Suspended Sediment Transport Model Research Articles

A two-phase numerical model for suspended-sediment transport in estuaries

This paper presents a full 2-D X/Z numerical model for sediment transport in open channels and estuaries using a two-phase (fluid–solid particle) approach. The physical concept and the mathematical background of the model are given and test-cases have been carried out to validate the proposed model. In order to illustrate its feasibility for a real estuary, the model has been applied to simulate the suspended-sediment transport and the formation of turbidity maximum in the Seine estuary. The numerical results show that the main characteristics of estuarine hydro-sediment dynamics in the Seine estuary are in fact reproduced by the proposed model. A qualitative agreement between the numerical results and the actual observations has been obtained and is presented in this paper.

Numerical Computation on Beach Erosion Control Function of Submerged Groin System

Numerical computations are made for the nearshore currents and morphology around a system of multiple submerged groins. They function in decreasing the speed of longshore currents and controlling beach erosion. Nearshore currents are computed with the PEGBIS model by Goda (2004) for wave transformation and beach morphology is estimated with the suspended sediment transport model by Katayama and Goda (2000). The computation indicates the efficacy of a submerged groin system for beach erosion control.

A Turbulent and Suspended Sediment Transport Model for Plunging Breakers

Extensive studies have suggested a high concentration of suspended sediment near the free surface induced by strong plunging breakers. However, prediction by models have not been successful because of the localized interactions among the plunging jet, turbulent production, and sediment movement. This study proposes a new calculation model for turbulent flow and suspended sediment transport in the surf zone.A numerical model was developed to simulate the flow and sediment motion in connection with plunging breakers in the surf zone. The Reynolds-Averaged Navier-Stokes (RANS) equations in two spatial dimensions were employed to simulate the flow field together with a κ-ε model for the turbulence and the Volume of Fluid (VOF) method for multiple free-surface tracking. An advection-diffusion equation was used for the suspended sediment concentration with a bottom boundary condition following the reference concentration formulation. Performance of the suspended sediment transport model under plunging breaking waves were examined through the comparison with experimental data.Good agreement between the model and experimental data was obtained for the surface elevation and velocity, turbulent kinetic energy, eddy viscosity and suspended sediment concentration. The overturning waves, plunging jet and transport of high concentration of suspended sediment near the free surface are reproduced by the present model with selected fine mesh resolution. The study shows the applicability of the present model in the turbulent and suspended sediment dominated region induced by strong plunging breakers.

Modeling diagnosis of suspended sediment transport in tidal estuarine system

A three-dimensional, time-dependent hydrodynamic and suspended sediment transport model was performed and applied to the Danshuei River estuarine system and adjacent coastal sea in northern Taiwan. The model was validated with observed time-series salinity in 2001, and with salinity and suspended sediment distributions in 2002. The predicted results quantitatively agreed with the measured data. A local turbidity maximum was found in the bottom water of the Kuan-Du station. The validated model then was conducted with no salinity gradient, no sediment supply from the sediment bed, wind stress, and different freshwater discharges from upstream boundaries to comprehend the influences on suspended sediment dynamics in the Danshuei River estuarine system. The results reveal that concentrations of the turbidity maximum simulated without salinity gradient are higher than those of the turbidity maximum simulated with salinity gradient at the Kuan-Du station. Without bottom resuspension process, the estuarine turbidity maximum zone at the Kuan-Du station vanishes. This suggests that bottom sediment resuspension is a very important sediment source to the formation of estuarine turbidity maximum. The wind stress with northeast and southwest directions may contribute to decrease the suspended sediment concentration. When the freshwater discharges increase at the upstream boundaries, the limits of salt intrusion pushes downriver toward river mouth. Suspended sediment concentrations increase at the upriver reaches in the Danshuei River to Tahan Stream, while decrease at Kuan-Du station.

Modelling the sedimentary signature of long waves on coasts: implications for tsunami reconstruction

We describe a process-based mathematical model of suspended and bedload sediment transport under long, non-breaking waves on a plane beach, and we use this model to investigate the relationship between the hydrodynamics of run-up and run-down and the resulting erosive and depositional ‘signature’ which the wave leaves. In particular, we compare the results of our ‘forward’ model with several recently proposed methods for reconstructing tsunami hydrodynamics from their deposits. We find that sediment transport, both as bedload and in suspension, is strongly controlled by asymmetries in the direction of maximum velocity; in the latter case it is also affected by settling lag, especially around the point of maximum run-up. The combination of these effects appears to preclude simple methods of reconstructing tsunami hydrodynamics from the large-scale features of their signatures; however, our results suggest some promising avenues for further investigation.

