Suspended Sediment Transport Model Research Articles

Distributed dynamic modelling of suspended sediment mobilization and transport from small agricultural catchments

Erosion, soil loss and consequent nutrient fluxes impair water quality and can degrade arable soils. Erosion rates in Sweden are generally low but episodic losses of suspended solids (SS) can affect water quality. Identifying critical source areas (CSAs) and “hot moments” is essential to reduce erosive losses from arable land. Here we use a distributed, dynamic high-resolution erosion model that simulates the sum of all transported material, i.e., erosion within the soil profile, on the soil surface and transport through drainage systems. We simulate monthly SS transport in six small agricultural catchments with varying soil texture over 8 years. Kling-Gupta Efficiency (KGE) was used as model performance statistics, and calibration (KGE = 0.45–0.78) and validation (KGE = 0.64–0.83) showed acceptable model performance for all catchments, with mean annual SS losses between 2.1 and 31.5 t km-2yr-1. Equifinality could be minimised by using more precise initial parameter values. We suggest that the model can be applied to comparable unmonitored catchments to identify erosion-sensitive periods and CSAs.

Phenomenological model of suspended sediment transport in a small catchment

Abstract. We develop a phenomenological model of suspended sediment transport on the basis of data acquired in the Capesterre river, which drains a small tropical catchment in Guadeloupe. The model correctly represents the concentration of suspended sediment during floods, provided that the relation between concentration and water level forms a counterclockwise loop. In the model, the properties of the sediment and of the river are all lumped into four parameters: a settling velocity related to the size of the suspended sediment, a threshold water level which acts as a proxy for the threshold shear stress, a characteristic entrainment rate, and a dimensionless exponent. The value of the parameters changes from one flood to the next, probably reflecting changes in the characteristics of the river and the fine sediment. Finally, a test of the model against data acquired in a small catchment in the French Alps suggests that the model is versatile enough to be used in diverse hydrological settings.

Development, calibration and validation of a phase-averaged model for cross-shore sediment transport and morphodynamics on a barred beach

Simulating cross-shore sediment transport and associated sandbar migration is still a challenging task for phase-averaged coastal morphological models. Numerical studies have mostly relied on beach morphology prediction for calibration and validation, without examining in much detail the underlying hydrodynamics, sediment concentrations and transport rates. This paper reports on a new three-dimensional coastal morphodynamic model based on the hydrodynamic model of Zheng et al. (2017), combined with an advection-diffusion type suspended sediment transport model and the extended SANTOSS near-bed sediment transport formula of Van der A et al. (2013), to represent the key cross-shore transport mechanisms. The model is are calibrated based on comprehensive measurements from a large-scale laboratory experiment involving regular plunging breaking waves over an evolving sandbar, covering detailed comparisons on hydrodynamics, sediment suspension, transport rates, and bed level evolution. Separate validation using large scale wave flume experiments were also conducted to confirm the model's performance on different conditions. Good agreements are obtained between measurements and model results, which demonstrates the model's ability to reproduce cross-shore sediment transport processes under breaking waves correctly, given that the appropriate parameterizations for intra-wave processes are included. Model results also reveal the onshore near-bed transport is related to wave-induced near-bed streaming, wave skewness and asymmetry, and bed slope effects at different locations across the beach surface. Wave breaking-induced turbulence enhances the near-bed transport within the bed boundary layer which needs to be taken into account in order to achieve good model prediction skills.

