The Not-So-Great Lakes: Rise and Fall of the Great Lakes
May - June 2008
This is the second article in a five part series
Even small changes in the levels of the Great Lakes are of huge importance to Michigan’s economy and the ecology of near-shore communities. Shipping, other industries, recreational boating, erosion, property values, coastal wetlands and wildlife are all affected by the rise and fall of the water.
When water levels drop, coastal wetlands dry up and become overgrown with shrubs and emergent plants like cattails. Valuable habitats for spawning fish and waterbirds are often lost. Beaches increase in size and may be invaded by exotic plants like Phragmites that take over nesting grounds for shorebirds. Fish can’t swim up certain spawning streams, and mudflats are formed that may be sites for diseases such as botulism. Algae in the shallows breaks off and piles up on beaches. During high water times, barrier dunes that protect rare coastal habitats are eroded, and nesting habitats for shorebirds may be flooded.
The decline of water levels in Lakes Huron and Michigan and the apparent recent increase in the level of Lake Superior are hot topics of discussion. Concerns about global warming provide a new backdrop for the finger-pointing that always accompanies lake level changes. The causes of the fluctuations that worry shoreline property owners, government officials, conservationists, and politicians are complicated. But if we are to protect the earth’s largest body of freshwater (excluding polar ice caps) the general public needs a better understanding of the dynamics.
Understanding Great Lakes water level fluctuations requires comparing data on a variety of timescales ranging from hours to thousands of years. Unfortunately, humans don’t like to think that way. We are confused by short-term changes caused by storms and momentum-driven wave actions (seiches), seasonal changes caused by variation in snow melt, precipitation and evaporation, and long-term changes caused by major climate trends and rebounding of the earth’s crust after the receding of the glaciers. And we have made the naturally-complex hydrology even more complicated by dredging, and building control structures at the outlets of Lakes Superior and Ontario.
Trends And Cycles
A recent study by the U.S. Geological Survey provides insights into the “nature of the beast.” Scientists examined sedimentary deposits and other information to reconstruct records of past variability in climate and lake levels. They found that the recorded fluctuations of the past century have been far less dramatic than those of other periods of similar length over the past several thousand years. Put another way, current conditions are well within the natural variability of long-term cyclical changes.
Does that mean global warming is a hoax? Not by any means. It simply shows that the climate and hydrology of the Great Lakes have always varied substantially.
About 4,500 years ago the level of Lakes Michigan and Huron was about 13 feet higher. Then came 500 years of rapid decline before the level approached what we think of as an “historical average.” There were high phases from 3,300 to 2,300 years ago, from 2,000 to 1,000 years ago, and from 800 years ago to present.
The data reveal fairly pronounced rise-and-fall cycles of about 160 +/- 40 years in duration, and within those, short-term fluctuations of 32 +/- 6 years in length. Thus, there seem to be cycles within cycles, and our historical data-set for the mid-1980s to present seems to correspond to one 32-year cycle within a 160-year cycle.
High water levels in Lakes Michigan and Huron have been recorded in the late 1800s, late 1920s, and 1950s, and from the early 1970s to mid 1980s. The two highest levels occurred in 1886 and 1986. The lows came in 1926, 1934, 1964, 2003 and this past year. The level is now about two feet lower than the long-term historical average. Lake Superior is about 11 inches below its average despite rising 6 inches in the past year. Similarly, Lake Erie is slightly below its long term average, but in May of 2007 the level was slightly above that of May 2006.
The Link Between Climate And Water Levels
While some aspects of the geologic and historic records are not well understood, it is clear that the water levels of the Great Lakes are strongly linked to climate variability. The large-scale drop in Lake Michigan between 4,500 and 4,000 years ago was the result of a well-documented drought that affected much of North America and was perhaps global in scale. The drought activated dunes, caused widespread fires, and changed the composition of forests. Southern Michigan experienced another forest-altering drought with a corresponding drop in Lake Michigan about 1,050 years ago. And there were wide fluctuations in water levels between 1,000 and 700 years ago during what geologists call the “Medieval Warm Period.”
The causes of such climate variability are likely rooted in the dynamics of the ocean-atmosphere system. Differences in sea and land temperatures, likely related to solar radiation and perhaps volcanic activity, cause changes in atmospheric circulation. The degree to which man-caused global warming affects this variability is the subject of sometimes fierce debate, but it is safe to say that even without man-caused changes in the atmosphere, the earth’s climate and Great Lakes water levels were and always will be highly variable.
