Hydrodynamic Sediment Transport Model Research Articles

Development of a Two-Dimensional Hybrid Sediment-Transport Model

This paper presents the development of a two-dimensional hydrodynamic sediment transport model using the finite volume method based on a collocated unstructured hybrid-mesh system consisting of triangular and quadrilateral cells. The model is a single-phase nonequilibrium sediment-transport model for nonuniform and noncohesive sediments in unsteady turbulent flows that considers multiple sediment-transport processes such as deposition, erosion, transport, and bed sorting. This model features a hybrid unstructured mesh system for easy mesh generation in complex domains. To avoid interpolation from vertices in conventional unstructured models, this model adopted a second-order accurate edge-gradient evaluation method to consider the mesh irregularities based on Taylor’s series expansion. In addition, the multipoint momentum interpolation corrections were integrated to avoid possible nonphysical oscillations during the wetting-and-drying process, common in unsteady sediment transport problems, to ensure both numerical stability and numerical accuracy. The developed sediment transport model was validated by a benchmark degradation case for the erosion process with armoring effects, a benchmark aggradation case for the deposition process, and a naturally meandering river for long-term unsteady sediment-transport processes. Finally, the model was successfully applied to simulate sediment transport in a reservoir that was significantly affected by typhoon events.

Assessing the nature of sediment transport with bridge scour by 1D sediment transport model in the sub-catchment basin of Bhagirathi–Hooghly river

Sediment deposition is a significant feature of a dynamic floodplain river. As the river's carrying capacity decreases, it is forced to deposit sediment on the river bed. However, due to the construction of some hydraulic structures over the river bed at different times (bridges, dams), the velocity of the river in the floodplain area decreases with accelerating sedimentation process, which hinders water transport. The sub-catchment basin (Nabadwip-Kalyani stretch) of the Bhagirathi–Hooghly river in West Bengal (Ghosh et al. 2020), India is frequently used as a means of water transport by local stakeholders. Because of sedimentation, the thalweg depth of the river is constantly decreasing in Nabadwip–Kalyani stretch and the water transport is being disrupted. Therefore, it is very important to know the function of hydraulic structures over the river bathymetry and resultant sediment flow, transportation, and sediment deposition in this region. Therefore, this article mainly assesses to develop a 1D hydro-dynamic sediment transport model on river morphological change through seasonal quasi-unsteady flow accumulation and sediment budget in a given year (2018). The hydro-dynamic model is calibrated by 1D HEC-RAS v 5.0.7 software (Gibson et al. 2017) based on seasonal quasi-unsteady flow using various empirical equations and Manning's roughness coefficient and validated with R2, NSE, and RSR. The model also examines the role of hydrodynamic structures in scouring and sedimentation due to the location of these structures above the river. This model output will help local stakeholders to understand the amount of sediment in the river and keep river transport viable in all seasons.

Analysis of riverine suspended particulate matter fluxes (Gulf of Lion, Mediterranean Sea) using a synergy of ocean color observations with a 3‐D hydrodynamic sediment transport model

AbstractThe export of riverine suspended particulate matter (SPM) in the coastal ocean has major implications for the biogeochemical cycles. In the Mediterranean Sea (France), the Rhone River inputs of SPM into the Gulf of Lion (GoL) are highly variable in time, which severely impedes the assessment of SPM fluxes. The objectives of this study are (i) to investigate the prediction of the land‐to‐ocean flux of SPM using the complementarity (i.e., synergy) between a hydrodynamic sediment transport model and satellite observations, and (ii) to analyze the spatial distribution of the SPM export. An original approach that combines the MARS‐3D model with satellite ocean color data is proposed. Satellite‐derived SPM and light penetration depth are used to initialize MARS‐3D and to validate its predictions. A sensitivity analysis is performed to quantify the impact of riverine SPM size composition and settling rate on the horizontal export of SPM. The best agreement between the model and the satellite in terms of SPM spatial distribution and export is obtained for two conditions: (i) when the relative proportion of “heavy and fast” settling particles significantly increases relative to the “light and slow” ones, and (ii) when the settling rate of heavy and light SPM increases by fivefold. The synergy between MARS‐3D and the satellite data improved the SPM flux predictions by 48% near the Rhone River mouth. Our results corroborate the importance of implementing satellite observations within initialization procedures of ocean models since data assimilation techniques may fail for river floods showing strong seasonal variability.

