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Water-Year Summary for Site 12305000

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  • Water-Year Summary reports summarize a year of hydrologic data in a printer-friendly format.
  • For water years 2014 onward, choose a water year and parameter and an on-demand Water-Year Summary report will be generated.
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  • Not all sites have reports available for every water year.
Available Parameters
00010 Temperature, water(Max.,Min.,Mean)  
00060 Discharge(Mean)  
00065 Gage height(Mean)  

Water year 2021: 2021-10-01 to 2022-09-30

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USGS Water-Year Summary 2021
LOCATION - Lat 48°37'03", long 116°02'47" referenced to North American Datum of 1983, in sec.20, T.33 N., R.34 W., Lincoln County, MT, Hydrologic Unit 17010104,

Leonia quad., on right bank at Leonia, 450 ft east of Montana-Idaho State line, 0.5 mi upstream from Boulder Creek, and at mile 171.6

DRAINAGE AREA - 11,740 mi².
PERIOD OF RECORD - March 1928 to current year.
GAGE - Water-stage recorder and crest-stage gage. Datum of gage is 1794.12 ft above NAVD of 1988. Prior to Oct. 1, 1970, at datum 90 ft lower. Prior to Nov. 13, 1928, non recording gage on bridge 250 ft upstream at datum 90.41 ft lower.
REMARKS - Flow regulated by Libby Dam and power plant, located about 50.5 river miles upstream, since Mar. 21, 1972.
EXTREMES OUTSIDE PERIOD OF RECORD - Floods of June 1894 and 1916 reached stages of 34.6 and 31.6 ft, respectively, present datum, from information by Great Northern Railway.
EXTREMES FOR PERIOD OF RECORD - UNREGULATED PERIOD (1929-71): Maximum discharge prior to regulation by Libby Dam and powerplant, 123,000 ft³/s May 28, 1948, gage height, 33.40 ft; minimum, 996 ft³/s Dec. 9, 1936, minimum gage height, 7.56 ft, Dec. 10, 1929. REGULATED PERIOD (1972 to current year): Maximum discharge since regulation began, 62,000 ft³/s Jan. 16, 1974, gage height, 24.15 ft; maximum gage height, 25.87 ft, June 17, 18, 2006; minimum daily, 2,270 ft³/s Dec. 9, 1972.
PERIOD OF RECORD - Continuous water temperature data were collected July 1962 to May 1963, April 1965 to Sept. 1986, Oct. 2012 to current year.
REMARKS - Numerical uncertainty is not currently computed for time-series water-quality records but qualitative ratings are provided based on professional judgment.
  • The practice of using qualitative ratings to describe data accuracy was discontinued in Water Year 2017.