Bed-load sediment transport on steep longitudinal slopes

The results of new experiments on bed load transport on steep longitudinal slopes are presented. The experiments were carried out in a large tilling duct with a fine sand (d(50) = 208 mu m) covering the range of slope angles beta of +/- angle of repose for the sand phi(s) (32 degrees), Measurements included bed shear-stress, flow discharge, and the sediment pickup rate on slopes. The results suggest that existing theories for bed load transport on slopes are not adequate for all bed slopes and the new data are used to formulate a semiempirical relation that satisfactorily predicts the transport rate on horizontal as well as mild and steep slopes. The following ate two important findings: (1) Correcting the threshold term (for slope) in the Meyer-Peter and Muller formula adequately describes the transport rate on positive slopes (elevation increasing in direction of flow) and on small negative slopes. On steeper negative slopes an extra correction term is required, although the value of beta/phi(s) at which this term becomes necessary is a function of shear stress; and (2) the influence of slope vanishes at high shear stresses.