Don't drain the swamp: report says wetlands help avert flood damage

Canada needs to stop draining its swamps in order to reduce flooding linked to climate change, warns a new report.

Wetlands, including swamps, marshes and bogs, are natural catch-basins that can quickly absorb much of the excess water dumped by increasingly fierce storms.

And research from Ontario's University of Waterloo has found that leaving wetlands intact can reduce the financial costs of floods by up to 38 per cent.

"The wetlands aren't there for decoration — they actually serve a purpose," Blair Feltmate, one of the researchers, said in an interview.

The $90,000 study, released today, examines in detail how wetlands in their natural state protect two sites, a rural area north of Mississauga, Ont., and an urban site in Waterloo, Ont., in the event of a major flood.

Both sites currently have adjacent wetlands, and the researchers estimated the impact of a major autumn flood if those wetlands somehow disappeared. The authors drew on the experience of massive floods in southern Ontario triggered by Hurricane Hazel in 1954, noting that such severe events are becoming more common with climate change.

Wetland absorber

Computer modeling, historic insurance data and recent damage estimates from floods in Ontario and Alberta showed the cost to repair major flood damage at the rural site at $8.9 million with wetlands absorbing the impact, compared to $12.4 million without.

At the Waterloo site, projected costs were $84.5 million with a wetland absorber compared to $135.6 million without.

The role of wetlands as catch-basins has long been recognized, but the study — from the university's Intact Centre on Climate Adaption, founded by a large insurance firm — is among the first to quantify the financial benefits.

The research was paid for by Ontario's Ministry of Natural Resources, which already supports wetland conservation, and Ducks Unlimited, a non-profit group operating in Canada since 1937 to preserve waterfowl habitats.

People have to understand that the actual dynamics of the system have changed ...- Climate-adaptation expert Blair Feltmate, University of Waterloo

Climate change has been associated with a range of weather-related disasters, including droughts, windstorms, ice storms and wildfires, but in Canada the costliest events are floods. Insured damage from natural disasters in 2016 hit a record $4.9 billion, according to the Insurance Bureau of Canada, which estimates up to a million Canadian homes are in high-risk zones for flooding.

Feltmate says things are getting worse.

"People have to understand that the actual dynamics of the system have changed, due to climate change and elevated CO2 (carbon dioxide, a greenhouse gas) loadings in the atmosphere," he told CBC News.

"So the intensity and the duration, and even the frequency, of rainfall events is already greater than it was in the past, and it's even growing in magnitude."

'Eyes wide open'

The study notes that about 14 per cent of Canada's land mass is wetland. In some populated areas, most of the historic wetlands have been drained to make way for farms, houses and roads. In southern Ontario, for example, some 72 per cent of the original wetlands have disappeared.

Feltmate says at the very least, Canadians should know the future flood risks and costs of draining swamps, muskeg, bogs, fens and marshes.

"We should do so with our eyes wide open, and make sure our decisions are well-informed," he said. "As an absolute minimum, let's be well informed as to the consequences."

Severe flooding this spring hit several regions, including areas around Montreal, Ottawa, Toronto and southwestern Ontario, and the British Columbia southern interior.

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