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QUADRANGLE: Delavan North, 7.5' series

LOCATION: Lat 40 27' 15", long 89 36'22", in SE1/4 SE1/4 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.

ESTABLISHMENT: Digital water-stage recorder (ADR), manometer, and Type-A wire-weight gage installed on June 24, 1988 by J. Bledsoe & J. Gookin, US Army Corps of Engineers, Rock Island District., and P. Hayes (U.S.G.S.). A data-collection platform (DCP) was installed Sept. 1988 and is maintained by the Rock Island, Corps of Engineers. A crest-stage gage was installed July 28, 1994. Sediment sampling began Oct. 1994 and was discontinued Oct. 1, 1997.

DRAINAGE AREA: 1,073 sq. mi. (from USGS topographic maps)

GAGE: Digital water-stage recorder (ADR) and a manometer housed in a 4 ft. X 4 ft. steel shelter on a wooden base on the right downstream side of bridge. A type-A wire-weight gage (WWG) attached to the downstream concrete handrail 120 ft. from right end. The US Army Corps of Engineers, Rock Island District maintains a Data Collection Platform (DCP) chain operated from the manometer. An 18 ff. pvc crest-stage gage mounted on the downstream side of the right bridge pier. Manometer orifice is mounted to an 8 ft. steel pipe, which is bracketed to fence posts at the downstream end of the right bridge pier. A U.S.G.S. solar panel is mounted to the roof of the gagehouse.

GAGE DATUM: Datum of the gage is 477. 10 ft, NGVD, datum of 1929.

HISTORY: At site located at Lat 40 26'43", Long 89 39'11 " on State Highway 29 bridge, 3 mi. north of Green Valley and 2.5 mi. downstream of present location with a drainage area of 1,089 sq. mi. Record is considered equivalent to present site.

A chain gage was installed and read daily from the railroad bridge about 200 ft. upstream from the State Highway 29 bridge during Mar. 1921. On Jan. 17, 1933 the chain gage was moved to the State Highway 29 bridge because the railroad bridge was being raised. On May 14, 1940, a wire-weight gage was also installed on the State Highway bridge and read daily. The gage was operated from Mar. 1921 to Oct. 31, 1956 as a daily discharge gaging station. The gage was then operated as a crest-stage partial record station Oct. 1956-88.

The gage was moved Oct. 1, 1988 to Tower Line Road, 2.5 miles east of Highway 29, to the present site. An ADR, manometer and wire-weight gage were installed and operated as a daily discharge station.

CHANNEL AND CONTROL: The streambed consists of sand and gravel. The channel is straight 100 ft. upstream of gage and 1500 ft. downstream of gage. The banks are steep, 10 to 12 ff. high, with levees about 6 ft. higher on each side. Low flows are contained to the right half of the channel near the gage.

Previous descriptions refer to the low-water control being a sand and gravel bar anywhere from 50 - 300 ff. downstream from the gage. The low-water control migrates due to moveable streambed materials (sand and gravel).

The low-water control is currently a sand and gravel bar about 500- 1000 ft downstream from the gage. The control is subject to vegetation, accumulation of debris, and scour and fill. Medium to high stages are channel controlled. Overbank flow begins at a stage of about 21 ff. with flow over the levees at about 27 ft.

DISCHARGE MEASUREMENTS: High stages are measured off of either side of the bridge. Stages below about 15.0 ft. may be waded about 50 ft. downstream or 100 - 300 ft. upstream of the bridge.

Traffic safety: The attached traffic safety plan must be followed when making discharge measurements from the bridge. It documents the appropriate sign(s), cones, and possibly flag persons needed to prevent traffic-related accidents. Vehicle hazard lights must be used when approaching the traffic-safety site and continued until after personnel and vehicles have safely left the site.

FLOODS: Dec. 6, 1982, 51,000 cfs (gage height 16-13 ft. at State Highway 29 site). Maximum gage height at the present site was above 28.29 ft. Sept. 16, 1993.

POINT OF ZERO FLOW: 12.6 ft. measured Sept., 1996.

WINTER FLOW: Ice cover during extreme cold weather.

REGULATION AND DIVERSION: None known.