Bedload Research Articles

Simulation of Bed Change in Al-Musayyab Canal using HEC-RAS Software

This study focuses on the simulation of the bed change and total sediment concentration in the Al-Musayyab Canal, which is a vital irrigation system located in the central region of Iraq, using HEC-RAS V 6.3 software. The 49.5 km canal, with 13 branches, faces challenges from sediment influx originating from the Euphrates River. The primary objective is to analyze sedimentation, erosion patterns, and sediment discharge variations to support effective canal management. Field sampling collected suspended and bed load samples for laboratory tests, providing input data for the sediment transport model. Simulation results show steady flow water surface elevations ranging from 26.32 to 33.16 m.a.s.l, with velocities from 0.24 to 0.98 m/s. Significant sediment deposition and erosion variations are observed as data for 2019 and 2020 are analyzed. Notable changes in the canal's invert levels occurred in both years, with maximum deposition depths reaching 14 cm in 2019 and 21 cm in 2020. Erosion depths ranged from 3 to 15 cm in 2019 and 5 to 25 cm in 2020. The total sediment discharge for 2019 in the Al-Musayyab Canal amounted to 17 tons/day, while 22 tons/day in 2020.

A Novel Laboratory Technique for Measuring Grain‐Size‐Specific Transport Characteristics of Bed Load Pulses

AbstractAlthough several laboratory studies on the propagation of bed load pulses were carried out in the last decades, most studies neglect grain‐size‐specific aspects or use invasive measurement techniques. To remedy the situation, we present a novel, time‐efficient and non‐destructive laboratory technique to investigate grain‐size‐specific transport characteristics of bed load pulses. The method consists of a through‐water, high‐resolution image acquisition followed by the application of a supervised color classification algorithm (Gaussian Maximum Likelihood Classification). The analyzed bed load pulse consisted of five different grain size classes of dyed quartz sand and gravel, each having a unique color. The initial experimental bed was uni‐colored and contained the same size fractions as the augmented pulse. Quality assessment based on a confusion matrix approach and basic random sampling showed a high classification performance. By statistically analyzing the temporal and spatial color distribution of the experimental reach, characteristic parameters to describe the propagation behavior were determined. The bed load pulse presented in the application example initially showed strong deviations in the grain‐size‐specific advection and dispersion, and advection proved to be predominant in the transport process.

Assessing the Status of Flood Hazard on the Bank of Mohana River in Kailari Rural Municipality

Purpose: Kailali holds number of rivers originating from Mahabharat range and Chure range which get flooded every year, causing high losses of agricultural land and the flooding at community level. In order to identify and understand the probable risks in the study area and the methodologies followed to get rid of the flood risk or to protect the land and community from the effect of flood. Design/Methodology/Approach: The study was conducted during the period from March 2022 to May 2023. Field observation, in-depth interview, focus group discussion and questionnaire survey were the major tool applied for the investigation. Findings/Results: The study found that the flood is the major hazard, and the earthquake is the minor one. River encroachment is the major one problem of the river training works and inadequate people’s awareness is the minor one. The river down to Chure carries lots of sediment and thus increasing the bed loads. Thus, Chure protection programs must be effectively executed so that the lower plain will be sediment less and the inundation of land will be reduced. Originality/Value: The paper contributes on the effective ways to protect community from flood hazards

Numerical investigation about effects of flow sediment-storage variation on capacity modelling of morphological evolutions

The capacity model based on the Exner equation has been widely used to simulate bed load sediment transport. However, most of their governing equations neglect a sediment storage term (∂hCe/∂t), of which the impact on bed load transport simulation is unknown and needs to be better comprehended. This paper has split the capacity model into two sub-models: one with the sediment storage term and the other without the sediment storage term. The two sub-models are applied to simulate a series of typical bed load transport processes, such as dam-break flooding and swash flows. A comparison of their results is used to shed light on the effect of sediment storage term on flows and morphological evolutions. It is shown that for both dam-break flooding and swash flows, neglection of the inflow sediment storage may lead to under-estimation of bed erosion or over-estimation of bed deposition, which further affects the computed hydrodynamics greatly. Moreover, it is shown that including this factor can improve quantitative accuracy of sediment transport estimation. These indicate an important role of this factor and accordingly the present work provide a numerical justification for using sediment storage terms in capacity models.

