PERMEABLE PAVERS

Permeable pavers refer to pervious concrete, porous asphalt or any other forms of pervious or porous paving material that allows passage of water through pavement sections and they often include an aggregate base that gives structural support and acts as stormwater reservoirs. They also absorb water and allow it to infiltrate through the paving material.

A subsurface layer of coarse gravel is underlain to the permeable pavers to allow stormwater to be stored as it percolates into the ground. They are mostly used in low traffic areas and are more suited for parking lots, low traffic roads residential driveways and pedestrian walkways.

Additionally, they can also be used alongside other stormwater management systems to collect and infiltrate the overflow of stormwater.

Benefits:

  • Improves the aesthetic appeal of paved areas.
  • Soil erosion control: in areas with loose soil such as the arid areas and areas with hills permeable pavers can be used to retain and prevent soil erosion.
  • Reduction of the heat island effect: with most towns covered with asphalt and concrete the surfaces absorb heat which increases temperatures and in turn leading to the heat island effect, installation of permeable pavers which allow the soil underneath to breathe would significantly reduce the heat island effect.
  • Flexible for use in areas of various shapes and sizes.
  • Reduces the need for traditional stormwater infrastructure.
  • Treats stormwater runoff.
  • Provides local flood control.
  • Reduction of stormwater runoff volume, flow rate and temperature.
  • Increase in groundwater recharge and infiltration.
  • Easy installation: they do not require expensive installation materials as compared to concrete and asphalt surfaces.
  • Reduce retention and drainage fees: conventional asphalt or concrete systems will require having systems of storm drains and water control pipes during the rain, however, permeable pavers allow any water that accumulates to drain through the surface and into the ground helping reduce flooding and also the construction cost.
  • Together with subgrade soil permeable pavements help filter and reduce the pollution of stormwater.
  • Choice of styles, colours and patterns: There are a variety of styles and colours to choose from as per one’s preferences and tastes.
  • Strong and durable: due to its floating surface a permeable pavement has joints that make it flexible and thus is not affected by expansion and contraction.
  • Factory-made and easy to install year-round.
  • Rainwater harvesting
  • Winter friendly; allows snowmelt to drain and minimizing icing and deicer use.
  • Cost competitive: permeable pavers are more cost-effective as compared to other means such as concrete and asphalt.
  • Pedestrian and vehicular friendly.
  • Sustainable: they are made of environment –friendly recycled materials which reduces the amount of waste in the system and reduces the energy required to acquire new materials, additionally they can be recycled at the end of their lifespan reducing their carbon cycle.

Maintenance

Below are the routine maintenance practices that must be done to maintain the pavements in good condition and their frequency.

Needs and Frequencies

  • Periodic replacement of sand, gravel and vegetation.
  • Inspecting paver blocks annually for deterioration.
  • Inspecting them periodically during and after the rains to ensure that infiltration is occurring.
  • Pavers will need complete replacement after 25 years.
  • Grass dippings must be collected and removed when they fill the infiltration spaces after infiltration has occurred to prevent dogging from occurring.

When considering permeable pavers there some concerns or unknowns that one must consider. Firstly, pavers are ideally situated in areas with not more than 2% of the slope. Permeable pavers also require a space of two feet between the bottom of the gravel base and the underlying bed
lock and or the seasonally high groundwater table. They should also be sited at least 10 feet downgradient of buildings and 100 feet away from drinking water wells. The cost to the volume of stormwater ratio treated is higher than many other stormwater management practices.

Are you concerned about the environment? Then permeable pavers should be an option you should consider, this is because runoff water has been tied to environmental concerns. This is because it picks up and carries pollutants into nearby storm drains that lead directly into streams, lakes and
rivers and ultimately into coastal areas where the contaminants affect aquatic life, fishing, swimming and even our drinking water, thus many cities, towns and homeowners have set limitations on areas impervious surfaces can cover.

And as the saying goes “necessity is the mother of invention” therefore with the construction of permeable pavements restrictions such as bans imposed on low water reservoirs, watering lawns, flash floods, wet yards, flooded basements and beaches could be avoided. Permeable pavers also help in reducing the heat flux from the pavement surface to the atmosphere thus helping mitigate against the urban heat island.

DESIGN FACTORS TO CONSIDER

  • Soil: before starting your project you must put into consideration the soil type of the area you plan on implementing the pavers on. For instance, clay soils provide less structural support to paving solutions than sandy soil meaning that the gravel layer will need to be deeper on clay soil than on sandy soils to provide additional strength and stability. Additionally, clay soils provide lesser infiltration as compared to sandy soils and may therefore require underdrains to able to effectively drain water.
  • Area: one must ensure that the pavements are not too close to areas that have soil disturbances or where plenty of soil sediments can get transferred to the paving.
  • Slope: steep slopes reduce the paving ability to store stormwater and can cause shifting in the paving material. Slopes should be made minimal as much as possible ( less than 5%). Some permeable pavement guidelines however state that there should be no slopes at all.
  • Load: permeable pavings are designed to handle moderately heavy loads and not high velocities, therefore make sure you consider the load to be carried by your paving when choosing your aggregate and the thickness of your pavement.

In conclusion adoption of permeable paving’s is not only necessary but also important in helping establish a more hydrological balance and reduce run off the volume by trapping and slowly releasing precipitation to the ground allowing easy flow of stormwater and helping in environmental conservation.

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