Work begins on grit interceptors
Project will clean runoff at Children's Bridge
Saturday, Jul 26, 2014 06:00 am
More interceptors for Sturgeon
The St. Albert Children’s Bridge is getting a double dose of interceptors this summer in order to help keep grit out of the Sturgeon River.
Crews started work on upgrades to Outfall No. 7 by the St. Albert Children’s Bridge earlier this week. The upgrades are meant to replace the outfall’s concrete structure, fence and grate, and to add two grit interceptors to the stormwater line.
This outfall catches the runoff from most of Grandin – about 165 hectares worth of land, said Leah Kongsrude, the city’s director of strategic services. This includes the Grandin Ravine, a major drainage channel and source of eroded soil.
As a result, a considerable amount of grit and dirt has piled up at this site on the Sturgeon over the years, creating a peninsula that stretches most of the way across the river.
Last year crews installed a series of mini-dams in the Grandin Ravine to reduce erosion and the amount of dirt running off to this outfall, Kongsrude said. But that still left a lot of sand from Grandin Road that could reach this point.
This outfall gets so much flow that, unlike all the other outfalls in town, it needs two interceptors instead of one, Kongsrude said. The two interceptors combined will have the same capacity as the giant one in front of St. Albert Place.
“It’s kind of like the shape of a seashell,” she said.
The interceptors send water spiralling into two cylindrical tanks to slow it down so that all the grit and oil separate out. Cleaner water flows out to the river, while grit collects in the bottom. Crews can later suck out the grit and skim off the oil from the top.
Crews also plan to replace the concrete structure at this outfall with a less blocky one that blends in with the shoreline, Kongsrude said.
The outfall’s chain-link fence and grate will also be replaced with ones similar to the ones now at the Perron Street Bridge outfall, reported Sue Howard, manager of the city’s capital projects office. That outfall has a sturdier fence that looks like bulrushes and a stainless steel blue grate that resembles waves.
“The grate that is on there is our new standard,” she noted, as it’s less likely to clog than the city’s traditional ones.
Crews plan to eventually change all downtown outfall grates to that design, Howard said. There were no plans yet to upgrade all the fences.
The Red Willow Park Trail will be closed at this spot until construction wraps up later this year, Howard said. Residents can get around the roadblock by taking the trail by Lions Park and going behind the Grandin Medical Clinic or by walking down the path through the forest by Millennium Park.
This $2 million project is part of a 10-year plan to reduce sediment going into the Sturgeon, Howard said. The city is now at the halfway point of that plan and will spend the next year evaluating its effects. If it’s working, crews will upgrade Outfall No. 4 by the grain elevators in 2016.