Theory and observation of currents and setup over a shallow reef

Over a shallow reef the absence of a shoreline allows both setup and mean cross shore flow to result from gradients in the radiation stress through the surf zone on the outer part of the reef. The relative magnitude of setup and currents depends on the magnitude of the forcing and the geometry of the reef. In this paper observations of currents and setup over natural reefs and in the laboratory are presented revealing interesting features of these flows. A one dimensional analytic model is described which explains the observed features and is able to simulate the observed currents on a natural reef by adjusting friction and the reef width.