Description Of Sediment Transport Research Articles

Mapping Microplastic Movement: A Phase Diagram to Predict Nonbuoyant Microplastic Modes of Transport at the Particle Scale.

Microplastics pose numerous threats to aquatic environments, yet understanding their transport mechanisms remains limited. Drawing from natural sediment research provides valuable insights to address this knowledge gap. One key dimensionless number used to describe sediment transport is the transport stage, referring to the ratio between the flow shear velocity and the particle settling velocity. However, variations in physical properties, such as shape and density, raise concerns about the applicability of existing sediment transport theories to microplastics. To address this challenge, we employed a physical modeling approach, examining 24 different nonbuoyant microplastic particles in a turbulent open channel flow. Utilizing 3D particle tracking, a total of 720 trajectories were recorded and analyzed. Microplastic particles exhibited transport modes akin to natural sediments, including rolling/sliding, saltation, and suspension. The transport stage strongly correlated with these modes, as well as with the mean forward velocity and mean position in the water column. Notably, particle shape emerged as a critical factor influencing transport dynamics. Due to their lower settling velocity, fibers tended to stay closer to the water surface with lower forward velocities compared to spheres. Based on the laboratory results, a new phase diagram for microplastics is introduced analogous to an existing diagram for sediments.

РАЗРАБОТКА ФИЗИКО-МАТЕМАТИЧЕСКОЙ МОДЕЛИ РАЗРУШЕНИЯ ПЛОТИН СМЕШАННОГО ТИПА

When the body of dams of various types is destroyed, the problems of interaction of water flows with soil from local materials and with the concrete base of the dam, as well as the development of filtration processes in the body of the dam, become relevant. This model allows us to describe both the mechanism of failure of mixed-type dams and the erosion of soil in the coastal zone, for example, formed as a result of a breakthrough wave, which leads to catastrophic consequences. To obtain practical results, there is a need to simplify the processes being studied. The main problem in problems of soil erosion by turbulent water flow is an adequate description of sediment transport. Typically, for these purposes, semi-empirical formulas are used, obtained for various conditions (extremely rarely specified) and giving very different results. In this work, to describe the processes of soil erosion, the theory of the bottom layer is used, which makes it possible to derive a formula for sediment consumption theoretically. The proposed model combines approaches developed in well-known models of continuum theory and hydraulics.

A sediment transport theory based on distortion-free-boundary nonhomogeneous fluid flows

Over the last 50 years several sediment transport models in coastal environments based on Shallow Water(SW) type models have been developed in the literature. The water flow over an abrupt moving topography quickly spatially variable becomes accelerated and strongly varied arising the turbulence (distortion). The acceleration and strong variation of the flow facilitate the transport of a large quantity of sediments present at the bottom while modifying it. The mathematical models based on SW type models widely used to describe the sediment transport phenomena do not account the distortion effects. Indeed, it is well-known that the SW models are derived from first order approximation of long wave theory. The acceleration and strong variation of the water flow near the bottom is due to the distortion of the horizontal velocity profile along the vertical direction. One can regard distortion as a combination of strain and rotation. The effect of the rotational component is to weaken the effect of the strain somewhat. In this work, we put in place a king theory of sediment transport derived from the second order approximation of long wave theory that can describe sediment transport processes in distortion-free-boundary nonhomogeneous fluid flows. The derived model accounts the distortion (fluctuation with great correlation lengths) that creates the turbulence. Moreover, the model differentiates the fluid velocity from sediment velocity (phase-lag) near the sediment bed. The proposed theory significantly reduces the modeling errors observed in several sediment transport models based on nonhomogeneous shallow water equations and has a great potential to increase the predictive power of sediment transport models in rivers, lakes, coastal flows, ocean basins and so on. The proposed theory improves several existing sediment transport theories recently developed in the literature and can be apply with some degree confidence.

