Determination of bed shear stress in gravel-bed rivers using boundary-layer parameters

The behaviour of the bed shear stress in the presence of a decelerating flow over a gravel bed has been examined. The collected observations revealed that the velocity distribution in the outer region of the boundary layer may be described by a parabolic law. The results obtained by parabolic law are comparable to the bed shear stress estimated via the St-Venant method. At a specific cross section, shear velocities estimated by the parabolic and the St-Venant methods divert considerably from the estimation by zero pressure gradient method. For constant bottom slope and relative roughness, the estimated bed shear stresses based on the parabolic and the St-Venant methods are proportional to the flow discharge, whereas this tendency is not accounted for by the zero pressure gradient model.Key words: velocity distribution, shear velocity, decelerating flows, gravel bed, boundary layer.

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SOLITARY-WAVE-INDUCED BOUNDARY LAYER FLOWS OVER PERMEABLE BEDS

Coastal Engineering Proceedings ◽

10.9753/icce.v36v.waves.9 ◽

2020 ◽

pp. 9

Author(s):

Nimish Pujara ◽

Claudio Meza-Valle ◽

Philip L.-F. Liu

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Solitary Wave ◽

Boundary Layers ◽

Accurate Determination ◽

Bed Shear Stress ◽

Boundary Layer Flows ◽

Viscous Effects ◽

Wave Induced

In the nearshore environment, viscous effects of wave- induced boundary layer flows above sea beds are important in evaluating sediment fluxes and wave damping. These effects need to be included in phase- resolved nearshore models for accurate determination of quantities such as the bed shear stress and the decrease in wave height due to frictional dissipation. In this work, we analyze the boundary layers induced by a solitary wave on permeable sea beds (extending previous work of wave-induced boundary layers on an impermeable bed). We find that the velocity profiles and bed shear stress are sensitive to the hydraulic conductivity of the bed, but not extremely sensitive to the precise boundary condition at the bed-fluid interface.

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The Effect of Habitat Structure Boulder Spacing on Near-Bed Shear Stress and Turbulent Events in a Gravel Bed Channel

Water ◽

10.3390/w12051423 ◽

2020 ◽

Vol 12 (5) ◽

pp. 1423

Author(s):

Amir Golpira ◽

Fengbin Huang ◽

Abul B.M. Baki

Keyword(s):

Shear Stress ◽

Habitat Structure ◽

Open Channel ◽

Reynolds Shear Stress ◽

Three Dimensional ◽

Quadrant Analysis ◽

Bed Shear Stress ◽

Gravel Bed ◽

Restoration Practices ◽

Ejections And Sweeps

This study experimentally investigated the effect of boulder spacing and boulder submergence ratio on the near-bed shear stress in a single array of boulders in a gravel bed open channel flume. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. Four methods of estimating near-bed shear stress were compared. The results suggested a significant effect of boulder spacing and boulder submergence ratio on the near-bed shear stress estimations and their spatial distributions. It was found that at unsubmerged condition, the turbulent kinetic energy (TKE) and modified TKE methods can be used interchangeably to estimate the near-bed shear stress. At both submerged and unsubmerged conditions, the Reynolds method performed differently from the other point-methods. Moreover, a quadrant analysis was performed to examine the turbulent events and their contribution to the near-bed Reynolds shear stress with the effect of boulder spacing. Generally, the burst events (ejections and sweeps) were reduced in the presence of boulders. This study may improve the understanding of the effect of the boulder spacing and boulder submergence ratio on the near-bed shear stress estimations of stream restoration practices.

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Boundary-layer flow and bed shear stress under a solitary wave: revision

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.52 ◽

2014 ◽

Vol 753 ◽

pp. 554-559 ◽

Cited By ~ 4

Author(s):

Yong Sung Park ◽

Joris Verschaeve ◽

Geir K. Pedersen ◽

Philip L.-F. Liu

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Solitary Wave ◽

Boundary Layer Flow ◽

Bottom Boundary Layer ◽

Bed Shear Stress ◽

Bottom Boundary ◽

Layer Flow

AbstractWe address two shortcomings in the article by Liu, Park & Cowen (J. Fluid Mech., vol. 574, 2007, pp. 449–463), which gave a theoretical and experimental treatise of the bottom boundary-layer under a solitary wave.

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