Bedload Research Articles

Confluence morphodynamics in mountain rivers in response to intense tributary bedload input

AbstractCoarse sediment transported by steep mountain tributaries during channelized flash flood events with intense bed load transport poses a significant threat to life, property, and infrastructure. Intense bedload transport occurring in tributary channels and insufficient transport capacity of the main channel flow can provoke flooding at the confluence. Deposition in the confluence can lead to overbank flooding and sedimentation into adjacent settlement areas. Extensive research has been carried out investigating lowland river confluences, where it has been determined that the confluence angle and discharge ratio have the most significant influence on channel morphology and hydraulics. However, there is a lack of information concerning confluences with low width and discharge ratios, high sediment concentrations, and gradients, typically found in steep mountain channels. This study presents results from large‐scale laboratory experiments coupled with numerical modelling with a standardized river confluence geometry. Bedload transport capacities, the shape, and volume of the deposition zone in the confluence, bedload dispersion characteristics, hydraulic and morphological dynamics, and spatial boundaries were analysed for various discharges and sediment concentrations. The confluence angle was 90°, sediment concentration was 5%, 7.5%, and 10%, and the discharge ratio was 0.1. The model was designed to accommodate scale factors of 20–40. With this configuration, a set of experiments based on steady‐state hydraulic conditions was accomplished. Results show that when the discharge ratio and confluence angle are constant, different morphologies occur, indicating that in addition to the confluence angle and the discharge ratio, the sediment concentration, flow velocity, and unit stream power significantly impact both hydraulic and morphologic zones in the confluences of mountain rivers. Additionally, backwater effects upstream of the confluence, and sedimentation in the tributary channel increases with increasing sediment concentration, which not only influences confluence morphodynamics and hydraulics but also the potential for overbanking of both channels.

Hochauflösende numerische Grundlagenuntersuchungen als Basis für ein verbessertes Prozessverständnis von Schwebstoff- und Geschiebetransport

ZusammenfassungIn dieser Arbeit werden zwei numerische Grundlagenuntersuchungen vorgestellt, die das Prozessverständnis von Schwebstoff- und Geschiebetransport erweitern. Die Modellierungen werden mittels der hochauflösenden Large-Eddy-Simulation durchgeführt. Im Fall des Schwebstofftransports werden die ersten Sekunden nach der Verklappung von Feinsediment simuliert und die Geschwindigkeiten der Partikel in der Schwebstoffwolke im Vergleich zur Fließgeschwindigkeit analysiert. Es zeigt sich, dass der Schwebstoff bereits nach wenigen Sekunden keine nennenswerten Geschwindigkeitsunterschiede zur Strömungsgeschwindigkeit in Hauptströmungsrichtung mehr aufweist und somit eine Modellierung mithilfe einer Advektions-Diffusions-Gleichung ab diesem Zeitpunkt zulässig ist. Hinsichtlich des Geschiebetransports werden die Einwirkungen von turbulenten kohärenten Strukturen auf die Geschiebekörner untersucht. Hierbei wird deutlich, dass insbesondere asymmetrische turbulente Strukturen in der Größe der Körner die Druckverteilung und das Verhältnis von Strömungswiderstands- zu Auftriebsbeiwerten so zu ändern vermögen, dass eine Bewegung des Geschiebes eintreten kann. Diese Erkenntnisse werden es zukünftig erlauben, Geschiebetransportmodelle mithilfe hydromechanischer Ansätze zu verbessern.

Experimental study on velocity distribution and bed load transport in compound channels: Effect of the floodplain’s wall parallel with the meandering main channel

