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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. Tidal impact on the division of river discharge over distributary channels in the Mahakam Delta

    NASA Astrophysics Data System (ADS)

    Sassi, Maximiliano G.; Hoitink, A. J. F.; de Brye, Benjamin; Vermeulen, Bart; Deleersnijder, Eric

    2011-12-01

    Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels. A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations. The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper the discharge division that would occur in the case without tides.

  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. 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.

  5. 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

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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.

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

    DOE PAGESBeta

    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 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

  12. Cyclic behavior of sandy shoals on the ebb-tidal deltas of the Wadden Sea

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Ebb-tidal deltas are bulges of sand that are located seaward of tidal inlets. Many of these deltas feature shoals that cyclically form and migrate towards the coast. The average period between successive shoals that attach to the coast varies among different inlets. In this study, a quantitative assessment of the cyclic behavior of shoals on the ebb-tidal deltas of the Wadden Sea is presented. Analysis of bathymetric data and Landsat satellite images revealed that at the majority of inlets along the Wadden Sea migrating shoals occur. The average period between succeeding shoals correlates to the tidal prism and has values ranging between 4 and 130 years. A larger tidal prism favors larger periods between successive shoal attachments. However, such a relationship was not found for wide inlets with multiple channels. There is a positive relationship between the frequency with which the shoals attach to the coast and their migration velocity, and a negative relationship between the migration velocity of the shoal and the tidal prism. Finally, the data were too sparse to assess whether the longshore sediment transport has a significant effect on the period between successive shoals that attach to the coasts downdrift of the observed tidal inlets.

  13. 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.

  14. 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

  15. Migration and morphologic evolution of an ebb-tidal delta shoal, Chincoteague Inlet, Virginia

    SciTech Connect

    Barlet, K.E.; Simpson, E.L. ); Venn, C. ); Zimmerman, R. )

    1994-03-01

    Ebb-tidal delta shoals form as a result of the dynamic interaction of tide-, wave-, and storm-generated currents. A limited number of studies have tracked the long-term migration of an ebb-tidal delta shoal and the morphologic changes that result from the passage of a hurricane or a northeaster. The authors examined an ebb-tidal delta shoal in chincoteague Inlet, virginia by two methods. Aerial photographs from 1974 to 1991 were used to track shoal position and shoreline changes. Plane table mapping of the shoal from 1990 through 1992 allowed assessment of morphologic changes before and after the passage of storms. Aerial photographs indicated that the shoal migrated southward from 1974 to approximately 1981; superimposed on the southward migration is a counterclockwise rotation of the shoal. From 1981 through 1991 the shoal moved first towards Wallops Island, VA, to the west, then traveled northward; superimposed on the northward migration is a clockwise rotation of the shoal. Overall the shoal is inscribing a large clockwise pattern possibly the result of wave and longshore drift interaction. Alternatively, the shift of the shoal towards Wallops Island during the overall clockwise movement may be in part the result of sediment transport landward during storms. The smaller apparent rotations during southward and northward migration may be the result of a stronger flood tidal current in the main channel during southward migration and in the smaller southern flood tidal channel during northward migration.

  16. Modeling the dynamics of barrier coasts and ebb-tidal deltas

    NASA Astrophysics Data System (ADS)

    van der Vegt, M.

    2006-03-01

    It is observed that the length of barrier islands is inversely related to the tidal range. A physical explanation for this behavior is missing. In Chapter 2 it is studied whether a straight coastline can become unstable for small rhythmic undulations of the position of the coastline. This mimics the initial evolution of a straight coast into a coast with barrier islands. The results show that, for typical Dutch shelf conditions, a straight coast is unstable for undulations with a length scale smaller than 8 km. These undulations grow due to a feedback mechanism between the position of the coastline and the shore-parallel tidal currents. When also the influence of sediment transport due to waves only is taken into account, it is found that for increasing magnitude of the shore-parallel tidal currents the length scale of the perturbation which grows fastest, decreases. For increasing influence of the sediment transport due to waves only the length scale of the perturbation which grows fastest is increasing. The results compare favorably well with the observed trend in the length of the islands along the Dutch and German coast. Between two barrier islands a tidal inlet is found. This tidal inlet connects a single backbarrier basin with the coastal sea. In the inlet a deep ebb-dominated channel is located in which the tidal currents during ebb are stronger than during flood. At its seaward end a shallow area is present, the ebb-tidal delta. This delta is flanked by two flood-dominated. A main question is whether the hydrodynamics, sediment transport and the bathymetry in the area of the ebb-tidal delta are such that, averaged over several tidal periods, the bottom patterns are steady (morphodynamic equilibrium). In Chapter 3 it is shown that, by using an idealized model, the symmetric ebb-tidal delta (typically found along the east coast of the USA) is in morphodynamic equilibrium. The modeled bathymetry compare well with that of observed ebb-tidal deltas. Furthermore

  17. 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).

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

    USGS Publications Warehouse

    Wright, Scott A.; Morgan, Tara

    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

  19. 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

  20. 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.

  1. River deltas: channelizing sandpiles with memory

    NASA Astrophysics Data System (ADS)

    Jerolmack, Douglas; Reitz, Meredith

    2013-03-01

    River deltas are wedges of sediment that are built via the lateral migration of self-channelizing rivers, but the timescale of this process is prohibitively long to observe in nature. Here we present laboratory results that allow us to examine how channels form and fill space to create a delta. Flow collapses into a single channel whose dimensions adjust to threshold transport conditions for the imposed sediment load. This channelization causes localized shoreline growth until the slope drops below a threshold value for sediment transport. This leads to deposition within the channel, with an upstream-migrating step akin to a stopping front in granular flows, which causes widespread flooding and the selection of a new (steeper) channel path. This cycle is remarkably periodic; delta slope oscillates between two thresholds - entrainment and distrainment - analogous to static and dynamic angles of repose. Selection of a new flow path is inherently stochastic, but previously abandoned channels act as significant attractors for the flow. Once a critical density of flow paths has been established, the flow oscillates among the same 3-5 channels indefinitely. These dynamics result in self-similar (quasi-)radial growth of delta lobes, which can be described using a simple geometric model. Despite its simplicity, the experimental system agrees well with what can be measured from natural deltas Thus, temporal and spatial patterns of deltas appear to be a robust result of mass conservation and transport thresholds.

  2. BAY DELTA CROSS CHANNEL OPERATIONAL STUDIES

    EPA Science Inventory

    The Delta Cross Channel was constructed in 1953 to deliver low-salinity water from the Sacramento River in Northern California to the South Delta where it is pumped to the San Francisco Bay Area and other parts of the State for public consumption and to the San Joaquin Valley for...

  3. 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.

  4. 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

  5. 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.

  6. Mapping of tide and tidal flow fields along a tidal channel with vessel-based observations

    NASA Astrophysics Data System (ADS)

    Li, Chunyan; Blanton, Jack; Chen, Changsheng

    2004-04-01

    We present the results of a study focused on the tidal regime of a shallow channel with a large intertidal area. Data from a vessel-towed acoustic Doppler current profiler (ADCP) were used to infer tidal constituents for both tidal elevation and tidal current along an upstream portion of the Okatee River, South Carolina. The tidal elevation is estimated from the depth recorded by the moving ADCP. This tidal elevation is then used to correct the vertical coordinates of each depth bin below the ADCP for the velocity profiles. The ability to resolve both tidal elevation and velocity allows us to determine that the tide is a standing wave. A statistical analysis demonstrates that the along-channel velocity has a stronger tidal signal (larger R2 values) than the across-channel velocity. When only the M2 and mean components are included in the harmonic analysis, about 75% of the covered area along the ship track has a "good fit," where at least 70% of the variability can be explained by the tidal and mean components. By adding the M4 component to the harmonic analysis, an additional 2% of the covered area has "good fit" for the elevation, depth-averaged velocity, and mid-depth velocity, but 12% for the near-surface velocity. The observed spatial distribution of the residual flow is in reasonable agreement with that predicted by an unstructured grid, finite-volume coastal ocean model (FVCOM).

  7. 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

  8. 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

  9. 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.

  10. 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

  11. Salt marsh vegetation promotes efficient tidal channel networks.

    PubMed

    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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. Controls on floc growth in an energetic tidal channel

    NASA Astrophysics Data System (ADS)

    Braithwaite, K. M.; Bowers, D. G.; Nimmo Smith, W. A. M.; Graham, G. W.

    2012-02-01

    Measurements of turbulence and suspended particle characteristics have been made continuously for 9 tidal cycles in a shallow, energetic tidal channel. Particle-size spectra were measured with a LISST-100 laser diffraction instrument placed on a frame on the seabed. A 1200 kHz ADCP in the same frame was used to measure vertical current profiles and from these the turbulent kinetic energy dissipation rate was determined using the structure function method. Median particle size is observed to change in a regular way by a factor of 3 or more over each tidal cycle, with the largest particles observed at slack tide and the smallest at times of maximum flood and ebb. The most likely explanation of this change is that particles are aggregating at times of low turbulence and breaking up during fast flows. A simple dynamical flocculation model that incorporates these processes gives good agreement with observations, particularly if tidal advection of a longitudinal gradient in particle size is allowed for. If particles have time to reach equilibrium with ambient conditions, the model predicts that the particle size will be proportional to the product of concentration and the Kolmogorov microscale. The observations support this prediction on most tidal cycles if a phase lag (of 30-60 min) is allowed between the measurements of particle size and Kolmogorov scale. This phase lag represents the adjustment time for flocs to respond to change in turbulence. The constant of proportionality between median particle size and Kolmogorov scale increases with particle volume.

  20. 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

  1. 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

  2. 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.

  3. 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

  4. Quantitative metrics that describe river deltas and their channel networks

    NASA Astrophysics Data System (ADS)

    Edmonds, Douglas A.; Paola, Chris; Hoyal, David C. J. D.; Sheets, Ben A.

    2011-12-01

    Densely populated river deltas are losing land at an alarming rate and to successfully restore these environments we must understand the details of their morphology. Toward this end we present a set of five metrics that describe delta morphology: (1) the fractal dimension, (2) the distribution of island sizes, (3) the nearest-edge distance, (4) a synthetic distribution of sediment fluxes at the shoreline, and (5) the nourishment area. The nearest-edge distance is the shortest distance to channelized or unchannelized water from a given location on the delta and is analogous to the inverse of drainage density in tributary networks. The nourishment area is the downstream delta area supplied by the sediment coming through a given channel cross section and is analogous to catchment area in tributary networks. As a first step, we apply these metrics to four relatively simple, fluvially dominated delta networks. For all these deltas, the average nearest-edge distances are remarkably constant moving down delta suggesting that the network organizes itself to maintain a consistent distance to the nearest channel. Nourishment area distributions can be predicted from a river mouth bar model of delta growth, and also scale with the width of the channel and with the length of the longest channel, analogous to Hack's law for drainage basins. The four delta channel networks are fractal, but power laws and scale invariance appear to be less pervasive than in tributary networks. Thus, deltas may occupy an advantageous middle ground between complete similarity and complete dissimilarity, where morphologic differences indicate different behavior.

  5. 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.

  6. 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.

  7. Effect of channel errors on delta modulation transmission

    NASA Technical Reports Server (NTRS)

    Rosenberg, W. J.

    1973-01-01

    We have considered the response of a variable step size delta modulator communication system, to errors caused by a noisy channel. For the particular adaptive delta modulation scheme proposed by Song, Garodnick, and Schilling (1971), we have a simple analytic formulation of the output error propagation due to a single channel error. It is shown that single channel errors cause a change in the amplitude and dc level of the output, but do not otherwise affect the shape of the output waveform. At low channel error rates, these effects do not cause any degradation in audio transmission. Higher channel error rates cause overflow or saturation of the step size register. We present relationships between channel error rate, register size, and the probability of register overflow.

  8. 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.

  9. 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.

  10. 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.

  11. Tidal bedform characteristics in the Jade and Weser tidal inlet channels, German North Sea coast

    NASA Astrophysics Data System (ADS)

    Feng, H. S.; Winter, C.; Svenson, C.; Maushake, C.

    2009-12-01

    Compound bedforms are ubiquitous in marine environments with sandy beds and sufficient hydrodynamic forcing. In tidal channels, these features can build up to several meters in height and hundreds of meters in length. Recent high-resolution bathymetric mapping has revealed the complex morphology and morphodynamics of superimposed bedforms of different sizes and geometries. In this study, high-resolution multibeam echo sounder bathymetry and parametric sediment echo sounder (SES) sub-bottom data were compiled and visualized in Fledermaus 7 to identify typical bedform geometries and internal structures along 40 km of the Jade tidal channel and 50 km of the tide-dominated Weser estuary at the German North Sea coast. These extensive bathymetric datasets show the confined occurrence and the diversity of shapes and dimensions of the bedforms, ranging from simple geometries to compound superpositions of large subsidiary dunes, from small bedforms with lengths of the order of 20 m and heights of 1 m to large features 200 m in length and 10 m in height, and from symmetrical shapes to ebb- or flood-dominated geometries. The parametric echo sounder imaged sub-bottom profiles up to 4 m deep, showing relatively simple foreset bedding in simple dunes and complex internal structures in compound bedforms. Cross-bedding signatures indicating an ebb orientation were recognized within symmetric and flood-directed bedforms, suggesting a temporal re-orientation of the whole structure. Locally small buried bedforms, overgrown by recent larger bedforms, were detected. These indicate changes in the local hydrodynamic conditions or variations in the sediment supply.

  12. 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.

  13. 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

  14. 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

  15. An ecogeomorphic model of tidal channel initiation and elaboration in progressive marsh accretional contexts

    NASA Astrophysics Data System (ADS)

    Belliard, J.-P.; Toffolon, M.; Carniello, L.; D'Alpaos, A.

    2015-06-01

    The formation and evolution of tidal networks have been described through various theories which mostly assume that tidal network development results from erosional processes, therefore emphasizing the chief role of external forcing triggering channel net erosion such as tidal currents. In contrast, in the present contribution we explore the influence of sediment supply in governing tidal channel initiation and further elaboration using an ecogeomorphic modeling framework. This deliberate choice of environmental conditions allows for the investigation of tidal network growth and development in different sedimentary contexts and provides evidences for the occurrence of both erosional and depositional channel-forming processes. Results show that these two mechanisms in reality coexist but act at different time scales: channel initiation stems from erosional processes, while channel elaboration mostly results from depositional processes. Furthermore, analyses suggest that tidal network ontogeny is accelerated as the marsh accretional activity increases, revealing the high magnitude and prevalence of the depositional processes in governing the morphodynamic evolution of the tidal network. On a second stage, we analyze the role of different initial topographic configurations in driving the development of tidal networks. Results point out an increase in network complexity over highly perturbed initial topographic surfaces, highlighting the legacy of initial conditions on channel morphological properties. Lastly, the consideration that landscape evolution depends significantly on the parameterization of the vegetation biomass distribution suggests that the claim to use uncalibrated models for vegetation dynamics is still questionable when studying real cases.

  16. Sand bypass and updrift beach evolution after jetty construction at an ebb-tidal delta

    NASA Astrophysics Data System (ADS)

    Garel, E.; Sousa, C.; Ferreira, Ó.

    2015-12-01

    The evolution of an ebb-tidal delta (Guadiana, South Portugal) and its updrift beach after jetty construction (in 1972-1974) is analysed based on 24 ortho-rectified aerial photographs (1940-2012) and 13 bathymetric maps (1969-2014). The objectives are to evaluate the re-establishment of the sand bypassing process and if the disruption of the historical delta may affect the updrift beach evolution. Post-jetty progradation of the updrift beach resulted from two large accretion events. The second (largest) event (110 m progradation in 1985-1994) was due to beach attachment of a shoal produced by the erosion of a broad shallow area relict of the historical delta. The reworking of sand from this relict area also enables the individualisation of a lateral updrift bar simultaneously with the new ebb shoal proper formation. Both morphological features were close to (volume) equilibrium in 1995, indicating that most of the sand was transported towards the downdrift side of the inlet at that time. This study shows that erosion of the historical delta may enhance significantly the updrift shoreline progradation and may promote the re-establishment of sand bypassing after jetty construction.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

    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

  1. 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

  2. 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 ...

  3. 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.

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

    PubMed Central

    Ralston, David K.; Stacey, Mark T.

    2011-01-01

    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. PMID:21499572

  5. 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.

  6. Delta distributary dynamics in the Skagit River Delta (Washington, USA): Extending, testing, and applying avulsion theory in a tidal system

    NASA Astrophysics Data System (ADS)

    Hood, W. Gregory

    2010-11-01

    Analysis of historical aerial photos shows that Skagit Delta (Washington, USA) distributary dynamics are consistent with the Slingerland and Smith model of avulsion dynamics where the ratio of the water surface slopes of the two branches of a bifurcation predicts avulsion stability. This model was extended to predict distributary inlet (upstream) width and bankfull cross-sectional area. The water surface gradient ratio for a bifurcation pair predicted distributary width well; the lowest R2 was 0.61 for the 1937 data points, but R2 ranged from 0.83 to 0.90 for other year-specific regression lines. Gradient ratios were not constant over the historical record; from 1937 to 1972 the mainstem river channel lengthened by 1250 m in the course of marsh progradation, while distributary lengthening was comparatively negligible. Consequently, the gradient advantage of the distributaries increased and their channels widened. After the mainstem river terminus stabilized from 1972 to the present, the distributaries continued to lengthen with marsh progradation, so that distributary gradient advantage steadily declined and the distributaries narrowed. While distributary cross sections were not available for the historical period, they were surveyed in 2007 near the distributary inlets. Gradient ratio was more closely related to distributary inlet bankfull cross-sectional area ( R2 = 0.95) than to minimum distributary width for any photo year examined. Applying this form of analysis to Skagit Delta distributaries that have been dammed in the course of agricultural development suggests that their restoration to stabilize eroding marshes at their outlets and recover salmon migration pathways would be feasible without significant risk of full river avulsion.

  7. Hydraulic Consequences of Hydrilla, an Invasive Submerged Aquatic Plant, in Freshwater Tidal Channels

    NASA Astrophysics Data System (ADS)

    Jenner, B. A.; Prestegaard, K. L.