Improve the Accuracy in Numerical Modeling of Suspended Sediment Concentrations in the Hangzhou Bay by Assimilating Remote Sensing Data Utilizing Combined Techniques of Adjoint Data Assimilation and the Penalty Function Method

Suspended sediment dynamics play an important role in controlling nearshore and estuarine geomorphology and the associated ecological environments. Modeling the transport of suspended sediment is a complicated and challenging research topic. The goal of this study is to improve the accuracy of modeling the suspended sediment concentrations (SSCs) with newly developed techniques. Based on a three-dimensional suspended cohesive sediment transport model, the transport of suspended sediment and SSCs are simulated by assimilating SSCs retrieved from the Geostationary Ocean Color Imager (GOCI) with the adjoint data assimilation in the Hangzhou Bay, a typical strong tidal estuary along the coast of the East China Sea. To improve the effect of the data assimilation, the penalty function method, in which the reasonable constraints of the estimated model parameters are added to the cost function as penalty terms, will be introduced for the first time into the adjoint data assimilation in the SSCs modeling. In twin experiments, the prescribed spatially varying settling velocity is estimated by assimilating the synthetic SSC observations, and the results show that the penalty function method can further improve the effect of data assimilation and parameter estimation, regardless of synthetic SSC observations being contaminated by random artificial errors. In practical experiments, the spatially varying settling velocity is firstly estimated by assimilating the actual GOCI-retrieved SSCs. The results demonstrate that the simulated results can be improved by the adjoint data assimilation, and the penalty function method can additionally reduce the mean absolute error (MAE) between the independent check observations and the corresponding simulated SSCs from 1.44 × 10−1 kg/m3 to 1.30 × 10−1 kg/m3. To pursue greater simulation accuracy, the spatially varying settling velocity, resuspension rate, critical shear stress and initial conditions are simultaneously estimated by assimilating the actual GOCI-retrieved SSCs to simulate the SSCs in the Hangzhou Bay. When the adjoint data assimilation and the penalty function method are simultaneously used, the MAE between the independent check observations and the corresponding simulated SSCs is just 9.90 × 10−2 kg/m3, which is substantially less than that when only the settling velocity is estimated. The MAE is also considerably less than that when the four model parameters are estimated to be without using the penalty function method. This study indicates that the adjoint data assimilation can effectively improve the SSC simulation accuracy, and the penalty function method can limit the variation range of the estimated model parameters to further improve the effect of data assimilation and parameter estimation.

A Physically Based Model of Deposition, Re‐Entrainment, and Transport of Fine Sediment in Gravel‐Bed Rivers

AbstractInterpreting the links between transient in‐channel fine sediment storage and the dynamics of suspended sediment transport during flood events helps the understanding of river geomorphology, and also the impacts of fine sediment on water quality and bed habitats of rivers and downstream receiving environments. We present a unique physically based model of suspended sediment transport which is intimately coupled with fine sediment deposition and re‐entrainment processes within the gravel bed. This multi‐size fraction theory provides unique information about the effect of fine sediment size classes due to their dynamics and associated river bed changes in net deposition. The data from a series of flood events from the Oreti River, located in Southland, New Zealand were used to test the ability of this theory to provide a description of the dynamics of the fine sediment size distribution, their concentration, load, and rate of river bed deposition and re‐entrainment. After calibration of the model using the data from one flood event, the model provides good agreement between observed and modeled fine sediment concentration and event load for seven subsequent test events. One of the main applications of this theory in future is for routing suspended sediment concentration and changes on fine sediment deposition down a river network.

Generalized non-equilibrium suspended sediment transport model with hindered settling effect for open channel flows

The present paper formulates a generalized model for non-equilibrium suspended sediment transport through an open channel turbulent flow that contains all the existing models in literature as special cases. The two-dimensional (2D) unsteady model for suspended concentration distribution contains the effect of hindered settling and the bottom boundary condition considers deposition velocity together with equilibrium bottom concentration. OpenFOAM, an open-source Finite Volume (FV) method based framework, has been used for the numerical approximation of the model. The proposed model addresses the non-linearity in the governing equation as well as the non-linearity in boundary conditions. Picard iteration approach has been utilized to ensure the convergence of the numerical solution. With different physical parameters and conditions, concentration profiles of suspended sediment particles have been analysed theoretically and graphically. It greatly extends the domain of the numerical solutions for determining sediment distribution in suspension through an open channel turbulent flow in a non-equilibrium state.

