Manitoba Update
The CBC reports Flood-threatened communities plead for volunteers and food
Usually, most properties in Winnipeg and the rural municipalities are protected from rising river levels by the floodway, which redirects the water through a 48-kilometre channel between St. Norbert and Lockport.
It can’t do anything, though, when ice is causing sections of river inside those protected areas to rise so quickly.
I don’t understand why they don’t just put a grid, say half meter squares, in front of the flood gates and open them? The ice floats on top, but the water underneath will flow into the channel and reduce the pressure and the rising level. I understand that they don’t want to just open the gates and have an ice jam form in channel, so filter out the ice. There has to be something I’m missing.
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I suspect the grid would be an object that ice could form on under the surface. Instead of filtering out the ice, it would become the foundation for an ice damn. At least, that’s my take on it.
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Maybe a 1-meter grid would be better, but this definitely shouldn’t be a permanent structure, because, as you say, it would form an ice wall. I was thinking of a something to hold back the ice on top, while letting the water underneath head down the channel. Sort of like using to pot lid to hold in the potatoes when you’re pouring out the water.
Too many flood control measures depend on overflow, which don’t work when there’s ice on top.
What happens is that the undertow from the water flowing underneath (but nothing flowing on top) sucks the ice downward, thus cutting off even more flow.
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The real missing piece is the design of the flood gates. If they can limit the flow at the gates, they need only divert the increase. If too much water is diverted the unsupported ice sheets will break and make the ice dams worse. Flow control is the key to avoiding the current effect.
A form of grating works with logs, but the buoyancy of the ice is unknown, and it doesn’t have the approximate uniformity of the logs.
I have more familiarity with canal locks because of family history and living near the old Eire Canal and the New York Barge Canal that replaced it. Gravity did most of the work in the stepping, i.e. raising or lowering the water level for the next stage. The valving was very controlled.