The effect of bed load sediments on self-purification of river – Experimental approach

Assessing the profitability of river restoration requires knowledge of the importance of individual ecosystem elements for the value of specific ecosystem services. The aim of this study was to experimentally estimate the effect of the presence of bed load on the processes of water self-purification from suspended solids, organic matter and microplastic fibres. The experiment was carried out in channels with and without bed load, simulating conditions in a lowland river. The system was supplemented with artificial sewage containing FPOM and polypropylene fibres. Changes in the amount of suspended solids in the water, as well as organic matter and microplastics in the water and sediment, were recorded over the course of a week. The presence of a bed load increased the rate of suspension removal from the river water many times over. The decomposition rate of organic matter in the sediment was much higher than in the water, reaching 1 g of organic carbon per week. Bed load favoured the immobilisation of large microplastic fibres, facilitating their incorporation into bottom biofilms. The fibres formed a 'skeleton' that led to the formation of larger bed load biofilms. The study suggests that, even without restoring the connection between river water and groundwater, the supply of bed load to the river significantly increases the efficiency of natural processes in the river ecosystem, including self-purification.

Study of local scour around rectangular and square subsea caissons under steady current condition

Numerical simulations were conducted to investigate steady current scour around rectangular and square subsea caissons. The caissons, which are representative of subsea structures, have a submerged height ranging from 0.5 to several times their longest base dimension. The flow model used is based on the Reynolds Averaged Navier-Stokes equations, and the scour model simulates bed load and suspended load transport to predict the evolution of the seabed profile. The aim of this study is to investigate the mechanisms of local scour, specifically the contribution of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour. The model is validated through comparisons with experimental measurements, indicating reasonable agreement. Based on the numerical model results, the mechanisms of local scour around square and rectangular caissons are found to be qualitatively similar. If the flow is directed perpendicular to one of the caisson faces, both the horseshoe vortex and the local streamline contraction contribute to scour. The maximum scour depth is located at the two upstream corners of the caisson due to the combined effects of the horseshoe vortex and streamline contraction. When the flow approaches the caisson with a diagonal attack angle of 45°, the two upstream faces act like a streamlined wedge that splits the incoming flow. The study found that the horseshoe vortex almost disappears and the scour is primarily caused by the local velocity amplification at the two side corners. If the flow attack angle is 45°, the scour does not initiate near the upstream corner without the contribution from the horseshoe vortex. These findings are expected to serve as a valuable theoretical foundation for the design of scour protection.

Integrated modelling of flow-sediment transport and power generation in the Three Gorges Reservoir

Reservoirs play a crucial role in regulating runoff and generating energy. However, they also lead to significant sedimentation in the reservoir area. In this study, we propose an integrated model that combines a 1-D hydro- and sediment dynamic module with a power generation module. The model considers both suspended and bed load transports. This model is applied to the Three Gorges Reservoir (TGR) and evaluate its performance against corresponding measurements. The results demonstrate that:① the proposed model accurately reproduces the processes of flow and sediment transport, bed deformation, and power generation during the hydrological years of 2019 and 2020. The relative errors for average discharge and bed deformation volume are <6 % and 10 %, respectively. Moreover, the calculated total power (982 × 108–1115 × 108 kW·h) closely agree with the measured values (969 × 108–1118 × 108 kW·h); ② the inflows of small tributaries have a noticeable impact on the calculated water discharge in the TGR. This impact will lead to a 16 % increase in average discharge and alter the magnitudes and occurrence times of flood peaks; ③ the flocculation of fine sediment particles significantly affects sediment transport, particularly in the sub-reach close to the dam. This flocculation will result in a 37 %–57 % reduction in average suspended sediment discharge and a 63 %–93 % reduction in peak sediment discharge. This research provides a comprehensive tool for simulating flow and sediment transport as well as power generation, which can support the optimal regulation of the TGR.

