Numerical simulation insights on salinity increase in estuaries around Ibu Kota Nusantara (IKN) due to Sepaku-Semoi Rivers damming I.P. Anwar1*, M.R. Putri1, A. Tarya1, I. Mandang2
1 Research Group of Oceanography, Faculty of Earth Sciences and Technology, Institut Teknologi Bandung, Bandung, Indonesia
2 Department of Physics, Faculty of Mathematic and Natural Sciences, Universitas Mulawarman, Samarinda, Indonesia
Abstract
The Indonesian national government has decided to relocate the national capital city to East Kalimantan. The new location, named Ibu Kota Nusantara (IKN), is situated in the coastal area of Balikpapan Bay. The development of the new capital city will have significant environmental impacts. Specifically, the construction of dams on the Sepaku-Semoi Rivers will reduce the availability of freshwater in Balikpapan Bay, thereby altering its hydrodynamic conditions. These changes are expected to lead to a crucial issue: increasing salinity levels, particularly in the estuaries of the main rivers. In this study, the primary focus is to investigate the salinity increase in the estuaries due to damming. The baroclinic mode of the Hamburg Shelf Ocean Model (HAMSOM) has been applied to estimate the hydrodynamic conditions in Balikpapan Bay. Crucial parameters output from the model, including sea level, current speed, salinity, and temperature in 3D, have been validated against field measurement data with root mean square error (RMSE) values of 0.1 m, 0.1 m/s, 0.67 PSU, and 1.41^{o}C, respectively. The coefficients of correlation for these parameters are 0.99, 0.85, 0.92, and 0.93, respectively. The prediction of saline water intrusion following dam development has been conducted using three scenarios: normal conditions (before damming), a 50\% reduction in river discharge, and a 95\% reduction in river discharge. The results indicate that salinity in the estuaries of four main rivers (Spaku, Semoi, Wain, and Riko) increased by 3.7-15.1 PSU after damming. This suggests that the estuaries of the main rivers in Balikpapan Bay will experience significantly higher levels of saline water in the future, underscoring the critical environmental impact of dam construction on the Sepaku-Semoi River.
Keywords: Salinity Increasing, Hydrodynamic Modeling, Ibu Kota Nusantara (IKN), Sepaku-Semoi River Damming, Estuarine Impact
