Permeable paving enables water to pass through the pavement and filter back to the drains or into the ground below. The process of treatment that occurs from permeable pavements prevent harmful contaminants from entering rivers and other storm water pools. These surfaces allow water to percolate through to a sub-surface course, from where it either infiltrates to the soil or is filtered back to the drainage system.
Porous paving achieve a number of key water management goals, these include:
- they reduce a significant volume of stormwater discharges
- increase the amount of groundwater recharged into the water tables below
- the filtration process improves stormwater quality
There are a number of ways to lay porous paving. There are pavements made from special asphalts or resins that allow stormwater to filter through the surface, there are concrete pavers that allow stormwater to filter through voids in between the paver and there are plastic modular grids that allow stormwater to filter through gravel fillings in the plastic.
To ensure effectiveness of the permeable paving, the best practice is to include water retention trenches that are placed below the sand/gravel layer and then an overflow pipe to the street drainage system to minimise chances of flooding.
The benefits of permeable pavement includes
- You retain pollutants close to source
- A reduction in site run-off, reduce flood peaks
- Recharge water table volumes directly below
- Permeable pavements can be more aesthetically pleasant than standard pavement
The cons of permeable pavement includes
- As they are still developing the technology behind it at this stage they can only support lighter traffic loads and not heavy vehicles
- Permeable pavements are prone to clogging, which can reduce effectiveness, as the gaps in the pavement get clogged with sediment
- In general they are only suitable for mildly sloped sites which can reduce its application across areas
What to do when permeable pavements are clogged?
When permeable pavements are clogged this can mean that they are not functioning properly. In general they are found to be at 50-70% effectiveness.
When surfaces are clogged, cleaning is required. This can be done through high pressure water applied to the pavement. Once cleaned, studies have found that the same permeable pavements can be used with confidence but must undergo regular clean in approximately 2-5 year intervals depending on the amount of sediment impacting that area.