The City of Calgary retained Kerr Wood Leidal Associates to design solutions to capture and treat stormwater at its Deerfoot Athletic Park. One of the City’s main goals was to demonstrate the successful use of Low Impact Development (LID) practices in reducing stormwater volumes – even at a site that has low native soil infiltration capacity and drains to a sensitive water body: Nose Creek.
The parking lot was redesigned and the driveway re-graded so that stormwater drained to a new, central bioretention cell. The design requirements were to capture the water quality event, meet specific annual runoff volume targets and to maintain a safe ponding depth during events up to the 1:100 year return period. The cell was designed based on City of Calgary’s Low Impact Development Technical Guidance, Module 2A, DRAFT, October 2012. (A final version of that document is available on the City’s website and is a great resource for bioretention and bioswale design.)
The cell feature an innovative growing medium that was specifically created, in collaboration with the supplier, to balance plant needs, infiltration capacity and local availability, and to work in the semi-arid climate of southern Alberta.
Many factors were considered in the design including: ponding depth, I/P (impervious to pervious area) ratio, sediment accumulation, growing media properties, drain rock depth, filtration layers, and mulching and vegetation.
Other features of the design include:
- easily cleanable scour protection;
- native vegetation that is resilient enough to withstand periods of drought, inundation and exposure to stormwater contaminants; and
- a system for keeping pedestrian and vehicular traffic out of the cells.