In this study, the effect of the floodplain’s parallel wall with a compound meandering main channel over the hydraulics flow has been analyzed experimentally. A constant sinuosity factor of 1.3 and relative flow depths of 0.3 to 0.55 were considered to illustrate the effect of the hydraulic parameters on the variations of the velocity components. Velocity components were measured by ADV velocimeter at seven cross sections with angles of zero, 30, and 60 degrees and mesh size of 2 cm × 2 cm. Furthermore, a laser meter measured the topographies of the sediment bed in the 33 cross-sections with an angle difference of 5 degrees to the bend apex. The results showed that in lower relative depths, due to vortexes and high turbulence intensity, the ability of flood damage will be more eminent. The CS04 section with the least longitudinal and transverse changes in the water level is the best position for hydraulic investigation of the meandering rivers. The left bank in sections CS03 to CS07 will be the place of deposit of sediment in nature with the formation of the stagnation area. The velocity of (Ud(fp-inner)) is 3 to 5 times higher than (Ud(fp-outer)). For this cause, the flow in the outer bank, unlike the inner bank, has a reduced effect on the flow velocity in the main channel. Increasing the relative depth, the ratio (Ud(mc)/Ud(T)) and (Ud(fp)/Ud(T)) decreased and increased, respectively. Therefore, the average velocity values in the main channel and the floodplains reached the average velocity of the whole section. The flow velocity in the main channel is always higher than in the floodplains, and the ratio (Ud(fp)/Ud(mc)) is less than one. The variation trend in the average values of bed shear stress, turbulence kinetic energy (TKE) and average kinetic energy (MKE) was decreased with increasing relative flow depth. Both factors of relative depth and Froude number will affect the location of the occurrence of the maximum values of velocity, bed shear stress, maximum depth hole and the peak of the sedimentary hill.

Assessment of the fraction of bed load concentration towards the sediment transport of a monsoon-dominated river basin of Eastern India

Assessment of the fraction of bed load concentration towards the sediment transport of a monsoon-dominated river basin of Eastern India

Interplay of flow and bed morphology caused by pool-riffle sequence formation without upstream sediment supply in gravel-bed rivers

Pool-riffle sequences (PRSs) are widely distributed in gravel-bed rivers, but their formation regimes under conditions with no sediment supply have not yet been explored. This study selected one field section of PRSs in the East River and measured the bed surface and bedload longitudinally and used these observations to design scaled, variable width flume experiments where we measured feedback of flow and bed morphology under different flows and slopes without a sediment supply. Experimental results show that there exists the critical value of width-depth ratio during PRS formation, corresponding to the aggregated velocity distribution. Meanwhile, the peak value of turbulent kinetic energy easily occurs in the middle riffle under flood discharge conditions, promoting the removal of fine sediment and its transport downstream. The formation and destruction of the periodic armoring layer in the PRS become common without sediment supply. In fact, downstream sorting effect of the armoring layer is the dominant factor to lead the formation-destruction of bed surface, and causes discontinuous surface GSD (grain size distribution) longitudinally in the field. The increase in the flow and slope can effectively promote PRS development, expanding the variation in the lateral sedimentation but shortening the length of pools and riffles. Furthermore, self-maintenance of adjacent riffles and pools response to the lack of sediment supply is faster and more frequent than that with sediment supply, and higher flow can promote incipient sediment and bedload transport on the bed surface. The PRS with variable-width largely increases the influence of sediment supply on the bedload transport, e.g., the increase of bed load transport rate with incoming sediment supply of the PRS is much higher than that of constant-width channel.

Pemodelan Pola Transport Sedimen di Perairan Desa Berakit dan Pengudang Kabupaten Bintan

Sedimentation and erosion processes can be influenced by hydro-oceanographic factors. These factors include waves, currents, and tides because they interact directly with the coastal/coastal area. Related to these problems, sedimentation and erosion is one thing that needs to be studied. One way that is used in providing information about these that is widely used is to use a hydrodynamic model. Based on this, it can be seen that it is important to conduct research to determine sediment properties such as the type and type of sediment with sediment transportt modeling in Berakit and Pengudang villages. This research was carried out using the MIKE21 Software hydrodynamic modeling for one month in June 2021 using hydrodynamic modeling, the Flow Model FM Sand Transportt module. Sediment transportt observed is bottom sediment or bed load. The research results are shown in 4 conditions, namely towards high tide, highest tide, towards low tide and lowest tide. Sediment transportt at high tide with erosion of -0.10 and sedimentation of 0.25 m/day and at the highest tide shows an erosion value of -0.24 and sedimentation of 0.32 m/day. Sediment transportt towards low tide with erosion of -0.15 and sedimentation of 0.20 m/day and at the lowest ebb erosion occurs with a value of -0.36 and sedimentation of 0.20 m/day.

