Flow Sediment Transport Research Articles

Modified stochastic diffusion particle-tracking model (MSDPTM) incorporating energy cascade theory and eddy intermittency for suspended sediment transport in open channel flow.

This study presents a modified stochastic diffusion particle tracking model (MSDPTM) that incorporates energy cascade theory to more accurately simulate suspended sediment transport. The impact of turbulent eddies on sediment particles is an intermittent process, which is also considered in this study. The study examines the time correlation between eddies using eddy turnover time and finds that closer-scale eddies exhibit higher correlations than those farther apart. The statistical properties of particle movement, such as the ensemble mean and variance of particle trajectories, have been calculated and compared with the stochastic diffusion particle tracking model (SDPTM) results. Notably, MSDPTM with intermittency demonstrates a significantly larger ensemble mean of particle trajectories in the streamwise direction than other particle tracking models. The proposed model is validated through comparison with available data, showing its enhanced performance. The results of the simulation indicate that MSDPTM outperforms SDPTM, especially when the intermittency effect of eddies is considered.

Modelling of Granular Sediment Transport in Steady Flow over a Mobile Sloped Bed

This paper introduces a three-layer system, proposing a comprehensive model of granular mixture transport over a mobile sloped bed in a steady flow. This system, consisting of the bottom, contact, and upper zones, provides complete, continuous sediment velocity and concentration vertical profiles. The aim of this study is to develop and experimentally verify this model for sediment transport over a bottom locally sloping in line with or opposite the direction of sediment flow. The model considers gravity’s effect on sediment transport in the bottom (dense) layer when the component of gravity parallel to the bottom acts together with shear stresses associated with water flow. This is a crucial factor often overlooked in previous studies. This effect causes an increase in velocity in the mobile sublayer of the dense layer and significantly affects the vertical distributions of velocity and concentration above this layer. The proposed shear variation due to the interaction between fractions and an intensive sediment mixing and sorting process over a mobile sloped bed adds to the novelty of our approach. The data sets used for the model’s validation cover various conditions, including slopes, grain diameters, densities, and grain mobility conditions, from incipient motion to a fully mobilized bed. This extensive validation process instils confidence in the theoretical description and its applicability to real-world scenarios in the design of hydraulic infrastructure, such as dams, barrages, bridges, and irrigation, and flood control systems.

CENTRAL PART OF NATURAL COASTAL SYSTEM TENDRA–JARYLGACH, THE BLACK SEA COAST

Problems of Research and Purpose. In the theory of general geomorphology, the section on coastal-marine processes at the genetic contact-zone between Land and Ocean assigns importance to the study of relief associations. One such complex of geomorphologic association on maritime coastlines is the winged-forelands. They consist of interconnected complex capes, active cliffs, typical benches, sandy beaches, and aeolian forms. Wind, sea wave, geobotanical, zoogeographical, geochemical, and other factors contribute to their development. Their morphology and dynamics are determined by lithodynamic interaction under the influence of a unified alongshore sediment flow transport. We conducted a study of one such winged-foreland on the non-tidal Black Sea coast, a classic foreland in "the Tendra–Jarylgach shore system". Practical issues were discussed, and identified development patterns allow for rational natural resource usage, emphasizing the relevance of the topic. Purpose of our scientific work is: Based on the obtained materials, identified patterns, and analyses of the development of the classic winged-foreland "the Tendra–Jarylgach" to determine optimal natural resource usage and ways to preserve the natural resources of the coastal environment. Data and Methods: During our research, we applied route and stationary methods, above-water and underwater methods, field descriptive and instrumental methods, cartographic techniques, geographical comparisons, aerial and space remote sensing, and analytical methods. Instruments for topographic and geodetic work, underwater profiling of the nearshore slope, lithological sampling, and laboratory data processing were used. Profiling of accumulative and abrasional forms of coastal relief, coastal intersections in different parts of the winged foreland, and specific descriptions of photo-reflectance were obtained. Special attention was paid to the efficiency of coastal protective structures on the abrasional front. Basical Results and Comments: The presented materials and their brief discussion revealed that the natural system of the winged-foreland "Tendra–Jarylgach" is a complex coastal-marine system of the physical-geographical subregion level with significant dynamics. All secondary elementary systems within it are closely connected by wave energy and sediment material flows in a unified sediment balance. Therefore, its conservation and the usage of its natural resources require a comprehensive systemic approach based on general-geographical principles. Within "the Tendra–Jarylgach" winged foreland, optimal natural resource utilization is achievable based on the general principles of geography and the fundamentals of coastal studies as an interdisciplinary geographical science. Key components of optimization include: a) adherence to rules and norms regarding anthropogenic pressure on the studied natural system; b) organization of the natural system to maintain high air and sea water quality; c) resistance to abrasive activities of the sea through the implementation of effective, operational engineering-geographical measures; d) preservation of sediment balance, as the creation of sediment mass is an exclusively long-term process, while disturbance is an instantaneous process. The leading source of sediment within the studied coastal-marine system is the abrasional input from coastal cliffs and benches. A minor contribution comes as a carbonate material. The coastal zone here experiences a significant deficit of coastal sediments, actively supporting further shoreline erosion. The development of the natural system of the researched winged-foreland is driven by the active action of the unified Tendra–Jarylgach alongshore sediment transport, involving the contribution of shell-detritus. This significantly distinguishes this type of foreland from others where two branches of sediment transport flows in opposite directions from the middle of the frontal part. During particularly strong storms, up to 5% of repetitions on accumulative forms typically result in new inlets and the expansion of existing old breaches. This undermines the stability of both spits, and the entire winged foreland in total. Such negative phenomena are exacerbated by disturbances to the sediment balance, especially artificial removals of beach sands for construction purposes.

