Design flood computation at ungauged catchments of Baitarani River Basin using scaling concept and probabilistic time distribution of design rainfall

Short-duration rainfall data are basic inputs to many rainfall-runoff models for generating the flood hydrographs. But these data are scarce in comparison to daily data, which is abundantly available, but cannot be directly used unless disaggregated to a shorter duration. This paper adopts a simple scaling approach for disaggregation of daily design precipitation into the desired duration and the time distribution of precipitation based on 3p Beta distribution herein referred to as the scaled 3p-Beta approach. The rainfall quantiles and their temporal distribution, when used as an input to the rainfall-runoff model, generate the design flood hydrograph at the ungauged location. The Upper Baitarani Basin under Mahanadi Sub-zone (3d) of India has been selected as the test catchment. The efficacy of the proposed scaled 3p-Beta approach, and also the rational approach coupled with CWC-2p Gamma UH was verified in the test catchment for design flood computation. The findings reveal that the methodology ensures encouraging results directly derivable from the abundantly available daily rainfall data and can be applied in any ungauged catchment in a region.