OVERTOPPING RISK AND FREEBOARD ASSESSMENT OF THE SIRENJA BEACH POLDER UNDER A 100-YEAR SEA LEVEL RISE SCENARIO

Abstract

Sirenja Beach, Donggala Regency, is one of the coastal areas affected by the 2018 Central Sulawesi earthquake and tsunami, which caused changes in coastal conditions and increased the risk of tidal flooding. The construction of a polder system was carried out as a mitigation effort; however, its influence on hydrodynamic conditions and its ability to withstand Sea-Level Rise due to climate change require further evaluation. This study aims to analyze the hydrodynamic conditions of Sirenja Beach after polder construction and evaluate its effectiveness under a 100-year future Sea-Level Rise scenario. The research method applies two-dimensional (2D) numerical modeling using Delft3D software to simulate current patterns, tides, and waves. The data used include bathymetry, topography, tidal data, and wind data from 2015–2024 for wave analysis. Simulations were conducted under two scenarios: the condition after polder construction and the Sea-Level Rise scenario based on climate change projections. The modeling results show that current patterns are influenced by tidal conditions, while the projected 100-year future scenario produces a maximum tidal elevation of 2.17 m. This value remains below the polder crest elevation of 4.67 m, indicating that the polder system is still capable of protecting the coastal area. This study demonstrates that the polder system is effective as coastal adaptation infrastructure against coastal dynamics and climate change impacts.