    2010-12-01

    Hydrilla is a non-indigenous submerged aquatic plant that has become common in the southeast and mid-Atlantic regions of the United States. The purpose of this research is to evaluate the effects of Hydrilla on flow resistance, velocity, and discharge in freshwater tidal channels along the Patuxent River, MD. Hydrilla height is limited by the level of average low tide in tidal channels; therefore, it has preferentially invaded larger, deeper channels. Geomorphic and hydraulic measurements were made at 6 sites in the channel network of a large, freshwater tidal marsh in the spring, prior to Hydrilla regrowth, and in late summer when vegetation height was at a maximum. Field measurements of vegetation height (Zo), gauge height, energy gradient, velocity profiles, and maximum velocity were used to calculate mean channel velocity, shear velocity, and flow resistance (u/u* and Manning’s n) for the two vegetative conditions. “At-a-station” and “Downstream” hydraulic geometry relationships (the power function relationships of discharge to width, depth, and velocity) were also determined for maximum and minimum vegetation conditions. Results indicate that flow resistance increased and velocity decreased by an order of magnitude between Hydrilla minima and maxima heights. Tidal marsh channels typically exhibit rapid decreases in channel width and cross sectional area in the up-marsh direction. These decreases in width serve to maintain channel velocities and bring sediment, organic matter, and other materials into tidal marshes. Therefore, the downstream hydraulic geometry exponents for width are large and exponents are near zero for velocity, in most measured tidal marsh systems. Our measurements indicate that mean channel velocity decreases significantly in the up-marsh direction during maximum vegetation. This generates an exponent for velocity in the downstream hydraulic geometry relationships that is significantly larger than observed in other tidal systems

  8. Extraction of tidal channel networks from airborne scanning laser altimetry and aerial photography

    NASA Astrophysics Data System (ADS)

    Mason, David C.; Wang, Hai-Jing; Lohani, Bharat

    2003-03-01

    The study of the morphodynamics of tidal channel networks is important because of their role in tidal propagation and the evolution of salt-marshes and tidal flats. Channel dimensions range from tens of meters wide and meters deep near the low water mark to only 20-30cm wide and 20cm deep for the smallest channels on the marshes. The conventional method of measuring the networks is cumbersome, involving manual digitizing of aerial photographs. This paper describes a semi-automatic knowledge-based network extraction method that is being implemented to work using airborne scanning laser altimetery. The channels exhibit a width variation of several orders of magnitude, making an approach based on multi-scale line detection difficult. The processing therefore uses multi-scale edge detection to detect channel edges, then associates adjacent anti-parallel edges together to form channels uing a distance-with-destination transform. Breaks in the networks are repaired by extending channel ends in the direction of their ends to join with nearby channels, using domain knowledge that flow paths should proceed downhill and that nay network fragment should be joined to a nearby fragment so as to connect eventually to the open sea.

  9. Observations of estuarine circulation and solitary internal waves in a highly energetic tidal channel

    NASA Astrophysics Data System (ADS)

    Groeskamp, Sjoerd; Nauw, Janine J.; Maas, Leo R. M.

    2011-11-01

    Despite vigorous tidal and wind mixing, observations in an estuarine tidal inlet in the Wadden Sea show that during part of the tidal cycle, vertical stratification and internal waves may still develop. Acoustic Doppler current profiler (ADCP) and conductivity, temperature, depth observations, collected over the past 6 years at 13 h anchor stations (ASs), reveal that these occur especially during slack tide, when there is little wind and large freshwater discharge from nearby Lake IJssel. Measurements with a moored ADCP show that in the same tidal phase, strong cross-channel circulation develops, which may suddenly reverse circulation sense due to passing density fronts. In the vertically stratified phase that follows after the front passage, propagating mode-one solitary internal waves are observed. These are resonantly generated during decelerating tidal ebb currents when the (shear) flow passes a transcritical regime (Froude number equal to 1). A combination of photographs (including one from the International Space Station), bathymetric data, and ASs data leads to the discovery of yet another source of internal waves in this area, produced during slackening tide by propagating lee waves that develop over a deep trench. We suggest that both the cross-channel circulation as well as the (solitary) internal waves may locally be of importance for the (re)distribution and transport of sediments and nutrients and may influence tidally averaged transports.

  10. Baroclinic tidal generation in the Kauai Channel inferred from high-frequency radio Doppler current meters

    NASA Astrophysics Data System (ADS)

    Zaron, Edward D.; Chavanne, Cedric; Egbert, Gary D.; Flament, Pierre

    2009-10-01

    A data-assimilating three-dimensional primitive equations model is used in conjunction with high-frequency radio Doppler current data to infer tidal conversion during two 3-month periods in Kauai Channel, Hawaii. It is estimated that the M barotropic tide loses energy at rates of 1.1 and 1.2 GW during these periods, values 25% lower than predicted with the prior model. Of this total conversion rate, approximately 85% exits the model domain to enter the deep ocean as a coherent propagating internal tide. Although the inferred tidal currents differ in detail during the 3-month periods, the domain-averaged tidal energetics do not. The tidal solutions obtained by the data-assimilative model do not exactly satisfy the primitive equations dynamics since a residual forcing is permitted in the horizontal momentum and mass conservation equations. An analysis of these residuals indicates that they are consistent with the expected amplitude of tidal-mesoscale interactions; however, the residual forcing in the mass equation, which represents refraction by the mesoscale buoyancy field, is much too small. An attempt to reconcile the forcing residuals with known processes suggests, by elimination, that tidal-mesoscale interactions are of leading-order significance and should be included in future analysis of baroclinic tidal energy budgets.

  11. A Parallel Double Front System along the Main Channel of a Barotropic Tidal Inlet

    NASA Astrophysics Data System (ADS)

    Li, C.

    2003-12-01

    In an estuary with a significant longitudinal density gradient, fronts can occur during flood stage if a cross channel shear of flow exists. In a wide estuary, models have suggested convergence on the right hand side when facing the downstream direction, because of Coriolis effect, favoring a single front line changing its position with tidal phase. If a front system occurs during different tidal stages including ebb and appears in pairs on both sides of a channel, then neither of the above mechanisms can explain it. Here I report such a front system observed in a barotropic tidal inlet - Sand Shoal Inlet, VA. The front system is observed during different tidal stages within a 13-hour observation period. A 25-ft boat is used to tow an acoustic Doppler current profiler (ADCP) to measure velocity profiles along an hour-glass shaped ship track. A harmonic-statistic analysis is used to analyze the tide, tidal velocity, and mean velocity. The transverse convergence and divergence of velocity are calculated. The rms errors of the harmonic-statistic analysis of the elevation and velocity are about 0.28 m and 0.13 m/s (with a maximum velocity of over 2 m/s), respectively. On average, about 83%, 95%, and 70% of the variabilities of the elevation, longitudinal and transverse velocities respectively can be explained by the M2 tidal and subtidal constituents. Strong transverse velocity convergences are identified by the analysis and are generally consistent with the observed front positions. The analysis shows that the front system is apparently generated by a combination of several mechanisms including (1) differential rotation of the tidal ellipses and spatial variations of the major axes of the tidal ellipses, owing to the strong bottom friction, and (2) a strong geometric convergence at the inlet. Density effect is found to be negligible and the planetary vorticity tilt effect is also unimportant because of a much higher relative vorticity. The observed front system is

  12. Inferring tidal wetland stability from channel sediment fluxes: Observations and a conceptual model

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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 anthropogenic loss.

  13. 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

  14. 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. PMID:16854806

  15. 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).

  16. 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.

  17. Influence of Aquatic Vegetation on Channel Hydraulics, Morphology, and Seasonal Accretion in Tidal Freshwater Marsh Inlet Channels

    NASA Astrophysics Data System (ADS)

    Prestegaard, K. L.; Statkiewicz, A. E.

    2014-12-01

    We examined interactions among aquatic vegetation, flow hydraulics, sediment (organic and inorganic) deposition, organic matter decomposition, and the channel form of tidal freshwater marsh inlet channels. Inlets chosen for study were partially covered by a dominate vegetation species (N.luteum, Z.aquatica, or H.verticullata). Vegetation cover, height, stem diameter, and stem density were measured monthly along each channel cross section. Water surface elevation was measured with multiple gauges in each tidal inlet and accompanied by measurements of velocity. These data were used to calculate total and effective channel shear stresses. Channel cross section elevations were surveyed bimonthly to determine elevation change in inlets occupied by each of the three dominate vegetation species. Sediment cores were obtained along each inlet cross section and analyzed for bulk density, grain size, and percentage of organic matter. Leaf litter experiments were conducted to determine plant decomposition rates. The three aquatic plants grew in significantly different water depths (Z. aquatica the shallowest and H. verticullata the deepest). Z. aquatica and N. luteum had similar stem diameters and densities and grew over well-defined platforms associated with low shear stresses during vegetation maxima. The central channel core, however, had higher summer shear stresses than predicted from depth and slope data. The zones of low shear stress persisted after vegetation die-back, but shear stresses in the central core decreased during non-vegetated periods. The deep central cores of these seasonally-vegetated inlets experienced erosion during the warm season and deposition during cool (unvegetated) periods. The H. verticullata channels had a parabolic channel form rather than the platform-central form observed in the other channels. Decomposition experiments indicated significantly higher decomposition rates for H. verticullata and N. luteum than for Z. aquatica. Comparison among

  18. 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

  19. The record of sea level rise by tidal sand bodies of the English Channel

    SciTech Connect

    Berne, S; Lericolais, G. ); Lafont, F. )

    1990-05-01

    Improvements of very high resolution seismic reflection provide new information about internal structures of modern sand bodies. This allows us to reconstruct their recent history, which is related to the Holocene sea level rise. A major distinction is found between inner shelf sand bodies, dominated by autocyclic processes, and outer shelf sand bodies, where allocyclic processes are invoked to explain the apparent contradiction between internal structures and present-day dynamics. On the inner shelf, evidence of the migration of tidal dunes (sand waves) has been obtained by repeated surveys using accurate positioning systems. Major bounding surfaces are thought to result from the action of tidal current and/or from episodic storms. A rough estimation of the age of these sand bodies can be proposed. On the outer shelf, some dunes of the English Channel exhibit cross-beds indicative of a past net bed-load transport at the opposite of present days dynamics, inherited from different tidal conditions when sea level was between 20 and 40 m lower. Some large tidal sand banks (e.g., the Sark Bank near the Channel Islands) display a more complicated pattern. The upper part of the sand bank is the result of the migration of very large dunes climbing at positive angles, whereas the lower part shows major erosional surfaces, attributed to the action of storms during lower sea levels.

  20. 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

  1. 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

  2. Tidal transformation and resonance in a short, microtidal Mediterranean estuary (Alfacs Bay in Ebre delta)

    NASA Astrophysics Data System (ADS)

    Cerralbo, Pablo; Grifoll, Manel; Valle-Levinson, Arnoldo; Espino, Manuel

    2014-05-01

    Tidal and subtidal waves are analyzed with sea-level data and numerical modeling in a short and micro-tidal embayment, Alfacs Bay (NW Mediterranean Sea). Data analysis exhibits tidal wave amplification and seiching (characteristic period of 3.5 h) along the bay. Numerical results show an eight-fold increase in quarter-wave resonant wave amplitudes from the mouth to the head of the bay. This amplification follows the classical description of a standing wave. Moreover, resonant wave velocities measured and computed at the bay mouth (node location) are about one order of magnitude higher than tidal currents. Analysis of astronomic tidal propagation in the bay reveals similar behavior for diurnal and semidiurnal constituents. Tidal waves amplify along the bay by 3% for diurnal and 10% for semidiurnal constituents. Numerical simulations conducted with different domains indicate that geometric effects dominate over frictional influences in causing the wave behavior. This behavior is consistent with the existence of a quasi-steady standing wave within the bay.

  3. Quantifying the signature of sediment composition on the topologic and dynamic complexity of river delta channel networks and inferences toward delta classification

    NASA Astrophysics Data System (ADS)

    Tejedor, Alejandro; Longjas, Anthony; Caldwell, Rebecca; Edmonds, Douglas A.; Zaliapin, Ilya; Foufoula-Georgiou, Efi

    2016-04-01

    Deltas contain complex self-organizing channel networks that nourish the surface with sediment and nutrients. Developing a quantitative understanding of how controlling physical mechanisms of delta formation relate to the channel networks they imprint on the landscape remains an open problem, hindering further progress on quantitative delta classification and understanding process from form. Here we isolate the effect of sediment composition on network structure by analyzing Delft3D river-dominated deltas within the recently introduced graph-theoretic framework for quantifying complexity of delta channel networks. We demonstrate that deltas with coarser incoming sediment tend to be more complex topologically (increased number of pathways) but simpler dynamically (reduced flux exchange between subnetworks) and that once a morphodynamic steady state is reached, complexity also achieves a steady state. By positioning simulated deltas on the so-called TopoDynamic complexity space and comparing with field deltas, we propose a quantitative framework for exploring complexity toward systematic inference and classification.

  4. The ebb-tidal delta model of shoreface ridge origin and evolution: Appraisal and applicability along the southern North Sea barrier island coast—a discussion

    NASA Astrophysics Data System (ADS)

    Antia, E. E.

    1994-03-01

    The ebb-tidal delta model of McBride and Moslow is the most comprehensive on the morphogenesis and distribution of shoreface ridges along the US Atlantic seaboard to date. This discussion evaluates the applicability of the above model to the southern North Sea barrier island coast. Results indicate that the characteristics of the North Sea shoreface-connected ridge sediments display a genetic relationship with those of the inlet ebb delta as implied by the ebb-tidal model. By contrast, ridge orientation is not well accounted for by lateral inlet migration and shoreline recession as suggested by the model. A possible reason for the aforementioned discrepancy is discussed.

  5. Tide and river influences on distributary channels of the Mekong River delta

    NASA Astrophysics Data System (ADS)

    Saito, Y.; Nguyen, V. L.; Ta, T. K. O.; Tamura, T.; Kanai, Y.; Nakashima, R.

    2015-12-01

    The Mekong River delta, one of the world's largest deltas, has extended from Phnom Penh in Cambodia (apex) to the coast from the Saigon River mouth to Cape Camau in Vietnam with a triangular-shape area of more than 60,000 km2. The delta has prograded more than 200 km over at least the last 6-7 ka. The river-mouth area of the delta is meso-tidal with the mean tidal range of 2.5 ± 0.1 m and the maximum tidal range is 3.2-3.8 m. The mean wave height is 0.9 m. Its water discharge is 470 km3/y and its sediment discharge is 160 million t/y, or tenth and ninth largest in the world, respectively. The water discharge varies by season because most of the drainage area is under a monsoonal tropical regime. The flow at Phnom Penh, Cambodia, reaches a maximum in October (typically 39,000 m3/s) and a minimum in May (about 1700 m3/s). Tidal water-level changes are observed in Cambodia, more than 200 km upstream from the river mouth. To understand the combined influenced of river and tide on river bottom sediments, we have collected ~210 surface samples from river bottoms of the whole Mekong River delta in Vietnam, covering five distributaries during dry season from January to May 2015. Sediment characteristics show clearly tide- and river-influenced areas, which are closely linked with river morphology.

  6. 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.

  7. 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.

  8. Bedding types in Holocene tidal channel sequences, Knik Arm, Upper Cook Inlet, Alaska.

    USGS Publications Warehouse

    Bartsch-Winkler, S.; Schmoll, H.R.

    1984-01-01

    Uplifted convoluted and horizontal to subhorizontal beds of varying thickness in intertidal silt as old as 3280 +- 90 yr BP are exposed in the banks of tidal channels of unknown depth in the intertidal zone in Knik Arm of Upper Cook Inlet. Internal discordances may occur both within convoluted beds and between convoluted and horizontal to subhorizontal beds. At the base of many convoluted beds, there is a rapid gradation upward into laminae which are severely deformed; that is, in some places, the contortions appear to have originated along a single bedding plane. Where the convoluted sequences are truncated by nearly horizontal sequences, the distortion must have resulted from syndepositional or postdepositional events prior to their burial by the overlying beds. Various forms of gravitational and tidal processes caused the deformation of the Knik Arm deposits. -from Authors

  9. 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.

  10. 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.

  11. Tidal currents in the Malta - Sicily Channel from high-frequency radar observations

    NASA Astrophysics Data System (ADS)

    Cosoli, Simone; Drago, Aldo; Ciraolo, Giuseppe; Capodici, Fulvio

    2015-10-01

    Two years of sea surface current measurements acquired since August 2012 by High-Frequency SeaSonde radars over the relatively shallow shelf area dividing the Maltese Islands from Sicily (the Malta - Sicily Channel), are used to characterize the surface tidal currents in the region. Tidal currents are generally weak and concentrated in the semidiurnal and diurnal bands, barely exceeding 3 cm s-1 in the semidiurnal band (M2, S2), and below 6 cm s-1 in the diurnal band (K1, O1). In the middle part of the basin, the M2 currents oscillate along the main Channel axis; on the contrary the S2 oscillations are oriented along the energetic Atlantic Ionian Stream (AIS) flow. Diurnal tides have a more circular pattern, also following the AIS path and with a significant intensification in proximity of the shelf break, thus suggesting a substantial contribution from internal tides in the region. Phase contours suggest the presence of amphidromic points for both the semidiurnal and diurnal constituents, located in the central area of the Channel for S2, O1 and K1, but slightly shifted towards north-west for the M2 component.

  12. Research Spotlight: What controls the shape of sediment channels in river deltas?

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-03-01

    When turbulent, sediment-filled rivers empty into oceans and lakes, the channels often divide repeatedly to form triangular deltas. Some channels, however, travel long distances before bifurcating, creating elongated channels. Understanding how these patterns arise could be useful for designing wetland restoration schemes on river deltas. Seeking to explain the conditions under which elongated channels form, Falcini and Jerolmack considered an analogy with cold filaments in ocean currents, in which high potential vorticity (a measure that combines the rotation of a flow with its thermal gradient) helps a filament hold a coherent structure over long distances. The researchers introduced a model that incorporates sediment concentration and fluid vorticity, to derive a new “potential vorticity” equation that describes sedimentation patterns at the river mouth. Their model shows that a high potential vorticity is needed for the creation of elongated channels, and their comparison to modeling, laboratory, and field studies confirms that potential vorticity is a primary control on channel morphology. The new model could help to understand the shape of the iconic Mississippi River delta and may aid in the design of proposed channel diversions there and in other deltas. (Journal of Geophysical Research-Earth Surface, doi:10.1029/2010JF001802, 2010)

  13. 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

  14. Fish species from a micro-tidal delta in the Caribbean Sea.

    PubMed

    Correa-Herrera, T; Jiménez-Segura, L F; Barletta, M

    2016-07-01

    A total of 66 fish species belonging to 32 families were recorded between November 2012 and April 2014 in the southern arm of the delta to the Atrato River. Total length (LT ; range: 1·7-48 cm), total mass (MT ), LT and MT relationships (b values ranged from 1·8 to 3·7, mostly with negative allometric growth), and LT frequency (for 25 species) were estimated for freshwater, estuarine and marine species. LT and MT of Porichthys pauciradiatus and Membras argentea are given for the first time and maximum LT records for 14 species exceed those in the literature. PMID:27401485

  15. Patterns of flow and sedimentation in channels with variable tidal and fluvial influence: observations from coastal Georgia.

