EHJ July 2005, pages 18-19

Climate changes mean wetter winters in the future. Deirdre Mason looks at sustainable urban drainage systems and what Scotland is doing to prepare for the downpour

Drainage systems that save and recycle surface water run-off instead of allowing it to flood overtaxed stormwater drains should be standard issue in all new developments. Yet, a recent conference organised by the Chartered Institute of Water and Environmental Management demonstrated that legislation is still not up to the job of making it simple for planning authorities to authorise sustainable urban drainage systems (SUDS). Ambitious development plans become caught in a tangle of standards - who is to adopt the new drainage systems, who is to be responsible for long-term repair and maintenance, and who pays for this upkeep.

It is not as if we have decades in which to sort these obstacles out. Meteorologist Dr Jean Palutikof, from the Hadley Centre for Climate Prediction and Research, says that even if one took the middle range of possible climate-change scenarios, by 2080, the UK is generally going to have wetter winters, with 20 per cent more rainfall and with an increased number of days when rainfall is especially heavy. Scotland and Northern Ireland are likely to suffer greater numbers of heavy rainfall days than England.

However, the UK is also going to have drier summers - 40 per cent less rain is likely, especially in the south. Allowing clean run-off to enter a sewerage system that either loses it to sea or mixes it with foul effluents that need expensive cleaning treatment makes less sense with each passing decade.

The technical hurdles have been the easiest to clear. SUDS is not one single system but rather a series of linked ideas. They range from simple open drainage ponds that allow water to soak away and collect there naturally, to complex porous paving systems that filter and clean rainwater, and either allow the clean rainwater to drain into the ground or divert it to a holding tank where it can be used for watering plants, for example.

"SUDS is a way of thinking, not any one particular system," says Phil Chatfield, an Environment Agency engineer who chairs the National SUDS Working Group. It also benefits from a strategic approach, he stressed.

Scotland, aware of its worsening weather, is ahead of the rest of the UK on implementing SUDS. Edinburgh University's Institute for Infrastructure and Environment has been working with Glasgow CC on innovative drainage systems for 79 sites in the city. Some are new developments. Others are existing sites that need to be retrofitted.

Dr Miklas Scholz, who heads the project, said: "A site being considered for a SUDS project needs sufficient run-off and then to be next to something that can take the run-off."

What is underway at the Glasgow sites is generally combinations of swales (grassed depressions that lead surface water overland from the drained surface to a storage or discharge system) or infiltration trenches with ponds or underground storage tanks.

Glasgow, however, has a problem: "Most of Glasgow is contaminated with heavy metals, such as lead," says Dr Scholz. The University set up an experimental wetland treatment site in its own grounds, treating nickel and copper-contaminated effluent from the gully pots that form part of road drainage systems. The results showed that the system could work, but it also demonstrated the problems that road gritting and salting could have for a wetlands drainage system. These additives destroy the natural microbiological process within the wetlands system that would normally trap and contain heavy metals.

What the conference made clear is the degree to which legislation has not caught up with the need for more sustainable drainage systems. In England, Telford & Wrekin BC's planners, engineers and building control officers have been trying to ensure that SUDS are installed in new developments. Engineering manager Graham Fairhurst said: "My experience is that by and large, developers are 'up for' SUDS and willing to design and produce good SUDS. However, they then find themselves trying to nail jelly to the wall over getting SUDS schemes adopted."

Others agreed: the enthusiasm and innovation is there, but the clarification of long-term responsibilities is missing. Section 106 of the Water Industry Act 1991, which allows an unrestricted right of connection, is also a problem. Simon Walster from OFWAT said: "If SUDS drainage is installed in a (private) development and no surface water sewer is provided, there could be problems in the future. Currently, a sewerage undertaker has no right to discharge surface water into private watercourses. Statutory undertakers' rights to lay pipes under notice should include the right to discharge."

Scotland has had a relatively good take-up of SUDS since the mid-1990s and has benefited from having its own assembly, which has pushed through much-needed reforms to legislation.

Francis Brewis, from the Scottish Executive's Environmental and Rural Affairs Department, explained how the Water Environment and Water Services (Scotland) Act 2003 provides a basis for vesting SUDS schemes in Scottish Water, provided that design and construction standards are met. This, he said, should make good-quality SUDS a normal feature of housing developments. "The controlled activities regulations to be made in 2005 require SUDS for surface water outfalls," he says. "Despite some reluctance, SUDS in Scotland are becoming part of routine practice."

England and Wales recognise the need for SUDS systems, and the government's consultation paper issued in 2004, Making space for water, generated an enthusiastic response. David Richardson, deputy chief engineer at Defra's flood management division, told delegates that the present review of research and identifying pilot sites will be completed this year, and that lead authorities for pilot studies will be brought in during 2006. The pilot schemes will be completed, and guidance issued, by the spring of 2008.

Crucial planning guidance document, PPG 23, is already under revision, with a new version containing an appendix covering SUDS. Also being revised is PPG 25, covering development and flood prevention, and the building regulations.

"We are aware of the barriers to implementation such as adoption and maintenance, and the potential some legislation has for constraint and disincentives", Mr Richardson told delegates. "We are taking action to resolve these issues."