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{{alert|The anticipated construction period for this page is January through March, 2013|alert-under-construction}}
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[[File:General information page image.png|left|100px|alt=image]]
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[[File:Univ of MN PICP Photograph.jpg|thumb|300px|alt=a photo illustrating porous concrete|<font size=3>Example of a new retrofit permeable parking lot at the University of Minnesota</font size>]]
  
{{alert|The anticipated review period for this page is January through March, 2013|alert-under-review}}
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{{alert|Permeable pavement can be an important tool for retention and detention of stormwater runoff. Permeable pavement may provide additional benefits, including reducing the need for de-icing chemicals, and providing a durable and aesthetically pleasing surface.|alert-success}}
  
[[File:picture of porous concrete 1.jpg|thumb|300px|alt=a photo illustrating porous concrete|<font size=3>This photo illustrates an example of pervious concrete.</font size>]]
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Permeable pavements allow stormwater runoff to filter through surface voids into an underlying stone reservoir where it is temporarily stored and/or infiltrated. The most commonly used [[Types of permeable pavement|permeable pavement surfaces]] are pervious concrete, porous asphalt, and permeable interlocking concrete pavers (PICP). Permeable pavements have been used for areas with light traffic at commercial and residential sites to replace traditionally impervious surfaces such as low-speed roads, parking lots, driveways, sidewalks, plazas, and patios. While permeable pavements can withstand truck loads, permeable pavement has not been proven in areas exposed to high repetitions of trucks or in high speed areas because its’ structural performance and surface stability have not yet been consistently demonstrated in such applications.
  
Permeable pavements allow stormwater runoff to filter through surface voids into an underlying stone reservoir where it is temporarily stored and/or infiltrated. The most commonly used [[Types of permeable pavement|permeable pavement surfaces]] are pervious concrete, porous asphalt, and permeable interlocking concrete pavers (PICP). Permeable pavements have been used for areas with light traffic at commercial and residential sites to replace traditionally impervious surfaces such as low-speed roads, parking lots, driveways, sidewalks, plazas, and patios. Permeable pavement is not ideal for high traffic/high speed areas because it has lower load-bearing capacity than conventional pavement.
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While the designs vary, all permeable pavements have a similar structure, consisting of a surface pavement layer, an underlying stone aggregate reservoir layer, optional underdrains, and geotextile over uncompacted soil subgrade. From a hydrologic perspective, permeable pavement is typically designed to manage rainfall landing directly on the permeable pavement surface area. Permeable pavement surface areas may accept runoff contributed by adjacent impervious areas such as driving lanes or rooftops. Runoff from adjacent vegetated areas must be stabilized and not generating sediment as its transport accelerates permeable pavement surface clogging. Additionally, the capacity of the underlying reservoir layer limits the contributing area.  
  
While the designs vary, all permeable pavements have a similar structure, consisting of a surface pavement layer, an underlying stone aggregate reservoir layer, optional underdrains, and geotextile over uncompacted soil subgrade.  
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[[File:Schematic showing infiltration.png|thumb|300px|alt=schematic showing process of infiltration into permeable pavement during and after a rain event.|<font size=3>Schematic showing the process of infiltration into permeable pavement during and after a rain event. Note how infiltrating water includes precipitation falling directly on the pavement and runoff from the adjacent street directed onto the pavement. Caution should be used when runoff is diverted from impervious surfaces to permeable pavement.</font size>]]
  
From a hydrologic perspective, permeable pavement is typically designed to manage rainfall landing directly on the permeable pavement surface area. Permeable pavement surface areas may accept runoff contributed by adjacent impervious areas such as driving lanes or rooftops. Runoff from adjacent vegetated areas is often discouraged because sediment in runoff from adjacent areas increases clogging of the permeable pavement, especially at the edges. Additionally, the capacity of the underlying reservoir layer limits the contributing area.  
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==Benefits and limitations==
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*'''Benefits''': Permeable pavements allow conversion and/or design of typical impervious areas (i.e. parking lots) to pervious areas that infiltrate stormwater runoff. When compared to typical impervious areas, properly designed and maintained permeable pavements can reduce the runoff quantity, reduce total suspended solids (TSS) and total phosphorus (TP) loads into receiving water bodies, and reduce runoff temperatures. In addition, permeable pavements can reduce nitrogen, metals and process oils. Permeable pavements are well suited for high density urban areas with limited space for other BMPs such as ponds, swales or bioretention systems.
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*'''Limitations''': As with all BMP’s, permeable pavement has limitations that need to be considered before design and construction. Limitations are discussed in detail in the permeable pavement [[Design criteria for permeable pavement|design section]].
  
