LOCATION.-- Lat 42°15'22", long 88°51'47" (NAD of 1927), in SE1/4SE1/4 sec.27, T.44 N., R.3 E., Boone County, Hydrologic Unit 07090006, on left bank at Belvidere sewage-treatment plant, 1.3 mi downstream from bridge on State Street in Belvidere, 3.0 mi downstream from Piscasaw Creek, and at mile 21.9.

DRAINAGE AREA.-- 538 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1939 to current year.

STAGE: Water years 1994 to current year.

REVISED RECORDS.-- WSP 1175: 1946. WSP 1508: 1940, 1942-43, 1947(M). WSP 1728: 1940(M). WDR IL-75-1: Drainage area. WDR IL-00: 1999.

GAGE.-- Water-stage recorder, phone telemeter and crest-stage gage. Datum of gage is 738.34 ft above NGVD of 1929 (U.S. Army Corps of Engineers bench mark) (738.16 ft NAVD 1988). Sept. 29, 1939, to Sept. 30, 1942, nonrecording gage at site 1.3 mi upstream at datum 3.99 ft higher, and Oct. 1, 1942, to Sept. 30, 1973, nonrecording gage at present site and datum.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 11,900 ft³/s, Feb. 20, 1994; gage height 14.19 ft; minimum discharge, 14 ft³/s, Sept. 19, 1988, observed.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Flood of Jan. 24, 1938, reached a stage of 16.9 ft, backwater from ice, from information by sewage-treatment plant employees.