LOCATION.-- Lat 41°53'30", long 87°38'30" (NAD of 1927), in NW1/4SW1/4 sec.12, T.40 N., R.13 E., Cook County, Hydrologic Unit 07120003, on right upstream side of Grand Avenue bridge in Chicago, 0.6 mi upstream from confluence with the main stem of the Chicago River, and at mile 36.0.

DRAINAGE AREA.-- 180 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: July 2, 2002 to current year.

SURFACE-WATER QUALITY

PHYSICAL AND CHEMICAL: Water years 2002 to current year.

WATER TEMPERATURE: September 2002 to current year.

GAGE.-- Water-stage recorder, acoustic velocity meter and water-temperature sensor. Datum of gage is 579.48 ft above NGVD of 1929 (Chicago City datum) (579.20 ft NAVD 1988).

REMARKS.-- This station provides data for a water-quality model. Discharges during winter periods may be underestimated due to bi-directional density currents. Flow is diverted from Lake Michigan and is regulated by the Wilmette Controlling Works upstream and the Chicago River Controlling Works on the main stem of the Chicago River and the Lockport Lock and Dam. The Metropolitan Water Reclamation District of Greater Chicago also discharges wastewater effluent from the Northside Treatment Plant to the North Branch of the Chicago River upstream of the gage.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 14,100 ft³/s, Aug. 22, 2002, minimum daily discharge, -20 ft³/s, Jan. 31, 2004, due to regulation or bi-directional density currents.

WATER TEMPERATURE: Maximum, 26.4°C, July 19, Aug. 2, 10, 2005; minimum recorded, 0.5°C, Jan. 31, 2004.

EXTREMES FOR CURRENT YEAR.-- Maximum recorded water temperature, 25.1°C, Sept. 10; minimum recorded, 22.6°C, Sept. 4.

REMARKS FOR CURRENT YEAR.-- Water-temperature data are from six temperature sensors on right bank with sensor #1 being the highest in the water column and sensor #6 being the lowest.