LOCATION.-- Lat 40°27'15", long 89°36'22" (NAD of 1927), in SE1/4SE1/4 sec.12, T.23 N., R.5 W., Tazewell County, Hydrologic Unit 07130004, on right downstream side of bridge on Towerline Road, 2.5 mi east of State Highway 29, 3.9 mi northeast of Green Valley, 5.8 mi south of Pekin, 10.2 mi north of U.S. Highway 136, and at mile 17.3.

DRAINAGE AREA.-- 1,073 mi². Area at site used prior to Oct. 1, 1988, 1,089 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: March 1921 to September 1956; June 1988 to current year.

STAGE: Water years 1994 to current year.

PARTIAL RECORD: Annual maximum, water years 1957-88.

SURFACE-WATER QUALITY

CHEMICAL: October 1997 to September 1998.

SEDIMENT: October 1994 to September 1997.

MISCELLANEOUS: Contaminants of streambed sediment, July 1997; contaminants of fish tissue, July 1997; streambank sediment size, October 1997; Streambed sediment size, October 1997; sediment concentration and particle size, water years 1996-98.

BIOLOGICAL

BENTHIC MACROINVERTEBRATES: Water year 1996 and 1997.

FISH: Water year 1997.

HABITAT: Water year 1996.

GAGE.-- Water-stage recorder, U.S. Army Corps of Engineers satellite telemeter and a crest-stage gage. Datum of gage is 477.10 ft above NGVD of 1929 (levels by U.S. Army Corps of Engineers). Prior to Jan. 17, 1933, chain gage at site 3.5 mi downstream on railroad bridge at datum 2.00 ft higher. Jan. 17, 1933, to May 13, 1940, chain gage, and May 14, 1940 to Sept. 30, 1952, wire-weight gage at site 3.6 mi downstream at datum 2.00 ft higher. Oct. 1, 1952 to Oct. 31, 1956, wire-weight gage, and Nov. 1, 1956 to Sept. 30, 1988, crest-stage gage at site 3.6 mi down stream at present datum.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 51,000 ft³/s, Dec. 6, 1982, gage height, 16.13 ft (backwater from ice), site then in use; maximum recorded gage height, 28.29 ft, Sept. 16, 1993 (discharge unknown); minimum discharge observed, 17 ft³/s, Oct. 26, 27, 1940.

SUSPENDED-SEDIMENT CONCENTRATIONS: Maximum daily, 6,160 mg/L, May 27, 1996; minimum daily, 4 mg/L, May 11, 1997.

SUSPENDED-SEDIMENT LOADS: Maximum daily 99,800 tons, May 27, 1996; minimum daily, 0.83 tons, Dec. 21, 1996.

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) sample was collected in accordance with the NAWQA protocols (Cuffney and others, 1993). The quantitative sample was a composite of macroinvertebrates from about 10 submerged tree branches. Branches were cut underwater, gathered in a 425µm 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. 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 reach begins 2,001 feet upstream of the Towerline Road bridge and continues upstream for 1,099 feet. The surface area sampled at reach A was 0.19 m².