Dynamics of lock-release gravity currents over sparse and dense rough bottoms

Dense oceanic overflows mix with surrounding waters along the descent down the continental slope. The existing parameterizations for entrainment in dense currents account primarily for the shear-induced entrainment at the interface between the dense flow and the ambient fluid. However, the turbulence generated by roughness elements at the bottom boundary, which produces an enhanced drag, can be intense and must be considered. This paper describes an experimental study investigating the dynamics of a lock-release dense gravity current propagating through ‘sparse’ and ‘dense’ bottom roughnesses. Two main regimes are observed in which the entrainment/dilution of the current is enhanced due to different mechanisms. For the sparse configuration the dense current is observed to propagate between the roughness elements while for the dense configuration it rides on top of the cylinders.