The report presents regional flood frequency curves developed by fitting L-moment based GEV distribution to annual maximum peak flood data of small to medium sized catchments of the seven hydrometeorological sub-zones of zone 3 and combined zone 3 of India. The effect of regional heterogeneity is studied by comparing the growth factors of various sub-zones and combined zone 3. The flood frequency curves based on probability weighted moment (PWM) approach have been compared with the flood frequency curves based on L moment approach.
The relationships developed between mean annual peak flood and catchment area are coupled with the respective regional flood frequency curves for derivation of regional flood formulae. The regional flood frequency curve developed for each sub-zone together with at-site mean annual peak floods may be used for gauged catchments. While, for ungauged catchments, regional flood formulae developed for the respective sub-zones may be adopted for obtaining rational flood estimates.
The conventional empirical formulae cannot provide floods of desirable return periods. However, the flood formulae developed in this study are capable of providing flood estimates for different return periods.
The form of the developed regional flood formula is very simple. For estimation of flood of desired return period for an ungauged catchment it requires only catchment area, which is readily available. These formulae may be used by the Field Engineers for estimation of floods of desired return periods.
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