Equilibrium scour depths around piles in noncohesive sediments under currents and waves

A universal formula for the estimation of equilibrium scour depth around a single cylindrical pile under the action of steady currents, tidal and short waves is presented. Following a dimensional analysis, the controlling parameters of scour was found to be the Keulegan-Carpenter number and the ratio between the flow velocity and the critical velocity for the initiation of motion of the sediment particles, u/u(c). Based on this finding a new formula for the prediction of equilibrium scouring depths was derived in this paper. Measurements of the scouring process and the action of waves and/or currents from literature are used with KC and u/u(c) ranging between 6 and 10(5), and 0.6 and 4.5, respectively for the parameterization and verification of the newly proposed formula. The predicted scour depths and the investigated measurements show clearly the influence of the bed properties which have not been reported before in the literature. Predictions using the new approach have been compared with previous measurements and other formulations presented in the specialized literature. The proposed empirical formula accounts for the effect of waves, currents and sediment characteristics on the scouring process and shows better results than previous ones. (C) 2011 Elsevier B.V. All rights reserved.