[[File:Schematic showing infiltration.png|thumb|400px|alt=schematic showing process of infiltration into permeable pavement during and after a rain event.|<font size=3>Schematic showing the process of infiltration into permeable pavement during and after a rain event. Note how infiltrating water includes precipitation falling directly on the pavement and runoff from the adjacent street directed onto the pavement.</font size>]]
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==Pretreatment considerations==
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Pretreatment that removes sediment from runoff draining onto permeable pavement from impervious surfaces is desirable since sediment can clog permeable pavements. For that reason, pretreatment areas should emit practically no sediment onto the permeable pavement surface. Locating such areas next to impervious surfaces upslope from the permeable pavement may not be possible on some sites. Permeable pavement itself can be considered a pre-treatment device and included in a stormwater treatment train if underdrains are utilized within the storage reservoir. The underdrains will typically be routed to a bioretention area.
  
==Benefits and limitations==
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==Permit applicability==
*'''Benefits''': Permeable pavements allow for conversion and/or design of typical Permeable pavements allow conversion and/or design of typical impervious areas (i.e. parking lots) to pervious areas that infiltrate stormwater runoff. When compared to typical impervious areas, properly designed and maintained permeable pavements can reduce the runoff quantity, reduce total suspended solids (TSS) and total phosphorus (TP) loads into receiving water bodies, and reduce runoff temperatures. In addition, permeable pavements can reduce nitrogen, metals and process oils. Permeable pavements are well suited for high density urban areas with limited space for other BMPs such as ponds, swales or bioretention systems.
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Permeable pavements can be utilized to assist in meeting stormwater [[Regulatory information|requirements]] for volume, total suspended solids, and total phosphorus. The section on [[Calculating credits for permeable pavement|credits]] provides guidance on the implementation of permeable pavements that may be utilized to meet various runoff volume and pollutant runoff reduction goals.
*'''Limitations''': As with all BMP’s, permeable pavement has limitations that need to be considered before design and construction. Limitations are discussed in detail in the permeable pavement [[Design criteria for permeable pavement|design section]].
 
  
==Pretreatment Considerations==
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==Retrofit suitability==
[[Glossary|Pretreatment]] to remove sediment from runoff draining onto permeable pavement from adjacent impervious areas is desirable since sediment tends to clog permeable pavements. This is usually accomplished through the use of a vegetative filter upstream of the pavement. Permeable pavement itself can be considered a pre-treatment device and included in a stormwater [[Using the treatment train approach to BMP selection|treatment train]] if [[Glossary#U|underdrains]] are utilized within the storage reservoir. The underdrains will typically be routed to [[Bioretention|bioretention]] or a raingarden.
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In most cases, existing impervious surfaces can be replaced with permeable pavements to achieve improved runoff conditions. Retrofit requires the removal of the old pavement and subgrade and the installation of the underlying reservoir layer and the permeable pavement. For the greatest water quality credits, avoid compaction of subgrade soils. If this is not possible, compacted subgrade soils should be removed or loosened to achieve the maximum infiltration rate possible.
  
==Permit Applicability==
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==Cold climate suitability==
Permeable pavements can be utilized to assist in meeting stormwater [[Regulatory information|requirements]] for volume, total suspended solids, and total phosphorus. The section on [[Calculating credits for permeable pavement|credits]] provides guidance on the implementation of permeable pavements that may be utilized to meet various credit goals.
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Favorable permeable pavement performance has been documented in cold climates. Air in the aggregate base acts as an insulating layer and the higher latent heat associated with higher soil moisture delays the formation of a frost layer while maintaining permeability and this condition also reduces frost depths when frozen. Winter sanding should be avoided when possible and if used, removed by vacuuming the following spring. Permeable pavements require significantly less use of, or in some cases, no deicing chemicals and sand to maintain a safe walking or driving surface. Other climate considerations include high wind erosion [http://www.casqa.org/ (California 2003)]. Dramatic reductions in life span of the infiltration properties of the pavement may occur in these areas due to particulate clogging and this may require additional surface vacuum cleaning.
  
