Everything you need to know about flooding this spring

Flooded Park Photo by Shutterstock/Artem Zavarzin

Cottage country flooding is always a concern come spring. In recent years, snow melt and heavy rainfall have put many Ontario communities at risk. For instance, in 2019, the District of Muskoka declared a flooding state of emergency as rising waters threatened properties, roads, and drinking water. And last March, cottagers in the Chatham-Kent area were forced to abandon their properties due to rising waters in Lake Erie.

No one wants to spend their spring shoring up waterfronts and praying that their property doesn’t get swept away, especially cottagers who don’t always have time to react to sudden flooding. That’s why it’s important to understand what causes flooding, so that you can take a proactive approach.

To find out whether your property could be at risk, Cottage Life spoke with Mark Peacock, the CAO of the Lower Thames Valley Conservation Authority, to get more information on flooding.

How are floods forecasted?

To predict whether an area is at risk of flooding, Peacock says conservation authorities must combine local knowledge of their particular watershed with an understanding of other systems that could impact water flow in the area. To grasp the bigger picture, conservation authorities rely on data from a provincial flood forecasting centre that looks at the overall water systems in Ontario.

Conservation authorities across Ontario are also in constant communication about water flow throughout the province. “Most of our systems either move from southwest or from northwest through Ontario,” Peacock says. “Therefore, we are able to talk to the other authorities and see through their gauges what is happening. So, it allows us a bit of a heads up on what we might experience.”

What causes flooding?

Flooding can be caused by a number of factors, with each watershed being affected differently. Peacock says one of the things they look at is snow depth. When forecasting flooding, the conservation authority will measure the snow depth and calculate the water equivalent within that snowpack.

Another major factor is the weather, especially heavy rainfall. In this situation, conservation authorities will look at North American-wide trends, such as whether we’re in El Nino and where the currents are driving different types of rainfall.

Peacock also says that soil saturation plays a part as conservation authorities determine how much water the soil can absorb.

How do different areas affect flooding?

Every watershed is susceptible to different conditions that can cause flooding. According to Peacock, it depends on a whole variety of factors, including the length of a river and the conditions of the watershed feeding into yours.

Flooding is also different depending on whether you’re on a river versus a chain of lakes. Peacock, who used to work as the engineer for the Otonabee system on the Kawartha Lakes, says that with the big lake systems, you have a longer lead time because it takes a while for them to flood.

When it comes to the Thames River, Peacock says their big spring concern is ice jamming, which is when floating river ice accumulates at a natural or man-made feature, impeding the progress of the ice downstream. “We’ve had major [ice jamming] events that blew out dikes and flooded square kilometres of land,” Peacock says.

Which properties are most at risk of flooding?

According to Peacock, it’s always the same properties. “It’s the buildings that shouldn’t have been there in the first place,” he says. In many Ontario regions, communities were built before the conservation authority had regulations. These properties, often built in floodplains, are not flood resilient and are susceptible to flooding every year.

Peacock says that across Ontario, there are approximately 100,000 buildings erected in floodplains. “It’s because our historic development was in the floodplain,” he says. Each time one of these buildings is wiped out by a flood and then rebuilt, the conservation authority, through the permitting process, tries to get the building flood proofed and removed from the flood plain.

How do you protect your property from flooding?

According to Peacock, the best type of flood proofing is what he calls “passive flood proofing,” which means you don’t have to barricade your property. “You want to flood proof so that your building is up and out [of the floodplain],” he says. This is especially true for cottagers who can’t get to their properties in time to deal with sudden flooding.

One of the ways to passively flood proof your property is to lift the building and mount it on a large mound of dirt so that it’s raised well above the water level, Peacock says. It’s also a good idea to avoid putting in a basement. “If you decide to finish your basement, you’re going to have significant loses.”

What does the Conservation Authority do when there is a flood?

If a flood is forecasted, Peacock says the first thing the conservation authority does is contact local municipalities, providing them with maps of the areas it believes will be hit by flooding.

“We get a hold of municipalities and say, this is where we’re at. We can give you three days notice, but we believe these are the houses that need to be talked to. Your emergency people need to talk to these people or this community. And there’s a potential the utilities will be turned off for these people,” he says.

Peacock remembers in 2018, when the town of Thamesville had to be evacuated, including nursing homes. “We had to give them as much notice as possible,” he says, “because we knew if we got water, all the utilities would have to be shut down. And at that point, you have to move senior people. You can’t have them in the dark or the cold. And you need to do it before there’s water in the building.”

What does the flood forecast look like this year?

The Lower Thames Valley has managed to make it through this spring unscathed. Peacock says the area’s spring freshet went through two weeks ago. “It wasn’t significant. Our ice moved very well. The upper watershed melted in a very even way without any rainfall,” he says.

In an email, the Ministry of Natural Resources and Forestry (MNRF) said that across the rest of the province it looked to be an average snow melt, giving little indication of severe flooding. But the ministry did warn that all it takes is a heavy rain event to quickly change those conditions.

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