scholarly journals Structural Properties of the Static Armor during Formation and Reestablishment in Gravel-Bed Rivers

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1845
Author(s):  
Qiang Wang ◽  
Yunwen Pan ◽  
Kejun Yang ◽  
Ruihua Nie
Keyword(s):  
Random Field ◽  
Structural Properties ◽  
Transport Rate ◽  
Surface Elevation ◽  
Bed Load ◽  
Two Dimensional ◽  
Statistical Parameters ◽  
Laboratory Flume ◽  
Load Transport ◽  
Bed Load Transport

The formation and reestablishment of bed structural properties in the static armor layer is an important research subject. To address this issue, we conducted a series of static armor layer experiments in a laboratory flume that focused on formation and reestablishment. Through an automatic measurement system, we obtained a real-time bed load transport rate. The bed surface elevation at different flow intensities was obtained using a PTS (Photo Terrain Scanning) system. The results show that the formation and reestablishment of the bed load transport rate in the static armor layer increased from zero to its peak before decaying. The bed structure response was found to be highly dependent on the unevenness of the bed surface elevation. The bed surface elevation of a static armor layer in a laboratory flume is considered as a two-dimensional random field. In a two-dimensional random field, the changes in bed elevation are characterized using statistical parameters. Statistical parameters are evaluated from precise digital elevation models (DEMs) of bed surfaces. Experimental results provide the change of probability distribution functions (PDFs) and second-order structure functions of bed elevations between formation and reestablishment after breaking the static armor layer. By quantitatively analyzing the changes in these statistical parameters, we quantified the difference between the bed structure in the static armor layer formation and the new static armor layer formed after being broken. Thus, this finding reveals that the bed structure of the static armor layer formed by different flow intensities is different, and this difference can be quantified using statistical methods.

scholarly journals Evaluation of an acoustic Doppler technique for bed-load transport measurements in sand-bed Rivers

2018 ◽  
Vol 40 ◽  
pp. 02053 ◽  
Author(s):  
S. Conevski ◽  
A. Winterscheid ◽  
N. Ruther ◽  
M. Guerrero ◽  
C. Rennie
Keyword(s):  
Transport Model ◽  
Transport Rate ◽  
Qualitative Assessment ◽  
Bed Load ◽  
Apparent Velocity ◽  
Digital Cameras ◽  
Statistical Correlations ◽  
Hydraulic Conditions ◽  
Load Transport ◽  
Bed Load Transport

The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load. Strong statistical correlations are reported between the ADCP BT velocity and the transport rate obtained by physical sampling or dune tracking; however, these relations are strictly site-specific and a local calibration is necessary. The direct physical sampling is very labor intensive and it is prone to high instrument uncertainty. The aim of this work is to develop a methodology for evaluating the bed load transport using commercial ADCPs without calibration with physical samples. Relatively long stationary measurements were performed in a sand-bed and sand gravel rivers, using three different ADCPs working at 3MHz, 1.2MHz and 0.6MHz. Simultaneously, bed load samples were collected with physical samplers, and the riverbed was closely observed with digital cameras mounted on the samplers. It is demonstrated that the kinematic transport model can yield a relatively good estimate of the transport rate by directly using filtered apparent velocity, the knowledge of the hydraulic conditions and instrument-related calibration coefficients. Additionally, the ADCP data can help in qualitative assessment of the physical sampling. Future investigation of the backscattering echo and further confirmation of the BT apparent velocity should be performed in laboratory-controlled conditions.

scholarly journals Comparison between Computations and Measurements of Bed Load Transport Rate in Nestos River, Greece

2016 ◽  
Vol 162 ◽  
pp. 172-180 ◽  
Author(s):  
Thomas Papalaskaris ◽  
Paraskevi Dimitriadou ◽  
Vlassios Hrissanthou
Keyword(s):  
Transport Rate ◽  
Bed Load ◽  
Nestos River ◽  
Load Transport ◽  
Bed Load Transport

scholarly journals Quantification of bed-load transport over dunes

2018 ◽  
Vol 40 ◽  
pp. 02010 ◽  
Author(s):  
Kenneth Lockwood ◽  
Patrick Grover ◽  
Ana Maria Ferreira da Silva
Keyword(s):  
Shear Stress ◽  
Bed Load ◽  
Bed Shear Stress ◽  
Complex Flows ◽  
Wall Model ◽  
Load Rate ◽  
Laboratory Flume ◽  
Load Transport ◽  
Bed Load Transport ◽  
End Use

