Wetland Drainage Increases Spring Flooding, Research Shows

It’s a long way from Broughton’s Creek in southwestern Manitoba to Lake Winnipeg smack in the middle of the province.

But to Pascal Badiou there is a relationship between this tiny rivulet in Prairie pothole country and the condition of one of Canada’s largest freshwater lakes.

There’s also a connection between the history of the Broughton’s Creek watershed and the spring floods currently threatening southern Manitoba, says Badiou, a Ducks Unlimited research scientist.

Recent research by Badiou and other DU scientists connects the dots leading from the drainage of Manitoba’s wetlands, including Broughton’s Creek, to the province’s chronic flooding and water quality problems.

Periodic floods in Manitoba are no accident. They are, at least in part, the direct result of decades of draining wetlands and potholes to make way for agricultural land, Badiou says.

Potholes and wetlands retain water on the land and release it in a controlled fashion. But because of all that drainage, water rushes off the landscape in an uncontrolled flow. Floods often result.

It’s true this year’s flooding is largely the product of an abnormally wet 2010, above-normal winter snowfall and saturated soils which increase run-off.

DRAINAGE CONNECTION

Even so, Badiou is convinced flooding wouldn’t be as bad if so many wetlands had not been drained over the years.

“It’s pretty clear that wetland drainage dramatically increases total flow – the total amount of water coming out of the watershed,” he said from his office in DU’s national headquarters at Oak Hammock Marsh.

“But more importantly, it increases peak flow. That’s usually when flood impacts are the greatest.

“Any increase in peak flow has the potential to cause damage. It’s very clear that wetland drainage increases peak flow.”

Another side-effect of drainage is nutrient loading. Decomposing plants release nitrogen and phosphorus into the water and are washed downstream. Ultimately, they end up in Lake Winnipeg and contribute to the algal blooms plaguing the lake.

Broughton’s Creek, located in the rural municipalities of Blanshard and Daly northwest of Brandon, is an example of that phenomenon, according to Badiou’s research.

STARTLING RESULTS

A computer model analyzing drainage patterns in the Broughton’s Creek watershed between 1968 and 2005 revealed some startling results.

During that time, excessive drainage increased the area of land collecting water by 31 per cent. The creek’s total stream flow grew by 62 per cent. Peak flows increased by 37 per cent. The amount of phosphorus and nitrogen in the water increased by 32 and 57 per cent respectively. The volume of sediment exported went up 85 per cent.

If you extrapolate the Broughton’s Creek results throughout southwestern Manitoba, the overall effect becomes even greater.

Badiou’s research calculates that 37 years of drainage in the southwest region increased the amount of land draining water into Lake Winnipeg by 4,500 square kilometres. It increased the amount of phosphorus reaching the lake by 167 tonnes a year. And it released nearly eight million tonnes of carbon, previously stored in sediment and vegetation, into the environment.

DISAPPEARING WETLANDS

The same sort of thing occurs in the rest of Manitoba as watersheds, which formerly stored water on the landscape, disappear, said Badiou.

And so Broughton’s Creek, a tiny watershed far from Lake Winnipeg, becomes a microcosm for what’s happening throughout Manitoba. This suggests too much emphasis is being placed solely on the Red River as a solution to Lake Winnipeg’s water quality problem, Badiou said.

Broughton’s Creek is part of the rolling Prairie pothole region stretching across much of southern Alberta, Saskatchewan and Manitoba and into the northern United States. Canada’s portion of the region covers about half of the Lake Winnipeg watershed.

Badiou compares potholes to bathtubs on the landscape which catch water and hold it.

But the water in those bathtubs is going down the drain. Up to 70 per cent of the wetlands in settled areas of Canada have vanished over the years to be replaced mainly by cultivated farmland.

The resulting environmental impacts – chronic flooding, nutrient loading, sedimentation, loss of habitat – point to the need to conserve wetlands that remain, DU researchers maintain.

CAN’T GO BACK

Badiou is the first to admit you can’t turn back the clock and restore what’s been lost since the settlers arrived. Nor does he advocate that.

But now that science has established a link between wetland loss and flooding, Manitobans may be willing to support programs which limit wetland drainage and encourage their restoration, he said.

“We’re at a point now where we can stop wetland loss and prevent further damage and degradation and, hopefully, flooding,” said Badiou.

“At the same time we can start looking at investing in restoration and maybe turning back the clock a little bit to reduce some of the impact.”

Badiou said he is heartened by Manitoba Water Council consultations last year on the need for a provincial wetland policy.

According to a document summarizing comments heard at public meetings: “There was a clear expectation that a wetland policy will be developed with the provincial government providing strong leadership.”

The document noted, however, that most wetlands in southern Manitoba are on private land. Some landowners feel the cost of maintaining wetlands outweighs the benefits they provide. [email protected]

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“It’sveryclearthatwetlanddrainageincreasespeakflow.”

– PASCAL BADIOU, DUCKS UNLIMITED

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