Numerical modeling of cohesive sediments dynamics in estuaries: Part I—Description of the model and simulations in the Po River Estuary

AbstractThe present work contributes to the numerical modeling of complex turbulent multiphasic fluid flows occurring in estuarine channels. This research finds its motivation in the increasing need for efficient management of estuaries by taking into account the complex turbulent stratified flows encountered in estuaries and costal zones. A time‐dependent, 3D finite element model of suspended sediment transport taking into account the effects of cohesiveness between sediments is presented. The model estuary is the forced time‐dependent winds, time elevation at open boundaries and river discharge. To cope with the stiffness problems a decoupling method is employed to solve the shallow‐water equations of mass conservation, momentum and suspended sediment transport with the conventional hydrostatic pressure. The decoupling method partitions a time step into three subcycles according to the physical phenomena. In the first sub‐cycle the pure hydrodynamics including the k–ε turbulence model is solved, followed by the advection–diffusion equations for pollutants (salinity, temperature, suspended sediment concentration, (SSC)), and finally the bed evolution is solved. The model uses a mass‐preserving method based on the so‐called Raviart–Thomas finite element on the unstructured mesh in the horizontal plane, while the multi‐layers system is adopted in vertical with the conventional conforming finite element method, with the advantage that the lowermost and uppermost layers of variable height allow a faithful representation of the time‐varying bed and free surface, respectively. The model has been applied to investigate the SSC and seabed evolution in Po River Estuary (PRE) in Italy. The computed results mimic the field data well. Copyright © 2007 John Wiley & Sons, Ltd.

Coupled changes in sand grain size and sand transport driven by changes in the upstream supply of sand in the Colorado River: Relative importance of changes in bed-sand grain size and bed-sand area

Sand transport in the Colorado River in Marble and Grand canyons was naturally limited by the upstream supply of sand. Prior to the 1963 closure of Glen Canyon Dam, the river exhibited the following four effects of sand supply limitation: (1) hysteresis in sediment concentration, (2) hysteresis in sediment grain size coupled to the hysteresis in sediment concentration, (3) production of inversely graded flood deposits, and (4) development or modification of a lag between the time of a flood peak and the time of either maximum or minimum (depending on reach geometry) bed elevation. Construction and operation of the dam has enhanced the degree to which the first two of these four effects are evident, and has not affected the degree to which the last two effects of sand supply limitation are evident in the Colorado River in Marble and Grand canyons. The first three of the effects involve coupled changes in suspended-sand concentration and grain size that are controlled by changes in the upstream supply of sand. During tributary floods, sand on the bed of the Colorado River fines; this causes the suspended sand to fine and the suspended-sand concentration to increase, even when the discharge of water remains constant. Subsequently, the bed is winnowed of finer sand, the suspended sand coarsens, and the suspended-sand concentration decreases independently of discharge. Also associated with these changes in sand supply are changes in the fraction of the bed that is covered by sand. Thus, suspended-sand concentration in the Colorado River is likely regulated by both changes in the bed-sand grain size and changes in the bed-sand area. A physically based flow and suspended-sediment transport model is developed, tested, and applied to data from the Colorado River to evaluate the relative importance of changes in the bed-sand grain size and changes in the bed-sand area in regulating suspended-sand concentration. Although the model was developed using approximations for steady, uniform flow, and other simplifications that are not met in the Colorado River, the results nevertheless support the idea that changes in bed-sand grain size are much more important than changes in bed-sand area in regulating the concentration of suspended sand.

