LOCATION.-- Lat 39°42'12", long 90°38'43" (NAD of 1927), in SE1/4NW1/4 sec.34, T.15 N., R.14 W., Scott County, Hydrologic Unit 07130011, on upstream side of Norfolk & Southern Corporation Railroad bridge at Flints Creek, 0.4 mi east of Valley City, 1.8 mi downstream from Mauvaise Terre Creek, and at mile 61.3. Auxiliary gage 10.0 miles upstream.

DRAINAGE AREA.-- 26,743 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

DISCHARGE: October 1938 to current year. Prior to October 1960, at site 0.2 mi upstream at same datum. Prior to October 1989, published as "at Meredosia." Records are considered equivalent.

STAGE: Water years 1994 to current year.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1975-93 and 1996 to current year.

SEDIMENT: February 1980 to current year.

SPECIFIC CONDUCTANCE: Water years 1975-81.

WATER TEMPERATURE: Water years 1975-81.

MISCELLANEOUS: Contaminants in streambed sediments, October 1996; contaminants in fish tissue, October 1996; sediment concentration and particle size, water years 1996-2003.

BIOLOGICAL

ALGAE: Water years 1980-81, 1997-98, and 2002-03.

BENTHIC MACROINVERTEBRATES: Water years 1997-98 and 2002.

FISH: Water year 1998 and 2003-04.

HABITAT: Water years 1997-98 and 2003.

GAGE.-- U.S. Army Corps of Engineer's water-stage recorder and satellite telemeter, crest-stage gage, and water-quality monitor. Datum of gage is 418.00 ft above NGVD of 1929 (levels by U.S. Army Corps of Engineers). Prior to Nov. 25, 1992 and Oct. 1, 1994 to current; auxiliary gage (05585500) at site 10.0 mi upstream. Nov. 25, 1992 to Sept. 30, 1994; auxiliary gage operated at this site (05586100).

REMARKS.-- Occasional regulation at low flow by navigation dam at La Grange. Since Jan. 17, 1900, flow has included diversion from Lake Michigan through Chicago Sanitary and Ship Canal. Suspended-sediment samples were collected by a local observer twice weekly with additional samples collected during high runoff periods. Since February 1994, samples used to compute sediment record have been collected at upstream side Rt. 106 bridge at Florence at mile 56.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 123,000 ft³/s, May 26-28, 1943; maximum gage height, 28.61 ft, May 26, 1943; minimum daily discharge, 1,330 ft³/s, Sept. 2, 1984.

SUSPENDED-SEDIMENT CONCENTRATIONS: Maximum daily, 3,720 mg/L, Apr. 14, 1981; minimum daily, 14 mg/L, Dec. 26, 1984, July 21, 1993.

SUSPENDED-SEDIMENT LOADS: Maximum daily, 410,000 tons, June 4, 1980; minimum daily, 172 tons, Sept. 2, 1984.

REMARKS FOR CURRENT YEAR.--Benthic macroinvertebrate community samples were collected as part of the National Water-Quality Assessment program (NAWQA) in the lower Illinois River Basin. One quantitative (Richest-Targeted Habitat) and one qualitative (Qualitative-Multiple Habitat) sample were collected in accordance with the NAWQA protocols (Moulton and others, 2002). The quantitative sample was a composite of macroinvertebrates from about ten submerged tree branches. Branches were cut underwater, gathered in a 500µm mesh net, and invertebrates were washed or picked from the branches. The average length and average diameter of each branch were measured and used to calculate an approximate surface area. The qualitative sample was collected from many habitat types within the sampling reach to obtain as complete a list of invertebrate taxa as possible. All samples were processed by the USGS National Water-Quality Laboratory. Phylum, Class, Order, Suborder, Family, Subfamily, and Tribe are listed and arranged according to the USGS National Water-Quality Laboratory taxonomic hierarchy. The sampling reach begins at river mile 59, upstream of Big Blue Island, and continues downstream for 2460 ft. The surface area sampled was 0.14 m².