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A GROWING CONCERN

While the world's lakes dry up, Lake Manitoba expands

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Among the world's largest bodies of water, Lake Manitoba is a special place.

But the reasons won't please flooded-out farmers or the owners of lakefront homes either ruined this week by storm-driven waves -- or doomed to a similar fate in the coming months and years.

Lake Manitoba is all but unique among the planet's 40 largest lakes in that it's growing larger. In other parts of the world, large lakes are shrinking in what amounts to one of the planet's most horrific environmental disasters.

In central Africa, freshwater Lake Chad has shrunk 95 per cent in 50 years due to increasing irrigation and drinking-water demands along its former shores. Farmers and fishermen in four African countries -- Chad, Niger, Cameroon and Niger -- are now fighting over what little water remains in what was once the world's sixth-largest lake.

In central Asia, the Aral Sea has gone from being the world's fourth-largest freshwater lake to a series of small, brackish basins in Kazakhstan and Uzbekistan, thanks to decades of disastrous Soviet irrigation policies. Dust storms laden with toxic chemicals stirred up from the exposed former lake bottom now blow over abandoned communities.

In the Middle East, Iran's brackish Lake Urmia (No. 25 by size) and the extremely salty Dead Sea (No. 27 by volume) on the Israeli-Jordanian border are also shrinking away, the victim of upstream irrigation and industrial mineral processing.

In stark contrast, Lake Manitoba -- officially the planet's 33rd-largest inland body of water -- is expanding to the point where it may have already overtaken Ontario's Lake Nipigon (No. 32) and what's now called the South Aral Sea (No. 31).

"Lake Manitoba is unique. On the list of the world's large lakes, it's the shallowest," said University of Manitoba aquatic ecologist Gordon Goldsborough, one of the few scientists to extensively study a body of water that has not attracted the extensive attention enjoyed by larger, more ecologically threatened Lake Winnipeg.

On average, Lake Manitoba is only five metres deep. Its deepest point is only seven metres. It's basically a large, flat baking pan, easily manipulated by wind -- and very sensitive to changes in the rivers that feed it.

"It doesn't take much for it to spill its banks. Any amount of increase in water level, and the results are noticeable almost immediately," Goldsborough said.

Since 1923, when the province began taking consistent water-level readings, Lake Manitoba fluctuated between 809.9 feet and 816.3 feet above sea level.

The upper level was reached in 1955 in a flood that submerged farms and settlements all along its shores. That led the province to build a control structure at the lake's sole outflow, the Fairford River, which drains Lake Manitoba into Lake St. Martin and eventually Lake Winnipeg.

Since the Fairford Dam's completion in 1961, Lake Manitoba had not risen higher than 813.5 feet above sea level -- that is, until the past year.

The lake now stands at 815.6 feet, its highest level since 1955 and similar to an even earlier significant flood, in 1881, Goldsborough said.

"There have been times when the lake has been as high as this. Anyone who tells you otherwise is not aware of the history," he said, dismissing theories the current level can be attributed solely to climate change or record inflows from the Portage Diversion, the artificial channel that carries in flood waters from the Assiniboine River.

The Portage Diversion, however, is a significant factor in Lake Manitoba flooding this year. During the middle of May, during the peak of the Assiniboine River flood, the diversion brought 33,000 cubic feet per second of water into the lake -- roughly 70 per cent of its total inflows.

Lake Manitoba has two major inflows. The Whitemud River flows in from the southwest. The Waterhen River, which enters at the northeast and drains a large basin that includes Waterhen Lake, Lake Winnipegosis and Dauphin Lake. Together with the Portage Diversion, they sent Lake Manitoba 47,250 cubic feet of water every second in the middle of May.

At the same time, outflows through the Fairford River were 15,250 cfs. That means 32,000 cfs -- slightly less than half an Olympic swimming pool -- was added to Lake Manitoba every second at the peak of the spring 2011 flood.