LES two-phase modelling of suspended sediment transport using a two-way coupled Euler–Lagrange approach

Sediment plume development was modelled using an Euler–Lagrangian two-way coupled large eddy simulation. Momentum exchange was calculated based on interaction forces in the Maxey–Riley equation. Validation showed good agreement with experimental data from literature. For analysis of interaction between sediment and fluid 6,859 particles were released into turbulent fluid flow. In order to ensure independence of the results from arbitrary turbulent velocity fluctuations in the initial fluid velocity field, 41 simulations of the test case starting from different initial flow fields were analysed. Results of these simulations are normally distributed. Mean values indicate three phases of the development of the sediment plume: (i) acceleration phase, (ii) transport phase and (iii) deposition phase. Significant slow down of fluid flow and particle sorting turned out to be relevant processes in the initial development of the sediment plume which are not accounted for in one-way coupled models.

Simulation Study of Scarp and Berm Formation Using a Suspended Sediment Transport Model

Vu, X.H. and Lee, J.L., 2021. Simulation study of scarp and berm formation using a suspended sediment transport model. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 504–508. Coconut Creek (Florida), ISSN 0749-0208. Beach berms and scarps are common morphological features that develop repetitively due to the cyclic incidence of mild and storm waves. However, beach scarp and berm formations, as well as their morphodynamics, have not been researched thoroughly. In particular, scarp generation is often observed at nourished beaches or under the incidence of oblique storm waves; scarps can pose severe risks to beach users and negatively impact local ecosystems. A numerical study was conducted using a suspended sediment transport model developed in a previous study to quantify the morphodynamic responses of beach berms and scarps to the foreshore region as well as offshore sand motion. In the present study, the destructive beach slope at the foreshore was controlled using Kim's empirical formula on the foreshore slope.

SOME QUESTIONS OF ESTIMATING SUSPENDED SEDIMENT IN WATERCOURSES OF NORTH-WEST RUSSIA

In the practice of water management for economic purposes, calculations of suspended sediment for various time scales – from per-second to annual, are important. The estimation of annual suspended sediment transport, as well as of the statistical parameters of turbidity and the reliability of the estimates, is extremely difficult because of irregular and insufficient light conditions in different phases of the water regime. At the same time, owing to the knowledge of the processes that shape the quality of natural waters and a sufficient toolkit of calculation methods, the main indicators of water quality with can be reproduced with acceptable accuracy. The capabilities of statistical analysis of water quality indicators can be expanded by an integrated approach to estimating the indicators by means of well-proven deterministic and stochastic calculation algorithms with arguments observed regularly and for a long time. In this case, a composite method can be used to estimate the parameters of the suspended sediment distribution or water turbidity, which permits finding the parameters of the distribution curve of the function from the parameters of the distribution curve of its arguments. The paper presents a deterministic-stochastic modeling system “weather-runoff-suspended sediments”, based on a stochastic weather model, a model of runoff formation in a catchment area, and a model of annual suspended sediment transport. The system can estimate the distribution parameters of daily suspended sediment load and turbidity values in the situation of observed data shortage or changes in runoff formation in the catchment resulting from natural causes or economic activities.

Estimation of initial conditions for surface suspended sediment simulations with the adjoint method: A case study in Hangzhou Bay

In this paper, an improved numerical scheme is developed to estimate the initial conditions (ICs) based on a three-dimensional suspended sediment transport model (3D SSTM) with adjoint data assimilation, and the method is then applied to Hangzhou Bay as an example. Specifically, the ICs are estimated by assimilating artificial observations in twin experiments and suspended sediment concentrations (SSCs) retrieved from the Geostationary Ocean Color Imager (GOCI) in practical experiments. In the twin experiments, the sensitivity of the estimated ICs to several influential factors is discussed. The results demonstrate that the conjugate descent algorithm of Fletcher is proven to be better than the steepest descent, finite memory BFGS, and five other conjugate gradient algorithms in estimating the ICs; the estimated ICs are sensitive to initial guess values, and appropriate initial values are necessary for improving the efficiency of convergence and obtaining good results. Additionally, the errors of observations can significantly influence the estimated results. In contrast, the estimated results are not very sensitive to cloud coverage, errors in the background flow field, and length of the assimilation time window. In practical experiments, according to the conclusions of twin experiments, an improved 3D SSTM with the adjoint method is developed for Hangzhou Bay, and the surface GOCI-retrieved SSCs during typical neap and spring tidal cycles are assimilated to estimate the practical ICs. The experimental results imply that with the present estimation method, more accurate ICs can be obtained, which indicates that the adjoint method is effective in the estimation of the ICs in SSTMs. Furthermore, this study verifies that accurate ICs are critical for the numerical modeling of SSCs on the tidal cycle scale. This study is not only useful for further improving the accuracy of ICs in SSTMs but also suggestive for the initialization schemes of other matter transport models.