    NASA Astrophysics Data System (ADS)

    Hughes, Z. J.; Howes, N. C.; Georgiou, I. Y.; FitzGerald, D.

    2014-12-01

    Significant differences exist between the sedimentology of fluvial and tidal channels. This is primarily the result of differences in the temporal and spatial patterns of the hydrodynamics, and, where the regimes overlap, complex interactions between the two. In this detailed study, we investigate flow and resulting sedimentation in six tidal meander bends with varying levels of fluvial influence. Tidal currents were recorded using a combination of continuous deployments and vessel-based synoptic measurements. Residual circulation patterns and estimates of tidal asymmetry were determined. A series of cores, taken along transects both parallel and perpendicular to the channel, were used to examine the spatial variation of mud and sand deposits. We observed a separation of flow into ebb and flood pathways, creating a residual circulation and encouraging the growth of point bars. At our study sites, the majority of the channels were found to be ebb dominant. At several tidal sites, we identified regions of the channel where the flow remained close to zero throughout much of the tidal cycle. This occurred in sections of the channel that were primarily active during the flood tide. In these areas, settling of fine sediment was not limited to slack water periods as is common to most systems and, instead, could occur over longer periods. This translated to sandier sediments being observed in parts of the channel that were primarily active during the ebb tide, compared to muddier sediments where the channel only was active during flood tides. In regions where there was a greater fluvial influence, flow reversal during flood tides was reduced, and the timing of slack water was altered. At the upstream limit of our observations, minimal flow reversal was observed during the tide and the current slowed to zero (slack) only once per tidal cycle (during the flood). Although water levels at this site indicated that the tidal wave was strongly flood dominated due to shallow water

  16. Quantifying the transition from fluvial- to wave-dominance for river deltas with multiple active channels

    NASA Astrophysics Data System (ADS)

    Nienhuis, J.; Ashton, A. D.; Giosan, L.

    2012-12-01

    The plan-view morphologies of fluvial- and wave-dominated deltas are clearly distinctive, but transitional forms are numerous. A quantitative, process-based description of this transition remains unexplored, particularly for river deltas with multiple active channels. Previous studies focused on general attributes of the fluvial and marine environment, such as the balance between wave energy and river discharge. Here, we propose that the transition between fluvial and wave dominance is directly related to the magnitude of the fluvial bedload flux to the nearshore region versus the alongshore sediment transport capacity of waves removing sediment away from the mouth. In the case of a single-channel delta, this balance can be computed for a given distribution of waves approaching shore. Fluvial dominance occurs when fluvial sediment input exceeds the wave-sustained maximum alongshore sediment transport for all potential shoreline orientations both up- and downdrift of the river mouth. However, deltaic channels have the tendency to bifurcate with increasing fluvial strength. Initial bifurcation splits the fluvial sediment flux among individual channels, while the potential sediment transport by waves remains constant for both river mouths. At higher bifurcation orders, multiple channels interact with each other alongshore, a situation more complicated than the single channel case and one that cannot be simple addressed analytically. We apply a model of plan-view shoreline evolution to simulate the evolution of a deltaic environment with multiple active channels. A highly simplified fluvial domain is represented by deposition of sediment where channels meet the coast. We investigate two scenarios of fluvial delivery. The first scenario deposits fluvial sediment alongshore on a self-similar predefined network of channels. We analyze the effects of different network geometrical parameters, such as bifurcation length, bifurcation angle, and sediment partitioning. In the

  17. Genistein potentiates wild-type and delta F508-CFTR channel activity.

    PubMed

    Hwang, T C; Wang, F; Yang, I C; Reenstra, W W

    1997-09-01

    Effects of genistein on wild-type (wt) and delta F508-cystic fibrosis transmembrane conductance regulator (CFTR) were studied in NIH/3T3 cells stably transfected with wt or mutant CFTR cDNA. As measured by I- efflux, half-maximal concentration of agonist (K1/2) for forskolin-dependent activation was greater for delta F508-CFTR than wt-CFTR. Genistein decreased the K1/2 for both forms of the channel and increased the maximal activity of delta F508-CFTR by 3.7-fold. In cell-attached patches, 10 microM forskolin induced minimal delta F508-CFTR activity with characteristic prolonged closed times (estimated time constant, > 30 s). Genistein increased the forskolin-induced macroscopic currents of wt-CFTR and delta F508-CFTR by 3- and 19-fold, respectively. Variance analysis suggested that in the presence of forskolin and genistein the open probabilities (Po) of wt- and delta F508-CFTR were identical. In single-channel studies, at maximal adenosine 3',5'-cyclic monophosphate (cAMP) stimulation, genistein increased the Po of wt-CFTR by prolonging the open time, but, at submaximal cAMP stimulation, the Po was increased by prolonging the open time and shortening the closed time. In excised patches with CFTR channels preactivated in the cell-attached mode, genistein increased ATP-dependent wt- and delta F508-CFTR current about twofold by prolonging the open time. Our results thus suggest that phosphorylation-dependent activation of delta F508-CFTR is defective and that genistein corrects this defect at least in part by binding to the CFTR protein. PMID:9316420

  18. The morphology and evolution of channels on the Wax Lake Delta, Louisiana, USA

    NASA Astrophysics Data System (ADS)

    Shaw, John B.; Mohrig, David; Whitman, Spencer K.

    2013-09-01

    deltas are classic depositional systems, but a growing body of literature shows that their channel networks can be erosional. Furthermore, this erosion can attack channel beds of consolidated mud that acts as bedrock. To better understand the channel networks of natural deltas and engineered river diversions, we investigate bathymetric and planimetric change, bed cover, and sediment transport in the Wax Lake Delta (WLD) in coastal Louisiana, USA. Channels have eroded up to 40% of modern flow depth between the WLD's initiation in 1973 and 1999. Aerial image analysis shows that channels have widened by 11% between 1991 and 2009, forcing the downstream migration of islands. Channel beds are composed of 85-98% muddy bedrock, with the remainder covered by alluvial sands. Water velocity, grain size, and suspended sand concentration measurements during the 2009 spring flood show that almost all available grain sizes are transported in suspension. Flow was supply limited during this period, with the calculated sand concentration at the height of the bed load layer is 1-4 orders of magnitude smaller than predicted for saturated sand transport. We test "the cover effect" and "the tools effect" previously proposed for bedrock erosion in upland river channels. Bedrock erosion and alluvial cover are anti-correlated (the cover effect), but the observations do not closely follow previously proposed relationships. The difference in erosion rate between clear water and sand-rich water shows that abrasion by sand (the tools effect) accounts for 51% ± 56% of bedrock erosion when it is present.

  19. Soil Phosphorus Forms and Profile Distributions in the Tidal River Network Region in the Yellow River Delta Estuary

    PubMed Central

    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. PMID:24971393

  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. Partitioning of Water Discharge by Distributary Channels in the Prograding, Wax Lake Delta, Coastal Louisiana, USA

    NASA Astrophysics Data System (ADS)

    Buttles, J.; Mohrig, D.; Nittrouer, J.; McElroy, B.; Baitis, E.; Allison, M.; Paola, C.; Parker, G.; Kim, W.

    2007-12-01

    How water and sediment is routed through distributary networks on river deltas is incompletely known and a topic of much active research. We have undertaken a study to determine the controls on partitioning of water and sediment discharge in distributary channels of the Wax Lake Delta and to connect these transport processes to the land building associated with the growth of islands that separate distributary channels from each other. Here we present first results from the field project that defines how water from the upstream primary channel is partitioned between the first set of five distributary channels. Measurements of water discharge and channel bathymetry were collected using a 22-ft research vessel equipped with an acoustic Doppler velocity profiler, a swath bathymetry profiler and dual differential GPS antennas. Wax Lake Delta is situated at the downstream end of Wax Lake Outlet, a man-made channel that diverts water and sediment from the lower Atchafalaya River, roughly 20 km upstream from Morgan City, LA. The subaerial delta has been building out into Atchafalaya Bay since roughly 1973 with a delta-front advance rate of about 0.27 km/yr. Associated with this growth has been development of a distributary network of channels that continues to evolve as the delta progrades seaward. Measurements collected in May, 2007 define properties of the upstream channel and the first set of five distributary channels. Characteristic width, depth and water discharge for the upstream channel are 420 m, 21.2 m, and 2900 m3/s. Characteristic values for width, depth and water discharge for the five distributary channels are 1) 270 m, 6.7 m, and 310 m3/s, 2) 300 m, 6.5 m, and 350 m3/s, 3) 650 m, 6.8 m, and 820 m3/s, 4) 395 m, 6.5 m, and 560 m3/s, and 5) 440 m, 6.0 m, and 440 m3/s. These data highlight a number of interesting points regarding the initial set of bifurcations. First, the transition from one to five channels is associated with a two-thirds reduction in

  2. 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

  3. Morphodynamic equilibrium in straight tidal channels: Combined effects of the Coriolis force and external overtides

    NASA Astrophysics Data System (ADS)

    Schramkowski, G. P.; de Swart, H. E.

    2002-12-01

    A new physical mechanism that is potentially relevant for the equilibrium morphodynamics of tide-dominated estuaries and in understanding the occurrence of lateral shoals in these systems is identified. The mechanism acts in relatively straight and wide channels (width of the order of the horizontal tidal excursion length) in which both external overtides and the Coriolis force affect sediment transport. This is investigated by analyzing an idealized model, which consists of the 3D shallow water equations, mass conservation for suspended load, and a bed evolution equation. The model is forced by a prescribed depth-averaged tidal current. It is demonstrated that, when viewed in the direction of the flood flow, a flood (ebb)-dominant current generates a net cross-sectional sediment transport to the left (right) in the Northern Hemisphere. A morphodynamic equilibrium is established by a counteracting dispersive sediment flux, generated by shear stresses that increase toward shallower water. This dispersive flux is much larger than the flux due gravitational downslope effects. The equilibrium bed profile has a constant slope in the lateral direction that varies as cos(φ), where φ is the phase difference between the M2 and M4 external horizontal tide. Hence, the smallest depths are found on the left (right) in case of a flood (ebb)-dominant current. Typical cross-channel depth differences may be as large as several meters. Velocity data collected in the Dutch Western Scheldt estuary are used to tune the hydrodynamic parameters in the model. Analysis of the bathymetric data seems to confirm the qualitative results of the model.

  4. 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.

  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. An overview on selected Middle Miocene slope channel complexes, offshore east Nile Delta of Egypt

    NASA Astrophysics Data System (ADS)

    F. Sharaf, Essam; Khaled, Khaled A.; Abushady, Ahmed I.

    2015-12-01

    Middle Miocene turbidite channel reservoirs offshore Nile Delta of Egypt are difficult to develop efficiently. The depositional mechanism of these channels defines sand bodies with variable thickness and quality over short distances. Akhen Field is a turbidite high pressure and high temperature reservoir offshore in the East Nile Delta, Egypt. The turbidite deposits at Akhen area reflect varied depositional fabrics from poorly to moderately sorted and non-graded to graded. Well logs and core data suggest at least 3 sand packages in a cyclic pattern. Each package exhibits variable sedimentological and petrophysical properties and forms a separate reservoir, sealed by shale. A conceptual geologic model showing facies geometry based on 3D seismic mapping and core analysis was used for evaluation of the reservoir quality of the Field. Integrating sedimentologic and other subsurface data such as seismic attributes, pressure data, core analysis, was crucial to predict the fluid flow between the different reservoir units.

  8. 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

  9. Tidal Forms

    NASA Astrophysics Data System (ADS)

    Bolla Pittaluga, M.; Seminara, G.; Tambroni, N.

    2003-04-01

    We give an overview of some recent investigations on the mechanics of the processes whereby forms develop in tidal environments. The viewpoint taken here is mechanistic. Some of the questions which deserve an answer may be summarised as follows: i) do tidal channels tend to some altimetric long term equilibrium? ii) why are they typically convergent and weakly meandering? iii) how is such equilibrium affected by the hydrodynamics and morphodynamics of tidal inlets? iv) what is the hydrodynamic and morphodynamic role played by tidal flats adjacent to the channels? Some of the above questions have received a considerable attention in the last few years. Schuttelaars and de Swart (1996), Lanzoni and Seminara (2002) and, more recently, Bolla Pittaluga (2003) have investigated the first problem. In particular, the latter two contributions have shown that a straight tidal channel connected to a tidal sea at one end and closed at the other end tends to reach a long term equilibrium profile, which is slightly concave seaward and convex landward where a beach forms. The equilibrium profile is strongly sensitive to the harmonic content of the tidal forcing as well as to the value of sediment concentration established by the coastal hydrodynamics in the far field of the inlet region. Less important are the effect of channel convergence and the role of settling lag in the transport of suspended load. Insufficient attention has been devoted to the understanding of what mechanisms control channel convergence and meandering, though some similarities and differences between tidal and fluvial channels have emerged from some recent works. In particular, free bars form in tidal channels due to an instability mechanism essentially similar to that occurring under steady conditions though the oscillatory character of the flow field makes the bar pattern non migrating (Seminara and Tubino, 2001). Similarly, forced bars in curved tidal channels are driven by the development of

  10. 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.

  11. Modeling bed shear-stress fluctuations in a shallow tidal channel

    NASA Astrophysics Data System (ADS)

    Mathis, R.; Marusic, I.; Cabrit, O.; Jones, N. L.; Ivey, G. N.

    2014-05-01

    Recently, Mathis et al. (2013) developed a model for predicting the instantaneous fluctuations of the wall shear-stress in turbulent boundary layers. This model is based on an inner-outer scale interaction mechanism, incorporating superposition, and amplitude-modulation effects, and the only input required for the model is a time series measurement of the streamwise velocity signal taken in the logarithmic region of the flow. The present study applies this new approach for the first time to environmental flows, for which the near-bed information is typically inaccessible. The data used here are acoustic Doppler velocimeter time series measurements from a shallow tidal channel (Suisun Slough in North San Francisco Bay). We first extract segments of data sharing properties with canonical turbulent boundary layers. The wall (bed) shear-stress model is then applied to these selected data. Statistical and spectral analysis demonstrates that the field data predictions are consistent with laboratory and DNS results. The model is also applied to the whole available data set to demonstrate, even for situations far from the canonical boundary layer case, its ability to preserve the overall Reynolds number trend. The predicted instantaneous bed stress is highly skewed and amplitude modulated with the variations in the large-scale streamwise velocity. Finally, the model is compared to conventional methods employed to predict the bed shear-stress. A large disparity is observed, but the present model is the only one able to predict both the correct spectral content and the probability density function.

  12. 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.

  13. 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

  14. 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. PMID:23319708

  15. Immunostaining of rat brain, spinal cord, sensory neurons and skeletal muscle for calcium channel alpha2-delta (alpha2-delta) type 1 protein.

    PubMed

    Taylor, C P; Garrido, R

    2008-08-13

    Alpha2-delta (alpha2-delta) is a membrane-spanning auxiliary protein subunit of voltage-gated calcium channels found in muscle and brain. Of the four subtypes of alpha2-delta, only alpha2-delta types 1 and 2 (alpha2-delta-1 and alpha2-delta-2) bind the drugs gabapentin (Neurontin) and pregabalin (Lyrica). Although recent findings indicate that drug binding to alpha2-delta-1 is required for pharmacology of pregabalin and gabapentin, previous work has not addressed the location of alpha2-delta-1 protein within nervous tissues. A monoclonal antibody to alpha2-delta-1 revealed intense immunostaining in certain areas of rat brain, spinal cord, dorsal root ganglia, and skeletal muscle, with weaker staining in heart muscle, gut and liver. Little immunostaining was seen in spleen, kidney, thymus and lung. Staining was dense in some regions of the CNS including spinal dorsal horn, anterior olfactory nucleus, anterior amygdala, basolateral (ventral) amygdala and cortical amygdala, and the piriform, perirhinal, insular and entorhinal cortices. In hippocampus, staining was heterogeneous with greater density in areas of glutamate terminals (mossy fiber endings on CA3 pyramidal cells and perforant path endings on granule cells and CA1 stratum radiatum). Moderate staining occurred in the lateral posterior nucleus of the thalamus, superficial layers of neocortex, periaqueductal gray, substantia nigra, stria terminalis, nucleus accumbens shell and tegmental nucleus. We propose that areas of dense alpha2-delta-1 staining in brain and spinal cord are likely sites of action for the analgesic, anticonvulsant and anxiolytic-like actions of pregabalin and gabapentin in animal models. PMID:18616987

  16. Upper Devonian deposystems of Catskill delta, West Virginia

    SciTech Connect

    Donaldson, A.C.; Lewis, J.S.; Mumcuoglu, C.; Boswell, R.; Peace, K.; Jewell. G.

    1984-12-01

    The oil and gas reservoir rocks of the Upper Devonian of West Virginia were deposited as shoreline sands along a coastal plain characterized by marine-dominant deltas (Catskill delta complex). The oil-bearing sandstones occur in strike trend (north-south) in north-central West Virginia connected by feeder channel sandstones with dip trends (east-west). In outcrop, the strike-trending sanstones contain occasional marine fossils, are well sorted, and exhibit sedimentary structures that suggest depositional environments ranging from shoreface to tidal delta and back barrier. Channel sandstones with herringbone bedding suggest tidal influence. These beds change to cross-bedding of unidirectional paleoflow origin in upstream fluvial counterparts of red-bed facies. The interpreted fluvial and tidal channels combine to represent distributary channels that supplied the sands to the barrier islands and delta front. Isolith maps show anastomosing belts trending east-west with both vertical and offset stacking. Stream avulsion and stream piracy probably account for lateral shifting of tidally influenced river distributaries. Gridlike patterns of sandstone belts result from the dynamic interference of tidal-fluvial channels with wave-constructed shoreline barrier islands and bars, complicated by onlap and offlap cycles. Subsurface informally named oil and gas sands generally are multiple sandstones.

