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:
Similarly, in Florida hurricanes have been recorded in virtually every month, but they are more likely to occur during the late summer and early fall, which is coincidentally the period of the year in which high water levels (or discharges) are most likely to oc cur. Accordingly, for this type of seasonal variation, the normal water level (or discharge) should be deter mined only for that period of the year during which the event is most likely to occur or for the ap propriate period as indicated by studies of the area. Floods are seasonal in many parts of the United States. While the surface water levels (or discharges) addressed in this guide are not applicable to floods, it is quite possible that the influence of flood levels on normal ground water levels must be considered. The following discussions of various water bodies assume that the seasonality of the design events are properly taken into account. 2. Nontidal Streams Data on stream discharge rates are readily available for thousands of stream-gaging stations operated by the U.S. Geological Survey; U.S. Army Corps of Engineers; Bureau of Reclamation; other Federal, State, and local agencies; power companies; and other organizations. Most such data are in the form of mean daily discharges for varying periods of record. Hydrology textbooks contain acceptable standard methods for transposing these data from the gaging stations to the plant site. Thus, relatively reliable information on stream discharge may be ob tained for a plant site located on a nontidal stream. Short-term discharge data are also frequently col lected at the sites and should be used to verify the transposed data. A period of record of at least 50 years is desirable for use in determining the normal water level and dis charge at sites on nontidal streams. For many loca tions, however, such long-term records do not exist. In such cases, periods of record of at least 12 years may be acceptable if it can be demonstrated that the period used