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  • Sediment transport  (6)
  • Estuarine mixing
  • Sediment trapping
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  • 1
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    Flood dispersal and deposition by near-bed gravitational sediment flows and oceanographic transport : a numerical modeling study of the Eel River shelf, northern California (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 110 (2005): C09025, doi:10.1029/2004JC002727.
    Description: A large flood of the Eel River, northern California, created a thick sediment deposit between water depths of 50 and 70 m in January 1997. The freshwater plume, however, confined sediment delivery to water depths shallower than 30 m. Mechanisms proposed to explain the apparent cross-shelf transport include dispersal by oceanographic currents, resuspension by energetic waves, and gravitationally forced transport of a thin layer of fluidized mud. Field observations indicate that these processes were all active but cannot determine their relative significance or whether these mechanisms alone explain the location, size, and timing of deposition. Approximately 30% of the sediment delivered by the Eel River is accounted for in the midshelf mud bed and inner shelf, but the fate of the remaining 70% is uncertain. A three-dimensional, hydrodynamic model was used to examine potential mechanisms of sediment transport on the Eel River shelf. The model includes suspended sediment transport and was modified to account for a thin, near-bed layer of fluidized mud. It was used to simulate flood dispersal on the Eel River shelf, to compare the relative importance of transport within the near-bed fluid mud layer to suspended sediment transport, and to evaluate sediment budgets for floods. Settling properties of fine-grained sediment, both within the flood plume and the fluid mud layer, critically impact depositional patterns. To a lesser degree, wind-driven ocean currents influence the volume of sediment that escapes the shelf, and wave magnitude affects the cross-shelf location of flood deposits. Though dilute suspension accounts for a large fraction of total flux, cross-shelf transport by gravitational forcing appears necessary to produce a midshelf mud deposit similar in volume, location, and timing to those seen offshore of the Eel River.
    Description: The Office of Naval Research’s Coastal Geoscience Program supported this through program N0014-01-1-008.
    Keywords: Flood sediment dispersal ; Northern California shelf ; Sediment transport
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Effects of estuarine and fluvial processes on sediment transport over deltaic tidal flats (2013)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 60, Suppl. (2013): S40–S57, doi:10.1016/j.csr.2012.02.004.
    Description: Tidal flats at a river mouth feature estuarine and fluvial processes that distinguish them from tidal flats without river discharge. We combine field observations and a numerical model to investigate hydrodynamics and sediment transport on deltaic tidal flats at the mouth of the Skagit River, in Puget Sound, WA during the spring freshet. River discharge over tidal flats supplies a mean volume flux, freshwater buoyancy, and suspended sediment. Despite the shallow water depths, strong horizontal density fronts and stratification develop, resulting in a baroclinic pressure gradient and tidal variability in stratification that favor flood-directed bottom stresses. In addition to these estuarine processes, the river discharge during periods of low tide drains through a network of distributary channels on the exposed tidal flats, with strongly ebb-directed stresses. The net sediment transport depends on the balance between estuarine and fluvial processes, and is modulated on a spring-neap time scale by the tides of Puget Sound. We find that the baroclinic pressure gradient and periodic stratification enhance trapping of sediment delivered by the river on the tidal flats, particularly during neap tides, and that sediment trapping also depends on settling and scour lags, particularly for finer particles. The primary means of moving sediment off of the tidal flats are the high velocities and stresses in the distributary channels during late stages of ebbs and around low tides, with sediment export predominantly occurring during spring low tides that expose a greater portion of the flats. The 3-d finite volume numerical model was evaluated against observations and had good skill overall, particularly for velocity and salinity. The model performed poorly at simulating the shallow flows around low tides as the flats drained and river discharge was confined to distributary channels, due in part to limitations in grid resolution, seabed sediment and bathymetric data, and the wetting-and-drying scheme. Consequently, the model predicted greater sediment retention on the flats than was observed.
    Description: This work was supported by the Office of Naval Research.
    Keywords: Tidal flats ; Sediment transport ; Sediment trapping ; Distributary channels ; Stratification ; Salinity fronts ; Tidal asymmetry ; Velocity skewness ; Numerical model
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Rapid sediment deposition and fine-scale strata formation in the Hudson estuary (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): F02004, doi:10.1029/2003JF000096.
