Illinois State Water Survey - Illinois Maps, University of Illinois at Urbana-Champaign

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Statewide Maps

Major Watersheds of Illinois

Countywide Vertical Datum Conversion Factors in Illinois - This map displays countywide, conversion values to adjust elevations from the National Geodetic Vertical Datum 1929 (NGVD 29) to the North American Vertical Datum 1988 (NAVD 88). Values indicated should be added to current NGVD 29 elevations (not displayed) to obtain the NAVD 88 elevation. Countywide values were calculated using the methodology outlined in the Federal Emergency Management Agency (FEMA) Guidelines and Specifications for Flood Hazard Mapping Partners Appendix B (

Point conversion factors were computed using the CORPSCON utility (

This map is available online as a 11" x 17" PDF file (450k).
Major Watersheds of Illinois

Major Watersheds of Illinois - This map illustrates general boundaries of major watersheds of Illinois. Shades of blue and green indicate watersheds in the Mississippi River basin. Watersheds with shades of green are located in the Illinois River basin. Shades of yellow and brown indicate watersheds in the Ohio River basin. The Cache River drains to both the Mississippi and Ohio Rivers. Drainage to Lake Michigan is in the Great Lakes basin. Its watershed is shaded pink. A watershed is often considered synonymous with drainage basin, and in this context it is the land area that directly drains to a common stream, river, or lake. Watershed boundaries follow topographic highs. Artificial drainage structures such as canals may convey water across topographic watershed boundaries in some areas shown. Features shown on this map are accurate to the scale at which they were originally developed. Communities are displayed as space allowed. To request a paper copy of the Major Watersheds of Illinois map from The Illinois State Water Survey, please fill out this form. Copies are available free of charge until supplies run out.

Lambert Conformal Conic projection based on standard parallels 30° and 45°

This map is available online as a 26" x 38" PDF file (730k).
Community Surface Water Supplies Year 2000

Community Surface Water Supplies Year 2000 - Community water supplies provide nearly 90% of Illinois' citizens with water for residential use. The Illinois Environmental Protection Agency (IEPA) defines a "community water supply" as a public water supply that provides potable water to a minimum of 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. The IEPA issues permits for operation of water supplies serving the public. Data from the Illinois State Water Survey (ISWS) Illinois Water Inventory Program (IWIP) show that 1998 total withdrawals by all public water supply systems exceeded 1,700 million gallons per day (mgd). Community systems withdrawing surface water accounted for 84% of those withdrawals, with Lake Michigan withdrawals exceeding 1,000 mgd. Other surface water sources include interstate rivers (Mississippi and Ohio), intrastate rivers (Fox, Illinois, Kankakee, Kaskaskia, and Little Wabash), and 96 reservoirs.

Due to Homeland Security issues, we can not freely distribute this map through the World Wide Web. For a copy, you will need to send a Letter of Intent on your company's letterhead, stating why you would like this map. This map is prohibited from being displayed publicly. Please include contact information, as we may call to verify the information. Upon receipt of the letter, it will be forwarded to the Survey Director for approval. You can fax it (217-333-4983 - Please include the web address/URL of this webpage on the FAX cover sheet) or mail it to:

Illinois State Water Survey
c/o Patti Hill
2204 Griffith Drive
Champaign, IL 61820-7495
Illinois River Watershed

Illinois River Watershed - The Illinois River watershed (shaded in light blue) is of vital importance to the State of Illinois. This large watershed covers 44 percent of the state and 90 percent of Illinois' population resides within 55 counties wholly or partially included in the watershed. The Illinois River, one of the major tributaries of the Mississippi River, is part of the only inland waterway linking the Great Lakes to the Gulf of Mexico. The Illinois River watershed has a drainage area of 28,906 square miles or sq mi (75,156 square kilometers or sq km), of which approximately 3,058 sq mi (4,920 sq km) are located in Indiana and 1,070 sq mi (1,722 sq km) in Wisconsin. The watershed contains the drainage basins of several of the Illinois' major rivers including the Des Plaines, Kankakee, Fox, Vermilion, Mackinaw, Spoon, Sangamon, and La Moine Rivers.

