Accelerating shear velocity in gravel-bed channels

Hydrological Sciences Journal

Rennie

2009

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The behaviour of velocity profiles and shear velocity for non-uniform flow in gravel-bed rivers is studied, with the objectives: (a) to test a new method of shear velocity estimation in gravel-bed rivers that is based on boundary layer parameters, and to compare it with the log law and parabolic law; (b) to consider the influence of flow non-uniformity on the outer layer region of velocity profiles; and (c) to investigate the effect of aspect ratio on velocity profiles. For the primary study river, mid-channel velocity profiles were analysed with relative submergence ranging from 9.7 to 33.3 in channel sections with aspect ratios ranging between 16.2 and 50. Velocity profiles deviated from the log law in the outer region due to flow nonuniformity or pressure gradient effects, and the vertical extent of the inner region was variable. Estimates of shear velocity using the boundary layer parameters (δ * and θ) compared well with estimates from the log law. In a second study river, boundary-layer parameter estimates of shear velocity compared well to shear velocity estimates from linear extrapolation of Reynolds stress profiles.

Section: Local Shear Velocity Estimatesmentioning

confidence: 99%

“…Using the laboratory data of , Afzalimehr & Anctil (2000) suggested the following formulation for determining shear velocity in non-uniform flows over gravel-bed channels:…”

Section: Introductionmentioning

confidence: 99%

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

Hydrological Sciences Journal

Rennie

2009

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“…Afzalimehr and Anctil (2000) and Afzalimehr and Rennie (2009) claimed C = 4.4 using based on laboratory experiments and field studies, respectively; u max is the maximum flow velocity in a velocity profile; δ * is the displacement thickness; and θ is the momentum thickness. According to Schlichting and Geresten (2000), these thicknesses are defined as:…”

Section: Calculations Friction Factor With Bedformsmentioning

confidence: 99%

“…where the total shear velocity (u * ) is calculated by using the BLCM method (Afzalimehr and Anctil, 2000) as follow:…”

Section: Calculations Friction Factor With Bedformsmentioning

confidence: 99%

Bedform characteristics in a gravel-bed river

Journal of Hydrology and Hydromechanics

Maddahi

Sui

2017

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Estimation of hydraulic and geometric parameters of a gravel-bed river such as dimensions of bedforms is very difficult task, although they play a fundamental role in river engineering projects. One of the methods to get essential information regarding the bedform characteristics is to find the relations between the flow parameters and bedform dimensions. We conducted this field study in the Babolroud River in northern Iran to investigate the application of double averaged method in unspecific gravel bedforms to evaluate friction factor. Using data collected from several river reaches with total length of 356 m of a gravel-bed river, the relationship between bedform geometry (height and the length of bedforms) and flow parameters including shear velocity, transport stage parameter with friction factor is investigated. Different methods for estimating bedforms dimensions are examined to assess the ability of predicting bedform parameters (length and height) in a gravel-bed river. Using bedform parameters, the contribution of particle and form friction is estimated. Results confirm the application of the double averaged method and existing bedform parameters for unspecific bedforms. There exists a similar trend between aspect ratio and friction factor in gravel bedforms.

“…This prevents the presentation of a general pattern of Reynolds normal stress distribution and to use it for evaluating shear velocity. Shear velocity u * was also calculated using the boundary layer characteristics method (BLCM) for each velocity profile as follows (Afzalimehr and Anctil, 2000):…”

Section: Fig 32 Fit Of the Log Law To The Inner Layer Data (Continmentioning

confidence: 99%

Effects of relative submergence and bed slope on sediment incipient motion under decelerating flows

Bolhassani

Journal of Hydrology and Hydromechanics

Dey

2015

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This paper presents the results of an experimental study to quantify the effects of bed slope and relative submergence on incipient motion of sediment under decelerating flows. Experiments were conducted in an experimental tilting-flume of 8 m long 0.4 m wide and 0.6 m deep with glass-walls. Three uniform sediments with median grain sizes of 0.95, 1.8 and 3.8 mm and three bed slopes of 0.0075, 0.0125 and 0.015 were used under decelerating flow. The main conclusion is that the Shields diagram, which is commonly used to evaluate the critical shear stress, is not suitable to predict the critical shear stress under decelerating flows.