USGS Water-Year Summary 2021
05587450 MISSISSIPPI RIVER AT GRAFTON, IL
LOCATION - Lat 38°58'04.7", long 90°25'44.4" referenced to North American Datum of 1983, in sec.15, T.6 N., R.12 W., Jersey County, IL, 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.
PERIOD OF RECORD - DISCHARGE: 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, IL" (05587500) Apr 1933 to September 1986.
GAGE HEIGHT: Aug 1879 through Sep 1892, 1929 to Sep 1986, Oct 1986 to current year. Stages also available from reports of the National Weather Service.
GAGE - Water-stage recorder. Datum of gage is 403.79 ft above National Geodetic Vertical Datum of 1929. Auxiliary water-stage recorder 15.3 mi downstream at Alton, Ill., headwater gage at Melvin Price Lock and Dam, used to determine fall for discharge computation.
EXTREMES OUTSIDE PERIOD OF RECORD - Flood of Jun 1844 reached an elevation of 435.89 ft, present datum.