Sediment Transport In Open Channels Research Articles

Unsteady two-dimensional distribution of suspended sediment transport in open channels

Unsteady two-dimensional distribution of suspended sediment transport in open channels

Effect of sediment transport on flow characteristics in non-prismatic compound channels

Sediment transport in open channels and rivers is considered one of the most important and complex processes in hydraulic engineering. In this study, we investigated the effect of sediment transport in non-prismatic compound channels on flow characteristics using the Computational Fluid Dynamics (CFD) software ANSYS-Fluent. Contrary to many previous numerical studies, the momentum exchange between both primary (water) and secondary (sediment) phases was considered by activating the Discrete Phase Model (DPM). The aim was thus, to investigate the behavior of particles from a Lagrangian viewpoint and a discrete perspective. This enabled to monitor the momentum lost or gained by transported sediment particles that were injected in the continuous phase. Moreover, the influence of discrete phase trajectories on the continuum continuous phase was considered. Four sediment particle sizes 1, 5, 50, and 500 µm and three sediment mass discharges 5.19, 10.38, and 15.56 kg/s were considered during simulations of the non-prismatic compound channel. Results showed that the stream-wise velocity of flow deceased along the length of the main channel and floodplain for sediments with small diameter. No considerable change was noted for larger particles. Sediment mass discharge had a considerable effect on flow velocity. As sediment mass discharge increased, flow velocity decreased. The flow velocity at the channel outlet was 0.52 and 0.50 m/s corresponding to sediment mass discharge of 5.19 kg/s and 15.56 kg/s, respectively. Results revealed that flow turbulence was attenuated in the presence of sediments and the degree of attenuation increased with increasing sediment mass discharge in flow, especially near the free channel surface. Moreover, suspended sediment concentrations were higher in the presence of gradual enlarged floodplain as compared to the straight one. Maximum concentrations were 13 and 190 kg/m 3 in the gradual enlargement reach for sediment diameter 1 and 5 µm, respectively, and 4.5 and 170 kg/m 3 in the same reach for the prismatic compound channel, respectively. Generally, and based on the results, it can be concluded that the effect of the secondary sediment phase on the primary water phase was more pronounced in case of small diameters and high mass discharge of sediments. In addition, the joint effect of floodplain width enlargement and sediment particle size on suspended sediment concentration was more pronounced for fine sediments than that for coarser sediment along the compound channel.

Semianalytical Solution for Nonequilibrium Suspended Sediment Transport in Open Channels with Concentration-Dependent Settling Velocity

Semianalytical Solution for Nonequilibrium Suspended Sediment Transport in Open Channels with Concentration-Dependent Settling Velocity

COMPUTER SIMULATION OF DETERMINING SILTATION VOLUMES OF WATER RESERVOIR STORAGE ON THE AKSAY RIVER

Objectives. The development of a mathematical model for the increased turbidity zones of the Aksay river in order to determine the siltation volumes of the Aksay water reservoir storage.Method. The mathematical model is developed using the theory of probability and the theory of random process outliers. The model takes the normal distribution of the horizontal and vertical components of the instantaneous flow velocities into account, as well as the Rayleigh law of the distribution of their maxima. The proposed model is used to calculate the “turbidity tail” of the Aksay river.Result. Due to the multifactorial nature of the continuously associated processes of siltation and deposition of suspended and bottom sediments in the upper pounds of the Aksay reservoir storage hydrological system, a mathematical model of the reservoir accretion process is developed. This model provides the reliability of accretion forecasting with spatial and temporal correlation with the siltation process model, which is actually feasible on the basis of computer simulation.Conclusion. The developed model, which is based on a probabilistic approach and the theory of random process outliers, reflects the overall process of sediment transport in open channels. The development and execution of simulation programmes is carried out using the Microsoft Developer Studio (MDS) and the Fortran Power Station algorithmic language, which comprises not only a programming system, but also a set of tools for supporting large software projects integrated into MDS.

3D numerical modeling of flow and sediment transport in rivers and open channels

Numerical model is a useful tool in studying the flow and sediment transport, change in river bed and is built on solving governing differential equations. Numerical model has many different levels and three-dimensional model is the highest level, allowing detailed simulation of flow and sediment transport process in 3D space. The paper presents a method calculating three - dimensional flow and sediment transport in the open channel. Water level and flow velocity are solved from three-dimensional equations with hydrostatic hypothesis. Concentration of suspended sediment, bottom sediment and bottom evolution is solved from transport equations. The governing differential equations in the "sigma" transform coordinate system are solved by finite volume method on unstructured grid of quadrilateral elements. Boundary condition of water level or flow will be imposed on open boundary. For suspended sediment concentrations in the injected phase, suspended sediment concentrations are applied and the outflow phase applies free drainage conditions. This method of calculation was tested with the problem of curved channel sediment transport which was studied experimentally by Odgaard and Bergs. Calculation results are quite consistent with the measured data. In order to test the practical applicability, this method is also tested with the problem of sediment transport in Cu lao Pho islet on Dong Nai river. To solve the matter of hydraulic boundary condition of this problem, the model of Cu lao Pho islet is integrated into the Sai Gon - Dong Nai river system model. Results of the calculation of the river bed evolution of the Cu lao Pho islet on the Dong Nai river also show that this calculation method gives results consistent with the rule and can be used in practical research.

