Regional Flood Frequency Analysis of the Red River Basin Using L-moments Approach

A basin-wide flood frequency analysis using Index flood and L-moments approach offers an attractive solution to provide flood quantile estimations at hundreds of ungauged sites within the Red River Basin of the North. L-moments diagrams and hierarchical clustering techniques were used initially to delineate hydrologic regions within the basin. Although the northern plain is relatively flat and almost monotonous, the analyses have shown that four homogeneous regions could be established for the basin. The whole basin as a region is also established for the purpose of flood estimations along the main stem. Appropriate probability distributions are fitted to the pooled regional flood peaks in each region. Monte Carlo simulations are performed to decide the best distribution for each region, and the dominant distributions found are the Log-Pearson Type III and the generalized Pareto distributions. The regression of index flood with the physical factors of drainage area and basin slopes for two of the five regions are not very satisfactory. However, the flood quantile estimates are sufficient for preliminary planning purposes.