Drain London

Our climate is changing and one of the important changes is that our rainfall is expected to come in more intense storms, increasing peak rainfall rates by up to 40 per cent. These heavy rainstorms put us at greater risk of surface flooding. To mitigate that risk we need to first better understand it.

Drain London

The Drain London project is looking at one of the most serious challenges that London will face in the near future – flooding from surface water.

Drain London will help us manage and reduce surface water flood risk in London by improving our knowledge of the surface water drainage system and identifying areas at greatest risk of flooding. We will also demonstrate some of the ways to reduce the risk.

The Mayor’s Regional Flood Risk Appraisal identifies surface water flood risk as the most likely cause of flooding in London. The operation of the surface water system is not well understood and we don’t have consistent records of when surface water flooding has happened in the capital. We need greater understanding of the issue to deal with the problem.

Read the Mayor’s Regional Flood Risk Appraisal

What is surface water flooding?

Surface water flooding happens when the volume of rainwater overwhelms the drainage system and begins to form puddles and pools on the ground. A small amount of this is normal but some storms completely overwhelm our drainage systems and we experience flooding. This can happen very quickly and can be followed by rivers and streams bursting their banks as they are inundated with water from the drainage system.

Our climate is changing and one of the important changes is that our rainfall is expected to come in more intense storms, increasing peak rainfall rates by up to 40 per cent. These heavy rainstorms put us at greater risk of surface flooding. To mitigate that risk we need to first better understand it.

What will the Drain London project achieve?

When the project is finished each London borough will have a Surface Water Management plan that will contain the Preliminary Flood Risk Assessment and a Flood Risk Management Plan, both being requirements under the Flood and Water Management Act  (2010). The Flood and Water Management Act requires boroughs to investigate (by 2015) and address flood risk problems and maintain a public register of Flood Risk Management assets and the Assessment and Plan will help them to do this.

Boroughs are the Lead Local Flood Authorities (LLFAs) and have full responsibility for managing flood risk from surface water, groundwater and ordinary watercourses. Once Drain London finishes, each London Borough will have to investigate (by 2015) measures to address remaining flood risk problems and develop and maintain a public register for Flood Risk Management Assets.

The Drain London Forum will continue to help boroughs with their responsibilities for managing flood risk by providing guidance on asset registers, helping to form multi-agency partnerships and sharing good practice, knowledge and expertise.

This will mean that London is better equipped to deal with one of the main threats we face from climate change.

Working across London

We are leading a partnership of 33 London boroughs, the Environment Agency, Thames Water, Transport for London and London Councils to deliver the project. We are also working with other agencies with drainage responsibilities in London. This partnership is called the Drain London Forum.

One of the first tasks for the project was to divide London into more manageable sub groups loosely based on their common risk of flooding. The groups will meet regularly throughout the project to take the programme forward.

The Drain London Subgroups

The programme of work

Tier One
(March 2010 to September 2010)
In this first stage the groups will gather information and establish the standards and framework for flood risk modeling for the next stage of the project.

Tier Two
(August 2010 to February 2011)
This is the key part of the project. We will model the surface water flood risk, using our framework, identifying the areas at risk of flooding and producing a Surface Water Management Plan for each London Borough, with a prioritised list of areas needing attention.

Tier Three
(November 2010 to July 2011)
During this final stage our consultants will undertake detailed modelling of high priority flood risk to develop demonstration solutions

Further information

The Drain London Forum meets quarterly and although the meetings are not open to the public the Forum newsletter is available for Londoners to read.

Read Newsletter No. 2
Read Newsletter No. 1

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