Marylebone Flyover underpass turned into network of rain gardens

A flood mitigation scheme featuring vegetation and permeable paving, with a water collection area of more than 3,500 square metres, has been completed in the disused underpass of Marylebone Flyover in central London. 

The ramps and stairs of the underpass, which led to the subway, have been turned into porous rain gardens, which can hold around 30,000 gallons of rainwater, estimates Transport for London (TfL). It added that the gardens are designed to help mitigate London’s increasing risk of extreme weather, and reduce the risk of localised flooding and the number of occasions in which sewer overflows occur.

The Marylebone Flyover rain garden scheme was a joint collaboration between TfL, the Greater London Authority (GLA) and Thames Water, with the Marble Arch London BID committed to fund and run the maintenance work on the gardens. 

The scheme was part-funded by Thames Water and the GLA under the Green Infrastructure Fund programme, with £1m allocated for greening projects on the TfL Road Network. TfL’s Business Plan sets out how TfL will invest £6m over the next four years to improve its understanding of the impacts of climate change, as well as help supplement existing projects to boost green infrastructure and SuDS (Sustainable drainage systems).

TfL has worked with Westminster City Council to deliver improved pedestrian crossings as part of the Safer Junctions programme. Since public access to the subway system under the Marylebone Flyover was closed, pedestrians can continue to use the safe surface level signal-controlled crossings at the junction, said TfL. As part of this, the pavement outside Edgware Road Underground Station has been extended and a left turn slip lane has been removed.

Penny Rees, TfL’s Head of Healthy Streets Investment, said the scheme will “improve the surface drainage system to protect a busy junction from flooding” as well as increasing biodiversity and contributing to the London Mayor’s aim to improve river water quality.

Mete Coban, Deputy Mayor for Environment and Energy, said: “This is a great initiative to help reduce flooding in the area, increase biodiversity and provide beautiful new gardens for residents and visitors to enjoy.

“Addressing the important issue of surface water flooding is one of many ways we are working with partners like TfL to make London more climate resilient, creating a fairer, greener city for all.”

Kay Buxton, Chief Executive of Marble Arch London BID, said: “We have been involved in this project since 2018 when the subway network was closed, so to see these rain gardens come to life marks such a significant milestone for Marble Arch BID. Our colleagues at TfL have a very strong commitment to delivering more green infrastructure on the capital’s main roads, to manage the impact of climate change and improve air quality. The delivery of these SuDS around the Marylebone flyover is a clear indication of the commitment of all the partners and funders involved.”

Craig Boorman, Principal Environment Engineer at Thames Water, said: "This unique regeneration project shows how sustainable drainage can help our capital city to adapt to the impacts of more intense rainfall, while also being beautiful and enhancing for local communities.

“Sustainable drainage systems like this play a vital role in capturing rainwater, slowing the flow entering sewers which can reduce the risk of flooding and untreated discharges from storm overflows. We regard all discharges as unacceptable, and by working in partnership with one of key stakeholders, TfL, this project is a small step that demonstrates how we are taking action to improve the health of rivers.

“A more ‘spongey’ London will be better able to deal with heavy rain now and in the future, and the solution is to turn our urban landscape from grey to green.”

TfL said it is on track to deliver its annual target of 5,000 square metres of additional sustainable drainage on its road network.

The gardens have been planted with 11 trees, 95 shrubs, more than 1,100 perennial plants and almost 2,300 bulbs in total and installed. 

TfL is planning to deliver schenmes on London Road Roundabout in Twickenham, which will add almost 2,000 square metres of SuDS collection area, and the Kingston Cromwell Road Bus station, which will add 1,620 square metres of SuDS collection area.

Find out more about rainwater garden schemes at Climate Resilient Streets