1D vertical model for suspended sediment transport in turbulent tidal flow: Application to the English Channel

A 1D dynamic model of a tidal boundary layer flow with suspended sediment is proposed (model of sediment transport and turbulence, MoSeTT). The model includes two linearized momentum equations for the horizontal velocity components and a series of advection–diffusion equations for concentration of suspended sediment of specific size. Turbulence generated at the sea-bed is computed with the aid of a two-equation closure describing the time-space evolution of the turbulent kinetic energy k, and the turbulent master length ℓ ( k - k ℓ model). Special attention is paid to the bottom boundary condition for the sediment concentration, which is mixed type in order to take into account downward fluxes around times of the flow reversal. The model is applied to conditions encountered in a shallow site located in the eastern part of the English Channel. The model is forced with pressure gradients computed with a 2D vertically integrated tidal model covering the eastern English Channel and the southern part of the North Sea. The tidal currents and the total suspended sediment load predicted by the model are compared with the field data collected over two levels at the water column. The vertical structure of flow properties is fairly well predicted by the present model. Better results are found at the measuring point located farther from the coastline where advective terms can be reasonably neglected.

A vertical 2-D numerical simulation of suspended sediment transport

Numerical simulation of sediment transport and bed evolution has become an important technique in the sediment research. In this article, a numerical model of suspended sediment transport was proposed, which was established in the vertical ω coordinate for fitting the free surface and bottom. In the research of the sediment transport, the predominant factors were found to be the eddy diffusion, the settling velocity, the bed condition and so on. By the aid of the model in the article, the contribution of the Rouse parameter to the vertical profile of sediment concentration was clarified, which was identical to the theoretical results. In the comparison of the numerical results with laboratory data, the agreement between experimental data and numerical results was reached except for some data. And the possible reasons for the disagreement were discussed.

Investigation of Analysis Method to Evaluate Countermeasures against Fairway Shoaling at Fishing Ports under Ocean Characteristics at Sea of Okhotsk

An analysis method is developed to evaluate countermeasure options against fairway shoaling for Yubetsu fishing port, which is located on Okhotsk coastal region. According to the field observation results, the discriminating ocean current, which is so-called Soya Current, could affect on the flow field even in the surf zone. In this study, the ocean current is successfully implemented to the existing nearshore current model and the results give a reasonable agreement with the observed flow conditions. Moreover, the suspended sediment transport model is applied and gives better agreement with the observed bathymetric changes especially in evaluating the scours around the port facilities.

Development and evaluation of a new catchment‐scale model of floodplain sedimentation

Fine‐sediment storage within floodplain systems typically represents a significant component of the catchment sediment budget and a primary control on sediment‐associated nutrient and contaminant fluxes at the basin scale. However, quantitative modeling of floodplain sedimentation within whole catchments represents a significant challenge, not least because hydraulic controls on sediment transport and deposition processes operate at fine spatial scales that cannot be resolved by basin‐scale models. This paper outlines a new approach to addressing this problem in order to develop a computationally efficient model of floodplain sedimentation, which retains a strong physical basis. The approach involves two stages. First, a simple theoretical model of overbank sedimentation is presented, which quantifies the relationship between floodplain geometry, overbank discharge, and total sedimentation rate. Second, the precise form that such a relationship should take is established by analysis of the output from high‐resolution flow and suspended sediment transport models applied to 22 floodplain reaches along three U.K. rivers. This analysis supports a simple power law model between discharge in excess of bankfull and sedimentation rate per unit valley floor length per unit sediment concentration. The power law model is then incorporated within a sediment budget framework and implemented using a Monte Carlo approach to allow an assessment of uncertainty in the model parameterization. The relative likelihood of competing model structures is determined using estimates of mean annual floodplain sediment storage derived by analysis of the 137Cs content of floodplain sediment cores. Comparison of 137Cs‐derived sedimentation rates with uncertainty‐bounded model predictions highlights the potential for assessing the significance of overbank sedimentation within catchment sediment budgets using the simple power law model.

Numerical modelling of floodplain hydraulics and suspended sediment transport and deposition at the event scale in the middle river Elbe, Germany

AbstractThe objective of this case study was to calibrate and verify detailed transport model of sediment in a 4‐kilometre stretch of the middle Elbe floodplains in Germany. The hydraulic RMA‐2 model and the SED2d‐WES sediment transport model were used. These models were calibrated and validated by detailed measurement of the surface water elevations, the velocities at six profiles, and the suspended sediment concentration and deposition (by means of 10 sediment traps). The flow was modelled for three steady‐state discharges. The surface water elevations were calculated to an accuracy of less than 5 cm compared to measurements. The differences between the calculated and measured velocities were with one exception smaller than 0.2 m/s (measured range 0.1…︁1.0 m/s). An average sediment input of 35 g/(m2 d) was calculated for the flood event studied. The highest calculated sedimentation rates of 700 g/(m2 d) (dry density 90 kg/m3) occurred in quiescent zones and abandoned channels. Twenty‐five percent of the deposited sediment settled in the quiescent zones (which only account for 13% of the area). The most sensitive parameters of the sediment transport model were the settling velocity and critical shear stress. The modelling techniques used allowed sediment deposition on the floodplains of the Elbe to be realistically depicted.