    Description: A 9 month time series of tripod-mounted optical and acoustic measurements of sediment concentration and bed elevation was used to examine depositional processes in relationship to hydrodynamic variables in the Hudson River estuary. A series of cores was also taken directly under and adjacent to the acoustic measurements to examine the relation between the depositional processes and the resulting fine-scale stratigraphy. The measurements reveal that deposition occurs as a result of sediment flux convergence behind a salinity front and that the accumulation rates are sufficient to deposit up to 25 cm of new high-porosity sediment in a single ebb-tidal phase. Subsequent dewatering and erosion reduces the thickness of the initial deposit to several centimeters. These depositional events were only observed on spring tides. Ten depositional events during two spring tidal cycles produced a seasonal deposit of 18 cm, consistent with estimates of seasonal deposition from cores. A proxy for near-bed suspended grain size variations was estimated from the combined acoustic and optical measurements, implying that the erosional processes resuspend only the finer-grained sediments, thus leaving behind silt and very fine grained sand beds. The thickness of the deposited homogenous clayey silt beds, and the vertical separation between beds interlaminated with silt and very fine sand, are roughly consistent with the acoustic measurements of changes in bed elevations during deposition and erosion. The variability in individual bed thickness is the result of variations of processes over an individual tidal cycle and is not a product of variations over the spring neap fortnightly timescale.
    Description: The authors would like to acknowledge the Hudson River Foundation, who provided funding for this work under grant 009/00A.
    Keywords: Sediment transport ; Estuarine processes ; Fluid mud
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Bathymetric controls on sediment transport in the Hudson River estuary : lateral asymmetry and frontal trapping (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C10013, doi:10.1029/2012JC008124.
    Description: Analyses of field observations and numerical model results have identified that sediment transport in the Hudson River estuary is laterally segregated between channel and shoals, features frontal trapping at multiple locations along the estuary, and varies significantly over the spring-neap tidal cycle. Lateral gradients in depth, and therefore baroclinic pressure gradient and stratification, control the lateral distribution of sediment transport. Within the saline estuary, sediment fluxes are strongly landward in the channel and seaward on the shoals. At multiple locations, bottom salinity fronts form at bathymetric transitions in width or depth. Sediment convergences near the fronts create local maxima in suspended-sediment concentration and deposition, providing a general mechanism for creation of secondary estuarine turbidity maxima at bathymetric transitions. The lateral bathymetry also affects the spring-neap cycle of sediment suspension and deposition. In regions with broad, shallow shoals, the shoals are erosional and the channel is depositional during neap tides, with the opposite pattern during spring tides. Narrower, deeper shoals are depositional during neaps and erosional during springs. In each case, the lateral transfer is from regions of higher to lower bed stress, and depends on the elevation of the pycnocline relative to the bed. Collectively, the results indicate that lateral and along-channel gradients in bathymetry and thus stratification, bed stress, and sediment flux lead to an unsteady, heterogeneous distribution of sediment transport and trapping along the estuary rather than trapping solely at a turbidity maximum at the limit of the salinity intrusion.
    Description: This research was funded by a grant from the Hudson River Foundation (#002/07A). D.R. was partially supported by the Office of Naval Research (N00014-08-1-0846).
    Description: 2013-04-17
    Keywords: Estuarine turbidity maximum ; Lateral sediment distribution ; Salinity fronts ; Sediment flux ; Sediment trapping ; Stratification
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Sediment transport and deposition on a river-dominated tidal flat : an idealized model study (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 115 (2010): C10040, doi:10.1029/2010JC006248.
