Intercomparison of Peak Flood Discharge Estimates Using Normal, Gamma and Extreme Value Families of Distributions

Abstract

Estimation of Peak Flood Discharge (PFD) for a given return period is utmost importance for planning, design and management of hydraulic structures. This can be achieved through Flood Frequency Analysis (FFA) that involves fitting normal, gamma and extreme value families of distributions to the series of observed annual maximum discharge data. Based on the intended applications and the variate under consideration, Method of Moments (MoM), Maximum Likelihood Method (MLM) and L-Moments (LMO) are used for determination of parameters of the distributions. In this paper, a study on comparison of PFD estimates by adopting eight probability distributions pertaining to normal, gamma and extreme value families of distributions for Bhuntar, Manali and Parvati sites is carried out. The adequacy of fitting distributions applied in FFA is evaluated by quantitative assessment using Goodness-of-Fit (viz., Chi-square and Kolmogorov-Smirnov) and diagnostic (viz., D-index) tests, and qualitative assessment using fitted curves of the estimated PFD. The outcomes of the study indicates the GEV (LMO) is better suited amongst eight distributions adopted in FFA for estimation of PFD at Bhuntar and Manali sites whereas EV1 (LMO) for Parvati.