Grain-Size Specific Suspended Sediment Transport and Flow Resistance in Large Sand-Bed Rivers

Abstract

Grain-size specific suspended sediment transport can be computed, given the mean velocity and concentration profiles, by integration of the sediment flux over the flow depth: $${q_{si}} = \int_\delta ^h {u{C_i}dy} $$ (1) where u is flow velocity, C i is volume concentration of grain-size i, δ is the top of the bedload layer, and h is the flow depth. Einstein (1950) used the standard logarithmic velocity profile and Rouse suspended sediment profile to develop the first grain-size specific suspended sediment transport predictor. The Rouse profile requires the nearbed concentration, and Einstein used his bedload predictor to provide this boundary condition. Also, the logarithmic velocity profile requires the near-bed velocity (or roughness height) as a boundary condition. Since Einstein, several advancements have been made in the solution of (1). Most of these have focused on the prediction of the near-bed concentration, for both uniform sediment and mixtures (see Garcia and Parker, 1991, for a review). Other researchers have focused on the roughness height, particularly in the presence of dune bedforms, and density stratification effects (Smith and McLean, 1977, McLean, 1991, 1992). This research follows along these lines, and has been driven by the desire to model large, low-slope, sand-bed rivers. Modifications to existing relations for near-bed concentration and roughness height are proposed which extend their validity to the range of interest.