Sustainable urban drainage systems (SUDS) seek to reduce surface water run-off and improve urban water quality by mimicking natural processes such as infiltration and attenuation through vegetation and wetlands.
Use of these systems has been promoted in national and local planning policy, and guidance on their design has been available for several years. Implementation of these techniques has been much lower than expected, however, and they are far from being accepted as standard practice in designing surface water drainage systems.
The Environmental Industries Commission’s (EIC) Water Pollution Control Working Group has recently investigated why this is so, and what needs to be done to remedy the position.
The EIC group found the main problems revolved around administrative and institutional issues rather than technical ones. In particular, the issue of adoption, by which a drainage authority agrees to accept a new system and maintain it as part of the surface water drainage network, forms a real barrier to the widespread use of SUDS.
In a more traditional, piped, drainage system, the water industry uses established guidelines, Sewers for Adoption, to state the design and performance levels required for a system to be acceptable for adoption. If a developer constructs a piped system – which may include storage – to these standards, and the system has an outlet, then adoption is likely.
The adopting authority, usually a water company or local authority, knows how the system is likely to behave and how much maintenance it will require. If the adopting authority is a water company, it can add a piped system to its asset base which is used by Ofwat in assessing its overall charges.
SUDS present a rather different aspect. The whole point of a SUDS system is often to encourage infiltration, to the extent that it may not actually have an outlet. It could include landscaped features, such as swales and ponds which require maintenance of vegetation – something quite alien to the more engineering-based maintenance programmes of adopting authorities.
So, while Sewers for Adoption does mention SUDS, the design standards and maintenance regimes are far less quantified than those for piped systems, and adoption is therefore much less prevalent.
Although the EIC found that adoption is the main problem, several other factors contributed to the take-up of SUDS systems despite the work that has been undertaken to promote their use. It made a number of recommendations to overcome these problems, focused on removing the obstacles and promoting the use of SUDS as standard practice:
- SUDS should be the default option on all new developments (i.e. where SUDS are not proposed there should be a requirement to prove that they cannot be implemented). This should be reflected in building regulations
- SUDS should not be dealt with any differently from pipe-only drainage systems, and therefore the appropriate adopting authority should be the same as for pipe-only drainage systems
- SUDs should normally be a planning requirement on all new developments. This should be reflected in planning guidance. The consultative role of sewerage undertakers should be reviewed in light of this
- The right to connect surface water drainage to a public sewerage system, as established in Section 106 of the Water Industry Act, should be repealed. The statutory obligation of a sewerage undertaker to effectually drain surface water from new developments should be reviewed in the light of this
- Sewers for Adoption should be reviewed to include all SUDS techniques and aligned with CIRIA advice and guidance so that sewerage undertakers have confidence that SUDS have been designed and installed to best practice standards. The title should be changed to reflect the extended scope
- The definition of a sewer should be extended to cover all SUDS. This may require legislation to effect
- A consequence of (7) and (8) is that Ofwat should recognise adopted SUDS as part of Water Company Assets.
- The housing density requirement of PPG3 should be reviewed to ensure that there is no incompatibility with the need to accommodate SUDS and/or surface pathways/storage to effectively manage extreme events, especially in areas of high risk
The EIC concluded that implementation of SUDS should not depend on the organisational structure of drainage responsibilities, and that no change to the current structure is required provided the above steps were taken.
Members of the EIC Water Pollution Control Working Group discussed the paper with officials at Defra, and the paper was forwarded to the minister for the environment, Phil Woolas, in February 2008.
Production of the paper was timely, coming as it did during a period of review of current arrangements for surface water drainage after the floods of last summer, and immediately before the publication of the government’s new water strategy.
It has received a warm response from the minister, who accepted that adoption is the key issue, and invited the EIC Water Pollution Control Working Group to assist in the implementation of the strategy through the consultation process.
There is a general view, shared by Defra and much of the water industry, that we must improve the way surface drainage is designed so that flood run-off is reduced and urban water quality improved. The drive to increase housing provision with urban extensions and eco-towns, while adapting to increasing rainfall intensity as a result of climate change, emphasises the need to urgently address this issue.
The EIC Water Pollution Control Working Group intends push hard for measures that will lead to the take up of SUDS, and thus promote implementation of them in future urban development.