Research and analysis

Thames water situation report: May 2024 summary

Updated 21 June 2024

Applies to England

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

1. summary

Thames area received 72mm of rainfall in May, 125% of the long term average (LTA). Areal units in the north-west received above normal rainfall and those in the south-east received normal rainfall. Soil moisture deficits (SMD) increased from last month to 20mm across the area, lower than expected for the time of the year (38mm). Monthly mean river flows at the majority of our indicator sites were notably high or exceptionally high with 3 rivers, the Thame, Kennet and Wye experiencing their second highest May flows. At the end of the month, groundwater levels at the majority of our indicator sites continued their seasonal decline, yet most remained above normal or higher for the time of year.

2. Rainfall

In May 72mm of rain fell in Thames area, 125% of the LTA. For the past 3 months, total accumulated rainfall was notably high or exceptionally high for all areal units. For the past 6 months and 12 months the total accumulated rainfall was exceptionally high for all areal units. Geographically, there was more rain in the north-west of Thames area (above normal), compared to the south-eastern units, which received normal rainfall.

3. Soil moisture deficit and recharge

Thanks to a wet winter and May’s above normal rainfall, the SMD for Thames area was 20mm. This meant soils were wetter than expected for the time of the year (38mm). However, there was a wide range of SMDs for the areal rainfall units, ranging between 9mm and 35mm, with wetter soils found towards the north of the area. Effective rainfall for the month was 7mm, which is typical for May, a change from the above average effective rainfall experienced most months over the last half year.

4. River flows

Due to another month of higher than average rainfall, and a wet spring in general, all our river flow indicator sites had notably high and exceptionally high monthly mean flows in May, except for the Blackwater at Swallowfield (above normal). For our groundwater fed rivers, this was due to high rainfall and aquifer recharge leading to high groundwater levels over the past 6 months. The River Thame at Wheatley had its second wettest May on record, as did the River Kennet at Marlborough and the River Wye at Bourne End, with the last 2 being supported by a strong baseflow thanks to elevated Chalk groundwater levels.

5. Groundwater levels

Most of the groundwater sites continued their seasonal decline typically expected for May. Thanks to the very wet winter, nearly all the groundwater indicator sites were higher than normal, with the exception of the Inferior Oolite aquifer at Jackaments Bottom, whose level was normal. The Great Oolite sites’ levels were above normal at Ampney Crucis and notably high at Fringford. Groundwater levels of all the Chalk indicator sites were exceptionally high, with Gibbet Cottages having exceptionally high levels for over half a year. Groundwater levels remained notably high for the Lower Greensand and receded to above normal for the Upper Greensand.

6. Reservoir stocks

The capacity for both of the Lower Thames and Farmoor reservoirs at the end of the month was at 98%, up from 96% and 95%, respectively, last month.

7. Environmental impact

There were 6 fluvial Flood Alerts issued on rivers during May. By month end, there were 5 groundwater Flood Alerts in force. At the end of May, 3 abstraction licences were 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