Policy paper

Thames: groundwater situation: 1 March 2024

Updated 1 March 2024

Applies to England

Current situation

Groundwater levels have responded to recent rainfall and have risen at some of our observation boreholes:

• Draycot in the Upper Og Valley
• Longacre in the Lambourn Valley
• Water Acre in the Upper Aldbourne Valley
• Northfield Farm in the Great Shefford area
• Chapel Wood in the Leckhampstead area
• Hodcott 2 in West Ilsley, East Ilsley, Compton, Chilton and West Hagbourne
• Piddington in the Wycombe area including Radnage and the lower Hughenden Valley
• Ray Farm in the Wycombe area including Radnage and the lower Hughenden Valley
• Farringdon in the Alton, Chawton and Lower Farringdon areas
• Tile Barn Farm1 in the Crondall, Sherborne St John, Basingstoke and Buckskin areas
• Frith Cottage in the Haslemere, Churt, Rushmoor, Godalming, Shackleford and Hambledon areas
• Stonor Estate in Turville, Skirmett, Stonor, Middle and Lower Assendon, and parts of Henley

Groundwater levels at these locations are currently above the level that requires early awareness. This briefing note has been issued to provide an update on these high levels.

Please note that Tile Barn Farm Observation Borehole is currently offline and levels are being derived from 2 nearby proxy sites. We have good confidence in the relationship between these levels. Works are underway to replace this site in the near future.

Upper Og Valley

In response to recent rainfall, groundwater levels have risen above the level that requires early awareness, and the level at which a groundwater flood alert is issued, determined from the Draycot borehole in the Upper Og Valley. The groundwater level at this location is higher than normal for this time of year and is currently slowly rising. This observation site is more responsive to individual rainfall events compared to our other observation boreholes in the Chalk aquifer. Therefore, it is likely for levels to continue rising as we receive further rainfall.

We issued a groundwater flood alert on 2 January 2024 for the areas at risk of groundwater flooding in the Upper Og Valley, and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

Lambourn Valley

In response to recent rainfall, groundwater levels have risen above the level at which groundwater flooding may affect communities and a groundwater flood alert has been issued determined from the determined from the Longacre borehole in the Lambourn Valley. The groundwater level at this location is higher than normal for this time of year and is currently slowly rising. The catchment remains sensitive to rainfall due to saturated ground and groundwater levels may continue to rise in response to any further rainfall.

We issued a groundwater flood alert on 27 November 2023 for the areas at risk of groundwater flooding in the Lambourn Valley and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

Upper Albourne Valley

In response to recent rainfall, groundwater levels have risen above the level that requires early awareness and the level at which a groundwater flood alert is issued, determined from the Water Acre borehole in the Upper Aldbourne Valley. The groundwater level at this location is higher than normal for this time of year and is currently stabilised at this high level. The catchment remains sensitive to rainfall due to saturated ground. Therefore, levels may start to rise again if we receive further rainfall.

A groundwater flood alert was issued on 10 January 2024 for the areas at risk of flooding in the upper Aldbourne Valley and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

Great Shefford area

In response to recent rainfall, groundwater levels have risen above the level that requires early awareness, and the level at which a groundwater flood alert is issued, determined from the Northfield Farm borehole in the Great Shefford area. The groundwater level at this location is higher than normal for this time of year and is currently slowly rising. The catchment remains sensitive to rainfall due to saturated ground and levels may continue to increase as we receive further rainfall.

A groundwater flood alert was issued on 2 January 2024 for the areas at risk of groundwater flooding in the Great Shefford area and this will remain in force. A pumping plan is available to mitigate groundwater flood impacts in this area. We will continue to monitor the situation closely and provide an update as this changes.

Leckhampstead area

In response to recent rainfall, groundwater levels have risen above the level at which groundwater flooding may affect communities and a groundwater flood alert has been issued, determined from the Chapel Wood borehole in the Leckhampstead area. The groundwater level is higher than normal at this location and is currently rising further. The catchment remains sensitive to rainfall due to saturated ground and levels may continue to increase again if we receive further rainfall.

A groundwater flood alert was issued on 23 January 2024 for the areas at risk of groundwater flooding the Leckhampstead area and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

West Ilsley, East Ilsley, Compton, Chilton and West Hagbourne

In response to recent rainfall, groundwater levels have risen above the level at which groundwater flooding may affect communities and a groundwater flood alert has been issued determined from the Hodcott 2 borehole in West Ilsley, East Ilsley, Compton, Chilton and West Hagbourne. The groundwater level is higher than normal for this time of year at this location and is currently slowly rising. The catchment remains sensitive to rainfall due to saturated ground and levels may continue to increase as we receive further rainfall.

A groundwater flood alert was issued on 6 January 2024 for the areas at risk of groundwater flooding in West Ilsley, East Ilsley, Compton, Chilton and West Hagbourne and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

Wycombe area including Radnage and the lower Hughenden Valley

In response to recent rainfall, groundwater levels have risen to the level that requires early awareness and the level at which a groundwater alert is considered determined from the Piddington borehole in the Wycombe area (including Radnage and the lower Hughenden Valley). The Ray Farm borehole in the same area has also risen to the level that requires early awareness. Groundwater levels at both Piddington and Ray Farm are currently rising. The catchment remains sensitive to rainfall due to saturated ground and levels may continue to increase as we receive further rainfall.

