USGS Water-Year Summary 2021
05578000 SANGAMON RIVER AT PETERSBURG, IL
LOCATION - Lat 40°00'48", long 89°50'18" referenced to North American Datum of 1983, in NE 1/4 SE 1/4 NW 1/4 sec.13, T.18 N., R.7 W., Menard County, IL, Hydrologic Unit 07130008, Downstream side of State Highway 123 bridge, 390 feet west of County Highway 15, 0.5 miles east of Route 97 (6th street) in Petersburg, 2.5 miles upstream of Indian Creek, and at mile 45.5.
DRAINAGE AREA - 3,063 mi².
PERIOD OF RECORD -
SURFACE-WATER DISCHARGE AND STAGE
DISCHARGE: January 1948 to September 1949 and April 2010 to current.
STAGE: Water Years 2010 to current.
PARTIAL RECORD: Miscellaneous discharge measurements, water years
1950-51, 1958-1974, 1976-1990.
CHEMICAL: Water years 1978-90.
GAGE - Water-stage recorder, satellite telemeter, and crest-stage gage. Datum of gage is 474.00 ft above NGVD of 1929 (473.67 ft NAVD 1988). Prior to December 1968, non-recording gage at site 0.4 miles upstream at datum 10.00 ft. higher. December 1968 to September 1977, non-recording gage at site 100 ft upstream at datum 10.00 ft. higher. October 1977 to August 1985, non-recording gage at site 100 ft upstream at current datum. September 1985 to Jan. 8, 1991, non-recording gage at current site and datum. During 1991-2010, non-recording gage maintained and operated by the U.S. Corps of Engineers at current site and datum. Apr. 13, 2010 to present, recording gage at current site and datum.
EXTREMES OUTSIDE PERIOD OF RECORD -
SURFACE-WATER DISCHARGE AND STAGE: Flood of May 1943 reached a gage height of 23.9 ft, from staff gage readings obtained by U.S. Corps of Engineers at site and datum then in use. Flood of May 19, 1943, reached 68,700 ft³/s at Riverton gage 37.2 mi. upstream.
EXTREMES FOR PERIOD OF RECORD -
SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 44,800 ft³/s, Dec. 31, 2015, gage height 30.55 ft.; minimum, 41 ft³/s, Aug. 26 and 29, 2012.