Characterization of Stream, Hyperconcentrated and Debris Flows from Seismic Signals: Insights into Sediment Transport Mechanisms and Flow Dynamics

AbstractSediments in steep channels can be mobilized to form stream flows, hyperconcentrated flows and debris flows, which can cause damage to downstream communities. However, the understanding of the sediment‐transport mechanisms that control these processes remains incomplete due to the lack of effective monitoring methods. In this study, we utilize seismic data captured during these sediment‐laden flows through field experiments and in situ monitoring to offer insights into flow mechanics and sediment transport mechanisms. Results show that sediment transport in stream flows and hyperconcentrated flows is primarily supported by viscous shear and turbulent stresses, whereas grain collisional stresses play a significant role in debris‐flow dynamics. By characterizing impact rates, basal impulses and flow discharge, seismic monitoring can reveal the internal flow dynamics and bulk flow characteristics as well as the characteristics of sediment transport. Increasing solid concentrations can elicit positive nonlinearities in the frequency‐based scaling relationships between seismic power and hydrographs, indicating transitions in the seismic signal from turbulence‐bedload‐dominated to bedload‐dominated, and grain collisional‐dominated regimes. By introducing the ratio of the real shear stress to the critical shear stress, we refined the phase space for sediment stability. Combining this criterion with the absolute seismic power enables us to establish ground‐motion thresholds for distinguishing different flow types. Our results highlight opportunities to use seismic data for the quantitative inversion of these fluvial processes and debris flows as well as early warning strategies.

Effect of equilibrium and non-equilibrium sediment transport flows on the shear velocity in an open channel.

Equilibrium and non-equilibrium sediment transport flow in natural rivers and artificial channels can result in degradation or aggradation of the river bed, which will affect many hydraulic parameters, one of which is shear velocity. This study evaluates the influence of sediment transport on shear velocity in open channels. In this study, laboratory experiments were carried out using a sediment-recirculating flume, and measurements of the velocity and Reynolds shear stress distributions were measured using a Sontek-acoustic Doppler velocimeter (ADV). This experimental study measured 120 velocity distributions, and Reynolds stress profiles, consisting of 12 different sets of measurements involving flow with sediment transport and movable sand bed. The results showed an average shear velocity, u*, difference between sediment feeding and without sediment feeding by 9.41%. For the integration constant Br value, the average difference between sediment feeding and without sediment feeding was 5.58%.

