The Benefits of Permeable Pavement System
The primary benefits of using a permeable pavement system are:
- Reducing the amount of rainfall runoff from pavement surfaces and, thereby, eliminating or minimizing the extent of the stormwater drainage system needed. This can lead to substantial savings in the overall development cost.
- Reducing the size or need for rainwater detention facilities in roadworks by using the pavement itself for retention. This is an excellent example of using land in a sustainable way.
- Reducing or avoiding downstream flooding.
- Recharging and maintaining aquifers and the natural groundwater.
- Trapping and treating pollutants that would otherwise contaminate groundwater or drainage systems.
- Assisting in the biological decomposition of hydrocarbon contaminants.
By infiltrating water through a permeable pavement system; reduces or avoids the direct surface runoff and standing water/puddles on the road surface. Most importantly, a permeable pavement system reduces the peak discharge directed to storm sewers. This means that if a new development takes place; instead of upgrading or building a new storm drainage system, the existing one can be usually utilized without overloading it. A further benefit of infiltrating water is that surface gradients can often be minimized or eliminated (e.g. pavements can be laid level where this improves the amenity of the surface such as in car parks or for container stacking in port areas).
Permeable pavements also provide interception storage whereby water is absorbed into the pavement and thereafter evaporates only once the rain has stopped. The consequence of this is that, the runoff during a storm does not occur until after the first 5 mm of rainfall.
An important function of permeable pavements is that it improves water quality by removing and treating the pollutants that are commonly found on road surfaces or which get washed on to roads from the roofs of adjoining properties. These pollutants are either trapped by the pavement acting as a filter or by sedimentation within the pavement. Pollutants are also broken down by biological and chemical action. This means that permeable pavement systems treat pollution “at source”, which is an important concept in water-sensitive urban design. By contrast, conventional pavements rapidly direct polluted rainfall into watercourses where it is difficult and expensive to remediate.
Permeable pavements system also can be used to harvest water for later use; an important function in the urban development context where water is often scarce and expensive. The harvested water is filtered to be free of debris and sediments and can be used for non-potable purposes.
Because permeable pavements combine the functions of managing runoff, water quality, and water harvesting within a single construction unit they make very efficient use of land because they do not require additional land to be dedicated for detention ponds or for water treatment. This means that land acquired for new developments can be minimized.
When to Use Permeable Pavement
- There is a need or by-law requirement to maintain the existing solid surface runoff volume or green site runoff conditions when developing a site.
- The existing stormwater sewer/drainage system is at its max capacity.
- The are by-law limitations on the extent of impermeable (solid) surface pavement that the councils/authorities will allow for the new development.
- There is insufficient land available to construct the traditional pavement and the detention ponds. Thus the use of permeable pavement can be the solution.
- When the local municipalities/councils wants to control the pollution of local streams, wetlands, water table, and water supplies.
- Where the water need to be conserved for re-use as non-portable water.
- When there is a need to recharge the local aquifers/water table.
When not to Use Permeable Pavement
- The road/site is a slope steeper than 5%. The surface water will not have suffice time to infiltrate into the permeable pavement layers.
- The existing water table is closer to the surface, which may cause backflow to the surface.
- The existing stormwater drainage is less than 1m below the surface of pavement.
- There is a risk of spillage of hazadous liquids which may affect the ground water quality (e.g. fuel, oil, detergent, pesticides, and etc.)
- There is possibilities of high sediment being washed onto the pavement surface; thus clogging up the whole system.
- When the pavement may be subjected to tidal.
