Our firm carried out a Class Environmental Assessment (EA) preliminary design, detailed design, contract document preparation, contract administration, and field inspection during construction of the Britannia Trunk Storm Sewer and Sedimentation Control Facilities. This project addressed ongoing flooding in the Britannia Village and Britannia Heights communities and provided a means of improving the quality of stormwater being released to the Ottawa River from these large upstream areas.
A number of alternative designs were reviewed and a preferred design concept was identified to remove total suspended solids (TSS) from stormwater discharges while protecting the fauna and wildlife in and around the provincially significant Mud Lake. The preferred solution consisted of a 1,200 m long cast-in-place rectangular trunk storm sewer, 1.5 m high and with varying widths up to 4.2 m. The trunk storm sewer included a specially designed siphon section under two large water transmission mains (1,525 mm diameter and 1,225 mm diameter) that supply a large portion of the City of Ottawa. Two “wet pond” sedimentation control facilities were incorporated into the design to provide both water quality and quantity control. To confirm sizing of the trunk storm sewer and sedimentation facilities, various analyses were conducted: hydrological to simulate synthetic design storm events, long-term simulations to evaluate removal of TSS, and hydrodynamic hydraulic analyses using XPSWMM (EXTRAN block) to evaluate hydraulic grade line elevations in the trunk and local storm sewer systems.
As the constructed works were in close proximity to the Mud Lake environmental area, extensive input and analyses from hydrogeologists, biologists, and botanists were required through all stages of the design and construction process. We also worked very closely with stakeholder groups representing the Britannia neighbourhoods as well as the National Capital Commission to ensure their requests were met throughout design and construction.