TR(BR)-134 : Development of regional flood formula for Mahanadi Subzone (3D)

Abstract

Most of the flood formulae developed for different regions of India are empirical in nature and do not provide flood estimates for desired return period. Based on the comparative flood frequency studies carried out at the Institute for some of the typical regions of India, Probability Weighted' Moment(PWM) based At Site and Regional General Extreme Value(SRGEV) method is found to be the most robust. In this study, regional flood frequency curves have been developed fitting the Probability Weighted Moment(PWM) based General Extreme Value(GEV) distribution to annual maximum peak flood data of 20 bridge sites of the Mahanadi subzone-3(d). The relationship between the mean annual peak floods and the physiographic characteristics of the bridge catchments of subzone-3(d) has also been developed. Flood frequency curves, thus developed, have been coupled with the relationship established between mean annual peak floods and the physio-graphic characteristics, in order to develop the regional flood formula for the subzone-3(d). The annual maximum peak flood data of 2 bridge catchments( test catchments) have been excluded while developing the regional flood frequency curves and the same have been utilized to compute the at site mean annual peak floods. These at site mean values together with the regional frequency curves have been used to compute the floods of various return periods for the 2 test catchments. Floods of various return periods have also been computed using the developed regional flood formula for these test catchments. The developed regional flood formula has also been represented in the form of the Dicken's formula and the return periods of the floods estimated by the Dicken's flood formula have also been computed. For estimation of floods of different return periods for the small catchments of the Mahanadi subzone-3(d), which are gauged the regional flood frequency curves together with at site mean annual peak flood may be used, while for the ungauged catchments the developed regional flood formula may be adopted.