Document: NUREG-0800
Document ID: 904b56ce-40c5-4058-b0ad-837d98f63c2a
Document Type: srp
Title: PROBABLE MAXIMUM FLOOD (PMF) ON STREAMS AND RIVERS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070730405.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.4.3
CFR Part: 
CFR Title: 

Content:
ates. In its independent analysis, the staff should use currently accepted runoff generation and flood routing methods, such as those made available by the USACE, and hydraulic characteristics such as velocities and momentum fluxes that may assist in estimation of dynamic effects of the PMF on SSC. The staff’s estimates are compared with the applicant’s estimates to determine conformity to the acceptance criteria in Subsection II of this SRP section. 2. Design Bases for Site Drainage. Flooding on the plant site is reviewed to determine if SSC important to safety are adequately protected. In response to locally intense precipitation, immediate flooding by ponding at the site may occur due to inadequate infiltration capacity and a lack of an efficient drainage system. The staff’s estimates of flooding potential are based on local PMP estimates from the appropriate HMRs published by NOAA and are reviewed in SER Section 2.4.2 as described in SRP Section 2.4.2. Runoff models, such as the unit hydrograph method (if applicable), or other runoff discharge estimates presented in standard texts, are used to estimate discharge on the site drainage system under local PMP. Where generalized runoff models are used, coefficients used for the site and region are compared to information available at documented locations to evaluate hydrological conditions used in determining the probable maximum flood for the site drainage system. The staff review should also determine appropriateness of the runoff model used. For example, if the watershed has sufficiently diverse hydrologic characteristics that justify the use of a distributed model, then the use of such a model is encouraged as compared to a lumped model. In its review of flooding of site drainage, the staff may verify the applicant’s estimate or perform its own independent analysis using currently accepted runoff 2.4.3-7 Revision 4 - March 2007 generation and flood routing methods. The staff’s estimates are compared