Policy paper

Thames: groundwater situation: 21 May 2024

Updated 21 May 2024

Applies to England

Current situation

Groundwater levels remain high due to rainfall over the winter but are now falling at our observation boreholes:

• Longacre in the Lambourn 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
• 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.

Lambourn Valley

Groundwater levels are above the level that requires early awareness at the Longacre borehole in the Lambourn Valley. The groundwater level at this location is higher than normal for this time of year but is currently declining. The catchment remains sensitive to rainfall due to saturated ground and high groundwater levels may be prolonged by 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.

Great Shefford area

In response to recent rainfall, groundwater levels are 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 but is currently declining. The catchment remains sensitive to rainfall due to saturated ground and high levels may be prolonged 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

Groundwater levels are above the level that requires early awareness, and the level at which a groundwater flood alert is issued determined from the Chapel Wood borehole in the Leckhampstead area. The groundwater level is higher than normal at this location but is currently declining. The catchment remains sensitive to rainfall due to saturated ground and high levels may be prolonged as 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

Groundwater levels are 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 but is currently declining. The catchment remains sensitive to rainfall due to saturated ground and high levels may be prolonged 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

Groundwater levels are above the level that requires early awareness at the Ray Farm borehole and above the level at which a groundwater alert is issued, determined from the Piddington borehole in the Wycombe area (including Radnage and the lower Hughenden Valley). Groundwater levels at both boreholes are currently declining. The catchment remains sensitive to rainfall due to saturated ground and high levels may be prolonged as we receive further rainfall. A groundwater flood alert was issued on 26 March 2024 for the areas at risk of groundwater flooding in the Wycombe area including Radnage and the lower Hughenden Valley and this will remain in force. We will continue to monitor the situation closely and provide an update as this changes.

Alton, Chawton and Lower Farringdon areas

Groundwater levels are currently 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 but is currently declining. The catchment remains sensitive to rainfall due to saturated ground and high levels may be prolonged or start to increase again 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.

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

Groundwater levels are above the level at which groundwater flooding may affect communities and a groundwater flood alert has been issued determined from the Stonor Estate borehole in Turville, Skirmett, Stonor, Middle and Lower Assendon, and parts of Henley. The groundwater level is higher than normal at this location but is currently slowly declining. The catchment remains sensitive to rainfall due to saturated ground and high levels may be prolonged as we receive further rainfall. A groundwater flood alert was issued on 8 March 2024 for the areas at risk of groundwater flooding in Turville, Skirmett, Stonor, Middle and Lower Assendon, and parts of Henley and this will remain in force. 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 remain high but have started to decline as we move through spring. This declining trend is expected to continue. However, any heavy rainfall may change these trends locally and/or prolong high levels. We continue to monitor groundwater levels and will update this briefing note and issue flood alerts as and when appropriate.

Forecast risk of flooding

The forecast for today (21 May) is mostly dry until the afternoon. There is an increasing chance of isolated heavy showers by the afternoon which may be thundery. Overnight it is forecast to be dry for most areas, although a few showers may continue through the evening. Wednesday is again forecast to be dry and cloudy to start, with some heavy (and perhaps thundery) showers forecast for the afternoon. The outlook for Thursday to Saturday is likely to be largely dry, with the odd light shower possible in places.

In the longer term (although more uncertain), some showers are expected over the bank holiday weekend. Once this rainfall clears, mostly drier conditions are expected as we move through next week, although there is still a chance of showers, which may be heavy and thundery.

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. This can be found at: Monthly Water Situation Report - 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 GOV.UK 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 GOV.UK.

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 Environment Agency for more information:

• customers and engagement: enquiries_THM@environment-agency.gov.uk
• national customer contact centre: 03708 506 506
• incident reporting hotline: 0800 807060