Five new pedestrian bridges spanning Cold Creek in Bolton, Ont. required careful environmental construction planning for YMCA Greater Toronto staff at its Cedar Glen Outdoor Centre and a design construction team.
Ranging from 17- to 20-metres long and supported by angled helical piles with concrete caps, the five new steel truss pedestrian bridges with wooden decks now span the environmentally-sensitive Cold Creek which flows through Cedar Glen.
Designed by AECOM, the new structures replace four old decades-old steel and wooden bridges and a causeway/culvert which were either washed out or rendered structurally unsafe by a pair of major storms in the summer of 2013.
Prefabricated by Eagle Bridge, they were installed in one-piece sections by McPherson-Andrews Contracting Limited using high hoes and a 135-ton crane in 2015.
Approximately 24,000 people a year participate in the centre's programs, many of which are centred at or near the bridges, and the loss of the original ones severely curtailed those activities, says general manager Brandon McClounie.
"There was a need to replace them quickly."
As the Cold Creek is a cold stream protected by the Ministry of Natural Resources due to the presence of the Redside Dace — a species at risk — that replacement had to be done in, "the least intrusive manner as possible and in an environmental sustained manner," says Don Scott, partner, with George Robb Architect.
Geotechnical studies undertaken by Terraprobe Consulting Inc. concluded that one method to achieve that goal was using helical piles, he points out.
Drilled into the sandy soils on along the sides of the creek bed, the supporting piles range from two to five metres deep for most of the bridges, although one required depths of between five and nine metres, says Scott.
Design commenced in the fall of 2014 and extended right through until the spring of 2015, with installation taking place that summer during the "short window of opportunity" between July 1st and September 15, which is the only time in water work can be conducted to protect the Redside Dace.
Of course, there was considerable pre-installation site preparation work including the erection of silt fences on both sides of the creek. Undertaken by the YMCA with the help of some volunteers, the site enclosures had to be approved by AECOM, says Scott.
Prior to the actual bridge construction timber-sectioned swamp mats were placed across the creek to prevent the contractors' equipment from actually entering the water.
Each bridge took approximately two weeks to install and they're longer, wider, and higher than the old structures where which were basically at bank level, says Scott.
As well, the $445,000 project was an opportunity to eliminate the causeway/culvert which had long been deemed an environmental liability by the Toronto Region Conservation Authority.
"It was choking the floodplain," says Scott, citing periodic stone washouts and the causeway's impediment to the movement of the Reside Dace, says Scott.
The project, however, is a long way from completion. A year before the 2013 flooding, a clear span steel span emergency access bridge known as Bridge F was closed by the Y after a structural report concluded it was unsafe.
Currently, the only vehicle access linking the centre's headquarters at the top of the valley with the northwest side of the property where a number of program fixtures — such as a rope climb — are located is a narrow steel bridge.
"It can only be used by light emergency vehicles, certainly not fire trucks," adds Scott.
A new 30.5-metre-long Bridge F was included in the original tender, but was deferred for budgetary reasons. To be built on 4.7-metre-long, 0.75-metre-wide, and two-metre-deep foundation piers which will sit on 10 helical piles (five per side), it will be erected either in the summer of 2018 or 2019, says Scott.
Meanwhile, master planning for a proposed redevelopment of the centre continues. Some of the proposed new features which would be added over several years include overnight accommodations, two swimming pools, and enhanced outdoor education facilities.
"We anticipate approval (of the master plan) this summer," says Scott, whose firm is the lead in a team of consultants which include AECOM, MHBC Planning Inc., Kuntz Forestry Consulting Inc. and Crozier & Associates Consulting Engineers.