Designing integrated SUDS

Local authorities should ensure that the design of SUDS form an integral part of neighbourhood and site planning.

Lakeland in Florida has been designed around an extensive SUDS. Photo by Robert Bray

Following the Pitt review the government have announced that local authorities should be responsible for adopting and maintaining new and redeveloped sustainable drainage systems on highways and the public realm, so as to increase their uptake and effectiveness.

This should be undertaken in a collaborative manner, with input from planners, urban designers, landscape architects, water engineers, ecologists and environmental scientists.

Local surface water management should be planned as part of the wider city and sub-regional network through the creation of drainage features that prevent the local network being swamped. At the neighbourhood scale these SUDS features can form part of a local network to facilitate a more natural response to weather events:

• French drains - features to catch surface water and allow filtration into groundwater - a linear trench filled with a permeable material often with a perforated pipe in the trench’s base to assist drainage
• swales - shallow vegetated channels designed to conduct and retain water. Can be considered for directing water over ground as an alternative to piped drainage.
• detention basins or ponds –vegetated depressions that are normally dry except following storm events constructed to store water temporarily to attenuate flows. May allow infiltration of water to the ground. A wet detention pond always contains water and attenuates flows by storing run-off during the peak flow and releasing at a controlled rate during and after the storm.
• retention basins or ponds –basins or ponds where run-off is detained for a sufficient time to allow settlement and possibly biological treatment of some pollutants
• below ground storage – enables retention of water for irrigation of green infrastructure.

Detailed guidance on the incorporation of these features in schemes can be found at the CIRIA website. Documents such as the advice paper Sustainable drainage systems and the SUDS Manual can be downloaded through the free to join members’ area.

The CIRIA SUDS Manual highlights that the variety of components and design options available allows designers and planners to consider locally responsive schemes taking account of land use, land take, future management scenarios, and the needs of local people.

Local planning guidance documents should consider the inclusion of design guidance and SUDs principles as required for neighbourhood and site scale developments.

At Upton, Northampton SUDS was fully incorporated in the design of the new neighbourhood to provide protection from flooding and quality green infrastructure

At a site scale, it is important to produce a management strategy including objectives and costs to ensure effective management of SUDS features. Redevelopment or retrofit solutions should reduce the volume, rate and frequency that water enters the combined sewer if no other route is available, the storm sewer and wherever possible open watercourses.

At the site scale it is important to integrate SUDS into both the design and long term management of development schemes. All new development and redevelopment should have fully accredited SUDS schemes with ‘source control’ to ensure flow, volume and frequency of runoff is equivalent to ‘greenfield’ conditions. These conditions are set out in the CIRIA SUDS manual and stipulate either that each development site should deal with its own run-off to ‘greenfield’ rates or:

• a site may elect to negotiate with local authorities to manage pre-treated runoff volumes in public open space.
• a clear responsibility for surface water management – particular storage features, source control and convergence mechanisms should rest with land owners to the boundary of their property.
• rain harvesting of clean run-off should be balanced with the need to recharge aquifers, base flows to watercourses and ground water.

Hopwood Park motorway service area was developed with a strong SUDS system as the basis for the scheme design and provides a good working example of such techniques.

Sustainable urban drainage channel, integrated into Manor Field District Park. Copyright Ian Stanyon, Sheffield City Council.

Manor fields park, Sheffield

Sheffield City Council led a masterplan for Manor Fields Park that was heavily influenced by sustainable water management objectives. The 25 hectare site had significant constraints to development, not least in being designated as a district park but also being of poor environmental quality with an associated stigma. The delivery programme was incremental, with slow manageable improvement at low cost.

Early on it was clear that a conventional water management system was proving too expensive because of the site’s topography. Drainage then became an abnormal of the development and was therefore financed through a reduction in payment for land. This decision freed up the partnership to consider a full SUDS scheme for the site which used the existing landscape and character as a basis for design.

The local authority adopted the scheme using a commuted sum. Delivery was eased through the design of a simple robust system that formed part of the overall landscape management requirements and this has proved to be of minimal liability.

Read more about Manor fields park, Sheffield.

Priority: manage surface water and flood risk
Tags: green infrastructure, public space, water, neighbourhoods