Replacing a defective culvert underneath a portion of a Credit River tributary in northwest Brampton, Ont. was no ordinary undertaking for Peel Region, consulting engineer Amec Foster Wheeler and general contractor Metric Contracting Services Corporation.
But the Credit River Culvert Rehabilitation Project garnered a major award from the Ontario Public Works Association (OPWA) earlier this year. It was named the association’s 2016 project of the year in the structures $2 to $10 million category.
"The complexity of this project was unlike typical culvert rehabilitations," public works commissioner Janette Smith pointed out in a report to Peel Region Council that cited the culvert’s location in a 14-metre-deep constrained and environmentally sensitive valley.
A major feature of the new, reconfigured and shorter Bovaird Drive culvert are wooden baffles that allow fish to rest as they pass through, says Peel Region transportation project manager Dan Bennington.
On the north side of the culvert are a series of "pools" that allow them to continue their journey upstream by jumping from one pool to the next.
Prior to the project, the culvert was comprised of three segments installed at different time periods underneath Bovaird Drive and the parallel Highway 7 which had been abandoned and closed years ago.
They included a 75-year-old, 20-metre-long masonry piece under Highway 7, a middle 20-metre-long old box portion installed several years ago and a more recent 60-metre-long box culvert.
A 2013 environmental assessment of Bovaird Drive revealed that both the original masonry part and the older box culvert were structurally deficient and insufficiently sized for a regional storm.
"A collapse could have a potential for major flooding," Bennington explains.
With a grade that climbed from 2.1 to 7.3 and a two-metre vertical drop from the middle box culvert to the newer one, the culvert was also a major barrier to fish passage, he says.
Several different design solutions were proposed and debated by the region, the consultant, the Ministry of Natural Resources and the Credit Valley Conservation Authority during the approximately two-year-long design, says Bennington.
A major innovative solution that emerged was to remove the Highway 7 road platform, thus eliminating the need for a replacement for the masonry piece. This also shortened the length of the overall culvert by 20 metres.
"By carving out Highway 7, which wasn’t needed, 10,000 cubic metres of flood storage space was created," he adds.
But that removal came later in the construction which started in mid-June 2016 after tree clearing earlier in the year.
The first step involved slicing off a large section of Bovaird Drive and then bracing it with shoring so that the faulty older box culvert could be removed and replaced.
Initially, just getting to the site was a logistical challenge because of the valley’s depth and environmental features. The original plan was to build a long, circuitous access road.
Instead, the contractor came up with a proposal to cut an approximate 20-per-cent slope into the valley using the old Highway 7 right-of-way, says Bennington.
The next step in the construction procedure was the removal of the box culvert and its replacement with a new 20-metre-long, 1.2-metre-wide, 2.8-metre-high precast box structure.
This phase of the project also included inserting the fish baffles in both the new piece and the structurally intact newer box culvert. After that was accomplished and Bovaird Drive regraded Metric proceeded with the concurrent construction of the stepped pools and the removal of the remaining portion of Highway 7, Bennington says.
About 7,000 cubic metres of excavated earth was reused as backfill, another 2,000 cubic metres used on site for the construction of small landscaping berms and the remaining 11,000 cubic metres hauled off site.
Using Highway 7 wasn’t the only innovative idea the contractor proposed.
As the culvert sections to be replaced were non-standard dimensions, the design specified they should be replaced with cast-in-place ones.
However, during construction, the contractor located a supplier willing to fabricate non-standard dimension units. That proposed change received the go-ahead after a review by the design team.
"This revision not only delivered the same end product, but allowed the contractor to reduce the duration of construction, as the culvert could be backfilled immediately rather than waiting for a cast-in-place structure to cure," says Bennington.
Another aspect of the project, which finished last October, was the periodic rescue of fish and releasing them downstream from the construction site, he says.
Apart from this year’s OPWA award, a major indicator of the project’s success was the recent sighting of rainbow trout upstream from the culvert.
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