Lake Michigan is one of the five Great Lakes in North America and the only one located entirely within the United States. At 22,300 square miles, it is the second largest of the Great Lakes by area and the third largest by volume, containing 1,180 cubic miles of water. With such a massive amount of water contained in the lake, many may wonder exactly how long it would take to completely drain it. In this article, we will explore the key facts and figures around Lake Michigan and do the math to determine how long it would take to empty it completely.
Key Statistics on Lake Michigan
Here are some key statistics on Lake Michigan:
- Surface area: 22,300 square miles
- Average depth: 279 feet
- Maximum depth: 923 feet
- Volume: 1,180 cubic miles
- Shoreline length (including islands): 1,640 miles
- Primary outflow: Straits of Mackinac into Lake Huron
Knowing the volume of the lake and its primary outflow will allow us to estimate the drainage time.
Outflow Through the Straits of Mackinac
The primary outflow of water from Lake Michigan is through the Straits of Mackinac, which connect it to Lake Huron. The flow rate through the straits can vary depending on water levels, but averages around 72,000 cubic feet per second. This is over 2 trillion gallons per day being discharged through the straits into Lake Huron.
To determine the total drainage time, we need to know the volume of Lake Michigan in cubic feet:
- Volume: 1,180 cubic miles
- 1 cubic mile = 147,197,952,000 cubic feet
- Total volume in cubic feet = 173,693,383,552,000 cubic feet
Given an outflow rate of 72,000 cfs through the Straits of Mackinac, we can now calculate the drainage time:
- Lake Michigan volume: 173,693,383,552,000 ft3
- Outflow rate: 72,000 ft3/s
- To drain 173,693,383,552,000 ft3 at 72,000 ft3/s would take:
- 173,693,383,552,000 ft3 / 72,000 ft3/s = 2,414,076 hours
- 2,414,076 hours / 24 hours per day = 100,586 days
- 100,586 days / 365 days per year = 275 years
Conclusion
Based on the volume of Lake Michigan and the outflow rate through the Straits of Mackinac, it would take approximately 275 years to completely drain the lake. This assumes the outflow rate remained constant at 72,000 cubic feet per second until the lake was emptied. In reality, the drainage rate would slow as the lake level dropped and the outflow pressure decreased, so full drainage would likely take even longer. Nonetheless, this estimate gives a sense of the massive scale of Lake Michigan and how much water is contained in the Great Lakes!
Other Major Outflows from Lake Michigan
In addition to the outflow through the Straits of Mackinac, there are some other significant flows of water leaving Lake Michigan:
Chicago River System
The Chicago River System drains into Lake Michigan and historically flowed west and south into the Mississippi River watershed. To prevent sewage and wastewater from flowing into Lake Michigan, the flow of the river was reversed in 1900 through civil engineering projects. The Chicago Sanitary and Ship Canal now forms an outflow from Lake Michigan down the Chicago River and into the Des Plaines River, ultimately connecting to the Mississippi River. This diversion averages around 3,200 cubic feet per second.
Indiana Harbor and Ship Canal
This canal provides an outflow from Lake Michigan at East Chicago, Indiana. It was constructed between 1901 and 1906 and is used heavily for harbor and shipping purposes. The flow out of Lake Michigan averages around 500 cubic feet per second.
Impact on Drainage Time
The additional outflows through the Chicago canal and Indiana harbor combine for around 3,700 cubic feet per second. If we factor this into the total outflow from Lake Michigan, the new drainage calculation would be:
- Total outflow = 72,000 (Straits of Mackinac) + 3,700 (Other outflows) = 75,700 cubic feet per second
- New drainage time = 173,693,383,552,000 ft3 / 75,700 ft3/s = 2,295,543 hours
- 2,295,543 hours / 24 hours per day = 95,648 days
- 95,648 days / 365 days per year = 262 years
By factoring in the other major outflows, the estimated drainage time for Lake Michigan decreases slightly to 262 years.
Drainage By Pumping
In addition to gravity drainage through outflow channels, Lake Michigan could theoretically be drained faster by active pumping. Here are some scenarios for drainage times by pumping:
Using Large Scale Pit Dewatering Pumps
Some of the biggest pumps used for dewatering open pit mines can pump 100,000 gallons per minute (22,000 cubic feet per second). If an array of these pumps were set up along the shoreline of Lake Michigan and pumped continuously, the drainage calculations would be:
- Pumping rate: 22,000 cubic feet per second
- Total volume: 173,693,383,552,000 cubic feet
- Drainage time: 173,693,383,552,000 ft3 / 22,000 ft3/s = 7,895,153 hours
- 7,895,153 hours / 24 hours per day = 328,965 days
- 328,965 days / 365 days per year = 901 years
Using a network of large 100,000 gpm pit dewatering pumps, Lake Michigan could be drained in around 900 years.
