Sediment Transport Submodel Research Articles

Numerical Study over the Effects of a Designed Submerged Breakwater on the Coastal Sediment Transport in the Pescara Harbour (Italy)

In 1997, in front of the Pescara Harbour (Italy), a detached breakwater was constructed. In the successive years, the sediment transport due to the combined action of waves and coastal currents, in the area between the detached breakwater and the entrance of the Pescara Harbour, produced an accumulation of about 40,000 m 3 of sediment per year. In this paper, the causes of the accretion of the bottom elevation in front of the Pescara Harbour entrance and the effects produced by the existing detached breakwater are investigated. The effects on the sediment transport of the introduction of a new submerged breakwater designed to protect the entrance of the harbour from sediment siltation are investigated. In particular, the ability of the designed submerged breakwater, located orthogonally to the longshore current, to intercept the aforementioned solid material and to significantly reduce the accretion of the bottom in the area in front of the harbour entrance, was numerically verified. Numerical simulations were carried out by means of a model of the bottom-change composed of two sub-models: a two-dimensional phase resolving model that is used to calculate the fluid dynamic variables changing inside the wave period and a second sediment transport sub-model to simulate the bottom changes, in which the suspended sediment concentration is calculated by the wave-averaged advection–diffusion equation. The equations of motion, in which the vector and tensor quantities are expressed in Cartesian components, are written in a generalised curvilinear coordinate system. The fully nonlinear Boussinesq equations are written in an integral form and used to simulate the velocity fields.

Distributed modeling of soil erosion and sediment transport

A mathematical model is used for the estimation of the annual sediment yield resulting from rainfall and runoff at the outlet of Nestos River basin (Toxotes, Thrace, Greece), where the ecologically interesting Nestos delta exists. The model is applied to that part of Nestos River basin (838 km2) which lies downstream of three dams. Two dams (Thissavros and Platanovryssi) have been already constructed, while the third one (Temenos) is under construction. The model consists of three sub-models: a rainfall-runoff sub-model, a surface erosion sub-model and a sediment transport sub-model for streams. This model is also capable of computing the annual erosion amount and sediment yield in the individual sub-basins

Modeling hydromorphological processes in a mountainous basin using a composite mathematical model and ArcSWAT

Hydromorphology is a matter of water and sediment. This constitutes the study of hydrological processes, as well as of the soil and streambed erosion processes imperative. This study presents two different models aiming at continuous simulations of hydromorphological processes at the basin scale. The first model is a Composite Mathematical Model (CMM), consisting of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a stream sediment transport submodel. The second model is the GIS version of the Soil and Water Assessment Tool, SWAT. The application of both models results to continuous hydrographs and sediment graphs at the basin outlet. The computed stream discharge and sediment discharge values are compared with field measurements and both models are evaluated, as to their competence of simulating the hydromorphological processes in a basin. The novelty of this research primarily lies in the fact that different ways for producing continuous sediment graphs, are presented. This can be achieved at any stream segment and provides a continuous assessment of the sediment discharge. Additionally, the application of all models is performed at an hourly time step, for long periods of time. This imparts high precision and detail to the hydromorphological study of a basin at the temporal scale. Sediment discharge is a highly nonlinear physical procedure and high levels of disaggregation (subdaily to hourly time steps) incorporate a very high degree of nonlinearity, especially in flooding periods. In this respect, this research highlights the importance of calculating sediment discharge at fine time scales and offers different methodologies to achieve it. Several statistic efficiency criteria were used to evaluate the models' efficiency to simulate the aforementioned processes. As far as the evaluation of CMM is concerned, values for Nash-Sutcliffe Efficiency (NSE), determination coefficient (r2) and Percent BIAS (PBIAS) amount to 0.974, 0.985 and −10.344, respectively, for water discharge, and 0.647, 0.660 and 12.371, for sediment discharge, whilst regarding the evaluation of SWAT the corresponding values for NSE, r2 and PBIAS are 0.978, 0.981 and −5.104, for water discharge, and 0.593, 0.664 and −37.155, for sediment discharge. It is considered that the efficiency criteria provide satisfying results.

