Tsable River Crossing

The Tsable River Bridge, undertaken by the Vancouver Island Highway Project (VIHP), and the Ministry of Transportation (MoT), was designed to minimize the environmental impact on the rich ecosystem in the Tsable River valley bottom. This bridge was constructed using a cast-in-place concrete single cell box girder and cellular pier design that was more cost effective than the steel design option and environmentally sensitive to the underlying valley. The Tsable River Bridge project was able to avoid a “Net Loss” of habitat at the construction site.

The Tsable River Bridge, completed in 1998, was built to ensure construction and operation would have very little impact on the valley’s ecosystem. Located between Mud Bay and Courtenay, this 400 meter span is Vancouver Island’s longest bridge. Unique construction methods were utilized to avoid environmental impact. The bridge was high and long enough to evade major environmental sensitivities in the Tsable River valley. Concern stemmed from the fact that the valley supported a variety of animal species including; Roosevelt elk, black bears, cougars, blacktail deer, hummingbirds, warblers, bald eagles and blue herons. The Tsable River also supports a variety of fish species including cutthroat trout, steelhead, and several species of salmon. An old-growth Douglas Fir forest filled the valley, some of the trees reaching above the proposed bridge height. Other factors that were considered in the planning process included the steep topography and the unstable terrain of the valley. The objective of the project was to achieve a “No Net Loss” of fish habitat. A “Net Gain” of fish habitat was the preferred option, incorporating both mitigation and enhancement activities.

1) The goal for the Vancouver Island Highway Project was to construct the Tsable River Bridge with “No Net Loss” of fish habitat. The underlying river and valley was to be disturbed as little as possible so as not to harmfully alter, disrupt, or destroy fish habitat.2) To ensure that construction techniques were environmentally sensitive. There was temporary support work on the valley floor but no permanent piers or other structures were erected in the river.3) To protect as many of the Douglas Fir surrounding the area as possible and to minimize impact on the old growth forests in the valley.

4) To construct a bridge that carried four lanes of traffic on the Inland Island Highway over the Tsable River valley.

5) To build a bridge that was earthquake resistant in a high seismic activity location primarily by reducing the superstructure’s weight.

VIHP identified and mitigated environmental fish and wildlife concerns for the Tsable River Bridge Project in three stages; Design/Review, Pre-Construction, and Construction.A primary goal of the bridge project was to develop construction methods that would minimize or alleviate disturbances to the underlying ecosystem as much as possible. The bridge had to be sensitive to the environment, earthquake resistant and meet safety standards. VIHP engaged with bridge design consultants N.D. Lea Consultants Ltd. of Vancouver in collaboration with T.Y. Lin International of San Francisco and developed the concrete single-cell box girder and construction methodologies that ensured the bridge design was compliant with seismic, geotechnical, hydraulic, and environmental concerns. A steel design was also developed and tendered simultaneously to promote industry competition for the purpose of realizing cost savings. The concrete tender price was approximately $1.3M lower than the steel design.During bridge construction, VIHP was involved with ongoing consultations with the Ministry of Environment, Lands and Parks (MELP), and Fisheries and Oceans Canada (DFO) to ensure the bridge design met environmental legislation. The project was also subject to environmental monitoring during the construction.

DESIGN / REVIEWThe bridge had to be environmentally sensitive to the crossing site. VIHP engaged in consultations with environmental agencies and bridge engineering designers. A concrete single cell box girder design was chosen as the most environmentally sensitive and economical bridge option.The location of the middle pier was critical. Locations were constrained by the steep and unstable terrain of the valley below. To protect fish habitat and to ensure very little impact to the ecosystem, a decision was made to construct the middle pier on an island in the river. This ensured no change to the hydraulic characteristics of the river and no change to fish habitat, protecting the various species of salmon (coho, pink and chum), steelhead, and sea-run cutthroat trout supported by the Tsable River.

PRE-CONSTRUCTION

Prior to the bridge construction, environmental assessments were completed to account for the various plant, animal, and fish species that were distributed throughout the valley. During the approval process, VIHP contracted qualified biologists and consulted with provincial and federal agencies, streamkeepers and conservation groups receiving input from the design of the new highway and bridge structure. This ensured the project complied with government policies and legislation for the protection of the environment.

CONSTRUCTION

Construction of the Tsable River Bridge began on April 25, 1996. Twenty-seven months were allotted for construction. An environmental monitor was employed throughout construction to ensure the contractor was meeting the obligations as specified in Standard Specifications for Highway Construction, Section 195, Protection of the Environment. That person also acted as a resource for construction methods performed in sensitive areas. The Environmental Monitor in turn reported to a VIHP Environmental Coordinator who was responsible for the scope of the project and certified that recommendations matched ministry policy and provided accountability for the project team on environmental issues.