Numerical Modeling of Sediment Transport and Bed Evolution in Nonuniform Open-Channel Flows

Abstract The shallow-water and multilayer hydrostatic models have been commonly used to analyze the problems of a sediment-laden, plane open-channel flow. The models are adequate to solve a quasi-hydrostatic flow problem, but their accuracy deteriorates as the e ects of the vertical acceleration gain in significance. Herein, a higher-order numerical model for treating the problems of unsteady, plane open-channel flow over a movable bed is proposed. In this model, the flow hydrodynamics is governed by the depth-averaged Boussinesq-type equations, and the bed morphodynamics is determined by an Exner-type equation and additional equations describing the non-equilibrium transports of suspended load and bed load. A hybrid finite-volume and finite-di erence scheme was used to discretize and solve the governing equations, yielding solutions that are in satisfactory agreement with the experimental data. Overall, the results of the proposed model for the temporal free-surface profile and bed evolution were fairly adequate. For the two particular cases considered, however, the quality of its results was moderately a ected by the e ects of the three-dimensional characteristics of the dam-break flow and the sliding of the dike body due to sub-surface flow. The results of this investigation highlight the importance of including a higher-order Boussinesq-type correction for refining sediment transport computations.

Sediment Transport Beneath a Simulated Partial Ice Cover: Effects of Asymmetric Border Ice

With the onset of winter in cold regions, border ice begins to form, impacting sediment transport rate and distribution. Understanding the effect of ice cover is crucial in regions with prolonged sub-freezing temperatures, as water bodies remain frozen for a considerable part of the year. While the existing literature includes many studies on sediment transport in open channel flow and several studies on completely ice-covered flow, there is limited research on sediment transport in partially ice-covered channels. Addressing this gap, the current study conducted laboratory experiments in a rectangular flume at the Hydraulics Research and Testing Facility, University of Manitoba, Canada. The investigation focused on examining the influence of asymmetric border ice, varying coverage ratios in asymmetric partially ice-covered flow, and changing flow strengths on bedload transport rate and distribution. Additionally, a comparison was made with symmetric partially ice-covered flow conditions. The findings indicate that the presence of asymmetric border ice indeed affected the bedload transport distribution within the channel, causing non-uniform bedload transport distribution across the channel width, with peak values concentrated in the center of the open flow section. Increased asymmetry in border ice leads to greater asymmetry in bedload transport rate distribution. Despite these pronounced differences in bedload transport rate across the channel width, the cross-section-averaged bedload transport rate could still be estimated utilizing the conventional equations, used for open channel flow, fully ice-covered flow, and symmetric partially ice-covered flow, with the effect of ice cover accounted for by incorporating an additional boundary in the calculation of the wetted perimeter, leading to adjustments in the flow strength.

Numerical Simulation of Sediment Transport in Unsteady Open Channel Flow

This paper presented a two-dimensional, well-balanced hydrodynamic and sediment transport model based on the solutions of variable-density shallow-water equations (VDSWEs) and the Exner equation for bed change for simulating sediment transport in unsteady flows. Those equations are solved in a coupled way by the first-order Godunov-type finite volume method. The Harten–Lax–van Leer–Contact (HLLC) Riemann solver is extended to find the local Riemann fluxes to maintain the exact balance between the momentum term and the bed slope term. A well-balanced scheme is superior to an unbalanced scheme to minimize numerical dispersion as demonstrated by the synthetic standing contact-discontinuity test case. Following this, the model is employed to simulate two laboratory experiments and a field case, the 1996 Lake Ha! Ha! flood event in Canada. The results of water surface elevations and bed surface profiles agree well with the measurements. The accuracy and robustness of the numerical schemes make the model a good candidate for practical engineering applications.

Experimental investigation of sediment transport in partially ice-covered channels

It is important to understand the effects of ice cover on sediment transport in cold climates, where sub-freezing temperatures affect water bodies for a significant part of the year. The literature contains many studies on sediment transport in open channel flow, and several studies on sediment transport in completely ice-covered flow. There has been little or no research on sediment transport in partially ice-covered channels. In the current study, laboratory experiments were done in a rectangular flume to quantify the impact of border ice presence on the sediment transport rate. The effects of ice cover extent and changing flow strengths on sediment transport distribution also were investigated, and the results were compared to those for fully ice-covered and open channel flow. The ice coverage ratios considered were 0 (representing the open water condition), 0.25, 0.50, 0.67, and 1 (representing fully ice-covered flow). The partial ice cover was found to impact the sediment transport distribution within the channel. The effect of ice coverage extent on sediment transport distribution was more significant at lower flow strengths and became negligible at higher flow strengths. The conventional equations for sediment transport in open channel flow and fully ice-covered flow that relate the dimensionless bedload transport rate to the flow strength were found to be applicable to estimate the total cross-section-averaged bedload transport for partially ice-covered flow when modified appropriately. Empirical coefficients for these equations were determined using the experimental data.

