Estimation of Overtopping-Induced Scour Behind Floodwalls

Floodwalls are commonly used as part of flood risk reduction systems when constraints on right of way restrict the construction of embankments. For extreme events, floodwalls will overtop. The overtopping flow can cause scour behind the floodwall that may compromise the structural integrity of the system. To assess risks associated with floodwall overtopping, it is necessary to estimate the expected scour depths over the full range of anticipated loads. This paper presents a physics-based approach for estimating scour behind floodwalls as a function of wall height, overtopping depth, tailwater depth, overtopping duration, and soil erodibility parameters. Application of the method to a case history provides more reasonable estimates of the maximum scour depth than empirical alternatives.