Computation of hourly sediment discharges and annual sediment yields by means of two soil erosion models in a mountainous basin

ABSTRACTThe objective of this study is the estimate of sediment discharges and sediment yields deriving from soil and streambed erosion, at the basin scale. For this reason, continuous simulations of soil and streambed erosion processes are performed in the mountainous part of the Nestos River basin, downstream of the Platanovrysi dam (Macedonia-Thrace border, northeastern Greece). For attaining the above, two composite mathematical models, each consisting of three submodels, are applied: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The two models only differ in the soil erosion submodel. The rainfall-runoff submodel that is used for the computation of the surface runoff and the streamflow in the sub-basins is the deterministic distributed hydrologic model HEC-HMS 4.2. The first soil erosion submodel, utilized for the estimate of soil erosion in a sub-basin, is based on the relationships of Poesen [1985. An improved splash transport model. Zeitschrift für Geomorphologie, 29, 193–211], while the second is the widely known Modified Universal Soil Loss Equation (MUSLE). The estimate of sediment yield at the outlet of a sub-basin, and finally at the outlet of the whole basin, is achieved by means of the stream sediment transport model of Yang and Stall [1976. Applicability of unit stream power equation. Journal of the Hydraulics Division, ASCE, 102 (5), 559–568]. The application of the latter mathematical models results in continuous hydrographs and sediment graphs at the basin outlet. The computed sediment discharge values are compared with field measurements. The statistic efficiency criteria utilized for the comparison between computed and measured values at the basin outlet provide satisfactory results. Therefore, it is concluded that the continuous hydromorphologic modelling can be successfully applied to the Nestos River basin.

2D numerical modelling of meandering channel formation

A 2D depth-averaged model for hydrodynamic sediment transport and river morphological adjustment was established. The sediment transport submodel takes into account the influence of non-uniform sediment with bed surface armoring and considers the impact of secondary flow in the direction of bed-load transport and transverse slope of the river bed. The bank erosion submodel incorporates a simple simulation method for updating bank geometry during either degradational or aggradational bed evolution. Comparison of the results obtained by the extended model with experimental and field data, and numerical predictions validate that the proposed model can simulate grain sorting in river bends and duplicate the characteristics of meandering river and its development. The results illustrate that by using its control factors, the improved numerical model can be applied to simulate channel evolution under different scenarios and improve understanding of patterning processes.

Estimate of Continuous Hydrographs and Sediment Graphs in Nestos River Basin

The objective of this study is to present continuous hydrologic simulations, as well as continuous simulations of soil and streambed erosion processes in the mountainous part of Nestos River basin (Macedonia-Thrace border, northeastern Greece). The characteristic of the basin is the presence of a dam at its upper boundary and two irrigation canals very close to the outlet of the basin. For attaining the above, a composite mathematical model, consisting of three submodels, is applied: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The application of the latter mathematical model results in continuous hydrographs and sediment graphs at the basin outlet. The computed stream discharge and sediment discharge values are compared with field measurements. Statistic efficiency criteria provide satisfactory results. Therefore, it is concluded that the continuous hydromorphologic modeling can be successfully applied to Nestos River basin.

Estimate of Continuous Sediment Graphs in a Basin, Using a Composite Mathematical Model

The aim of this study is to present continuous simulation efforts of soil and streambed erosion processes, as well as the comparison of computed sediment load values with field measurements. For this reason, a composite mathematical model, consisting of three submodels, is applied to the basin of Kosynthos River (district of Xanthi, Thrace, northeastern Greece): a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The rainfall-runoff submodel that is used for the computation of the surface runoff and the streamflow in the sub-basins, is the deterministic distributed hydrologic model HEC-HMS 3.5. For the estimate of soil erosion in a sub-basin, the model of Poesen (1985) is used, while for the estimate of sediment yield at the outlet of a sub-basin, and finally at the outlet of the whole basin, the stream sediment transport model of Yang and Stall (1976) is used. The statistic efficiency criteria utilized for the comparison between computed and measured sediment discharge values at the outlet of the whole basin, provide satisfactory values. Therefore, it is concluded that the continuous hydromorphologic modeling can be successfully applied to Kosynthos River basin.

Development and application of a braided river model with non-uniform sediment transport

This paper presents the development and application of a physics-based morphological model for simulating the evolution processes of braided channels. This model comprises a depth-integrated hydrodynamic sub-model for rapidly varying unsteady flows and a bed load sediment transport sub-model for non-uniform sediments. The sheltering effects of non-uniform particles and the lateral sediment transport due to bed slope and secondary flow are taken into account in the sediment sub-model. Channel bed level change is calculated according to the erosion/deposition rate, and the bank movement is modelled according to the submerged angle of repose, which is valid for braided rivers in natural and experimental conditions. The model has been applied to a braided river produced in a flume experiment, and the numerical model-predicted channel patterns are shown to generally well resemble the experimental river. Most of the morphodynamic processes observed in the experiment can be found in the numerical predictions, including the evolution of the channel from a single straight channel to a multi-thread pattern and local morphologic changes. The mechanisms of the morphodynamic evolution of multi-thread flows are investigated, in which the process of grain sorting occurs under the interaction of fluid and sand, and the effect on channel migration is identified.

