The water industry is starting to realise that conventional surface-water management has polluted urban water courses and exacerbated flooding risk.

New legislation in the form of the Water Framework Directive (WFD) now provides greater protection to the quality of streams and rivers. And recent changes in planning policy mean that new development is protected to higher standards than ever before in terms of flooding frequency.

As a result, the conventional engineering approach no longer meets the demands of new legislation, in both investment and environmental terms.

Atkins has been involved at the forefront of sustainable urban drainage systems (SUDS) research in Scotland, where SUDS is progressing with greater momentum than is currently the case in England and Wales. The company has recently done research for Scottish Water, which examined the feasibility of retrofitting SUDS to reduce spills at combined sewer overflows (CSOs) to improve bathing-water quality.

This project was run jointly with the Scottish Environment Protection Agency and funded by the Scottish Executive. The intention was to examine whether SUDS could be retrofitted in towns and cities to reduce CSO spill, and whether SUDS was cheaper than conventional engineering.

The results are available on the Scottish Executive website, and conclude that the costs of retrofitting SUDS in the urban environment are likely to be comparable with conventional engineering in capital terms because both approaches have the same constraints on services, land, access requirements and standard building issues.

However, SUDS is more likely to offer significant savings over conventional practice in dealing with diffuse pollution, particularly agricultural runoff, where there are fewer building constraints and cheaper solutions can be implemented as a result.

Retrofitting on a site-by-site basis is also unlikely to be effective at removing enough flow to significantly reduce CSO spill. However, retrofitting in this way can be effective for other benefits, particularly the facilitation of urban regeneration and new development.

Atkins is now working with Glasgow City Council to retrofit SUDS in an area identified for redevelopment, and will have an opportunity to see how effective SUDS is in creating capacity within the sewer system to accommodate new development.

The system will redirect surface water flow from a highly constrained combined sewer system, in order to provide capacity for connection of new development, and significantly enhance the amenity within a valuable public open space.

An exciting aspect of this particular project is the desire to incorporate renewable energy into the drainage scheme to aid surface water management within the site. This is the first project of many in which Glasgow intends to use SUDS as a tool for facilitating regeneration and new development.

Regular and effective maintenance of SUDS and other drainage systems is essential. A legal process for SUDS maintenance and adoption has been a barrier to their wider implementation. Two mechanisms to overcome this barrier have been developed in Scotland, England and Wales. In Scotland, a change in legislation permits Scottish Water to adopt and maintain SUDS. In England and Wales a mechanism through planning legislation ensures an appropriate maintenance regime is put in place.

The Water Environment and Water Services (Scotland) Act, which was intended to transpose the requirements of the WFD into Scottish Law, was introduced in 2003 and came into force in 2005. This allows Scottish Water to adopt “public SUDS” which meet certain design criteria. It is likely that a connection agreement will be required and Scottish Water has the power to require payment before adopting SUDS.

This change in legislation will remove many of the uncertainties associated with SUDS in Scotland. The design and construction requirements will be set out in a new edition of Sewers for Scotland, due in Autumn 2005.

No changes in legislation have taken place in England and Wales, so a mechanism for SUDS-implementation through planning was developed by Atkins on behalf of CIRIA. This was published in 2004 as C625 Model Agreements for SUD. A summary of this work was also included in the Interim Code of Practice for SUDS, published in 2004 by the Department for Environment, Food and Rural Affairs (DEFRA), ODPM and the Welsh Assembly.

This mechanism presents a framework for ongoing maintenance, enforced through the planning process, with maintenance carried out by different organisations depending on the type of SUDS and experience of the public bodies. Model legal documents were produced, which can be adapted for use with any scheme. These include:

  • SUDS as a Planning Obligation under the Town and Country Planning Act 1990
  • A SUDS Maintenance Framework Agreement
  • A Private SUDS Agreement

Sustainable Drainage Systems (SUDS) are now being recognised as a way of dealing with quality and quantity issues as well as offering aesthetic and environmental benefits.

As more research into the performance, design, life costs and maintenance of SUDS becomes available, and an increasing number of demonstration sites is proving the efficacy of SUDS in the field, the barriers which previously prevented widespread adoption of these systems are beginning to fall.

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