SCIENTISTS STUDYING Lake Michigan are developing disturbing theories about the record high water levels swelling the Great Lakes: They may not be record high levels after all.
These researchers believe that lake levels were much higher before scientists started measuring them in the middle of the 19th Century. They fear that the swollen lakes, which pose grave threats to long stretches of lakefront property, could rise as much as 5 feet over the next 100 years.
Although the theories are far from proven and further research is needed, scientists say that if they turn out to be correct, beaches, homes, buildings and roads along the shorelines of eight states and Canada could be submerged.
Vast stretches of the Chicago area, including entire lakefront neighborhoods and much of Lake Shore Drive, could be flooded.
And the Chicago River, artificially reversed in a landmark engineering feat in 1900, will disgorge massive torrents of lake water down through the Illinois River, spreading floods along its length.
In the face of such a massive rise in water levels, lake experts say, protective measures such as seawalls or dikes could be constructed. But the costs would be so prohibitive–at least $2 million per mile of shoreline, by some estimates–that such structures could be built only in limited areas to protect small portions of the lakefront.
The Great Lakes are abnormally high, as even the most infrequent visitors to what`s left of the Chicago area`s beaches have noticed. They have been surpassing record monthly levels all spring and are nearly as high as they have ever been in the 126 years scientists have been measuring them.
Experts forecast that all but Lake Ontario will reach all-time record levels by the time they reach their seasonal peaks in June and July.
The surface of Lake Michigan, for example, stood at 580.86 feet above sea level as of late May, nearly 2 1/2 feet higher than its average level during the period of recordkeeping. The water is predicted to rise another 6 inches by July, which would exceed the previous record high of 581.05 feet, set in July, 1974.
Such record levels are sobering enough for property owners in cities like Grand Haven, Mich., many of whose homes have been lost to ravaging effects of lake erosion. Each one-foot rise in the lake can easily chew away 20 feet of beach.
But scientists believe that the entire 126-year period of recordkeeping
–the period when most of the shoreline area was planned and intensively developed–could well represent a low cycle in the longer history of the Great Lakes. Only recently have researchers begun charting the ancient histories of the Great Lakes, and what they have found is unnerving.
Geologic evidence suggests that every 500 years over the last 2,000, Lake Michigan seems to have risen to about 585 feet, or nearly 5 feet higher than its current levels and stayed near there for decades. Those peak periods, first documented by geologist Curtis Larsen of the U.S. Geological Survey in 1983, occurred from 400 and 650 A.D., 900 to 1200 and 1450 to 1800.
”If the future repeats the past,” Larsen said in a recent interview,
”it would seem that for the next century, the dominant movement will be upward. It kind of puts in perspective the kind of levels we are seeing now.” No scientist is predicting imminent floods, or even that the Great Lakes will definitely follow these apparently regular historical trends. Too little is known, for example, about climate during the last 10,000 years–the period Larsen studied–to determine if history will repeat itself.
But a broad consensus seems to be emerging that what geologists and hydrologists always assumed to be true about the Great Lakes may not be true after all.
Old ideas that the Great Lakes basin is a fixed, unmoving land mass and that the lakes rise and fall in regular, dozen-year cycles are being abandoned amid growing recognition that there is still much to be learned.
”If the cycle analysis were completely correct,” noted Frank Quinn, chief hydrologist at the Great Lakes Environmental Research Laboratory in Ann Arbor, Mich., ”the lake levels ought to be falling now. It`s 12 years now since 1973, when we had a string of record levels. But we are obviously not getting low levels now.”
”Scientists simply assumed,” Larsen said, ”that they knew the Great Lakes so well that they really didn`t need to study them any more. The problem has been that so much of the environmental history and geology of the Great Lakes was based on 19th Century geology theories that have been updated and hammered to fit over the years. But those theories don`t fit.”
Larsen, a geologist in the Reston, Va., office of the U.S. Geological Survey, first started studying the Great Lakes in the early 1970s as a graduate student at the Univerity of Chicago. He began collecting soils and lake sediments in an area north of Waukegan, where beach ridges built up over thousands of years had protected ancient soil samples from being washed away. The samples were examined to determine whether they came from ancient marshes–which meant they had been under water–or from stream banks–which meant they had been above water. They were then dated using the radiocarbon process, which can fix the age of an ancient geologic or archeologic sample by measuring the extent to which radiocarbon atoms in the sample have decayed.
From this analysis, the results of which were published last year, Larsen discerned the long-range ebb-and-flow patterns that could threaten dire consequences if they are repeated in the future.
