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:
am discharge and ground water data, and weather records. As with nontidal streams, a shorter record may be acceptable if it can be demonstrated that major wet and dry periods are included. As with the Great Lakes, if a trend can be identified, the data should be adjusted for this trend. Consideration should also be given to potential changes in water use that could significantly alter this median. In many cases, mean monthly data may be used to compute the median level. However, a study should be made to determine whether the median based on mean monthly records is sufficiently accurate or whether mean daily data should be used. Such a study could consist of computing medians for a short period (e.g., two or three years) from both monthly and daily information and comparing the results. 5. Regulated Lakes and Reservoirs At their outlets many lakes have dams or other regulating structures, which in effect convert the lake into a reservoir. Regulated lakes are therefore addres sed as reservoirs in this guide. Most reservoirs have at least one level designated as "normal pool" elevation. For some reservoirs, more than one elevation, usually varying with the time of the year, may be considered normal pool. Those reservoirs that have reserved flood control space are frequently of this type. For example, a reservoir in the Sierra Nevada of California might have a given normal pool level for the July-to November period, followed by a November-to December period when the level must be drawn down to accommodate potential flood runoff, and a December-to-June period when the level must be kept as closely as possible to the drawndown level but may rise to as high as the top of the flood control pool. Normal water level should be considered the nor mal pool level of the reservoir, with due considera tion for variations in normal pool level during the year. If the reservoir includes flood control storage, the median of the flood control pool levels for the life of the reservoir