Research and analysis

South London groundwater situation: 20 March 2024

Updated 22 March 2024

Applies to England

© Crown copyright 2024

This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@nationalarchives.gov.uk.

Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.

This publication is available at https://www.gov.uk/government/publications/mole-and-south-london-groundwater-situation/south-london-groundwater-situation-10-february-2020

Current situation

Since the end of October, the South London area has been receiving notably high amounts of rain for this time of the year. This, combined with a slightly wet summer and widespread rain that continued to fall during the first half of November resulted in a sharp rise in groundwater levels. The rise in levels slowed down after a drier second half of November and then rose more steeply due to a wetter December and early-January. After a small decline early in February, levels started to rise again in response to the rainfall received between February and early March. Levels are now rising less sharply again due to the lower rainfall intensity since mid-March.

Across the South London area, groundwater levels began to rise suddenly in the early weeks of November. Levels typically begin to increase towards the end of November and early December. The sharp and early rise of groundwater levels was responsible for groundwater fluctuating between levels that are considered exceptionally high, notably high or above normal since November. 

Due to the rise in groundwater levels in East Surrey and South London that occurred since late February, a flood alert for groundwater flooding was issued earlier this month, and it is now in effect for South East London area.

Find out more information about this alert and other flood alerts and warnings on GOV.UK.

Short term forecast  

After somewhat drier conditions that were prevailing earlier in March, for next week, the forecasts predict weather systems with more unsettled conditions. This could result in less stable conditions with the Caterham Bourne (that started to flow last week) flowing more intensively at times.

Longer term forecast  

Trends of groundwater levels are dependent on the amount and intensity of rainfall we receive in South London until the end of the groundwater recharge season. The recharge season typically comes to an end in the spring.  

Caterham Bourne is now flowing in its full extent between Woldingham and Purley and these conditions are likely to continue through to April and possibly May. Bournes are rivers that flow in winter because of high groundwater levels. 

For the next three to four weeks, across the south of the UK, conditions are forecast to remain unsettled. If these unsettled, wet spells result in heavy and frequent rainfall events, then it is possible for the winter bourne to flow more intensively with more widespread effects of groundwater flooding to occur later in March or April.

Graph showing the trend of groundwater levels since June 2022 at Woldingham Observation Borehole in South London overlying a background of colour banding indicating relatively high and low conditions.

What the Environment Agency is doing  

We will continue to monitor groundwater levels across South London and provide situation report updates throughout the remainder of this winter. The next report will be published next month unless the situation changes significantly.   

We will take evidence-based decisions. If conditions deteriorate, we will notify our partners (including lead local flood authorities and water companies). We will also actively engage with our partners to help them prepare for incident response.

Actions and advice

There is practical advice on what to do before, during and after groundwater flooding, and further guidance about groundwater flooding, how it might affect you and what to do.

Next update

We will continue to monitor groundwater levels closely and we will provide a further update next month unless there are any significant changes.

Further information

You can view:

Contacts

If you have any questions, please email enquiries@environment-agency.gov.uk.

The Environment Agency offers free Groundwater Flood Alerts. You can:

Back to top