Permeable Pavements

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.

An Illustration of Permeable Pavements

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.