Connecting Lake Simcoe's Community

Homes on flood plains prone to Spring flooding

2020 03 21 watersheds with pic

By David Hawke -- In the coming week, if you watch the 6pm news or, if you’re still young enough to stay up, the 11pm news, I predict that one of the top stories you’ll see has to do with, not the lack of toilet paper, but the abundance of water. Spring floods are upon us once again, and the TV reporters are digging out their hip waders and will soon be seen out standing in the field as they document the spring freshet.

          Simcoe County has a wonderful array of rivers and streams, each carrying water down to the shores of the Trent-Severn Waterway and Georgian Bay, so why is it that only a couple make the news each year, those being the Black and the Nottawasaga. Okay, so yes, the Coldwater and North also flood but we don’t hear about them so much… why is that?

          Some of the factors that lead to flood coverage are the length and location of the river, soil substrate and adjacent wetlands, but the biggest factor in news coverage is whether or not somebody’s house is about to float away. Now that’s news!

          This whole situation starts on the top of a high hill, probably one of the highest hills in that immediate area, although not always. So, a heavy spring rainfall happens and raindrops fall on the deep snow that’s atop that hill. Each raindrop will soak into that snow and eventually flow down either the west side or the east side of the hill, and thus a watershed is defined.

          As more and more water is shed to the sides of the hill, the bottom of the slope suddenly finds itself with the urge to purge all this gathering water… and that little summer creek suddenly finds itself flush with a fair bit of fresh water. Now here’s where a cool sciencey thing that comes into play: water is quite dense and therefore fairly heavy and has no choice but to become a victim of gravity. (Why do you think raindrops fall down, and never up?)

As the topography of the hillside is by definition a slope, the water just keeps sliding downward until things level out a bit. Now, if nature has been left alone to do her work, that level part at the bottom of the hill is where the water can now soak into the soil and be retained for a while. A common name for this sponge area is “a wetland”. But of course nature has not been left alone, so that wetland has in all probability been ditched to ensure the water that came down from the hilltop just keeps on going without time to soak in.

As over 80% of the natural wetlands in southern Ontario are no longer allowed to exist, a whole lot of flushing takes place. The longer the river the more chances of wetland loss and the greater and faster the river fills up with water that should actually be somewhere deep in the soil.

The Nottawasaga River is like that, a long stretch of waterway that meanders through a lot of farmland as it heads down to Wasaga Beach. Not only have numerous wetlands been eliminated over time, but field drainage systems and municipal ditches ensure the water does not have a chance to soak in.

Other times it’s just the plain and simple fact that the river starts in an area on the Canadian Shield, where there is no deep soil to collect the water, just a whole lot of rock. Whoosh and it’s gone. This is the challenge with the Black River, which starts way up around Algonquin Park and slices through central Ontario before emptying out near Washago. That’s a huge collection area (known as a watershed) with only one outlet, so by the time the Black River water gets down to meet the Green River, the volume can get to be a bit more than the riverbanks can handle.

On both of these rivers there is also the added spring thrill of ice jams.  Pans of ice, once attached to the shores but now floating, hit a fallen tree and tilt on an angle. This flat ice sheet is now a dam, holding back a bit of the current. Add together a whole lot of ice dams and the water does slow down, and collect, and rise, and tops over the banks until it can flow across the pretty cottage lots all in a row. 

And here’s where the Big Concern comes into play… real estate values are challenged! Insurance claims will be made! Water damage to house foundations will occur! Woe! Damn you Nature! Somebody call a TV crew!

Flood prone areas are often near the end run of the river, as all that upstream water has finally come together to create quite a volume. And river systems usually have a natural delta formation to some extent, where eons of spring flooding have deposited silt and debris carried down from far upstream. This delta is what is mapped on land use planners’ maps as a flood plain. It’s going to get wet here folks, every year, almost guaranteed.

And for some unknown reason these flood plains were, historically, granted building permits. And for some reason the owners claim confusion each year when the river water rises up and enters their basement. What’s up with that? Who knew, eh?

Maybe there will be a few soft-hearted toilet paper hoarders who will drop off a few thousand of their rolls to help soak up the flood waters? Stranger things have happened.

                                       

Dave’s Notebook: Hello from my isolation chamber (aka my house).

Despite our health dilemma, the rest of Nature is carrying on just like usual: birds are coming back and plants are starting to grow. However, I just saw a Varied Thrush in our yard, a visitor from B.C., and that is indeed unusual, so what do I know.

Stay safe. Stay home. Stay healthy. Stay sane.

© 2020 David J. Hawke

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Tuesday, 31 March 2020

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