Stormwater: Simon Fraser UniverCity

CH2M Hill

Simon Fraser University atop Burnaby Mountain outside Vancouver has always been a striking symbol of higher learning. Now the institution is to be a beacon for sustainable design as it prepares to develop a new community on the campus. Over 10,000 people will be living and working in UniverCity when it is finished in 25 years. Already the roads and water infrastructure on the eastern sector are due to start construction this June.

Because of land agreements, only the top 20% of the mountain can be developed and the rest has to be preserved in its natural forest state. Besides the legal requirement for limiting the area of development, the university has a sustainable development policy and wants to build a tightly knit urban form to discourage car dependency and suburban-type sprawl. No single-family homes are to be built on the 160-acre site, only townhouse residences. There will be university buildings, a main street, and commercial area, with towers up to 10 stories tall.

The high density of the development (40-80 units per acre) has a potential down side, however. It disturbs the ground and means up to 70% of the surface is paved. Rain run-off from Burnaby Mountain goes into Stoney Creek, which is one of the few remaining high quality fish-bearing tributaries in the Brunette River Basin. The public is very concerned that the creek’s ecology be protected.

Kim Stephens, P.Eng., project manager for CH2M Hill which is in charge of the watercourse and stormwater management plan, believes that unless they found a way of protecting the creek’s ecology, the entire project might have foundered.

The engineers say they returned to first principles and “re-invented” urban hydrology for the project. They decided to design for the full spectrum of rainfall, rather than for just extreme storms. Burnaby has rain on average 170 times a year, and according to Stephens, it is these small rainfall events that create wear and tear on the receiving waterways. Traditionally stormwater engineers have been concerned with extreme storm flows — “Let’s pipe it and get rid of it” — but Stephens believes they should be more concerned with managing volume at the source.

At UniverCity the first 35 millimetres of rainfall will be retained on site. Water will soak into the ground and percolate in the “interflow” zone just below the surface, to be held there and released slowly through natural pathways. In heavier rainfall of up to 100 mm, the overflow goes to 12 stormwater ponds until it can be slowly released. When there is a major storm of more than 100 mm (which amounts to only 2% of the total rainfall), the overflow is conveyed down the mountain via the existing open channel system to flow into Stoney Creek.

Since rainfalls of less than 35mm are the most common event, the on-site retention strategy is critical. Buildings will have on-site cisterns that will release at natural flow rates to the shallow ground zone described above. The long-term goal is to have buildings use and re-use the stored water.

All parking structures will be underground and topped with vegetative roofs that soak up the rain. Roads will be only 3 metres wide, with 2.5-metre wide shoulders with pervious paving. Between the road curb and the sidewalk is a swale with a gravel-filled infiltration trench underneath. The run-off seeps through the trench bottom and sides into the surrounding media, but the trench will hold the water for several days. It has a perforated overflow pipe in case the water level builds up. Many man-made ditches are being realigned and existing piped watercourses are being opened up to the daylight.

The project team will follow a plan of “adaptive management” which means constantly monitoring and adjusting design plans over the 25-year development period. Based on the principles adopted in this project, CH2M has developed a decision support software program called the Water Balance Model. Under contract to the B.C. Government, the consultants have also published a guideline, Stormwater Management Planning intended for municipalities to implement a watershed-based approach to land planning.CCE

Client: Simon Fraser University

Prime consultant: Hotson Bakker Architects