By Mary Muter, Georgian Bay Association
Back in 1999 when water levels began to decline, no one was surprised as the levels had been well above average for 30 years, and we all knew that Great Lakes water levels are cyclical. In others words we expected the decline. But when levels stayed low for five years and approached record lows, some people began to ask questions. And in the relatively shallow waters among the 30,000 islands on Georgian Bay, the impact of sustained low levels was significant. The main concern was that the wetlands not only dried up but also began to convert to grassy meadows. Wetland biologists told us that once that happened it would take a decade or more for the wetlands to re-establish if and when the water levels returned to more normal levels. And even more worrisome was the reality that the aquatic life forced out of these particular wetlands could not find similar habitat on the adjacent steep granite shorelines. Since wetlands are needed by over 70% of Great Lakes fish at some point in their life cycle for spawning, nursery or feeding habitat, we knew that this loss of wetlands could further threaten the already declining Georgian Bay/Lake Huron native fishery.
It was then that the Georgian Bay Association (GBA) began its own investigation into what might be causing this steep decline in water levels. It is a very complex topic, for many factors influence levels; so from our membership we formed a committee with several engineers reviewing extensive historical data.We came to the conclusion that, at the place where Lake Huron drains out, there appeared to be an increase in the conveyance capacity of the St. Clair River that could be contributing to the lower lake levels. Then GBA Foundation decided to retain the internationally respected coastal consulting engineering firm W.F. Baird and Associates to review our findings. This was a huge undertaking by a relatively small non-governmental organization (NGO), and GBA Foundation had certainly not done anything like it before. Baird then confirmed our findings and added more shocking ones. The research report is available on our website: www.georgianbay.ca.
According to the Baird Report, Lakes Michigan and Huron – considered one body of water because they are connected at the Straits of Mackinac – have permanently lost an additional 12 inches since 1970 because of ongoing erosion at the mouth of the St. Clair River. This erosion has gone undetected since the 1962 dredging for navigation.
All told, the dredging and erosion have accounted for a water loss from the lakes equivalent to 28 Lake St. Clairs or 1/4 of Lake Erie, according to the Baird Report.
Because the extra water moves so quickly through Lake St. Clair, the Detroit River, and Lake Erie on its way over Niagara Falls, it has not raised the levels of those waters appreciably, reported Dr. Rob Nairn, the principal researcher. A modest resurgence in Great Lakes water levels during the past two years is part of a natural cycle, but doesn’t mask the fact that the Huron/Michigan waters are still a foot below where they would be without the erosion, Nairn said. During the last half of 2005, the resurgence seems to have ebbed away. And the problem can’t be explained by natural forces, said Nairn. Geologists say that erosion in the St. Clair River basin stopped between 2,000 and 3,000 years ago. But it began again in the 1900s because of man-made factors including:
– Dredging of the channel to 27 feet deep to accommodate ships;
– Erosion at the sites of sand and gravel mining that took place in the river in the early part of the 1900s; and
– Erosion-control structures protecting beaches on lower Lake Huron that deprive the St. Clair River of sediment that normally would have washed into it and filled holes in the river bottom.
The Georgian Bay Association took the Baird Report to the International Joint Commission (IJC), and we were told that this level of work by an NGO was unheard of.We are pleased that the IJC recently announced a revised Upper Lakes Levels Study that includes best mitigation designs and costs.
Unfortunately we have learned that the IJC had looked at this loss of Huron/Michigan water on at least three previous occasions.The last time was in the early 1960’s, when they knew engineers were again lowering lake levels by dredging for the 27-foot channel. But at that same time the IJC discovered that Chicago was taking too much water; so it forced Chicago to cut back. Then water levels rose, and the interest in mitigation was lost. The problem has now come back as the ongoing erosion continues to allow more water out. Recent bathymetry data shared with us by the US Geological Survey show that additional erosion at the outflow of Lake Huron took place between 2000 and 2003.
We are hopeful that a solution can finally be put in place. The first action will be to cover over the eroding areas with hard rock substrate to stop the erosion of exposed soft clay. This may actually improve a resurgent sturgeon spawning habitat in the very deep, fast flowing part of the river, where it is now over 60 feet deep. (Ships need only 30 feet of depth.) And then flexible control gates such as were designed previously could be put in place. One thing we know we don’t want, or need is locks. They would lead to very challenging ecological problems.
Until something is done though, the forecast for future water levels is not good – especially if climate change is added to the mix. The other Great Lakes have the capacity to hold back water under any scenario. Something has to be put in place for Lakes Michigan and Huron.
For more information:
Georgian Bay Association, Georgian Baykeeper, GBA Foundation