Further results to time-dependent local scour at bridge elements

This research intends to clarify the limitations of a local scour equation recently proposed, based on extended laboratory data collected at VAW, Zurich, Switzerland. The present project is concerned with four items: (1) clarification of the minimum laboratory dimensions required to apply Froude similitude; (2) effect of sloping abutments on scour advance; (3) extension of scour formula to spur dikes; and (4) effect of unsteady flow on scour development. These items were investigated mainly from an experimental point of view based on some 150 laboratory experiments and accounted for by a hydraulic approach. It was found that the basic scour equation mentioned may be applied provided additional limitations are specified. These are discussed in the light of the densimetric particle Froude number, the threshold Froude number, and other important parameters that influence the progress of local scour. The results of this study may be applied to practice, provided the limitations of the computational approach are respected.