Rise Of The Earth’s Crust Affects Lake Superior
Another source of water level variability is associated with the retreat of the glaciers. When the massive ice bodies moved north, the depressed land crust slowly rebounded as the weight of the ice was removed. This phenomenon has been most pronounced in the northern part of the Great Lakes basin where the glaciers were thickest, heaviest, and last to retreat. The rise in the crust in parts of the Lake Superior watershed has been more than 21 inches per century. It is most pronounced on the east side of the lake. Lake Superior is like a tipped cup, with the water coming closer to the edge of the cup on the west side and farther from the edge on the east side. This tipping has less significance for the other Great Lakes as there is little or no movement in the southern parts of the Great Lakes basin.
Short-term Fluctuations
During our relatively brief period of actual record-keeping, the difference between the record high and low monthly averages were 3.8 feet for Lake Superior, 6.2 feet for Lakes Michigan and Huron, 6.0 feet for Lake Erie, and 6.5 feet for Lake Ontario. Every year, storms and other wind shifts cause seiches or short-term water surges against downwind shorelines that raise Great Lakes water levels several feet for just minutes to a few hours. In Lake Erie, storm surges of up to 8 feet have been recorded with a similar drop at the upwind end of the lake.
A “normal” seasonal difference in levels of the Great Lakes is about one foot with the peak occurring in the summer and the low in winter. This fact surprises many people who assume evaporation is greater and water levels lower in summer. Actually, evaporation increases as dry winter air masses pass over the Great Lakes, and spring runoff of melting snow and ice boosts summer water levels. Cold weather that increases ice cover minimizes winter-time evaporation and can reduce seasonal water level differences.
Human Caused Changes
The extensive dam-building, dredging, and other man-caused changes to runoff in the Great Lakes watershed aren’t nearly as important as climate and weather in determining the magnitude of water level fluctuations. The levels of Lakes Superior and Ontario can be adjusted somewhat by a series of control gates in dams, but this can only change the levels of those lakes less than a foot over periods of six months to a year. Lake Erie water levels could be influenced by manipulation of gates at the Welland Canal and the upper reaches of the Niagara River, but those structures were built to facilitate shipping and production of hydro-electric power, and even if lake level control was made a top priority, they likely could not change Lake Erie much.
Lakes Michigan and Huron were lowered about 16 inches by dredging of the St. Clair River between the 1880s and 1962. The 16-inch drop has been acknowledged by the U.S. Army Corp of Engineers which oversaw the effort in modern times. But the agency has not yet agreed with a Canadian citizens’ group, the Georgian Bay Association, which released a study three years ago that suggested the dredging caused ongoing erosion (downcutting) that is lowering the water level even more. The Association’s report says the river bottom may have down-cut about one centimeter per year between 1975 and 2000 and three centimeters per year between 2000 and 2007.
Since Lakes Michigan and Huron are now within a foot of their record low, and about five feet below their record high in 1986, officials are being pressed to take a close look at the erosion question in the St. Clair River and the diversion of about 2.1 billion gallons per day of Lake Michigan water to Chicago and its suburbs. That diversion was authorized by a U.S. Supreme Court consent decree, and is about equal in quantity to the loss that some environmental groups charge is occurring due to erosion of the St. Clair River’s bottom. The International Joint Commission of Canada and the U.S. is starting a major study to determine whether the regulation of Lake Superior outflows can be improved, investigate physical changes in the St. Clair River that might be affecting water levels and flows, and develop and test potential new regulations under various climate change scenarios. The study area includes all of the Great Lakes and interconnecting waters bordered by Michigan downstream to Niagara Falls and is outlined at www.ijc.org/en.activities/upperlakes/upperlakes.htm.
Everyone’s Problem
The IJC study should be considered important to all Michigan citizens. Millions of people depend on vulnerable lakeshore and harbor facilities for drinking water, electricity, sewage treatment, manufacturing supplies and a host of other services that are affected by high as well as low water levels. Historically, we have invested in property and infrastructure based on a poor understanding and appreciation for the variability in Great Lakes levels. From beach-front property owners to public officials operating sewage treatment plants, we have not planned for worst-case scenarios. We build just above the “100-year flood level,” reasoning that since we won’t live 100 years, we won’t have a problem. But thousands of homeowners in Michigan can testify that they have lived through several “100-year floods.” The fact is that predicting fluctuations based on about 140 years of data is silly when the geologic history of water level fluctuations in the Great Lakes is considered. Advice and regulations to protect shoreline structures during high water times are outdated, and planning to mitigate the impacts of low water levels has been inadequate.