The bridge superstructure was supported by three piers. The exterior piers were constructed with the use of a crane from the roadway and a smaller crane on the valley floor. The construction access to the valley was built at the north bank and included a small temporary bridge to an island. The middle pier was constructed on an island in the river with a small crane on the valley floor. The construction of the middle pier had to be completed during the fisheries window, June 15th to September 15th, when the chance of disturbing the salmonid habitat would be at a minimum. When construction of the middle pier was finished the small bridge and most of the access road was removed. The exposed land was then hydroseeded with a Standard Island Highway Mix.

The bridge superstructure was constructed of concrete cast into single cell box segments. As each segment was cast, it was attached to the previous segment using post-tensioning tendons. This process was repeated alternating from each side of the piers until closure of each span was achieved. This process was referred to as cast-in-place cantilever segmental construction utilizing a traveling form. A total of 137 segments were cast to complete the bridge superstructure.

Transverse ribs were incorporated into the top slab to stiffen the structure and to maximize structural efficiency. Silica fume cement was used throughout the superstructure to provide high strength concrete resulting in the reduction of structural mass and penetration of corrosion caused from water and dissolved deicing chemicals. High density, high quality concrete with an average thickness of 50 millimeters was cast over the top slab as a final wearing surface. The completed structure was 400 meters long, 24 meters wide, and 60 meters above the valley floor.

The final bridge design was cost-effective and successful at minimizing impact to the ecosystem. The Tsable River was virtually undisturbed and only one island on the valley bottom was impacted. Bridge construction was conducted in a 27-month time span, and work along the river occurred only during the fisheries window, June 15th to September 15th. Work conducted during this period ensured that the fisheries resources were not impacted. The bridge avoided significant impact on the valley below as a result of building individual bridge segments from each of the piers using the traveling form process. Further, the contractor was constrained by the need to protect and preserve as many Douglas Fir trees as possible at the site in order to minimize impact on the old growth forest. The cantilever system used a tower crane minimizing the need for any tree removal.The use of cast in place cantilever segmental construction utilizing a traveling form resulted in a structure that was inherently aesthetically pleasing, satisfied the operational requirements and minimized environmental intrusion into the valley below.The building of the Tsable River Bridge had a near perfect safety record over the two years of construction. This was particularly important since there was considerable risk to the on-site workforce particularly since the work often took place 60 meters above the valley floor. VIHP ensured that the safety pre-qualification process was followed. Contractors were required to provide evidence of an acceptable safety record as well as a commitment to providing safe work sites and practices by maintaining a project specific Occupational Safety and Health Program for the duration of construction.

Construction finished on July 15, 1998 at a cost of $15 million and the bridge was opened to the public on September 25, 1999. The construction of the Tsable River Bridge used 254 construction workers and 150,000 hours of work to complete the project. The Tsable River Bridge was successfully constructed on schedule and under budget.

MoT strives to reduce and ultimately eliminate human and wildlife accidents, and motor vehicle damage. To protect both motorists and wildlife, MoT is currently installing fencing to impede animals from entering the highway corridor. The east/west migration of animals was facilitated under the bridge structure, and in the event animals found their way onto the roadway, one-way gates were installed as a primary deterrent that led the animals to safety. Where fencing was not present, special roadside reflectors were placed at major deer crossings along the Inland Island Highway to discourage animals from crossing the road.A wildlife ungulate exclusion treatment under the Tsable River Bridge was proposed to further prevent the possibility of vehicle collisions with a resident Roosevelt Elk herd. In order for the one-way fencing to be effective at preventing the elk from accessing the highway from the west side of the fence, it was imperative that the valley bottom was sealed with a visual barrier. Installing alternating clear and solid colour panels across the main river channel would reduce the possibility of elk traveling along the river corridor and accessing the east side of the highway.No post construction monitoring has been undertaken by VIHP, DFO, or MELP since there was no impact to the valley bottom. However, the Fanny Bay Enhancement Society is actively monitoring Tsable River and its side channels to ensure that salmon passages remain clear.

N.D. Lea Consultants Ltd. received the Consulting Engineers of British Columbia’s (CEBC) 1999 Award of Engineering Excellence for the design of the Tsable River Upstream Bridge.

Fisheries and Oceans Canada
Habitat Management
Richard Eliasen
Senior Eng. Technolo
3225 Stephenson Pt. Road
Nanaimo, BC Canada
V9T 1K3
Phone: (250) 756-7278
Email: eliasenr@pac.dfo-mpo.gc.caMinistry of Transportation
Vancouver Island Highway Project
Larry Louis
Bridge Design Coordi
200 – 546 Yates Street
Victoria, BC Canada
V8W 1K8
Phone: (250) 953-4944
Email: Larry.Louis@gems4.gov.bc.ca