Experimental study of transmission of waves over coastal reef systems

• Main Author: Sim, Denise Zi Qing
• Other Authors: Lo Yat-Man, Edmond
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Civil engineering
• Online Access: http://hdl.handle.net/10356/64467
• Institution: Nanyang Technological University

Reef ridge is the highest point of reef structures. It is usually exposed during low tide and is prone to the highest wave action across the reef. However, in previous reported modelling investigations, the ridge structures are generally ignored and the reef structure is simplified such that it consists of a constant fore-reef slope and a horizontal reef flat. This experimental study was motivated by the previous experimental results of Yao (2012), which showed that the presence of a reef ridge increased the wave-induced setup on the reef flat. This study served as a continuation and it focused on reef ridges with narrower widths that could be caused by erosion due to intensive wave action, and its effects on the wave-induced setup. The experiment was modeled on a fringing reef that was directly attached to the coastline, with a rectangular ridge placed on the reef edge. During the experiment, ridge models of various widths were interchangeably used and placed at the same location. Parameters such as wave height, water depth and wave period were used to determine the response of the wave breaking and the effect of the wave setup on the reef flat. Several cases from Yao’s (2012) previous study were repeated and the present experimental study was validated with no major discrepancy seen. This report investigated the level of wave setup under different wave parameters. The study concluded that with a narrower ridge, the wave setup increases with an increasing wave height, and decreases with the increasing water depth. An increase in wave setup was also observed as the wave period increases. However, Gourlay (1996) observed that the wave period has an upper limit whereby the wave period no longer increases the wave setup and further investigation is required to prove this hypothesis. This study found that the use of Gourlay and Colleter’s (2005) analytical model is applicable for the present ridges modelled and the finding is useful for improving existing analytical models in wave-induced setup over fringing reefs.