Tidal circulation, sediment and pollutant transport in Cádiz Bay (SW Spain): A modelling study

A numerical model to simulate the dispersion of particle-reactive tracers in Cádiz Bay (SW Spain) has been developed. It includes a hydrodynamic submodel to provide water currents, a sediment transport submodel, which provides suspended matter concentrations and sedimentation rates and the pollutant dispersion model. Pollutant exchanges between the liquid and solid phases are described in a dynamic way, using kinetic transfer coefficients. Results of the hydrodynamic and sediment transport models have been compared with observations. The contamination of sediments of the bay by fallout 137Cs has been simulated. The existence of an accumulation area in the inner bay, found in field measurements, has been reproduced by the model. Dispersion experiments for Zn and 226Ra have also been carried out. Flushing-times of the inner bay have been finally determined through numerical experiments.

Formation process of meandering channel by a 2D numerical simulation

A 2D depth-averaged model for hydrodynamic, sediment transport and river morphological adjustment is presented. The sediment transport submodel considers non-uniform sediment, bed surface armoring, impact of secondary flow on the direction of bed-load transport, and transverse slope of river bed. The bank erosion submodel incorporates a simple simulation method for updating bank geometry during either degradational or aggradational bed evolution. The model is applied to a 180° bend with a constant radius under unsteady flow conditions, and to Friedkin's laboratory meander channels. The results are in acceptable agreement with measurements, confirming the two dimensional model's potential in predicting the formation of river meandering and improving understanding of patterning processes. Future researches are needed to clarify some simplifications and limitations of the model.

A Distributed Soil Erosion and Sediment Transport Sub–Model in Non-Point Source Pollution and Its Application in Guishui Watershed

Abstract: Soil erosion was very serious in the Guishui area of Guanting reservoir. In order to control the non-point source (NPS) pollution of soil loss there, a distributed soil erosion and sediment transport sub-model with less parameters and more convenient application was built in this paper, which was composed of the USLE model and the sediment transport model. Firstly, USLE was used to calculate soil erosion after suitable calculation formulae of its factors were selected. And then the watershed was generalized into river network, we applied the relation between S-curve and pollutant-collecting area coefficient we had established into the solution of one-dimensional water quality transportation equation gained from Laplace transform and inverse Laplace transform, and derived the distributed sediment transport model. Finally, relied on DEM, this paper made research on the model application in Guishui watershed by picking up geographical information from the soil map and land-use map of Guishui waters...

Estimate of sediment inflow into Vistonis Lake, Greece

In the present study, the mean annual sediment inflow into Vistonis Lake (Thrace, northeastern Greece) was calculated. The sediment quantity originates mainly from the basins of Kossynthos, Kompsatos and Travos (Aspropotamos) Rivers. The whole basin area (mountainous part) contributing to the lake amounts to about 845 km 2. The above mean annual sediment quantity was compared with the mean annual sediment accumulation in the lake. The latter quantity was estimated from the mean annual decrease of the lake water volume for a period of 22 years, which was determined by means of older and newer topographic maps (isobath contours). For the calculation of the mean annual sediment yield at the outlets of the three above mentioned basins, a mathematical model consisting of three submodels was used: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The comparison of the computational results by means of the mathematical model with the estimation results by means of the topographic maps is satisfactory and encouraging.

Numerical Simulation of Longitudinal and Lateral Channel Deformations in the Braided Reach of the Lower Yellow River

Bank erosion frequently occurs in the Lower Yellow River (LYR), playing an important role in the evolution of this braided river. A two-dimensional (2D) composite model is developed herein that consists of a depth-averaged 2D flow and sediment transport submodel and a bank-erosion submodel. The model incorporates a new technique for updating bank geometry during either degradational or aggradational bed evolution, allowing the two submodels to be closely combined. Using the model, the fluvial processes in the braided reach of the LYR between Huayuankou and Laitongzhai are simulated, and the calculated results generally agree with the field measurements, including the water-surface elevation, variation of water-surface width, and variations of cross-sectional profiles. The calculated average water-surface elevation in the study reach was 0.09m greater than the observed initial value, and the calculated mean bed elevation for six cross sections was 0.11m lower than the observed value after 24 days. These errors are attributed to the large variability of flow and sediment transport processes. Sensitivity tests of three groups of parameters are conducted, and these groups of parameters are related to flow and sediment transport, bank erosion, and model application, respectively. Analysis results of parameter sensitivity tests indicate that bank erodibility coefficient and critical shear stress for bank material are sensitive to the simulated bank erosion process. The lateral erosion distance at Huayuankou will increase by 19% as the value of bank erodibility coefficient changes from 0.1 to 0.3, and it will decrease by 57% as the value of critical shear stress for bank increases from 0.6 to 1.2N∕m2. Limited changes of other parameters have relatively small effects on the simulated results for this reach, and the maximum change extent of calculated results is less than 5%. Because the process of sediment transport and bank erosion in the braided reach of the LYR is very complicated, further study is needed to verify the model.

