Development of A Gis-Based Rainfall Mapping System Using Isohyet and Interpolation for Flood Control in the Babak Watershed

Abstract

Accurate and spatially distributed rainfall data are crucial for effective water resource management, particularly in flood control and infrastructure planning. This study develops a GIS-based rainfall mapping system for the Babak Watershed by integrating Isohyet mapping with spatial interpolation techniques—specifically Inverse Distance Weighting (IDW) and Spline methods—to address the limitations in rainfall data coverage due to the sparse distribution of Automatic Rainfall Recorder (ARR) stations. Secondary rainfall data from 17 Automatic Rainfall Recording (ARR) stations in the Lombok River Basin were analyzed alongside observed values from two Manual Rain Gauge (MRG) stations: MRG Bendung Babak and MRG Bendung Batu Riti. Using ArcGIS 10.2, rainfall distributions were estimated and visualized within a spatial decision-support system.

Results show rainfall estimates at MRG Bendung Babak of 2013 mm/year (IDW), 2210 mm/year (Spline), and 3098 mm/year (Observed); and at MRG Bendung Batu Riti of 1691 mm/year (IDW), 1402 mm/year (Spline), and 1446 mm/year (Observed). Error analysis indicates that Spline had a slightly lower error at Bendung Babak (34%) compared to IDW (37%), while IDW showed superior performance at Bendung Batu Riti (206% vs. 212%). Correlation coefficients further validate IDW’s accuracy, with values of 68% and 81% at the two respective sites.

This study demonstrates that integrating Isohyet and interpolation methods within a GIS environment enhances the reliability of regional rainfall estimation. The GIS-based system developed offers a practical tool for hydrological analysis, flood risk assessment, and strategic planning of water infrastructure, particularly in data-scarce regions. To the best of our knowledge, this is the first application of such integrated techniques for rainfall mapping in the Babak Watershed.