Two Dimension Vertically Integrated Numerical Suspended Sediment Transport Model (Dept.C)

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Simultaneously assimilating multi-source observations into a three-dimensional suspended cohesive sediment transport model by the adjoint method in the Bohai Sea

The performance of the suspended cohesive sediment transport model can be improved by using data assimilation; however, only one source of observations of suspended sediment concentrations (SSCs) is assimilated in the previous studies. This study investigates the simultaneous assimilation of multi-source SSC observations, including in-situ SSC observations and GOCI-retrieved SSCs, into a three-dimensional suspended cohesive sediment transport model by the adjoint method in the Bohai Sea.The artificial SSC observations obtained by running the suspended cohesive sediment transport model are firstly assimilated in the twin experiments. When the initial surface condition obtained using GOCI-retrieved SSCs was used, the model performance after assimilating multi-source artificial SSC observations was improved than that after assimilating only artificial GOCI-retrieved SSCs or in-situ SSC observations. The real multi-source SSC observations are then assimilated in practical experiments. The experimental results indicate that the initial conditions are not only important for SSC simulations, but also significant for data assimilation. Except for the surface layer, assimilating only GOCI-retrieved SSCs can significantly improve the simulated SSCs in the middle and bottom layers. On the whole, the results of simultaneously assimilating multi-source SSC observations are just slightly closer to the SSC observations than those after assimilating only GOCI-retrieved SSCs, but the convergence of adjoint data assimilation is accelerated and the model performance in deep layers is further improved, demonstrating the effectiveness of simultaneously assimilating multi-source SSC observations.

A robust model for rapidly varying flows over movable bottom with suspended and bedload transport: Modelling and numerical approach

We propose a coupled model for suspended and bedload sediment transport in the shallow water framework. The model is deduced under hydrostatic pressure assumptions and will not assume any Boussinesq hypothesis. The numerical resolution is carried out in a segregated way. First the underlying system of conservation laws is solved by using a first order path-conservative Riemann solver. Then, the source terms corresponding with the erosion and depositions rates are approximated in a semi-implicit way. The final scheme preserves the positivity of the density. Several numerical experiments were carried out in order to validate the model and the numerical scheme. The results obtained are in good agreement with the experimental data.

Numerical modelling of suspended-sediment transport in a geographically complex microtidal estuary: Sydney Harbour Estuary, NSW

A numerical study was conducted to investigate the sediment dynamics in a geographically complex estuary, the Sydney Harbour Estuary (SHE). The SHE is a good example of a microtidal estuary, with irregular shorelines and a complex bathymetry, characterized by many headlands and islands forming a meandering main channel. Horizontal sediment transport showed a local estuarine turbidity maximum (ETM) as a result of complex topography, independent of salinity fields and river flows during dry weather. The along-estuary advection of sediment was mainly driven by the mean advection, with a minor contribution by tidal pumping. Mean advection associated with barotropic forcing drives sediment flux seaward in the upper estuary and landward in the middle estuary, leading to a longitudinal convergence of sediment transport, without upstream or downstream migration of ETM during high river flows. The interactions between tidal currents, complex topography and asymmetric vertical mixing led to spring-neap and flood-ebb variations in sediment distribution. The Singular Spectrum Analysis (SSA) method was used to calculate the relative contributions of the identified environmental forcing frequencies (tidal range, tidal frequency, river discharges, wind stress) to the variability in suspended-sediment concentration. Tidal frequency and river discharges were the major contributors to this variability. Tidal range made the highest contribution in the middle estuary, where the ETM was located, driving the spring-neap cycle of the ETM.

