Everyone has seen the photos, after heavy rainfall events and during the spring melt: homes in the Belle Ewart area, between Lines 5 and 6 of Innisfil, that are surrounded by floodwaters, even partially submerged.
For several years, the Lake Simcoe Region Conservation Authority (LSRCA) has been investigating options to address flooding in areas that include the Belle Aire Creek floodplain.
“As part of our Strategic Plan, we’ve been looking at flood relief programs,” said Mike Walters, LSRCA Chief Administrative Officer – and last year, the Authority was successful in winning a grant, under the National Disaster Mitigation Program, to launch the Alcona Flood Relief Project.
A Class Environmental Assessment was carried out to look at a whole suite of options and tools that might be used to offset the impacts of flooding and climate change, in a 350-hectare study area between Lines 5 and 6 of Innisfil, east of 20 Sideroad.
It's not possible to stop the impact of all flooding, Walters was quick to note. “If someone’s in a regional flood plain, and it’s a Hurricane Hazel event, we’re not going to stop it,” he said - but measures can certainly be taken to address frequent flooding and provide some relief for homeowners.
There are two creeks within the study area. Little Cedar Creek is described as a “healthy, undisturbed stream” capable of handling the peak flows of a “100-year storm” – the kind of major event that happens, on average, once in 100 years.
The other is Belle Aire Creek – the source of the flooding problems.
The study described Belle Aire Creek as “compromised, due to urban development.” Not only is it a source of sediment, pollutants and phosphorus washing into Lake Simcoe, its capacity has been so reduced that it can't even handle a two-year storm event without flooding.
Peak flow, during a two-year storm, is 2 cu. m. per second; the creek currently has a capacity of only 0.4 cu. m. per second.
Flood damage, over the long term, averages $2 million per year, and without action, the situation will only worsen. The study area actually drains a larger upstream area of 802.23 ha., which includes properties expected to see a 62 percent increase in urbanization, as part of the Alcona South Secondary Plan.
The increased development will change runoff patterns: reducing the amount of precipitation that can infiltrate into the soil, and increasing runoff, peak flows and flooding.
Climate change is adding to the issue. “Our Junes are wetter. These storms we are seeing now are much worse,” said Walters – leading to more frequent and higher peak flows, and an increase in flood events.
The Class EA looked at a number of options, including increasing the capacity of the existing waterway, preventing ice-jamming during the spring break-up, and providing additional storage for runoff.
The preferred solution is a combination of minor channel improvements for Belle Aire Creek, and the use of existing “Green Infrastructure”: the Little Cedar Creek wetland.
It was clear, through the EA, that simply upgrading Belle Aire Creek along the 670 metres from 20 Sideroad to Lake Simcoe would not work. The alteration in grade and channel-widening required to improve the stream capacity beyond a two-year storm event, in an area already built up, was “not technically viable.”
Some channel improvements were proposed, including clearing the creek of sediment and improving and replacing culverts, at an estimated cost of $690,000.
But the key to flood prevention and mitigation is the use of the Provincially Significant Little Cedar Creek wetland in the northeast portion of the study area.
The Class EA concluded, “Preliminary modelling currently indicates that there is sufficient volume for storage of all storm events up to the 100-year storm event within the existing wetland footprint,” with the addition of a 1.2 metre berm encircling the wetland.
“The idea of using existing wetlands – enhancing them, making them bigger” can be looked at as a viable option for flood control, “as long as you’re not impacting the health of the wetland,” Walters noted.
In this case, a new by-pass flow channel would redirect floodwaters from Belle Aire Creek to the wetland area – providing an increased area for evaporation and infiltration, and for biofiltering of pollutants within the channel.
The additional flows are also expected to contribute to the overall health of the wetland. Walters noted that climate change, with its higher summer temperatures and increased evaporation, has contributed to a loss of natural wetlands. They have been dryng out, in recent years, and invaded by trees.
The proposed project, in addition to mitigating flooding for residents of the area, may actually increase the lifespan of the Little Cedar Creek Wetland.
“It’s enhancing our natural heritage system,” Walters said. “It’s win-win. The more benefits you can get from this, the better… It just makes sense.”
The cost of creating the by-pass flow from Belle Aire Creek to Little Cedar Creek wetland, and adding a 30 metre buffer zone and new berming, is estimated at $6.11 million; total cost of all the mitigation proposed is $6.8 million.
With annualized flood losses estimated at $2 million per year, the project will pay for itself in less than four years.
The LSRCA intends to apply for additional grant funding, in addition to working with its partners in the project, including the Town of Innisfil, as it moves forward.
Notice of Completion for the EA was filed on March 31; the appeals period has now closed.
The EA is now “essentially completed,” said Walters, and has been submitted to the Ministry of Environment, Conservation and Parks for review.
Next steps include any additional studies required, a final design, and then construction. The goal is to begin the project in 2021, although that will be dependent on funding, Walters noted.
Affected property owners will be notified in advance of the construction schedule – with all work to be carried out during daylight hours only, and both dust and stormwater controls in place.
“It’s flood mitigation. It’s climate change. It’s enhancing our natural heritage system,” said Walters of the Alcona Flood Relief Project. “It makes perfect sense.”
And then there’s the bottom line: Over the 50-year lifespan of the proposed works, construction and maintenance costs are expected to come to $11.47 million. If no action is taken, the expected cost of flood damage is expected to exceed $41 million.
For more information on the Alcona Flood Relief Project, click here.