Assessing Adequacy of a Probability Distribution for Estimation of Design Flood

Estimation of design flood for a desired return period is of prime importance for safe design of hydraulic structures such as dams, spillways, bridges, culverts, urban drainage systems and flood plain zoning. Frequency analysis enables estimation of the probability of occurrence of a certain hydrological event of practical importance by fitting a probability distribution to one that is empirically obtained from recorded annual maximum discharge (AMD) data. This study deals with the fitting of Extreme Value Type-1, Gamma, 2-parameter Lognormal (LN2) and Log Pearson Type-3 (LP3) distributions to the AMD data; and examines the use of goodness-of-fit tests and diagnostic analysis in assessing the adequacy of suitable probability distribution for estimation of design flood. Results of the study showed that LN2 distribution is better suited for modelling flood data for Tapi at Burhanpur, Girna at Dapuri and Bori at Malkheda sites; and LP3 is the best for Purna at Lakhpuri.