Permeable pavements

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Conceptual diagram illustrating an adjustable storage underdrainA perforated pipe used to assist the draining of soils. configuration beneath permeable interlocking pavers

Overview

Permeable pavements are an alternative to conventional imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. pavement that allows stormwater to drain through the surface and into a stone reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe., where it infiltrates into the underlying native soilThe natural ground material characteristic of or existing by virtue of geographic origin. or is temporarily detained. Depending on the native soilThe natural ground material characteristic of or existing by virtue of geographic origin. properties and physical constraints, the system may be designed with no underdrainA perforated pipe used to assist the draining of soils. for full infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., with an underdrainA perforated pipe used to assist the draining of soils. for partial infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., or with an impermeable liner and underdrainA perforated pipe used to assist the draining of soils. for a non-infiltrating, or detentionThe temporary storage of stormwater to control discharge rates, and allow for sedimentation. and filtrationThe technique of removing pollutants from runoff as it infiltrates through the soil. only practice.

Permeable pavementAn 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. types include:

  • Permeable interlocking pavers (concrete and composite materials)
  • Permeable grid systems (concrete or composite materials)
  • Permeable articulated block systems
  • Pervious concrete (poured-in-place or pre-cast)
  • Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

Permeable pavingAn 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. is ideal for:

  • Sites with limited space for other surface stormwater BMPs
  • Projects such as low traffic roads, parking lots, driveways, pedestrian plazas and walkways

The fundamental components of a permeable pavingAn 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. system are:

  • Pavement surface: interlocking pavers with open joints, grid systems, precast pervious slabs or pavers, poured in place asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. or concrete Bedding layer as a levelling course (for precast systems)
  • Subsurface base storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. of open graded aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.
  • Edge restraints

Additional components may include:

  • an underdrain system
  • geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils., at the discretion of design professional
  • impermeable geomembrane on sites where soil infiltration is not desired
  • geo-grids for sites with heavy vehicle loadingThe 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.
  • monitoring wells and clean-outs

Planning considerations

InfiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.

Permeable pavements can be constructed over any soil type, but hydrologic soil group (HSG) A and B are best for achieving water balanceThe accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle. objectives. Native soilThe natural ground material characteristic of or existing by virtue of geographic origin. infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. at the proposed facility location and depth should be confirmed through in-situ measurements of hydraulic conductivityA parameter that describes the capability of a medium to transmit water. under field saturated conditions. A liner will be required if native soils are contaminated.

Systems located in low permeability soils with an infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. of less than 15 mm/hr (i.e., hydraulic conductivityA parameter that describes the capability of a medium to transmit water. of less than 1x10-6 cm/s), require incorporation of a perforated pipe underdrainA perforated pipe used to assist the draining of soils.. Pavements require an impermeable geomembrane where the underlying soils are contaminated or the pavement is within two year time-of-travel wellhead protection area (see local drinking water source protection plan)

Space

Permeable pavementAn 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. in the IMAX parking lot, Mississauga ON

Permeable pavements can be used for the entire parking lot, driveway or road surface, or be designed to to receive runoffThat potion of the water precipitated onto a catchment area, which 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. from adjacent imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. surfaces. For example, the parking spaces of a parking lot or road can be permeable pavements while the drive lanes are conventional asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.. The imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. area draining on to the permeable pavementAn 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. should not exceed the area of the permeable pavementAn 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. itself. Relatively clean drainage areas such as roofs may be up to 4 times the size of the pavement but should include filtrationThe technique of removing pollutants from runoff as it infiltrates through the soil. pretreatmentInitial 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. to remove coarse debris prior to being conveyed directly to the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe..

Permeable pavements should be located down-gradient from building foundations. If the pavement does not receive drainage from other surfaces, no setback is required. If the pavement receives drainage from other surfaces a minimum setback of four metres down-gradient is recommended. A smaller setback may be permissible where foundations are protected by a geomembrane.

Site Topography

Permeable pavementAn 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. surface slope should be at least 1% and no greater than 5%. Steeper slopes may require additional features (see subgrade section below). Pervious areas should not drain onto permeable pavements.

GroundwaterThe water below the surface, and typically below the groundwater table.

