Investigation of flood incidence causes and mitigation: Case study of Ribb river, northwestern Ethiopia

Abstract

Land degradation due to population growth, climate change and variability and other anthropogenic activities are main factors for the occurrence of flooding in Ethiopia. This study aimed to investigate flood incidence causes in the Ribb river. Possible causes of flooding were identified from literature. To recognize the causes, trend analysis of rainfall to know possible climate change, stream flow analysis to know possible land cover change and lake water level trend analysis to know backwater effect were conducted using the Mann-Kendall test. Land use land cover change review was also conducted. El Niño Southern Oscillation (ENSO) correspondence on rainfall extremes to know the climate pattern effect was conducted using correlation of Southern Oscillation Index (SOI) with summer rainfall anomaly. Structured interview with purposely and systematically selected flood plain community, focus group discussion with Woreda level early warning and response group leaders and natural resource conservation experts were used to confirm causes of flooding. At the end, landscape based mitigation measures from watershed morphometric analysis were proposed using integrated mission for sustainable development (IMSD) and FAO guidelines. The results indicated that the causes of flooding are combination of factors such as anthropogenic activities (expansion of cultivated land, significant lake water level rise and decreasing channel conveyance), climate change (significant increase in wet conditions), inadequate drainage and torrential rainfall. From the landscape based mitigation measures, a total of 7 check dams, 55 farm ponds, 29 percolation ponds and terracing were proposed.