Bed Sediment Transport Research Articles

Impact of emergent vegetation on three-dimensional turbulent flow properties and bed morphology in a partially vegetated channel

The study aimed to explore three-dimensional turbulent flow properties and bed morphology in a partially vegetated channel with sand bed conditions. Presence of flexible vegetation in the river and its interaction with the flow are of great significance in understanding the momentum and mass transport in the flow. Experiments were conducted in a straight, tilting rectangular flume with staggered emergent vegetation covering half of the channel width. The results show that the presence of vegetation diverts streamwise velocity from the vegetated side to the non-vegetated side. The study reveals that the presence of vegetation leads to an increase in turbulent intensity, turbulent kinetic energy, and Reynolds shear stress at the transition area between the vegetated and non-vegetated sides of the channel. This increase is attributed to higher transverse flow and momentum exchange in the transition area between the vegetated and non-vegetated sides. In the vegetated side, the vegetation serves as an obstruction, reducing turbulent intensity, turbulent kinetic energy, and Reynolds shear stress compared to the transition area between the vegetated and non-vegetated sides. This reduction in turbulence supports the stability of bed materials and promotes sediment deposition. The presence of vegetation significantly alters the secondary current in the channel. Scour depth along the non-vegetated side was higher than the vegetated side, mainly because the flow concentrated in the centre and non-vegetated side of the channel. The investigation determines that the existence of vegetation on the vegetated side effectively protects against bed erosion and sediment transport. Understanding the impact of emergent flexible vegetation on flow properties and sediment transport can inform decisions about vegetation layouts in river ecosystems.

Effects of Leafy Flexible Vegetation on Bed‐Load Transport and Dune Geometry

AbstractThe development of sustainable river management strategies requires knowledge of the effect of vegetation on hydrodynamics and sediment transport. To date, the complex physical processes involving the combined effects of leafy flexible vegetation and mobile bedforms are not completely understood. Most sediment transport models have been developed for bare bed conditions so that their performance in the presence of leafy flexible vegetation remains unclear. On the other hand, recently developed models consider vegetated conditions but they typically account only for the presence of rigid cylinders and in some cases scour at their base. For this purpose, laboratory experiments were conducted with mobile dune bed conditions and artificial flexible plants with varying Leaf Area Index to investigate the effect of flexible vegetation on bed morphology and sediment transport. Sediment transport rates and bedform characteristics such as height, wavelength and celerity, were measured in specifically designed experimental runs. The collected data show that the presence of leafy vegetation alters bed morphology, tending to reduce the average dune wavelength and leading to the formation of complex 3D geometries. Bed‐shear‐stress‐based models for predicting sediment transport were verified to be valid under conditions of low vegetation roughness density. On the contrary, the collected data emphasize that the measured bed‐load transport rate increased in the presence of leafy flexible vegetation with higher frontal area. Recent bed‐load models for vegetated channels provide a better interpretation for dense leafy vegetation but are less effective when predominant effects related to dunes are present.

Experimental Investigation on Flow and Bed Sediment Transport around a Semi-Circular Abutment in the Presence of Irregular Vegetation

Experimental Investigation on Flow and Bed Sediment Transport around a Semi-Circular Abutment in the Presence of Irregular Vegetation

Field observations on the characteristics of sand ripples on tidal flats

Ripples on tidal flats significantly influence bedform roughness and near-bed turbulence, yet their dynamics in sandy and muddy environments remain incompletely understood. While laboratory studies have elucidated the effects of mud content and extracellular polymeric substances (EPSs) on ripple formation and stability, the interactions between ripple characteristics, EPS, and mud content in natural settings are more complex and not thoroughly explored. To address this gap, we conducted field studies on sand ripples at the central Jiangsu coast, China, using high-resolution drone photogrammetry to accurately measure ripple dimensions. We performed bedload sampling at both ripple crests and troughs to analyze median grain size, mud content, and EPS concentrations. Our results show that the investigated ripple wavelengths range from 34 to 46 mm, and heights vary between 2.7 and 5.3 mm. Ripples developed near tidal creeks show pronounced asymmetry. Significantly, EPS concentrations are markedly higher at the ripple crests than at the troughs, and it follows a power-law relationship with the median grain size. These results highlight the complex intricate relationship between the ripple morphology, environmental forcing conditions, and EPS content. Our findings enrich the understanding of ripple development and the factors influencing current-dominated ripples in natural environments. This research also adds to the better prediction of the bedform roughness and quantification of the near bed sediment transport.

