U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3113

November 2005 Printed on recycled paper

Great Lakes Basin Water Availability and Use

A study of the National Assessment of Water Availability and Use Program

At the request of Congress, the U.S. 

Geological Survey (USGS) is assessing 

the availability and use of the Nation’s 

water resources to gain a clearer understanding of the status of our water 

resources and the land-use, water-use, 

and natural climatic trends that affect 

them. The goal of the National Assessment of Water Availability and Use Program is to improve our ability to forecast 

water availability for future economic 

and environmental uses. Simply put, the 

assessment will help characterize how 

much water we have now, how water 

availability is changing, and how much 

water we can expect to have in the future. 

Currently (2005), the assessment 

is focused on the Great Lakes Basin 

(fig.1) to determine the best methods to 

evaluate water resources and to develop 

strategies for delivering information 

about water availability and use. Other 

water-resources regions will be added 

to the assessment as evaluation methods 

improve and as funding permits. 

Water-Resources Issues in 

the Great Lakes Basin

The Great Lakes Basin, which 

encompasses Lakes Superior, Michigan, Huron, Erie, and Ontario (fig. 1), 

contains 95 percent of the fresh surface 

water in North America and 18 percent 

of the fresh surface water in the world. 

Ground water underlying the basin 

constitutes another large volume of 

freshwater. Humans, animals, and plants 

have adapted to this abundance in water 

resources. Yet, even in this water-rich 

area, water withdrawals, diversions, and 

use sometimes conflict with the needs of 

other users and ecosystems in the basin. 

For example, pumping of large watersupply wells in Wisconsin and Illinois 

has lowered ground-water levels in other 

wells in the area, reducing the yield 

of water to those wells and increasing 

pumping costs. Because the Great Lakes 

Basin contains so many communities, 

industries, and ecosystems that depend 

on present sources of water, and because 

competition for available water is intensifying, there is a need to quantify the 

region’s water resources and the trends 

affecting them so that the potential for 

possible future water-use conflicts can be 

reduced or avoided. 

In recent years, numerous government agencies, commerce, industry, and 

the general public all have expressed 

concern about potential large withdrawals 

of water within the Great Lakes Basin. 

In response, the Great Lakes States and 

Canadian Provinces signed an Annex 

to the Great Lakes Charter in 2001. The 

Annex commits the States and Provinces 

to sci­ence-based water-resources management. This commitment requires a more 

detailed understanding of the region’s 

water resources and a synthesis of available data and information. The USGS 

Water Availability and Use assessment 

will provide information to fill this need 

for the U.S. part of the Great Lakes, their 

tributary streams, and the ground-water 

system that feeds the Great Lakes and its 

tributaries.

Great Lakes Basin Study

Water availability is a function of 

many factors, including the quantity and 

quality of water and the laws, regulations, economics, and environmental 

factors that control its use. The focus 

of the Great Lakes Basin study is on 

improving fundamental knowledge of the 

water balance of the basin, including the 

flows, storage, and water use by humans. 

An improved quantitative understanding of the basin’s water balance not only 

provides key information about water 

quantity but also is a fundamental basis 

O N T A R I O

90 80

45

50

0 0

0

0

Base from ESRI, 2001; U.S. Army Corps of Engineers,1998; and Environment Canada,1995.

Q U E B E C

LAKE

HURON

LAKE

ERIE

LAKE

ONTARIO

LAKE SUPERIOR

LAKE MICHIGAN

ILLINOIS

INDIANA OHIO

PENNSYLVANIA

NEW

YORK

W I S C O N S I N

JAMES

BAY 

CANADA

U. S. A.

CANADA

U. S. A.

St. Lawrence 

River

St. Marys 

River

St. Clair 

 River

Detroit 

River

Niagra

River

Straits of 

Mackinac

GREAT LAKES BASIN

EXPLANATION

Lake St. Clair

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

M I C H I G A N

Figure 1.  Location of the Great Lakes Basin in the United States and

Canada.
for many analyses of water quality and 

ecosystem health.

Water Levels of the Great Lakes

The water-level elevations of Lakes 

Michigan, Huron, Erie, and Ontario have 

varied about 6 feet since 1860, when 

accurate records of lake levels were first 

recorded. Water levels in Lake Superior varied about 3 feet during the same 

interval. Prehistoric variations were much 

greater and were strongly correlated with 

climate change. Changes in water levels 

of the Great Lakes constitute the largest 

changes in the amount of water in the 

region. The Great Lakes Basin study will 

summarize what is known about lake 

levels over the past 4,700 years. This 

analysis of lake levels will help put recent 

low lake levels into perspective, especially given the prospect of future global 

warming. 

