Experts have warned that the overly idealistic interpretation of Sustainable Drainage Systems (SuDS) as natural above-ground drainage is holding back progress.
"It's time to get real about the principles and practice we need for surface water drainage – not just for new development, but also for much-needed improvements to the existing surface water drainage infrastructure,” said Alex Stephenson, chair of the British Water Sustainable Water Management (SuWM) Focus Group and director of Hydro International's UK Stormwater division. “This will be essential to combat flooding and tackle pollution of our rivers and watercourses.”
Mr Stephenson’s comment comes as Defra confirms a delay to plans to make SuDS compulsory for new developments and redevelopments. The new regulations, as part of the Flood and Water Management Act, will make SuDS subject to approval by new local authority SuDS Approving Bodies, who will then be responsible for adopting and maintaining the them. This is largely to avoid a repeat of 2007, when floods devastated the UK.
He continued: "Housebuilders and developers are worried about the costly loss of land required to build space-hungry, above-ground 'natural' features such as ponds, wetlands and swales. There are also questions surrounding the proper funding for local authorities to maintain SuDS effectively.
"It's not that housebuilders are anti-SuDS - many have been installing good SuDS schemes for the past 10 years or more and these issues are not new to our industry. The question is: why are they the focus of attention now?
"I believe a significant contributory factor is a tendency to interpret SuDS too rigidly as 'natural' or above-ground drainage features, and this is what threatens to hold back progress. It's time to go back to the first principles of what we are trying to achieve in sustainable surface water control, as well as treatment of pollutants from runoff, in particular from highways. The key principle of SuDS is to mimic natural drainage paths and processes, and to deal with rainwater as close as possible to where it falls – by infiltration where possible. By doing so, the unsustainable outcome of directing surface water into the over-burdened sewer network is avoided.
"Innovative technologies – many developed and well-proven by UK companies – are available to reduce the amount of space needed for surface water features. Proprietary solutions can also help to deliver predictable and repeatable maintenance schedules that local authorities can effectively cost. Technologies such as vortex flow controls, underground storage/infiltration systems and treatment devices are available to use alongside – or instead of – natural features.
"A pragmatic approach is essential if we are to realise the full potential of sustainable drainage systems. It was 2007 when devastating surface-water flooding first prompted the Pitt Review, which led to the Flood and Water Management Act. Six years later, after persistent delays and repeated calls for action by politicians on the Efra committee, it seems unbelievable that we are still waiting. Technologies are already available that can deliver a satisfactory compromise.
"It's vital that Defra gets the all-important design guidance that will accompany the legislation absolutely right. It's essential that this, and future, design guidance for SuDS takes full account of the toolbox of well-proven technologies available to support natural design features."
The proposed new legislation is applicable in England and Wales. Different regulations are already in place in Scotland, where SuDS have been compulsory since 2003.