Figure 1: Hydrologic Cycle and the
Effects of Urbanization
Courtesy: Conservation Ontario
It has become abundantly apparent
that extensive and more frequent
flooding has been occurring over
the past several decades not only
in New Brunswick but throughout
Canada. The consequences have forced
many Canadian municipalities into a
mode of crisis or reactive stormwater
management using the bandage
approach to control runoff.
Stormwater management can be
defined as: functions associated with
the planning, design, construction,
maintenance and financing of both
natural and constructed facilities that
collect, control and convey stormwater.
The objectives of stormwater management
are to prevent loss of life,
reduce hazards to human health and
well being, minimize damage both to
property and to the environment. This
article is an overview of the historic
approaches to municipal stormwater
management, the resulting problems
and the emerging needs and rationale
for changes to this approach.
Historically, stormwater management
in municipal settings generally
has been limited to selected individual
developments.
The overall large-scale management
of stormwater has primarily been
reactive (i.e. waiting for recurring
flooding problems to manifest themselves
before action is taken). It
appears that this historic piecemeal
and reactive approach is beginning to
result in more frequent and severe
flooding of streets and properties, primarily
in downtown areas.
The two primary processes that
influence increased flooding are
urbanization and climate change.
Urbanization is the often gradual conversion
of previously natural or undeveloped
areas into developed areas.
Urbanization which impacts drainage
includes: an increase in hard surfaces, such as roads, driveways, roofs, walkways
and parking lots, and a reduction
in natural stormwater storage provided
by low-lying areas such as wetlands
and floodplains. Figure 1 illustrates
these effects which result in reduced
evaporation and infiltration of surface
water (recharge), and more runoff both
as larger peak flows and larger runoff
volumes.
As the magnitude of the increase in
runoff is a function of the amount and
the density of development in a given
area, a certain critical mass of development
has to be reached before its
effects on drainage become severe
enough to be clearly evident. Also, as
new development in a watershed primarily
affects existing downstream
development, the cumulative effects of
new development on stormwater
drainage (such as flooding) are most
likely to appear in the downstream
areas of a watershed, rather than in the
areas of new development.
Climate change, the second process
that drives the increase in flooding, is
expected to result in gradual changes
in weather patterns, increased climate
variability and increases in weather
extremes. The net effect of climate
change on municipal drainage infrastructure
is an increase in the frequency
of severe storm events that have the
potential to exceed the capacity of
drainage infrastructure which results
in flooding.
These two processes support the
conclusion that the relatively recent
increases in flooding of downtown
areas is a reality, rather than perception.
The reasons for this type of flooding
are that the effects of climate
change are gradual, that flooding in
many areas is caused by additional
upstream development (rather than
changes in the downtown areas themselves),
and that upstream development
had to reach a critical mass
before its effects on stormwater
drainage became readily apparent.
An illustration of these two processes
would be the 1999 flooding events
in Moncton, NB. Two very severe rainfall
events (both were deemed to have
a return period of 100 years), caused
serious flooding in areas of Moncton
that were located primarily in the lower
and middle sections of the watersheds.
The following illustrates the need
for a more proactive and comprehensive
approach to stormwater management:
The initial development in most
Canadian municipalities occurred in
low-lying areas on the banks of rivers
and lakes, with new development generally
radiating uphill from these older
sections of town. This development
pattern results in the more frequent
and severe flooding occurring in
downtown areas of municipalities
which generally have the highest
development densities and highest real estate values. These increase the damages
associated with flooding and
drastically increase the difficulty and
costs associated with implementing
stormwater management measures
retroactively.
Attempts at alleviating local flooding
by increasing the capacity of the local
drainage system (e.g. storm sewers,
culverts and waterways) have the
potential to amplify and transfer the
flooding to a location further downstream.
Increased and recurring flooding is
also resulting in escalating insurance
claims, expensive and cumbersome
civil litigation, and an increase in public
concern with regard to inconvenience
and property damage related to
flooding.
Increased public awareness of the
stormwater impacts of new development
and the transfer of flooding to
downstream locations, complicates
public planning and community meetings
related to the approval and zoning
of new development.
The lack of foresight with regard to
stormwater management may limit or
prevent new development within sections
of a municipality.
