LANDSCAPING & EXTERNAL WORKS 67 The growing demand for SuDs
With UK weather seemingly wetter than ever and flooding causing problems across the country, demand for sustainable drainage systems has never been higher. Hannah Hyslop of Cemex discusses the role of permeable paving
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ncreased urbanisation and construction, such as impermeable roads, driveways, car parks and pedestrian schemes, has resulted in a greater likelihood of surface water flooding. This urbanisation, combined with the fact that weather data shows there has been a 50% rise in the number of three consecutive day storm occurrences since the 1960s, means continuing growth in the volume of surface water run-off, which we must now handle effectively.
Of the 57,000 homes affected in the 2007 summer floods, Government figures demonstrated that over two thirds were the result of surface water run-off, not swollen rivers. Another severe flooding event in 2015/16 changed the landscape of planning applications with many new schemes being required to include a full, compliant sustainable drainage system (SuDS) as part of the standard detail.
In light of these flooding events, the UK Government introduced a requirement for SuDS on developments in England, which is implemented through the planning system. Its expectation is ‘that Sustainable Drainage Systems will be provided in new developments wherever this is appropriate.’ The measures are applied by local planning authorities on major developments of 10 or more dwellings and equivalent non-residential or mixed sites, however, smaller developments may also incorporate SuDS installations. SuDS are designed to reduce the likelihood of flooding due to surface water run-off.
As part of our work with architects, one of the main questions we deal with is a request to explain the different types of SuDS that are available. There are many different SuDS techniques, including retention ponds, green rooftops, and pervious pavements, however it is pervious pavements that suppliers such as ourselves offer to architects, and construction projects, and which we focus on in our RIBA certified CPD online training.
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Pervious pavements provide two functions; to effectively capture the maximum theoretical rainfall and flooding event (known as a design storm event) and discharge it in a controlled manner to the subgrade or drainage system; and to provide sufficient structural resistance to withstand the loadings imposed by vehicles travelling on the surface. Pervious pavements do this by providing a hardened surface suitable for pedestrian and/or vehicular traffic, while also allowing rainwater to infiltrate through the surface and into underlying structural layers. Cemex’s Permaflow is a pervious concrete mixture that works perfectly for SuDs, and is carefully designed to have a network of interconnecting voids which allow the movement of water, providing the optimal solution for surface and stormwater management.
Once it has reached the underlying structural layers, rainwater can be processed in three different ways. It can be temporarily stored beneath the overlying surface before alternative use, such as flushing toilets. This is usually achieved with the use of a geo-cellular system in conjunction with a rainwater harvesting
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Of the 57,000 homes affected in the 2007 summer floods, over two- thirds were the result of surface water run-off, not swollen rivers
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