Flood forecast and inundation mapping using a combined hydrologic and hydraulic model on Muga River Abay Basin, Ethiopia

Abstract This study presents an integrated flood forecasting and inundation mapping framework using coupled SWAT, HEC‐HMS, and HEC‐RAS models for the Muga River basin in the Abay Basin, Ethiopia. The study addresses the limited application of integrated hydrologic–hydraulic modeling and the uncertainty associated with digital elevation model (DEM) resolution in data‐scarce regions. Flood discharges corresponding to 2‐, 5‐, 10‐, 25‐, 50‐, and 100‐year return periods, which are commonly used for flood risk assessment and infrastructure design, were simulated. SWAT was applied for continuous hydrological simulation, while the Hydrologic Engineering Center's Hydrologic Modeling System (HEC‐HMS) supported event‐based peak flow estimation. Model performance was evaluated using observed streamflow and the 2017 historical flood event. Flood inundation characteristics were assessed using ALOS 30 m, SRTM 30 m, and SRTM 90 m DEMs to quantify terrain‐related uncertainty. Results show that SWAT produced slightly higher peak discharges than HEC‐HMS, providing conservative estimates for flood risk planning; therefore, SWAT‐derived flows were used for final inundation mapping. Among the tested DEMs, ALOS 30 m exhibited the closest agreement with observed flood extent and depth. The proposed framework is transferable to other sub‐basins of the Abay Basin with similar hydro‐geomorphic characteristics and offers practical support for flood hazard mitigation and planning.