Sediment transport modeling in rigid boundary open channels using generalize structure of group method of data handling

Sediment transport in open channels has complicated nature and finding the analytical models applicable for channel design in practice is a quite difficult task. To this end, behind theoretical consideration of the open channel sediment transport through incorporating of four fundamental characteristics of fluid, flow, sediment and channel, recently, machine learning techniques are used for modeling of sediment transport in open channels. However, most of the studies in the literature used limited number of data for model development neglecting some effective parameters involved which may affect their performances. Moreover, most of this studies had not provided a comprehensive explicit equation for future use. Accordingly, this study applied four machine learning techniques of Gene Expression Programming (GEP), Extreme Learning Machine (ELM), Generalized Structure Group Method of Data Handling (GS-GMDH) and Fuzzy c-means based Adaptive Neuro-Fuzzy Inference System (FCM-ANFIS) to model sediment transport in open channels. Four existing data sets in the literature with wide ranges of pipe size, sediment size, sediment volumetric concentration, channel bed slope and flow depth are used for the model development. The recommended models are compared with their corresponding conventional regression models taken from the literature in terms of different statistical performance indices. Results indicate superiority of the machine leaning techniques to the conventional multiple non-linear regression models. Although, developed GEP, ELM, GS-GMDH and FCM-ANFIS models have almost same performances, GS-GMDH gives slightly better performance which can be linked to the generalized structure of this approach. A MATLAB code is provided to calculate the sediment transport in open channel for practical engineering.

Design of a Hybrid ANFIS–PSO Model to Estimate Sediment Transport in Open Channels

In the present study, a new hybrid evolutionary method is presented for estimating the minimum densimetric Froude number required for sediment transport with no solid substance deposition in channel pipes. This method is based on a combination of particle swarm optimization (PSO) algorithm with adaptive neuro-fuzzy inference system (ANFIS). The PSO algorithm is utilized for optimization of fuzzy membership function value. Three different sets of data measured at different times as well as a vast range of parameters are used to test and train the suggested models. The results of ANFIS–PSO (R2 = 0.976, RMSE = 0.260, MAPE = 5.743, BIAS = − 0.004, SI = 0.059) are compared with the results of ANFIS (R2 = 0.929, RMSE = 0.452, MAPE = 9.107, BIAS = − 0.077, SI = 0.101) and regression-based equations obtained from the literature.

A Comparative Study of Extreme Learning Machines and Support Vector Machines in Prediction of Sediment Transport in Open Channels

The limiting velocity in open channels to prevent long-term sedimentation is predicted in this paper using a powerful soft computing technique known as Extreme Learning Machines (ELM). The ELM is a single Layer Feed-forward Neural Network (SLFNN) with a high level of training speed. The dimensionless parameter of limiting velocity which is known as the densimetric Froude number (Fr) is predicted using ELM and the results are compared to those obtained using a Support Vector Machines (SVM). The comparison of the ELM and SVM methods indicates a good performance for both methods in the prediction of Fr. In addition to being computationally faster, the ELM method has a higher level of accuracy (R2=0.99, MAE=0.10; MAPE=2.34; RMSE=0.14; CRM=0.02) compared with the SVM approach.

Derivation of Rouse equation for sediment concentration using Shannon entropy

Abstract Sediment concentration is fundamental for determining sediment transport in open channels. The Rouse equation, one of several methods for computing sediment concentration, has been derived using deterministic hydraulic principles. This study derives the Rouse equation using the Shannon entropy theory. The derivation requires a hypothesis on the cumulative probability distribution function of sediment concentration in terms of flow depth which is formulated in a general form and can specialize in several specific forms reported in the literature. The advantage of using the entropy theory is that it permits quantification of uncertainty associated with concentration and determination of parameters in terms of specified information, such as mean concentration.

Developing a 2D vertical flow and sediment transport model for open channels using the Youngs-VOF method

A 2D vertical (2DV) numerical model, without σ-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs-VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.

