositional environments such as the Niger Delta) should ideally be made together with other raw data for accuracy and those based solely on well log signatures should be treated with

  17. Enceladus' tidal dissipation revisited

    NASA Astrophysics Data System (ADS)

    Tobie, Gabriel; Behounkova, Marie; Choblet, Gael; Cadek, Ondrej; Soucek, Ondrej

    2016-10-01

    A series of chemical and physical evidence indicates that the intense activity at Enceladus' South Pole is related to a subsurface salty water reservoir underneath the tectonically active ice shell. The detection of a significant libration implies that this water reservoir is global and that the average ice shell thickness is about 20-25km (Thomas et al. 2016). The interpretation of gravity and topography data further predicts large variations in ice shell thickness, resulting in a shell potentially thinner than 5 km in the South Polar Terrain (SPT) (Cadek et al. 2016). Such an ice shell structure requires a very strong heat source in the interior, with a focusing mechanism at the SPT. Thermal diffusion through the ice shell implies that at least 25-30 GW is lost into space by passive diffusion, implying a very efficient dissipation mechanism in Enceladus' interior to maintain such an ocean/ice configuration thermally stable.In order to determine in which conditions such a large dissipation power may be generated, we model the tidal response of Enceladus including variable ice shell thickness. For the rock core, we consider a wide range of rheological parameters representative of water-saturated porous rock materials. We demonstrate that the thinning toward the South Pole leads to a strong increase in heat production in the ice shell, with a optimal thickness obtained between 1.5 and 3 km, depending on the assumed ice viscosity. Our results imply that the heat production in the ice shell within the SPT may be sufficient to counterbalance the heat loss by diffusion and to power eruption activity. However, outside the SPT, a strong dissipation in the porous core is required to counterbalance the diffusive heat loss. We show that about 20 GW can be generated in the core, for an effective viscosity of 1012 Pa.s, which is comparable to the effective viscosity estimated in water-saturated glacial tills on Earth. We will discuss the implications of this revisited tidal

  18. Tidal disruption of inviscid planetesimals

    NASA Technical Reports Server (NTRS)

    Boss, A. P.; Cameron, A. G. W.; Benz, W.

    1991-01-01

    In view of previous efforts' demonstration that strongly dissipative planetesimals are immune to tidal disruption, an examination is presently conducted of the complementary case of inviscid planetesimals arising from collisions that are sufficiently energetic to entirely melt the resulting planetesimal and debris. The tidal disruption is numerically simulated by means of the smoothed particle hydrodynamics (SPH) code of Cameron and Benz (1991), concentrating on the tidal disruption of 0.01 earth-mass planetesimals passing by the earth with variations in the impact parameter at perigee and velocity at infinity. The SPH models show that tidal forces during a close encounter can efficiently convert orbital angular momentum into spin angular momentum, thereby initiating equatorial mass-shedding to inviscid planetesimals that have been spun up beyond the limit of rotational stability.

  19. Using Modern Processes to Understand Postglacial Delta Evolution: Elwha River Delta

    NASA Astrophysics Data System (ADS)

    Lee, K. M.; Ogston, A. S.; Nittrouer, C. A.; Holmes, M.

    2008-12-01

    The post-glacial shoreline of the Elwha River delta in the Strait of Juan de Fuca, Washington State, is thought to have been 4 km seaward and approximately 50 m lower than the modern shoreline. Nearshore transport processes throughout this rapid transgression are poorly constrained. Previous work suggests storm-driven waves and relative sea level are the primary forcings of the Elwha River delta over the past 10,000 years. Net eastward sediment transport formed a series of drowned paleospits at -25 m, -8 m, and -6 m depths in the Strait of Juan de Fuca. Sea-level rise slowed at 4,500 years BP and created the well- developed modern spit, Ediz Hook. In recent times, the Elwha River was dammed (starting in 1916) and later the surrounding coastal bluffs were armored. The resulting cutoff of sediment to the nearshore created a period of net shoreline erosion, when storm waves, tidal currents, and sediment supply shaped the modern delta morphology. We created a base map of the subaqueous delta morphology using multibeam swath mapping and seismic reflection profiles to test the conceptual model (Galster, 1978) of shoreline evolution over the past 10,000 years. In addition, we quantified the modern sediment-transport pathways and mapped the seasonal surface plume of the river along with current measurements and suspended-sediment concentrations collected in the bottom boundary layer using an instrumented tripod. The modern sediment- transport system can be linked to the ancient morphology and stratigraphy though the pairing of the water- column energetics with high-resolution bathymetry and seismic-reflection data. Data indicate that sediment is focused by a tidally-driven, thin bidirectional surface plume and an eddy in the lee of the protruding delta. The strong currents (over 1 m/s) direct net transport to the east and may smooth the delta morphology. Newly acquired seismic-reflection data show outbuilding foresets on the subaqueous delta front and accretionary features

  20. Modelling the transverse distribution of velocity and suspended sediment in tidal estuaries

    NASA Astrophysics Data System (ADS)

    Huijts, K. M. H.

    2011-01-01

    An estuary is a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. Examples are the Western Scheldt River Estuary and the Chesapeake Bay. Within these environments complex patterns of velocity and suspended sediments are observed in the transversal plane (across-estuary and vertical), and sediments are trapped laterally (across-estuary). The transverse structure of velocity is relevant to the transport of salt, sediment, contaminants, oxygen and other material. High sediment concentrations affect water quality, ecology and wildlife, and may cause siltation of navigation channels and harbors. This work aims at a fundamental understanding of the transverse distributions of estuarine velocity and suspended sediment. The thesis provides two-dimensional (cross-sectional) analytical models to identify the effect of individual forcing mechanisms on the transverse distribution of velocity and suspended sediment in tidally-dominated estuaries. The models are based on the shallow water equations and sediment mass balance. Considered are the residual and the semi-diurnal tidal components of the along-estuary, across-estuary and vertical velocity and of the suspended sediment concentration. The models apply to partially to well-mixed tidal estuaries, relatively uniform along-channel conditions and weakly to moderately nonlinear flow. Horizontal density gradients are prescribed based on numerical or observational data. The analytical flows are decomposed into components induced by individual mechanisms. Considered are tides, horizontal residual density gradients, river discharge, stokes return flow, wind, the earth’s rotation, tidal variations in the across-channel density gradient and channel curvature. In addition, two tidally rectified along-channel residual flow mechanisms are considered, which result from net advection of along-channel tidal

  1. Tidal Power for San Francisco

    DTIC Science & Technology

    2003-09-01

    venturi created by design of the subsea tidal station. All mechanical moving parts for the system are on land including conventional air-driven...energy has a global resource base of approximately 30 Tera Watt (TW) (see Table 1). TABLE 1. GLOBAL RENEWABLE RESOURCES Resource Potential...www.sfports.wr.usgs.gov) couples over 20 years of USGS tidal data with a 3-D computational model [4] to provide real-time information from deployed instruments in SF

  2. The tidally averaged momentum balance in a partially and periodically stratified estuary

    USGS Publications Warehouse

    Stacey, M.T.; Brennan, Matthew L.; Burau, J.R.; Monismith, Stephen G.

    2010-01-01

    Observations of turbulent stresses and mean velocities over an entire spring-neap cycle are used to evaluate the dynamics of tidally averaged flows in a partially stratified estuarine channel. In a depth-averaged sense, the net flow in this channel is up estuary due to interaction of tidal forcing with the geometry of the larger basin. The depth-variable tidally averaged flow has the form of an estuarine exchange flow (downstream at the surface, upstream at depth) and varies in response to the neap-spring transition. The weakening of the tidally averaged exchange during the spring tides appears to be a result of decreased stratification on the tidal time scale rather than changes in bed stress. The dynamics of the estuarine exchange flow are defined by a balance between the vertical divergence of the tidally averaged turbulent stress and the tidally averaged pressure gradient in the lower water column. In the upper water column, tidal stresses are important contributors, particularly during the neap tides. The usefulness of an effective eddy viscosity in the tidally averaged momentum equation is explored, and it is seen that the effective eddy viscosity on the subtidal time scale would need to be negative to close the momentum balance. This is due to the dominant contribution of tidally varying turbulent momentum fluxes, which have no specific relation to the subtidal circulation. Using a water column model, the validity of an effective eddy viscosity is explored; for periodically stratified water columns, a negative effective viscosity is required. ?? 2010 American Meteorological Society.

  3. Tidal and residual flows in the western Dutch Wadden Sea III: Vorticity balances

    NASA Astrophysics Data System (ADS)

    Ridderinkhof, H.

    A vorticity-dynamics approach is used to examine the origin of the small-scale residual current field in the western Dutch Wadden Sea. For a representative part of the Wadden Sea, the magnitude of vorticity and of terms in the balance equation for vorticity is determined on the basis of results from a two-dimensional numerical model. The torque from bottom friction along the side walls of the tidal channels appears to be the dominating mechanism in generating tidal relative vorticity, the magnitude of which is much larger than planetary vorticity. Especially near a tidal inlet, stretching and squeezing of fluid columns is of importance in increasing/decreasing relative vorticity. Averaging over a tidal period shows, compared to the tidal equations, an increased influence of the non-linear advective and streching/squeezing terms in the tidally-averaged balance. However, although the relative influence of these strong non-linear terms increases, the influence of the weak non-linear terms originating in bottom friction cannot be ignored. The mechanism responsible for the headland eddies near a tidal inlet and the topographical eddies in the channels of the Wadden Sea is essentially the same, viz. the transfer of vorticity from a source region where this vorticity is produced by differential bottom friction, to adjacent regions. This transfer of tidal vorticity, or advection, is most effective near a transition from straight to curved isobaths where a gradient in the production of tidal vorticity occurs. This is illustrated by showing the vorticity possessed by a particular fluid column during a tidal excursion. The dominant influence of the bathymetry on the small scale residual current pattern is used for a qualitative discussion of the residual flow field in other parts of our numerical model.