==Retrofit Suitability==
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==Special receiving waters suitability==
In most cases, existing impervious surfaces can easily be replaced with permeable pavements to achieve improved runoff conditions. Retrofit requires the removal of the old pavement and subgrade and the installation of the underlying reservoir layer and the permeable pavement. When possible, compacted subgrade soils should be removed or loosened to achieve the maximum infiltration rate possible.  
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Many of the same design considerations and limitations apply to permeable pavement as to other infiltration practices.
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*Infiltration of runoff from [[Potential stormwater hotspots|hotspots]] (e.g., gas stations, chemical storage areas, etc.) should be carefully considered and in many cases avoided.
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*Special consideration also needs to be taken near wellhead areas and [[Stormwater infiltration and constraints on infiltration|basement foundations]].
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*Some designs may require consideration of storms in excess of the infiltration capabilities of the pavement. For these situations the design should ensure the excess runoff does not negatively impact [[Special waters and other sensitive receiving waters|special surface waters]] (e.g.,trout streams) through the implementation of additional BMPs.
  
==Cold Climate Suitability==
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==Water quality==
The effective use of permeable pavement has been documented in a variety of climates. However, special consideration is necessary for [[Cold climate impact on runoff management|cold climates]], arid regions, or areas with high wind erosion [http://www.casqa.org/ (California 2003)]. Dramatic reductions in life span of the infiltration properties of the pavement may occur in these areas due to particulate clogging. In cold climates like Minnesota, the most notably special consideration is regarding the application of sand in the winter for added traction. This is not recommended. Fortunately, permeable pavements require significantly less use of de-icing sand and chemicals to maintain a safe walking or driving surface.
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In general, permeable pavement provides removal of TSS and other pollutants through processes similar to other filtration and infiltration BMPs. However, permeable pavements are not suggested for areas that may receive high loading rates of TSS due to their propensity for surface clogging. The expected annual volume and pollutant reductions for designs without an underdrain are a function of the underlying reservoir storage volume. The greater the storage volume, the greater the annual volume and pollutant reductions.
  
==Special Receiving Waters Suitability==
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For designs with underdrains, reductions are typically lower depending on the drain outflow location that determines the volume of water removed by the underdrains before infiltration. Of the water intercepted and draining through the underdrain, 45 percent (with upper and lower 90 percent confidence bounds of 65 percent and 24 percent, respectively) of the total phosphorus and 74 percent (with upper and lower 90 percent confidence bounds of 93 percent and 33 percent, respectively) of total suspended solids removal can be expected. These event mean averages and ranges are derived from a literature review on research on permeable pavements. The literature includes 19 studies on pollutant reductions and 10 studies on volume reductions. (See the section on [[Calculating credits for permeable pavement|credits]] for more information on pollutant reduction credits and their relationship to the MIDS credit calculator).
Many of the same design considerations and limitations apply to permeable pavement as to other infiltration practices. Infiltration of runoff from [[Potential stormwater hotspots|hotspots]] (e.g., gas stations, chemical storage areas, etc.) should be carefully considered and in many cases avoided. Special consideration also needs to be taken near [[Wellhead protection areas|wellhead areas]] and [[Stormwater infiltration and constraints on infiltration|basement foundations]]. Some designs may require consideration of storms in excess of the infiltration capabilities of the pavement. For these situations the design should ensure the excess runoff does not negatively impact [[Special waters and other sensitive receiving waters|special surface waters]] (e.g.,trout streams) through the implementation of additional BMPs.
 
  
==Water Quality==
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==Water quantity==
In general, permeable pavement provides removal of TSS and other pollutants through processes similar to other filtration and infiltration BMPs. However, permeable pavements are not suggested for areas that may receive high loading rates of TSS due to their propensity for surface clogging. The expected annual volume and pollutant reductions for designs without an underdrain are a function of the underlying reservoir storage volume. The greater the storage volume, the greater the annual volume and pollutant reductions. If a system is designed to infiltrate the MIDS performance standard of 1.1 inches of runoff from the tributary impervious surfaces, it would result in a 91% annual runoff volume reduction from a site with hydrologic soil group (HSG) C soils (infiltration rate of 0.2 inches/hr). Annual pollutant load reductions for this example are approximately equal to the volume reduction. A site with HSG A soils (infiltration rate of 1.6 inches/hr) would result in higher annual reductions.
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The primary advantage of permeable pavements is providing volume reduction by reducing runoff from a site and/or providing attenuation from outflows. The volume of water that will be reduced during a given rainfall event will be equivalent to the volume available for storage below the pavement or underdrain (if an underdrain is present). More discussion on this item is available in the section on [[calculating credits for permeable pavement|credits]].
  
