LID opportunities on public land

Small- and large-scale projects

The scale of your LID project will largely determine how to proceed. While you can usually complete small-scale LID projects with in-house expertise and resources, large-scale projects require external support from consultants and contractors.

Small-scale projects

A no-mow zone is a landscape alternative that does not require construction activities. (Source: Aquafor Beech)

Starting with small-scale projects is a good strategy to increase public interest in LID practices, gauge municipal support, and gain retrofit experience. Small-scale projects include retrofitting your site with landscape alternatives, rain barrels, enhancements of existing swales, or using pollution prevention strategies and practices. Small-scale projects require fewer resources and a smaller project budget:

• They do not require integration into capital works projects
• Engineering consultants are not required
• Contractors may not be not required
• External approvals are not required
• Consultation with the public is limited

Due to less financial commitment, it can be easier to build colleague support and to gain supervisor approval for small-scale projects. However, small-scale projects like landscape alternatives and pollution prevention may not be easily identified as LID practices by the public. Your project team should consider establishing educational signage to inform the public.

Pollution prevention (P2) projects are great small-scale projects for municipal facilities, such as schools and public works yards. Many P2 techniques and strategies do not require construction, consultants or contractors. In fact, simply adding signage to a site is a simple and easy to implement pollution prevention at municipal facilities.

A successful small-scale LID retrofit project is a good indication that you are ready to take on a more intensive retrofit project. You now know the resources that are available and understand the internal municipal processes required to move a LID project from planning to finished product.

Large-scale projects

When installing new parks equipment, consider whether the LID practices can be integrated into the design. Here a bioswale has been built into the landscape between a playground and sidewalk. (Source: CVC)

Large-scale projects require significantly more effort, budget and staff than small-scale projects. Large-scale LID practices include:

• Bioretention
• Enhanced grass swales
• Bioswales
• Perforated pipe systems
• Permeable pavement
• Soakaways
• Infiltration chambers
• Rainwater harvesting
• Prefabricated modules
• Green roofs

Consider a large-scale project if your municipality, school or place of worship would like to be a leader in sustainability. Large-scale projects are often highly visible and attract more public attention. Large-scale projects may also be the only solution to site-specific challenges. For example, if the parking lot on your site does not have existing stormwater controls, small-scale projects are not likely to fully achieve compliance with water quality and quantity objectives. Consider using an infiltration chamber or bioswale project to meet those objectives. Before starting a large-scale retrofit project, consider the following distinctions that set these retrofits apart from small-scale projects.

Integration with capital works programs

Most large-scale LID retrofits must function with existing site infrastructure, such as storm sewers, catch basins, and pavement systems. The construction of large-scale LID practices often requires these systems to be removed, exposed, or replaced. The best time for this type of project to occur is when an infrastructure replacement or rehabilitation project is already planned.

When LID retrofits are worked into other construction projects, such as parking lot repaving, or grading or drainage improvements, there can be substantial cost savings. Whether big or small, every municipality, school and place of worship spends relatively large sums of money and substantial time planning for major capital projects. This includes redevelopment of public buildings and spaces. Many communities which have undertaken retrofits recognize that even if a relatively small portion of the project funds goes towards LID retrofits, they can retrofit large impervious surfaces and avoid new stormwater management infrastructure projects.

Municipal facility rehabilitation is typically forecast well in advance of the project. Parking lot paving is typically worked into municipal budgets based on expected life cycle and observed wear. As such, funds may be set aside prior to the project planning phases. Long-term forecast budgets may also be available for site revitalization or expansion. These budget forecasts provide opportunities to compare the capital and life-cycle costs and benefits of conventional construction projects against LID retrofits.

Regulatory compliance

The objectives, technologies and standard practices associated with stormwater management are constantly evolving. It is unlikely that the stormwater management practices on your site meet modern industry standards. When you are making changes to your site, it is important to stay ahead of regulation. Your school, park, place of worship or municipal facility may not be required to improve on-site stormwater management infrastructure, but those retrofits can be beneficial and save money and time over the long term. Consider both current and future water regulations which may affect your property. Consulting with your municipality will help you determine if LID retrofits can reduce taxes or prevent costly upgrades required at a later date.

