Thames water situation report: March 2024 summary
Updated 15 April 2024
Applies to England
© Crown copyright 2024
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1. Summary
March was another wet month with 174% of the monthly long term average (LTA) rainfall being recorded across Thames area. The winter period, comprising the last 6 months, had exceptionally high rainfall and was the second wettest winter since records began in 1871. The soil moisture deficit (SMD) in Thames area was 1mm at the end of the month, allowing high levels of effective rainfall to occur (222% LTA). After several months of significantly high rainfall, exceptionally high river flows were recorded at all our indicator sites in March. Groundwater levels remained high across Thames Area and were exceptionally high at the majority of our indicator sites for the time of the year.
2. Rainfall
March was another wet month in Thames Area, with a total of 102mm of rain, 174% of the LTA. In the last week of March 44% of the month’s rain fell, with the highest daily rainfall total (26mm) recorded on the 28th at Shalbourne in the Berkshire Downs. Notably high and exceptionally high rainfall was recorded right across Thames Area, with higher rainfall totals typically falling on the westernmost areal units. March marked the end of the hydrological winter, which started in October 2023. During the winter period, rainfall was exceptionally high throughout all of Thames Area, ranging from 165% (Enborne and Chilterns-West) to 186% (Berkshire Downs and Upper Thames) of the LTA. It was the second wettest winter since records began in 1871.
3. Soil moisture deficit and recharge
As a result of rainfall in March, soils remained saturated and wetter than expected for the time of the year. The SMD in Thames area was 1mm at the end of the month and this allowed a high amount of effective rainfall to occur in March (222% LTA). Effective rainfall for the previous 6 month winter period was 243% of the LTA.
4. River flows
Exceptionally high monthly mean river flows were recorded at all our indicator sites in March, as significant rainfall and high groundwater levels combined in many catchments. The Rivers Evenlode at Cassington, Thames at Windsor, Kennet at Marlborough and Wey at Tilford recorded their highest monthly mean flow for March since records began at those sites. Despite the high river flows, 11 out of 15 indicator sites had lower monthly mean flows in March compared to February.
5. Groundwater levels
Following a wet winter, groundwater levels at all sites reported notably high or higher levels, with the only exception being Jackaments Bottom in the Inferior Oolites which was above normal for the time of year. By the end of the month, groundwater levels of the Chalk were exceptionally high at the Berkshire Downs and South-west Chilterns; and notably high at the North Downs. Lower Greensand sites have remained notably high for the second month in a row.
6. Reservoir stocks
Reservoir stocks in Farmoor reservoir were 89% at the end of March, an increase from 85% at the end of February. Stocks at the Lower Thames reservoir has also increased to 96.4% at the end of this month from 96% at the end of February. Reservoir levels remain below the LTA at Farmoor while levels at Lower Thames remain just above the LTA for the time of year.
7. Environmental impact
During March, there were 74 flood alerts and 3 flood warnings issued on rivers in Thames area. At the end of the month, 1 abstraction licence was being constrained in the area to protect water resources and the environment.
Author: Thames Area Groundwater Resources and Hydrology, enquiriesWT@environment-agency.gov.uk
Contact Details: 020302559659
All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained in this report.