Research and analysis

South-east England 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

The south-east of England received 70% of the long term average (LTA) rainfall for August. The highest daily rainfall was 54.6mm, recorded at Eden Vale sewage treatment works (STW), Kent and South London (KSL) on 1 August, with 80% of this falling in just 30 minutes between 6:15pm and 6:45pm Greenwich Mean Time (GMT). Soil moisture deficits (SMDs) fluctuated following early and mid-month rainfall but rose steadily towards the end of August, finishing above the LTA for August. River flows displayed a range of responses, with 6 indicator sites recording normal flows. However, 4 sites, including chalk-fed rivers, recorded exceptionally high flows. Groundwater levels showed seasonal declines but remained notably high at several sites due to prior rainfall. A total of 14 fluvial flood alerts and 1 flood warning were issued during August

2. Rainfall

The south-east of England received 70% of the LTA rainfall for August. The wettest day was 24 August, contributing 24% of the monthly total on average, closely followed by 23 August (18%), and the third wettest day was 1 August (13%). Together, the days from 22 to 24 August accounted for 47% of the monthly rainfall total, on average, while these 4 wettest days, including 1 August, contributed to 60% of the total monthly rainfall on average.

The highest daily rainfall was 54.6mm, recorded at Eden Vale STW, KSL on 1 August, with 80% of this falling in just 30 minutes between 6:15pm and 6:45pm GMT. The heavy rainfall on 1 August was largely confined to the Thames Area (THM), Solent and South Downs (SSD), and parts of KSL. The wettest area was SSD, which received 80% of its LTA rainfall for August, while Hertfordshire and North London (HNL) was the driest at 40%. Overall, August ended hot and dry, with 20 ‘dry’ days (a dry day being 0.2mm rainfall or less recorded), on average across the south-east.

3. Soil moisture deficit and recharge

In August, SMDs rose steadily, briefly decreasing after rainfall on the 1 and 23 to 24 August. By month end, SMDs were above the LTA for the end of August, with minimal recharge and most areas experiencing significant dry conditions.

4. River flows

During August, the key indicator flow sites displayed a range of responses to the rainfall on 1 August and 22 August to 24 August. Some sites barely reflected any rainfall at all, whereas other sites showed relatively significant increases in flow. Some of the largest responses were unusually in the Chalk rivers of the Mimram at Panshanger and the Ver at Colney Street reflecting the very high local groundwater levels. Of the 21 indicator sites, 6 were in the normal category. These included the Coln at Bibury (THM), the Thames at Farmoor and Kingston (both THM), the Lymington at Brockenhurst (SSD), and the Rother at Udiam (KSL). The remaining 15 sites exhibited varied flows, with 4 of these in the exceptionally high category, 3 of which were chalk groundwater-fed rivers.

The Teise at Stonebridge (KSL) recorded exceptionally high flows, primarily driven by compensation flows. Some notable observations for August include:

• Colney Street (HNL) recorded the second highest August flow, after 2001
• Panshanger (HNL) ranked the third highest August flow, after 1979 and 2001
• Allbrook and Highbridge (SSD) experienced its fourth highest August flow, after 2007, 2021, and 2012
• Stonebridge (KSL) recorded the highest August flow on record, surpassing the previous high in 2021

Please note, the data for Alfoldean is incomplete this month due to ongoing issues with the station. As a result, its recorded values are not included in this report.

A total of 14 fluvial flood alerts and 1 fluvial flood warning were issued during August.

5. Groundwater levels   

In August, groundwater levels showed seasonal declines and the influence of high rainfall in previous months. Despite the levels falling as expected at this time of year, many sites continued to maintain high groundwater levels.

The following sites recorded significant rankings for August:

• Ashley Green (HNL): third highest on record, highest since 2001
• Lilley Bottom (HNL): third highest on record, highest since 2001
• Stonor Estate (THM): third highest on record, highest since 2001
• Clanville Lodge (SSD): third highest on record, highest since 2001
• West Meon (SSD): third highest on record, highest since 2007
• Chipstead (KSL): second highest on record, highest since 2016
• Wolverton (KSL): second highest on record, highest since 2007

6. Reservoir stocks

The reservoirs remain above average for August at all of the reservoirs across the south-east with just 3 exceptions. Arlington (SSD), Powdermill (KSL) and Bewl (KSL) ended the month just below the monthly LTA.

Author: groundwaterhydrology@environment-agency.gov.uk     

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.