Abstract

Tg. Piai, located on the southern tip of westMalaysia in Johor, is subject to critical coastal erosion on theeast side of the headland, and, as a consequence, severe loss ofprotected mangrove coastline has been observed over the past 20years. Various triggers for this erosion have been proposed, allbeing linked to the extensive developments of the region, and theincrease in marine activities in the waters of Singapore Strait. Inthis study, impacts on the regional (ambient) wave field, by thepresence of ships in the Strait of Singapore, are investigated.Waves are partially reflected off the hulls of the ships, and theextensive presence of ships in the Strait of Singapore thusmanifests itself as a blocking of the ambient wave field, resultingin a wave climate near Tg. Piai that depend on the congestion ofships. The integrated effect of the ship hull-induced wavereflections on the ambient wave field is evaluated by using thenumerical modelling tool MIKE 21. Information on the number,the positions and the sizes of the ships are determined fromsatellite images. It is found that the impacts of ship hull-induced wave reflections on the near shore wave field at Tg. Piai aresignificant, and, in particular, that the impacts on near shorewave periods are pronounced. The MIKE 21 model predictssignificant reductions in the wave periods at Tg. Piai whenincluding the ships. These changes in the wave periods canexplain the changes to the coastal morphology observed at Tg.Piai, including the coastal erosion, from the notion that thelonger waves in the wave spectrum tend to push sediment in thecoastal profile onshore, whereas the shorter waves movessediment seaward.