Stopping Chilliwack's snow, one fence at a time

In snowy winter weather, it’s orange fences that make good neighbours.

Each year, the City of Chilliwack installs nearly 4,000 metres of snow fences—temporary barriers that defend local roads against blowing snowdrifts. Together with the city’s snow removal teams, they keep some of Chilliwack’s key transportation arteries from becoming traffic nightmares when wind and snow begin to blow.

But the physics of fencing in the weather is more complicated than one might expect. And although Chilliwack has found success with snow fences, not every Fraser Valley community with big fields uses the humble fence to stop snow from covering its streets.

If you’ve driven down one of Chilliwack’s north-south arterial roads in the winter, you’ve probably seen the city’s snow fences. The fences, placed parallel to the roadway on neighbouring fields, are an important part of Chilliwack’s snow management strategy and are installed each year before flakes start to fall.

This year, the city’s operations department assembled 3,900 metres of fencing in more than a dozen spots, including along Prest Road and Evans Road, two of Chilliwack’s busiest routes. The snow fences are used to protect roads surrounded by open fields, across which strong winds propel vast amounts of snow considerable distances.

The snow fences slow the wind and allow snow to settle in a controlled area rather than drifting haphazardly across local roads. The hope is that the fences can reduce snow removal costs and also improve driving visibility.

In order to set up a snow fence, Chilliwack must first get permission from the property owner where the fence will be installed. Once that happens, the city sends out teams to erect fences across the municipality.

It takes between two and three hours for each crew to install each fence. Chilliwack staff stick each heavy-duty post into the soil, then zap-strap the removable fence to the stakes. The fences are placed away from the road at a set distance—usually between 30 and 50 times their height—so that the snow can accumulate around the fence rather than the road.

After that, all that is left is to wait for the snow to arrive.

It wasn’t always this way. Chilliwack began installing fences only within the last five years or so.

(Chilliwack staff aren’t entirely sure when the program started: a February 2019 Chilliwack Progress article said the city altered its snow program after back-to-back bad winters, with snow fences described as one of the additions. A Chilliwack spokesperson said that “2019 being the first year sounds accurate to the best of our knowledge.”)

The snow fences are used in areas that have long-standing issues with snow drifts, like Prest Road. Snow has been an issue along Prest as long as vehicles have been trying to navigate the road in winter. A January 1950 newspaper article describes how residents had resorted to using sleighs after snow drifts prevented residents from using their vehicles for weeks. In 2006, Chilliwack Progress photographer Jenna Hauck captured an image six people trying fruitlessly to push a car out of a snow drift. It was eventually towed out by a passing pickup truck, and Chilliwack later closed the road.

The introduction of snow fences aimed to reduce crews’ need to clear the same section of road over, and over, and over again. Around the same time, the city had also begun to establish more-permanent forms of snow fencing: planting roadside shrubs along some roads to act as wind blocks, and asking some farmers to leave a strip of corn standing at the edge of their fields.

The program was a call back to some of the earliest uses of snow fences, which—like other elements of society—have faded in and out of popularity over time.

The first written reference to snow fences as a piece of infrastructure was a small book published by Norwegian roadmaster G.D.B. Johnson in 1852. His book, which featured sketches of snow collecting around barriers like fences, helped spark an interest in the use of physical structures to prevent snow from gathering on the tracks of railways springing up across North America. In the United States, an 1880 tourist guidebook for those riding the rails through the Wyoming prairie highlighted “innumerable” snow fences along the tracks.

Snow fences increased in popularity as cars became more common, but later fell from favour as force overpowered infrastructure. The physics of how snow fences collected snow was poorly understood, and stronger trucks and plows made it seem easier to push snow off roads instead.

Brute force was expensive, however. In 1957, BC spent more than 1% of its budget on snow removal. A report from the time noted that “this cost is a very serious matter, and yet public demand today is such that there is no way to cut these costs and still provide the demanded service.”

(That demand once resulted in a woman jumping onto a plow operator’s bed, undressing and threatening to scream if he didn’t plow the five miles to her home.)

In the 1950s, Russian scientists began to research how snow fences actually worked—and how they could be more effective. At that time, snow fences were used to protect about half the roads in Russia, one paper said, but some believed temporary fences along roadways in places like Siberia could collect even more snow if applied properly. Researcher A.A. Komarov published a formula in 1954 that, for the first time, allowed officials to calculate the storage capacity of a temporary snow fence.

Canada’s National Research Council translated the paper in 1963, saying it would help engineers understand the “theoretical aspects of the problem” of snow drifts. Americans began their own work into the physics of snow drifts around the same time. The return of the snow fence in North America had begun.

Snow fences work not because they actually stop snow, but because they reduce the speed of the wind. Snow begins to drift when winds reach around 15km/hr (a speed that would give a respectable, but not outstanding, showing in the Boston Marathon). As wind speed increases, even by small amounts, it can pick up exponentially more snow. (A 19km/hr wind has about twice the energy of a 15km/hr wind.)

When the wind hits a barrier, the energy drops and the snow slows and collects on the ground. (The physics are similar to how sediment moves within river systems, which we’ve reported on here.)

Snow will naturally collect wherever the wind slows: around ditches, near trees, by buildings, or at road embankments. By slowing the wind in a specific area, fences can keep drifts away from roadways.

How much snow a fence can collect depends on how the fence is built, and how “porous” it is. A solid fence will create a large pile of snow on the side where the wind hits the fence, and very little on the other side. A fence with gaps, on the other hand, will primarily collect snow on the leeward side, rather than the windward side.

A fence with more gaps can collect more snow—albeit over a longer “drift” area. That means there has to be enough space between the fence and the road for the snow to collect, otherwise crews will be right back where they started. Drifts can be more than 10 times longer than the fence is tall, which is why Chilliwack places its fences so far from the road.

Each year, Chilliwack revisits its list of “strategic locations” to determine where it should add more fencing. The city has been adding around 150m of fences to its program each year.

It’s not the only community in the Fraser Valley to use snow fences. The District of Kent also uses snow fences at four locations in the community: Tranmer Road, McDonald Road, Cameron Road, and McCartney Rd.

Abbotsford on the other hand, despite also having open fields and blustery weather in Sumas Prairie, doesn’t use snow fences in any systematic way. It uses heavy equipment like graders and plows—and crews working on 12-hour shifts during storms—to manage blowing snow on Sumas Prairie, which the city says is too large an area to manage with fences.

“To properly deploy and implement a snow-fencing program would require large areas of land which the City doesn’t own,” an Abbotsford spokesperson wrote in an email to The Current. “A snow-fencing program is not considered required at this time.”

Chilliwack also doesn’t own the land where it puts its fences—a spokesperson there said they contact property owners each year for permission and to negotiate locations, installation and cleanup. And those owners—many of whom live near the roads protected by the snow fences—seem eager to volunteer their land.

“The majority of property owners are happy to help support the program as they recognize the benefits to the community,” the Chilliwack spokesperson said in an email.