Sediment deposition from tropical storms in the upper Chesapeake Bay: Field observations and model simulations

Episodic flood and storm events are important drivers of sediment dynamics in estuarine and marine environments. Event-driven sedimentation has been well-documented by field and modeling studies, though both techniques have inherent limitations. A unique opportunity to integrate field observations and model results was provided in late August/early September 2011 with the passage of Hurricane Irene and Tropical Storm Lee in the Chesapeake Bay region. Because these two storms occurred within a relatively short period of time, both are potentially represented in the sediment record obtained during rapid-response cruises in September and October 2011. Associated sediment deposits were recognized in cores using classic flood-sediment signatures (fine grain size, uniform 7Be activity, physical stratification in x-radiographs) and were found to be <4cm, thickest in the upper Bay. A coupled hydrodynamic-sediment transport model is used to simulate the sediment plume and sediment deposition onto the seabed. The predicted deposition thickness for TS Lee is in general agreement with the observational estimates. One exception with physical stratification but no 7Be activity appears to be due to extreme wave activity during Hurricane Irene. Integration of observations and modeling in this case greatly improved understanding of the transport and fate of flood sediments in the Chesapeake Bay.

Dispersal of Mississippi and Atchafalaya sediment on the Texas–Louisiana shelf: Model estimates for the year 1993

A three-dimensional coupled hydrodynamic-sediment transport model for the Texas–Louisiana continental shelf was developed using the Regional Ocean Modeling System (ROMS) and used to represent fluvial sediment transport and deposition for the year 1993. The model included water and sediment discharge from the Mississippi River and Atchafalaya Bay, seabed resuspension, and suspended transport by currents. Input wave properties were provided by the Simulating WAves Nearshore (SWAN) model so that ROMS could estimate wave-driven bed stresses, critical to shallow-water sediment suspension. The model used temporally variable but spatially uniform winds, spatially variable seabed grain size distributions, and six sediment tracers from rivers and seabed. At the end of the year 1993, much of the modeled fluvial sediment accumulation was localized with deposition focused near sediment sources. Mississippi sediment remained within 20–40 km of the Mississippi Delta. Most Atchafalaya sediment remained landward of the 10-m isobath in the inner-most shelf south of Atchafalaya Bay. Atchafalaya sediment displayed an elongated westward dispersal pattern toward the Chenier Plain, reflecting the importance of wave resuspension and perennially westward depth-averaged currents in the shallow waters (<10 m). Due to relatively high settling velocities assumed for sediment from the Mississippi River as well as the shallowness of the shelf south of Atchafalaya Bay, most sediment traveled only a short distance before initial deposition. Little fluvial sediment could be transported into the vicinity of the “Dead Zone” (low-oxygen area) within a seasonal–annual timeframe. Near the Mississippi Delta and Atchafalaya Bay, alongshore sediment-transport fluxes always exceeded cross-shore fluxes. Estimated cumulative sediment fluxes next to Atchafalaya Bay were episodic and “stepwise-like” compared to the relatively gradual transport around the Mississippi Delta. During a large storm in March 1993, strong winds helped vertically mix the water column over the entire shelf (up to 100-m isobath), and wave shear stress dominated total bed stress. During fair-weather conditions in May 1993, however, the freshwater plumes spread onto a stratified water column, and combined wave–current shear stress only exceeded the threshold for suspending sediment in the inner-most part of the shelf.

Discontinuous hindcast simulations of estuarine bathymetric change: A case study from Suisun Bay, California

