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.
UNDULAR BORE DEVELOPMENT OVER A LABORATORY FRINGING REEF