December 4, 2017

Is Vancouver a "Sponge City?"

Internationally water management is the purview of the Dutch, who consulted in the rebuilding of New Orleans after the horrific hurricane and also worked with China on the concept of Sponge Cities to improve drainage and provide flooding mitigation. This is achieved by innovative sewage and waste water techniques, and combining spatial planning and water management, an interdisciplinary approach to flood proofing cities.
Similar work has been successful in the Dutch city of Nijmegen where flooding capacity of a river was enlarged by creating an extra stream channel, which  as part of that City’s policy also enhanced economic development and place making.  In Rotterdam plazas have been created that hold rainwater in extreme weather events replacing infrastructure basins. There have also been pioneering work on the use of dry river bed “wadis” incorporated  in new residential housing developments to mitigate flooding.
As reported to the World Economic Forum  China is utilizing the spongy city design concept in 30 cities including Shanghai, Wuhan and Xiamen. With an investment of 12 billion US dollars the project hopes to have 80 per cent of urban areas in China reusing almost 3/4 of their rainwater in the next three years.
Vancouver is riddled with underground streams, many lost in development~and there is a treasure trove of materials available at the University of British Columbia. There are great stream stories-by mistake the Mount Pleasant stream that used to move logs and power wood mills was excavated during work near Main Street and Broadway decades ago. There is also a large aquifer and flowing stream below the Oakridge Mall. City Engineers have calculated that the Oakridge aquifer can supply 120 US gallons a minute or approximately 7.5 litres of water per second. Indeed the water is used by the mall as a coolant, and has been used that way since the 1970’s.
New York City’s urban ecologist Eric Sanderson has created a “digital elevation” of New York  pre-development and is discussing how these ancient watersheds and streams can be reincorporated into city landscapes for resiliency and public amenity. It is this interdisciplinary approach to flooding, flora and fauna that will bring streams back to New York City and provide a new amenity in the concrete signature of the city. As outlined in this piece from Mountain View’s Vancouver Street Stories, everything old is new again~and streams and old river beds have a renewed purpose in weatherproofing  and providing new recreational spaces in  spongy cities.

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  1. Is Vancouver a “sponge city”?
    Absolutely not. The Burrard Peninsula rise is underlain by hard, impermeable glacial till often just a few centimetres below the surface, then again by even harder sandstone. Attempts to dig below the till layer can be met by pressurized ground water (i.e. one humongous artesian well) that will never drain out. That’s what killed the formerly-approved Oakridge project, and is causing a multi-million problem with an artesian well on a private Southlands lot.
    These geotechnical circumstances in a high-rain region make drainage and stormwater management challenging, but also tend to highlight how silly and token some planning codes are here. One of them is enforcing the provision of small strips and patches of lawn or planting beds on open lots all in the name of infiltration. Well, these bits become mud after the first rainfall event of the season, and remain completely saturated and therefor ineffective during every other storm that follows until summer. The reason? Dense silty soil and glacial till just below the surface.
    The most effective way to store and treat runoff here is to provide underground cisterns than can store winter rainfall from the roof for use in summer. If the cisterns are large enough (e.g. at least 3,000 litres on residential lots) then the use of the Metro’s potable water supply is offset. Scaling up to the neighbourhood level, roof and street runoff could be directed into even larger underground cisterns placed in public parks for non-potable summer irrigation of planting beds. I don’t think we’re ready yet to consider city-wide greywater collection and recycling.
    City and region-wide stormwater treatment is most effective with large artificial wetland complexes placed downstream before they empty into the Fraser or the ocean, with input from the upstream storm sewer network. This was done with Burnaby’s Byrne Creek, a watershed where even more daylighting is planned. Vancouver cannot accomplish anything close because it culverted all 26 major salmon-bearing streams. Requiring little bits of lawn on open lots and tiny garbage-collecting ditches romantically termed “bioswales” is like colouring a paper leaf and placing on a stump in a 130 km2 clear cut and calling it “green.”

  2. I’m quite suprised that so little is actually required here in terms of ‘blue’ roofs and on-site stormwater retention … especially considering how many sites have lightwells which require sumps and pumping anyway, increasing the tank capacity seems a totally low hanging fruit to capture and slow the runoff of a huge amount of rainfall … as Alex’s comment suggests, a few thousand liters or gallons each would go a huge way to both lessening the need for summer water-rationing, and also go some way to the whole ‘green city’ thing.
    On another note … the fact that so few people remember where these streams are was very evident on the redevelopment of ‘The Ridge’ on Arbutus … a friend of mine worked construction on that site and they were mystified as to why they had so much water on site … having seen the rewilding show at MOV and having seen the stream map very similar to that on ‘lost streams’ site I could immediately tell him why they had a river through the site.
    The fact that the Geotechnical Engineer didn’t seem to know, and that they hadn’t therefore planned to deal with that much site water is a bit troubling.

    1. I’ve worked on a handful of projects where the geotechnical engineer warned us to not puncture the hard till layer. The old streams eroded the earth and created steep side banks where the groundwater seeped, and in some cases flowed, out of the sides of the embankment. The water still flows and had to be contained by pipes deep underground. One of the greatest causes of erosion of the UBC Wreck Beach cliffs is groundwater seeping out from between the layers of till.
      The pioneer farmers in Langley and the Fraser Valley never lacked for water even in the hottest summers because they could always find it by driving a pipe several metres into the ground, and had a 5 cm standing column of low pressure water always flowing out of the top, enough to fill livestock watering troughs overnight. I would wonder about the water quality today, though, given the half century of chemical farming practiced there.

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