  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. Analytical and numerical analysis of tides and salinities in estuaries; part II: salinity distributions in prismatic and convergent tidal channels

    NASA Astrophysics Data System (ADS)

    Kuijper, Kees; van Rijn, Leo C.

    2011-11-01

    Estuaries, commonly, are densely populated areas serving the needs of the inhabitants in multiple ways. Often the interests are conflicting and decisions need to be made by the local managers. Intake of fresh water for consumption, agricultural purposes or use by industries may take place within a region not far landward of the limit of salt intrusion. Human interventions (e.g. deepening of the navigation channels) or climate changes (sea level rise, reduction of the river discharge) can bring these intake locations within the reach of saline or brackish water and consequently endanger their function. To support policy and managerial decisions, a profound knowledge of processes associated with the salinity structure in estuaries is required. Although nowadays advanced numerical three-dimensional models are available that are able to cope with the complexity of the physics there is still a need for relatively simple tools for quick-scan actions in a pre-phase of a project or for instructive purposes. The analytical model described in this paper may serve these needs. It computes the maximum salinity distribution using the dispersion coefficient in the mouth as the only model parameter. The model has been calibrated using observational data in a large number of estuaries and experimental data in a tidal flume. The dispersion coefficient was successfully related to geometric and hydrodynamic parameters resulting in an expression that can be used for convergent estuaries as well as prismatic channels, see Eqs. 25a and 25b. Application of the model in a predictive mode showed its promising capabilities. Comparison with three-dimensional numerical models indicates that the channel geometry in the estuary mouth largely influences dispersive processes. The analytical model for salt intrusion may be used in combination with the analytical model for tidal propagation in convergent estuaries and tidal channels by Van Rijn (part I). In this way, input is obtained on the tidal

  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. 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.

  2. 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.

  3. Tide-dominated delta model for coal-bearing Wilcox strata in south Texas

    SciTech Connect

    Breyer, J.A.

    1984-04-01

    Coal-bearing Wilcox strata near Uvalde in south Texas are the deposits of a tide-dominated delta. The delta of the Klang and Langat Rivers, Malaysia, provides a modern analog for these strata. Five facies have been identified from a study of core and well logs: lignite; underclay; interbedded sand and mud with lenticular, wavy, and flaser bedding; ripple-laminated or cross-bedded sand; and greenish, very strongly bioturbated sand. On the Klang-Langat delta, the modern equivalents of these facies are peat formed in fresh water swamps; root horizons developed beneath the peat; interbedded sand and mud deposited on tidal flats; channel sands; and shallow marine sand and mud. Tidal flat deposits are the most abundant type of sediment on the Klang-Langat delta and in the coal-bearing Wilcox strata. The tidal flats of the modern delta are crossed by small tidal creeks and by larger tidal streams. The tidal channels are cut into tidal flat sediments and separate peat-forming areas. Channel sands in the Wilcox are cut into tidal flat deposits and form washouts in the lignite. Two types of channel-fill sand are present in the Wilcox, sands 5-15 ft (1.5-4.5 m) thick and sands more than 30 ft (9m) thick. The thinner sands, deposits of small tidal creeks, have sharp, erosive bases, fine upward and pass into interbedded sand and mud. The thicker sands have sharp tops as well as sharp bases and show no grain-size trends; they are fills of larger tidal streams.

  4. 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

  5. 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.

  6. Reservoir geology of Crystal Viking field, Lower Cretaceous estuarine tidal channel-bay complex, south-central Alberta

    SciTech Connect

    Reinson, G.E.; Clark, J.E.; Foscolos, A.E.

    1988-10-01

    The Lower Cretaceous Viking Formation in the Crystal field of south-central Alberta contains a linear sandstone body, as much as 30 m thick, that forms a complicated dual-pool hydrocarbon reservoir. This contrasts sharply with most other Viking reservoirs, which are much thinner, are commonly oriented northwest, and are composed of a single hydrocarbon pool. Thickness, orientation, and pool duality are attributed to the complicated depositional history of the Viking in the Crystal region. The sandstone body is interpreted as a multistage tidal channel-fill deposit within a larger estuarine channel-bay complex, which rests unconformably on inner shelf-lower shoreface facies. A major lowstand of sea level that occurred approximately 97 m.y. ago is believed to be responsible for incisement of the estuarine valley, which was filled during rising sea level. A depositional model of progressive estuarine valley fill under transgressive conditions readily accounts for the occurrence of two hydrodynamically separated oil pools, and also for differences in reservoir continuity and performance trends within the main oil-bearing A pool. Highly productive wells in the main pool correspond to specific channel-fill deposits, or are situated in areas where deposits of successive channel stages are highly superimposed. Conversely, marginally productive wells and poor reservoir communication between producing wells occur in areas where the different channel-stage deposits diverge. 22 figures, 2 tables.

  7. Study of performance scaling of 22-nm epitaxial delta-doped channel MOS transistor

    NASA Astrophysics Data System (ADS)

    Sengupta, Sarmista; Pandit, Soumya

    2015-06-01

    Epitaxial delta-doped channel (EδDC) profile is a promising approach for extending the scalability of bulk metal oxide semiconductor (MOS) technology for low-power system-on-chip applications. A comparative study between EδDC bulk MOS transistor with gate length Lg = 22 nm and a conventional uniformly doped channel (UDC) bulk MOS transistor, with respect to various digital and analogue performances, is presented. The study has been performed using Silvaco technology computer-aided design device simulator, calibrated with experimental results. This study reveals that at smaller gate length, EδDC transistor outperforms the UDC transistor with respect to various studied performances. The reduced contribution of the lateral electric field in the channel plays the key role in this regard. Further, the carrier mobility in EδDC transistor is higher compared to UDC transistor. For moderate gate and drain bias, the impact ionisation rate of the carriers for EδDC MOS transistor is lower than that of the UDC transistor. In addition, at 22 nm, the performances of a EδDC transistor are competitive to that of an ultra-thin body silicon-on-insulator transistor.

  8. Mapping the Transverse Structure of Tidal Velocity in the Channel of a Saltmarsh Creek

    NASA Astrophysics Data System (ADS)

    Armstrong, S. J.; Arega, F.; Styles, R.

    2008-12-01

    The tidal exchange through the Scott Creek saltmarsh estuary was measured near Big Bay Creek, in Edisto, South Carolina. The techniques used for data collection stemmed from those recommended in previous studies. A bottom-mounted ADCP was used to sample data for 35 days, from the thalweg. A vessel-mounted ADCP was used for 13- hour durations, repeatedly surveying Scott Creek's 50m width. These surveys were performed during 4 different tidal cycles, capturing 1.2, 1.5, 2.3, and 2.4m amplitude events. Survey data were then spatially segregated into 3m wide bins along the transverse axis of the creek. Data in each bin were then depth-integrated, treated as distinct time series of data, and analyzed for 14 significant harmonic frequencies. Resultant constituents were used to construct individual time series for axial current speed through each transverse bin and were compared with both the bottom-mounted and vessel-mounted ADCP datasets. Correlations, between transversely segregated measurements and each constructed time series, averaged 0.88, and varied between 0.71 and 0.93. Standard deviations were 8-14cm/s. This effort was completed to provide both the boundary forcing function to drive a 2-D hydrodynamic model and the baseline to evaluate the effect of tidal restoration for the Scott Creek estuary.

  9. 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.

  10. 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

  11. 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

  12. Interplay between river discharge and tides in a delta distributary

    NASA Astrophysics Data System (ADS)

    Leonardi, Nicoletta; Kolker, Alexander S.; Fagherazzi, Sergio

    2015-06-01

    The hydrodynamics of distributary channels has tremendous impact on nutrient and dissolved oxygen circulation, transport of sediments, and delta formation and evolution; yet many processes acting at the river-marine interface of a delta are poorly understood. This paper investigates the combined effect of river hydrograph and micro-tides on the hydrodynamics of a delta distributary. As the ratio between river flow to tidal flow increases, tidal flood duration at the distributary mouth decreases, up to the point when flow reversal is absent. Field measurements in a distributary of the Apalachicola Delta, Florida, USA, reveal that, once the flow becomes unidirectional, high-discharge events magnify tidal velocity amplitudes. On the contrary, while the flow is bidirectional, increasing fluvial discharge decreases tidal velocity amplitudes down to a minimum value, reached at the limit between bidirectional and unidirectional flow. Due to the different response of the system to tides, the transition from a bidirectional to a unidirectional flow triggers a change in phase lag between high water and high water slack. In the presence of high riverine flow, tidal dynamics also promote seaward directed Eulerian residual currents. During discharge peaks, these residual currents almost double mean velocity values. Our results show that, even in micro-tidal environments, tides strongly impact distributary hydrodynamics during both high and low fluvial discharge regimes.

  13. 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.

  14. Tidal meanders

    NASA Astrophysics Data System (ADS)

    Marani, Marco; Lanzoni, Stefano; Zandolin, Diego; Seminara, Giovanni; Rinaldo, Andrea

    2002-11-01

    Observational evidence is presented on the geometry of meandering tidal channels evolved within coastal wetlands characterized by different tidal, hydrodynamic, topographic, vegetational and ecological features. New insight is provided on the geometrical 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 local 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 transitions 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 evolution 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 sensitive 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.

  15. 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.

  16. Differential Effects of Voltage-Gated Calcium Channel Blockers on Calcium Channel Alpha-2-Delta-1 Subunit Protein Mediated Nociception

    PubMed Central

    Chang, E.; Chen, X.; Kim, M.; Gong, N.; Bhatia, S.; Luo, Z.D.

    2014-01-01

    Background Overexpression of the voltage gated calcium channel (VGCC) alpha-2-delta1 subunit protein (Cavα2δ1) has been shown to cause pain states. However, whether VGCC are involved in pain states driven by abnormal Cavα2δ1 expression is not known. Methods Intrathecal injection of N-, P/Q-, and L-type VGCC blockers were tested in two models: a transgenic neuronal Cavα2δ1 overexpression (TG) model with behavioral hypersensitivity and a spinal nerve ligation (SNL) model with Cavα2δ1 overexpression in sensory pathways and neuropathy pain states. Results The nociceptive response to mechanical stimuli was significantly attenuated in both models with ω-conotoxin GVIA (an N-type VGCC blocker) and nifedipine (a L-type VGCC blocker), in which ω-conotoxin GVIA appeared more potent than nifedipine. Treatments with ω-agatoxin IVA (P-VGCC blocker), but not ω-conotoxin MVIIC (Q-VGCC blocker) had similar potency in the TG model as the N-type VGCC blocker, while both ω-agatoxin IVA and ω-conotoxin MVIIC had minimal effects in the SNL model compared to controls. Conclusion These findings suggest that, at the spinal level, N- and L-type VGCC are likely involved in behavioral hypersensitivity states driven by Cavα2δ1 overexpression. Q-type VGCC have minimal effects in both models. The anti-nociceptive effects of P-type VGCC blocker in the Cavα2δ1 TG mice, but minimally at the SNL model with presynaptic Cavα2δ1 upregulation, suggest that its potential action site(s) is at the post-synaptic and/or supraspinal level. These findings support that N-, L- and P/Q-type VGCC have differential contributions to behavioral hypersensitivity modulated by Cavα2δ1 dysregulation at the spinal cord level. PMID:25158907

  17. 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.

  18. 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

  19. 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

  20. Water and suspended sediment division at a stratified tidal junction

    NASA Astrophysics Data System (ADS)

    Buschman, F. A.; Vegt, M.; Hoitink, A. J. F.; Hoekstra, P.

    2013-03-01

    Tidal junctions play a crucial role in the transport of water, salt, and sediment through a delta distributary network. Water, salt and sediment are exchanged at tidal junctions, thereby influencing the transports in the connecting branches and the overall dynamics of the system. This paper presents observations of water, salt and sediment transports in three channels that connect at a stratified tidal junction. Flow variation in one channel was found to lag behind flow variation in a connected channel by more than 1 h, which is largely attributed to channel length differences from the junction to the sea. The water columns in the three channels were periodically stratified during spring tide, whereas the salinity structure represented a salt wedge during neap tide. Salinity differences between the three channels were substantial. The channels contain water bodies of different salinity and act largely independently. Flow velocities in the upper and lower layers differed substantially. Flow in the lower layer was generally in the direction of acceleration produced by the baroclinic pressure gradient. Interestingly, baroclinic pressure gradients were sometimes directed landward, indicating the presence of saltier water at the land side of the estuary. In sharp channel bends close to the junction, secondary flow was strongest at the highest axial flow velocity during spring tide. In one channel bend, these circulations steered the suspended sediment toward the inner bend, which affected the suspended sediment division.

  1. Aromatic Residues {epsilon}Trp-55 and {delta}Trp-57 and the Activation of Acetylcholine Receptor Channels.

    PubMed

    Bafna, Pallavi A; Jha, Archana; Auerbach, Anthony

    2009-03-27

    The two transmitter binding sites of the neuromuscular acetylcholine (ACh) receptor channel contain several aromatic residues, including a tryptophan located on the complementary, negative face of each binding pocket. These two residues, Trp-55 in the epsilon subunit and Trp-57 in the delta subunit, were mutated (AEFHILRVY), and for most constructs the rate constants for acetylcholine binding and channel gating were estimated by using single channel kinetic analyses. The rate constants for unliganded channel opening and closing were also estimated for some mutants. From these measurements we calculated all of the equilibrium constants of the "allosteric" cycle as follows: diliganded gating, unliganded gating, dissociation from the C(losed) conformation, and dissociation from the O(pen) conformation. The results indicate the following. (i) These aromatic side chains play a relatively minor role in ACh receptor channel activation. (ii) The main consequence of mutations is to reduce the affinity of the O conformation of the binding site for ACh, with the effect being greater at the epsilon subunit. (iii) In epsilon (but not delta) the aromatic nature of the side chain is important in determining affinity, to a slightly greater degree in the O conformation. Phi value analyses (of both tryptophan residues) show Phi approximately 1 for both the ACh binding and diliganded gating reactions. (iv) This suggests that the structural boundaries of the dynamic elements of the gating conformational change may not be subunit-delimited, and (v) the mutated tryptophan residues experience energy changes that occur relatively early in both the ligand-binding and channel-gating reactions. PMID:19171937

  2. 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.

  3. 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

  4. 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.

  5. delta-Opioid receptors are more efficiently coupled to adenylyl cyclase than to L-type Ca(2+) channels in transfected rat pituitary cells.

    PubMed

    Prather, P L; Song, L; Piros, E T; Law, P Y; Hales, T G

    2000-11-01

    Opioid receptors often couple to multiple effectors within the same cell. To examine potential mechanisms that contribute to the specificity by which delta-receptors couple to distinct intracellular effectors, we stably transfected rat pituitary GH(3) cells with cDNAs encoding for delta-opioid receptors. In cells transfected with a relatively low delta-receptor density of 0.55 pmol/mg of protein (GH(3)DOR), activation of delta-receptors produced inhibition of adenylyl cyclase activity but was unable to alter L-type Ca(2+) current. In contrast, activation of delta-receptors in a clone that contained a higher density of delta-receptors (2.45 pmol/mg of protein) and was also coexpressed with mu-opioid receptors (GH(3)MORDOR), resulted in not only the expected inhibition of adenylyl cyclase activity but also produced inhibition of L-type Ca(2+) current. The purpose of the present study was to determine whether these observations resulted from differences in delta-opioid receptor density between clones or interaction between delta- and mu-opioid receptors to allow the activation of different G proteins and signaling to Ca(2+) channels. Using the delta-opioid receptor alkylating agent SUPERFIT, reduction of available delta-opioid receptors in GH(3)MORDOR cells to a density similar to that of delta-opioid receptors in the GH(3)DOR clone resulted in abolishment of coupling to Ca(2+) channels, but not to adenylyl cyclase. Furthermore, although significantly greater amounts of all G proteins were activated by delta-opioid receptors in GH(3)MORDOR cells, delta-opioid receptor activation in GH(3)DOR cells resulted in coupling to the identical pattern of G proteins seen in GH(3)MORDOR cells. These findings suggest that different threshold densities of delta-opioid receptors are required to activate critical amounts of G proteins needed to produce coupling to specific effectors and that delta-opioid receptors couple more efficiently to adenylyl cyclase than to L-type Ca(2

  6. 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.

  7. CFTR gating I: Characterization of the ATP-dependent gating of a phosphorylation-independent CFTR channel (DeltaR-CFTR).

    PubMed

    Bompadre, Silvia G; Ai, Tomohiko; Cho, Jeong Han; Wang, Xiaohui; Sohma, Yoshiro; Li, Min; Hwang, Tzyh-Chang

    2005-04-01

    The CFTR chloride channel is activated by phosphorylation of serine residues in the regulatory (R) domain and then gated by ATP binding and hydrolysis at the nucleotide binding domains (NBDs). Studies of the ATP-dependent gating process in excised inside-out patches are very often hampered by channel rundown partly caused by membrane-associated phosphatases. Since the severed DeltaR-CFTR, whose R domain is completely removed, can bypass the phosphorylation-dependent regulation, this mutant channel might be a useful tool to explore the gating mechanisms of CFTR. To this end, we investigated the regulation and gating of the DeltaR-CFTR expressed in Chinese hamster ovary cells. In the cell-attached mode, basal DeltaR-CFTR currents were always obtained in the absence of cAMP agonists. Application of cAMP agonists or PMA, a PKC activator, failed to affect the activity, indicating that the activity of DeltaR-CFTR channels is indeed phosphorylation independent. Consistent with this conclusion, in excised inside-out patches, application of the catalytic subunit of PKA did not affect ATP-induced currents. Similarities of ATP-dependent gating between wild type and DeltaR-CFTR make this phosphorylation-independent mutant a useful system to explore more extensively the gating mechanisms of CFTR. Using the DeltaR-CFTR construct, we studied the inhibitory effect of ADP on CFTR gating. The Ki for ADP increases as the [ATP] is increased, suggesting a competitive mechanism of inhibition. Single channel kinetic analysis reveals a new closed state in the presence of ADP, consistent with a kinetic mechanism by which ADP binds at the same site as ATP for channel opening. Moreover, we found that the open time of the channel is shortened by as much as 54% in the presence of ADP. This unexpected result suggests another ADP binding site that modulates channel closing. PMID:15767295

  8. 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

  9. Nutrition literacy status and preferred nutrition communication channels among adults in the Lower Mississippi Delta.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Our objective was to explore cultural perceptions of the MyPyramid key messages and identify factors that may impact adoption of these recommendations. Participants were 23 adults, primarily African American females, residing in the Lower Mississippi Delta. When asked to identify good reasons to fol...

