Peeling back the Pavement - POLIS Water Sustainability Project

and focus for local government incentive programs, as well as benchmarks against
which future development can be measured. Mandating “runoff neutral” standards
or site-level regulations, such as release rates for all new redevelopments, can help
achieve the overall permeability target for a region.
Using green infrastructure to manage rainwater in new developments is one thing,
but what about the existing infrastructure in a Stormwater City? When retrofitting,
changes will inevitably be made in stages. Although some small-scale green
infrastructure retrofit projects can be more expensive than conventional approaches,
green infrastructure is generally cost-effective when incorporated into larger
redevelopment projects or when major infrastructural improvements are already
needed. In these cases, the costs of green infrastructure are often minimized
relative to the scope and cost of the overall project. 25 In the City of Philadelphia
redevelopment projects are exempt from various regulatory requirements if they
reduce impervious area by 20 per cent or more. Almost all redevelopment projects
now reach this 20 per cent reduction target 26 with most developers now building
on infill sites instead of undeveloped, natural areas. 27
Fixing and Retrofitting Obsolete Infrastructure…
Even with widespread adoption of green infrastructure that reduces a city’s overall
impermeability, the presence of roads, sidewalks, and extreme storm events
means that there will still be a need to manage some amount of runoff. In a
Rainwater City, existing hard infrastructure complements green infrastructure to
accommodate these particular drainage priorities. So, while green infrastructure
is the focus, identifying, repairing, and upgrading conventional drainage infrastructure
is also relevant in Rainwater Cities. For example, the City of Toronto is
installing tanks and tunnels to capture and hold combined sewer overflows and
runoff. Before the water is slowly released into Lake Ontario, it is subjected to
ultraviolet light to kill bacteria. In addition, the City will use a technique known
as "flow balancing" to capture runoff and treat it through the use of ponds and
wetlands. The City’s Wet Weather Flow Management Master Plan calls for the
creation of 180 ponds/wetlands. 28
Canada’s communities have billions of dollars invested in conventional stormwater
infrastructure and in many cases are projecting a financial shortfall in addressing
the future upkeep of aging infrastructure. 29 An opportunity lies in making evolutionary
changes during the lifecycle of the infrastructure. For example, the City of
Calgary is taking a two-tiered approach to transitioning to infrastructure that better
mimics the natural water cycle. New developments are being built to capture approximately
80 per cent of their runoff volume. The City is working with developers
to promote new practices for lot and block developments to achieve pre-development
flow profiles. In older areas, the City prioritizes redevelopment opportunities
such as end-of-pipe retrofits.
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