WC129 MarApr2023 - Flipbook - Page 24
STORMWATER
Shifting Stormwater Capacity
New solutions for reducing our stormwater
management footprint BY STEVEN VAN HAREN, P.ENG.
“An undergroundbased system
with a treatment
train-based water
quality approach,
depending on site
considerations,
is likely better
at removing fine
particulates
from the runoff
stream via media
filtration than a
surface stormwater
management pond.“
Steven van Haren, P.Eng.
is a Manager of
Land Development /
Water Resources for
WSP Canada.
24
WATER C AN ADA • M ARCH/APRIL 2023
T
HE COST OF LAND in Canada’s major cities and their
surrounding areas is skyrocketing. New housing stock are
going for astronomical prices and there is no concrete evidence to suggest that this trend will change.
So how do we make more of our new residential
footprints, especially with the need to factor in climate change
and resiliency measures in these developments? How do we build
greener communities while still making the most of the valuable
existing land mass?
One solution that has emerged is the opportunity to bury our
stormwater management capacity, removing the need for aboveground stormwater ponds and, in turn, freeing up additional space
for desperately needed housing stock and recreational space.
The value of going underground
Shifting stormwater storage underground allows for the reuse of
the surface area above it for parkland or other low-loading urban
uses such as turfed playing fields and amphitheatres. These forms
of land use work well in this setting, allowing the large surface
area associated with the underground stormwater management
facility to double as parkland dedication, freeing up the space that
would have been reserved for a pond, a normal factor in urban
development that is viewed as a cost for developers. Normally,
the pond area and a separate park area would be considered
a requirement of a traditional development application but
combining them allows for significant savings in land value.
Other items that are in underground detention’s favor are
hydraulically related. Open-air stormwater management ponds
have maximum depth requirements for public safety that constrain
outlet system design. Underground systems are not accessible
to the public, so water depths can be higher, reducing facility
footprint for the same volume and adding flexibility in the design
of outlet controls to dial-in performance for the sensitive receiving
water systems.
Another benefit of underground systems is the reduction of
thermal load on receiving watercourses. Many Ontario watercourses are considered cold-water fisheries with aquatic life that is
sensitive to contributions of warm water discharges from open-air
stormwater management ponds that typically sit in direct sunlight
most of the year. Underground stormwater management facilities
typically have significant amounts of concrete in thermal equilibrium with the subsurface soil, so any water stored in the facility
doesn’t warm up from sunlight and inflowing water can be cooled
WAT E R C A N A D A . N E T
