FLOOD INUNDATION AND HAZARD MAPPING ON SHABELLE RIVER BASIN: CASE STUDY OF JOWHAR TOWN IN SOMALIA

Abstract

Floods present a significant threat to Jowhar Town, Somalia, due to its location in a riverine area. This study aimed to assess flood risk and identify vulnerable areas through a comprehensive analysis using GIS and Remote Sensing techniques. High-resolution Digital Elevation Models (DEMs) were utilized to delineate the watershed, while the Analytic Hierarchy Process (AHP) was applied to assign weights to factors influencing flood hazards, such as elevation, slope, land cover, rainfall, soil texture, proximity to the river, and drainage density. A weighted overlay analysis produced a flood hazard map, and a weighted sum analysis evaluated flood risk, considering factors like population density, land use, elevation, slope, and flood hazard. Hydrological modeling using the Generalized Extreme Value (GEV) distribution estimated peak discharges for various return periods. The results revealed high flood hazards and risks in downstream areas with minimum area coverage while the upstream showed maxim flood hazard with maximum area coverage. The 1D Hydraulic models for inundation mapping using HEC-RAS showed the 100-year return period flood depth was maximum immediate upstream of Jowhar town with a discharge of 1017.01 m3/s using Gumbel distribution function. To reduce these risks, both structural and non-structural measures are recommended. Structural solutions include the construction of levees, floodwalls, dams, and enhancing river channels particularly around Jowhar town. At the same time, non-structural approaches involve land-use planning, early warning systems, emergency response plans, and public awareness initiatives in the Jowhar sub-watershed. By implementing these strategies, Jowhar Town can significantly reduce its flood vulnerability and better protect its residents and infrastructure from unexpected flood.