For designs with underdrains, the reductions are less because a portion of the water is captured by the underdrains before it can be infiltrated. Of the water intercepted and draining through the underdrain, 45% (with upper and lower 90% confidence bounds of 65% and 24%, respectively) of the total phosphorus and 74% (with upper and lower 90% confidence bounds of 93% and 33%, respectively) of total suspended solids removal can be expected.
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<noinclude>
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==Related articles==
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*[[Overview for permeable pavement]]
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*[[Types of permeable pavement]]
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*[[Design criteria for permeable pavement]]
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*[[Construction specifications for permeable pavement]]
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<!--[[Construction observations for permeable pavement]]-->
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*[[Assessing the performance of permeable pavement]]
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*[[Operation and maintenance of permeable pavement]]
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*[[Calculating credits for permeable pavement]]
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<!--[[Cost-benefit considerations for permeable pavement]]-->
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*[[Case studies for permeable pavement]]
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*[[Green Infrastructure benefits of permeable pavement]]
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*[[Summary of permit requirements for infiltration]]
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*[[Permeable pavement photo gallery]]
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*[[Additional considerations for permeable pavement]]
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*[[Links for permeable pavement]]
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<!--*[[External resources for permeable pavement]]-->
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*[[References for permeable pavement]]
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<!--*[[Supporting material for permeable pavement]]-->
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*[[Fact sheets for permeable pavement]]
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*[[Requirements, recommendations and information for using permeable pavement BMPs in the MIDS calculator]]
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<!--#[[Permeable pavement credits]]-->
  
==Water Quantity==
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[https://stormwater.pca.state.mn.us/index.php?title=Permeable_pavement Permeable pavement main page]
The primary advantage of permeable pavements is their ability to provide volume reduction by reducing runoff from a site and/or providing attenuation during runoff events. The volume of water that will be reduced during a given rainfall event will be equivalent to the volume available for storage below the pavement or underdrain (if an underdrain is present). More discussion on this item is available in the section on [[calculating credits for permeable pavement|credits]].
 
  
[[category: Overview]]
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[[Category:BMP overview]]
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[[category:Permeable pavement]]
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</noinclude>

Revision as of 18:45, 13 August 2019

image
a photo illustrating porous concrete
Example of a new retrofit permeable parking lot at the University of Minnesota
Green Infrastructure: Permeable pavement can be an important tool for retention and detention of stormwater runoff. Permeable pavement may provide additional benefits, including reducing the need for de-icing chemicals, and providing a durable and aesthetically pleasing surface.

Permeable pavements allow stormwater runoff to filter through surface voids into an underlying stone reservoir where it is temporarily stored and/or infiltrated. The most commonly used permeable pavement surfaces are pervious concrete, porous asphalt, and permeable interlocking concrete pavers (PICP). Permeable pavements have been used for areas with light traffic at commercial and residential sites to replace traditionally impervious surfaces such as low-speed roads, parking lots, driveways, sidewalks, plazas, and patios. While permeable pavements can withstand truck loads, permeable pavement has not been proven in areas exposed to high repetitions of trucks or in high speed areas because its’ structural performance and surface stability have not yet been consistently demonstrated in such applications.

While the designs vary, all permeable pavements have a similar structure, consisting of a surface pavement layer, an underlying stone aggregate reservoir layer, optional underdrains, and geotextile over uncompacted soil subgrade. From a hydrologic perspective, permeable pavement is typically designed to manage rainfall landing directly on the permeable pavement surface area. Permeable pavement surface areas may accept runoff contributed by adjacent impervious areas such as driving lanes or rooftops. Runoff from adjacent vegetated areas must be stabilized and not generating sediment as its transport accelerates permeable pavement surface clogging. Additionally, the capacity of the underlying reservoir layer limits the contributing area.

schematic showing process of infiltration into permeable pavement during and after a rain event.
Schematic showing the process of infiltration into permeable pavement during and after a rain event. Note how infiltrating water includes precipitation falling directly on the pavement and runoff from the adjacent street directed onto the pavement. Caution should be used when runoff is diverted from impervious surfaces to permeable pavement.

