Regional Flood Frequency Analysis of Kashafrood River Basin using L-Moments Method

Design of different types of hydraulic structures, flood plain zoning, and economic evaluation of flood protection projects require information on flood magnitudes and their frequencies. Regional flood frequency analysis resolves the problem of estimation of the extreme flood events for the catchments having short data records or ungauged catchments. One of the most common methods which are applied for frequency analysis is L-moment method. Superiority of this method to other ones is its less sensitivity to outlaying data. In this research, the L-Moments method is used to analyze the regional flood frequency of Kashafrood basin. Two kinds of homogeneity statistics, discordancy measure and heterogeneity measure, are used for studying the station matching and regional homogeneity. Based on the L-moment ratio diagram and statistic criteria, general extreme value (GEV) distribution is identified as the robust distribution for the study area. On the other hand, both the Log Pearson-III and the three-parameter lognormal distributions are acceptable at the at-site level.