scholarly journals Sediment Bed-Load Transport: A Standardized Notation

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 368
Author(s):  
Ulrich Zanke ◽  
Aron Roland
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Basic Structure ◽  
Structural Formula ◽  
Bed Load ◽  
Viscous Effects ◽  
Data Set ◽  
Sediment Bed ◽  
Load Transport ◽  
Bed Load Transport

Morphodynamic processes on Earth are a result of sediment displacements by the flow of water or the action of wind. An essential part of sediment transport takes place with permanent or intermittent contact with the bed. In the past, numerous approaches for bed-load transport rates have been developed, based on various fundamental ideas. For the user, the question arises which transport function to choose and why just that one. Different transport approaches can be compared based on measured transport rates. However, this method has the disadvantage that any measured data contains inaccuracies that correlate in different ways with the transport functions under comparison. Unequal conditions also exist if the factors of transport functions under test are fitted to parts of the test data set during the development of the function, but others are not. Therefore, a structural formula comparison is made by transferring altogether 13 transport functions into a standardized notation. Although these formulas were developed from different perspectives and with different approaches, it is shown that these approaches lead to essentially the same basic formula for the main variables. These are shear stress and critical shear stress. However, despite the basic structure of these 13 formulas being the same, their coefficients vary significantly. The reason for that variation and the possible effect on the bandwidth of results is identified and discussed. A further result is the finding that not only shear stress affects bed-load transport rates as is expressed by many transport formulas. Transport rates are also significantly affected by the internal friction of the moving sediment as well as by the friction fluid-bed. In the case of not fully rough flow conditions, also viscous effects and thus the Reynolds number becomes of importance.

scholarly journals INFLUENCE OF GRAIN SIZE ON LITTORAL DRIFT

1970 ◽  
Vol 1 (12) ◽  
pp. 56 ◽  
Author(s):  
Jose Castanho
Keyword(s):  
Grain Size ◽  
Shear Stress ◽  
Bed Load ◽  
Flow Conditions ◽  
Littoral Drift ◽  
Flow Shear ◽  
Load Transport ◽  
Bed Load Transport ◽  
Flow Shear Stress ◽  
Load Discharge

Influence of grain size in sediment transport depends on flow conditions For bed load transport a maximum probably exists for load discharge as a function of gram size The important parameter seems to be the ratio To/T between the threshold shear stress and the flow shear stress.

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.

Initiation of motion conditions for shale sediments

1983 ◽  
Vol 10 (3) ◽  
pp. 549-554 ◽  
Author(s):  
L. Magalhaes ◽  
T. S. Chau
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Single Particles ◽  
Channel Stability ◽  
High Lift ◽  
Flume Tests ◽  
Load Transport ◽  
Bed Load Transport ◽  
Bed Material

Critical shear stresses for erosion of alluvial shale particles were investigated in a laboratory flume. Tests in the incipient motion conditions of individual particles showed that entrainment of shale bed particles takes place at mean shear stress values 40–50% smaller than other types of non-cohesive and coarse granular material. The low density and platy shape of the shale particles may induce high lift forces, which would account for a decrease in the resistance to erosion of shale channels and greater rates of bed-load transport. Keywords: channel stability, critical shear stress, flume tests, initiation of motion, shale gravels, single particles, weak bed material movement.

Discussion of “Bed-Load Transport at High Shear Stress”

1967 ◽  
Vol 93 (5) ◽  
pp. 303-307
Author(s):  
David I. H. Barr ◽  
John G. Herbertson
Keyword(s):  
Shear Stress ◽  
Bed Load ◽  
High Shear ◽  
High Shear Stress ◽  
Load Transport ◽  
Bed Load Transport

scholarly journals Impact of the regularity of the sediment bed on bed-load transport

PAMM ◽  
2016 ◽  
Vol 16 (1) ◽  
pp. 583-584
Author(s):  
Ramandeep Jain ◽  
Bernhard Vowinckel ◽  
Jochen Fröhlich
Keyword(s):  
Bed Load ◽  
Sediment Bed ◽  
Load Transport ◽  
Bed Load Transport

scholarly journals BED LOAD TRANSPORT OF FINE SAND BY LAMINAR AND TURBULENT FLOW

1982 ◽  
Vol 1 (18) ◽  
pp. 96
Author(s):  
Anthony J. Grass ◽  
Ragaei N.M. Ayoub
Keyword(s):  
Shear Stress ◽  
Turbulent Flows ◽  
Time History ◽  
Fine Sand ◽  
Great Sensitivity ◽  
Bed Load ◽  
Test Range ◽  
Laminar And Turbulent Flow ◽  
Load Transport ◽  
Bed Load Transport

An experimental study is described in which the rate of transport of fine sand over a flat bed was measured as a function of the shear stress exerted on the bed by both laminar and turbulent flows, for a range of water temperatures. The results confirm the great sensitivity of the transport rate to changes in both shear stress and temperature over the test range. The hypothesis is propounded that in certain specified circumstances, the net rate of local bed load transport generated by an arbitrary unsteady flow, can be estimated by integration, using the measured steady laminar flow transport relationships in conjunction with the time history or probability distribution of the fluctuating bed shear stress. The concept has been tested using the measured data with encouraging results. It is suggested that this method of linking the characteristics of the near bed flow field to the local induced rates of sediment transport could be productively applied in a range of studies including the initiation and development of bed sand ripples by the action of various combinations of waves and steady currents.

scholarly journals A bed load transport equation based on the spatial distribution of shear stress – Oak Creek revisit

2020 ◽  
Author(s):  
Angel Monsalve ◽  
Catalina Segura ◽  
Nicole Hucke ◽  
Scott Katz
Keyword(s):  
Shear Stress ◽  
Flow Field ◽  
Transport Equation ◽  
Bed Load ◽  
Bankfull Discharge ◽  
Wide Range ◽  
Average Shear ◽  
Load Transport ◽  
Two Dimensional Flow ◽  
Bed Load Transport

Abstract. Bed load transport formulations for gravel bed-rivers are often based on reach-averaged shear stress values. However, the complexity of the flow field in these systems results in wide distributions of shear stress, whose effects on bed load transport are not well captured by the frequently used bed load transport equations, leading to inaccurate estimates of sediment transport. Here, we modified a subsurface-based bed load transport equation to include the complete distributions of shear stress generated by a given flow within a reach. The equation was calibrated and verified using bed load data measured at Oak Creek, OR. The spatially variable flow field characterization was obtained using a two-dimensional flow model calibrated over a wide range of flows between 0.1 and 1.0 of bankfull discharge. The shape of the distributions of shear stress was remarkably similar across different discharge levels which allowed it to be parameterized in terms of discharge using a Gamma function. When discharge is high enough to mobilize the pavement layer (1.0 m3/s in Oak Creek), the proposed transport equation had a similar performance to the original formulation based on reach-averaged shear stress values. In addition, the proposed equation predicts bed load transport rates for lower flows when the pavement layer is still present because it accounts for bed load transport occurring in a small fraction of the channel bed that experience high values of shear stress. This is an improvement over the original equation, which fails to estimate this bed load flux by relying solely on reach-average shear stress values.

scholarly journals The bed load transport in rivers. Part I: Start moving, shear stress

2015 ◽  
Vol 13 (4) ◽  
pp. 109-120
Author(s):  
Mateusz Hämmerling ◽  
◽  
Paweł Zawadzki ◽  
Natalia Walczak ◽  
Michał Wierzbicki ◽  
...  
Keyword(s):  
Shear Stress ◽  
Bed Load ◽  
Load Transport ◽  
Bed Load Transport
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