Shoreline Change Forecast Modeling at Bahoi Beach, North Minahasa Regency, Using Numerical Simulation

Abstract

This study models shoreline changes at Bahoi Beach, West Likupang, North Minahasa Regency, to support sustainable planning and use of the coastal zone. The method is numerical modeling using the Coastal Engineering Design Analysis System (CEDAS) equipped with the Nearshore Evolution Modeling System (NEMOS) module. The main input data comprise wave, tidal, and bathymetric data. Simulations were run for return-period scenarios of 10, 15, and 20 years. Model validation against the historical shoreline extracted from 2023 satellite imagery yielded a root-mean-square error (RMSE) of 3.5 m, indicating acceptable accuracy for medium-term prediction. Results for the 20-year horizon show a stable, though slight, dominance of accretion, with an accretion–erosion difference of +20.95 m² (0.20%). These results indicate a condition of dynamic coastal equilibrium. It is concluded that Bahoi Beach is stable with a mild accretion tendency, so major structural intervention is not required; however, continuous monitoring and preparation of mitigation scenarios remain necessary.