Theoretical analysis of the laminar boundary layer beneath forward-leaning waves

Wave-induced sediment transport is an important issue in coastal engineering. It is of fundamental significance to manifest the boundary layer behavior of nonlinear waves to accurately describe sediment transport in coastal areas, where wave forms are typically cnoidal or forward leaning rather than sinusoidal or symmetrical. In the present work, a novel expression of the near bed orbital velocity beneath forward-leaning waves is worked out. It is a series in which the coefficients are invariable for arbitrarily forward-leaning waves and just depend on the order of expansion. Based on this new expression, a theoretical solution of the laminar boundary layer beneath forward-leaning waves is derived by solving the governing equation via the method of variable separation. With this theoretical solution, it is convenient to acquire the velocity and shear stress (especially at the bottom) of the boundary layer beneath forward-leaning waves, which are different from those beneath sinusoidal waves as the degree of forward leaning increases. The phase lag between the bottom shear stress and the free-stream velocity is also analyzed, as well as the boundary layer thickness. In addition, the applicability of the present theory is discussed by comparing theoretical results with numerical results of different flow regimes.

Spatiotemporal Variation in Total Sediment Load Concentration and Related Factors of Shoreline Waters Based on Disorder Power Index

Entropy is a property of a system which measures the uncertainty or disorder within the system. In hydraulics, uncertainties occur in flow variables, such as velocity, sediment concentration, wave. Using entropy, it is possible to establish connections between deterministic and probabilistic domains. To describe sediment transport distributional/autocorrelation properties, including scaling behavior both in state and in time, the well-founded physical and mathematical entropy theory is generally used wherein the spatiotemporal disorder power index (STDPI) is considered to have the maximum uncertainty. Effort has been made in this research to propose a novel entropy method capable of accurately calculating the total sediment load concentration (TSLC) in the shoreline region. Accordingly, STDPI and entropy method have been suggested for finding the TSLC to analyze the spatiotemporal patterns/reports based on a shoreline zone case study because STDPI is quite suitable for marine and hydrological ecosystem components analyses. The method makes use of the monthly data of six shoreline sections in Makran Ocean region in the time period between 1970 and 2015 and investigates the spatiotemporal patterns of the wave height and TLSC variables both of which depend on time and play important parts in terrestrial hydrological studies. These variables usually show meaningful spatiotemporal variability, but explanation of their combined performance is not an easy task. As the results show, STDPI can simulate TSLC and wave when concentration, flow conditions, and granulometry vary.

Coastal Processes and Longshore Sediment Transport along Zemmouri Bay, Central East Coast of Algeria

Abstract The coastline of Zemmouri Bay on the northeast coast of Algeria with about 50 km of shoreline has been eroding since 1970. Changes of the sandy shoreline are continuous and occur at diverse spatial and temporal scales. This erosion is a major crisis and it potentially impacts the coastal population and natural environment. In order to understand and predict these morphological changes, an accurate description of sediment transport by waves and currents and shoreline change is important. This paper presents a comprehensive study of wave refraction, current-driven sediment transport and shoreline change. Results show that the study area exhibits a great variety of shoreline evolution trends, with erosion prevailing in the eastern and central sectors and stability or even accretion in the Western area.

Einstein conjecture and resting-time statistics in the bed-load transport of monodispersed particles

Sediment transport in rivers consists, at moderate discharge stage, of individual grains that undergo a series of step movements and rest periods (bed-load). Following a large number of grain trajectories in time and space is difficult and the results are affected by bias due to censorship of the time-spatial window. Therefore, the data sets available for the description of the statistics of resting-times, travel-time and lengths of the steps, are still insufficient. In this paper, an innovative experimental methodology has been designed and applied to get data representing the evolution of a bed surface and to support a robust statistical analysis of sediment transport. The methodology is based on image sequences taken of a flat bed made of well-sorted (mono-dispersed) particles. The acquired data are interpreted analytically through equations that describe the effects of grain entrainment and deposition. We show that grains’ displacement have a mean value independent of bed-load rate under low to moderate transport intensity for a given sediment type and bed-slope. Hence, we provide a strong validation of the seminal conjecture of Einstein in his theoretical statistical description of sediment transport. Finally, we describe the probability density functions of the resting-time for a few values of the sediment discharge.

