Lack of data boosts flood risk in B.C.
Many communities working with out-of-date floodplain maps — or have no maps at all
B.C. communities that lack upto-date floodplain maps risk billions of dollars in property damage and even the lives of their citizens when disaster strikes, experts say.
“The flood in Calgary and High River is a perfect example of what happens when your maps are wrong,” said Tamsin Lyle, a Vancouver consulting engineer. “The events of 2013 showed that their maps were out of date, so the areas they thought were going to flood didn’t flood and the areas where it flooded weren’t shown on the map.”
“Planning decisions and emergency response plans were based on poor information, resulting in a lot more damage than might have otherwise happened,” she said.
Many B.C. communities lack recent floodplain data, according to a study commissioned by the British Columbia Real Estate Association. Changes in the topography of developed land, silt accumulation in rivers and changing weather patterns can render a floodplain map obsolete in as little as five years.
One of the biggest data gaps is in the Fraser Valley floodplain, said Lyle, a principal of Ebbwater Consulting who was an adviser on the study. The Fraser Valley suffered widespread damage due to flooding in 1894 and 1948, when 2,000 homes were destroyed.
A similar flood today would cause several billion dollars in damage in Chilliwack and Richmond, according to the Ministry of Forests, Lands and Natural Resource Operations.
“It’s an unmapped territory,” said Lyle. “We can make some good guesses, because it’s flat … but we don’t really have a designated map.”
The provincial government created a floodplain mapping program in 1974 to help towns and cities direct and limit development in floodplains. The program identified and designated 90 floodplains before the program was cancelled in 2004, leaving municipalities to conduct their own research.
Only 21 per cent of the communities and First Nations that participated in the study have updated their floodplain maps since the provincial program was discontinued, according to the authors. More than 30 per cent have no floodplain maps at all and the remaining 48 per cent are working with out-of-date information, most of it at least 20 years old.
A federal floodplain mapping program was killed in the mid’90s, but there are signs that may change since the Calgary flood, which killed five people, said Lyle.
Lyle will attend a flood mapping workshop next week organized to coincide with the federal National Disaster Roundtable in Calgary.
“The tools that you can launch once you have a map can save you billions and billions of dollars down the line,” she said. “It’s just a matter of convincing folks that this is important.”
Ottawa should be ripe to take notice of the potential advantages, she said. The federal government spent $6.1 billion on flood relief in Calgary and Toronto in 2013.
Insurance companies complained in the aftermath of the floods that most floodplain maps are badly out of date, which is part of the reason most home insurance policies do not cover flood damage.
A University of Waterloo study released that same year found that flooding has become the biggest payout category for Canadian insurers. Private insurers paid out $2.25 billion for damage in southern Alberta in 2013.
New laser-based mapping technology has revolutionized floodplain mapping in recent years, according to Nathan Vadeboncoeur, an engineering consultant who worked on that study.
It’s a level of detail that is vital as extreme weather events become more frequent.
New aerial LiDAR surveys provide topological data accurate to within centimetres, making it easier to predict how flood waters will move over the land.
“There can be little ruts that channel water that you can’t see on older maps,” Vadeboncoeur said.