23. Morphometric Characterization and Flash Flood Zonation of a Mountainous Catchment Using Weighted Sum Approach

Uttarakhand is a hill state of North India with a unique and diverse topographic, morphologic, and climatic setting. The higher elevation areas have been experiencing repeated flash flood events caused by cloud bursts or heavy precipitation. This study demonstrates the potential of remotely sensed data and geographical information system for assessing the flash flood risk in the Alaknanda River Basin (ARB) located in the Northwestern Himalayan Region in India. Multiple sub-watersheds in this river basin experience flash flood events almost every year, causing massive property damages and life loss. SRTM 30 m DEM was processed and utilized for conducting morphometric analysis to prepare a flash flood risk prioritization map for the 7 sub-watersheds of ARB. The morphometric parameters considered for this purpose were sub-watershed area, perimeter, stream order, stream length, basin length, bifurcation ratio, drainage density, stream frequency, texture ratio, form factor, circularity ratio, and elongation ratio. The correlation matrix for all these morphometric parameters for each sub-watershed was analyzed to obtain a compound parameter value using weighted sum approach (WSA), which was used for performing flash flood zonation (low, medium, high, and very high). The analysis results indicate that out of the 7 sub-watersheds, SW-2 and SW-3 were categorized under the high-risk zone, and SW-5 was categorized under the very high-risk zone.