Temporal and Spatial Variability of Sediment Transport in a Mountain River: A Preliminary Investigation of the Caldone River, Italy

Sediment transport is a key evolution process of rivers and water basins. This process can pose flood hazards to nearby areas. The Eulerian and Lagrangian methods are usually employed to describe sediment transport in mountain rivers. The application of different methods was proposed by scientists to analyze specific aspects of solid transport, however a complete understanding still alludes us. After a brief review of the most common methods, the coupling of three different methods is proposed and tested in order to study sediment dynamics, and its spatial and temporal variability, in mountain rivers. Tracers, painted bed patches, and digital elevation model (DEM) comparisons are used to characterize sediment transport at both a micro-scale short-term and a macro-scale long-term level on a test reach on Caldone River, Italy. Information about travel distance, critical diameters, active width, and morphological evolution was sought. We focused on how water discharge is changing the relationships between different measurement techniques. High discharge events force the channel to behave in a unique way, while low discharge events generate more intrinsic variability. Only measurement technique coupling can overcome this issue. Results are encouraging and show the potential of a mixed Eulerian-Lagrangian approach.

Combining Predictions and Assessing Uncertainty from Sediment Transport Equations Using Multivariate Bayesian Model Averaging

AbstractA key assumption in the use of numerical sediment transport models is the selection and application of an equation to describe sediment transport capacity. This assumption introduces uncert...

Experimental and numerical simulation of bed load transport over steep slopes

ABSTRACTMathematical models used to describe sediment transport are updated to include more physical characteristics resulting in more accurate numerical predictions. Hence, the present work studies the influence of gravity effects in the bed load transport over steep sloping beds. For this purpose the 2D gravity projections on global coordinates have been included not only in the sediment fluxes, which is the classical approach, but also in the water fluxes and in the pressure/friction terms. Additionally, a set of experiments involving steep slopes has been designed and carried out. Comparisons between the numerical and the experimental results are reported. The gravity projections included in the hydrodynamic and morphodynamic models lead to more accurate predictions in two situations: (i) at the initial stages of experiments where the bed slopes angles are higher; and (ii) under large water and solid discharges, where the interaction between the bed and the water is stronger.

RANS-based simulation of wave-induced sheet-flow transport of graded sediments

A one-dimensional vertical (1DV) turbulence-closure flow model, coupled with sediment transport capabilities, is extended to incorporate graded sediment mixtures. The hydrodynamic model solves the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equations coupled with k–ω turbulence closure. The sediment transport description includes both bed and suspended load descriptions. So-called high-concentration effects (turbulence damping and hindered settling velocities) are likewise included. The sediment transport model treats the bed and suspended load individually for each grain fraction, including effects associated with increased exposure of larger particles within a mixture. The suspended sediment transport model also makes use of modified reference concentration approach, wherein reference concentrations computed individually for each fraction are translated to a common level, conveniently enabling use of a single computational grid for the simulation of suspended sediments. Parametric study shows that these two effects combine to help alleviate an otherwise systematic tendency towards over- (under-) predicted transport rates for fine (coarse) sand fractions. The sediment transport model is validated against sheet-flow experimental oscillatory tunnel measurements beneath velocity-skewed wave signals, and demonstrates similar accuracy (transport rates generally within a factor of two) for both graded and uniform sands. The model is likewise validated against an extensive data set involving sheet-flow transport beneath acceleration-skewed wave signals (limited to uniform sands). It is then utilized to study potential effects of gradation on the net transport beneath such flows. The simulations suggest that gradation effects can both increase, as well as decrease, the total transport rate, depending largely on the behavior of the fine sand fraction. The model is implemented within the Matlab environment, and is freely available upon request to the corresponding author.

Rheology of sediment transported by a laminar flow.

Understanding the dynamics of fluid-driven sediment transport remains challenging, as it occurs at the interface between a granular material and a fluid flow. Boyer, Guazzelli, and Pouliquen [Phys. Rev. Lett. 107, 188301 (2011)]PRLTAO0031-900710.1103/PhysRevLett.107.188301 proposed a local rheology unifying dense dry-granular and viscous-suspension flows, but it has been validated only for neutrally buoyant particles in a confined and homogeneous system. Here we generalize the Boyer, Guazzelli, and Pouliquen model to account for the weight of a particle by addition of a pressure P_{0} and test the ability of this model to describe sediment transport in an idealized laboratory river. We subject a bed of settling plastic particles to a laminar-shear flow from above, and use refractive-index-matching to track particles' motion and determine local rheology-from the fluid-granular interface to deep in the granular bed. Data from all experiments collapse onto a single curve of friction μ as a function of the viscous number I_{v} over the range 3×10^{-5}≤I_{v}≤2, validating the local rheology model. For I_{v}<3×10^{-5}, however, data do not collapse. Instead of undergoing a jamming transition with μ→μ_{s} as expected, particles transition to a creeping regime where we observe a continuous decay of the friction coefficient μ≤μ_{s} as I_{v} decreases. The rheology of this creep regime cannot be described by the local model, and more work is needed to determine whether a nonlocal rheology model can be modified to account for our findings.

