GROUNDWORKS & DRAINAGE 49 Absorb the ‘sponge city’ theory


With recent flooding reminding everyone of the results of climate change and sealing up urban areas, Chris Hodson from trade body MPA Precast (Interpave) explains how taking collective responsibility for the issue is leading to a new ‘sponge city’ concept


Permeable paving and swales helping maintain street trees as part of the Lamb Drove SuDS scheme in Cambridgeshire Photo: Chris Hodson


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e all need to become involved with the flood resilience of our communities, and consider the wider implications of our designs within rainwater catchment areas, as highlighted by the recent flooding across the UK. A change of approach is needed. By moving towards a ‘sponge city’ paradigm, we can reverse the addition of impermeable surfaces due to urbanisation. With examples internationally, sponge cities essentially soak up rainwater and retain excess stormwater, then filter and release the water gradually – much like a sponge. This approach is recognised in government proposals for mandatory sustainable drainage systems (SuDS) on developments in England, action on surface water flooding from existing impermeable surfaces, and enforcement of planning permitted


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development rules for ‘unplanned paving.’ SuDS are nature-based, and manage surface water by attenuation and filtration with the aim of replicating, as closely as possible, greenfield (pre-development) conditions with natural losses and reduced discharge rates. As well as reducing flooding, they must also improve water quality and provide amenity and biodiversity through multifunctionality. SuDS are based on a design philosophy, using a range of techniques in a sequence known as a ‘management train.’


Mandatory SuDS Although the 2010 ‘Flood and Water Management Act’ included provisions for mandatory SuDS on developments, these provisions were not implemented at the time in England under Schedule 3 of the Act – although they were in Wales – relying


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We should now see a growing application of permeable surfaces, reversing the sealing-up of urban areas


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