Bedload Research Articles

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.

The statistical parameters analysis of bed load grains in Sungai Kakap Waters, Kubu Raya Regency

This study aims to analyze the statistical parameters of bed load grains in Sungai Kakap Waters, Kubu Raya Regency, West Kalimantan Province. Bed load sampling was carried out at seven stations, with five sampling points each. The hydrometer test on the sample was carried out to determine the grain type and size of the bed load, and statistical parameter analysis to determine the mean size, sorting, skewness, and kurtosis. The results showed that the fraction of bed load in the form of sand was 38.54%, silt was 42.11%, and clay was 19.28%. The bed load was dominated by three types, clayey clay, clay, and dusty clay. Based on the grain size parameters of the bed load, the mean size (in units) is 0.94 – 2.24, with the classification of coarse sand to fine sand. The results also showed that the sorting obtained is poorly sorted, the skewness of the sediment is very fine skewed, and the kurtosis is platykurtic.Keywords: bed load; sorting; skewness; kurtosis

Bedload Estimation: Case of Wadi El-Hammam in the North-West of Algeria

In Algeria, only the transport of suspended sediment is measured, the rate of bedload in the global transport of solids is estimated, approximately. Measures of bed load transport in the field are very costly, due to flow disturbances. As a result, evaluations of this type of sediment transport are difficult to carry out in the absence of databases. In this article, we tried to quantify this mode of transport at the wadi El-Hammam using the formula of Meyer-Peter and Müller. Formula that seems best adapted to the physical characteristics and flow conditions of the wadi studied. The results obtained show that the calculated bedload ratio is between 0.6 and 28 % of the suspension. The quantities transported annually are very large and irregular as they vary from 2.3 to 32 Mg.km-2.year-1, characterising the Mediterranean mountains and semi-arid environments. A good correlation was found between the daily bedload flow and the liquid flow, the obtained model Qs = aQb, can be easily used to estimate the bedload transport at the Hacine hydrometric station, located at the output and without data concerning this phenomenon. Keywords: Bed load transport; Fergoug; Meyer–Peter and Müller formula; Suspension; Wadi El-Hammam.

The statistical parameters analysis of bed load grains in Sungai Kakap Waters, Kubu Raya Regency

This study aims to analyze the statistical parameters of bed load grains in Sungai Kakap Waters, Kubu Raya Regency, West Kalimantan Province. Bed load sampling was carried out at seven stations, with five sampling points each. The hydrometer test on the sample was carried out to determine the grain type and size of the bed load, and statistical parameter analysis to determine the mean size, sorting, skewness, and kurtosis. The results showed that the fraction of bed load in the form of sand was 38.54%, silt was 42.11%, and clay was 19.28%. The bed load was dominated by three types namely clay loam, loam, and silt loam. Based on the grain size parameters of the bed load, the mean size (in φ units) is 0.94 – 2.24, with the classification of coarse sand to fine sand. The results also showed that the sorting obtained is poorly sorted, the skewness of the sediment is very fine skewed, and the kurtosis is platykurtic.Keywords: bed load; sorting; skewness; kurtosis

First Evidence of Microplastic Presence in Bed Load Sediments of a Small Urban Stream in Warsaw

Microplastics (MPs) are considered as a contaminant of widespread global concern. Due to their small size, MPs become bioavailable to many types of organisms and affect them. However, there is still little known about MP release on land, storage in soils and sediments, or their transport by runoff in rivers. Thus, the aim of this work was to present the results of the first, initial investigation on microplastic presence in an urban stream located in Warsaw, Poland. A simple and relatively inexpensive procedure that leads step-by-step to the detection of microplastics in bed load sediment is presented. It consists of sampling, sieving, density separation, organic matter reduction, and Nile Red staining. The presence of MP in the channel of Służew Creek was confirmed. The estimated amount of particles ranged from 191 to 279 pieces per 30 g of bed load sediment for the selected sampling sites. The number of particles seemed to increase with the catchment area. There is a need for further broad research focusing, among others, on the standardization of methods and laboratory procedures leading to microplastic detection.