Study of Velocity Changes Induced by Posidonia oceanica Surrogate and Sediment Transport Implications

An analysis of the interactions between wave-induced velocities and seagrass meadows has been conducted based on the large-scale CIEM wave flume data. Incident irregular wave trains act on an initial 1:15 sand beach profile with measurement stations from the offshore of a surrogate meadow until the outer breaking zone, after crossing the seagrass meadow. The analysis considers variability and peaks of velocities, together with their skewness and asymmetry, to determine the effects of the seagrass meadow on the near bed sediment transport. Velocity variability was characterized by the standard deviation, and the greatest changes were found in the area right behind the meadow. In this zone, the negative peak velocities decreased by up to 20.3%, and the positive peak velocities increased by up to 11.7%. For more onshore positions, the negative and positive peak velocities similarly decreased and increased in most of the studied stations. A progressive increase in skewness as the waves passed through the meadow, together with a slight decrease in asymmetry, was observed and associated with the meadow effect. Moving shoreward along the profile, the values of skewness and asymmetry increased progressively relative to the position of the main sandbar. The megaripple-like bedforms appeared earlier when the meadow was present due to the higher skewness, showing a belated development in the layout without the meadow, when skewness increased further offshore due to the proximity of the breaker sandbar. To assess the sediment transport capacity of a submerged meadow, the SANTOSS formula was applied, showing that in front of the meadow, there was a higher sediment transport capacity, whereas behind the meadow, that capacity could be reduced by up to 41.3%. In addition, this formula was able to produce a suitable estimate of sediment transport across the profile, although it could not properly estimate the sediment volumes associated with the bedforms generated in the profile.

Flood simulation with the RiverCure approach: the open dataset of the 2016 Águeda flood event

Abstract. Floods are among the most common natural disasters responsible for severe damages and human losses. Numerically produced data, managed by user-friendly tools for geographically referenced data, have been adopted to increase preparedness and reduce vulnerabilities. This paper describes the locally sensed and numerically produced data that characterize a flood event that occurred in February 2016 in the Portuguese Águeda River, referred to as Agueda.2016Flood for short. The data were managed through the RiverCure portal, a collaborative web platform connected to a validated shallow-water model featuring modelled dynamic bed geometries and sediment transport. The dataset provides a synthesis of topo-bathymetric, hydrometric and numerically produced data from a calibrated hydrodynamic model. Due to the lack of measured hydrometric data near the city, the numerically produced data are crucial for a complete description of the flood event. The Agueda.2016Flood dataset constitutes a complete validation test for flood forecasting models and a tool to better mitigate floods in this river and in similar rivers. Thus, Agueda.2016Flood is a relevant dataset for Águeda River stakeholders as well as for the community of flood modellers, as it provides a well-documented validation event for forecasting tools. The dataset can be accessed at https://doi.org/10.4211/hs.937927473a3a4e66a07a2e2fdd9d581e (Ricardo et al., 2024).

Hydro-morphodynamic responses of rivers to the construction of hydropower dams: a case study – the Kor River, Iran

Rivers are one of the main components of the ecosystem that has changed because of more pressing human activities, such as the building of small and large dams along rivers. The impact of dams on fluvial hydro-morphology in arid and semi-arid regions, such as the Middle East, has received little attention, even if such fluvial corridors represent major sources of livelihood for the local population. In this study, the influence of the Mollasadra Dam, on the hydro-morphological conditions of the Iranian Kor River is numerically investigated using iRIC MFlow_02, by considering different flooding conditions. Simulating different scenarios with and without the dam, and looking at key parameters like flow rate and velocity, sediment transport rate, and bed topography, it is evident that the dam significantly reduces the water discharge and the relative flow velocities, while it has a relatively reduced impact of the bed morphology and sediment transport. This can be ascribed to the fact that the Kor River is a capacity-limited watercourse, characterized by rather coarse material and reduced sediment transport.