    Description: A 3-D hydrodynamic model is used to investigate how different size classes of river-derived sediment are transported, exported and trapped on an idealized, river-dominated tidal flat. The model is composed of a river channel flanked by sloping tidal flats, a configuration motivated by the intertidal region of the Skagit River mouth in Washington State, United States. It is forced by mixed tides and a pulse of freshwater and sediment with various settling velocities. In this system, the river not only influences stratification but also contributes a significant cross-shore transport. As a result, the bottom stress is strongly ebb-dominated in the channel because of the seaward advance of strong river flow as the tidal flats drain during ebbs. Sediment deposition patterns and mass budgets are sensitive to settling velocity. The lateral sediment spreading scales with an advective distance (settling time multiplied by lateral flow speed), thereby confining the fast settling sediment classes in the channel. Residual sediment transport is landward on the flats, because of settling lag, but is strongly seaward in the channel. The seaward transport mainly occurs during big ebbs and is controlled by a length scale ratio Ld/XWL, where Ld is a cross-shore advective distance (settling time multiplied by river outlet velocity), and XWL is the immersed cross-shore length of the intertidal zone. Sediment trapping requires Ld/XWL 〈 1, leading to more trapping for the faster settling classes. Sensitivity studies show that including stratification and reducing tidal range both favor sediment trapping, whereas varying channel geometries and asymmetry of tides has relatively small impacts. Implications of the modeling results on the south Skagit intertidal region are discussed.
    Description: SNC is supported by a WHOI/USGS postdoctoral scholarship. The field program on the Skagit intertidal region is supported by an ONR grant N00014-08-1-0790.
    Keywords: Sediment trapping ; Tidal flat
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Comparison of physical to numerical mixing with different tracer advection schemes in estuarine environments (2020)
    MDPI
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    Publication Date: 2022-10-27
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Kalra, T. S., Li, X., Warner, J. C., Geyer, W. R., & Wu, H. Comparison of physical to numerical mixing with different tracer advection schemes in estuarine environments. Journal of Marine Science and Engineering, 7(10), (2019): 338, doi: 10.3390/jmse7100338.
    Description: The numerical simulation of estuarine dynamics requires accurate prediction for the transport of tracers, such as temperature and salinity. During the simulation of these processes, all the numerical models introduce two kinds of tracer mixing: (1) by parameterizing the tracer eddy diffusivity through turbulence models leading to a source of physical mixing and (2) discretization of the tracer advection term that leads to numerical mixing. Physical and numerical mixing both vary with the choice of horizontal advection schemes, grid resolution, and time step. By simulating four idealized cases, this study compares the physical and numerical mixing for three different tracer advection schemes. Idealized domains only involving physical and numerical mixing are used to verify the implementation of mixing terms by equating them to total tracer variance. Among the three horizontal advection schemes, the scheme that causes the least numerical mixing while maintaining a sharp front also results in larger physical mixing. Instantaneous spatial comparison of mixing components shows that physical mixing is dominant in regions of large vertical gradients, while numerical mixing dominates at sharp fronts that contain large horizontal tracer gradients. In the case of estuaries, numerical mixing might locally dominate over physical mixing; however, the amount of volume integrated numerical mixing through the domain compared to integrated physical mixing remains relatively small for this particular modeling system.
    Description: This study was funded through the Coastal Model Applications and Field Measurements Project and the Cross-shore and Inlets Project, US Geological Survey Coastal Marine Hazards and Resources Program.
    Keywords: Physical mixing ; Numerical mixing ; Advection schemes ; Estuarine mixing
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  • 7
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    Observations and modeling of wave-supported sediment gravity flows on the Po prodelta and comparison to prior observations from the Eel shelf (2007)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 27 (2007): 375-399, doi:10.1016/j.csr.2005.07.008.
    Description: A mooring and tripod array was deployed from the fall of 2002 through the spring of 2003 on the Po prodelta to measure sediment transport processes associated with sediment delivered from the Po River. Observations on the prodelta revealed wave-supported gravity flows of high concentration mud suspensions that are dynamically and kinematically similar to those observed on the Eel shelf (Traykovski et al., 2000). Due to the dynamic similarity between the two sites, a simple one-dimensional across-shelf model with the appropriate bottom boundary condition was used to examine fluxes associated with this transport mechanism at both locations. To calculate the sediment concentrations associated with the wave-dominated and wave-current resuspension, a bottom boundary condition using a reference concentration was combined with an “active layer” formulation to limit the amount of sediment in suspension. Whereas the wave-supported gravity flow mechanism dominates the transport on the Eel shelf, on the Po prodelta flux due to this mechanism is equal in magnitude to transport due to wave resuspension and wind-forced mean currents in cross-shore direction. Southward transport due to wave resuspension and wind forced mean currents move an order of magnitude more sediment along-shore than the downslope flux associated wave-supported gravity flows.
