A flood hazard study has found that about 36 per cent of the total assessed value of improvements within the Regional District of East Kootenay, including municipalities, lies in an area prone to flooding.
That is equal to $2.4 billion of building infrastructure, according to the report prepared by Vancouver applied earth sciences company BGC Engineering.
"The first surprising result is the proportion of infrastructure that is located in areas that have been mapped as potentially subject to flood hazard," engineer Kris Holm told the Regional District of East Kootenay (RDEK) board of directors at a committee meeting on Thursday, April 4.
"It's not an estimate of the potential building damage costs that could happen during any particular flood hazard scenario – that would be much lower," he said.
"This is likely an overestimate of the damage that could occur during any particular flood event, although it is perhaps a proxy for the importance of flooding as something to think about in the district."
Most of the flood hazard areas are outside of municipalities, the study found. Area A – around Fernie and Sparwood — has the highest priority rating; followed by Area F — between Canal Flats and Invermere; then Area C — around Cranbrook; Area E — Wasa and Skookumchuck; Area G — north of Radium; and finally Area B — around Koocanusa.
Within municipalities, Fernie has the highest rating, followed by Elkford and Canal Flats, then Invermere, Radium Hot Springs, and finally Cranbrook, Kimberley and Sparwood.
The report also took in climate change predictions and applied them to flood hazards in the regional district. The study summarized projected climate change over the next 100 years.
“To sum it up, by the year 2070-2099, models suggest we will see in the district a general increase in annual temperatures, a decrease in summer precipitation, an increase in winter precipitation, a decrease in spring snowfall, a general decrease in extreme snowpacks, an increase in the intensity and frequency of short, high intensity precipitation events, and somewhat of an increase in extreme precipitation for the northern versus the southern areas of the region,” said Holm.
“Some of the projected results (of climate change) are that we may see extended flood hazard seasons: later autumn floods, earlier spring floods, increased secondary peak flows for the flows occurring in the autumn, potentially an increase in the number of high flow events if there is an increase in intense precipitation, and increased frequency of rain on snow events, which is a driving factor for flooding.”
Landslides have different triggers, he went on. For example, more forest fires could bring more intense run-off, which could bring landslides.
“In general, there is potential for increased debris flow activity over the next 100 years, an increase in peak discharge rates which may result in increased landslide activities, changed tidal patterns, and possibly, depending on the processes, a reduced effectiveness of existing dykes and flood infrastructure,” said Holm.
The flood hazard study was prepared using existing data as the first step towards a comprehensive regional flood management plan.
The RDEK board of directors have not yet approved funding for the next steps of the plan. On Friday, April 5, the board postponed consideration of the study to wait for further information.