Sustainable drainage schemes (SuDS) are popping up everywhere if you know where to look. A new, interactive map highlights the spread of retrofit SuDS across London. Holly Smith reports

London is adding sustainable drainage systems (SuDS) so rapidly that it can be difficult to keep track of all the schemes springing up across the capital. Now, the mayor of London has launched a retrofit SuDS map to highlight and celebrate them.

This live, interactive site shows which schemes have been fitted where. It’s colour-coded to show schools, highways, social housing, parks, wetlands and river-restoration schemes. Filters can narrow your search to find tree-planting schemes, attenuation storage, bioretention, wetlands, green roofs, filter strips and other specific SuDS.

Whether you live in London, work in water management there or are delivering SuDS in other regions, the map creates a snapshot to highlight where and how quickly schemes are being added across the capital.

From wetlands to rain planters, each SuDS is helping to manage and slow the way water flows across the capital. Here are four pioneering projects.

Dig-once SuDS in Enfield

Roadworks create problems for cities, disrupting traffic and making life unpleasant for local people, businesses, the wider environment and even road users. One way to reduce that disruption is to use what planners call a dig-once approach – timing multi-utility works so that they’re carried out and completed together.

Dig once demands better co-ordination and partnerships – for planning and for delivery. The mayor of London’s Infrastructure Co-ordination Service (ICS) aims to do just that.

Based on the number of major and standard permits issued, London utilities dig up the capital’s roads at least 165,000 times a year. By this autumn, the ICS had saved London more than 1,000 days of disruption by supporting more effective collaboration.

Adapting to climate change – and managing flood risk and road run-off – strengthens the case to fit SuDS alongside road works, and the ICS enables innovation, finding ways to collaborate on street works to also benefit the environment – so that works to improve roads can also build in SuDS.

Park Lane in Enfield, part of the Haselbury neighbourhood-improvements scheme carried out in 2022, is a successful example. Local gas-distribution company Cadent Gas needed to replace a cast-iron gas main, which meant large excavations along both the footway and carriage way.

The ICS spotted a chance for Enfield Council and Cadent to work together. The project partners used the Greater London Authority’s (GLA) Infrastructure Mapping Application, a web-based mapping tool with data on growth, development, construction and factors that affect growth and infrastructure in Greater London, including utilities works.

Working alongside Cadent, including on traffic management, Enfield fitted a rain garden and carriageway buildouts to calm traffic – spending less than it would have had it been working alone. And so Park Lane bridged the gap between potentially competing priorities: utilities upgrades and climate adaptation.

The pilot opens new ways to install SuDS in tandem with utilities’ mains-replacement works. Other local authorities, inspired by Park Lane, are rolling out their own schemes alongside local utility upgrades.

It’s an innovative approach to SuDS that we can and should scale up – across London and nationwide. Indeed, thanks to support from the Regulators Pioneer Fund, the ICS is exploring new ways to scale up SuDS delivery by taking a market-based approach to street works.

Space for SuDS – Fleet Valley Pocket Park

Turning a densely built-up street in central London into a park is no mean feat.

Mount Pleasant occupies one of Camden’s critical drainage areas. It’s a local flood-risk zone; the now-culverted River Fleet flows below.

The Fleet is one of London’s most famous hidden rivers. It rises on Hampstead Heath as two separate springs – you can see it above ground on the heath – before flowing underground and joining in Camden, where you can hear and see it where grates have been fitted in the road. From Camden, the Fleet flows east to join the Thames below Blackfriars Bridge.

Below ground, the Fleet is a sewer. But above ground, Mount Pleasant neighbourhood has been transformed, impermeable pavements replacing permeable paving and new tree pits and rain gardens installed to manage run-off.

The Thames Water Surface Water Management Programme part-funded the scheme, which improves the area’s sewer capacity. Its other benefits include creating green spaces to increase biodiversity and amenity space and produce cleaner air. And the scheme is educational, too; a River Fleet explorer path winds through the space.

The London Borough of Camden invited poets and artists to respond to the hidden river. Their artworks and poems appear along the path.

The SuDS team worked with the Mount Pleasant Neighbourhood Forum to design the scheme. Having that local feedback helped to create an outcome that’s sympathetic to the area and that local people value. It was local residents who named the scheme Fleet Valley Pocket Park.

Camden Council learned a lot from the scheme. It brought together the Green Space and Lead Local Flood Authority teams, who learned to work together more effectively. The Green Space team managed and is maintaining the project, helping it to improve its own SuDS-delivery skills, which will come in handy for developing SuDS in other neighbourhoods in Camden.

Climate-resilient schools for London

Even small interventions can have a big impact. On its own, a SuDS rain planter might not seem to do much to cut flood risk but installing 564 SuDS rain planters across 72 sites makes a huge difference.

The Climate Resilient Schools programme brings together mayor of London Sadiq Khan, the Department for Education and Thames Water. Using the GLA’s climate-risk maps, the project partners picked out 95 of London’s most vulnerable schools. They installed SuDS rain planters in 72 schools and drew up tailored climate-adaptation plans for the remaining schools, which receive Smarter Business visits from Thames Water and access to climate education material.

Project teams surveyed the schools to work out where best to put rain planters. Each school selected received up to ten planters. GLA teams worked with AmbioTEK and researchers from Kings College London to evaluate the planters’ impact, installing weather stations on the roofs of 24 schools and fitting soil-moisture sensors in 30 planters.

The data on rainfall and soil moisture that these have gathered indicates that the 564 planters have a storage capacity of 157 cu metres that can capture and store the first 3mm of precipitation that falls during a storm.

And the planters provide many other benefits to schools, creating both new habitats that attract wildlife and green spaces, which help to boost people’s health and wellbeing.

Not everyone was on board at first. Some schools worried about how they would maintain the planters. The project found that what matters most is keeping gutters clear so that the water flows into the planters.

By March, the project will have gathered a full year of data to find out how effectively the planters have held and managed water – and on how the schools have benefited from having more greenery and a reduced flood risk.

Grow Back Greener – Community resilience in Lambeth

The mayor of London’s Grow Back Greener programme has been giving small grants to create and improve green spaces across London since 2020. The programme is tackling unequal access to open spaces. It targets neighbourhoods with high levels of deprivation and where access to green spaces is limited.

Grow Back Greener funding is open to charities, community groups, boroughs and schools. In Lambeth, partners Froglife and Streatham Common Co-operative received £20,000 to create a corridor of ponds alongside the River Graveney on Streatham Common.

The scheme uses swales to divert heavy rain into ponds that are connected by leaky dams. Using natural flood-management techniques to reduce flooding has made the site easier to access, shrinking muddy areas, while also creating new habitats for amphibians. The local community steered the project to focus on disadvantaged young people.

More than 150 locals volunteered for the project and 68 attended sessions on art in training. The scheme has also been working with the Wild Times dementia-friendly volunteering programme for people aged over 55. Wild Times activities include wildlife gardening, nature walks and talks, creative work with nature and events to share memories and spend time with other people.

Scaling up

The London SuDS retrofit map features many more case studies that celebrate the capital’s growing SuDS network. It highlights the many different ways in which partnerships across London have worked together to deliver retrofit SuDS.

The GLA wants to fill in all of the gaps in the map. Please get in touch if your scheme isn’t yet on there. But what we see from the information we’ve gathered so far is that all of us – from partnerships to upgrade our streets to community groups – need to get moving to deliver more SuDS.

Find out more: https://apps.london.gov.uk/suds

Holly Smith is surface-water-flooding project manager at the Greater London Authority

This story is published in the December 2023 / January 2024 issue of The Environment magazine