A groundwater flood alert may be issued later this week for the areas at risk of groundwater flooding in the Wycombe area (including Radnage and the lower Hughenden Valley) depending on how levels respond to rainfall over the next few days. We will continue to monitor the situation closely and provide an update as this changes.

Alton, Chawton and Lower Farringdon areas

In response to recent rainfall, groundwater levels have risen above the level that requires early awareness and the level at which a groundwater flood alert is issued, determined from the Farringdon borehole in the Alton, Chawton and Lower Farringdon areas. The groundwater level is higher than normal at this location and is currently rising. The catchment remains sensitive to rainfall due to saturated ground and levels may continue to increase as we receive further rainfall.

A groundwater flood alert was issued on 9 January 2024 for the areas at risk of groundwater flooding in Alton, Chawton and Lower Farringdon and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

Crondall, Sherborne St John, Basingstoke and Buckskin areas

In response to recent rainfall, groundwater levels had risen above the level that requires early awareness at our indicator sites in the Crondall, Sherborne St John, Basingstoke and Buckskin areas. The groundwater level is higher than normal at this location and levels are currently rising. The catchment also remains sensitive to rainfall due to saturated ground and levels may continue to increase as we receive further rainfall.

Currently, no groundwater flood alert has been issued for this area. We will continue to monitor the situation closely and provide an update as this changes.

Haslemere, Churt, Rushmoor, Godalming, Shackleford and Hambledon areas

In response to recent rainfall, groundwater levels have risen close to the level that requires early awareness at the Frith Cottage borehole in the Haslemere, Churt, Rushmoor, Godalming, Shackleford and Hambledon areas. The groundwater level is higher than normal at this location and is currently fluctuating around the threshold for early awareness. The catchment remains sensitive to rainfall due to saturated ground and levels may rise above the threshold for early awareness in the next few days.

Currently, no groundwater flood alert has been issued for this area. We will continue to monitor the situation closely and provide an update as this changes.

Turville, Skirmett, Stoner, Middle and Lower Assendon, and parts of Henley

In response to recent rainfall, groundwater levels are rising close to the level that requires early awareness at the Stonor Estate borehole in Turville, Skirmett, Stoner, Middle and Lower Assendon, and parts of Henley. The groundwater level is higher than normal at this location and levels are currently rising. The catchment remains sensitive to rainfall due to saturated ground and levels may rise above the threshold for early awareness this weekend.

Currently, no groundwater flood alert has been issued for this area. We will continue to monitor the situation closely and provide an update as this changes.

Summary of other groundwater sites

Groundwater levels at the majority of our indicator sites are higher than normal for this time of year. Groundwater levels across the area have risen following heavy rainfall events. Groundwater levels remain high, but there is some variance in their site-specific trends due to local factors. An overall increasing trend is expected in response to rainfall over the winter period. We continue to monitor groundwater levels and will update this briefing note and issue flood alerts as or when appropriate.

Forecast risk of flooding

The forecast for today (1 March) is dry to start, with rain arriving in the afternoon. Showers are forecast to continue overnight and into Saturday with a brief risk of snowfall in the west of the region. Sunday is anticipated to be drier, although more rainfall is forecast to arrive around Monday evening. Heavy showers are forecast on Tuesday.

In the longer term, (although more uncertain), drier spells of weather are likely to develop, with some sunshine forecast from the middle of next week.

We will:

• closely monitor the need for groundwater flood alerts
• add more sites to this briefing note in the coming weeks, if required
• keep this under review and continually monitor the rainfall received

More details of the forecast predictions can be found in the monthly Water Situation Report for England.

What we’re doing

We are:

• continuing to monitor groundwater levels across the area
• removing blockages from rivers in the area to ensure they flow freely
• talking with the local authority and other responding partners to ensure they are aware of the situation

Actions and advice

Call Floodline on 0345 988 118 or visit check for flooding on AMSTRAD to find out if you can register to receive free flood alerts for flooding from groundwater.

Check the river, sea, groundwater and rainfall levels on AMSTRAD.

You should:

• review your individual and community group flood plans
• check pumps and any other flood protection equipment you have
• keep drains and gullies around your property free of debris
• move valuables from basements and cellars

Next update

As flood risk increases with the continuing rising groundwater trends, we will update this briefing note weekly (or sooner if the situation significantly changes).

Further information

See more information on groundwater levels and the water situation report.

You can also get practical advice on what to do before, during and after groundwater flooding. Visit check for flooding in England. The 5 day flood risk outlook can be found here for reference.

Contacts

For more information on the flood alert service and to find out what messages you are registered to receive, call the Floodline on 0345 988 118.

Alternatively, you can contact the following for additional information:

• Environment Agency Customers and Engagement: enquiries_THM@environment-agency.gov.uk
• Environment Agency National Customer Contact Centre: 03708 506 506
• Environment Agency Incident Reporting Hotline: 0800 807060