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15 Jun 2023

Defra Report Highlights Exemplary Project

Defra’s review in January this year identified that SuDS delivery via the planning system hasn’t worked. Its recommendation, accepted by government, is to implement mandatory SuDS in England during 2024. To demonstrate the government’s ‘SuDS approach’, Defra’s report cited one particular project as an exemplar: Lamb Drove in Cambourne, Cambridgeshire, a SuDS demonstration project monitored by Royal Haskoning.

Completed in 2006, Lamb Drove is a 35 homes development on 1-hectare with a conventional layout while still delivering SuDS. It was compared with a similar, neighbouring development using piped drainage and it demonstrates various techniques to collect, clean, convey, infiltrate or store and release runoff at greenfield runoff rates (2 l/s/hectare) from developments to watercourses or sewers.

It quickly became apparent to the SuDS scheme designer, Bob Bray, that the whole site could contribute to storage using sub-catchments defined by flow controls at or near the surface. The Lamb Drove site is considered as two discrete sub-catchments, each with a micro-catchment of permeable paved roads – all managed by flow control chambers. This enables full storage within landscape features and permeable paving, while roof-water discharges directly to green space. Lamb Drove is an integrated SuDS system with predictable performance and is still operating successfully today.

The monitoring report highlights lower capital costs – saving £314 per property at the time – and lower maintenance costs, with potential for further improvements and savings. It identifies that the scheme successfully attenuates surface water flows and significantly reduces peak flows, with reductions in concentrations of pollutants and other water quality indicators, and with an increase in wildlife species and diversity.

The report also confirms that only limited manual sweeping of the permeable paving has taken place. Nonetheless, it concludes that: “The permeable pavement infiltration study specifically illustrates the robustness of the performance of this feature to limited maintenance. The infiltration capacity of the permeable pavement is able to adequately cope with the highest recorded rainfall intensity at the Study Site.”

  • A case study on this innovative scheme is also available.