Regional flood frequency analysis using L-moment approach

Flood frequency analysis is essentially a problem of information scarcity in arid and semi-arid regions. Particularly in three regions, the lengths of records are usually too short to ensure reliable quantile estimates. Regional flood frequency analysis (RFFA) involves two major steps: (1) Grouping of sites into homogenous regions, and (2) Regional estimation of flood quantiles at the site interest. The main objectives of this study were to estimate regionalized parameters and indentification of the best-fit distribution by L-moments approach in several gauging stations. In central Iran. After determination of main influencing variables by factor analysis discordancy and homogeneity tests were done by L-moment –based measures. In this study, five three parameter distributions generalized logistic (GLO) , generalized extreme value (GEV) , generalized pareto (GPA) , three – parameter lognormal (LN3) , and pearson type III (PE3) were fitted to the two homogeneous regions. The three parameters of these distributions are estimated by the L-moments approach. The results of factor analysis showed that length of main waterway. ompactness coefficient , mean annual precipitation , and mean annual temperature were the main variables affecting on flood magnitude. The study area was divided into two regions based on the Ward’s method. The results of goodness –of-fit analysis for the two regions indicates that the GEV-LN3 for the regions (1) and (2) give acceptably close fits to the regional average L-momets. In general, the GEV distribution could be adopted as the appropriate distribution for the study area.

کلیدواژه ها:

best-fit distribution ، cluster analysis ، L-moments ، regional flood frequency