  4. A method for using shoreline morphology to predict suspended sediment concentration in tidal creeks

    NASA Astrophysics Data System (ADS)

    Ensign, Scott; Currin, Carolyn; Piehler, Michael; Tobias, Craig

    2017-01-01

    Improving mechanistic prediction of shoreline response to sea level rise is currently limited by 1) morphologic complexity of tidal creek shorelines that confounds application of mechanistic models, and 2) availability of suspended sediment measurements to parameterize mechanistic models. To address these challenges we developed a metric to distinguish two morphodynamic classes of tidal creek and tested whether this metric could be used to predict suspended sediment concentration. We studied three small tidal creeks in North Carolina, U.S.A. We collected suspended sediment at one non-tidal and two tidal sites in each creek and measured the wetland and channel width using a geographic information system. In each creek, tidal harmonics were measured for one year, sediment accretion on the salt marsh was measured for three years, and shoreline erosion was measured from aerial photographs spanning 50 years. Additional total suspended solids measurements from seven creeks reported in a national database supplemented our analysis. Among the three intensively studied creeks, shoreline erosion was highest in the most embayed creek (having a wider channel than the width of adjoining wetlands) and lowest in the wetland-dominated creek (having a channel narrower than the width of adjoining wetlands). Wetland sediment accretion rate in the wetland-dominated creek was four times higher than the accretion in the embayed creek. The wetland-dominated tidal creek had over twice the suspended sediment as the most embayed creek. Based on these results, we conclude that our metric of embayed and contrasting wetland-dominated creek morphology provides a guide for choosing between two types of morphodynamic models that are widely used to predict wetland shoreline change. This metric also allowed us to parse the 10 tidal creeks studied into two groups with different suspended sediment concentrations. This relationship between suspended sediment concentration and creek morphology provides

  5. Sediment Dynamics in Shallow Tidal Landscapes: The Role of Wind Waves and Tidal Currents

    NASA Astrophysics Data System (ADS)

    Carniello, L.; D'Alpaos, A.

    2014-12-01

    A precise description of sediment dynamics (resuspension and re-distribution of sediments) is crucial when investigating the long term evolution of the different morphological entities characterizing tidal landscapes. It has been demonstrated that wind waves are the main responsible for sediment resuspension in shallow micro-tidal lagoons where tidal currents, which produce shear stresses large enough to carry sediments into suspension only within the main channels, are mainly responsible for sediment redistribution. A mathematical model has been developed to describe sediment entrainment, transport and deposition due to the combined effect of tidal currents and wind waves in shallow lagoons considering both cohesive and non-cohesive sediments. The model was calibrated and tested using both in situ point observations and turbidity maps obtained analyzing satellite images. Once calibrated the model can integrate the high temporal resolution of point observations with the high spatial resolution of remote sensing, overcoming the intrinsic limitation of these two types of observations. The model was applied to the specific test case of the Venice lagoon simulating an entire year (2005) which was shown to be a "representative" year for wind and tide characteristics. The time evolution of the computed total bottom shear stresses (BSS) and suspended sediment concentration (SSC) was analyzed on the basis of a "Peaks Over Threshold" method once a critical value for shear stress and turbidity were chosen. The analyses of the numerical results enabled us to demonstrate that resuspension events can be modeled as marked Poisson processes: interarrival time, intensity of peak excesses and duration being exponentially distributed random variable. The probability distributions of the interarrival time of overthreshold exceedances in both BSS and SSC as well as their intensity and duration can be used in long-term morphodynamic studies to generate synthetic series statistically

  6. Carbonate tidal flat in mixed carbonate-siliciclastic clore formation (upper chesterian) in Southern Illinois

    SciTech Connect

    Abegg, F.E.

    1988-01-01

    The upper Chesterian Clore Formation consists primarily of delta-front sandstones of the Tygett Sandstone Member and interbedded offshore mud-rich carbonates and prodelta shales of the Cora and Ford Station Limestone Members. The basal Ford Station limestone in south-central Illinois contains a carbonate sequence 1.0 m thick marked by (1) laminated pelletal lime mudstones, (2) bird's-eye structures containing internal sediment, (3) vertical burrows, (4) horizontal shrinkage cracks, (5) autoclastic brecciation, (6) root. tubes, and (7) calciphers. These features indicate tidal-flat deposition. Other examples of peritidal carbonate deposition are unknown in the Chesterian of the Illinois basin. Tidal-flat strata overlie 1.9 m of interbedded shale and lime mudstones containing linguloid brachiopods, pectin bivalves, and ostracods. The lime mudstones and shales are interpreted as shallow-subtidal, restricted-shelf deposits overlying crevasse-splay deposits of the upper Tygett sandstone. Carbonate tidal-flat deposition in the upper Chesterian of the Illinois basin is an exception to the generally accepted model of nearshore terrigenous and offshore carbonate sedimentation. Delta switching is the most plausible explanation for development of the Clore tidal flat. Following deposition of the deltaic Tygett sandstone, peritidal carbonate deposition occurred in the basal Ford Station limestone when terrigenous sedimentation was deflected westward, as indicated by thin delta-front sandstones in the basal Ford Station limestone in southwestern Illinois. The tidal flat developed locally because south-central Illinois was the region of maximum progradation of the Tygett delta and because upper Tygett crevasse-splay deposits compacted less than adjacent shales.

  7. Elwha River Delta: Geomorphology of a Mixed-Sediment Beach

    NASA Astrophysics Data System (ADS)

    George, D. A.; Warrick, J. J.

    2007-12-01

    The Elwha River drains the Olympic Peninsula of Washington and forms a mixed grain-size delta in the Strait of Juan de Fuca. The Elwha River has been dammed for almost a century, and a pending dam removal project is expected to reconnect upstream sediment sources to the river mouth. Topographic and grain-size mapping of the delta during 1939-2007 is synthesized and the geomorphology and shoreline changes of this system are described. Data sources include historical aerial photographs, airborne LIDAR, semiannual RTK DGPS topographic surveys and grain-size analyses from digital photographs. The delta is divided into three geomorphic regions: west delta, river mouth and east delta. The river mouth is the most complex region due to the river channel movement, side-channels, and bars immediately offshore of the mouth. The east and west delta differ in beach profile and shoreline change rates. The west delta is steep, cuspate and lacks a low-tide terrace. Further, the west delta has exhibited little semi-annual or inter-annual shoreline change. In contrast, the east delta has a steep foreshore, flat low tide terrace that is dominated by cobble, and a consistent trend of erosion during the surveys. These observations can be used to track coastal changes following dam removal on the Elwha River..

  8. Hurricane-dominated carbonate tidal flats, Caicos Platform, British West Indies

    SciTech Connect

    Wanless, H.R.; Tyrrell, K.M.; Tedesco, L.P.

    1987-05-01

    Hurricane-generated, thinly bedded grainstones are the dominant style of stratification throughout the carbonate tidal flat complex on Caicos Platform, BWI. This is in dramatic contrast to the winter storm-generated, millimeter laminae which dominate stratification on the Andros tidal flats and have become the general criteria for recognizing ancient carbonate tidal flat sequences. Hurricane Kate, which passed directly across the Caicos tidal flats on November 18, 1985, provided an opportunity both to document the character and distribution of a specific storm sediment layer and to evaluate the role of hurricanes in molding the geometry of the tidal flat system. Though moderate in strength and producing only incomplete flooding, Hurricane Kate deposited a 0.5-2-cm thick layer of fine peloidal grainstone across significant portions of the extremely broad low-relief shore and channel levees and minor sections of the sequence beneath both the channel levees and the inland algal marsh. These storm layers are interbedded with organic-rich layers which represent prolonged periods of Scytonema algal mat growth between hurricanes. Recognition that centimeter-thick grainstone layers dominate entire tidal flat complexes necessitates both a thorough modification of criteria for defining ancient tidal flat deposits and a reevaluation of supposedly subtidal thinly bedded limestones.

  9. Facies transition and depositional architecture of the Late Eocene tide-dominated delta in northern coast of Birket Qarun, Fayum, Egypt

    NASA Astrophysics Data System (ADS)

    Abdel-Fattah, Zaki A.

    2016-07-01

    Late Eocene successions in the Fayum Depression display notable facies transition from open-marine to brackish-marine realms. Stratigraphic and sedimentologic characteristics of the depositional facies are integrated with ichnological data for the recognition of four facies associations (FA1 to FA4). The transition from open-marine sandstones (FA1) to the brackish-marine deposits (FA2) heralds a transgressive - regressive dislocation. The shallowing- and coarsening-upward progradation from the basal prodelta mudstone-dominated facies (FA2a) to deltafront heterolithics (FA2b) and sandstone facies (FA2c) are overlain by finning-upward delta plain deposits which are expressed by the delta plain mudstone (FA2d) and erosive-based distributary channel fills (FA4). Prodelta/deltfront deposits of FA2 are arranged in thinning- and coarsening-upward parasequences which are stacked in a shallowing-upward progressive cycle. Shallow-marine fossiliferous sandstones (FA3) mark the basal part of each parasequence. Stratigraphic and depositional architectures reflect a tide-dominated delta rather than an estuarine and incised valley (IV) model. This can be evinced by the progressive facies architecture, absence of basal regional incision or a subaerial unconformity and the stratigraphic position above a maximum flooding surface (MFS), in addition to the presence of multiple tidally-influenced distributary channels. Stratigraphic and depositional characteristics of the suggested model resemble those of modern tide-dominated deltaic systems. Accordingly, this model contributes to our understanding of the depositional models for analogous brackish-marine environments, particularly tide-dominated deltas in the rock record.