Simulations of estuarine bathymetric change over decadal timescales require methods for idealization and reduction of forcing data and boundary conditions. Continuous simulations are hampered by computational and data limitations and results are rarely evaluated with observed bathymetric change data. Bathymetric change data for Suisun Bay, California span the 1867–1990 period with five bathymetric surveys during that period. The four periods of bathymetric change were modeled using a coupled hydrodynamic-sediment transport model operated at the tidal-timescale. The efficacy of idealization techniques was investigated by discontinuously simulating the four periods. The 1867–1887 period, used for calibration of wave energy and sediment parameters, was modeled with an average error of 37% while the remaining periods were modeled with error ranging from 23% to 121%. Variation in post-calibration performance is attributed to temporally variable sediment parameters and lack of bathymetric and configuration data for portions of Suisun Bay and the Delta. Modifying seaward sediment delivery and bed composition resulted in large performance increases for post-calibration periods suggesting that continuous simulation with constant parameters is unrealistic. Idealization techniques which accelerate morphological change should therefore be used with caution in estuaries where parameters may change on sub-decadal timescales. This study highlights the utility and shortcomings of estuarine geomorphic models for estimating past changes in forcing mechanisms such as sediment supply and bed composition. The results further stress the inherent difficulty of simulating estuarine changes over decadal timescales due to changes in configuration, benthic composition, and anthropogenic forcing such as dredging and channelization.

Diagnosis of the sediment transport in the Belgian Coastal Zone

Estimating the age of particles in marine environment constitutes an invaluable tool to understand the interactions between complex flows and sediment dynamics, particularly in highly energetic coastal areas such as the Belgian Coastal Zone (Southern Bight in the North Sea). To this end, the Constituent Age and Residence time Theory – CART – introduced by Delhez, E.J.M., Campin, J.-M., Hirst, A.C., Deleersnijder, E. [1999a. Toward a general theory of the age in ocean modelling. Ocean Modelling 1, 17–27] for passive water constituents is extended to describe the sediment dynamics. It is then used in combination with a three-dimensional coupled hydrodynamic-sediment transport model to investigate sediment processes in the Belgian Coastal Zone focusing on two complementary aspects of the sediment dynamics: the internal sediment motion and redistribution within the Belgian coast; and the horizontal transport.

Effects of resuspended sediments and vertical mixing on phytoplankton spring bloom dynamics in a tidal estuarine embayment

As a preliminary multidisciplinary modeling approach encompassing physical and ecological systems, a 1-D biogeochemical model was coupled with a 3-D hydrodynamic-sediment transport model through an off-line mode. The resulting modeling system was used to investigate the main controlling factors for the onset of phytoplankton spring blooms in 2001 at the Youngsan River Estuarine Bay (YREB), where tidal currents are relatively weak and the freshwater discharge from the river is artificially regulated by sluice gates on a dyke. The model simulations suggested that the strong vertical mixing caused by sea-surface cooling was a major controlling factor in the development of phytoplankton blooms in the YREB during the period from January to April 2001. In relation to the reduction in vertical mixing rates, frequent freshwater inflows from the reservoir during the neap tides contributed to the onset of phytoplankton spring blooms in 2001. Furthermore, sensitivity tests with different conversion factors for the estimation of the ‘photosynthetically active radiation’ (PAR) revealed that further examination and parameterization of PAR is required for improvement of the ecosystem model. It also showed that an increase in the PAR attenuation coefficient, taking into account the tidally varying structure of suspended sediment concentrations, inhibited phytoplankton blooms. Finally, it can be emphasized that in order to predict variability in phytoplankton production in turbid estuarine bays, it is essential to incorporate an ecosystem model with a 3-D hydrodynamic model coupled to a sediment transport model capable of resolving the variable vertical dynamics of sediment resuspension and mixing.

Fluvial suspended sediment dynamics: Implications for particulate organic carbon transport modeling

The effect of fluvial suspended sediment aggregation on the hydrodynamic transport properties of particulate organic carbon (POC) was investigated using a combination of field measurement and numerical modeling. Field‐based settling tube experiments were conducted to obtain particle settling velocity frequency distributions of a 4‐km‐long section of a lake outlet river at two distinct discharge levels (6.8 and 29.7 m3 s−1). Results of field studies conducted in April 2001 and April 2002 showed that the lacustrine settling velocity frequency distributions of suspended particulate matter (SPM) and POC were altered owing to the formation of riverine aggregates having comparatively higher settling velocities. Data suggest that aggregation promoted deposition fluxes of POC; these fluxes were in turn closely tied to the processes that controlled deposition of SPM. Data interpretation was aided by the employment of a hydrodynamic sediment transport model. The approach used to integrate aggregation in the sediment transport simulations represents the interaction of multiple settling velocity mass fractions. Both field data and modeling demonstrated the effect of aggregation on the increase in deposition fluxes of POC.

