Hydraulic forces on debris accumulations: a preliminary analysis

Understanding the hydraulic forces exerted on bridge decks is critical for assessing structural safety during flood events, especially at low Froude numbers ( Fru < 0.6). This study provides preliminary insights into the complex interactions between flow and debris accumulations. To this end, isolated wood debris logs were tested in a hydraulic flume under various submergence levels. Results show that even at low Froude numbers, the presence of debris significantly alters the flow field, increasing both drag and uplift forces. Specifically, data analysis reveals that both horizontal and vertical components of the hydrodynamic loads depend on debris characteristics as well as backwater and difference in water levels across debris, suggesting that current hydraulic design practices may underestimate the forces acting on bridge superstructures under low-velocity and floating debris. This study offers useful design indications which are worth further analyses, including numerical, experimental and theoretical.