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Flood worries on the rise; Lake Simcoe could surge as much as 30 centimetres

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Flood worries on the rise; Lake Simcoe could surge as much as 30 centimetres

 

 

Colin McKim / thebarrieexaminer.com

March 5, 2008

 

 

With water levels in Lake Simcoe abnormally high due to a record-breaking January thaw and heaps of February snow yet to melt, there is a risk of the worst flooding in almost 50 years, says a water-control expert with the Trent-Severn Waterway

 

"I don't want to alarm anybody with doom and gloom about a big flood," said Dave Ness. "But the potential is there."

 

A quick thaw boosted by heavy spring rain could cause Lake Simcoe to rise by as much as 30 centimetres and spill over earthen dikes into the Holland Marsh, causing widespread flooding in the low-lying agricultural area, something that last occurred in 1960.

 

"All the emergency-management people have been given a heads up," said Tom Hogenbirk, manager of engineering and technical services with the Lake Simcoe Region Conservation Authority.

 

"The biggest danger is a wholesale breach in one of the dikes when there's no one around."

 

The Holland Marsh Joint Municipal Service Board Drainage Committee is monitoring the water levels in Lake Simcoe and developing an emergency plan to shore up low points in the dikes with sandbags, said Hogenbirk.

 

"They're out there checking the situation every day."

 

Hogenbirk asked members of the public to notify authorities if they see water spilling over dikes or roads in the marsh area, where much of the land is lower than Lake Simcoe.

 

A major breach would flood 6,000 acres of farmland, barns, houses, churches, processing plants, fuel tanks and other structures, said drainage committee chair John McCallum: "If the levee breaks - it doesn't matter where - the whole thing floods."

 

Docks, boathouses and other structures on Lake Simcoe could be damaged if water levels rise rapidly in the spring thaw, said McCallum.

 

There is also a risk of flooding along the Severn River system between Lake Couchiching and Port Severn, with Sparrow Lake, Six Mile Lake and Gloucester Pool being most at risk, said Ness.

 

Water levels in Lake Simcoe are controlled by numerous dams and valves in the locks, fluctuating up to 37 centimetres from a peak of 219.06 metres above sea level to a low of 218.69 metres.

 

Water levels typically peak in May and June following the spring runoff and hit bottom at the end of October.

 

Every fall, the water in Lake Simcoe should be at least 20 centimetres below peak to create capacity for the spring runoff.

 

At the beginning of January this year, the water level in the lake was at the desired level - 218.85 metres - low enough to accommodate typical winter thaws and the spring runoff.

 

However, rain and melting snow in January pumped 20 centimetres back into the lake, bringing it virtually back to capacity at 219.05 metres.

 

The waterway took the unusual step of opening dams and valves downstream to bring the water level down again.

 

But it has been slow going and the water level in Simcoe, 218.93 metres, is still about 17 centimetres higher than average for this time of year, said Ness.

 

"It's surprising," he said. "We're discharging as much as possible. The valves are wide open."

 

And the heavy snow load dumped in February is still waiting to melt and flow down rivers and creeks into the system, Ness noted: "There's a pile of snow out there."

 

If there is a gradual melt this spring, with minimal rainfall, the flooding risk will be greatly reduced.

 

But, if temperatures leap to 10 C or higher, accompanied by significant rainfall, the lake will spill over, Ness predicted, noting the overflow could be as much as 30 centimetres.

 

One wild card is the Black River, which drains into the Severn system at the north end of Lake Couchiching and can carry huge volumes of water in the spring.

 

Normally, the flow from Lake Simcoe can be held back while the Black crests to minimize flooding along the Severn.

 

This spring, however, the valves and dams will have to remain wide open to keep draining Lake Simcoe, so there will be no way to ease back when the Black lets go, said Ness.

 

"We could be in quite a pickle."

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