On the vertical structure of non-buoyant plastics in turbulent transport

Plastic pollution is overflowing in rivers. A limited understanding of the physics of plastic transport in rivers hinders monitoring, the prediction of plastic fate and restricts the implementation of effective mitigation strategies. This study investigates two unexplored aspects of plastic transport dynamics across the near-surface, suspended and bed load layers: (i) the complex settling behaviour of plastics and (ii) their influence on plastic transport in river-like flows. Through hundreds of settling tests and thousands of 3D reconstructed plastic transport experiments, our findings show that plastics exhibit unique settling patterns and orientations, due to their geometric anisotropy, revealing a multimodal distribution of settling velocities. In the transport experiments, particle-bed interactions enhanced mixing beyond what established turbulent transport theories (Rouse profile) could predict in low-turbulence conditions, which extends the bed load layer beyond the classic definition of the bed load layer thickness for natural sediments. We propose a new vertical structure of turbulent transport equation that considers the stochastic nature of heterogeneous negatively buoyant plastics and their singularities.

Numerical investigation of dam break flow over erodible beds with diverse substrate level variations

Abstract This study aimed to comprehensively investigate the influence of substrate level difference and material composition on dam break wave evolution over two different erodible beds. Utilizing the Volume of Fluid (VOF) method, we tracked free surface advection and reproduced wave evolution using experimental data from the literature. For model validation, a comprehensive sensitivity analysis encompassed mesh resolution, turbulence simulation methods, and bed load transport equations. The implementation of Large Eddy Simulation (LES), non-equilibrium sediment flux, and van Rijn’s (1984) bed load formula yielded higher accuracy compared to alternative approaches. The findings emphasize the significant effect of substrate level difference and material composition on dam break morphodynamic characteristics. Decreasing substrate level disparity led to reduced flow velocity, wavefront progression, free surface height, substrate erosion, and other pertinent parameters. Initial air entrapment proved substantial at the wavefront, illustrating pronounced air-water interaction along the bottom interface. The Shields parameter experienced a one-third reduction as substrate level difference quadrupled, with the highest near-bed concentration observed at the wavefront. This research provides fresh insights into the complex interplay of factors governing dam break wave propagation and morphological changes, advancing our comprehension of this intricate phenomenon.

Gravity‐Driven Differences in Fluvial Sediment Transport on Mars and Earth

AbstractThere is abundant evidence from fluvial landforms and deposits that Mars had rivers that actively transported sediment and shaped its surface. Sediment transport equations are playing a key role in quantifying river processes from these observations, which continue to increase in quality and quantity. In this study, we review sediment transport equations developed on Earth and isolate the effect of gravity for the case of an alluvial channel. We compare 33 formulas used to calculate the sediment transport rate, under transport‐limited conditions, for grain sizes that range from silt to boulders and a lognormal sediment distribution. Results indicate that for a given discharge, channel morphology and grain size, the lower gravity on Mars compared to Earth results in: (a) larger grains mobilized on Mars and transported in suspension, and (b) larger suspended sediment transport rates on Mars and therefore larger total transport rates. Importantly, the effect of gravity is different for bed load and suspended load, with nonlinearity at the bed load‐suspended load transition zone. Therefore, typical total‐load transport relations that do not distinguish between bedload and suspended load are not appropriate for other planets as they simplify the effect of gravity. Gravity‐driven differences in fluvial sediment transport should produce differences in sediment sorting, morphology and stratigraphy between Earth and Mars. Additionally, our results show how Earth‐derived fluvial sediment transport theory can be applied beyond Mars to other planets and moons.

