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The Great July Flood

July 13, 2014

It’s unusual.  We do get floods in the spring some years, but this time it was in July.  I’ve been hearing reports on CBC radio and reading news articles about the flood in southern Manitoba.  Last weekend, when I went to Brandon, one of the two entrances to the city from the Trans-Canada highway was closed because of flooding.

Most of the complaints I heard about were about large man-made flood control structures.  All of these are operated intentionally during a flood event.  People complained that they caused an artificial flood, and that the government did this to protect other areas some distance away.  There are three of these structures in Manitoba.  The Winnipeg floodway protects Winnipeg by diverting Red River water around the city.  The Portage diversion also protects Winnipeg by sending Assiniboine River water north into Lake Manitoba.  The third one is quite new.  It’s the Lake St. Martin channel, which provides an outlet from Lake Manitoba.

The argument seems to be that these structures are completely artificial, creating an artificial flood.  This is the same argument that’s used for food products.  Somehow, natural food is good for you, but artificial food is bad for you.  Would they rather have a natural flood?  There’s no such thing.

The major rivers in southern Manitoba are the Red River, flowing northward from the US border and emptying into Lake Winnipeg, and the Assiniboine River, flowing eastward from the Saskatchewan border and joining the Red River at Winnipeg.  People in Manitoba, at least the western part, blame Saskatchewan for the flooding this summer.  It’s true that there were heavy rains there, but that’s only part of the problem.

All of the agricultural land in Manitoba and Saskatchewan has been drained.  That’s a major contribution.  Farmers want to get the water off their land as quickly as possible, especially in the spring.  Because of the short summer, they want to complete seeding as early as possible.  The land has to be dry for seeding.  In addition, drainage increases the amount of arable land on each farm, and accomodates large machinery.  It’s almost impossible to prevent farmers from draining their land.

Winnipeg is at the centre of the ancient Lake Agassiz basin.  All of this land has been drained, some over a century ago.  When I was doing research in Soil Science, I remember discovering a layer of peat at the surface of a piece of land just east of Winnipeg.  Clearly this land had never been cultivated.  At the time, we were studying lead levels in soild adjacent to roadways.  The peat layer was a vivid reminder that all of the Lake Agassiz basin had originally been a wet meadow with tall grasses and other marsh plants growing on it.  Now this entire basin is covered with a network of drains, all leading into the Red or Assiniboine Rivers.  It’s entirely artificial.  Undoubtedly this drainage contributes to the rapid rise of these rivers during the spring melt and in response to rainfall events.

It’s going to get worse.  Climate change is going to lead to more extreme weather events.  We’ve created a situation that’s going to cause devastating floods every few years.  What should we do?  Do we protect people or protect land?  Do we flood the upstream end or the downstream end of the hydrologic system?  Do we compensate people who have lost their homes or lost their income because of flooding?  Do we force people to move to higher ground?  Regardless of what we do, there’s going to be a cost.

 

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