Sediment transport capacity equation for soils from the Loess Plateau and northeast China

Sediment transport capacity (Tc) is a relevant component in physical-process-based soil erosion models. At present, the sediment transport capacity prediction model for soils with a low median grain diameter is not fully understood. In this study, the Tc values of three different soils (median grain diameter d50 = 0.015, 0.040, and 0.095 mm) were investigated by conducting indoor experiments at unit flow discharges of 0.19 – 1.89 × 10-3 m2·s−1 and slopes of 0.07–0.21. In addition, data describing the overland flow sediment transport capacity of black soil (d50 = 0.01 mm) were obtained from Yu et al. (2018). First, the performance of seven shear stress, unit stream power, stream power, and mean flow velocity concept-based Tc equations were evaluated based on the measurements. The results confirmed that none of the existing formulas performed well over the entire experimental range. Tc equations derived using soils with a large particle size generally underestimate the Tc of soils containing small particles. The Zhang equation, when calibrated based on the data in this study, can predict overland flow Tc with a PoP of 66 % (PoP refers to the percentage of predictions in which the discrepancy ratio falls between 0.5 and 2.0, whilst the discrepancy ratio is the ratio of the predicted and measured Tc). Based on the general flow parameter concept, a more accurate Tc equation was developed for the four types of soils, which was characterized by a PoP of 83 %. When these equations are beyond the scope of their development conditions, they should be verified further.

Erosion depth and concentration profile formulae for graded sediment transport in asymmetric oscillatory sheet flow

The transport of graded sediments is much more complex and universal compared with that of uniform sediments. This paper proposes formulae of erosion depth and concentration profile for graded sediments in asymmetric oscillatory sheet flow. The erosion depth is obtained by taking the summation of each size fraction whilst considering the phase residual, phase shift and acceleration modification. The erosion depth includes a hiding-exposure factor of exposure height and a phase shift correction of gradation, which represent the selective transport (promotion or inhibition) of graded sediments. The sediment concentration for each size fraction is proposed using the idealised exponential or power function, which is based on erosion depth considering mass conservation. The upper sheet flow boundary and sheet flow layer thickness are further identified from the erosion depth and concentration profile. Experimental data for validation are recalculated by an improved method that considers mass conservation and actual stationary bed. The proposed formulae demonstrate a better performance in predicting the erosion depth and concentration profile of graded sediments compared with previous uniform and graded sediment formulae. The proposed formulae are able to identify the selective transport and grade recombination on mobile sediment bed. The hiding-exposure effect and phase lag discrepancy for different size fractions are also discussed.

A multi-dimensional two-phase mixture model for intense sediment transport in sheet flow and around pipeline

A two-phase mixture model is developed to simulate intense sediment transport covering the bed-load layer and suspended load layer. The proposed model maintains high accuracy as an Eulerian two-phase model but requires low computational cost. The proposed model applies an analytical formula for relative velocity between phases. The dense granular flow rheology is employed to close particle stress economically. The closure of Reynolds stress considers turbulence damping and small-scale fluctuation of fluid–particle interaction and particle collision. A damping function is adopted in eddy viscosity for extra turbulence damping from inter-particle interaction. The optimal exponent of the damping function refers to sediment shape and size. The sediment diffusion includes turbulence diffusion and shear-induced self-diffusion originating from dense sediment. The proposed model is validated by several sets of sheet flow cases (Shields number Θ = 0.44–2.20 and particle Reynolds number Res = 1.6–603.0) and shows a wide applicable range and good accuracy. The small-scale fluctuation and shear-induced self-diffusion improve the computation in the lower sheet flow layer where volumetric sediment concentration is larger than 0.2. Furthermore, the proposed model shows reasonable applicability on the multi-dimensional pipeline scour development. The scour profiles are well predicted and the Brier Skill Score = 0.809. However, the proposed model does not perform the wake characteristic around the pipeline sufficiently, and slight scour difference exists between the simulation and experiment.

