Housing estates trial tool for SUDS analysis

Groundwork London is close to working out the true value of retrofitting sustainable urban drainage systems (SUDS) on housing estates thanks to a new purpose-made analysis tool.

Richard Knight House: Benefits of SuDS Tool is being used in unique pilot project at three London housing estates - image: Groundwork
Richard Knight House: Benefits of SuDS Tool is being used in unique pilot project at three London housing estates - image: Groundwork

The Benefits of SuDS Tool (BeST) was launched by construction research group CIRIA in 2015. It is being used in a unique pilot project across three housing estates in the London Borough of Hammersmith & Fulham to crunch the numbers on the monetary value such interventions provide, across a range of measures from reduced flooding to lowered temperatures.

The estates were chosen to showcase many climate proofing options while also providing benefits such as biodiversity, play areas and better air quality. All the features - from green roofs to basins, rain gardens and swales - have been used elsewhere but not on a housing estate in this way, said Groundwork landscape architect Mark Bentley. Residents were extensively consulted about the changes they would like to see and local people carried out the work through Groundwork's Green Teams apprenticeship scheme, which helps long-term unemployed people get into work.

Bentley said it is hoped that other local authorities and social housing providers will be able to apply similar retrofits to their own properties because widespread retrofitting of SUDS is essential to reduce London's surface water flooding. So far the measures have performed well even in heavy rain, contrasting with bad flooding in nearby streets. However, many property owners still want a full cost-benefit analysis before they will invest in SUDS retrofitting.

Funding for the pilot projects came from the EU's Life+ programme. As a condition of the £1m grant, the project's effects must be monitored, so flow meters, time-lapse and thermal imaging cameras were installed. Groundwork must also calculate aspects such as social return on investment.

While the EU funding allowed Hammersmith & Fulham to carry out the work as a pilot, "the question is how someone would finance these schemes in the future", said Bentley. "One argument is that having better information on the benefits will help, but even then green infrastructure's benefits don't all apply to the same organisation.

"We could have put a pipe or tank under the ground and that would have provided a similar benefit for managing water but it wouldn't help biodiversity, it wouldn't provide informal play areas or better access to amenity or improve the estate visually."

However, other groups such as Thames Water or the Wildlife Trust will benefit. Ideally if the BeST tool can quantify the monetary value then they will be more likely to help fund future projects.

Without the monitoring aspects the work itself is not particularly expensive. Projects are also roughly "maintenance-neutral", so where Tarmac has been replaced by gardens that require maintenance, they have been offset by turning grass areas to meadow.

Simple low-maintenance plant mixes that suit the conditions and provide colour for residents were also used. Contractors and council officers are being trained so they can replicate these measures elsewhere.

Estates Housing - landscapes climate proofed at three sites

Cyril Thatcher, Eric MacDonald and Richard Knight Houses sit on a compact, organised site with well-defined green spaces with large, flat, slightly leaky roofs and internal downpipes. A residential block and smaller bin stores now have extensive green roofs, food-growing beds are sited over permeable paving and a grass swale redirects water that used to pool on paths. A small area of car park has been removed to install an unusual storm water tree pit — a tree trench combined with a rain garden.

Queen Caroline Estate has large areas of unused green space and pitched roofs, with around half the downpipes running through private houses with gardens. Changes include de-paving to plant a garden, a grass swale ending in attenuation basin, roadside rain garden, green roofs on bin stores and a hybrid green wall. Extensive vegetable gardens that have quickly become well used and areas that were used as a dog toilet are now gardens with colour and interest. A trial with one resident to divert water through their garden and through an open channel across a public path to a swale has been successful and is set to be rolled out further.

Cheesemans Terrace, which is still to be completed, is a large but densely built housing estate with small pockets of green. The focus is on small interventions near the buildings, including raised beds and water butts on communal balconies, green roofs on porches and permeable paving combined with rain gardens.

Groundwork has created an online 360° virtual tour of the two completed sites where anyone can take a look at the interventions. To take a closer look, see www.groundwork.org.uk/lifeplus-lon.

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