PROGRAMS & PLANS--Water Resources Division (WRD) Policy on Probable Maximum Floods In Reply Refer To: September 7, 1983 WGS-Mail Stop 415 SURFACE WATER BRANCH TECHNICAL MEMORANDUM NO. 83.05 Subject: PROGRAMS & PLANS--Water Resources Division (WRD) Policy on Probable Maximum Floods Recently we have been asked by the National Park Service (NPS) to reevaluate our policy concerning the estimation of probable maximum floods (PMF) as expressed in Surface Water Branch Technical Memorandum No. 77.03. NPS uses PMF as a criterion for management of flood plains in National Parks and would like us to delineate areas of PMF inundation. While the various procedures for computing PMF's are useful in an engineering sense to the agencies that must protect life and property from extremely rare flood events, the concept of PMF is not compatible with the data-based probabilistic description of flood hydrology, which is the mainstay of WRD in flood hydrology. Thus, PMF is outside the scope of the WRD missions and projects requiring its estimation should not be accepted. Although the preclusion of PMF determinations from our projects apparently may diminish our utility to NPS in the short run, we should endeavor to assist NPS in any way possible within the scope of our mission. Marshall E. Moss Chief, Surface Water Branch Attachment Distribution: A, B, S, FO, PO