ANNUAL MAXIMA AND PARTIAL DURATION FLOOD SERIES ANALYSIS BY PARAMETRIC AND NONPARAMETRIC METHODS

Annual maxima (AM) and partial duration (PD) flood series are modelled by parametric and non-parametric methods. In PD analysis the number o f threshold exceedances is assumed to be Poisson distributed; the peak exceedances are described by the generalized Pareto (GP) and non-para metric (NP) distributions. The generalized extreme value (GEV) and non -parametric (NP) distributions are used to describe the AM series. L-m oments are employed for parameter estimation for GEV and GP distributi ons. Analysis of data from the provinces of Quebec and Ontario, Canada , shows that both AM and PD series can be inferred as being unimodal a nd bimodal, both of which can be described by the NP method. Also, thi s method is found not to be sensitive to the choice of threshold level ; however, it was also observed that parametric methods cannot detect biomodality, give different quantile estimates for AM and PD data and PD estimates are sensitive to the selection of threshold level. Theref ore, the NP method is more advantageous than the parametric methods in flood frequency analysis for both AM and PD series. (C) 1998 John Wil ey & Sons, Ltd.