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November/December, 1996
Canadian Geographic
How does the Seine River get over Winnipeg’s Red River Floodway,
which blocks its path? John Gent, Milton, Ont.
IF YOU LOOK at a map, the Seine flows up to the edge of the floodway,
then disappears, then starts flowing again on the other side.
The answer is this: it goes underneath. The water falls into a
big pipe just south of the floodway, flows under it, and comes
up via the siphon principle on the other side.
What to do with the Seine was one of the problems engineers faced
when the Red River Floodway was built in the 1960s, says Eugene
Kozera, a flood damage reduction engineer with the Manitoba Department
of Natural Resources. The floodway was required because the Red
River, with its shallow banks and northerly flow, is given to
springtime flooding, a point driven home by the massive Winnipeg
flood of 1950, which inundated a sixth of Winnipeg and drove 100,000
people from their homes. The flood lasted 51 days, was caused
by snowmelt and heavy rains and was responsible for the death
of one person. Damages were estimated at $606 million.
The floodway is a huge ditch, up to 300 meters across and 48
kilometers long. In the Western Hemisphere, only the construction
of the Panama Canal required more earth to be moved. Usually the
floodway is just grassy hillsides. But if the Red rises too high,
gates south of Winnipeg divert river water into the floodway,
which carries it safely up the eastern outskirts of Winnipeg until
turning it into the Red River again.
Small streams were run into the floodway when it was dug, but
this couldn’t be done with the relatively major and marvelously
meandering Seine. Rather, a concrete water collecting box was
built on the south side of the floodway, and a 1.5 meter-diameter
corrugated metal pipe run more than 450 meters beneath it and
up again to the Seine’s streambed on the other side. A drop in
elevation from south to north keeps the inverted siphon working
– and the Seine River running. In the interests of absolute accuracy,
Kozera adds that there still are times – especially in spring-
when the Seine is running so high that some water from the river
flows into the floodway rather than under it.
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