ANALISIS LAJU ANGKUTAN SEDIMEN UNTUK MENGANTISIPASI RESIKO BENCANA SEJAK DINI PADA SUNGAI CILEUEUR KABUPATEN CIAMIS

This study uses the Duboy's method and the Englund -Hunsen method to calculate bed load transport which aims to determine the volume of sedimentation in the Cileueur River, Ciamis Regency as a form of early anticipation of disaster risk.This research was carried out with stages starting from hydrological analysis, determining the planned rainfall, analyzing the design discharge, and analyzing the average velocity of the river.This research is based on considerations to anticipate disaster risks, especially in the Cileueur River, Ciamis Regency, this river has a length of 25,000 m and an area of 13,660.7 ha of watershed. In the Cileueur River there are several problems including silting of the river which results in frequent occurrence of large enough water overflows exceeding the cross-sectional area capacity of the river during the rainy season. Seeing the impact of the occurrence of these problems, it is necessary to conduct research in order to anticipate risks before a disaster occurs.Based on the results of the analysis and discussion, it can be concluded that the results of bed load transport calculations in the Cileueur river, Ciamis Regency using the Duboy's method obtained an average of 357.5619 tonnes/year and the Englund and Hunsen method of 317.379 tonnes/year. Then the comparison of the results of calculating the amount of bottom sediment from the two methods is 6%.

Study effect of slope change on sediment transport in the Dujila irrigation canal


 One of the main elements influencing the Dujila River's river shape is sediment. The characteristics of sediment supplied within reach when creating hydraulic constructions like a dam, irrigation canal, maybe even to use the stream for navigation purposes, would be one of the design engineer's main concerns.. The shallow depth brought on by riverbed aggradation may have an impact on the Dujila River's utilization as a source of drinking water and agricultural irrigation. Investigating sediment movement and the features of the river bed is essential to reducing the problems caused by River morphology changes. Utilizing the River Analysis System of the Hydrologic Engineering Center, a hydraulic examination of the transfer of sediment model was produced for this project (HEC-RAS). Along the Dujaili's 57 kilometers Information was gathered. The Manning coefficient was calculated for seven sections after calibration and verification. For 6 sections, samples from the river bed and suspended loads were taken in order to calculate the amount of silt. The model's output displays the pattern of river reach sections that follow erosion or deposition as well as the pattern of bed change. The model has been tested with various slope values to determine how slope affects sediment transport.

Seabed morphodynamics of a coastal lagoon of the Gulf of California

A two-dimensional, vertically integrated, non-linear numerical model was applied to investigate the Urias coastal lagoon’s (URCOL) tide-driven currents, bed load sediment transport, and seabed morphodynamics. The coastal body of water, located on the eastern side of the Gulf of California, includes the Mazatlán harbour, the most important port on the Pacific Mexican coast due to the relevant activities like the heavy vessel traffic. URCOL also includes an extensive aquaculture infrastructure at the lagoon head. The tidal hydrodynamic modelling revealed the mixed character of tides predominantly semidiurnal in the lagoon. The numerical computation at the harbour entrance showed an ebb-dominant tidal distortion. The distribution patterns of the erosion and accretion rates are consistent with the convergent and divergent character of the vectors of sediment transport rates. The sediment accretion has been predicted mainly in the middle part of the channel, right where the channel starts curving, changing the alignment of the lagoon. The tidal hydrodynamics, sharp topographic gradient, and geometric features of the lagoon seem to determine the location of accretion and erosion areas.

Numerical Simulation of Hydrodynamics and Sediment Transport in the Surf and Swash Zone Using OpenFOAM®

This study focuses on the numerical investigation of the 3D hydrodynamic processes of coastal zones such as wave breaking, wave-induced currents, and sediment transport, using the multiphase, interFoam solver of OpenFOAM® (a state-of-the-art, open-source CFD numerical tool). The numerical scheme is suitably framed by initial conditions of wave propagation and absorption using waves2Foam wave library. The turbulence closure problem is handled using a buoyancy modified k–ω SST model. In order to predict the sediment transport rate due to waves and currents (bed load, sheet flow, and suspended load over ripples), a transport-rate formula involving unsteady aspects of the sand transport phenomenon is implemented. For the suspended load in the surf zone, the Bailard formula is adopted after considering that the dissipation mechanism is the wave breaking. Results concerning wave height, longshore current, turbulence kinetic energy, and sediment transport are compared against experimental data and semi-empirical expressions.

