Flood Risk Analysis in Illu Floodplain, Upper Awash River Basin, Ethiopia
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Date
2015-12
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Addis Ababa University
Abstract
A flood has negative effect to human beings and properties even if it has positive effect. Because less attention is paid for risk, it should be analyzed and quantified properly. The Upper Awash River and flooding remain inseparable for long time in cultivated area. The objective of this study is to quantify and estimate the risk of flooding on crop production in the study area. The basic assumptions in statistical flood frequency analysis are the independence and stationarity of the data series and that the data come from the same distribution. Homogeneity and stationarity tests at different significance levels were made using Wald-Wolfowitz and Mann-Whitney tests. Using the method of moments of parameter estimation technique, the time series of the flow data was fitted to extreme value type one (EV I). The flood hazard mapping was done through HEC-GEORAS and HEC-RAS software’s. Finally, by comparing the amount of crop yield produced previously from a hectare of land and the expected crop yield from the inundated area the flood damage could be estimated. Thus indicates that, improved Awash Bello stream flow gauge station which measures flow data appropriately for the entire period i.e. it properly records the flow data without any disturbance from 1960 to 2010. The flow data of Awash Bello s station was found to be independent, homogenous, stationary and no outlier at 5% significance level. The quantile estimates of the 2, 5, 50, 100, and 500 year return periods for the site were also found to be 39.30, 50.38, 73.86, 80.69 and 96.46 m3/s, respectively. These floods inundated croplands having sizes of 1,959.50, 2,107.38, 2,299.16, 2,318.84, 2,354.06 hectares, respectively. These corresponded to losses of 44,088.66, 47,415.96, 51,731.03, 52,173.84, 52,966.25 quintals of crop, respectively. This study has shown that the upper most part of the cultivated is more inundated than the middle and lower parts. The areas affected by the flooding are found closer to the Awash River. Therefore, the affected areas is to be free of any agricultural activities, infrastructure development, investment and residence of people in order to avoid the risk of flooding in the area especially closer to the Awash River Keywords: Hec-Ras, Hec-GeoRAS, Flood hazard map and Crop production.
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Hec-Ras, Hec-GeoRAS, Flood hazard map and Crop production