Evolution of Flood Frequency Analysis with Bulletin 17

The current methodology recommended for flood-frequency analyses by U.S. Federal agencies is presented in Bulletin 17B. Bulletin 17 was first published in 1976, minor corrections were made in 1977 resulting in Bulletin 17A, which was later succeeded by Bulletin 17B published in 1982. Bulletin 17B sought to resolve ambiguities in the recommended procedures, including the treatment of low outliers, and the use of both regional skew and historical flood information. As the 25th anniversary of the publication of Bulletin 17B approaches, this paper provides a discussion and evaluation of the procedures that document recommends. The fields of hydrology and flood frequency analysis have substantially evolved since Bulletin 17 was first published. New techniques are now available which should become part of these standard procedures. A comparison is provided which demonstrates how the standard and weighted Bulletin 17B quantile estimators perform relative to alternative LP3 quantile estimators that also make use of regional information.