Using Smaller Agricultural Irrigation Pumps
Typical agricultural irrigation pumps have more modest capacities of around 1,000 gpm (2,200 cubic feet per second). Arranging an array of these smaller pumps along the lakeshore would have the following drainage effect:
- Pumping rate: 2,200 cubic feet per second
- Drainage time: 173,693,383,552,000 ft3 / 2,200 ft3/s = 78,995,199 hours
- 78,995,199 hours / 24 hours per day = 3,291,466 days
- 3,291,466 days / 365 days per year = 9,018 years
With many smaller 1,000 gpm irrigation pumps, Lake Michigan could potentially be drained in around 9,000 years.
Using Small Sump Pumps
For a more extreme scenario, we can consider an array of small electric sump pumps, each with a capacity of just 10 gallons per minute (0.22 cubic feet per second). The drainage figures would be:
- Pumping rate: 0.22 cubic feet per second
- Drainage time: 173,693,383,552,000 ft3 / 0.22 ft3/s = 789,951,990,000 hours
- 789,951,990,000 hours / 24 hours per day = 32,914,666,250 days
- 32,914,666,250 days / 365 days per year = 90,159,103 years
With small electric sump pumps, draining Lake Michigan would take over 90 million years!
Pumping Conclusions
Using active pumping, the drainage time for Lake Michigan could be reduced from over 275 years for gravity drainage to as little as 900 years with huge pit pumps. Smaller pumps would take much longer, with small sump pumps requiring tens of millions of years to drain the lake. In all cases, the massive volume of water contained in Lake Michigan still makes complete drainage an extremely lengthy process.
Lowering Lake Michigan Levels
While completely draining Lake Michigan may seem fanciful, there are periodic discussions around intentionally lowering lake levels to restore shorelines or alleviate coastal flooding. Here are some key considerations around feasibly lowering the lake:
Current Low Water Level Impacts
Lake Michigan recently experienced record low water levels from 2013-2020. Impacts included:
- Exposed and wider beaches
- Reefs and shoals emerging, posing boating hazards
- Marinas and harbors having reduced access and more dredging needs
- Disruptions to commercial shipping and hydropower production
Legal Constraints
There are legal agreements between the U.S. and Canada that regulate water levels in the Great Lakes. Actions to intentionally lower Lake Michigan levels would likely violate the International Joint Commission treaty unless agreed upon by both nations.
Feasible Reduction Scenarios
While large intentional reductions are unlikely, some smaller scenarios could be feasible:
- Reducing outflows through Chicago River locks and dams by 10-20% during low water years
- Opening the Portage Lake control structure to increase outflows from Lake Superior into Lake Huron/Michigan
- Drawing down the lake 1-2 feet to provide periodic beach restoration
However, even these modest reductions require extensive study of potential impacts.
Major Factors Limiting Lake Level Control
Some key factors that make it difficult to control Lake Michigan’s water levels:
- Massive scale and volume of water in the lake
- Variability in precipitation, runoff, and evaporation
- Outflows divide between Lake Huron and Lake Erie
- Requirement to work jointly with Canada
Environmental Impacts of Draining Lake Michigan
Conceptually draining Lake Michigan provides an interesting thought experiment to grasp its immense scale. However, attempting to intentionally drain the lake would have monumental environmental impacts:
Loss of Habitat
Draining Lake Michigan would destroy the habitat for many fish species and other aquatic life. The lake contains over 85 species of fish including prized sportfish like salmon and trout. These species would lose their entire ecosystem.
Shipping and Transportation Disruptions
With over 1,500 miles of shoreline and many harbors, Lake Michigan supports immense commercial shipping and recreational boating. Draining the lake would devastate these industries.
Disappearance of Coastal Wetlands
The shoreline contains extensive coastal wetlands that provide habitat for birds and filter runoff entering the lake. These sensitive ecosystems rely on lake levels and would be destroyed if it were drained.
Compacted Lakebed Soils
The soft lakebed sediments would compact under their own weight without the buoyancy of water. This would make the lakebed extremely difficult to restore if the lake were refilled.
Loss of Water Supply
Many towns and cities draw drinking water from Lake Michigan. Draining the lake would force over 40 million people to find new water sources.
Violation of Conservation Laws
Draining Lake Michigan would violate a range of federal, state, and international conservation laws focused on protecting the Great Lakes ecosystems.
Conclusion
Draining massive Lake Michigan would be an enormous undertaking requiring hundreds of years through natural outflow, decades with large pumps, or millennia using small pumps. Large intentional reductions in lake level face major legal, environmental, and economic obstacles. While the thought experiment provides perspective on the lake’s enormous scale, attempting to actually drain Lake Michigan would have catastrophic ecological consequences. The lake supports invaluable natural habitats, communities, industries, and recreation that would be devastated by draining it. Responsible management focused on conservation is crucial for ensuring Lake Michigan remains a sustainable freshwater asset for generations to come.