Flood hazard management and identification of mitigation measures along river Nyamugasani in Kyarumba, Kasese district

Abstract

On a global basis, there is evidence that the number of people affected by floods are on the rise. Floods have for a long period put areas in Kasese district at risk for settlement with many displaced and many lives lost. A comprehensive study on flood hazard management and identification of mitigation measures along Nyamugasani river was carried out. Hydrological and hydraulic modeling was carried out considering the storm of different return periods in Nyamugasani. Flood hazard maps in consideration of different return periods of 10, 25, 50 and 100 years were generated. Flood vulnerability level was carried out by index-based approach to get a better understanding of the sensitivity, resilience and exposure of the community to the flood hazard. Suitable mitigation measures associated with the community experience to floods were identified in this study. Rainfall run-off analysis was done using HEC HMS having generated the basin model from ArcGIS. Weighted curve numbers for the various sub-basins and precipitation values were entered into the hydrological model from which the rainfall runoff response of Nyamugasani was determined. This was done for hydrological models for different return periods of 10, 25, 50 and 100 years considering the rainfall data from 2000 to 2015, thus generation of peak discharges of the area. Hydraulic modeling to generate flood hazard maps was done using HEC-RAS having generated the hydraulic model partly from ArcGIS and HEC-RAS itself. Hydraulic models were then calibrated and used to simulate the 10, 25, 50 and 100-year floods to aid in determination of maximum channel flood depths for all cross sections along the Nyamugasani channel reach in Kyarumba. This research study assessed the level of community exposure, sensitivity and resilience and the households’ risk perceptions to floods in Kyarumba. The research design for this study involved an index-based approach. The primary data was obtained using a semi-structured questionnaire, where 156 households were purposefully selected. The research study revealed that Kyarumba community was highly exposed to flood. About 8.3% of the households were found living less than two kilometers from the flooding river. The households were also found to be highly susceptible to flood hazard with 79.5% had a monthly average income of about US$50,000- 290,000. However, the community had high capacities to cope with the flood hazard impacts with only 26.9% of the households surveyed had gone to the local authority for assistance in the last 5 years. About 98.1% thought that the community area is vulnerable to flood risk and 57.1% very worried about the floods in their locality. Flood adaptation measures Respondents were asked the community was not willing to pay with 76.9% claiming its governments work to fund the flood control projects. Suitable mitigation measures were identified in this research study and it was discovered that the largest percent of people in Kyarumba, about 88.5% agreed with construction of a diversion channel. More people agreed with installation of flood warning systems, flood forecasting techniques and flood plan zoning to mitigate floods in Kyarumba along Nyamugasani river. Willingness to pay was carried for the identified community based adaptation strategies and 42.9% of the households were affirmative while 57.1% were negative to the process.