Flash flood susceptibility assessment using geospatial technology-based morphometric analysis in Waya watershed, Volta River basin, Ghana

Abstract

The present study aims to assess the flash flood susceptibility of Waya watershed in the Lower Volta River Basin, Volta region, Ghana using geospatial technology-based morphometric analysis. Morphometric characteristics were determined using Advanced Spaceborne Thermal Emission and Reflection Radiometer DEM (30 m) in a GIS 10.7 environment. The morphometric ranking method was applied to prioritize sub-watersheds' susceptibility to flash floods. The results revealed that the watershed is a seventh-order drainage system with a dendritic drainage pattern. The mean bifurcation ratio (4.48), and form factor (0.20) are indicative of higher levels of surface runoff and high flash flood events. The stream frequency (3.27–4.14 km²), drainage density (2.24–2.51 km/km²), and infiltration number (8.05–10.22 km³) showed higher runoff and flash floods. Watershed relief (553 m), relative relief (194.4), ruggedness number (1.36), and mean slope (10.31 %) are indicative of flash flood susceptibility. The results further showed that seven sub-watersheds (SW1, SW5, WS6, SW8, SW9, SW10 and SW12) constituted 63.00 % of watershed ranked as high to very high susceptibility to flash flood, while two sub-watersheds (SW 2 and WS 7) 12.20 % of the watershed classified under moderate flood susceptibility zone for which specific sub-watersheds flood risk reduction strategies are required to mitigate the hazard of flash flood. Four sub-watersheds (SW3, SW4, SW11, and SW13) represented 24.80 % of the watershed ranked as low susceptibility to flash floods. The study recommends the construction of retention bunds and embankments in the inland valleys and wetlands as sustainable soil and water conservation measures to mitigate flash floods and promote sustainable inland valleys and wetlands rice production.