Analysis of Hydro morphometric Characteristics and Flood Hazard Risk in the Bawa Shaswar Watershed

Abstract

The Bawa Shaswar Dam watershed represents one of the most significant hydrological basins in Garmian Governorate, encompassing a total catchment area of 280.84 km² and comprising two principal sub-watersheds: the Bakrasha sub-watershed with an area extent of 102.9 km² (36.64%), and the Balak sub-watershed covering 177.94 km² (63.36%). This investigation was undertaken with the objective of conducting a comprehensive analysis of hydro morphometric characteristics and assessing flood hazard risk, employing a Digital Elevation Model (DEM 12.5M) at 12.5-meter resolution, ArcMap 10.8.1 geographic information system software, and mathematical hydrological models including Kirpich (1940) and Snyder methodologies. The physical characterization analysis revealed that the watershed is underlain by five distinct geological formations (Fatha, Injana, Mukdadiya, Bai Hassan, and Recent Deposits) and encompasses three primary soil types: brown reddish soil (77.88%), stony soil (7.94%), and valley bottom soil (14.18%). From a morphometric perspective, the analytical results demonstrated that the watershed exhibits a circularity ratio of 0.30 km²/km, an elongation ratio of 0.35, and a form factor of 0.19, collectively indicating substantial deviation from circular geometry and approximation toward elongated configuration, thereby amplifying susceptibility to flash flood events. Drainage network analysis revealed a total of 205 stream channels, with drainage density of 1.23 km/km² and stream frequency of 0.73 streams/km², all representing relatively low values indicative of limited erosional activity. From a hydrological standpoint, the Bakrasha sub-watershed exhibited a time of concentration of 4.58 hours, lag time of 0.84 hours, and peak flood discharge of 245.30 m³/s, whereas the Balak sub-watershed demonstrated a time of concentration of 6.48 hours, lag time of 1.06 hours, and peak flood discharge of 336.79 m³/s. Hazard assessment utilizing 14 morphometric variables revealed that the Bakrasha sub-watershed falls within the high-risk category (34 points), while the Balak sub-watershed occupies the moderate-risk classification (26 points). Furthermore, hydrological hazard evaluation employing 12 mathematical equations indicated that both sub-watersheds are classified under the high-risk category; however, the Bakrasha sub-watershed presents elevated risk with a score of 32 points compared to 27 points for the Balak sub-watershed. The investigation conclusively established that the hydro morphometric characteristics of the Bawa Shaswar watershed demonstrate direct correlation with flood hazard potential, necessitating the formulation and implementation of comprehensive flood control strategies and management plans to safeguard the environmental integrity and water resource sustainability of the region.