Suspension flows in open channels; experimental study

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' = nuss/(β) over bar kappau(.). The (β) over bar -value has been subject of much research, being (β) over bar (greater than or equal to)(less than or equal to) 1. This study focuses on the experimental determination of the depth-averaged (β) over bar -value, given by the ratio of the sediment, epsilon(s), and the momentum, epsilon(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 (β) over bar -values at capacity condition are smaller than unity, (β) over bar <1. However, it could also be shown that for flows over a movable bed with bed forms the <(beta)over bar>-values are larger than unity, (β) over bar >1; this is notably the case in natural waterways.