Maintaining a separation of one metre between the elevations of the base of the practice and the seasonally high water tableThe upper surface of the zone of saturation, except where the surface is formed by an impermeable body.Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone., or top of bedrock is recommended. Lesser or greater values may be considered based on groundwater mounding analysis. See Groundwater page for further guidance and a spreadsheet tool.

To protect groundwater from possible contamination, runoffThat potion of the water precipitated onto a catchment area, which 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. from pollution hot spots should not be treated by permeable pavements designed for full or partial infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.. Facilities designed with an impermeable liner (filtrationThe technique of removing pollutants from runoff as it infiltrates through the soil.-only) can be used. Also see the Site considerations page.

Private Sites

If permeable pavingAn 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. systems are installed on private lots, property owners or managers will need education on their routine maintenance needs, understanding the long-term maintenance plan. They may also be subject to a legally binding maintenance agreement. An incentive program, such as a storm sewer user fee based on the area of imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. cover on a property that is directly connected to a storm sewer, could be used to encourage property owners or managers to maintain existing practices.

Design

Subgrade

For infiltrating pavements, subgrade slopes should be minimized so that runoffThat potion of the water precipitated onto a catchment area, which 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. will be able to infiltrate evenly through the entire surface. For steeply sloped sites (>5%), check damsStructures constructed of a non-erosive material, such as suitably sized aggregate, wood, gabions, riprap, or concrete; used to slow runoff water. Can be employed in practices such as bioswales and enhanced grass swales., berms or weir structures on the native soils of the pavement should be considered. If the system is not designed for infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., the bottom should be sloped at 1 to 5% toward the underdrainA perforated pipe used to assist the draining of soils.. Subgrades should be compacted to 95% Standard Proctor Density. If a lesser value is desired to promote infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., a thicker sub-base should be considered. Subgrade soils should not be scarified.

PretreatmentInitial 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.

In most designs, the permeable surface acts as pretreatmentInitial 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. to the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. below. Since sedimentSoil, 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. accumulates in the permeable areas of the pavement, periodic vacuum sweeping and preventative measures like not storing snow, construction materials or landscaping materials on the pavement are critical to prevent clogging.

UnderdrainA perforated pipe used to assist the draining of soils.

The diagram below displays permeable pavementAn 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. cross sections showing full and partial infiltration designs.[1] See Underdrains page for further guidance. Permeable Pavement cross sections showing full and partial infiltration designs. Source: GVRD, 2005

Access Structures

Access structures are used for periodic inspection and flushing. It could be a maintenance hole or vertical standpipe connected to the perforated pipe. For accessing the underdrainA perforated pipe used to assist the draining of soils. pipe with camera or cleaning equipment, 45° couplings should be used for standpipe connections.

Overflow

Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. system with overflow edge draining to a reservoir. Source: Pennsylvania Department of Environmental Protection (PDEP). 2006.

All designs require an overflow outlet connected to a storm sewer with capacity to convey larger storms. This is normally achieved with a catch basinGround depression acting as a flow control and water treatment structure, that is normally dry. outlet, but water may also be directed to a downstream practice (e.g. bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation., swaleA 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.). Another option is a gravel diaphragmA level spreading device placed at a runoff discharge location, perpendicular to flow, to maintain sheet flow and distribute runoff as evenly as possible across a pervious area or stormwater infiltration practice. A gravel diaphragm acts as a pretreatment device, settling out suspended sediments before they reach the practice. or trench along the downgradient edge of the pavement that drains to the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. below.

The diagram to the left is an example of a porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. system with overflow edge draining to a reservoir.[2] A flush curb extending into the base may be required as an edge restraint for some permeable pavementAn 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. types. Decorative stone is lined with a geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils. to prevent migration of fine sedimentSoil, 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. into the pavement base and facilitate maintenance.

Finish course

Consult the manufacturer for the design specifications of their product. In pervious concrete and porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. systems, the concrete or asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. mix specifications and construction procedures are key to proper functioning. These systems require well-trained and experienced contractors for installation.

