SUDS drainage systems mimic mother nature by slowing down rainwater flow.

To the untrained eye, thE picture above might look like a bit of boggy ground in need of decent drainage. But it isn’t. It’s part of a SUDS (Sustainable (Urban) Drainage System) designed by Robert Bray Associates for Matchborough First School in Redditch.

SUDS works by trying to mimic nature, slowing down the flow of rainwater from roofs and hard surfaces, rather than channelling it all into pipes and water courses as quickly as possible. This puts less strain on the sewage system, and therefore less chance of flooding, and in some cases creates habitats for wildlife and an amenity for locals. The ponds and channels at Matchborough provide a learning opportunity for the children.

More and more local authority planners are latching onto it because it ticks their sustainability boxes. Matchborough First School’s system is a ‘pure’ version of SUDS, matching nature as closely as possible. But permeable paving or an underground storage device (such as AquaCell, as featured on page 27) with a mechanism to slow outflow are also classed as SUDS.

As Pete Sykes, MD of MPSL points out, ‘man-made’ solutions too can make a huge difference to the environment. And of course not all sites will be on permeable ground. A standard outfall would produce a flow of 120-130 litres per second during the sort of storm that happens once every 30 years, and there could be many outfalls into a river. By using a concrete storage pipe with a hydrobreak you can reduce that amount to an easier-to-handle six litres per second.

The Environment Agency and the Scottish Environment Protection Agency are keen to encourage the use of SUDS. The guidance PPG25: development and flood risk specifically recommends SUDS be considered. But it isn’t compulsory, so developers struggle to get the systems adopted. So while the council’s planning department may encourage it, the maintenance department won’t take it on. And the water companies won’t touch them with a barge pole.

One of the big problems is that some duff systems have been built, says Bob Bray of Robert Bray Associates who has been a SUDS enthusiast since 1996.

“You have to take a bit of time to work out how to do it properly. It’s labour intensive. It’s environmental engineering.”

Some local authorities are supportive, however, and with flooding on the rise, SUDS could be compulsory within 10 years.

Persimmon proves perfect for Pure SUDS

Pete Sykes is excited. The MD of MPSL Civil Engineering invested around £5,000 in SUDS software three years ago and he’s only just getting to use it now.

The job is a 300-dwelling development for Persimmon Homes in Newcastle-under-Lyme. The 30-acre site next to marshland and criss-crossed by brooks is ideal for a full SUDS solution. For smaller developments, there’s seldom enough land to construct ponds or swales (long shallow channels).
For the Persimmon site, water will be carried from roofs and roads by conventional concrete pipes. This is necessary if the water company is to adopt them.

Persimmon will construct two balancing ponds of around 50m to 80m diameter within the marsh area. Various plants and micro-organisms will be introduced to purify the water before it drains slowly back into the ground. The local authority will take on the maintenance.

It’s important when designing ponds to make them safe, says Sykes. So the sides will be gently sloping to reduce the danger to local children. The scheme is still going through planning, but is due to start on site in January.

Suffolk’s simple SUDS

Suffolk County Council wanted something sustainable and cost effective for its park-and-ride scheme at Martlesham. The solution was 14,000 sq m of Marshalls’ permeable block paving Priora.

The blocks have gaps in their interlocking joints that allow surface water to pass through. Marshalls carried out tests on contractor Breheny’s proposed sub-base to check the blocks remained fully permeable after heavy traffic. The aggregate contains hydrocarbons to absorb
contamination and spillages before the water reaches the water courses.
Enquiry number 205

Source

Construction Manager

Postscript

For more information and guides visit see www.ciria.org.uk/suds