Flushing a finite volume of dense fluid from a square street canyon by a turbulent overflow

►In flushing process, both, skimming and mixing process were observed. ► The thickness of the interface layer decreased with increasing Ri. ► Layer buoyancy decreases linearly till the shear layer reaches the cavity bottom. ► Density interface is thinner than the shear layer that is driving the mixing. ► The initial exponential decay rate was estimated by an empirical equation.