Transport and distribution of manganese in tidal estuarine system in Taiwan.

Based on the observed heavy metals in the Danshui River estuarine system, the concentration of manganese (Mn) exceeds the water quality standards. High concentrations of manganese in aquatic environment can cause disturbances in the sodium balance, disturb the metabolism of carbohydrates, and impair the immunological functions of fish. Therefore, a three-dimensional heavy metal transport model was developed and incorporated into the hydrodynamics, salinity, and suspended sediment transport model to evaluate the concentration distribution of the heavy metal manganese (Mn) in the Danshui River estuarine system of northern Taiwan. The model was validated with observational data for water level, tidal current, salinity, suspended sediment concentration, and heavy metal (Mn) concentration that was measured in 2015. The indicators of statistical error, including mean absolute error (MAE), root mean square error (RMSE), and skill score (SS), were adopted to evaluate the model performance. There was good quantitative agreement between the simulation results and measurements. Sensitivity analysis of suspended sediment and heavy metal transport model was carried out to understand which parameters were important to be cautiously determined. Furthermore, the validated model was used to investigate the influence of suspended sediment on the concentration distribution of heavy metals (Mn) in tidal estuaries. If the suspended sediment transport module was excluded in model simulations, the predicted results for the heavy metal (Mn) concentration underestimated the measured data. The modeling results showed that the inclusion of the suspended sediment transport module in the model simulations was critically important to the results of the heavy metal (Mn) concentration in the tidal estuarine system in Taiwan.

Three-dimensional modelling of suspended sediment transport in the far wake of tidal stream turbines

A three-dimensional tidal turbine simulation based on an oceanographic numerical model has been tested for suspended sediment calculation, particularly in the wake of a standalone tidal turbine. The results suggest a need for further improvement of the model in order to obtain correct predictions of suspension strength of the wake and suspended sediment concentration under the influence of a turbine (compared to measured data). Due to the wide use of FVCOM in coastal applications where turbines are commonly installed, it proves necessary to address this issue. Two approaches with respect to modifying bed shear stress and turbulent mixing calculations in the presence of a turbine are proposed and tested in this research. Using data collected in the laboratory as reference, the turbulent mixing enhancement approach is shown to be effective. A series of tests are carried out to identify the impact of the turbine on suspended sediment transport in its vicinity. The results suggest that the impact is highly dependent upon the sediment grain size.

Investigation of the fecal coliform plumes induced by river discharge and wind stress using a three-dimensional model

A three-dimensional hydrodynamic, suspended sediment, and fecal coliform transport model was developed and applied to characterize the fecal coliform plume in the Danshuei River estuarine system and its adjacent coastal sea. The numerical model was calibrated and validated with time-series water levels and spatial distributions of suspended sediment and fecal coliform concentrations in 2012 and 2013, respectively. Three indices (i.e., mean absolute error, root-mean-square error, and skill score) were used to compare the predicted results and measured data for assessing the performance of the model. Quantitatively, there was good agreement between the simulation and the measurement results. The validated model was later applied to explore the influence of river discharge and wind stress on the fecal coliform plume in the Danshuei River coastal area. In the absence of wind stress, no cyclonic circulation occurs as a result of river discharge under flood conditions. However, anticyclone circulation occurs on the east coast of the Danshuei River mouth at low river discharge. The plume distances of fecal coliform from the Danshuei River mouth reach 17 km and 5 km under flood flow and Q50 flow conditions, respectively. In the absence of river discharge, the plume distance of fecal coliform is confined to the Danshuei River mouth. Consequently, the wind directions control the upwelling and downwelling plumes. If the river discharge and wind stress are included in the model simulations, the surface fecal coliform concentrations are flushed out of the Danshuei River mouth and move to the southwestern coast as a result of the wind’s favoring downwelling. Conversely, the fecal coliform concentrations are flushed out of the Danshuei River mouth and flow to the northeastern coast, with the wind favoring upwelling. Comparing simulated results with and without wind stresses, the plume distance/area of fecal coliform decreases with the inclusion of wind stress.

