Assessment of Probable Maximum Precipitation Using Gumbel Distribution and Hershfield Method

Assessment of Probable Maximum Precipitation (PMP) has utmost importance for planning, design, management and risk analysis of hydraulic and other structures in a region. This paper details the procedures involved in estimation of Extreme Rainfall (ER) for Bhavnagar region using five parameter estimation methods of Gumbel distribution. Goodness-of-Fit test involving Kolmogorov-Smirnov (KS) statistics is used for checking the adequacy of fitting of the method for determination of parameters of the distribution. Root Mean Square Error (RMSE) is used for selection of a suitable method for estimation of ER. The paper presents that the Probability Weighted Moments (PWM) is better suited for modelling daily maximum rainfall and Order Statistics Approach (OSA) for 24-hour maximum rainfall for the region under study. The results obtained from Gumbel distribution are compared with PMP value given by Hershfield method. The study shows that the Mean+SE(where Mean denotes the estimated ER and SE the standard error) value of 1000-year return period one-day ER given by PWM may be considered for design purposes for Bhavnagar region.