Wetland draining contributing to high water flows

July 10, 2014 - 12:02pm
A flooded-out road on the west side of Moosomin. Photo by CJME's Andrew Shepherd
A flooded-out road on the west side of Moosomin. Photo by CJME's Andrew Shepherd

Decades of draining prairie wetlands are now contributing to high water flows during major flooding events according to a researcher in Saskatchewan.

John Pomeroy is the Director of the Centre for Hydrology at the University of Saskatchewan who studies detailed models outlining how water flows across the landscape in Saskatchewan, Alberta and Manitoba.

“We took it back to how it was in 1958 as measured by aerial photographs of the slough extent and then we looked at the drainage since then and what that has done to the stream flow,” Pomeroy explained. “The short story is that it has doubled the volume of stream flow for the flood of 2011, and increased the peak daily flow by one third compared to how the stream would have behaved if that flood had hit in the 1950s.”

In many areas, up to a quarter of the land would naturally be sloughs or wetlands that would hold more water back and release it slowly. In a year with significant rainfall, such as this one, Pomeroy points out that all of that extra water has to go somewhere, so it spills over the larger sloughs that are left and flows into the river system.

“It’s like a series of bathtubs, one spills into the other, spills into the other...so eventually the bathtub or the slough at the end of the line is going to cause stream flow even if it normally wouldn’t because of all the others streaming into it,” Pomeroy explained.

He recognizes that flooding this year was caused by the very heavy rainfall but he says draining sloughs and wetlands has contributed to the higher flows. The water no longer sits in natural basins and drains slowly into ground water or evaporates.

“They have incredible flood protection capability,” he said. “It’s like having tens of thousands of dams across your landscape, holding back the water.”

Pomeroy noted that it is understandable that farmers would want to drain wetlands in order to produce a bigger crop and add to their cultivated acreage. He suggested that farmers should be rewarded for preserving their wetlands.

“If farmers are conserving their (sloughs) and their wetlands or restoring them, then they’re providing a service in flood mitigation downstream,” Pomeroy said.

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