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