October 2014 Vol. 2 No. 2

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Eregno FE

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Original Research Articles

Regional Flood Frequency Analysis Using L-Moment in the Tributaries of Upper Blue Nile River, South Western Ethiopia

Fasil Ejigu Eregno

Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway.

E-mail: efasilejigu@yahoo.com OR fasil.eregno@nmbu.no; Telephone: +4741488518

Accepted September 22, 2014

Abstract

Flood estimation with a certain frequency is one of the most important factors for the design of hydraulic structures. It is a big problem in an area where river gauging stations are limited, or the length of records is too short to insure reliable quantile estimates. Regional flood frequency analysis using L-moments is one of the recently innovated methods to overcome this problem. In this study, the flood records of six gauged tributaries of Didessa sub-basin, Ethiopia, are examined based on L-moments procedure to investigate the hydrologically homogeneity of the region, to identify and establish the regional statistical distribution, to develop regional frequency curve and to extend the methodologies to the case of ungauged site. The result of the analysis shows that, the region is homogeneous, and Generalized Extreme Value (GEV) distribution is found to describe the distribution of extreme flood event in the region. Then regional dimensionless growth curves for the region are derived. The results presented herein can be used in Didessa sub-basin while the methodology may be applied in any other regions in Ethiopia, provided flood records are available.

Keywords: Flood frequency, Index flood, L-moments, Regionalization, Upper Blue Nile River