Developing a Lagrangian sediment transport model for open channel flows

A three-dimensional stochastic Lagrangian particle tracking sediment transport model is developed to solve the discrete advection–dispersion equation using a combination of empirical dispersion equations. The performance of three widely-used longitudinal dispersion coefficient equations was examined to select one of them as the primary dispersion equation term in the developed model. Also, a conditional empirical equation was used to consider the effect of vertical dispersion term in top layers near the water surface. The performance of particle tracking model (PTM) to calculate the sediment concentration was evaluated for various sediment classes (very fine sand, fine sand, and medium sand) using available laboratory dataset. Multiple statistical measures were calculated using the Taylor diagram for each dispersion equation. Based on the result, the developed particle tracking model estimated the suspended sediment concentration in a rectangular open channel with a correlation coefficient (R) of 0.96, standard deviation (STD) of 0.262, and root mean square deviation (RMSD) of 0.06 for three different sediment classes proving the acceptable accuracy of the developed model for different range of sediment gradations. In addition, the accuracy of PTM was compared to recently developed models. Comparison between the particle tracking model and the analytical solution of the advection–dispersion equation showed that the developed model predicted the maximum concentration of suspended sediment 6% and 9.4% lower than the analytical solution result for 30 and 50 s simulation time in the straight channel, respectively. However, there was a good agreement between the longitudinal and transverse sediment concentration distribution from the model and the analytical solution approach. The result of the sensitivity analysis and validation process showed that the model could be used to simulate sediment transport in open channel flows.

PARAMETERS OF SEDIMENTS TRANSPORT IN RIVERS WITH A SIDE TYPE OF THE CHANNEL PROCESS

At present, in practice, to model channel reformations in rivers with a deformable bottom, a large number of different formulas are used to calculate the flow of bottom sediments. However, the reliability of channel forecasts performed using the apparatus of mathematical modeling, in most cases, still remains quite low. The quality of channel forecasts performed when designing engineering measures to ensure navigation on rivers is determined, on the one hand, by the correct assessment of the physical nature of sediment transport in natural channel flows, and, on the other hand, by the quality of the applied numerical models. This work is devoted to the verification of the sediment transport model based on studies in hydraulic flumes, in which microforms and mesoforms of a river channel with a secondary type of channel process were simultaneously reproduced. Such problems have not been considered yet. The previous experiments were carried out with a uniform steady-state mode of water movement at one structural level of bottom sediment movement - with the movement of bottom sediments in the form of microforms (dunes) - i. e. on a flat day. The results obtained in the course of the research make it possible to obtain new data, using which it seems possible to improve the quality of modeling of sediment transport in natural channel flows. This line of research, based on the use of the methodology for calculating the discharge of channel sediments using the parameters of dunes, can objectively lead to an increase in the reliability of forecasts of channel reformations when keeping navigation on free and regulated rivers with a moving bottom.

A multilayered shallow water model for sediment transport in flows over heterogeneous erodible beds

A multilayered shallow water model for sediment transport in flows over heterogeneous erodible beds

A bedload transport in shallow water model applied for sediment transport in open channel flows

This paper presents the numerical approximation of bedload sediment transport due to shallow layer flows. The hydrodynamical component is modelled by a 2D shallow water system and the morphodynamical component by a solid transport discharge formula that depends on the hydrodynamical variables. The coupled system can be written as a non-conservative hyperbolic system. To discretize it, first we consider a Non-Homogeneous Riemann Solver scheme as well as a variant based on the use of flux limiters. In order to develop second-order scheme, we use a MUSCL method incorporating slope limiters in the spatial approximation and a two-step Runge-Kutta method for time integration. The comparison between results based on the proposed scheme and analytical results shows good agreement..

A splitting method for the numerical simulation of free surface flows with sediment deposition and resuspension

AbstractWe present a numerical model for the simulation of 3D sediment transport in a Newtonian flow with free surfaces. The Navier–Stokes equations are coupled with the transport, deposition, and resuspension of the particle concentrations, and a volume‐of‐fluid approach to track the free surface between water and air. The numerical method relies on operator splitting to decouple advection and diffusion phenomena, and a two‐grid method. An appropriate combination of characteristics, finite volumes, and finite elements methods is advocated. The numerical model is validated through comparisons with numerical experiments, sediment flushing, shear flow erosion, and the formation of dunes.

