Wessex water situation: July 2024 summary
Updated 14 August 2024
Applies to England
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1. Summary
July marked the return to wetter conditions following the driest June in 6 years. An average of 79mm fell across Wessex equating to 151% of the long term average (LTA). This increase in rainfall from last month also helped make this the wettest 6 month and 12 month periods on record since 1871. Soil moisture deficit (SMD) initially decreased during July in response to the high rainfall towards the beginning of the month but then increased to near the LTA by the end of the month. The majority of monthly mean flows in the north of Wessex were normal or above normal, while flows in the south were largely above normal or notably high. Groundwater sites at the end of July varied between normal and notably high across most sites including those monitoring the Chalk aquifer. Throughout July, reservoir levels continued to decrease with Wessex Water ending the month at approximately 76% capacity and Bristol Water ending July at approximately 75% capacity.
2. Rainfall
An average of 79mm of rain fell across Wessex in July (151% of the LTA). Recorded monthly rainfall ranged from 115% to 221% of the July LTA with the lowest relative rainfall recorded in the Mendips and River Chew and the highest in the West Dorset Streams. Rainfall was concentrated on a couple of days towards the beginning of the month with an average of 22mm falling on 5 July (27% of rain during July) and 21mm falling on 8 July (26% of rain during July). In total, 61% of the month’s total rainfall fell between 5 July and 8 July. Hydrological areas across the north of Wessex received normal rainfall while those to the south of Wessex received either normal or above normal rainfall. Over the past 3 months, the picture in the north of Wessex is similar as most hydrological areas received normal quantities of rainfall. In the south of Wessex however, 3 of the areas which received above normal rainfall in July recorded notably high rainfall across the past 3 months. Due to the wet winter and spring, both the last 6 and 12 months recorded exceptionally high rainfall across all hydrological areas. This has been both the wettest 6-month period (February to July) and 12-month period (August to July) since records began in 1871.
3. Soil moisture
SMD in Wessex initially decreased for the first couple of weeks of July, before increasing again for the remainder of the month. At the end of July, the majority of Wessex recorded a SMD in the range of 71mm to 100mm. Small areas in the east of Wessex recorded a higher SMD in the range of 101mm to 130mm while a couple of small areas in the west of Wessex recorded lower SMD values in the range of 41mm to 70mm and 11mm to 40mm. When compared to the LTA, the majority of the south of Wessex recorded an SMD within 5mm of the LTA at the end of July. In the north east of Wessex, SMD was between 6mm and 25mm above the LTA. However in the north west of Wessex, SMD was between 6mm and 25mm below the LTA.
4. River flows
In July, the majority of sites to the north and west of Wessex reported normal or above normal mean monthly flows. Sites to the south and east of Wessex, including those on the Chalk aquifer largely recorded above normal or notably high flows. Flows were higher on the Chalk largely because of groundwater supplied by the aquifer contributing towards river flows. East Stoke Combined and Baggs Mill, on the Dorset Frome and the Piddle respectively both recorded exceptionally high mean monthly flows. Most sites recorded flows peaking around 9 July and recorded falling flows towards the end of the month.
5. Groundwater levels
Groundwater levels at the end of July varied between normal and exceptionally high across Wessex. Didmarton 1 (monitoring the Inferior Oolite formation) was the only site to record exceptionally high levels at the end of the month. Amongst sites monitoring the Chalk aquifer, Kingston Russell Road was the only site to record notably high levels at the end of the month. The remaining sites monitoring the Chalk recorded either normal or above normal groundwater levels. Allington 2 (monitoring the Great Oolite formation) recorded normal levels and Overcompton (monitoring the Bridport Sand formation) recorded notably high levels at the end of July.
6. Reservoir stocks
Reservoir levels in Wessex continued to decrease throughout July. At the end of the month, Wessex Water reported reservoirs at approximately 76% capacity which is very similar to this time last year. Bristol Water reported reservoir levels of approximately 75% capacity at the end of July which is approximately 5% lower than this time last year.
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.