Finite Element Numerical Simulation of Local Scour of a Three-Dimensional Cylinder under Steady Flow

Pile safety has received increasing attention in marine engineering, especially in the field of local scour. In this paper, a finite element numerical model is established for local scour around a cylinder in steady currents. The flow is described by unsteady Reynolds–averaged Navier–Stokes equations with a traditional turbulent closure model. The proposed scour model takes bed load into account. The Exner equation is solved to determine the bed variation and the moving mesh approach is used to capture the evolution of the bed. When the resulting slope exceeds the angle of repose, a novel sand-slide model based on Rodrigues' rotation formula is used to prevent simulation distortion. All the equations are discretized by the two-step Taylor–Galerkin algorithm, and the resulting approach is fast to implement with second-order accuracy in space. The numerical results are found to be in good agreement with the experimental data.

On Bed Form Resistance and Bed Load Transport in Vegetated Channels

A set of laboratory experiments were conducted to study the impact of vegetation on bed form resistance and bed load transport in a mobile bed channel. Vegetation stems were simulated by using arrays of emergent polyvinyl chloride (PVC) rods in several staggered configurations. The total flow resistance was divided into bed, sidewall, and vegetation resistances. Bed resistance was further separated into grain and bed form (i.e., ripples and dunes) resistances. By analyzing experimental data using the downhill simplex method (DSM), we derived new empirical relations for predicting bed form resistance and the bed load transport rate in a vegetated channel. Bed form resistance increases with vegetation concentration, and the bed load transport rate reduces with vegetation concentration. However, these conclusions are obtained by using experimental data from this study as well as others available in the literature for a vegetated channel at low concentration.

Numerical modelling of local scour around a spur dike with porous media method

ABSTRACT A 3D numerical model is developed to investigate the flow motion and sediment transport around a spur dike. In this model, fluid motion is described by the Navier–Stokes equations, adopting large eddy simulation to capture turbulent transport and dissipation. The spur dike and sand bed are treated by the porous media method. The suspended load concentration and the bed load transport rate is calculated separately, and then the bed variation is updated using the mass-balance equation. A series of flume experiments are employed to validate the model’s performance before being applied for the case of partially emergent spur dikes and submerged spur dikes, respectively. Detailed analyses on the spatial-temporal variation of flow intensity, sediment concentration and shapes of scour holes are made, based on which some innovative findings are discussed such as the scouring process patterns, as well as the influence of flow conditions on the maximum scour depth and location, and then useful engineering suggestions are provided to improve structural safety.

Multi Grain‐Size Total Sediment Load Model Based on the Disequilibrium Length

AbstractIn natural rivers, sediment heterogeneity and flow variability control the diversity of transport modes that occur. Although these different modes contribute to the total sediment transport, a law extending from bed load to suspended load that is, relevant for a wide range of sediment mixtures and flow conditions is lacking. Besides, a transport‐limited assumption is often made in modeling of fluvial morphodynamics and thus potentially misses under‐/over‐capacity regimes associated with a particular range of grain sizes and hydraulic conditions. We present a Multi Grain‐Size Total Load model based on widely accepted concepts of sediment transport and developed within the transport length framework in combination with an erosion‐deposition formulation. The new transport length model captures the diversity of transport modes as a physical continuum. Transport capacities for single or bimodal grain sizes are reasonably predicted when compared to published data and scale with the bed shear stress through a continuously varying exponent linked to the characteristic transport height. Modeled transport lengths extend over several orders of magnitude at given flow conditions. Extremely long distances suggest that suspended transport is probably never at capacity. The model can be extended to populations of various grain sizes with a threshold of motion corrected from hiding‐exposure. However, further experimental constraints are needed to better describe entrainment and saltation in strongly heterogeneous bed load transport. The new theoretical formalism we introduce paves the way for a Multi Grain‐Size Total Load Sediment Transport model that includes the variety of transport modes in both non‐stationary and stationary regimes.

Applicability of several machine learning models in estimation of vortex tube trapping efficiency

Abstract A vortex tube ejector comprises a tube with a slitted crown that lies flush across the entire width of a channel bed surface. The bed and suspended loads are ejected with minimal flushing water through the slit with the same efficacy as any other alternative extractor. The whirling flow phenomena through the vortex duct are very complex, so ordinary classical models have results contrary to required design guidelines. So, the machine learning (ML) models of the artificial neural network (ANN), deep neural network (DNN), gradient boosting machine (GBM), stacked ensemble (SE), and adaptive neuro-fuzzy inference system (ANFIS) are used to predict vortex tube trapping efficiency (VTE). The input dataset takes the size of the sediment (Sz), concentration (I) of the sediment, the ratio of slit thickness to diameter of the tube (th/dia), and extraction ratio (Extro) while trapping efficiency (TE) is taken as output. Based on statistical assessments, GBM appears to be better than all proposed models. However, other proposed ML models give comparable performance. The classical models, multivariate linear, and nonlinear regression techniques also provide comparatively good results. According to sensitivity analyses, the extraction ratio is the most relevant parameter in evaluating the VTE.

