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For example, the parking spaces of a parking lot may be permeable pavers while the drive lanes are impervious asphalt.
For example, the parking spaces of a parking lot may be permeable pavers while the drive lanes are impervious asphalt.
In general, the impervious area should not exceed 1.2 times the area of the permeable pavement which receives the runoff.
In general, the impervious area should not exceed 1.2 times the area of the permeable pavement which receives the runoff.
A hybrid permeable pavement/soakaway design can feature connection of a roof downspout directly to the stone reservoir of the permeable pavement system, which is sized to store runoff from both the pavement surface and the roof drainage area.
A hybrid permeable pavement/soakaway design can feature connection of a roof downspout directly to the stone reservoir of the permeable pavement system, which is sized to store runoff from both the pavement surface and the roof drainage area.
{{:Gravel}}
{{:Gravel}}
<h5>Sizing Stone Reservoirs</h5>
<h5>Sizing Stone Reservoirs</h5>
The following calculation is used to size the stone storage bed (reservoir) used as a base course for designs without underdrains. It is assumed that the footprint of the stone bed will be equal to the footprint of the pavement. The following equations are taken from the ICPI Manual (Smith, 2006).
The following calculation is used to size the stone storage bed (reservoir) used as a base course for designs without underdrains. It is assumed that the footprint of the stone bed will be equal to the footprint of the pavement. The following equations are taken from the ICPI Manual <ref>Smith, D. 2006. Permeable Interlocking Concrete Pavements; Selection, Design,
Construction, Maintenance. 3rd Edition. Interlocking Concrete Pavement Institute.
Burlington, ON.</ref>
The equation for the depth of the stone bed is as follows:
The equation for the depth of the stone bed is as follows:
<math>db= [Qc\times R + P - i\times T ] / V</math>
<math>db= [Qc\times R + P - i\times T ] / V</math>
where:
where:{{plainlist|}}
{{plainlist|}}
*''db'' = Stone bed depth (m)
*''db'' = Stone bed depth (m)
*''Qc'' = Depth of runoff from contributing drainage area, not including permeable paving surface(m)
*''Qc'' = Depth of runoff from contributing drainage area, not including permeable paving surface(m)
<math>Ap= [Qc \times Ac] / [Vr \times dp – P + i \times T] </math>
<math>Ap= [Qc \times Ac] / [Vr \times dp – P + i \times T] </math>
<h4>Geotextile</h4>
<h4>Geotextile</h4>
{{:Geotextiles}}
Geotextiles can be used to prevent downward migration of smaller particles in to larger aggregates, and slump of heavier particles into finer underlying courses. The formation of biofilm on geotextiles has also been shown to improve water quality:
*By degrading petroleum hydrocarbons<ref>Newman AP, Coupe SJ, Spicer GE, Lynch D, Robinson K. MAINTENANCE OF OIL-DEGRADING PERMEABLE PAVEMENTS: MICROBES, NUTRIENTS AND LONG-TERM WATER QUALITY PROVISION. https://www.icpi.org/sites/default/files/techpapers/1309.pdf. Accessed July 17, 2017</ref>
*By reducing organic pollutant and nutrient concentrations<ref>Paul P, Tota-Maharaj K. Laboratory Studies on Granular Filters and Their Relationship to Geotextiles for Stormwater Pollutant Reduction. Water. 2015;7(4):1595-1609. doi:10.3390/w7041595.</ref>
*When installing geotextiles an overlap of 150 - 300 mm should be used.
Material specifications should conform to OPSS 1860 for Class II geotextile fabrics<ref>ONTARIO PROVINCIAL STANDARD SPECIFICATION METRIC OPSS 1860 MATERIAL SPECIFICATION FOR GEOTEXTILES. 2012. http://www.raqsb.mto.gov.on.ca/techpubs/OPS.nsf/0/2ccb9847eb6c56738525808200628de1/$FILE/OPSS%201860%20Apr12.pdf. Accessed July 17, 2017</ref>
*Fabrics should be woven monofilament or non-woven needle punched.
*Woven slit film and non-woven heat bonded fabrics should not be used, as they are prone to clogging.
In choosing a product, consider:
{{plainlist|}}
*''The maximum forces that will be exerted on the fabric (i.e., what tensile, tear and puncture strength ratings are required?)'',
*''The load bearing ratio of the underlying native soil (i.e. is the geotextile needed to prevent downward migration of aggregate into the native soil?)'',
*''The texture (i.e., grain size distribution) of the overlying and underlying materials, and''
*''The suitable apparent opening size (AOS) for non-woven fabrics, or percent open area (POA) for woven fabrics, to maintain water flow even with sediment and microbial film build-up''
==Performance==
==Performance==
*Full Infiltration: Full infiltration designs are more effective because little if any of the pollutants generated on the impermeable surfaces leave the site as surface runoff.
*Full Infiltration: Full infiltration designs are more effective because little if any of the pollutants generated on the impermeable surfaces leave the site as surface runoff.
*Partial Infiltration: Partial infiltration designs with underdrains generate more runoff.
*Partial Infiltration: Partial infiltration designs with underdrains generate more runoff.
Studies in North Carolina have shown the average curve number of permeable pavements to range from a low of 45 to a high of 89 <ref>Bean, E.Z., Hunt, W, F., Bidelspach, D.A. 2007a. Evaluation of Four Permeable Pavement Sites in Eastern North Carolina for Runoff Reduction and Water Quality Impacts. Journal of Irrigation and Drainage Engineering. Vol. 133. No. 6. pp. 583-592.</ref>
==Construction Considerations==
==Construction Considerations==
Construction of permeable pavement is a specialized project and should involve experienced contractors. The following general recommendations apply:
Construction of permeable pavement is a specialized project and should involve experienced contractors. The following general recommendations apply:
*Sediment Control: The treatment area should be fully protected during construction so that no sediment reaches the permeable pavement system and proper erosion and sediment controls must be maintained on site.
*Sediment Control: The treatment area should be fully protected during construction so that no sediment reaches the permeable pavement system and proper erosion and sediment controls must be maintained on site.
*Weather: Porous asphalt and pervious concrete will not properly pour and set in extremely high and low temperatures (City of Portland, 2004; U.S. EPA, 1999). One benefit to using permeable pavers is that their installation is not weather dependent.
*Weather: Porous asphalt and pervious concrete will not properly pour and set in extremely high and low temperatures <ref>City of Portland. 2004. Portland Stormwater Management Manual. Prepared by the
Bureau of Environmental Services (BES). Portland, OR.</ref>. One benefit to using permeable pavers is that their installation is not weather dependent.
*Pavement placement: Properly installed permeable pavement requires trained and experienced producers and construction contractors.
*Pavement placement: Properly installed permeable pavement requires trained and experienced producers and construction contractors.
==Life Cycle Costs==
==Life Cycle Costs==
Initial construction costs for permeable pavements are typically higher than conventional asphalt pavement surfaces, largely due to thicker aggregate 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 savings and benefits may also be realized, including reduced need for storm sewer pipes and other stormwater practices, less developable land consumed for stormwater treatment, and ancillary benefits such as 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 infiltration, retention, and detention into one facility.
Initial construction costs for permeable pavements are typically higher than conventional asphalt pavement surfaces, largely due to thicker aggregate 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 savings and benefits may also be realized, including reduced need for storm sewer pipes and other stormwater practices, less developable land consumed for stormwater treatment, and ancillary benefits such as 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 infiltration, retention, and detention into one facility.
==References==
<references/>
==Proprietary Links==
==Proprietary Links==