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Basin Information

The Lower Illinois River Basin (LIRB) is located in central and western Illinois. The basin extends from the confluence of the Illinois and Fox Rivers near Ottawa, IL. down to the confluence of the Illinois and MIssissippi Rivers at Grafton, IL. Major rivers in the basin include:

River Length Area
Illinois River 240 mi 17,960 mi2
Sangamon River 241 mi 5,420 mi2
Spoon River 164 mi 1,860 mi2
La Moine River 126 mi 1,350 mi2
Vermilion River 76 mi 1,330 mi2
Mackinaw River 130 mi 1,140 mi2

The flat topography of the LIRB in central Illinois is dissected by the Illinois River. Glacial features are the major landforms. The LIRB is mostly (99.5%) in the Till Plains Section of the Central Lowland physiographic province.

The altitude of the land surface ranges from 600 to 800 feet above sea level. The area of greatest topographic relief is along the river valley, where topographic relief can range from 200 to 400 feet.

The 1990 population in the LIRB was 1.3 million, which equates to a poulation density of 72 people per square mile. The four most populated cities in the basin in 1990 were:

Major City Population Note
Peoria 339,000
Springfield 190,000 State Capital
Bloomington-Normal 129,000
Decatur 117,000

The population density reflects the extent of rural areas. Agriculture is the predominant land use (87%). The major crops grown are corn and soybeans. The remaining 13% of the land area in the basin are forests (8%), urban areas (2%), water and wetlands (2%), and miscellaneous land-use areas (1%).

The climate in the LIRB is humid continental, with cold, relatively dry winters and warm, wet summers. The mean annual temperature in the LIRB ranges from 50 degrees Fahrenheit in the north to 55 degrees Fahrenheit in the south. Precipitation is normally 35-38 inches per year. Variations in precipitation and temperature may occur in any year because the basin is far from large physical features such as oceans or mountains ranges that modify regional weather patterns.


Personnel to contact about a specific subject are listed on the staff page.
U.S. Department of the Interior
U.S. Geological Survey
221 North Broadway, Urbana, IL 61801, USA
URL: http://il.water.usgs.gov/proj/lirb/info/index.html
Maintainer: djfazio@usgs.gov
Last modified: 10:57 CST Thurs 11 May 2000