Generalized approach for clear-water scour at bridge foundation elements

Extensive studies on the temporal evolution of scour were recently conducted at Versuchsanstalt fur Wasserbau, Hydrologie und Glaziologie VAW, ETH Zurich, Switzerland, along with a computational model for the scour depth estimation. The VAW scour data are revisited in the present study to present a further refinement. Additional experiments conducted on the scour entrainment at piers, at rectangular and sloping abutments, as well as at singular and multiple spur dikes are reported. A general criterion is proposed to determine the densimetric particle Froude number for scour entrainment. A new relationship for the temporal scour evolution at bridge foundation elements is then developed based on the similitude of Froude by relating the scour depth to the difference between the actual and the entrainment densimetric particle Froude numbers. The new relationship is validated by the complete VAW scour data set, and verified by the available literature data. The combination of sediment characteristics, approach flow velocity, and obstruction geometry leading to an end scour are identified and a relationship is proposed for determining the corresponding time scale. The limitations of the present work are outlined.