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Great Lakes Water Availability

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Detailed Description

Though the Great Lakes are the largest freshwater system on Earth, the basin has the potential for local shortages, according to a new basin-wide water availability assessment by the U.S. Geological Survey. Kara Capelli spoke with Howard Reeves, USGS scientist and lead author on the report, about why uneven distribution of water can cause local shortages and conflicts. 




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[Intro Music]


Kara Capelli: Hello and welcome to the USGS Corecast. I'm your host, Kara Capelli.


Many areas in the United States face potential water shortages. The Great Lakes are the largest freshwater system on earth, with its five lakes, thousands of tributaries and streams, and abounding groundwater, it would be seem that there is ample water for now and well into the future.

I spoke with USGS Hydrologist Howard Reeves who recently led a basin-wide assessment of the Great Lakes to find out where water  is abundant or not, both  in the ground and on the surface, and how it is being used. The study is a pilot for others like it across the  nation.


Howard Reeves: For any system, water availability is a balance between  the storage of water in the system, the flow of water in the system and existing uses. This is a five-year  project and we looked at many aspects of water availability. We looked at trends we have seen over the last 70-90 years in both precipitation and  stream-flow. We tried to identify the groundwater system better in response to questions about location of groundwater divides and how these divides move in response to pumping.

We looked at how the groundwater system has responded to development since 1865 in the Lake Michigan basin. And we looked at water use, both  at how water use is distributed across the basin and how consumptive use or the water that is actually removed from the system  is estimated across the basin.

So in the Great Lakes, there is an abundance of water in storage in the Great Lakes themselves and there is a great deal of water that flows through the system every year. But it is not distributed equally through the whole system and it is not being used equally through the systems.


So in the Great Lakes region, although we have an abundance of water through the whole system, it doesn’t really tell us how the local system will act if  there is a change either in local use or in external factors such a climate. Local dynamics are what are going to determine the water use in the area. If we introduce a new use, we want to understand how that use will impact the groundwater system, how it impacts the local stream-flow, and  then how those changes will impact existing users.

Kara Capelli: Many areas in the Great  Lakes basin are already seeing some of these local effects .

Howard Reeves: Groundwater pumping has had very little effect on the overall water  budget  in the Great Lakes but if we look locally at the Chicago-Milwaukee areas, we see the groundwater levels have declined in the deep aquifers there as much as 1,000 feet.


As part of thee project, we developed a groundwater flow model for this area. If the pumping were to increase as anticipated in the region, water levels in these aquifers are estimated to decline an additional 100 feet by 2040. If you increase the drawdown to decrease the pumping cost, so the water becomes more expensive for the people who rely on that, it also has the potential to lower the water quality by inducing the flow from lower quality areas towards the pumping wells.

Kara Capelli: Understanding the effect of climate variation on water use, lake levels, stream-flow and groundwater levels in the Great Lakes basin was also a part of this five-year investigation.

Howard Reeves: The Great Lakes is so large that climate is a major factor determining water levels and flow in the system. We are not trying to predict what would happen under  a clearly decreasing water levels or clearly increasing, but  rather illustrate the variability that we have  seen in the past and  help people understand  that there will  be variability in the future.


Kara Capelli: Information from studies like this one that examine water quantity and quality is crucial for making science-based decisions about water use. Results of the study will improve the ability to forecast the balance of water supply and demand for future  economic and environmental uses.

Howard Reeves: USGS provides this information to water managers and the public to try to help understand how  the system will change in the future  in response to new use or changes in use or changes in the climate. Most water management decisions are made in the local level. Ultimately, water managers and  the society will have to decide if changes to stream ecology, let’s say, or impacts on other users are acceptable or not when they make a water management decision.

Kara Capelli: This water availability study was conducted through the USGS Groundwater Resources program.


Reports from this project as well as additional information on USGS water availability studies in the Great Lakes basin are available online at More information about the Groundwater Resources Program is available online at


An don't forget to follow the USGS on Twitter at or visit our other social media channels at

I'm Kara Capelli and this Corecast is a product of the US Geological Survey, Department of the Interior.  

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