Queen Caroline Estate, London

142m2 of extensive biodiverse green roofs have been installed on bin stores and pram sheds (Figure 2). These buildings have flat or shallow-domed concrete slab roofs and drain via downpipes to the adjacent paving. A new waterproofing liner was applied to the concrete roofs and a pebble filled gabion edge used to create a retaining structure for the green roof substrate. The roofs were planted with wildflower seeds and plugs.

Rain gardens have been installed within paved areas and alongside estate roads to drain the adjacent hard-standing and, in one case, a section of the roof of an adjacent building. The rain gardens were filled with an engineered rain garden soil and planted with a mix of shrubs and perennials. Each rain garden has a vertical entry overflow which connects via a flow control chamber back to the sewer. The weir in the flow control chamber is set to the design storm water limit. If the water level exceeds this limit, water will overtop the weir in the flow control chamber and be released back to the sewer un-impeded.

Queen Caroline Estate has an open structure with fairly large areas of open space between the residential blocks. Many of the residential blocks have pitched roofs that drain to external downpipes. This combination opened the possibility of introducing vegetated channels, swales (Figure 3), rain gardens and small-medium sized basins to manage run-off from roofs and paving. The majority of components are connected via flow control chambers to the sewer, with the exception being the segmented swale at Alexandra House which, if required, overflows to a soakaway. The main features adjacent to Beatrice, Margaret, Adella, Phillippa and Alexandra Houses have the capacity to manage a 1 in 100 year storm event. The overflows comprise horizontal entry pipes set 75-100mm off the base of the feature. The flow control chambers are of a slide-up weir design with a 20mm orifice protected by a debris screen. The weir in the flow control chamber is set to the design water limit, which is typically 300-350mm off the base of the feature.

In soft landscape areas runoff has been diverted from downpipes via pebble or vegetated channels to shallow basins/rain gardens planted with wildflower turf (Figure 4). In paved areas, “stony” basins have been introduced which combine an outer skirt of permeable resin bound aggregate and planting beds, with a central area of loose aggregate and planting at their base. The use of stony basins reflects the Council’s requirement to minimise increases in soft landscape to avoid significant changes to maintenance. The basins are approximately 30% soft landscape and 70% hard landscape. Their design was developed through consultation with residents, who were concerned that larger loose aggregate might be picked up and thrown as a weapon, and with maintenance contractors, who were concerned that loose aggregate near path edges might be easily transferred to grass areas where it would interfere with grass cutting. The basins and adjacent landscaping include informal play features, including bridges, mounds, stepping logs, balance beams and boulders.

Prior to the works the estate had several large unused paved areas, which were originally installed as drying areas. These have been replaced with permeable hard landscape, comprising stoney basins (described above) permeable paving, composite decking and schotterrasen (Austrian gravel lawn).  

A vertical rain garden is proposed for the end façade of Mary House, which will combine sections of plug-planted green wall with climbing plants. Both will be irrigated from water collected from the roof of Mary House. One of the existing downpipes will be diverted into a series of narrow stacked tanks which will drip-irrigate the plug planted section of the wall. The overflows from the tanks and the plug planted section of the wall will feed into a raised planter at the base of the wall which will be planted with climbing plants. Any remaining overflow from the system will drain to the adjacent rain gardens.  

Monitoring and evaluation 

The University of East London is undertaking monitoring on the site. Performance of the ground-level SuDS components is being monitored using weather stations, flow sensors (downpipes), pressure sensors (in basins) and time-lapse photography. In addition, thermal imaging is being used to record the cooling effect of both the ground-level SuDS components and green roofs.

Wider benefits of the scheme, for instance for health and recreation, crime reduction and environmental education benefits, are being evaluated using a combination of the CIRIA’s BeST and the Social Return On Investment (SROI) model designed by the New Economics Foundation. The monitoring and evaluation reports are available on the project website.

Benefits 

• Unused uninspiring landscape converted to diverse, attractive, multi-functional space;
• Run-off from 1750m2 of impermeable surface has been diverted from draining directly to the sewer (i.e., green roof, SuDS with controlled overflow or total disconnection);
• The capital works were delivered at the same £/m2 rate as equivalent non-SuDS landscape improvements (based on a sample of 15 Groundwork London projects undertaken on social housing estates in the London over the past 3 years).
• The scheme won a prestigious Landscape Institute Award for the use of Landscaping and SuDS.

The project received almost universal support from local residents:

• “Every time I come outside, it looks so beautiful I could cry”. Shirley Culpit, Chair of Tenants & Residents Association (TRA)
• “The project has made many improvements to the look of the estate, as well as helping to gel our community together.” Ros O’Connell, Treasurer of TRA
• “It looks beautiful and has brightened up the estate. Walking along it, I felt as if I was walking through a new private development.” Phillip Lee, Housing Officer, LBHF

Further Information for the project can be found on the Susdrain website: https://www.susdrain.org/case-studies/case_studies/queen_caroline_estate_london.html