The resulting lake flood this year has inundated thousands of acres of farmland, displaced cattle and threatened or destroyed hundreds of homes, forcing at least 425 evacuations.

The property damage to homes is especially severe at communities on the spit of land that lines the lake's heavily wind-exposed southern and southwestern edge, a narrow sandbar formed by sediment brought in 2,500 years ago, when the Assiniboine River flowed into Lake Manitoba and created a delta.

At least 38 cottages at what's now Delta Beach were severely damaged Tuesday by a 96-kilometre-per-hour windstorm that sent waves and debris crashing through sandbag dikes, over breakwalls and into living rooms.

Some cottages kept their walls but got flooded. Others suffered so much erosion, their foundations are unstable. One cottage appeared bent as one side of the home collapsed into a sinkhole, buckling the floor.

A century-old two-storey cottage belonging to Sandy and Ron Brooks was split into two, cleaved by waves as high as eavestroughs.

"I've had Delta Beach my whole life and so have my boys," said a distraught Sandy Brooks, who bought her property in 2008 after years of renting. Framed photos of the cottage when it was built 100 years ago -- a gift from the previous owner -- were washed away.

Despite this lengthy pedigree of settlement, the long-term prospects for properties at the south end of the lake are dim, as flooding itself is not the only threat.

Storm-driven waves can be as high as 1.5 metres. And that's on top of a massive standing wave called a seiche (pronounced "saysh") that may add another metre when the wind blows from the north.

That means the potential storm surge at Delta Beach or Twin Lakes Beach can exceed the height of the tallest basketball player in the NBA.

"There are two separate things happening -- the waves and the seiche -- but since they occur at the same time, you can't discern the effects," said Shawn Clark, a hydraulic engineer at the University of Manitoba.

The height of waves is determined by wind speed, the duration of the winds and what's called the fetch, or the distance the wave travels before it hits the shore, he said.

The seiche effect, meanwhile, is caused when high winds push water horizontally from one side of an enclosed body to another. In shallow lakes such as Lake Manitoba, the seiche effect is stronger because there is less room on the floor of the lake for water from the massive wave to flow back, Clark explained.

"That's why the effects of wind are so dramatic on this lake," said Goldsborough, who has even more depressing news for residents at the south end of the lake: Lake Manitoba is slowly creeping southward towards Portage la Prairie.

When the glaciers that covered most of Manitoba melted, the compressed surface of the province started bouncing back, most dramatically in the north, where old docking rings at Churchill now sit metres away from the shore of Hudson Bay. Geologists call the process isostatic rebound.

Lake Manitoba's northern basin is rebounding faster than its south, when means the lake is slowly tilting over Delta Beach into Delta Marsh, said Goldsborough, who used to run the U of M's field station at the beach.

"The lake is moving southward, so you will see the erosion of the whole strip of land. Eventually, the lake and the marsh will be one," said.

"The problem of course is, development has been going on for more than 100 years. That was one of the first cottage developments in Manitoba. So if you retroactively say 'We're not allowing development there,' you're going to get some strong sentiment," Goldsborough said.

Residents at the south end of the lake, many of which remain in shock, are not ready to contemplate the idea of leaving for good.

"I don't even want to think about it," said Duke Andrich, a 15-year Delta Beach cottager who has spent a week trying to figure out how to stop his Frank Lloyd Wright-style property from tipping into the lake. The earth, rocks and underpinnings have been scooped away by the lake.

Manitoba Water Stewardship has ideas of its own. Executive director Steve Topping has floated the concept of placing barriers offshore to break waves, a practice borrowed from North Carolina, or placing homes on stilts to allow storm surges to pass underneath, as they do in storm-prone stretches of Costa Rica and other tropical nations.

Clark, the engineer, is not certain about the offshore-barrier idea. He believes barriers can break waves offshore but would do nothing about the seiche effect on Lake Manitoba. The scale of the project may also be a problem.

"It's a long, long shore," Clark said. "I don't know if there's any physical means of actually accomplishing this task. In the long term, I don't know if it's a viable option. And there are also ecological concerns."

