Derbyshire Street
This pocket park in Tower Hamlets shows that sustainable drainage (permeable paving, rain gardens, green roofs, swales and stormwater planters) can be attractive and improve how the local area looks.

Action on flooding in London

02 February 2017

You might not know what surface water is, or why it’s a problem. But you’ve almost certainly been affected by it, as Katherine from the Environment team explains…

  • Have you ever walked along a pavement in London after a rainstorm and got your shoes soaked by the puddle underneath a loose paving stone? This is called the ‘beau trap’ or ‘affpuddle’ and is a form of surface water flooding.
  • Have you ever been drenched when a driver hits a huge puddle of water on the road and sprays it over the pavement? That’s another form of surface water flooding.
  • Have you ever had your basement toilet or shower back up with sewage after heavy rainfall? Again, the reason is surface water flooding.
  • Have you ever walked along a London river or stream and wondered what the beige or grey strands on the aquatic vegetation are? It’s sewage fungus – bacteria that thrive in polluted and nutrient-rich watercourses. It can be caused by surface water flooding.

London’s population is growing and our climate is changing. This is increasing the chance of heavier rainstorms. It means surface water flooding and its impacts will become a bigger problem. That’s one reason why the Thames Tideway Tunnel is being built. On its own, it won’t be enough.

To help, the Mayor has published his London Sustainable Drainage Action Plan. It recognises the need to rethink how we deal with rainfall. Sustainable drainage systems (SuDS) are one way of doing just that.

SuDS mimic nature and usually manage rainwater close to where it falls. They can stop or reduce the amount of rainwater reaching the drainage system, or slow it down so the system has time to empty. SuDS can be ‘green’, like green roofs and rain gardens (like these rain gardens in Enfield), or ‘grey’ solutions, like permeable paving, and underground storage tanks.

We need both types. However, green SuDS also improve water quality, support biodiversity, help to clean the air, and make areas look more attractive.

But for SuDS to work we need them everywhere. Not just in new developments but in pavements, parks, roofs, and alongside train lines all over London. That’s where the action plan comes in.

The plan urges people and organisations to think about installing SuDS at the same time as other works that are already set to happen to reduce costs and hassle. This includes installing SuDs while carrying out roof repairs or while digging up pavements for maintenance and resurfacing. That way, SuDS cost very little, or sometimes have no net cost. Here are some examples of SuDS retrofit projects that the Mayor supported.

Londoners can do their bit as well. More and more gardens have been paved over. This stops rainwater from soaking into the soil, contributing to surface water flooding. Taking up some of the paving stones or concrete and replacing it with soil or gravel can make a big difference.

Find out more about how you can get involved.

Surface water facts and figures

  • 80%
    full drainage network
    Parts of London’s drainage network are 80% full even in dry weather
  • 18m
    tonnes of sewage
    18m tonnes of untreated waste water enter the River Thames each year
  • 68k
    residential properties
    More than 68k homes are at high risk of surface water flooding
  • 70%
    of surface water runoff
    SuDS could deal with up to 70% of the runoff from a 1 in 30 year storm