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. Basin contains so many communities, Water Availability and Use assessment Geological Survey (USGS) is assessing industries, and ecosystems that depend will provide information to fill this need the availability and use of the Nation’s on present sources of water, and because for the U.S. part of the Great Lakes, their water resources to gain a clearer under- competition for available water is inten- tributary streams, and the ground-water standing of the status of our water sifying, there is a need to quantify the system that feeds the Great Lakes and its resources and the land-use, water-use, region’s water resources and the trends tributaries. and natural climatic trends that affect affecting them so that the potential for them. The goal of the National Assess- possible future water-use conflicts can be Great Lakes Basin Study ment of Water Availability and Use Pro- reduced or avoided. Water availability is a function of gram is to improve our ability to forecast In recent years, numerous govern- water availability for future economic ment agencies, commerce, industry, and many factors, including the quantity and and environmental uses. Simply put, the the general public all have expressed quality of water and the laws, regula- assessment will help characterize how concern about potential large withdrawals tions, economics, and environmental much water we have now, how water of water within the Great Lakes Basin. factors that control its use. The focus availability is changing, and how much In response, the Great Lakes States and of the Great Lakes Basin study is on water we can expect to have in the future. Canadian Provinces signed an Annex improving fundamental knowledge of the Currently (2005), the assessment to the Great Lakes Charter in 2001. The water balance of the basin, including the is focused on the Great Lakes Basin Annex commits the States and Provinces flows, storage, and water use by humans. (fig.1) to determine the best methods to to science-based water-resources manage- An improved quantitative understand- evaluate water resources and to develop ment. This commitment requires a more ing of the basin’s water balance not only strategies for delivering information detailed understanding of the region’s provides key information about water about water availability and use. Other water resources and a synthesis of avail- quantity but also is a fundamental basis water-resources regions will be added able data and information. The USGS to the assessment as evaluation methods 0 0 90 80 improve and as funding permits. JAMES BAY Water-Resources Issues in O N T A R I O the Great Lakes Basin EXPLANATION 0 GREAT LAKES BASIN The Great Lakes Basin, which 50 encompasses Lakes Superior, Michi- CA gan, Huron, Erie, and Ontario (fig. 1), U. NA S. DA ERIOR A. SUP Q U E B E C KE contains 95 percent of the fresh surface LA St. Marys water in North America and 18 percent River Straits of of the fresh surface water in the world. Mackinac St. Lawrence Ground water underlying the basin River LAKE WISCONSIN constitutes another large volume of N HURON A G I freshwater. Humans, animals, and plants H C LAKE I 0 M MICHIGAN ONTARIO have adapted to this abundance in water 45 E K St. Clair A River Niagra L River NEW resources. Yet, even in this water-rich Lake St. Clair YORK DA CANA A. area, water withdrawals, diversions, and Detroit U. S. River LAKE use sometimes conflict with the needs of ERIE PENNSYLVANIA other users and ecosystems in the basin. ILLINOIS For example, pumping of large water- INDIANA OHIO supply wells in Wisconsin and Illinois has lowered ground-water levels in other wells in the area, reducing the yield Base from ESRI, 2001; U.S. Army Corps of Engineers,1998; and Environment Canada,1995. 0 50 100 150 200 MILES of water to those wells and increasing 0 50 100 150 200 KILOMETERS pumping costs. Because the Great Lakes Figure 1. Location of the Great Lakes Basin in the United States and Canada. U.S. Department of the Interior Fact Sheet 2005–3113 U.S. Geological Survey Printed on recycled paper November 2005 USGS Minnesota stream gage during 2001 spring flood (photograph by Eric S. Wakeman, U.S. Geological Survey). for many analyses of water quality and characterized in a variety of ways. For of these streamflow changes could be ecosystem health. many uses, an appropriate measure of far greater. Another aspect of quantify- streamflow is the “minimum daily flow,” ing future water availability is to quan- Water Levels of the Great Lakes which is especially important during tify trends—especially those related to The water-level elevations of Lakes droughts. For municipal wastes, a mea- floods, droughts, and seasonal timing. Michigan, Huron, Erie, and Ontario have sure of the low flow of a stream quanti- If significant trends are detected, subse- varied about 6 feet since 