Scour control at bridge piers using macro-roughness elements

A new approach involving macro-roughness elements is proposed as a scour countermeasure at circular bridge piers subject to debris accumulation. Experiments were carried out under clear water conditions with the approaching flow velocity set at the threshold of sediment motion. The efficiency of the method was investigated in terms of scour morphology reduction and temporal scour evolution. The results show the effectiveness of the method in reducing maximum scour depth. In some cases, the elements did not reduce the maximum scour depth but were effective in reducing the volume of the scour hole. Based on the experimental data, empirical equations were derived to estimate the temporal local scour depth in the presence of debris accumulation and macro-roughness elements.