Contrasting modes of sediment infilling and geomorphic change within a sand dominated dredge pit on the inner Louisiana shelf

While many sediment transport studies have been performed on mud capped dredge pits (MCDP), there is a paucity of sediment infilling data for sand dominated dredge pits (SDDP) in the Northern Gulf of Mexico (NGoM). In this study, bathymetry, sidescan, and subbottom data were collected in 2018, 2019, and 2020 and sediment cores were collected between the 2019 and 2020 surveys at Block 88: a dredge pit sitting on the sand-dominated Ship Shoal of Louisiana's inner shelf. The crest of Ship Shoal was 5 m below mean sea level before dredging and was excavated to a depth of 10 m below mean sea level after the dredging of 8.4 million m3 of sediment. Two years after dredging, the northern end of the eastern pit wall accumulated ∼0.09 million tons (approximately 500 m long × 50 m wide × 2.5 m deep) of sediment, driven by westward longshore sediment transport and the deposition of bed load on the shoal crest. Sediment accumulation on the pit bottom was mainly driven by suspended load at a rate of ∼0.1 m yr−1 from 2018 to 2019 and ∼0.2 m yr−1 from 2019 to 2020. Thus, the sediment infilling in Block 88 was from both bed- and suspended-loads from contrasting sources. These pit-bottom sediment accumulation rates are approximately one order of magnitude lower than the predicted rate from a previous empirical modeling study conducted on Ship Shoal and lower than the rates (0.5–2 m yr−1) of three other MCDPs on the inner Louisiana shelf. The infilling sediment was patchy and predominantly silt and clay, with lower sidescan reflectivity. The slopes of Block 88's pit walls decreased from ∼20° in 2018 to ∼8° in 2020. These values were smaller than the values of pit wall slopes in MCDPs at a similar stage (i.e., 2–3 years after dredging). Our results indicate that the highest sediment accumulation rates occur immediately adjacent to the eastern pit wall of Block 88, which is down-current of the longshore transport direction. This study helps sand resource managers and policymakers to better plan and design future sediment dredging projects on sandy shoals. This study concludes that the longest axis of a dredge pit should be aligned perpendicular to the longshore transport direction to trap the most sediments for possible reuse. Additionally, both bed load and suspended load should be considered in future modeling to better predict sediment infilling.

Sediment sources and delivery of Norwegian mountain rivers in a changing climate

AbstractThe projected climate change for Norway through the 21st century predicts that the temperature will increase significantly. Events with heavy rainfall will be more intense and occur more frequently. Rain floods will increase in magnitude and also occur more frequently. Extreme flooding and heavy rain will significantly impact the sediment dynamics in rivers. In the mountain areas, floods are often associated with erosion, transport and deposition of coarse sediment along the streams. These processes are related to bed load transport and pose a hazard in addition to the elevated water discharge and have to be included in management plans for river basins. This article studies the bed load delivery from sources that contribute the most to the sediment budget in the Gudbrandsdalslågen river basin during the large magnitude floods in 2011 and 2013. More than 100 debris slides and debris flow were triggered in the tributary river Veikleåi by the heavy rain and snowmelt during these floods. The volume of the contribution from debris flows and erosion and deposition of the river bed was determined by subtracting digital elevation models acquired during repeated airborne LIDAR surveys. In the river Dørja the supply of sediment from a number of debris flows caused extensive aggradation and channel changes. In their new position, lateral erosion by these channels triggered slides on the adjacent slopes. The contributing volumes of debris flows, lateral erosion, and river bed erosion and deposition were determined from the LIDAR surveys. Relations obtained from studies of sediment transport in modern glacier rivers were used to obtain estimates of the ratio of bed load versus suspended load derived from the Pleistocene moraine deposits. Several monitoring stations using conventional methods for measuring bed load and suspended load recorded very large volumes of sediment delivery during both of the extreme floods. The results of the study may be used to identify necessary locations for check‐dams and erosion protection works in order to adapt to climate change.

