Peeling back the Pavement - POLIS Water Sustainability Project

PRoblem 1
“CONCRETE JUNGLES”: DESIGN THAT CREATES RUNOFF
New Development and Urban Sprawl
Building cities has always meant replacing the natural landscape—forests, wetlands,
and grasslands—with streets, parking lots, rooftops, and other hard surfaces.
Rather than designing urban infrastructure to absorb water the way nature does,
the use of impermeable materials creates the problem of runoff. Over the past
several decades, the proportion of impervious surfaces has increased dramatically
in Canada’s urban areas. Hard surfaces constitute almost half of urban land cover,
and in downtown commercial settings cover up to 96 per cent (with as much as 70
per cent being roof surfaces). 4
The problem of runoff is compounded by the zoning decisions and subdivision
design characteristics common in most Canadian communities. Since the 1950s,
population growth has been met by developing more land, roads, and water and
sewage treatment infrastructure to meet demand for housing. This has resulted in
urban sprawl across the country. When urban sprawl replaces natural landscapes
with impervious surfaces, significant changes in the natural patterns of water
movement occur.
1951
1981
2010
Built form - 40 km 2
Built form - 261 km 2
Built form - 469 km 2
City limit - 104 km 2 City limit - 509 km 2
City limit - 848 km 2
Concrete Creates the Problem. A supply-side approach to population growth has led to soaring rates
of urban sprawl outside of Calgary, Alberta. This sprawl translates into a loss of natural surfaces and
increased runoff.
Source: City of Calgary
Maintaining Expensive Infrastructure
The Stormwater City drains runoff into a system of pipes where it is conveyed to
streams, lakes, oceans, or other bodies of water that are often several kilometres
from where the rain initially fell. This drainage infrastructure tends to be designed
based on the “major flow” of extreme storm events rather than regular patterns
of precipitation, thus creating an expensive, overbuilt network of infrastructure.
Managing stormwater runoff through hard infrastructure costs Canadian taxpayers
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