Comparative application of two mathematical models to predict sedimentation in Yermasoyia Reservoir, Cyprus

The Yermasoyia Reservoir is located northeast of the town of Limassol, Cyprus. The storage capacity of the reservoir is 13·6 × 106 m3. The basin area of the Yermasoyia River, which feeds the reservoir, totals 122·5 km2. This study aims to estimate the mean annual deposition amount in the reservoir, which originates from the corresponding basin. For the estimate of the mean annual sediment inflow into the reservoir, two mathematical models are used alternatively. Each model consists of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. In the first model, the potential evapotranspiration is estimated for the rainfall-runoff submodel, and the soil erosion submodel of Schmidt and the sediment transport submodel of Yang are used. In the second model, the actual evapotranspiration is estimated for the rainfall-runoff submodel, and the soil erosion submodel of Poesen and the sediment transport submodel of Van Rijn are used. The deposition amount in the reservoir is estimated by means of the diagram of Brune, which delivers the trap efficiency of the reservoir. Daily rainfall data from three rainfall stations, and daily values of air temperature, relative air humidity and sunlight hours from a meteorological station for four years (1986–89) were available. The computed annual runoff volumes and mean annual soil erosion rate are compared with the respective measurement data. Copyright © 2006 John Wiley & Sons, Ltd.

Estimate of sediment yield in a basin without sediment data

In this study, three mathematical models for the estimate of sediment yield, due to soil and stream erosion, at the outlet of a basin are presented. Each model consists of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The rainfall-runoff and the stream sediment transport submodels are identical in the three mathematical models. The rainfall-runoff submodel that is used for the computation of the runoff in a sub-basin is a simplified water balance model for the soil root zone. For the estimate of soil erosion in a sub-basin, three different submodels are used alternatively, owing to the fact that erosion or sediment yield data are not available. The soil erosion submodels are (a) a modified form of the classical Universal Soil Loss Equation (USLE, [Foster, G.R., Meyer, L.D., Onstad, C.A., 1977. A runoff erosivity factor and variable slope length exponents for soil loss estimates. Transactions of the ASAE, 20 (4), 683–687]) taking into account both the rainfall erosion and the runoff erosion, (b) the relationships of Poesen [Poesen, J., 1985. An improved splash transport model. Zeitschrift für Geomorphologie, 29, 193–211] quantifying the splash detachment, as well as the upslope and downslope splash transport, (c) the relationships of Schmidt [Schmidt, J., 1992. Predicting the sediment yield from agricultural land using a new soil erosion model. Proceedings of the 5th International Symposium on River Sedimentation. Karlsruhe, Germany, pp. 1045–1051] including the momentum flux exerted by the droplets and the momentum flux exerted by the runoff. The sediment transport submodel for streams aims to estimate the sediment yield at the outlet of a sub-basin. This quantity results by comparing the available sediment amount in the main stream of a sub-basin with the sediment transport capacity by stream flow, which is computed by the relationships of Yang and Stall [Yang, C.T., Stall, J.B., 1976. Applicability of unit stream power equation. Journal of the Hydraulics Division, ASCE, 102, 559–568]. The mathematical models were applied to the basin of Kompsatos River, in northeastern Greece, with an area of about 565 km 2. The whole basin was divided into 18 natural sub-basins for more precise calculations. Monthly rainfall data were available for 27 years (1966–1992); therefore, the calculations were performed on a monthly basis. The deviation between the three mean annual values of sediment yield at the basin outlet, for 27 years, resulting from the three mathematical models is relatively small.

