• ROUGHNESS
• FLOW

Rock chutes or block ramps represent a valid and low environmental impact alternative as fishway passages. The interaction between the free surface and the bed material in flow over rock chutes under leads macro-roughness conditions to a
high air entrainment into the flow. This improves the re-aeration in rivers with low dissolved oxygen content, due to the turbulence enhanced by the threedimensional macroroughness conditions. Thus the two-phase flow properties over macro- and intermediate roughness condition have got greater awareness in recent years. Air concentration properties and frictional properties were studied in uniform flow condition over different roughness conditions and general expressions were developed. Moreover, this study gives a general expression for estimating the air
inception length. The turbulence nature and the energy dissipation characteristics of the flows over the macro- and intermediate roughness conditions were also studied.