A basin-wide flood frequency analysis using Index flood and L-moments approachoffers an attractive solution to provide flood quantile estimations at hundreds ofungauged sites within the Red River Basin of the North. L-moments diagrams andhierarchical clustering techniques were used initially to delineate hydrologic regionswithin the basin. Although the northern plain is relatively flat and almostmonotonous, the analyses have shown that four homogeneous regions could beestablished for the basin. The whole basin as a region is also established for thepurpose of flood estimations along the main stem. Appropriate probabilitydistributions are fitted to the pooled regional flood peaks in each region. Monte Carlosimulations are performed to decide the best distribution for each region, and thedominant distributions found are the Log-Pearson Type III and the generalized Paretodistributions. The regression of index flood with the physical factors of drainage areaand basin slopes for two of the five regions are not very satisfactory. However, theflood quantile estimates are sufficient for preliminary planning purposes.
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