The results are described of systematic research for three-dimensional local scour in loose sediments. Relationships were determined between time-scale and scales for velocity, length and material density. As for two-dimensional flow the shape and the extent of the scour-hole due to vortices are in a high degree time dependent; originally the development as a function of time is very fast, but in a later phase the progress is slower until eventually an equilibrium situation is reached. In many practical cases the equilibrium will not be attained. Geometry, dam-height, length and roughness of bottom protection, flow velocity and density of sediments were varied. A relationship for the time-scale was derived. somewhat similar to that for two-dimensional scour. For practical cases the scour has to be determined for a number of longitudinal sections which have each a different time-scale. Restrictions of the results like permanent flow and neglect ion of upstream material supply can be tackled with additional computation methods.
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