Saltwater Intrusion at Kapuas Besar Estuary Using 1-Dimensional Analytical Method

The Kapuas Besar Estuary in West Kalimantan is vital for both the local community’s ecological and economic well-being. One major issue faced in this estuary is saltwater intrusion. This study aims to investigate saltwater intrusion variation using a one-dimensional (1D) analytical model. The model input data includes estuary geometry, tides, salinity, and river discharge. Simulation results demonstrate the effectiveness of the 1D analytical model in predicting saltwater distance based on the Root Mean Square Error (RMSE), Percent Bias (PBIAS), and Nash-Sutcliffe Efficiency (NSE) values between the analytical model results and observed data ranging from 0.82-1.70 psu, 1.64-2.85%, and 0.96-0.99 respectively. The model proves applicable during the May-October period, subject to the condition that the river discharge remains below 3,200 m3/s. However, during November-April the model tends to underestimate compared to actual distance. Model results show saltwater intrusion increasing from December to June by 49 km, then decreasing from July to November by 38 km. The minimum distance of saltwater intrusion occurred in May (1 km from the estuary mouth) when river discharge of 8,853.82 m 3 /s. Conversely, the maximum saltwater intrusion distance was observed in June (71 km from the estuary mouth) with a river discharge of 1,034.55 m 3 /s.