Flood Hazard Analysis Based on the Modified Geomorphic Flood Index (MGFI) using Effective Rainfall in the Bekasi Watershed

Abstract

This study analyzes flood hazards in the Bekasi watershed using the Modified Geomorphic Flood Index (MGFI) weighted by effective rainfall for return periods of 2, 5, 10, 25, and 50 years. Effective rainfall was calculated using the SCS-Curve Number method and subsequently used as a weight in the calculation of the contributing area. Flood depth was estimated based on the relationship between river water levels and elevation relative to the river network. The results indicate that the hazard area expanded from 31,179.03 ha for the 2-year return period to 38,466.39 ha for the 50-year return period. Maximum flood depth also increased from 1.159 m to 1.554 m, with the high-hazard class emerging only at the 50-year return period. ROC–AUC validation using 110 points yielded values between 0.9326 and 0.9491, demonstrating high discrimination capability between flood points and pseudo-non-flood points. These findings suggest that the effective-rainfall-weighted MGFI is suitable for preliminary flood hazard mapping in watersheds with limited data.