LID opportunities in park lands

LID opportunities in 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)

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’). These areas should be targeted when introducing LID in your park.

Targeting hard surfaces

Hard surfaces like parking lots and internal driveways are the most obvious areas to target for both stormwater quality and water balance improvements. These features produce more runoff than any other area on your site. Water quality of 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, and hydrocarbons (gasoline) and metals from vehicle breakdowns.

Runoff from vegetated areas of parks will be relatively clean and more closely match 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 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. Apathway paved with permeable paving is another LID option for your park. They will reduce runoff volumes and encourage on-site infiltration. Exfiltration trenches are a viable option on many parks sites as well. They can be 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

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 bioretention range from 5:1 to 15:1. (Source: CVC)

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 roads 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 change 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 will 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. arborist 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 funding LID retrofits. This is a federal transfer that provides long term funding for municipalities to build and revitalize public infrastructure. Up to 30% of municipalities yearly GTF allotment can be used towards stormwater management.

Source Areas

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)

The LID option that best fits 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 Options for Parks

Source area	Permeable paving	Bioretention	Enhanced grassed swales	Bioswales	Soakaways and infiltration 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	**
** Common option			* Possible option			o Unlikely

Making it happen: Approaches to getting LID into parks=

The scale of your LID project will largely determine how you will proceed. This guide provides two tiers of LID park retrofit projects. You can usually complete small-scale LID projects with in-house expertise and resources. Large-scale projects will 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 parks site with landscape alternatives or rain barrels, or using pollution prevention strategies and practices.

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

• 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 the less significant financial commitment, it can be easier to build colleague and supervisor support for small-scale projects. 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

Large-scale projects require significantly more effort, budget, and staff than small-scale projects. Large-scale LID projects 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. 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. For example, installing bioretention, infiltration chambers, or permeable pavement in a parking lot requires removal of existing pavement. Budget and resources set aside for parking lot replacement could be transferred to a retrofit project that includes replacement of this 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

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)

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 cost significantly more taxpayer dollars. 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.

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 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.

Credit Valley Conservation

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.

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 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.

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

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.

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.

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

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.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

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.

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.

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.

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

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.