Seven schools in the London Borough of Merton have received new sustainable drainage systems designed to reduce surface water runoff and localised flood risk.
The schools had been identified by the council as being at high risk of surface water flooding, with previous incidents including water pooling in playgrounds and flooding affecting classrooms and learning environments.
29 rain gardens installed across schools
The project has seen 29 modular rain gardens installed across the seven sites by Sudsplanter.
The systems intercept rainwater from school roofs through existing downpipes, temporarily storing the runoff rather than allowing it to immediately enter the sewer network.
Each unit combines attenuation, filtration and storage, with rainwater passing through a specially designed soil layer before being held within an underlying reservoir.
The captured water can then be released gradually, reducing the volume entering the drainage network during periods of heavy rainfall.
The project was part-funded through the SuDS in Schools programme with support from the Department for Education and forms part of wider efforts to manage surface water in London.
Modelling assesses impact on sewer flows
Before installation, surface water specialists assessed drainage systems, roof areas and downpipes at each school alongside a council officer to identify suitable locations.
Modelling was then used to calculate projected storage and attenuation capacity and assess the scheme against Department for Education performance requirements.
According to the project calculations, the 29 installations are expected to reduce peak discharge to the sewer from individual downpipes by between 81% and 95%.
The systems are also calculated to withhold 24.49m³ of rainwater upstream of the sewer network for later controlled release, while providing a total roof rainwater attenuation volume of 14.7m³.
Schools combine flood resilience with education
Between three and six units were installed at each school, with plant species selected according to conditions at individual sites.
The project also incorporates an educational element, with pupils taking part in sessions covering the water cycle, sustainable drainage systems and the maintenance of the planted habitats.
Individual schools will be responsible for the long-term day-to-day maintenance of their systems, while Merton Council plans to conduct annual check-ins to gather information about their performance.
“Surface water flooding is one of the primary sources of flood risk in Merton, occurring during heavy rain when the ground is unable to absorb the water and the drainage system is overwhelmed,” said Bethan McGregor, Climate Projects Officer at London Borough of Merton.
McGregor said schools provide an opportunity to combine flood-risk management with educational and biodiversity benefits.
“The SuDSPlanters have delivered tangible benefits. In just one of many examples, one school reported its playground, which usually floods after rain, has not flooded since the planters were installed in December.”
SuDS form part of local flood management
Sustainable drainage systems, commonly known as SuDS, are designed to manage rainfall closer to where it falls and reduce the rate at which surface water reaches conventional drainage infrastructure.
For schools and other developed sites, interventions such as rain gardens can provide additional temporary storage without requiring major changes to existing underground drainage networks.
“By installing SuDSPlanter units, Merton Council has provided these schools with an ongoing engagement resource which provides water quality benefits, flood protection, biodiversity enhancements, education tools and health and wellbeing benefits,” said Lorna Davis, Director at Sudsplanter.
Davis also encouraged other local authorities in areas affected by flooding to investigate funding opportunities for similar projects.
Further information about the systems is available from Sudsplanter.
What are sustainable drainage systems (SuDS)?
Sustainable drainage systems, or SuDS, are designed to manage rainfall and surface water closer to where it falls. They can temporarily store, filter and gradually release rainwater, helping to reduce pressure on conventional drainage and sewer networks.
How are the Merton schools managing surface water?
A total of 29 modular rain gardens have been installed across seven schools in the London Borough of Merton. They intercept runoff from roofs and temporarily store the water before releasing it at a controlled rate.
How much rainwater can the Merton school SuDS manage?
Project calculations indicate that the installations can withhold 24.49m³ of rainwater upstream of the sewer network and provide 14.7m³ of roof rainwater attenuation volume.
How many schools are involved in the Merton SuDS project?
Seven schools in the London Borough of Merton are involved, with between three and six modular rain garden units installed at each site.
