Document: NRC Regulatory Guide
Document ID: 0b3f08e9-b342-468d-a869-a00f19278ecb
Document Type: regulatory_guide
Title: Normal Water Level and Discharge at Nuclear Power Plants
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740143.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.135
CFR Part: 
CFR Title: 

Content:
t mospheric Administration, U.S. Army Corps of Engineers, or others. A stage-duration curve should be used to estimate the median water level as the nor mal water level. This procedure may be used for loca tions upstream and downstream from the site with the normal water level at the site estimated by inter polation. A period of record of 20 years (to account for cyclic tidal variations) is acceptable if it can be demonstrated that the period includes major wet and dry periods. 8. Ground Water Normal ground wa'ýýr level should be the median level over a 20-year period. This length of record will not be available at most sites for nuclear power plants. However, most sites will have one or more short-term records of a year or two. The staff will ac cept extension of these short-term records by correla tion with longer records in the region. The effect of future changes in water use should be considered. The U.S. Geological Survey collects and publishes records for thousands of observation wells throughout the United States and may advise where other data in the region may be obtained. For those sites at which the applicant plans to lower the ground water level permanently by use of an underdrain system, either pumped or gravity flow, the staff will accept, as normal, the anticipated lower water level for which the system is designed. Ground water levels to be used for soil liquefaction analyses will be discussed in a regulatory guide now under preparation on liquefaction. C. REGULATORY POSITION Analyses of the capability of safety-related struc tures, systems, and components to resist combina tions of loading conditions often require identifica tion of normal water levels or discharges. For the purposes of this guide, normal water level (or dis charge) means the water level (or discharge) that can be expected at the time of occurrence of design basis natural or accidental events.' Subject to the excep tions below, the normal water level (or discharge) will generally