Bed shear stress and sediment transport equations for predicting morphological and shoreline changes: a review

Coastal sediments can be transported as bedload and suspended-load transport by waves and currents. The waves stir up the sediments, then currents transport sediments. Waves on the bottom can generate bed-shear stress. Meanwhile, the combination of bedload and suspended-load transport is known as total sediment transport. Prediction of total sediment transport has become important related to coastal morphological change and also shoreline change. Most of the sediment transport equations and approaches are developed from the physical principles. There are so many researchers proposed some formulas and methods with some considerations and difficulties. Due to the complexity of coastal conditions, the existing sediment transport rate prediction formulas are still not finished yet. Several well-known equations of bed-shear stress, bedload-suspended transport, and cross shore-longshore sediment transport; are discussed and reviewed in the present study. Thus, an overview of approaches and formulations that are reliable and nearly accurate for calculating the total sediment transport rate based on the characteristics of each coastal waters will be obtained. Accurate estimation of sediment transport rates will provide good results for predicting and monitoring changes in coastal morphology and shoreline changes. Moreover, coastal monitoring can be used for actions related to coastal protection system and coastal management.

The influence of coarse particle abundance and spatial distribution on sediment transport and cluster evolution in steep channels under sediment-starved conditions

Large particles strongly influence flow resistance, energy dissipation, bed stability, and channel morphology in mountain streams. We conducted flume experiments to evaluate effects of the density and spatial distribution of coarse particles (i.e., keystones) on bed stability, surface texture and sediment transport in steep channels. Keystones were placed on the channel bed surface at the beginning of each experiment, both in clustered and in uniformly spaced (i.e., anti-clustered) configurations and in different numbers (i.e., for different values of keystone density). The flow rate was increased by 20 % every hour and each experiment continued until the bed was completely scoured. Sediment transport was measured with a sediment trap located at the flume outlet. Topographic data from high-resolution surface imagery and second-order structure functions (SSF) of bed elevations, were used to characterize bed surface structuring while the Ripley’s K function was used to assess the degree of clustering of keystones relative to random spatial distributions. Our results indicate that (1) the density and spatial distribution of keystones exert a minor control on the bed surface grain-size distribution (GSD), (2) for increasing flow rates, the spatial distribution of keystones naturally evolves towards a random distribution, regardless of the initial spatial arrangment, and (3) sediment transport has a higher correlation with the proportion of dislodged keystones than with flow discharge.

Erosion and accretion patterns on intertidal mudflats of the Yangtze River Estuary in response to storm conditions

Understanding of erosion and accretion patterns over intertidal mudflats during storm periods is vital for the management and sustainable development of coastal areas. This study aimed to investigate the effect of the 2014 storm Fung-wong on the erosion and accretion patterns of the Nanhui intertidal mudflats in the Yangtze estuary, China, based on field measurements and Delft3D numerical modeling. Results show that prolonged easterly winds during the storm enhance the flood velocity, weaken the ebb velocity, and even change the current direction. The current velocity, wave heights, and bed-level changes increased by 1–1.43 times, 2.40–3.88 times, and 2.28–2.70 times than those of normal weather, respectively. The mudflats show a spatial pattern of overall erosion but increasing erosion magnitude from the high (landward) mudflat to the low (seaward) mudflat during the storm. The magnitude of bed-level change increases with increasing wind speed, but the spatial pattern of erosion and accretion remains the same. The main reason for this pattern is the longer submersion duration of the low mudflat compared with the high mudflat, so the hydrodynamic process is longer and stronger, leading to an enhancement in bed shear stress and sediment transport rate. Wind speed increases the hydrodynamic intensity but does not affect on the submersion duration over each part of the intertidal mudflat. This study is helpful to improve the understanding of physical processes during storms on intertidal mudflats and provides a reference for their protection, utilization, and management, as well as for research in related disciplines.

