An improved equation for potential discharge estimation in groundwater basin delineated watershed

Abstract

Indonesia is delineated by 128 river basins and 7,977 watersheds, with 47 % consisting of groundwater basins and 53 % classified as non-potential groundwater areas. Groundwater basins, defined by hydrogeological boundaries, contain both confined and unconfined aquifers, with a total potential discharge of 517.217 m³/s. Effective water resource management, given the interaction between surface and groundwater, requires analyzing water availability using dependable flow, which includes direct runoff, interflow, and baseflow. This study proposes an improved equation based on modified rational method, for estimating potential discharge in groundwater basins, offering a simplified method compared to existing approaches. The new equation was tested in two locations—the Cidanau Watershed in Banten Province and the Kupang Watershed in Central Java—using data such as AWLR observations, climate, runoff coefficients, land use, groundwater basin maps, and soil permeability. The improved equation was then compared to the F.J. Mock, Sacramento, and NRECA methods, which are widely used in water resources development. Results showed that the improved equation had the low RSR value and the high correlation in both watersheds, suggesting greater accuracy. In the Cidanau Watershed, it achieved the lowest RSR value (0.071) and highest correlation (79.6 %) compared to other methods. Though the Kupang Watershed had a slightly higher RSR (0.083), the difference was not significant. Furthermore, in this case, the improved equation demonstrates the highest correlation value (63.18 %). These findings highlight the equation's potential for estimating discharge and its applicability in water resources management policy and planning in Indonesia.

Keywords

• Improved equation
• Rational method
• Groundwater basin
• Cidanau watershed
• Kupang watershed