  10. Tidal circulation alteration for salt marsh mosquito control

    NASA Astrophysics Data System (ADS)

    Resh, Vincent H.; Balling, Steven S.

    1983-01-01

    Mosquito control ditches designed to increase tidal circulation are widely used as a physical control alternative to insecticidal applications The impact of such ditching on Pacific Coast marshlands was largely unknown before this five-year study of impact in two types of San Francisco Bay salt marshes, a Salicornia virginica (pickleweed) monoculure and a mixed vegetation marsh Results of our studies suggest that ditches cause less environmental disturbance than insecticidal applications The article describes the following environmental consequences of ditching for mosquito control: increased tidal flushing of soils occurs adjacent to ditches compared with that in the open marsh, thereby reducing ground water and soil surface salinities and water table height; primary productivity of S. virginica, as determined by both the harvest method and infrared photographic analysis, is higher directly adjacent to ditches than in the open marsh, distribution of selected arthropod populations is similar at ditches and natural channels, although arthropod community response differs seasonally; aquatic invertebrate biomass is similar within ditched and natural ponds, but diversity is lower in ditched habitats, ditching increases fish diversity and density by improving fish access from tidal channels; ditches provide additional salt marsh song sparrow habitat, although ditches are less preferred than natural channels or sloughs. Management criteria can be used to design ditches that provide effective mosquito control and reduced environmental impact

  11. Tidal disruption event demographics

    NASA Astrophysics Data System (ADS)

    Kochanek, C. S.

    2016-09-01

    We survey the properties of stars destroyed in tidal disruption events (TDEs) as a function of black hole (BH) mass, stellar mass and evolutionary state, star formation history and redshift. For M_{BH} ≲ 10^7 M_{⊙}, the typical TDE is due to a M* ˜ 0.3 M⊙ M-dwarf, although the mass function is relatively flat for M_{ast } ≲ M_{⊙}. The contribution from older main-sequence stars and sub-giants is small but not negligible. From MBH ≃ 107.5-108.5 M⊙, the balance rapidly shifts to higher mass stars and a larger contribution from evolved stars, and is ultimately dominated by evolved stars at higher BH masses. The star formation history has little effect until the rates are dominated by evolved stars. TDE rates should decline very rapidly towards higher redshifts. The volumetric rate of TDEs is very high because the BH mass function diverges for low masses. However, any emission mechanism which is largely Eddington-limited for low BH masses suppresses this divergence in any observed sample and leads to TDE samples dominated by MBH ≃ 106.0-107.5 M⊙ BHs with roughly Eddington peak accretion rates. The typical fall-back time is relatively long, with 16 per cent having tfb < 10-1 yr (37 d), and 84 per cent having longer time-scales. Many residual rate discrepancies can be explained if surveys are biased against TDEs with these longer tfb, which seems very plausible if tfb has any relation to the transient rise time. For almost any BH mass function, systematic searches for fainter, faster time-scale TDEs in smaller galaxies, and longer time-scale TDEs in more massive galaxies are likely to be rewarded.

  12. Tidal Boundary Conditions in SEAWAT

    USGS Publications Warehouse

    Mulligan, Ann E.; Langevin, Christian; Post, Vincent E.A.

    2011-01-01

    SEAWAT, a U.S. Geological Survey groundwater flow and transport code, is increasingly used to model the effects of tidal motion on coastal aquifers. Different options are available to simulate tidal boundaries but no guidelines exist nor have comparisons been made to identify the most effective approach. We test seven methods to simulate a sloping beach and a tidal flat. The ocean is represented in one of the three ways: directly using a high hydraulic conductivity (high-K) zone and indirect simulation via specified head boundaries using either the General Head Boundary (GHB) or the new Periodic Boundary Condition (PBC) package. All beach models simulate similar water fluxes across the upland boundary and across the sediment-water interface although the ratio of intertidal to subtidal flow is different at low tide. Simulating a seepage face results in larger intertidal fluxes and influences near-shore heads and salinity. Major differences in flow occur in the tidal flat simulations. Because SEAWAT does not simulate unsaturated flow the water table only rises via flow through the saturated zone. This results in delayed propagation of the rising tidal signal inland. Inundation of the tidal flat is delayed as is flow into the aquifer across the flat. This is severe in the high-K and PBC models but mild in the GHB models. Results indicate that any of the tidal boundary options are fine if the ocean-aquifer interface is steep. However, as the slope of that interface decreases, the high-K and PBC approaches perform poorly and the GHB boundary is preferable.

  13. Observations of Currents in Two Tidally Modulated Inlets

    NASA Astrophysics Data System (ADS)

    Lippmann, T. C.; Irish, J. D.; Hunt, J.

    2012-12-01

    Observations of currents obtained in two tidally modulated inlets are used to examine the spatial evolution of the vertical structure in hourly averaged mean flow and at tidal frequencies. Field experiments of 30 day duration were conducted at Hampton/Seabrook Harbor, NH, in the Fall of 2011 and again at New River Inlet, NC, in the spring of 2012. The temporal variation and vertical structure of the currents were observed with 600 khz and 1200 khz RDI Acoustic Doppler Current Profilers (ADCP) deployed on low-profile bottom tripods just outside and within the inlet mouth, and with a Nortek Aquadopp Profiler mounted on a jetted pipe on the flank of the inlet channel. Across-inlet current profiles were obtained at each site at various tidal stages with a 1200 khz RDI vessel-mounted ADCP onboard the personal watercraft (the Coastal Bathymetry Survey System, or CBASS) that transited the inlet multiple times at various spatial locations. Flows within the inlet were dominated by semi-diurnal tides, ranging from 2.5 to 4 m in elevation at Hampton/Seabrook Harbor with velocities exceeding 3 m/s, and tides ranging from 1 to 1.5 m in elevation at New River Inlet with velocities exceeding 2 m/s. Flows sampled with the CBASS will be used to examine the horizontal and vertical variation in mean currents (averaged over about 20 - 40 min) at various tidal stages. Currents sampled with the fixed instruments will be used to examine the temporal variation in amplitude and direction of mean currents (averaged over 30 - 60 min) as a function of depth, as well as the amplitude, phase, and rotational structure at tidal frequencies. Observations from the two field sites will be compared and discussed in terms of the spatial and temporal evolution from outside the river mouth to the inner inlet channels over the fortnightly sampling period.

  14. Seismic facies analysis of shallowly buried channels, New Jersey continental shelf: understanding late Quaternary paleoenvironments during the last transgression

    NASA Astrophysics Data System (ADS)

    Nordfjord, S.; Goff, J. A.; Austin, J. A.; Gulick, S. P.; Sommerfield, C.; Alexander, C.; Schock, S.

    2004-12-01

    is more variable in amplitude and configuration, and includes a laminated acoustic response, small erosional surfaces, and some wavy reflections. We think the complexity of this facies likely reflects deposition of an estuary mouth complex in a dynamic environment, including frequent lateral variations in sedimentary facies from tidal inlets, washovers, tidal-deltas and barriers. A seismic transition upward from chaotic to flat-lying reflections and a more transparent acoustic response indicates less depositional energy, suggesting replacement of fluvial systems by tidal/estuarine environments. This has been confirmed by vibra-coring of one channel. Our paleo-flow reconstructions also yield velocities in the range of 0.5-1.5 m/s, which are reasonable estimates for flows in estuarine environments.

  15. TIDAL LIMITS TO PLANETARY HABITABILITY

    SciTech Connect

    Barnes, Rory; Jackson, Brian; Greenberg, Richard; Raymond, Sean N.

    2009-07-20

    The habitable zones (HZs) of main-sequence stars have traditionally been defined as the range of orbits that intercept the appropriate amount of stellar flux to permit surface water on a planet. Terrestrial exoplanets discovered to orbit M stars in these zones, which are close-in due to decreased stellar luminosity, may also undergo significant tidal heating. Tidal heating may span a wide range for terrestrial exoplanets and may significantly affect conditions near the surface. For example, if heating rates on an exoplanet are near or greater than that on Io (where tides drive volcanism that resurfaces the planet at least every 1 Myr) and produce similar surface conditions, then the development of life seems unlikely. On the other hand, if the tidal heating rate is less than the minimum to initiate plate tectonics, then CO{sub 2} may not be recycled through subduction, leading to a runaway greenhouse that sterilizes the planet. These two cases represent potential boundaries to habitability and are presented along with the range of the traditional HZ for main-sequence, low-mass stars. We propose a revised HZ that incorporates both stellar insolation and tidal heating. We apply these criteria to GJ 581 d and find that it is in the traditional HZ, but its tidal heating alone may be insufficient for plate tectonics.

