Recent innovations with concrete block permeable paving help meet regulatory requirements for sustainable drainage systems (SuDS) while cutting costs and maximising development potential, as consultant to Interpave Chris Hodson explains.
SuDS and techniques such as concrete block permeable paving are essential tools in the fight against flooding and pollution – particularly with overloaded sewers, urbanisation and climate change. They are also a firm requirement around the UK and the National Planning Policy Framework (NPPF) requires SuDS on new developments of 10 or more dwellings in England. In addition, NPPF prioritisation of SuDS in areas of flood risk and requirements that developments should not make flood risk worse elsewhere apply to developments of any scale. Localised planning policies are also appearing, spelling out what local authorities expect from sustainable drainage on the ground.
By its very nature, concrete block permeable paving is uniquely placed to help meet the multifunctional requirements for SuDS on developments. Of course, hard surfaces are necessary anyway – whether for traffic, parking, cycling, walking or play. But permeable paving also provides an inherent drainage system, addressing both flooding and pollution issues by attenuating and cleaning water runoff at source. Concrete block permeable paving can simply infiltrate to the ground where conditions allow or, more commonly, collect water for transmission to other SuDS features along the ‘management train’ or to conventional drainage and watercourses.
After more than two decades of use, it has proved to be a predictable, reliable and low-cost SuDS technique. Its capability to attenuate water flow during rainfall for gradual discharge is well known. But this principle is transformed by considering distinct storage ‘sub-catchments’ of permeable paving using straightforward devices with an orifice – accessible for observation and adjustment if needed – controlling outlet flows.
This enables water storage to be strategically deployed around a site, with the flow controls demonstrating straightforward compliance to local authorities as part of the SuDS design approval process. Dedicated water storage on valuable land and associated excavation and construction costs are avoided, and this technique can help satisfy SuDS requirements on high-density urban schemes without expensive storage structures. It is also useful for controlling flows within the pavement construction, maximising storage on sloping sites and increasing treatment times to optimise removal of pollutants.
A real strength of concrete block permeable paving is its ability to remove water-borne pollution, offering the important – and often missed – opportunity of a gradual flow of clean water for landscape and biodiversity. This capability is also central to the role of permeable paving as a source control, gradually passing clean water to open SuDS features such as swales.
Of course, paving will help to define the design and character of any development. The growing choice of concrete block permeable paving products available from Interpave manufacturers – with numerous shapes, styles, finishes and colours – allows real design freedom. At the same time, they can provide completely level, well-drained, firm and slip-resistant surfaces that are accessible to all, without the need for cross-falls, channels, gulleys or other interruptions. Rainwater ‘ponding’ is eliminated, reducing the risk of ice forming on the surface and preventing splashing from standing water.