Involvement of consultants and contractors

Consultants are required for large-scale retrofit projects, specifically for the final screening of options, pre-design, detailed design, tender and contract documents, construction supervision and administration, and assumption and verification. Site contractors are also required for large-scale LID retrofits.

Ideally, contractors should be pre-qualified based on previous experience with similar LID projects.

Intensive public consultation

Stakeholders must be closely involved in the retrofit process for large-scale LID projects. These projects have longer construction windows, may have significant impacts on long term public use patterns of the site and will have significantly higher costs. Gaining public insight before LID implementation can help address public concerns and information gaps, as well as identify public supporters and champions. Public consultation can help designers tailor the project to address community concerns, values and use-patterns.

External approvals

Large-scale retrofits may require a variety of approvals at the municipal, watershed, provincial, and/or federal level. Since LID is still relatively new, you may encounter policies or bylaws that present barriers to LID retrofit projects. Alternatively, the municipality may have to amend or enforce some policies and bylaws to facilitate the implementation of LID projects on your site.

Parks

The bioretention area installed at O’Connor Park in Mississauga is part of a stormwater management system that treats parking lot runoff prior to discharging to a local wetland. (Source: CVC)

Urban parkettes may look small, but they have the potential to treat a large surface area of road. Typical ratios of impervious drainage area to a bioretention range from 5:1 to 15:1. (Source: CVC)

The road surface (left) contributes significantly more stormwater pollutants than the parkland area (right). To achieve maximum watershed benefit a designer could consider accepting runoff from this external area. (Source: CVC)

Source areas within a typical park

Parks range from simple parcels of municipal property to complex outdoor recreational facilities that include parking, sidewalks, trails, sports fields, field houses, operations facilities and washrooms. Each distinct area of your site can be a source for runoff (referred to as a ‘source area’). Target these areas when introducing LID in your park.

Targeting hard surfaces

Hard surfaces like parking lots and internal driveways are the most obvious targets for both stormwater quality and water balance improvements. These features produce more runoff than any other area on your site. Runoff from parking lots and driveways is typically more polluted than other source areas. Common water quality concerns include sand and salt from winter de-icing operations, hydrocarbons (gasoline) and heavy metals from vehicle breakdowns.

Runoff from vegetated areas of parks will be relatively clean and more closely matches the natural water balance. On municipal park properties, hard surfaces are usually located adjacent to pervious areas such as lawns, gardens or naturalized areas. This makes parks an ideal location for a LID retrofit. Where grading allows, you can construct bioswales and bioretention areas in these green areas to pre-treat water prior to infiltration.

You can also design parking surfaces and internal roadways as infiltration systems using permeable pavement. This retrofit strategy can be combined with other LID practices. Pathways paved with permeable paving are another LID option for your park. They reduce runoff volumes and encourage on-site infiltration. Exfiltration trenches are a viable option on many parks sites as well, as they provide an alternative to conventional conveyance systems (such as storm sewers). They encourage infiltration from hard surfaces and can be used to convey water to other LID features.

Accepting drainage from off-site areas

Does municipally owned land drain into your retrofit site? If so, this is an opportunity to provide stormwater controls for these areas. Roads are the most common source of runoff from external properties into parks. Treating municipal road runoff in a park requires planning input from municipal roads department staff. For these projects, the team must understand how all road activities, including winter maintenance and potential roadwork, will affect the operation of LID practices in the park.

Inter-municipal transfer of funds

Integrating LID practices into the municipal stormwater management framework may require a change in how municipal funds are managed. Traditional stormwater management maintenance resources and funds may have to be transferred to a more landscape-based stormwater management maintenance program. Instead of infrequent but expensive stormwater management pond sediment removal operations, time and resources would be spent on more frequent but inexpensive maintenance projects, including pruning and weeding bioretention practices or sweeping permeable pavement. Municipalities generally have the required staff and infrastructure within departments (e.g. arborists and horticulturalists in parks departments) to manage the maintenance of LID measures. However, funding this maintenance may require a transfer of funding and additional training. The federal Gas Tax Fund (GTF) is another funding option for LID retrofits. This federal transfer provides long-term funding for municipalities to build and revitalize public infrastructure. Up to 30% of a municipality's yearly GTF allotment can be used for stormwater management.

