Scour evaluation in space and time – the challenge of dam designers

The main questions arising during a dam project in view of safety against scour formation downstream of spillways and bottom outlets are discussed. First the physical processes involved in scour formation are analyzed based on the state-of-the-art of the knowledge and understanding. Then the different scour evaluation methods from simple empirical formula to complex scour models are briefly presented. The main difficulties encountered when estimating scour depth are discussed, such as the choice of the appropriate theory, interpretation of hydraulic model tests and prototype observations, scour rate and prevailing discharge. Furthermore the selection of the return period of the flood event is discussed, for which the scour formation and the control measures have to be evaluated. Finally the options of measures for scour control are presented and discussed.