ABSTRACT
A mathematical model of the deployment of rock riprap falling aprons at bridge piers and abutments is developed based on a conceptual kinematic representation of apron formation. The model, which is founded on results of scale-model experiments of falling apron behavior and on practical experience that has influenced current design theory, accounts for the regularly repeated processes of slope erosion followed by rock settlement that take place along a receding convex, conical underwater slope. Apron parameters that are quantified include the needed thickness of a horizontal riprap layer, the amount of stone lost during deployment, and the lateral extent of erosion before complete slope coverage is established. The model is uncomplicated and can be applied without difficulty to design rock riprap falling aprons used to counteract the threat of bridge pier and abutment undermining by scour.
