FLOOD FREQUENCY-ANALYSIS WITH HISTORICAL AND PALEOFLOOD INFORMATION

An investigation is made of flood quantile estimators which can employ 'historical' and paleoflood information in flood frequency analyses. Two categories of historical information are considered: 'censored' data, where the magnitudes of historical flood peaks are known; and 'binomial' data, where only threshold exceedance information is available. A Monte Carlo study employing the two-parameter lognormal distribution shows that maximum likelihood estimators (MLEs) can extract the equivalent of an additional 10-30 years of gage record from a 50-year period of historical observation. The MLE routines are shown to be substantially better than an adjusted-moment estimator similar to the one recommended in Bulletin 17B of the United States Water Resources Council Hydrology Committee (1982).