A You Tube video clip that refers to the decision making behind the design of Canmore’s Cougar Creek mitigation measures as “stupid” is representative of a misunderstanding of the nature of the creek before and after the measures were implemented, according to the Town of Canmore’s senior engineer.
The statement comprises two slides and barely a minute of an hour-long keynote address titled Canada’s Freshwater in the 21st Century presented by David Schindler, University of Alberta professor of ecology, former director of Canada’s world-class Experimental Lakes Area, acid rain authority and Stockholm Water Prize recipient whose current studies focus on freshwater shortages and the effects of climate change. Schindler made the presentation at the University of Waterloo, Ontario’s Water Institute on June 18, close to the one-year anniversary of the 2013 flooding of southern Alberta.
The two slides show images of Cougar Creek in its natural state, and the basin as it is now, widened and lined with articulated concrete mats.
“It just leaves you grinding your teeth,” Schindler said in the video. “We have really learned nothing in 50 years. We still let engineers do this to natural streams. This might be good news for Canmore; I can tell you it’s not good news for Calgary. This is like building an outhouse, and then having somebody put in a second layer of holes above your head. It’s absurd to see human beings still stupid enough to be doing this sort of remediation.”
When asked to further explain his comments, Schindler replied to the RMO by email, saying that in addition to a straight, rocky channel being very poor habitat for any sort of organisms, “the wetlands that used to hold back some water from hitting the river have been destroyed, replaced by concrete, so now all of the water hits the river at once.
“All this does is hurry the water through Canmore and get it to Calgary faster. Part of the reason why we are seeing more flooding is this very sort of mentality … get the water off my property and send it downstream.”
Similar mitigation was done in Europe for many years, Schindler said, until about 20 years ago when engineers began building meandering streams with gravel bars that support biota.
Schindler’s comments, said Canmore’s manager of engineering Andy Esarte, show a misinterpretation of the work that has been done on Cougar Creek.
“Philosophically, I agree with Professor Schindler, and his desire to limit how quickly we allow the flow to get to the main rivers,” Esarte said. “But Cougar Creek’s discharge is relatively small in relation to the Bow River basin. It is neither straighter nor flowing faster. Both those assumptions are false. Cougar Creek is a minor contributor relative to the flows coming into Calgary from hundreds of tributaries. By the time you get to Calgary, the mitigation work has zero impact on the City of Calgary.”
The main focus behind the Cougar Creek mitigation measures was two-fold, Esarte said: to protect people and property and to control erosion, not to slow water flow in the channel. The mitigation measures have left Cougar Creek with the same channel roughness and the same infiltration properties as it had before, he added.
“While it has the appearance of a concrete-lined viaduct like Los Angeles, that’s not what it is,” Esarte said.
“Cougar Creek is a pre-existing channel that functions differently than it would if it had not been built on. We can’t turn back time, we can’t remove 4,000 residents and one third of Canmore’s business community.”
Robert Newbury, a Kewlona, B.C.-based engineer who specializes in stream restoration, said he doubted the articulated mats would serve to slow any flow of water during a flood, particularly of the magnitude of the 2013 event. He also said he didn’t think the mitigation would have any significant effect on the amount or speed of water Cougar Creek would send to Calgary during a flood.
“The water will still go tearing through so fast it won’t make a difference,” Newbury said.
The big problem, he explained, is that alluvial fans, such as Cougar Creek’s, are built by having floods occur that have so much debris that as they reach the lower gradient at the end of the creek, they fill in one channel and the water jumps over and begins a new channel, and the process is repeated again and again.
Cougar Creek’s alluvial fan has been doing this for 7,000 years, he said.
“We build on these sloping river landforms, alluvial fans like Cougar Creek's for example, that are still building themselves,” Newbury said. “Once in a while we can steer some of their energy away by breaking their gradients and storing floods in reservoirs. Trying to contain the energy with dykes and riprap is a lot more difficult and very often unsuccessful.”
The net installed at the mouth of the creek, he estimated, might stop a debris flood once.
Having flown over Cougar Creek upstream of Canmore, Newbury echoed what is visible on a topo map and to any hiker or rock climber who has ever walked all the way to the Canadian Forks crag – upstream, where creek water does flow through the summer, the creek is wider than it is closer to Canmore. That widened creekbed creates natural space to store debris.
“You have to stop this fan building process because you sold off all the storage area,” Newbury said. “You do that by wresting the sediment and accumulating the materials upstream.”
The solution, he suggested would be to build a reservoir upstream, beyond the town boundaries.
In an April interview with the RMO, Esarte said the current work would not fully contain a flood of the magnitude of last year’s, and that further mitigation would be pursued. A detailed risk and hazard assessment is in the process of being finalized, and is expected to be released for community engagement in the not too distant future.
He also said the debris net was designed in a way that it would need to have sediment removed after an event and through regular upkeep and removal should last for more than one flood event.
