Study looks at river flow
Written by Port Huron Times-Herald   
Sunday, 03 May 2009 07:52
The good thing about a study looking at water flows in the St. Clair River, laughs Roy Schatz, is that it's only a draft.

"There are still seven verification studies that they haven't incorporated into that draft," said Schatz, founding president of the Georgian Bay Association, a group of Canadian residents concerned about rapidly declining water levels in the Georgian Bay area of Lake Huron. "We'd like to see those, and we'd like the public to see those, but they're all likely going to be reported on after the public meetings are over."

The International Upper Great Lakes Study Board, a body of the binational International Joint Commission, released a report Friday called "Impacts on Upper Great Lakes Water Levels: St. Clair River."

The study found that in the years from 1962 to 2006, water levels in Lake Michigan-Huron declined 9 inches relative to Lake Erie.

The last major dredging project on the St. Clair River was completed in 1962.

Significantly, the draft report does not recommend any remedial measures be taken in the St. Clair River to correct changes in conveyance, the water-carrying capacity of the river.

Jill Wingfield, a public information officer for the study board, said the group's mandate was to determine whether there was a change in conveyance and whether it could be linked to manmade or natural changes.

The draft study, which took two years to complete, found there had been changes in conveyance in the 34 years from 1962 to 2006.

But Eugene Stakhiv, U.S. co-chairman of the study group, said researchers found manmade changes -- such as maintenance dredging since 1962 -- had a minimal impact on the river's conveyance.

"The nature of maintenance dredging is simply to keep the original channel at that depth," he said. "The channel does silt in over time.

"We did notice though looking at the maintenance dredging records since the 1980s there was a lot less maintenance dredging compared to the previous era."

Dredging's impact since 1962, he said, "is so minimal to the extent that our models do not pick up the changes in whatever maintenance dredging there was."

Researchers believe three key factors have contributed to the change in conveyance though the St. Clair River, according to Wingfield.

They found episodic events such as ice jams have increased the river's capacity to carry water, she said, pointing to a major ice jam in April 1984.

That ice jam, the largest in recorded history on the river, was 21 miles long and lasted about 28 days, she said.

"According to the study board, the weight of the ice was so significant it pressed down on the water and increased the flow velocity of the water moving under the ice," Wingfield said.

The increased flow scoured the bottom of the river, she said. Ice in the lower reaches of the river also moved down the channel like a massive plow, according to Wingfield, eroding the banks and increasing the river's width.

The study board said the ice jam accounted for 3.9 to 4.7 inches of the decline in the level of Lake Michigan-Huron.

Other factors include changes in climate patterns, said Wingfield, and isostatic glacial rebound -- some parts of the Great Lakes Basin, including the Georgian Bay, still are rising about 10,000 years after the massive weight of the continental glaciers was removed.

"In certain areas of the basin the land is uplifting, which means the water is receding," she said. "In other areas the weight is increasing so the water is getting higher."

The study found 6 billion more gallons of water per day are leaving Lake Michigan-Huron compared to 1971 -- but that the increase is due to natural causes.

A study commissioned in 2004 by the Georgian Bay Foundation, however, blamed increased conveyance on dredging, shoreline alterations and sand and gravel mining.

Schatz said the draft released Friday is incomplete. He pointed to what he believes are flaws in the methodology for the study, including use of a flow meter that only goes two-thirds of the way across the St. Clair River.

He also said researchers relied too much on extrapolation and that they should have looked at dredging projects in the river prior to 1962.

Stakhiv, however, said other studies had looked at the impact of dredging projects done in the 1930s and 1960s.

Schatz said despite increased precipitation, Lake Michigan-Huron and the Georgian Bay remain below long-term lake level averages, while levels in Lakes St. Clair, Erie and Ontario have increased.

"We are coming up this year because of the increased precipitation and because of the terrific freeze-over this past winter," he said. "This is the first time in 10 years that the Georgian Bay froze over.

"But why is this triple lake (Michigan, Huron and Georgian Bay) the one that's still 10 inches below its long-term average?" Schatz said.

"That other factor has to be the only drain hole, which is the St. Clair River."

Wingfield said the study board will be accepting public comment until July 1. A final report is expected Oct. 1.

 
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