Integrating channel design and assessment methods based on sediment transport capacity in gravel bed streams

AbstractNatural channel design (NCD) and analytical channel design (ACD) are two competing approaches to stable channel design that share fundamental similarities in accounting for sediment transport processes with designs based on hybrid fluvial geomorphology and hydraulic engineering methods. In this paper, we highlight the linkage between ACD's capacity/supply ratio (CSR) and NCD's sediment capacity models (FLOWSED/POWERSED), illustrating how ACD and NCD have reached a point of convergent evolution within the stream restoration toolbox. We modified an existing CSR analytical spreadsheet tool which enabled us to predict relative channel stability using both conventional bed load transport equations and regional sediment regression curves. The stable channel design solutions based on measured data most closely matched the Parker (ACD) and/or Pagosa good/fair (NCD) relationships, which also showed the greatest CSR sensitivity in response to channel alterations. We found that CSR differences among the transport relationships became more extreme the further the design width deviated from the supply reach, suggesting that a stable upstream supply reach may serve as the best design analog. With this paper, we take a step toward resolving lingering controversy in the field of stream restoration, advancing the science and practice by reconciling key differences between ACD and NCD in the context of reach scale morphodynamics.

Analysis of Bedforms in the Mississippi River at Vicksburg, Mississippi, for Select Flows 2011–2016

Quantification of sediment transport rates is necessary for river management but remains difficult due to large volumes of sediment in motion, spatiotemporal heterogeneity in discharge, depth, and morphology, the need for expensive equipment, and personnel costs. During efforts to quantify sediment bed load in the Mississippi (MS) River near Vicksburg, MS, US, the US Army Corps of Engineers-Engineer Research and Development Center (USACE-ERDC) collected acoustic multibeam topographic data during the 2011 MS River flood. Bed topography data were analyzed to quantify the effect of changing flow rates on bed topography. Bedforms were much higher and longer in the center section than near either bank, and superimposed bedforms were found during the falling limb of the 2011 flood hydrograph. Bedform amplitudes and lengths were positively correlated with flow depths, but amplitudes were typically higher and lengths shorter than predicted in previous research. Topography data from three lower flows are included to illustrate the morphometric variation induced by a wide range of discharges.

Bimodal Bed Load Transport Characteristics under the Influence of Mixture Ratio

The transport of a non-uniform bed load in a river is a complicated process and has enormous implications on the sediment flux and anomalous riverbed evolution. To investigate the transport characteristics of the non-uniform bed load and the related particle interactions, a real-time monitoring system of the bed load transport was developed to determine the instant transport rate and grain composition of the bed load. Doppler Velocimetry was used to synchronously measure the fluctuating velocity in high frequency. A total of 211 cases of flume experiments were conducted, focusing on non-uniform sediment with a bimodal pattern. The experimental results indicate that the random fluctuation of the bed load transport amount closely depends on the flow-intensity fluctuation caused by the turbulence burst near the bed. When the value of the flow-fluctuation peak is bigger than 2.5 σ, the coarse sands tend to incipient motion in high probability but are mostly fine sand transport when the peak is less than 1.5 σ. The transport rate of fine particles remains continuous throughout the process, while that of coarse particles is intermittent because the incipient motion mechanism of bed load sands mainly follows three modes. If the difference in diameter between the coarse and fine particles is large, the transport of coarse particles may undergo supernormal transport because of the effect of the fine particles on the coarse particles. The bed load flux of total, fine, and coarse sand present different trends with changes in the bed material composition, in which the transport rate of coarse sands and total bed load sands presents a humped curve in terms of the mixture ratio, and the optimal corresponding mixture ratio ηc is about 3:7. The optimal mixture ratio is not fixed, and it depends on the grain composition and size differential of bed material. With a proper mixture ratio, the transport rate of a non-uniform bed load is higher than the uniform bed load of related size. These findings might provide valuable support for predicting bed load transport and bed evolution in rivers.