Experimental validation of a cohesive suspended sediment transport model for two Mexican rivers

BackgroundThe south of Mexico is the least developed part of the country but its basins generate more than 60% of the country’s available water. Though disturbances to the rivers caused by development are still low, there is concern about the environmental health of the rivers. The calculation of the sediment load with a focus in fine fraction, where nutrients are found, is a priority. However, models for suspended sediment transport in large rivers are difficult to formulate because they carry a large amount of cohesive sediments, those cohesive sediments form aggregates or flocs with primary particles that are less than 65 μm. The hydrodynamic behavior of flocs depends on their size, density and shape, which differs from that of non-cohesive sediments as theirs depends on their interaction with the water column. A classical model to calculate suspended sediment concentration profiles for steady flow conditions is the Rouse equation, which has been extensively validated for non-cohesive suspended sediment. Some authors have demonstrated that when applied in some large rivers in conjunction with non-cohesive settling velocity models it does not perform very well. The difficulty comes from the fact that most of the suspended sediment charge in large rivers is constituted by cohesive sediments.ResultsSuspended sediments from Mexico’s two largest rivers Usumacinta and Grijalva, with a mean flow rate near river mouth of 2020 m3/s and 1150 m3/s respectively, were analyzed in a rotating annular flume (RAF). The shear velocity obtained in the field by ADCP was reproduced in the annular flume, the size and shape of flocs were obtained by means of PTV. Settling velocity was also obtained to calibrate a settling velocity model appropriate for cohesive sediments.ConclusionsThe settling velocity model developed for cohesive sediments in conjunction with the Rouse equation allowed the reproduction of suspended sediment concentration profiles for the rivers Usumacinta and Grijalva. The estimated concentration profiles were compared and validated with the measured concentration profiles in the field. Thus, the model obtained through this research can be used to estimate nutrient delivery to the sea from the largest rivers in Mexico.

Experimental Modeling of Suspended Sediment Transport Considering the Flow Rate and Grain Size

Bong, T.; Son, Y., and Kim, K.-S., 2019. Experimental modeling of suspended sediment transport considering the flow rate and grain size. Journal of Coastal Research, 35(3), 637–647. Coconut Creek (Florida), ISSN 0749-0208.In this study, laboratory sediment disposal tests were performed using an open channel, and the behavior of soil particles underwater was analyzed according to flow rate and grain size. For each grain size, the deposition distributions of soil particles were demonstrated to have log-normal distributions regardless of the flow rate. The relationships between the average and standard deviation of the deposition distance and the flow rate can be expressed using a quadratic regression equation, and the relationships between the average and standard deviation of deposition distance and the grain size can be expressed using a two-term exponential decay equation. As a result, a simple experimental model was proposed for predicting the soil transportation and deposition distribution considering the flow rate and grain size. The proposed model was validated by comparison with the test results for each grain size and a mixed soil, which was collected from another area, and the proposed model showed good agreement with the experimental results.

Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load

Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2−5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes. Cross-sectional currents, bed shear stress and erosion-deposition patterns are discussed. The flow in cross-section exhibits significant stratification and even an opposite flow direction during the tidal rise and fall; the vertical velocity profile deviates from the logarithmic distribution. During the flow reversal between flood and ebb tides, sediment deposits, which is affected by slack-water durations. The bed deformation is dependent on the meander asymmetry and the interaction between the fresh water flow and tides. The flood tides are attributable to the deposition, while the ebb tides, together with run-offs, lead to slight erosion. The flood tides play a key role in the morphodynamic changes of the meander reach.