Numerical Model for Bank Erosion in the Brahmaputra River

A method is proposed to predict bank erosion and sand bar migration in river reaches where suspended sediment transport is dominant. The method focuses on the influence of the lateral bed slope on the erosion and deposition rate of suspended sediment, as well as on the profile of lateral bedload transport, assuming that geometric similarity holds in the bank region. In the proposed model, the erosion and deposition rate can be evaluated using either the bed shear stress at a reference location or the average bed shear stress in the bank region. In order to simulate bank erosion and associated bank shifting with a depth-integrated-base treatment, stretchable grids were added to the conventional coarse grid system near the bank. The proposed method, including the bank erosion model, is applied to the lower reach of the Brahmaputra River, which is ∼90 km long and ∼12.50 km wide. The computed results on bank shifting, sand bar migration, and sediment transport rates are compared with data obtained from field investigations and remote sensing. These results suggest that the proposed method is applicable for predicting sediment issues in river reaches dominated by suspended sediment.

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A PIV-based method to measure spatial gradients in bedload transport over a dune

E3S Web of Conferences ◽

10.1051/e3sconf/20184004012 ◽

2018 ◽

Vol 40 ◽

pp. 04012 ◽

Cited By ~ 1

Author(s):

Renske C. Terwisscha van Scheltinga ◽

Heide Friedrich ◽

Giovanni Coco

Keyword(s):

Shear Stress ◽

Sediment Transport ◽

Particle Velocity ◽

Particle Tracking ◽

Bedload Transport ◽

Sediment Flux ◽

Bed Shear Stress ◽

Spatial Gradients ◽

Accelerating Flow ◽

Dune Crest

Traditional sediment transport equations calculate sediment flux from bed shear stress and the equations predict that transport increases nonlinearly with an increase in flow velocity. In a dune field, the dune geometry affects the flow velocity causing accelerating flow over the dune crest and de- and reattachment of the flow downstream of the dune crest. Sediment flux predicted from the reach-averaged bed shear stress gives fairly good results for dune fields, though their simplification is discordant for the complexity of the processes involved. Measurements of the displacement of sand particles over the dune bed were derived from highfrequency image capturing. The two main methods to measure particle velocities from images are particle tracking velocimetry (PTV) and particle image velocimetry (PIV). We compare individual particle tracking with a PIV-based correlation method. The PIV-based method promises to be a more efficient and effective approach to track particle motion. It is more suitable for the conditions of high bedload transport, as present in our experiments. The PIV-based method is based on using images of difference (IoD) and is fully automated and identifies spatial gradients at a support scale in the order of centimetres. Findings align with our general knowledge of accelerating flow over the dune crest. The mean streamwise particle velocity and activity over a dune stoss slope increase. At the scale of 0.026 m the observed particle velocity variability can be explained in the context of general onset and cessation of sediment transport, the effect of the reattachment zone and observed sweep/burst events. By decreasing the streamwise distance between cross-sections, the variations in mean particle velocity induced by superimposed bed defects are distinguished as well. The maximum particle velocity and activity occurred at the same location and consequently the location of the maximum transport over the dune crest was identified. The measurements bridge the gap between individual particle motion studies and (non-local) sediment transport flux measurements.

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Bed Shear Stress Influence on Local Scour Geometry Properties in Various Flume Development Conditions

Water ◽

10.3390/w11112346 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2346 ◽

Cited By ~ 3

Author(s):

Kiraga ◽

Popek

Keyword(s):

