Model Test Results of Scour Along Breakwaters

Abstract

Waves impacting on breakwaters, even of rubble‐mounds, are reflected efficiently from them, so producing almost standing waves for normal approach and a complex short‐crested wave system for oblique approach. In the former, sediment is accreted one half wavelength intervals from the face at the expense of material at the nodes, at odd multiples of quarter wavelength intervals. With angled waves similar erosion takes place, either at the nodal or antinodal regions depending upon the obliquity. These are determined in fractions of the distance of island crests, formed at wave interactions, termed the crest length. Kinematics of the water particles exhibit high bed velocities and also vortices at alignments one eighth of the crest length from the structure. The associated mass transport exceeds that of the incident waves. Model studies in Japan have exhibited scouring capacity for waves at all angles, including normal, and those results are re‐examined herein. New relationships exhibit the need for long duration tests.