Source Areas

The best LID option for your site will depend what types of source areas are present. Source areas may include:

• Active use areas
• Passive use areas
• Pedestrian walkways
• Internal driveways
• Parking lots

On park sites, pollution prevention is often associated with changes to operations and maintenance practices and has not been included in the table below. Options and implementation strategies for a few of these source areas will give you some ideas for your park site.

LID opportunities in parks
(** = Common, * = Possible, o = Unusual)

Source area	Permeable paving	Bioretention	Enhanced grass swales	Bioswales	Infiltration trenches and chambers	Exfiltration trenches	Landscape alternatives	Prefabricated modules
Active use area	**	o	*	*	**	*	o	o
Passive use area	o	**	**	**	**	**	**	**
Pedestrian walkway	**	**	**	**	**	*	*	o
Internal driveway	**	**	**	**	**	**	o	*
Parking lot	**	**	**	**	**	**	o	**

Making it happen: Approaches to getting LID into parks

The scale of your LID project will largely determine how to proceed. While you can usually complete small-scale LID projects with in-house expertise and resources, large-scale projects require external support from consultants and contractors.

Small-scale projects

A no-mow zone is a landscape alternative that does not require construction activities. (Source: Aquafor Beech)

Starting with small-scale projects is a good strategy to increase public interest in LID practices, gauge municipal support and gain experience. Small-scale projects include retrofitting your park with landscape alternatives, rain barrels, or by using pollution prevention strategies and practices.

Small-scale projects require fewer resources and a smaller project budget:

• They do not require integration into capital works projects
• Engineering consultants are not required
• Contractors may not be not required
• External approvals are not required
• Consultation with the public is limited

Due to less financial commitment, it can be easier to build colleague support and to gain supervisor approval for small-scale projects. However, small-scale projects like landscape alternatives and pollution prevention may not be easily identified as LID practices by the public. Your project team should consider establishing educational signage to inform the public.

Large-scale projects

When installing new parks equipment, consider whether the LID practices can be integrated into the design. Here a bioswale has been built into the landscape between a playground and sidewalk. (Source: CVC)

Large-scale projects require significantly more effort, budget, and staff than small-scale projects. Large-scale LID practices include:

• Bioretention
• Enhanced grass swales
• Bioswales
• Perforated pipe systems
• Permeable pavement
• Soakaways
• Infiltration chambers
• Rainwater harvesting
• Prefabricated modules

Consider a large-scale project if your municipality or department would like to be a leader in sustainability. Large scale projects are often highly visible and attract more public attention. Large-scale projects may also be the only solution to site-specific challenges. For example, if the parking lot on your site does not have existing stormwater controls, small-scale projects are not likely to fully achieve compliance with water quality and quantity objectives. Consider using an infiltration chamber or bioswale project to meet those objectives.

Before starting a large-scale retrofit project, consider the following distinctions that set these retrofits apart from small-scale projects.

Integration with capital works programs

Most large-scale LID retrofits must function with existing site infrastructure, such as storm sewers, catch basins and pavement systems. Constructing large-scale LID practices often requires these systems to be removed, exposed or replaced. Planned infrastructure replacement or rehabilitation projects provide opportunities for implementing LID practices. For example, if a planned project requires removing existing pavement, infiltration chambers, permeable pavement or bioretention can be incorporated. Budget and resources already set aside for infrastructure projects can be set aside for a retrofit project including replacement existing infrastructure.

Involvement of consultants and contractors

Consultants are required for large-scale retrofit projects, specifically for the final screening of options, pre-design, detailed design, tender and contract documents, construction supervision and administration, and assumption and verification. Site contractors are also required for large-scale LID retrofits.

Ideally, contractors should be pre-qualified based on previous experience with similar LID projects.

