Flood Hazard Mapping and Damage Analysis for Meki River Using Hec-Ras And Hec-Fda Models

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Date

2017-12

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Addis Ababa University

Abstract

Flooding causes major damage on the economic, social and environment of the affected area. Overflow of Meki River has affected and displaced the people and destroyed farm land along the river in the flood plain area of Dugda Woreda in the summer season. In late March and early April 2016 floods destroyed 485.75 hectares farm land and damage 80 farmer houses. This research develops flood hazard maps and damage analysis along Meki River. The digital elevation model of the study area was used to extract the physical characteristics of the catchment using HEC-GeoHMS GIS extension. HEC-HMS hydrological model was used to generate flow hydrograph for different return periods at the outlet of the catchment using the design rainfall. Flood inundation and hazard maps along Meki River have been developed based on the flow hydrographs for different return periods using the HEC-RAS model, GIS for spatial data processing and HEC-GeoRAS for interfacing between HEC-RAS and GIS. Based on the output of HEC-RAS hydraulic model, using HEC-FDA, flood damages were estimated quantitatively. The areas along the Meki River simulated to be inundated for 2, 5, 10, 20, 25, 50 and 100 years return period. The flooded areas were high from Meki town to Lake Ziway for all return periods. The flood inundated area along the Meki River for a return period of 100, 50, 25, 20, 10, 5, and 2 years were 15.52, 14.99, 14.02, 13.57, 12.95, 12.50 and 11.52 km respectively. The flood hazard map results were low, moderate, high and very high hazard levels based on the flood depths generated using HEC-GeoRAS GIS extension. Finally, the cost of flood damages was evaluated using HEC-FDA and mitigation measures were proposed to reduce the damages due to flooding in study area. The sum of expected annual damage for eight return period intervals was 707,193,871 birr. The major findings in the study indicate that inundated areas in the lower part of Meki River were made economic damage on agricultural farm land and settlement. Therefore, increasing the width of the river channel or construction of levees has been proposed to reduce the economic damage of flooding in lower river parts.

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Keywords

Meki River, Flood Plain, HEC-HMS, HEC-RAS, HEC-FDA, DEM

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