This map is available online as a 26" x 38" PDF file (6mb).

Illinois Community Water Supply Wells

Illinois Community Water Supply Wells - Illinois has abundant buried groundwater reserves that supply millions of gallons of groundwater per day for public, agricultural, and industrial/commercial use. These aquifers are unevenly distributed throughout the state. Fortunately, surface water or a combination of groundwater and surface water is available to meet required needs in most cases where groundwater resources are marginal.

This map depicts community water supply wells in relation to the major aquifer systems in Illinois. A community water supply is defined as "a public water system which serves at least 15 service connections used by residents or regularly serves at least 25 residents for at least 60 days per year." Only community wells classified as active in the ISWS Public-Industrial-Commercial Survey database for the Year 2003 are shown.

This map is available online as a 28" x 40" PDF file (3.7mb).

County-Level Maps

Illinois Community Water Supply Wells

2012 Center Pivot Irrigation in Mason County, Illinois - Mason County has the most irrigated acreage in the state, nearly double that of any other Illinois county. Sandy soils and annual precipitation of about 38 inches promote significant groundwater recharge. An extensive shallow aquifer provides an abundant source of water that, historically, has not led to any long-term lowering of water levels or depletion of the aquifer even as irrigation has significantly expanded. The Imperial Valley Water Authority, a local government entity that regulates non-agricultural high capacity wells in Mason County and four townships in Tazewell County, estimated groundwater withdrawals for irrigation in Mason County in 2012 to be a little over 70 billion gallons, which equates to 587 million gallons a day (MGD) across a 120-day growing season.

This map displays the center pivot irrigation systems in use in Mason County, Illinois during the 2012 growing season. Center pivot irrigation imprints identifiable circular patterns on the landscape which can be visible in aerial images. The USDA collects aerial imagery (National Agricultural Imagery Program) and makes them available through the USDA Geospatial Data Gateway. The NAIP images were examined for circular irrigation patterns, and field boundaries were digitized using ArcGIS version 10.0 to create a map layer. In total, 1553 fields were identified as using center pivot systems in Mason County during the summer of 2012, representing 135,684 acres of farmland and approximately 50 percent of all farmland in Mason County.

This map is available online as a 34” x 22” PDF file (4.7Mb)

Examples of Other Survey Maps (Many more are available on our web site, and in our publications and brochures)

1996 Peoria Lake Bathymetry

1996 Peoria Lake Bathymetry - The bathymetric contours in this map were derived from a triangulated irregular network (TIN) built using the Z values from the surveyed cross-section points. Lambert Conformal Conic projection based on standard parallels 30° and 45°.
This map is available online as a 35" x 46" PDF file (3.1mb).

7-Day 10-Year Low Flow Maps

7-Day 10-Year Low Flow Maps - This site provides electronic copies of the paper maps that are contained in Illinois State Water Survey contract reports ISWS CR 440, ISWS CR 441, and ISWS CR 545 . These maps provide information on low flow conditions that might be expected to occur only during droughts (once in 10 years), and associated effluent discharges, water withdrawals, and flow regulations for most Illinois rivers and streams. You may view and download the maps at the 7-Day 10-Year Low Flow Maps web site.
A 7-day low flow for a stream is the average flow measured during the 7 consecutive days of lowest flow during any given year. The 7-day 10-year low flow (Q7,10) is a statistical estimate of the lowest average flow that would be experienced during a consecutive 7-day period with an average recurrence interval of ten years. Because it is estimated to recur on average only once in 10 years it is usually an indicator of low flow conditions during drought.

