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WCEL
> Issues > Urban Growth and
Development > Smart Bylaws Guide > Part
2 > Integrated Stormwater Management >
Chilliwack
Smart Bylaws Guide – Chilliwack
Chilliwack requires new developments to manage
stormwater so that there is no net increase in post-development
flows into receiving watercourses. The City’s objective is
“…to control run-off volume so that watersheds behave as though
they have less than 10% impervious area.” The City is
changing its approach from reacting to rainfall problems to
preventing them by reducing the volume and rate of runoff. To
achieve this goal, the City’s regulations in its Subdivision
Development Control Bylaw (titled Policy
and Design Criteria Manual for Surface Water Management) were
developed as a case study application for the provincial
Stormwater
Planning: A Guidebook for British Columbia.
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Stormwater Management Goal
Implement integrated
stormwater management that maintains or restores the water balance
and water quality characteristics of a healthy watershed, manages
flooding and geotechnical risks to protect life and property, and
improves fish habitat values over time.
Stormwater Management Objectives
- To manage development to
maintain stormwater characteristics that emulate the pre-development
natural watershed.
- To predict the
cumulative stormwater impacts of development and to integrate this
information with other economic, land use, and sustainability
objectives and policies when considering land use change.
- To regulate
watershed-specific performance targets for rainfall capture, run-off
control, and flood risk management during development, and to refine
these targets over time through an adaptive management program.
- To identify, by example
and pilot studies, means of meeting the performance targets by
application of best management practices, and to remove barriers to
use of these practices.
- To support innovation
that leads to affordable, practical stormwater solutions and to
increased awareness and application of these solutions.
Policy
and Design Criteria Manual for Surface Water Management, p.6
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The City published its Policy
and Design Criteria Manual for Surface Water Management in 2002
to define the City’s drainage planning approach and to provide
developers and City officials with the necessary design criteria to
implement the stormwater management objectives at a site level.
It addresses stormwater management at both watershed/neighbourhood
scales and at the subdivision scale. It provides the City with
a comprehensive framework within which Integrated Master Drainage
Plans can be implemented. It also provides developers with
site-specific sustainable stormwater management approaches.
The Manual is divided into five sections:
Section 1 – Context and Overview: Provides an
overview of the Manual and the City’s approach to stormwater
management.
Section 2 – Stormwater Goals &
Objectives: Defines the objectives that summarize the City’s
drainage planning philosophy and approach.
Section 3 – Action Plan: Defines the actions
that are needed over the next five years to achieve the City’s
stormwater management objectives, and who is to take the lead role
in achieving each of the actions.
Section 4 – Design Guidelines: Defines the
City’s design criteria for drainage systems and provides guidance
to city staff, developers and consultants regarding how to implement
these design criteria at the site level. This section includes
a methodology for developing performance targets and design
criteria.
Section 5 – Submission Requirements: Defines
the information that land developers must submit to the City in
order to obtain development approval.
For new developments on the ground, the City
has committed to capturing the first 30 millimetres of rainfall per
day at the source and restoring it to natural hydrologic pathways
(infiltration, evapo-transpiration, or re-use). The next 30
millimetres of rain will be detained and released into storm sewers
or streams at natural interflow rates. This approach means
that Chilliwack will restore 75 percent of annual rainfall volume
into natural hydrologic pathways, and will detain a further 20
percent.
The City has been monitoring three subdivisions
that incorporate some infiltration strategies, and is using the
information to revise their standards through adaptive management.
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