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Homeowner Storm Water Management
Permeable Pavement
The Problem with Impermeable Surfaces

   Impervious surfaces have played a large role in the decline of watershed integrity in urban and urbanizing areas, causing:

    • higher discharges
    • more bank erosion
    • increased sediment transport
    • reduced groundwater recharge
    • increased pollutant loads to streams
What is Permeable Pavement ?

   Permeable pavement is an alternative to conventional concrete and asphalt materials that allows for infiltration of stormwater into a storage area with void spaces that provide temporary storage. Traditional paved surfaces do not allow water to infiltrate and instead converts almost all rainfall into runoff.

            

    Permeable paving materials include, but are not necessarily limited to:

    • porous concrete
    • permeable interlocking concrete pavers
    • concrete grid pavers
    • porous asphalt

            

              Some advantages to permeable pavement are that it:

    • replaces completely impervious surfaces with partially impervious surfaces
    • reduces stormwater runoff rate and volume
    • reduces loads of some pollutants in surface runoff by reducing the volume of stormwater leaving a site
Benefits of Using Permeable Pavement Found in Studies

In a study comparing the stormwater runoff quality and quantity of asphalt, paver, and stone it was found that:

    • asphalt had the most runoff
    • stone had the least
    • paver was in the middle

           The average filtration rates were as follows:

    • asphalt=0 cm/h
    • paver=11.2 cm/h
    • crushed stone=9.0 cm/h

          

           The reduction in runoff from asphalt to paver surface was 72% and to crushed stone was 98%. There were no seasonal differences in runoff depth among driveway types from the repeated measures analysis.

            Runoff from paver driveways contained significantly lower concentrations of all pollutants measured than runoff from asphalt driveways. Runoff from crushed stone driveways was similar in concentrations to runoff from asphalt driveways, except for total phosphorus.

             Total phosphorus concentration levels were lower in runoff from crushed stone driveways than runoff from asphalt driveways. Total phosphorus results were as follows:

    • asphalt=0.244 mg/L
    • paver=0.162 mg/L
    • crushed stone=0.155 mg/L

             The results of the nitrogen concentrations in stormwater runoff were as follows:

    • asphalt=0.6 mg/L
    • paver=0.3 mg/L
    • crushed stone=0.3 mg/L

 

           Another study found that after one year’s use of four permeable pavement areas there was no measurable surface runoff from the permeable pavement areas. After returning to the site after an additional five years all four permeable pavement systems showed no major signs of wear or clogging. Virtually all rainwater continued to infiltrate through every permeable pavement system, with little or no surface runoff. However, uniformly good performance cannot be presumed everywhere, as the experimental site has particularly favorable soil conditions and rainfall intensities in the area are typically low.

 

Possible Disadvantages of Permeable Pavement

Disadvantages of permeable pavement are:

    • its applicability being limited to the Coastal Plain and Sandhills regions
    • the potential for clogging of porous media by sediment, which could lead to reduced effectiveness without proper maintenance
    • it’s not applicable for high-traffic areas or for use by heavy vehicles
    • completed permeable pavement installation must have a slope less than 0.5% and the top 3-ft of soil must have no finer texture than “LoamyVery Fine Sand” as determined by a soil analysis done by the NC Division of Water Quality

           

             Maintenance requirements consist of:

    • vacuum sweeping permeable pavement surface annually
    • ensuring that permeable pavement is free of sediment monthly
    • verifying monthly that the permeable pavement system dewaters between storms
 

 

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