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Created page with "the mid 1970s, attempts to control runoff flow rates from urban developments were initiated. By the late 1980s, water quality became an additional focus and in the late 1990s,..."
the mid 1970s, attempts to control runoff flow rates from urban developments were
initiated. By the late 1980s, water quality became an additional focus and in the late
1990s, approaches to mitigate accelerated stream channel erosion were introduced.
Lot level stormwater management approaches have been advocated in Ontario since
1995 (OMMAH, 1995), but widespread application has yet to occur. Today, with
improvements in our understanding of watershed systems and the potential impacts
urbanization can have on aquatic ecosystems, stormwater management addresses a
broad suite of issues including fluvial geomorphology (stream channel forming
processes), groundwater resources and the protection of aquatic and terrestrial habitats
(Figure 1.2.1).
Municipalities, with the support of conservation authorities, review stormwater
management facilities and plans designed to address this multitude of concerns. This has led to an increasing complexity in stormwater management planning and design
including:
* increasingly complex stormwater management facilities and best management practices;
* the need to involve more inter-disciplinary expertise in studies to define environmental opportunities and constraints;
* expanding requirements for multi-purpose stormwater management facilities; and,
* increased emphasis on the treatment train approach and use of multiple types of controls to address environmental issues.
CVC and TRCA have been extensively involved in integrated watershed-wide
environmental monitoring for many years. The results of this monitoring have shown
that the environmental health of many watersheds continue to decline as urbanization
increases. This environmental deterioration has taken place despite widespread
compliance with provincial and conservation authority requirements for stormwater
management planning and facility design. Conventional stormwater management,
which focuses on controlling peak flow rate and the concentration of suspended solids,
has failed to address the widespread and cumulative hydrologic modifications in watersheds that increase the volume of stormwater, increase the runoff rate, and cause
excessive erosion and degradation of stream channels. Conventional stormwater
management also fails to adequately treat other pollutants of concern, such as
nutrients, pathogens and metals.1
CVC’s recent Credit River Water Management Strategy Update concludes that
continued use of what are currently considered “state of the art” stormwater
management practices will lead to continued degradation of the watershed, jeopardizing
the health of the Credit’s world class fishery and other valued environmental resources
(CVC, 2007b). To protect the health of the Credit River watershed, the updated water
management strategy calls for an immediate shift to more proactive and innovative
stormwater management systems that include low impact development practices.
TRCA’s Rouge River Watershed Plan (TRCA, 2007c), Humber River Watershed Plan
(TRCA, 2008a) and Don River Watershed Plan (TRCA, 2009a) reach similar
conclusions about the inability of conventional stormwater management practices to
protect the health of rivers and the need for low impact development approaches. In
addition, the Rouge River Watershed Plan concludes that widespread implementation of
LID practices in new and existing developments could increase the resiliency of the
watershed system to some anticipated impacts of climate change on baseflow and
channel erosion (TRCA, 2007d).
Recent research (Aquafor Beech Ltd., 2006) has suggested that current practices to
offset the hydrologic effects of urbanization are insufficient to prevent increased channel
erosion and deterioration of aquatic habitats. In many cases, even small incremental
changes in watershed hydrology commensurate with an increase in impermeable
surfaces of 4%, can result in changes to stream channel characteristics and aquatic
communities. To offset these impacts, an increased emphasis on maintaining natural
water balance and replicating the predevelopment hydrologic cycle is required (Aquafor
Beech Ltd., 2006).
Finally the 2003 OMOE Stormwater Management Planning and Design Manual, though
reflective of current technology is rapidly becoming dated, since much of the material it
reviewed dates from 1999. In the last five years, over 30 state-of-the-science
stormwater management manuals and guidelines have been released in locations such
as Maryland, Washington State, British Columbia, Minnesota, Pennsylvania and
Oregon. The objective of maintaining predevelopment water balance, use of the
treatment train approach and application of low impact development practices are all
becoming common practice in these jurisdictions.