Dynamics of suspended sediment transport: A Direct Numerical Simulation study

The dynamics of suspended sediment transport in horizontal open channel flow is analysed using point-particle one-way coupling Direct Numerical Simulations (DNS), with a virtual wall as a simple particle resuspension model. In sediment transport, the bed-load is dominated by the inter-particle interactions, but the suspended sediments are transported essentially in a one-way coupling situation. The validity of one-way coupling DNS with point-particle approach for the transport of suspended sediment is analysed, by comparing the simulations with existing well-designed experiments performed under very similar conditions. The range of the relevant non-dimensional parameters of the simulations is roughly the same as in actual sediment transport, except for the flow Reynolds number. Good agreement is observed between the simulations and the experiments; furthermore, the simulation results of the motion of the suspended sediment are insensitive to the position of the virtual wall, provided this wall is placed in a region where the fluid velocity fluctuation in the wall-normal direction is comparable to the particle settling velocity. Using the simulation results, the interplay between the different fluid–particle interaction forces is analysed, with and without gravity. In the absence of gravity, the dynamics is dominated by the balance between the stress-gradient force and the turbophoretic effects; as the particle-to-fluid density ratio for the sediment particles is on the order of one, the situation is quite different when compared to the dynamics with a density ratio on the order of 1000. When gravity is included, the dynamics is dominated by the interplay between the drag and gravitational forces, and they balance each other. Both with and without gravity, the lift and added-mass forces have only secondary effects and do not play an important role.

A random displacement model of sediment transport in ice-covered alluvial channel flows.

There is a need for developing efficient models to simulate the sediment transport phenomenon in ice-covered alluvial channel flows, which is essential in enriching the theory of riverbed evolution. This study establishes a random displacement model parameterized with the time-averaged streamwise velocity U(z), the sediment settling velocity ωs(z), and the turbulent diffusion coefficient Dz(z) to calculate the suspended sediment concentration and the longitudinal dispersion coefficient for ice-covered alluvial channels. The proposed model is first validated to determine if it could be used to predict the sediment concentration profiles by comparing to limited experiments published in the literature. Results show that the simulations agree well with the measurements except for the underestimated concentration near the ice cover boundary. Once validated, the random displacement model is applied to explore the variation law of the suspended sediment concentration and the longitudinal dispersion with different sediment particle release modes. The sediment concentration and the stable value of the longitudinal dispersion coefficient for a given flow condition in the dynamic equilibrium state are not affected by the change of the particle release mode. The Fickian time required for the longitudinal dispersion coefficient converging to a constant, however, has a close relationship with the particle release mode and increases as the water depth increases.

Modeling of sediment transport in rapidly-varying flow for coastal morphological changes caused by tsunamis

Tsunamis can cause significant coastal erosion and harbor sedimentation that exacerbate the concomitant flood hazards and hamper recovery efforts. Coupling of the non-hydrostatic model NEOWAVE and the sediment transport model STM provides a tool to understand and predict these morphological changes. The non-hydrostatic model can describe flow fields associated with tsunami generation, wave dispersion as well as shock-related and separation-driven coastal processes. The sediment transport module includes non-equilibrium states under rapidly-varying flows with a variable exchange rate between bed and suspended loads. A previous flume experiment of solitary wave runup on a sandy beach provides measurements for a systematic evaluation of sediment transport driven by shock-related processes. The extensive impacts at Rikuzentakata, Iwate, Japan and Crescent City Harbor, California, USA from the 2011 Tohoku tsunami provide pertinent case studies for model benchmarking. We utilize a self-consistent fault-slip model to define the tsunami source mechanism and field survey data to determine the characteristic grain sizes and morphological changes. The near-field modeling at Rikuzentakata gives reasonable fits with observed large-scale erosion and sedimentation associated with transition of the incoming wave into a surge and formation of a hydraulic jump in the receding flow. The non-hydrostatic module becomes instrumental in resolving tsunami waves at the far-field shore of Crescent City. The results show good agreement with local tide-gauge records as well as observed scour around coastal structures and deposition in basins resulting from separation-driven processes. While the erosion patterns in the laboratory and field cases can be explained by suspended sediment transport in the receding flow, bed load transport can be a dominant mechanism in sediment laden flows and scour around coastal structures.