Streamflow

Streamflow maintains the water levels 

of the Great Lakes, nourishes ecosystem 

habitats, furnishes an essential raw material for a variety of industries, and carries 

away municipal wastes. Corresponding 

to these uses, streamflow availability is 

characterized in a variety of ways. For 

many uses, an appropriate measure of 

streamflow is the “minimum daily flow,” 

which is especially important during 

droughts. For municipal wastes, a measure of the low flow of a stream quantifies water available for effluent dilution 

or “assimilative capacity” for which a 

treatment plant is designed. Other statistics characterize the seasonal distribution 

or persistence of streamflow. As a first 

step toward quantifying water availability, 

this project will assemble published statistics and compute relevant new statistics 

for streams now or previously gaged. 

 Trends in Streamflow.—Streamflow 

is affected by climatic factors (primarily 

precipitation) and watershed characteristics including human factors such 

as urbanization, stream regulation, and 

water diversions. Changes among these 

factors have altered the timing and 

rates of streamflow and, in some places 

(especially urban areas), have affected 

the magnitude and frequency of floods 

and low flows. In the past, these effects 

were either unrecognized or dispersed 

through a sparse, rural population and 

economy. Today, the economic, environmental, and political consequences 

of these streamflow changes could be 

far greater. Another aspect of quantifying future water availability is to quantify trends—especially those related to 

floods, droughts, and seasonal timing. 

If significant trends are detected, subsequent investigations may determine the 

cause. That information will help inform 

plans for future water use or watershed 

development and will help water-resource 

managers determine an appropriate 

network for monitoring streamflow in the 

basin.

Unmeasured streamflow. —The USGS 

currently measures streamflow for only 

about 70 percent of the U.S. part of 

the Great Lakes Basin. Streamflow for 

the remaining ungaged tributaries will 

be estimated for this study by means 

of regional regression and correlation 

techniques to determine the contribution 

of those areas to the water balance. This 

method will allow USGS scientists to 

make monthly estimates of total tributary 

streamflow to the Great Lakes, which 

will be provided online by way of USGS 

Web sites.

USGS Minnesota stream gage during 2001 spring flood (photograph by Eric S. Wakeman, U.S. Geological Survey).
Ground-Water Flow and Storage

Ground water is a major natural 

resource in the Great Lakes Basin 

because it is, in effect, a large subsurface reservoir. Ground water discharges 

naturally to streams, lakes, and wetlands. 

It is also tapped for drinking water by 

many water suppliers and residents of 

the basin who do not use water directly 

from the lakes. Two major ground-water 

resource issues in the Great Lakes Basin 

are the amount of ground water available 

at a given location and the interaction 

of ground water with surface water. The 

Great Lakes Basin Water Availability 

and Use assessment will address various 

aspects of these ground-water issues.

Ground-water divides. —Groundwater divides are like watershed (landsurface) divides in that their location 

determines whether ground water will 

flow toward or away from one of the 

Great Lakes. Locations of ground-water 

divides in the uppermost aquifers underlying the basin commonly coincide with 

watershed divides. In deeper aquifers, 

however, ground-water divides may not 

coincide with watershed divides. Additionally, the location of ground-water 

divides can change if water is pumped 

from aquifers or if natural changes take 

place in the ground-water system. The 

Great Lakes Water Availability and Use 

assessment will delineate ground-water 

divides for most aquifers in the Great 

Lakes hydrologic system. This delineation will be a synthesis of data and 

information from previous and current 

regional and local studies. Where possible, areas where divides have shifted as 

a result of ground-water withdrawals or 

natural causes will be delineated. 

Recharge. —Areal recharge is the primary source of water to the ground-water 

system; however, regional estimates of 

ground-water recharge in the Great Lakes 

Basin can differ substantially depending on the methods used. Consistent and 

accurate estimates are needed to understand how recharge to the ground-water 

system relates to water availability and 

use. Locally, areal recharge rates range 

from less than 1 inch per year to more 

than 20 inches per year on the basis of 

hydrograph analysis for large watersheds. The rates depend on precipitation 

and other climatic factors, in addition 

to watershed characteristics such as 

soil type. Seasonal, year-to-year, and 

decade-to-decade changes all can affect 

computed recharge rates. The recharge 

component of this assessment will evaluate new and existing methods to determine spatial recharge rates and trends in 

recharge over time. 

Great Lakes Basin Hydrogeologic 

Summary. —Previous hydrogeologic 

studies in the Great Lakes Basin consist 

of a variety of regional and subregional 

investigations that were appropriate for 

a specific purpose but are difficult to 

synthesize into a broader view of water 

availability and use basinwide. As part of 

the hydrogeologic summary effort, results 

from published studies will be compiled, evaluated, and synthesized. Where 

possible, the amount of ground water in 

storage will be determined, and changes 

in ground-water storage through time will 

be assessed. In addition, water levels in 

observation wells with several decades of 

record will be analyzed for trends related 

to climatic factors. An analysis of available data will be done to determine if current monitoring of ground-water levels in 

the basin is adequate to support regional 

and national decisionmaking for effective 

water management. Analysis of groundwater monitoring programs will include 

Golf-course irrigation well and water distribution system (photograph by N. Grannemann, U.S. Geological

Survey).
data networks operated by Federal, state, 

and local agencies in the United States. 

