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Monday, Jul 20, 2020

New storm sewer improves conveyance and stormwater quality

37 Street Stormtrunk

Previously, we featured an article on Contract 1 of this project

As part of the Calgary Southwest Ring Road project, Alberta Transportation sought to have The City of Calgary replace a stormwater trunk running through Tsuut’ina First Nation land with a new trunk within the 37 Street SW right-of-way, south of Lakeview Drive SW, along with a new outfall to the Glenmore Reservoir/Elbow River. As The City of Calgary’s Prime Consultant, Associated Engineering’s team proposed to divide the project into two phases. This approach allowed The City of Calgary and Associated Engineering to perform the required due diligence by conducting the necessary environmental assessments in the park area, including a biophysical impact assessment and fish habitat assessment. 

The optimal storm trunk installation route was through North Glenmore Park, a park frequented by locals and known for recreational activities, such as dragon boat races. The park is heavily treed with both natural and manicured vegetation, including large, mature trees. The team coordinated with Calgary Water Resources and Calgary Parks’ Urban Forestry, Natural Areas and Pathways. To refine the installation alignment, Calgary Parks provided an estimated valuation of existing trees and identified areas to avoid impact. The City took the opportunity to incorporate planned public amenity improvements as part of the park restoration.  

37 Street Stormtrunk

The existing untreated stormwater discharged to the Elbow River, immediately upstream of the Glenmore Reservoir, a major drinking water source for the City. Project Manager, Nadeer Lalji, says, “We mitigated water quality issues by installing an oil-grit separator treating a peak flow of 4.5 cubic metres per second (the largest such installation in Calgary at the time) prior to discharge to the Glenmore Reservoir.”

The work required installing the storm trunk and outfall in an unstable slope. To prevent slope movement from negatively affecting this infrastructure, we installed a 30 metre long, piled, slope stabilization wall. The outfall was installed on weak, lacustrine deposit soils. To provide the required strength to support the outfall and to mitigate structural concerns due to the reservoir eroding the bank under the outfall, the outfall was installed on concrete piles. 

37 Street Stormtrunk

The portion of the trunk upstream of the outfall enters the outfall on a steep slope, creating significant energy in the stormwater flow. Releasing flow with this energy into the Glenmore Reservoir would cause significant erosion. Nadeer explains, “We designed a cast-in-place, concrete energy dissipation structure integrated with a cast-in-place, concrete outfall structure to effectively resolve the issue.” 

Construction was primarily completed during the fall, winter and early spring, when park use is lower, to reduce impact on the public. 

Our key personnel on the project included Nadeer Lalji, Oz Podolski, Gabriel Jean, Duane Strayer, Corinne Arkell, Joe Lisella, Risto Protic, Andrew Rushworth, Craig Pass, Ryan Jalowica, Eliman Camara, Jason Bennett, and Matt Freeman.