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:
tidal 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 includes major wet and dry periods. Where shorter-term data or no data exist, records should be estimated on the basis of weather records and records for other streams in the region. In all cases, watershed development conditions anticipated during the plant lifetime should be considered. For nontidal streams, the median discharge will be considered the normal discharge. The median dis charge may be determined as the 50% point on a flow-duration curve2 (discharge vs. percent of days when indicated discharge was equalled or exceeded). Acceptable methods of constructing a flow-duration curve are outlined in many publications, e.g., U.S. Geological Survey Water-Supply Paper 1542-A, "Flow Duration Curves," 1959.1 It would be desirable to determine the normal water level on nontidal streams by similar means, i.e., use of a stage-duration curve (water level vs. percent of days when indicated level was equalled or ex ceeded). However, stages (water levels) at gaging sta tions are not as readily available as are the cor 2 The U. S. Geological Survey computes data for most of their gaging stations from which a flow-duration curve may be plotted. It should be noted, however, that such a curve will cover only the period of record available for the gaging station. ' Copies are available from the Branch of Distribution, U.S. Geological Survey, 1200 South Eads Street, Arlington, VA 22202. 1.135-2 responding discharge data. Therefore, the NRC staff will accept, as the normal water level, the water level corresponding to the normal discharge. Computation of the normal water level by this method requires the establishment of the relationship between river level and discharge (the rating curve) and the application of that relationship to the normal discharge. If the stream has a movable