Experimental and numerical study on the breaching mechanisms of landslide dams with non-uniform structures

Landslide dams often exhibit non-uniform structures due to the rapid and dynamic accumulation of various types of landslide materials. These variations in dam composition significantly impact breach progression, causing significant errors in current model tests and numerical simulations with uniform structure assumptions This adversely affects peak flow predictions and decisions related to risk prevention and control. This study conducted a series of flume tests to examine the influence of non-uniform structures on the failure mechanisms of landslide dams. A 3D dam breach model was used to replicate these flume experiments and obtain more detailed information. Large Eddy Simulation (LES) captures the hydraulic features of dam-break flow, while equilibrium equations model morphological changes in landslide dams amid complex terrains using suspended and bed load transport. The findings indicate that in a uniform dam, the presence of coarse particles shifts erosion characteristics from layered erosion to step-pool development. Furthermore, as the content of coarse particles increases, the number of steps also rises. In the vertically non-uniform structure, the upper layer affects the formation of the breach, the middle layer affects the dam break and the breach flow, and the bottom layer affects the remaining dam height. The presence of an armor layer results in a higher water level and accelerates breach formation with a larger breach flow. In the horizontally non-uniform structure, the upper part of the overflow side is the core area of the breach, the lower part of the overflow side and the upper part of the opposite side affect the downcutting and widening rates of the breach, respectively. Preferentially, the breach tends to develop towards the relatively weaker of the two sides.

Under cover ice transport processes under equilibrium and non-equilibrium conditions

The transport of ice particles beneath a stable ice cover (referred to as cover load transport), and the processes leading to ice deposition and erosion are highly dynamic and complex. Based on the strong analogous relationship between bed load and cover load transport processes, knowledge from bed load transport research can be used when developing experiments for cover load transport processes. This paper presents a detailed experimental study of cover load transport rate in a laboratory flume with simulated ice particles and a simulated ice cover. The effect of the particle shape and size on cover load transport rate is quantified using the buoyant velocity and its velocity coefficient. The critical dimensionless flow strength is identified as an important parameter which determines the incipient motion of the under cover ice particles, and was calculated using hydraulic measurements obtained through laboratory experiments. A new cover load transport formula is introduced based on regression analysis of experimental data for a wide range of dimensionless flow strength conditions. The impact of incoming ice supply rate on the under cover ice transport rate was also investigated by altering the ice supply rate to the flume. A control volume analysis of ice discharge underneath the ice cover is used as the approach to quantify the dimensionless ice transport rate at different sections of the flume. The concept of equilibrium ice transport rate is introduced based on the experimental observations with variable incoming ice supply rates. The experimental observations on the impact of incoming ice supply were supported by an analysis of field data from Hequ Reach, China (Sun et al., 1986; Wang, 1992). The introduction of a cover load transport formula developed exclusively with simulated ice particles that have similar physical properties to ice forming in a natural environment, and the discussion on equilibrium ice transport rate are important contributions to advance the present understanding on under cover ice transport processes.

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.

Assessing shoreface sediment transport at Costinha beach, Aveiro, Portuguese Northwest coast

Coastal zones are dynamic environments where sediment transport significantly influences erosion, deposition, and ecosystem stability. Accurate modelling of the complex interactions between hydrodynamics, sediment transport, and morphological changes in high-energy shoreface areas is crucial for sustainable coastal management. This study aims to assess sediment dynamics and understand the dominant physical drivers of sediment transport in the shoreface by coupling high-resolution numerical modelling with a shoreface sand tracer experiment. Results from the field experiment showed high diffusion and a net onshore and downdrift movement of the tracer in agreement with the observed hydrodynamic data. The numerical modelling strategy, validated with in situ hydrodynamic data and tracer results, demonstrated good performance and highlighted the dominant modes of shoreface sediment transport. While during low energetic wave conditions, the dominant transport mechanism involves the slow-rate bed load sediment movement toward the shore, under moderate energetic wave conditions, longshore wave-induced suspended transport becomes the prevailing mode of transport. The study provides valuable insights to increase the understanding of sediment transport in the shoreface and highlights the importance of coupling numerical modelling with sediment tracer experiments.

