Wave set-up

Abstract

Waves breaking on a reef or beach create an increase in m.w.l in the surf zone called wave set-up. This set-up increases with increasing height and period of the ocean waves and decreases with increasing water depth over the reef, becoming negligible when waves pass over the reef without breaking. Maximum set-up occurs when the ocean water (tide) level is about the same level as the reef top. The water level differences caused by wave set-up drive reef-top current systems and the flushing on many atoll lagoons. Wave set-up may contribute significantly to the groundwater elevation in cays and the sedimentary margins of continental islands. Wave set-up caused by both local storm waves and swells from distant storms may cause significant flooding, erosion and damage on reef islands, particularly where resonant oscillations occur on a reef top.