Dr. Patrick J. Rusz
Director of Wildlife Programs
This is the second article in a five part series
Even small changes in the levels of the Great Lakes are of huge importance to Michigan’s economy and the ecology of near-shore communities. Shipping, other industries, recreational boating, erosion, property values, coastal wetlands and wildlife are all affected by the rise and fall of the water.
When water levels drop, coastal wetlands dry up and become overgrown with shrubs and emergent plants like cattails. Valuable habitats for spawning fish and waterbirds are often lost. Beaches increase in size and may be invaded by exotic plants like Phragmites that take over nesting grounds for shorebirds. Fish can’t swim up certain spawning streams, and mudflats are formed that may be sites for diseases such as botulism. Algae in the shallows breaks off and piles up on beaches. During high water times, barrier dunes that protect rare coastal habitats are eroded, and nesting habitats for shorebirds may be flooded.
The decline of water levels in Lakes Huron and Michigan and the apparent recent increase in the level of Lake Superior are hot topics of discussion. Concerns about global warming provide a new backdrop for the finger-pointing that always accompanies lake level changes. The causes of the fluctuations that worry shoreline property owners, government officials, conservationists, and politicians are complicated. But if we are to protect the earth’s largest body of freshwater (excluding polar ice caps) the general public needs a better understanding of the dynamics.
Understanding Great Lakes water level fluctuations requires comparing data on a variety of timescales ranging from hours to thousands of years. Unfortunately, humans don’t like to think that way. We are confused by short-term changes caused by storms and momentum-driven wave actions (seiches), seasonal changes caused by variation in snow melt, precipitation and evaporation, and long-term changes caused by major climate trends and rebounding of the earth’s crust after the receding of the glaciers. And we have made the naturally-complex hydrology even more complicated by dredging, and building control structures at the outlets of Lakes Superior and Ontario.
Trends And Cycles
A recent study by the U.S. Geological Survey provides insights into the “nature of the beast.” Scientists examined sedimentary deposits and other information to reconstruct records of past variability in climate and lake levels. They found that the recorded fluctuations of the past century have been far less dramatic than those of other periods of similar length over the past several thousand years. Put another way, current conditions are well within the natural variability of long-term cyclical changes.
Does that mean global warming is a hoax? Not by any means. It simply shows that the climate and hydrology of the Great Lakes have always varied substantially.
About 4,500 years ago the level of Lakes Michigan and Huron was about 13 feet higher. Then came 500 years of rapid decline before the level approached what we think of as an “historical average.” There were high phases from 3,300 to 2,300 years ago, from 2,000 to 1,000 years ago, and from 800 years ago to present.
The data reveal fairly pronounced rise-and-fall cycles of about 160 +/- 40 years in duration, and within those, short-term fluctuations of 32 +/- 6 years in length. Thus, there seem to be cycles within cycles, and our historical data-set for the mid-1980s to present seems to correspond to one 32-year cycle within a 160-year cycle.
High water levels in Lakes Michigan and Huron have been recorded in the late 1800s, late 1920s, and 1950s, and from the early 1970s to mid 1980s. The two highest levels occurred in 1886 and 1986. The lows came in 1926, 1934, 1964, 2003 and this past year. The level is now about two feet lower than the long-term historical average. Lake Superior is about 11 inches below its average despite rising 6 inches in the past year. Similarly, Lake Erie is slightly below its long term average, but in May of 2007 the level was slightly above that of May 2006.
The Link Between Climate And Water Levels
While some aspects of the geologic and historic records are not well understood, it is clear that the water levels of the Great Lakes are strongly linked to climate variability. The large-scale drop in Lake Michigan between 4,500 and 4,000 years ago was the result of a well-documented drought that affected much of North America and was perhaps global in scale. The drought activated dunes, caused widespread fires, and changed the composition of forests. Southern Michigan experienced another forest-altering drought with a corresponding drop in Lake Michigan about 1,050 years ago. And there were wide fluctuations in water levels between 1,000 and 700 years ago during what geologists call the “Medieval Warm Period.”
The causes of such climate variability are likely rooted in the dynamics of the ocean-atmosphere system. Differences in sea and land temperatures, likely related to solar radiation and perhaps volcanic activity, cause changes in atmospheric circulation. The degree to which man-caused global warming affects this variability is the subject of sometimes fierce debate, but it is safe to say that even without man-caused changes in the atmosphere, the earth’s climate and Great Lakes water levels were and always will be highly variable.