Plot investigation on rill flow resistance due to path tortuosity

The path tortuosity t is an indicator of rill morphology accounting for the deviation of the thalweg from a straight alignment. The effect of t on flow resistance has been little investigated for rills. This paper reports the results of a plot investigation aimed to establish the suitable accuracy of the rill thalweg measurement to determine the tortuosity parameter and to test the reliability of a theoretical flow resistance law. Four rills were incised in clay soil (CS) and clay-loam soil (LS) and shaped by a clear flow discharge. The three-dimensional Digital Terrain Models were created by the Structure from Motion technique. For rills on LS, an approximate thalweg was tracked by photo-interpretation, and a specific calculation routine was applied to identify the cross sections with a constant spacing d. The actual rill thalweg was obtained as the line joining the lowest points of these cross-sections. Among the different tested d values, d = 0.075 m was chosen to determine t. For both CS and LS, the Darcy-Weisbach friction factor f featured a non-monotonic relation with t, which was explained as the result of three additive components due to bed roughness, sediment transport, and localized energy losses due to curves. The effect of the former two components on f contrasts that of the third, resulting in a linearly decreasing f-t relationship and constant flow velocity for the three lowest tortuosity values, and an increased friction factor and reduced flow velocity for the highest tortuosity value. The flow resistance law was positively tested, and the predicted friction factor was dependent on t.

The impacts of near-bed flow characteristics on river bed sediment transport under ice-covered conditions in 2016–2021

Global climate change has been projected to affect hydrology, the ice-covered flow period and river morphology (including changed sediment transport conditions) in northern high-latitude regions. To understand the impact of the expected shortening of the ice-covered period on bedload transport, one needs to understand the present sediment transport in these high-latitude rivers with annually occurring ice cover. Thus, the aims are (1) to define the impacts of ice cover on near-bed flow characteristics during hydrologically varying years, and (2) to analyse the impacts of these mid-winter flow characteristics on the bed sediment transport potential. The analyses are based on Acoustic Doppler Current Profiler (ADCP: 2016–21) and Acoustic Doppler Velocimeter (ADV: 2020–21) measurements performed in mid-winter ice-covered conditions of the sandy and small (circa 20 m wide) Pulmanki River in northern Finnish Lapland.Despite the ice-covered river conditions in winter, sediment transport occurs even during these harshest mid-winter conditions. The critical velocities and shear velocities of mid-winter conditions were exceeded in winters 2016–2021, and bedload transport occurred according to bedload measurements. Three different situations occurred regarding the bed sediment transport and near-bed velocity conditions: (1) high measured mid-winter discharges indicate high velocities throughout the meander bend; (2) low measured mid-winter discharges cause low near-bed velocities throughout the meander bend; (3) winters having intermediate discharges indicate near-bed velocities and sediment transport potential being higher at the upstream inlet and apex sections of the meander bend but clearly lower downstream of the apex. The confinement by the river ice cover, i.e. bottom-fast ice, explains the velocity variation. The near-bed velocities were the highest at the upstream inlet section of a symmetrical meander bend, where the measurement cross-sections were narrower and shallower. The velocities were the lowest downstream of the apex, where the channel changed from relatively narrow to wider and deeper.

Morphodynamics of vortex ripple creation under constant and changing oscillatory flow conditions

