Critical Scour: New Bed Protection Design Method

Abstract

A new design philosophy for granular bed protection is given; this is referred to as the “critical scour” method. Critical scour is defined as the scour that is admissible for protection of a granular bed during its lifetime. First the traditional “critical shear” design method is discussed, and some of its shortcomings are described. These shortcomings can be overcome by application of the critical scour method. The basic philosophy of the critical scour method is given, and the two main parameters (load on the cover layer and strength of the cover layer, defined as expected and admissible scour, respectively) are discussed in more detail. The load and strength functions are then combined in a risk analysis. An example from engineering practice demonstrates the advantages of the critical scour method, namely that: (1) It deepens insight into the actual scour and failure processes; and (2) it incorporates additional strength parameters, such as layer thickness, which enables the risk of damage to be predicted more accurately.