When the big storms hit : The role of wetlands to limit urban and rural flood damage / Natalia Moudrak, Anne-Marie Hutter, and Blair Feltmate.

"Intact Centre on Climate Adaptation."

"July 2017."

Includes bibliographical references (pages 52-53).

This report assesses the potential for wetlands to
affect the financial impacts associated with rural
and urban flooding. Working with the Grand River
Conservation Authority (Ontario), Credit Valley
Conservation (Ontario) and Ducks Unlimited Canada,
the Intact Centre on Climate Adaptation (Intact
Centre) determined that wetlands, if maintained in
their natural state, can substantially reduce flood
damage costs to buildings (ranging from residential
homes and apartment buildings, to industrial,
commercial and institutional structures).
These findings have national applicability, albeit the
research focused on two Southern Ontario pilot sites,
one rural and one urban. For both sites, computer
models simulated a major Fall flood, to compare
flood damages under conditions where wetlands
were maintained in their natural state and where
they were replaced with agricultural land use. The
researchers found that flood damages were lower if
wetlands were maintained in their natural state, with
financial cost savings of 29 and 38 per cent in rural
and urban areas, respectively.
The rural pilot site was located near the City of
Mississauga (Ontario) and the urban pilot site was
located within the City of Waterloo (Ontario). The
magnitude of the modelled flood was based on
a severe, yet realistic, flood event (i.e., Hurricane
Hazel, 1954, approximately equivalent to a 1-in-500
year flood), that had historically caused substantial
property damage and loss of life in the Greater
Toronto Area (Ontario).
At the rural pilot site, if wetlands were maintained in
their natural state, flood damages would have been
$8.9 million. This was $3.5 million, or 29 per cent,
lower than the $12.4 million cost that would have
been realized if wetlands had been replaced with
agricultural development.
Executive Summary
Residential Wetlands @DUC
For the urban pilot site, if wetlands were maintained
in their natural state, the cost of flood damages would
be $84.5 million, which was $51.1 million, or 38 per
cent, lower than $135.6 million cost that would have
occurred had wetlands been replaced with agricultural
development.
If the modeling assumed that wetlands were
replaced by urban, largely impervious surfaces
(such as buildings, roads and parking lots), rather
than agricultural development, the value of flood
damages avoided would have exceeded 29 - 38 per
cent. Accordingly, the additive value of wetlands to
reduce flood damage, as profiled in this report, is
conservative.
This report demonstrates quantitatively that wetlands
conservation is a cost-effective means to reduce flood
risk in Canada. As such, the findings are consistent
with, and reinforcing of, directives outlined in the
Wetland Conservation Strategy for Ontario, the
Province of Ontario’s Climate Change Action Plan, and
the Government of Canada’s Pan-Canadian Framework
on Clean Growth and Climate Change.
In summary, maintaining wetlands in their natural state
offers a broadly-applicable and cost-effective means to
reduce the financially and socially pervasive impacts of
flooding that are increasingly affecting all Canadians.