Unraveling flow hydraulics for intermediate roughness conditions in sediment motion over loose block ramps

ABSTRACT The block ramps are characterized by large randomly dumped macro-rugged elements on the riverbed, which are aquatic-friendly river restoration structures used for stabilizing riverbed. A special case of loose block ramp (LBR) with varying slopes of (S = 0.1, 0.15, and 0.2) is considered to investigate the ramp stability and the ramp behavior in intermediate roughness conditions. Erosion of ramp material may affect the stability of the LBR, which may in turn leads to significant damages. The present paper addresses the factors that affect the flow resistance, relative submergence, and intensity of block movement for various flow regimes. It was found that the critical Shield’s stress increases with ramp slope, and the intensity of ramp motion is also expected to increase with the shear stress. The results indicated that friction resistance increases with relative submergence for the tested range of experiments. A comparison with several model predictions with uniform sediment transport indicates that relative roughness of block is responsible for increasing the critical Shield’s stress in the present experimental study.