Extreme learning machine assessment for estimating sediment transport in open channels

The minimum velocity required to prevent sediment deposition in open channels is examined in this study. The parameters affecting transport are first determined and then categorized into different dimensionless groups, including "movement," "transport," "sediment," "transport mode," and "flow resistance." Six different models are presented to identify the effect of each of these parameters. The feed-forward neural network (FFNN) is used to predict the densimetric Froude number (Fr) and the extreme learning machine (ELM) algorithm is utilized to train it. The results of this algorithm are compared with back propagation (BP), genetic programming (GP) and existing sediment transport equations. The results indicate that FFNN-ELM produced better results than FNN-BP, GP and existing sediment transport methods in both training (RMSE = 0.26 and MARE = 0.052) and testing (RMSE = 0.121 and MARE = 0.023). Moreover, the performance of FFNN-ELM is examined for different pipe diameters.

An effective Euler–Lagrange model for suspended sediment transport by open channel flows

An Euler–Lagrange two-phase flow model is developed to study suspended sediment transport by open-channel flows with an Eddy Interaction Model (EIM) applied to consider the effect of fluid turbulence on sediment diffusion. For the continuous phase, the mean fluid velocity, the turbulent kinetic energy and its dissipation rate are directly estimated by well-established empirical formulas. For the dispersed phase, sediment particles are tracked by solving the equation of motion. The EIM is applied to compute the particle fluctuation velocity. Neglecting the effect of particles on flow turbulence as usually suggested for dilute cases in the literature, the Euler–Lagrange model is applied to simulate suspended sediment transport in open channels. Although the numerical results agree well with those by the well-known random walk particle tracking model (RWM) and with the laboratory data for fine sediment cases, it is clearly shown that such an Euler–Lagrange model underestimates the sediment concentration for the medium-sized and coarse sediment cases. To improve the model, a formula is proposed to consider the local fluid turbulence enhancement around a particle due to vortex shedding in the wake. Numerical results of the modified model then agree very well with laboratory data for not only the fine but also the coarse sediment cases.

A one-dimensional model of mixed cohesive and non-cohesive sediment transport in open channels

A one-dimensional model has been developed to simulate mixed cohesive and non-cohesive sediment transport in open channels. Flocculation is considered by determining the floc settling velocity as function of sediment size, concentration, and bed shear stress. The critical shear stress of cohesive sediment erosion is related to the dry bed density that varies with time due to consolidation, and the critical shear stress of non-cohesive sediments is corrected when the cohesive fraction exceeds a certain limit such as 10%. Cohesive and non-cohesive sediment transport, bed change and bed-material sorting equations are solved in a coupled form. The model is tested using two field cases of mixed sediment transport in the Lower Fox River in USA and the Three Gorges Reservoir in China. The calculated results agree generally well with measured data.

Removing sediment transport in open channel with submerged aquatic vegetation: Laboratory study

Vegetation affects fluvial processes and is key role in river management in particular sediment transport. Vegetation characteristics such as vegetation’s density, height and distributions have significant effect on sediment transport in vegetated channel. This paper studied the role of aquatic vegetation characteristics in sediment transport. Laboratory experiments were conducted in a fabricated channel with real vegetations (Hydrilla verticillata) planted on its bed. The total suspended solid (TSS) was applied for sediment rate measurement. As results, it is found that vegetation density and distribution has significant impact to the sediment entrapment capacity of the vegetation. An increased coverage of the vegetation from 33 to 66% of the flow area has increased the sediment trapping capacity in average by 15%. To sum up, the present study was designed to determine the effect of the vegetation properties on sediment transport rate. Key words: Sediment transport, aquatic vegetation, Flow, vegetation open channel.

A general two-phase turbulent flow model applied to the study of sediment transport in open channels

A numerical model for the general description of the sediment-laden flow is developed based on an Euler–Euler approach of the two-phase turbulent flow theory. The basic equations of the model are the Reynolds averaged equations of motion for both the fluid and the sediment phase in addition to the Reynolds averaged continuity equations for the mixture and for the sediment phase. The fluid phase and the sediment phase are coupled through their interaction forces including resistance force, inertia force, and lift force. Turbulence closure of the fluid phase is based on the conventional k– ε model while an algebraic particle turbulence model is applied to the sediment phase. The numerical method is based on the modified SIMPLE scheme. The model is applied to the computation of saturated sediment-laden flows and also the non-equilibrium transport of sediment by unidirectional flows under simple erosion and simple deposition conditions. The numerical results are well verified by the available experimental data. The vertical velocity of the sediment phase is also shown to be in very good agreement with the fall velocity of the sediment particles, which strongly support the assumption of Rouse’s diffusion theory for suspended sediment under steady state.