The morphodynamics of orbital vortex ripples due to oscillatory flow and induced sediment transport was studied numerically. The methodology was based on large-eddy simulations of the full coupling of turbulent oscillatory fluid flow, bed and suspended sediment transport, and bed evolution. The Immersed Boundary method was implemented for the imposition of fluid and sediment boundary conditions on the mobile bed surface. Results are presented for ripple creation starting from flat or rippled beds, as well as results of ripples adapting to changing flow (wave) direction. The computed equilibrium ripple dimensions are in agreement with existing empirical predictions; however, the computed ripple profile is not as steep in the vicinity of the ripple crest as the analytical one in Sleath (1984). The time needed for the bed geometry to reach equilibrium, in cases where the initial bed is almost flat or it is formed by ripples that shorten towards equilibrium, is longer than in cases where the initial bed is formed by ripples that widen towards equilibrium. Moreover, the ripple crests are reoriented when the flow changes direction by 45°; the new equilibrium ripple crestline is perpendicular to the flow direction. Finally, the numerical results are compared with corresponding results of flow above fixed ripples. The bed load flux does not present substantial differences between the fixed and mobile bed cases. On the contrary, a strong increase of the suspended load flux is observed for the mobile bed case in comparison to the fixed bed case. • LES Coupling between oscillatory flow, sediment transport, and bed morphodynamics. • Same flow forcing results into same bed equilibrium regardless of initial bed form. • Evolution of ripples longer than equilibrium ones is slower than for shorter ones. • Ripples are reoriented perpendicular to the flow direction. • Suspended load over mobile rippled bed is larger than over fixed ripples.

Depth-Resolved Modelling of Intra-Swash Morphodynamics Induced by Solitary Waves

We present a fully coupled 2DV morphodynamic model, implemented in OpenFOAM® that is capable of simulating swash-zone morphodynamics of sandy beaches. The hydrodynamics are described by the Reynolds-averaged Navier–Stokes (RANS) equations with a k−ω turbulence model and the Volume of Fluid (VoF) approach for discriminating between air and water. Sediment transport is described in terms of bedload and suspended load transport. We show that the default divergence scheme in OpenFOAM can become numerically unstable and lead to negative sediment concentrations, and propose a solution to avoid this problem. The model performance is assessed in terms of surface elevation, flow velocities, runup, suspended sediment concentrations, bed profile evolution and sediment transport volumes by comparing with measurements of field-scale (wave height of 0.6 m) solitary waves. The model shows reasonable agreement in terms of hydrodynamics and predicts the correct sediment transport volumes, although the deposition is predicted more onshore compared to the measurements. This is partially attributed to an overprediction of the runup. The model shows that the suspended sediment concentration displays a strong vertical dependence. These results show the potential of depth-resolving models in providing more insight into morphodynamic processes in the swash zone, particularly with respect to vertical structures in the flow and suspended sediment transport.

Hydraulic model of a braided channel to aid design of a grade-building structure

Presented here are considerations for designing a hydraulic model involving a broad reach of braided, sand-bed channel used to aid the design of a grade-building structure (GBS) for retaining bed sediment upstream of a sediment-deposition plain formed by a sediment-retention dam. The results focus on the similitude and calibration considerations needed to simulate bed-sediment transport along a large braided channel. Key variables in this regard were flow discharge, channel slope and sediment-transport rate. Additionally, the results describe how the GBS evolved in design from initially comprising four walls that lengthened flow path (thereby causing sediment deposition) to being four walls with openings that dispersed flow and consequently spread sediment deposition across the reach. The addition of rock aprons and wall bunds (curved, wall ends), enhanced sediment retention, reduced scour, and mitigated an under-wall seepage concern. In final design, the GBS retained approximately 83% of the bed sediment entering the reach over the test duration.

Coupled modelling of flow and non-capacity sediment transport in sewer flushing channel

Flushing is cost-effective for mitigating sediments and constraining environmental problems in sewer systems. Previous mathematical models are almost exclusively built upon simplified governing equations evoking the assumptions of slow bed evolution and sediment transport capacity, of which the applicability remains open to question. Here a 1D coupled non-capacity model is presented for non-uniform sediment transport in sewer flushing channels, as adapted from recently established shallow water hydro-sediment-morphodynamic models for fluvial processes. The present model is tested for an experimental flushing case in Paris's Des Coteaux catchment system. The computational results agree with observed data more closely than those of a previous decoupled capacity model. While the differences between decoupled and capacity models and the present coupled non-capacity model are minor for flushing processes of short-durations, they are more pronounced for sustained long-duration flushing processes. Physically, the adaptation of suspended sediments to capacity regime cannot be fulfilled quickly, though bedload sediments can adapt to capacity regime instantly. Also, the bed deformation rate is comparable to its counterpart of the flow depth. Therefore, coupled non-capacity modelling is suggested for general applications to sewer flushing channels, of which the computing cost is essentially equivalent to simplified models built upon decoupling and capacity assumptions.