Ground-Water-Flow Models

Application of ground-water-flow 

models is one of the most comprehensive 

ways to synthesize ground-water data and 

to analyze the response of a ground-water 

system to changes in the system, such 

as increased pumping rates, changes in 

pumping locations, changes in recharge, 

and climate variations. Regional models 

that simulate ground-water flow will 

greatly improve the overall understanding of ground-water conditions in the 

Great Lakes Basin and provide a quantitative framework to help manage water 

resources in ways consistent with the 

Great Lakes Charter Annex. Comprehensive ground-water-flow models are 

complex and time consuming to develop; 

therefore, the entire Great Lakes Basin 

could not be modeled for this study. 

Instead, a ground-water-flow model of 

the Lake Michigan subbasin is being 

developed because (1) the entire watershed is in the United States, and many 

datasets already are available within the 

USGS; (2) ground water is withdrawn 

from bedrock and glacial-deposit aquifers, both of which are important aquifer 

systems throughout the Great Lakes 

Basin; (3) important issues related to 

ground-water and surface-water interaction can be simulated with the model; (4) 

ground-water withdrawals in the Lake 

Michigan subbasin may affect the locations of ground-water divides with Lakes 

Superior, Huron, and Erie; and (5) problems caused by large-scale ground-water 

withdrawals have been documented in the 

subbasin. In addition, one or more separate models within the Lake Michigan 

subbasin will be developed specifically to 

simulate ground-water and surface-water 

interaction in smaller watersheds because 

this is an important component of the 

water balance not only here but elsewhere 

in the Great Lakes Basin. These models 

will be used to test new techniques for 

simulating the interactions of ground 

water and surface water at the appropriate 

scale. 

Water Use

The USGS plans to compile water-use 

data (fig. 2) to assist Great Lakes Basin 

stakeholders in water-supply management efforts and to test compilation 

approaches that may have nationwide 

applicability. Preliminary discussions 

with state agencies have indicated that 

refinement of consumptive-use factors 

for all types of water use is the area of 

greatest interest and value to water-supply managers. Initial plans are to conduct 

a focused study on either (1) a small 

geographic area for a comprehensive 

understanding of consumptive use or (2) 

selected water-use categories (fig. 2) to 

refine the understanding of consumptive 

use for those categories basinwide. As 

an initial assessment of consumptive-use 

factors, the USGS has begun work on an 

annotated bibliography for consumptiveuse coefficients in the Great Lakes and 

climatically similar regions.

—Norman G. Grannemann and

Howard W. Reeves

For additional information about the 

USGS National Assessment of Water 

Availability and Use in the Great Lakes 

Basin, please contact:

Howard W. Reeves, Project Chief

USGS Michigan Water Science Center

6520 Mercantile Way, Suite 5

Lansing, MI 48911

hwreeves@usgs.gov

References Cited

Baedke, S.J., and Thomas, T.A., 2000, 

A 4,700-year record of lake level and 

isostasy for Lake Michigan; Journal of 

Great Lakes Research, v. 26, no. 4, p. 

416–426. 

Council of Great Lakes Govenors, 

2001, The Great Lakes Charter 

Annex, accessed October 27, 2005, at

http://www.cglg.org/projects/water/

Annex2001.pdf 

National Oceanic and Atmospheric 

Administration, Great Lakes Water 

Levels, accessed October 27, 2005, at 

http://www.glerl.noaa.gov/data/now/

wlevels/levels.html

Solley, W.B., Pierce, R.R., and Perlman, 

H.A., 1998, Estimated use of water in 

the United States in 1995: U.S. Geological Survey Circular 1200, 71 p.

Surface

Water

Public

Supply

Ground

Water

Domestic Commercial Industrial

Irrigation Thermoelectric Mining Livestock

31,160

3,830

4,415

1,507

585

1.0 354

355

108 44

152

3,900 270

4,170

145 170

315

22,800 0

22,800

356 34

390

20 50

70

Surface-water source

Ground-water source

31,160

1,507

4,415 Public-water-supply use

22,800 Self-supplied water use

TOTAL WATER SUPPLY OR USE FOR CATEGORY, IN MILLION GALLONS 

PER DAY

Figure 2.   Pipe diagram of the source and use of the estimated 32,667 million

gallons per day of freshwater withdrawals in the Great Lakes Basin in 1995

(Solley and others, 1998).