Benefits and limitations

  • Benefits: Permeable pavements allow conversion and/or design of typical impervious areas (i.e. parking lots) to pervious areas that infiltrate stormwater runoff. When compared to typical impervious areas, properly designed and maintained permeable pavements can reduce the runoff quantity, reduce total suspended solids (TSS) and total phosphorus (TP) loads into receiving water bodies, and reduce runoff temperatures. In addition, permeable pavements can reduce nitrogen, metals and process oils. Permeable pavements are well suited for high density urban areas with limited space for other BMPs such as ponds, swales or bioretention systems.
  • Limitations: As with all BMP’s, permeable pavement has limitations that need to be considered before design and construction. Limitations are discussed in detail in the permeable pavement design section.

Pretreatment considerations

Pretreatment that removes sediment from runoff draining onto permeable pavement from impervious surfaces is desirable since sediment can clog permeable pavements. For that reason, pretreatment areas should emit practically no sediment onto the permeable pavement surface. Locating such areas next to impervious surfaces upslope from the permeable pavement may not be possible on some sites. Permeable pavement itself can be considered a pre-treatment device and included in a stormwater treatment train if underdrains are utilized within the storage reservoir. The underdrains will typically be routed to a bioretention area.

Permit applicability

Permeable pavements can be utilized to assist in meeting stormwater requirements for volume, total suspended solids, and total phosphorus. The section on credits provides guidance on the implementation of permeable pavements that may be utilized to meet various runoff volume and pollutant runoff reduction goals.

Retrofit suitability

In most cases, existing impervious surfaces can be replaced with permeable pavements to achieve improved runoff conditions. Retrofit requires the removal of the old pavement and subgrade and the installation of the underlying reservoir layer and the permeable pavement. For the greatest water quality credits, avoid compaction of subgrade soils. If this is not possible, compacted subgrade soils should be removed or loosened to achieve the maximum infiltration rate possible.

Cold climate suitability

Favorable permeable pavement performance has been documented in cold climates. Air in the aggregate base acts as an insulating layer and the higher latent heat associated with higher soil moisture delays the formation of a frost layer while maintaining permeability and this condition also reduces frost depths when frozen. Winter sanding should be avoided when possible and if used, removed by vacuuming the following spring. Permeable pavements require significantly less use of, or in some cases, no deicing chemicals and sand to maintain a safe walking or driving surface. Other climate considerations include high wind erosion (California 2003). Dramatic reductions in life span of the infiltration properties of the pavement may occur in these areas due to particulate clogging and this may require additional surface vacuum cleaning.

Special receiving waters suitability

Many of the same design considerations and limitations apply to permeable pavement as to other infiltration practices.

  • Infiltration of runoff from hotspots (e.g., gas stations, chemical storage areas, etc.) should be carefully considered and in many cases avoided.
  • Special consideration also needs to be taken near wellhead areas and basement foundations.
  • Some designs may require consideration of storms in excess of the infiltration capabilities of the pavement. For these situations the design should ensure the excess runoff does not negatively impact special surface waters (e.g.,trout streams) through the implementation of additional BMPs.

Water quality

In general, permeable pavement provides removal of TSS and other pollutants through processes similar to other filtration and infiltration BMPs. However, permeable pavements are not suggested for areas that may receive high loading rates of TSS due to their propensity for surface clogging. The expected annual volume and pollutant reductions for designs without an underdrain are a function of the underlying reservoir storage volume. The greater the storage volume, the greater the annual volume and pollutant reductions.

For designs with underdrains, reductions are typically lower depending on the drain outflow location that determines the volume of water removed by the underdrains before infiltration. Of the water intercepted and draining through the underdrain, 45 percent (with upper and lower 90 percent confidence bounds of 65 percent and 24 percent, respectively) of the total phosphorus and 74 percent (with upper and lower 90 percent confidence bounds of 93 percent and 33 percent, respectively) of total suspended solids removal can be expected. These event mean averages and ranges are derived from a literature review on research on permeable pavements. The literature includes 19 studies on pollutant reductions and 10 studies on volume reductions. (See the section on credits for more information on pollutant reduction credits and their relationship to the MIDS credit calculator).

Water quantity

The primary advantage of permeable pavements is providing volume reduction by reducing runoff from a site and/or providing attenuation from outflows. The volume of water that will be reduced during a given rainfall event will be equivalent to the volume available for storage below the pavement or underdrain (if an underdrain is present). More discussion on this item is available in the section on credits.


Related articles

Permeable pavement main page