This paper examines the motion of a dense fluid that develops as an inertial gravity current of decreasing mass above a horizontal porous bed, while flow described by Darcy's law occurs in the bed. Measurements of the mass and the front position of the current in a set of laboratory experiments performed by changing different parameters are presented. The results are explained by means of a global analytical model that suggests practical correlations combining the parameters. Thus, previous experimental, numerical and theoretical findings are extended to describe lock-release gravity currents above more realistic porous beds.