Testing Bed Load Transport Formulas: A Case Study Of The Lower Amur Using Bed Load Yield Data Obtained With Multi-Beam Echo-Sounders (Mbes)

The development of bed load calculation methods directly depends on the reliability of the measurement data. The most reliable measurement data remains the data obtained by the volumetric method when observing the filling of reservoirs, borrows, ditches etc. Nevertheless these data are the rarest. In this paper on the base of the data obtained when observing the process of filling of a ditch across the Amur River a comparison of a number of bed load calculation methods is performed. The observations were carried out with a multi-beam echo-sounder during summer floods of 2018, from 21st of July to 22nd of August. Over this time 5 surveys were performed, that allows to have 4 calculation periods for determining bed load yield. The total number of the measurements at different calculation verticals is 108. These data are used for verification of 80 bed load formulas. Four methodological approaches are considered: bed form approach, critical velocity approach, critical water discharge approach and regression approach. The bed form approach has shown the greatest accuracy: 17 formulas out of 26 gave the error less than 60%. For the other 56 methods which were considered only 5 formulas showed the error less than 60%, all of them correspond to the critical velocity approach.

Grain shape effects in bed load sediment transport.

Bed load sediment transport, in which wind or water flowing over a bed of sediment causes grains to roll or hop along the bed, is a critically important mechanism in contexts ranging from river restoration1 to planetary exploration2. Despite its widespread occurrence, predictions of bed load sediment flux are notoriously imprecise3,4. Many studies have focused on grain size variability5 as a source of uncertainty, but few have investigated the role of grain shape, even though shape has long been suspected to influence transport rates6. Here we show that grain shape can modify bed load transport rates by an amount comparable to the scatter in many sediment transport datasets4,7,8. We develop a theory that accounts for grain shape effects on fluid drag and granular friction and predicts that the onset and efficiency of transport depend on the coefficients of drag and bulk friction of the transported grains. Laboratory experiments confirm these predictions and reveal that the effect of grain shape on sediment transport can be difficult to intuit from the appearance of grains. We propose a shape-corrected sediment transport law that collapses our experimental measurements. Our results enable greater accuracy in predictions of sediment transport and help reconcile theories developed for spherical particles with the behaviour of natural sediment grains.

Modelling sediment trapping in vegetative filter strips on steep slopes

AbstractThe slope effects on sediment trapping process in vegetative filter strips (VFS) are usually neglected in current modelling practices for VFS operation, which hamper the VFS design and performance evaluation, especially on steep slopes. To fill the knowledge gap, 12 laboratory experiments of sediment trapping in VFS were conducted with three different inflow discharge (80, 100, and 120 ml s−1) and four slope angles (5,10, 15, and 20°). The experimental results show that, on steep slopes (10, 15, and 20°), a part of trapped sediment particles in VFS can be eroded again and then dragged to the downstream as bed load, whilst they do not move on gentle slope (5°). To describe the complex processes, a simple and effective modelling framework was developed for sloped VFS by coupling the slope infiltration, runoff, and modified sediment transport model. The model was tested against the experimental results and good agreements between the modelled and observed results were found in both runoff and sediment transport processes for all cases. On steep slopes, the sediment trapping performance of VFS decreases significantly because the erosion of deposited sediment particles can account for more than 60% of the sediment load in the outflow. The slope effect on sediment trapping efficiency of VFS varies greatly with soil, VFS, and slope properties. The model was compared with previous sediment transport equation and found that both methods can satisfactorily predict the sediment trapping of VFS on gentle slopes, but previous sediment transport equation is likely to overestimate the sediment trapping efficiency in VFS on steep slopes. This model is expected to provide a more realistic and accurate method for predicting runoff and sediment reduction in VFS on sloping surfaces.