A Coupled Upland-Erosion and Instream Hydrodynamic-Sediment Transport Model for Evaluating Sediment Transport in Forested Watersheds

This article describes a prototype modeling system for assessing forest management-related erosion at its source and predicting sediment transport from hillslopes to stream channels and through channel networks to a watershed outlet. We demonstrate that it is possible to develop a land management tool capable of accurately assessing the primary impacts of spatiotemporally varied forest management practices on sediment yield and delivery at hillslope to watershed scales in a single simulation. The modeling system consists of four components: (1) the TOpographic ParameteriZation (TOPAZ) model for discretizing hillslope and channel elements, (2) the Water Erosion Prediction Project (WEPP) model for evaluating hillslope-scale surface erosion processes, (3) the National Center for Computational Hydrodynamics and Engineering's one-dimensional (CCHE1D) hydrodynamic-sediment transport model, and (4) an interface program to manage relational databases and data transfer between modules. The coupled models were calibrated and validated with observed flow and sediment load data from the North Fork Caspar Creek Experimental Watershed in coastal northern California. The coupled models' predictions of peak flow rate and total flow volume were not significantly different from observed values. Predicted sediment concentrations were significantly different from observed values, but within typical ranges for sediment transport equations. We recommend that the WEPP model be improved to allow access to sub-daily time scale results so that it can be better integrated with other watershed models.

Significance of particle interaction to the modelling of cohesive sediment transport in rivers

AbstractAggregation processes of fine sediments have rarely been integrated in numerical simulations of cohesive sediment transport in riverine systems. These processes, however, can significantly alter the hydrodynamic characteristics of suspended particulate matter (SPM), modifying the particle settling velocity, which is one of the most important parameters in modelling suspended sediment dynamics. The present paper presents data from field measurements and an approach to integrate particle aggregation in a hydrodynamic sediment transport model. The aggregation term used represents the interaction of multiple sediment classes (fractions) with corresponding multiple deposition behaviour. The k–ε–turbulence model was used to calculate the coefficient of vertical turbulent mixing needed for the two‐dimensional vertical‐plane simulations. The model has been applied to transport and deposition of tracer particles and natural SPM in a lake‐outlet lowland river (Spree River, Germany). The results of simulations were evaluated by comparison with field data obtained for two levels of river discharge. Experimental data for both discharge levels showed that under the prevailing uniform hydraulic conditions along the river reach, the settling velocity distribution did not change significantly downstream, whereas the amount of SPM declined. It was also shown that higher flow velocities (higher fluid shear) resulted in higher proportions of fast settling SPM fractions. We conclude that in accordance with the respective prevailing turbulence structures, typical aggregation mechanisms occur that continuously generate similar distribution patterns, including particles that settle toward the river bed and thus mainly contribute to the observed decline in the total SPM concentration. In order to determine time‐scales of aggregation and related mass fluxes between the settling velocity fractions, results of model simulations were fitted to experimental data for total SPM concentration and of settling velocity frequency distributions. The comparison with simulations for the case of non‐interacting fractions clearly demonstrated the practical significance of particle interaction for a more realistic modelling of cohesive sediment and contaminant transport. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Modeling Suspended Sediment Transport in Nonequilibrium Situations

A mathematical model is presented for calculating suspended sediment transport in unidirectional channel flow under general, non-equilibrium conditions. The model consists of a flexible hydrodynamic component for calculating the flow field and the turbulence characteristics and a scalar transport model. The former employs the \Ik\N-e turbulence model and provides, as input to the latter, the distribution of velocity and eddy diffusivity as well as the friction velocity. The settling process is simulated with an empirical settling velocity appearing in the particle concentration equation. As a boundary condition for this equation, the net flux of sediment to and from the bed is prescribed with a new model which covers both fixed-bed and erodable-bed situations. The net flux is expressed as the difference between deposition to and entrainment from the bed and, while the deposition rate is known from the local concentration and settling velocity, the entrainment is assumed to occur at the same rate as it does under equilibrium conditions, provided sufficient sediment material is available. With the aid of a finite volume procedure, the combined hydrodynamic sediment transport model is applied to a variety of flume experiments involving zero net flux, net-deposition, and net-entrainment situations. The predicted development of the vertical concentration profiles is compared with the measurements and generally good agreement is obtained.