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How is Squamish holding up with all this rain?

Experts discuss natural flood mitigation.

The Squamish area has been getting pounded by rain in another round of exceptionally wet weather.

On Nov. 30, Environment Canada held a technical briefing, during which meteorologist Armel Castellan said that the Sea to Sky would be seeing more downpours.

“Towards Squamish, things are going to certainly amp up to amounts that are above 120 millimetres, potentially, in that elevated and particularly southwest-facing terrain that’s feeling the direct hit of this atmospheric river,” Castellan said.

He noted that this is the third atmospheric river that the province has had to face in a week.

Holding our own

The District of Squamish spokesperson Rachel Boguski said the town’s Emergency Operations Centre has been activated since Nov. 15, and municipal staff conducted inspections and preparation of all flood protection infrastructure in advance of these incoming storm systems. All dikes and road systems are performing as intended with no major issues, she said.

“The Mamquam berm that protects spawning channel trails adjacent to the Mamquam River saw evidence of erosion as a result of heavy rainfall, however, this was repaired on Nov.  29. There are no current washouts or new areas of concern. The gravel portion of Mamquam Road below Quest University remains closed due to significant public safety risk.”

For much of the province, Castellan said, this will be the wettest fall on record, if predictions hold true.

This deluge of rain poses some risks, as a result, not only because of the amount of rain, but also because the weather is triggering snow melt, he noted.

“Those quantities [of rain] are going to be perhaps dangerous and impactful, not only because the rain is plentiful and copious, not only because the freezing levels are extraordinarily high — upwards of 3,000 metres above most mountain tops and melting snow on those mountains — but, also, snow has fallen in certain places along the central and north coast recently, and that will also melt,” he said.

“We’ve also had the difficulty of having had three back-to-back storms with very little respite in the overnight or in the in-between period.”

On Tuesday, the River Forecast Centre declared that river levels around much of the coast, including Squamish, are rising and are at risk of creating floods in adjacent areas.

With many communities witnessing the impacts of flooding in real-time, much attention has been drawn to the impacts that natural land features, such as forests and estuaries, have with respect to flood mitigation — or the lack thereof.

“We know that the ecosystem is ultimately connected, and one thing has an impact on another, and we don’t have to look too much deeper than just this past summer,” said Castellan.

“In fact, three of the last five summers, with extreme wildfire behaviour and knowing how drought and wildfire burn scars have an impact on the landscape and can be manifested in the wet season a few months later.”

Estuaries help ease impact

Patricia Heintzman, spokesperson for the Squamish River Watershed Society, said that she witnessed firsthand the effects that wetlands can have on mitigating disasters.

Heintzman was part of a delegation visiting Sri Lanka after it was hit by a major tsunami in 2004, as Squamish was helping a village in that country rebuild from the destruction.

“It was like a war zone, for one,” she said.

“But one thing that really stuck out to me was the areas where mangroves and sort of that coastal wetland environment had been deforested or taken out were absolutely decimated by the tsunami, and areas where the mangroves were still healthy and provided that amazing buffer between the energy of the waves and the shore were essentially intact.”

She said it pointed to the important role wetland areas have in mitigating flooding, and, in Squamish, would include the estuary.

“You can think of the estuary as a big sponge and a big area that absorbs energy whether it’s wave or current energy and dissipates it,” she said.

“Nature provides all that way better than a lot of man-made structures do. And, certainly, [this] needs to be considered as part of the solution to withstand a variety of different climatic situations, whether it’s caused by warming and climate change and/or these more intense storms that we’re getting as a result.”

She added that removing the Spit would help restore the estuary to its full functioning potential.

Alex Boston, executive director at SFU’s Renewable Cities program, compared how a wetland or estuary might differ from man-made flood protections.

“Hard engineering infrastructure solutions have benefits but also costs. They can provide defence that meets a certain flood risk threshold, but often fail completely above that threshold in terms of wave height or force of storm. The result is big overtopping or destruction of the infrastructure” wrote Boston in an email to The Chief.

“Natural systems can be superior at being able to dissipate waves or currents because they can absorb a share of the energy. They are almost always superior in terms of supporting ecosystems. Interestingly, they typically don’t have to be as high to provide the equivalent protection in terms of wave height or runoff volume. Natural systems can require a greater horizontal allowance for protection.”

Catastrophic events tend to involve the convergence of multiple factors, he said.

In the case of Abbotsford, floods were prompted by intense rain, massive runoff from both early snow accumulation, rising temperatures, forest fires that reduced absorption and big tides and extensive development in the floodplain, Boston noted.

“To understand the best defence mechanism for Squamish it is critical to understand how similar events can converge and then plan accordingly,” he said.

In Squamish, the municipality should be on guard against channelled wind coming up the sound, as that can produce large waves.

“That, when combined with big tides and big runoff, are the type of scenario the city should be planning for and, interestingly, it is approximately the time of year when we have our biggest tides,” said Boston.

“Almost invariably a combination of systems that are natural and inspired by nature and standard engineering solutions are best for reducing vulnerability.”