L-moments approach for flood frequency analysis of river Okhuwan in Benin-Owena River basin in Nigeria

Abstract

The flood frequency analysis of River Okhuwan at Ugonoba site in Benin Owena River Basin in Nigeria was carried out using annual maximum stream flow series for 20 years (1989-2008). The objective of the study was to determine the best fit probability distribution model applicable to the site from amongst three selected 3-parameter distribution models namely: Generalized Extreme Value distribution (GEV), Generalized Logistic distribution (GLO) and generalized Pareto distribution (GPA) whose parameters were estimated by the method of L-moments. The best fit distribution was selected based on result of four goodness-of-fit tests applied to the candidate distributions. The results indicate that GPA is the best fit distribution model for analyzing the annual maximum flood series at the study site for return period less than or equal to 25 years but for return periods between 25years and 200 years, GLO or GEV is recommended in that order.

Keywords: Flood frequency Analysis,L-moments, Probability distribution, Return period, Parameter estimation