Component: Pervious surfaces

 

Description

Pervious surfaces can be either porous or permeable. The important distinction between the two is:

 

• Porous surfacing is a surface that infiltrates water across the entire surface.
• Permeable surfacing is formed of material that is itself impervious to water but, by virtue of voids formed through the surface, allows infiltration through the pattern of voids.

 

Pervious surfaces provide a surface suitable for pedestrian and/or vehicular traffic, while allowing rainwater to infiltrate through the surface and into underlying layers.

 

The water can be temporarily stored before infiltration to the ground, reused, or discharged to a watercourse or other drainage system. Surfaces with an aggregate sub-base can provide good water quality treatment.

 

Advantages and disadvantages

 

Advantages

Reduced peak flows to watercourses reducing the risk of flooding downstream Reduced effects of pollution in runoff on the environment Can be used in high density developments with a range of surface finishes that accept surface waters over their area of use Reduced need for deep excavations for drainage, which can have significant cost benefits Flexible and tailored solution that can suit the proposed usage and design life Lined systems can be used where infiltration is not desirable, or where soil integrity would be compromised Allows dual use of space, so no additional land take Removes need for gully pots and manholes Eliminates surface ponding and surface ice Often very resilient to a lack of maintenance Good community acceptability.

Disadvantages

Cannot be used where large sediment loads may be washed/carried onto the surface In the UK, current practice is to use on highways with low traffic volumes, low axle loads and speeds of less than 30 mph Risk of long-term clogging and weed growth if poorly maintained

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Where component can be used

Residential:  Yes

Commercial/industrial:  Yes

High density:  Yes

Retrofit:  Yes

Contaminated sites:  Yes

Sites above vulnerable groundwater: Yes

 

Performance

Peak flow reduction:  Good

Volume reduction:  Good

Water quality treatment: Good

Amenity potential:  Poor

Ecology potential:  Poor

 

Read more on:

• Source control

• Benefits of pervious surfaces

• Hydraulic performance

• Pervious surface types

• Other permeable surfaces