Regional Frequency Analysis of Wabash River Flood Data by L-Moments

Abstract

Regional frequency analysis is used to estimate flood quantiles in a region. It is also used to identify parent distributions by analyzing the data from a number of stations within a region. The basic idea behind regional frequency analysis is to make use of similarities in the characteristics of floods at different sites in a region. Consequently, regional homogeneity is essential for such an analysis. L-moments are used in this study to investigate the feasibility of regional frequency analysis in the Wabash River basin. The Wabash River basin is shown to be hydrologically heterogeneous. It is divided into smaller subregions by using L-moment ratio diagrams. The generalized extreme value distribution is recommended to be the regional parent distribution. Both the Pearson-III and the three-parameter lognormal distributions are acceptable at the at-site level. The goodness of fit at both the at-site and regional levels is compared for a homogeneous and for a heterogeneous region.