Research and analysis

Kent and South London water situation: September 2024 summary

Updated 11 October 2024

Applies to England

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

The whole of the Kent and South London (KSL) area received 193% of the long-term average (LTA) rainfall during September. Rainfall received across catchments in the area ranged from normal to exceptionally high. Soil moisture deficits (SMDs) decreased in most catchments in September due to the increase in the effective rainfall received. Monthly mean flows (MMFs) ranged from notably high to exceptionally high in September. Groundwater levels during September continued to fall across most of the KSL area and are still ranging from normal to exceptionally high for this time of the year. Levels in 3 of 5 reservoirs in KSL decreased in September; Bewl, Darwell and Bough Beech. Powdermill and Weirwood reservoirs levels increased slightly.

1. Rainfall

The whole of the Kent and South London (KSL) area received 193% of the long-term average (LTA) rainfall during September. Rainfall received across catchments in the area ranged from normal to exceptionally high. Exceptionally high rainfall was recorded in 8 of the 13 catchments in across the south and west of KSL. Notably high rainfall was recorded in North Kent Chalk, while above normal rainfall was recorded in Northwest Grain, Stour and Dover Chalk. Normal rainfall was recorded in Sheppey and Thanet Chalk catchments. The percentage of LTA rainfall received across catchments ranged from 95% across Thanet Chalk rainfall area to 278% in the Medway rainfall area. The highest daily rainfall total of 60.3mm for September was recorded at Sundridge PS rain gauge in the Darent catchment on the 22 September. The next highest daily rainfall totals were on 5, 8, 20 and 29 September and ranged from 31.3mm to 60.3mm. In September, 2 dry days where less than 0.2mm of rainfall was received were recorded on 17 and 31 September. The Medway and Eastern Rother catchments recorded the wettest September on record since records began in 1871.  The Lower Mole catchment saw the third wettest September on record. Analysis of the rainfall over the last 12 months from September 2024 to October 2023 shows that the whole KSL area recorded the second wettest 12 months since records began in 1871. Individual catchments saw lower Mole, Darent, Medway, Eastern Rother and Romney Marsh recorded the second wettest 12 months on record.  

2. Soil moisture deficit and recharge

At the end of September, SMDs in the south and west of the patch ranged from less than 10mm to 40mm. SMDs in the north and east of the patch were higher and ranged from 41mm to 130mm. SMDs decreased in most catchments in September due to the increase in the effective rainfall received. Across the whole area, on average, effective rainfall received this month was at 208% of the LTA.

3. River flows

MMFs ranged from notably high to exceptionally high in September. Three key flow sites saw notably high MMFs all located in the east of the patch.  Eight flow sites across the remaining areas of the catchment saw exceptionally high MMFs during September. Rother at Udiam recorded the highest percentage LTA of 622% for the month of September. Stour at Horton recorded the lowest percentage LTA of 142%. The Rother at Udiam recorded the second highest flows for the month of September since records began in 1961 with 4 cubic metres per second. The Medway at Teston recorded the third highest flows for the month of September since records began in 1961 with 15.3 cubic metres per second.  

4. Groundwater levels   

Generally, groundwater levels continued to fall across the KSL area. This is with the exception of Riverhead and Fleet Reservoir, where the fall of groundwater levels has discontinued. The fall in groundwater levels has also slowed down at Sweeps Lane and Wolverton. In general, the slowdown or discontinuation of the fall of groundwater levels is consistent with the effective rainfall that in September was relatively high.

At the end of September, groundwater levels across the whole KSL area were still ranging from normal to exceptionally high. The Lower Greensand aquifer at Riverhead continues to register groundwater levels that for this time of the year are notably high, with a slight rise this month. Groundwater levels in the chalk aquifer are also mostly notably high. An exception are the key monitoring points in the west of the patch registering levels in the Chalk at Chipstead and Sweeps Lane that are assessed as normal and above normal, respectively. 

5. Reservoir stocks

Levels in 3 of the 5 reservoirs in KSL decreased in September; Bewl, Darwell and Bough Beech. Powdermill and Weirwood reservoir levels increased. Weirwood reservoir is currently offline.

At the end of September, reservoir levels were:

• normal at Powdermill with 61% and Bewl with 64%
• notably high at Darwell with 67% and Bough Beech with 66%
• exceptionally high at Weirwood with 100%

6. Environmental impact 

Hands off flow constraints were removed for certain licensed abstractions within the Rother, Medway and Stour catchments during September. Eighteen fluvial flood alerts and 9 flood warnings were issued from 22 September to 30 September.

Author: Groundwater and Hydrology Team, ksl.gwh@environment-agency.gov.uk

Contact details: 03708 506 506

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.