Integrated hydrologic and hydrodynamic modeling for flood hazard assessment in Ajay River Basin, West Bengal, India

The Ajay River, originating from the Chotanagpur Plateau (Bihar) and flowing through Jharkhand into West Bengal before merging with the Bhagirathi‐Hugli near Katwa, is among the most flood‐prone rivers in the region. Its lower reaches frequently experience rainfall‐induced flooding and embankment breaches during the mid‐ to late‐monsoon season. Here, an integrated hydrologic‐hydraulic approach was adopted to better understand flood hazards, a practice that is rarely applied in this basin. Using Intensity‐Duration‐Frequency (IDF) curves derived from Indian Meteorological Department data, rainfall‐runoff simulations were performed on HEC‐HMS for 25‐, 50‐, 100‐, and 500‐year storm events. Simulated peak discharges ranged from 6627.5 to 12098.4 m 3 /s. Further, hydrodynamic simulation using HEC‐RAS revealed that the 500‐year event inundated the largest area, with 214.76 km 2 under flood depths of 2–3 m and 279.00 km 2 under flood depths exceeding 3 m. These findings offer critical insights into the basin's flood response and emphasize the importance of integrated modeling for effective flood risk assessment and management.