  16. Artificial delta growth

    NASA Astrophysics Data System (ADS)

    Mikeš, Daniel

    2010-05-01

    A deltaic sedimentary system has a point source; sediment is carried over the delta plain by distributary channels away from the point source and deposited at the delta front by distributary mouth bars. The established methods to describe such a sedimentary system are "bedding analysis", "facies analysis", and "basin analysis". We shall call the ambient conditions "input" and the rock record "output". There exist a number of methods to deduce input from output, e.g. "Sequence stratigraphy" (a.o. Vail et al. 1977, Catuneanu et al. 2009), "Shoreline trajectory" (a.o. Helland-Hansen & Martinsen 1996, Helland-Hansen & Hampson 2009) on the one hand and the complex use of established techniques on the other (a.o. Miall & Miall 2001, Miall & Miall 2002). None of these deductive methods seems to be sufficient. I claim that the common errors in all these attempts are the following: (1) a sedimentary system is four-dimensional (3+1) and a lesser dimensional analysis is insufficient; (2) a sedimentary system is complex and any empirical/deductive analysis is non-unique. The proper approach to the problem is therefore the theoretical/inductive analysis. To that end we performed six scenarios of a scaled version of a passive margin delta in a flume tank. The scenarios have identical stepwise tectonic subsidence and semi-cyclic sealevel, but different supply curves, i.e. supply is: constant, highly-frequent, proportional to sealevel, inversely proportional to sealevel, lagging to sealevel, ahead of sealevel. The preliminary results are indicative. Lobe-switching occurs frequently and hence locally sedimentation occurs shortly and hiatuses are substantial; therefore events in 2D (+1) cross-sections don't correlate temporally. The number of sedimentary cycles disequals the number of sealevel cycles. Lobe-switching and stepwise tectonic subsidence cause onlap/transgression. Erosional unconformities are local diachronous events, whereas maximum flooding surfaces are regional

  17. Environmental threats to tidal-marsh vertebrates of the San Francisco Bay estuary

    USGS Publications Warehouse

    Takekawa, J.Y.; Woo, I.; Spautz, H.; Nur, N.; Letitia, Grenier J.; Malamud-Roam, K.; Cully, Nordby J.; Cohen, A.N.; Malamud-Roam, F.; Wainwright-De La Cruz, S.E.; ,

    2006-01-01

    The San Francisco Bay and delta system comprises the largest estuary along the Pacific Coast of the Americas and the largest remaining area for tidal-marsh vertebrates, yet tidal marshes have been dramatically altered since the middle of the 19th century. Although recent efforts to restore ecological functions are notable, numerous threats to both endemic and widespread marsh organisms, including habitat loss, are still present. The historic extent of wetlands in the estuary included 2,200 km2 of tidal marshes, of which only 21% remain, but these tidal marshes comprise >90% of all remaining tidal marshes in California. In this paper, we present the most prominent environmental threats to tidal-marsh vertebrates including habitat loss (fragmentation, reductions in available sediment, and sea-level rise), habitat deterioration (contaminants, water quality, and human disturbance), and competitive interactions (invasive species, predation, mosquito and other vector control, and disease). We discuss these threats in light of the hundreds of proposed and ongoing projects to restore wetlands in the estuary and suggest research needs to support future decisions on restoration planning.

  18. Tidal dynamics in a changing lagoon: Flooding or not flooding the marginal regions

    NASA Astrophysics Data System (ADS)

    Lopes, Carina L.; Dias, João M.

    2015-12-01

    Coastal lagoons are low-lying systems under permanent changes motivated by natural and anthropogenic factors. Ria de Aveiro is such an example with its margins currently threatened by the advance of the lagoonal waters recorded during the last decades. This work aims to study the tidal modifications found between 1987 and 2012 in this lagoon, motivated by the main channels deepening which induce higher inland tidal levels. Additionally it aims to study the impact that protective walls designed to protect the margins against flooding may have in those modifications under sea level rise predictions. The hydrodynamic model ELCIRC previously calibrated for Ria de Aveiro was used and tidal asymmetry, tidal ellipses and residual currents were analyzed for different scenarios, considering the mean sea level rise predicted for 2100 and the implementation of probable flood protection walls. Results evidenced that lagoon dominance remained unchanged between 1987 and 2012, but distortion decreased/increased in the deeper/shallower channels. The same trend was found under mean sea level rise conditions. Tidal currents increased over this period inducing an amplification of the water properties exchange within the lagoon, which will be stronger under mean sea level rise conditions. The deviations between scenarios with or without flood protection walls can achieve 60% for the tidal distortion and residual currents and 20% for the tidal currents, highlighting that tidal properties are extremely sensitive to the lagoon geometry. In summary, the development of numerical modelling applications dedicated to study the influence of mean sea level rise on coastal low-lying systems subjected to human influence should include structural measures designed for flood defence in order to accurately predict changes in the local tidal properties.

  19. Littoral steering of deltaic channels

    NASA Astrophysics Data System (ADS)

    Nienhuis, Jaap H.; Ashton, Andrew D.; Giosan, Liviu

    2016-11-01

    The typically single-threaded channels on wave-influenced deltas show striking differences in their orientations, with some channels oriented into the incoming waves (e.g., Ombrone, Krishna), and others oriented away from the waves (e.g., Godavari, Sao Francisco). Understanding the controls on channel orientation is important as the channel location greatly influences deltaic morphology and sedimentology, both subaerially and subaqueously. Here, we explore channel orientation and consequent feedbacks with local shoreline dynamics using a plan-form numerical model of delta evolution. The model treats fluvial sediment delivery to a wave-dominated coast in two ways: 1) channels are assumed to prograde in a direction perpendicular to the local shoreline orientation and 2) a controlled fraction of littoral sediment transport can bypass the river mouth. Model results suggest that channels migrate downdrift when there is a significant net littoral transport and alongshore transport bypassing of the river mouth is limited. In contrast, river channels tend to orient themselves into the waves when fluvial sediment flux is relatively large, causing the shoreline of the downdrift delta flank to attain the orientation of maximum potential sediment transport for the incoming wave climate. Using model results, we develop a framework to estimate channel orientations for wave-influenced deltas that shows good agreement with natural examples. An increase in fluvial sediment input can cause a channel to reorient itself into incoming waves, behavior observed, for example, in the Ombrone delta in Italy. Our results can inform paleoclimate studies by linking channel orientation to fluvial sediment flux and wave energy. In particular, our approach provides a means to quantify past wave directions, which are notoriously difficult to constrain.

  20. 2007 NWFSC Tidal Freshwater Genetics Results

    SciTech Connect

    David Teel

    2008-03-18

    Genetic Analysis of Juvenile Chinook Salmon for inclusion in 'Ecology of Juvenile Salmonids in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, lower Columbia River, 2007. Final report submitted to the Bonneville Power Administration, Contract DE-AC05-76RLO1830.' Genotypic data were collected for 108 Chinook salmon and used in the genetic stock identification analysis. Results of the mixture analysis are presented in Table 1. Percentage estimates for four genetic stock groups (West Cascade Tributary Fall, Willamette River Spring, Deschutes River Fall, and Upper Columbia River Summer/Fall) ranged from 11% to 43%, all with non-zero lower 95% confidence intervals. Small contributions were also estimated for the West Cascade Tributary Spring (3%) and Snake River Fall (6%) stock groups. Results of individual fish probability assignments were summed by collection date (Figure 1) and site (Figure 2). Assignment probabilities for the most likely stock group for each individual ranged from 0.51 to 1.00 with approximately 60% of the assignments greater than 0.90 (data not shown). Nearly all of the low probability assignments were fish with assignments split between the Deschutes River Fall and Upper Columbia River Summer/Fall groups.

  1. Comparative Geomorphology of Salt and Tidal Freshwater Marsh Environments

    NASA Astrophysics Data System (ADS)

    Pasternack, G. B.

    2002-05-01

    Temperate estuaries include a spectrum of coastal marshes ranging from highly saline near the ocean to fresh in tributaries with substantial watershed drainage. While the hydrologic, sedimentary, and geomorphic dynamics of salt marshes have been thoroughly investigated, those aspects of tidal freshwater marshes have only begun to be addressed. Based on a recent burst in research on tidal freshwater systems in Chesapeake Bay by different universities, an attempt is made here to provide comparative geomorphology. In terms of similarities, both have tidal channels whose hydraulic geometry is primarily controlled by the tidal prism. Both show decreasing sedimentation and increasing organics with elevation and distance from channels. At seasonal to interannual time scales, the morphodynamics of both show similarities in the interplay among hydroperiod, vegetation, and geomorphology. Rather than simply evolving from youth to maturity, both systems exhibit strong evidence for dynamic equilibrium between process and morphology. Despite these similarities, there are key differences that motivate further research of tidal freshwater marshes. First, whereas salt marshes are limited by sediment supply, tidal fresh ones may not be limited depending on upstream basin size. E.g., fringing marshes along Pumunkey River have very low sediment supply, while deltaic marshes in Bush River and Sassafras River are not supply-limited. Instead, the growth of deltaic fresh marshes is transport limited, as winds and tides can only generate low momentum and turbulence for sediment transport. As illustrated in multiple systems, a constant availability of sediment leads to higher sedimentation in fresh marshes. Second, in high latitude salt marshes where the tidal range is large and the climate cold, ice acts as a strong erosional agent. In fresh marshes, ice serves to sequester sediment and buffer the erosional impact of autumnal vegetation dieback. Third, the high spatial variation in plant

  2. Tidal variations of earth rotation

    NASA Technical Reports Server (NTRS)

    Yoder, C. F.; Williams, J. G.; Parke, M. E.

    1981-01-01

    The periodic variations of the earths' rotation resulting from the tidal deformation of the earth by the sun and moon were rederived including terms with amplitudes of 0.002 millisec and greater. The series applies to the mantle, crust, and oceans which rotate together for characteristic tidal periods; the scaling parameter is the ratio of the fraction of the Love number producing tidal variations in the moment of inertia of the coupled mantle and oceans (k) to the dimensionless polar moment of inertia of the coupled moments (C). The lunar laser ranging data shows that k/C at monthly and fortnightly frequencies equals 0.99 + or - 0.15 and 0.99 + or - 0.20 as compared to the theoretical value of 0.94 + or - 0.04.

  3. Tidal disruption of inviscid protoplanets

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.; Cameron, A. G. W.; Benz, W.

