Evaluating the contribution of weir and canal towards flooding in river Ngenge.

Abstract

A significant natural hazard that annually affects various regions of the world is flooding. This is due to climate change, both urban and rural areas are more susceptible to floods. One of the most notable events that cause flooding is heavy rainfall received in the Ngenge watershed. As a result of the failure of mitigation measures, the majority of experts now advise a shift in thinking from structural measures to flood risk zoning and non-structural management measures. Recently, the development of models for flood calculation and hazard assessments has made full use of the advancement in computer-aided technology. This study focuses on applying ArcGIS, HEC-HMS and HECRAS in assessing the contribution of the weir and canal towards flooding in Ngenge sub county, kween district. The models were used to obtain inundation maps, flood depth, and water surface elevation of 2,10,25,50,100, & 200-year return periods. This research included reading a variety of literary works and gathering supplemental information in the form of journals and reports, which aided in developing the project. The data used included; DEM, discharge flow, land use/cover, rainfall, and soil data were all collected. These datasets were prepared and processed in the ArcGIS environment in order to generate curve number grid with the help of land use and soil data, HEC Geo-HMS extension was used to set up a project involving basin features, processing, and exporting into HMS to generate hydrographs for use in HEC-RAS. Flood frequency analysis was calculated using the Gumbel method to attain the peak flows at various return periods. The HEC-RAS program was used to compute for 1D steady and 2D unsteady flow simulation. The computed peak discharges of 19.8m3/s, 42.3m3/s, 80m3/s, 108.2m3/s, 124.3m3/s and 151.5m3/s and output flow hydrographs were used as inputs in performing 1D steady and 2D unsteady flow respectively in HEC RAS. This study shows that the robust modelling approach presented here yielded insightful results that can be used by relevant authorities to implement flood management measures and define priorities for flood catastrophe risk planning, and preparedness.