Sediment Transport Equations Research Articles

Simulation of River Bed Changes Upstream Merowe Dam

The main objective of this paper is to address long term morphological changes for Merowe Dam Reservoir located in Sudan using River Analysis System Software (HEC-RAS 5.0.3) , The trend of three different sediment transport equations (Laursen/Copeland, Yang and Ackre/White) had been represented in terms of the volumetric bed changes. The results obtained by the model had been calibrated and validated, furthermore, Sensitivity analysis was conducted. For the model, Two different boundary conditions had been used, one is the Sediment rating curve and the other is equilibrium load. Using the predictive model concept, three bed changes scenarios were simulated, assuming repeated flows, assuming wet and dry flows, Model limitations were considered and further recommendations were highlighted.

Scouring mechanism of suspended and partially-buried pipelines under steady flow

Offshore pipelines are often suspended or partially-buried during operating process. Understanding the scouring mechanism of the suspended and partially-buried pipelines is important for protecting the pipelines. The numerical models of pipelines under steady flow are established, in which Reynolds Averaged Navier-Stocks equation (RANS) with the k-ω turbulence closure, as well as the sediment transport equation, are solved with the finite volume method. After experimental verification, the models are applied to a series of parametric analysis for the suspended and partially-buried pipelines under steady flow. The effect of different variables such as the pipe diameter D , the suspension height e , the pipe shape, the embedment depth, on the scour process of the pipelines are investigated in detail based on more than 150 simulation results. For the suspended pipelines, the gap-to-diameter ratio e / D is the key parameter to predict scour depth. The pipe shape has an influence on the scour depth and the position of the scour hole. A formula to predict scour depth in terms of e/D and the relation between gap velocity and scour depth is obtained. For the partially-buried pipelines, the block height and the curvature of the pipeline is proposed as the key parameters to analyze the flow field around the pipeline. • The numerical model of pipelines under steady flow are established and verified. • Effect of different parameters on scour process of offshore pipelines are studied. • Formula to predict scour depth in terms of e / D is proposed for suspended pipelines. • Block height and curvature are key data to analyze flow of partially-buried pipelines.

Computational investigation of scour characteristics of USAF in multi-specie sand under steady current

The seabed sediment in marine is typically composed of complex mixtures of materials thereby it is of paramount importance to consider a multi-specie sand bed in scouring tests since most of the researches only take individual specie sand bed into account. In this work, a series of scouring tests were conducted computationally by using a VOF method to capture the sharp interface and finite-volume-finite-difference method to solve the RANS equation combined with sediment transport equations, with the purpose of investigating the characteristics of local scour around a novel offshore foundation, USAF, in a multi-specie (two-specie) sand seabed under steady current state. The three-dimensional scour model was established and validated against available experimental data. Furthermore, the effect of very fine sand on the scouring process in medium sand sediment bed is clarified. Meanwhile, the influence of the Froude number is also determined. The predicted results suggest that scour characteristics in the multi-specie sand seabed is significantly different from that in sole one, which depends on both amount of very fine sand and Froude number.

A Predictor–corrector scheme for simulation of two-phase granular flows over a moved bed with a variable topography

In this paper, we propose a numerical simulation of two-phase shallow granular flows through a moved bed with a variable irregular topography via a predictor corrector scheme. This method consists of predictor and corrector stages. The predictor stage contains a parameter to control the numerical diffusion that is performed by utilizing limiters and Riemann invariant theory. The corrector stage recovers the balance conservation equation. In the first part, we solve numerically the one-dimensional equation for two-phase shallow granular flows over a fixed bed with irregular topography. In the second part, we consider the model equations for the bed-load sediment transport, the governing model equations consist of two components, specifically, a geophysical flows part and interstitial fluid. The sediment part is described by the Exner equation when the velocity can be considered to be the solid velocity, fluid velocity or a mean value of both of them.

Decoupled solution of the sediment transport and 2D shallow water equations using the finite volume method

In this paper was successfully implemented a numerical solution of the sediment transport and 2D shallow water equations using the decoupled approach. Different discharge formulas to approximate the solid discharge of the sediment were used. The flow field was calculated by solving the shallow water equations and was discretized using the finite volume method; the Godunov's method along with the Roe's Riemann solver was used to approximate the numerical fluxes. The sediment transport was modeled with the Exner equation which was discretized using the Roe's scheme and the finite volume method. In addition, it was proposed an algorithm to guarantee the mass balance in the whole domain for water and sediment at all time steps. The results were compared with experimental measurements reported by other authors to validate the implemented solution.