Sediment Transport Capacity in a Gravel-Bed River with a Sandy Tributary

Bedload transport in a river is a deeply analyzed problem, with many methodologies available in the literature. However, most of the existing methods were developed for reaches of rivers rather than for confluences and are suitable for a particular type of material, which makes them very inaccurate in cases where the sediments are comprised of a mix of different types of soil. This study considers the effect of two different bed sediment sizes, gravel and sand, in relation to bed load transport in a confluence. Five well-known and validated equations (namely Meyer-Peter and Müller, Parker + Engelund and Hansen, Ackers and White, and Yang) are applied to the case study of the Tagus–Alberche rivers confluence (in Talavera de la Reina, Spain), where main and tributary rivers transport different materials (sand and gravel). Field works in the area of the confluence were conducted, and a set of alluvial samples were collected and analyzed. The previously mentioned methods were employed to analyze the geomorphology in the confluence area and downstream of it under different flooding scenarios, concluding different trends in terms of deposition/erosion in the area under historic flooding scenarios. When the trends show erosion, all methods are very consistent in terms of numerical predictions. However, the results present high disparity in the estimated values when the predictions suggest deposition, with Parker + Engelund and Hansen yielding the highest volumes and Meyer-Peter and Müller the lowest (the latter being around 1% of the former). Yang and Ackers and White predict deposits in the same range in all cases (around 15% of Parker and Engelund Hansen). Yang’s formula was found to be suitable for the confluences of rivers with different materials, allowing for the estimation of sediment transport for different grain sizes. The effect of different flow regimes has been analyzed with the application of Yang’s formula to the Tagus-Alberche confluence.

Addendum: Grain shape effects in bed load sediment transport.

Addendum: Grain shape effects in bed load sediment transport.

Flow resistance at lowland and mountainous rivers

Abstract This study initially examines the various sources of flow resistance in sand-bed (lowland) and gravel-bed (mountainous) rivers along with the limitations of traditional estimation methods. The nondimensional hydraulic geometry approach, relating dimensionless flow discharge (q *) to the Darcy-Weisbach friction factor (f), has demonstrated good performance for both river types, covering shallow to moderately deep flows. However, accuracy in estimating f is affected by simplifications like assuming uniform and deep flow, neglecting bed load transport and vegetation effects, which require further evaluation. To address these issues, the proposed method is evaluated using data from four sand-bed rivers in Slovakia (with vegetation), and three gravel-bed rivers in Iran (dominated by cobbles and boulders). Bedforms prove to be significant resistance sources in all studied rivers. The approach yields separate predictors for each river type, showing a satisfactory agreement between observed and calculated values within a maximum deviation of ±20% error bands. These predictors are further validated using field data and established equations from rivers with similar physiographic characteristics. Results indicate the method performs well in predicting flow resistance in sand-bed rivers, slightly overestimating overall (+40%). It effectively captures riverbed features and vegetation influence under small-scale roughness conditions. However, the predictor’s validity for gravel-bed rivers is somewhat limited due to high variability in water-surface profiles, making it challenging to accurately capture flow dynamics under large-scale roughness conditions. Addressing complex characteristics of gravel-bed riverbeds, including boulders and local energy extraction, is crucial for improving the estimation of water-surface profile variations and flow resistance using the hydraulic geometry approach.

