LOCATION.-- Lat 40°23'37", long 91°22'27" (NAD of 1927), in SE1/4 SW1/4 sec.30, T.65 N., R.4 W., Lee County, Hydrologic Unit 07080104, near right bank in tailwater of dam and powerplant of Union Electric Co. at Keokuk, 0.2 mi upstream from bridge on U.S. Highway 136, 2.7 mi upstream from Des Moines River, and at mile 364.2 upstream from Ohio River.

DRAINAGE AREA.-- 119,000 mi², approximately.

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: January 1878 to current year.

GAGE.-- Water-stage recorder. Datum of gage is 477.41 ft above NGVD of 1929 (levels by U.S. Army Corps of Engineers). Jan. 1, 1878 to May 1913, nonrecording gage at Galland (formerly Nashville), 8 mi upstream; zero of gage was set to low-water mark of 1864, or 496.52 ft above NGVD of 1929.

REMARKS.-- Discharge computed from records of operation of turbines in powerplant and spillway gates in dam. Minor flow regulation caused by powerplant since 1913 and navigation dams. Records for May 1913 to September 1937 adjusted for change in contents in Keokuk Reservoir, those after September 1937 unadjusted.

COOPERATION.--Records provided by Ameren-Union Electric Co.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 446,000 ft³/s, July 10, 1993, gage height, 27.58 ft; from floodmark; minimum daily discharge, 5,000 ft³/s, December 27, 1933.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Flood of June 6, 1851, reached a stage of 21.0 ft, present site and datum, estimated as 13.5 ft at Galland, discharge, 360,000 ft³/s.