Uniform Flood‐Frequency Estimating Methods for Federal Agencies

Abstract

Large-scale planning for improved flood-plain management and expanding water-resources development has made it increasingly important that a consistent approach be adopted for estimating flood frequencies, a major analytical component in studies required in flood-plain management and, in a larger sense, in river-basin management. A Federal interagency group has studied the most commonly used methods of flood-frequency analysis and has compared the results of applying these methods to a selected group of long-record representative sites in different parts of the country. Based on these comparisons and on other considerations, it is recommended that all government agencies adopt a uniform procedure for flood-frequency analysis at sites where records are available. The log-Pearson Type III distribution has been selected as the base method, with provisions for departures from the base method where justified. Continuing study leading toward improvement or revision of methods is recommended. (Key words: Floods; rivers; statistics) •A•V• A. S•SO• These circumstances were recognized by a Bureau of Standards and Geoffrey S. Watson Task Force on Federal Flood Control Policy of The Johns Hopkins University. which, in August 1966, transmitted a report to the President entitled 'A Uniform National INVESTIGATIONS Program for Managing Flood Losses.' This re-The Work Group decided that several methport was subsequently submitted to the Con-ods of flood-frequency analysis in common use gress [House Doc. •,65, 1'966]. In the report among Federal agencies and elsewhere would the following statements are included relating be applied to a group of 10 long-term records to flood-frequency methods: of annual flood peaks at selected locations in Techniques for determining and reporting the frequency of floods used by the several Federal agencies are not now in consistent form. This results in misunderstanding and confusion of interpretation by State and local authorities who use the published information. Inasmuch as wider, discerning use of flood information is essential to mitigation of flood losses, the techniques for reporting flood frequencies should be resolved.

Probability distribution of flood flows in Tunisia

“…The proponents of each distribution have been able to show some degree of confirmation for their particular distribution by comparing theoretical results and measured values. However, there is no theoretical basis for justifying the use of one specific distribution for modeling flood data and long term flood records show no justification for the adoption of a single type of distribution (Benson, 1968).…”

“…A working group in the USA (US Water Resources Council (Benson, 1968) recommended the LP3 distribution whereas a similar study in the United Kingdom (NERC, 1975) proposed the GEV distribution as a standard. The generalized gamma distribution was recommended in the former USSR (Kritsky and Menkel, 1969) while the P3 and the LP3 distributions were generally recommended in West Germany.…”

Statistical distribution of rainfall in Uttarakhand, India

“…The choice of a best-fit distribution also has been applied to a discharge series in the USA (Benson 1968;Vogel et al 1993), the UK (NERC 1975), Australia (McMahon and Srikanthan 1981), and Turkey (Haktanir 1991). A review of the selection of the best distribution was given by (Curmane 1989).…”

Fractal theory and the estimation of extreme floods

“…One estimate of the severity of a flood is the peak discharge at a station V. The magnitude of the peak discharge is affected by a variety of circumstances including: (1) The amount of rainfaU produced by the storm or storms in question, (2) the upstream drainage area, (3) the saturation of the soil in the drainage area, (4) the topography. soil type, and vegetation in the drainage area, and (5) whether snow melt is involved.…”