Gravity currents impact significantly the environment and human's life. Understanding their internal structure and their dynamics is fundamental for modelling purposes. In this study we observe experimentally how bed porosity affects the dynamics of density currents. We will focus on density and velocity profiles of currents traveling over porous bed, sinking and entraining water from its cavities. This abstract presents the preliminary results of this study which are relative to density currents travelling over the reference substratum, a smooth impermeable bed. The tests presented will be used as a reference to observe how the water entrained from the bottom cavities can change the structure of the current and are herein used to validate the experimental techniques. Brine water is injected at constant discharge in a 7.5 m long, 0.3 m wide and 0.3 m deep flume while instantaneous velocity and density profiles are simultaneously acquired 3 m downstream of the inlet. Initial excess densities and inlet velocities allow to reproduce gravity flows in sub and super-critical regime.