Skip to main content

Aerial views of two sections of land in the Smith Creek Basin during high rainfall in April 2011. The section on the left has no artificial drainage, allowing water to pool up in small, shallow depressions. The section on the right shows the impact of an artificial drainage network, which clears the land of water and increases the flow rate downstream leading to higher water levels on the Assiniboine River.

University of Saskatchewan

Heavy rain is not the only reason the Assiniboine River is flooding in the height of summer and threatening a swath of communities across southern Manitoba this week, a new report suggests.

The elimination of vast numbers of small ponds and wetlands across the Canadian prairie has removed a crucial buffer that can temporarily store water on the landscape during periods of excessive precipitation.

So profound is the effect, the report's authors find, that had the same amount of rain fallen in the 1950s as has this past year, the swollen Assiniboine might have reached only half of its current peak level.

Story continues below advertisement

"It's one of the strongest land-use impacts [on water movement] I've seen anywhere in the world," said John Pomeroy, a hydrologist at the University of Saskatchewan, lead author of the report.

Some of the lost "wetlands" would hardly qualify as wet. They are no more than slight dips in the flat prairie terrain where water pools up after abundant rainfall. But farmers have plenty of incentive to create drainage systems that efficiently clear these temporary reservoirs and keep water flowing downstream, while increasing the fraction of land that can be cultivated. Over time, this has led to a steady growth in drainage networks across the prairie.

To better understand the impact of these networks, Dr. Pomeroy and his colleagues made a detailed study of the Smith Creek basin near the Saskatchewan-Manitoba border.

Using airborne lasers, they created a precise elevation map to show where water should be collecting in the basin and how it drains.

The team also looked back more than half a century to a time when 24 per cent of the region was covered by wetlands, as compared with 11 per cent at the start of 2009, and developed a computer model to compare water flow then and now.

The analysis shows peak water flow during the last major flooding event, in 2011, would have been 32 per cent lower had a similar flood occurred in 1958. The researchers also found the same flood would be 78 per cent higher with no wetlands at all, a likely scenario if drainage networks continue to proliferate unchecked.

As climate change brings more extreme weather to the region, the report suggests that flooding along the Assiniboine as well as Lake Manitoba, where flood waters are diverted, will be more frequent.

Story continues below advertisement

And flood damage is only part of the problem, experts say, as the fast-draining water carries fertilizer downriver toward Manitoba's lakes. This sets the stage for massive algal blooms that can suck up oxygen and kill off aquatic habitats.

"My great fear is that we will see the world's largest Jell-O bowl," in Lake Manitoba, said Scott Forbes, an ecologist with the University of Winnipeg.

Dr. Pomeroy said the issue of drainage regulation should be a priority for the Prairie Province Water Board, which oversees water use across provincial boundaries.

Manitoba has recently moved toward improving its own regulations and has requested the board to "follow up on the issue of Saskatchewan drainage impacts to Manitoba," said Steve Topping, who represents Manitoba on the board.

Report an error Editorial code of conduct
Comments

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff. Non-subscribers can read and sort comments but will not be able to engage with them in any way. Click here to subscribe.

If you would like to write a letter to the editor, please forward it to letters@globeandmail.com. Readers can also interact with The Globe on Facebook and Twitter .

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff. Non-subscribers can read and sort comments but will not be able to engage with them in any way. Click here to subscribe.

If you would like to write a letter to the editor, please forward it to letters@globeandmail.com. Readers can also interact with The Globe on Facebook and Twitter .

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff.

We aim to create a safe and valuable space for discussion and debate. That means:

  • All comments will be reviewed by one or more moderators before being posted to the site. This should only take a few moments.
  • Treat others as you wish to be treated
  • Criticize ideas, not people
  • Stay on topic
  • Avoid the use of toxic and offensive language
  • Flag bad behaviour

Comments that violate our community guidelines will be removed. Commenters who repeatedly violate community guidelines may be suspended, causing them to temporarily lose their ability to engage with comments.

Read our community guidelines here

Discussion loading ...

Due to technical reasons, we have temporarily removed commenting from our articles. We hope to have this fixed soon. Thank you for your patience. If you are looking to give feedback on our new site, please send it along to feedback@globeandmail.com. If you want to write a letter to the editor, please forward to letters@globeandmail.com.
Cannabis pro newsletter