LOCATION.-- Lat 41°00'05", long 90°51'15" (NAD of 1927), in NE1/4SW1/4 sec.28, T.12 N., R.4 W., Henderson County, Hydrologic Unit 07080104, on left bank at downstream side of bridge on State Highway 94, 1 mi south of Bald Bluff, 6.5 mi northeast of Oquawka, and at mile 20.8.

DRAINAGE AREA.-- 432 mi².

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1934 to September 1996. October 1997 to current year. Prior to October 1938, published as Henderson River. Monthly discharge only for some periods, published in WSP 1308.

STAGE: Water years 1994-1996;1998 to current year.

SURFACE-WATER QUALITY

CHEMICAL: Water years 1978 to 1991. Additional chemical data for water years 1972-77 are published in Water-Resources Investigations 78-23 and 79-24 as site LD 02.

SEDIMENT: April 1978 to September 1981.

REVISED RECORDS.-- WSP 1208: 1939, 1942-43, 1948. WSP 1308: 1935-38(M), 1941(M). WDR IL-75-1: Drainage area.

GAGE.-- Water-stage recorder, U.S. Army Corps of Engineers satellite telemeter, and crest-stage gage. Datum of gage is 541.21 ft above NGVD of 1929 (levels by U.S. Army Corps of Engineers) (540.99 ft NAVD 1988). Prior to Mar. 4, 1941, nonrecording gage at same site and datum.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 34,600 ft³/s, July 8, 1982, gage height, 31.05 ft; maximum gage height, 32.65 ft, July 25, 1993, discharge 30,800 ft³/s; minimum daily observed, 1.7 ft³/s, Sept. 22, 23, 1940.

SUSPENDED-SEDIMENT CONCENTRATIONS: Maximum daily mean, 7,070 mg/L May 27, 1981; minimum daily mean, 6 mg/L Feb. 10, 11, 1981.

SUSPENDED-SEDIMENT LOADS: Maximum daily, 33,900 tons Apr. 14, 1981; minimum daily, 0.87 tons Feb. 2-4, 1980.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Flood of June 1924 reached a stage of 27.8 ft, from flood profile, and an estimated discharge of 20,000 ft³/s.