Research on flood frequency analysis has taken place with varying intensity over the last couple of decades. The eighties proved to be important years with many significant contributions, reviewed for instance by Greis [1983], Potter [1987], Kirby and Moss [1987], Cunnane [1987], NRC [1988], WMO [1989], and Bobée and Ashkar [1991]. Due to its large economical and environmental impact, flood frequency analysis remains a subject of great importance and interest, and the research on improved methods for obtaining reliable flood estimates has continued into the nineties, although with different emphasis. In the seventies and eighties much effort was spent on developing efficient at-site flood frequency procedures. New distributions and estimation methods were introduced in the hydrologic journals, some of them developed specifically for flood frequency analysis. It seems that this tendency has decelerated somewhat in the beginning of the nineties. Researchers are increasingly realizing that the lack of sufficiently long data series imposes an upper limit on the degree of sophistication that can reasonably be justified in at-site flood frequency analysis. It has been emphasized by many that instead of developing new methodologies for flood frequency analysis, effort should be spent on comparing existing ones and on looking for other sources of information [ Potter, 1987; Bobée et al., 1993a]. Regionalization is probably the most viable avenue for improving flood estimates, and fortunately this seems to be the direction that the research in flood frequency analysis has taken in the nineties.
We make the classical distiction between at-site and regional flood frequency analysis. Only the parametric analysis of flood data is reviewed here, as the case of nonparametric analysis is treated elsewhere in this volume [ Lall, 1995, this issue]. Approaches to flood frequency analysis involving deterministic and/or hydraulic components (e.g. rainfall-runoff models, unit hydrographs, derived distributions) also fall outside the scope of this review, although we recognize that significant contributions have been made in this field in recent years [e.g. Bradley and Potter, 1992; Durrans, 1994].
We extend our review to cover also part of what was published in the late eighties. The main reason for doing so is that a chapter on flood frequency analysis was not included in the last U.S. National Report to the IUGG (1987-1990). Some quite significant contributions to flood frequency analysis occurred in that period, especially in the years 1989 and 1990, and we think they deserve to be covered in the present review.