  10. 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

  11. 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.

  12. Interactions of Growth-faulting with Incised Valleys and Channels on the Late Miocene to Recent Mississippi River Delta, LA

    NASA Astrophysics Data System (ADS)

    Armstrong, C. P.; Mohrig, D.; Steel, R. J.

    2011-12-01

    The interaction between incised valleys and growth-fault related subsidence is poorly understood in the Late Miocene to Recent Mississippi River Delta. Previous work has found little evidence that growth-faults are able to affect the course or geometry of small (< 200m in width and 20m in depth) channels. However, the relationship between growth-faults and larger scale valleys (> 1km in width and 25m in depth) has not been previously evaluated in this area. We use a 1400 km2 3D seismic volume located under Breton Sound, LA, integrated with a selection of well logs to document the effect of growth-faults on 12 valleys and 14 channels present within the upper 1.5 kilometers of the seismic volume. In contrast to the majority of smaller distributary channels found within the survey, valleys appear to be steered along or away from growth-faults. This observation suggests that faults are able to affect the course of valleys to a greater extent than small channels. We suggest that this is because valleys are long lived features which do not avulse before being influenced by shorter time scale faulting events. This study contributes to our understanding of the dynamics of growth-faults and valleys in the subsurface and has important long term societal implications for populations living near large rivers in areas with active growth-faulting.

  13. Testing river surveying techniques in tidal environments: example from an actively meandering channel surveyed with TLS (Mont Saint-Michel bay, France)

    NASA Astrophysics Data System (ADS)

    Leroux, J.; Lague, D.

    2013-12-01

    Tidal channel developed in mega-tidal salt marsh offer a unique set of characteristics to study the interaction between hydraulics, riparian vegetation and sedimentation using Terrestrial Laser Scanner (TLS). The recession of water allows a nearly complete survey of the channel that is otherwise impossible in rivers. Moreover, the predictability of tide amplitude allows to target surveys large events. Finally, the hydro-sedimentary processes and peak flow velocities in excess of 2 m/s in mega-tidal estuaries (e.g. Mont Saint Michel (MSM) bay) allow to explore conditions that are similar to river during flood conditions. This has motivated a 3 years study of a sinuous tidal channel located on the fringe of the marsh with the aim to understand its dynamics at daily to annual scales. We have acquired 36 high resolution topographic surveys with TLS, whose 13 daily surveys were acquired during annual largest tides. A local reference network of targets is used to yield a high registration accuracy with uncertainty varying between 1.5 mm and 3.4 mm. We use the CANUPO algorithm for classifying riparian vegetation and ground in 3D data, and use the point cloud comparison algorithm M3C2 to resolve 3D topographic changes down to 5 mm. ADCP, ADV and a turbidimeter were installed to constrain flow velocities and suspended sediment concentration (SSC). Our analysis is focused on three active compartments: (1) the inner bar on which riparian pioneer vegetation is developing and where sedimentation reaches up to 5 cm/tide; (2) the actively eroding outer bank which exhibits local retreat rates up to 2 m/tide; (3) the channel itself for which we document fluctuations of up to 0.2 m in elevation at daily to monthly timescales. We find that High Water Level (HWL) is a good predictor of the mean rate of evolution of these compartments with different empirical relationships. Spatially averaged sedimentation on the inner bend tends to increase linearly with HWL and is increased by a

  14. 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

  15. Application of a Novel Automatic Erosion and Deposition Monitoring System at a Channel Bank Site on the Tidal River Trent, U.K.

    NASA Astrophysics Data System (ADS)

    Lawler, D. M.; West, J. R.; Couperthwaite, J. S.; Mitchell, S. B.

    2001-08-01

    There is a well-defined need to improve understanding of the dynamics of sediment erosion and deposition on intertidal channel banks, given their importance to channel stability, sediment budgets, depth maintenance, pollutant and nutrient transport, and ecological processes in estuarine systems. Conventional, manual methods for field monitoring of erosion and deposition, however, normally deliver information of low temporal resolution conditioned by infrequent field resurveys. To address this problem, this paper discusses a recently developed and improved automatic erosion and deposition monitoring technique, the Photo-Electronic Erosion Pin (PEEP) system, and its application to a tidal channel bank site at Burringham on the River Trent, U.K. The PEEP system allows the magnitude, frequency and timing of individual erosion and deposition events to be monitored much more precisely than with conventional manual methods. PEEP sensors also monitor light intensity and sediment temperature, variables which can influence bank stabilizing and destabilizing processes. Example results at both the event and spring-neap timescales are presented from a short PEEP system deployment between March and May 1997 at Burringham. These establish that discrete erosion events of >60 mm and 100 mm can occur in response to individual tidal cycles, events which are readily monitored automatically and quasicontinuously by the PEEP system. The capability of the PEEP approach to enhance temporal resolution of monitoring is demonstrated by the determination of the timing of the 100-mm bank erosion incident to an ' event window ' of 2·75 h: this converts to mean bank erosion rate of 36 mm h -1over the period of inundation. In addition, the PEEP system defines the magnitude and date of two example deposition events of 47 and 92 mm on the lower bank during a sequence of rising spring tides. These represent mean deposition rates of 4·5 and 8·4 mm h -1respectively over the periods of inundation

  16. Activation of peripheral delta opioid receptors eliminates cardiac electrical instability in a rat model of post-infarction cardiosclerosis via mitochondrial ATP-dependent K+ channels.

    PubMed

    Maslov, L N; Lishmanov, Yu B; Solenkova, N V; Gross, G J; Stefano, G B; Tam, S W

    2003-07-01

    The effects of the selective delta-1 (delta(1)) opioid receptor agonist, DPDPE, and the selective delta(2) opioid receptor agonist, DSLET, have been studied on the ventricular fibrillation threshold (VFT) in rats with an experimental post-infarction cardiosclerosis (CS). It has been found that CS induced a significant decrease in VFT. This CS-induced decrease in VFT was significantly reversed by intravenous administration of DPDPE (0.1 mg/kg) 10 min before VFT measurement. On the contrary, intravenous injection of DSLET (0.5 mg/kg) exacerbated the CS-induced cardiac electrical instability. Pretreatment with the selective delta opioid receptor antagonist, ICI 174,864 (0.5 mg/kg), completely abolished the changes in VFT produced by both DPDPE and DSLET. Previous administration of a nonselective peripherally acting opioid receptor antagonist, naloxone methiodide (5 mg/kg) also completely reversed the antifibrillatory action of DPDPE. Naloxone methiodide and ICI 174,864 alone had no effect on VFT. Pretreatment with the nonselective K(ATP) channel blocker, glibenclamide (0.3 mg/kg), or with the mitochondrial selective K(ATP) channel blocker, 5-hydroxydecanoic acid (5-HD, 5 mg/kg), completely abolished the DPDPE-induced increase in cardiac electrical stability. Glibenclamide and 5-HD alone had no effect on VFT. These results demonstrate that the delta opioid receptor plays an important role in the regulation of electrical stability in rats with post-infarction cardiosclerosis. We propose that peripheral delta(1) opioid receptor stimulation reverses CS-induced electrical instability via mitochondrial K(ATP) channels. On the contrary, delta(2) opioid receptor stimulation may exacerbate the CS-induced decrease in VFT. Further studies are necessary to determine the delta opioid receptor subtype which mediates the antifibrillatory effect of DPDPE and pro-fibrillatory effect of DSLET. PMID:12798419

  17. Functional properties of the CaV1.2 calcium channel activated by calmodulin in the absence of alpha2delta subunits.

    PubMed

    Ravindran, Arippa; Kobrinsky, Evgeny; Lao, Qi Zong; Soldatov, Nikolai M

    2009-01-01

    Voltage-activated CaV1.2 calcium channels require association of the pore-forming alpha1C subunit with accessory CaVbeta and alpha2delta subunits. Binding of a single calmodulin (CaM) to alpha1C supports Ca2+-dependent inactivation (CDI). The human CaV1.2 channel is silent in the absence of CaVbeta and/or alpha2delta. Recently, we found that coexpression of exogenous CaM (CaMex) supports plasma membrane targeting, gating facilitation and CDI of the channel in the absence of CaVbeta. Here we discovered that CaMex and its Ca2+-insensitive mutant (CaM1234) rendered active alpha1C/CaVbeta channel in the absence of alpha2delta. Coexpression of CaMex with alpha1C and beta2d in calcium-channel-free COS-1 cells recovered gating of the channel and supported CDI. Voltage-dependence of activation was shifted by approximately +40 mV to depolarization potentials. The calcium current reached maximum at +40 mV (20 mM Ca2+) and exhibited approximately 3 times slower activation and 5 times slower inactivation kinetics compared to the wild-type channel. Furthermore, both CaMex and CaM1234 accelerated recovery from inactivation and induced facilitation of the calcium current by strong depolarization prepulse, the properties absent from the human vascular/neuronal CaV1.2 channel. The data suggest a previously unknown action of CaM that in the presence of CaVbeta; translates into activation of the alpha2delta-deficient calcium channel and alteration of its properties. PMID:19106618

  18. Electrical resistivity mapping of the buried stream channel of the Canopic branch in the western Nile Delta, Egypt

    NASA Astrophysics Data System (ADS)

    El-Gamili, M. M.; Shaaban, F. F.; El-Morsi, O. A.

    1994-08-01

    Buried stream channels, which can often be mapped accurately by resistivity, are favoured targets for exploration. Horizontal profiling, electrical soundings, or both, are generally used. In the western Nile Delta, the electrical sounding method was applied using a Schlumberger electrode array with the maximum AB distance being 200 m. The field survey was conducted along profiles extending NE-SW, perpendicular to the expected historical Canopic buried stream channel. About 107 vertical electrical soundings (VES) were measured along eleven profiles. The (VES) field curves were interpreted using the automatic interpretation method of Zohdy and Bisdorf (1989) in which a layered model is obtained directly from a digitized sounding curve. The interpreted results were correlated with borehole data to delineate the main lithological units and to help construct geoelectrical cross-sections based on layer thicknesses and their corresponding ranges in litho-resistivity. The lithological information from borehole data, surface geology and the present layer resistivities indicate three major lithofacies: Holocene clay and silt at the top, Pleistocene sands, and then gravelly sands and gravels (El-Tahrir gravels) at the bottom. From the thickness of the riverine topmost clay-silt facies and the paleotopograph of the Pleistocene sands, the buried stream channels can be delineated. It is evident that two streams existed for the defunct Canopic branch. These defunct streams are discussed and correlated with the historical records.

  19. 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

  20. Tidal power

    SciTech Connect

    Hammons, T.J. )

    1993-03-01

    The paper reviews the physics of tidal power considering gravitational effects of moon and sun; semidiurnal, diurnal, and mixed tides; and major periodic components that affect the tidal range. Shelving, funneling, reflection, and resonance phenomena that have a significant effect on tidal range are also discussed. The paper then examines tidal energy resource for principal developments estimated from parametric modeling in Europe and worldwide. Basic parameters that govern the design of tidal power schemes in terms of mean tidal range and surface area of the enclosed basin are identified. While energy extracted is proportional to the tidal amplitude squared, requisite sluicing are is proportional to the square root of the tidal amplitude. Sites with large tidal amplitudes are therefore best suited for tidal power developments, whereas sites with low tidal amplitudes have sluicing that may be prohibitive. It is shown that 48% of the European tidal resource is in the United Kingdom, 42% in France and 8% in Ireland, other countries having negligible potential. Worldwide tidal resource is identified. Tidal barrage design and construction using caissons is examined, as are alternative operating modes (single-action generation, outflow generation, flood generation, two-way generation, twin basin generation, pumping, etc), development trends and possibilities, generation cost at the barrage boundary, sensitivity to discount rates, general economics, and markets. Environmental effects, and institutional constraints to the development of tidal barrage schemes are also discussed.

  1. The alpha-5 segment of Bacillus thuringiensis delta-endotoxin: in vitro activity, ion channel formation and molecular modelling.

    PubMed Central

    Gazit, E; Bach, D; Kerr, I D; Sansom, M S; Chejanovsky, N; Shai, Y

    1994-01-01

    A peptide with a sequence corresponding to the highly conserved alpha-5 segment of the Cry delta-endotoxin family (amino acids 193-215 of Bacillus thuringiensis CryIIIA [Gazit and Shai (1993) Biochemistry 32, 3429-3436]), was investigated with respect to its interaction with insect membranes, cytotoxicity in vitro towards Spodoptera frugiperda (Sf-9) cells, and its propensity to form ion channels in planar lipid membranes (PLMs). Selectively labelled analogues of alpha-5 at either the N-terminal amino acid or the epsilon-amine of its lysine, were used to monitor the interaction of the peptides with insect membranes. The fluorescent emission spectra of the 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD)-labelled alpha-5 peptides displayed a blue shift upon binding to insect (Spodoptera littoralis) mid-gut membranes, reflecting the relocation of the fluorescent probes to an environment of increased apolarity, i.e. within the lipidic constituent of the membrane. Moreover, midgut membrane-bound NBD-labelled alpha-5 peptides were protected from enzymic proteolysis. Functional characterization of alpha-5 has revealed that it is cytotoxic to Sf-9 insect cells, and that it forms ion channels in PLMs with conductances ranging from 30 to 1000 pS. A proline-substituted analogue of alpha-5 is less cytolytic and slightly more exposed to enzymic digestion. Molecular modelling utilizing simulated annealing via molecular dynamics suggests that a transbilayer pore may be formed by alpha-5 monomers that assemble to form a left-handed coiled coil of approximately parallel helices. These findings further support a role for alpha-5 in the toxic mechanism of delta-endotoxins, and assign alpha-5 as one of the transmembrane helices which form the toxic pore. The suggested role is consistent with the recent finding that cleavage of CryIVB delta-endotoxin in a loop between alpha-5 and alpha-6 is highly important for its larvicidal activity [Angsuthanasombat, Crickmore and Ellar (1993) FEMS

  2. Evolution of the Parnaíba Delta (NE Brazil) during the late Holocene

    NASA Astrophysics Data System (ADS)

    Szczygielski, Agata; Stattegger, Karl; Schwarzer, Klaus; da Silva, André Giskard Aquino; Vital, Helenice; Koenig, Juliane

    2015-04-01

    Sedimentary processes and the evolution of the wave- and tide-dominated, asymmetric Parnaíba Delta during the late Holocene were investigated based on geochemical and sedimentological analyses of sediment cores collected in 2010, as well as satellite images and historical maps. This is a rare case of pristine deltas essentially unaffected by human activities worldwide. The lowermost part of the main Parnaíba River distributary exhibits several low-sinuosity bends and several anastomosing bifurcation patterns in the east, whereas three NW-SE-oriented tidal channels drain a large mangrove area in the west. Dating of various materials in sediment cores from the tidal flats, tidal channels and supratidal marshes revealed that the oldest sediment (4,853 to 4,228 cal. years BP) is paleo-mangrove soil from the main river distributary. Present-day mangroves and marshes up to 200 years old exhibit high sedimentation rates reaching 3.4 cm/year. The asymmetry of the delta is explained not only by the wind- and wave-induced westward-directed longshore drift but also by neotectonic processes, as revealed by satellite images. Faulting and eastward tilting may have triggered delta lobe switching from west to east. This would explain the erosional character and unusual updrift orientation of the main river-mouth channel. Consistent with existing knowledge on mangrove ecosystems worldwide, sediment carbon and nitrogen signatures lie in the range of freshwater or marine dissolved organic carbon and C3 terrestrial plants. In the western tidal channels, the low Corg/Ntot ratios (16-21) of young mangrove soil (deposited in the last 16 years) reflect a stronger influence of marine plants compared to older mangroves (1,390-1,525 cal. years BP; ratios of 20-37). Thus, there would have been a greater influence of the Parnaíba River on tidal-channel sedimentology 1,400 to 1,500 years ago, entailing a natural connection between the present-day tidal channels and the river in ancient times

  3. The Role of Sea Level Rise and in Situ Carbonate Accumulation on the Morphodynamic Evolution of a Carbonate Tidal Channel. The Case of the Bahamas Islands.

    NASA Astrophysics Data System (ADS)

    Borhani, S.; Viparelli, E.; Imran, J.; Mahjabeen, N.; Abdo, K.; Kendall, C.; Rankey, E. C.

    2015-12-01

    We explore the problem of morphodynamic evolution of carbonate tidal channels, bounded seaward by the ocean and shoaling landward, as observed in coastal lagoons and estuaries. Governing model equations are the conservation of mass and momentum for the flow, and the conservation of sediment mass in the water column and in the bed deposit. We model carbonate accumulation in terms of a specified depth-dependent carbonate "production rate" based on modern rates of carbonate accumulation rate. We further assume that 1) there is no input of clastic sediments to the system, 2) cementation processes are slow when compared to carbonate accumulation, 3) there is an absence of particles in the silt/mud range, and 4) we treat the carbonate sediments as non-cohesive particles. Governing equations are integrated with finite volume for unsteady, two-dimensional, depth averaged shallow-water flow over arbitrary topography. This method is known to capture sharp fronts accurately. We use Roe's approximate Riemann solver for the computation of fluxes at the interfaces between one finite volume and the other. For second order accuracy we implement MUSCL (Monotone Upstream Scheme for Conservation Laws) and a predictor-corrector time stepping scheme. We validate the model at field scale by comparing the numerical results with field data collected in the Bahamas channels. The comparison is presented in terms of flow velocities, bed profiles and grain size distributions of the bed surface. Finally, we use the validated model to explore how different rates of sea level rise will affect the morphodynamic evolution of the tidal channels under different "production rate" scenarios, e.g. constant, depth dependent.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. Limits to Tidal Power

    NASA Astrophysics Data System (ADS)

    Garrett, C.

