Dredging in process; the lake was divided into 16 dr3ede zones, partly to contain turbidity.
Associated Engineering led and completed a complex and innovative process to sustainably restore the pristine environment of Burnaby Lake, a 36-hectare body of water in the City of Burnaby east of Vancouver in B.C.
Over the past 30 years, natural sedimentation, and development and construction activities in the 7,300 hectare Brunette River watershed in which Burnaby Lake resides had resulted in the steady accumulation of heavy layers of contaminated sediments on the bottom of the lake. In addition, the lake had become overgrown with vegetation and its precious open water characteristics had gradually disappeared. The aquatic quality had also degraded.
In 2009, with $20 million in funding from the City of Burnaby and the province, the city launched a project that has resulted in the lake being restored. The project helped to reverse the effects of sediment infilling and increase the area of deeper open water. It also removed the contaminated sediments and improved the water quality conditions, thus protecting fish and wildlife, including salmonids, and improving the lake tributory for fish migration.
Time constraints, strict regulatory conditions, and the need for cost efficiency all combined to demand a high level of dedication, collaboration, and innovation from Associated Engineering’s project team.
Watching for turtles and cutting weeds
The overall challenge was to develop an effective system to dredge the lake that would have a limited impact on the environment. Several approaches were created that had never been previously implemented together on this type of project.
First, the BC Ministry of Environment decreed that no dredging could take place during the winter season without confirming that the lake’s population of Western Painted Turtles – an endangered species – would not be harmed. The team developed a wildlife detection program using ground penetrating radar and a high resolution sonar camera that gave near-video quality images. The camera enabled the team to monitor the turtles in the lake’s water column. They tagged 45 individuals over the 20 month period and showed that the turtles remain active during the winter months. Not a single endangered turtle was harmed during the course of dredging the lake.
The team also developed a tailor-made train of technologies to dredge, transport, and process the polluted and contaminated lake sediments. They recommended a hydraulic suction dredge with a cutter head auger to handle the removal of the vast quantities of aquatic vegetation.
They divided the lake into 16 separate dredge zones, with each zone isolated by a double turbidity barrier. The barriers (a) aided in the capture and relocation of sensitive species prior to the dredging; (b); contained the turbidity caused by the dredging; and (c) enabled the effective monitoring of the lake quality post-dredging. Up to three zones were set up at any one time to complete the activities. The creation of 16 zones also protected the existing migratory routes for spawning salmonid species and allowed the public to have continued access to the lake while dredging was taking place (in most cases at a depth of 2 to 3 metres).
By using suction dredge, lake and land-based booster pumps and a flexible pipeline, the dredgeate was efficiently moved five kilometres away to a processing plant stationed in a parking lot at the western edge of the lake. An advanced treatment technology was developed to allow treated effluent to be discharged back into the lake. The process included shaker screens, inline grinders, equalization/mixing tanks, centrifuges, centrate tank clarifiers, sand filters, flow return pumps, and a return pipeline. The use of an on-site electrical substation at the treatment plant rather than diesel generatores reduced the project’s carbon emissions.
During the project 945,000 cubic metres of lake dredgeate and garbage were cleaned and processed. The material included contaminated sediments, automobile tires and parts, wire cables, metal poles, used beverage containers (cans, plastic bottles) and other plastic and paper waste. The lake sediments were reused as sub-grade for a future sports field nearby.
As a result of the work, Burnaby Lake Park has been revitalized as an attractive natural environment, and transformed into a destination spot popular with Burnaby’s families and sports and wildlife enthusiasts. It has been re-established as a world-class rowing venue, with the Burnaby Lake Rowing Club once again considered a top training facility in North America.cce
Name of project: Burnaby Lake
Rejuvenation, Burnaby, B.C.
Award-winning firm (lead engineering consultant): Associated Engineering (Peter Degroot, P.Eng., Larry Martin, P.Eng., Dean Shiskowski, P.Eng., Dave Forgie, P.Eng.)
Owner/client: City of Burnaby
Lead environmental consultant:
Prime contractor: Tervita Corporation
Other key players: EBA Engineering
(environmental and remote sensing);
Atek Hydrographic Surveys
Through the designers taking great care in environmental control and in the protection of fish and wildlife, a valuable natural resource was rejuvenated. These factors, together with the reuse of on-site resources like lake sediments, were key considerations in making this award.