Flood Frequency Analysis Using Box-Cox Transformation Based Gumbel EV-I Distribution

Box-Cox transformation is one of the powerful procedure for transforming the data series to near normalization which has been employed in flood frequency analysis. In this study, an attempt has been develop methodlogy for transforming the annual peak flood series to the form of Gumbel EV-I distribution using Box-Cox transformation The exponent λ of the Box-Cox transformation has been estimated by trial and error using the method of maximum likelihood (MML) and method of probability weighted moments (MPWM), so as to obtain nearly the same estimates of log likelihood functions by both the methods. This methodology has been applied to 1000 sample of various sample sizes of randomly generated synthetic “flood” series which follow the pearson type-III distribution. The statistical estimates of the reduced variates of the Gumbel EV-I distributed transformed series, viz.mean and standard deviation,have been found nearer to 0.5772 and 1.2825 as required from theoretical considerations and thus verifying the applicability of the proposed methodlogy for transforming to Gumbel EV-I distribution.