Science.gov

Sample records for channel tidal delta

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    SciTech Connect

    Schatzinger, R.A.; Tomutsa, L.

    1997-08-01

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

  4. Tidal controls on river delta morphology

    NASA Astrophysics Data System (ADS)

    Hoitink, A. J. F.; Wang, Z. B.; Vermeulen, B.; Huismans, Y.; Kästner, K.

    2017-09-01

    River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Despite global concerns about these issues, human activity in the world’s largest deltas intensifies. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure. Emerging insights into tidal controls on river delta morphology suggest that--despite the active morphodynamics in tidal channels and mouth bar regions--tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows. Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide. These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas, including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  6. 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.

  7. On funneling of tidal channels

    NASA Astrophysics Data System (ADS)

    Lanzoni, S.; D'Alpaos, A.

    2015-03-01

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

  8. Computer Simulations of Deltas with Varying Fluvial Input and Tidal Forcing

    NASA Astrophysics Data System (ADS)

    Sun, T.

    2015-12-01

    Deltas are important depositional systems because many large hydrocarbon reservoirs in the world today are found in delta deposits. Deltas form when water and sediments carried by fluvial channels are emptied to an open body of water, and form delta shaped deposits. Depending on the relative importance of the physical processes that controls the forming and the growth of deltas, deltas can often be classified into three different types, namely fluvial, tidal and wave dominated delta. Many previous works, using examples from modern systems, tank experiments, outcrops, and 2 and 3D seismic data sets, have studied the shape, morphology and stratigraphic architectures corresponding to each of the deltas' types. However, few studies have focused on the change of these properties as a function of the relative change of the key controls, and most of the studies are qualitative. Here, using computer simulations, the dynamics of delta evolutions under an increasing amount of tidal influences are studied. The computer model used is fully based on the physics of fluid flow and sediment transport. In the model, tidal influences are taken into account by setting proper boundary conditions that varies both temporally and spatially. The model is capable of capturing many important natural geomorphic and sedimentary processes in fluvial and tidal systems, such as channel initiation, formation of channel levees, growth of mouth bars, bifurcation of channels around channel mouth bars, and channel avulsion. By systematically varying tidal range and fluvial input, the following properties are investigated quantitatively: (1) the presence and the form of tidal beds as a function of tidal range, (2) change of stratigraphic architecture of distributary channel mouth bars or tidal bars as tidal range changes, (3) the transport and sorting of different grainsizes and the overall facie distributions in the delta with different tidal ranges, and (4) the conditions and locations of mud drapes

  9. 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

  10. Tidal hydrodynamics and erosional power in the Fly River delta, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Canestrelli, A.; Fagherazzi, S.; Defina, A.; Lanzoni, S.

    2010-12-01

    A two-dimensional numerical model is used to study tidal hydrodynamics and distribution of bed shear stresses in the Fly River delta, Papua New Guinea. The model describes the propagation of the tidal wave within the delta and along the river. Model results indicate that tidal discharge at the mouths of the distributary channels is between 10 and 30 times larger than the river discharge, and that the upstream part of the delta is flood-dominated, whereas near the mouth, the delta is ebb-dominated. Numerical simulations allow us to investigate the sensitivity of fluxes and bottom stresses with respect to the variations of sea level and the area of delta islands. The results suggest that a decrease in the total area of the delta occupied by islands increases the tidal prism and, therefore, the bed shear stresses. Similarly, an increase in sea level reduces the dissipation of the tidal signal and speeds up the propagation of the tidal wave within the delta, thus yielding higher discharges and increased bed shear stresses.

  11. 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

  12. 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

  13. An unstructured grid model of tidal intrusion in a complex mega delta

    NASA Astrophysics Data System (ADS)

    Bricheno, Lucy; Wolf, Judith; Islam, Saiful

    2017-04-01

    The finite volume community ocean model (FVCOM) has been applied to the Ganges-Brahmaputra-Meghna (GBM) delta, in the northern part of the Bay of Bengal, in order to simulate tidal hydrodynamics and freshwater flow in a complex river system. This is the first 3D baroclinic model covering the whole GBM delta from deep water beyond the shelf break to 250 km inland, the limit of tidal penetration. The delta region is limited in observations of bathymetry and water level, which poses a challenge for configuration and validation of accurate hydrodynamic models in this area. We examine the controls on tidal penetration from the open coast into the intricate system of river distributary channels and creeks. The tidal simulation was validated against the limited available data in order to have confidence in the delta model results when it is used to investigate baroclinic processes, river salinity and future change in this area. The performance of the FVCOM tidal model configuration has been evaluated at a range of sites in order to assess its ability to capture water levels, which vary over both a tidal and seasonal cycle. This modelling approach has been used to improve understanding of the hydrodynamics of the GBM delta system. Tidal penetration into the delta distributaries is controlled by a combination of bathymetry, channel geometry, bottom friction, and river flow. FVCOM is seen to capture the leading tidal constituents satisfactorily at coastal tide gauge stations, with small root-mean-squared errors of 10 cm on average. Inland, the model compares favourably with twice-daily observed water levels at thirteen stations where it is able to capture both tidal and annual timescales in the estuarine system. When the river discharge is particularly strong the tidal range can be reduced, as the tide and river flows oppose each other. The bathymetry is found to be the most influential control on water levels within the delta, though tidal penetration can be significantly

  14. Tidal impacts on the subtidal flow division at the main bifurcation in the Yangtze River Delta

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Feng, Haochuan; Hoitink, A. J. F.; Zhu, Yuliang; Gong, Fei; Zheng, Jinhai

    2017-09-01

    Flow division at bifurcations in the Yangtze Estuary has received ample attention, since it may control the pathways of terrestrial sediments over downstream river branches including the 12.5 m Deepwater Navigation channel. While some efforts have been made to interpret flow division at the bifurcations of the Yangtze Estuary, little attention has been paid to the role of tides. Flow division at estuarine bifurcations is made complicated by tides that propagate from the outlet of the tidal channels into the delta. To quantify the tidal influence on the distribution of river discharge, and more generally, to understand the mechanisms governing the subtidal flow division at the tidally affected bifurcation in the Yangtze River Delta, a two-dimensional hydrodynamic model is employed. In this model, the landward boundary is chosen beyond the tidal limit, where the tidal motion has faded out entirely. The seaward boundary is chosen such that the river discharge does not influence the water level. Subtidal discharges are decomposed using the method of factor separation, to distinguish between the effects of tides, river discharge and river-tide interactions on the subtidal flow division. Results indicate that tides modify the river discharge distribution over distributary channels in the Yangtze River Delta, particularly in the dry season. A significant difference in the subtidal flow division during spring tide and neap tide shows that the tidally averaged flow division over the distributaries in the delta greatly depends on tidal amplitude. By varying the river discharge at the landward boundary and amplitudes and phases of the principal tidal constituents at the seaward boundary of the established model, the sensitivities of the subtidal flow division to the river discharge and tidal amplitude variation were investigated in detail. Generally, the tidal impacts on the subtidal flow division are around 12% to 22%, with river discharge varying from 30,000 m3s-1 to 20

  15. 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.

  16. 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.

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

    DOE PAGES

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

    2014-12-17

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  19. 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.

  20. 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

  1. Distributary channels in the fluvial to tidal transition zone

    NASA Astrophysics Data System (ADS)

    Kästner, K.; Hoitink, A. J. F.; Vermeulen, B.; Geertsema, T. J.; Ningsih, N. S.

    2017-03-01

    Coastal lowland plains under mixed fluvial-tidal influence may form complex, composite channel networks, where distributaries blend the characteristics of mouth bar channels, avulsion channels, and tidal creeks. The Kapuas coastal plain exemplifies such a coastal plain, where several narrow distributaries branch off the Kapuas River at highly asymmetric bifurcations. A comprehensive geomorphological analysis shows that trends in the channel geometry of all Kapuas distributaries are similar. They consist of a short, converging reach near the sea and a nonconverging reach upstream. The two parts are separated by a clear break in scaling of geometrical properties. Such a break in scaling was previously established in the Mahakam Delta, which suggests that this may be a general characteristic in the fluvial to tidal transition zone. In contrast to the geometrical trend similarities, a clear difference in bed material between the main and side distributaries is found. In the main distributary, a continuous trend of downstream fining is established, similar to what is often found in lowland rivers. In the side distributaries, bed material coarsens in the downstream direction. This indicates an undersupply of sediment to the side distributaries, which may contribute to their long-term stability as established from historical maps. Tides may be the main agent preventing fine sediment to settle, promoting residual transport of fine material to the coastal ocean.

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

    NASA Astrophysics Data System (ADS)

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

    2006-11-01

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

  3. 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).

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

    USGS Publications Warehouse

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

  6. 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

  7. 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.

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

    DTIC Science & Technology

    1991-08-01

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

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

    DTIC Science & Technology

    1993-02-01

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

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

    USGS Publications Warehouse

    Morgan, Tara; Wright, Scott A.

    2016-01-01

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

  11. 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.

  12. Stage-discharge relationship in tidal channels

    NASA Astrophysics Data System (ADS)

    Kearney, W. S.; Mariotti, G.; Deegan, L.; Fagherazzi, S.

    2016-12-01

    Long-term records of the flow of water through tidal channels are essential to constrain the budgets of sediments and biogeochemical compounds in salt marshes. Statistical models which relate discharge to water level allow the estimation of such records from more easily obtained records of water stage in the channel. While there is clearly structure in the stage-discharge relationship, nonlinearity and nonstationarity of the relationship complicates the construction of statistical stage-discharge models with adequate performance for discharge estimation and uncertainty quantification. Here we compare four different types of stage-discharge models, each of which is designed to capture different characteristics of the stage-discharge relationship. We estimate and validate each of these models on a two-month long time series of stage and discharge obtained with an Acoustic Doppler Current Profiler in a salt marsh channel. We find that the best performance is obtained by models which account for the nonlinear and time-varying nature of the stage-discharge relationship. Good performance can also be obtained from a simplified version of these models which approximates the fully nonlinear and time-varying models with a piecewise linear formulation.

  13. 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

  14. 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.

  15. 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

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

    USGS Publications Warehouse

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

    2014-01-01

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

  17. On the tidal prism-channel area relations

    NASA Astrophysics Data System (ADS)

    D'Alpaos, Andrea; Lanzoni, Stefano; Marani, Marco; Rinaldo, Andrea

    2010-03-01

    We verify the broad applicability of tidal prism cross-sectional area relationships, originally proposed to relate the total water volume entering a lagoon during a characteristic tidal cycle (the tidal prism) to the size of its inlet, to arbitrary sheltered cross sections within a tidal network. We suggest, with reasonable approximation defining a statistical tendency rather than a pointwise equivalence, that the regime of tidal channels may be anywhere related to local landscape-forming prisms embedded in a characteristic spring tide oscillation. The importance of the proposed extension stems from its potential for quantitative predictions of the long-term morphological evolution of whole tidal landforms, in response to forcings affecting tidal prisms. This is the case, in particular, for alterations of relative mean sea levels possibly driven by climate change. Various 1-D and 2-D morphodynamic and hydrodynamic models are employed to evaluate peak flow rates, bottom shear stresses, and the ensuing local tidal prisms. One-dimensional morphodynamic models describing both the longitudinal and cross-sectional evolution of tidal channels are used to verify the validity of the relationship for sheltered sections. Relevant hydrodynamic features determined through accurate 2-D numerical models are compared with those obtained through time-invariant equivalents, defining a mean watershed by an energy landscape from averaged free surface gradients. Empirical evidence gathered within the lagoon of Venice (Italy) supports the proposed extension. We conclude that the geomorphic law relating tidal prisms to channel cross-sectional areas anywhere within a tidal landscape is a valuable tool for studies on long-term tidal geomorphology.

  18. Predicting the Evolution of Tidal Channels in Muddy Coastlines

    DTIC Science & Technology

    2010-09-01

    marshes. We deployed a Nortek ADCP at the mouth of the creek to measure tidal elevation, water velocity, and concentration of suspended sediment in...time. A Sontek ADV was deployed in the bay in front of the channel mouth to record wave characteristics during the studied period. 2.2 TIDAL CHANNEL...Willapa Bay. Preliminary results show that wave characteristics during extreme events are well simulated by the wave model SWAN (Boij et al. 1999

  19. Tidal Energy Resource Assessment in Chacao Channel, Chile

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Vegetation causes channel erosion in a tidal landscape

    NASA Astrophysics Data System (ADS)

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

    2007-07-01

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

  1. 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.

  2. Salt marsh vegetation promotes efficient tidal channel networks.

    PubMed

    Kearney, William S; Fagherazzi, Sergio

    2016-07-19

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

  3. 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

  4. In the Balance: Natural v. Embanked Landscapes in the Ganges-Brahmaputra Tidal Delta Plain

    NASA Astrophysics Data System (ADS)

    Wallace Auerbach, L.; Goodbred, S. L.; Mondal, D. R.; Wilson, C.; Ahmed, K.; Roy, K.; Steckler, M. S.; Gilligan, J. M.; Nooner, S. L.

    2013-12-01

    sediment, accounting for decades-worth of normal sedimentation, but only partly restoring the elevation lost over the previous five decades. This work implements field measurements and a conceptual model of the lower delta plain to establish a budget for observed elevation differences among local, relative water levels and the natural and human-altered landscapes. We demonstrate that embanked regions of the lower delta are more vulnerable than pristine areas to changes in sea level caused by impeded sediment delivery as a result of decoupling the tidal channel-landscape system. The elevation disparity that has developed in the past 50 years is equivalent to ~2 cm/yr of RSL rise. This rate is more than twice the upper end of Intergovernmental Panel on Climate Change projections for future sea-level rise, making these poldered landscapes a very useful, albeit troubling, analog for studying the impact of increased SLR in coming decades.

  5. Tidally-Driven Flow through a System of Interconnected Tidal Channels with Varying Hydraulic Geometry and Planform Configuration

    NASA Astrophysics Data System (ADS)

    Bain, R. L.; Goodbred, S. L., Jr.; Hale, R. P.

    2016-12-01

    In tidally-dominated environments such as the Ganges-Brahmaputra-Meghna Delta in Bangladesh and India, bidirectional flow interacts with the landscape to produce densely interconnected distributary channel networks. The exchange of discharge between adjacent channels results in counterintuitive hydrodynamic behavior throughout the system. Here, we present complementary field and modeling results to evaluate the propagation of mass and energy through two major tidal channels in the Polder 32 region of southwest Bangladesh. The Sibsa and Pussur Rivers initiate at an estuarine bifurcation 30 km north of the Bay of Bengal before extending an additional 60 km inland to our study area, where four secondary channels (from south to north, the Bhadra, Dhaki, Gorkhali, and Shengrali Rivers) reconnect these two primary conduits. In August/September 2015, we deployed an array of seven pressure sensors to collect high-resolution time series of water surface elevation over a monsoon season spring-neap cycle. Our data reveal several unexpected phenomena in tidal waveform propagation: (1) during spring tides, high water occurs at Sibsa RK 60 (RK—river kilometer; all distances measured from the Sibsa/Pussur bifurcation) approximately twenty minutes before Sibsa RK 51, despite distance from the coast suggesting that the opposite should occur; (2) high water at Pussur RK 50 precedes Sibsa RK 51 by over an hour, although the Pussur is significantly shallower than the Sibsa and should display a lower waveform celerity; and (3) the region experiences up to two hours of high water slack during spring tides. Using a numerical solution to the Saint Venant equations for a network of channels, we test several hypotheses concerning the physical processes responsible for our field observations. Specifically, our modeling results assess the effect of river discharge on tidal phasing throughout the system, the importance of secondary channel size and configuration, and the possibility of a

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

    DTIC Science & Technology

    2013-09-30

    Walfir, P. W.; Silva, M. S.; Silveira, O. F.; Fricke, A. T.; Water and sediment transport in the Amazon tidal river and its tributaries (Abstract ID...transport dynamics that act to effect the delivery and retention of fine-grained sediment through tidal rivers and in shallow- water coastal regions. We...system. We report here on preliminary results from the Tropical Deltas DRI on the Mekong River , along with results from the Amazon River delta system

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    DTIC Science & Technology

    2013-09-30

    scales), and thereby validate localized measurements and numerical models of sediment transport for diverse tidal systems (tidal flats, mangrove forests...likely transported landward from the continental shelf. 3) bathymetry – A simple single-beam depth finder gave good cross-channel bathymetric data...and A.S. Ogston, in preparation, Fluvial sediment dispersal through an insular sea: modern sedimentation associated with the Skagit River delta

  9. Modelling channel network formation: the effect of tidal range and initial bathymetry

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    morphological behaviour of the tidal system to changes in tidal range and initial bathymetry. Initial bathymetric conditions have been varied in terms of the initial depth of the basin. In the case of a shallow basin and a large tidal range, significant bathymetric changes occur in the first few decades with the rapid formation of channels and intertidal areas. The formation of a well developed channel network is accompanied by a transition from flood-dominated to ebb-dominated sediment transport. When the basin is deeper, large tidal range conditions facilitate the transport of large volumes of sediment from the offshore area into the basin. A flood-tidal delta forms which, over long time scales, channelizes and a complete tidal channel network develops. Analysis of the hypsometry of the tidal basins indicates that large-scale bathymetric changes result in hypsometric curves which resemble those of natural systems. However, when the tidal basin is deep and the tidal range small, channel initiation and adaptation in the hypsometry are slowed down and an underdeveloped channel network remains present.

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

    USGS Publications Warehouse

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

    2003-01-01

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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

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

    NASA Astrophysics Data System (ADS)

    Nhan, Nguyen Huu

    2016-12-01

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

  17. Scaling of equilibrium bed profiles in short tidal channels

    NASA Astrophysics Data System (ADS)

    Toffolon, M.; Lanzoni, S.

    2009-04-01

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

  18. 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

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

    NASA Astrophysics Data System (ADS)

    Tanaka, A.

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  1. Sedimentary facies of distributary channels of the whole Mekong River delta

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    The Mekong River delta, one of the world's largest deltas, has extended from Phnom Penh in Cambodia (apex) to the Vietnam coast from the Saigon River mouth in its eastern end to Cape Camau in its western end, and has the delta plain area of > 50,000 km2. The delta has prograded more than 200 km for 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. Sea level in winter (dry season) is higher than summer by 30-40 cm due to setup in the South China Sea basin by northerly. Mean wave height is 0.9 m. The water discharge of the Mekong 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, controlled by a monsoonal tropical-subtropical regime. The flow at Phnom Penh, Cambodia, reaches a maximum in October and a minimum in May. SSC has also a seasonal change from more than 300 mg/L in a wet season to less than 50 mg/L in a dry season at the Cambodia-Vietnam border. 1m tidal water-level changes are observed at the border in a dry season. To understand the combined influences of rivers and tides on river-bottom sediments, we have collected 210 surface samples from distributary channels of the whole Mekong River delta in Vietnam from the Cambodia border to five river mouths during a dry season from January to May 2015. Additional sampling expedition in a wet season will be conducted in October 2015 for one distributary channel from the border to its river mouth. The characteristics of channel bottom sediments in a dry season show clearly river- and tide-dominated areas spatially, based on sedimentary facies (grain size and sedimentary structures). Tidal rhythmites are well recognized within 100km from the river mouths and mud balls are well found in the middle reach of the survey area. The spatial distribution of river- and tide-dominated areas is closely linked with the morphology

  2. Bottom morphology in the Song Hau distributary channel, Mekong River Delta, Vietnam

    NASA Astrophysics Data System (ADS)

    Allison, Mead A.; Dallon Weathers, H.; Meselhe, Ehab A.

    2017-09-01

    Field studies in the Song Hau distributary of the Mekong Delta in Vietnam conducted at high (Sept.-Oct 2014) and low (March 2015) Mekong River discharge are utilized to examine channel bottom morphology and links with sediment transport in the system. Multibeam bathymetric mapping surveys over the entire channel complex in the lower 80 km of the distributary channel, and over 12- to 24-h tidal periods at six transect locations in the reach are used to characterize bottom type and change on seasonal and tidal timescales, supplemented by bottom sampling. The results of this study indicate that the largest proportion of channel floor (up to 80% of the total area) is composed of substratum outcrops of relict sediment units deposited during the progradation of the delta in the last 3.5 ka. These take the form of outcrops that are either (1) steep-sided, tabular channel floor, (2) steep-sided sidewall, or (3) relatively flat channel floor. Flatter outcrops of channel floor substratum are identified by the presence of sedimentary furrows (<0.5 m deep) incised into the channel bottom that are exposed at high discharge and oriented along channel and laterally continuous for kilometers. These furrows are persistent in location and extent across tidal cycles and appear to be incised into relict units, sometimes with a thin surficial layer of modern sediment observable in bottom grabs. The extent of substratum exposure, greater than that observed previously in low tidal energy systems like the Mississippi River, may relate both to a relatively low sand supply from the catchment, and/or to an efficient transfer of both sand and mud through this tidally energetic channel. Sand bottom areas forming dunes, comprise about 19% of the channel floor over the study area and are generally less than a few meters thick except on bar extensions of mid-channel islands. Both sandy and substratum areas are mantled by soft muds 0.25-1 m thick during low discharge in the estuarine section of

  3. 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

  4. 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

  5. Sedimentation in the tidal marshes of the Sacramento-San Joaquin Delta, CA

    NASA Astrophysics Data System (ADS)

    Reed, D. J.

