This project arose from the City of Calgary’s water quality policy that commits to a no net increase in sediment loads to the Bow River beyond 2005 levels, while maintaining a projected 30% population growth by the year 2030. Existing regulatory controls on new developments will not reduce sediment loads sufficiently to meet this target, therefore Calgary also needs to develop stormwater quality retrofit facilities for existing developed areas.
Fish Creek East was selected as a site offering a significant water quality benefit from a retrofit project. The existing stormwater facilities at Fish Creek East occupy a former gravel pit which was reclaimed in 2001 by Alberta Transportation and the Rotary Club of South Calgary, and were established as part of the overall stormwater management facilities for the Deerfoot Trail South Extension. Outfall B117 was located at the south end of the site and was originally constructed to discharge full stormwater runoff from the Cranston and Auburn Bay catchments direct into the Bow River. However, subsequent construction of three stormwater ponds in the upper catchment has resulted in much lower peak flows, and KCB determined that full diversion of Outfall B117’s 1:100 year flow could be accommodated and treated by the existing Main Pond, allowing demolition of this large outfall structure and rehabilitation of the riverbank. The stormwater retrofit for the Fish Creek East included the following:
- A diversion pipe and channel to divert the total stormwater flow from Outfall B117 into the existing Main Pond.
- Demolition of the existing Outfall B117 structure and reinstatement of the riverbank.
- A forebay formed by a cross-dyke in the existing pond to facilitate maintenance and improve pollutant removal of larger particles.
- An overflow channel to convey excess water during a 1:5 year or greater event from the existing pond to the Bow River. Routine stormwater inflow from small rainfall events will leave the pond via exfiltration through the permeable gravels, and will not surcharge the pond enough to reach the overflow channel invert.
The final project was significantly more compact and had much lower construction impacts and cost than the original concept (by others). The construction activities occupied only the southern 30% of the park area. No significant historical resource impacts or environmental/habitat issues for the project were identified by appropriate evaluations carried out as part of the preliminary design work. Overall, the project has resulted in the removal of a large and intrusive stormwater outfall structure from the riverbank and the elimination of an average of approximately 167,000 kg/year sediment load from the Bow River.
- Watershed modelling
- Erosion and sediment control
- Hydraulic structures design
- Construction management