Microplastic trapping in dam reservoirs driven by complex hydrosedimentary processes (Villerest Reservoir, Loire River, France)

Dam reservoirs can strongly influence the spatial distribution of sediment pollution by microplastics (MP). The Villerest reservoir (Loire River, 36 km long) is a good candidate to study the relationship between MP pollution and hydrosedimentary processes. Sediments were collected from the dam-controlled river section and from 3 km downstream. Geomorphological and sedimentological analyses were performed and microplastics were analysed using µFTIR imaging (polymer identification for particle sizes ≥ 25 µm). This paper highlights strong MP levels (on an order of 104 items/kg dw) over the section characterized by fine-grained sediments (FGS). In coarse-grained sediments (CGS), at the upstream part of the reservoir and downstream of the dam, levels are one order of magnitude lower. FGS are indicator of long-time settling processes. Such conditions lead to foster the MP trapping as low-density suspended materials in the water column. CGS deposits originate from the river bed load. These sediments are transported in high-velocity and high-turbulent flow conditions. Moreover, post-depositional reworking of the finest fraction can occur according to hydrofluctuations. Here are adverse conditions for the MP trapping. The polymer diversity is also higher in FGS than in CGS. However, the range of plastic particle sizes is similar in FGS and CGS and is not related to the sediment grain-size distribution. Moreover, in both FGS and CGS, the polymer abundance is not correlated with the grain-size distribution or with the organic matter content. In the reservoir context, a change in the polymer partition appears over the FGS section in the downstream direction, depending on the polymer density. From a fundamental point of view, this work contributes to improving our understanding of the key role played by hydrosedimentary processes in MP repartition. These findings also have operational scopes, providing significant elements to advocate for a better consideration of MP pollution during sediment management operations.

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.

Planform Dynamics and Cut-Off Processes in the Lower Ucayali River, Peruvian Amazon

The Ucayali River is one of the most dynamic large rivers in the world, with high rates of channel migration regularly producing cutoffs. In the lower portion of the Ucayali River, before its confluence to the Marañon River where the Amazon River is born, the increase in water and sediment discharge triggers bends with secondary channels (transitional stage from purely meandering to anabranching), which influence the planform migration rates and patterns of the sinuous channels. Based on remote sensing analysis, a comparison of planform dynamics of bends with and without secondary channels is presented. For the case of a bend with secondary channels (Jenaro Herrera, JH), detailed field measurements for bed morphology, hydrodynamics, bed and suspended load are performed for low-, transitional- and high-flow conditions (August, February and May, respectively). Additionally, a two-dimensional depth average hydraulic model is utilized to correlate observed migrating patterns with the hydrodynamics. Results indicate that the secondary channels have disrupted typical planform migration rates of the main meandering channel. However, at high amplitudes, these secondary channels reduce their capacity to capture flow and start a narrowing process, which in turn increases migration rates of the main channels (meandering reactivation process), suggesting that an imminent cutoff along the JH bend is underway by pure lateral migration or by the collapse into the existing paleochannels.

Experimental investigation of flow pattern over a fully developed bed at a 60° river confluence in large floods

River confluences have a complex flow and sedimentation pattern that have vital influences on the hydraulic and bed morphology of river reach and the surrounding area. Confluences can be observed in waterways with various situations such as live bed conditions. This condition is a hydro-morphological situation with a high densimetric Froude number, i.e., bed load transport is supplied from upstream. According to the literature review, most of the experimental studies investigate the flow pattern on the flatbed and not on the developed riverbed, or/and in the low densimetric Froude number, or/and without supplying the sediment from upstream. Therefore, in the present study for the quantification of the flow pattern under these conditions, each developed bed was fixed with the cement blanket method in the laboratory. Then, the 3D velocity was measured at specific points at the confluence. The current study was designed to understand the flow pattern corresponding to the river bed behavior in the case of large floods. It is expected that the morphological features downstream of the confluence have a different pattern than the ones in the condition described in other literature. Thus, this paper describes briefly what are the different bed features and investigates the corresponding flow pattern. The results of the flow pattern on the developed bed show that all zones at the river confluence can be observed except the point bar due to the approximate equality of the mean longitudinal velocity of the separation zone and the main channel upstream of the confluence. Moreover, results show that by increasing the bedload ratio (sediment discharge to water discharge of the main channel of upstream of the confluence) from 0 to 3 × 10−4, flow deflection to the outer bank of the channel decreased down to 45%, the stagnation equivalent area decreased down to 2.5 times, and bed shear stress decreased down to 40%. Hence, the momentum of lateral flow decreased with increasing bedload. Besides, the recovery zone occurred at a longer distance after the confluence compared to the case without bedload. Hence, the location of the maximum velocity zone, vortices, and secondary flows changed downstream of the confluence, by changing the bed load value.

