Engineering nature to rebuild a creek
It's not nice to fool Mother Nature.
Michael MacLatchy knows it can be a challenge mimicking her.
MacLatchy is a watershed management specialist for Associated Engineering. He was in charge of the restoration of John Matthews creek in South Burnaby.
The company recently received an award of excellence from the Association of Consulting Engineering Companies British Columbia for its reconstruction of the creek and surrounding ravine after erosion caused part of it to collapse more than 30 feet in 2012.
Fixing the creek was no easy task. The ravine slopes as much as 18 or 19 per cent. It's steep walls border mostly on private property. Getting heavy equipment in and out without decimating the habitat took a light touch and careful attention to detail.
The erosion that caused the collapse had come from years of heavy run-off of rain water from the surrounding neighbourhood. The area's expansive road network and homes left little soil to absorb moisture. When the erosion began to undermine the clay that supported the ravine, it gave way, explained MacLatchy.
To prevent that problem from recurring, a 2-foot diameter pipe was run down the ravine. A catch basin was built at the top. If rainwater run-off from surrounding streets gets too high or fast, it acts like the overflow drain in a sink and diverts the excess water into the pipe. Two city blocks down the ravine, that overflow then spills out over a jumble of rocks and boulders, slowing it to a more manageable rate for the creek to handle.
The creek was then rebuilt over the pipe, it's bed lined with a special geosynthetic material to keep it watertight.
MacLatchy's challenge was to not only ensure it worked as designed, but to also make the habitat look as if Mother Nature had placed it there, not backhoes and shovels.
"To have this in an urban area is extremely challenging," said MacLatchy. "It's a crude approximation of Mother Nature."
Rocks and boulders were reclaimed from the site and brought in from elsewhere. Material to create the stream bed, like stones, pebbles and sand, came from Coquitlam. Tree stumps and rotting logs were reused. Grasses and vegetation were replanted, along with 10 species of trees like dogwood and willow.
MacLatchy even consulted with an avid birder who lives next to the ravine for suggestions of plants and bushes that would attract birds.
"The emphasis was on the kinds of plants you would find in a natural stream corridor," said MacLatchy.
The result, said Kel Coulson, an environmental engineer for the City of Burnaby, is "a beautiful ravine."
Although it's not one the public can access. The top is fenced off to give the rebuilt habitat a chance to take hold.
For MacLatchy, the accolades are nice. But the real reward is from the fish. They're rediscovering the creek; steelhead have been spotted leaping their way towards spawning beds halfway up.
"The fact the fish like it is most important," said MacLatchy.