Mussel relocation necessary for Britannia Beach project
Caption: The project has reinstated Ottawa’s Britannia Beach gradient to a depth of up to 2.4m
Dredging of Ottawa’s Britannia Beach was completed in October, but before work could begin in August an extensive mussel relocation programme took place.
The project has reinstated the beach gradient to a depth of up to 2.4m, which involved removal of around 9000m3 of contaminant-free sediment from a 110mx80m section of the Ottawa River. It also, however, required the tagging and relocation of 45,000 mussels.
Mussel relocation was required under one of many environmental permits that City of Ottawa’s Susan Johns, manager, Design & Construction – Facilities had to navigate before dredging could commence.
Under a permit with the department of Fisheries and Oceans Canada, the city had an “obligation to locate any mussels buried in the sand,” Johns told CEDA Industry News. “There are species at risk at a federal level. We could have found an endangered mussel”.
The beach, a popular leisure site, needs to be dredged every 30 years to maintain suitable depths for swimming. Johns said that there has been an “incremental requirement for the environment” – with far more planning and permits necessary than there would have been when it was last dredged in 1988.
Closing the beach during the summer months when the beach is at its most popular was also a decision driven by environmental requirements. In-water work is not permitted during spring, explained Johns, to protect aquatic species that use the river as a mating site.
Work on the CD3 million (USD2.3 million) projected was carried out by local company Thomas Fuller Construction. A temporary causeway was constructed out of dredged sand-filled geotextile bags topped with granulars, from which a long-armed excavator dredged sediment from the riverbed, Johns explained. In the far reaches of the work zone, when the arm of the excavator could not reach land, trucks transited the causeway to transport the sediment back to the beach.
The dredged sediment was then stockpiled on the beach to allow water to dissipate. From there, the majority of sediment was moved to a nearby landfill site where it was placed as the final layer.
Thomas Fuller Construction’s project manager, Sam Fuller, told CEDA Industry News that this decision was driven by the sediment meeting the landfill site’s specific requirements.
Johns explained that the characteristics of the sand were evaluated during design to determine suitable options for disposal. Testing showed the sand was not contaminated, and was therefore not subject to Ministry of Environment, Conservation and Parks regulations for soils.
“Conversation with the City’s landfill site found the sand was suitable for re-use since it meets the quality and gradation requirements for final cover,” said Johns. “The City beneficially re-used approximately 4,600 m3 of sand for final cover capping material at the Trail Road Waste Facility, saving clean aggregate in local pits for other better suited projects. This reduced costs to the City by eliminating the need to purchase similar material for the job. The re-use of sand was both a benefit to the Britannia Beach dredging project and the Trail Road Waste Facility.”
Prior to construction, various options were explored to re-use the dredged sand, confirmed Johns. Consideration was given to re-purposing the sediment at other City of Ottawa beaches, for winter operations and for potential future flooding events. “After further investigation, these three options were not feasible due to cost constraints and insufficient means to store the material,” she noted.
More information about the Britannia Beach dredging project can be found here: https://ottawa.ca/en/city-hall/public-engagement/projects/britannia-beach-dredging