    2001-05-01

    One of the major goals of the CALFED Bay/Delta Program is "restoring ecosystem health" and the restoration of shallow-water habitat within the Sacramento-San Joaquin Delta is deemed a key strategy in meeting this goal. Over 90% of the once vast tidal-freshwater wetlands of the Sacramento-San Joaquin Delta have been leveed and removed from tidal and floodwater inundation. The main approach in these areas is to breach and/or remove the levees surrounding Delta islands. However, experience so far with levee-breach occurrences, both planned and unplanned, has shown that the transition from shallow open water habitats to tule marshes occurs slowly if at all. Sedimentation rates in tidal marshes are an important control on this transition. This study encompasses three regions of the delta that are characterized by different regimes of sediment supply and tidal energy - potential controlling factors on vertical accumulation processes. In each region a natural site and a breached levee site were selected for study. Measured rates of accretion are in excess of 10 mm/yr. The main control on variations in soil accumulation appears to be mineral sediment accumulation. The pattern of mineral sediment accumulation among our sites confirms the original hypotheses governing site selection. The northern delta has higher rates of mineral sediment accumulation than other areas while rates of organic accumulation are remarkably similar among areas. Interannual changes in vegetation associated with minor variations in salinity, particularly in the western delta, may influence subsurface biotic contributions to marsh elevation change.

  6. Sediment and Vegetation Controls on Delta Channel Networks

    NASA Astrophysics Data System (ADS)

    Lauzon, R.; Murray, A. B.; Piliouras, A.; Kim, W.

    2016-12-01

    Numerous factors control the patterns of distributary channels formed on a delta, including water and sediment discharge, grain size, sea level rise rates, and vegetation type. In turn, these channel networks influence the shape and evolution of a delta, including what types of plant and animal life - such as humans - it can support. Previous fluvial modeling and flume experiments, outside of the delta context, have addressed how interactions between sediment and vegetation, through their influence on lateral transport of sediment, determine what type of channel networks develops. Similar interactions likely also shape delta flow patterns. Vegetation introduces cohesion, tending to reduce channel migration rates and strengthen existing channel banks, reinforcing existing channels and resulting in localized, relatively stable flow patterns. On the other hand, sediment transport processes can result in lateral migration and frequent switching of active channels, resulting in flow resembling that of a braided stream. While previous studies of deltas have indirectly explored the effects of vegetation through the introduction of cohesive sediment, we directly incorporate key effects of vegetation on flow and sediment transport into the delta-building model DeltaRCM to explore how these effects influence delta channel network formation. Model development is informed by laboratory flume experiments at UT Austin. Here we present initial results of experiments exploring the effects of sea level rise rate, sediment grain size, vegetation type, and vegetation growth rate on delta channel network morphology. These results support the hypothesis that the ability for lateral transport of sediment to occur plays a key role in determining the evolution of delta channel networks and delta morphology.

  7. The Coastline Evolution of an Abandoned Deltaic Lobe and the Fate of its Relict Distributary Channel: A Case Study from the Huanghe (Yellow River) Delta, China.

    NASA Astrophysics Data System (ADS)

    Carlson, B.; Nittrouer, J. A.; Kineke, G. C.; Moodie, A. J.; Ma, H.; Kumpf, L.

    2016-12-01

    A high sediment load and frequent flooding events drive rapid modification to the coastline of the Huanghe (Yellow River) delta, China. Distributary channel avulsions occur every 7-10 years, and each event results in the shifting of fluvial sediment supply over hundreds of square kilometers across the deltaic coastline. Upon lobe abandonment, the shoreline erodes at rates that reach kilometers per year, and low-lying regions of the delta are routinely inundated by tides. These processes rework the sediment deposit, and while much of this material is advected basinward, some is transported landward via tidal channels that occupy the abandoned distributary channel. Over a yearly timescale, the relict channel fills with sediment, the delta lobe converts to a tidal flat, and the rate of coastline retreat decreases. The focus of this study is to validate a physical model of the time evolution of the morphodynamics using data collected from field studies, as well as time-series satellite imagery. Sedimentological analysis of seventeen 6-m cores extracted from a lobe abandoned in 1996 documents the abrupt transition from the relict channel bed (comprised of sand) to the ongoing tidal flat sedimentation (comprised of mud). The thickness of the tidally-influenced mud deposit varies across the old channel, and is based on the inherited bed morphology and proximity to the active tidal channel. For example, sedimentation rates, as estimated using a numerical model, are higher near the tidal channel and decrease with lateral distance from this source, and are also a function of the local elevation of the tidal flat surface relative to the tidal amplitude. Overall, predicted sedimentation rates on the tidal flat - reaching several centimeters per year - are in agreement with field observations. Our results indicate that after 20 years of morphological adjustment following abandonment, this particular Yellow River delta lobe remains highly dynamic as result of active reworking of

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

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

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

  9. 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

  10. Effect of environmental change on the morphology of tidally influenced deltas over multi-decadal timescale

    NASA Astrophysics Data System (ADS)

    Angamuthu, Balaji; Darby, Stephen; Nicholls, Robert

    2017-04-01

    An understanding of the geomorphological processes affecting deltas is essential to improve our understanding of the risks that deltas face, especially as human impacts are likely to intensify in the future. Unfortunately, there is limited reliable data on river deltas, meaning that the task of demonstrating the links between morphodynamic and environmental change is challenging. This presentation aims to answer the questions of how delta morphology evolves over multi-decadal timescales under multiple drivers, focussing on tidally-influenced deltas, as some of these, such as the Ganges-Brahmaputra-Meghna (GBM) delta are heavily populated. A series of idealised model simulations over 102 years were used to explore the influence of three key drivers on delta morphodynamics, both individually and together: (i) varying combinations of water and sediment discharges from the upstream catchment, (ii) varying rates of relative sea-level rise (RSLR), and (iii) selected human interventions within the delta, such as polders, cross-dams and changing land cover. Model simulations revealed that delta progradation rates are more sensitive to variations in water discharge than variations in fluvial sediment supply. Unlike mere aggradation during RSLR, the delta front experienced aggradational progradation due to tides. As expected, the area of the simulated sub-aerial delta increases with increasing sediment discharge, but decreases with increasing water discharge. But, human modifications are important. For example, the sub-aerial delta shrinks with increasing RSLR, but it does not when the sub-aerial delta is polderised, provided the polders are restricted from erosion. However, the polders are vulnerable to flooding as they lose relative elevation and can make the delta building process unsustainable. Cross-dams built to steer zones of land accretion within the delta accomplish their local goal, but may not result in net land gain at the scale of the delta. Applying these

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  12. Eddy Generation and Shedding in a Tidally Energetic Channel

    NASA Astrophysics Data System (ADS)

    McIlvenny, J.; Gillibrand, P. A.; Walters, R. A.

    2016-02-01

    The Pentland Firth in northern Scotland, and its subsidiary channel the Inner Sound, are currently under scrutiny as the first tidal energy array in the world is installed during 2016. The tidal flows in the channel and sound have been intensively observed and modelled in recent years, and the turbulent nature of the flow, with features of eddy generation and shedding, is becoming increasingly well known. Turbulence and eddies pose potential risks to the turbine infrastructure through enhanced stress on the blades, while understanding environmental effects of energy extraction also requires accurate simulation of the hydrodynamics of the flow. Here, we apply a mixed finite element/finite volume hydrodynamic model to the northern Scottish shelf, with a particular focus on flows through the Pentland Firth and the Inner Sound. We use an unstructured grid model, which allows the open boundaries to be far removed from the region of interest, while still allowing a grid spacing of 40m in the Inner Sound. The model employs semi-implicit techniques to solve the momentum and free surface equations, and semi-Lagrangian methods to solve the material derivative in the momentum equation, making it fast, robust and accurate and suitable for simulating flows in irregular coastal ocean environments. The model is well suited to address questions relating to tidal energy potential. We present numerical simulations of tidal currents in The Pentland Firth and Inner Sound. Observed velocities in the Inner Sound, measured by moored ADCP deployments, reach speeds of up to 5 m s-1 and the model successfully reproduces these strong currents. In the simulations, eddies are formed by interactions between the strong flow and the northern and southern headlands on the island of Stroma; some of these eddies are trapped and remain locked in position, whereas others are shed and transported away from the generation zone. We track the development and advection of eddies in relation to the site of

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  15. 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

  16. Sediment- and hydro-dynamics of the Mekong Delta: From tidal river to continental shelf

    NASA Astrophysics Data System (ADS)

    Ogston, A. S.; Allison, M. A.; Mullarney, J. C.; Nittrouer, C. A.

    2017-09-01

    This introduction to the special issue entitled, "Sediment- and hydro-dynamics of the Mekong Delta: from tidal river to continental shelf", describes the setting and program design of collaborative studies with integrated field and modeling experiments in 2014-2015, along with associated research in the region. The Mekong River is among the largest on Earth in terms of water discharge, and much of the sediment delivered from the Tibetan Plateau has accumulated in the subaerial and subaqueous components of the Mekong Delta. As a group, the papers in this special issue describe the portion of the system where the sediment source signal is altered along the tidally influenced river and is delivered to the shorelines and continental shelf. The linked studies provide a holistic view of the system, and emphasize the interactions between hydrodynamics and sediment transport processes in sub-environments as sediment makes its way along the path from source to sink.

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

    DTIC Science & Technology

    1985-09-01

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

  18. Changes in surf zone morphodynamics driven by multi-decadal contraction of a large ebb-tidal delta

    NASA Astrophysics Data System (ADS)

    Hansen, J. E.; Barnard, P.; Elias, E.

    2012-12-01

    The impact of large-scale deflation (76 million m3 of sediment loss) and contraction (~1 km) of a 150 km2 ebb-tidal delta over a half-century on hydrodynamics and sediment transport at Ocean Beach in San Francisco, CA (USA), onshore of the delta, 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 indicate that along north/south trending Ocean Beach the contraction and deflation of the ebb-tidal delta has 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 north ~1 km toward the inlet while a persistent alongshore flow and transport divergence point migrated south by ~500 m (Figure 1). Alongshore migration of these features has resulted in an increasing portion of onshore migrating sediment from the ebb-tidal delta, inferred by the contraction, 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. The approach described here is broadly applicable for investigating the causes of long-term morphological changes along urbanized beaches adjacent to inlet mouths worldwide.Figure 1. Ebb-tidal delta bathymetry in 1956 (A) and 2005 (B), 2 m contour interval to 20 m. Schematized pattern of alongshore transport along Ocean Beach and transport of onshore migrating sediment from the ebb-tidal delta in 1956 (C) and 2005 (D).

  19. Temperature independent quantum well FET with delta channel doping

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  20. 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.

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

    USGS Publications Warehouse

    Hood, W. Gregory; Grossman, Eric E.; 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.

  2. 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.

  3. 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.

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

    SciTech Connect

    Yang, Zhaoqing; Wang, Taiping; Copping, Andrea

    2014-04-18

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

  5. 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.

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

    PubMed

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

    2014-04-01

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

  7. Monitoring bacterial indicators of water quality in a tidally influenced delta: A Sisyphean pursuit.

    PubMed

    Partyka, Melissa L; Bond, Ronald F; Chase, Jennifer A; Atwill, Edward R

    2017-02-01

    The Sacramento-San Joaquin Delta Estuary (Delta) is the confluence of two major watersheds draining the Western Sierra Nevada mountains into the Central Valley of California, ultimately terminating into San Francisco Bay. We sampled 88 sites once a month for two years (2006-2008) over 87 separate sampling events for a total of 1740 samples. Water samples were analyzed for fecal indicator bacteria (Escherichia coli, enterococci and fecal coliforms), and 53 other physiochemical, land use, and environmental characteristics. The purpose of the study was to create a baseline of microbial water quality in the Delta and to identify various factors (climatic, land use, tidal, etc.) that were associated with elevated concentrations of indicator bacteria. Fecal indicator bacteria generally had weak to modest relationships to environmental conditions; the strength and direction of which varied for each microbial indicator, drainage region, and across seasons. Measured and unmeasured, site-specific effects accounted for large portions of variance in model predictions (ρ=0.086 to 0.255), indicating that spatial autocorrelation was a major component of water quality outcomes. The effects of tidal cycling and lack of connectivity between waterways and surrounding landscapes likely contributed to the lack of association between local land uses and microbial outcomes, though weak associations may also be indicative of mismatched spatiotemporal scales. The complex nature of this system necessitates continued monitoring and regular updates to statistical models designed to predict microbial water quality. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  10. 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

  11. Suspended sediment transport under estuarine tidal channel conditions

    USGS Publications Warehouse

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

    1988-01-01

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

  12. 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.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    SciTech Connect

    Friedrichs, C.T.

    1993-02-01

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

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

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

    EPA Science Inventory

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

  19. 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 ...

  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.; Barnard, P.L.; Jaffee, B.E.; Schoellhamer, D.H.

    2013-01-01

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

  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. 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.

  3. Combining satellite photographs and raster lidar data for channel connectivity in tidal marshes.

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Hodges, Ben

    2017-04-01

    High resolution airborne lidar is capable of providing topographic detail down to the 1 x 1 m scale or finer over large tidal marshes of a river delta. Such data sets can be challenging to develop and ground-truth due to the inherent complexities of the environment, the relatively small changes in elevation throughout a marsh, and practical difficulties in accessing the variety of flooded, dry, and muddy regions. Standard lidar point-cloud processing techniques (as typically applied in large lidar data collection program) have a tendency to mis-identify narrow channels and water connectivity in a marsh, which makes it difficult to directly use such data for modeling marsh flows. Unfortunately, it is not always practical, or even possible, to access the point cloud and re-analyze the raw lidar data when discrepancies have been found in a raster work product. Faced with this problem in preparing a model of the Trinity River delta (Texas, USA), we developed an approach to integrating analysis of a lidar-based raster with satellite images. Our primary goal was to identify the clear land/water boundaries needed to identify channelization in the available rasterized lidar data. The channel extraction method uses pixelized satellite photographs that are stretched/distorted with image-processing techniques to match identifiable control features in both lidar and photographic data sets. A kmeans clustering algorithm was applied cluster pixels based on their colors, which is effective in separating land and water in a satellite photograph. The clustered image was matched to the lidar data such that the combination shows the channel network. In effect, we are able to use the fact that the satellite photograph is higher resolution than the lidar data, and thus provides connectivity in the clustering at a finer scale. The principal limitation of the method is the where the satellite image and lidar suffer from similar problems For example, vegetation overhanging a narrow

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

    PubMed

    Ralston, David K; Stacey, Mark T

    2007-06-01

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

  5. Numerical Modeling of Tidal Dynamics and Transport in the Multi-channel Estuary of the Mekong River

    NASA Astrophysics Data System (ADS)

    Vo, T. Q.; Reyns, J.; Kernkamp, H.; Roelvink, J. A.; Van der Wegen, M.

    2016-02-01

    The Mekong estuary is an area of high biodiversity in which the ecosystem has been influenced not only by natural factors but also by anthropogenic impacts (Quang et al., 2010). The former determine the water circulation such as tide propagation, river discharge and outflow plume behavior, while the latter consist of full-dyke systems in the flood zone, saline protection systems along the coast and in general much reduced mangrove forests along the river banks and coasts. These factors influence the coastal system directly and indirectly by changing the sediment dynamics. This study aims at understanding the tidal characteristics of this multi-channel estuary by simulating the water circulation and investigating impacts of tidal forcing on the flow regime. In order to achieve these objectives, a process-based approach by using Delft3D Flexible Mesh is applied to calculate the water regime in the delta. In addition, the model has been calibrated and validated through comparison of simulated and observed tidal harmonics during different discharge stages. The results show a good agreement between simulation and observation. The model will be used to understand the system-wide sediment dynamics in all the main branches of the tide-influenced Mekong delta, from Kratié in Cambodia to the East Sea shelf. An overview of the grid is given in the attached figure. The model includes a large stretch of shelf to enable studying the seasonal plume characteristics and is driven by astronomical boundary conditions at the seaward boundary and imposed discharges at Kratié; the Tonle Sap lake in Cambodia is included as it exerts a strong control on the upstream water levels. Acknowledgements: This study was funded by ONR under Grant N00014-12-1-0433 Modeling the Mekong Delta at three different scales

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Reungoat, David; Leng, Xinqian; Chanson, Hubert

    2017-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Toffolon, Marco; Lanzoni, Stefano

    2010-12-01

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

  9. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  12. Modeling delta growth concurrently with self-formed channels. Preliminary results on Lake Nasser Delta, Sudan and Egypt

    NASA Astrophysics Data System (ADS)

    Ezz, H.; Moussa, A.; Viparelli, E.; Parker, G.

    2012-12-01

    A one-dimensional model of delta growth, in which the channels are assumed to have self-constructed their cross sections, is presented. Preliminary validation results using field data collected on Lake Nasser Delta, Egypt and Sudan, where the effects of vegetal encroachment can be reasonably neglected, are discussed. The novel characteristic of the present model is that the average geometry of the channels on the delta top is computed by combining a criterion for channel formation with the standard backwater equation. As in previous models of delta growth, the delta top is divided into channelized and an unchannelized zones. Due to channel avulsion, bifurcation and migration on the delta top, sediment is gradually spread across the delta top, so that the average time rate of change of mean delta elevation is reasonably constant along a transect, but can vary in the downdelta direction. The overall geometry of the channelized portion of the delta, where significant transport of bed material occurs, is approximated as a rectangular channel. Channel width and depth are determined by the flow conditions. In particular, it is assumed that during floods, when the channel is morphologically active, the Shields number in the channels attains a constant formative value. This requires the delta evolution to be sufficiently slow to allow for the construction of the channels. Not far from the shoreline, where the channels are still actively building their cross-sections, the assumption of self-formed channels does not strictly hold. Flood discharge is described in terms of a morphologically active flood flow that lasts for a specified fraction of the year. This flood flow is assumed to be the formative discharge for the rectangular channel. Sediment is modeled in terms of bed material and washload. While transport rates of bed material are computed with an Engelund-Hansen-type total load relation, the equation of mass conservation of washload in suspension in the water column

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  14. Linking Sediment Management Practices, Ebb-Tidal Delta Evolution, and Shoreline Change in the San Francisco Bay Coastal System

    NASA Astrophysics Data System (ADS)

    Dallas, K. L.; Barnard, P. L.

    2008-12-01

    San Francisco Bay, California, is among the most anthropogenically-altered estuaries in the United States, but the effect of human activities on sediment transport to the coastal ocean has not been quantified. Since the discovery of gold in 1848, the bay floor has been regularly altered by a range of activities, including infill by hydraulic mining debris, mining of sand for bay development, dredging of harbors and waterways, and mining of sand and gravel for use as construction aggregate. Results from the compilation of historical records indicate that over 60 million m3 of sand-sized material has been removed for development and aggregate use alone. Long-term effects on the amount of sediment delivered to the coastal ocean are assessed using hydrographic survey data of the San Francisco Bar, a 120 km2 ebb tidal delta at the mouth of the bay. Data from 1855, 1873, 1900, 1955, and 2005 are compiled to create bathymetric models and compared to quantify net sedimentation volumes and rates of sediment deposition and erosion. Results from the last 50 years demonstrate that the ebb tidal delta has lost approximately 92 million m3 of material. Historical shoreline positions of ~20 km of adjacent beaches are also analyzed to determine if there is a statistical link between bay sediment removal, ebb tidal delta change, and beach evolution. This system-wide approach is unique to the region and emphasizes the often overlooked connection between San Francisco Bay and the coastal ocean.

  15. 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.

