Oceanographic conditions and sediment dynamic of the Barrang Caddi Island (Spermonde Archipelago, Indonesia)

Abstract

Small islands are vulnerable to long-term natural disasters like coastal erosion due to their size and topography. Barrang Caddi is one the small island in the Spermonde Archipelago (South Sulawesi) that encountered serious coastal erosion. Several attempts have been done by the relevant parties like by building a wave breaker to prevent erosion. But in fact some parts of the island are still eroded. A comprehensive oceanographic study of the wave climate and coastal processes at work to delineate the factors responsible for shoreline chance and to identify the location that need protection is needed. In this study, physical oceanographic data including waves, currents, tide, bathymetry, sediment characteristics and sediment transport were collected in the Barrang Caddi Island to analyze the factors responsible for shoreline chance (erosion) in the island. Results of the study showed that tide in the study site is mixed tide, predominantly semidiurnal with tidal range of 118 cm. Current measurements using a electromagnetic current meter revealed that current velocities at the study site were relatively low and vary spatially and temporally with magnitude of 0.02 – 0.58 m/s. Under normal conditions (no storms) the significant wave height (H 1/3) varied from 0.04 to 0.20 m. The wave height decreases from the fore reef to the reef flat due to the presence of coral reefs that reduce wave energy (wave height). Sediments were dominated by biogenic sand with grain diameter of 0.38 – 1.04 mm. Island erosion analysis showed that wave action was a main factor that responsible for shoreline chance (erosion) at the island. Current velocity alone with average of 0.19 m/s was not strong enough to move (erode) sediments at the island.