London is synonymous with water. From the River Thames flowing through its city centre, to the lakes and tributary streams stretching across the suburbs.
But as the city has become more urbanised, there are fewer green spaces to absorb water when it rains. Instead of slowly being absorbed into the soil, now, when it rains, runoff is flushed rapidly into the ageing sewer network which can become overwhelmed during storms, leading to surface water flooding. Many of London’s rivers, like the Effra and Peck in south London, were also culverted – buried and hidden underground – in the early 1800s. Instead of conveying runoff during storms and providing wildlife habitats, these ‘Lost Rivers’ have been relegated to the city’s sewer system.
But building ever larger sewers is expensive and unsustainable. So, in the London Borough of Southwark, the Council is taking a Sustainable Drainage Systems (SuDS) approach to managing surface water by working with, or mimicking, natural processes to slow down and clean surface water.
Southwark Council initiated the Greener Delawyk scheme in partnership with the London Wildlife Trust and the Delawyk Crescent Residents Association to implement green infrastructure, including SuDS, at a Council-owned housing estate. Delawyk Crescent is dominated by impermeable surfaces and the existing green spaces which consisted of grass verges could do with some enhancement. By retrofitting multifunctional SuDS features and using depaving, the scheme has helped to create greener spaces for residents and wildlife to enjoy, whilst reducing flood risk locally. The scheme consisted of three main elements: a rain garden, de-paving and a mini-wildflower meadow, and permeable paving footpaths.
The benefits of SuDS go beyond managing flood risk, enhancing biodiversity, and delivering localised air quality and microclimate improvements
By installing approximately 270 m2 of new SuDS and enhanced green spaces, the scheme has delivered substantial benefits via relatively small-scale interventions. For instance, a downpipe draining a roof was diverted into the new 37 m2 rain garden bioretention system, which was planted with shrubs and flowers by residents. The rain garden provides both attenuation and water quality treatment by filtering stormwater through soils, before releasing it slowly into the sewer system.
Existing footpaths were also upgraded with permeable resin bound surfaces, whilst hardstanding areas were depaved and replaced with planting, allowing direct rainfall to infiltrate, and reducing runoff rates. This included planting a new 36 m2 wildflower meadow, a 20 m2 lawn, as well as removing hardstanding areas between existing beds and replacing with 74 m2 of new lawns with enhanced planting.
Delawyk Crescent is located in a Critical Drainage Area (CDA), where managing surface water flood risk is a priority. By providing local-scale stormwater attenuation, the Greener Delawyk scheme is helping to reduce peak flows of surface water entering the combined sewer system. At the other end of the scale are larger projects that Southwark is developing at Peckham Rye Park and Common, using green engineering in the form of earth bunds to protect local properties from flooding by holding back 15,000 m3 of surface water.
But the benefits of SuDS go beyond managing flood risk. The design focused on enhancing biodiversity and also delivers localised air quality and microclimate improvements, helping to reduce the urban heat island effect. The new multifunctional spaces have improved Delawyk Crescent for both residents and wildlife, whilst design consultations and planting events brought together local people and promoted social cohesion. The scheme was supported with a £50,000 grant from the Mayor of London’s Greener City Fund and £5,000 from Southwark Council’s Cleaner Greener Safer Fund. Considered ‘radical’ only a few years ago, SuDS are now on their way to becoming the new norm and Southwark is currently developing more of such schemes across several housing facilities in the borough.