Research and analysis

South East water situation report: March 2024 summary

Updated 15 April 2024

Applies to England

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

1. Summary

March was another wet month with 159% of the monthly long term average (LTA) rainfall recorded across the south east of England.  March marks the end of the hydrological winter from October 2023 where 5 of the 6 months received significantly higher than average rainfall.  It was the wettest winter on record (from 1871) for the south east as a whole.  After the particularly wet last few days of March, the soil moisture deficit (SMD) dropped to end below the LTA for the end of March, close to zero.  The recharge was on average twice what would be expected for March and 231% of the LTA for the 6 month period ending March.  As would be expected after a wet month, and in particular a wet winter, the monthly mean flows for the indicator sites were in the notably high or exceptionally high category for March.  There were 129 fluvial flood alerts and 8 fluvial flood warnings issued during the month.  The groundwater levels remained high during the month in response to the winter recharge.  Levels at Chilgrove, Solent and South Downs (SSD) were the highest since March 1951.  There were 8 groundwater flood alerts issued during the month.  

2. Rainfall

March was another wet month with 159% of the monthly LTA rainfall recorded across the south east of England.  Overall the weather was unsettled, with a succession of frontal systems bringing rain and wind.  The highest daily rainfall totals were recorded at the beginning and end of the month, with the highest, 26.8mm, recorded at Chiddingfold, (SSD) on March 1.  The highest daily total recorded for Hertfordshire and North London (HNL) for March was also on the first, but for Kent and South London (KSL) it was 10 March and for Thames (THM) it was 28 March. For the south east as a whole, the days with the highest totals were 1, 4, 27, 28 and 31 March.  These 5 days accounted for an average of 37% of the monthly total rainfall.  Generally, the west was wetter than the east, where the maximum number of days with greater than 10mm was 9 for SSD and 7 for THM.  HNL and KSL recorded only a maximum of 5 days with greater than 10mm.

March marks the end of the hydrological winter from October 2023 where 5 of the 6 months received significantly higher than average rainfall.  It was the wettest winter on record (from 1871) for the south east as a whole, and a number of areal rainfall units including Cotswolds West and Berkshire Downs (both THM) and the Isle of Wight (SSD). For the remaining areal units, it was either the second wettest winter after 2001, including Chilterns East (HNL), Dover Chalk (KSL) and Thame (THM) or the third wettest winter after 2014, including Chilterns West (THM), Upper Mole (KSL), and Test (SSD).  There were also some significant statistics for the 12 month period ending in March, with both Berkshire Downs (THM) and Lymington (SSD) recording the wettest year ending in March on record (from 1871).  The remainder of the areal units were split between being the second wettest year since 2001 and the third since 2013. 

3. Soil moisture deficit and recharge

After the particularly wet last few days of March, the SMD dropped to end below the LTA for the end of March, close to zero.  For the winter as a whole, the SMDs reached zero in October, generally a month earlier than the LTA, allowing a longer period for recharge to the groundwater.  The SMDs remained close to zero for most of the winter.  The recharge was on average twice what would be expected for March and 231% of the LTA for the 6 month period ending March. 

4. River flows

As would be expected after a wet month, and in particular a wet winter, the monthly mean flows for the indicator sites were in the notably high or exceptionally high category for March.  The 3 sites which had notably high flows were the Lee at Feildes Weir (HNL), the Lymington River at Lymington (SSD) and the Teise at Stonebridge (KSL).  The remaining 18 indicator sites were all in the exceptionally high range for March.  The groundwater-fed rivers have maintained high flows in response to the winter recharge and the rivers draining impermeable catchments responded quickly to the frontal systems which crossed the south east during the month.  The Thames at Farmoor, Kennet at Marlborough and Wey at Tilford (all THM); the Arun at Alfoldean (SSD) and the Dour at Crabble Mill (KSL) all recorded the highest monthly flow for March on record.  The majority of the remaining sites had the highest March flows since 2001, including the Ver at Colney Street and the Lee at Feildes Weir (both HNL), the Thames at Kingston (THM) and the Medway at Teston and East Farleigh (KSL).  The Mimram at Panshanger (HNL) and the Test at Broadlands recorded the highest March flows since 2014.  There were 129 fluvial flood alerts and 8 fluvial flood warnings issued during the month.

5. Groundwater levels   

The groundwater levels remained high during the month in response to the high rainfall and the winter recharge.  Levels at Clanville Lodge (SSD) and Rockley (THM) flattened off during the month. Carisbrooke, Houndean Bottom and Chilgrove levels all fell slightly and the levels at the remaining 11 indicator sites continued to rise during March.  Ten sites recorded exceptionally high levels, including Stonor (THM), Ashley Green (HNL) and Chilgrove (SSD); 4 sites were in the notably high band, including West Meon Hut (SSD) and Riddles Lane (KSL) and 2 were above normal, including Jackaments (THM).  Levels at Chilgrove (SSD) were the highest since March 1951; Ashley Green levels (HNL) were the highest since 2001 and most of the remaining sites recorded the highest levels since 2014.  There were 8 groundwater flood alerts issued during the month.

6. Reservoir stocks

Reservoir stocks ended March below the LTA at Farmoor (THM), and Arlington (SSD) reservoirs and at or above the LTA at Lower Thames (THM), Lee Valley (HNL), Ardingly (SSD), Bough Beech, Darwell, Bewl, Powdermill & Weir Wood (all KSL) reservoirs.

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.