On the north side of the Bow River across from downtown Calgary, a paved pathway follows the top of a berm, giving cyclists and pedestrians excellent views of the fast-moving river, views not available to motorists on Memorial Drive.

During the 2013 flood, the river water flowed on both sides of that berm, covering Memorial and spreading through the community of Sunnyside.

Now, as part of a suite of possible flood protection measures, the city is proposing even higher berms and floodwalls — a solution that might keep communities like Sunnyside safer, but could drastically change the look and feel of large parts of the city.

On Oct. 18 at the Hillhurst/Sunnyside community centre, Calgarians filed in to take part in one of six citizen workshops about flood mitigation measures. The aim of these workshops were to give Calgarians a platform to voice their concerns and opinions about possible flood mitigation projects.

City staff said projects already underway will reduce flood risk by about one-third from where it stood in 2013. For further reductions, they offered three major options.

First, dams could hold back water upstream, at the Springbank Off-Stream Reservoir already proposed on the Elbow River and at one or more location on the Bow River.

Second, the city could build extensive berms and flood walls along one or both banks of the Elbow and the Bow.

Finally, “non-structural measures” such as changes to building codes and bylaws could help reduce damage in areas that can’t be protected from flooding.

Tony Morris, co-president of the Calgary River Communities Action Group, says studies show that “upstream mitigation is the way to go.”

But with the proposed Springbank reservoir still mired in reviews and opposed by local residents three years after the flood, and upstream options on the Bow not even narrowed down yet, the upstream option could leave some areas unprotected for many years.

Flood barriers within the city limits could be built much more quickly, but they come with a cost. To protect from a 1-in-200-year flood — a flood expected to occur at least once in two centuries, but possible in any year — berms and flood walls would reach up to one storey high (roughly three to four metres) in places, blocking not only floodwaters but also river access and views.

New or elevated barriers would be needed — on one or both banks — through roughly half the Bow’s length within the city and along nearly all of the Elbow where it runs through communities below the Glenmore Dam.

The savings in damages from a major flood can be calculated, but it’s hard to measure the barriers’ cost to river access, aesthetics and environmental quality. Citizens discuss flood mitigation projects proposed by the city at a workshop at the Hillhurst/Sunnyside community centre on Oct. 18. A decorative border on the wall above them states in green lettering, “When the flood came, she’d open up the front door and the back door and just let the water go through.” Photo by Logan Peters.

Frank Frigo, Calgary’s lead river engineer, says, “I think that Calgary is a very outdoors-oriented type of community that is looking for opportunities to recreate with our natural resources and especially our rivers.”

Even if the priority is to protect human lives, homes and livelihoods, flood barriers have drawbacks. They don’t protect from groundwater unless they are extended underground, and the city estimates doing that could double their cost.

And the cost of construction and maintenance is already high, at $1.8 billion almost equalling the expected benefits of $1.9 billion in damages saved.

Finally, if a flood overtops a flood wall or berm, the barrier becomes a trap holding water behind it and possibly doing more harm than good.

Frigo said the city wants Calgarians to understand how barriers could affect their communities. “If we’re going that route, we want to think really carefully about how we’re doing it. And before we go that route, we want to make sure that all the other alternatives don’t make more sense from a cost, social and environmental standpoint,” he says.

The reservoir option is expected to cost slightly more at $1.9 billion, but supposedly offers benefits of $2.6 billion.

Unlike barriers, Frigo says, a reservoir will always have a positive impact even if it only holds back part of a flood — at least the flood will be smaller.

Still, Morris, from the Calgary River Communities Action Group, says it makes sense that those living in the floodplain would be interested in short-term mitigation measures such as barriers and flood walls.

“It’s achievable,” he said. “And that’s what people want to see, they want to see something done.”

Every option comes with trade-offs. And every trade-off comes with uncertainty. To get dollar figures for Calgarians to compare, the city estimated damages from many different flood levels, combined those amounts with estimates of flood frequency, and boiled it all down to a dollar figure for each option to predict overall damages over the next century.

But predictions are a problem. According to John Pomeroy, the Canada Research Chair in Water Resources and Climate Change, Canada’s observations of the Bow River only go back about 100 years and there are only a few large floods to study within that timeframe.

Pomeroy says researchers are looking at alternative methods to predict the size and frequency of large floods. But each of these methods has its weaknesses.

One method looks at paleoclimate records such as tree rings and sediment cores. This gives an idea of the range of events that are possible, and the trends that occurred in the past, but it says little about future directions of change.

Another method uses an atmospheric model — the kind used to study climate change. But these models are designed to work at a global scale, so they can’t predict local weather events, such as heavy rainfall on snow, that can produce large floods.

Weather models can simulate these events, but they can’t account for climate change.

Pomeroy hopes a combined model could help. Currently, at the University of Saskatchewan, Pomeroy is working with the U.S. National Center for Atmospheric Research in Boulder, Colorado to nest a weather model inside a climate model and make local predictions based on global trends.

But these huge long-term simulations take time to refine and run, and early results are still about a year away. In the meantime, Pomeroy says, “You do the best calculation you can, you try to estimate how uncertain that is, and then you build in the safety factor to account for some of the uncertainty.”

If you get it wrong, lives are at stake. Both Pomeroy and Frigo mentioned the problem that flood mitigation projects can give false reassurances to people who assume they are protected.

Calgary’s consultations also asked participants about “non-structural measures” to make floodplain areas less vulnerable and also less crowded with structures that back up floodwater higher than it would otherwise reach.

Pomeroy contrasted Alberta’s 1-in-100-year flood design standard with Saskatchewan’s standard of a 1-in-500-year mark. He gave examples of cities like Toronto, Saskatoon and Lethbridge where tougher and at times painful planning decisions in the past created river parkways where floods can now pass through with little or no damage.

But in Calgary, even a 1-in-100-year flood reaches well into the downtown core. And even though the city appears to have recovered well from the devastation of 2013, big decisions are still to be made.

This story is part of a Calgary Journal project called Calgary Builds. To view more stories highlighting Calgary’s infrastructure, visit CalgaryBuilds.ca.

lstewart@cjournal.ca & lpeters@cjournal.ca

The editor responsible for this piece is Josie Lukey an can be reached at jlukey@cjournal.ca