    2008-12-01

    Ocean tides have been proposed as a source of renewable energy, though the maximum available power may be shown to be only a fraction of the present dissipation rate of 3.5 TW, which is small compared with global insolation (nearly 105 TW), wind dissipation (103 TW), and even human power usage of 15 TW. Nonetheless, tidal power could be a useful contributor in some locations. Traditional use of tidal power, involving the trapping of water behind a barrage at high tide, can produce an average power proportional to the area of the headpond and the square of the tidal range; the power density is approximately 6 W per square meter for a tidal range of 10 m. Capital costs and fears of environmental damage have put barrage schemes in disfavor, with interest turning to the exploitation of strong tidal currents, using turbines in a manner similar to wind turbines. There is a limit to the available power, however, as adding turbines reduces the flow, ultimately reducing the power. For sinusoidal forcing of flow in a channel connecting two large open basins, the maximum available power may be shown to be given approximately by 0.2ρ g a Q_max, where ρ is the water density, g gravity, a the amplitude of the tidal sea level difference along the channel, and Q_max is the maximum volume flux in the natural state. The same formula applies if the channel is the entrance to a semi-enclosed basin, with a now the amplitude of the external tide. A flow reduction of approximately 40% is typically associated with the maximum power extraction. The power would be reduced if only smaller environmental changes are acceptable, and reduced further by drag on supporting structures, dissipation in turbine wakes, and internal inefficiencies. It can be suggested that the best use of strong, cold, tidal currents is to provide cooling water for nuclear reactors.

  10. Electrophysiological characterization of spinal neuron sensitization by elevated calcium channel alpha-2-delta-1 subunit protein

    PubMed Central

    Zhou, Chunyi; Luo, Z. David

    2013-01-01

    Background Voltage-gated calcium channel α2δ1 subunit is the binding site for gabapentin, an effective drug in controlling neuropathic pain states including thermal hyperalgesia. Hyperalgesia to noxious thermal stimuli in both spinal-nerve-ligated (SNL) and voltage-gated calcium channel α2δ1 over-expressing transgenic (Tg) mice correlates with higher α2δ1 levels in dorsal root ganglia and dorsal spinal cord. In this study, we investigated whether abnormal synaptic transmission is responsible for thermal hyperalgesia induced by elevated α2δ1 expression in these models. Methods Behavioral sensitivities to thermal stimuli were test in L4 SNL and sham mice, as well as in α2δ1 Tg and wild-type mice. Miniature excitatory (mEPSC) and inhibitory (mIPSC) postsynaptic currents were recorded in superficial dorsal spinal cord neurons from these models using whole-cell patch clamp slice recording techniques. Results The frequency, but not amplitude, of mEPSC in superficial dorsal horn neurons was increased in SNL and α2δ1 Tg mice, which could be attenuated by gabapentin dose dependently. Intrathecal α2δ1 antisense oligodeoxynucleotide treatment diminished increased mEPSC frequency and gabapentin's inhibitory effects in elevated mEPSC frequency in the SNL mice. In contrast, neither the frequency, nor the amplitude, of mIPSC was altered in superficial dorsal horn neurons from the SNL and α2δ1 Tg mice. Conclusions Our findings support a role of peripheral nerve injury-induced α2δ1 in enhancing presynaptic excitatory input onto superficial dorsal spinal cord neurons that contributes to nociception development. PMID:24151064

  11. Three-dimensional numerical simulation of turbidity currents in a submarine channel on the seafloor of the Niger Delta slope

    NASA Astrophysics Data System (ADS)

    Abd El-Gawad, S.; Cantelli, A.; Pirmez, C.; Minisini, D.; Sylvester, Z.; Imran, J.

    2012-05-01

    In the present work, we use a three-dimensional numerical model to simulate turbidity currents in a large-scale submarine environment. The model solves the Reynolds Averaged Navier-Stokes equations, along with a two-equation turbulence closure model, the sediment conservation equations for multiple grain-size classes and the Exner equation of bed sediment conservation. Four different grain-size classes (30, 64, 125, and 250μm) are considered. The model is applied to a modern seafloor environment in the continental slope of the Niger Delta where bathymetric data and seven piston cores were collected in and around a sinuous channel. Detailed analyses show the grain-size distribution for different beds within each core. Since the flow events responsible for the formation of this modern depository are unknown, we perform simulations with different inflow conditions in order to match the grain-size data. The model realistically predicts the flow field and its evolution over the complex topography and shows the spatial distribution of different grain-size classes. A strong lateral flow from the inner to the outer bank is observed at the bends of the low-relief channel. From the computed deposition rate, we obtain the fraction of each grain-size class at the core locations and compareD50 and D90 predicted from the model with the core data. The discrete values predicted from the model fall within the range of D50 and D90observed in different beds in the cores. The results demonstrates that a 3-D numerical model can be a useful tool for understanding the distribution pattern, thickness, and grain size of the turbidity currents and their deposits at the field scale and can help constrain the variabilities of reservoir architecture.

  12. Sediment transport in response to changes in river discharge and tidal mixing in a funnel-shaped micro-tidal estuary

    NASA Astrophysics Data System (ADS)

    Gong, Wenping; Jia, Liangwen; Shen, Jian; Liu, James T.

    2014-03-01

    Huangmaohai Estuary is a micro-tidal funnel-shaped estuary, located along the southwestern side of the Pearl River Delta complex. Variations of sediment transport patterns under different conditions of river discharge and tidal mixing are investigated by using field measurements and data analysis during both dry and wet seasons, respectively. The intratidal variation of sediment dynamics is largely controlled by the tidal asymmetry. The typical pattern of 25-hour mean sediment transport during the dry season is that the transport is landward in the channel and seaward on the shoals. A bifurcation pathway of sediment transport shows that sediments are imported from the East Opening and exported through the Middle Opening. However, this pattern can be altered by mixing processes and river discharge. Enhanced mixing or increased discharge can result in a predominantly seaward transport. Conversely, weak mixing can result in an emphatic landward transport. In general, the sediment transport is closely associated with the morphological evolution in the estuary.

  13. Suppression of Random Dopant-Induced Threshold Voltage Fluctuations in Sub-0.1-(micron)meter MOSFET's with Epitaxial and (delta)-Doped Channels

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Saini, Subhash

    1999-01-01

    A detailed three-dimensional (3-D) statistical 'atomistic' simulation study of fluctuation-resistant sub-0.1-(micron)meter MOSFET architectures with epitaxial channels and delta doping is presented. The need for enhancing the fluctuation resistance of the sub-0.1-(micron)meter generation transistors is highlighted by presenting summarized results from atomistic simulations of a wide range of conventional devices with uniformly doped channel. According to our atomistic results, the doping concentration dependence of the random dopant-induced threshold voltage fluctuations in conventional devices is stronger than the analytically predicted fourth-root dependence. As a result of this, the scaling of such devices will be restricted by the "intrinsic" random dopant-induced fluctuations earlier than anticipated. Our atomistic simulations confirm that the introduction of a thin epitaxial layer in the MOSFET's channel can efficiently suppress the random dopant-induced threshold voltage fluctuations in sub-0.1-(micron)meter devices. For the first time, we observe an "anomalous" reduction in the threshold voltage fluctuations with an increase in the doping concentration behind the epitaxial channel, which we attribute to screening effects. Also, for the first time we study the effect of a delta-doping, positioned behind the epitaxial layer, on the intrinsic threshold voltage fluctuations. Above a certain thickness of epitaxial layer, we observe a pronounced anomalous decrease in the threshold voltage fluctuation with the increase of the delta doping. This phenomenon, which is also associated with screening, enhances the importance of the delta doping in the design of properly scaled fluctuation-resistant sub-0.1-(micron)meter MOSFET's. Index Terms-Doping, fluctuations, MOSFET, semiconductor device simulation, silicon devices, threshold.

  14. Bi-objective analysis of water-sediment regulation for channel scouring and delta maintenance: A study of the lower Yellow River

    NASA Astrophysics Data System (ADS)

    Kong, Dongxian; Miao, Chiyuan; Wu, Jingwen; Jiang, Lin; Duan, Qingyun

    2015-10-01

    Long-term hydrological data and remotely-sensed satellite images were used to analyze the effects of the water-sediment regulation scheme (WSRS) implemented in the lower Yellow River (LYR), China, between 1983 and 2013. The WSRS aimed to control channel scouring in the LYR and maintain the Yellow River Delta (YRD). Channel erosion in the LYR has primarily depended on the incoming sediment concentration at Xiaolangdi, where the concentration must be lower than approximately 9.17 × 10- 3 t m- 3 to avoid rising of the riverbed. In 1996, an artificial diversion altered the evolution of the YRD. To maintain delta equilibrium, an average sediment load of about 441 × 106 t year- 1 was required before 1996, after which this value decreased to 167 × 106 t year- 1. We provide a preliminary estimate of the incoming water and sediment conditions required at the Xiaolangdi station to guarantee both LYR channel scouring and maintenance of the YRD. Our results show that it is feasible to transport sediment originally deposited in the LYR to the river mouth to maintain the delta, which is of great significance for the future management and environmental protection of the LYR.

  15. 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.

  16. Upper Devonian Catskill delta of West Virginia

    SciTech Connect

    Donaldson, A.C.; Lewis, J.S.; Mumcuoglu, C.; Boswell, R.; Peace, K.; Jewell, G.

    1984-12-01

    Oil and gas reservoir rocks of the Upper Devonian of West Virginia were deposited as shoreline sands along a coastal plain characterized by marine-dominant deltas (Catskill delta complex). These sandstones exhibit facies relationships between red beds and interbedded sandstones and shales that shift westward and eastward with offlap and onlap. Outcrop equivalents at Elkins, West Virginia, are correlated with the interval of Balltown to Fourth sands. Subsurface correlation indicates that maximum westward progradation occurred during deposition of the Gordon and Gordon Stray sands, and that transgression mainly characterized the younger Devonian sands of the Thirty-foot, Fifty-foot and Gantz. Regional correlations suggest that the Bradford-Balltown and Speechly (B sands of Pennsylvania Geological Survey) sands are better developed in northwestern Pennsylvania, whereas the Bayard through Gantz (D sands of Pennsylvania Geological Survey) sands are better developed in northern and central West Virginia, decreasing also in buildup toward southeastern West Virginia. The oil-bearing sandstones occur in strike trend (north-south) in north-central West Virginia connected by feeder channel sandstones with dip trends (east-west). The interpreted fluvial and tidal channels combine to represent distributary channels that supplied the sands to the barrier islands and delta front. Shoreline shifts, with regression and transgression of the ancient sea, caused corresponding changes in distal-fan accumulations with time.

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

    USGS Publications Warehouse

    Carlson, P.R.; Powell, R.D.; Phillips, A.C.

    1992-01-01

    Side-scan sonar images provide a view of an actively changing delta front in this marine outwash fjord. 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. -Authors

  18. Calcium channel alpha-2-delta-1 protein upregulation in dorsal spinal cord mediates spinal cord injury induced neuropathic pain states

    PubMed Central

    Boroujerdi, Amin; Zeng, Jun; Sharp, Kelli; Kim, Donghyun; Steward, Oswald; Luo, Z. David

    2011-01-01

    Spinal cord injury (SCI) commonly results in the development of neuropathic pain, which can dramatically impair the quality of life for SCI patients. SCI induced neuropathic pain can be manifested as both tactile allodynia (a painful sensation to a non-noxious stimulus) and or hyperalgesia (an enhanced sensation to a painful stimulus). The mechanisms underlying these pain states are poorly understood. Clinical studies have shown that gabapentin, a drug that binds to the voltage gated calcium channel alpha-2-delta-1 subunit (Cavα2δ-1) proteins is effective in the management of SCI induced neuropathic pain. Accordingly, we hypothesized that tactile allodynia post SCI is mediated by an upregulation of Cavα2δ-1 in dorsal spinal cord (DSC). To test this hypothesis, we examined if SCI-induced dysregulation of spinal Cavα2δ-1 plays a contributory role in below-level allodynia development in a rat spinal T9 contusion injury model. We found that Cavα2δ-1 expression levels were significantly increased in L4-6 dorsal, but not ventral, spinal cord of SCI rats that correlated with tactile allodynia development in the hindpaw plantar surface. Furthermore, both intrathecal gabapentin treatment and blocking SCI induced Cavα2δ-1 protein upregulation by intrathecal Cavα2δ-1 antisense oligodeoxynucleotides could reverse tactile allodynia in SCI rats. These findings support that SCI induced Cavα2δ-1 upregulation in spinal dorsal horn is a key component in mediating below-level neuropathic pain development and selectively targeting this pathway may provide effective pain relief for SCI patients. PMID:21239111

  19. 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.

  20. Holocene evolution of a wave-dominated fan-delta: Godavari delta, India

    NASA Astrophysics Data System (ADS)

    Saito, Y.; Nageswara Rao, K.; Nagakumar, K.; Demudu, G.; Rajawat, A.; Kubo, S.; Li, Z.

    2013-12-01

    The Godavari delta is one of the world's largest wave-dominated deltas. The Godavari River arises in the Western Ghats near the west coast of India and drains an area of about 3.1x10^5 km^2, flowing about 1465 km southeast across the Indian peninsula to the Bay of Bengal. The Godavari delta consists of a gentle seaward slope from its apex (12 m elevation) at Rajahmundry and a coastal beach-ridge plain over a distance of about 75 km and covers ~5200 km^2 as a delta plain. The river splits into two major distributary channels, the Gautami and the Vasishta, at a barrage constructed in the mid-1800s. The coastal environment of the deltaic coast is microtidal (~1 m mean tidal range) and wave-dominated (~1.5 m mean wave height in the June-September SW monsoon season, ~0.8 m in the NE monsoon season). Models of the Holocene evolution of the Godavari delta have changed from a zonal progradation model (e.g. Nageswara Rao & Sadakata, 1993) to a truncated cuspate delta model (Nageswara Rao et al., 2005, 2012). Twelve borehole cores (340 m total length), taken in the coastal delta plain during 2010-2013, yielded more than 100 C-14 dates. Sediment facies and C-14 dates from these and previous cores and remote-sensing data support a new delta evolution model. The Holocene coastal delta plain is divided into two parts by a set of linear beach ridges 12-14 km landward from the present shoreline in the central part of the delta. The location of the main depocenter (lobe) has shifted during the Holocene from 1) the center to 2) the west, 3) east, 4) center, 5) west, and 6) east. The linear beach ridges separate the first three from the last three stages. These lobe shifts are controlled by river channel shifts near the apex. Just as the current linear shoreline of the central part of the delta and the concave-up nearshore topography are the result of coastal erosion of a cuspate delta, the linear beach ridges indicate a former eroded shoreline. An unconformity within the deltaic

  1. Using delta-front bathymetry to understand river delta progradation

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    We investigate the delta-front bathymetry of the Wax Lake Delta in Louisiana, USA; a sand rich river delta prograding quickly (~100 m/yr) into a shallow (~2.5 m) basin. The delta-front is the zone separating the bottomset from the topset of the delta. Bottomset sedimentation covers the bed evenly whereas topset sediment transport is focused by flow through distributary channels. The delta front connects these two disparate transport regimes and has a profound effect on channel-network evolution and sedimentary structure of river deltas. Predictions of delta-front topography made by models of delta progradation have rarely been compared to the bathymetry of field-scale deltas. We have mapped 60 km2 of delta front bathymetry immediately seaward of two sub-aerial distributary channels. Subaqueous channels extend up to 2 km seaward of their subaerial portions. These channels lose definition at their distal ends through a combination of channel-bed shoaling and loss of bank relief. Little bathymetric relief is observed at the fronts of the subaqueous channels, calling into question the role of channel-mouth bars in generating the bifurcations observed in this delta-channel network. Near the subaerial to subaqueous transition, steep and eroding sidewalls transition to constructional banks with gentle grades. Grab samples of bed material have been collected throughout the study area in order to detect proximal to distal fining and to constrain the shear stresses connected with delta-front sedimentation. A better understanding of sediment transport in the delta front and its affiliated patterns of erosion and deposition is essential for progress in understanding how river deltas prograde and fill their basins.

  2. Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia

    NASA Astrophysics Data System (ADS)

    Storms, Joep E. A.; Hoogendoorn, Robert M.; Dam, Rien A. C.; Hoitink, A. J. F.; Kroonenberg, S. B.

    2005-10-01

    The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide-fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons. This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand-mud couplets. The distribution of the sand-mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand-mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments. Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first

  3. 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)

  4. Agonist-dependent single channel current and gating in alpha4beta2delta and alpha1beta2gamma2S GABAA receptors.

    PubMed

    Keramidas, Angelo; Harrison, Neil L

    2008-02-01

    The family of gamma-aminobutyric acid type A receptors (GABA(A)Rs) mediates two types of inhibition in the mammalian brain. Phasic inhibition is mediated by synaptic GABA(A)Rs that are mainly comprised of alpha(1), beta(2), and gamma(2) subunits, whereas tonic inhibition is mediated by extrasynaptic GABA(A)Rs comprised of alpha(4/6), beta(2), and delta subunits. We investigated the activation properties of recombinant alpha(4)beta(2)delta and alpha(1)beta(2)gamma(2S) GABA(A)Rs in response to GABA and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3(2H)-one (THIP) using electrophysiological recordings from outside-out membrane patches. Rapid agonist application experiments indicated that THIP produced faster opening rates at alpha(4)beta(2)delta GABA(A)Rs (beta approximately 1600 s(-1)) than at alpha(1)beta(2)gamma(2S) GABA(A)Rs (beta approximately 460 s(-1)), whereas GABA activated alpha(1)beta(2)gamma(2S) GABA(A)Rs more rapidly (beta approximately 1800 s(-1)) than alpha(4)beta(2)delta GABA(A)Rs (beta < 440 s(-1)). Single channel recordings of alpha(1)beta(2)gamma(2S) and alpha(4)beta(2)delta GABA(A)Rs showed that both channels open to a main conductance state of approximately 25 pS at -70 mV when activated by GABA and low concentrations of THIP, whereas saturating concentrations of THIP elicited approximately 36 pS openings at both channels. Saturating concentrations of GABA elicited brief (<10 ms) openings with low intraburst open probability (P(O) approximately 0.3) at alpha(4)beta(2)delta GABA(A)Rs and at least two "modes" of single channel bursting activity, lasting approximately 100 ms at alpha(1)beta(2)gamma(2S) GABA(A)Rs. The most prevalent bursting mode had a P(O) of approximately 0.7 and was described by a reaction scheme with three open and three shut states, whereas the "high" P(O) mode ( approximately 0.9) was characterized by two shut and three open states. Single channel activity elicited by THIP in alpha(4)beta(2)delta and alpha(1)beta(2)gamma(2S) GABA

  5. 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

  6. Sandwave movement under tidal and wind-driven currents in a shallow marine environment: Adolphus Channel, northeastern Australia

    NASA Astrophysics Data System (ADS)

    Harris, Peter T.

