V-3-Regional Flood Frequency Analysis using L-moments for Mahi and Sabarmati Subzone 3(a).

Abstract

Estimation of flood frequencies and their magnitudes is needed for taking up various structural and non-structural measures of water resources planning, development and management. Regional flood frequency relationships are developed based on the L-moments approach. The annual maximum peak floods data are screened using the Discordancy measure (D.) and homogeneity of the region is tested employing the L-moments based heterogeneity measure (H). For computing heterogeneity measure H, 500 simulations are performed using the Kappa distribution. Twelve frequency distributions namely Extreme value (EV1), Generalized extreme value (GEV), Logistic (LOS), Generalized logistic (GLO), Normal (NOR), Generalized normal (GNO), Uniform (UNF), Pearson Type-HI (PE3), Exponential (EXP), Generalized Pareto (CPA), Kappa (KAP) and five parameter Wakeby (WAK) are employed. Based on the L-moments ratio diagram and 1Z,d'I -statistic criteria, PE3 is identified as the robust frequency distribution for the study area. For estimation of floods of various return periods for gauged catchments of the study area, the regional flood frequency relationship is developed using the L-moments based PE3 distribution. Also, for estimation of floods of various return periods for ungauged catchments, the regional flood frequency relationships developed for gauged catchments is coupled with the regional relationship between mean annual maximum peak flood and catchment area.