    Description: This work funded by the U.S. Office of Naval Research under grant number #N00014-02-10378, under the direction of program manager, Tom Drake.
    Keywords: Po River ; Adriatic Sea ; Sediment transport ; Turbidity currents ; Fluid mud
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Large-eddy simulation of the tidal-cycle variations of an estuarine boundary layer (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 115 (2010): C08003, doi:10.1029/2009JC005702.
    Description: The estuarine boundary layer affected by a horizontal density gradient exhibits temporal evolution over a tidal cycle, in a manner similar to the diurnal cycle of the ocean surface mixed layer. A large eddy simulation (LES) model is developed to investigate the physics controlling the growth of the boundary layer during the flood tide and restratification during the ebb tide. Turbulent kinetic energy, momentum and salt fluxes, bottom stress, and energy dissipation rates calculated from the LES model all show a strong flood-ebb asymmetry. Analysis of the turbulent kinetic energy (TKE) budget shows a primary balance between shear production and dissipation in the well-mixed boundary layer over the tidal cycle. However, TKE transport term is found to be important across the edge of the boundary layer during the flood tide so turbulent energy generated in the bottom boundary layer can be transferred to the stratified pycnocline region. Tidal straining leads to a small and weakly convective region inside the boundary layer during the flood tide but the strain-induced buoyancy flux does not make a significant contribution to the turbulence generation. Additional LES runs are conducted by switching off the baroclinic pressure gradient term in the momentum equation and the tidal straining term in the salinity equation to show that the baroclinic pressure gradient is the main mechanism responsible for generating the flood-ebb mixing asymmetry.
    Description: This work is supported by grants OCE-0451699 (M.L.), OCE-0452380 (U.P. and S.R.), and OCE-0451740 (W.R.G.) from the National Science Foundation.
    Keywords: Estuarine mixing ; Large Eddy Simulations ; Tidal straining
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Sediment transport due to extreme events : the Hudson River estuary after tropical storms Irene and Lee (2014)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 5451–5455, doi:10.1002/2013GL057906.
    Description: Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 megaton, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that approximately two thirds of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms and only about one fifth of the new sediment reached the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest that this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.
    Description: This research was supported by grants from the Hudson Research Foundation (002/07A) and the National Science Foundation (1232928).
    Description: 2014-04-18
    Keywords: Sediment transport ; Tidal river ; Estuary ; Sediment trapping
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Sediment transport time scales and trapping efficiency in a tidal river (2018)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 122 (2017): 2042–2063, doi:10.1002/2017JF004337.
    Description: Observations and a numerical model are used to characterize sediment transport in the tidal Hudson River. A sediment budget over 11 years including major discharge events indicates the tidal fresh region traps about 40% of the sediment input from the watershed. Sediment input scales with the river discharge cubed, while seaward transport in the tidal river scales linearly, so the tidal river accumulates sediment during the highest discharge events. Sediment pulses associated with discharge events dissipate moving seaward and lag the advection speed of the river by a factor of 1.5 to 3. Idealized model simulations with a range of discharge and settling velocity were used to evaluate the trapping efficiency, transport rate, and mean age of sediment input from the watershed. The seaward transport of suspended sediment scales linearly with discharge but lags the river velocity by a factor that is linear with settling velocity. The lag factor is 30–40 times the settling velocity (mm s−1), so transport speeds vary by orders of magnitude from clay (0.01 mm s−1) to coarse silt (1 mm s−1). Deposition along the tidal river depends strongly on settling velocity, and a simple advection-reaction equation represents the loss due to settling on depositional shoals. The long-term discharge record is used to represent statistically the distribution of transport times, and time scales for settling velocities of 0.1 mm s−1 and 1 mm s−1 range from several months to several years for transport through the tidal river and several years to several decades through the estuary.
    Description: Hudson River Foundation Grant Number: 004/13A; National Science Foundation Grant Number: 1325136
    Description: 2018-05-02
    Keywords: Tidal river ; Sediment age ; Trapping efficiency ; Estuary ; Sediment transport
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