Comment on “Depth‐integrated modeling of suspended sediment transport” by M. Bolla Pittaluga and G. Seminara

Comment on “Depth‐integrated modeling of suspended sediment transport” by M. Bolla Pittaluga and G. Seminara

Reply to comment by Z. B. Wang and H. J. De Vriend on “Depth integrated modeling of suspended sediment transport”

[1] Let us first thankWang and De Vriend [2004] for their attention and their careful scrutiny of our paper. Let us also clarify that the motivation of our work was not to show that Galappatti’s [1983] model (hereinafter referred to as G83) was incorrect, but rather to develop a depth-averaged formulation of suspended sediment transport suitable for long-term morphological predictions, able to take into account weak non equilibrium effects of the kind often encountered in tidal as well as fluvial environments. Unfortunately, the mathematical framework appropriate to perform such investigation is precisely that proposed in G83, which forced us to revisit critically the latter work. [2] Let us come to the points raised by the Wang and De Vriend, which do concern G83’s approach rather than our formulation, whose validity does not seem to be questioned. The issue underlined in the discussion is whether or not G83’s perturbation scheme is correct and the basis for the Wang and De Vriend’s defense are the works of Wang [1992] and Wang and Ribberink [1986] (hereinafter referred to as W92 and WR86, respectively). We then also need to revisit the latter works.

Two dimensional modelling of flood flows and suspended sedimenttransport: the case of the Brenta River, Veneto (Italy)

Abstract. The paper presents a numerical model for the simulation of flood waves and suspended sediment transport in a lowland river basin of North Eastern Italy. The two dimensional depth integrated momentum and continuity equations are modified to take into account the bottom irregularities that strongly affect the hydrodynamics in partially dry areas, as for example, in the first stages of an inundation process or in tidal flow. The set of equations are solved with a standard Galerkin finite element method using a semi-implicit numerical scheme where the effects of both the small channel network and the regulation devices on the flood wave propagation are accounted for. Transport of suspended sediment and bed evolution are coupled with the hydrodynamics using an appropriate form of the advection-dispersion equation and Exner's equation. Applications to a case study are presented in which the effects of extreme flooding on the Brenta River (Italy) are examined. Urban and rural flood risk areas are identified and the effects of a alleviating action based on a diversion channel flowing into Venice Lagoon are simulated. The results show that this solution strongly reduces the flood risk in the downstream areas and can provide an important source of sediment for the Venice Lagoon. Finally, preliminary results of the sediment dispersion due to currents and waves in the Venice Lagoon are presented.

Cross‐shore sediment transport and the equilibrium morphology of mudflats under tidal currents

We describe a mathematical model of suspended sediment transport under cross‐shore tidal currents on an intertidal mudflat. We employ a Lagrangian formulation to obtain periodic solutions for the sediment transport over idealized bathymetries and use these to investigate the process of settling lag. In deep water away from the shoreline the concentration of suspended sediment tends to a constant value, and we may invert the relation between bathymetry and offshore concentration to estimate how the gradient of a flat in a state of equilibrium varies with the sediment properties and supply. These analytical estimates are compared successfully with the numerical experiments of previous studies. We discuss the robustness of our modeling framework and demonstrate its application to different descriptions of sediment transport and tidal regimes.