2-Year 7-Day Low Flows

2-Year 7-Day Low Flows - Taken from A Plan for Scientific Assessment of Water Supplies in Illinois 2001, Illinois State Water Survey, Champaign, IL v, 22 p. : col. Ill, ISWS IEM 2001-03.
Abstract Excerpt: Demand for water in Illinois is increasing, and water shortages in the Chicago metropolitan area have been projected. There are, however, limits to the availability of clean water at a reasonable cost. Limits to water availability are imposed by a number of factors including droughts, legal requirements to maintain minimum flows in rivers and streams, water recharge rates, and a decree of the United States Supreme Court limiting withdrawal of water from Lake Michigan. In addition, the specter of regional climate change could pose the greatest threat to Illinois water supplies over the long term: some projections show the possibility of persistent floods, whereas other projections show persistent droughts.
Additional sources of water do exist and can be tapped, but the cost of providing clean water increases with the necessity of water treatment, storage, and distribution, and the mitigation of impacts of new withdrawals on existing water supplies. Long lead times also are needed to construct major water projects. Unless the water supplies of Illinois are planned and managed in a comprehensive, regional, and visionary manner--based on the concept of renewable water supply capacity--water shortages could soon occur in some parts of the state. Water supply planning and management should be based on improved understanding and prediction of water supply and demand, and risk assessment.
The goal of this plan is to provide a framework for Illinois State Water Survey (ISWS) water supply programs and to document those studies that ISWS, working with others, needs to conduct to provide Illinois with comprehensive technical data and information, models, and training for water supply planning and management. Full Abstract
This map is available online as an 8.5" x 11" PDF file (450k).

View and download a full text version of this publication:
Average Annual Snowfall
Climate Atlas of Illinois
Atlas of
Illinois Precipitation Departures - Figure 7-1, left, is from Climate Atlas of Illinois published by the Illinois State Water Survey. The figure shows precipitation departures, in percent of average, for the four worst 12-month droughts during the 20th century.
Excerpt: The four most severe one-year long droughts (based on water supply and agricultural problems) had patterns of very deficient precipitation (Figure 7-1). During the worst drought, 1933 1934 (ending in May 1934), half of the state had less than 60 percent of average precipitation. The second worst drought, 1930-1931, had less than 50 percent of average precipitation in extreme southern Illinois. The 1930s are well known for the worst Illinois droughts during the 20th Century. The third-ranked drought, 1953-1954, actually had above average precipitation in northern Illinois but less than 50 percent of average amounts across south-central Illinois.
For planning and design purposes, likely deficiencies of precipitation for periods from six months up to three years are important. Deficiencies in shorter periods, a year or less, can be devastating to crops, whereas most urban water supplies in Illinois are not seriously affected until a drought period has lasted two years or more. The 5-, 10-, 25-, and 50-year frequency patterns for 6-month, 12-month, 24-month, and 36-month precipitation droughts reveal that expected precipitation deficiencies for any return period are greater in southern Illinois than elsewhere in Illinois.
Details about purchasing a copy of Climate Atlas of Illinois are available on our web site.
Estimated Potential Yield of Sand and Gravel Aquifers

Estimated Potential Yield of Sand and Gravel Aquifers - Taken from An Analysis of Groundwater Use to Aquifer Potential Yield in Illinois, Wehrmann, H. Allen, Sean V. Sinclair, and Timothy P. Bryant., 2003 Illinois State Water Survey, Champaign, IL, ISWS CR 2004-11.
Abstract Excerpt: Proper water resource planning and management requires a firm understanding of water use and water resource availability. This report summarizes a comparison of Year 2000 groundwater withdrawals against estimated aquifer potential yields. The comparison is presented as a ratio of groundwater use (withdrawals) to groundwater yield (i.e., potential aquifer yield) on a township basis. Geographical Information System (GIS) technology was used to determine township yield ratios for three aquifer types (sand-and-gravel, shallow bedrock, and deep bedrock). Full Abstract
This map is available online as a 24" x 36" PDF file (800k).
View and download a full text version of this publication:



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