  16. High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon.

    PubMed

    Madricardo, Fantina; Foglini, Federica; Kruss, Aleksandra; Ferrarin, Christian; Pizzeghello, Nicola Marco; Murri, Chiara; Rossi, Monica; Bajo, Marco; Bellafiore, Debora; Campiani, Elisabetta; Fogarin, Stefano; Grande, Valentina; Janowski, Lukasz; Keppel, Erica; Leidi, Elisa; Lorenzetti, Giuliano; Maicu, Francesco; Maselli, Vittorio; Mercorella, Alessandra; Montereale Gavazzi, Giacomo; Minuzzo, Tiziano; Pellegrini, Claudio; Petrizzo, Antonio; Prampolini, Mariacristina; Remia, Alessandro; Rizzetto, Federica; Rovere, Marzia; Sarretta, Alessandro; Sigovini, Marco; Sinapi, Luigi; Umgiesser, Georg; Trincardi, Fabio

    2017-09-05

    Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system.

  17. High resolution multibeam and hydrodynamic datasets of tidal channels and inlets of the Venice Lagoon

    PubMed Central

    Madricardo, Fantina; Foglini, Federica; Kruss, Aleksandra; Ferrarin, Christian; Pizzeghello, Nicola Marco; Murri, Chiara; Rossi, Monica; Bajo, Marco; Bellafiore, Debora; Campiani, Elisabetta; Fogarin, Stefano; Grande, Valentina; Janowski, Lukasz; Keppel, Erica; Leidi, Elisa; Lorenzetti, Giuliano; Maicu, Francesco; Maselli, Vittorio; Mercorella, Alessandra; Montereale Gavazzi, Giacomo; Minuzzo, Tiziano; Pellegrini, Claudio; Petrizzo, Antonio; Prampolini, Mariacristina; Remia, Alessandro; Rizzetto, Federica; Rovere, Marzia; Sarretta, Alessandro; Sigovini, Marco; Sinapi, Luigi; Umgiesser, Georg; Trincardi, Fabio

    2017-01-01

    Tidal channels are crucial for the functioning of wetlands, though their morphological properties, which are relevant for seafloor habitats and flow, have been understudied so far. Here, we release a dataset composed of Digital Terrain Models (DTMs) extracted from a total of 2,500 linear kilometres of high-resolution multibeam echosounder (MBES) data collected in 2013 covering the entire network of tidal channels and inlets of the Venice Lagoon, Italy. The dataset comprises also the backscatter (BS) data, which reflect the acoustic properties of the seafloor, and the tidal current fields simulated by means of a high-resolution three-dimensional unstructured hydrodynamic model. The DTMs and the current fields help define how morphological and benthic properties of tidal channels are affected by the action of currents. These data are of potential broad interest not only to geomorphologists, oceanographers and ecologists studying the morphology, hydrodynamics, sediment transport and benthic habitats of tidal environments, but also to coastal engineers and stakeholders for cost-effective monitoring and sustainable management of this peculiar shallow coastal system. PMID:28872636

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  19. 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

  20. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  2. Hydrometeorological controls on water level in a vegetated Chesapeake Bay tidal freshwater delta

    NASA Astrophysics Data System (ADS)

    Pasternack, Gregory B.; Hinnov, Linda A.

    2003-10-01

    Wind vectors, watershed discharge, and subestuarine water levels were monitored in a vegetated delta at the head of the Bush River, an upper Chesapeake Bay tributary in Maryland, during an El Niño/La Niña cycle 1995-1996 to investigate hydrometeorological processes that affect the tidal freshwater ecosystem located there. Time series of these processes were analyzed in both the time and frequency domains using such methods as flood frequency analysis, harmonic analysis, averaged and evolutionary power spectral analysis, and coherency spectral analysis. Wind speed variations with periods of 3-4 and 7 days were found to have both high spectral power and high statistical significance. The frequencies of these variations fluctuated over weeks to months and the amplitudes modulated seasonally, but the variations persisted interannually. Significantly greater subtidal wind speed variations in the prinicipal wind direction occurred during the cold and stormy La Niña winter of 1996 relative to the warm and dry El Niño winter of 1995. Data from five hurricanes occurring in the region during the study provided high-resolution snapshots of the mechanisms revealed by the time series analyses. Water level quickly responded to south-north directed wind speed fluctuations during the aperiodic hurricanes, illustrating the strong coupling between wind and water levels in this system. The magnitude of the response was large enough to determine the extent and duration of flooding over tens of hectares in important intertidal marsh habitats. Subtidal water level variations were greater during the La Niña period. During El Niño conditions, the east-west wind component played a larger role than during the La Niña period. Variations in local watershed discharge as well as Susquehanna River outflow had no measurable impact on water levels in the upper reaches of the Bush River tributary during the study.

  3. Large-Scale Numerical Simulations of Ocean and Tidal Channel Boundary Layers

    NASA Astrophysics Data System (ADS)

    Hamlington, P.; Smith, K.; Van Roekel, L. P.; Fox-Kemper, B.; Suzuki, N.; Sullivan, P. P.

    2016-12-01

    Ocean and tidal channel boundary layers are dynamically complex fluid environments that can span an enormous range of scales, from sub-meter scale vertical gradients to horizontal features extending to tens of kilometers or more. Resolving this full scale range in numerical simulations is a profoundly difficult computational challenge that requires modern petascale high-performance computing (HPC) resources. In this talk, we describe new scientific insights learned from large-scale numerical simulations of open ocean and tidal channel boundary layers performed on the Yellowstone and Janus supercomputers. All of the simulations were performed using the National Center for Atmospheric Research (NCAR) large-eddy simulation (LES) model, and the largest simulations required over one thousand computational cores. We describe results from a series of studies focused on four topics in particular: (i) the interactions between submesoscale eddies and Langmuir turbulence in the ocean mixed layer, (ii) frontogenesis in the ocean mixed layer, (iii) transport of reactive and non-reactive tracers in the upper ocean, and (iv) turbulence properties of tidal channel boundary layers for a range of conditions. The first three topic areas required HPC resources in order to resolve horizontal scales from 20km down to 5m and vertical scales from 100m down to roughly 1m over a period spanning tens of eddy turnover times. The fourth topic area used HPC resources to perform a broad-ranging parametric study of tidal channel boundary layers. We describe lessons learned while performing these simulations and provide an outlook for the future of ocean and tidal channel boundary layer simulations on exascale HPC resources. This research utilized the Janus supercomputer, supported by NSF (award CNS-0821794) and the University of Colorado at Boulder, and the Yellowstone supercomputer (ark:/85065/d7wd3xhc) provided by NCAR's Computational and Information Systems Laboratory, sponsored by NSF.

  4. 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.

  5. In situ measurements of shear stress, erosion and deposition in man-made tidal channels within a tidal saltmarsh

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    A field study was conducted in man-made ditches in a tidal saltmarsh in Lewes, Delaware, USA. Ditches are prevalent throughout tidal marshes along the Atlantic US coast, and influence hydrodynamics and sediment transport. The field study focused on measuring near-bed velocity, shear stress, sediment concentration, and bed level variability at 5 stations over a 3-week period. Velocities in the ditch (2-5 m wide, 1 m deep) peaked between 0.4 and 0.6 m/s and were slightly ebb dominated. Velocity and shear stress were maximum during a storm event, with peak shear stresses of 2 N/m2. Bed levels were estimated from acoustic amplitude return of a downward-looking velocity profiler. The bed level in the ditch at the landward locations increased ∼ 0.03 m over 3 weeks, while there was ∼ 0.01 m bed level decrease at the most seaward site suggesting a net import of sediment into the channel. At all sites, erosion (∼ 0.005-0.015 m) occurred during the accelerating phase of the flood tide, and accretion of a similar magnitude occurred during the decelerating phase of the ebb tide. This erosion-deposition sequence resulted in small net changes in bed level at the end of each tidal cycle. The intratidal behavior of the bed level was simulated using erosion and deposition flux equations based on shear stress, critical shear stress, and suspended sediment concentration. Erosion was predicted well with RMS errors on the order of 2 ṡ10-3 m. The bed level during the deposition phase could not be reproduced using the simple approach. Model inaccuracies for deposition were attributed to advection and variations in fall velocity due to flocculation that were not modeled due to lack of ground-truth observations.

  6. Influence of changes in hydrodynamic conditions on cadmium transport in tidal river network of the Pearl River Delta, China.

    PubMed

    Dou, Ming; Zuo, Qiting; Zhang, Jinping; Li, Congying; Li, Guiqiu

    2013-09-01

    With rapid economic development, the Pearl River Delta (PRD) of China has experienced a series of serious heavy metal pollution events. Considering complex hydrodynamic and pollutants transport process, one-dimensional hydrodynamic model and heavy metal transport model were developed for tidal river network of the PRD. Then, several pollution emergency scenarios were designed by combining with the upper inflow, water quality and the lower tide level boundary conditions. Using this set of models, the temporal and spatial change process of cadmium (Cd) concentration was simulated. The influence of change in hydrodynamic conditions on Cd transport in tidal river network was assessed, and its transport laws were summarized. The result showed the following: Flow changes in the tidal river network were influenced remarkably by tidal backwater action, which further influenced the transport process of heavy metals; Cd concentrations in most sections while encountering high tide were far greater than those while encountering middle or low tides; and increased inflows from upper reaches could intensify water pollution in the West River (while encountering high tide) or the North River (while encountering middle or low tides).

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Jerolmack, Douglas J.

    2009-08-01

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

  9. 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).

  10. A study of long period forced waves in a tidal channel

    NASA Astrophysics Data System (ADS)

    Tejedor, B.; Martin, P.; Vidal, J.

    2003-04-01

    The study of long period forced waves, in rivers and water bodies connected to lakes, where the bottom friction forces are of importance, have been described by different authors (LeBlond, 1979; Robison et al., 1983; Hill, 1994). Godin, (1999) studies these forced waves and suggests that they are of a friction due origin, where the components of the incoming tidal interaction with the outgoing current cause their mutual damping and the creation of low-frecuency. Other authors (Aubrey and Speer, 1985), however, detect these waves in shallow estuaries, suggesting that the wind can also play an important role in the low-frequency wave generation. In this paper, the behaviour of these waves in a tidal channel is studied, explaining the origin of both forthnightly and monthly modulation of the frictional forces due to the variation in tidal velocities. The Sancti Petri tidal channel connects the inner Bay, a semi-closed body of water, to the Atlantic Ocean, with several smaller branching canals. Situated in the Southwest of the Coast of Spain, it has a longitude of 16 Km and little depth (3 m respect to the sea-mean level). The main hydrodynamic characteristics of the tidal wave propagation and associated currents have been described by Tejedor (2001) and Vidal (2002). This canal bears the peculiarity of being a canal whose extremes are connected to water bodies of different dynamic characteristics (Inner Bay and Atlantic Ocean), causing that the tidal wave propagation, which is of basically semi-diurnal character, occur almost simultaneously through each end of the canal. On the study of the of the sub-tidal sea-level fluctuation, carried out with the use of the tidal elevation measures taken in more than 9 stations throughout the canal, the presence of forced waves with monthly and fortnightly periods have been determined and not presenting any substantial differences of phases with the synodic tides. Resulting from this study, the wave amplitudes have been observed

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  12. General morphology and sediment patterns in tidal inlets

    NASA Astrophysics Data System (ADS)

    Hayes, Miles O.

    1980-04-01

    Tidal inlet sediments make up a significant portion of most barrier island complexes. Inlet-affiliated sedimentary units usually include an ebb-tidal delta (seaward shoal), a flood-tidal delta (landward shoal) and inlet-fill sequences created by inlet migration and recurved spit growth. The morphological components of ebb-tidal deltas include a main ebb channel flanked by linear bars on either side and a terminal sand lobe at the seaward end. This channel is bordered by a platform of sand dominated by swash bars which is separated from adjacent barrier beaches by marginal flood channels. The ebb-delta sand body is coarser-grained than other sedimentary units of the inlet and contains polymodal cross-bedding with a slight ebb dominance. Flood-tidal deltas consist of a flood ramp and bifurcating flood channels o the seaward side, which are dominated by flood currents and flood-oriented sand waves, and ebb shields, ebb spits and spillover lobes on the landward side, which contain an abundance of ebb-oriented bedforms. A proposed stratigraphic sequence for a typical flood-tidal delta contains bidirectional, large-scale crossbedded sand at the base, predominantly large-scale (flood-oriented) crossbedded sand in the middle, and finer-grained tidal flat and marsh sediment at the top. Inlets migrate at rates that vary from a few to several tens of meters per year, depending upon such variables as rate of longshore sediment transport and depth of the inlet. Inlet-fill sequences, which fine upward, contain coarse, bidirectional crossbedded sediments at the base, polydirectional crossbedded sands in the middle, and finer-grained aeolian sand at the top. Both tidal-delta morphology and relative size and abundance of ebb- and flood-tidal deltas are considerably different in different oceanographic settings. Microtidal (tidal range T.R. = 0-2 m) areas tend to have smaller ebb-tidal deltas and larger flood-tidal deltas; whereas, mesotidal (T.R. = 2-4 m) areas show just the

  13. 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

  14. 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

  15. 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

  16. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Residual flow, bedforms and sediment transport in a tidal channel modelled with variable bed roughness

    NASA Astrophysics Data System (ADS)

    Davies, A. G.; Robins, P. E.

    2017-10-01

    The frictional influence of the seabed on the tidal flow in shelf seas and estuaries is usually modelled via a prescribed, spatially/temporally invariant drag coefficient. In practice, the seabed exhibits considerable variability, particularly spatially, that should in principle be included in simulations. Local variations in the seabed roughness (ks) alter the flow strength and, hence, local sediment transport rates. The effect of using a spatially/temporally varying ks is assessed here with reference to a tidal channel (Menai Strait, N. Wales) in which the variability of the bedforms has been monitored using multi-beam surveying. The channel not only exhibits strong tidal flow, but also a residual induced flow that is used here as diagnostic to assess various bed roughness formulations tested in a Telemac model. Tidal simulations have been carried out with both constant and temporally/spatially variable ks, and the predicted residual flow is shown to be sensitive to these representations. For a mean spring-neap (SN) cycle with variable ks, the average residual flow is calculated to be 525 m3 s- 1, consistent with observations. This residual flow can be recovered using imposed, constant values of ks in the range 0.15 m to 0.3 m. The results suggest that the overall, effective roughness of the seabed is less than half of the maximum local roughness due to the dunes in mid-channel, but more than the spatially-averaged ks value in the channel as a whole by about 50%. Simulations carried out with an M2-alone tide using variable ks produce a somewhat smaller (by 7%) residual flow of 491 m3 s- 1. The use of an 'equivalent M2' tide of amplitude enhanced by 7.3% reconciles these estimates. The main contribution to ks is made by dunes which are modelled using Van Rijn's (2007) formulation subject to an additional 'history effect'. The modelled ks is found to equal approximately the observed height of the dunes along mid-channel transects rather than half the height as

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  3. 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

  4. Multi-scale temporal patterns in fish presence in a high-velocity tidal channel.

    PubMed

    Viehman, Haley A; Zydlewski, Gayle Barbin

    2017-01-01

    The natural variation of fish presence in high-velocity tidal channels is not well understood. A better understanding of fish use of these areas would aid in predicting fish interactions with marine hydrokinetic (MHK) devices, the effects of which are uncertain but of high concern. To characterize the patterns in fish presence at a tidal energy site in Cobscook Bay, Maine, we examined two years of hydroacoustic data continuously collected at the proposed depth of an MHK turbine with a bottom-mounted, side-looking echosounder. The maximum number of fish counted per hour ranged from hundreds in the early spring to over 1,000 in the fall. Counts varied greatly with tidal and diel cycles in a seasonally changing relationship, likely linked to the seasonally changing fish community of the bay. In the winter and spring, higher hourly counts were generally confined to ebb tides and low slack tides near sunrise and sunset. In summer and fall of each year, the highest fish counts shifted to night and occurred during ebb, low slack, and flood tides. Fish counts were not linked to current speed, and did not decrease as current speed increased, contrary to observations at other tidal power sites. As fish counts may be proportional to the encounter rate of fish with an MHK turbine at the same depth, highly variable counts indicate that the risk to fish is similarly variable. The links between fish presence and environmental cycles at this site will likely be present at other locations with similar environmental forcing, making these observations useful in predicting potential fish interactions at tidal energy sites worldwide.

  5. Multi-scale temporal patterns in fish presence in a high-velocity tidal channel

    PubMed Central

    Viehman, Haley A.

    2017-01-01

    The natural variation of fish presence in high-velocity tidal channels is not well understood. A better understanding of fish use of these areas would aid in predicting fish interactions with marine hydrokinetic (MHK) devices, the effects of which are uncertain but of high concern. To characterize the patterns in fish presence at a tidal energy site in Cobscook Bay, Maine, we examined two years of hydroacoustic data continuously collected at the proposed depth of an MHK turbine with a bottom-mounted, side-looking echosounder. The maximum number of fish counted per hour ranged from hundreds in the early spring to over 1,000 in the fall. Counts varied greatly with tidal and diel cycles in a seasonally changing relationship, likely linked to the seasonally changing fish community of the bay. In the winter and spring, higher hourly counts were generally confined to ebb tides and low slack tides near sunrise and sunset. In summer and fall of each year, the highest fish counts shifted to night and occurred during ebb, low slack, and flood tides. Fish counts were not linked to current speed, and did not decrease as current speed increased, contrary to observations at other tidal power sites. As fish counts may be proportional to the encounter rate of fish with an MHK turbine at the same depth, highly variable counts indicate that the risk to fish is similarly variable. The links between fish presence and environmental cycles at this site will likely be present at other locations with similar environmental forcing, making these observations useful in predicting potential fish interactions at tidal energy sites worldwide. PMID:28493894

  6. Multi-scale temporal patterns in fish presence in a high-velocity tidal channel

    DOE PAGES

    Viehman, Haley A.; Zydlewski, Gayle Barbin; Hewitt, Judi

    2017-05-11

    The natural variation of fish presence in high-velocity tidal channels is not well understood. A better understanding of fish use of these areas would aid in predicting fish interactions with marine hydrokinetic (MHK) devices, the effects of which are uncertain but of high concern. To characterize the patterns in fish presence at a tidal energy site in Cobscook Bay, Maine, we examined two years of hydroacoustic data continuously collected at the proposed depth of an MHK turbine with a bottom-mounted, side-looking echosounder. The maximum number of fish counted per hour ranged from hundreds in the early spring to over 1,000more » in the fall. Counts varied greatly with tidal and diel cycles in a seasonally changing relationship, likely linked to the seasonally changing fish community of the bay. In the winter and spring, higher hourly counts were generally confined to ebb tides and low slack tides near sunrise and sunset. In summer and fall of each year, the highest fish counts shifted to night and occurred during ebb, low slack, and flood tides. Fish counts were not linked to current speed, and did not decrease as current speed increased, contrary to observations at other tidal power sites. As fish counts may be proportional to the encounter rate of fish with an MHK turbine at the same depth, highly variable counts indicate that the risk to fish is similarly variable. The links between fish presence and environmental cycles at this site will likely be present at other locations with similar environmental forcing, making these observations useful in predicting potential fish interactions at tidal energy sites worldwide.« less

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

    PubMed

    Essien, J P; Antai, S P

    2009-06-01

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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    York, Carly C.

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

  15. Sediment Transport Between Deep Navigation Channels and Shallow Side Banks Under Variable Tidal and Meteorological Forcing

    NASA Astrophysics Data System (ADS)

    Burke, P. B.; Bruno, M. S.; Rankin, K. L.; Herrington, T. O.

    2002-12-01

    Newark Bay, within the Hudson-Raritan estuary, is characterized by complex bathymetry, with shallow side banks adjacent to deeply dredged ship channels. The discontinuity in bathymetry leads to complicated hydrodynamic behavior, which gives rise to complex sediment transport processes throughout the estuary. Since certain hydrophobic contaminants are preferentially bound to sediments, the complexities of the sediment processes in the region will influence pollutant dynamics and overall ecosystem health. Thus, it is essential to understand these dynamics including the exchange of sediment between the channels, which act primarily as conduits, and the side banks, which act principally as storage areas for sediment. Intermittent processes, such as wind waves, are the primary driving force producing sediment suspension and transport in shallow estuarine flats. The bottom shear stresses generated by such intermittent forcings are the combined effect of non-linear interactions between tidal currents and the waves at the sediment bed. We sought to demonstrate how continuous (tidal currents) and intermittent (waves) processes interact to control sediment entrainment and transport for Newark Bay. Continuous velocity, turbidity, and sediment concentration measurements were made in the navigation channel and on side-banks in Newark Bay for a two-year period using fixed bottom mounted instrument platforms and vessel-supported hydrographic surveys. These observations have allowed for the correlation of sediment transport events with a variety of forcing conditions, including significant wind/storm events. The connectivity between the side bank and channel regions of the estuary for fluid and sediment exchange was examined through concurrent measurements with high-frequency velocimeters and optical and laser-based turbidity meters. Frequency analysis indicated that the semidiurnal tide is the dominant forcing of the current structure in Newark Bay; however, bottom sediment

  16. Tidal Marsh Vegetation Pattern and Channel Network Complexity Linked in Alternative Stable States

    NASA Astrophysics Data System (ADS)

    Moffett, K.; Gorelick, S.