Investigation of the overtopping-induced breach of tailings dams

Using a 400 g-ton geotechnical centrifuge, a centrifugal model test system was developed to investigate the overtopping-induced breach process of tailings dams. According to abrupt changes in the erosional characteristics and breach morphological evolution, the breach processes of tailings dams could be divided into three stages, namely, the initial, acceleration, and stable stages. The breach mechanisms mainly consisted of backward erosion during the initial stage, followed by rapid downcutting and widening accompanied by intermittent lateral expansion caused by the collapse of breach-side slopes until the rebalancing of the breach channel occurred. Furthermore, a detailed physical hydrodynamic model was used to simulate dam breaching. The Reynolds-averaged Navier–Stokes (RANS) equations combined with the renormalization group (RNG) k-ε turbulence model were adopted to calculate the complex hydrodynamic conditions. In addition, the model considered the sediment transport equations for bedload and suspended load, as well as the breach-side slope sliding. The governing equations of the model were computed using the finite volume method on a rectangular grid. The calculated breach hydrograph and dynamic breach evolution were consistent with the observations made using the centrifugal tests. This study can provide a scientific reference to estimate the failure process of tailings dams.

ASSESSMENT OF STEADY FLOW BEHAVIOUR OF KULSI RIVER USING HEC-RAS AND QGIS

Sediment transport study is important tools of Kulsi River in the context of river bank erosion, Sedimentation, and water quality management. The initiation of computer technologies has enabled engineers to resolve sediment transport equations through computer simulations. In this study, it is intended to carry out a sediment transport study in the Kulsi River reach with the help of Hydrologic Engineering Centre-River Analysis System (HEC-RAS) and Quantum Geographic information System (QGIS). From the analysis of the model, total sediment erosion and deposition were obtained at different cross sections between the study reach. Kulsi river is Southern tributary of Brahmaputra and it’s originate in Meghalaya (2538N, 9138E) and after travelling 12 km its enter Assam from the place of its origin and linked with Brahmaputra at Nagarbara in Kamrup Metro. The initial version of this sediment model will leverage the wide range of hydraulic capabilities existing in HEC-RAS to compute a series of steady flow profiles used to develop hydrodynamic parameters for sediment transport. In this model where sufficient data is not available, So QGIS and remote sensing used as tools for extraction of bed profile of Kulsi River. HEC-RAS and QGIS are the Software used in this study. This study is carried out to simulate the process of erosion and sedimentation using HEC- RAS model to assess sedimentation and erosion processes in 2.5 Km stretch of Kulsi River from upstream to downstream. The model was calibrated manually for hydraulic parameters of river flow and then sediment transport model was simulated from January 2016 to December 2016. Key Words: Steady flow, HEC-RAS 5.05, QGIS, TCX converter.

Modeling and simulation sedimentation process using finite difference method

Abstract The goal of this research is to develop a numerical model that can be used to simulate the sedimentation process under two scenarios: first, the flocculation unit is on duty, and second, the flocculation unit is out of commission. The general equation of flow and sediment transport were solved using the finite difference method, then coded using Matlab software. The result of this study was: the difference in removal efficiency between the coded model and operational model for each particle size dataset was very close, with a difference value of +3.01%, indicating that the model can be used to predict the removal efficiency of a rectangular sedimentation basin. The study also revealed that the critical particle size was 0.01 mm, which means that most particles with diameters larger than 0.01 mm settled due to physical force, while most particles with diameters smaller than 0.01 mm settled due to flocculation process. At 10 m from the inlet zone, the removal efficiency was more than 60% of the total removal rate, indicating that increasing basin length is not a cost-effective way to improve removal efficiency. The influence of the flocculation process appears at particle sizes smaller than 0.01 mm, which is a small percentage (10%) of sieve analysis test. When the percentage reaches 20%, the difference in accumulative removal efficiency rises from +3.57% to 11.1% at the AL-Muthana sedimentation unit.

Preliminary Experimental Study on Effectiveness of Aquatic Vegetation on Sediment Transport Capacity

Vegetation affects sediment transport by obstructing the flow and changing the turbulence characteristics. Common sediment transport equations are not applicable to situations with submerged vegetation. A laboratory experiment was carried out in which flow, vegetation, and sediment transport were measured in an open channel model with a 240 cm long section of 50 cm high x 50cm width with submerged vege-tation in a sand bed. Measured data from various vegetation density and height were analyzed to obtain estimates of the trapping efficiency. Results show an increment of the trapping efficiency with 86.7% and 94.2% reduction in sediment concentration compared to a case without vegetation.