    1991-01-01

    Roche showed that equilibrium is impossible for a small fluid body synchronously orbiting a primary within a critical radius now termed the Roche limit. Tidal disruption of orbitally unbound bodies is a potentially important process for planetary formation through collisional accumulation, because the area of the Roche limit is considerably larger then the physical cross section of a protoplanet. Several previous studies were made of dynamical tidal disruption and different models of disruption were proposed. Because of the limitation of these analytical models, we have used a smoothed particle hydrodynamics (SPH) code to model the tidal disruption process. The code is basically the same as the one used to model giant impacts; we simply choose impact parameters large enough to avoid collisions. The primary and secondary both have iron cores and silicate mantles, and are initially isothermal at a molten temperature. The conclusions based on the analytical and numerical models are summarized.

  4. Suspended-sediment flux and retention in a backwater tidal slough complex near the landward boundary of an estuary

    USGS Publications Warehouse

    Morgan-King, Tara L.; Schoellhamer, David H.

    2013-01-01

    Backwater tidal sloughs are commonly found at the landward boundary of estuaries. The Cache Slough complex is a backwater tidal region within the Upper Sacramento–San Joaquin Delta that includes two features that are relevant for resource managers: (1) relatively high abundance of the endangered fish, delta smelt (Hypomesus transpacificus), which prefers turbid water and (2) a recently flooded shallow island, Liberty Island, that is a prototype for habitat restoration. We characterized the turbidity around Liberty Island by measuring suspended-sediment flux at four locations from July 2008 through December 2010. An estuarine turbidity maximum in the backwater Cache Slough complex is created by tidal asymmetry, a limited tidal excursion, and wind-wave resuspension. During the study, there was a net export of sediment, though sediment accumulates within the region from landward tidal transport during the dry season. Sediment is continually resuspended by both wind waves and flood tide currents. The suspended-sediment mass oscillates within the region until winter freshwater flow pulses flush it seaward. The hydrodynamic characteristics within the backwater region such as low freshwater flow during the dry season, flood tide dominance, and a limited tidal excursion favor sediment retention.

  5. Ecosystem attributes related to tidal wetland effects on water quality.

    PubMed

    Findlay, S; Fischer, D

    2013-01-01

    Biogeochemical functioning of ecosystems is central to nutrient cycling, carbon balance, and several ecosystem services, yet it is not always clear why levels of function might vary among systems. Wetlands are widely recognized for their ability to alter concentrations of solutes and particles as water moves through them, but we have only general expectations for what attributes of wetlands are linked to variability in these processes. We examined changes in several water quality variables (dissolved oxygen, dissolved organic carbon, nutrients, and suspended particles) to ascertain which constituents are influenced during tidal exchange with a range of 17 tidal freshwater wetlands along the Hudson River, New York, USA. Many of the constituents showed significant differences among wetlands or between flooding and ebbing tidal concentrations, indicating wetland-mediated effects. For dissolved oxygen, the presence of even small proportional cover by submerged aquatic vegetation increased the concentration of dissolved oxygen in water returned to the main channel following a daytime tidal exchange. Nitrate concentrations showed consistent declines during ebbing tides, but the magnitude of decline varied greatly among sites. The proportional cover by graminoid-dominated high intertidal vegetation accounted for over 40% of the variation in nitrate decline. Knowing which water-quality alterations are associated with which attributes helps suggest underlying mechanisms and identifies what functions might be susceptible to change as sea level rise or salinity intrusion drives shifts in wetland vegetation cover.

  6. Hydrodynamic Modeling, Optimization and Performance Assessment for Ducted and Non-ducted Tidal Turbines

    NASA Astrophysics Data System (ADS)

    Shives, Michael Robert

    This thesis examines methods for designing and analyzing kinetic turbines based on blade element momentum (BEM) theory and computational fluid dynamics (CFD). The underlying goal of the work was to assess the potential augmentation of power production associated with enclosing the turbine in an expanding duct. Thus, a comparison of the potential performance of ducted and non-ducted turbines was carried out. This required defining optimal turbine performance for both concepts. BEM is the typical tool used for turbine optimization and is very well established in the context of wind turbine design. BEM was suitable for conventional turbines, but could not account for the influence of ducts, and no established methodology for designing ducted turbines could be found in the literature. Thus, methods were established to design and analyze ducted turbines based on an extended version of BEM (with CFD-derived coefficients), and based on CFD simulation. Additional complications arise in designing tidal turbines because traditional techniques for kinetic turbine design have been established for wind turbines, which are similar in their principle of operation but are driven by flows with inherently different boundary conditions than tidal currents. The major difference is that tidal flows are bounded by the ocean floor, the water surface and channel walls. Thus, analytical and CFD-based methods were established to account for the effects of these boundaries (called blockage effects) on the optimal design and performance of turbines. Additionally, tidal flows are driven by changes in the water surface height in the ocean and their velocity is limited by viscous effects. Turbines introduced into a tidal flow increase the total drag in the system and reduce the total flow in a region (e.g. a tidal channel). An analytical method to account for this was taken from the field of tidal resource assessment, and along with the methods to account for ducts and blockage effects, was

  7. Tidal disruption of dissipative planetesimals

    NASA Technical Reports Server (NTRS)

    Mizuno, H.; Boss, A. P.

    1985-01-01

    A self-consistent numerical model is developed for the tidal disruption of a solid planetesimal. The planetesimal is treated as a highly viscous, slightly compressible fluid whose disturbed parts are an inviscid, pressureless fluid undergoing distortion and disruption. The distortions were constrained to being symmetrical above and below the equatorial plane. The tidal potential is expanded in terms of Legendre polynomials, which eliminates the center of mass acceleration effects, permitting definition of equations of motion in a noninertial frame. Consideration is given to viscous dissipation and to characteristics of the solid-atmosphere boundary. The model is applied to sample cases in one, two and three dimensions.

  8. Tidal disruption of viscous bodies

    NASA Technical Reports Server (NTRS)

    Sridhar, S.; Tremaine, S.

    1992-01-01

    Tidal disruptions are investigated in viscous-fluid planetesimals whose radius is small relative to the distance of closest (parabolic-orbit) approach to a planet. The planetesimal surface is in these conditions always ellipsoidal, facilitating treatment by coupled ODEs which are solvable with high accuracy. While the disrupted planetesimals evolve into needlelike ellipsoids, their density does not decrease. The validity of viscous fluid treatment holds for solid (ice or rock) planetesimals in cases where tidal stresses are greater than material strength, but integrity is maintained by self-gravity.

  9. Primary production in the Delta: Then and now

    USGS Publications Warehouse

    Cloern, James E.; Robinson, April; Richey, Amy; Grenier, Letitia; Grossinger, Robin; Boyer, Katharyn E.; Burau, Jon; Canuel, Elizabeth A.; DeGeorge, John F.; Drexler, Judith Z.; Enright, Chris; Howe, Emily R.; Kneib, Ronald; Mueller-Solger, Anke; Naiman, Robert J.; Pinckney, James L.; Safran, Samuel M.; Schoellhamer, David H.; Simenstad, Charles A.

    2016-01-01

    To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function. Primary production is a crucial ecosystem process, which directly limits the quality and quantity of food available for secondary consumers such as invertebrates and fish. The Delta has a low rate of primary production, but it is unclear whether this was always the case. Recent analyses from the Historical Ecology Team and Delta Landscapes Project provide quantitative comparisons of the areal extent of 14 habitat types in the modern Delta versus the historical Delta (pre-1850). Here we describe an approach for using these metrics of land use change to: (1) produce the first quantitative estimates of how Delta primary production and the relative contributions from five different producer groups have been altered by large-scale drainage and conversion to agriculture; (2) convert these production estimates into a common currency so the contributions of each producer group reflect their food quality and efficiency of transfer to consumers; and (3) use simple models to discover how tidal exchange between marshes and open water influences primary production and its consumption. Application of this approach could inform Delta management in two ways. First, it would provide a quantitative estimate of how large-scale conversion to agriculture has altered the Delta's capacity to produce food for native biota. Second, it would provide restoration practitioners with a new approach—based on ecosystem function—to evaluate the success of restoration projects and gauge the trajectory of ecological recovery in the Delta region.

  10. Pen Branch delta expansion

    SciTech Connect

    Nelson, E.A.; Christensen, E.J.; Mackey, H.E.; Sharitz, R.R.; Jensen, J.R.; Hodgson, M.E.

    1984-02-01

    Since 1954, cooling water discharges from K Reactor ({anti X} = 370 cfs {at} 59 C) to Pen Branch have altered vegetation and deposited sediment in the Savannah River Swamp forming the Pen Branch delta. Currently, the delta covers over 300 acres and continues to expand at a rate of about 16 acres/yr. Examination of delta expansion can provide important information on environmental impacts to wetlands exposed to elevated temperature and flow conditions. To assess the current status and predict future expansion of the Pen Branch delta, historic aerial photographs were analyzed using both basic photo interpretation and computer techniques to provide the following information: (1) past and current expansion rates; (2) location and changes of impacted areas; (3) total acreage presently affected. Delta acreage changes were then compared to historic reactor discharge temperature and flow data to see if expansion rate variations could be related to reactor operations.

  11. Tidal frequency estimation for closed basins

    NASA Technical Reports Server (NTRS)

    Eades, J. B., Jr.

    1978-01-01

    A method was developed for determining the fundamental tidal frequencies for closed basins of water, by means of an eigenvalue analysis. The mathematical model employed, was the Laplace tidal equations.

