Research and analysis

Kent and South London water situation: December 2024 summary

Updated 14 January 2025

Applies to England

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

1. Summary

The whole of the Kent and South London (KSL) area received 78% of the long-term average (LTA) rainfall during December. The rainfall received was below normal across catchments in the North-west and one catchment in the east. The rest of the Kent and south London area saw normal rainfall. At the end of December, soil moisture deficits (SMDs) were 10mm or less in most catchments, except for three catchments in the northeast of KSL. Monthly mean flows (MMFs) are mostly normal in December with two key flow sites above normal in the northeast of the patch. Groundwater levels in the Chalk at most locations across the KSL area have begun to rise. Although they are rising, which for this time of the year is typical, groundwater levels in the Chalk in the KSL area can be described as normal or above normal. Only the Lower Greensand aquifer at Riverhead continued to register groundwater levels that are notably high for this of the year. Levels at the end of the month at the five water company reservoirs in the area ranged from normal to exceptionally high. 

2. Rainfall

The whole of the KSL area received 78% of the LTA rainfall during December. Rainfall across the Kent and South London area received below normal across catchments in the north-west and one catchment in the east. The rest of the Kent and south London area saw normal rainfall. The LTA rainfall received across catchments ranged from 57% in the South London area to 91% in the Stour and Dover chalk area. The highest daily rainfall total of 25.9mm for December was recorded at Charing PS rain gauge in the Stour catchment on 8 December. The next highest daily rainfall totals were on 9, 4, 18 and 5 December and ranged from 21.3mm to 13.8mm. Dry days, where less than 1mm of rainfall was received, were registered at the middle and end of the month. 

3. Soil moisture deficit and recharge

At the end of November, SMDs were 10mm or less in almost all catchments, with exception of the Isle of Grain, Sheppey and Thanet. At the end of December SMDs were 10mm or less in almost all catchments again, with exception of the Isle of Grain, Sheppey and Thanet which saw slightly lower deficits than November. At the end of November, the difference in LTA ranged from -75 in the west and centre of the patch to -6 in the north and south. In December the difference in LTA decreased in many of the catchments ranging from minus 25 to 5.

4. River flows

MMFs are mostly normal in December with two key flow sites above normal. Eight out of the eleven key flow sites saw normal MMFs. Two key flow sites located in the North-west of the patch saw above normal MMFs, River Wandle at Connolly’s mill and river Darent at Hawley, and one key flow site located also in the North-west of the area, saw below normal MMFs at river Ravensbourne at Catford. Dour at Crabble recorded the highest MMF highest percentage LTA of 127% for the month of December. Ravensbourne at Catford recorded the lowest percentage LTA of 61%.

5. Groundwater levels   

At the end of December, groundwater in the Chalk can be found at levels that for this time of year are either normal or above normal. At the end of the month, levels at Wolverton and Little Bucket in the east but also Sweeps Lane in the west of the patch were normal. The Lower Greensand aquifer at Riverhead continued to register groundwater levels that are notably high. Groundwater levels in the Chalk at most locations across the KSL area have started to rise except Riddles Lane and Sweeps Lane which are levelling off.  The rise in groundwater levels is consistent with the effective rainfall of 96% of the LTA. It is also consistent with the continued depletion of SMDs seen in most areas by the end of December.

6. Reservoir stocks

At the end of December, reservoir levels were: 

• Normal at Darwell with 79% and Bewl at 63%
• Above normal at Bough Beech at 92%
• Weir Wood and Powdermill reservoirs were full at the end of this month. Weir Wood reservoir remained offline during December.

7. Environmental impact 

Five fluvial flood alerts were issued from 5 to 10 December.

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.