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! We're replacing this page with a Next Generation Monitoring Location Page.
We're modernizing Water Data for the Nation delivery. Find out what this means for you. This page will be discontinued Jan.1, 2023.



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NOTICE (06/01/2022) -- Continuous water quality data collection of specific conductance, pH, dissolved oxygen, and turbidity at this streamgage will be discontinued on 09/30/2022.
Although historic data will remain accessible, no new data will be collected unless one or more new funding partners are found.
Potential funding partners or those with general questions concerning continuance of operations may contact Chuck Walker (cwwalker@usgs.gov;443-498-5523).

Click for larger image LOCATION.--Lat 38°56'59.2", long 77°07'39.5", Montgomery County, MD, Hydrologic Unit 02070008, on left bank just upstream from Little Falls Dam, 1 mi upstream from District of Columbia boundary line, 1.2 mi upstream from Chain Bridge, 1.8 mi east of Langley, Fairfax County, and at mile 117.4.
DRAINAGE AREA.--11,560 mi2.
  • WSP 726: Drainage area.
  • WDR MD-DE-75-1: 1973-74(M).
  • https://waterdata.usgs.gov/nwis/dv/?site_no=01646500: 2018.
  • https://waterdata.usgs.gov/nwis/uv/?site_no=01646500: 2021.
  • Discharge for Measurement 385 made on 06/25/2021 was revised on 09/22/2021 due to an error in computation.
PERIOD OF RECORD.--March 1930 to current year.
GAGE.--Water-stage recorder, crest-stage gage, and concrete control. Datum of gage is 37.20 ft above North American Vertical Datum of 1988. Prior to Jun 7, 1930, nonrecording gage, and June 7, 1930 to Jan. 22, 1965, water-stage recorder at site 1 mi upstream on right bank at same gage datum.
REMARKS.--Diversions since June 1959. U.S. Geological Survey satellite data-collection platform at station.
EXTREMES OUTSIDE PERIOD OF RECORD.--Flood of June 2, 1889, was of approximately the same magnitude as that of March 19, 1936.
COOPERATION.--Funding for the operation of this station is provided by the U.S. Geological Survey. Access to gage site provided by the Baltimore District, U.S. Army Corps of Engineers.
Boating safety tips
This station managed by the MD-DE-DC Water Science Center Baltimore office.

Available Parameters Available Period
2019-07-24  2022-06-30
2007-10-01  2019-10-01
2007-10-01  2019-10-01
2007-10-01  2019-10-01
2013-11-23  2019-05-27
1972-06-09  2022-06-30
2007-10-01  2022-06-30
2019-07-24  2022-06-30
2007-10-01  2019-10-01
2013-11-23  2019-05-27
2019-07-24  2022-06-30
2013-11-23  2019-05-27
2019-07-24  2022-06-30
2013-11-23  2019-05-27
2019-07-24  2022-06-30
2013-11-23  2019-05-27
2019-07-24  2022-06-28
2011-12-03  2019-06-11


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Summary of all available data for this site
Instantaneous-data availability statement