There is disagreement in the literature as to whether a shear stress-based approach can be used to accurately predict sediment transport over dunes. This study aims to address this disagreement. To this end, use is made of an experiment involving the study of naturally formed, fully developed dunes produced in a laboratory flume. The bed shear stress is estimated through a combination of velocity, Reynolds stress measurements, and results of a CFD RANS rough wall model. The validity of using Bagnold’s equation to predict the bed-load rate is subsequently analyzed. In contrast to what has been previously suggested by some authors, it is found from the present experiment that the bed-load rate correlates well with the bed shear stress, and that Bagnold’s equation yields realistic values of the bed-load rate over the stoss side of the dune downstream of the reattachment point. This work also highlights the difficulties in reliably estimating the bed shear stress in complex flows. Such difficulties are overcome in this paper through a combination of flow velocity measurements and modeled results.

scholarly journals Advection and dispersion of bed load tracers

2018 ◽  
Vol 6 (2) ◽  
pp. 389-399 ◽  
Author(s):  
Eric Lajeunesse ◽  
Olivier Devauchelle ◽  
François James
Keyword(s):  
Steady State ◽  
Steady Flow ◽  
Constant Velocity ◽  
Transport Rate ◽  
Bed Load ◽  
Deposition Model ◽  
Advection Diffusion ◽  
Maximum Value ◽  
Load Transport ◽  
Bed Load Transport

Abstract. We use the erosion–deposition model introduced by Charru et al. (2004) to numerically simulate the evolution of a plume of bed load tracers entrained by a steady flow. In this model, the propagation of the plume results from the stochastic exchange of particles between the bed and the bed load layer. We find a transition between two asymptotic regimes. The tracers, initially at rest, are gradually set into motion by the flow. During this entrainment regime, the plume is strongly skewed in the direction of propagation and continuously accelerates while spreading nonlinearly. With time, the skewness of the plume eventually reaches a maximum value before decreasing. This marks the transition to an advection–diffusion regime in which the plume becomes increasingly symmetrical, spreads linearly, and advances at constant velocity. We analytically derive the expressions of the position, the variance, and the skewness of the plume and investigate their asymptotic regimes. Our model assumes steady state. In the field, however, bed load transport is intermittent. We show that the asymptotic regimes become insensitive to this intermittency when expressed in terms of the distance traveled by the plume. If this finding applies to the field, it might provide an estimate for the average bed load transport rate.

Estimation of Bed Load Transport Rate Based on Grain Froude Similarity Considering the Existence of Sand Waves

2010 ◽  
Vol 148-149 ◽  
pp. 30-35
Author(s):  
Bing Qian Wei ◽  
Hong Yun Xun ◽  
Xiao Jun Sun ◽  
Rong Ge Xiao
Keyword(s):  
Froude Number ◽  
Satisfactory Result ◽  
Model Experiment ◽  
Transport Rate ◽  
Bed Load ◽  
Sand Waves ◽  
Estimation Formula ◽  
Bed Forms ◽  
Load Transport ◽  
Bed Load Transport

It is very important for reservoir management to estimate the sedimentation amount deposited in a reservoir. Firstly, the formula for estimating the bed load transport rate in the bed of sand waves of prototype by model experiment was derived based on the similarity of grain Froude number; Secondly, several model experiments that the bed forms is similar with the prototype were carried, and the formula was verified. As a result, when the ratio of grain diameter in the prototype and model is great enough, and the bed forms in the model is similar with that in the prototype, a satisfactory result can be obtained by using the estimation formula for estimating the bed load transport rate of the prototype that sand waves occur in the bed.

On the development of dunes in erodible channels

1974 ◽  
Vol 64 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Jørgen Fredsøe
Keyword(s):  
Stability Analysis ◽  
Order Approximation ◽  
Experimental Fact ◽  
Bed Load ◽  
Two Dimensional ◽  
Alluvial Channel ◽  
Load Transport ◽  
Bed Load Transport ◽  
The Stability ◽  
Vorticity Transport

A two-dimensional stability analysis of the flow in a straight alluvial channel has been carried out, using the vorticity transport equation. In the analysis an attempt has been made to account for the influence of gravity on bed-load transport, and this turned out to change the stability quite significantly.In the case of instability, the further growth of the dunes has been investigated using a second-order approximation, This nonlinear theory explains the experimental fact that the dunes very soon become asymmetric.

scholarly journals BED LOAD TRANSPORT DUE TO NON-LINEAR WAVE MOTION

1988 ◽  
Vol 1 (21) ◽  
pp. 133 ◽  
Author(s):  
Hitoshi Tanaka
Keyword(s):  
Sediment Transport ◽  
Wave Motion ◽  
Surf Zone ◽  
Function Theory ◽  
Transport Rate ◽  
Bed Load ◽  
Linear Wave ◽  
Wave Flume ◽  
Load Transport ◽  
Bed Load Transport

The bed load transport rate due to wave motion is measured in a wave flume. The modified stream function theory of the author ( Tanaka (1988) ) is applied to the formulation of the sediment transport rate in order to include the non-linearity. The proposed formula predicts well except near the surf zone where the effect of the acceleration plays an important role.

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