  12. Geomorphic modeling of macro-tidal embayment with extensive tidal flats: Skagit Bay, Washington

    DTIC Science & Technology

    2012-09-30

    DISTRIBUTION A: Distribution approved for public release; distribution is unlimited. Geomorphic modeling of macro- tidal embayment with extensive... tidal flats: Skagit Bay, Washington Lyle Hibler Battelle-Pacific Northwest Division Marine Sciences Laboratory Sequim, WA 98382 phone: (360) 681...of muddy tidal flats and to quantify the effects of tidal action, river discharge, and shoreline development (e.g. dikes and jetties) on these

  13. The effect of interference on delta modulation encoded video signals

    NASA Technical Reports Server (NTRS)

    Schilling, D. L.

    1979-01-01

    The results of a study on the use of the delta modulator as a digital encoder of television signals are presented. The computer simulation was studied of different delta modulators in order to find a satisfactory delta modulator. After finding a suitable delta modulator algorithm via computer simulation, the results are analyzed and then implemented in hardware to study the ability to encode real time motion pictures from an NTSC format television camera. The effects were investigated of channel errors on the delta modulated video signal and several error correction algorithms were tested via computer simulation. A very high speed delta modulator was built (out of ECL logic), incorporating the most promising of the correction schemes, so that it could be tested on real time motion pictures. The final area of investigation concerned itself with finding delta modulators which could achieve significant bandwidth reduction without regard to complexity or speed. The first such scheme to be investigated was a real time frame to frame encoding scheme which required the assembly of fourteen, 131,000 bit long shift registers as well as a high speed delta modulator. The other schemes involved two dimensional delta modulator algorithms.

  14. Delta hepatitis in Malaysia.

    PubMed

    Sinniah, M; Dimitrakakis, M; Tan, D S

    1986-06-01

    Sera from one hundred and fifty nine Malaysian individuals were screened for the prevalence of delta markers. These included 15 HBsAg positive homosexuals, 16 acute hepatitis B cases, 9 chronic hepatitis B patients, 13 healthy HBsAg carriers and 106 intravenous (i.v.) drug abusers, of whom 27 were positive for HBsAg only and the rest were anti-HBc IgG positive but HBsAg negative. The prevalence of delta markers in the homosexuals was found to be 6.7%, in the HBsAg positive drug abusers 17.8%, in acute hepatitis B cases 12.5%. No evidence of delta infection was detected in healthy HBsAg carriers, chronic hepatitis B cases and HBsAg negative i.v. drug abusers. With reference to i.v. drug abusers, the prevalence of delta markers was higher in Malays (23%) than in Chinese (7%) although the latter had a higher HBsAg carrier rate. Although the HBsAg carrier rate in the homosexuals was high, their delta prevalence rate was low as compared to drug abusers. In Malaysia, as in other non-endemic regions, hepatitis delta virus transmission appeared to occur mainly via the parenteral and sexual routes. This is the first time in Malaysia that a reservoir of delta infection has been demonstrated in certain groups of the population at high risk for hepatitis B.

  15. TIDAL DWARF GALAXIES AROUND A POST-MERGER GALAXY, NGC 4922

    SciTech Connect

    Sheen, Yun-Kyeong; Jeong, Hyunjin; Lee, Young-Wook; Ferreras, Ignacio; Lotz, Jennifer M.; Olsen, Knut A. G.; Dickinson, Mark; Barnes, Sydney; Park, Jang-Hyun; Ree, Chang H.; Madore, Barry F.; Barlow, Tom A.; Conrow, Tim; Foster, Karl; Friendman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Neff, Susan G.; Schiminovich, David; Yi, Sukyoung K.

    2009-12-15

    One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy (TDG) candidates in the post-merger galaxy NGC 4922 in the Coma cluster. Based on a two-component population model (combining young and old stellar populations), we find that the light of tidal tail predominantly comes from young stars (a few Myr old). The Galaxy Evolution Explorer ultraviolet data played a critical role in the parameter (age and mass) estimation. Our stellar mass estimates of the TDG candidates are {approx}10{sup 6-7} M {sub sun}, typical for dwarf galaxies.

  16. Morphology and Sediment Transport Dynamics of the Selenga River Delta, Lake Baikal, Russia

    NASA Astrophysics Data System (ADS)

    Dong, T. Y.; Il'icheva, L.; Nittrouer, J. A.; Pavolv, M.

    2013-12-01

    The Selenga River fan delta is a lacustrine system located in southeastern Siberia, Russia, where Selenga River flows into Lake Baikal. The Selenga River is the largest source of sediment and water entering Lake Baikal. Covering ~550 km2, the Selenga delta is one of the largest freshwater deltas in the world. Evaluating the Selenga delta and its morphology is very important for local residents who rely upon the delta for both ecological and agricultural welfare. However, a sediment budget remains poorly constrained, as do estimates for the partitioning of water and sediment amongst the numerous bifurcating delta channels. This information is critical for addressing how the delta morphology evolves and influences the stratigraphic composition of the delta. To investigate the morphological characteristics of the delta, a field expedition was undertaken during July 2013 in collaboration with Russian scientists. The overall goal of the field work was to constrain delta dynamics through data collection. Field measurements included single-beam bathymetry data and sidescan sonar data to characterize: 1) channel geometries of the delta; 2) bedform sizes and distribution; and 3) grain-size composition of the channel bed. Flow velocity measurements were collected within the bifurcating channels to measure water discharge. Bedload samples were obtained within the active distributary channels to measure downstream sediment fining. Additionally, channel island cores were collected in order to analyze the internal architecture of the delta. The data reveal a systematic downstream sediment fining, from a predominantly gravel bed near the delta apex, to a fine-sand bed at the delta-lake interface (~40 km total distance). Bathymetry data document how width-to-depth ratios systematically decrease downstream in association with increasing channel bifurcations and decreasing channel-bed grain size. Furthermore, the investigations reveal that the delta is actively terraced, with the

  17. Building a delta: Interactions between water, sediment, and vegetation in an experimental system

    NASA Astrophysics Data System (ADS)

    Piliouras, A.; Kim, W.; Carlson, B.

    2013-12-01

    Vegetation is an important part of morphodynamics in river deltas, but it has not been thoroughly investigated in physical delta models. We conducted a set of experiments in the Sediment Transport and Earth-surface Processes (STEP) Basin at the University of Texas at Austin to examine the effects of vegetation on delta growth and dynamics. One experiment was conducted without vegetation (Run 1), and four (Runs 2-5) were conducted using alfalfa (Medicago sativa) as a proxy for riparian vegetation, one of which included cycles between flood and normal flow discharges (Run 5). Results indicate that vegetation increased sediment trapping on the delta topset, increasing delta slope and decreasing progradation rate as compared to the unvegetated experiment. Vegetation also caused a lack of channelization when the topset reached 20% plant cover, after which progradational delta lobes were no longer evident. Discharge fluctuations in Run 5, however, led to more topset reworking, resulting in lower vegetation density (< 20%) and the persistence of highly incisional channels. Experiments run only at flood stage resulted in consistently net depositional deltas with very little channel incision, regardless of the amount of vegetation. The addition of water and sediment discharge fluctuations in Run 5, however, created a cyclic pattern between periods of topset aggradation and periods of channel incision that were net erosional. We conclude that there is a two-way interaction between the vegetation and the channels through discharge fluctuations that aid in delta growth. (1) During floods, vegetation acts an efficient sediment trapper on the floodplain to aid in topset aggradation and maintain channel relief. During normal flow, vegetation also stabilizes channel banks, allowing channels to focus their flow and erode sediment from the bed. (2) During floods, channels transport sediment to the shoreline to create new deposits that can be colonized by vegetation and deliver

  18. Nile River Delta, Egypt

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The Nile River Delta of Egypt (30.0N, 31.0E) irrigated by the Nile River and its many distributaries, is some of the richest farm land in the world and home to some 45 million people, over half of Egypt's population. The capital city of Cairo is at the apex of the delta. Just across the river from Cairo can be seen the ancient three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta.

  19. Delta Scuti stars: Theory

    NASA Technical Reports Server (NTRS)

    Guzik, J. A.

    1998-01-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.

  20. Dwarf Galaxies Swimming in Tidal Tails

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This false-color infrared image from NASA's Spitzer Space Telescope shows little 'dwarf galaxies' forming in the 'tails' of two larger galaxies that are colliding together. The big galaxies are at the center of the picture, while the dwarfs can be seen as red dots in the red streamers, or tidal tails. The two blue dots above the big galaxies are stars in the foreground.

    Galaxy mergers are common occurrences in the universe; for example, our own Milky Way galaxy will eventually smash into the nearby Andromeda galaxy. When two galaxies meet, they tend to rip each other apart, leaving a trail, called a tidal tail, of gas and dust in their wake. It is out of this galactic debris that new dwarf galaxies are born.

    The new Spitzer picture demonstrates that these particular dwarfs are actively forming stars. The red color indicates the presence of dust produced in star-forming regions, including organic molecules called polycyclic aromatic hydrocarbons. These carbon-containing molecules are also found on Earth, in car exhaust and on burnt toast, among other places. Here, the molecules are being heated up by the young stars, and, as a result, shine in infrared light.

    This image was taken by the infrared array camera on Spitzer. It is a 4-color composite of infrared light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange), and 8.0 microns (red). Starlight has been subtracted from the orange and red channels in order to enhance the dust features.

  1. 2010-2015 Juvenile fish ecology in the Nisqually River Delta and Nisqually Reach Aquatic Reserve

    USGS Publications Warehouse

    Hodgson, Sayre; Ellings, Christopher S.; Rubin, Steve P.; Hayes, Michael C.; Duval, Walker; Grossman, Eric E.

