If an extreme storm unleashed its fury on our region, Collingwood would be more at-risk of high damage by flooding than its nearby neighbours.
Such an event would likely mean access to the town's hospital, paramedic station and police station would be, at best, limited, while residents in some areas could be cut off from entering or exiting their neighbourhoods.
That's what a report by the Nottawasaga Valley Conservation Authority has revealed. The report, titled Watershed Flood Risk Assessment identifies three areas of concern within Collingwood including:
- Batteaux Creek along Beachwood Road, Georgian Manor Drive and toward the bay;
- Pretty River from Poplar Sideroad to the Bay; and
- Silver Creek along Osler Bluff Road and Grey Road 19.
Kristopher Robinson, the NVCA’s water resource/GIS technologist, and Peter Alm, the agency's water resource engineer, co-authored the report with Hendrick Amo, manager of GIS and IT, and presented it to the NVCA board of directors at their recent meeting. The study was funded by the National Disaster Mitigation Program.
"Collingwood was identified as the most at-risk of flooding ... which reflects that it has the largest number of buildings and roads within the floodplain compared to other communities," said Alm. "Collingwood has a relatively large population compared to other towns in our watershed, with a few streams passing through areas historically developed within the floodplain. Collingwood's ranking as most at-risk of flooding is therefore not unexpected."
There were eight communities in the NVCA boundaries selected for this report including Alliston, Angus, Collingwood, Creemore, Elmvale, Shelburne, Stayner and Wasaga Beach.
"The study completed is a high-level look at which communities are most prone to flooding," said Alm.
However, Wasaga beach was not included in the report as there are other flood risk assessment projects ongoing there with more accurate data predicted.
The communities received a risk assessment score based on flood event warning time, population impacted, affected roads for pedestrian access, affected roads for vehicle access and expected annual damages. The study looked at flooding via rivers and creeks as that's the most likely source of a flood in town.
Staff used different modeling technology to predict the outcome of various levels of floods identified by their likelihood.
So a two-year event has a one in two (fifty-fifty) chance of occurring in any given year. A 100-year event has a one in 100 chance of occurring in any year. The report also uses the Timmins Storm Model to predict flooding in an extreme storm event.
The Timmins storm was a flash flood that took place Aug. 31, 1961, in Timmins. There was a torrential downpour that lasted just a few hours, but destroyed roads, homes, building foundations and personal property. A mother and her four children drowned in a home by the bank of Town Creek, where the flooding originated.
According to the NVCA report, the biggest issue should flooding occur along the Batteaux River is the potential for residents to be stranded in their homes and emergency crews could be unable to reach them. Flooding in the area would cover Beachwood Road and prevent or make emergency access difficult. In a 100-year event or Timmins Storm event, most of the homes on Georgian Manor Drive on the waterside would be underwater.
Along pretty River from Poplar Sideroad to the Bay, flood waters would rise from the river and onto the banks from 50 to 500 metres from the river depending on the severity of the storm. The report predicts there would be many buildings and residential homes in peril in the case of a major rain event.
“The hospital, as well as the paramedic station and the police station, would have limited access due to flooded roads,” states the report.
It further indicates major roadways such as Highway 26, Pretty River Parkway, Huron Street and First Street would be flooded causing loss of access and egress to the area.
Along Silver Creek, flooding will threaten new housing developments on Osler Bluff Road and Grey Road 19.
Jannett Mays, communication officer for the town of Collingwood, said the town does have a flood contingency plan included in the official Emergency Management Plan, which was developed and reviewed by the fire department, public works and NVCA.
"Our full emergency management plan is reviewed and updated annually, and will take into account the assessment by the NVCA; however much of the information has already been incorporated into the flood contingency plan."
According to the engineer and technologist predictions, even a more common event like a 2-year or 10-year flood would have a significant impact on major roadways in Collingwood along Batteaux Creek and Pretty River.
After Collingwood, of the eight communities studied, Stayner, Creemore, and Alliston are most at-risk of flooding.
Stayner’s entire downtown could be flooded in a Timmins Storm-like event; a similar fate would befall Creemore. In Alliston, the residential area south of Victoria Street West to the river would be most impacted.
The NVCA notes a major flood with water levels that exceeded what would be expected in a 100-year flood event, occurred on June 23, 2017, in Shelburne, Mono, New Tecumseth and Adjala-Tosorontio.
“Climate change could affect the frequency of storm events, making extreme storms such as the 100-year return period event more common in the future,” states the flood risk assessment report. “With large storms becoming more frequent, there is a higher chance of threat to property and life.”
As time goes on, if climate change continues at similar rates, a 100-year flood event could be more like an 85-year flood event, with a one-in-85 chance of occurring in any given year.
According to the report, the NVCA will use this information to work with municipal staff to update floodplain mapping in the most-at-risk communities, including Collingwood. NVCA staff will also continue to work with municipalities and landowners where opportunities for flood mitigation projects are possible. The NVCA staff also suggest there should be more done to educate municipal staff, councils and the public on the impacts of flooding.
"We are planning to share the results directly with Collingwood flood response and engineering staff so that they have a better understanding of the areas in town that will likely flood first," said Alm. "This will help to prioritize emergency response during a flood event. The risk assessment is also the first step at identifying where engineered floodplain mapping updates may be beneficial."
According to Mays, the town does have a number of its watercourses already floodplain mapped.
"As new information becomes available, these maps are updated," said Mays. "The NVCA is the lead in mapping, and we work closely with them as our partner."
The NVCA does run a flood forecasting system and will post warnings and messages on its website here.