Sediment transport through self‐adjusting, bedrock‐walled waterfall plunge pools

AbstractMany waterfalls have deep plunge pools that are often partially or fully filled with sediment. Sediment fill may control plunge‐pool bedrock erosion rates, partially determine habitat availability for aquatic organisms, and affect sediment routing and debris flow initiation. Currently, there exists no mechanistic model to describe sediment transport through waterfall plunge pools. Here we develop an analytical model to predict steady‐state plunge‐pool depth and sediment‐transport capacity by combining existing jet theory with sediment transport mechanics. Our model predicts plunge‐pool sediment‐transport capacity increases with increasing river discharge, flow velocity, and waterfall drop height and decreases with increasing plunge‐pool depth, radius, and grain size. We tested the model using flume experiments under varying waterfall and plunge‐pool geometries, flow hydraulics, and sediment size. The model and experiments show that through morphodynamic feedbacks, plunge pools aggrade to reach shallower equilibrium pool depths in response to increases in imposed sediment supply. Our theory for steady‐state pool depth matches the experiments with an R2 value of 0.8, with discrepancies likely due to model simplifications of the hydraulics and sediment transport. Analysis of 75 waterfalls suggests that the water depths in natural plunge pools are strongly influenced by upstream sediment supply, and our model provides a mass‐conserving framework to predict sediment and water storage in waterfall plunge pools for sediment routing, habitat assessment, and bedrock erosion modeling.

Can Suspended Fine-Sediment Transport in Shallow Lakes Be Predicted Using MVRVM with Limited Observations?

AbstractThe study of sediment transport in water natural bodies is a challenging task. There have been several attempts to describe sediment mathematically using hydraulic characteristics of water bodies. Most researchers who developed empirical formulas to describe sediment transport performed laboratory experiments with assumptions that did not take into account variations of hydraulic parameters and the fine sediment sizes that are part of this phenomenon. Recently, new approaches for studying sediment transport have been developed involving the use of machine-learning algorithms that have proven accuracy and efficiency in predicting sediment transport. A novel machine-learning method, the Multivariate Relevance Vector Machine (MVRVM), has yet to be tested to model sediment transport and water quality in estuaries and lakes. The selection of the MVRVM is suggested by the limited field observations that present challenges for alternative statistical learning machines, and by the promise of using the MVR...

Numerical modeling of shoreline undulations part 1: Constant wave climate

This paper presents a numerical study of the non-linear development of alongshore undulations up to fully developed quasi-steady equilibrium. A numerical model which describes the longshore sediment transport along arbitrarily shaped shorelines is applied, based on a spectral wave model, a depth integrated flow model, a wave-phase resolving sediment transport description and a one-line shoreline model.First the length of the shoreline undulations is determined in the linear regime using a stability analysis. Next the further evolution from the linear to the fully non-linear regime is described. In the fully non-linear regime down-drift spits and migrating shoreline undulations are described.Three different shoreline shapes are found depending on the wave conditions: undulations with no spits, undulations with shore parallel spit and undulations with reconnecting spits.

New approach to understanding sediment transport

Sediment transport is an important factor in the evolution of river channels. Bed load sediment flux, defined as the volume of particles crossing a vertical surface per unit time per unit width, is a common way to describe sediment transport. However, quantifying bed load sediment flux in terms of conceptually simple quantities is challenging, as the motion of particles in turbulent water is very complex. In a set of four related papers, Furbish et al. developed a new probabilistic definition of bed load transport and verified their approach using laboratory experiments and model simulations. Their approach, which treats particle positions and motions as stochastic quantities, shows how the particle activity and velocity distributions are key elements in describing sediment flux. Their experiments, using high‐speed imaging of sand particle motions in a laboratory tank, allowed them to directly observe particle behavior and test their theory. Model simulations also verified their approach. (Journal of Geophysical Research‐Earth Surface, doi:10.1029/2012JF002352, 2012, doi:10.1029/2012JF002353, 2012, doi:10.1029/2012JF002355, 2012, and doi:10.1029/2012JF002356, 2012)

