Effects of subaqueous debris accumulations on local scour around the pier and riverbed morphology

During floods, debris accumulates around the pier in the channel. The depth of debris accumulation beneath the water surface significantly influences on local scouring around the pier, and affecting its flood-fighting capacity. Flume experiments were carried out to investigate local scour around the pier when debris accumulations occurred at three distinct levels: on the water surface (<i>H</i>_a/<i>H</i> = 0), in the middle of the water body (<i>H</i>_a/<i>H</i> = 0.5), and near the riverbed (<i>H</i>_a/<i>H</i> = 0.8). Through numerical simulation verified by experiments, the flow characteristics were obtained, and the impact of the subaqueous debris position on the flow field was analyzed. The results show that the debris accumulations significantly aggravate the local scouring around the piers. Longitudinal and transverse maximum scour depths around the pier increase progressively as the debris accumulates from the water surface toward the riverbed. The maximum scour depth is directly proportional to the extent of debris penetration beneath the water surface. Specifically, when the debris is near the riverbed (<i>H</i>_a/<i>H</i> = 0.8), the scour depth reaches its maximum. Compared to without debris, the maximum longitudinal scour depth increases by 28.3%, while the maximum transverse scour depth increases by 53.8%.