More intensive public consultation

Stakeholders must be closely involved in the retrofit process for large-scale LID projects. These projects have longer construction windows, may have significant impacts on long term public use patterns of the park, and will have significantly higher costs. Gaining public insight in advance of LID implementation can help address public concerns and information gaps, as well as identify public supporters and champions. Public consultation can help designers tailor the project to address community concerns and values.

External approvals

Large-scale park retrofits may require a variety of approvals at the municipal, watershed, provincial and/or federal level. Since LID is still relatively new, you may encounter policies or bylaws that present barriers to LID retrofit projects. Alternatively, the municipality may have to enforce some policies and bylaws to facilitate the implementation of LID projects within parks.

Municipal facilities

Each distinct area of your site can be a source for runoff (referred to as a ‘source area’). Target these areas when introducing LID in your municipal facility.

Targeting hard surfaces

Municipal facilities have large parking lots to accommodate public demand. Parking areas represent the most significant source of pollutant loading from these sites and contribute significantly to increased runoff rates in comparison to natural conditions. Parking lots include areas for parking, areas for driving, and islands or landscape planters used for calming traffic, directing vehicles and improving pedestrian safety.

LID practices can be incorporated into all areas of a parking lot. You can use bioretention in parking lot islands and along the lot perimeter. Standard curbs with small cut-outs (called ‘curb cuts’) can allow water to easily enter biorentention practices while also preventing damage from cars.

Bioswales are excellent options in parking lot islands or along lot perimeters. Parking lots with existing perimeter ditching are ideal for bioswale integration due to their extended continuous flow path.

Prefabricated modular infiltration chambers are gaining acceptance for their easy integration with parking lot functions. These subsurface systems are typically installed over a coarse granular reservoir to provide storage and allow infiltration into native soils. Infiltration chambers under conventional asphalt system work well on sites where parking demand and other site uses do not allow space for a stormwater feature.

Stormwater planters beautify this building entrance. The entrance receives a lot of traffic during business hours, making it an ideal location for a high visibility LID practice. (Source: Aquafor Beech)

Permeable pavements are also an option in large municipal parking lots. Pervious concrete, permeable interlocking concrete pavers, and porous asphalt can detain stormwater and increase infiltration.

Municipal facilities provide excellent opportunities for integrating rainwater harvesting systems. Rainwater harvesting systems have two requirements: an area for catchment of relatively clean runoff and a nearby demand for water usage. Municipal facilities often have large rooftop areas producing relatively clean runoff. Installing a cistern internal to the building or buried adjacent to the building can provide a sustainable source of water for site irrigation needs for landscaped areas, recreational fields and indoor use (e.g. flushing toilets and urinals).

Targeting highly visible areas

If your LID integration strategy involves highly visible LID practices, consider targeting areas with high-volume pedestrian traffic. This can help promote LID's visibility among the public and increase support for future LID projects.

Targeting pollution prevention opportunities

On some municipal sites, pollution prevention techniques and strategies are the best approaches to mitigating the environmental impact of your site. Retrofits of municipal works yards require a different approach than other land uses discussed in this guide. Works yards do not offer substantial opportunities for public interaction. LID retrofits should focus primarily on reducing pollution generated on-site. Fueling stations, waste storage areas, truck washing stations, sand and salt storage, staging areas and water conveyance features are ideal for pollution prevention.

Source areas

The best LID option for your site will depend what source areas are present. Types of source areas include:

Source areas within a typical community centre.

• Active use areas
• Passive use areas
• Pedestrian walkways
• Internal driveways
• Parking lots

On municipal sites, pollution prevention is often associated with changes to operations and maintenance practices and has not been included in the table below.

LID opportunities in municipal buildings
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavements	Bioretention	Enhanced grass swales / bioswales	Green roofs	Soakaways and infiltration chambers	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Pollution prevention
Active use area	**	**	**	o	**	*	o	*	o	**
Passive use area	o	**	*	o	**	**	o	**	**	**
Pedestrian walkway	**	**	**	o	**	*	o	*	*	**
Internal driveway	**	**	**	o	**	**	o	o	**	**
Parking lot	**	**	**	o	**	**	o	o	**	**
Building	*	*	*	**	**	*	**	o	o	**

Schools

The Peel District School Board's Adult Education Centre South school partnered with the City of Mississauga to manage runoff from the adjacent street, Elm Drive, on their property. This partnership benefits the City by giving it space to provide an enhanced level of stormwater treatment, and benefited the school through the construction of new parking lay-bys for students. The site is maintained by the City of Mississauga. Source: CVC

Each distinct area of your site can be a source for runoff (referred to as a ‘source area’). These areas should be targeted when introducing LID at your school.

