REGIONAL FLOOD FORMULAS USING L–MOMENTS FOR SMALL WATERSHEDS OF SONE SUBZONE OF INDIA

Abstract

Estimation of flood frequency and magnitude is essential for design of soil and water conservation measures. Datafrom 12 stream flow gauges within the Sone region were screened using the discordancy measure (Di) in terms of theLmoments. Homogeneity of the region was then tested using the Lmoments based heterogeneity measure, H. For computingthe heterogeneity measure H, 500 simulations were performed using the four parameter Kappa distribution. Comparativeregional flood frequency analysis studies were performed using the Lmoments based frequency distributions: viz. Extremevalue, General extreme value, Logistic, Generalized logistic, Normal, Generalized normal, Uniform, Pearson TypeIII,Exponential, Generalized Pareto, Kappa, and five parameter Wakeby. Based on the Lmoment ratio diagram and |Zidist|statistic criteria, the GEV distribution was identified as the robust distribution for the study area. For estimation of floodsof various return periods for gauged watersheds of the study area, a regional flood formula was developed using theLmoments based GEV distribution. Also, for estimation of floods of desired return periods for ungauged watersheds, aregional flood formula was developed by coupling the regional flood formula with the regional relationship between meanannual peak flood and watershed area.