Specifications for pervious concrete, porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces., and permeable pavers
Material Specification Quantity
Pervious concrete
  • NO4-RG-S7 mix with air entrainment proven to have the best freeze-thaw durability after 300 freeze-thaw cycles.
  • 28 day compressive strength = 5.5 to 20 MPa.
  • PorosityThe porosity (n) of a mixture is the ratio of the volume of void-space to the total or bulk volume of the mixture. It is closely related to the concept of void ratio (e) where void ratio is the ratio of the volume of void-space to the volume of solids. n = Volume of voids/Total volume of mixture = e/(1+e) between 14% to 31%.
  • Permeability = 900 to 21,500 mm/hr.
  • Proprietary pre-cast slabs meeting required specifications are also available.
Thickness will range from 100 mm - 150 mm depending on the expected loads.
Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.
  • Open-graded asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. mix with a minimum porosityThe porosity (n) of a mixture is the ratio of the volume of void-space to the total or bulk volume of the mixture. It is closely related to the concept of void ratio (e) where void ratio is the ratio of the volume of void-space to the volume of solids. n = Volume of voids/Total volume of mixture = e/(1+e) of 16%.
  • Polymers can be added to provide additional strength to heavy loads.
  • The University of New Hampshire Stormwater Center has detailed design specifications for porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces..
Thickness will range from 50 mm - 100 mm depending on the expected loads.
Permeable Interlocking Pavements
  • Pavers shall meet the minimum material and standard specifications for precast concrete pavers (CSA A231.2 in Canada; ASTM C936 in United States).
  • Open space between pavers (i.e. joint space) typically ranges between 5 and 15% of the total surface area.
  • ASTM No. 8 (5 mm dia.) crushed aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. is recommended for fill material in the paver joints (typically HPB).
  • For narrow joint pavers, a smaller sized aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. may be used. Narrow joints are required where pavement must be AODA compliant.
  • For vehicle applications the minimum paver thickness is 80 mm
  • For pedestrian applications the minimum paver thickness is 60 mm and joint widths should be no greater than 15 mm.

Foundation AggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

All aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. should meet the following criteria:

  • PorosityThe porosity (n) of a mixture is the ratio of the volume of void-space to the total or bulk volume of the mixture. It is closely related to the concept of void ratio (e) where void ratio is the ratio of the volume of void-space to the volume of solids. n = Volume of voids/Total volume of mixture = e/(1+e) of 0.4
  • Maximum wash loss of 0.5%
  • Minimum durability index of 35
  • Maximum abrasion of 10% for 100 revolutions and maximum 50% for 500 revolutions

Most OPSS aggregates are not recommended for use in permeable pavements, with the exception of 'GranularGravel, 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. O' type.

GranularGravel, 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. Subbase Should be clear, crushed 50 mm diameter stone, graded in accordance with ASTM D2940. 'Rain ballast' aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. (63 mm) would also be suitable

GranularGravel, 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. Base Should be clear, crushed 20 mm diameter stone conforming to ASTM C33 No 57

Bedding Should be clear, crushed 5 mm diameter stone, graded in accordance with ASTM C33 No 8, High Performance Bedding (1-9 mm diameter), or equivalent. Typical bedding thickness is between 40 mm and 75 mm.

For more information, also see Aggregates page.

Sizing Stone Reservoirs

The stone reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. must meet both runoffThat potion of the water precipitated onto a catchment area, which 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. storage and structural support requirements. The bottom of the reservoir should be level so that water infiltrates evenly.

Permeable pavements: Sizing

GeotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

Permeable pavers in Hoboken, NJ used around trees which allow air and water to reach the roots (Source: Bruce Ferguson)

Geotextiles are non-woven needle punched, or woven monofilament geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils. fabric that may be placed between the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. and native soilThe natural ground material characteristic of or existing by virtue of geographic origin. to maintain separation. Geotextiles are commonly used on low strength soils (CBR <4). Where expansive clays are present, a non-infiltrating design may be necessary. If used, geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils. socks around perforated pipes should conform to ASTM D6707 with minimum water flow rate conforming to ASTM D4491 (12,263 L/min/m2 at 5 cm head).

Edge Restraints

Pavers must abut tightly against the restraints to prevent rotation under load and any consequent spreading of joints. The restraints must be able to withstand the impact of temperature changes, vehicular traffic and snow removal equipment. Metal or plastic stripping is acceptable in some cases, but concrete curbs are preferred. Concrete curbs should be supported on a minimum base of 150 mm of aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations..

Landscaping

Adjacent landscaped areas should drain away from permeable pavementAn 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. to prevent sedimentsSoil, 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. from running onto the surface. Urban trees also benefit from being surrounded by permeable pavementAn 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. rather than imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. cover, because their roots receive more air and water.