Temporal evolution of backward erosion piping in small-scale experiments

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.

A Numerical Study of Sheet Flow Driven by Skewed-Asymmetric Shoaling Waves Using SedWaveFoam

SedWaveFoam, an OpenFOAM-based two-phase model that concurrently resolves the free surface wave field, and the bottom boundary layer is used to investigate sediment transport throughout the entire water column. The numerical model was validated with large-scale wave flume data for sheet flow driven by shoaling skewed-asymmetric waves with two different grain sizes. Newly obtained model results were combined with previous nonbreaking and near-breaking wave cases to develop parameterization methods for time-dependent bed shear stress and sediment transport rate under various sediment sizes and wave conditions. Gonzalez-Rodriguez and Madsen (GRM07) and quasi-steady approaches were compared for intra-wave bed shear stress. The results show that in strongly asymmetric flows, considering the separated boundary layer development processes at each half wave-cycle (i.e., GRM07) is essential to accurately estimating bed shear stress and highlights the impact of phase-lag effects on sediment transport rates. The quasi-steady approach underpredicts (∼60%) sediment transport rates, especially for fine grains under large velocity asymmetry. A modified phase-lag parameter, incorporating velocity asymmetry, sediment stirring, and settling processes is proposed to extend the Meyer-Peter and Mueller type power law formula. The extended formula accurately estimated the enhanced net onshore sediment transport rate observed under skewed-asymmetric wave conditions.

Numerical Analysis of Sand Bed Degrading and Sediment Transport Rate Under Tailings Dam Break

Dam-breaking accidents in tailings ponds may result in loss of tailings, damage to the downstream bridges and houses, flooding of farmland and roads, hazards to the local environment, and even loss of property and lives. Therefore, research on dam breaks in tailings reservoirs and prediction of subsequent impacts are of great significance. This paper describes theoretical and numerical analyses of the retrogressive erosion model and calculations of the sand bed surface profile and sediment transport rate following tailings dam break events. The calculation results show that the degrading rate of the bed surface in the reservoir area reaches a maximum when the breach is formed and then rapidly decreases to a stable value. Farther away from the breach, the peak degrading rate of the bed surface is lower. The time of the peak tailings outflow rate is related to the formation of the breach. A larger breach has a shorter formation time and a greater peak flow.

Hierarchical Fractional Advection-Dispersion Equation (FADE) to Quantify Anomalous Transport in River Corridor over a Broad Spectrum of Scales: Theory and Applications

Fractional calculus-based differential equations were found by previous studies to be promising tools in simulating local-scale anomalous diffusion for pollutants transport in natural geological media (geomedia), but efficient models are still needed for simulating anomalous transport over a broad spectrum of scales. This study proposed a hierarchical framework of fractional advection-dispersion equations (FADEs) for modeling pollutants moving in the river corridor at a full spectrum of scales. Applications showed that the fixed-index FADE could model bed sediment and manganese transport in streams at the geomorphologic unit scale, whereas the variable-index FADE well fitted bedload snapshots at the reach scale with spatially varying indices. Further analyses revealed that the selection of the FADEs depended on the scale, type of the geomedium (i.e., riverbed, aquifer, or soil), and the type of available observation dataset (i.e., the tracer snapshot or breakthrough curve (BTC)). When the pollutant BTC was used, a single-index FADE with scale-dependent parameters could fit the data by upscaling anomalous transport without mapping the sub-grid, intermediate multi-index anomalous diffusion. Pollutant transport in geomedia, therefore, may exhibit complex anomalous scaling in space (and/or time), and the identification of the FADE’s index for the reach-scale anomalous transport, which links the geomorphologic unit and watershed scales, is the core for reliable applications of fractional calculus in hydrology.