Flume Investigation Into Mechanisms Responsible for Particle Sorting in Gravel‐Bed Meandering Channels

AbstractMeandering gravel‐bed rivers tend to exhibit bed surface sorting patterns with coarse particles located in pools and fine particles on bar tops. The mechanism by which these patterns emerge has been explored in sand‐bed reaches; however, for gravel‐bed meandering channels it remains poorly understood. Here we present results from a flume experiment in which bed morphology, velocity, sediment sorting patterns, and bed load transport were intensively documented. The experimental channel is 1.35 m wide, 15.2 m long, and its centerline follows a sine‐generated curve with a crossing angle of 20°. Water and sediment input were held constant throughout the experiment and measurements were collected under quasi‐equilibrium conditions. Boundary shear stress calculated from near‐bed velocity measurements indicates that in a channel with mild sinuosity, deposition of fine particles on bars is a result of divergent shear stress at the inside bend of the channel, downstream of the apex. Boundary shear stress in the upstream half of the pool was below critical for coarse particles (>8 mm), leading to an armored pool. Inward directed selective transport was responsible for winnowing of fine particles in the pool. Fine and coarse sediment followed similar trajectories through the meander bend, which contrasts earlier studies of sand‐bedded meanders where the loci of fine and coarse particles cross paths. This suggests a different sorting mechanism for gravel bends. This experiment shows that a complex interaction of quasi‐equilibrium bed topography, selective sediment transport, and secondary currents are responsible for the sorting patterns seen in gravel‐bed, meandering channels.

Field quantification and spatial variation of bed load transport in mountain stream: a case study of Gujarat (India)

Field quantification and spatial variation of bed load transport in mountain stream: a case study of Gujarat (India)

A finite element method for partially erodible bed evolution coupled with multiphase flows

This paper introduces a continuous finite element model for two phase flows coupled with evolving bedforms. The method extends the positive definite non-oscillatory finite element algorithm (NFEM) capabilities to predict sediment transport, multiphase flow, and evolution of the resulting interfaces limiting fluids, erodible sediment layers and non-erodible strata. Free surface hydrodynamics is simulated by the integration of the governing equations for incompressible multiphase flows, including the advection and reinitialization of a phase function to update the interface location. Sign preservation of the algorithm is essential both for fluid interface tracking procedure and for the landform tracking. In the first case, the property avoids unphysical overshoots along the free surface. In the second case, a positive definite thickness of the erodible layer of sediment is mandatory to account for interaction between evolving cohesionless sediment layers and rigid beds. To compute sediment layer thickness, the method incorporates a conservation law to balance evolution of the bed position with sediment mass flux, including a general template for saturated flux calculation. The framework permits the simulation from bed load dominant transport to saltation dominant transport. Fluid/terrain interface is explicitly captured by a surface tracking methodology whereby the mesh is adapted to the bedform. Numerical experiments explore several saturated sediment flow formulae for interactive evolution of dune/atmosphere system, as well as stringent dam-break type problems on channels with dry beds and partially and totally erodible beds.

Characteristics of Sediment Transport After Morphological Changes at Palu Estuary, Sulawesi, Indonesia as The Impact of 2018 Tsunami

The tsunami triggered by the 2018 Palu Earthquake has not only caused the collapse of public infrastructure, but also damaged beaches along Palu Bay. Based on direct investigation along the beaches, the coastlines have shifted inland up to 30 meters. This shoreline change was caused by the attack of the tsunami waves at high speed followed by massive abrasion. Another impact of the wave attackis a change in the morphology of the beach bed, including in the Palu Estuary. This study aims to investigate the impact of changes in bed morphology around the Palu Estuary as a result of the tsunami attack on transport sediment characteristics, as one of the determinants of bed morphology. Quantitative analysis was carried out by numerical simulation based on 2D hydrodynamic modeling using the Surface-water Modeling System (SMS). The geometry of the model is formed from the mesh generated from the bed elevation based on the after-tsunami bathymetry survey. Two boundary conditions and one main input data are applied to this model: discharge data, tidal data and bed load data. Discharge data as an upstream boundary condition consists of minimum discharge, average discharge and maximum discharge. The downstream boundary is defined by a tidal curve predicted from 15 daily data. The bed load data is presented in the form of a gradation curve that describes the distribution of sediment grains. The simulation output indicates that sediment settles intensively downstream of the river mouth at high discharge and low tide. At low discharge and high tide, sediment tends to settle before the flow reaches the river mouth. Referring to the results of previous studies, the direction and velocity of sediment motion changed slightly after the tsunami. Changes in the direction and speed of movement are related to changes in bed morphology at the river mouth due to the 2018 Palu Tsunami.