Flood risk assessment in Namisindwa district using GIS.

Abstract

Throughout the human history floods have been an integral part of the civilization. Still men have not quite coped well to live with floods. Flooding is the most frequent global natural disaster; rural areas are becoming more vulnerable to flooding due to effect of climate change. Flash flood is one of the most prominent phenomena caused by heavy rains. In developing countries drainage channels is the most common strategy employed for flood control. The failure of preventive measures has led to most authors and researchers to advocate a shift in thinking from preventive measures to flood risk and structural management measures. Recently, the advancement in computer-aided technology has been extensively used in formulating models used for flood calculation and hazard analysis. This study focuses on using a hydraulic model HEC-HMS and HEC-RAS in a GIS environment for the affected areas of Namisindwa, generates the inundation area and the return period for the specified flood events. The research involved studying various literature and collecting ancillary data in form of journals and reports. This helped to formulate the methodology for the whole project. Hydrological modeling was performed using HEC HMS software, after delineating the catchment basin model using HEC GeoHMS in ArcGIS environment, populating the meteorological model with design storm data and defining control specifications. The 2, 5, 10, 20, 50- and 100-year design storms data input into the model generated design floods of 33.8m 3 /s, 52.0m 3 /s, 66.2m 3 /s, 80.6m 3 /s, 99.9m 3 /s and 114.9m 3 /s magnitudes respectively. Hydraulic modelling was performed using HEC RAS software. The model output channel flood depths at the gauging station were 1.29m, 1,53m, 1.68m, 1.81m, 1.98m and 2.09m for stimulated 2, 5, 10, 20, 50 and 100year design floods respectively. Flood hazard maps were generated by exporting the HEC RAS model output results to Arc GIS where they were processed to identify the flood prone areas. From the flood hazard maps, the most flood prone areas were around the river middle reach.