Research and analysis

Wessex water situation: April 2025 summary

Updated 14 May 2025

Applies to England

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

1. Summary

April largely saw a continuation of the dry weather from March with a few interspersed days of higher rainfall in the latter half of the month. An average of 36mm, 68% of the long term average (LTA) fell across Wessex. In total, 90% of rain in April fell between 15 April and 22 April. When considered alongside an exceptionally dry March, this has been the fifth driest 2 month period (March to April) since records began in 1871. Soil moisture deficit (SMD) was at a historic maximum for the time of year at the beginning of April and initially continued to increase. Following rain between 15 April and 22 April, SMD briefly decreased, dipping below the historic maximum. By the end of April, SMD was rising again following a week of dry weather. Monthly mean flows recorded across the north and west of Wessex were largely below normal to exceptionally low while the majority of sites to the south of Wessex reported normal monthly mean flows due to baseflow from the Chalk aquifer. Groundwater sites monitoring the Chalk reported between normal and notably low levels at the end of April while Didmarton in the north of Wessex monitoring the Inferior Oolite recorded above normal levels. Reservoirs ended April at approximately 90% capacity for both Wessex Water and Bristol Water.

2. Rainfall

An average of 36mm of rain fell across Wessex in April (68% of the LTA). This came after an exceptionally dry March, resulting in the fifth driest 2 month period (March to April) since records began in 1871. Most rain in April fell in the latter half of the month. A total of 16% of the month’s rain fell on 15 April and 36% and 30% of the total rain in April fell on 18 April and 22 April respectively. The lowest relative rainfall was recorded in the Upper Hampshire Avon and Bourne in the east of Wessex (35% of the LTA). The highest relative rainfall was recorded in the West Somerset Streams (128% of the LTA). Hydrological areas in the west and south of Wessex received normal rainfall while areas to the east and north of Wessex received below normal to notably low rainfall during April.

Over the past 3 months, all hydrological areas received at most below normal rainfall with most areas to the north and east receiving notably low rainfall. The Little Avon in the north of Wessex was the only hydrological area to receive exceptionally low rainfall. Over the past 6 months, most of Wessex has received normal rainfall except for 2 areas to the north west which received below normal. Over the past 12 months, most areas of Wessex have received between normal and above normal rainfall except for the West Dorset Streams which received notably high rainfall.

3. Soil moisture

SMD in Wessex initially increased for the first couple of weeks of April. Following rain on 18 and 22 April, SMD briefly decreased, dipping below the historic maximum in the latter half of April. At the end of April, SMD was rising again following a dry week. At the end of the month, most hydrological areas to the south and west of Wessex recorded a SMD in the range of 41mm to 70mm. In the north east of Wessex, most hydrological sites recorded a SMD between 71mm and 100mm at the end of April. In the south and west, SMD was 26mm to 50mm higher than the LTA. In the north east SMD was largely 51mm to 75mm higher than the LTA.

4. River flows

In April, the majority of flow sites in the north of Wessex reported between below normal and notably low monthly mean flows. The exceptions were the Bristol Frome at Frenchay and Bristol Avon at Great Somerford which both recorded exceptionally low monthly mean flows and Isle at Ashford Mill which recorded normal flows reflecting higher rainfall in the west of Wessex. Most sites monitoring flows on and downstream of the Chalk aquifer recorded normal monthly mean flows in April as the flows are supported by strong baseflow from the Chalk aquifer. The only exception was the Dorset Stour at Throop which recorded below normal flows. The River Washford at Beggearn Huish was the only flow site with higher flows at the end of April than the beginning of the month. For most sites, daily mean flows fell throughout most of April. A few sites recorded peaks in daily mean flows following rain on 18 April such as the Isle at Ashford Mill and Asker at Bridport East Bridge.

5. Groundwater levels

The majority of groundwater sites monitoring the Chalk aquifer ended April reporting either below normal or notably low levels. The 2 exceptions were Tilshead and Chitterne Down which both reported normal levels. In the north of Wessex, Didmarton (monitoring the inferior Oolite) recorded above normal levels at the end of April. Over Compton (monitoring the Bridport Sand) reported normal levels at the end of the month. Across all sites, groundwater levels were decreasing throughout most of April.

6. Reservoir stocks

Reservoir levels continued to decrease during April. For Wessex Water, reservoir levels steadied in the latter half of the month while for Bristol Water they continued to decrease until the end of April. The current combined levels for both Wessex Water and Bristol Water are approximately 90% capacity. For both water companies this is lower than reservoir levels recorded this time last year. For Wessex Water, reservoir levels are still slightly higher than in April 1995 but for Bristol Water they are now lower.

Author: Wessex Hydrology, hydrologywessex@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.