FLOOD HAZARD ASSESSMENT AND MAPPING OF FLOOD INUNDATION AREA OF LOKA-ABAYA WOREDA OF SIDAMA ZONE IN S/N/N/P/R/S ETHIOPIA

Abstract

Loka-Abaya woreda is found in S/N/N/P/R/S Rift Valley, surrounded by Bilate catchment. The area is dominated by undulating terrain with relatively steep to moderately steep and flatter slopes in the downstream of the catchment. This flood plain has been vulnerable to high flooding from rainfall during rainy season. This study focuses on estimation of flooding of the woreda due to the out-braking of Bilate River. The data used for generating the peak discharge for different return period related to the hydro metrological data of past events, and geometrical characteristics of the river channel and the reach boundary conditions are prepared in SCS method, HEC-RAS and HEC-GeoRAS models and Arc GIS environment. It was found that simulation result for return period of 5, 10, 25, 50 and 100-yearflood discharges of magnitude are 405.38, 551.48, 707.20, 745.37 and 898.12 in m3 /s respectively. The maximum flood hazard and flow depth for the return periods are found to be 3699.3 and 3.42; 3851.4 and 5.52; 4011.2 and 6.18; 4067.0 and 6.29; and 4224.5 hectare and 6.78 m respectively with a maximum velocity of 5.6m/s. The percentages of area inundated by floods are found increasing from 18.6 (3699.3ha) for 5 years to 21.3 (4224.5 ha) 100-year return period. Billate erisha lemat, Billate chricho, Thinbaho erisha lemat, Billate Eta and Boro shebela Keble of the woreda is found as flood prone area. It is observed that the findings of the research lead to key inputs in the designing of sustainable mitigation measures to minimize the impact of floods and the associated risks; it supports policy and decision makers to decide about how to allocate resources, flood forecasting, ecological studies, and significant land use planning in