    1989-11-01

    Synoptic bathymetric surveys and current meter data collected over a sandwave field in Adolphus Channel (20 m water depth), Australia, yield average estimated celebrities of 0.75 and 0.25 m day -1, respectively. The sandwaves average 3.9 m in height, 102 m in wavelength and are comprised of up to 96% carbonate, consisting primarily of intact and fragmented calcareous alga Halimeda, benthic foraminifers, bryozoans and molluscs. The sand has a modal grain size of 0.8 mm. Current speeds measured 1 m above the bed averaged 0.42 m -1 and reached a peak of 1.36 m -1. Surveys carried out in September and February show that the sandwaves reversed their asymmetric orientation over this time interval, which is attributed to a change in the direction of the wind-driven currents during the monsoon season. The reversal of asymmetry was accompanied by a statistically significant change in the degree of sandwave asymmetry (ratio of stoss and lee slope lengths) whereas no change in mean wavelength was detected. The reversal is estimated to have required 47 days to occur based upon estimates of average sandwave cross-sectional area and bedload transport rates predicted from the current meter data.

  7. 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.

  8. Meandering: fluvial versus tidal. (Invited)

    NASA Astrophysics Data System (ADS)

    Seminara, G.

    2009-12-01

    Tidal meanders (Marani et al, Water Resour Res, 2002) display similarities as well as important differences from fluvial meanders (Seminara, J Fluid Mech, 2006). Like fluvial meanders they have characteristic wavelengths scaling with channel width: this is why the convergent character of tidal channels leads to meander wavelengths decaying landward. Unlike fluvial meanders, the typical curvature spectra of tidal meanders contain even harmonics: hence, meander skewing does non display any distinct correlation with the flow direction and the known Kinoshita curve, which approximates the shape of fluvial meanders, is not appropriate to tidal meanders. Additional constraints are brought up by the spatial gradients of the basic bed profile connected to the finite length of tidal channels at equilibrium. In fact, it has been theoretically established (Schuttelaars and De Swart, Eur J Mech, B/Fluids, 1996, Seminara et al, J Fluid Mech submitted, 2009) and confirmed by controlled laboratory experiments (Tambroni et al., J Geoph Res, 2005) that tidal channels closed at one end and connected at the other end with a tidal sea, evolve towards an equilibrium configuration characterized by a ‘slow’ landward decay of the average flow depth. An equilibrium length of the channel is then determined by the formation of a shoreline. Channel curvature affects the lateral equilibrium topography and gives rise to a pattern of point bars and scour pools resembling that of fluvial channels. With some notable differences, though. In fact, Solari et al (J Fluid Mech, 2001) showed that long sequences of weakly sinuous identical meandering channels subject to a symmetrical tidal forcing develop a symmetrical bar-pool pattern with small symmetrical oscillations during the tidal cycle. However, in the laboratory investigations of Garotta et al. (Proceedings RCEM5,2007) the bar-pool pattern was somehow unexpected. In a first experiment, it was in phase with curvature only in the inner half of

  9. Correlations Between Fluvial Morphologic Changes and Vegetation, and Fluvio-deltaic Behavior on Deltas Using Remote Sensing

    NASA Astrophysics Data System (ADS)

    Felicia, A. L.; Weissmann, G. S.; Scuderi, L. A.; Hartley, A. J.

    2015-12-01

    Large deltas (>30 km in length) provide the majority of sediment to the world's oceans and contain important aquifers and hydrocarbon reservoirs; however, a comprehensive analysis of the geomorphic influence of factors (e.g., tides, groundwater interaction, and upstream discharge and sediment supply) controlling fluvio-deltaic deposition and morphology has not been conducted. To document the geomorphological changes occurring from the apex to the toe of deltas, a database of 84 large modern deltas was compiled. Of these deltas, several were specifically selected to gauge the interplay of tidal, groundwater, and fluvial influence on the modern river channels on these deltas. On these selected deltas, we analyzed the river width and sinuosity with distance downstream from the apex using Shuttle Radar Topography Mission (SRTM) and LANDSAT imagery. Additionally, we analyzed a time-series from the year 2000 to 2015 of interpreted vegetation density using the Normalized Difference Vegetation Index (NDVI). Since vegetation density and type are related to both salinity and groundwater conditions, we are able to observe systematic changes in vegetation across different portions of the delta, depending on the major hydrologic influences in each area (e.g., tidal, fresh groundwater, brackish groundwater, or direct fluvial influence). In this study, we evaluate correlations between fluvial morphologic changes and vegetation density and type, thus helping to improve our understanding of the significance of tides and groundwater on fluvio-deltaic behavior globally.

  10. Identification of the alpha2-delta-1 subunit of voltage-dependent calcium channels as a molecular target for pain mediating the analgesic actions of pregabalin.

    PubMed

    Field, Mark J; Cox, Peter J; Stott, Emma; Melrose, Heather; Offord, James; Su, Ti-Zhi; Bramwell, Steve; Corradini, Laura; England, Steven; Winks, Joanna; Kinloch, Ross A; Hendrich, Jan; Dolphin, Annette C; Webb, Tony; Williams, Dic

    2006-11-14

    Neuropathic pain is a debilitating condition affecting millions of people around the world and is defined as pain that follows a lesion or dysfunction of the nervous system. This type of pain is difficult to treat, but the novel compounds pregabalin (Lyrica) and gabapentin (Neurontin) have proven clinical efficacy. Unlike traditional analgesics such as nonsteroidal antiinflammatory drugs or narcotics, these agents have no frank antiinflammatory actions and no effect on physiological pain. Although extensive preclinical studies have led to a number of suggestions, until recently their mechanism of action has not been clearly defined. Here, we describe studies on the analgesic effects of pregabalin in a mutant mouse containing a single-point mutation within the gene encoding a specific auxiliary subunit protein (alpha2-delta-1) of voltage-dependent calcium channels. The mice demonstrate normal pain phenotypes and typical responses to other analgesic drugs. We show that the mutation leads to a significant reduction in the binding affinity of pregabalin in the brain and spinal cord and the loss of its analgesic efficacy. These studies show conclusively that the analgesic actions of pregabalin are mediated through the alpha2-delta-1 subunit of voltage-gated calcium channels and establish this subunit as a therapeutic target for pain control. PMID:17088553

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. Cloned delta-opioid receptors in GH(3) cells inhibit spontaneous Ca(2+) oscillations and prolactin release through K(IR) channel activation.

    PubMed

    Piros, E T; Charles, R C; Song, L; Evans, C J; Hales, T G

    2000-05-01

    Opioid receptors can couple to K(+) and Ca(2+) channels, adenylyl cyclase, and phosphatidyl inositol turnover. Any of these actions may be important in the regulation of neurotransmitter and hormone release from excitable cells. GH(3) cells exhibit spontaneous oscillations of intracellular Ca(2+) concentration ([Ca(2+)](i)) and prolactin release. Activation of cloned delta-opioid receptors stably expressed in GH(3) cells inhibits both spontaneous Ca(2+) signaling and basal prolactin release. The objective of this study was to examine a possible role for K(+) channels in these processes using the patch-clamp technique, fluorescence imaging, and a sensitive ELISA for prolactin. The selective delta receptor agonist [D-Pen(2), D-Pen(2)]enkephalin (DPDPE) inhibited [Ca(2+)](i) oscillations in GH(3) cells expressing both mu and delta receptors (GH(3)MORDOR cells) but had no effect on control GH(3) cells or cells expressing mu receptors alone (GH(3)MOR cells). The inhibition of [Ca(2+)](i) oscillations by DPDPE was unaffected by thapsigargin pretreatment, suggesting that this effect is independent of inositol 1,4,5-triphosphate-sensitive Ca(2+) stores. DPDPE caused a concentration-dependent inhibition of prolactin release from GH(3)MORDOR cells with an IC(50) of 4 nM. DPDPE increased inward K(+) current recorded from GH(3)MORDOR cells but had no significant effect on K(+) currents recorded from control GH(3) cells or GH(3)MOR cells. The mu receptor agonist morphine also had no effect on currents recorded from control cells but activated inward K(+) currents recorded from GH(3)MOR and GH(3)MORDOR cells. Somatostatin activated inward currents recorded from all three cell lines. The DPDPE-sensitive K(+) current was inwardly rectifying and was inhibited by Ba(2+) but not TEA. DPDPE had no effect on delayed rectifier-, Ca(2+)-, and voltage-activated or A-type K(+) currents, recorded from GH(3)MORDOR cells. Ba(2+) attenuated the inhibition of [Ca(2+)](i) and prolactin release

  16. 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.

  17. Sequence stratigraphic model of the Rio Grande Delta, south west Texas: Potential analog for the Niger Delta

    SciTech Connect

    Banfield, L.A.; Anderson, J.B.; Vail, P.R. )

    1996-01-01

    A sequence stratigraphic model developed from the ancient Rio Grande Delta in South West Texas is suggested as an analog for the Niger Delta. The two delta systems are characterized by high sand bedloads, shale diapirism with associated listric normal faulting, and large amounts of tidal and wave influence forming lower coastal plains characterized by swamps and estuaries. The sequence stratigraphic model of the ancient Rio Grande delta is based on approximately 1200 kilometers of single channel, 15 cubic inch water gun data, lithologic descriptions from approximately 25 long cores (28-30 m) located in 17-94 meters water depth, three gamma ray logs, paleontologic data from two cores, and oxygen isotopic data from one core (152 meters in length and located in 94 meters water depth). The combined data indicate that considerable quantities of sand are sequestered on the continental shelf and point sourcing the slope. The Rio Grande sequence stratigraphic model provides an improved understanding of sand deposits on the shelf, of the role of sediment bypass during lowstands, and of the base of slope deposits formed by headward eroding canyons ( ) or channels ( ) located at the shelf break. This information regarding the distribution of sand in the Rio Grande system can provide valuable insight into the reservoir distribution in the Niger system, improving existing reservoir predictions.

  18. Sequence stratigraphic model of the Rio Grande Delta, south west Texas: Potential analog for the Niger Delta

    SciTech Connect

    Banfield, L.A.; Anderson, J.B.; Vail, P.R.

    1996-12-31

    A sequence stratigraphic model developed from the ancient Rio Grande Delta in South West Texas is suggested as an analog for the Niger Delta. The two delta systems are characterized by high sand bedloads, shale diapirism with associated listric normal faulting, and large amounts of tidal and wave influence forming lower coastal plains characterized by swamps and estuaries. The sequence stratigraphic model of the ancient Rio Grande delta is based on approximately 1200 kilometers of single channel, 15 cubic inch water gun data, lithologic descriptions from approximately 25 long cores (28-30 m) located in 17-94 meters water depth, three gamma ray logs, paleontologic data from two cores, and oxygen isotopic data from one core (152 meters in length and located in 94 meters water depth). The combined data indicate that considerable quantities of sand are sequestered on the continental shelf and point sourcing the slope. The Rio Grande sequence stratigraphic model provides an improved understanding of sand deposits on the shelf, of the role of sediment bypass during lowstands, and of the base of slope deposits formed by headward eroding canyons (?) or channels (?) located at the shelf break. This information regarding the distribution of sand in the Rio Grande system can provide valuable insight into the reservoir distribution in the Niger system, improving existing reservoir predictions.

  19. Peripheral G protein-coupled inwardly rectifying potassium (GIRK) channels are involved in delta opioid receptor-mediated anti-hyperalgesia in rat masseter muscle

    PubMed Central

    Chung, Man-Kyo; Cho, Yi Sul; Bae, Young Chul; Lee, Jongseok; Zhang, Xia; Ro, Jin Y.

    2014-01-01

    Background Although the efficacy of peripherally administered opioid has been demonstrated in preclinical and clinical studies, the underlying mechanisms of its anti-hyperalgesic effects are poorly understood. G protein-coupled inwardly rectifying potassium (GIRK) channels are linked to opioid receptors in the brain. However, the role of peripheral GIRK channels in analgesia induced by peripherally administered opioid, especially in trigeminal system, is not clear. Methods Expression of GIRK subunits in rat trigeminal ganglia (TG) was examined with RT-PCR, western blot and immunohistochemistry. Chemical profiles of GIRK expressing neurons in TG were further characterized. Behavioral and Fos experiments were performed to examine the functional involvement of GIRK channels in delta opioid receptor (DOR)-mediated anti-hyperalgesia under an acute myositis condition. Results TG expressed mRNA and proteins for GIRK1 and GIRK2 subunits. Majority of GIRK1- and GIRK2-expressing neurons were non-peptidergic afferents. Inhibition of peripheral GIRK using Tertiapin-Q (TPQ) attenuated anti-nociceptive effects of peripherally administered DOR agonist, DPDPE, on mechanical hypersensitivity in masseter muscle. Furthermore, TPQ attenuated the suppressive effects of peripheral DPDPE on neuronal activation in the subnucleus caudalis of the trigeminal nucleus (Vc) following masseteric injection of capsaicin. Conclusions Our data indicate that peripheral DOR agonist-induced suppression of mechanical hypersensitivity in the masseter muscle involves the activity of peripheral GIRK channels. These results could provide a rationale for developing a novel therapeutic approach using peripheral GIRK channel openers to mimic or supplement the effects of peripheral opioid agonist. PMID:23740773

  20. Remarked morphological change in a large tidal inlet with low sediment-supply

    NASA Astrophysics Data System (ADS)

    Wang, Ya Ping; Gao, Shu; Jia, Jianjun; Liu, Yunling; Gao, Jianhua

    2014-11-01

    Sediment transport within small tidal inlets is sensitive to natural processes, whilst large tidal inlets are relatively robust systems because of their large tidal prism. However, remarked morphological changes may be initiated even under the condition of low sediment supply, as illustrated by Jiaozhou Bay, a large coastal embayment on the Shandong Peninsula, eastern China. Jiaozhou Bay is characterized by its relatively slow rate of natural change, and while the embayment has a flood-dominated entrance channel and muddy seabed, the suspended sediment concentration is generally low due to the lack of abundant source material. Observations of sediment dynamics show that net suspended sediment transport is directed towards outside of the bay, with an order of magnitude of 103 t during a tidal cycle. The export of sediment associated with this flood-dominated environment implies that the net transport pattern is controlled by tidal exchange processes rather than the strength of the seabed shear stress. Sediment budget calculations show that supply of artificial sediment into the bay can account for up to 72% of the total input, which is in agreement with the 210Pb and 137Cs radioisotope geochronologies, and this leads to accumulation rates of 100-101 mm yr-1; without this, the deposition rate would be low under natural conditions. The flood tidal delta area is also influenced by the input of anthropogenic material, and acts as a depocenter with relatively high accumulation rates. Furthermore, although the inlet system has not yet reached its equilibrium state (i.e., the entrance cross-sectional area is still larger than the equilibrium cross-sectional area), land reclamation activities have resulted in a rapid reduction of the embayment area (by 37%) over the last 80 years. Our findings indicate that the rapid changes observed in the tidal basin area and seabed morphology are mainly the result of human activity rather than natural processes.

  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. 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.

  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. 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.'

  5. 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

  6. 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.

  7. 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

  8. Regulation of the tidal volume and ventilatory responses to CO2 in normal man and in scoliosis.

    PubMed

    Kafer, E R

    1981-01-01

    The variation of the ventilatory response to CO2 and its pattern among normals and in the presence of pulmonary disease is wide. In normal subjects the relationship between the slopes of the ventilatory (delta V/delta PCO2), tidal volume (delta VT/delta PCO2) and the frequency (delta f/delta PCO2) responses and body size, metabolic rate, resting ventilation and pattern, lung volumes or mechanical properties of the respiratory system have only been demonstrated in a few studies. In idiopathic scoliosis there is a positive correlation between the delta V/delta PCO2 and delta VT/delta PCO2 and body size, resting ventilation and tidal volume, lung volumes and compliance of the respiratory system. Although there were significant correlations between the delta V/delta PCO2 and the delta VT/delta PCO2 and th delta f/delta PCO2 the correlation between the delta VT/delta PCO2 and delta f/delta PCO2 was not significant. Correlations between the delta f/delta PCO2 and lung volumes, compliance or body size were also not significant. Therefore variation in the frequency response to CO2 contribute to the variation between individuals of the delta V/delta PCO2 and this variation is unrelated to respiratory mechanics or body size. We conclude that in human studies any examination of possible relationships between ventilatory response to CO2 and body size, lung volumes and mechanics should examine separately the tidal volume and frequency response to CO2. We postulate that the tidal volume response is the most appropriate variable to normalize for lung volumes, e.g., vital capacity (delta VT/VC/delta/ PCO2). PMID:6781570

  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. Holocene tidal back-barrier development at decelerating sea-level rise: a 5 millennia record, exposed in the western Netherlands

    NASA Astrophysics Data System (ADS)

    Beets, Dirk J.; De Groot, Thomas A. M.; Davies, Huw A.

    2003-05-01

    A succession of tidal back-barrier deposits, ranging in age from about 6000 to 0 cal BC, was recently exposed in an up to 17-m-deep excavation in the western Netherlands. The lower part of the succession shows the flooding of the area and the establishment of a tidal back-barrier basin during high rates of relative sea-level rise; the upper part of the succession consists mainly of estuarine channel and tidal flat deposits. Medieval lake deposits cover the estuarine sequence. The development of the Holocene Holland Tidal Basin took place in the Atlantic and Early Subboreal sub-stages between ˜7000 and 3500 cal BC after which the tidal inlets closed and fresh water marshes developed. Its evolution was largely controlled by both the rates of sea-level rise and of sediment supply. All the sediment was derived from the North Sea and the shoreface. During initial flooding of the outcrop area, the rate of sea-level rise (0.1-0.06 cm/year) far outran that of sediment supply. Facies zones developed controlled by the inundated topography and sediment supply. Fresh water reed marshes evolved along the landward side of the tidal basin. The Basal Peat that formed in these marshes is overlain by a thin layer of organic-rich clays, which represent the deposits in a lagoon separating the marshes from the tide-influenced sands and clays of the proximal zone of the tidal basin. The latter consisted of sand-rich channel sequences separated by mud-rich interchannel areas. Position of the channels was controlled by the pre-existing topography; the channels were confined by levees consisting of overbank and crevasse deposits. The interchannel areas consisted of sub-tidal mudflats. The studied outcrop showed a subtidal fan or delta, connecting a non-exposed channel to a mud-rich sequence of subtidal interchannel sediments. The latter graded upwards into inter- and supratidal flats deposited when the rate of sea-level rise decelerated after ±5000 cal BC and sediment supply eventually

  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

    2016-09-01

    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). Totally, 28 sets of binary models combined with different input parameters are studied. For each set of binary model, we presented the range of initial orbital periods which 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 is 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. Activation of delta-opioid receptors inhibits neuronal-like calcium channels and distal steps of Ca(2+)-dependent secretion in human small-cell lung carcinoma cells.