The continued use of historic
approaches to stormwater management
may result in municipal councils
becoming victims of their municipality’s
development success, as negative
consequences of this approach only
become apparent when repairs or
upgrades to the drainage system are
urgently needed. Often these seem
economically impractical and involve
high levels of public inconvenience
and disruption. Proactive approach to
stormwater management will result in
a cost-effective way to control the
impacts of development on drainage, it
makes sense to implement this new
approach to stormwater management
for all new developments, and implement
remedial upgrades to drainage
systems of existing development when
and where possible and practical.
The required new approach to
stormwater management should
include the following components:
Integration of planning and stormwater
engineering. The design of the
stormwater drainage system (both the
minor or traditional storm sewer system,
and the major or overland
drainage system) should be included
as part of each new development (both residential subdivisions as well as
commercial and industrial developments).
These designs should assess
the drainage effects on existing downstream
development as well as the
drainage effects from potential future
upstream development.
Development of consistent guidelines
for the design of stormwater drainage
infrastructure. These guidelines should
include: acceptable design methods,
minimum design parameters, both the
minor and major drainage systems,
both stormwater quantity and quality,
the effects of climate change and guidance
with regard to effective management
measures.
Development of a stormwater implementation
plan. This type of plan
would assess the drainage dynamics of
all the watersheds throughout the
entire municipality as well as the
capacity of all drainage infrastructures.
The uses of this type of plan include:
the ability to determine the reserve
capacity of major drainage infrastructure
(culverts and bridges), the identification
of potential flooding “hot
spots”, the assessment of the potential
effects of proposed new development on existing drainage infrastructure,
and the identification of areas that
require additional design and construction
to accommodate future development.
Integration of potential stormwater
effects from sections of natural watersheds
that extend beyond municipal
boundaries. These can be under the jurisdiction
of another municipality or service
district, which may operate under different
guidelines. Consideration may be
given to provincial guidelines to address
these issues.
The intent of a comprehensive
stormwater management plan is the
ability to ensure sustainable growth by
controlling changing drainage conditions.
This type of approach will ensure
the fair and equitable sharing of both the
costs and benefits of stormwater management
by both existing and future
development, regardless of its relative
location within a watershed. Due to the
many different ways in which changing
drainage conditions can be controlled at
the individual development level, the
stormwater management plan intends to
provide large-scale watershed-based
guidance for drainage. This does not
eliminate the need for detailed design by a professional engineer, nor is it intended
to stifle innovation in planning and
design.
The new approach to stormwater
management can be implemented as a
capital works planning tool, by directing
capital spending on stormwater
infrastructure to areas most in need of
upgrading, while postponing spending
in other areas until the need for
upgrades becomes more urgent. In
many cases, upgrades to stormwater
drainage infrastructure can be coordinated
with improvements to traffic,
sanitary sewer, and water systems as
part of the capital works planning
process such as upgrading a culvert
under a street scheduled for improvement
or repaving.
The City of Dieppe has endeavored
to take this approach to capital spending
related to existing storm sewer
infrastructure upgrades, by monitoring
the reserve capacity of the storm
drainage system. To this end, the City
recently completed a Storm Water
Management Implementation Plan,
and is in the process of developing
Storm Water Design Guidelines for all
new developments.
The City of Moncton has developed Storm Water Design Guidelines as part
of its Design Criteria Manual for
Municipal Services, and is in the
process of revising these guidelines to
accommodate the water quality aspects
of stormwater management. The City
of Fredericton is presently completing
Storm Water Design Guidelines, while
other municipalities are following suit.
In summary, a well-prepared
stormwater management plan, once
implemented, can protect the natural
and built environments within municipalities,
and lessen potential problems
that could adversely affect the sustainable
growth of municipalities and wellbeing
of residents. The increasing challenges
faced by municipalities due to
urbanization and climate change can be
faced successfully with a comprehensive,
integrated and pro-active
stormwater management plan.
Rodney Hopper is Regional Manager
of Touchie Engineering in Moncton,
Contact: rhopper@rvanderson.com
Hans Arisz is Senior Associate of
Hydro-Com Technologies in
Fredericton.
Contact: harisz@rvanderson.com
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