Introduction
A pavement with base and
sub-base that allows the water to infiltrate or pass through the
surface is known as Permeable Pavement. It not only helps to reduce
the surface run off but also effectively traps the pollutants and solid
particles in the water avoiding ground water pollution.
Evaporation of water at
or below the surface also produces surface cooling, as opposed to the
traditional heating of paved areas. This is especially beneficial in cities
which experience extremely high temperatures in summer – traditional “blacktop”
temperatures can make some public spaces unusable in warmer weather.
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An
Illustration of Permeable Pavements
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Generally permeable
pavement structure consists of a pervious / permeable surface course which may
be of Asphalt concrete or Portland cement concrete laid over a layer of
fine aggregates, which acts as a filter layer for infiltrating storm or rain water.
Underneath this filter layer is uniformly graded gravel course to
store water, which ultimately penetrates in the natural ground. General
design practice requires an un-compacted natural ground, which allows
relatively easier discharge of water and to avoid any standing water under
the pavement structure that may cause structure failure.
Permeable pavements
are generally recommended for residential, commercial and urban areas but
not feasible for highways, motorways and streets with heavy traffic loading as these
pavements are not designed with structural capacities to support such loads.
Advantages
Permeable pavements
offer many benefits, both aesthetic and practical. Some of the benefits are
listed below:
- Reduces storm water runoff, including reduction of temperature, total water volume, and flow rate.
- Treats water runoff.
- Increases groundwater infiltration and recharge.
- Provides local flood control.
- Improves the quality of local surface waterways.
- Reduces soil erosion.
- Reduces the need for traditional storm water infrastructure, which may reduce the overall project cost.
- Increases traction when wet.
- Reduces splash-up in trafficked areas.
- Extends the life of paved area in cold climates due to less cracking and buckling from the freeze-thaw cycle.
- Reduces the need for salt and sand use during the winter, due to little or no black ice.
- Requires less snow-plowing.
- Reduces groundwater pollution.
- Creates green space (grass ground cover, shade from tree canopies, etc.
- Offers evaporative cooling.
- Porous pavements reduce the volume of storm water, increase the recharge, control the peak rate, and offer a high out flowing water quality.
Disadvantages
Some of the
disadvantages associated with these pavements are listed below:
- Highly contaminated runoff can be generated by some land uses where pollutant concentrations exceed those typically found in storm water.
- Heavy traffic loads can cause severe distresses which leads to pavement failure.
- In cold climates, salts used for removal of snow, contains chlorides that could migrate through the porous pavement into groundwater.
- Frequent maintenance is required to prevent the blockage of pores.
- Additional maintenance cost compared to conventional pavement.
