Extreme precipitation causes flooding, not drainage: Expert

A Manitoba hydrologist with 30 years of experience says extreme precipitation causes flooding, not drainage.

Eric Blais, who works for an engineering consulting firm in Winnipeg, said the debate over drainage in Saskatchewan and whether it causes flooding on the Assiniboine River misses the point.

The amount and frequency of rain and snow are the key variables behind flooding, not drainage.

“If you look at the 2014 flood event, that came completely out of left field. We’ve never had a flood like 2014 before. It set records on the Upper Assiniboine…. It’s probably still a one in 200 year event, or better.”

Approximately 150-200 mm of rain fell on a broad area of eastern Saskatchewan and western Manitoba in late June, leading to record water levels on the Assiniboine in July.

In the aftermath of the flood, which cost Manitoba an estimated $200 million in flood protection measures and damages, politicians, conservation groups and farmers said unauthorized and rampant drainage in eastern Saskatchewan was responsible.

Blais said there’s “no doubt” that farmland drainage changes the hydrologic regime and reduces the amount of water stored on the land.

“In the long run it’s probably not a great thing…. You’re also altering groundwater levels and you’re changing water quality,” he said. “(But) when you’re talking about these really, really extreme hydrologic events, I don’t think you can point the finger solely at the producer…. If you’re in a very wet climatic period and all the storages (on the land) get used up, all bets are off. Your normal assumption about how much water will run off the land is wrong because the soil can’t hold any more water and all the wetlands are full of water.”

Earlier this year John Pomeroy, a University of Saskatchewan water expert, released a report on the Smith Creek in eastern Saskatchewan and how the loss of wetlands has increased flows in the creek.

Ducks Unlimited and other organizations have pointed to Pomeroy’s research, saying it proves flooding severity is related to the loss of wetlands.

Blais said wetlands are a factor but flooding occurred on the Prairies before the arrival of the backhoe and the drainage plow.

“One of the largest floods on the Assiniboine was in 1888,” he said. “Same, the biggest flood on the Red (River) was in 1826, before there was any drainage.”

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Comments

  • Chelsea

    Another expert who is the Canada Research Chair in water resources and climate change, professor of geography and director of centre for hydrology at U of S says otherwise: http://www.usask.ca/hydrology/papers/Pomeroy_et_al_2014.pdf

  • Chelsea

    Just wanting to also point out that the expert interviewed above says:”the debate over drainage in Saskatchewan and whether it causes flooding on the Assiniboine River misses the point.” DUC has never stated drainage “causes” flooding. The exact quote is “contributes to flooding”. There is a difference in context. Also it seems like Eric agrees with the science DUC stands behind where he states:
    “There’s “no doubt” that farmland drainage changes the hydrologic regime and reduces the amount of water stored on the land.“In the long run it’s probably not a great thing…. You’re also altering groundwater levels and you’re changing water quality”. One of the exact (word for word) conclusions from the Pomeroy Report is: “Continued wetland drainage will have a very strong impact on streamflow in flood conditions. For the flood of 2011, complete drainage of the existing wetlands would increase the 2011 flood peak by 78% and the yearly volume of streamflow by 32%.”

    This is basically the same message. If we continue to alter the landscape and reduce the amount storage on the land, then flood conditions will worsen as the precipitation (extreme or normal) continues throughout the years.

    • Jeff

      It is important to clarify, that Blais is not at all associated with the Pomeroy report. The Pomeroy report is very flawed. It is based on modeling, which is complex, problematic,and unreliable. The numbers you have posted of 78% and 32% are only believed by those who wish to push their idealistic agendas. They are viewed with an incredible amount of scepticism by unbiased third parties. Furthermore, each basin is different. You can’t extend conclusions from one basin and apply them to other basins.

  • Habo

    I have seen the effects of flooding. Even with wet lands, when there is so much precipitation, there eventually is no where else for it go. I am a farmer, I have lost about 40% of my crop due to flooding and soaked out areas. Even with insurance and the programs out there, I’ll basically be told you don’t qualify. Also with your set of skills, it’ll be easy to get a job. So lady, unless you will get another job to support your first one. Or support farming financially, or quit eating altogether, I wouldn’t talk.

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