A gritty situation


Grit interceptors keep dirt out of the river

St. Albert has passed the halfway point on a crusade to keep sediment out of the Sturgeon River and the next two years will mark more key milestones.

The sixth of nine sediment filters is slated for installation along Meadowview Lane this winter, near Heritage Park, while two more are coming in 2019.

The concrete box-like structures, called grit interceptors, are an important piece of St. Albert’s stormwater infrastructure, keeping truckloads of dirt out of the Sturgeon River every year.

“(The amount) is massive. It’s seven or eight dump trucks worth of grit we collect – it’s pretty cool,” said Leah Kongsrude, director of environment with the city’s infrastructure and development services department.

The capacity of the five interceptors the city has is 175 cubic metres of dirt – or 17 dump trucks full. In one year, city staff usually clean out half that volume.

In most cases, you’d never know a grit interceptor existed. They are installed below ground and work the same way stormwater ponds do: as water runs into the stormwater system from roads and parking lots, they slow that water down and allow the sediment carried with the water to settle. The result is cleaner water being expelled into the Sturgeon River through stormwater outfalls.

Kongsrude estimates there are around 40 outfalls along the Sturgeon River. Until 2004, when the city did its stormwater master plan and Big Lake stormwater management plan, sediment flowed freely with the water.

Those plans, Kongsrude said, were the seeds for sediment control.

“When those two reports were done, we found a couple interesting and kind of disturbing impacts. One of the things we found was that, especially here in St. Albert, the river was actually starting to accumulate sediment – and largely, when we tested it, it turned out to be our road sand.”

Over time, that sand had changed the depth of the river as well as its configuration.

‘We said, ‘We really need to do something about this,’ ” Kongsrude said.

Making a plan

In 2005, St. Albert installed its very first grit interceptor. The project was such a success and collected so much sand that a couple of years later it became the inception of a $20-million project that would span more than a decade.

After monitoring that first interceptor, Kongsrude got together with city staff to look at each of the city’s outfalls and come up with a priority list for the ones releasing the most amount of sediment. The result was a list of eight – later nine – outfalls that would need to be retrofitted with grit interceptors.

“After we proved that, yeah, this is making a really big difference, we put in a capital charter to council for approval,” Kongsrude said.

A majority of them are in the downtown area, where sediment accumulates more quickly.

Sediment, safety and aesthetics

When it comes to stormwater infrastructure, St. Albert is proof you can preserve the environment and look good doing it.

In 2012, while installing on a grid interceptor beside the Perron Street bridge, city staff decided to get creative. Instead of replacing a chain link fence around the outfall, the city put up a delicate stainless steel fence crafted with the silhouette of a bird.

“That was an incredibly fun project,” Kongsrude said. The fence was for safety but also helped to make the project look a little nicer and has a longer lifespan than chain link.

Now, three such fences can be seen in the downtown area, with a red-winged blackbird, magpie and great blue heron silhouetted against the structures.

“They just look a million times better, and they’re so functional,” Kongsrude said.

Likewise, the look of the actual outfalls began to change. Instead of covering the outfall pipes with a grate that looked like jail bars, the city began installing grates with bars that look like waves.

The design helps keep branches and debris from clogging the grate, is easier for staff to access and gives the structure a more natural look.

“It was probably one of the most fun things I’ve done at the city,” Kongsrude said.

Making progress

As grit interceptors went into the ground, the city’s public works staff embarked on a spring cleanup program. Targeted before the spring melt, staff go around the city with street sweepers and brushes, cleaning boulevards and medians.

“Say we put down 100 dump trucks worth of sand – at least 50 per cent of what we put down, we collect just through that (program),” Kongsrude said.

“The rest, if it happens to get into the storm system, we can collect in our grit interceptors. Obviously there’s still going to be a small portion that ends up getting in the river, but it’s significantly less than before.”

Those measures, combined with efforts by public works staff to control how much sand they put down during the winter, all work to keep the river cleaner.

Currently, grit interceptor installation is slated until 2024. Between 2018 and then, there is $11.8 million on the books for sedimentation and erosion control. $2 million of that is for 2018 alone.

While there are four locations yet to be retrofitted with grit interceptors, Kongrude said there are also plans to completely replace four stormwater outfalls. Those will be fitted with interceptors at the same time.

Kongsrude credits the project’s slow-but-steady progress to the decision of city council to approve it all those years ago.

“That was a big chunk of money. And everybody just said, ‘Our residents are concerned about the river – let’s do something about it,’ ” she said.

“We’ve been puttering away ever since.”


About Author

April Hudson

April is the editor of the St. Albert Gazette