Development of a 2D hydraulic model for prediction of floods in the River Nyamwamba catchment

Abstract

River Nyamwamba is located in the western part of Uganda and it flows through kasese district. The river is majorly known for its seasonal flooding every year during the May season and besides that, the river is also a great tourism centre in Kasese district. The river’s flooding interrupts social economic activities such as transport, studying, farming and many others. This study focused on conducting a flood risk assessment through the utilization of software and these were QGIS 4.42, HEC-HMS, and HEC-RAS. We used QGIS 4.42 to delineate the catchment and Hydrological and Hydraulic models for the river catchment were developed in HEC-HMS 4.12 and HEC-RAS 6.6 respectively. The curve number method was used as the loss method with the Muskingum method adopted as the routing method to simulate runoff from the catchment. The precipitation was downloaded from CopernicusServices,https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels?tab=download and was later bias corrected. The simulated river flows for the different return periods of 2, 5, 10, 25, 50 and 100 years after which the basin model was calibrated and validated in HEC-HMS by using observed River flow data from the kyembago station since River Nyamwamba is ungauged. HECRAS 6.6 was used to carry out Hydraulic modeling for the catchment using simulated streamflow results from HEC-HMS 4.12 and the subsequent flood plain maps were developed for each return period. Analysis of each obtained data was made to ensure proper validation of the model. A flood plain management program has been recommended to reduce the impact of floods on the communities living in the catchment.