Monitoring Wells: see “Deeper Wells” section

Heavy Vehicle Traffic

Permeable pavingAn 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. is not typically used in locations subject to heavy loads. However, some permeable pavements are designed for heavy loads and have been used in commercial port loadingThe 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. and storage areas. A flexible geogrid structure may be used to improve the structural capacity of the pavement by spreading loads over a larger area. Increasing the base thickness will also improve structural capacity.

Modelling permeable pavements in the Treatment Train Tool

Permeable pavements: TTT

Construction Considerations

Properly installed permeable pavementAn 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. requires trained and experienced construction contractors. The following general recommendations apply:

  • SedimentSoil, 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. Control: The treatment area should be fully protected during construction so that no sedimentSoil, 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. reaches the permeable pavementAn 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. system. Construction vehicle traffic should not be permitted on the permeable pavementAn 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. and its drainage areas once the pavement has been installed.
  • Base Construction: AggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. should be placed in 100 mm to 150 mm lifts and compacted with a minimum 9 ton steel drum vibratory roller. A light weight deflectometer may be used to test compaction level of open graded stone and compare to specifications.
  • Weather: Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. and pervious concrete require a specific temperature range to set properly and the setting time can be several days[3].

Inspection and Maintenance

Permeable pavements require regular inspection and maintenance to ensure proper functioning. The limiting factor for permeable pavements is clogging of the surface course or joint filler between pavers. As these start to fill, the trapped sedimentSoil, 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. becomes finer and finer until they eventually become clogged. Ideally, signs should be posted on the site identifying permeable pavementAn 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.. This can also serve as a public awareness and education opportunity. See: Permeable pavements: Maintenance

Life Cycle Costs

Initial construction costs for permeable pavements are typically higher than conventional asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. pavement surfaces, largely due to the price of the surface course and thicker aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. base needed for stormwater storage. However, the cost difference is reduced or eliminated when total life-cycle costs, or the total cost to construct and maintain the pavement over its lifespan, are considered. Other potential savings and benefits include reduced need for storm sewer pipes and other stormwater practices, less developable land consumed for stormwater treatment, and ancillary benefits (improved aesthetics and reduced urban heat island effect). These systems are especially cost effective in existing urban development where parking lot expansion is needed, but there is not sufficient space for other types of BMPs. They combine parking, stormwater infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., retention, and detentionThe temporary storage of stormwater to control discharge rates, and allow for sedimentation. into one facility. See also: Cost analysis resources

Performance

Ability of Permeable Pavements to Meet Stormwater Management Objectives
BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls. Water Balance Water Quality Erosion Control
Permeable pavementAn 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. with no underdrainA perforated pipe used to assist the draining of soils. Yes Yes-size for water quality storage requirement Partial-based on available storage volume and native soilThe natural ground material characteristic of or existing by virtue of geographic origin. infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour.
Permeable pavementAn 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. with underdrainA perforated pipe used to assist the draining of soils. Partial-based on available storage, native soilThe natural ground material characteristic of or existing by virtue of geographic origin. infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. and if a flow restrictor is used Yes-size for water quality storage requirement Partial-based on available storage, native soilThe natural ground material characteristic of or existing by virtue of geographic origin. infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. and if a flow restrictor is used
Permeable Interlocking Pavements No-some volume reduction occurs through evaporationAbiotic transfer of water vapour to the atmosphere. Yes-size for water quality storage requirement Partial-based on available storage volume and if a flow restrictor is used

Water Balance

Research on the volumetric runoffThat potion of the water precipitated onto a catchment area, which 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. reduction performance of permeable pavements have been conducted on pavements with and without an underdrainA perforated pipe used to assist the draining of soils. in the base. Volumetric performance improves when:

  • Native soils have high infiltration capacity.
  • ImperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. surface draining onto the permeable pavementAn 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. is limited or absent.
  • UnderdrainA perforated pipe used to assist the draining of soils. is elevated above the native soilThe natural ground material characteristic of or existing by virtue of geographic origin. and/or a flow restrictor is installed on the underdrainA perforated pipe used to assist the draining of soils..

All permeable pavements have very high surface infiltration rates when appropriately maintained. Therefore, the surface course type (i.e. PICP, pervious concrete) is not a key factor in determining volumetric runoffThat potion of the water precipitated onto a catchment area, which 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. reduction performance.

