The influence of upstream riverbed topography on local scouring around bridge piers

Human activities such as sand mining, dredging, and dam construction have altered the topography of riverbeds, creating irregular undulations that change the flow patterns in rivers and pose risks to the safety of downstream bridge foundations. Research on the impact of riverbed topography on local scouring around bridge foundations remains limited. This study investigates the effects of three types of riverbed topography—flat, concave, and convex—on local scouring around downstream bridge piers through laboratory flume experiments. Factors considered include the size of the concave and convex topographies, the distance from the bridge pier, and the flow velocity. Results show that, compared to flat riverbeds, concave topographies reduce horizontal velocity gradients in front of piers, while convex topographies increase them. Both concave and convex topographies accelerate the scouring process and increase scouring intensity around the piers. The influence of riverbed topography on velocity distribution upstream of the piers and the morphology of scour pits is positively correlated with the relative height of the topography and negatively correlated with the distance between the topography transition point and the pier. Based on experimental data, a formula for calculating local scour depth considering topographical factors is proposed. The concept and prediction method for the boundary distance of topographical influence on local scour are also introduced, providing a reference for practical engineering management.