Dartmouth Crossing brook boasts surprising trout life
Brook has been revived and now has about 110 trout per 100 square metres
Trout are making a comeback at a brook in a business park near Halifax thanks to a storm drain system introduced by a biologist and a boutique planning firm.
Grassy Brook — tucked between wide roads, a sea of parking lots and big box stores in Dartmouth Crossing — runs several kilometres through the eastern edge of Burnside Industrial Park, down through Dartmouth Crossing and drains into Lake Micmac.
In 2005, the developers behind Dartmouth Crossing hired biologist Bob Rutherford and Environmental Design and Management Limited to realign part of the waterway and develop a storm drain system that would help bring trout back to the brook.
"The developers wanted this as the signature part of Dartmouth Crossing, and keep the stream and fix it up," said Rutherford.
"But all the literature will tell you that you can't do a trout stream in something that's 90 per cent paved and hard-roofed and solid."
Yet, turning Grassy Brook into a healthy trout spawning stream is exactly what Rutherford and EDM Ltd. have accomplished.
"Today, there's about 110 trout per 100 square metres in the brook," Rutherford said. "The environmental assessment in 2005 said there were maybe one or two trout per 100 square metres, so that's quite an increase.
"We would normally expect in a stream like this to have maybe 20 or 30 trout per 100 square metres."
Rutherford says the trout levels in Grassy Brook compare favourably to the best rehabilitated natural trout streams in the province, which flow into the Northumberland Strait. Those streams have about 150 trout per 100 square metres, and gravel beds where water seeps in to allow the trout to spawn.
"There's nothing in this brook that a trout can move to dig away and bury their eggs in the bottom for the winter," he said.
"But what they're doing is they're getting down in between all this cobble and small boulder and just letting their eggs stay down in there. It's working really well for them — not a traditional trout habitat."
Storm water management key
Rutherford says stormwater drain controls and the rebuilding of the brook bed west of Finlay Drive were instrumental in making the waterway healthy.
EDM Ltd. worked with Rutherford to build a berm near Finlay Drive and create an artificial marsh to slow the flow of water downstream and help it cool.
Large sections of the upper part of Grassy Brook used to disappear below ground alongside the site of a former quarry.
EDM Ltd. and Rutherford worked to rebuild the brook there and bring it all to the surface, further helping trout life.
They also convinced the developer to build wide road culverts that wouldn't interfere with the path of the stream. Provincial regulations only require that culverts be 1.2 metres in diameter to accommodate existing streams, but the ones along Grassy Brook are 12 to 15 metres wide.
"It's seamless, they've been kept out of the stream's path," Rutherford said.
Further downstream, several "storm jails" — fenced-in, rock-lined holes where stormwater from nearby streets and parking lots pools, cools down and trickles out slowly — also help prevent any sudden surges in water levels that would affect trout life.
Man-made springs, cool water — and vigilance
Still further along in Grassy Brook Park, about 75 man-made springs pipe water in slowly from surrounding buildings and parking lots. That water helps feed a large man-made gravel spawning pool.
"The nice thing is that all the water coming in here is about nine or 10 degrees. It stays nice and warm for the trout all winter so they actually hatch earlier in this pond than they do in the stream because it's colder.
"Because we've got all the water going into the ground in this watershed the way it should in a forested situation, the stream never gets hotter than 16 or 17 degrees in the summer time. Trout like that."
Rutherford is also working with the developer to build a few more pedestrian bridges across the Brook — wooden bridges, to allow for a continuous path from Grassy Brook Park along the brook all the way to the end of the man-made marsh north-west of Finlay Drive. There's one pedestrian bridge already near the park.
Groups such as the Sackville Rivers Association and the Adopt-a-Stream Program have helped with managing the brook rehabilitation. The Clean Foundation is also helping with efforts to clean up wayward garbage blown in from the surrounding parking lots.
Rutherford says Grassy Brook is a great success, but he needs to remain vigilant about what sort of stormwater systems developers in the upper part of the watershed plan on building.
With files from CBC Halifax's Information Morning