ASSESSING THE IMPACT OF WATERSHED MANAGEMENT ON FLOOD DYNAMICS UNDER CLIMATE CHANGE IN THE SWAT VALLEY, KP, PAKISTAN

Abstract

Frequent flooding in the Swat River basin, draining the hilly terrain of Hindukush Mountains in the Northern Pakistan, has been intensifying due to rapid urbanization, inadequate flood planning, and climate change particularly in the monsoon season. This study addressed the need to assess future flood hazards and evaluated mitigation strategies for the basin. The research aimed to quantify peak river discharge in different scenarios obtained from the recorded precipitation data and future modeled based scenarios data to explore the flooding characteristics (height and discharge) in the River Swat thematic layer (DEM plus Satellite Image) geometry at the most vulnerable zones of river reaches. A coupled modeling approach integrated HEC-HMS for rainfall–runoff simulation and HEC-RAS for river routing and floodplain inundation. Historical simulations used observed precipitation and derived intensity–duration–frequency (IDF) curves, while future flows were estimated using down scaled climate projections for RCP4.5 and RCP8.5 for years 2032, 2042, 2052, 2062, and 2072 respectively. Results indicated that the historical design flood discharge was approximately 1168.8 m³/s at the basin outlet. Under RCP4.5, projected peak flows increased moderately, whereas under RCP8.5, flood magnitudes increased up to 1441.3 m³/s by 2072. Mitigation simulations revealed that an upstream reservoirs of area 57,507,700 sq meters could effectively attenuate peak flows up to 40.92%. while levee embankments up to 7 meters restrict the discharge within river floodplain and alleviate the flood risk. Combined application of both levees and reservoirs in catchment provided the greatest reduction 39.6% in flood extent. This study    highlighted climate change predictions in storm events for the future and ultimate its alliance with River Swat peak flow rates to assess the present river geometry and levees application for flooding conditions which can support policy makers to assess the significance of different flood alleviation measures in the Swat Valley and similar regions in South Asia.