    PubMed

    Sher, E; Cesare, P; Codignola, A; Clementi, F; Tarroni, P; Pollo, A; Magnelli, V; Carbone, E

    1996-06-01

    Human small-cell lung carcinoma (SCLC) cells express neuronal-like voltage-operated calcium channels (VOCCs) and release mitogenic hormones such as serotonin (5-HT). Opioid peptides, on the other hand, have been shown to reduce SCLC cell proliferation by an effective autocrine pathway. Here we show that in GLC8 SCLC cells, only delta-opioid receptor subtype mRNA is expressed. Consistently, the selective delta-opioid agonist [D-Pen2-Pen5]-enkephalin (DPDPE), but not mu and kappa agonists, potently and dose-dependently inhibits high-threshold (HVA) VOCCs in these cells. As in peripheral neurons, this modulation is largely voltage-dependent, mediated by pertussis toxin (PTX)-sensitive G-proteins, cAMP-independent, and mainly affecting N-type VOCCs. With the same potency and selectivity, DPDPE also antagonizes the Ca(2+)-dependent release of [3H]serotonin ([3H]5-HT) from GLC8 cells. However, DPDPE inhibits not only the depolarization-induced release, but also the Ca(2+)-dependent secretion induced by thapsigargin or ionomycin. This suggests that besides inhibiting HVA VOCCs, opioids also exert a direct depressive action on the secretory apparatus in GLC8 cells. This latter effect also is mediated by a PTX-sensitive G-protein but, contrary to VOCC inhibition, it can be reversed by elevations of cAMP levels. These results show for the first time that opioids effectively depress both Ca2+ influx and Ca(2+)-dependent hormone release in SCLC cells by using multiple modulatory pathways. It can be speculated that the two mechanisms may contribute to the opioid antimitogenic action on lung neuroendocrine carcinoma cells. PMID:8642411

  14. 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 competition among the above interactions determines the FDA and TDA, whereas for the FVA, aside from the interaction among different tidal constituents, an extra component, the residual flow, plays an important role. The results

  15. 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

  16. 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

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

    NASA Astrophysics Data System (ADS)

    Marineau, M. D.; Wright, S. A.

    2015-03-01

    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.

  18. 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.

  19. 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

  20. Recent research on the hydrodynamics of the Sacramento - San Joaquin River Delta and north San Francisco Bay

    USGS Publications Warehouse

    Burau, J.R.; Monismith, S.G.; Stacey, M.T.; Oltmann, R.N.; Lacy, J.R.; Schoellhamer, D.H.

    1999-01-01

    This article presents an overview of recent findings from hydrodynamic research on circulation and mixing in the Sacramento-San Joaquin Delta (Delta) (Figure 1) and North San Francisco Bay (North Bay) (Figure 2). For the purposes of this article, North Bay includes San Pablo Bay, Carquinez Strait, and Suisun Bay. The findings presented are those gained from field studies carried out by the U.S. Geological Survey (USGS), as part of the Interagency Ecological Program (IEP), and Stanford University beginning about 1993. The premise behind these studies was that a basic understanding of circulation and mixing patterns in the Bay and Delta is an essential part of understanding how biota and water quality are affected by natural hydrologic variability, water appropriation, and development activities. Data collected for the field studies described in this article have significantly improved our understanding of Bay and Delta hydrodynamics. Measured flows ,in the Delta have provided valuable information on how water moves through the Delta's network of channels and how export pumping affects flows. Studies of the shallows and shallow-channel exchange processes conducted in Honker Bay have shown that the water residence time in Honker Bay is much shorter than previously reported (on the order of hours to several tidal cycles instead ofweeks). Suisun Bay studies have provided data on hydrodynamic transport and accumulation mechanisms that operate primarily in the channels. The Suisun Bay studies have caused us to revise our understanding of residual circulation in the channels of North Bay and of "entrapment" mechanisms in the low salinity zone. Finally, detailed tidal and residual (tidally averaged) time-scale studies of the mechanisms that control gravitational circulation in the estuary show that density-driven transport in the channels is governed by turbulence time-scale (seconds) interactions between the mean flow and stratification. The hydrodynamic research

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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.

  2. 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.

  3. Avulsion in action: Reconstruction and modelling sedimentation pace and upstream flood water levels following a Medieval tidal-river diversion catastrophe (Biesbosch, The Netherlands, 1421-1750 AD)

    NASA Astrophysics Data System (ADS)

    Kleinhans, Maarten G.; Weerts, Henk J. T.; Cohen, Kim M.

    2010-05-01

    Deltaic land inundated by storm surges may reform by sedimentation from natural or human-induced river diversions. This is a well-known trigger mechanism for creation of new channels in coastal plains and deltas, which may develop into main channels and lead to abandonment of older (avulsion), particularly in the downstream parts of deltas that host tidal rivers. These new channels develop as part of deltaic splay complexes that heal initial diversion scars and fill up flooded basins at a certain pace. We study a case with excellent historical and geological data of a diversion of the river Rhine following catastrophic inundations (1421-1424 AD) into medieval reclaimed land. Numerical modelling of deltaic splay and channel development is combined with reconstructions from historical maps and geological data. This yields detailed insight in pacing of splay sedimentation and changing hydrodynamics in the channel upstream of the diversion in the two centuries following the inundation. The equivalent of the full sand budget of the river Rhine was effectively trapped in the developing splay. The tidal-avulsion splay evolution on aspects is similar to that of fluvial crevassing into flood basins documented for settings lacking 'downstream' tidal control. The typical small-scale delta-lobe avulsion cycles: mouth bar formation, backward sedimentation, upstream avulsion, channel progradation and mouth bar formation are reproduced in the splay-modelling. The pacing of splay development, however, is relatively fast due to the presence of tides and the water depth in the receiving basin. The diversion had a strong upstream impact, in particular on water levels in the feeding river channel at stages of peak flow. For two centuries levels were significantly raised, because bifurcation-imposed reduced transport capacity and associated sedimentation at the diversion site increased hydraulic roughness and hampered flow. These findings have implications regarding flood mitigation

  4. 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. PMID:21329199

  5. 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.

  6. Triggering Mechanism of Subaqueous Sediment Density Flows on the Fraser Delta Slope: What Can be Gained through Continuous Observation from Venus?

    NASA Astrophysics Data System (ADS)

    Davidson, E.; Hill, P. R.; Moran, K.

    2014-12-01

    Recent observations on the Fraser Delta slope (British Columbia, Canada) confirm that unconfined turbidity currents occur on the delta slope close to the mouth of the main river channel. However the conditions that trigger these events are not understood. This study attempts to characterize the triggering conditions using data from the Delta Dynamics Laboratory (DDL), part of the VENUS Coastal Network in the Ocean Networks Canada Observatory, collected over four years. Data collection focused on the freshet season (May-July), a period believed to have the highest occurrence of submarine sediment density flows due to a high river discharge from snow melt combined with high tidal excursions resuspending bottom sediment. ADCP backscatter profiles reveal sediment settling through the water column from the river plume to the delta slope during ebb tide when the salt wedge is likely pushed out of the river channel and into the basin. Combined with measurements of tidal excursions and Fraser River discharge, quantitative measurements of the sediment settling process were analyzed on a daily and seasonal time scale. It is found that while sediment settling events occur throughout the entire year, the most intense and longest duration events occur on a higher frequency during the freshet season. In addition, the intensity of the ADCP backscatter has a strong positive correlation with the height of the major tide each day. This suggests that the tidal excursion has a larger direct control on the near bottom sediment concentration the delta slope than the river discharge. Continuous data collection is able to capture a clearer picture of the conditions in which submarine sediment density flows are created. From this, the aim is to produce more accurate predictions of when and where the flows will occur. With this information, improved geohazard monitoring on delta slopes can be achieved.

  7. 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.

  8. 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.

  9. Understanding pesticides in California's Delta

    USGS Publications Warehouse

    Kuivila, Kathryn M.; 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.

  10. 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 ...

  11. 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

  12. Preliminary results of a finite-element, multi-scale model of the Mahakam Delta (Indonesia)

    NASA Astrophysics Data System (ADS)

    de Brye, Benjamin; Schellen, Sébastien; Sassi, Maximiliano; Vermeulen, Bart; Kärnä, Tuomas; Deleersnijder, Eric; Hoitink, Ton

    2011-08-01

    The Mahakam is a 980-km-long tropical river flowing in the East Kalimantan province (Borneo Island, Indonesia). A significant fraction of this river is influenced by tides, the modelling of which is the main subject of this study. Various physical and numerical issues must be addressed. In the upstream part of the domain, the river flows through a region of three lakes surrounded by peat swamps. In the lowland regions, the river is meandering and its hydrodynamics is mostly influenced by tides. The latter propagate upstream of the delta, in the main river and its tributaries. Finally, the mouth of the Mahakam is a delta exhibiting a high number of channels connected to the Makassar Strait. This article focusses on the flow in the delta channels, which is characterised by a wide range of time and space scales. To capture most of them, the depth-integrated and the section-integrated versions of the unstructured mesh, finite-element model Second-Generation Louvain-la-Neuve Ice-Ocean Model are used. Unstructured grids allow for a refinement of the mesh in the narrowest channels and also an extension of the domain upstream and downstream of the delta in order to prescribe the open-boundary conditions. The Makassar Strait, the Mahakam Delta and the three lakes are modelled with 2D elements. The rivers, from the upstream limit of the delta to the lakes and the upstream limit of the domain, are modelled in 1D. The calibration of the tidal elevation simulated in the Mahakam Delta is presented. Preliminary results on the division of the Eulerian residual discharge through the channels of the delta are also presented. Finally, as a first-order description of the long-term transport, the age of the water originating from the upstream limit of the delta is computed. It is seen that for May and June 2008, the time taken by the water parcel to cross the estuary varies from 4 to 7 days depending on the channel under consideration.

  13. 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.

  14. 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

  15. 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.

  16. 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).

  17. 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

  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. Influence of tidal range on the stability of coastal marshland

    USGS Publications Warehouse

    Kirwan, Matthew L.; Guntenspergen, Glenn R.

    2010-01-01

    Early comparisons between rates of vertical accretion and sea level rise across marshes in different tidal ranges inspired a paradigm that marshes in high tidal range environments are more resilient to sea level rise than marshes in low tidal range environments. We use field-based observations to propose a relationship between vegetation growth and tidal range and to adapt two numerical models of marsh evolution to explicitly consider the effect of tidal range on the response of the marsh platform channel network system to accelerating rates of sea level rise. We find that the stability of both the channel network and vegetated platform increases with increasing tidal range. Our results support earlier hypotheses that suggest enhanced stability can be directly attributable to a vegetation growth range that expands with tidal range. Accretion rates equilibrate to the rate of sea level rise in all experiments regardless of tidal range, suggesting that comparisons between accretion rate and tidal range will not likely produce a significant relationship. Therefore, our model results offer an explanation to widely inconsistent field-based attempts to quantify this relationship while still supporting the long-held paradigm that high tidal range marshes are indeed more stable.

  20. Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03693 Channel

    This channel is located south of Iani Chaos.

    Image information: VIS instrument. Latitude -10.9N, Longitude 345.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  1. 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

  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. 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

  4. Avulsion in Action: Reconstruction and Modelling Sedimentation Pace and Upstream Flood Water Levels Following a Medieval Tidal-River Diversion and Storm Surge Catastrophe, The Netherlands, 1421-1750 AD

    NASA Astrophysics Data System (ADS)

    Cohen, K.; Kleinhans, M. G.; Weerts, H.

    2010-12-01

    Deltaic land inundated by storm surges may reform by sedimentation from natural or human-induced river diversions. This is a well-known trigger mechanism for creation of new channels in coastal plains and deltas, which may develop into main channels and lead to abandonment of older (avulsion), particularly in the downstream parts of deltas that host tidal rivers. These new channels develop as part of deltaic splay complexes that heal initial diversion scars and fill up flooded basins at a certain pace. We study a case with excellent historical and geological data of a diversion of the river Rhine following catastrophic inundations (1421-1424 AD) into medieval reclaimed land. Numerical modelling of deltaic splay and channel development is combined with reconstructions from historical maps and geological data. This yields detailed insight in pacing of splay sedimentation and changing hydrodynamics in the channel upstream of the diversion in the two centuries following the inundation. The equivalent of the full sand budget of the river Rhine was effectively trapped in the developing splay. The tidal-avulsion splay evolution on aspects is similar to that of fluvial crevassing into flood basins documented for settings lacking ‘downstream’ tidal control. The typical small-scale delta-lobe avulsion cycles: mouth bar formation, backward sedimentation, upstream avulsion, channel progradation and mouth bar formation are reproduced in the splay-modelling. The pacing of splay development, however, is relatively fast due to the presence of tides and the water depth in the receiving basin. The diversion had a strong upstream impact, in particular on water levels in the feeding river channel at stages of peak flow. For two centuries levels were significantly raised, because bifurcation-imposed reduced transport capacity and associated sedimentation at the diversion site increased hydraulic roughness and hampered flow. These findings have implications regarding flood

  5. Coastal Dynamics of the Ganges-Brahmaputra Delta: 1988-2014

    NASA Astrophysics Data System (ADS)

    Chiu, S.; Sousa, D.; Mondal, D. R.; Small, C.

    2014-12-01

    In this study we quantify erosional and depositional processes in the coastal zone (including tidal flats and river channels) of the lower Ganges Brahmaputra delta (GBD). Recent availability of accurately coregistered, radiometrically intercalibrated, Landsat TM, ETM+ & OLI collected since 1988 allows for spatiotemporal (ST) analyses of both natural and anthropogenic processes in the coastal zone on seasonal to interannual time scales. We quantify changes in the coastal zone using 106 cloud-free acquisitions in the area of the 3 Landsat scenes spanning the lower delta. Changes are quantified using multitemporal spectral mixture analysis of exoatmospheric reflectance to represent land cover and water bodies as continuous fields of soil and sediment substrates (S), vegetation (V), and dark surfaces (D; water & shadow). We also use MODIS 16-day EVI composite time series and high spatial resolution (2-4 m) imagery post-2000 to extend and vicariously validate the Landsat-derived observations. Because water levels on the lower delta change by several meters on time scales of hours (tides), months (discharge) and years (relative sea level rise), we use a network of 11 tide gauges to distinguish the effects of these changes in the coastal zone imaged by Landsat. Cross spectral analysis of this network of tide gauge records quantifies the dominant periods and relative magnitudes as well as phase of water level variations across these time scales. Tide gauge records are used to identify Landsat scenes acquired at similar water levels as well as the effects of water level on variations in tidal flats. Water level and water leaving radiance are used to map spatiotemporal variations in suspended sediment. Tri-temporal change maps of SVD fractions show progressive changes of coastlines throughout the study period. We find significant change in tidal flats in acquisitions from different tidal heights, alluding to the importance of tidal phase in coastal analyses. Erosion of

  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. Tidal influence on subtropical estuarine methane emissions

    NASA Astrophysics Data System (ADS)

    Sturm, Katrin; Grinham, Alistair; Werner, Ursula; Yuan, Zhiguo

    2014-05-01

    The relatively unstudied subtropical estuaries, particularly in the Southern Hemisphere, represent an important gap in our understanding of global greenhouse gas (GHG) emissions. These systems are likely to form an important component of GHG budgets as they occupy a relatively large surface area, over 38 000 km2 in Australia. Here, we present studies conducted in the Brisbane River estuary, a representative system within the subtropical region of Queensland, Australia. This is a highly modified system typical of 80% of Australia's estuaries. Generally, these systems have undergone channel deepening and straightening for safer shipping access and these modifications have resulted in large increases in tidal reach. The Brisbane River estuary's natural tidal reach was 16 km and this is now 85 km and tidal currents influence double the surface area (9 km2 to 18 km2) in this system. Field studies were undertaken to improve understanding of the driving factors behind methane water-air fluxes. Water-air fluxes in estuaries are usually calculated with the gas exchange coefficient (k) for currents and wind as well as the concentration difference across the water-air interface. Tidal studies in the lower and middle reaches of the estuary were performed to monitor the influence of the tidal stage (a proxy for kcurrent) on methane fluxes. Results for both investigated reaches showed significantly higher methane fluxes during the transition time of tides, the time of greatest tidal currents, than during slack tide periods. At these tidal transition times with highest methane chamber fluxes, lowest methane surface water concentrations were monitored. Modelled fluxes using only wind speed (kwind) were at least one order of magnitude lower than observed from floating chambers, demonstrating that current speed was likely the driving factor of water-air fluxes. An additional study was then conducted sampling the lower, middle and upper reaches during a tidal transition period

  8. 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.

  9. 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

  10. Radar remote sensing for levee health assessment in the Sacramento-San Joaquin Delta

    NASA Astrophysics Data System (ADS)

    Sharma, P.; Jones, C. E.; Dudas, J.; Bawden, G. W.; Deverel, S. J.

    2014-12-01

    Levees and dikes form extensive flood protection infrastructure that often also serve critical water conveyance functions. We have studied the use of radar remote sensing for providing health assessment of levees, focusing on California's levee system. The Sacramento-San Joaquin Delta, which lies directly east of San Francisco Bay, is an area comprised of tidal marshland and reclaimed land in the form of ~60 islands surrounded by 1700 km of levees. Improved knowledge of subsidence across the region is needed to maintain the integrity of the Delta levee system, which protects the integrity and quality of the state's primary water supply. The western Delta is particularly critical because levee failure in this area would rapidly draw water of high salinity content into the channels conveying the fresh water supply. Here we report on a study that uses radar interferometry to measure the spatially and temporally varied levee movement and subsidence in the area, focusing particularly on Sherman Island, the westernmost island of the Delta. We use data from NASA's L-band (23.79 cm) Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) collected at 6-week average interval from July 2009 through the current day. We show preliminary results for localized movement on and near the levees and for island-scale subsidence and discuss the techniques used for these measurements and how they could contribute to emergency response.