    2016-12-01

    Intertidal marsh ecosystems may emerge from alternative mudflat and subtidal states; meanwhile, nested within them there develops patchy marsh vegetation zonation. System organization at both these coastal- and patch-scales may be controlled by biogeomorphic feedbacks. But what of the intermediate, marsh-scale? What features and feedbacks reconcile patch-scale and coastal-scale organizational tendencies and guide the full 2D structure of a whole salt marsh-and-tidal channel system? This intermediate scale has been a gap in analyses to date. We used an empirical approach to first document the variety of such 2D whole-marsh vegetation-and-channel patterns that can be achieved within a common physiographic region, surveying 113 tidal marshes in San Francisco Bay estuary. Decision-tree pattern categorizations and pattern-quantifying metrics from object-based image analysis were then assessed in relation to key site characteristics. Site vegetation pattern complexity was significantly related to site salinity but independent of marsh age or elevation. Channel complexity was significantly related to marsh age but independent of salinity or elevation. Vegetation pattern and channel complexity were significantly related, suggesting two prevalent biogeomorphic states at the intermediate scale questioned above: a linked, complex vegetation-and-channel configuration, or a simple vegetation-and-channel configuration. This correspondence held across marsh ages (decades to millennia) and at both high and low marsh elevations. We conclude that marshes of shared physiography can exhibit highly variable ecosystem structures, and young marshes are not necessarily simple nor necessarily develop vegetation complexity with age and elevation. Salt marshes may tend to occupy two alternative stable states at the marsh-scale, characterized by linked complexity in vegetation and channel organization. The channel network configuration is a lynchpin of this organization, possibly serving a

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

    PubMed

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

    2008-08-01

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

  18. Field studies of velocity, salinity and suspended solids concentration in a shallow tidal channel near tidal flap gates

    NASA Astrophysics Data System (ADS)

    Mitchell, S. B.; Burgess, H. M.; Pope, D. J.; Theodoridou, A.

    2008-06-01

    The design and operation of mathematical models of solute mixing and sediment transport in estuaries rely heavily on the provision of good-quality field data. We present some observations of salinity, suspended sediment concentration and velocity at one of the tidal limits of a semi-enclosed tidal lagoon in Southern England (Pagham Harbour, West Sussex, UK) where the natural processes of tidal incursion and solute mixing have been heavily modified as a result of the construction of sea walls dating back to the 18th Century. These observations, made immediately downstream of two parallel tidal flap gates by conductivity-temperature-depth (CTD) profiler, and also using bed-mounted sensor frames to measure velocity at 2 fixed depths, have yielded a set of results covering 11 tidal cycles over the period 2002-04. It is clear from the results obtained that over a typical tidal cycle, the greatest vertical salinity gradients occur in the 1-2 h immediately after the onset of the flood tide, and that subsequently, energetic mixing acts to rapidly break down this stratification. Under moderate-to-high fresh water flows (>0.5 m 3/s), the break-down in vertical salinity gradient is more gradual, while under low fresh water flows (<0.2 m 3/s), the vertical salinity gradient is generally less pronounced. Estimates of Richardson number during the early flood-tide period reveal values that vary rapidly between <1 and about 20, with lower values occurring after around 1.5-2 h after low water. Observations of suspended sediment concentration vary widely even for similar tidal and fresh water flow conditions, revealing the possible influence of wind speed, the storage effects of the water in the lagoon downstream of the observation site, and the complexity of the hydrodynamics downstream of tidal flap gates. The data also show that most of the sediment transport is landward, and occurs during flood tides, with estimated total tidal landward flood tide flux of fine sediment of the

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  1. 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

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

    PubMed

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

    2015-08-08

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

  3. 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. © 2016 The Fisheries Society of the British Isles.

  4. Multi-frequency inversion of FDEM data for the study of ancient meandering channels in tidal landscapes

    NASA Astrophysics Data System (ADS)

    Cassiani, G.; Boaga, J.; Ghinassi, M.; D'Alpaos, A.; Deidda, G. P.; Rodriguez, G.

    2016-12-01

    We present, for the first time in tidal landscapes, an innovative inversion process of multi-frequency electromagnetic measurements (Frequency Domain Electro-Magnetic - FDEM) to unravel the vestiges of ancient meandering channels. This technique allows us to characterize the dynamics of a salt-marsh paleo-meander in the Venice Lagoon (Italy) and to emphasize interesting and peculiar features of meander migration in tidal landscapes. An interesting result, emerging from FDEM geophysical data and validated by ancillary sedimentological analyses and boreholes, is that tidal meanders migrate laterally while aggrading vertically, the surface bounding the top of the bar describing a "spoon-shaped geometry", which is then filled up with salt-marsh deposits. This particular behavior challenges current assessments of tidal meander morphodynamics and the possibility of applying depositional models developed for their fluvial counterparts. Our analyses emphasize in fact that tidal meanders migrate laterally while vertically aggrading, differently from their fluvial counterparts, thus challenging current assessments of tidal meander morphodynamics. The results are of broad interest for the fields of hydrology and geomorphology and with important consequences for quantitative analyses of the long-term morphodynamic evolution of tidal meanders.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  6. 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.

  7. Persistence of large-scale, 3-dimensional morphologic features in regions with large, alongshore sediment transport: observations of ebb tidal deltas using X-band radar (RIOS)

    NASA Astrophysics Data System (ADS)

    McNinch, J.; Humberston, J. L.

    2016-12-01

    The persistence of large-scale, nearshore morphologic features, such as shore-oblique bars and ebb tidal deltas, are difficult to reconcile on beaches with large, wave-driven alongshore transport volumes without assuming that: 1) hydrodynamic processes maintaining these features are sustained through a variety of oceanographic conditions, and 2) large volumes of sediment bypasses the features during periods of strong alongshore transport. One would otherwise expect wave events to diffuse shore-oblique features into more 2-D, linear forms typically observed on shore-parallel sand bars in the inner surf zone. Understanding the modes of sediment transport occurring (e.g. small, migrating sand waves as observed in riverine settings; bedload transport along existing large-scale morphological features; and/or event-driven suspended sediment transport) is important to accurately model alongshore, 3-D beach morphology and tidal inlet morphodynamics. Part of the challenge is the paucity of observational data and the difficulty in measuring bathymetry over these features at high temporal and spatial resolutions in all conditions. We explore the morphologic evolution of shoals comprising two ebb tidal deltas in regions with significant wave-driven, alongshore sediment transport using data collected by Radar Inlet Observing System (RIOS). RIOS utilizes hourly X-band radar data (1Hz, 10-min duration) to define shoal positions and morphology from measured wave breaking and wave speed. Extended time series (>3 months) of RIOS-defined shoals at Oregon Inlet, NC and St. Augustine Inlet, FL are used to test the hypothesis that the large-scale shoals comprising the ebb tidal deltas remain relatively static while still allowing a substantial volume of alongshore sediment throughput. Early results support this hypothesis, suggesting bed load transport and shore-parallel bedform migration may dominate inlet bypassing in these systems instead of the more traditionally accepted bulk

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

    PubMed

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

    2014-01-01

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

  9. 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

  10. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  12. 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

  13. Evans blue is a specific antagonist of the human epithelial Na+ channel delta-subunit.

    PubMed

    Yamamura, Hisao; Ugawa, Shinya; Ueda, Takashi; Shimada, Shoichi

    2005-11-01

    The epithelial Na(+) channel (ENaC) regulates Na(+) homeostasis in cells and across epithelia. Four homologous ENaC subunits (alpha, beta, gamma, and delta) have been isolated in mammals. Combination of alpha-, beta-, and gamma-subunits or delta-, beta-, and gamma-subunits forms fully functional channels. Amiloride is a well known blocker of the ENaC family that inhibits both channel complexes. However, no specific antagonists are currently known that distinguish them. Here, we show that Evans blue, a diagnostic aid for the measurement of blood volume and vascular permeability, inhibits the activity of the delta-subunit expressed in Xenopus oocytes. The inward currents at a holding potential of -60 mV in human ENaCdeltabetagamma-expressing oocytes were inhibited by the application of Evans blue in a concentration-dependent manner with an IC(50) value of 143 muM. Evans blue markedly inhibited the delta-subunit current but did not block the alpha-subunit current. In conclusion, Evans blue is the first known delta-subunit-specific antagonist of ENaC. This finding provides us with a key compound for elucidating the physiological and pathological functions of ENaCdelta in humans and for drug development in the ENaC family.

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

    PubMed Central

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

    1999-01-01

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

  15. Ion channel formation by synthetic analogues of staphylococcal delta-toxin.

    PubMed

    Kerr, I D; Dufourcq, J; Rice, J A; Fredkin, D R; Sansom, M S

    1995-06-14

    Ion channel formation by three analogues of staphylococcal delta-toxin, an amphipathic and alpha-helical channel-forming peptide, has been evaluated by measurement of ionic currents across planar lipid bilayers. Replacement of beta-branched, hydrophobic residues by leucine and movement of a tryptophan residue from the hydrophilic to the hydrophobic face of the helix does not significantly alter ion channel activity. Removal of the N-terminal blocking group combined with the substitution of glycine-10 by leucine changes the single channel properties of delta-toxin, without altering macroscopic conductance/voltage behaviour. Truncation of the N-terminus by three residues results in complete loss of channel-forming activity. These changes in channel-forming properties upon altering the peptide sequence do not mirror changes in haemolytic activity. The results lend support to the proposal that channel formation and haemolysis are distinct events. Channel properties are discussed in the context of a model in which the pore is formed by a bundle of approximately parallel transbilayer helices.

  16. Blade design and performance analysis on the horizontal axis tidal current turbine for low water level channel

    NASA Astrophysics Data System (ADS)

    Chen, C. C.; Choi, Y. D.; Y Yoon, H.

    2013-12-01

    Most tidal current turbine design are focused on middle and large scale for deep sea, less attention was paid in low water level channel, such as the region around the islands, coastal seas and rivers. This study aims to develop a horizontal axis tidal current turbine rotor blade which is applicable to low water level island region in southwest of Korea. The blade design is made by using BEMT(blade element momentum theory). The section airfoil profile of NACA63-415 is used, which shows good performance of lift coefficient and drag coefficient. Power coefficient, pressure and velocity distributions are investigated according to TSR by CFD analysis.

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

    PubMed

    Divett, T; Vennell, R; Stevens, C

    2013-02-28

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

  18. 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.

  19. Observations of tidal flow, waves and drag within a fringing coastal mangrove forest in the Mekong delta

    NASA Astrophysics Data System (ADS)

    Mullarney, J. C.; Bryan, K. R.; Henderson, S. M.; Norris, B. K.; Vo Luong, H. P.

    2016-02-01

    In recent years attention has focused on the ability of mangroves to protect shorelines against damage from the combined hydrodynamic forces of waves and tides, owing to the presence of roots (pneumatophores) and tree trunks enhancing vegetative drag. However, field measurements within these dynamic environments are limited. We report on field observations from the seaward side of Cù Lao Dung Island (Soc Trang Province) in the Mekong Delta, Vietnam. The island encompasses two contrasting environments from a sandy, prograding flat with gentle topographic slope on the southwest side to a steep, eroding and muddy fringe region on the northeast side. The data capture the flow transitions from mudflat across the fringing region to the forest interior. We observe a rotation of the obliquely incident flows to an orientation perpendicular to the vegetated/unvegetated boundary. The balances governing the large scale flow are assessed and indicate the relative importance of friction, winds and depth-averaged pressure forces. We find drag coefficients of 10-30 times greater than the usual values associated with bottom friction, with values particularly elevated in the regions of dense pneumatophores that are important during the early stages of the tidal cycle. The field observations are used in the set-up of a simple one-dimensional process model. The model predicts the movement of the tide across the vegetated flat, associated sediment transport and evolution of the across flat profile. Preliminary results indicate that mangrove profiles may evolve towards a close to linear shape in contrast to systems with temperate species or no vegetation.

  20. 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.

  1. Subtidal flow division at a shallow tidal junction

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Tides influence distribution of river discharge at tidally affected channel junctions. At the apex of a channel network in an Indonesian delta, observations of flow division suggest that tidally averaged flow division depends on the tidal range. To understand the mechanisms governing the subtidal flow division, an idealized hydrodynamic junction model inspired by the observations has been set up. The barotropic model consists of two exponentially converging tidal channels that connect to a tidal river at the junction and solves the nonlinear shallow water equations. By varying the depth, length, e-folding length scale of the channel width, and hydraulic roughness in one of the two tidal channels, the sensitivity of the subtidal flow division to those four parameters was investigated. For depth, length, and e-folding length scale differences between channels the effect of tides is generally to enhance unequal subtidal flow division that occurs in the case of river flow only. In contrast, for hydraulic roughness differences, the tidal effect partly cancels the inequality in river flow division. The tidal effect may even reverse the horizontal flow circulation that would occur in the absence of tides.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  3. Molecular cloning and characterization of the human voltage-gated calcium channel alpha(2)delta-4 subunit.

    PubMed

    Qin, Ning; Yagel, Susan; Momplaisir, Mary-Lou; Codd, Ellen E; D'Andrea, Michael R

    2002-09-01

    The voltage-gated calcium channel is composed of a pore-forming alpha(1) subunit and several regulatory subunits: alpha(2)delta, beta, and gamma. We report here the identification of a novel alpha(2)delta subunit, alpha(2)delta-4, from the expressed sequence tag database followed by its cloning and characterization. The novel alpha(2)delta-4 subunit gene contains 39 exons spanning about 130 kilobases and is co-localized with the CHCNA1C gene (alpha(1C) subunit) on human chromosome 12p13.3. Alternative splicing of the alpha(2)delta-4 gene gives rise to four potential variants, a through d. The open reading frame of human alpha(2)delta-4a is composed of 3363 base pairs encoding a protein with 1120 residues and a calculated molecular mass of 126 kDa. The alpha(2)delta-4a subunit shares 30, 32, and 61% identity with the human calcium channel alpha(2)delta-1, alpha(2)delta-2, and alpha(2)delta-3 subunits, respectively. Primary sequence comparison suggests that alpha(2)delta-4 lacks the gabapentin binding motifs characterized for alpha(2)delta-1 and alpha(2)delta-2; this was confirmed by a [(3)H]gabapentin-binding assay. In human embryonic kidney 293 cells, the alpha(2)delta-4 subunit associated with Ca(V)1.2 and beta(3) subunits and significantly increased Ca(V)1.2/beta(3)-mediated Ca(2+) influx. Immunohistochemical study revealed that the alpha(2)delta-4 subunit has limited distribution in special cell types of the pituitary, adrenal gland, colon, and fetal liver. Whether the alpha(2)delta-4 subunit plays a distinct physiological role in select endocrine tissues remains to be demonstrated.

  4. 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.

  5. 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.

  6. 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

  7. Evolution and stability of tidal river bifurcations

    NASA Astrophysics Data System (ADS)

    Kleinhans, M. G.

    2011-12-01

    At bifurcations, water and sediment are partitioned, so that long-term evolution of fluvial and deltaic channels is determined by the bifurcation stability. Recent work in fluvial environments showed that bifurcations are commonly unstable so that avulsion results. For tidal rivers it could be argued that the discharge fluctuation enhances transport so that it simply closes of faster than in steady flow, but it could also be argued that tidal phase differences between the bifurcates cause a residual flow that counteracts the closing trend and keeps both bifurcates open. A physics-based numerical model (Delft3D) was used to model fixed-bank fork-shaped bifurcations with and without tides, and with short and long length relative to tidal wavelength. In all cases the bifurcations remained as unstable as without tides and ended invariably in avulsion. Tidal bifurcations unbalanced more rapidly than fluvial bifurcations, because of the increased ebb current and nonlinearity of sediment transport. On the other hand, discharge partitioning at the final bifurcation was much less asymmetrical with tides than without. Tidal wave deformation and production of higher harmonics in the longer channels affected sediment partitioning in the unstable phase but seems to have no effect on equilibrium morphology. Significant phase differences between the bifurcates caused a tidal floss effect, which scoured the bifurcation. In conclusion, symmetrical bifurcations affected by tides are unstable, but their final equilibrium is more symmetrical than without tides unless bifurcates have significant tidal phase differences. Furthermore I modelled growing deltas with self-formed distributary channels with and without cohesive sediment and with and without tides. Here, tides cause the flow to be more focussed in fewer and larger channels, whilst the few bifurcations are relatively stable. Combined fluvial discharge and tidal ebb flow in the channels transports more sediment than in fluvial

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

    NASA Astrophysics Data System (ADS)

    Kubicki, Adam; Kösters, Frank; Bartholomä, Alexander

    2017-02-01

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

  9. 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.

  10. Tidal Channel Dynamics and Muddy Substrates: a Comparison Between a Wave Dominated and a Tidal Dominated System

    DTIC Science & Technology

    2011-09-30

    C. A. Ruhl , and J . R. Burau (2004), Flood tide pulses after low tides in shallow subembayments adjacent to deep channels, Estuarine Coastal and... b . ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 Constance Bayou waves...sediment transport. WORK COMPLETED Figure 1 Figure 1. A) Location of Willapa Bay, Washington State, USA. B ) Detail of the inner mudflat of

  11. 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

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

    NASA Astrophysics Data System (ADS)

    Wegen, M.; Jaffe, B. E.

    2014-05-01

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

  13. Interaction between Fresh and Sea Water in Tidal Influenced Navigation Channel

    NASA Astrophysics Data System (ADS)

    Hwang, J. H. H.; Nam-Hoon, K.

    2016-02-01

    Nam-Hoon, Kim 1, Jin-Hwan, Hwang 2, Hyeyun-Ku 31,2,3 Department of Civil and Environmental Engineering, Seoul National University, Republic of Korea; 1nhkim0426@snu.ac.kr; 2jinhwang@snu.ac.kr; 3hyeyun.ku@gmail.com; We have conducted field observations after freshwater discharges of sea dike during ebb tide in Geum River Estuary, Korea to understand the interaction between fresh and sea water. To measure spatial variability of the stratified flow, an Acoustic Doppler Current Profiler (ADCP) and a portable free-fall tow-yo instrument, Yoing Ocean Data Acquisition Profiler (YODA profiler) which can continuously measures three-dimensional velocity profiles and vertical profiles of the fine-scale features, respectively, within water column were used in a vessel moving at a speed of 1-2 m/s. The flow observations show the strong stratification and dispersion occurred near field region because of the ebb tide advection (Fig. 1). As moving toward the far field region, the stratification and dispersion was getting thin and weak but still remaining. The presence of mixing process between fresh and sea water was represented by the gradient Richardson Number. The mixing occurred throughout the near field region and potentially mixed in the far field region. This study have been conducted to serve as a basic research of understanding the Region Of Freshwater Influence (ROFI) in the tidal influenced navigation channel. We are going to perform a few more observations in the future. Key words: Richardson number, stratification, mixing, ROFI, ADCP, CTDFigure 1. High-resolution observation data of salinity (psu) from YODA Profiler Acknowledgement: This research was supported by grants from the Korean Ministry of Oceans and Fisheries entitled as "Developing total management system for the Keum river estuary and coast" and "Integrated management of marine environment and ecosystems around Saemangeum". We also thank to the administrative supports of Integrated Research Institute of

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

    NASA Astrophysics Data System (ADS)

    Drexler, J. Z.

    2012-12-01

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

  15. Characterizing the differences in bankfull channel geometry across the tidal-fluvial zone of micro- to macro- tidal fluvial systems: Lower Trinity River, TX, USA vs Chehalis River, WA, USA

    NASA Astrophysics Data System (ADS)

    Parsons, D. R.; Prokocki, E.; Best, J.; Ashworth, P. J.; Simpson, C.; Constantine, S.

