Sensitivity Analysis of Mock and NRECA Method Parameters on Water Availability in the Jangkok Hulu Watershed

Abstract

The Jangkok watershed, as one of the watersheds with high utility, plays an important role as a supplier of supplementary water to the communities living in the surrounding area. If there is a decrease in base flow in the Jangkok Watershed, it will have a significant impact on the irrigation water supply in Jangkok-Babak-Jurang Sate, raw water supply, and industrial water in Mataram City and West Lombok Regency. Because the Jangkok watershed is widely used for low flow management in the form of river and spring water, water flow availability can be obtained using the F.J Mock and NRECA methods. Each parameter has its own sensitivity that can directly affect changes in water availability. The parameter with the greatest sensitivity is determined based on the average deviation percentage and discharge change. The initial stage involved a calibration process with Qdefault results for the Mock and NRECA methods of 1.261 m³/dt and 0.968 m³/dt, respectively. Next, sensitivity analysis was performed using calibrated default parameters with overestimate and underestimate conditions of 5%, 10%, 15%, and 20%. Based on the results of the sensitivity analysis of the F.J. Mock Method, the parameter with the highest sensitivity was the Groundwater Recession Constant (k) under an underestimate condition of 20%, which affected the increase in water availability discharge in January 2024 to 6.457 m³/dt with an average deviation of 245.90%. In the NRECA Method, the parameter with the highest sensitivity was Percent Sub Surface (PSUB) under the 20% underestimate condition, which influenced the increase in water availability discharge in January 2024 to 0.993 m³/dt with an average deviation of 20.08%.