Is Lake Michigan draining?
Written by Milwaukee Journal Sentinel   
Monday, 18 September 2006 17:15

People are worried Lake Michigan water levels are lower than normal, but most have no grasp of what "normal" is for the world's fifth largest freshwater lake.

When you chart the lake's levels over the past century, the picture you get looks something like a cardiogram - almost rhythmic pulses of highs and lows. It is never a flat line for a lake where levels can swing by about 6 feet in just a matter of years. That means the lake is rarely at its "normal" level; it's either on the way above it, or on the way below it. At the moment, the lake is about 18 inches below it but still about a foot above its all-time low for September, recorded in 1964.

Yet there are signs of trouble ahead.

The U.S. and Canadian governments are about to embark on a $14.7 million study of water levels on the upper Great Lakes, and one of the first things scientists will be looking at is the theory of an expanding drain hole in Lakes Michigan and Huron that the Army Corps of Engineers might have accidentally opened while dredging a shipping channel in the St. Clair River in the early 1960s.

The St. Clair River is the main outflow for Lakes Michigan and Huron, which are actually two lobes of one big lake, connected by the Straits of Mackinac.

A Canadian property owners group called the Georgian Bay Association contends that the 1960s St. Clair River dredging removed the rocky riverbed down to erosion-prone clay and sand, and the river has been carving a deeper channel ever since. The group's argument was bolstered by $200,000 hydrologic study it released last year, conducted by the respected engineering firm of W.F. Baird & Associates Coastal Engineers, that shows ongoing erosion has created a faster-flowing, bigger river that is steadily draining water from Lakes Michigan and Huron.

Everyone agrees that the 1960s dredging permanently dropped the long-term average levels of Lakes Michigan and Huron, because it did create a wider drain hole. Federal engineers have long believed that it, combined with earlier dredging and riverbed mining on the St. Clair, resulted in a permanent loss of about 16 inches from Lakes Michigan and Huron's long-term average.

The Georgian Bay study, however, argues that Lakes Michigan and Huron have dropped about another 12 inches since the dredging in the early 1960s, and the loss is continuing at a rate of about an inch every five years. In other words, on any day you go to the shore of Lake Michigan, the water is about 28 inches lower than it would be had its outflow never been tampered with.

Authors of the Georgian Bay study say the problem has been masked during much of the 1980s and `90s because Lakes Michigan and Huron were well above their historic average level.

But how can anyone tell what is missing when lake levels are in constant flux? The Georgian Bay study measured Lakes Michigan and Huron basin levels against Lake Erie's.

Although both basins of water fluctuate, the relative difference between the two had historically remained constant. If, for example, Lakes Michigan and Huron dropped 12 inches, so did Lake Erie. That is no longer happening.

"There is no doubt due to dredging ... the lakes (Michigan and Huron) have been lowered," said Frank Quinn, a retired hydrologist for the U.S. Army Corps of Engineers and National Oceanic and Atmospheric Administration who was a paid consultant for the Georgian Bay study.

No major dredging has occurred in more than 40 years, but Quinn said measurements show the difference in levels between Lake Erie and Lakes Michigan and Huron continues to shrink.

"The real question is," Quinn said, "why have water levels in Michigan-Huron dropped since the 1990s, relative to Lake Erie?"

Georgian Bay study author and hydrologist Rob Nairn blames it on a disappearing river bottom.

"It's erosion," he said, "but why it's occurring and how long it will continue is something we have to study."

That study is about to begin.

The International Joint Commission, which oversees U.S.-Canadian boundary waters issues, is embarking on a five-year analysis of overall water levels in the upper Great Lakes. One of the first things it will look at is the St. Clair question.

There are a number of potential explanations beyond ongoing erosion for the shrinking difference in water levels between Lakes Michigan and Huron and Lake Erie, including the theory that the Lake Erie drainage basin is receiving more precipitation than the Michigan-Huron basin.

Climate change could also affect lake levels. Warm winters mean less ice, and that can lead to increased evaporation.

Another explanation is that the earth under Lakes Michigan and Huron is rising faster than the riverbed of the St. Clair as the region literally rebounds from the last glaciers.

All of these will be examined in the study by the international commission, said Dennis Schornack, the commission's U.S. chairman.

Retired Army Corps hydrologist Roger Gauthier, however, worries the upper Great Lakes study is too broad to actually determine precisely what is going on in the St. Clair River. That, he said, would take a full-blown "geophysical investigation" by the Corps of Engineers into what precisely is happening in the riverbed. He said such a study, which could be done in conjunction with the international commission's upper Great Lakes study, has been proposed by Michigan Congresswoman Candice Miller, but lawmakers so far have been cool to the estimated $2.5 million it would take for the corps to do the job.

Gauthier, who now works for the Great Lakes Commission, said the erosion question is one the region can't afford to ignore in a century when water is becoming an increasingly precious commodity. He said the raging debate over Great Lakes water diversions to cities outside the region "pales in significance" to what could be happening on the St. Clair River right now, in terms of the volume of water being lost.

"This St. Clair outlet is one of the most sensitive places in the Great Lakes, in terms of affecting the retention of water on the lakes," he said. "If we have a situation where we have reduced water supply, retaining water on Michigan and Huron is going to be the most significant concern we have."

Gauthier said we might be able to fix any erosion problems by placing structures in the river bottom to slow the flow and raise lake levels.

"We can engineer a solution," he said.

We actually already have.

Retired hydrologist Quinn said the corps designed such a project in the late 1960s and even constructed a working scale model of the St. Clair River, replete with flowing water.

But he said there was a reason it was never built. Water levels soared so high in the 1970s and `80s that the public actually wanted more done to lower lake levels.

Gauthier said anything that would be built today would allow for fluctuations in the flow to maintain more constant - if unnatural - lake levels. Such controls are already employed to regulate the levels of Lakes Superior and Ontario.

He knows that could lead to a fierce debate among shorefront property owners, industry and environmentalist who all might have different ideas of what Lakes Michigan and Huron's new "normal" should be.

"You can't please all the people all the time, so somebody is going to get gored," he said. "The social costs have to be factored in."

 
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