    2017-01-01

    The return of tidal inundation to over 750 acres of the U. S. Fish and Wildlife Service Billy Frank Jr. Nisqually National Wildlife Refuge (NNWR) in fall of 2009 was the crowning moment in the effort to protect and restore the Nisqually Delta. The Nisqually NWR project complemented three earlier restoration projects completed by the Nisqually Indian Tribe (Tribe) on tribal property to restore over 900 acres of the estuary, representing the largest estuary restoration project in the Pacific Northwest and one of the most significant advances to date towards the recovery of Puget Sound (USFWS 2005). In 2011 the Washington Department of Natural Resources (WADNR established the over 14000 acre Nisqually Reach Aquatic Reserve (Reserve), complementing the protection and restoration successes in the Nisqually Delta. The Reserve includes all state-owned aquatic lands around Anderson, Ketron and Eagle islands and part of McNeil Island (Figure 1, WDNR 2011). The Reserve also includes a diverse assemblage of nearshore and offshore habitats important to resident and migratory fish including federal endangered species act listed fish like Chinook salmon (Oncorynchus tshawytscha) and steelhead (O. mykiss). Studies in the Nisqually Estuary (Ellings and Hodgson 2007, David et al. 2014, Ellings et al. 2016) and South Puget Sound (Duffy 2003) have summarized fish use of the area. However, the fish ecology of the reserve had not been systematically surveyed. The Tribe, U.S. Geological Survey (USGS), NNWR, Nisqually River Foundation (NRF), and others are currently conducting a multi-year, interdisciplinary, hypothesis-based research and monitoring study investigating the impact of delta restoration on estuarine processes, habitat structures, and functions. Our interdisciplinary monitoring framework enables us to link key estuarine processes with habitat development and biological response at multiple scales across the restored footprint, reference marshes, and throughout the Nisqually

  2. Long-term evolution in the location, propagation, and magnitude of the tidal shear front off the Yellow River Mouth

    NASA Astrophysics Data System (ADS)

    Wang, Nan; Li, Guangxue; Qiao, Lulu; Shi, Jinghao; Dong, Ping; Xu, Jishang; Ma, Yanyan

    2017-04-01

    Characteristics and formation of the tidal shear front off the Yellow River Mouth had been previously studied based on observations and models. However, its long-term variability and thus related mechanisms have not been investigated. In this study, a three-dimensional hydrodynamic model was used to examine the long-term evolution on the location, propagation, and magnitude (length, duration, and shear strength) of the tidal shear front from 1976 to 1996. Over the 20 years, a peninsula of about 27 km long and 7 km wide (above the high water line) was formed off the new river mouth, while the coastline retreated by 5-10 km, and the water depths increased by about 2 m in the north (the abandoned river mouth). Results also show that for the period of each flood and ebb tidal cycle, the tidal shear front originated in the north of the delta, then propagated southeastwards and finally disappeared at the south of the river mouth. During the two decades, the front had an obvious shoreward movement, and its duration within a tidal cycle increased slightly. Furthermore, the length of the front decreased, while the shear strength of the front increased. The propagation of the front was determined by flood and ebb process in the delta, where both of them were from north to south due to tidal phase distribution. Long-term characteristic variations of the front were mainly caused by morphology change, which had a significant influence on the tidal current gradient and the location of maximum bottom stress gradient area. The morphology change also had a slight impact on the tidal current phase in the front area, which may have caused the slight duration variation of the front.

  3. PEAT ACCRETION HISTORIES DURING THE PAST 6000 YEARS IN MARSHES OF THE SACRAMENTO - SAN JOAQUIN DELTA, CALIFORNIA, USA

    SciTech Connect

    Drexler, J Z; de Fontaine, C S; Brown, T A

    2009-07-20

    Peat cores were collected in 4 remnant marsh islands and 4 drained, farmed islands throughout the Sacramento - San Joaquin Delta of California in order to characterize the peat accretion history of this region. Radiocarbon age determination of marsh macrofossils at both marsh and farmed islands showed that marshes in the central and western Delta started forming between 6030 and 6790 cal yr BP. Age-depth models for three marshes were constructed using cubic smooth spline regression models. The resulting spline fit models were used to estimate peat accretion histories for the marshes. Estimated accretion rates range from 0.03 to 0.49 cm yr{sup -1} for the marsh sites. The highest accretion rates are at Browns Island, a marsh at the confluence of the Sacramento and San Joaquin rivers. Porosity was examined in the peat core from Franks Wetland, one of the remnant marsh sites. Porosity was greater than 90% and changed little with depth indicating that autocompaction was not an important process in the peat column. The mean contribution of organic matter to soil volume at the marsh sites ranges from 6.15 to 9.25% with little variability. In contrast, the mean contribution of inorganic matter to soil volume ranges from 1.40 to 8.45% with much greater variability, especially in sites situated in main channels. These results suggest that marshes in the Delta can be viewed as largely autochthonous vs. allochthonous in character. Autochthonous sites are largely removed from watershed processes, such as sediment deposition and scour, and are dominated by organic production. Allochthonous sites have greater fluctuations in accretion rates due to the variability of inorganic inputs from the watershed. A comparison of estimated vertical accretion rates with 20th century rates of global sea-level rise shows that currently marshes are maintaining their positions in the tidal frame, yet this offers little assurance of sustainability under scenarios of increased sea-level rise in

  4. Tidal flow separation at protruding beach nourishments

    NASA Astrophysics Data System (ADS)

    Radermacher, Max; de Schipper, Matthieu A.; Swinkels, Cilia; MacMahan, Jamie H.; Reniers, Ad J. H. M.

    2017-01-01

    In recent years, the application of large-scale beach nourishments has been discussed, with the Sand Motor in the Netherlands as the first real-world example. Such protruding beach nourishments have an impact on tidal currents, potentially leading to tidal flow separation and the generation of tidal eddies of length scales larger than the nourishment itself. The present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions, based on extensive field observations and numerical flow simulations. Observations of the flow field around the Sand Motor, obtained with a ship-mounted current profiler and a set of fixed current profilers, show that a tidal eddy develops along the northern edge of the mega-nourishment every flood period. The eddy is generated around peak tidal flow and gradually gains size and strength, growing much larger than the cross-shore dimension of the coastline perturbation. Based on a 3 week measurement period, it is shown that the intensity of the eddy modulates with the spring-neap tidal cycle. Depth-averaged tidal currents around coastline perturbations are simulated and compared to the field observations. The occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape. Results show that several different types of behavior exist, characterized by different combinations of the nourishment aspect ratio, the size of the nourishment relative to the tidal excursion length, and the influence of bed friction.

  5. Maine Tidal Power Initiative: Environmental Impact Protocols For Tidal Power

    SciTech Connect

    Peterson, Michael Leroy; Zydlewski, Gayle Barbin; Xue, Huijie; Johnson, Teresa R.

    2014-02-02

    The Maine Tidal Power Initiative (MTPI), an interdisciplinary group of engineers, biologists, oceanographers, and social scientists, has been conducting research to evaluate tidal energy resources and better understand the potential effects and impacts of marine hydro-kinetic (MHK) development on the environment and local community. Project efforts include: 1) resource assessment, 2) development of initial device design parameters using scale model tests, 3) baseline environmental studies and monitoring, and 4) human and community responses. This work included in-situ measurement of the environmental and social response to the pre-commercial Turbine Generator Unit (TGU®) developed by Ocean Renewable Power Company (ORPC) as well as considering the path forward for smaller community scale projects.

  6. Federal Funding in the Delta.

    ERIC Educational Resources Information Center

    Reeder, Richard J.; Calhoun, Samuel D.

    2002-01-01

    The Lower Mississippi Delta region, especially the rural Delta, faces many economic challenges. The rural Delta has received much federal aid in basic income support and funding for human resource development, but less for community resource programs, which are important for economic development. Federal aid to the Delta is analyzed in terms of…

  7. Simulation of unsteady flow and solute transport in a tidal river network

    USGS Publications Warehouse

    Zhan, X.

    2003-01-01

    A mathematical model and numerical method for water flow and solute transport in a tidal river network is presented. The tidal river network is defined as a system of open channels of rivers with junctions and cross sections. As an example, the Pearl River in China is represented by a network of 104 channels, 62 nodes, and a total of 330 cross sections with 11 boundary section for one of the applications. The simulations are performed with a supercomputer for seven scenarios of water flow and/or solute transport in the Pearl River, China, with different hydrological and weather conditions. Comparisons with available data are shown. The intention of this study is to summarize previous works and to provide a useful tool for water environmental management in a tidal river network, particularly for the Pearl River, China.

  8. A meeting of the waters: interdisciplinary challenges and opportunities in tidal rivers

    USGS Publications Warehouse

    Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.; Fagherazzi, Sergio

    2012-01-01

    At the interface of estuarine tides and freshwater rivers lie wetland and aquatic ecosystems, which experience dramatic effects of sea level rise. There, nontidal channels and riparian floodplains are transforming into tidal ecosystems, and tidal freshwater ecosystems are receiving increasing salinity. These river-floodplain systems have both fluvial characteristics, including meandering channels and expansive floodplain forests, and estuarine characteristics, including tides and intertidal wetlands [see Barendregt et al., 2009; Conner et al., 2007, and references therein]. Because tidal rivers lie at the disciplinary divide between fluvial and estuarine science, a knowledge gap has developed in scientists' understanding of the geomorphic and biogeochemical response of these environments to sea level rise, climate change, and anthropogenically driven variations in watershed exports.