Two recent documents, one prepared by the City of Toronto and the other prepared by
the Greater Vancouver Regional District summarize how the approach to stormwater
management needs to change.
Rainwater should be treated as a resource to nourish and enhance the
City’s environment. Management should begin where precipitation hits
the ground according to the priority of source, conveyance, end-of-pipe
and finally, stream restoration measures (City of Toronto, 2006).
There is a need for a change in the philosophy of treating runoff from
one of stormwater management to rainwater management (GVRD,
2005).
This is why CVC and TRCA commissioned the development of a stormwater
management guide to provide guidance on the kind of cutting edge practices that are
needed to protect the health of the CVC and TRCA watersheds. The LID SWM Guide
draws on published research, literature and local studies to provide planning and design
guidance that reflects regional policies, practices and climate. It provides information
and guidance on the following:
* how to integrate stormwater management into the urban planning process;
* how to design, construct and maintain a range of LID stormwater management
practices; and
* the kinds of environmental and performance monitoring that should be carried
out.
Acknowledging that it will not always be possible to maintain the predevelopment water
budget of a site, predicted increases in runoff from land development that cannot be
mitigated through stormwater infiltration practices should be minimized through
practices that either evapotranspire (e.g., green roofs, bioretention), or harvest runoff for
non-potable uses (i.e., rainwater harvesting). In areas where development has already
taken place, LID can be used as a retrofit practice to reduce runoff volumes, pollutant
loadings, and the overall impacts of existing developments on receiving waters. LID
practices can include:
* conservation site design strategies (i.e., non-structural LID practices);
* infiltration practices;
* rainwater harvesting;
* runoff storage and evapotranspiration;
* runoff conveyance;
* filtration practices; and landscaping.
Studies show that implementing LID practices can have multiple positive environmental effects including:
* protection of downstream resources;
* abatement of pollution;
* recharge of groundwater;
* improvement of water quality;
* improvement of habitat;
* reduced downstream flooding and erosion;
* conservation of water and energy; and
* improved aesthetics in streams and rivers.
These combined benefits help to mitigate potential negative impacts of climate change
on groundwater levels, risk of flooding and stream channel erosion.
initiated. By the late 1980s, water quality became an additional focus and in the late
1990s, approaches to mitigate accelerated stream channel erosion were introduced.
Lot level stormwater management approaches have been advocated in Ontario since
1995 (OMMAH, 1995), but widespread application has yet to occur. Today, with
improvements in our understanding of watershed systems and the potential impacts
urbanization can have on aquatic ecosystems, stormwater management addresses a
broad suite of issues including fluvial geomorphology (stream channel forming
processes), groundwater resources and the protection of aquatic and terrestrial habitats
(Figure 1.2.1).
Municipalities, with the support of conservation authorities, review stormwater
management facilities and plans designed to address this multitude of concerns. This has led to an increasing complexity in stormwater management planning and design
including:
* increasingly complex stormwater management facilities and best management practices;
* the need to involve more inter-disciplinary expertise in studies to define environmental opportunities and constraints;
* expanding requirements for multi-purpose stormwater management facilities; and,
* increased emphasis on the treatment train approach and use of multiple types of controls to address environmental issues.
CVC and TRCA have been extensively involved in integrated watershed-wide
environmental monitoring for many years. The results of this monitoring have shown
that the environmental health of many watersheds continue to decline as urbanization
increases. This environmental deterioration has taken place despite widespread
compliance with provincial and conservation authority requirements for stormwater
management planning and facility design. Conventional stormwater management,
which focuses on controlling peak flow rate and the concentration of suspended solids,
has failed to address the widespread and cumulative hydrologic modifications in watersheds that increase the volume of stormwater, increase the runoff rate, and cause
excessive erosion and degradation of stream channels. Conventional stormwater
management also fails to adequately treat other pollutants of concern, such as
nutrients, pathogens and metals.1
CVC’s recent Credit River Water Management Strategy Update concludes that
continued use of what are currently considered “state of the art” stormwater
management practices will lead to continued degradation of the watershed, jeopardizing
the health of the Credit’s world class fishery and other valued environmental resources
(CVC, 2007b). To protect the health of the Credit River watershed, the updated water
management strategy calls for an immediate shift to more proactive and innovative
stormwater management systems that include low impact development practices.
