LOCATION.-- Lat 41°38'27", long 88°03'34" (NAD of 1983), in SE1/4SW1/4 sec.35, T.37 N., R.10 E., Will County, Hydrologic Unit 07120004, on left bank 40 ft upstream from bridge on Romeoville Road (135th Street) in Romeoville, 5.2 mi upstream from Lockport Lock and Dam, and at mile 6.2.

DRAINAGE AREA.-- 739 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1984 to current year.

STAGE: Water years 1994 to current year.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1987-92 and 1999 to 2001.

WATER TEMPERATURE: Water years 1974-77.

REVISED RECORDS.-- WDR IL-86-2: 1985. WDR IL-89-2: 1986. WDR IL-92-2: 1986-89.

GAGE.-- Water-stage recorder, acoustic-velocity meter and phone telemeter. Datum of gage is 551.89 ft above NGVD of 1929 (U.S. Army Corps of Engineers bench mark) (551.60 ft NAVD 1988).

REMARKS.-- Estimated daily discharges determined from a regression relation between present site and the previous site 5.2 mi downstream. This gaging station provides flow data essential to determine Illinois' diversion of Lake Michigan water. A U.S. Supreme Court Decree limits Illinois' diversion to an average of 3,200 ft³/s. Illinois' diversion includes water diverted from the lake for domestic water supply, for navigation and water-quality improvement in the Chicago Sanitary and Ship Canal system, and the stormwater runoff from a 673 mi² diverted watershed area. Flows recorded at this station also include nondiversion flows.

EXTREMES FOR PERIOD RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 19,466 ft³/s, Feb. 21, 1997, gage-height, 23.95 ft; maximum gage-height, 26.43 ft, Feb. 4, 1996, discharge, 2,876 ft³/s; no flow or periods of reverse flow at times in most years.