Document: NUREG-0800
Document ID: aee3277d-bcab-4cf4-bdb2-fb607503b041
Document Type: srp
Title: PROBABLE MAXIMUM FLOOD (PMF) ON STREAMS AND RIVERS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340529.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.4.3
CFR Part: 
CFR Title: 

Content:
nditions to be evaluated in establishing the applicable stream and river flooding design basis referred to in General Design Criterion 2, Appendix A, 10 CFR Part 50. PMF estimates are required for all adjacent streams or rivers and site drainage (including the consideration of PMP on the roofs of safety- related structures). The criteria for accepting the applicant's PMF-related design basis depend on one of the following three conditions: 1. The elevation attained by the PMF (with coincident wind waves) establishes a required protection level to be used in the design of the facility. 2. The elevation attained by the PMF (with coincident wind waves) is not controlling; the design basis flood protection level is established by another flood phenomenon (e.g., the probable maximum hurricane). 3. The site is "dry," that is, the site is well above the elevation attained by a PMF (with coincident wind waves). When condition 1 is applicable, the staff will assess the flood level (described in subsection III). The assessment may be made independently from basic data, by detailed review and checking of the applicant's analyses, or by comparison with estimates made by others that have been reviewed in detail. The applicant's estimates of the PMF level and the coincident wave action are acceptable if the estimates are no more than 5% less conservative than the staff's estimates. If the-applicant's estimates of discharge are more than 5% less conservative than the staff's, the applicant should fully document and justify its estimates or accept the staff's estimates and redesign applicable flood protection. When conditions 2 or 3 apply, the staff analyses may be less rigorous (described in subsection III). For condition 2, acceptance is based on the protection level estimated for another flood-producing phenomenon exceeding the staff estimate of PMF water levels. For condition 3, the site grade must be well above the staff assessment of PMF water levels. The evaluation of the