Effects of Flow Unsteadiness on the Transport of Bimodal Bed Material

The grain size distribution of the transported bed load was experimentally investigated under unsteady flow conditions with bimodal mixture of sand and gravel in a laboratory flume. Five various triangular hydrographs were generated. A clockwise behavior for the total bed load versus shear velocity was observed meaning that the bed load during rising limb was higher than that of falling limb. It was found that the percent finer at the plateau of bimodal sediment size distribution curve had higher values during the initial and final phases compared to those obtained during the peak time. At all plateaus, the percent finer values related to the hydrograph peak discharge were in the same order of magnitude with that of the bed material. The sand content of the transported bed material initially decreased, then maintained a constant value during a certain time interval and finally returned to its original value. The sand percent of the bed load decreased in the falling limb showing a counterclockwise loop and the duration of the hydrograph did not affect the results considerably. The greater the peak flow rate of the hydrograph, the greater was the hysteresis. The bimodality index was calculated for all transported sediment samples and it was revealed that its initial and final values were less than that of the bed material but it was approximately the same elsewhere. The 5% finer sediment amount was nearly equal during rising and falling limbs. It was revealed that D50 value of the bed load decreased in the rising limb showing a clockwise loop. The hysteresis was not considerably changed according to the hydrograph characteristics. The clockwise type hysteresis was also observed for the size group of D95. The lag increased as the peak flow rate increased. A strong relation was found between the dimensionless total bed load Wt* and the total work index Wk as well as Wk and the ratio WR/WF. The correlations between the dimensionless total bed load and the unsteadiness parameters P, and Pmod were very weak, whereas a high value of determination coefficient was obtained with the unsteadiness parameter Pgt, implying an appreciable interdependence.

Numerical investigation of swash–swash interaction effects on beachface evolution using Nonlinear Shallow Water Equations

This paper presents a numerical investigation of multiple identical swash events to study the swash–swash interaction processes and their impacts on beachface evolution. The numerical model, based on the Nonlinear Shallow Water Equations, is first calibrated/validated against two different single-event-based data-sets. Multiple swash events are generated by identical solitary waves separated by different time intervals, to achieve weak and strong wave-backwash interactions. After a small number of weak interaction events the main feature is erosion from lower and mid swash region and deposition seaward of the swash in a bed-step, created by a backwash bore, primarily due to bed-load. As the number of waves increases, the strength of this backwash bore reduces because of the reduced beach slope caused by the growing bed-step. This eventually leads to a net quasi-equilibrium between bed- and suspended-load per period in most of the swash and surf zones. For strong interaction, initial bed evolution per event is much slower, due to interactions, and is bed load dominated. A quasi-equilibrium is also established as the influence of suspended load grows. Overall bed change per period within the domain eventually converges in both cases. Final bed profiles (i.e. after the same elapsed time, but different numbers of waves) are fairly similar, both with an offshore swash bar. Both profiles continue to evolve on the offshore side of this bar. However, this evolution is driven by suspended load for the weak interactions and bed load for strong interactions. The implication is that similar swash morphological features can emerge from different swash processes, and also be maintained distinctly.

Improved XBeach model and its application in coastal beach evolution under wave action

ABSTRACT Beach evolution is one of the key issues in coastal engineering. High computational efficiency model of beach evolution is limited by strong wave nonlinearity, flow acceleration, and sediment phase lag. The XBeach model is improved to cover the three limitations in the study. First, the near-bed velocity of nonlinear wave is reconstructed by using nonlinear parameters. Second, flow acceleration and sediment phase lag are taken into account for the near-bed sediment conditions to calculate the equilibrium concentration of suspended sediment and the transport rate of bed load. The response of sediment is not necessarily instantaneous to near-bed velocity in practical problems, but separated into a phase (time) shift between sediment concentration and velocity and a phase residual denoting sediment amount in moving at flow reversal. The improved XBeach model performs better results than the original XBeach model. Numerical experiments are carried out using the improved XBeach model to investigate the effects of wave height and sediment size. The numerical experiments show that the volume and range of erosion/deposition increase with the increase of wave height and decrease of sediment size, and deposition center moves to offshore. The perspective of wave energy and phase lag can explain the erosion/deposition variation.