Friday, December 10, 2021

Our House is on a Floodplain. Why? Clay Stratification

Our house in North York/Toronto is on a floodplain.

I learned this recently thanks to a helpful neighbour. I was walking home from dropping off my son at school, and one of our neighbours was doing the same after dropping off his son, and we were both looking at the new construction of a building near the school.

The new building has a giant basement. Two stories. Something similar to an "iceberg home" where most of the house is actually below ground.

My neighbour was laughing at it however and predicted that it was going to get flooded...

And that was when I learned our entire neighbourhood was on a floodplain.

It wasn't something we were told about when we leased the property, but it is definitely an issue.

Now you might think, like I did: "Wait, isn't our house on a hill? How can it be on a floodplain?"

The problem is the soil.

Clay Stratification

Most drainage issues are caused by clay soil. A minor issue will be that you have standing water after a heavy rainfall for less than a day, and it will be more noticeable in your front yard and backyard. Clay soil is more dense than sandy or loamy soil, and therefore, is slower to allow rainwater to filter through it.

Clay Stratification is when you have multiple layers of dense clay, the result of millions of years of rainfall, rivers and flooding, etc. When one layer of clay stratification becomes flooded it acts like a barrier, so that water above it just sits there and can only move sideways, but not down.

Get too much water all at once, and the next thing you know your basement is flooded because it acts like a well where the water can collect. Many basements aren't designed to withstand that much water trying to get in. This is a big problem for many parts of Toronto because clay stratification is actually surprisingly common.

Why does Toronto have so much clay stratification?

Go back 12,000 years ago and all of Toronto, the GTA and the Great Lakes region was under a big inland sea. As time went by the water levels receded and it left behind layers of clay bits and loamy bits, resulting in many layers of clay and loam.

Factor in that Toronto is also effectively an ancient river delta, and yeah... That's a lot of clay.

So what can you do about it?

Knowledge is key.

#1. You need to ask "Is this property on a floodplain?"

And make a note of how the owners respond.

#2. Get it in writing.

Because people do lie about floodplains and it can lead to lawsuits when people later find out that they bought property on a flood plain. (Or bought a house with mold problems. Or bought a house with termites. The previous owners need to be disclosing these problems.)

#3. Ask "What steps have been taken to prevent flooding?"

Because chances are likely if your property is in Toronto, then it is probably on a flood plain. Even if it is on top of a hill.

#4. Get home owners insurance.

But you might also get other types of insurance too. Eg. Buyer's Title Insurance for example. Or Mortgage Insurance if you are getting a mortgage.

And flood insurance if you are in a high risk location.

Basement Flooding on the Rise thanks to Climate Change

Yeah... So this isn't a problem that is just going to go away. Places that aren't traditionally thought as being flood prone these days are getting flooded anyway. Climate Change means that Toronto now has a rainy season from April to May.

And we can still get large deluges of water thanks to freak rainstorms like that one on July 8th 2013.

I was outside when that flood happened. Toronto got 126 mm of rain in only a few hours. And while that doesn't seem like much, remember that water flows downhill and will flood basements, parking garages, subway stations, floodplains, lower streets, etc along the way.

Here's some video of what happened on July 8th 2013:

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