If you are concerned about getting into deep water – use permeable paving. Jamie Gledhill, Brett Landscaping’s Engineering Technical Manager, examines the issue.
In 2020, Water UK put pressure on developers to create more sustainable and resilient surface water drainage using SuDS rather than “end of pipe” solutions, such as balancing ponds or attenuation basins. One of the most effective methods for improving drainage without negatively impacting on land-use is the use of permeable paving solutions.
Permeable pavements work by replicating the drainage patterns of an undeveloped site where up to 95 per cent of rainfall is absorbed into the land, with only 5 per cent becoming surface water runoff. In this way the flow of water is attenuated, removing the early spike in surface water run-off, which creates the greatest risk and pressure on downstream water management.
Utilising the permeable blocks as both paving and the drainage solution, simplifies the process and reduces construction and environmental costs. When compared to using balancing/retention ponds, it also increases the amount of land that can be used for building – as the drainage solution is simply part of the carriageway. This, in turn, means that the housing density could increase.
Permeable pavements are also straightforward in terms of installation, the simplest of these being an infiltration system. Once the level of the sub-grade is chosen, a geotextile is laid before a permeable sub-base (4 – 20mm Coarse Graded Aggregate) is set across the area. This is covered with a 50mm thick laying course (2 – 6.3mm Graded Aggregate) – before the permeable paving blocks are installed on top and jointed with the same 2 – 6.3mm aggregate. The normal flow of rainwater then evaporates within that system.
In the event of storms with high-volume heavy rain, the permeable paving system will attenuate the surface water until the storm passes, and then slowly release the storm water back into the natural environment.
Research, in 2004, by the Construction Industry Research and Information Association has shown that permeable pavements can remove between 60 per cent and 95 per cent of suspended solids, and up to 90 per cent of hydrocarbons.
The research demonstrated that permeable paving systems are more effective in removing pollution from rainwater run-off than attenuation tanks. The same research also showed that permeable pavements can remove a wider range of pollutants than oil separators.
This means that permeable paving effectively cleans the water as it goes through the system. Tyre residue on road surfaces causes a considerable amount of plastics pollution and ends up in the drainage system along with hydrocarbons, detritus, silts, microplastics. All of these pollutants can be captured by permeable paving.
Larger particles are stopped at the surface, while finer materials, hydrocarbons and heavy metals are trapped as they penetrate the supporting layers. Organic materials, once trapped, break down over time, reducing the amount of contaminants that reach watercourses.
The result is that the water which infiltrates into the ground – or is drained to the next stage of a water management system, is of a much higher quality than if using an impermeable surface, relying on attenuation tanks. There are a number of other practical advantages to using permeable paving. Not least among these is that there is a greater range of products and finishes available across the market all designed with SuDS legislation and system longevity in mind.
For example, Brett Landscaping’s residential permeable paving systems Omega Flow and Alpha Flow, with existing pavements still offer between 15 and 20 years of low maintenance service. There is also Brett’s new Invicta Flow which uses a blend of specially sourced aggregates to create new paving finishes, which are unique to Brett Landscaping.
The new Invicta range came about after a programme of significant investment and expansion of manufacturing capacity. This investment has allowed Brett to develop its manufacturing processes to be able to blend the aggregates to create new paving finishes which are unique to Brett Landscaping.
Through this new AggTech process unique natural aggregates are used on the surface of each paving block to create a stunning durable finish. The Invicta Flow is available in four colours: Pearl, Moonstone, Onyx and Citrine. The colours are complementary so the different shades can be laid and arranged to meet a bespoke design brief, or to the preferred style and taste of the homeowner or client.
With obligations on contractors and sub-contractors to adhere to statutory regulations – as well as pressures on time, space and budget – the advantages to using permeable paving to meet sustainable drainage requirements are clear.
For further information on the range of permeable paving solutions from Brett Landscaping visit https://www.brettlandscaping.co.uk/