WCW24

Rossdale and E.L. Smith Water Treatment Plants (WTPs) provide drinking water to the City of Edmonton and surrounding areas and are operated by EPCOR Water Services Inc. (EPCOR). These plants are critical infrastructure identified as vulnerable to overland flood damage from the adjacent North Saskatchewan River. Stantec Consulting Ltd. (Stantec) was commissioned in 2020 to quantify the flood risk further and undertake the preliminary design of flood mitigation measures at both WTP sites. The project is now in the detailed design phase, with construction scheduled to commence in Summer 2024. The design consists of a combination of earthen embankments and cast-in-place concrete floodwalls at each site that meets the design basis of a 1:500-year river flood plus 1.0 m of freeboard. Temporary flood control measures also form part of the design at Rossdale WTP. The flood mitigation infrastructure is designed following the United States Army Corps of Engineers (USACE) standards. Several supporting studies and investigations were required to support the design phase. These included geotechnical soil sampling, non-intrusive geophysical investigation, hydrotechnical analysis of the river, stormwater and civil grading design, underground utility review, waste stream mitigations, landscape architecture design, and regulatory approval planning. The design considers ground conditions, groundwater seepage, underground infrastructure, and floodwater erosion potential. It also adapts to local constraints such as minimizing tree removals, reducing total wall height, and maintaining a naturalized aesthetic to match its river valley setting while still meeting the appropriate design standards. Each WTP site presented unique challenges to the design team. Rossdale WTP is situated centrally within the City of Edmonton and bordered by a residential neighborhood, the river, the historic Rossdale Generating Station, and RE/MAX® Field. Each bordering stakeholder required specific attention to minimize the impacts of the project. Rossdale WTP has been an operational facility since the early 1900s, which presented challenges with existing underground infrastructure and space constraints. E.L. Smith WTP is a more straightforward site than Rossdale WTP; however, a specific challenge was the river's proximity to critical infrastructure. A complex structural design was required to situate a floodwall between existing buildings and the river. The project uses a Construction Management at Risk (CMAR) delivery approach, with Graham Infrastructure LP as the construction contractor. This approach allowed for greater collaboration and enhanced the design process by having regular feedback on constructability, schedule, and cost. The CMAR team also adopted the practice of regularly meeting in a dedicated boardroom at Stantec's office to work closely together and develop a sense of mutual ambition to deliver the project successfully.