The Value of Historical Data in Flood Frequency Analysis

A common problem in flood frequency analysis is estimation, from a short gauged record, of the flood corresponding to a return period of 50–1000 years. One would expect that an estimate of the historical maximum event; i.e., the maximum flood in a period of perhaps 100–200 years, would, if properly included in the estimation procedure, improve the resulting estimate of the flood magnitude at the given return period. We attempt to assess the value of historical information using computer simulation. An annual flood sequence and a historical maximum event are generated from ah extreme‐value distribution (of type I or II) and quantitiles of the distribution are estimated by maximum likelihood, both including the excluding the historical event. After many such simulations have been performed the accuracy of the quantile estimates is assessed. We also consider the effect of errors in the magnitude of historical discharge estimates and the use of historical data in regional flood frequency analysis.