Volumetric runoffThat potion of the water precipitated onto a catchment area, which 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. reduction from permeable pavements
LIDLow 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. Practice Location RunoffThat potion of the water precipitated onto a catchment area, which 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. Reduction* Reference
Permeable pavementAn 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. without underdrainA perforated pipe used to assist the draining of soils. Guelph, Ontario 90% James (2002)[4]
Pennsylvania 90% Kwiatkowski et al. (2007)[5]
France 97% Legret and Colandini (1999)[6]
Washington 97 to 100% Brattebo and Booth (2003)[7]
Connecticut 72%* Gilbert and Clausen (2006)[8]
King City, Ontario 99%* TRCA (2008)
Permeable pavementAn 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. with underdrainA perforated pipe used to assist the draining of soils.
Vaughan, Ontario 45%* Van Seters and Drake (2015)
North Carolina 98 to 99% Collins et al. (2008)[9]
United Kingdom 50% Jefferies (2004)[10]
United Kingdom 53 to 66% Pratt et al. (1995)[11]
Maryland 45% to 60% Schueler et al. (1987)[12]
Mississauga 61 to 99% CVC (2018)
RunoffThat potion of the water precipitated onto a catchment area, which 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. Reduction Estimate* 85% without underdrainA perforated pipe used to assist the draining of soils.;

45% with underdrainA perforated pipe used to assist the draining of soils.

Water Quality

Like other stormwater practices, the water quality performance of permeable pavements is closely tied to the reduction of runoffThat potion of the water precipitated onto a catchment area, which 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. volumes through infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., However, permeable pavements are also very effective stormwater runoffThat potion of the water precipitated onto a catchment area, which 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. filters. Most sedimentsSoil, 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. and associated contaminants are trapped within the surface pores or gravel filled joints between the pavers. A five year study of three permeable pavementAn 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. surfaces in Vaughan showed total suspended solids (TSSTotal suspended solids) concentration reductions between 88 and 89% (Van Seters and Drake, 2015). Other STEPSustainable Technologies Evaluation Program studies in the Greater Toronto Area have displayed similar results, with only 7% of 181 permeable pavementAn 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. effluent samples having TSSTotal suspended solids concentrations above 30 mg/L (median = 7 mg/L)TRCA, 2015.

Another group of studies of permeable pavements examines the quality of water infiltrated through soils beneath the installations. In these studies the quality of infiltrated water is used as a measure of the potential for contamination of groundwaterThe water below the surface, and typically below the groundwater table.. One such study of a permeable interlocking concrete pavement installed in a college parking lot in King City, Ontario, showed that stormwater infiltrated through a 60 cm granularGravel, 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. reservoir and 1 metre of native soilThe natural ground material characteristic of or existing by virtue of geographic origin. had significantly lower concentrations of several typical parking lot contaminants relative to runoffThat potion of the water precipitated onto a catchment area, which 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. from an adjacent asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. surface (TRCA, 2008). These results are consistent with research on the quality of infiltrated water from permeable pavements in Washington[7] and Pennsylvannia[5]. As with all stormwater infiltration practices, risk of groundwater contamination from infiltration of runoffThat potion of the water precipitated onto a catchment area, which 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. laden with road de-icing salt constituents (typically sodium and chloride) may be a concern in lands designated as source protection areas. Chloride ions are extremely mobile in the soil and are readily transported by percolating water to aquifersLayer of rock or soil that holds or transmits water..

Stream Channel Erosion(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

Permeable pavements help address stream erosion and flood flows by attenuating peak flows through temporary storage and release. A STEPSustainable Technologies Evaluation Program study in Vaughan showed a 91% peak flow reduction due in part to flow restriction on the underdrainA perforated pipe used to assist the draining of soils. (Van Seters and Drake, 2015). A later study of three permeable pavements in a parking lot in Mississauga showed peak flow reductions between 39 and 84% for events greater than 25 mm (CVC, 2018).

