Research and analysis

Thames water situation report: August 2024 summary

Updated 13 September 2024

Applies to England

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

1. Summary

Thames area received 42mm of rainfall in August, 71% of the long term average (LTA). Most of the area’s areal units received normal rainfall, though the 5 north-eastern areal units received below normal rainfall. Soil moisture deficits (SMDs) increased slightly from last month to 92mm across the area and ended the month slightly higher than the LTA (87mm). Monthly mean river flows at all our indicator sites were normal or above, with the River Wye at Bourne End the only site to record exceptionally high flow. At the end of the month, levels at the majority of our groundwater sites continued their expected seasonal decline, and levels were normal or above for the time of year.

2. Rainfall

August was drier than typical, with Thames area receiving 42mm of rainfall for the month, 71% of the LTA. There was a geographic distribution of rainfall across the area, with normal rainfall in the southwestern areal units and below normal rainfall for the 5 northeastern units. Total accumulated rainfall for the past 3 months was below normal or normal for all areal units and rainfall remains exceptionally high across the entire area over the past 12 months.

3. Soil moisture deficit and recharge

SMDs increased slightly in August, ending the month at 94mm for the area, slightly higher than the LTA (87mm). SMDs were generally lower in the north of the area and higher in the south. Due to the month’s low rainfall and high evapotranspiration, effective rainfall in August was low.

4. River flows

Monthly mean river flows at most of our indicator sites were normal or above normal in August despite low rainfall, due to high rainfall in July. Almost all sites continued their usual seasonal decline. Many of the groundwater fed rivers (such as River Blackwater, River Wey, River Wye) were still supported by the continued contribution of groundwater baseflow resulting from the exceptionally wet winter. The River Wye at Bourne End was the only site in August with an exceptionally high flow.

5. Groundwater levels   

Except for the Lower Greensand aquifer at Frith Cottage, whose level remained largely unchanged, all our groundwater sites continued their expected seasonal declines, though their levels were still normal or above, following the exceptionally wet winter. These were largely in the same banding as last month, with only the Inferior Oolite aquifer at Marcham moving from exceptionally high to notably high and the Great Oolite aquifer at Ampney Crucis moving from above normal to normal. The Chalk aquifer at Stonor Estate was the only site to remain at an exceptionally high level for the time of year for the seventh month in a row.

6. Reservoir stocks

Reservoir capacity at Farmoor was steady for most of August, starting the month at 99%, before declining slightly to end the month at 96%, above the LTA. Capacity at the Lower Thames reservoirs decreased steadily over August from 91% at the beginning to 80% at the end on the month, remaining above the LTA for the time of year.

7. Environmental impact 

There were 3 flood alerts issued across Thames area during August. At the end of August, 11 abstraction licences were being constrained in Thames area to protect water resources and the environment.

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

Contact Details: 030708 506 506