LOCATION.-- Lat 39°09'37", long 90°36'55" (NAD of 1927), in NW1/4NW1/4 sec.26, T.10 S., R.2 W., Calhoun County, Hydrologic Unit 07130011, on right bank at downstream side of State Highways 16 and 100 bridge at north edge of Hardin, 1.6 mi downstream from Macoupin Creek and at mile 21.5.

DRAINAGE AREA.-- 28,690 mi², does not include diversion from Lake Michigan through the Chicago Sanitary and Ship Canal, which has occurred since Jan. 17, 1900.

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

STAGE: October 1986 to current year. Gage-height record for February 1932 to Sept. 30, 1986, available in files of U.S. Army Corps of Engineers. Partial gage-height records from 1878 through 1880 available in files of U.S. Army Corps of Engineers.

PARTIAL RECORD: Miscellaneous discharge measurements, water years 1997-98.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1978-91.

WATER TEMPERATURE: Water years 1973-77.

MISCELLANEOUS: Contaminants in streambed sediments, October 1996; contaminants in fish tissue, October 1996; sediment concentration and particle size, water years 1997-98.

GAGE.-- Water-stage recorder, U.S. Army Corps of Engineers satellite telemeter, and crest-stage gage. Datum of gage is 400.00 ft above NGVD of 1929 (levels by U.S. Army Corps of Engineers).

EXTREMES FOR PERIOD OF RECORD.--

STAGE: Maximum gage height, 42.40 ft, Aug. 3, 1993; minimum, 18.06 ft, Dec. 22, 1989.

EXTREMES OUTSIDE PERIOD OF RECORD.--

STAGE: Maximum gage height, 38.2 ft Apr. 29, 1973; minimum observed, 7.33 ft, Oct. 7, 1879, from records of U.S. Army Corps of Engineers.