Hamilton homeowners should think about where water would go in a flood, group says

With so-called one-in-100-years storms happening at least once a year now in Hamilton, Miranda Burton says preparing for potential flooding is more urgent than ever.

And that's why her organization is trying to mobilize people to do just that.

Burton, program manager for the Hamilton not-for-profit Green Venture, says they're trying to get Hamiltonians to look at overland water flow differently. 

Climate change is leading to more severe storms throughout the region, while development in Hamilton is expected to intensify significantly following city council's decision to maintain a firm urban boundary – meaning more pavement and fewer water-absorbing natural areas, she says.

"We're looking at wetlands that are being paved over, and we're running out of space for this water to go," says Burton, the program manager for Hamilton not-for-profit organization Green Venture. "It has to go somewhere. It's not just going to disappear."

Instead of directing water away from our houses and into the sewers — the traditional approach — Green Venture is urging people to create water-trapping green infrastructure on their own properties, she says. This can include swails, green roofs, and rain gardens – specially-constructed plant plots designed to soak up water and hold it there longer.

"When rain and snow falls in a natural environment, only 10 per cent will be runoff," Burton says. "In an urban environment, it's 55 per cent runoff."

Green Venture is offering a rebate of up to $500 for about 30 Hamiltonians who add green infrastructure projects to their properties this year through its Naturhoods program, which has been expanded following a previous pilot. Those interested can visit greenventure.ca/naturhoods and add their name to the rebate program email list to get more information.

"We want to be creating neighbourhoods that are able to deal with this issue of flooding, which is becoming more and more apparent," she said, noting the city gets the most flooding complaints from Wards 1, 2 and 13 – downtown, the west end and Dundas. 

The onus to prevent flooding may be more on the individual than some residents realize. Hamilton Water, the city's water management division, lacks an accurate picture of where excess water goes in major storms, according to a report presented by senior project manager Cassandra Kristalyn to the city's public works committee in December.  

"The city is lacking a comprehensive model that accurately captures both minor and major [stormwater] systems," the report says. "As a result, the city is limited in its ability to rapidly conduct post-flooding studies to identify and address any contributing factors to the flooding event. The city has insufficient visibility on where these systems are undersized or where flooding risks may exist."

'Streets and neighbourhoods vulnerable'

In her comments to council, Kristalyn indicated that flood risk is very likely to increase.

"Climate change is altering the intensity, overall duration and frequency of climatic events and causing increases in precipitation volumes and patterns," she said. "This presents a critical challenge for city infrastructure. 

"There is also a risk that major stormwater paths do not exist in some parts of the city leaving streets and neighbourhoods vulnerable to flooding."

Hamilton Water is working on a long-term project to update its modelling, but director of planning and capital Mark Bainbridge says it's a process that could continue indefinitely as the models improve.

"There's a lot of work that needs to be done," he said in a recent interview with CBC Hamilton, noting there is no modelling of overland water flow for most of the city, except Ancaster. "It is an ongoing process on a long timeline… It's a multi- multi-year program."

'People wake up when they have the big one'

He says it's much more complicated to accurately model in the parts of the city with combined sewer and stormwater pipes – most of the lower city and a section of the Mountain closest to the brow – but says it is possible.

With a rapidly changing climate that will increase the risk of flooding, hydrologic modelling expert Paulin Coulibaly says urgency is needed.

"People wake up when they have the big one," says Coulibaly, a professor of civil engineering at McMaster University and a director of Floodnet, a national network of researchers working on projects including flood and precipitation forecasting.

Citing Edmonton and Calgary as examples, he said, "some cities are already moving quickly and are well ahead" when it comes to flood preparedness, with measures such as policies preventing development in areas likely to flood.

He said recent research shows southern Ontario will have increasingly intense "storm events" as warming continues, and notes the area below the Niagara Escarpment is particularly vulnerable to runoff. "This area between (the Great Lakes), we will have more evaporation in this area, and that water will dump heavily on us. It's just a matter of time. Really, the prediction is the issue." 

City is trying to prepare people

He said Hamilton had the opportunity to participate in Floodnet, and thus benefit from its localized precipitation modelling, in 2014 but declined. 

Hamilton's senior project manager of air quality and climate change, Trevor Imhoff, says the city "is working toward preparing our entire community for the future impacts of climate change. This includes better understanding what future climate scenarios Hamilton may experience including but not limited to precipitation events and intensity, number of heat days and extreme heat, and number of extreme weather events such as wind and ice storms."

He says the city uses climate models from the Climate Atlas of Canada, and pointed to Hamilton's Climate Science Report, which says "100-year rainfall events" are forecast to go from a five-minute downpour rate of 190 millimetres of rain per hour to 215 millimetres per hour by 2050. 

Imhoff says the city is also part of a pilot project with other GTHA municipalities to help guide adaptation projects.

"This pilot also uses these future climate modelling projections in order to better assess the potential risks on the City's infrastructure assets," he said. "This will ultimately work to reduce potential flooding events, protect local waterways and contribute to a safer and healthier Hamilton."