New stormwater management works mitigate flooding in southwest Calgary

Over the years, several neighbourhoods in southwest Calgary have experience flooding during rainstorms. Remedial measures implemented in the 1980’s and 1990’s provided homeowners with some flooding relief. However, after a major storm and resultant flooding in July 1996, the City of Calgary decided to conduct an updated analysis of the local stormwater management systems. As a result of this analysis, the City prioritized five flood remediation projects, and retained Associated Engineering, together with subconsultants AMEC Earth & Environmental and landscape architects, Lim Associates, to complete design and construction of these projects.

The objectives of this project were to design and construct a dry pond and storm sewer upgrades that would reduce the frequency of flooding in the project area, considering impacts to local residents, traffic, and overall project costs. During the preliminary design phase of the project, the team developed a computer model of the storm sewer system to fine-tune the design of the storm sewer and dry pond. DDSWMM was used to determine hydrologic flow rates for each catch basin and XPSWMM was used to analyze the hydraulic capacities of the proposed storm sewer system. QHM was used for continuous rainfall simulations for the proposed detention pond, to estimate how often and to what degree the pond would retain stormwater during rainfall events.

The project team also conducted an extensive constructability review of the 20,000 cubic metres dry pond and 4000 metres of storm sewer, which ranged in size up to 1500 millimetres diameter. The challenge was to determine the best alignment that minimized conflict with existing infrastructure, mature trees, and a playground in this well-established neighbourhood. The team also had to find the best location for a 1500 millimetre diameter section of the storm sewer to cross Crowchild Trail, a six-lane urban arterial roadway.

“Retrofitting major infrastructure improvements in an existing urban community is not only technically challenging, but can have significant impacts on the lives of residents as well,” advises Project Manager, Dale Loewen. “We held a public open house during detailed design to present the proposed improvements to residents and to receive their comments.” As a result of the public open house and ongoing dialogue with community representatives, a number of design modifications were made. For example, the design of the detention pond was modified to include landscaping improvements to an existing park and a new baseball diamond.

During construction, the team, the City, and the Contractor worked together to ensure that construction minimized impact to residents’ daily lives and minimized traffic impact. Work adjacent to two neighbourhood schools was completed during the summer to avoid conflicts during the school year. The open-cut crossing of Crowchild Trail was planned well ahead of time with City of Calgary traffic planning staff, and was completed in two stages in successive weekends. Completed in 2004, the project met the City’s objectives for flood relief, and provided improved park space for the neighbourhood.

Other Associated Engineering staff involved in the project included Duane Strayer, Corinne Wotton, Sarah Huber, Tony Hasiuk, Scott Mills, Dieter Foessel, Shane Hemenway, Harry Vandenberg, Justin Fox, and Malcolm Cooper.

The design of the dry pond, completed by AMEC, received an Award of Merit at the 2005 Consulting Engineers of Alberta Showcase Awards.