Experimental study of the lock-release gravity current propagates on a rough upslope

In this paper, the simultaneous effects of boundary roughness and upslope on lock-release gravity currents were investigated by laboratory experiments, focusing on current propagation, entrainment processes, local vorticity fields, and velocity profiles. Based on the depth-averaged momentum equation, a new theoretical model that predicts the current front velocity on a rough upslope was developed and verified by experimental data. The results reveal that the entrainment coefficient E is negatively correlated with the boundary relative roughness k_s and positively correlated with the upslope angle θ . Both the reflected bores in front of the upslope toe and the backflow on the upslope move upstream and compose the accumulation of dense currents jointly. These two hydrodynamic processes should be considered in the current entrainment. When the current propagates on an upslope, the directions of part velocity vectors point to the upslope toe, the distribution regions of vorticity bands reverse behind the current front, and the signs for velocity peaks of vertical profiles change, all of which suggest the occurrence of a backflow phenomenon. In addition, as the upslope roughness increases, the vertical profiles of streamwise velocity trend to present multiple peaks accompanied by the wall region of gravity currents expanded.