Depth‐integrated modeling of suspended sediment transport

We derive a depth‐averaged model of suspended sediment transport. The development of the analysis leads us to revisit the asymptotic approach originally developed by Galappatti [1983], more recently generalized by >Wang [1992] and widely employed in commercial codes. We show that Galappatti's approach is formally incorrect as it differs from the formal asymptotic expansion of the exact solution. Moreover, the correct approach rather than leading to a differential equation for the depth‐averaged concentration actually provides higher order corrections for the leading order equilibrium approximation of the depth‐averaged concentration. Such corrections can be expressed in terms of spatial and temporal derivatives of the leading order solution. The latter picture is demonstrated on a model problem which is easily amenable to analytical treatment. On the basis of the formal asymptotic expansion of the exact solution we are then able to derive an analytical form for the flux of suspended sediment in slowly varying flows, which is suitable to applications to a variety of morphodynamic contexts including tidal and fluvial environments. An example of potential applications of the present approach is provided by examining the problem of suspended sediment transport due to a flood wave.

Stable lead isotopes, contaminant metals and radionuclides in upper Hudson River sediment cores: implications for improved time stratigraphy and transport processes

Radionuclide, stable lead isotope and trace metal analyses on fine-grained sediment cores collected along a 24-mile reach of the upper Hudson River were used to establish temporal trends of contaminant loadings, to establish stable lead isotopes as an additional stratigraphic tool, and as tracers for resolving particle transport fluxes over periods of decades. Very large contaminant inputs of Cd, Sb, Pb and Cr were evident in the sediment record. One potential large source for these metals was from a pigment manufacturing facility in Glens Falls, NY. The total range in stable lead isotope ratios observed in well-dated cores from about 15 miles downstream of the potential metal inputs was large (e.g., maximum difference in 206Pb/ 207Pb is 10%) and characterized by four major shifts occurring in the 1950s, 1960s, 1970s and 1980s. The temporal trend in 206Pb/ 207Pb has been used to establish precise dating of a sediment core from 24 miles further downstream. The large magnitude and abrupt shifts in stable lead isotope ratios preserved in upper Hudson sediment cores provide a way to significantly improve dating models, based only on radionuclide analyses. Cadmium, lead and antimony were identified as quite sensitive tracers of upper Hudson sediments due to the magnitude of contamination and the lack of significant additional downstream sources of these contaminant metals. Metal measurements in a pair of sediment cores located 24 miles apart were used to constrain relative fluxes of sediment entering the river between the two coring locations, with sediment sections deposited between the early 1960s and the late 1970s in these two cores suggesting that 3–4 times more sediment entered the river between the two coring sites than was transported from upstream. These dilution factors agree very well with estimates based on suspended sediment measurements during a flood event in April 1994 and with estimates based on mechanistic model of suspended sediment transport between 1977 and 1992.

Variational inverse parameter estimation in a cohesive sediment transport model: An adjoint approach

Parameter estimation in the sediment deposition and resuspension process is an important issue in numerical modeling of suspended sediment transport. The sediment settling velocity and resuspension rate are two critical parameters controlling the sediment exchange process between the water column and sediment bed. In this paper a variational inverse data assimilation scheme for estimation of the sediment settling velocity and resuspension rate is developed and tested with a three‐dimensional cohesive sediment transport model. The sediment settling velocity and resuspension rate are treated as poorly known parameters in the model and are estimated by the variational inverse scheme using an adjoint approach. A limited‐memory quasi‐Newtonian conjugate gradient algorithm is used in the minimization process. The variational inverse model is tested in the James River estuary in Virginia by identical twin experiments. Numerical experimental results show that variational inverse data assimilation is a useful tool for retrieving poorly known parameters in a cohesive sediment transport model.

An inversion method for reflectance in stratified turbid waters

Most methods for interpreting water-leaving reflectance assume vertical homogeneity in the water column. This approach is relevant to quite homogeneous waters or to very turbid waters where reflectance is related to the optical properties of a thin upper surface layer. In weakly turbid and stratified waters, water-leaving reflectance depends on the vertical profile of each optically significant component. This study presents a semi-empirical inversion method to estimate Total Suspended Matter (TSM) concentrations from reflectances in sediment-dominated and stratified waters. The method derives from the concept of a remote sensing estimate of concentration, which is calculated from the profile of suspended matter concentration and from the profile of diffuse attenuation coefficient. A simplification is introduced when the diffuse attenuation profile is not known. The simplified method can be applied to satellite data to retrieve 'optically-effective' concentrations showing better correlations with reflectances than subsurface concentrations. The method is extensively described in the paper and is applied, as an example, to field measurements and to SPOT data over the Ebro river mouth area. Its potential use in connection with numerical modelling of suspended sediment transport is also discussed.