Quinn has deemed Larsen`s findings ”very reasonable,” but he, like Larsen, is careful to back away from firm predictions. ”It`s very hard to say what is going to happen,” Quinn said, ”even though these rises did seem to occur at about 500 years apart.”
Quinn noted that two factors could mitigate the dramatic rise in the lake levels, if it occurs at all. Through various navigation dredging projects, he noted, the levels of Lakes Michigan and Huron, which hydrologists consider a single lake system, have been artificially lowered by almost a foot.
Also, the capacity of the St. Clair River, the principal natural drainage point for the two lakes, has been increased through dredging and widening projects, permitting a greater outflow of water.
Moreover, both Quinn and Larsen point out, significant questions linger about both the ancient and future climate trends in the Great Lakes region.
”The trends I`m dealing with ought to be related to past changes in climate–periods of cooler, wetter climate,” Larsen said. ”But we`re only now beginning to study climate for this time period, through studying peat bogs and cores taken from the bottom of Lake Michigan.
”There is a chance for a worst-case scenario, but we need to understand the hydrology of the lake better, the climatic record. We need studies from other parts of the Great Lakes basin to see if similar kinds of changes are present there.”
”We do know,” said Quinn, ”that the 30-year period ending in 1960 was warmer than normal and we had low lake levels. Now we`re in a cool, wet regime, and we have had relatively high lake levels. What we don`t know for certain is which regime is closer to normal.”
Whatever the historical temperature trends might have been, the much-discussed ”greenhouse effect” could alter them and skew all predictions.
The greenhouse effect theory suggests that greater amounts of carbon dioxide pumped into the upper atmosphere by the increasingly industrialized nations of the world are trapping the earth`s heat, encasing the earth in a thermal blanket that is causing a gradual increase in global temperatures.
Scientists generally agree that some global warming is occurring–and causing a slow but steady rise in worldwide ocean levels as it accelerates the melting of the polar ice caps. But the extent of this greenhouse warming is unclear.
”If the greenhouse effect occurs, it would lower lake levels due to increased evaporation,” Quinn said. ”But there`s no evidence in temperature records on the Great Lakes that we`re getting any increased temperatures based on the greenhouse effect.”
Lakeshore residents are not, of course, absolute hostages to the natural vicissitudes of the Great Lakes. Seawalls and dikes could be built along portions of the shoreline, such as McCormick Place, that authorities felt could not be sacrificed to the rising waters.
Such structures would be effective in protecting limited areas, lake experts say, but, at a cost of about $400 a foot, they are far too costly to be considered for large stretches of lakefront property.
”There is no economically feasible way to protect the entire Lake Michigan shoreline,” said Orrin Pilkey, a Duke University geologist and expert on shoreline problems. ”You could take the Dutch solution and build massive dikes. But the Dutch spent something on the order of our entire defense budget to do that. It`s not likely to be an American priority.”
The lake levels can be reduced by increasing outflows at points such as the Chicago River and holding back water in Lake Superior. But those remedies are not without their side effects–such as flooding down the Illinois River
–and, at any rate, they would provide only limited relief of a few inches, scientists say.
”Over the short term, there`s very little impact we can have on lake levels,” said Martin Jannereth of Michigan`s Department of Natural Resources. ”If we were to apply all the possible controls and ignore the adverse impacts, over the next six months we could probably lower Lake Michigan and Huron maybe four to five inches. But we would cause a lot of flooding down the Illinois River.”
Piping Great Lakes water to more arid parts of the country, an idea floated every few years by officials of western states but steadfastly resisted by Great Lakes governors, would have no appreciable effect on the water levels, scientists say.
”You just couldn`t pump enough water to make a real difference,” said Charles Collinson, principal geologist for the Illinois Geological Survey and an expert on Great Lakes erosion. ”It`s like a pinhole in a bathtub.”
Whether or not the longer-range predictions about lake levels prove correct, the Great Lakes will undoubtedly recede from their current record levels to more normal readings in the short term, the scientists say. The process will take from 4 to 10 years, depending on the amount of precipitation during the period, Quinn said.
But that expected drop leaves the scientists with a further concern: Will city planners and lakefront residents have the foresight to plan for the worst when things begin to look better?
”I have studied press clippings from three high-water periods–1952, 1974 and 1985,” Larsen said. ”At each peak period, there has been a public outcry over shore erosion and then a flurry of activity to try to stop it. Then the lake levels fall back in a year or two and nothing more is done.
”It`s maddening because we haven`t come to grips with long-term lake patterns. We take a postage-stamp approach.”