    2015-12-01

    Bankfull channel width measurements and bankfull stage-discharge relationships, coupled with published and/or collected channel depth sounding readings, were utilized to examine bankfull channel geometries (in the single-thread meandering channel reaches only) spanning from the fluvial 'normal flow' moving downstream through the tidal-fluvial 'backwater' hydraulic regime of two rivers that are micro- (lower Trinity River) and macro- tidally influenced (Chehalis River). This analysis reveals that moving downstream from the fully-fluvial 'normal flow' regime through to the tidal-fluvial 'backwater' regime, the micro-tidal lower Trinity River displays: (a) a decrease in bankfull channel width and an increase in bankfull channel depth, (b) a decrease in bankfull channel width/depth ratio, (c) a bankfull channel cross-sectional area that remains nearly constant, and (d) both measured and calculated bankfull discharge remains constant at approximately 900 m3sec-1. Conversely, the macro-tidal lower Chehalis River displays: (a) an increase in both bankfull channel width and depth, (b) bankfull channel width/depth ratios that remain constant, (c) a bankfull channel cross-sectional area that increases significantly, and (d) both measured and/or calculated bankfull discharge values range from approximately 800 (normal flow) to 10,000 m3sec-1 (downstream end of backwater regime). Importantly, along the Chehalis River a maximum of ~ 2,000 m3sec-1 of the total bankfull water discharge (10,000 m3sec-1), at the downstream end of the 'backwater flow' regime, can be accounted for by the Chehalis River proper and two tributary inputs. This suggests, at this channel cross-sectional location, that the additional 8,000 m3sec-1 of total bankfull water discharge must be supplied by the downstream tidally-sourced component of total water discharge. These results, coupled with the rates of change of measured and/or computed metrics from above, will be utilized to provide insight into the

  16. 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.

  17. 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

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

    PubMed

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

    2008-06-06

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

  19. 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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

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

    PubMed

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

    2005-04-01

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

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

    USGS Publications Warehouse

    Downing-Kunz, Maureen; Schoellhamer, David H.

    2015-01-01

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

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Falcini, Federico; Jerolmack, Douglas J.

    2010-12-01

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

  7. 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.

  8. Tidal Channels of Skagit Bay: Three-Dimensional Hydrodynamics and Morphodynamic Evolution

    DTIC Science & Technology

    2011-09-30

    is good. ] IMPACT/APPLICATIONS The fronts we measured are clear to remote sensors. Hydraulic control processes , which closely link frontal...journal. RESULTS We have found that hydraulic control theory explains the formation of intense baroclinic fronts along the edges of tidal...these researchers to compare turbulent dissipation rates estimated using our current meters with sediment flocculation estimated using their co

  9. 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

  10. Isolation and pharmacological characterisation of delta-atracotoxin-Hv1b, a vertebrate-selective sodium channel toxin.

    PubMed

    Szeto, T H; Birinyi-Strachan, L C; Smith, R; Connor, M; Christie, M J; King, G F; Nicholson, G M

    2000-03-31

    delta-Atracotoxins (delta-ACTXs) are peptide toxins isolated from the venom of Australian funnel-web spiders that slow sodium current inactivation in a similar manner to scorpion alpha-toxins. We have isolated and determined the amino acid sequence of a novel delta-ACTX, designated delta-ACTX-Hv1b, from the venom of the funnel-web spider Hadronyche versuta. This 42 residue toxin shows 67% sequence identity with delta-ACTX-Hv1a previously isolated from the same spider. Under whole-cell voltage-clamp conditions, the toxin had no effect on tetrodotoxin (TTX)-resistant sodium currents in rat dorsal root ganglion neurones but exerted a concentration-dependent reduction in peak TTX-sensitive sodium current amplitude accompanied by a slowing of sodium current inactivation similar to other delta-ACTXs. However, delta-ACTX-Hv1b is approximately 15-30-fold less potent than other delta-ACTXs and is remarkable for its complete lack of insecticidal activity. Thus, the sequence differences between delta-ACTX-Hv1a and -Hv1b provide key insights into the residues that are critical for targeting of these toxins to vertebrate and invertebrate sodium channels.

  11. 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.

  12. 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.

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

    PubMed Central

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

    2000-01-01

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

  14. Human factors and tidal influences on water quality of an urban river in Can Tho, a major city of the Mekong Delta, Vietnam.

    PubMed

    Ozaki, Hirokazu; Co, Thi Kinh; Le, Anh Kha; Pham, Viet Nu; Nguyen, Van Be; Tarao, Mitsunori; Nguyen, Huu Chiem; Le, Viet Dung; Nguyen, Hieu Trung; Sagehashi, Masaki; Ninomiya-Lim, Sachi; Gomi, Takashi; Hosomi, Masaaki; Takada, Hideshige

    2014-02-01

    In this study, we focused on water quality in an urban canal and the Mekong River in the city of Can Tho, a central municipality of the Mekong Delta region, southern Vietnam. Water temperature, pH, electrical conductivity, BOD5, CODCr, Na(+), Cl(-), NH4 (+)-N, SO4 (2-)-S, NO3 (-)-N, and NO2 (-)-N for both canal and river, and tide level of the urban canal, were monitored once per month from May 2010 to April 2012. The urban canal is subject to severe anthropogenic contamination, owing to poor sewage treatment. In general, water quality in the canal exhibited strong tidal variation, poorer at lower tides and better at higher tides. Some anomalies were observed, with degraded water quality under some high-tide conditions. These were associated with flow from the upstream residential area. Therefore, it was concluded that water quality in the urban canal changed with a balance between dilution effects and extent of contaminant supply, both driven by tidal fluctuations in the Mekong River.

  15. Chronic inflammatory injury results in increased coupling of delta opioid receptors to voltage-gated Ca2+ channels.

    PubMed

    Pradhan, Amynah; Smith, Monique; McGuire, Brenna; Evans, Christopher; Walwyn, Wendy

    2013-03-04

    Opioid receptors regulate a diverse array of physiological functions. Mu opioid receptor agonists are well-known analgesics for treating acute pain. In contrast, animal models suggest that chronic pain is more effectively relieved by delta opioid receptor agonists. A number of studies have shown that chronic pain results in increased function of delta opioid receptors. This is proposed to result from enhanced trafficking of the delta opioid receptor to the cell membrane induced by persistent tissue injury. However, recent studies have questioned this mechanism, which has resulted in some uncertainty as to whether delta opioid receptors are indeed upregulated in chronic pain states. To clarify this question, we have examined the effect of chronic inflammatory pain over time using both an ex vivo measure of delta function: receptor-Ca2+ channel coupling, and an in vivo measure; the relief of chronic pain by a delta opioid receptor agonist. In addition, as beta-arrestin 2 can regulate delta opioid receptor trafficking and signaling, we have further examined whether deleting this scaffolding and signal transduction molecule alters delta opioid receptor function. We used the Complete Freund's Adjuvant model of inflammatory pain, and examined the effectiveness of the delta agonist, SNC80, to both inhibit Ca2+ channels in primary afferent neurons and to attenuate mechanical allodynia. In naïve beta-arrestin 2 wildtype and knockout mice, SNC80 neither significantly inhibited voltage-dependent Ca2+ currents nor produced antinociception. However, following inflammatory pain, both measures showed a significant and long-lasting enhancement of delta opioid receptor function that persisted for up to 14 days post-injury regardless of genotype. Furthermore, although this pain model did not alter Ca2+ current density, the contribution of N-type Ca2+ channels to the total current appeared to be regulated by the presence of beta-arrestin 2. Our results indicate that there is an

  16. Tidal Channels of Skagit Bay: Three-Dimensional Hydrdynamics and Morphodynamic Evolution

    DTIC Science & Technology

    2010-09-30

    Model-data agreement is good.] IMPACT/APPLICATIONS The fronts we measured are clear to remote sensors. Hydraulic control processes , which...results from our tidal flats experiments to the (peer reviewed) Journal of Geophysical Research. RESULTS We have found that hydraulic control...researchers to compare turbulent dissipation rates estimated using our current meters with sediment flocculation estimated using their co-located

  17. 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.

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

    USGS Publications Warehouse

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

    2009-01-01

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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  1. 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.

  2. A reduced complexity approach to morphodynamic modeling: Validation of DeltaRCM and prediction of fluviodeltaic channel dynamics

    NASA Astrophysics Data System (ADS)

    Van Dyk, C.; Liang, M.; Passalacqua, P.

    2014-12-01

    DeltaRCM is a reduced-complexity model of delta formation and evolution based on a set of simple physical rules for routing water and sediment. The hydrodynamic component of the model has been previously validated against analytical and 3D numerical modeling results and has been shown to accurately reproduce flow field features critical to delta dynamics at the level of channel processes such as backwater profile, flow around a mouth bar, flow through a single bifurcation, and flow partitioning at the network scale. Here we focus on the morphodynamic component of DeltaRCM to: (1) identify a set of robust metrics to be used for validating morphodynamic models; (2) validate DeltaRCM results against a set of experimental and field data; and (3) investigate delta morphodynamics, especially the evolution of the channel network over time and the distribution of sand and mud in the stratigraphic record. The metrics analyzed span surface (e.g., channel density and wet fraction) and subsurface properties (e.g., sedimentograph and index of compensational stacking), as well as the system's dynamic behavior (e.g., avulsion time scale and shoreline trajectory). These metrics are used to compare the model's behavior to field and experimental data representing a range of boundary conditions, such as varying basin geometry, base-level cycles, and sediment input. The validation results show the range of applicability of our reduced complexity approach to modeling morphodynamics. DeltaRCM is then applied to investigate the deposition of sand and mud as a function of time and location for varying basin depth.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. Decoupling flood and interflood deposits for delta island formation and channel bifurcation

    NASA Astrophysics Data System (ADS)

    Daniller-Varghese, M. S.; Kim, W.

    2016-12-01

    Channel islands' size and organization dictate delta networks' morphology. To understand their complex network organization, a single channel island node within that network should be investigated first as the fundamental building block. When a sediment-laden flow enters slack water, it loses momentum and carrying capacity, depositing its sediment. As sediment accumulates, flow moves around it and a mouth bar island develops. We present an experimental investigation of island formation and channel bifurcation using the Sediment Transport and Earth-surface Processes (STEP) basin. We made mouth bar deposits and flow bifurcations in transport-limited turbulent conditions. Time-lapse images, elevation scans on the deltaic surface, and a low-cost particle imaging velocimetry system allow us to characterize the flow and depositional evolution of our experimental islands. Using two flow discharges (0.355 l/s, 6 l/s) and uniform sediment, our experiments have two characteristic advection lengths and corresponding deposit types. One, associated with interflood bedload transport, and the other with flood-suspended transport: proximal low-angle deposits and distal steep deposits, respectively. By varying the frequency of floods (one every 20s-20 mins) while keeping sediment and water mass constant across experiments, we are able to control the time and spatial organization of these two deposit types and examine the effect on bifurcation length and bifurcation incidence time. As the interflood flow deposit and flood deposit accumulate sediment over time, the interflood deposit encroaches onto the flood deposit. Flow is routed from the interflood deposit to the flood deposit but does not have the momentum to uniformly cover it. The flow becomes unsteady, and bifurcates around an island. After the bifurcation, the island's vertical aggradation rate also increases. The experiments suggest that the interaction between deposits stemming from different particle advection lengths is

  8. 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

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

    PubMed

    Joshi, Indu; Taylor, Charles P

    2006-12-28

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    SciTech Connect

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

    1985-02-01

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

  13. Path-averaged ocean measurements in the deep, stratified tidal channel of Hood Canal using acoustical scintillation

    NASA Astrophysics Data System (ADS)

    di Iorio, D.; Barton, A. D.

    2003-10-01

    Path-averaged current speed, effective refractive index fluctuations, and stratification measurements were made using high-frequency (67 kHz) acoustical scintillation measurements in the northern entrance to Hood Canal, Puget Sound, Washington. This experiment made use of a four-transmitter and four-receiver array configured in a T-shape; the two-dimensional feature of this array was designed to measure both along-channel small-scale properties as a result of advection and vertical properties as a result of acoustic refraction from temperature/salinity stratification. With long path lengths and stratified conditions, acoustic propagation resulted in multipath arrivals which were separable for most of the measurement period. A maximum likelihood estimation algorithm is developed that tracks both the direct path signal at approximately 25-30 m depth and the upward refracted signal into the near surface and calculates amplitude, phase, and travel time for each. The acoustical signals are then inverted to estimate path-averaged along-channel flow properties, turbulent effective refractive index levels, and changes in stratification. Along-channel flows approach 50 cm s-1, and the acoustic measurement agrees very well with a simple tidal model of the currents and shows some deviations from independent measurements during maximum flood tide. Current velocity contributions to the effective refractive index fluctuations are analyzed, and results indicate that both sound speed and velocity fluctuations contribute to the acoustic scattering. The vertical acoustic arrival angle to first order appears to be a sensitive indicator of small changes in stratification.

  14. Tidal surge in the M2 proton channel, sensed by 2D IR spectroscopy.

    PubMed

    Ghosh, Ayanjeet; Qiu, Jade; DeGrado, William F; Hochstrasser, Robin M

    2011-04-12

    The M2 proton channel from influenza A virus transmits protons across membranes via a narrow aqueous pore lined by water and a proton sensor, His37. Near the center of the membrane, a water cluster is stabilized by the carbonyl of Gly34 and His37, the properties of which are modulated by protonation of His37. At low pH (5-6), where M2 conducts protons, this region undergoes exchange processes on the microsecond to second timescale. Here, we use 2D IR to examine the instantaneous conformational distribution and hydration of G34, and the evolution of the ensemble on the femtosecond to picosecond timescale. The channel water is strongly pH dependent as gauged by 2D IR which allows recording of the vibrational frequency autocorrelation function of a (13)C = (18)O Gly34 probe. At pH 8, where entry and exit of protons within the channel are very slow, the carbonyl groups appear to adopt a single conformation/environment. The high-pH conformer does not exhibit spectral dynamics near the Gly34, and water in the channel must form a relatively rigid ice-like structure. By contrast, two vibrational forms of G34 are seen at pH 6.2, neither of which is identical to the high-pH form. In at least one of these low-pH forms, the probe is immersed in a very mobile, bulk-like aqueous environment having a correlation time ca. 1.3 ps at pH 6.2. Thus, protonation of His37 at low pH causes liquid-like water molecules to flow into the neighborhood of the Gly34.

  15. 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.

  16. Synthesis, solution structure, and phylum selectivity of a spider delta-toxin that slows inactivation of specific voltage-gated sodium channel subtypes.

    PubMed

    Yamaji, Nahoko; Little, Michelle J; Nishio, Hideki; Billen, Bert; Villegas, Elba; Nishiuchi, Yuji; Tytgat, Jan; Nicholson, Graham M; Corzo, Gerardo

    2009-09-04

    Magi 4, now renamed delta-hexatoxin-Mg1a, is a 43-residue neurotoxic peptide from the venom of the hexathelid Japanese funnel-web spider (Macrothele gigas) with homology to delta-hexatoxins from Australian funnel-web spiders. It binds with high affinity to receptor site 3 on insect voltage-gated sodium (Na(V)) channels but, unlike delta-hexatoxins, does not compete for the related site 3 in rat brain despite being previously shown to be lethal by intracranial injection. To elucidate differences in Na(V) channel selectivity, we have undertaken the first characterization of a peptide toxin on a broad range of mammalian and insect Na(V) channel subtypes showing that delta-hexatoxin-Mg1a selectively slows channel inactivation of mammalian Na(V)1.1, Na(V)1.3, and Na(V)1.6 but more importantly shows higher affinity for insect Na(V)1 (para) channels. Consequently, delta-hexatoxin-Mg1a induces tonic repetitive firing of nerve impulses in insect neurons accompanied by plateau potentials. In addition, we have chemically synthesized and folded delta-hexatoxin-Mg1a, ascertained the bonding pattern of the four disulfides, and determined its three-dimensional solution structure using NMR spectroscopy. Despite modest sequence homology, we show that key residues important for the activity of scorpion alpha-toxins and delta-hexatoxins are distributed in a topologically similar manner in delta-hexatoxin-Mg1a. However, subtle differences in the toxin surfaces are important for the novel selectivity of delta-hexatoxin-Mg1a for certain mammalian and insect Na(V) channel subtypes. As such, delta-hexatoxin-Mg1a provides us with a specific tool with which to study channel structure and function and determinants for phylum- and tissue-specific activity.

  17. 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

  18. Lime-mud layers in high-energy tidal channels: A record of hurricane deposition

    USGS Publications Warehouse

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

    1993-01-01

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

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

    PubMed

    Owsianik, Grzegorz; Cao, Lishuang; Nilius, Bernd

    2003-11-06

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

  20. Lime-mud layers in high-energy tidal channels: A record of hurricane deposition

    NASA Astrophysics Data System (ADS)

    Shinn, Eugene A.; Steinen, Randolph P.; Dill, Robert F.; Major, Richard

    1993-07-01

    During or immediately following the transit of Hurricane Andrew (August 23-24, 1992) across the northern part of the Great Bahama Bank, thin laminated beds of carbonate mud were deposited in high-energy subtidal channels (4 m depth) through the ooid shoals of south Cat Cay and Joulters Cays. During our reconnaissance seven weeks later, we observed lime-mud beds exposed in the troughs of submarine oolite dunes and ripples. The mud layers were underlain and locally covered by ooid sand. The mud beds were lenticular and up to 5 cm thick. Their bases cast the underlying rippled surface. The layers were composed of soft silt- and sand-sized pellets and peloids and in some areas contained freshly preserved Thalassia blades and other organic debris along planes of lamination. The beds had a gelatinous consistency and locally had been penetrated by burrowers and plants. Layers of lime mud had also settled on bioturbated, plant-stabilized flats and in lagoonal settings but were quickly reworked and made unrecognizable by the burrowing of organisms. Thicker, more cohesive (and therefore older) mud beds and angular mud fragments associated with ooids from Joulters Cays have similar characteristics but lack fresh plant fragments. We infer that these older beds were similarly deposited and thus record the passage of previous hurricanes or tropical storms. Storm layers are preserved within channel sediments because migrating ooids prevent attack by the burrowing activity off organisms.

  1. 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

  2. Processes Controlling Transfer of Fine-Grained Sediment in Tidal Systems Spanning a Range of Fluvial Influence

    DTIC Science & Technology

    2012-09-30

    cycle . Transects of water -column currents and suspended-sediment concentrations over complete tidal cycles along the tidal river show complex...Prescribed by ANSI Std Z39-18 2 with results from the Amazon River delta system that are guiding our efforts. Our objectives focus on the...characteristics of channel/flat water and sediment discharge and also the external stresses (e.g., winds, precipitation, and river discharge) that modify

  3. Delta receptors are required for full inhibitory coupling of mu-receptors to voltage-dependent Ca(2+) channels in dorsal root ganglion neurons.

    PubMed

    Walwyn, Wendy; John, Scott; Maga, Matthew; Evans, Christopher J; Hales, Tim G

    2009-07-01

    Recombinant micro and delta opioid receptors expressed in cell lines can form heterodimers with distinctive properties and trafficking. However, a role for opioid receptor heterodimerization in neurons has yet to be identified. The inhibitory coupling of opioid receptors to voltage-dependent Ca(2+) channels (VDCCs) is a relatively inefficient process and therefore provides a sensitive assay of altered opioid receptor function and expression. We examined micro-receptor coupling to VDCCs in dorsal root ganglion neurons of delta(+/+), delta(+/-), and delta(-/-) mice. Neurons deficient in delta receptors exhibited reduced inhibition of VDCCs by morphine and [D-Ala(2),Phe(4),Gly(5)-ol]-enkephalin (DAMGO). An absence of delta receptors caused reduced efficacy of DAMGO without affecting potency. An absence of delta receptors reduced neither the density of VDCCs nor their inhibition by either the GABA(B) receptor agonist baclofen or intracellular guanosine 5'-O-(3-thio)triphosphate. Flow cytometry revealed a reduction in micro-receptor surface expression in delta(-/-) neurons without altered DAMGO-induced internalization. There was no change in micro-receptor mRNA levels. D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)-sensitive mu-receptor-coupling efficacy was fully restored to delta(+/+) levels in delta(-/-) neurons by expression of recombinant delta receptors. However, the dimerization-deficient delta-15 construct expressed in delta(-/-) neurons failed to fully restore the inhibitory coupling of micro-receptors compared with that seen in delta(+/+) neurons, suggesting that, although not essential for micro-receptor function, micro-delta receptor dimerization contributes to full micro-agonist efficacy. Because DAMGO exhibited a similar potency in delta(+/+) and delta(-/-) neurons and caused similar levels of internalization, the role for heterodimerization is probably at the level of receptor biosynthesis.

  4. Connectivity of Multi-Channel Fluvial Systems: A Comparison of Topology Metrics for Braided Rivers and Delta Networks

    NASA Astrophysics Data System (ADS)

    Tejedor, A.; Marra, W. A.; Addink, E. A.; Foufoula-Georgiou, E.; Kleinhans, M. G.

