Regional Flood Estimations in Red River Using L-Moment-Based Index-Flood and Bulletin 17B Procedures

Abstract

L-moment-based index-flood method (LMIF) is used in a regional flood frequency analysis of the Red River of the North basin. The results are appraised with respect to the traditional methods based on the 1982 Interagency Advisory Committee on Water Data (Bulletin 17B) procedure. The L-moments approach detects the necessity of subdividing the basin into three main homogeneous hydrologic regions through hierarchical clustering techniques, regionalization, distribution fittings, and simulations. Each region has a unique index-flood growth curve. The dominant distributions include the Pearson Type III, the generalized Pareto, and the generalized extreme value. For a certain number of gauged sites, the quantiles obtained by the LMIF differ significantly from those obtained by pursuing the Bulletin 17B-regression procedures. Generally, the latter gives lower quantiles for most sites. Overall, the LMIF is effective in identifying homogeneous regions, coherent in statistical distribution fitting, and free from state boundary issues. The investigation also illustrates the flexibility of the method in allowing flood estimations for a special regulated region and a main stem region. Further studies on the use of the LMIF on a national or global scale are recommended.