Design storm estimation for flood risk assessment in the temperate Himalayan basin using hydrological modelling

Area of Science:

• Hydrology and Water Resource Management
• Environmental Modeling
• Climate Change Adaptation

Background:

• Flood frequency analysis and hydrological modeling are vital for managing water resources and mitigating floods, particularly in areas prone to extreme weather events.
• The Jhelum Basin in Kashmir is vulnerable to significant flood impacts, necessitating detailed risk assessment.
• Previous studies have not provided sub-watershed-scale, event-based design storm analyses for this region.

Purpose of the Study:

• To apply the HEC-HMS hydrological model for simulating rainfall-runoff processes and generating event-based design storms for various return periods.
• To assess flood risk patterns at the sub-watershed scale within the Jhelum Basin, Kashmir.
• To provide high-resolution insights for flood mitigation and infrastructure planning in a mountainous region.

Main Methods:

• Utilized the Hydrologic Engineering Center's Hydrologic Modeling System (HEC-HMS) for rainfall-runoff simulation.
• Employed ModClark for rainfall transformation, Linear Reservoir Method for baseflow, and Muskingum approach for flood routing.
• Incorporated satellite-based gridded rainfall data and sub-basin-specific hyetographs, with model calibration and validation using observed discharge data (2020-2023).

Main Results:

• The HEC-HMS model demonstrated strong performance in simulating observed hydrographs (R² > 0.78, NSE > 0.56).
• Sensitivity analysis identified curve number, time of concentration, and infiltration rates as critical model parameters.
• Identified varied hydrological responses across sub-watersheds, with specific areas showing high peak discharges or prolonged flood retention, and urbanized areas exhibiting vulnerability.

Conclusions:

• The study successfully generated event-based design storms at the sub-watershed scale in Kashmir using HEC-HMS, offering novel high-resolution flood risk insights.
• The findings highlight the effectiveness of the HEC-HMS model as a non-structural flood mitigation tool for mountainous regions.
• Results provide crucial data for informed infrastructure planning and risk management strategies to enhance flood resilience in the Jhelum Basin.