    2016-12-01

    Advancing quantitative understanding of the structure and dynamics of complex networks has transformed research in many fields as diverse as protein interactions in a cell to page connectivity in the World Wide Web and relationships in human societies. However, Geosciences have not benefited much from this new conceptual framework, although connectivity is at the center of many processes in hydro-geomorphology. One of the first efforts in this direction was the seminal work of Smart and Moruzzi (1971), proposing the use of graph theory for studying the intricate structure of delta channel networks. In recent years, this preliminary work has precipitated in a body of research that examines the connectivity of multiple-channel fluvial systems, such as delta networks and braided rivers. In this work, we compare two approaches recently introduced in the literature: (1) Marra et al. (2014) utilized network centrality measures to identify important channels in a braided section of the Jamuna River, and used the changes of bifurcations within the network over time to explain the overall river evolution; and (2) Tejedor et al. (2015a,b) developed a set of metrics to characterize the complexity of deltaic channel networks, as well as defined a vulnerability index that quantifies the relative change of sediment and water delivery to the shoreline outlets in response to upstream perturbations. Here we present a comparative analysis of metrics of centrality and vulnerability applied to both braided and deltaic channel networks to depict critical channels in those systems, i.e., channels where a change would contribute more substantially to overall system changes, and to understand what attributes of interest in a channel network are most succinctly depicted in what metrics. Marra, W. A., Kleinhans, M. G., & Addink, E. A. (2014). Earth Surface Processes and Landforms, doi:10.1002/esp.3482Smart, J. S., and V. L. Moruzzi (1971), Quantitative properties of delta channel networks

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

    PubMed

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

    2014-12-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  8. 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.

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

    PubMed

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

    2016-08-01

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

  11. Assignment of the human amiloride-sensitive Na{sup +} channel {delta} isoform to chromosome 1p36.3-p36.2

    SciTech Connect

    Waldmann, R.; Bassilana, F.; Voilley, N.

    1996-06-01

    This report describes the localization of the human amiloride-sensitive Na{sup +} channel {delta} isoform to human chromosome 1p36.3-p36.2 using in situ hybridization. Mutations in this group of ion channels have been implicated in various hereditary diseases. 18 refs., 1 fig.

  12. [Pregabalin: new therapeutic contributions of calcium channel alpha2delta protein ligands on epilepsy and neuropathic pain].

    PubMed

    Horga de la Parte, J F; Horga, A

    To review and update the contributions of a new class of drugs, named calcium channel alpha2delta protein ligands, on the treatment of epilepsy and neuropathic pain. A novel class of anticonvulsants are ligands for the auxiliary-associated protein alpha2delta subunit of voltage-gated calcium channels in the central nervous system. Gabapentin and pregabalin are members of this group. Pregabalin is a higher-potency and higher-effective analogue of gabapentin that act as a potent ligand for this site. The anticonvulsant action of pregabalin is probably due to its ability to reduce neurotransmitter release from activated epileptogenic neurons, without demonstrated effects on GABAergic receptors or mechanisms. In well-done clinical trials, pregabalin 150-600 mg/day has been shown to be highly effective and well tolerated as adjunctive therapy in patients with partial seizures. In several randomized, double-blind, clinical trials, oral pregabalin 150-600 mg/day was superior to placebo in relieving neuropathic pain associated with diabetic neuropathy and postherpetic neuralgia. Pregabalin demonstrates in humans an extensive and rapid absorption and a highly predictable and linear pharmacokinetics, a profile that makes it easy to use in clinical practice. The pharmacological activity of pregabalin is similar but not identical to that of gabapentin, and pregabalin shows possible advantages. Pregabalin and calcium channel alpha2delta protein ligands showed relevant advances on epilepsy and neuropathic pain treatment. In peripheral neuropathic pain conditions, if the criteria for efficacy are based on both pain relief and quality of life measures, pregabalin/gabapentin are suggested as choice treatment.

  13. 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.

  14. Integrating remote sensing and subsurface geological data to characterize a tidally-influenced paleodrainage from the mid-late Holocene succession of the Po Delta Plain (Italy)

    NASA Astrophysics Data System (ADS)

    Giacomelli, Serena; Rossi, Veronica; Amorosi, Alessandro; Bruno, Luigi; Campo, Bruno; Ciampalini, Andrea; Civa, Andrea; de Souza Filho, Roberto Carlos; Sgavetti, Maria

    2017-04-01

    A tidally-influenced, mid-late Holocene paleodrainage system from the Po Delta Plain (N Adriatic Sea, Italy) is reconstructed coupling remote sensing (RS) and subsurface geological data. Optical satellite images, DTM LiDAR, soil reflectance spectral features and core stratigraphy were combined in a GIS environment following a fully integrated methodological approach. The stratigraphic significance of RS-derived data (traces) was defined in terms of both depositional facies and depth, furnishing new insights on the role of RS in reconstructing the recent evolution of paleodrainages in coastal-deltaic settings. Sixteen images from Landsat 7 ETM+ (Enhanced Thematic Mapper Plus), Landsat 8 OLI (Operational Land Imager), Sentinel-2 MSI (Multispectral Instruments), and Hyperion satellites were collected from the USGS and the Scientific Hub ESA-Copernicus on-line databases, and integrated with Google Earth imagery. The visual interpretation of the images, mostly based on the brightness contrast (high and low reflectance values) and aimed to the recognition of traces, has been facilitated by the RGB combinations of the spectral bands most sensitive to lithology and moisture content and supported by a semi-automatic processing, including unsupervised classification and the spectral bands Principal Component Analysis (PCA). Multitemporal analysis of satellite imagery have been also performed. Two main traces, interpreted as meanders, have been analyzed for their sedimentological and stratigraphic characteristics. Following a field survey aimed to describe the morphology, grain-size, colors, and accessory materials of surface deposits, 11 soil samples have been collected for the extraction of the reflectance spectral signature and coring along the traces and in adjacent areas (bright and dark portions). Cores have been sampled for benthic foraminifer/ostracod analysis (42 samples) and stratigraphic cross-sections were constructed transversal to the meandering traces. Nine

  15. 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

  16. 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

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

    PubMed

    Warwick, R M; Somerfield, P J

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  19. Zambezi River Delta

    NASA Image and Video Library

    2013-08-29

    , upsetting the ecological balance for aquatic plant and animal species. Researchers have found that the freshwater table in the delta has dropped as much as five meters in the 50 years since dams were placed on the river. Less river flow also affects the shape and extent of the delta. Today there is less sediment replenishing the marshes and beaches as they are scoured by ocean waves and tides. "What strikes me in this image is the suspended sediment offshore," said Liviu Giosan, a delta geologist at the Woods Hole Oceanographic Institution. "Sediment appears to be transferred from the delta offshore in plumes that not only originate in active river mouths but also from deactivated former mouths, now tidal channels. This shows the power of tidal scouring contributing to the slow but relentless erosion of the delta." http://photojournal.jpl.nasa.gov/catalog/PIA18155

  20. 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

  1. 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.

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

    DTIC Science & Technology

    2012-05-01

    morphology. ADDITIONAL INDEX WORDS: Tidal inlet, tidal prism, tidal inlet morphology, tide dominated, wave dominated, mixed energy inlets. INTRODUCTION...shore that allows exchange of water between the ocean and bays, lagoons , and marsh and tidal creek systems, and for which the tidal current maintains...Because mixed- energy inlets can exhibit a wide range of varying energy forcing (both wave and tidal ), their ebb deltas are not as easily defined and may

  3. 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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  5. 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

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

    SciTech Connect

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

    2005-07-01

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

  7. Field estimates of floc dynamics and settling velocities in a tidal creek with significant along-channel gradients in velocity and SPM

    NASA Astrophysics Data System (ADS)

    Schwarz, C.; Cox, T.; van Engeland, T.; van Oevelen, D.; van Belzen, J.; van de Koppel, J.; Soetaert, K.; Bouma, T. J.; Meire, P.; Temmerman, S.

    2017-10-01

    A short-term intensive measurement campaign focused on flow, turbulence, suspended particle concentration, floc dynamics and settling velocities were carried out in a brackish intertidal creek draining into the main channel of the Scheldt estuary. We compare in situ estimates of settling velocities between a laser diffraction (LISST) and an acoustic Doppler technique (ADV) at 20 and 40 cm above bottom (cmab). The temporal variation in settling velocity estimated were compared over one tidal cycle, with a maximum flood velocity of 0.46 m s-1, a maximum horizontal ebb velocity of 0.35 m s-1 and a maximum water depth at high water slack of 2.41 m. Results suggest that flocculation processes play an important role in controlling sediment transport processes in the measured intertidal creek. During high-water slack, particles flocculated to sizes up to 190 μm, whereas at maximum flood and maximum ebb tidal stage floc sizes only reached up to 55 μm and 71 μm respectively. These large differences indicate that flocculation processes are mainly governed by turbulence-induced shear rate. In this study, we specifically recognize the importance of along-channel gradients that places constraints on the application of the acoustic Doppler technique due to conflicts with the underlying assumptions. Along-channel gradients were assessed by additional measurements at a second location and scaling arguments which could be used as an indication whether the Reynolds-flux method is applicable. We further show the potential impact of along-channel advection of flocs out of equilibrium with local hydrodynamics influencing overall floc sizes.

  8. Morphodynamic behaviour of a tidal inlet system in a mixed-energy environment

    NASA Astrophysics Data System (ADS)

    Michel, D.; Howa, H. L.

    This paper deals with the morphodynamic evolution of the Arcachon lagoon inlet (South West France) subjected to a mixed-energy regime. Patterns of erosion and deposition within this inlet are strongly influenced by ebb-tidal delta processes. Using an extensive data set, we propose a two stage conceptual model explaining the interactions between this transitional inlet and the adjacent shorelines. When only one channel is present, it is observed that: i) the longshore drift bypasses the inlet towards the south; ii)each year, 10 9 m 3 of sediment is eroded from the ebb-tidal delta. At the same time, large migrating swash bars accrete along the downdrift beach causing a progradation of the shoreline. With the opening of a new channel to the north, most of the longshore transport will be trapped in the inlet and the downdrift beaches are submitted to strong erosion.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  10. Wetlands: Tidal

    USGS Publications Warehouse

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

    2014-01-01

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

  11. 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

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

    NASA Astrophysics Data System (ADS)

    Paola, C.; Baumgardner, S. E.

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Vaughan, Garrett

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

  14. The signature of bankfull hydraulic conditions reflected by properties of the channel bank: a case study from the Selenga River delta, Lake Baikal, Russia

    NASA Astrophysics Data System (ADS)

    Dong, T. Y.; Nittrouer, J. A.; Czapiga, M. J.; Ma, H.; McElroy, B. J.; Il'icheva, E.; Pavlov, M.; Parker, G.

    2016-12-01

    A recent model developed to describe variable river channel Shields number proposed that the bankfull shear velocity value is nearly independent of bed material grain size, and instead is dependent on the kinematic viscosity of water. This fluid property has an important influence on the settling velocity of washload sediment, which is material generally not found on the channel bed, but is deposited on the adjacent levees during overbank flow. It is therefore hypothesized that bankfull shear velocity values for a lowland fluvial channel can be estimated based on the grain size properties of the bank sediment, after considering the vegetated state of the bank. This hypothesis is tested using a variety of data collected during two field expeditions (2014, 2016) to the Selenga River Delta, Lake Baikal, Russia, because this system demonstrates significant changes in bank material and flow hydraulic conditions across the distributary channel network. The data include: 1) channel geometry measurements, 2) bank and floodplain sediment samples, 3) water samples to measure washload concentration and grain size, 4) flow velocity measurements, and 5) bank vegetation type, to estimate sediment trapping efficiency. Analyses of the data document a downstream fining of bank sediment grain size, with medium sand present near the delta apex, to mud at the delta margin. Bankfull channel depth decreases downstream, from meter-scale near the apex, to decimeter-scale at the delta margin, where the channel banks transition from subaerial to subaqueous expression. Flow velocity - decreasing downstream - is used to calculate shear velocity. An analytical framework is developed to explore the physical connections between grain size of the bank material, bankfull depth, and shear velocity. This analysis is the first to establish a connection between bankfull geometry, bank material properties, and Shields number, and therefore provides insights regarding fluvial-deltaic morphodynamics.

  15. 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.

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

    USGS Publications Warehouse

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

    2001-01-01

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

  17. 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

  18. 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

  19. 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.

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

    USGS Publications Warehouse

    Smith, Lawrence H.; Cheng, Ralph T.

    1987-01-01

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

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

    SciTech Connect

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

    1985-01-01

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

  2. Development of tidal inlet on Mississippi River deltaic plain

    SciTech Connect

    Howard, P.C.

    1983-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Restrepo, Juan D.; Kjerfve, Björn

    2002-05-01

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

  4. 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.

  5. Identifying river channel characteristics of the Niger Inner Delta from altimeter data

    NASA Astrophysics Data System (ADS)

    Neal, Jeffrey; Bates, Paul; Trigg, Mark

    2014-05-01

    To date, much flood inundation research has focused on the simulation of hydrodynamics within a framework where detailed river and floodplain bathymetry is used to construct a physically-based numerical model. This framework is fundamentally limited in scale by the lack of observed river bathymetry for most of the world's rivers and wetlands. To simulate floodplain inundation across large spatial scales requires a different approach that will need to estimate bathymetry and friction as reach averaged components of the hydraulic model, using remotely observable variables such as water level and channel width. This research presents a model where the river channel depth, shape and friction can be described by three physically meaningful but continuous parameters. We attempt to estimate these parameters using satellite altimeter data from a test site along ~1000 km of the River Niger, Mali. For calibration the model was split into 1, 2 or 3 reaches and we used a DEM at 2 arcminutes or ~4 km. River and fl¬oodplain dynamics were simulated from 2002 to 2009, with each simulation taking ~2.5 minutes. Each reach had two parameters if assumed rectangular and three if the cross-section shape was allowed to change. Therefore there were between two and nine parameters to calibrate, depending on the number of reaches and parameters. Infl¬ow boundary conditions were based on gauge observations. Water surface elevation observations were available from ICEsat and Envisat altimeters, with parameters estimated from these using a Gauss-Marquardt-Levenberg method, with an objective function where observations were weighted given an estimate of their uncertainty. A twinned calibration experiment indicated that the information content of the data was sufficient to identify the parameters in an error free model and that the gradient based optimise was capable of finding the minimum of the objective function. Simulated levels were most sensitive to model friction and became more so with

  6. Flood Inundation Modelling in Data Sparse Deltas

    NASA Astrophysics Data System (ADS)

    Hawker, Laurence; Bates, Paul; Neal, Jeffrey

    2017-04-01

    An estimated 7% of global population currently live in deltas, and this number is increasing over time. This has resulted in numerous human induced impacts on deltas ranging from subsidence, upstream sediment trapping and coastal erosion amongst others. These threats have already impacted on flood dynamics in deltas and could intensify in line with human activities. However, the myriad of threats creates a large number of potential scenarios that need to be evaluated. Therefore, to assess the impacts of these scenarios, a pre-requisite is a flood inundation model that is both computationally efficient and flexible in its setup so it can be applied in data-sparse settings. An intermediate scale, which compromises between the computational speed of a global model and the detail of a case specific bespoke model, was chosen to achieve this. To this end, we have developed an intermediate scale flood inundation model at a resolution of 540m of the Mekong Delta, built with freely available data, using the LISFLOOD-FP hydrodynamic model. The purpose of this is to answer the following questions: 1) How much detail is required to accurately simulate flooding in the Mekong Delta? , 2) What characteristics of deltas are most important to include in flood inundation models? Models were run using a vegetation removed SRTM DEM and a hind-casting of tidal heights as a downstream boundary. Results indicate the importance of vegetation removal in the DEM for inundation extent and the sensitivity of water level to roughness coefficients. The propagation of the tidal signal was found to be sensitive to bathymetry, both within the river channel and offshore, yet data availability for this is poor, meaning the modeller has to be careful in his or her choice of bathymetry interpolation Supplementing global river channel data with more localised data demonstrated minor improvements in results suggesting detailed channel information is not always needed to produce good results. It is

  7. The inorganic chemistry of peat from the Maunachira channel-swamp system, Okavango Delta, Botswana

    NASA Astrophysics Data System (ADS)

    McCarthy, T. S.; McIver, J. R.; Cairncross, B.; Ellery, W. N.; Ellery, Karen

    1989-05-01

    The Okavango Delta is a large (18000 km 2), low gradient (1:3600), alluvial fan situated in the semi-arid Kalahari basin of northern Botswana. Seasonal floodwaters from tropical Angola disperse on the fan creating both perennial (6000 km 2) and seasonal (7000 to 12000 km 2) swamps. Ninety-five percent of this water is lost annually by evapotranspiration. Organic rich sediment (peat) is a major sediment of the perennial swamps. Peat formation commences during senescence of the plants, when certain nutrients are recycled while others are lost by rainwater leaching. Further changes in chemistry occur during subaqueous decay of the plants which involve both gains and losses of constituents. Decaying plants trap detrital mineral matter which becomes an integral part of the peat. The main sources and forms of inorganic matter in the peat are: allochthonous kaolinite (40%) and quartz (20%) and both allochthonous and autochthonous phytolithic silica (30%). Several inorganic components (Fe, K, P, Na, Ca and Mg) which make up the remaining 10% are associated with the organic fraction. Ion exchange plays only a minor part in their uptake and it seems that these metals are taken up during bacterial activity in the peat. The weight proportion of inorganic matter (ash) decreases downstream, mainly due to a decrease in allochthonous mineral matter. Volume percentage also decreases but is low throughout, generally less than five percent. This study has revealed that the low-quantity allochthonous mineral matter is the main reason for the long-term survival of this ecosystem. Uptake of soluble ions by the peat is important in off-setting evaporative concentration of metals.

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

    PubMed

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

    1999-10-01

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

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

    PubMed

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

    2017-04-13

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

  11. 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.

  12. 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, D.; Miao, C.; Duan, Q.

    2016-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. 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.

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

    USGS Publications Warehouse

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Poulain, Pierre-Marie

    2013-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Restrepo, Juan D.; López, Sergio A.

    2008-02-01

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

  18. Shaken, Not Stirred: How Tidal Advection and Dispersion Mechanisms Rather Than Turbulent Mixing Impact the Movement and Fate of Aquatic Constituents and Fish in the California Central Valley

    NASA Astrophysics Data System (ADS)

    Sridharan, V. K.; Fong, D.; Monismith, S. G.; Jackson, D.; Russel, P.; Pope, A.; Danner, E.; Lindley, S. T.

    2016-12-01

    River deltas worldwide - home to nearly a billion people, thousands of species of flora and fauna, and economies worth trillions of dollars - have experienced massive ecosystem decline caused by urbanization, pollution, and water withdrawals. Habitat restoration in these systems is imperative not only for preserving endangered biomes, but also in sustaining human demand for freshwater and long term commercial viability. The sustainable management of heavily engineered, multi-use, branched tidal estuaries such as the Sacramento-San Joaquin Delta (henceforth, the Delta) requires utilizing physical transport and mixing process models. These inform us about the movement and fate of water quality constituents and aquatic organisms. This study identifies and quantifies the effects of various hydrodynamic mechanisms in the Delta across multiple spatio-temporal scales. A particle tracking model with accurate channel junction physics and an agent based model with realistic biological hypotheses of fish behavior were developed to study the movement and fate of tracers (surrogates for water quality constituents) and fish in the Delta. Simulations performed with these models were used to (1) determine the transport pathways through the Delta, (2) quantify the magnitude of transport and mixing processes along those pathways, and (3) describe the effects of physical stressors on fates of juvenile salmon. The Delta is largely dominated by large spatial scale advection by river flows, tidal pumping, and significantly increased dispersion through chaos due to the interaction of tidal flows with channel junctions. The movement and fate of simulated tracers and juvenile salmon are governed largely by the water diversion and pumping operations, transport pathways and chaotic tidal mixing mechanisms along those pathways. There is also a significant effect of predation on fish. These transport pathway and mechanistic dependencies indicate that restoration efforts which are harmonious

  19. Characterizing Delta-Scale Connectivity Using Entropic Measures

    NASA Astrophysics Data System (ADS)

    Sendrowski, A.; Passalacqua, P.; Twilley, R.; Castaneda, E.