The province is also considering cutting larger or new channels out of Lake Manitoba into Lake St. Martin, which itself is heavily flooded, and somehow increasing the capacity of the Dauphin River, which drains Lake St. Martin into Lake Winnipeg.

"I think we have a lot of different options for flood protection," said Topping.

But in the long term, large-scale engineering projects are destined to fail in the face of natural disasters, said Michael Glantz, one of the world's foremost experts on changes to the planet's largest lakes, including Lake Chad and the Aral Sea.

"We think we know what we're doing. We have this blind faith in science and technology. We think it will save our ass, but what will save our ass is better policy," said Glantz, the director for the Consortium for Capacity Building at the University of Colorado Boulder.

Good policy would be to not allow anyone to live closer to a lake than the level of any previous flood, he suggested.

"Engineering is great, but when nature tests stuff, these tests often fail," he said, citing decades of failed attempts to revive declining lakes.

The Portage Diversion has brought Lake Manitoba one benefit, however: Its water has become less salty. Once considered too brackish to be a source of irrigation or drinking water, Lake Manitoba is close to being suitable for both, Goldsborough said.

"The water in Lake Manitoba is on the threshold of being useful," he said, theorizing it could be pumped to potato-growing fields near Portage la Prairie.

Consider this a tiny silver thread lining the edge of a massive storm cloud that is not going away.

-- with files from Mary Agnes Welch

bartley.kives@freepress.mb.ca

Lake Manitoba

Surface area: 4,624 square kilometres.

Rank among the world's largest lakes: 33.

Rank in Manitoba: No. 3, after Lake Winnipeg and Lake Winnipegosis

Volume: 22.7 cubic kilometres (not among world's largest lakes by volume).

Average depth: Five metres.

Maximum depth: Seven metres.

Major inflows: The Waterhen River, Whitemud River and seasonally, the Portage Diversion.

Outflow: The Fairford River.

What keeps the water high?

Factors affecting Lake Manitoba's water level:

Flooding

Before the completion of the Fairford Dam in 1961, water levels on Lake Manitoba fluctuated between 809.9 and 816.3 feet above sea level. Since 1961, the range was flattened to 810 to 813.5 feet.

The lake level is at 815.6 feet right now and expected to rise several more inches because more water has entered from the Portage Diversion, Waterhen River and Whitemud River than has flowed out at the Fairford River.

Historically, evaporation accounted for half of the lake's water loss. But the shallow lake is highly variable, as this year's flood follows similar events in 1955 and 1881.

Height of this year's flood, above Lake Manitoba's maximum ideal level: 3.1 feet and rising.

Seiche

In a phenomenon known as a seiche, or wind setup, sustained winds on Lake Manitoba drive water from one side of lake to the other in what amounts to a massive standing wave. While this happens in all enclosed bodies of water, the shallow nature of Lake Manitoba -- only five metres deep, on average -- prevents water below the surface from flowing back as quickly as it would in a deeper body of water.

Maximum seiche on Lake Manitoba: Three feet.

Waves

The height of waves is determined by three factors: wind speed, wind duration and fetch, the latter being how far a wave travels before it hits the shore. Computer models can predict wave height, to varying degrees of accuracy. Lake depth is not as great a factor in determining the height of waves as it is for determining seiches.

Maximum waves on Lake Manitoba: Five feet.

Isostatic rebound

Lake Manitoba is slowly tilting south and creeping towards Portage la Prairie because the province is rebounding from the pressure exerted by glaciers that only melted 8,000 years ago, a blink of the eye in geological time. This means Lake Manitoba is slowly merging with Delta Marsh.

Rate of Lake Manitoba movement due to isostatic rebound: Undetermined, but calculable.

Sources: Manitoba Water Stewardship, Environment Canada, U of M aquatic ecologist Gordon Goldsborough, U of M civil engineer Shawn Clark

Republished from the Winnipeg Free Press print edition June 13, 2011 A6

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