Large flow interchanges occur between free surface and subsurface flows of river training structures, such as in rock loose chutes based on pervious beds. The filtering action of the base pervious layer can improve the water quality but, at the mean time, reduce the minimum vital flow discharge. This paper, hence, aims to analyse the flow interchanges between the base material and the surface flow in presence of rock loose river structures (block ramps or rock chutes). Tests have been carried out in macro-roughness conditions for slopes ranging from 0.125 to 0.25. Different seepage inlet and outlet conditions have been tested in order to asses their influence on the maximum seepage capacity of both stilling basin and ramp base material. Finally, the effect of the seepage on the energy dissipation which occurs along the ramp has been studied.