Drain London

Drain London

Heavy rainstorms can put London at risk of flooding. This can lead to costly disruptions and damage, for example, by flooding properties or closing roads and rail stations. Our Drain London programme helps to predict and manage surface water flood risk in London.

What is Drain London?

Drain London is improving our knowledge of the surface water drainage system and identifying those areas at most risk of flooding. It is also trying to find ways to reduce flood risk. It was created in response to the Mayor’s Regional Flood Risk Appraisal, which identified surface water flood risk as the most likely cause of flooding in London. Read the Mayor’s Regional Flood Risk Appraisal.

Flood risk modelling through Drain London has helped London’s boroughs to better understand the risks in their borough and to produce a Surface Water Management Plan to help manage and reduce those risks. The Environment Agency has also produced a national set of flood risk maps.

Drain London is also working on several projects that show how surface water can be managed in a more sustainable way. This includes converting impermeable surfaces into green permeable surfaces, diverting rainwater pipes into landscaped areas and restoring river corridors to absorb more water.

What is surface water flooding?

Surface water flooding happens when rainwater can’t soak into the ground. This overwhelms the drainage system and leads to puddles, pools and temporary flows. Minor surface flooding is normal. However some storms completely overwhelm our drainage systems and cause more extensive flooding.

This can also be followed by rivers and streams bursting their banks as they overflow with water from the drainage system.This can be a particular problem in urban areas that have a large proportion of impermeable surfaces such as roofs, roads and car parks. To help manage this problem we run the Drain London project.

Working across London

Drain London is leading a partnership of 33 London boroughs, the Environment Agency, Thames Water and Transport for London. We also work with other bodies that have drainage responsibilities in London through the Drain London Forum.