Riverine flood management :

Abstract

This study covered the investigation of the flood mitigation measures required to protect River Namatala watershed, which is located in eastern Uganda and has been subject to frequent floods recently. Personal Computer Storm Water Management Model (PCSWMM) was applied to investigate the hydrological responses in the River Namatala watershed, precipitation data and the Digital Elevation Model (DEM) of the watershed were used as input. The observed discharge in the Namatala river was imported into the model to compare with the discharge values simulated by the model. Flood hazard maps were generated through hydrodynamic modelling using the 1D HEC-RAS model. The flood vulnerability maps were generated through the use of Multi Criteria Decision Analysis (MCDA) and Analytical Hierarchy Process (AHP) in a Geographic Information System (GIS) environment, considering the following factors, slope, elevation, land use land cover (LULC), soil type, rainfall and distance from river. The flood hazard and vulnerability maps were then overlayed to generate the flood risk maps. Using Multi Criteria Analysis (MCA) and basing on different factors, levees and river channel improvement were found to be the most appropriate structural flood mitigation measures for River Namatala watershed. Preliminary designs of the levees and river channel improvement were simulated in the 1D HEC-RAS model in order to determine their effectiveness in flood risk reduction, considering the evaluation criteria of flood depth and inundation extent. Finally, the effectiveness of a combination of levees and river channel improvement in flood risk reduction was evaluated. Key words; PCSWMM, 1D HEC-RAS model, Hydrodynamic modelling, MCDA, AHP, GIS