Experimental analysis on flow resistance for different macro scale roughness arrangements

Macro-roughness elements superimposed on the original river bed are increasingly being applied as a restoration measure in natural streams. Under these conditions, due to the interaction of these large boulders with the flow, the classic resistance formulae are no longer valid, preventing their use for design purposes. The paper shows the results of an experimental study conducted on a rough channel with the insertion of protruding boulders, under different hydraulic and geometric conditions, for a total of 66 tests. The effects on flow resistance of channel slope, discharge, boulder size, density and arrangement were investigated in order to obtain useful information (in terms of boulder arrangement, concentration and dimension) for designing bed stabilization systems in natural streams.