Background information

Progressive urban development has resulted in rapid increases in run-off to watercourses following storm events. Because rainfall can travel quickly to the watercourse via impermeable surfaces there is very little natural infiltration or retention to reduce levels of pollutants such as silt, organic matter and petrol/oil derivatives.

In recent years there has been a rising rate of flooding incidents, some on a very large scale.  The reasons for these are complex and inter-related, but they include:

• An increase in occurrences of very heavy rainfall over short periods; this may be a side effect of global warming;

• Raised water tables arising from higher rainfall;

• Increases in the speed at which rainfall finds its way into rivers and streams.  This can be caused by large new developments (including roads) which have surfaces which do not absorb water, or changes to agricultural practice which reduce water retention at times of heavy rainfall;

• New development in areas which should be reserved for flood management;

• Alterations to drainage patterns and systems (whether designed or accidental) which reduce capacity to handle peak flows;

• poor maintenance of surface water drains.

What are SUDS?

Sustainable drainage systems (known as SUDS) offer an alternative approach to traditional drainage.  SUDS employ a whole suite of techniques to effectively manage drainage at source including dry ditches (swales), detention/attenuation ponds, and integrated constructed wetlands, all of which aim to detain run-off and release it slowly into watercourses or to ground.  Source control techniques are also increasingly popular - such as the use of porous (as opposed to impermeable) paving and 'green roofs' which allow rainwater re-use.

These techniques reduce the likelihood of flash flooding and result in greatly improved water quality.  SUDS schemes are often cheaper and easier to maintain than traditional engineered drainage solutions involving gully pots and petrol interceptors.  In larger SUDS systems such as wetlands added value is provided by improved wildlife habitat and recreational potential.

The use of SUDS to reduce levels of diffuse pollution and flooding is common in Europe and North America, and is rapidly becoming more widespread in the UK as local authorities see the benefits to water quality and flood management.  Scotland has been particularly active in this area for some years, and the EA works with SEPA (the Scottish Environment Protection Agency) and the Environment and Heritage Service in Northern Ireland to develop guidance and encourage their use.  The EA drive the use of SUDS in the UK.

Working closely with the EA, the Partnership is implementing SUDS at various sites in the catchment area, and will promote the concept to local developers, monitoring the results over a period of time.   

SUDS in the Bourne Valley

Bournemouth Pier bathing beach has failed to comply with the Bathing Water Directive Guideline standards in 10 out of the last 12 years, despite significant investment in reducing point source inputs. The main reason for this non-compliance is the Bourne stream, which discharges close to the bathing beach.

The Bourne Stream was identified as offering an ideal opportunity to focus research on SUDS and a range of related issues; the Environment Agency has played a key role through it Research & Development (R&D) programme with the aim of improving water quality in the stream and at the bathing beach at Bournemouth Pier.

The lagoons and wetlands project at Alderney were established to install in-stream SUDS in the catchment.

Created by Borough of Poole, with a financial contribution from English Nature, they have been successful at improving water quality and demonstrating the environmental benefits of SUDS techniques to the local community.

Since then further projects at Coy Pond Gardens and Bourne Valley Park have utilised external funding to improve water quality & amenity value in other areas.

We have also been busy talking about them:

• In March 2002 the Partnership, led by the Environment Agency, initiated a SUDS workshop for Poole and Bournemouth local authority planners and other delegates.  Both LAs have since issued a supplementary planning guidance (SPG) to advise developers and builders on the use of SUDS.

• The Bourne Stream SUDS were described in an article in the CIRIA Sustainable Drainage newsletter (Issue 4, July 2003) written by Neil Smith of the Environment Agency.

• In April 2005 the Partnership hosted a SUDSnet group visit to the Bourne Valley when delegates had a chance to see and hear at first hand about our SUDS design and performance.  See also SUDSnet News (Issue 2, June 2005, pdf) and CIRIA Sustainable Drainage News (Issue 8, August 2005)

Students from Bournemouth University utilise the Bourne Valley SUDS for research purposes; we publish their papers here.

SPG for Developers

Sustainable Drainage Systems (SUDS) June 2002

Borough of Poole Supplementary Planning Guidance (SPG) document

• An electronic version (pdf) is available from Borough of Poole website

• A hard copy of the document is available from:

Borough of Poole

Strategic Planning Services

Civic Centre

Poole BH12 2BH

Email: strategic.planning@poole.gov.uk

Tel: 01202 633360

SUDS and the Law

Two papers from Coventry University consider SUDS from the point of view of habitat quality and public safety:

• Newman A.P., Whitehouse D. and Smith S.J. (c. 2001) Wildlife Protection Law as a Barrier to Sustainable Drainage Wetlands and Pools in the UK and Elsewhere: A Proposal for Legislative Change (pdf, 91kb)

• Chaplin N. (2003) Personal Injury Litigation as a Barrier to the Adoption of Sustainable Drainage Ponds - A Proposal for Legislative Reform

Further information