Modeling of 1D sediment transport in the langat river using quasi-unsteady HEC-RAS

The primary goal of this research was to investigate the sediment transport characteristics of the Langat River. The Langat River is situated in the state of Selangor, Malaysia, and is prone to flooding on a regular basis. The River Analysis System tool from the Hydraulic Engineering Center (HEC-RAS) was used to determine the sediment transport capacity of the river. The sediment transport and hydraulic models were created using elevation and cross-sectional data in HEC-RAS. The sediment transport model employed several approaches to calculate sediment transport capacity. HEC-RAS contains some useful built-in functions which were used in this study to visualize the sediment transport, calibration and calculation of Manning’s roughness coefficients, and forecast changes in bed elevation. The investigation reveals that urban development has resulted in a large rise in riverbed depth, implying that is no difference in flooding pattern in the short period of time. This paper focuses only on bed load sediment. The results of three years of stream flow show that some areas have experienced silt transport and river deposition. The river had changed slightly after utilizing the Laursen-Copeland method in HEC-RAS. The simulation outcome shows the segment that experienced sediment transport at River Stations RS 12926 from Lui, RS 9362 from Langat upper reach, and RS 3730 from Langat Lower Reach are experiencing sediment deposition activities.

Hybrid Modeling for Solutions of Sediment Deposition in a Low-Land Reservoir with Multigate Sluice Structure

At the multigate sluice structure on a fluvial river, undesired sediment deposition affects the normal operation of the reservoir in question. Physical and numerical models are hybridized to help explore flow and sedimentation patterns. Field and laboratory investigations show that the deposition is attributable to the formation of large recirculation zones at low and medium discharges. As a potential countermeasure, an array of guide vanes is recommended to cope with the concern. Their attack angle with the flow is a dominant parameter that needs to be evaluated. Tests in the fixed-bed model demonstrate that the vanes bend the reservoir flow towards the sluice and suppress the circulation zones along both banks. The favorable range of attack angle is 15–20°. With the examination of sedimentation of both bed and suspended loads, the numerical modeling indicates that the sediment-removal efficiency increases with an increase in attack angle. By weighing the flushing efficiency and the risk of local scouring at the vanes, the 15° vane layout is recommended. This study is expected to provide a reference for guide-vane design in similar situations.

Experiments on the Sediment Transport Along Pool‐Riffle Unit

AbstractThis study examines channel dynamics and bed load transport through a riffle and pool sequence forced by downstream channel width variations within an experimental flume. The experiment consisted of four runs across, which we compare and contrast local and spatially averaged bed surface texture and topography, sediment transport rates, and sediment mobility at five locations across a pool‐riffle pair. Sediment transport was measured using mini Helley‐Smith samplers and particle tracers seeded in the monitored riffle and pool. In this study, “local” sediment transport rates were highly variable across the five monitoring locations. The lowest sediment transport rate was recorded at the riffle tail whereas the highest rates were measured at the riffle head and the pool center. The texture of the bed surface and transported load do not explain measured bed load transport trends and depending on how the measurements are aggregated differing interpretations are supported. In general, the bed texture in the pool was finer than the texture in the riffle, however, specific grain‐size percentile classes derived from pooled population analysis suggests little to no difference between pool and riffle texture. The combined results highlight the importance of acknowledging and applying analysis techniques to better understand the inherent variability of bed load transport within channel reaches where morphology differs, such as pools and riffles.

СЕЗОННЫЕ ИЗМЕНЕНИЯ СОДЕРЖАНИЯ ЗАГРЯЗНЯЮЩИХ ВЕЩЕСТВ В НАНОСАХ ОВРАЖНО-БАЛОЧНЫХ КОМПЛЕКСОВ НА ТЕРРИТОРИИ САРАТОВА

The observation results of pollutant (heavy metals, oil products) concentrations in the bed load of perennial stream outlets of ravine and gully complexes in the city of Saratov are presented. A multiple exceeding of the background content for the analyzed indicators, primarily in the watercourses of industrial zones, is found. The bed load of the maximum water and solid runoff in spring is more polluted than for the minimum water discharge of the watercourses in summer. It can be concluded that it is necessary to create a surface flow treatment system on the territory of Saratov, since solid and water runoff from ravine and gully complexes enters the Volgograd Reservoir, which is a source of drinking water supply and a recreational and fishery object.