Laboratory experiments on the propagation of bores induced by offshore soliton forcing over reef flats

Abstract

This study investigates, in a two-dimensional wave flume, how idealized reef-flat roughness and reef-flat length affect the transformation of solitary-wave-induced bores. Field surveys following natural disasters show that there is some confusion about the degree of protection reef flats can actually offer, and various theories have been put forward. Some researchers claim that coral reefs offer protection from tsunamis, others that they enhance damage to settlement by accelerating the velocity of the wave, and a third group that they neither protect nor exacerbate the damage due to these events. In this study, the authors aim to examine the effect that coral reef analogues have on bores propagating over reef flats by means of laboratory experiments conducted on a two-dimensional wave flume, in order to provide some guidance regarding the effect that idealized reef flats can play on disaster risk mitigation. Forty-eight cases of experiments were tested by using two different water depths, two lengths of reef flat, three types of surfaces (to represent different types of idealized corals), and four different input wave heights into the wave generator. The results indicate that the reduction in both wave heights and wave front velocities was greater in the cases where there were structures representing corals, and for longer reef flats. Also, the attenuation of wave energy was greater with reduced water depth, which in nature usually correlates with a healthy reef system.