The fifth meeting of the Hydrologic Frequency Analysis Work Group was convened at the office of Michael Baker, Jr., 3601 Eisenhower Ave., Alexandria, Virginia. The following people were in attendance:

David Goldman, Martin Becker, Joe Krolak (Federal Highway Administration), and Gary Estes participated in the meeting by teleconference.

The following topics were discussed.

Ungaged Paper

Martin Becker asked if both the Ungaged Paper and the minority report should be posted on the HFAWG web page. After some discussion, it was suggested that this issue be discussed at the Subcommittee on Hydrology (SOH) meeting on January 10, 2002. (This issue was actually discussed at the April 25, 2002 meeting of the SOH and it was decided to remove the minority report from the web page and prepare a response addressing the concerns in the minority paper.)

Other questions discussed relative to the Ungaged Paper included:

• What has been the effect of this paper on the hydrologic community?
• What is the status of responses and comments on the paper?
• Will this paper be mandatory for programs like the National Flood Insurance Program?

Will Thomas responded that no one has provided review comments on the Ungaged Paper or contacted him regarding the paper. Therefore, it is unlikely that the Ungaged Paper has affected any hydrologic practices. Will pointed out that the introductory material on the HFAWG web page indicates that the Ungaged Paper " . is not a guideline or standard but a possible approach for evaluating the reasonableness of flood frequency estimates for ungaged watershed." Will also noted that the hydrologic review procedures in the Ungaged Paper are essentially the same as the review procedures described in FEMA's Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix C: Guidance for Riverine Flooding Analyses and Mapping that is on the web at http://www.fema.gov/pdf/fhm/frm_gsac.pdf.

Frequently Asked Questions (FAQs)

Bill Kirby indicated that the most recent distribution of the FAQs was January 2, 2002. A new question was suggested on the quality of data and the process of reviewing data. It was suggested that the FEMA web site for FAQs be consulted to make sure that our response is not in conflict.

The work group is to provide Bill Kirby any comments on the FAQs in the next two weeks and Bill will provide a final draft by February 15, 2002. Will Thomas will send the FAQs to the SOH for their review before their April 2002 meeting.

Regulated Flood Frequency

David Goldman asked the question what principles or strategy are we to use for regulated frequency analysis. He indicated that he was not in favor of using continuous simulation. He suggested the major issue was in determining the regulated-unregulated relation and the distribution of residuals about this relation is a major question. David suggested a direct transformation of the unregulated flows to regulated conditions.

Don Woodward suggested we form a subcommittee of about four people to identify major issues related to regulated flood frequency, and draft some guidelines for use by the hydrologic community. (This group was formed with Rocky Durrans as chairperson and the first meeting of the group was in Knoxville, TN on May 23, 2002.)

Mike Grimm redistributed five examples of regulated frequency analysis that were performed for flood insurance studies for FEMA.

Zhida Song-James suggested that we evaluate what was done right and wrong for the Savannah River regulated frequency analysis that was completed by the USACE and USGS in 1990 and later revised by FEMA in 1993 for a flood insurance study. This was one of the first applications of the total probability theorem for regulated flood frequency analysis.

The work group agreed that a major problem was how to provide guidance on applying the total probability theorem for flood frequency analysis and agreed that lack of data in applying this method was a critical issue.

Ken Bullard discussed the Stochastic Event Flood Model (SEFM) developed by Mel Schaefer with MGS Engineering Consultants, Inc. In essence, the HEC-1 watershed model is applied thousands of times using actual and simulated precipitation data and adjusting the loss rates and hydrograph shape parameters. The model utilizes reservoir data, antecedent moisture conditions and is appropriate for regulated frequency analysis. The objective in applying the model many times for varying watershed conditions is to be able to estimate extreme events with recurrence intervals as high as 10,000 years. The Bureau is using the SEFM for the American River in the Sacramento, California area. Ken indicated that Mel Schaefer does not have a problem with the HFAWG citing his model as an approach for regulated frequency analysis.

Ken agreed to provide Bureau of Reclamation examples of regulated flood frequency analyses.

Ken also discussed the joint proposal by USGS and the Bureau of Reclamation on "Improvements to Flood Frequency Analysis Techniques". He indicated that the Bureau provided $25K for seed money to prepare the proposal and to seek additional funding. As part of this effort, the Expected Moments Algorithm (EMA) manual will be completed by the Bureau. Jerry Coffey commented that there may be stationarity problems associated with the use of paleohydrology which is one method cited for further research in the joint USGS-Bureau proposal.

Based on discussion of the joint USGS-Bureau proposal, Mike Grimm asked what is the role of the SOH and the HFAWG in reviewing proposals. This topic will be discussed at the January 10, 2002 meeting of the SOH. The HFAWG will comment on the joint USGS-Bureau proposal if requested.

Rocky Durrans asked about policy issues relative to floodplain management if Bulletin 17B is revised in the future. Will Thomas commented that revisions to Bulletin 17B should not be a problem as future floodplain mapping would be based on the new flood frequency procedures. Revisions to flood frequency procedures alone should not be a reason for remapping the Nation's floodplains.

Next meeting

The next meeting of the Hydrologic Frequency Analysis Work Group (HFAWG) will be in July 2002 a day prior to the SOH meeting.

Will Thomas, Chair
Hydrologic Frequency Analysis Work Group
October 16, 2002