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Building Products October 2017

BRICKS, BLOCKS AND PAVING multifunctional SuDS technique. Of course, hard surfaces are necessary for developments anyway – whether for roads, parking, shared spaces or play. But permeable paving also provides an inherent drainage system that requires no additional land take for water storage, treatment or conveyance. It also addresses both flooding and pollution issues by storing and cleaning water runoff at source. This technology eliminates pipework, gulleys and manholes, and should therefore cost less than conventional drainage and paving. In fact, concrete block permeable paving can also accept runoff from other impermeable paving and roofs, giving further savings. It can simply infiltrate rainwater falling on it straight into permeable ground, after removing pollutants. But, more commonly in the UK, less permeable conditions – such as clay – will limit infiltration and on brownfield sites existing pollutants may preclude infiltration. Here, permeable paving is used to collect and store water on site during storms, before gradual discharge to other SuDS features along the ‘management train’, surface water or combined sewers, or watercourses. This attenuation and delayed discharge from the permeable paving avoids drains surcharging and downstream flooding. Where a comprehensive SuDS scheme is planned incorporating landscape features, concrete block permeable paving removes water-borne pollution and provides a gradual flow of clean 60 BUILDING PRODUCTS | OCTOBER 2017 water at the head of the ‘management train’. Water in open SuDS features on the surface can then be used to enhance landscape design and biodiversity. Following some 25 years use in the UK and abroad, concrete block permeable paving 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 optimised for greater cost efficiency by considering distinct storage ‘compartments’ of permeable paving using straightforward flow control devices with an orifice – accurately sized and accessible for observation or adjustment if needed – on the outlet. This technique enables water storage to be strategically deployed around a development within permeable paving compartments, each with a flow control demonstrating compliance to local authorities as part of the SuDS design approval process. It maximises the potential for water to be stored on site beneath paving that is needed anyway. 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. Similar techniques maximise storage in permeable paving on sloping sites, using terraces of compartments separated by simple check dams incorporating flow controls. And flow controls can <<< Continued from page 59 be used to retain water and make the most of available infiltration, so reducing discharge. And concrete block permeable paving is being used in other innovative ways too. For example, retrofit overlay systems can be applied on existing road bases allowing treated, attenuated water to simply discharge sideways into adjacent rain-gardens or other SuDS, providing sustenance for planting. 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, paved surfaces help to define the character of any development. The growing choice of concrete block permeable paving products available from manufacturers – with numerous shapes, styles, finishes and colours – allows real design freedom. At the same time, permeable paving can provide a completely level, well-drained, firm and slipresistance surface 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. Chris Hodson is a consultant with Interpave


Building Products October 2017
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