Wave-Induced Scour Prediction at Vertical Walls

Scour at the foot of a vertical wall is examined for the special case of normally-incident, nonbreaking irregular waves that are perfectly reflected by the wall. The bottom is initially flat. An expression for the root-mean-squared horizontal velocity (u rms ) near the bottom is given in terms of the incident spectrum and spatial location relative to the wall, and the validity of the expression is supported by laboratory measurements over a wide range of conditions. Movable-bed physical model tests indicate that maximum scour depths are related to variations in bottom u rms for fine sediments that are moved in suspension, and a predictive equation is proposed. Maximum scour depth magnitudes are substantially less than the corresponding regular wave case, possibly to the point that this particular case is not an important design concern.