Editor: Does anyone remember the June 2013 flood and how destructive it was?
The badly damaged houses along Cougar Creek? The destroyed homes in Exshaw? The disruption to the community?
Of course we do. If you were anywhere in this part of Alberta at that time it is impossible to forget the most costly natural disaster in Canadian history ($6 billion).
However, it would appear that those pushing for the new subdivisions in Dead Man’s Flats have had a lapse of memory regarding the damage that large floods can do, and are potentially putting people and property in harm’s way of Pigeon Creek.
Here’s why.
There are three big alluvial fans (ie. mountain creek flood zones) in our part of the Bow Valley – Cougar Creek, Exshaw Creek and at Dead Man’s Flats – each formed as a result of flood events over the years.
It is difficult to grasp the amount of material these creeks (nay, ephemeral rivers) have moved. The lead researcher of the comprehensive 2013 Mountain Creek Hazard Mitigation Plan (the 2013 flood study), the $600,000 study of flood risk in the Canmore region, put it this way: the amount of creek material (gravel, cobble, boulders) in the Cougar Creek alluvial fan (where all the houses currently sit) would fill enough dump trucks to wrap around the world twice. That’s a lot of material moved by a lot of floods.
Now here is some equally sobering information. According to the 2013 flood study, (1) the Wind Valley watershed is about 20 per cent larger than the Cougar Creek watershed, (2) the land where Dead Man’s Flats sits has been formed as a result of similar Cougar Creek-like flood events, and (3) that around 1923 there was a massive Pigeon Creek flood, much larger than the recent 2013 one (the hamlet began in the 1960s with arrival of the Trans-Canada Highway there).
But it gets worse. If you walk in the Wind Valley watershed, where Pigeon Creek originates, like I regularly do, you will see the most impressive June 2013 destruction of all the local creeks, much more so than Cougar Creek or Exshaw Creek. In June 2013, the various creeks in the Wind Valley watershed, which are all tributaries of Pigeon Creek, enlarged their widths from a few meters to nearly 50 meters or more in places, for many kilometres.
The many thousand uprooted trees absorbed much of this fearsome kinetic energy, lessening the destructive potential further downstream in Pigeon Creek and in Dead Man’s Flats. In other words, the trees took the hit, but those trees are no longer standing and so next time the flood will likely be much worse, and the creek/river heads straight into a portion of the proposed new development.
In late 2013, after a flood study presentation, I asked one of the BGC Engineering hydrogeologists what findings had surprised him. The researcher said one surprise was that the Dead Man’s Flats alluvial fan appears to have formed as a result of large sudden flood events rather than a succession of smaller ones, implying that Pigeon Creek was a potent wild card.
Further, John Pomeroy, one of Canada’s foremost mountain hydrologists, has expressed concern about Pigeon Creek’s flood potential.
In light of the above, what does the development plan (ASP) being considered have to say about Pigeon Creek? Surely, it would have taken such long-term risks into account. Unfortunately, the very brief hydrological report simply states in Section 6.2 that it is not possible to evaluate long-term flood risk for Pigeon Creek because there is no long-term flood mitigation plan currently available. Sad but true.
Yet the 2013 flood study on page 24 recommends that a detailed flood risk assessment for Pigeon Creek precede new development plans in Dead Man’s Flats, such as the proposed subdivisions and such.
In short, the approach should be: step 1, figure out long-term risk of large, destructive Pigeon Creek floods (frequency and magnitude); step 2, look at possible solutions to deal with those risks; step 3, consider development options in light of 1 and 2.
Alarmingly, step 3 is being done before step 1 and 2. The detailed flood risk assessment that would feed into a credible long-term flood mitigation plan for Pigeon Creek has not been done (it has only been done for Cougar Creek). Dead Man’s Flats currently only has short-term flood measures which are almost certainly inadequate for larger Pigeon Creek floods.
People now living in Dead Man’s Flats would also benefit from a proper, comprehensive long-term Pigeon Creek flood mitigation plan. BGC Engineering determined that it is a statistical certainty that Cougar Creek will experience a flood significantly larger than the June 2013 one; unavoidably, this also applies to Pigeon Creek.
Two short years after the destructive 2013 flood new developments are being located in risky flood zones. Are memories that short? If the development plan being considered proceeds and people or property are harmed in a flood, I believe those who planned, approved and/or promoted the development should be held personally accountable.
Let’s hope common sense prevails and that Dead Man’s Flats does not turn out to be an eerie prophecy. At a minimum, people who buy second homes (and investment properties) there should know that provincial flood compensation excludes second homes, as such owners along Cougar Creek found out in 2013.
Jacob Herrero,
Canmore