Shear Stress ◽

Sediment Transport ◽

Mutual Influence ◽

Three Dimensional ◽

Critical Shear Stress ◽

Water Structure ◽

Correlation Coefficients ◽

Bed Shear Stress ◽

Hole Dimensions ◽

Bed Material

Numerous approaches in sediment mobility studies highlighted the key meaning of channel roughness, which results not only from bed material granulation but also from various bed forms presence, caused by continuous sediment transport. Those forms are strictly connected with the intensity of particle transport, and they eventuate from bed shear stress. The present paper comprised of local scours geometric dimensions research in three variants of lengthwise development of laboratory flume in various hydraulic properties, both in “clear-water” and “live-bed” conditions of sediment movement. Lots of measurements of the bed conformation were executed using the LiDAR device, marked by a very precise three-dimensional shape description. The influence of the bed shear stress downstream model on scours hole dimensions of water structure was investigated as one of the key factors that impact the sediment transport intensity. A significant database of 39 experimental series, lasting averagely 8 hours, was a foundation for delineating functional correlations between bed shear stress-and-critical shear stress ratio and geometry properties of local scours in various flume development cases. In the scope of mutual influence of bed shear stress and water depth, high correlation coefficients were attained, indicating very good and good functional correlations. Also, the influence of bed shear stress and the total length of the scour demonstrated a high correlation coefficient.

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Relationship between bed shear stress and suspended sediment concentration: annular flume experiments

International Journal of Sediment Research ◽

10.1016/s1001-6279(12)60009-2 ◽

2011 ◽

Vol 26 (4) ◽

pp. 513-523 ◽

Cited By ~ 12

Author(s):

Yunwei WANG ◽

Qian YU ◽

Shu GAO

Keyword(s):

Shear Stress ◽

Suspended Sediment ◽

Suspended Sediment Concentration ◽

Sediment Concentration ◽

Bed Shear Stress ◽

Flume Experiments ◽

Annular Flume

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Contributions of catchment and in-stream processes to suspended sediment transport in a dominantly groundwater-fed catchment

Hydrology and Earth System Sciences ◽

10.5194/hess-22-3903-2018 ◽

2018 ◽

Vol 22 (7) ◽

pp. 3903-3921 ◽

Cited By ~ 5

Author(s):

Yan Liu ◽

Christiane Zarfl ◽

Nandita B. Basu ◽

Marc Schwientek ◽

Olaf A. Cirpka

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Urban Areas ◽

Transport Model ◽

Bank Erosion ◽

Main Stem ◽

Shear Stresses ◽

Sediment Transport Model ◽

Bed Erosion ◽

River Hydraulics

Abstract. Suspended sediments impact stream water quality by increasing the turbidity and acting as a vector for strongly sorbing pollutants. Understanding their sources is of great importance to developing appropriate river management strategies. In this study, we present an integrated sediment transport model composed of a catchment-scale hydrological model to predict river discharge, a river-hydraulics model to obtain shear stresses in the channel, a sediment-generating model, and a river sediment-transport model. We use this framework to investigate the sediment contributions from catchment and in-stream processes in the Ammer catchment close to Tübingen in southwestern Germany. The model is calibrated to stream flow and suspended-sediment concentrations. We use the monthly mean suspended-sediment load to analyze seasonal variations of different processes. The contributions of catchment and in-stream processes to the total loads are demonstrated by model simulations under different flow conditions. The evaluation of shear stresses by the river-hydraulics model allows the identification of hotspots and hot moments of bed erosion for the main stem of the Ammer River. The results suggest that the contributions of suspended-sediment loads from urban areas and in-stream processes are higher in the summer months, while deposition has small variations with a slight increase in summer months. The sediment input from agricultural land and urban areas as well as bed and bank erosion increase with an increase in flow rates. Bed and bank erosion are negligible when flow is smaller than the corresponding thresholds of 1.5 and 2.5 times the mean discharge, respectively. The bed-erosion rate is higher during the summer months and varies along the main stem. Over the simulated time period, net sediment trapping is observed in the Ammer River. The present work is the basis to study particle-facilitated transport of pollutants in the system, helping to understand the fate and transport of sediments and sediment-bound pollutants.

