Rain and snow spell relief for Great Lakes
Fri May 2, 2008 1:26pm EDT By Jonathan Spice
TORONTO (Reuters) – Twice as much autumn rain and early winter ice helped Lake Superior, the biggest of North America’s Great Lakes, bounce back from record low water levels reached last year.
The deep, cold lake on the Canada-U.S. border — the largest freshwater body of water in the world by surface area — rose about 31 cm (1 foot) in seven months, with half of that in April alone as the spring thaw melted heavy winter snowfall that arrived late in the season.
The turnaround in the uppermost of the Great Lakes could literally trickle down to its four lower cousins, spelling relief for shippers who use the major waterway and residents concerned over shallow channels and receding shorelines.
“The spring runoff was much anticipated, and conditions have appeared to return to normal,” said Melissa Kropfreiter, a hydraulic engineer with the U.S. Army Corps of Engineers, which studies the water levels.
In the last 30 years, precipitation has decreased while evaporation has increased. That led to higher water temperatures and, in recent years, lower water levels in the three upper Great Lakes — Superior, Huron and Michigan.
With the inland waterway a key route for shipping bulk commodities like grain, steel or coal, the low water forced ships to lighten their loads. Last summer, some of the shallows and riverbeds used by fish for spawning dried up.
But that pattern, seen by many as a mark of global climate change, appears to have reversed at least over the last half year.
HURON, MICHIGAN ALSO RISING
Lake Huron and Lake Michigan, which share the same water level, also rose through the winter and spring as 50 percent more snow fell in a region that includes the U.S. states of Wisconsin and Michigan, and parts of the Canadian province of Ontario.
Ice on the water curbs winter evaporation, helping to maintain levels. But much of the snowpack evaporates before the spring thaw and never reaches the lakes, which may explain why Huron and Michigan are still slightly lower than last year, experts say.
“If there are a lot of cool, sunny days, the snow goes straight into water vapor,” said Ralph Moulton, a senior engineer at Environment Canada who studies Canada-U.S. boundary waters.
The new data on water levels comes as the International Joint Commission, an independent body formed by the U.S. and Canadian governments, studies whether dredging on the St. Clair River has contributed to declining levels on the upper lakes.
The St. Clair River is a major shipping route near Detroit that connects the lower lakes of Lake Erie and Lake Ontario with the upper trio.
While the upper lakes remain below their long-term averages, water levels in the smaller, lower lakes are above average.
The massive waterway connects to the Atlantic Ocean through the St. Lawrence Seaway, a system of locks and canals that opened in 1959, allowing ocean-going vessels into the industrial heartland of North America.
The largest ships on the Great Lakes forfeit some 267 tonnes of cargo for every inch of water level lost, said Stuart Theis, executive director of the United States Great Lakes Shipping Association.
“Every inch lost is revenue the shipping companies can’t get out of a trip, and can’t get back.”
(Reporting by Jonathan Spicer; editing by Rob Wilson)
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