Toward two‐phase flow modeling of nondilute sediment transport in open channels

In this paper, we generalize several models based upon the multiphase flow theory to address the nondilute transport of suspended sediment in open channels. These models naturally include the dilute condition as a special case. We assess the range of validity of models through simulations of the experimental tests by Vanoni (1946), Einstein and Chien (1955), Taggart et al. (1972), Coleman (1986), and Wang and Qian (1992). The K − ɛ model is used to represent the turbulence in the carrier phase, and the kinetic theory of gases is employed for the closure of stresses due to inter‐particle collisions. We test various closures for the eddy viscosity of the disperse phase; we show the effects of increasing sediment concentration on the interaction forces between the two phases and on the stresses developed due to inter‐particle collisions. We determine the values of the Schmidt number required to approximate the experimental profiles of the volumetric concentration of sediment, suggesting that while the Schmidt number is smaller than one for dilute mixtures, it is larger than one for nondilute flows. Results indicate that nondilute models of increasing complexity are indeed necessary for flows having high solid volume fractions. Our results also suggest a more tested range of values for the threshold of sediment concentration of nondilute flows; this threshold can be located between 2 and 5%. It is observed that the virtual mass force becomes important in the simulation of nondilute flows. The eddy viscosity of the carrier phase is found to decrease with the increasing volumetric concentration in the flow.

Numerical modelling of non-equilibrium graded sediment transport in a curved open channel

The computer code FAST3D has been developed to calculate flow and sediment transport in open channels. In the code, the flow field is calculated by solving the full Reynolds-averaged Navier–Stokes equations with k–ε turbulence model; the bed-load transport is simulated with a non-equilibrium model containing an important parameter, the so-called non-equilibrium adaptation length, which characterizes the distance for sediment to adjust from a non-equilibrium state to an equilibrium state; the bed deformation is obtained from an overall mass-balance equation for sediment transport. The governing equations are solved numerically with a finite volume method on an adaptive, non-staggered grid. The former model assumed uniform bed material. In order to take into account the influence of grain-size distribution of the bed-surface on the evolution of the bed topography and consequently also on the flow field, a sediment transport module has been presently developed by the authors at the Institute of Hydraulic and Water Resources Engineering, Technische Universität München, Germany, for fractional sediment transport using a multiple layer model. This paper presents the numerical results for sediment sorting and the bed deformation in a curved alluvial channel under unsteady-flow conditions according to Yen and Lee (1995). The calculations were compared with data from laboratory measurements. Further, the sensitivity of the simulated results to the non-equilibrium adaptation length is investigated.

One‐dimensional numerical modeling of sediment transport and bed deformation in open channels

A one‐dimensional numerical model for simulating unsteady flow and sediment transport in open channels is presented and tested. The flow hydrodynamics is represented by the shallow water equations, and the bed morphodynamics is represented by the Exner equation and an additional equation describing the nonequilibrium sediment transport. Sediment size distribution is represented by the median grain diameter and the standard deviation, instead of the usual modeling with multiple particle size classes. Various methods for computing bed elevation changes at a cross section due to erosion or deposition of sediment are proposed and tested, including an innovative approach that relates the spatial pattern of erosion and deposition rates to boundary shear stress distribution, which is calculated by the Merged Perpendicular Method. An explicit finite difference scheme is employed for solving the water and sediment governing equations. The pertinence of the model is examined for two hypothetical cases. The model is then tested on one set of laboratory experiments on bed degradation under steady flow, showing excellent model data fit, and indicating that incorporating a nonequilibrium sediment transport equation into the model structure is an important element in reproducing the bed degradation process. Finally, the model is applied to simulate the morphological changes taking place in the Ha!Ha! River (Quebec) after the failure of the Ha!Ha! Dyke on July 1996. Relevant results can be obtained in terms of changes in longitudinal bed profile and cross‐sectional geometry as well as water levels, although some discrepancies are obtained between the simulated and surveyed cross‐sectional geometries, mainly because bank failure and channel widening are not modeled.

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.

Analysis of Suspended Sediment Transport in Open-Channel Flows: Kinetic-Model-Based Simulation

This paper presents a comprehensive analysis of suspended sediment transport in open channels under various flow conditions through a kinetic-model-based simulation. The kinetic model, accounting for both sediment-turbulence and sediment-sediment interactions, successfully represents experimentally observed diffusion and transport characteristics of suspended sediments with different densities and sizes. Without tuning any model coefficients, the nonmonotonic concentration distribution and the noticeable lag velocity with a negative value close to the wall are reasonably reproduced. Examination of flow conditions typical of suspension dominated rivers shows that the conventional method may overestimate or underestimate unit suspended-sediment discharge, depending on the Rouse number, sediment size, as well as shear velocity. The error may be less than 20% for dp 1.0 mm under typical flow conditions where shear velocity ranges from 1.0 to 12.5 cm∕s and flow depth ranges...