Applicability of modified SWAT model (SWAT-Twn) on simulation of watershed sediment yields under different land use/cover scenarios in Taiwan.

Climate change leads to increasing intensity and frequency of extreme rainfalls, especially in Taiwan with steep slopes and rapid currents. Heavy rainfalls trigger serious erosion and landslides on hillslopes, which increase sand concentration in rivers, and thus affect the water quality of reservoirs and the ecohydrological functions of rivers. We take the Zhuoshui River basin as an example and applied the modified Soil Water Assessment Tool (SWAT) model, SWAT-Twn, to simulate sediment in the basin. In SWAT-Twn, estimation of sediment yield is carried out by integrating the Taiwan Universal Soil Loss Equation (TUSLE) and the landslide simulation. Results of daily streamflow simulation showed that the model performances were above the satisfactory level, while simulations of daily sediment loads showed that the SWAT-Twn model performed better than the official SWAT (SWAT664), in terms of PBIAS of - 46.6 to 16.0% (SWAT-Twn) and - 1.2 to - 107.0% (SWAT664). Two scenarios of land use/cover, scenario 1 with fixed land use/cover and scenario 2 with updated land use/cover in each year, were applied to simulate annual sediment in the river basin for investigating the effects of landslide area variation on sediments. Results of sediment simulation under the two scenarios showed that although updating landslide area may facilitate sediment yield simulation at the subbasin level, the sediment transport equation, Bagnold equation, does not reflect the variation in sediment loads in the watershed. With further modifications, SWAT-Twn is expected to be an effective tool for simulating the impacts of landslide on sediment loads in the watersheds with rainfall-induced landslide.

CFD modelling of local scour around Tri-USAF in sand with different arrangements under steady current

The complex offshore foundation is required to adapt to the extreme marine climate, such as tripile, tripod, pile group foundations. For this reason, it is of great importance to consider an advanced tri-USAF, analogous to tripile, since previous studies only take into account monoUSAF in which scouring tests of a USAF were performed and influences of steady currents, waves, as well as the combination of waves and currents were evaluated. In this work, a series of scouring tests were conducted computationally by using a VOF method to capture the sharp interface and finite-volume-finite-difference method to solve RANS equations combined with sediment transport equations, in order to explore the characteristics of local scour around a tri-USAF, with different arrangements, in sand seabed under steady current state. The three-dimensional scour model was established and validated against available experimental data reported in the literature and own measured data. Furthermore, parametric analysis was performed regarding the influence of spacing ratio and Froude number. The predicted results imply that flow field and scour characteristics involving a tri-USAF are more complicated than those of monoUSAF, and the impact of the neighbouring structure is interpreted differently compared with piles, as tri-USAF possesses several specific components.

The Artificial Intelligence of Things Sensing System of Real-Time Bridge Scour Monitoring for Early Warning during Floods.

Scour around bridge piers remains the leading cause of bridge failure induced in flood. Floods and torrential rains erode riverbeds and damage cross-river structures, causing bridge collapse and a severe threat to property and life. Reductions in bridge-safety capacity need to be monitored during flood periods to protect the traveling public. In the present study, a scour monitoring system designed with vibration-based arrayed sensors consisting of a combination of Internet of Things (IoT) and artificial intelligence (AI) is developed and implemented to obtain real-time scour depth measurements. These vibration-based micro-electro-mechanical systems (MEMS) sensors are packaged in a waterproof stainless steel ball within a rebar cage to resist a harsh environment in floods. The floodwater-level changes around the bridge pier are performed using real-time CCTV images by the Mask R-CNN deep learning model. The scour-depth evolution is simulated using the hydrodynamic model with the selected local scour formulas and the sediment transport equation. The laboratory and field measurement results demonstrated the success of the early warning system for monitoring the real-time bridge scour-depth evolution.

Barrier Breaching Versus Overwash Deposition: Predicting the Morphologic Impact of Storms on Coastal Barriers

AbstractWaves and water level setup during storms can create overwashing flows across barrier islands. Overwashing flows can cause erosion, barrier breaching, and inlet formation, but their sediments can also be deposited and form washover fans. These widely different outcomes remain difficult to predict. Here we suggest that a breach develops when the sediment volume transported by overwashing flows exceeds the barrier subaerial volume. We form a simple analytical theory that estimates overwashing flows from storm characteristics, barrier morphology, and dune vegetation, and which can be used to assess washover deposition and breaching likelihood. Our theory suggests that barrier width and storm surge height are two important controls on barrier breaching. We test our theory with the hydrodynamic and morphodynamic model Delft3D as well as with field observations of 21 washover fans and 6 breaches that formed during Hurricane Sandy. There is reasonable correspondence for natural but not for developed barrier coasts, where traditional sediment transport equations do not readily apply. Our analytical formulations for breach formation and overwash deposition can be used to improve long‐term barrier island models.