Other Benefits

Permeable pavements (left) in Bartholdi Park, DC provides air and water to root systems contributing to healthier, longer lasting trees (Source: USCapitol)
  • Winter Performance: Snow plow and deicing costs are reduced due to rapid drainage of snow melt. Puddling on parking lots is also reduced. A two year study of PICP in Vaughan found that the PICP provides equivalent or higher levels of safety compared with asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. when treated with de-icing products at medium (0.049 kg/m2) or low (0.024 kg/m2) salt application rates[13].
  • Urban Heat Island Effect Reduction: Porous materials have less thermal conductivity and thermal capacity than traditional imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. pavement, thereby reducing the urban heat island effect [14]. Year round measurements of asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. and PICP surface temperatures in King City, Ontario showed asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. temperatures above 20°C approximately 12% more often than the adjacent permeable pavers (TRCA, 2008).
  • Improved Street Tree Health: Permeable pavements installed around tree planting zones in hardscapes help provide air and water to root systems, thereby contributing to healthier, longer lasting trees that require less manual irrigationHuman application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47.
  • Quiet Streets: Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. surfaces absorb sound energy and dissipate air pressure around tires before any noise is generated. Tire noise is lower in loudness and pitch for a porous surface than a corresponding dense pavement [14]. Segmented pavers do not share this benefit and are generally noisier than asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. roads.
  • LEED Credits: Permeable pavementAn 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. has the potential for earning Canadian Green Building Council LEED sustainable sites credits for reducing stormwater pollution and runoffThat potion of the water precipitated onto a catchment area, which 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., urban heat island mitigation, and conservation of materials and resources.

Proprietary Links

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

Pre-cast with joints

Pre-cast pervious

Cast in place

Plastic grid

Gallery

References

Also see references as direct web page links above.
  1. Greater Vancouver Regional District (GVRD). 2005. Stormwater Source Control Design Guidelines 2005. Prepared by Lanarc Consultants Limited, Kerr Wood Leidal Associates Limited and Goya Ngan.
  2. Pennsylvania Department of Environmental Protection (PDEP). 2006. Pennsylvania Stormwater Best Management Practices Manual. Prepared by Cahill Associates Inc., Harrisburg, PA.
  3. City of Portland. 2004. Portland Stormwater Management Manual. Prepared by the Bureau of Environmental Services (BES). Portland, OR.
  4. James, W. 2002. Green Roads: Research into Permeable Pavers. Stormwater. March/April.
  5. 5.0 5.1 Kwiatkowski, M., Welker, A.L., Traver, R.G., Vanacore, M., Ladd. T. 2007. Evaluation of an infiltration best management practice utilizing pervious concrete. Journal of the American Water Resources Association. Vol. 43. No. 5. pp. 1208-1222.
  6. Legret, M and V. Colandani. 1999. Effects of a porous pavement structure with a reservoir structure on runoff water: water quality and fate of metals. Water Science and Technology. 39(2): 111-117
  7. 7.0 7.1 Brattebo, B. and D. Booth. 2003. Long term stormwater quantity and quality performance of permeable pavement systems. Water Research 37(18): 4369-4376
  8. Gilbert, J. and J. Clausen. 2006. Stormwater runoff quality and quantity from asphalt, paver and crushed stone driveways in Connecticut. Water Research 40: 826-832.
  9. Collins, K., W. Hunt and J. Hathaway. 2008. Hydrologic comparison of four types of permeable pavement and standard asphalt in eastern North Carolina. Journal of Hydrologic Engineering.
  10. Jefferies, C. 2004. Sustainable drainage systems in Scotland: the monitoring programme. Scottish Universities SUDS Monitoring Project. Dundee, Scotland
  11. Pratt, C.J., Mantle, J.D.G., Schofield, P.A. 1995. UK research into the performance of permeable pavement reservoir structures in controlling stormwater discharge quantity and quality. Water Science Technology. Vol. 32. No. 1. pp. 63-69.
  12. Schueler, T. 1987. Controlling urban runoff: a practical manual for planning and designing urban BMPs. Metropolitan Washington Council of Governments. Washington, DC.
  13. Marvin, J., Scott, J., Van Seters, T., Bowers, B., Drake, J. Winter Maintenance of Permeable Interlocking Concrete Pavement: Evaluating Opportunities to Reduce Road Salt Pollution and Improve Winter Safety, submitted to Transportation Research Record May 2020, under review
  14. 14.0 14.1 Ferguson, B.K. 2005. Porous Pavements. Integrative Studies in Water Management and Land Development. Taylor and Francis: New York.