The City of Calgary’s Carburn Park was in need of stormwater management upgrades. The City retained Kerr Wood Leidal Associates (KWL) to design solutions that would capture and treat stormwater on site. One of the City’s main goals was to showcase examples of successful retrofits to existing infrastructure using Low Impact Development (LID) stormwater practices.

KWL’s design included re-grading the parking lot so that stormwater drained to new, central bioretention cells. The design requirements were to capture the water quality event, meet specific annual runoff volume targets, and maintain a safe ponding depth during events up to the 1:100 year return period. The cells were 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 cells 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.