Regression models for sediment transport in tropical rivers.

The investigation of sediment transport in tropical rivers is essential for planning effective integrated river basin management to predict the changes in rivers. The characteristics of rivers and sediment in the tropical region are different compared to those of the rivers in Europe and the USA, where the median sediment size tends to be much more refined. The origins of the rivers are mainly tropical forests. Due to the complexity of determining sediment transport, many sediment transport equations were recommended in the literature. However, the accuracy of the prediction results remains low, particularly for the tropical rivers. The majority of the existing equations were developed using multiple non-linear regression (MNLR). Machine learning has recently been the method of choice to increase model prediction accuracy in complex hydrological problems. Compared to the conventional MNLR method, machine learning algorithms have advanced and can produce a useful prediction model. In this research, three machine learning models, namely evolutionary polynomial regression (EPR), multi-gene genetic programming (MGGP) and M5 tree model (M5P), were implemented to model sediment transport for rivers in Malaysia. The formulated variables for the prediction model were originated from the revised equations reported in the relevant literature for Malaysian rivers. Among the three machine learning models, in terms of different statistical measurement criteria, EPR gives the best prediction model, followed by MGGP and M5P. Machine learning is excellent at improving the prediction distribution of high data values but lacks accuracy compared to observations of lower data values. These results indicate that further study needs to be done to improve the machine learning model's accuracy to predict sediment transport.

Two-dimensional (2D) numerical modelling of rainfall induced overland flow, infiltration and soil erosion: comparison with laboratory rainfall-runoff simulations on a two-directional slope soil flume

Abstract This paper presents a two-dimensional (2D) numerical model of soil erosion and sediment transport resulting from rainfall induced overland flow. It is a spatial and temporal dynamic model combining physical and empirical laws and comprises: i) An overland flow module that solves the two-dimensional unsteady water flow equations on an infiltrating surface; ii) A soil infiltration module that uses a combined Horton-SCS scheme; and iii) A soil erosion and sediment transport module that solves the two-dimensional sediment transport equation, distinguishing between rill erosion, interrill erosion and sediment deposition. The performance of the model was evaluated by comparing its results with observed data from laboratory rainfall-runoff experiments on a two-directional 2.00 × 2.00 m2 soil flume set at 1% and 10% slopes in the x- and y-directions, respectively. The x-direction produced remarkably lower runoff and transported sediments than the y-direction. The numerical model significantly underestimated x-direction lower values of runoff and transported sediments. However, in the y-direction the model presented very good performance. Overall, in total terms (x- plus y-direction), the numerically simulated graphs of runoff and sediment transport were in very good agreement with corresponding experimental measurements, demonstrating the laboratory proof-of-concept of the model.

The estimation of bedload in poorly-gauged mountain rivers

Bedload transport is one major driver of gravel-bed river morphodynamics, and its quantification is capital for many environmental issues and river engineering applications, as well as for landscape evolution studies. To this point, bedload transport rates and volumes have been classically computed by means of sediment transport formulae. The most used bedload transport equations compute the bulk bedload mass based on section-averaged hydraulic parameters. However, due to the non-linear behavior of sediment transport, bedload formulae are sensitive to the input parameters. Then, some doubts arise when applying bedload equations on poorly gauged river reaches, i.e. rivers where there are no hydrological records and rating curves. In this paper, we assess the application of bedload equations in the case of poorly gauged river reaches, and we test a workflow to follow in such situations. This workflow consists of three steps: (i) Reconstructing the flow duration curve, based on gauging records from neighboring river basins; (ii) Solving the hydraulic geometry relations of the study-case river-reach, based on a flow friction equation; and finally, (iii) Computing bedload with a sediment transport equation. We tested this approach against the bedload information available in the literature for Idaho streams and we found that it could potentially approximate annual bedload volumes in ungauged reaches under certain conditions. To illustrate the potential of this workflow, we also computed bedload volumes for two ungauged river reaches from the Cantabrian mountains (NW Spain).

