Assessment of Wave Attenuation Performance of the Tanjung Piai Breakwater Using Spectral Wave Analysis

Abstract

Tanjung Piai is a Malaysian heritage site situated at the southernmost tip of the Asian continent. Tanjung Piai provides a conducive coastal habitat for many mangrove species. Coastal erosion resulting in shoreline retreat was detected dating back to the 1930s. The erosion rate had accelerated until the early 21stcentury due to various factors including to coastal developments in the vicinity of Tanjung Piai. This led to significant land mass losses threatening the coastal eco-system. Previously, various measures were adopted to permanently harden the shoreline. Nevertheless, these approaches prevented sea water from reaching the mangroves, which in turn resulted in significant mangrove depletion along the shoreline. A series of offshore breakwaters were subsequently planned and constructed to reduce the wave energy prior to reaching the mangrove shoreline. The breakwaters are anticipated to be able to mitigate the erosion problems and extend the width of the existing mangroves belts along the wave-exposed coastline. The wave climate of Tanjung Piai has changed drastically in the past decades, potentially due to rapid coastal development in the vicinity. This study aims at re-evaluating the wave attenuation performance of the Tanjung Piai breakwaters subjected to the latest wave climate (i.e., offshore waves, squalls, and wind-generated waves) and bathymetry by means of two-dimensional numerical modelling –MIKE21 SW. The latest survey of the site and the most recent breakwater design details have been incorporated in this modelling study. Two scenarios have been conducted to determine the wave climates i.e., pre-and post-construction of the breakwaters. The alterations of the wave heights for both scenarios are taken as a basis to ascertain the actual wave attenuation performance of the breakwaters. The numerical results show that the breakwaters are able to reduce offshore wave heights up to 66%. The breakwaters can attenuate offshore waves more effectively than squalls and wind-generated waves.