HYDRODYNAMIC MODELING OF POLLUTANT DISTRIBUTIONS FROM THE BERA WATERSHED AND ITS IMPACT TO THE COASTAL AREA OF SALEH BAY, WEST NUSA TENGGARA, INDONESIA

Amar Malikal RAHMAN , Dini PURBANI , Syamsul B. AGUS , Taslim ARIFIN , Yulius YULIUS , Aprizon PUTRA , Aida HERIATI , Joko PRIHANTONO , Rudhy AKHWADY , Agus SUFYAN , Eva MUSTIKASARI , Sri Endah PURNAMANINGTYAS , Rinny RAHMANIA , Muhammad RAMDHAN , Arya NINGSIH , Sadad SADAD , Didik Wahju HENDRO TJAHJO

DOI: 10.21163/GT_2025.202.03

ABSTRACT: Pollutant distribution from the Bera Watershed may impacts the coastal environment of Saleh Bay. This study aims to map pollutant distribution and assess its ecological effects using a hydrodynamic modeling approach in the coastal waters of Saleh Bay, particularly around the estuaries of the Bera Watershed. The MIKE 21 software with the EcoLab module was used to simulate hydrodynamics and pollutant dispersion. The hydrodynamic model was validated using tidal data from Nao Tide Model, which had been previously compared with observed tidal measurements and showed good agreement. This validation showed a Root Mean Square Error (RMSE) of 0.19423 in April and 0.27589 in September, confirming the model’s reliability in simulating pollutant dispersion. Pollutant data, including Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Nitrate (NO₃-N), and Phosphate (PO₄-P), were collected from the Brang Bera, Brang Maronge, and Brang Kolong Rivers in the Bera Watershed during April and September. Simulations were conducted for both periods. Since discharge data were unavailable, the Manning equation was applied to estimate river discharge at the mouths of these three rivers based on cross-sectional area, hydraulic radius, wetted perimeter, and a consistent roughness coefficient (n = 0.045). Bathymetric analysis revealed depth variations ranging from, 5 to 500 m, while wind data indicated stronger winds in September (5.70–8.80 m/s). Pollutant concentration modeling indicated fluctuating levels, with BOD ranging from 1.2 to 1.8 mg/L, COD from 18 to 28 mg/L, NO₃-N from 3 to 5 mg/L, and PO₄-P from 1.2 to 1.8 mg/L. Peak concentrations occurred during high tides, while localized accumulation was observed during low tides. These findings emphasize the urgent need for effective pollutant management and mariculture to ensure the long-term ecological stability of Saleh Bay.

Keywords: Pollutant, Hydrodynamic modeling, Bera watershed, Environmental quality, Saleh Bay.

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