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.

Measuring Bed Load Transport Rates by Grain-Size Fraction Using the Swiss Plate Geophone Signal at the Erlenbach

2016 ◽  
Vol 142 (5) ◽  
pp. 04016003 ◽  
Author(s):  
Carlos R. Wyss ◽  
Dieter Rickenmann ◽  
Bruno Fritschi ◽  
Jens M. Turowski ◽  
Volker Weitbrecht ◽  
...  
Keyword(s):  
Grain Size ◽  
Size Fraction ◽  
Bed Load ◽  
Load Transport ◽  
Bed Load Transport

scholarly journals Studying of flow model and bed load transport in a coarse bed river: case study – Aland River, Iran

2010 ◽  
Vol 13 (4) ◽  
pp. 850-866 ◽  
Author(s):  
Kiyoumars Roushangar ◽  
Yousef Hassanzadeh ◽  
Mohammad Ali Keynejad ◽  
Mohammad Tagi Alami ◽  
Vahid Nourani ◽  
...  
Keyword(s):  
Grain Size ◽  
Unsteady Flow ◽  
Relative Error ◽  
Flow Rate ◽  
Bed Load ◽  
Main Role ◽  
Step Method ◽  
Discharge Data ◽  
Load Transport ◽  
Load Discharge

This paper describes a mathematical model which solves the 1D unsteady flow over a mobile bed. The model is based on the Richtmyer second-order explicit scheme. Comparison of the model results with the experimental flume data for alluvial steady flow (aggradation due to overloading) and unsteady flow shows that, by using the two-step method of Richtmyer, one can solve the equations, governing the phenomenon, in a coupled method with the desired accuracy. Firstly, the Badalan reach located at the Aland River is considered. Variations of flow rate, water level and bed level profiles due to flood hydrographs are assessed. Secondly, bed load discharge data were collected from the Aland River and a variety of bed load discharge formulae were compared with measured data. Results show that, by using the grain size of the bed surface layer to predict the bed load discharge, a larger relative error will occur compared to the other two cases and a proper choice of grain size has the main role in reduction of the relative error of bed load discharge estimation in gravel bed rivers. The applicability of formulae varies depending on flow rate, and should be split into low and high flow transport formulae.

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 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.

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 Conditions at interfaces of layered flow with intense bed load transport

2019 ◽  
Vol 213 ◽  
pp. 02056
Author(s):  
Václav Matoušek ◽  
Jan Krupička ◽  
Tomáš Picek ◽  
Štěpán Zrostlík
Keyword(s):  
Kinetic Theory ◽  
Transport Model ◽  
Bed Load ◽  
Flow Conditions ◽  
Laser Stripe ◽  
Load Transport ◽  
Uppermost Layer ◽  
Bed Load Transport ◽  
Layered Flow ◽  
The Individual

Intense bed load transport in open channel flow is typically associated with a layered structure of the flow, in which individual layers exhibit different mechanisms of support and friction of transported sediment grains. In the lowermost layer adjacent to the channel bed, the grains slide over each other and maintain virtually permanent contact. In the uppermost layer below the water surface, typically no grains are transported. In the central layer, the grains collide with each other producing typical distributions of granular concentration and velocity across the collisional layer. Mathematical models describing the layered flow with intense bed load (as models based on kinetic theory of granular flows) consider flow conditions at interfaces of the individual layers in their flow predictions. Usually, experimental verification of interfacial predictions is lacking. We exploit results of our new experiments with plastic cylindrical sediment to identify a variation of the conditions at the interfaces (local interfacial granular concentrations and velocities) with varying flow discharge, depth and slope in a laboratory tilting flume. The experimental results include local granular concentration using an improved laser stripe method. The experiments are compared with predictions using our kinetic-theory based transport model with the aim to evaluate a match for experimentally-determined and model-predicted interfacial parameters.

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