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Effect of vegetation on flows and sediment transport

E3S Web of Conferences ◽

10.1051/e3sconf/20184002017 ◽

2018 ◽

Vol 40 ◽

pp. 02017

Author(s):

Hela Romdhane ◽

Amel Soualmia ◽

Ludovic Cassan ◽

Gilles Belaud

Keyword(s):

Shear Stress ◽

Sediment Transport ◽

Open Channel ◽

Sediment Accumulation ◽

Bedload Transport ◽

Reasonable Accuracy ◽

Physical Processes ◽

Flow Measurements ◽

Flow And Sediment Transport ◽

Movable Bed

Vegetation is a common feature in natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and associated morphodynamics in a vegetated environment. In this context, an experimental study was conducted in laboratory with a movable bed trapped in artificial vegetation. The experimental flume is a rectangular open channel 5.75 m long and 0.29 m wide. For flow measurements, the channel is equipped with a fast camera and ADV probe. This work focuses on identifying the vegetation effects on flows and sediment transport. In fact, it was shown that the vegetation presence in a watercourse promotes deposition and sediment accumulation. This is explained by a reduction of the bed shear stress, since the friction occurs mainly by the drag force effect exerted by the vegetation. It was shown too that the vegetation reduced the bedload transport. Thanks to the partitioning of shear stress, it was possible to predict the bedload transport using standard formulas with a reasonable accuracy.

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Laboratory studies on bedload transport under unsteady flow conditions

Journal of Hydrology and Hydromechanics ◽

10.1515/johh-2017-0032 ◽

2018 ◽

Vol 66 (1) ◽

pp. 23-31 ◽

Cited By ~ 5

Author(s):

Magdalena M. Mrokowska ◽

Paweł M. Rowiński ◽

Leszek Książek ◽

Andrzej Strużyński ◽

Maciej Wyrębek ◽

...

Keyword(s):

Shear Stress ◽

Sediment Yield ◽

Water Surface ◽

Bedload Transport ◽

Bed Shear Stress ◽

Surface Slope ◽

Stream Power ◽

Transport Dynamics ◽

Water Surface Slope ◽

Total Sediment

Abstract Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m3 s-1 to 0.0456 m3 s-1, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.

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Spectral estimates of bed shear stress using suspended-sediment concentrations in a wave-current boundary layer

Journal of Geophysical Research Atmospheres ◽

10.1029/2001jc001279 ◽

2003 ◽

Vol 108 (C7) ◽

Cited By ~ 11

Author(s):

Guan-Hong Lee

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Suspended Sediment ◽

Bed Shear Stress ◽

Spectral Estimates ◽

Suspended Sediment Concentrations

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Efficient non-hydrostatic modelling of flow and bed shear stress in a pier scour hole

Canadian Journal of Civil Engineering ◽

10.1139/cjce-2013-0160 ◽

2014 ◽

Vol 41 (5) ◽

pp. 450-460 ◽

Cited By ~ 2

Author(s):

S. Pournazeri ◽

S.S. Li ◽

F. Haghighat

Keyword(s):

Experimental Data ◽

Shear Stress ◽

Local Maximum ◽

Bedload Transport ◽

Bed Shear Stress ◽

Pier Scour ◽

Law Of The Wall ◽

Scour Hole ◽

The Law ◽

Wall Method

Predicting 3-D flow in a pier scour hole and the associated bed shear stress τb is important for the safe and economical design of bridge piers. This paper combines layered, hydrostatic hydrodynamic computations with non-hydrostatic pressure corrections, exploring a new modelling approach for efficient and reliable predictions of 3-D flow velocity. The law of the wall method is used for estimating τb. Its suitability for incorporation into layered models for bedload transport and pier scour simulations is also discussed. The predicted flow shows realistic features: strong downward flow adjacent to the upstream nose of a circular pier, vortex motions in the vertical and horizontal direction, and meandering flow wakes. The velocity results compare well with available experimental data. In the approach region, τb is uniform. It attains a local maximum immediately before flow enters the scour hole and then drops non-linearly in the scour-hole region toward the pier. In the wake region, τb has very low values. The τb predictions are consistent with the experimental data. In multi-layer models, when applying the law of wall method, one should use near-bed velocities as opposed to bottom-layer velocities to obtain more reliable τb estimates and avoid noisy results, which can cause a numerical instability problem in bedload transport simulations.

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