Equilibrium approach for modeling erosional failure of granular dams

Erosional failure of granular dams by an overtopping body of water is investigated using a depth-averaged morphodynamic model. The transport of sediment by the flow assumes the sediment flux to remain in equilibrium with the local bed shear stress. Accordingly, the shallow-water hydrodynamic equations are coupled with the Exner equation for mass conservation of the sediment. The system of equations is solved using a fully coupled well-balanced finite volume method, second-order accurate in time and space. The effect of the steep bed slope of a dam face is incorporated into both the hydrodynamics and sediment transport equations, leading to improved predictions. Comparison with results obtained from nonequilibrium sediment transport models indicates that such models perform poorly while predicting the bed evolution near the toe of an eroding dam. Observations from experimental studies demonstrate that the amount of sediment entrained by the flow is not significant, except during the initial moments of failure. This suggests that the vertical exchange of mass between the bed and the flow layer, as assumed by the nonequilibrium models, may not be completely valid during the failure. The equilibrium model results, reproducing the key flow features of the overtopping failure process, are validated by experimental measurements. The study provides fresh insights into the sediment transport processes associated with the erosion of a granular dam by overtopping, establishes the appropriateness of the equilibrium approach for its numerical modeling, and proposes a well-balanced second-order accurate solution technique for solving the resulting coupled equations of flow and sediment transport.

A transient backward erosion piping model based on laminar flow transport equations

Backward erosion piping is an internal erosion process, which compromises the stability of water retaining structures such as dams and levees. In this paper, we propose a numerical solution that combines a 2D Darcy groundwater solution with Exner’s 1D sediment transport mass conservation equation. As an estimate of sediment transport, we tested four different empirical transport equations for laminar flow. The model performance was evaluated based on the results of the real-scale IJkdijk experiment. Through this, we were able to demonstrate the applicability of existing sediment transport equations to the description of particle motion during piping erosion. The proposed transient piping model not only predicts the pipe progression in time, it also allows for an identification of pore pressure transitions due to the erosion process. A major conclusion of the study is that from the four different modeling approaches for laminar flow, it is recommended to follow the approach of Yalin et al. regarding the simulation of backward erosion piping for dike configurations similar to those of the IJkdijk experiment.

Unsteady two-dimensional suspended sediment transport in open channel flow subject to deposition and re-entrainment

The present paper aims to investigate the transport of suspended sediment in an open channel turbulent flow. The method of moments is used to solve the unsteady two-dimensional suspended sediment transport equation where the moment equations are evaluated using a standard finite difference implicit scheme. The distribution of concentration is obtained using the Hermite polynomial representation of central moments. The solution exists for arbitrary form of eddy diffusivity and in contrast to other existing works, the present model considers the most general boundary condition at the channel bed which may be absorbing, reflecting or both. According to such nature of channel bed, the transport process has been distinguished into two phases, viz., suspension phase and deposition phase together with re-entrainment of particles. The model in its present form can be well applicable for sediment transportation in environmental processes.

One-Line Modeling of Mega-Nourishment Evolution

Whitley, A.E.; Figlus, J.; Valsamidis, A., and Reeve, D.E., 2021. One-line modeling of mega-nourishment evolution. Journal of Coastal Research, 37(6), 1224–1234. Coconut Creek (Florida), ISSN 0749-0208. As many coastal areas of the world suffer from chronic erosion, innovative solutions beyond traditional local nourishment must be explored. One such solution is the implementation of mega-nourishments (MNs), where a large sediment volume is deposited in a single location and redistributed via natural processes, thereby feeding adjacent beaches. Robust numerical modeling methods are needed to evaluate potential MN sites at coastal locations around the world. Two one-line numerical modeling approaches of MN evolution are presented using the Coastline Evolution Model (CEM) and GENESIS + Cascade (GenCade). Both models are parameterized for the Sand Motor (SM) that has been constructed on the Dutch coast to explore the feasibility of the MN approach. Here, a variety of K coefficients in the Coastal Engineering Research Center (CERC) sediment transport equation are tested since traditionally calibrated and used values may not apply for MN features. Both models are found capable of reproducing the shoreline morphological patterns observed at the SM over the first 3.5 years. GenCade shows a low difference between measured and modeled coastline position overall, showing accurate predictions of absolute shoreline position. CEM is able to capture feature tip migration due to its wave shadowing algorithm. The best results from both models can be obtained for higher K values than those commonly suggested in the literature. Given the size of a mega-nourishment relative to traditional nourishments, it is likely that a higher-than-usual K value may be a better fit when simulating mega-nourishments in a one-line model.