WC133 NovDec 2023 - Magazine - Page 26
STORMWATER
Green Solutions in Tight Spaces
Sustainable design solves stormwater facility retrofit
BY SARAH ANDREW
I
Sarah Andrew
Sarah Andrew is an associate and senior
water resources engineer for the Ontario
Integrated Water Management team at
GHD. She specializes in surface water
quality and quantity monitoring, as
well as green infrastructure design and
performance monitoring.
26
WATER C AN ADA • NOV EMBER/ DECEMBER 2023
the Region of Peel, Credit Valley Conservation Authority, and GHD took on the challenge of integrating GI into an innovative and sustainable solution for
the Bovaird facility.
Challenges of traditional stormwater management
Stormwater originates as precipitation, most commonly in the form of rainfall, which accumulates on
impervious surfaces such as streets, sidewalks, roofs,
and driveways and then ultimately discharges into
wetlands, streams, rivers, and lakes, ideally travelling
through SWM infrastructure first. As stormwater
flows over these surfaces two key things happen: It
picks up almost everything in its path (including
garbage, dirt, and other pollutants such as oil and
grease, fertilizers, and pesticides); and absorbs the
heat impervious surfaces give off, thereby raising the
water’s temperature.
The heating of stormwater is further exacerbated
by SWM facilities themselves. The purpose of these
facilities—specifically wet ponds—is to provide
temporary storage and/or treatment of stormwater.
However, they come with an unfortunate drawback:
their large surface areas mean that the captured water
begins to warm. This becomes problematic when the
water flows downstream into habitats that require
cooler temperatures.
To reduce the thermal impacts of SWM facilities,
designers typically look to incorporate best management practices, such as shading, bottom draw outlets,
and/or cooling trenches. However, for cooling to be
effective with a bottom draw outlet, a pond needs adequate depth and cooling trenches must be installed
outside the pond footprint, requiring sufficient
horizontal space.
The Bovaird facility was originally designed to
manage stormwater runoff from an upstream drainage
WAT E R C A N A D A . N E T
GHD
N RECENT YEARS, municipalities have turned
to green infrastructure (GI) to address the many
challenges associated with population growth,
aging infrastructure, declining ecosystem health,
and climate change. However, as municipalities
work toward introducing or scaling up their GI initiatives, they are faced with a common dilemma: how
to implement GI within a limited footprint while still
achieving the objective of sustainable design.
Due to growing urban landscapes, municipalities
are running out of room. Traditional stormwater
management (SWM) facilities that once functioned
as intended are now forced to manage increased
impervious areas within their catchment areas. The
consequence? Degraded treatment efficiency and
flooding. As part of a recent SWM facility retrofit,