1860, when fies water available for effluent dilution quent investigations may determine the accurate records of lake levels were first or “assimilative capacity” for which a cause. That information will help inform recorded. Water levels in Lake Supe- treatment plant is designed. Other statis- plans for future water use or watershed rior varied about 3 feet during the same tics characterize the seasonal distribution development and will help water-resource interval. Prehistoric variations were much or persistence of streamflow. As a first managers determine an appropriate greater and were strongly correlated with step toward quantifying water availability, network for monitoring streamflow in the climate change. Changes in water levels this project will assemble published sta- basin. of the Great Lakes constitute the largest tistics and compute relevant new statistics Unmeasured streamflow. —The USGS changes in the amount of water in the for streams now or previously gaged. currently measures streamflow for only Trends in Streamflow.— region. The Great Lakes Basin study will Streamflow about 70 percent of the U.S. part of summarize what is known about lake is affected by climatic factors (primarily the Great Lakes Basin. Streamflow for levels over the past 4,700 years. This precipitation) and watershed charac- the remaining ungaged tributaries will analysis of lake levels will help put recent teristics including human factors such be estimated for this study by means low lake levels into perspective, espe- as urbanization, stream regulation, and of regional regression and correlation cially given the prospect of future global water diversions. Changes among these techniques to determine the contribution warming. factors have altered the timing and of those areas to the water balance. This rates of streamflow and, in some places method will allow USGS scientists to (especially urban areas), have affected Streamflow make monthly estimates of total tributary the magnitude and frequency of floods streamflow to the Great Lakes, which Streamflow maintains the water levels and low flows. In the past, these effects will be provided online by way of USGS of the Great Lakes, nourishes ecosystem were either unrecognized or dispersed Web sites. habitats, furnishes an essential raw mate- through a sparse, rural population and rial for a variety of industries, and carries economy. Today, the economic, envi- away municipal wastes. Corresponding ronmental, and political consequences to these uses, streamflow availability is Golf-course irrigation well and water distribution system (photograph by N. Grannemann, U.S. Geological Survey). Ground-Water Flow and Storage from aquifers or if natural changes take computed recharge rates. The recharge place in the ground-water system. The component of this assessment will evalu- Ground water is a major natural Great Lakes Water Availability and Use ate new and existing methods to deter- resource in the Great Lakes Basin assessment will delineate ground-water mine spatial recharge rates and trends in because it is, in effect, a large subsur- divides for most aquifers in the Great recharge over time. face reservoir. Ground water discharges Lakes hydrologic system. This delin- Great Lakes Basin Hydrogeologic naturally to streams, lakes, and wetlands. eation will be a synthesis of data and Summary. —Previous hydrogeologic It is also tapped for drinking water by information from previous and current studies in the Great Lakes Basin consist many water suppliers and residents of regional and local studies. Where pos- of a variety of regional and subregional the basin who do not use water directly sible, areas where divides have shifted as investigations that were appropriate for from the lakes. Two major ground-water a result of ground-water withdrawals or a specific purpose but are difficult to resource issues in the Great Lakes Basin natural causes will be delineated. synthesize into a broader view of water are the amount of ground water available Recharge. —Areal recharge is the pri- availability and use basinwide. As part of at a given location and the interaction mary source of water to the ground-water the hydrogeologic summary effort, results of ground water with surface water. The system; however, regional estimates of from published studies will be com- Great Lakes Basin Water Availability ground-water recharge in the Great Lakes piled, evaluated, and synthesized. Where and Use assessment will address various Basin can differ substantially depend- possible, the amount of ground water in aspects of these ground-water issues. ing on the methods used. Consistent and storage will be determined, and changes Ground-water divides. —Ground- accurate estimates are needed to under- in ground-water storage through time will water divides are like watershed (land- stand how recharge to the ground-water be assessed.