Research and analysis

Thames water situation report: April 2024 summary

Updated 15 May 2024

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

1. Summary

Thames area received 74mm of rainfall in April, which is 146% of the long term average (LTA). All the areal units recorded above normal or notably high rainfall. Total rainfall over the past 3, 6 and 12 months was exceptionally high, with the last 12 months being the wettest on record. Soil moisture deficits (SMDs) increased to 6mm across the area with effective rainfall being 196% of the LTA at the end of the month. Monthly mean river flows at the majority of the indicator sites reported notably high or exceptionally high; with 3, the Evenlode at Cassington, the Kennet at Marlborough, and the Wey at Tilford, recording their highest April flows on record. At the end of the month, groundwater levels at the majority of the indicator sites began their seasonal decline, yet remained either notably high or exceptionally high for the time of year.

2.  Rainfall

April was another wet month, receiving a total of 74mm of rain, 146% of the LTA for the month. All areal rainfall units were above normal, apart from Cotswolds West, which was notably high. A third of April’s rain occurred in the first 4 days of the month, receiving a total of 23mm of rain, while the wettest day, 27 April, had 26mm. Looking at the last 3, 6, and 12 month rainfall values, all areal units have recorded exceptionally high rainfall. The last 12 months have been the wettest on record.

3. Soil moisture deficit and recharge

Following a wet winter and April’s above normal rainfall, the SMD for Thames area in April was at 6mm. This meant that soils were wetter than the typical April value of 20mm. This was consistent for each of the areal units, primarily at either 5mm or 6mm. As such, the effective rainfall of Thames Area was high, at 23mm, which is 196% of the LTA.

4.  River flows

With the continuing above average rainfall and high effective rainfall throughout Thames area, all river flow indicator sites remained above average. Seven sites were exceptionally high, including 3, the Evenlode at Cassington, the Kennet at Marlborough, and the Wey at Tilford, which had their highest April flows on record. Apart from the River Thame at Wheatley, which had above normal flow, all remaining sites had notably high flows. Additionally, the Wye at Bourne End had its second highest April flows, and for the Coln at Bibury it’s fourth. Most of these exceptionally high flow sites responded markedly to April’s rain thanks to a strong baseflow contribution following a very wet winter season.

5.  Groundwater levels   

Groundwater levels at most of the indicator sites began the typical seasonal decline, albeit somewhat delayed due to the very wet winter and a wet April. By month end all but one of the indicator sites were either notably high or exceptionally high. The Corallian, Upper Greendsands, and all the Chalk sites were exceptionally high. Both Lower Greensands and Great Oolites were notably high, while the Inferior Oolite at Jackaments Bottom was normal for the time of year.

6. Reservoir stocks

Farmoor reservoir capacity at the end of the month was 95% after peaking at 98% during the month. Capacity at the Lower Thames reservoirs was 96% at the end of the month.

7. Environmental impact 

There were 15 fluvial Flood Alerts issued on rivers during April. By month end, there were 7 groundwater Flood Alerts in force. At the end of April, 1 abstraction licence was being constrained in Thames Area in order to protect water resources and the environment.

Author: Thames Area Groundwater Resources and Hydrology, enquiriesWT@environment-agency.gov.uk

Contact details: 020 3025 9659