GROUNDWORKS & DRAINAGE 47 Placemaking for fl ood resilience
To avoid surface water fl ooding, holistic urban design include the ‘sponge city’ concept should include sustainable drainage from the very start, explains Chris Hodson, consultant to trade body MPA Precast Paving.
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n projects across the world, the ‘sponge city’ concept is gaining traction amongst policymakers, masterplanners,
architects, landscape architects and others. It recognises the growing risk of fl ooding with climate change and the need for nature-based rainfall management solutions, in place of the previous sealing- up of urban areas. The UK Rivers Trust offers a useful summary of this concept: ‘A Sponge City is designed to mimic natural processes, allowing urban areas to absorb, store, and purify rainwater, much like a sponge soaks up water. Sponge Cities can effectively reduce the risk of fl ooding while simultaneously enhancing the quality of urban life.’
A Sponge City future The term ‘sponge city’ was coined by landscape architect Kongjian Yu, a professor at Peking University, for his concept of using a range of nature-based techniques inspired by traditional landscape management. He says: ‘The sponge city concept adapts these ancient principles into urban planning, by incorporating permeable surfaces, green spaces, and constructed wetlands.’ Sponge cities were accepted in China as a nationwide urban construction policy in 2014 applying to new build, expanded and rebuilt buildings and communities, roads and squares, parks, green spaces and urban water systems. Some 30 cities in China are already implementing this policy.
While the concept takes a city-wide, ‘catchment-based’ approach, sponge city techniques can be applied at any scale. These techniques are used in various countries and known as: ‘green/blue infrastructure’, ‘water-sensitive urban design,’ ‘best management practice’ (BMP) or ‘low-impact development.’ In the UK, ‘sustainable drainage systems’ (SuDS) have been in use with similar aims since the mid- 1990s, albeit with slow uptake and ongoing
ADF FEBRUARY 2025
delayed government implementation. The principles and techniques involved are all fundamentally the same, with some differences in scale of application and responses to local weather or ground conditions. In essence, they make extensive use of green infrastructure – but permeable paving plays an essential role as well. As the Rivers Trust says: ‘One of the key components of a Sponge City is permeable pavements... these surfaces allow rainwater to infi ltrate the ground, reducing surface runoff and replenishing groundwater. These pavements not only reduce the risk of fl ooding but also mitigate the heat island effect, making urban areas more comfortable during hot weather. Other benefi ts include eliminating ‘ponding,’ reducing the risk of ice forming on the surface and no rain splashing from standing water.’
Masterplanning with water In the UK – as the name suggests – sustainable drainage systems began by focusing on drainage techniques to reduce fl ooding and pollution (‘quantity’ and ‘quality’), with a growing appreciation of their other multifunctional benefi ts (‘amenity’ and ‘biodiversity’, completing the four pillars of SuDS). Today, SuDS are often designed by drainage engineers and effectively grafted onto previously designed layouts. At this late design stage, the multiple potential benefi ts of SuDS techniques like permeable paving are easily missed. However, with the sponge city approach water is a fundamental consideration as part of holistic master- planning – from the very start. Now is the time for architects to take a lead with sponge cities and fully integrate SuDS techniques, such as permeable paving, within the design process to optimise their multifunctional benefi ts. Of course, safe and attractive hard surfaces are needed in any development and
Concrete block permeable paving overlay on an existing road base conveys water to tree-planted basins © Robert Bray Associates
Retrofi t SuDS include permeable paving to collect runoff from existing streets, then providing a gradual source of clean water to rain gardens and existing trees © Chris Hodson
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