Computing river suspended load over bedforms in the lower, transition and upper hydraulic regime

摘要

The classical Rouse-Schmidt procedure to compute the vertical distribution of suspended solids (SS) concentrations in open-channel flows relies on the simplifying assumption that the law du/dy = u_*/κy ("universal" logarithmic velocity profile) is applicable to the full boundary layer depth (although this is generally considered to apply only for the 15―20% lower part closest to the boundary). An alternative double-layer model has therefore been proposed (linear-constant model with threshold at quarter-depth), leaning on the continuum theory of mixtures. The application of the new suspended-load model to the complex situation of river flow over bedforms (in the lower, transition and upper alluvial regimes) is explored, based on Willis et al. (1972) laboratory studies conducted with 0.1 mm sand. Results are encouraging, suggesting that the basic dual-layer formulation keeps validity in the various alluvial regimes. One calibration coefficient, called profile steepness a, is shown to be controlled by the type of bedforms and is therefore a strong positive function of the actual Froude number of the open-channel flow.