The provincial government is expanding the number of possible flood scenarios it will consider in a hydrology assessment of the Bow River in a new hazard study currently underway.
In the past, flood hazard studies have only considered three different return periods for the range of possible river flows during floods along the Bow River. Now, Environment and Parks spokesperson Jason Penner said, that range will include 13 different return periods; from one in two years, to one in 1,000 as part of work currently underway as part of the province’s flood hazard identification program.
“In the new study we have more information and a greater range of possible floods that we want to assess and map,” Penner said. “The hydrology assessment will cover 13 different scenarios … what that will lead to is flood inundation mapping for those 13 different sized floods as well.”
The key result of conducting the extensive study, he said, is to build safer communities in the longer term by identifying risks posed by flooding in communities and help guide development. Penner said it would also equip municipalities with information that can be used for emergency response planning.
“What that gives you for higher populated areas is more information about where water will go for a variety of events and how deep it will be,” he said. “So when we talk about the broad goal of flood hazard mapping helping to build safer communities, it is not just helping municipalities make those development decisions, but also flood hazard maps are an important tool for emergency response planning.
“If you find yourself in an emergency situation and you are able to look at one of 13 different possible flood scenarios for the one that most closely matches what you are experiencing it can provide some pretty critical information about where you might have to evacuate people (for example).”
The hydrology assessment results in flood inundation maps that can be accessed by municipalities and the public for planning. The range of possible floods along the Bow River will include: two, five, 10, 20, 35, 50, 75, 100, 200, 350, 500, 750 and 1,000-year floods and will include looking at the 2013 flood.
The Upper Bow River Hazard Study began in fall when contractors were out along the river channel from its headwaters through 220 kilometres of the river. Penner said it is one of several river channels currently being studied by the government – 525 kilometres worth.
“It is an ambitious amount of work,” he said. “ We are looking at mapping 525 kilometres of river and that is along the Bow, the Elbow, the Sheep, the Highwood and up north, the Peace River as well. Just to put that into context, we currently have 1,100 kilometres of river mapped in Alberta.”
After the 2013 flood, the Town of Canmore began conducting comprehensive flood risk and hazard assessments for its mountain creeks, which saw debris flows that caused significant damage to homes along Cougar Creek.
At the same time, concern in the community grew about the potential of the Bow River flooding, as river levels during the 2013 event were quite high, although it did not breach the berm along the river. That berm was built after a flood in 1974 affected much of the valley bottom of Canmore.
Manager of engineering Andy Esarte said the municipality considered conducting a hazard assessment of the Bow River as well, but the fact the province is undertaking a more comprehensive analysis took precedence.
“We were happy to defer to the province for the hazard and risk assessment of the Bow River,” Esarte said. “Because they are looking at it comprehensively, it does not make sense for the municipality to look at our section as a one off.”
The province also established guidelines for hazard assessments on steep mountain creeks and Canmore and the MD of Bighorn used those over the past two years to analyze various creeks that affect developed areas in both communities.
Penner said there would also be new guidelines for developing around mountain creek hazards as they are currently under final review.
In addition to the hydrology assessment, the study will complete hydraulic river modelling, flood inundation mapping for the 13 different sized floods, a new flood hazard map, flood risk assessment and inventory and a channel stability investigation.
Penner said the new flood hazard map would continue to use a one-in-100 year return period to look at the floodplain. The map separates the floodplain into floodway and flood fringe zones to show where flooding would be deepest and most destructive.
“The lines on the map might change, but the process and the goal of saying this is where we define the floodway and flood fringe is still the same criteria,” Penner said.
Part of the Upper Bow River Hazard Study area lies within the national park system and those areas will not see new mapping produced. While there is no new map for inside the park, the hydrology assessment does go up to the headwaters of the river.
“If you don’t reassess the areas in the headwaters, you have a missing piece in your calculations that feed into the model and that is why it is important,” he said.
