Hydrodynamic and Morphodynamic Assessment of Low-Crested Breakwaters Using Geotube for Coastal Protection at Kilo 5 Beach, Banggai Regency, Indonesia

In recent years, the Kilo 5 Beach area of Banggai Regency, Central Sulawesi, Indonesia, has experienced hydrodynamic pressure leading to coastal abrasion. This study analyzed the effectiveness of low-crested breakwaters (LCB) constructed using Geotube materials in reducing wave energy and enhancing sediment accretion at Kilo 5 Beach. The method used was an integrated approach that comprehensively combined field data, sediment characteristics, bathymetry, and numerical hydrodynamic modeling. The numerical simulations showed that the low-threshold breakwater structure could reduce the average wave energy by 76%, enhance sediment deposition, and support natural accretion processes behind the breakwater structure. Morphodynamic simulations showed sediment accretion of up to 20 m behind the structure, while localized erosion of up to 15 m occurred around the gaps and sides of the structure due to flow acceleration. These findings show that low-crested breakwaters are effective in redistributing the hydrodynamic energy and accelerating shoreline stabilization and natural reclamation. Nevertheless, the potential for localized scouring at the toe of the structure must be considered in the technical design. Overall, low-crested breakwaters represent an adaptive and environmentally friendly alternative for coastal protection against abrasion, particularly in semi-enclosed tropical coastal areas.