Comparison of Normal, Gamma and Extreme Value Families of Distributions for Estimation of Peak Flood

 Vivekanandan

Chi-square | D-index

Volume: 6; Issue: 8; Aug-2020 | ISSN: 2454-5422

Estimation of Peak Flood (PF) for a given return period at a desired location on a river is required for planning, design and management of civil and hydraulic structures. This can be achieved by using deterministic models with extreme storm events or through frequency analysis by fitting probability distributions to the series of observed Annual Peak Flood (APF) data. In the latter approach, suitable probability distributions and associated parameter estimation methods are applied. In this paper, the parameters of normal, gamma and extreme value families of probability distributions are determined by method of moments, maximum likelihood method and L-moments, and are used for estimation of PF. The adequacy of fitting probability distributions to the series of observed APF data is quantitatively assessed by applying Goodness-of-Fit (GoF) tests viz., Chi-square and Kolmogorov-Smirnov. In addition to GoF tests, diagnostic test of D-index is used for identifying a suitable probability distribution for estimation of PF. However, the results of GoF and diagnostic tests offered diverging inferences, which leads to adopting qualitative assessment by using fitted curves of the estimated values for the selection of best fit probability distribution for estimation of PF. This paper presents a study on comparison of  normal, gamma and extreme value families of probability distributions for estimation of peak flood with illustrative examples and the results obtained thereof.