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

Abstract

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.

Effect of non‐uniformity of flow on velocity and turbulence intensities over a cobble‐bed

“…The Log Law, presented by von Karman (1930) and Prandtl (1932) for smooth boundaries, was extended by Nikuradse (1933) for sand beds. Altinakar (1993, 1998); Song and Graf (1994); Kironoto and Graf (1995); Anctil (1999, 2000) and Afzalimehr and Rennie (2009) among the others extended this law for gravel beds and Afzalimehr and Anctil (2001) for cobblebed streams as…”

Effect of accelerating and decelerating flows on incipient motion in sand bed streams

“…Song and Chiew [27] studied the effect of non-uniformity on the mean velocity and turbulence characteristics in accelerating and decelerating flows under equilibrium conditions analytically and experimentally. More recently, Afzalimehr and Rennie [3] determined the bed shear stress in a gravel-bed river having a non-uniform flow using the boundary layer displacement thickness and the boundary layer momentum.…”

Effects of Bed Forms and Large Protruding Grains on Near‐Bed Flow Hydraulics in Low Relative Submergence Conditions

“…Changes in turbulence intensities (Bathurst, ; Canovaro, Paris, & Solari, ; Nelson, McLean, & Wolfe, ; Papanicolaou et al, ; Papanicolaou, Bdour, & Wicklein, ; Thompson, ), local pressure distributions (Pournazeri, Li, & Haghighat, ; Zeng, Constantinescu, & Weber, , ), and water surface elevations (Vallé & Pasternack, ; Yager et al, ) also can occur. Flow variability has important consequences for the spatial distribution of shear stresses (Afzalimehr & Rennie, ; Clayton, ; Clayton & Pitlick, ; Cooper et al, ; Ferguson, ; Maddux, McLean, et al, ; Papanicolaou, Tsakiris, & Kramer, ), water aeration (Chanson, , ; Straub, Killen, & Lamb, ; Straub & Lamb, ), mixing (Chanson, ; Claxton, Bates, & Cloke, ; Tonina & Buffington, ), and transport of scalar properties such as water temperature and dissolved oxygen, all of which are key factors for aquatic habitat quality and riverine ecosystems (Cienciala & Hassan, ; Ouellet, Secretan, & Morin, ). In particular, the spatial distribution of shear stress has significant influence on sediment transport rates, sediment deposition patterns, and channel stability (Lisle et al, ; Monsalve et al, ; Nelson, Dietrich, & Venditti, ; Segura & Pitlick, ; Yager & Schmeeckle, ).…”