Application and Validation of Three-Dimensional Model in a Shallow Lake

This paper describes the validation and application of a hydrodynamic and sediment transport submodel of the Lake Okeechobee environment model (LOEM). This model simulates the sediment resuspension and transport due to wind driven current and waves. The LOEM simulated conditions in Lake Okeechobee from October 1, 1999 to September 30, 2000. The model reasonably simulated water depth, water temperature, current velocity, and suspended sediment concentrations in the validation period. To model sediment resuspension, the processes of wind generated waves and the resulting stresses on the lake bed were simulated. The LOEM is used to predict the impact of sediment processes in the lake under different management scenarios and environmental conditions (high/low lake stages and storm events/hurricanes). This model also is used to estimate light extinction coefficient. Results from the LOEM allow managers to predict how phosphorus-rich mud sediments move in the lake between the marsh and open water areas, and under what conditions they are most likely to be resuspended and transported.

Two-Dimensional Composite Mathematical Alluvial Model for the Braided Reach in the Lower Yellow River

The fluvial processes are considerably complicated in the braided reach of the Lower Yellow River, and the lateral or transverse channel deformation process is especially pronounced. The state-of-the-art of simulation techniques for the channel deformation in the Lower Yellow River was analyzed in this paper, and such a conclusion was drawn that existing mathematical alluvial models only can simulate the longitudinal channel deformation and cannot simulate such the lateral deformation as lateral erosion and failure of bank. Then a new two-dimensional (2D) composite model was developed herein, consisting of a 2D flow and sediment transport submodel and a riverbank-erosion submodel. This model not only can simulate the longitudinal and lateral channel deformations, but also can be used to simulate the fluvial processes of natural alluvial rivers with complex bed morphology. Through using the proposed composite model, the flood routing and channel deformation processes during the August 1982 flood were simulated. The maximum stage along the reach and the discharge hydrograph at the outlet so obtained were in good agreement with the observed data. Simulated results of the channel deformation processes showed that during the flood season, the main channel scours and the flood plain deposits; during the dry season, the main channel deposits and banks of the floodplain retreat due to lateral erosion by the flow and failure under gravity. Such results accord with the annual varying law of bed scouring and deposition in the braided reach.

Two-dimensional numerical modeling of the longitudinal and lateral channel deformations in alluvial rivers

Two kinds of bank erosion mechanisms were analyzed, including fluvial and non-fluvial controlled mechanisms, and mechanical methods of simulating the erosion processes of cohesive, non-cohesive and composite riverbanks were improved. Then a two-dimensional numerical model of the channel deformation was developed, consisting of a 2D flow and sediment transport submodel and bank-erosion submodels of different soil riverbanks. In the model, a new technique for up dating the bank geometry during the bed evolution was presented, which combines closely two kinds of submodels. The proposed model is capable of not only predicting the processes of flood routing and longitudinal channel deformation in natural rivers, but also simulating the processes of lateral channel deformation, especially the processes of lateral erosion and failure of cohesive, non-cohesive and composite river banks.

Simulation Modeling of Runoff, Groundwater Flow and Sediment Transport into Kastoria Lake, Greece

Kastoria Lake is located in northwestern Greece. The whole basin of the lake is about 253 km2. For the computation of the surface water volume inflowing into the lake from the main streams of the sub-basins located around Kastoria Lake, a rainfall-runoff sub-model is used. A quasi-three-dimensional simulation model of the Kastoria basin aquifer is also realized, in order to estimate the groundwater contribution to the volumetric budget of the lake and the whole basin as well. For the computation of sediment load inflowing into the lake from the main streams of the sub-basins, the rainfall-runoff sub-model is combinedwith a soil erosion sub-model and a sediment transport sub-model for streams. A GIS was developed in the hydrologic basin with all data needed for parameter identification and model application. The data base was enriched by a series of on site measurements of water discharge made in all main streams for one whole hydrologic year. By means of the resulting mathematical sediment model, those sub-basins, which deliver most sediment load to the lake, are identified. On the basis of this identification, a series of control measures, for the reduction of sediment inflowing into the lake, at certain places of the above mentioned sub-basins is proposed.

Comparative application of two erosion models to a basin

Two mathematical models were used to estimate the annual sediment yield resulting from rainfall and runoff at the outlet of the Nestos River basin (Toxotes, Thrace, Greece). The models were applied to that part of the Nestos River basin (838 km2) which lies downstream of three dams. Both models consist of three submodels: a simplified rainfall-runoff submodel, a physically-based surface erosion submodel and a sediment transport submodel for streams. The two models differ only in the surface erosion submodel: that of the first model is based on the relationships of Poesen (1985) for splash detachment and splash transport, while the corresponding submodel of the second model is based on the relationships of Schmidt (1992) for the momentum flux exerted by the droplets and the momentum flux exerted by the overland flow. The degree of conformity between the annual values of sediment yield at the basin outlet according to both models is satisfactory.