Numerical and experimental investigation of flow and scour around a half-buried sphere

The paper describes the results of a numerical and experimental investigation of flow and scour around a half-buried sphere exposed to a steady current. Hot-film bed shear stress and Laser Doppler Anemometer measurements were made with a half sphere mounted on the smooth bed in an open channel. The hydrodynamic model is a 3-D general purpose N–S flow solver. The k-omega SST turbulence model was used for closure. The flow model was used to study the horseshoe vortex and lee-wake vortex flow processes around the sphere. The flow model was coupled with a morphologic model to calculate scour around the half-buried sphere in currents. The morphologic model includes a sediment-transport description, and a description of surface-layer sand slides for bed slopes exceeding the angle of repose. The sediment transport description includes, for the first time, the effect of externally-generated turbulence (induced by the horseshoe-vortex flow and the lee-wake flow processes) on sediment transport. The results show that the scour depth increases and time scale decreases when the effect of externally-generated turbulence is incorporated in the calculations. Empirical expressions representing the numerically obtained data on the equilibrium scour depth and the time scale are presented. The results show that the equilibrium maximum scour depth in the live-bed regime can be approximated by 0.5 D in which D is the sphere diameter.

MORPHOLOGICAL MODELLING OF THE RESPONSE TO A SHIPWRECK - A CASE STUDY AT CAPE TOWN

A simulation of the morphological development and degrade of a salient behind a shipwreck located north of Cape Town, South Africa is presented. The morphological model is based on a hybrid morphological model concept which combines a 2D coastal model for calculating sediment transport with a simplified 1D morphological evolution model for the coastline. The model concept is applied to the case study in order to show how the modelling concept may be applied to real coastlines with general bathymetric features. The results show that the model captures the overall morphological response fairly well without the need for extensive calibration which is often required by traditional 2D morphological models. This is attributed by the authors to the fact that the sediment transport description is based on a process based model that captures the most important features, while neglecting the often challenging description of the cross-shore sediment transport.

Vegetated filter effects on sedimentological connectivity of agricultural catchments in erosion modelling: a review

AbstractThe sedimentological connectivity of agricultural catchments may be affected by anthropogenic structures (land management practices) established to reduce sediment exportation from agricultural plots to water streams. Distributed erosion models may in theory provide information about where and how these structures should be installed in catchments to reduce sediment exportation. The interaction between sediment exportation and land management practices is very complex from both theoretical and experimental points of view. Vegetated filters are a widely used land management practice. They interact with water flow, change turbulence conditions, and ultimately affect sediment transport and deposition processes. Experimental results have shown that the efficiency of sediment trapping in vegetated filters is influenced by flow characteristics, sediment size, and vegetation type, as well as by the slope and width of the filter in the streamwise direction. At the catchment scale, the spatial organisation of management practices is crucial for the global sedimentological connectivity. Present‐day erosion models propose different approaches to simulate the influence of management practices on soil loss and sediment export for agricultural catchments. Some of them use the Sediment Delivery Ratio (SDR) or P‐factor to describe sediment transport from source to sink areas. Others, such as in the TRAVA and VSFMOD, rely on process‐based descriptions involving changes in roughness and infiltrability along flow paths to study the effect of management practices. From the literature review conducted herein, we identified the lack of an approach of intermediate complexity, that would be more physically relevant than SDR and P‐factor approaches, but simpler and easier to spatialise than TRAVA and VSFMOD‐type models. Copyright © 2010 John Wiley and Sons, Ltd.

Large eddy simulation of sediment transport in open-channel flow

Large Eddy Simulation (LES) is used to investigate the 3D-transport of sediment suspension in an open channel flow at a Reynolds number based on the frictional velocity.An Eulerian model was employed to represent the fluid and the sediment phases. The subgrid-scale fluid stresses were modeled with the Smagorinsky model, whereas subgrid-scale sediment fluxes were based on a gradient approach. To avoid tuning constants, a dynamic procedure was applied. A two-way coupling between sediment and fluid improved the computational description of sediment transport. Sediment concentration profiles and the statistics of sediment fluxes are presented and compared with the Rouse profile and the RANS solution. The results obtained agree well with the theory and with measurements. The LES results also indicate that the assumption of a constant Schmidt number, as is mostly assumed in RANS simulations is erroneous.