LID opportunities at 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 paving is 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 outlined in Chapter 2 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. Fuelling 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:

• 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 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	**

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

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.

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.

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.

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

Penetration of water through the ground surface.

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

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