LOCATION.-- Lat 38°58'05", long 90°25'42" (NAD of 1927), in NE 1/4 sec.15, T.6 N., R.12 W., Jersey County, Hydrologic Unit 07110009, on left bank 0.2 mi downstream from the mouth of Illinois River, 15.3 mi above Lock and Dam 26, 23.0 mi above mouth of Missouri River, and at mile 218.6 upstream of the mouth of Ohio River.

DRAINAGE AREA.-- 171,300 mi², approximately.

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1986 to current year. Intermittently from 1880 to 1928, computed daily 1928 to 1932 by the National Weather Service and/ or the U.S. Army Corps of Engineers. Discharge previously published as "Mississippi River at Alton, Illinois" (05587500) for October 1927 to September 1986.

STAGE: August 1879 through September 1892, 1929 to September 1986. Stages also available from reports of the National Weather Service.

GAGE.-- Water-stage recorder and U.S. Army Corps of Engineers satellite telemeter. Datum of gage is 403.79 ft above NGVD of 1929. Auxiliary water-stage recorder 15.3 mi downstream.

REMARKS.-- Natural flow of river affected by many navigation dams in upper Mississippi River Basin. Flood water from Missouri River overtops or breaches the levees at extremely high stages.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 598,000 ft³/s, August 1, 1993, gage height, 441.96 ft, maximum gage height, 432.15 ft, April, 28, 1973, at Alton; minimum discharge, 7,960 ft³/s, November 7, 1948, at Alton, result of temporary storage in pool of Lock and Dam 26.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Flood of June 1844 reached an elevation of 435.89 ft, present datum.