Suspension flows in open channels; experimental study

Abstract

The vertical distribution of the concentration of suspended particles is usually determined by solving the diffusion-convection equation under appropriate boundary conditions. The exponent in the resulting Rouse equation is the Rouse number, defined as z′ = v_ss /κu. The -value has been subject of much research, being ⋛ 1.

This study focuses on the experimental determination of the depth-averaged -value, given by the ratio of the sediment, ∊ _s , and the momentum, ∊ _m , diffusion coefficients. These coefficients were evaluated under laboratory conditions from measurements of instantaneous velocity and concentration profiles, obtained simultaneously by using a non-intrusive sonar instrument, the Acoustic Particle Flux Profiler (APFP). In suspension flows over a movable bed without bed forms the measured -values at capacity condition are smaller than unity, < 1. However, it could also be shown that for flows over a movable bed with bed forms the -values are larger than unity, > 1; this is notably the case in natural waterways.