Regional Flood Frequency Analysis for Zeway – Shala Sub Basin, Rift Valley Basin, Ethiopia

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Date

2020-07

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Addis Ababa University

Abstract

In this study index flood method based on L-moments were used for regional flood frequency analysis of Zeway – Shala sub basin. The purpose of this study is to develop the regional flood frequency (growth) curve and index flood estimation equation which is essential for computing flood quantiles for ungauged catchments in Zeway – Shala sub basin. The index-flood method was applied to Zeway – Shala sub basin, based on the records of annual maximum instantaneous discharges at 10 stream gauging stations. Delination of comparatively homogeneous regions was performed on the basis of catchment characteristics and their similarity in certain parameters like slope, elevation, soil type, and flood statistics of the sub basin. Accordingly, Zeway – Shala sub-basin has been divided in to two nearly homogeneous regions. Goodness of fit test measure using the statistical test like kolmogorove simirnove test and chi-squared testes to identify how well the selected distribution fit to the data was followed. For this study among the fitted distributions, Generalized Extreme Value distribution is selected for region one and Log Pearson Type III distribution is selected for region two based on statistical value, because of its simple to apply and widely acceptance nature. For the selected distributions the statistical parameter estimated by Methods of Moment and the regional growth curve were developed for each regions by using the quantiles of the selected distributions. Finally the index flood estimation equation were developed by regression analysis with a coefficient of determination (R ) 0.72 for region one and 0.63 for region two to predicted mean annual flood flow from ungagged catchment

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Keywords

regional flood frequency analysis, annual maximum discharges, index-flood

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