Targeting hard surfaces

Parking areas represent the most significant source of pollutant loading from school sites and contribute significantly to increased runoff rates in comparison to natural conditions. Parking lots of all sizes can be targeted for permeable pavement retrofits. As an added benefit, permeable pavement systems have a longer lifespan compared to conventional asphalt. High schools often have large parking lots where the capacity outweighs the demand. These areas represent opportunities to install bioswales or bioretention areas in parking lot islands. Standard curbs with small cut-outs (called ‘curb cuts’) can allow water to easily enter biorentention practices while also preventing damage from cars. Often the existing drainage patterns and catch basin locations can be preserved and integrated into the design. These practices will also function to improve pedestrian safety and calm traffic.

Other types of infiltrating practices like infiltration chambers are gaining acceptance for their easy integration with parking lot functions. These subsurface systems are typically installed over a coarse granular reservoir to provide storage and allow infiltration into native soils. Infiltration chambers under conventional asphalt systems work well on sites where parking demand does not allow space for a stormwater feature. Grassed areas adjacent the parking lots are ideal areas to implement bioswales or bioretention areas. Perforated pipe systems may also work in areas adjacent to parking lots.

Roof options

Schools typically have large flat roofs that produce a significant amount of runoff that is drained internally via rain leaders. Schools also consume large quantities of water for flushing toilets and urinals. Rainwater harvesting systems can tackle both of these issues by intercepting this rooftop runoff and re-using it for toilet flushing as well as outdoor irrigation. This option has the benefit providing an ongoing financial benefit through reduced water bills. Roof runoff can also be directed to soakaways located on passive use areas around the building. As this runoff comes into contact with fewer hard surfaces, it produces better quality runoff than roads and does not require pretreatment devices. Green roof retrofits are another retrofit option for schools. When applying for external funding from organizations, highlight the fact that green roofs reduce energy usage by providing insulation during the winter and evaporative cooling during the summer.

Pollution prevention (P2)

On school sites, P2 strategies and practices, such as modifying de-icing programs and isolating drainage from waste storage areas, can be applied to operations and maintenance activities. Discuss these changes with your school board and operations staff.

School board partnerships with municipalities

LID practices located on school grounds can also be used to treat stormwater from external properties. These partnership opportunities give schools the potential to create new revenue. Accepting and treating runoff on your existing property can make funds available through:

• Contributions to capital projects like parking lot rehabilitations which include rain gardens, permeable

pavements, or subsurface infiltration facilities

• Ongoing revenues from long-term land leases to accommodate surface or subsurface LID retrofits
• Funds for maintenance of on-site LIDs

The table below identifies the LID practices that are common, possible and unlikely options for the source areas that you are likely to find on your school site. These source areas are:

• Active use area
• Passive use area
• Pedestrian walkway
• Internal driveway
• Parking lot

Source areas within a typical school site.

See the landforms of a school picture on the right for information on how to target these areas. The table below gives a more detailed breakdown of LID options for different source areas.

A student helps with planting at Fletchers Creek Senior School. Small-scale LID projects are a great way to engage with young children. Source: CVC

LID opportunities at schools
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavement	Bioretention	Enhanced grass swales / bioswales	Green roofs	Soakaways and infiltration trenches	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Pollution prevention
Active use area	**	**	**	o	**	*	o	*	o	**
Passive use area	o	**	*	o	**	**	o	**	**	**
Pedestrian walkway	**	**	**	o	**	*	o	*	o	**
Internal driveway	**	**	**	o	**	**	o	o	*	**
Parking lot	**	**	**	o	**	**	o	o	**	**
Building	*	*	*	**	**	*	**	o	o	**

Places of worship

Source areas within a typical place of worship

Each distinct area of a place of worship can be a source for runoff (referred to as a ‘source area’). One or more of these areas should be targeted when introducing LID at your place of worship.

