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Thursday, November 01, 2007

Science - Erosion

By JOHN FLESHER, Associated Press Writer 49 minutes ago

TRAVERSE CITY, Mich. - Video images from the St. Clair River bottom show no evidence that erosion is causing water levels on Lakes Michigan and Huron to drop, scientists working for a U.S.-Canadian advisory group said Thursday.


Although preliminary, the findings intensified a debate over whether people or nature are more to blame for the two lakes' steady decline since the late 1990s. Leaders of the research team said it was too early to judge the validity of a Canadian group's contention that erosion on the upper portion of the river is the leading culprit.

But they said the underwater video — taken in September along a roughly 30-mile stretch — showed the riverbed is covered with gravel, pebbles and stones up to 10 inches long. The rock layer is stable, meaning "the bed cannot be eroding," the team's report said.

"On a preliminary basis, we're finding that ongoing erosion does not appear to be a cause of low water levels," said John Nevin, spokesman for the International Joint Commission (IJC), which advises the U.S. and Canadian governments on Great Lakes issues.

The commission released its findings during a meeting and telephone news conference in Toronto.

A spokeswoman for the Georgian Bay Association, whose engineering studies have promoted the erosion hypothesis, said the IJC's report was unconvincing and contained errors. The association wants the two nations to look for ways to reduce water flow out of Lake Huron.

"It's premature for them to be releasing this information," said Mary Muter, chairwoman of the group's environment committee. "They're wasting time and wasting money."

Researchers acknowledged many questions remained unanswered, such as whether river flow rates have changed over time and how long the riverbed has been stable. The rock layer holding it steady may have been covered previously by sediment that washed away, said Ted Yuzyk, co-chairman of the study team.

Additional measurements will be taken to provide further information, he said.

The video was taken by Bommanna Krishnappan, a research scientist with the National Water Research Institute Ontario, who also reviewed previous reports of sediment movement in the river.

Low water is causing ecological and economic problems on the Great Lakes, particularly for commercial shippers and recreational marinas.

Lakes Michigan and Huron, which geographically are considered the same lake, are about 20 inches below their historical average levels for this time of year. Lake Superior, meanwhile, hit a record monthly low in September.

Many scientists say the dropoff is caused by drought and milder temperatures, which promote evaporation.

But engineers hired by the Georgian Bay Association, which represents thousands of Lake Huron waterfront property owners, place much of the blame on human activities in the St. Clair River — particularly dredging to deepen the shipping channel during the 1960s.

In an August report, the association said erosion from the dredging is causing Lake Huron to lose an extra 2.5 billion gallons per day. The excess water flows into the lower Great Lakes and eventually the Atlantic Ocean, the group said, likening the widened river channel to an enormous drain hole.

The IJC this year began studying the issue. It initially promised a final report by 2010 but recently said results would be produced a year earlier after getting pressure from U.S. senators and other political leaders.

Gov. Jennifer Granholm and U.S. Sen. Debbie Stabenow last month asked the U.S. Army Corps of Engineers to consider placing underwater barriers in the river to limit its flow even before the commission's study is finished.

The IJC has long acknowledged that dredging caused Lakes Huron and Michigan to drop nearly 16 inches from the mid-1800s to the 1960s. The debate is over whether it also is causing the present low-water period, which began in 1999.

Frank H. Quinn, a retired hydrologist with NOAA's Great Lakes Environmental Research Laboratory in Ann Arbor, said his studies over the past two years had found that 80-90 percent of the lakes' current dropoff could be attributed to weather.

In a presentation during the Toronto meeting, Quinn said the lakes probably would have fallen even more during recent decades. But their outflow has been slowed by a buildup of the water supply in Lake Erie caused primarily by increased precipitation, he said.

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On the Net:

_Georgian Bay Association: http://www.georgianbay.ca/index.html

_International Joint Commission: http://www.ijc. org.

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Editor's note — John Flesher is the AP correspondent in Traverse City and has covered environmental issues since 1992.

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