Permeable paving systems

Brett Landscaping offer a range of permeable pavement solutions – a proven source control technique
in handling surface water run off and controlling pollution. Our technical experts have been associated
with the development of Industry guidance and have a wealth of experience in the practical application
of permeable paving as SuDS solutions.

Run-off and pollution control

Run off control

Conventional pavements, car parks and hardstanding areas are designed to simply shed water from their surface, whereas permeable pavements allow the water to pass between each block and into the underlying sub-base. Here it can be stored, channelled or slowly released in one of three ways – into the ground, passed on to a further stage of the SuDS management train or passed into the drainage system. But it is the attenuation of water that is important, enabling permeable paving systems to reduce first flush, control peak rates and total volume and frequency of run off by employing the principle of source control.

Permeable pavements can also be used to handle run off from surrounding impermeable areas such as roofs and impermeable landscaping so long as a factor of approximately 2:1 is not exceeded, thereby maximising the hydraulic storage capability of the permeable pavement.

Pollution control

The second major benefit of permeable pavements is their ability to reduce pollutants, at or close to, the source. Pollutants can be retained on the surface of the pavements (especially where there is little or no fall), before being carried through to the laying course and sub-base layers during a rainfall event, where they can be trapped and degraded over time.

Pollution

Another direct result of the increase in urbanisation is the environmental pollution from hydrocarbons and heavy metals resulting from vehicle usage and power generation. Fast and uncontrolled surface water run off carries this pollution with it almost undiluted, directly into our water courses, where it can be harmful to our environment wildlife.

CIRIA*, the leading body in the research for SuDS, states that 60-95% of suspended solids and 70-90% of hydrocarbons can be removed by permeable pavements in this way. This means that not only do they not require oil separators, but are also more efficient at removing a wider range of pollutants than conventional oil separators would be so that water finally leaving the site is of a higher quality than if left untreated and passing into an attenuation tank.

*Construction Industry Research and Information Association

Space efficiency

Permeable pavements are a very space-efficient solution and ideal for high density housing and construction projects. The removal of the need for oil separators and attenuation tanks results in greater space efficiency and cost savings. The ability to install some pavements without the associated underground pipework used in conventional drainage systems, provides additional cost benefits to projects.

System A: Total infiltration

All water falling onto the pavement infiltrates down through the joints between the concrete blocks, passing through the constructed layers below and eventually into the sub-grade. The sub-base layer may act as a temporary storage device.


System B: Partial infiltration

Similar to System A, but with a series of perforated pipes or fin drains at the formation level at the bottom of the sub-base, to allow the remaining water to be drained to other systems such as sewers, swales and ponds or watercourses.


System C: No infiltration

Allows for the complete capture or attenuation of the water using an impermeable membrane placed on top of the formation level. Pipes or fin drains restrict the outflow of water from the pavement.