    2015-12-01

    Hydrologic connectivity in river deltas between distributary channels and inter-channel islands brings sediment and nutrients onto islands resulting in distinct vegetation zonation patterns on island interiors. Deltaic islands can also remain inundated for long periods of time, providing the conditions for denitrification to occur. To understand these dynamics and the overall complexity of the deltaic plain, water, sediment, and nutrient fluxes need to be considered at the network scale. Some key questions are what effect does external environmental forcing, such as river discharge, wind, and tides, have on spatial patterns in the delta, and what role do internal dynamics play in deltaic evolution. We apply the mutual information and transfer entropy metrics to quantify couplings between environmental controls and delta variables on islands and channels in Wax Lake Delta, a naturally prograding 100km2 river delta in coastal Louisiana, USA. Mutual information measures the amount of shared information in a coupling, while the transfer entropy measures the information transfer between two variables. With this method, we are able to analyze different dimensional variables across a variety of spatial and temporal scales. Continuous water levels, water temperature, and turbidity data were collected in three channels and on five islands from November 2013 to August 2014. Continuous surface water nitrate concentrations were collected at six locations on one island in the delta during the summer of 2015. The data occur over a suite of discharge, wind, and tidal conditions. While discharge is a predominant force, winds and tides play a significant role in water movement and residence time inside the islands. Nitrate fluctuations, in response to environmental forcing, vary spatially and temporally at the island scale, which will have an effect on nitrate dynamics on island interiors. Turbidity and water levels show variation at the network scale, leading to patterns of

  20. 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)

  1. 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)

  2. Defining a relationship between incident wave parameters and morphologic evolution of shoals on ebb tidal deltas using long term X-band radar observation from RIOS

    NASA Astrophysics Data System (ADS)

    Humberston, J. L.; McNinch, J.; Lippmann, T. C.

    2016-12-01

    The morphology of tidal inlet ebb-shoals varies dynamically over time, particularly in response to large wave events. Understanding which wave qualities most influence shoals' evolution would support advancements in sediment bypassing models as well as targeted maintenance dredging for hydrographic purposes. Unfortunately, shallow and rapidly changing bathymetry, turbid waters and ambiguous wave speeds resulting from multiple shoaling and de-shoaling areas limits many traditional surveying techniques from obtaining the spatial and temporal resolution necessary to effectively characterize shoal development. The Radar Inlet Observing System (RIOS) is a uniquely designed mobile X-band radar system that can be deployed to inlet environments and, using roof-mounted solar panels and an automatically triggered highly efficient diesel generator, run automated hourly collections and wirelessly stream data for up to several months at a time in nearly all weather and water conditions. During 2015 and early 2016, RIOS was deployed to St. Augustine Inlet, FL., New River Inlet, N.C., and Oregon Inlet, N.C. for periods of one to six months to allow for measureable shoal evolution. During deployments, ten minute collections (at 1 Hz) were conducted every hour and the data gridded to a 5m alongshore/cross-shore grid. Raw intensity returns were time-averaged and analyzed to define three metrics of shoal evolution: movement direction, movement velocity and inferred bathymetry. For each location and time period, wave frequencies, wave directions and significant wave heights were collected from the nearest wave-buoy. Time lapse videos of shoal positions were inspected and used in concert with cross-correlations values from each pair of shoal and wave parameters to determine the incident wave qualities most strongly relating to shoal evolution. Preliminary results suggest wave height, more than frequency, controls shoal movement. Wave direction and size collaboratively appear to direct

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

    PubMed

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

    1995-07-07

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

  4. 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

  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. Tidal Hydraulics and Morphological Response to Wetland Loss in Barataria Bay, Louisiana

    NASA Astrophysics Data System (ADS)

    Howes, N.; Fitzgerald, D. M.; Georgiou, I.; Hughes, Z. J.; Miner, M.; Kulp, M.

    2008-12-01

    Relative sea level rise (RSLR) in Barataria Bay, Louisiana is on the order of 1 cm/yr due to high rates of subsidence coupled with eustatic sea-level rise. The most pronounced physical response to this RSLR is wetland loss. Barataria is a large, shallow, interdistributary bay separated from the Gulf of Mexico by a chain of barrier islands. Four principal tidal inlets control the flux of water and nutrients between Barataria Bay and the Gulf of Mexico (west to east): Caminada Pass, Barataria Pass, Pass Abel, and Quatre Bayou. Between 1935 and 2006 wetland loss increased bay area by 1125 km2 resulting in greater tidal exchange and increasing tidal prism. During this period, inlet cross sectional areas enlarged by a combined 13,000 m2 and ebb-tidal deltas doubled in volume. The tidal wave in Barataria Bay is largely progressive, with only a minor standing wave component, consistent with a shallow estuary that contains additional frictional elements due to extensive marshlands and islands. Tides in Barataria Bay are diurnal and gradually reduce in amplitude from 0.53 m (tropic tide conditions) at the entrance to Barataria Pass to 0.07 m at Lake Cataouatche, located 70 km up basin. Much of the reduction in the upper reaches of the basin is due to bottlenecks, where narrow tidal channels connect to shallow lakes. The tidal wave crest reaches Lake Cataouatche 13 hours after propagating through Barataria Pass. Historically, the expanding inlet dimensions have increased tidal conductivity leading to an increase in tidal range throughout the bay. Tide gage records at Grand Isle and at eight other locations within the basin show that during the past 10 to 30 years (depending on station) tidal ranges increased from 9.8 mm/yr inside Barataria Pass to 3.1 mm/yr in Lake Salvador (60 km up basin). The magnitude of this change is significant due to the microtidal conditions that exists within the bay (TRAve = 0.32 m). Thus, the increasing extent of open water and dimensions of the

  7. Tidal Power Exploitation in Korea

    NASA Astrophysics Data System (ADS)

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

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

  8. Deficiency in the glycerol channel Fps1p confers increased freeze tolerance to yeast cells: application of the fps1delta mutant to frozen dough technology.

    PubMed

    Izawa, Shingo; Ikeda, Kayo; Maeta, Kazuhiro; Inoue, Yoshiharu

    2004-12-01

    Intracellular glycerol content affects the freeze-thaw stress tolerance of Saccharomyces cerevisiae. We have recently reported that intracellular-glycerol-enriched cells cultured in glycerol medium acquire tolerance to freeze stress and retain high leavening ability even in dough after frozen storage [Izawa et al. (2004) Appl Microbiol Biotechnol http://dx.doi.org/10.1007/s00253-004-1624-4]. A deletion mutant of the FPS1 gene, which encodes a glycerol channel, accumulates glycerol inside the cell without an exogenous supply of glycerol into the medium. We found that the fps1delta cells acquired tolerance to freeze stress and retained high leavening ability in dough after frozen storage for 7 days. These results suggest that the fps1delta mutant is a useful strain for developing better frozen-dough with a commercial advantage.

  9. Hydrodynamics and sediment transport in a southeast Florida tidal inlet

    PubMed Central

    Fiechter, Jerome; Steffen, Kelley L.; Mooers, Christopher N.K.; Haus, Brian K.

    2009-01-01

    A three-dimensional ocean circulation model is used to investigate the hydrodynamics of a tidal inlet and deltas system in Southeast Florida, and to understand the consequences for suspended and bedload sediment transport patterns. The model reproduces observed tidal currents and provides insight about residual currents caused by spatial asymmetries in the inlet throat and tidal deltas during ebb and flood flows. A particle-tracking approach for suspended and bedload sediment transport is used to simulate deposition patterns for different particle sizes. The simulation results qualitatively correlate with the distribution of sediment characteristics within the tidal inlet and deltas system and demonstrate sensitivity to the choice of advection velocities (e.g., near-bottom versus depth-averaged) and regions of sediment origin. Furthermore, the distinction between suspended and bedload transport as a function of particle size indicates significant differences in deposition patterns and their potential connection to geomorphologic features of the tidal inlet and deltas system. PMID:19838314

  10. 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

  11. Analysis and numerical modeling of the flow and sand dynamics in the lower Song Hau channel, Mekong Delta

    NASA Astrophysics Data System (ADS)

    Xing, F.; Meselhe, E. A.; Allison, M. A.; Weathers, H. D.

    2017-09-01

    Two- and three-dimensional Delft3D Flow and Morphology models were constructed for the lower Song Hau distributary channel of the Mekong River in Vietnam to provide insights into the hydrodynamics and sand transport of the channel system. The models were calibrated and validated with data for observed water level, water discharge, velocity, and suspended-sand concentration during the high- and low-flow seasons of 2014 and 2015. The water and sand budgets of the Dinh An and Tran De channels, the two sub-distributaries of the lower Song Hau channel, were calculated, showing that 73% of the fluvial water discharge and 90% of suspended sand were transported through the Dinh An channel, while the rest was transported through the Tran De channel in the high-flow season. In the low-flow season, the total fluvial water discharge was < 20% of that in the high-flow season; and 96% of it was transported through the Dinh An channel and the rest was transported through the Tran De channel. Sand was transported from channels into the ocean in both the Dinh An and Tran De channels during the high-flow season, but from the ocean into the two channels during the low-flow season. The reversed sand flux from ocean into river channels during low-flow season was not observed in field studies. The different behaviors between models and field observations might be caused by the absence of baroclinic effects in the model set up. The Dinh An channel was found to be dominated by ebb tide, in favor of transporting water and sediment to the ocean, and the Tran De channel was dominated by flood tide. In the high-flow season, the residual currents were directed toward the ocean for both the Dinh An and Tran De channels. In the low-flow season, the magnitude of the residual currents decreased in the river channels. Under these conditions, the residual-current direction changed to be ambiguous in the Tran De channel, but remained seaward in the Dinh An channel. The low fluvial discharge combined

  12. 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.

  13. Implications of tidally-varying bed stress and intermittent estuarine stratification on fine-sediment dynamics through the Mekong's tidal river to estuarine reach

    NASA Astrophysics Data System (ADS)

    McLachlan, R. L.; Ogston, A. S.; Allison, M. A.

    2017-09-01

    River gauging stations are often located upriver of tidal propagation where sediment transport processes and storage are impacted by widely varying ratios of marine to freshwater influence. These impacts are not yet thoroughly understood. Therefore, sediment fluxes measured at these stations may not be suitable for predicting changes to coastal morphology. To characterize sediment transport dynamics in this understudied zone, flow velocity, salinity, and suspended-sediment properties (concentration, size, and settling velocity) were measured within the tidal Sông Hậu distributary of the lower Mekong River, Vietnam. Fine-sediment aggregation, settling, and trapping rates were promoted by seasonal and tidal fluctuations in near-bed shear stress as well as the intermittent presence of a salt wedge and estuary turbidity maximum. Beginning in the tidal river, fine-grained particles were aggregated in freshwater. Then, in the interface zone between the tidal river and estuary, impeded near-bed shear stress and particle flux convergence promoted settling and trapping. Finally, in the estuary, sediment retention was further encouraged by stratification and estuarine circulation which protected the bed against particle resuspension and enhanced particle aggregation. These patterns promote mud export ( 1.7 t s-1) from the entire study area in the high-discharge season when fluvial processes dominate and mud import ( 0.25 t s-1) into the estuary and interface zone in the low-discharge season when estuarine processes dominate. Within the lower region of the distributaries, morphological change in the form of channel abandonment was found to be promoted within minor distributaries by feedbacks between channel depth, vertical mixing, and aggregate trapping. In effect, this field study sheds light on the sediment trapping capabilities of the tidal river - estuary interface zone, a relatively understudied region upstream of where traditional concepts place sites of deposition

  14. Mississippi River Delta, Louisiana as seen from STS-62

    NASA Image and Video Library

    1994-03-05

    STS062-85-021 (4-18 March 1994) --- The Mississippi River is the largest river system in North America. Its delta is a typical example of the bird's foot class of river deltas. It drains nearly 3 1/2 million square kilometers of real estate and is estimated to carry 2.4 billion kilograms (more than 500 million tons) of sand, silt, and clay to the Gulf of Mexico annually. Most of this sediment is deposited as a delta at the mouth of the river where the velocity of the river water is slowed and its ability to transport sediment is accordingly diminished. Continued deposition at such a site progrades the delta or extends it seaward into the Gulf as much as 150 meters each year until such time as a flooding episode finds a shorter more efficient channel to deliver sediment-laden river waters to the Gulf. At that time the old delta is abandoned and the river begins to build a new delta. In time, compaction of the sediment in the old delta causes it to subside forming first marshes, then bays. This and the modifying effects of coastal waves eventually allow the sea to reclaim much of the temporary land area of the delta. This sequence has repeated itself over and over again at the Mississippi Delta. In this photograph, the present day active Balize delta is shown. According to NASA scientists it is the youngest of the recent delta lobes having begun its seaward pro-gradation only some 600 - 800 years ago. The main channel of the river is 2 kilometers wide and 30 - 40 meters deep. Natural levees here are almost 1 kilometer wide and 3 to 4 meters above sea level. Along the active distributaries of the lower delta, natural levees are less than 100 meters wide and generally less than 0.5 meters above sea level. The bird's foot appearance of deltas such as this is characteristic of low coastal energy conditions - that is, low levels of tidal fluctuation and generally low wave energy. The interdistributary bays are extremely shallow, usually less than a few meters, and contain

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed

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

    2007-05-08

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

  17. Delta in Terra Cimmeria

    NASA Image and Video Library

    2011-02-18

    This unnamed crater in northern Terra Cimmeria has a small channel that created a delta feature. Such features are important indicators of liquid water in Mars past as shown in this image from NASA Mars Odyssey.

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

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  19. Changing Course - the Baird Team Solution: a Delta for All

    NASA Astrophysics Data System (ADS)

    Nairn, R. B.

    2016-02-01

    The Changing Course Design competition was initiated to evaluate options for re-positioning the mouth of the Mississippi River and modifying the management of the Lower Mississippi River to support the 2017 Master Plan for the Louisiana coast. This paper will present the findings of one of the selected competitors: the Baird Team and their "Delta for All" approach. A key to success in the future management of the lower Mississippi River is the development of an integrated, holistic approach to management that recognizes the need to harness the full land/wetland building and restorative potential of the river at the same time as improving flood protection and navigation. Fundamentally the Baird solution recognized the underlying geomorphic challenges of the Delta: it receives three to four times less sediment from the Mississippi River than it did historically and sea level is rising two to three times faster than it did historically and is predicted to rise much faster in the future. The result will be a smaller delta in the future. Our approach seeks to harness as close to 100% of the land building potential of the river to make the smaller future delta as large as possible. This compares to the 2012 State Master Plan which would harness approximately 50% of the land-building potential. Our approach also recognizes that the further inland new distributary mouths and associated sub-deltas are located, the greater the delta building potential. Our approach builds with the river by creating and managing new river distributaries that are opened and closed every 50 years or so to build new sub-deltas within a defined sustainable delta footprint. By placing the last outlet somewhere in the vicinity of English Turn the lower Mississippi River would become a tidal channel. These two simple concepts of harnessing 100% of the river and placing the last outlet near English Turn result in immediate and significant benefits for flood protection and navigation. Through the

  20. 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.

  1. Sand Waves in Tidal Channels

    DTIC Science & Technology

    2007-01-01

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

  2. 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.

  3. 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

  4. 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

  5. Sedimentary signatures of tidal bores: a brief synthesis

    NASA Astrophysics Data System (ADS)

    Tessier, Bernadette; Furgerot, Lucille; Mouazé, Dominique

    2017-08-01

    This article aims at presenting a brief synthesis of sedimentary signatures assigned to tidal bore dynamics and impacts. According to the few studies published until now on tidal bore-induced facies within inner estuarine tidal channel infilling successions, only two major signatures can be reported: (1) soft sediment deformations (SSDs) due to overpressure linked to sudden water level elevation, high shear stress and vertical velocity acceleration below the tidal bore front and secondary waves; SSDs may be present throughout the channel infill succession, with the general exception of the uppermost part; tidal bore-induced SSDs have been described only in modern facies; (2) tidal bore couplets (TBCs) formed by an erosional surface overlain by massive sand drapes, related to the reworking of the sediment bottom during tidal bore passage; TBCs were first described in the ancient record. Studies in modern estuaries demonstrate that TBCs evolve towards tidal bore sequences from the tidal channel bottom (subtidal to low intertidal facies) to tidal channel bank (low to mid intertidal facies). In mid to upper intertidal facies, the occurrence of thicker-than-average tidal rhythmites, reflecting higher-than-average suspended sediment concentrations, are also considered as a possible signature of tidal bore dynamics.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  7. 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.

  8. Ganges River Delta, Bangladesh, India

    NASA Image and Video Library

    1994-11-14

    The Ganges River Delta is the largest inter-tidal delta in the world. With its extensive mangrove mud flats, swamp vegetation and sand dunes, it is characteristic of many tropical and subtropical coasts. As seen in this photograph, the tributaries and distributaries of the Ganges and Brahmaputra Rivers deposit huge amounts of silt and clay that create a shifting maze of waterways and islands in the Bay of Bengal.

  9. Ganges River Delta, Bangladesh, India

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The Ganges River Delta is the largest inter-tidal delta in the world. With its extensive mangrove mud flats, swamp vegetation and sand dunes, it is characteristic of many tropical and subtropical coasts. As seen in this photograph, the tributaries and distributaries of the Ganges and Brahmaputra Rivers deposit huge amounts of silt and clay that create a shifting maze of waterways and islands in the Bay of Bengal.

  10. 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.

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

    PubMed Central

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

    2012-01-01

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

  12. Channels

    NASA Image and Video Library

    2014-04-29

    Two channels are visible in this image from NASA 2001 Mars Odyssey spacecraft . The smaller one near the bottom did not carve as deeply as the larger channel at the top. The channel near the top of the image is near the origin of Mamers Valles.

  13. The Relative Effects of Wave Climatology and Tidal Currents on Beach Processes Adjacent to a Major Tidal Inlet, Ocean Beach, San Francisco, California

    NASA Astrophysics Data System (ADS)

    Barnard, P. L.; Hanes, D. M.; Ruggiero, P.

    2004-12-01

    the typical northwest swell returns. Over longer time periods (i.e. decades), tidal processes emerge as the dominant control on coastal evolution is this region, as changes in sediment supply and depositional patterns exert a strong influence on the ebb tidal delta volume and morphology. The tidal delta, in turn, strongly influences wave shielding, refraction, and focusing patterns on adjacent beaches. An accurate assessment of the interaction between wave and tidal processes is crucial for evaluating coastal management options in an area that includes the annual dredging and disposal of ship channel sediment and an erosional hot spot that is posing a major threat to local infrastructure.

  14. 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.'

  15. Linking hydrologic connectivity and nutrient dynamics in a deltaic island of prograding Wax Lake Delta, coastal Louisiana

    NASA Astrophysics Data System (ADS)

    Sendrowski, A.; Passalacqua, P.; Castaneda-Moya, E.; Twilley, R.

    2016-12-01

    River deltas are self-organizing systems that exhibit complex non-linear dynamics. Deltas consist of highly connected distributary channels and inter-channel islands that exchange fluxes leading to ecologically rich island platforms. Deltaic islands have been suggested as areas of enhanced biological and biogeochemical processing that display high spatial and temporal variability in terms of vegetation succession, island size and shape, and hydroperiod. Nutrient dynamics within an island are influenced by the structural connectivity of channels and islands and the process connectivity between ecohydrologic variables and external geophysical forcings such as river discharge, wind, and tides. The aim of this study is to quantify the connectivity between delta variables and geophysical drivers within an island, with a focus on nutrient dynamics across space and time. Six permanent telemetry platforms installed on an island in Wax Lake Delta, a naturally prograding river delta in coastal Louisiana, measure continuous (March 2014 to present) in situ surface water nitrate, temperature, turbidity, and water level over time, thus covering different river discharge, wind, and tidal conditions. The platforms were installed in different locations within the island to capture the distinct flow paths and vegetation dynamics strongly associated with the Mississippi River flood-pulse season. We quantify the spatial and temporal variability of process connections on nutrient dynamics with information theory, a statistical method that quantifies the information flow between variables. With information theory, we can quantify the direction, strength, timescale of relationships, and the locations of enhanced nitrate processing under variable discharge, wind, and tidal conditions. Distinct spatial patterns emerge in water level and turbidity in response to riverine and tidal forcing that affect nitrate and temperature couplings. Implications for these relationships at the network

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. A preliminary study of tidal current ridges

    NASA Astrophysics Data System (ADS)

    Liu, Zhenxia; Xia, Dongxing

    1985-06-01

    Tidal current ridges, widely distributed geomorphological phenomena over the continental shelf of the world, are studied. They are formed by tidal current and the trend of their sand bodies runs parallel to the direction of tidal current. There are two types of the plane shapes: the parallel and the fingered. Conditions of forming tidal current ridges are the velocities of tidal current ranging from 1 to 3.5 knots and the supply of abundant sediments. Tidal current ridges often develop in following morphological locations: the bays, estuaries, the mouths of channels, as well as the offshore area with strong tidal current. Tidal current ridges occur generally at a water depth of less than 35 metres. The sediments of tidal current ridges are mainly composed of sand. The grain size of the sediments is uniform and well sorted. The characteristics of grain size of the sand imply that their formation mechanism is similar to that of river sand, that is, both of them are the result of flow movements in a trongth channel controlled by boundary. There is however difference between them that the river sand is formed by one-way flow movement while the tidal current sand by two-way movement. There are two saltation populations in the log-probability curves of tidal current sand, the sorting of first saltation population is better than the second one, and having positive skewness, which differs from beach sand. In the C-M grain size pattern tidal current sand is most found in graded suspension segment. The continental shelves of the Yellow Sea, the East China Sea and the South China Sea have favourable conditions for developing tidal current ridges in massive scale and special shape, such as the tidal current ridges in the offshore of Jiangsu, the Gulf of Korea, the shoal of Liaodong, the east and west mouths of the channel of Qiongzhou, Jiaozhou Bay, the shoal of Taiwan, Lingdingyang, the north branch of Changjiang estuary. The studies of them are of vital significance in

  8. Tidal power in Argentina

    SciTech Connect

    Aisiks, E.G.

