Research and analysis

South East 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

April was the seventh consecutive month of above average rainfall with 146% of the long term average (LTA) for April. Most of the south east of England received above normal rainfall. The highest daily total was 43.8mm recorded at Duncton rain gauge (SSD) during 18 hours of nonstop rain on 27 April. This was also the wettest day of the month. The soil moisture deficits began to rise in the second week of April and continued to rise until the rainfall at the end of the month. They then declined rapidly to single figures and were well below the LTA for the end of April across the south east of England. The heavy rainfall at the end of the month allowed recharge to reach almost twice the LTA for April for the south east of England. Overall, river flows fell during April, but responded to the rainfall at the beginning and end of the month. Half of the key indicator sites remained at exceptionally high flows for April, a quarter of the sites were at notably high levels and the remaining sites were at above normal flows. There were 37 fluvial flood alerts and 2 fluvial flood warnings issued during the month. Groundwater levels remained high reflecting the high rainfall and recharge over the month and preceding months. Most of the key indicator sites ended April at exceptionally high levels with a few exceptions that ranged from notably high to normal. There were a total of 21 groundwater flood alerts in force during April.

2. Rainfall

April was the seventh consecutive month of above average rainfall with 146% of the LTA for April. Most of the south east of England received above normal rainfall. There were a few exceptions in the Cotswold west areal unit (Thames, THM), West Sussex Chalk, Western Rother Greensand, the Arun and Adur areal units all in Solent and South Downs (SSD) and the Stour, Dover Chalk and Romney Marsh areal units in Kent and South London (KSL) which all received notably high rainfall. 

The highest daily total was 43.8mm recorded at Duncton rain gauge (SSD) during 18 hours of nonstop rain on 27 April. This was also the wettest day of the month when, on average, 32% of the monthly total rainfall was recorded. April began quite wet and for the first four days, on average, 34% of the monthly total was recorded. During the middle of the month there were on average 13 dry days when less than 0.2mm of rainfall was recorded.

For the 7 months ending in April most of the areal units were the third wettest or higher, on record. The wettest units included Cotswolds West, Berkshire Downs (all THM) and the Isle of Wight and Lymington (SSD).

3. Soil moisture deficit and recharge

The soil moisture deficits began to rise in the second week of April and continued to rise until the rainfall at the end of the month. They then declined rapidly to single figures and well below the LTA for the end of April across the south east of England. Similarly, recharge was above the monthly average within the first week due to the heavy rainfall. It remained reasonably static through the middle of the month until the heavy rainfall at the end of the month. This allowed recharge to reach almost twice the LTA for April for the south east of England.

4. River flows

Overall, river flows fell during the month, but responded to the rainfall at the beginning and end of the month. Half of the key indicator sites remained at exceptionally high flows for April, a quarter of the sites were at notably high levels and the remaining sites were at above normal flows. These latter sites were generally in and around the Wealden clay area of KSL. The sites with the higher flows were generally those fed by groundwater reflecting the continuing high groundwater levels. Flows in the Kennet at Marlborough and the Wey at Tilford (both THM) were the highest on record for April. Flows in the Itchen at Allbrook and Highbridge (SSD) were the joint highest on record with 2001. Many other sites were the highest since 2001 including the Ver at Colney Street, Mimram at Panshanger (both HNL), the Test at Broadlands (SSD), the Great Stour at Horton and Dour at Crabble Mill (both KSL). There were 37 fluvial flood alerts and 2 fluvial flood warnings issued during the month.

5. Groundwater levels   

Groundwater levels remained high reflecting the rainfall and recharge over the month and preceding months. Most of the key indicator sites ended April at exceptionally high levels with a few exceptions, mainly in KSL where groundwater levels in and around the Weald ended the month at notably high levels. In THM, Jackaments was normal for the time of year. It is a responsive site and clearly reacted to the dry weather in the middle of April. Despite the high levels, the groundwater at most of the key indicator sites fell during the month as is expected at this time of year. There were 3 exceptions where levels continued to rise, albeit more slowly than over the past months. They were Lilley Bottom (HNL), Sweeps Lane and Riddles Lane (KSL). In addition, groundwater at Stonor (THM) levelled off but remained exceptionally high for April. Twelve of the key indicator sites were all the third highest or higher on record, often since 2001. These included Ashley Green (HNL), Rockley (THM), Little Bucket (KSL) and West Meon (SSD). There were a total of 21 groundwater flood alerts in force during April.

6. Reservoir stocks

The continuing high rainfall has ensured that reservoir stocks remain above the LTA for April at all of the reservoirs across the south east of England with only Farmoor (THM) and Arlington (SSD) at their 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.