UNDULAR BORE DEVELOPMENT OVER A LABORATORY FRINGING REEF

Abstract

Several studies have reported the development of
 undular bores over fringing coral reefs (e.g, Gallagher,
 1976; Nwogu and Demirbilek, 2010) but the importance
 of this phenomenon for reef hydrodynamics has never
 been studied. Yet, the transformation of a long wave
 (e.g., swell or infragravity wave) into an undular bore
 leads to significant modifications of the wave field. The
 formation of undulations is for example associated to a
 significant increase of the leading bore height. Moreover,
 if the undulations have enough time to develop (i.e. if the
 reef flat is wide enough), the initial long wave will
 ultimately split into a series of solitons (e.g., Grue et al.,
 2008). All this is likely to affect wave run-up. As reeffronted
 coastlines are particularly vulnerable to flooding,
 a good understanding of long wave transformation over
 the reef flat, including their possible transformation into
 undular bores, is crucial.
 In this study, we investigate undular bore development
 over reef-type profiles based on a series of laboratory
 experiments. More specifically, we aim to characterize
 the conditions under which undular bores develop, and
 analyse how their development affect the hydrodynamics
 at the toe of the reef-lined beach and the resulting wave
 run-up.