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WCEL
> Issues > Urban Growth and
Development > Smart Bylaws Guide > Part
2 > Integrated Stormwater Management
Smart Bylaws Guide – Integrated Stormwater Management
A significant cost of the infrastructure for new development is
to ensure that water drains away from buildings and roads. Covering
over natural vegetation with hard surfaces means less water
naturally infiltrates into the ground, creating more surface runoff
that needs to be removed and delivered through stormwater systems of
underground pipes and ditches to receiving watercourses. Stormwater
runoff from developed areas flows to the receiving waters much
faster and in greater volume than under natural conditions. This
causes channel erosion, flooding, loss of aquatic habitat, and water
quality degradation. As more development occurs, more municipal
infrastructure must be built to deal with the increase in stormwater
runoff.
Because of the cost and problems associated with this
volume-based approach to stormwater, over the past decade
municipalities and the provincial government have been developing an
integrated stormwater planning approach. Integrated stormwater and
watershed management planning attempts to address the complex
interdependent effects of water, land, human activities, and aquatic
and wildlife resources.
What is Integrated Stormwater Management?
"In British
Columbia, the term Integrated Stormwater Management Plan (ISMP) has
gained widespread acceptance by local governments and the
environmental agencies to describe a comprehensive approach to
stormwater planning. The purpose of an ISMP is to provide a clear
picture of how to be proactive in applying land use planning tools
to protect property and aquatic habitat, while at the same time
accommodating land development and population growth… At the
highest level of effort and complexity, all watershed stakeholders
work together to achieve watershed management objectives while
considering inter-related social, economic, and environmental
issues. These high level watershed management plans include not only
the hydrology aspects of [master drainage plans] but also consider
other issues, such as the environment, water quality (surface and
groundwater), fisheries and aquatic life, wetlands, riparian
corridors, transportation, and agriculture.
An urban watershed is an ecosystem with a complex system of
interacting natural and man-made components. Managing such
watersheds involves planning and caring for its water, land,
land/water interactions, human activities, wildlife and wildlife
habitat, and aquatic resources to protect the health of the
ecosystem. Government agencies, other stakeholders, and watershed
residents must work together to accomplish watershed management
objectives while considering inter-related social, economic and
environmental issues."
Stormwater
Planning: A Guidebook for British Columbia
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The key to reducing property damage, poor water quality and
damage to aquatic habitat is to decrease the volume of runoff that
flows to streams. The idea is to mimic the water balance of a
naturally vegetated watershed by controlling stormwater at its
source or where it falls onto the ground.
This new approach of source control seeks to capture rainfall (on
lots or within road right-of-ways) and return it to its natural
hydrologic pathways by ensuring that it infiltrates into the soil or
is used. This reduces the volume of water and speed at which
stormwater flows into watercourses.
Municipalities and developers are using a variety of engineered
solutions to detain stormwater on sites. Most rainfall in
southwestern British Columbia occurs in light showers of less than
three centimeters that can typically be handled through landscape
solutions.
Source controls include:
- Vegetated swales (bioswales) – grassy or vegetated areas
that retain and infiltrate stormwater and improve water quality
beside roads and parking areas;
- Bioretention areas – a layer of absorbent soil and ground
surface that allows for water to infiltrate into the surrounding
soil;
- Infiltration trenches - an excavated trench that is filled
with gravel or stone (may have absorbent landscaping on top) to
form a sub-surface infiltration basin. With proper engineering,
paving and light vehicle traffic may be allowed on the
surface;
- Infiltration ponds - unlined ponds designed to promote
infiltration;
- Foundation planters - planter boxes into which rooftop runoff
can be diverted along building exteriors. Planters are most
useful for land uses where lack of space is a key
constraint;
- Pervious paving - paving materials (porous concrete, permeable
interlocking paving blocks, concrete grid pavers, perforated
brick pavers and compacted gravel) that allow water to flow
through them into the soil. Best used where vehicle traffic is
light (e.g. driveways, roadway shoulders, overflow parking
areas, sidewalks, patios);
- Green roofs – rooftops on which a layer of lightweight,
absorbent growing media is underlain by a drainage layer that
retains rainfall and allows it to evaporate or transpire from
the rooftop vegetation; and
- Rainwater capture and reuse on landscaping.
Most municipalities and projects employ a combination of the
above source controls, and sometimes limited hard infrastructure, to
achieve maximum infiltration and to ensure that major storm events
will not cause flooding.
Municipalities can achieve source control by using a variety of
tools, from OCP policies to zoning and subdivision servicing
requirements.
From City of Chilliwack Policy
and Design Criteria Manual for Surface Water Management (p.11)
Tools for Integrated Stormwater Management Planning
Local Government Integrated
Stormwater Management Initiatives (Policies and Bylaws)
For More Information
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