When it comes to flooding in Calgary, it's not the snowpack we need to worry about

With flooding being reported near Taber, many Calgarians wonder what the snowpack means for Calgary's chances of being flooded, too.

The Homestretch spoke with Frank Frigo, Calgary's leader of the Watershed Analysis, about what the city is doing to prepare for the snow melt of 2018.

Q: How concerned should we be?

A: We are seeing a reduced volume of calls around the operation of the drainage system and improved function of drainage systems, because we've had a number of warm days and we've had trickle or runoff that's been going through the system and effectively melting it out.

Our crews have been able to respond to the 311 calls we've had coming in and we are not seeing quite the same temperature regime we are seeing down in Taber. It's not quite as warm in Calgary. We're expecting some snow Wednesday, we're expecting some Friday, two to five centimetres — possibly as many as eight or 10 — but nothing that should be overly problematic.

Q: What about the impact of all this snow we've had this winter?

A: We've had around 160 centimetres, 170% of normal in most of the area around Calgary, and getting further up in the mountains — the area that feeds our rivers — we've got 120 centimetres or 130% of our normal snowpack.

In a lot of ways — from a river perspective — we're not discouraged at all to see the higher snowpack.

We've had a couple dry years and this higher snowpack does help us be more confident that we'll have less risk of low water levels heading into the open water season in springtime.

From a river flooding perspective, snow melt by itself tends not to drive river flooding. It's really rain on the steep mountain catchment that tends to drive that

Q: What about our storm drains?

A:  The higher snow locally can challenge with a freeze-thaw cycle that we do get some icing of some of our catch basins. That's something our crews have been working on. Certainly there have been some issues with localized ponds and ice forming, so we want to remind Calgarians to be very careful and always thinking of their own safety — where possible to remove snow, but if they do have a catch basin that isn't draining within three to nine hours, we do recommend they call 311, so our crews can respond in a prioritized way.

Q: What lessons did you learn from the flood of 2013?

A: Rain — more than snow — was the driver of the story in 2013. There was a healthy snowpack in 2013 — about 400-600 millimetres out there in mountains, up above the 2,000 metre elevation — not a record snowpack, but again that snow comes off a little slower than the rainfall process, and the story of 2013 was really the intensity and the wide coverage of the rainfall.

That is truly what drove the flooding we saw on the Elbow and Bow Rivers.

Q: What has changed since 2013?

A: Continual work has been going on since 2013 — so a good four years of work has occurred.

Recent work we've done on damage estimates for Calgary show that about a third of the risk that existed in 2013 has been now addressed by infrastructure we've put in place.

But a couple important pieces of that are the work the province has done with TransAlta.

TransAlta has agreed to operate their Ghost Reservoir as well the reservoirs on the Kananaskis Rivers, so Upper and Lower Kananaskis and Barrier Lake — in a new way, to offer additional flood resilience. That's a very important improvement for the Bow River.

Along the Elbow River, very important work is occurring right now. The second phase of a two-phase project to place new gates on the crest of Glenmore Reservoir is underway.

Q: What did you learn from studying the drainage situation around Calgary?

A:  A  number of communities have new gates on their storm water systems to prevent the ingress of water from the river — to prevent water from coming in.

Another important piece that we learned about [was that] 2013 occurred at a much more rapid rate — we were talking about the intense rainfall that drove that system, it occurred at a rate about three times faster, that rising limb of the hydrograph the speed of the response was about three times quicker than anything we'd modelled or analyzed before. 

So very much a focus for us has been looking at our warning systems, our communications systems, and educating and getting out to talk to the public that live in the areas that may have some risk, so they can be as prepared as possible as we enter spring runoff season.

There's great information on the city's website that helps Calgarians understand what they can do.

With files from The Homestretch

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