The refraction of groups and of the waves which they generate in shallow water

Abstract

A process is described which may be of importance in beach and nearshore development and which may account for surging in the surf zone as well as other phenomena. It is shown how a group front may be refracted according to one law as it approaches a coast and then, after reflection, proceed seaward under quite a different law. This permits the outgoing wave to move in a direction that it could not ordinarily attain, and causes “trapping” under many conditions. Stoneley's theory of refraction of energy fronts is further developed to permit quantitative investigation of group refraction on various types of shores. On the basis of the assumed hypothesis, the outgoing surf beat may be totally reflected from deep water, then reflected from the beach, a process which can occur repeatedly and result in newly arriving groups with variable phase relationships. Theory and techniques are developed for the investigation of the surf‐beat path. The refraction of the reflected groups is shown to display regions of high convergence, divergence, and reinforcement.