SuDS: Go For Green!

Sustainable Drainage Systems (SuDS) are not a new concept but with environmental issues intensifying in our urban areas should we be doing more to integrate ‘Green’ SuDS into our developments?

Historically drainage networks were built to direct rainfall away as quickly as possible in piped conduits and engineered channels.  This drainage strategy achieved its designed function, however it also inadvertently aggravated urban flooding.  As more and more surfaces are converted to impervious materials the drainage networks and rivers are not able to cope; the drains surcharge and the waterways burst their banks, all at a huge economic cost. For example in the UK between the winters of 2015 and 2016 economic damages from floods were estimated to be between £1.3 and £1.9 billion.  Unfortunately climate change is exacerbating the issue.  A recent Met Office report has shown that extreme winter rainfall in the UK is now seven times more likely.

The National Planning Policy Framework (NPPF) states ‘priority should be given to sustainable drainage’ and discusses the impact of new developments on flood risk.  It is then up to the local planning authorities to prepare local plans that produce policies addressing flood risk, whilst keeping climate change in consideration.

Often to expedite a development through planning the bare minimum is done for the drainage strategy.  Many schemes opt for an underground attenuation tank which captures surface water runoff and outfalls to the surrounding drainage network at a controlled rate.  The tank capacity is easily quantifiable and because its underground it is seen as an efficient use of space.  Therefore the attenuation tank is a convenient way to satisfy the target surface water run off rate set by the local authority, but what does this accomplish apart from addressing flood mitigation?

Why not ‘put the water in the landscape’ and reap the environmental and social benefits?  Rainfall can be directed via planting for natural irrigation or captured to form detention ponds; this can enrich biodiversity, create beautiful amenity spaces, filter out water pollutants, reduce the urban heat island effect, improve air quality AND achieve flood mitigation!

SuDS can even be designed to integrate dynamic play features into the landscape.  For example, stepping stones in swales entice children to ‘play on the way’.  Alternatively rainfall captured on roof tops can create playful water features at ground level by using the water head pressure for power.  If attenuation tanks must be used, then aim to direct the surface water through planters first and then recycle the captured water for irrigation or a grey water system.  Water is becoming more scarce due to climate change, the growing population and urbanisation – so lets treat it is as the valuable resource that it is!

One concern for specifying these ambitious SuDS features could be management costs.  For instance is managing raingarden planting more expensive than the maintenance of conventional drainage systems?  Professor Nigel Dunnett from Sheffield University posted on Instagram that the ‘Grey To Green’ scheme (a raingarden retrofit in Sheffield city centre) has reportedly cost less to manage than the previous maintenance of the road surfaces, drains and highway infrastructure it replaced.  The ‘Grey To Green’ scheme is proof that ‘Green’ SuDS can be environmentally and socially beneficial and also cost effective!

Here at Outerspace we are in the construction stage of an exciting high density residential project that incorporates a series of raingardens, green roofs and a naturalistic swale channel terminating to a wildlife detention pond.  The ‘Green’ SuDS features play a key role in our landscape strategy and maximises both the amenity and biodiversity value of the scheme; achieving one of our core principles – promoting ‘Human Nature’.  Keep an eye on our website and social media for updates!

By Alex Lowenhoff (Assistant Landscape Architect)