  9. A meeting of the waters: Interdisciplinary challenges and opportunities in tidal rivers

    NASA Astrophysics Data System (ADS)

    Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.; Fagherazzi, Sergio

    2012-11-01

    At the interface of estuarine tides and freshwater rivers lie wetland and aquatic ecosystems, which experience dramatic effects of sea level rise. There, nontidal channels and riparian floodplains are transforming into tidal ecosystems, and tidal freshwater ecosystems are receiving increasing salinity. These river-floodplain systems have both fluvial characteristics, including meandering channels and expansive floodplain forests, and estuarine characteristics, including tides and intertidal wetlands [see Barendregt et al., 2009; Conner et al., 2007, and references therein]. Because tidal rivers lie at the disciplinary divide between fluvial and estuarine science, a knowledge gap has developed in scientists' understanding of the geomorphic and biogeochemical response of these environments to sea level rise, climate change, and anthropogenically driven variations in watershed exports.

  10. Seasonal transfer and net accumulation of fine sediment on a muddy tidal flat: Willapa Bay, Washington

    NASA Astrophysics Data System (ADS)

    Boldt, Katherine V.; Nittrouer, Charles A.; Ogston, Andrea S.

    2013-06-01

    Tidal flats act as natural laboratories in which fundamental sediment-transport processes can be directly related to resulting seabed deposits. These environments represent important repositories for terrestrial particles (including organic carbon) entering marine dispersal systems. Along the coast of the US Pacific Northwest, tides, waves, currents, and storms create year-round energetic environments that evolve on myriad time scales, from semi-diurnal to interannual. In southern Willapa Bay, WA, an extensive tidal flat is accreting at a distance away from local fluvial sources. During winter, freshwater input and the peak suspended-sediment concentration (SSC) are one-to-two orders of magnitude greater than in summer, and wind- and wave-generated shear stresses prevent sediment from accumulating on the tidal flat. Temporary deposits form as a drape across secondary channels off the Bear River Channel. Sedimentary structures from these deposits reveal 15-30cm of physically stratified sediment underlain by a discrete shell-hash layer 2-8cm thick. The presence of relatively uniform excess 210Pb activities in the sediment above the shell hash, and only supported activities below indicate rapid deposition of the surficial sediment. During summer, the distribution of bed shear stresses is not significantly weaker than in winter due to the effect of local basin geometry on fetch, yet the SSC is much less, likely due to reduced fluvial sediment supply and enhanced benthic biological factors. Progressively through the summer, tidal currents and wind waves remove the temporary channel deposits and expose the buried shell-hash layer, and concurrent seabed changes allow the tidal flats to trap this remobilized sediment. Accumulation rates determined by 210Pb analysis for cores collected on the tidal flats show mean accretion at 1.4mm/yr, which can be accounted for by local river sources. The mass of sediment stored in the temporary channel drapes during winter is

  11. The Selenga River delta - a geochemical barrier for the waters of Lake Baikal

    NASA Astrophysics Data System (ADS)

    Chalov, Sergey; Thorslund, Josefin; Pietron, Jan; Jarsjö, Jerker

    2016-04-01

    Delta systems play an important role in retention of sediments and contaminants to downstream recipients, through processes such as gravitational sedimentation, flocculation and biofiltration. The Selenga river delta is one of the world's largest inland deltas, providing a huge buffer zone between Lake Baikal and upstream waters of the Selenga river basin. Understanding the delta functioning is critical for the planning of water management measures in the Selenga River Basin and for protection of the waters of Lake Baikal. We here study the current state and functioning of the delta's ecosystem and hydrogeochemical processes. More specifically, we considered spatio-temporal changes in water flow, morphology and transport of sediments and metals within the delta and what potential impacts these changes may have on the delta functions. Results show that the delta network has a large influence on the mass of metals reaching the Lake Baikal at the delta outlet. Regions with high density of wetlands and small channels, in contrast to main channel regions, show a consistent pattern of considerable contaminant filtering and removal (between 77-99% for key metals), during both high and low flow conditions, following with a significant increase (2-3 times) of bottom sediment pollution. Geomorphological processes also governs the barrier function of the delta, due to partitioning of flow between different channel systems. These results are particularly relevant in the light of recent and expected future changes involving both the hydrology and water quality in the Lake Baikal basin. Taken together, this emphasizes the importance of understanding the interface between flow partitioning, delta morphology, and sediment and metal patterns and storage rates for fully capturing and quantifying the variety in delta functions. This is particularly relevant coupled to hydroclimatic changes in the region, which could lead to significant decline in barrier functions of the delta due to

  12. Prediction of CBS tidal evolution

    NASA Astrophysics Data System (ADS)

    Dryomova, G. N.

    The time series of basic processes, accompanying the tidal evolution of star components of Close Binary Systems (CBS) are predicted in the framework of evolutionary stellar models by Claret (2004). The series includes the apsidal motion period, timescale of synchronization of axial rotation of a star with the orbital revolution, the orbit circularization timescale, and the age. Data from the catalogues by Svechnikov & Perevozkina (1999) and by Torres, Andersen, Gimenez (2010) are used for testing the sensitivity of the numerical prediction algorithm.

  13. Trans World Tidal Gravity Profile.

    DTIC Science & Technology

    1984-12-31

    America Curitiba (BraziZ) This station, situated at the Universidade Federal do Parana, in the Instituto de Ciencias Geod6sicas under Professor C...SUL COMPOSANTE VEPTICALE ERESIL 29 40 17S 53 49 22W H 700M P 2M 0 330KM DEPOTS SEDIMENTAIRES SUk BASALTE DEPT* DE INGENIERIA RURAL-UNIV. FED. DE SANTA...PRECAMBRIENIGNEISS * UNIVERSIDADE FEDERAL DO RIO GRANDE DO NORTE - DEPARTAMENTO DE FISICA TRANS WORLD TIDAL GRAVITY PROFILES P. MELCHIOR CENTRO POLITECNICO

  14. Tidally-Induced Thermonuclear Supernovae

    SciTech Connect

    Rosswog, S.; Ramirez-Ruiz, E.; Hix, William Raphael

    2009-01-01

    We discuss the results of 3D simulations of tidal disruptions of white dwarfs by moderate-mass black holes as they may exist in the cores of globular clusters or dwarf galaxies. Our simulations follow self-consistently the hydrodynamic and nuclear evolution from the initial parabolic orbit over the disruption to the build-up of an accretion disk around the black hole. For strong enough encounters (pericentre distances smaller than about 1/3 of the tidal radius) the tidal compression is reversed by a shock and finally results in a thermonuclear explosion. These explosions are not restricted to progenitor masses close to the Chandrasekhar limit, we find exploding examples throughout the whole white dwarf mass range. There is, however, a restriction on the masses of the involved black holes: black holes more massive than 2x105M{circle_dot} swallow a typical 0.6M{circle_dot} white dwarf before their tidal forces can overwhelm the star's selfgravity. Therefore, this mechanism is characteristic for black holes of moderate masses. The material that remains bound to the black hole settles into an accretion disk and produces an Xray flare close to the Eddington limit of L{sub Edd} {approx} 10{sup 41}erg/s (Mbh/1000M{circle_dot}), typically lasting for a few months. The combination of a peculiar thermonuclear supernova together with an X-ray flare thus whistle-blows the existence of such moderate-mass black holes. The next generation of wide field space-based instruments should be able to detect such events.

  15. North American tidal power prospects

    NASA Astrophysics Data System (ADS)

    Wayne, W. W., Jr.

    1981-07-01

    Prospects for North American tidal power electrical generation are reviewed. Studies by the US Army Corps of Engineers of 90 possible generation schemes in Cobscook Bay, ME, indicated that maximum power generation rather than dependable capacity was the most economic method. Construction cost estimates for 15 MW bulb units in a single effect mode from basin to the sea are provided; five projects were considered ranging from 110-160 MW. Additional tidal power installations are examined for: Half-Moon Cove, ME (12 MW, 18 ft tide); Cook Inlet, AK, which is shown to pose severe environmental and engineering problems due to fish migration, earthquake hazards, and 300 ft deep silt deposits; and the Bay of Fundy, Canada. This last has a 17.8 MW plant under construction in a 29 ft maximum tide area. Other tidal projects of the Maritime Provinces are reviewed, and it is noted that previous economic evaluations based on an oil price of $16/barrel are in need of revision.

  16. Tidally dominated sediment dispersal offshore of a small mountainous river: Elwha River, Washington State

    NASA Astrophysics Data System (ADS)

    Eidam, E. F.; Ogston, A. S.; Nittrouer, C. A.; Warrick, J. A.

    2016-03-01

    Sediment supplied by small mountainous rivers (SMRs) represents a major fraction of the global ocean sediment budget. Studies from the past two decades have shown that much of this sediment is dispersed by episodic wind and wave energy along storm-dominated coasts. In tidally dominated environments, however, different transport styles and deposits may result from persistent tidal dispersal. This study investigates episodic sediment releases generated by dam removal from a SMR in Washington State, in order to evaluate the mechanics of tidally dominated sediment dispersal in an energetic marine environment. The results indicate that asymmetric tidal currents with peak magnitudes of ∼50 to >80 cm/s produce daily sediment export in the direction of the dominant tidal phase (i.e., the semi-diurnal phase with faster currents and longer duration), resulting in dispersal of fluvially derived fine sediment to distal sinks. These effects are observed throughout all seasons in the presence or absence of wave events. During the first two years of dam removal, more than 8 million tonnes of sediment were discharged to the coast. The net result was little to no change in grain size at 10-60 m water depth across >70% of the seabed offshore of the river mouth. Over the remaining ∼2 to 3 km2 of the subaqueous delta, several cm of mud and sand accumulated in a sheltered coastal embayment adjacent to the river mouth. These results demonstrate that SMR discharge events may form patchy, isolated deposits-or even no deposits-along coastlines with strong tidal