Targeting hard surfaces

Hard surfaces such as parking lots are a great opportunity to implement LID. Parking lots are the main source of runoff and represent the most significant source of stormwater pollutants coming from your site. Parking lots at places of worship are typically busy only on select days of the week when groups gather for prayer or other community activities. Due to this intermittent schedule, parking lots at these facilities are often rented for other purposes during times of low usage. On sites where peak demand does not approach the total capacity of the lot, consider reducing the parking surface. Retrofit options for these large parking lot areas include permeable pavement, bioswales and bioretention areas. A benefit of permeable pavement systems is that they often have a longer lifespan than conventional infrastructure. The freeze-thaw cycle of the Ontario climate is tough on pavement. Frost heaving and slumping can cause cracks and potholes because of the expansion and contraction of water. The expected lifespan for conventional asphalt pavement in a northern climate, such as Ontario, is approximately 15 to 20 years. A well-maintained porous asphalt system can last for over 30 years, and permeable interlocking concrete pavers can have a design life of 20 to 25 years or greater. Using LID techniques to manage stormwater can also eliminate or reduce the need for an on-site storm sewer system. By eliminating piping, failure points in the pavement, such as areas around catch basins and manholes, can be eliminated. A design that does not use storm sewers also negates the need to replace on-site piping, thereby saving long-term infrastructure replacement costs. Prefabricated modular infiltration chambers are gaining acceptance because they are easy to integrate with parking lot functions. These subsurface systems are typically installed over a coarse granular reservoir to provide water storage and allow infiltration into native soils. Infiltration chambers under conventional asphalt systems work well on sites where parking demand does not allow space for a stormwater feature.

Landscaped areas

Landscaped or lawn areas adjacent to the parking lot or building present opportunities for implementation of LID practices such as bioswales and bioretention areas. These areas typically accept runoff from nearby hard surfaces and provide water quality and water balance benefits.

Roof options

Rainwater harvesting systems can be simple or complex depending on the architecture and roof drainage patterns of your building. Many places of worship have peaked roofs with piping to convey water from the rooftop. If your site is set up this way, it can be easy to integrate harvesting systems into the landscape surrounding your building.

Roof runoff can also be directed to soakaways located on passive use areas around your building. Due to the relatively good quality of this runoff, pre-treatment devices are not required.

Source Areas

The LID option that best fits your site will depend what types of source areas are present. Types of source areas include:

• Active use area
• Passive use area
• Pedestrian walkway
• Internal driveway
• Parking lot

At places of worship, pollution prevention is often associated with changes to operations and maintenance practices and has not been included in the table below.

LID opportunities at Places of Worship
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavement	Bioretention	Enhanced grass swales / bioswales	Green roofs	Soakaways and infiltration trenches	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Pollution prevention
Active use area	**	**	**	o	**	*	o	*	o	o
Passive use area	o	**	*	o	**	**	o	**	**	o
Pedestrian walkway	**	**	**	o	**	*	o	*	o	o
Internal driveway	**	**	**	o	**	**	o	o	*	*
Parking lot	**	**	**	o	**	**	o	o	**	*
Building	*	*	*	**	**	*	**	o	o	*

stuff to maybe integrate into the above

Figure 6.3.1: When considering any parking lot retrofit, first determine if the parking spaces provided are consistent with the demand. In place of worship, the demand will fluctuate. (Source: CVC)

Did you know that green roofs can help reduce your heating and cooling costs? These systems absorb heat and act as insulators for buildings. It has been estimated that a 3,000 m2 green roof on a one story building in Toronto could reduce the cost of cooling a building in the summer by 6% and the cost of heating a building by 10% in the winter23.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

Credit Valley Conservation

Ground depression acting as a flow control and water treatment structure, that is normally dry.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

The drainage area of a river.

An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

A vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

A body of water smaller than a lake, often artificially formed.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Tank used to store rainwater (typically roof runoff) for later use.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

The property of a material that allows the infiltration or passage of water (or other liquids).

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.