Regional Flood Frequency Analysis Upstream of Awash With the Confluence of Kesem River

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Addis Ababa University


Regionalization is the most viable way of improving flood quantile estimation in index flood method of frequency analysis. Systematic ways of estimating flood quantiles for the design of hydraulic structures for the cases of both gauged and ungauged catchments are presented. These have been carried out on Awash river upstream of Awash with the confluence of Kesem river. The Sub- Basin has been regionalized into similar flood producing characteristics based on established flood frequency procedures. The basin was delineated in to five homogeneous regions. Accordingly, region one includes Berga,Holeta, Ginchi, Teji and Awash-Bello river catchments, Region two covers Melka-Hombola, Melka-Kountera ,Akaki, Little-Akaki and Mojo catchments, Region three includes Awash-Below Koka dam, Wonji, Kelata and Nura-Hera, Region four includes Methara, Awash at Awash Station, Arba-Abomsa and Melka-Sedi catchments, Region five incorporates Kesem-Baka and Kesem-Awara Melka. All regions have shown satisfactory results for homogeneity tests. For the identified homogeneous regions three different best fitted distribution types and robust parameter estimation methods were selected to fit the standardized flow data for various return period. General extreme value type of distribution is found to be the best fitting distribution for region one. Whereas, Gama distribution for region two and four, Person-III for region three and five are selected for flood quantil estimation. For all distributions types method of moment parameter estimation is more efficient. Based on this, regional flood frequency curves are developed for all regions using standardized flow data for the purpose of estimating flood quantiles in the ungauged catchments of the basin .This study is believed to benefit regional states, NGOs and the country at large in providing new information on flood quantiles for designing of hydraulic structures, culverts, bridges, dams, weirs, etc.



hydraulic structures; culverts, bridges; dams; weirs.