    1993-03-01

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

  9. The effects of tidal range on saltmarsh morphology

    NASA Astrophysics Data System (ADS)

    Goodwin, Guillaume; Mudd, Simon

    2017-04-01

    Saltmarshes are highly productive coastal ecosystems that act simultaneously as flood barriers, carbon storage, pollutant filters and nurseries. As halophytic plants trap suspended sediment and decay in the settled strata, innervated platforms emerge from the neighbouring tidal flats, forming sub-vertical scarps on their eroding borders and sub-horizontal pioneer zones in areas of seasonal expansion. These evolutions are subject to two contrasting influences: stochastically generated waves erode scarps and scour tidal flats, whereas tidally-generated currents transport sediment to and from the marsh through the channel network. Hence, the relative power of waves and tidal currents strongly influences saltmarsh evolution, and regional variations in tidal range yield marshes of differing morphologies. We analyse several sheltered saltmarshes to determine how their morphology reflects variations in tidal forcing. Using tidal, topographic and spectral data, we implement an algorithm based on the open-source software LSDTopoTools to automatically identify features such as marsh platforms, tidal flats, erosion scarps, pioneer zones and tidal channels on local Digital Elevation Models. Normalised geometric properties are then computed and compared throughout the spectrum of tidal range, highlighting a notable effect on channel networks, platform geometry and wave exposure. We observe that micro-tidal marshes typically display jagged outlines and multiple islands along with wide, shallow channels. As tidal range increases, we note the progressive disappearance of marsh islands and linearization of scarps, both indicative of higher hydrodynamic stress, along with a structuration of channel networks and the increase of levee volume, suggesting higher sediment input on the platform. Future research will lead to observing and modelling the evolution of saltmarshes under various tidal forcing in order to assess their resilience to environmental change.

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  13. Tidal Asteroseismology

    NASA Astrophysics Data System (ADS)

    Burkart, Joshua

    2012-01-01

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

  14. 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.

  15. Avulsion in inhabited deltas triggered by human-induced sea ingressions: a historical analogue from the first millennium AD in the Netherlands

    NASA Astrophysics Data System (ADS)

    Pierik, Harm Jan; Stouthamer, Esther; Schuring, Tim; Cohen, Kim

    2017-04-01

    The shifting of river channels (avulsion) has consequences for people living in deltas as it is a key process in the distribution of sediment and water and thus transport and resources. These avulsions have many causes which are either upstream or downstream induced, such as base level rise, flooding events, or levee superelevation. However, a so far unexplored decisive factor in determining avulsion success is the development of sea ingressions and the role of human activities in forming them. The landward expansions of tidal channels significantly reduce the distance to sea for a potential new river course. In this contribution we infer the role of sea ingressions from a historical case study from the first millennium AD of a multiple-staged avulsion in the Rhine-Meuse delta, the Netherlands. This avulsion resulted in a major reorganisation of the river channel network: it was the first avulsion which successfully crossed an extensive peat area that separated the rivers Rhine and Meuse, thereby distributing a major part of the Rhine discharge towards another tidal inlet. This tidal inlet expanded into the peat area and connected to an active crevasse splay. Archaeological evidence surrounding this ingression strongly suggests that its expansion was accelerated by human-induced soil subsidence related to peat land reclamation. This case study demonstrates that an increase in tidal influence in a low gradient delta plain is an important mechanism determining avulsion success. Considering major subsidence and sediment depletion problems that many deltas are nowadays facing, human-induced sea ingressions will presumably become increasingly important for successful avulsions.

  16. 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

  17. 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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  19. 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.

  20. 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.

  1. Storm surge and tidal range energy

    NASA Astrophysics Data System (ADS)

    Lewis, Matthew; Angeloudis, Athanasios; Robins, Peter; Evans, Paul; Neill, Simon

    2017-04-01

    The need to reduce carbon-based energy sources whilst increasing renewable energy forms has led to concerns of intermittency within a national electricity supply strategy. The regular rise and fall of the tide makes prediction almost entirely deterministic compared to other stochastic renewable energy forms; therefore, tidal range energy is often stated as a predictable and firm renewable energy source. Storm surge is the term used for the non-astronomical forcing of tidal elevation, and is synonymous with coastal flooding because positive storm surges can elevate water-levels above the height of coastal flood defences. We hypothesis storm surges will affect the reliability of the tidal range energy resource; with negative surge events reducing the tidal range, and conversely, positive surge events increasing the available resource. Moreover, tide-surge interaction, which results in positive storm surges more likely to occur on a flooding tide, will reduce the annual tidal range energy resource estimate. Water-level data (2000-2012) at nine UK tide gauges, where the mean tidal amplitude is above 2.5m and thus suitable for tidal-range energy development (e.g. Bristol Channel), were used to predict tidal range power with a 0D modelling approach. Storm surge affected the annual resource estimate by between -5% to +3%, due to inter-annual variability. Instantaneous power output were significantly affected (Normalised Root Mean Squared Error: 3%-8%, Scatter Index: 15%-41%) with spatial variability and variability due to operational strategy. We therefore find a storm surge affects the theoretical reliability of tidal range power, such that a prediction system may be required for any future electricity generation scenario that includes large amounts of tidal-range energy; however, annual resource estimation from astronomical tides alone appears sufficient for resource estimation. Future work should investigate water-level uncertainties on the reliability and

  2. Tidal wave transformations in the German Bight

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Winterwerp, Johan C.

    2011-03-01

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

  5. On the migration rate of tidal meanders

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Sinuous channels shaped by periodically reversing tidal flows are a ubiquitous feature of tidal landscapes. Despite their fundamental role on the morphology and sedimentary patterns of these landscapes, tidal meanders have received less attention than their fluvial counterparts, particularly as far as migration processes are concerned. We have analyzed the migration of about 300 meander bends in the Northern Venice Lagoon (Italy), from 1968 to nowadays, through observations and modeling interpretation. Similarities with fluvial meanders occur, although important difference also emerge. Meanders cutting through salt-marshes in the Venice Lagoon follow the relationship between Cartesian length and channel width, typical of meanders developed within different settings. We find a mean migration rate of about 0.20 m/year. However, the potential migration rate can reach values of about 0.20 channel widths per year thus suggesting similarities with fluvial meanders. In addition, tidal channel migration dynamics displays features which qualitatively agree with theories developed for the fluvial setting. We deem our results are valuable for the understanding of the morphological evolution and architecture of tidal landscapes, with implications for restoration strategies, also in the face of changes in environmental conditions.

  6. Hydraulic geometry of a small tidal estuary

    USGS Publications Warehouse

    Myrick, Robert M.; Leopold, Luna Bergere

    1963-01-01

    A tidal channel in a marsh bordering the Potomac River near Alexandria, Va., was mapped, and current-meter measurements of discharge were made at various locations and at various stages in the tidal cycle. These measurements allowed analysis of the change of width, depth, and velocity with discharge at various cross sections and along the length of the channel.There is also presented a theoretical development of some, of these same relations based on hydraulic principles and on the assumption of a uniform distribution of energy and a minimum rate of work in the system as a whole.The change of width, depth, and velocity with discharge downstream developed from the field data checked closely with the theoretically derived values.The estuarine channel differs from a terrestrial one in that discharge at any section in an estuary varies depending on how the flow shaped the entire length of the channel between the point in question and the main body of tidal water. The result is that a tidal channel changes more rapidly in width and less rapidly in depth as discharge changes downstream than does a terrestrial channel.

  7. Understanding pesticides in California's Delta

    USGS Publications Warehouse

    Kuivila, Kathryn; Orlando, James L.

    2012-01-01

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

  8. 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

  9. 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 ...

  10. Channels

    NASA Image and Video Library

    2015-11-20

    Today's VIS image shows a number of unnamed channels located on the northeastern margin of Terra Sabaea. Orbit Number: 61049 Latitude: 33.5036 Longitude: 58.6967 Instrument: VIS Captured: 2015-09-18 12:54 http://photojournal.jpl.nasa.gov/catalog/PIA20097

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

    USGS Publications Warehouse

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

    2005-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-11-01

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

  13. Volga Delta

    Atmospheric Science Data Center

    2013-04-17

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  15. 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.

  16. 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

  17. 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

  18. 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.

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

    USGS Publications Warehouse

    Takesue, Renee K.

    2016-10-03

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

  20. 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).

  1. Simulating hydrodynamics on tidal mudflats

    NASA Astrophysics Data System (ADS)

    Cook, S.; Lippmann, T. C.

    2014-12-01

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

  2. 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.

  3. Tidal creek changes at the Sonoma Baylands restoration site

    USGS Publications Warehouse

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

    1998-01-01

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

  4. Offshore Deterioration in the Mekong Delta, Vietnam

    NASA Astrophysics Data System (ADS)

    Stattegger, K.; Unverricht, D.; Heinrich, C.

    2016-02-01

    The interplay of river, tide and wave forcing controls shape and sedimentation at the front of the Mekong Delta. Specific hydro- and morphodynamic conditions in the western subaqueous part of the asymmetric Mekong Delta generate a sand ridge - channel system (SRCS) which is unique in subaqueous delta formation. This large-scale morphological element extends 130 km along the delta front consisting of two sand ridges and two erosional channels. Three different zones within SRCS can be distinguished. The eastern initial zone stretches along delta slope and inner shelf platform southwest of the Bassac river mouth, the largest and westernmost distributary of the Mekong Delta. In the central zone SRCS covers the outer part of the subaqueous delta platform with a pronounced sand-ridge and erosional channel morphology. Cross-sections of the SRCS reveal an asymmetric shape including steeper ridge flanks facing into offshore direction. Channels incise down to 18.2 m water depth (wd) and 10.5 down the ridge top at the outer subaqueous delta platform, respectively. Towards the west the sand ridges pinch out while the two channels merge into one and form a giant erosional scour of up to 33 m wd within the subaqueous delta platform. In the western zone, the channel gets shallower and vanishes along the south-western edge of the subaqueous delta platform around Ca Mau Cape. Sediment transport from the Mekong River nourishes the sand ridges. In contrast, tide and wind-driven currents cut the erosional channels, which act also as fine-sediment conveyor from eroding headlands to the distal part of the delta front that is 200 km apart of the Bassac river mouth. SRCS in the subaqueous Mekong Delta is a relevant indicator of delta-front instability and erosion.

  5. Delta-doping of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schubert, E. F.

    2005-08-01

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

  6. 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.

  7. Constraining Daily-To-Annual Carbon Budgets in a Brackish Tidal Marsh in the San Francisco Bay Delta: Insights on Methane and Carbon Dioxide Fluxes from Eddy Covariance Measurements

    NASA Astrophysics Data System (ADS)

    Saraceno, J.; Anderson, F. E.; Knox, S.; Windham-Myers, L.; Bergamaschi, B. A.

    2016-12-01

    Carbon cycling in coastal wetlands is difficult to measure and model due to extremely dynamic atmospheric (vertical) and hydrologic (lateral) fluxes, as well as sensitivities to dynamic land- and ocean-based drivers. Whereas atmospheric carbon is sequestered in accreted carbon stocks over millennia to maintain balance with sea level rise, annual or seasonal carbon fluxes from tidal wetlands can become net negative or net positive, as key drivers of carbon cycling, such as inundation area, soil and air temperature and salinity change over short time periods. Few studies have documented the interannual variability in the net ecosystem carbon balance for tidal-driven ecosystems. Using the eddy covariance technique, we present 2.5 years (March 2014-September 2016) of net ecosystem exchanges (NEE) for CO2 and CH4 from a historic wetland (the National Estuarine Research Reserve's Rush Ranch) in the Suisun Marsh complex of San Francisco Bay, California, where salinity ranges from oligohaline to mesohaline. Preliminary estimates show that daily rates of CO2 NEE were approximately -15 gC m-2 d-1 during the peak growing season in the summer to +10 gC m-2 d-1 during the winter months. CH4 emissions, ranged from 0 to +30 mgC m-2 d-1, a small fraction of observed rates from neighboring freshwater marshes. We have also found that using standard parameters (e.g. temperature and radiation) in an artificial neural network approach to gap-fill missing fluxes and estimate random error uncertainty were insufficient, suggesting that daily and seasonal shifts in salinity, water levels, and plant community phenology may help to reduce uncertainty in estimated values of both CO2 and CH4 fluxes. An additional aspect of this study is to investigate the significance of carbon exported through tidal exchanges, especially considering that regional estimates of carbon accretion in the soils to be only 100 gC m-2. Here we will estimate the aquatic carbon flux using proxies for dissolved

  8. 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

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

    NASA Astrophysics Data System (ADS)

    Nienhuis, Jaap H.; Ashton, Andrew D.

    2016-11-01

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

  10. Depositional System Transition from Braided River to Tide Dominated Delta-A Case Study of the MPE3 Block in the Eastern Venezuelan Basin

    NASA Astrophysics Data System (ADS)

    Huang, Wensong; Chen, Heping; Xu, Fang; Meng, Zheng; Li, Yonghao

    2017-04-01

    The Eastern Venezuelan basin is a world-class petroliferous area, with the sedimentary environment controlled by the interaction between the Caribbean plate and the American plate. Based on interpretation of 3D seismic data, description of electrical well-logging facies and analysis of the sedimentary phenomena on the cores, we distinguished different types of sedimentary associations and clarified the evolution progress of the sedimentary system in the study area, the MPE3 Block. We put forward that depositional system in the study area changed from braided river in the early Miocene to tide dominated delta in the middle Miocene. Paralleled with sedimentary progress, the depositional hydrodynamic mechanism altered from the inertia dominated setting into the buoyancy dominated setting. During the middle Miocene, the tidal effect obviously reworked and formed tidal bars and tidal channels, both severing as the sedimentary framework. From the perspective of the tectonic movement, the study area varied from the foreland stage during the early Miocene to the compression and inverse stage during the middle Miocene. At the same time, the study area located in the southern part of the foreland basin began to extend and marine transgression occurred due to the tectonic extensional movement. We pointed out that critical factors influencing the transition from braided river to tidal dominate delta include palaeogeomorphology, sea level fluctuation, feeder system and the distance to catchment area.

  11. 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.

  12. Vertical and Lateral Changes in Facies, Bed Thickness, and Grain Size in Submarine Channels from an Ultra-High Resolution Dataset, Western Niger Delta Slope: Implications for Turbidity Current Stratification

    NASA Astrophysics Data System (ADS)

    Jobe, Z. R.; Pirmez, C.; Sylvester, Z.; Frascati, A.; Bolla Pittaluga, M.; Howes, N. C.

    2015-12-01

    Modern seafloor and shallow subsurface studies offer a high-resolution view into the morphology, architecture, and evolution of submarine channels. In addition to architecture derived from seismic data, lithologic and age calibration are needed to constrain the evolution of submarine channels and the properties of the flows that sculpt them. Near-seafloor seismic and core data from the western Niger Delta slope allow for the quantification of lateral and vertical changes in facies, bed thickness, and grain size in a well-constrained channel system. The dataset consists of a 3D seismic volume, high-resolution 2D seismic profiles, 21 sediment cores, and more than 500 grain-size analyses. Core and seismic data reveal that the channel axis consists of thick-bedded, amalgamated, coarse-grained sands. Channel margin deposits are thin-bedded and heterolithic, and show a pronounced decrease in bed thickness and grain size with increasing distance above and away from the channel thalweg. Margin deposits exist in 'scallops' that correspond to bends of an older, more sinuous channel. While individual scallops are disconnected from each other, beds can be correlated over hundreds of meters between cores within the same scallop. Multiple core transects across the channel demonstrate a rapid decrease in bed thickness and deposition rate (calculated from radiocarbon ages) with increasing height above channel thalweg. Grain size distributions obtained with a laser particle-size analyzer also show a strong fining with height above thalweg. These trends reflect the stratification of grain size and sediment concentration in channelized turbidity currents. Simple theoretical concentration and grain-size profiles match the observed trends, providing constraints for numerical and rule-based modeling approaches. Although facies models for submarine channels often assume quasi-horizontal fill with rapid lateral facies changes, this dataset suggests that there is a significant difference

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

    PubMed

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

    2007-03-01

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

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

    PubMed

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

    2004-05-17

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

  15. Mississippi River Delta

    NASA Image and Video Library

    2002-06-11

    As the Mississippi River enters the Gulf of Mexico, it loses energy and dumps its load of sediment that it has carried on its journey through the mid continent. This pile of sediment, or mud, accumulates over the years building up the delta front. As one part of the delta becomes clogged with sediment, the delta front will migrate in search of new areas to grow. The area shown on this image is the currently active delta front of the Mississippi. The migratory nature of the delta forms natural traps for oil. Most of the land in the image consists of mud flats and marsh lands. There is little human settlement in this area due to the instability of the sediments. The main shipping channel of the Mississippi River is the broad stripe running northwest to southeast. This image was acquired on May 24, 2001 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet. http://photojournal.jpl.nasa.gov/catalog/PIA03497

  16. Tale of Two Deltas: Permafrost Dynamics on the Colville and Yukon-Kuskokwim Deltas

    NASA Astrophysics Data System (ADS)

    Jorgenson, T.; Shur, Y.

    2016-12-01

    Arctic deltas are the predominant coastline in the Arctic and are greatly modified by permafrost aggradation and degradation. In comparing the Colville Delta (CD) along the Beaufort Sea (MAAT -11 °C) with the Yukon-Kuskokwim Delta (YKD) along the Bering Sea (MAAT -1 °C), permafrost characteristics respond to differences in climate, flooding, salinization, and vegetation-soil development. Both deltas have an inner zone dominated by fluvial processes and nonsaline ecosystems, and an outer zone affected by both tidal and fluvial processes and has salt-affected ecosystems. In the CD, closed taliks develop under the deeper channels and surface permafrost starts to form on channel bars where water is <2 m deep. During early floodplain development with active sedimentation, syngenetic permafrost is climate driven, ice-poor, and dominated by pore and lenticular cryostructures. On inactive floodplains, where flooding is infrequent and fine-grained sedimentation is greatly diminished, climate-driven, ecosystem-modified permafrost aggrades upward in response to thickening organics and thinning active layer. Here a 2-m-thick intermediate layer develops that is ice-rich and dominated by reticulate and ataxitic cryostructures. On the oldest abandoned floodplains, permafrost becomes sufficiently ice rich from segregated and wedge ice that thermokarst lakes develop. Large storm surges up to 3 m amsl, such as those in 1963 and 1970, have caused extensive salt killed and ice-wedge degradation. Thus, thermokarst is abundant even at low temperatures. In the YKD, permafrost develops only during late floodplain stages in response to sphagnum accumulation and creates extensive permafrost plateaus that rise 1 m above the floodplain. This ecosystem-driven permafrost is epigenetic, ice-poor, and dominated by pore and lenticular cryostructures. Permafrost develops around existing water bodies, but thermokarst lakes are uncommon. Large storm surges up to 3.5 m amsl, such those in 1974 and

  17. 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.

  18. TIDEV: Tidal Evolution package

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  19. Delta II

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The Delta II expendable launch vehicle with the ROSAT (Roentgen Satellite), cooperative space X-ray astronomy mission between NASA, Germany and United Kingdom, was launched from the Cape Canaveral Air Force Station on June 1, 1990.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    USGS Publications Warehouse

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

    2005-01-01

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

  2. 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

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

    NASA Astrophysics Data System (ADS)

    Nienhuis, J.; Ashton, A. D.

    2015-12-01

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

  4. 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