Assessing Flood Risk and Vulnerability in River Manafwa Catchment.

Abstract

River Manafwa is a natural river found in Eastern Uganda. The river originates from Mount Elgon in eastern Uganda and traverses the districts of Bududa, Manafwa, Mbale, and Butaleja. It joins the Mpologoma River, which empties into Lake Kyoga. The river basin is prone to flooding, which disrupts transportation of goods and services between the Bududa and Manafwa districts and damages buildings with several deaths recorded.

This study focused on conducting a flood risk assessment through the utilization of software and these were ArcGIS 10.8, HEC-HMS, and HEC-RAS. We used ArcGIS 10.8 to delineate the catchment and Hydrological and Hydraulic models for the river catchment were developed in HEC-HMS and HEC-RAS 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.

We simulated river flows for the different return periods of 10, 25, 50 and 100 years after which we basin model was calibrated and validated in HEC-HMS by using observed River flow data of River Manafwa from the DWRM, Ministry of Water and Environment. HECRAS 6.1.0 was used to carry out Hydraulic modeling for the catchment using simulated streamflow results from HEC-HMS 4.8 and the subsequent flood plain maps were developed for each return period. A flood plain management program has been recommended to reduce the impact of floods on the communities living in the catchment .