Rise Of The Earth’s Crust Affects Lake Superior
Another source of water level variability is associated with the retreat of the glaciers. When the massive ice bodies moved north, the depressed land crust slowly rebounded as the weight of the ice was removed. This phenomenon has been most pronounced in the northern part of the Great Lakes basin where the glaciers were thickest, heaviest, and last to retreat. The rise in the crust in parts of the Lake Superior watershed has been more than 21 inches per century. It is most pronounced on the east side of the lake. Lake Superior is like a tipped cup, with the water coming closer to the edge of the cup on the west side and farther from the edge on the east side. This tipping has less significance for the other Great Lakes as there is little or no movement in the southern parts of the Great Lakes basin.
Short-term Fluctuations
During our relatively brief period of actual record-keeping, the difference between the record high and low monthly averages were 3.8 feet for Lake Superior, 6.2 feet for Lakes Michigan and Huron, 6.0 feet for Lake Erie, and 6.5 feet for Lake Ontario. Every year, storms and other wind shifts cause seiches or short-term water surges against downwind shorelines that raise Great Lakes water levels several feet for just minutes to a few hours. In Lake Erie, storm surges of up to 8 feet have been recorded with a similar drop at the upwind end of the lake.
A “normal” seasonal difference in levels of the Great Lakes is about one foot with the peak occurring in the summer and the low in winter. This fact surprises many people who assume evaporation is greater and water levels lower in summer. Actually, evaporation increases as dry winter air masses pass over the Great Lakes, and spring runoff of melting snow and ice boosts summer water levels. Cold weather that increases ice cover minimizes winter-time evaporation and can reduce seasonal water level differences.
Human Caused Changes
The extensive dam-building, dredging, and other man-caused changes to runoff in the Great Lakes watershed aren’t nearly as important as climate and weather in determining the magnitude of water level fluctuations. The levels of Lakes Superior and Ontario can be adjusted somewhat by a series of control gates in dams, but this can only change the levels of those lakes less than a foot over periods of six months to a year. Lake Erie water levels could be influenced by manipulation of gates at the Welland Canal and the upper reaches of the Niagara River, but those structures were built to facilitate shipping and production of hydro-electric power, and even if lake level control was made a top priority, they likely could not change Lake Erie much.
Lakes Michigan and Huron were lowered about 16 inches by dredging of the St. Clair River between the 1880s and 1962. The 16-inch drop has been acknowledged by the U.S. Army Corp of Engineers which oversaw the effort in modern times. But the agency has not yet agreed with a Canadian citizens’ group, the Georgian Bay Association, which released a study three years ago that suggested the dredging caused ongoing erosion (downcutting) that is lowering the water level even more. The Association’s report says the river bottom may have down-cut about one centimeter per year between 1975 and 2000 and three centimeters per year between 2000 and 2007.
Since Lakes Michigan and Huron are now within a foot of their record low, and about five feet below their record high in 1986, officials are being pressed to take a close look at the erosion question in the St. Clair River and the diversion of about 2.1 billion gallons per day of Lake Michigan water to Chicago and its suburbs. That diversion was authorized by a U.S. Supreme Court consent decree, and is about equal in quantity to the loss that some environmental groups charge is occurring due to erosion of the St. Clair River’s bottom. The International Joint Commission of Canada and the U.S. is starting a major study to determine whether the regulation of Lake Superior outflows can be improved, investigate physical changes in the St. Clair River that might be affecting water levels and flows, and develop and test potential new regulations under various climate change scenarios. The study area includes all of the Great Lakes and interconnecting waters bordered by Michigan downstream to Niagara Falls and is outlined at www.ijc.org/en.activities/upperlakes/upperlakes.htm.
Everyone’s Problem
The IJC study should be considered important to all Michigan citizens. Millions of people depend on vulnerable lakeshore and harbor facilities for drinking water, electricity, sewage treatment, manufacturing supplies and a host of other services that are affected by high as well as low water levels. Historically, we have invested in property and infrastructure based on a poor understanding and appreciation for the variability in Great Lakes levels. From beach-front property owners to public officials operating sewage treatment plants, we have not planned for worst-case scenarios. We build just above the “100-year flood level,” reasoning that since we won’t live 100 years, we won’t have a problem. But thousands of homeowners in Michigan can testify that they have lived through several “100-year floods.” The fact is that predicting fluctuations based on about 140 years of data is silly when the geologic history of water level fluctuations in the Great Lakes is considered. Advice and regulations to protect shoreline structures during high water times are outdated, and planning to mitigate the impacts of low water levels has been inadequate.
Dr. Patrick J. Rusz
Director of Wildlife Programs