Spreading of a Gravity Current over a Permeable Surface

Plane inertial gravity currents running over horizontal permeable surfaces are studied. An analytical simple model based on local and global balances is derived which describes the propagation and infiltration of an incompressible dense fluid on and through the surface. Results of laboratory experiments are presented which are in accordance with scaling laws suggested analytically. It is found that the loss of mass, the velocity, and the position of the front of the current follow exponential relationships. The dynamics is governed by a particular decay time related to the initial volume released and reduced gravity g0′. However this decay time exhibits a different functional relationship from that obtained for currents evolving over thin permeable bottoms when the downward flow is viscous. As a consequence of the loss of mass, the distance to extinction of the current is found to be independent of g0′.