TRCA’s Rouge River Watershed Plan (TRCA, 2007c), Humber River Watershed Plan
(TRCA, 2008a) and Don River Watershed Plan (TRCA, 2009a) reach similar
conclusions about the inability of conventional stormwater management practices to
protect the health of rivers and the need for low impact development approaches. In
addition, the Rouge River Watershed Plan concludes that widespread implementation of
LID practices in new and existing developments could increase the resiliency of the
watershed system to some anticipated impacts of climate change on baseflow and
channel erosion (TRCA, 2007d).
Recent research (Aquafor Beech Ltd., 2006) has suggested that current practices to
offset the hydrologic effects of urbanization are insufficient to prevent increased channel
erosion and deterioration of aquatic habitats. In many cases, even small incremental
changes in watershed hydrology commensurate with an increase in impermeable
surfaces of 4%, can result in changes to stream channel characteristics and aquatic
communities. To offset these impacts, an increased emphasis on maintaining natural
water balance and replicating the predevelopment hydrologic cycle is required (Aquafor
Beech Ltd., 2006).
Finally the 2003 OMOE Stormwater Management Planning and Design Manual, though
reflective of current technology is rapidly becoming dated, since much of the material it
reviewed dates from 1999. In the last five years, over 30 state-of-the-science
stormwater management manuals and guidelines have been released in locations such
as Maryland, Washington State, British Columbia, Minnesota, Pennsylvania and
Oregon. The objective of maintaining predevelopment water balance, use of the
treatment train approach and application of low impact development practices are all
becoming common practice in these jurisdictions.
Two recent documents, one prepared by the City of Toronto and the other prepared by
the Greater Vancouver Regional District summarize how the approach to stormwater
management needs to change.
Rainwater should be treated as a resource to nourish and enhance the
City’s environment. Management should begin where precipitation hits
the ground according to the priority of source, conveyance, end-of-pipe
and finally, stream restoration measures (City of Toronto, 2006).
There is a need for a change in the philosophy of treating runoff from
one of stormwater management to rainwater management (GVRD,
2005).
This is why CVC and TRCA commissioned the development of a stormwater
management guide to provide guidance on the kind of cutting edge practices that are
needed to protect the health of the CVC and TRCA watersheds. The LID SWM Guide
draws on published research, literature and local studies to provide planning and design
guidance that reflects regional policies, practices and climate. It provides information
and guidance on the following:
* how to integrate stormwater management into the urban planning process;
* how to design, construct and maintain a range of LID stormwater management
practices; and
* the kinds of environmental and performance monitoring that should be carried
out.
Acknowledging that it will not always be possible to maintain the predevelopment water
budget of a site, predicted increases in runoff from land development that cannot be
mitigated through stormwater infiltration practices should be minimized through
practices that either evapotranspire (e.g., green roofs, bioretention), or harvest runoff for
non-potable uses (i.e., rainwater harvesting). In areas where development has already
taken place, LID can be used as a retrofit practice to reduce runoff volumes, pollutant
loadings, and the overall impacts of existing developments on receiving waters. LID
practices can include:
* conservation site design strategies (i.e., non-structural LID practices);
* infiltration practices;
* rainwater harvesting;
* runoff storage and evapotranspiration;
* runoff conveyance;
* filtration practices; and landscaping.
Studies show that implementing LID practices can have multiple positive environmental effects including:
* protection of downstream resources;
* abatement of pollution;
* recharge of groundwater;
* improvement of water quality;
* improvement of habitat;
* reduced downstream flooding and erosion;
* conservation of water and energy; and
* improved aesthetics in streams and rivers.
These combined benefits help to mitigate potential negative impacts of climate change
on groundwater levels, risk of flooding and stream channel erosion.