A self‐similar scaling for cross‐shelf exchange driven by transient rip currents

Abstract

AbstractTransient rip currents, episodic offshore flows from the surf zone to the inner shelf, present a recreational beach hazard and exchange material across the nearshore ocean. The magnitude and offshore extent of transient rip‐current‐induced exchange and its relative importance to other inner shelf exchange processes are poorly understood. Here 120 model simulations with random, normally incident, directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self‐similar. The nondimensional exchange velocity, surf zone flushing time, and cross‐shore decay length scale are scaled by beach slope and wave properties, depending strongly on wave directional spread. Transient rip‐current‐driven exchange can be compared to other cross‐shelf exchange processes. For example, transient rip‐current‐driven exchange is stronger than wave‐induced Stokes‐drift‐driven exchange up to six surf zone widths from shore.