Monthly water situation report South East England Summary – August 2021 August was the first month since April when the rainfall recorded was below the long term average across the South-east of England. Only 88% of the LTA rainfall was recorded during the month, with the distribution of the rainfall skewed towards the first half of the month. The soil moisture deficits ended the month slightly below the average, and no significant recharge occurred. The rivers draining impermeable catchments responded to the heavy rainfall, with nearly half of the key indicator sites in the exceptionally high category. There were 16 fluvial flood alerts and 3 fluvial flood warnings. Levels fell at most of the groundwater sites during the month and remained at normal or higher levels. Rainfall August was the first month since April when the rainfall recorded was below the long term average (LTA) across the South-east of England. Only 88% of the LTA rainfall was recorded during the month, with the distribution of the rainfall skewed towards the first half of the month, with the days with the highest totals the 1st, 6th, 8th, 9th and 21st. The highest daily total of 53.4mm was recorded at Westergate, Sussex Coast, Solent and South Downs (SSD) on the 8th August. Just under a half of this was recorded in 75 minutes. The heavy rainfall on the 8th formed a band from the Isle of Wight to Kent. By contrast, the distribution of the rain on the 21st was from the Cotswolds (Thames, THM) to the Chilterns (Hertfordshire and North London,HNL). On average, there were 19 ‘dry’ days (<0.2mm rainfall) across the South-east of England, half of which were at the end of the month. Soil Moisture Deficit/Recharge Unsurprisingly the soil moisture deficits (SMDs) reflected the pattern of rainfall during the month, falling significantly in the south between the 6th and 8th and on the 21st across the Chilterns in the north. The SMDs increased during the dry weather after the 21st. Generally, the SMDs ended the month slightly below the LTA across the South east, although there were local variations. No significant recharge occurred during August. River Flows The rivers draining impermeable catchments responded quickly to the heavy rainfall at the beginning of the month and declined very quickly. These daily peaks were high enough to affect the monthly average flows, resulting in nearly half of the indicator sites recording flows in the exceptionally high category. These included the Medway at Teston and East Farleigh (Kent and South London,KSL) and the Arun at Alfoldean (SSD). The Rother at Udiam (KSL) recorded the highest August flows on record. The groundwater-fed rivers were generally in the above normal category or higher and recorded the highest flows since 2014. The exceptions included the Wey at Tilford (THM) and the Ver at Colney Street (HNL) both with the highest flows since August 2001. There were 16 fluvial flood alerts and 3 fluvial flood warnings during August. HNL THM SSD KSL Total Fluvial Flood Alerts 0 3 9 4 16 Fluvial Flood Warnings 0 0 3 0 3 Groundwater Levels Groundwater levels across the South-east of England remained mainly at normal or above during the month. The exception was Jackaments (Oolites, THM) which was below normal. Levels for most of the Chilterns, Berkshire Downs and Hampshire Chalk remained in the normal range, including Stonor (THM) and Lopcombe (SSD). Levels for 14 of the 16 indicator boreholes fell during the month. However, the more responsive sites at Carisbrooke Castle (IOW) and Chilgrove (South Downs), both SSD, responded to the rainfall during the month and levels fell slightly to the record the highest August levels since 2012. West Meon (Hampshire Chalk, SSD) recorded the 3rd highest August level on record, the highest since 2007. About half of the key indicator sites had their highest levels since August 2014. Reservoir Storage/Water Resource Zone Stocks Reservoir storage was above the LTA for all reservoirs with the exceptions of Darwell (KSL) and Farmoor (THM). Author: [email protected] 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 herein. www.gov.uk/environment-agency © Environment Agency 2021 Rainfall Map Total rainfall for hydrological areas across South East England for the current month, the last 3 months, the last 6 months and the last 12 months classed relative to an analysis of respective historic totals. Data source:HadUK data based on the Met Office 1Km gridded rainfall dataset derived from raingauges. (Source:Met Office © Crown Copyright, 2021). Provisional data based on Environment Agency 1Km gridded rainfall dataset derived from Environment Agency intensity raingauges. Some features of this map are based on digital spatial data licensed from the Centre for Ecology and Hydrology, © CEH. Includes material based on Ordnance Survey 1:50 000 maps with the permission of the controller of Her Majesty’s Stationery Office © Crown copyright. All rights reserved. Environment Agency, 100026380, 2021. www.gov.uk/environment-agency © Environment Agency 2021 River Flow and Groundwater Status Map Groundwater site status based on end of month level. Surface water site status based on mean monthly flow. Some features of this map are based on digital spatial data licensed from the Centre for Ecology and Hydrology, © CEH. Includes material based on Ordnance Survey 1:50 000 maps with the permission of the controller of Her Majesty’s Stationery Office © Crown copyright. All rights reserved. Environment Agency, 100026380, 2021 Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC www.gov.uk/environment-agency © Environment Agency 2021 Thames – Page 1 Monthly total rainfall (mm) Long term average rainfall (mm) Cotswolds West - Rainfall Berkshire Downs - Rainfall 180 200 160 180 160 140 140 120 120 100 100 80 80 60 60 Rainfall (mm) Rainfall (mm) Rainfall 40 40 20 20 0 0 Sep-20 Sep-20 Oct-20 Oct-20 Nov-20 Nov-20 Dec-20 Dec-20 Jan-21 Jan-21 Feb-21 Feb-21 Mar-21 Mar-21 Apr-21 Apr-21 May-21 May-21 Jun-21 Jun-21 Jul-21 Jul-21 Aug-21 Aug-21 Cotswolds West - Effective Rainfall Berkshire Downs - Effective Rainfall 160 120 140 100 120 80 100 80 60 60 40 40 Effective (mm) Effective Rainfall Effective (mm) Effective Rainfall 20 20 0 0 Sep-20 Sep-20 Oct-20 Oct-20 Nov-20 Nov-20 Dec-20 Dec-20 Jan-21 Jan-21 Feb-21 Feb-21 Mar-21 Mar-21 Apr-21 Apr-21 May-21 May-21 Jun-21 Jun-21 Jul-21 Jul-21 Aug-21 Aug-21 RIVER COLN AT BIBURY RIVER KENNET AT MARLBOROUGH Ranking used data from 01/10/1963 to 31/12/2017 Ranking used data from 01/02/1972 to 31/12/2017 7 5 4 6 4 5 3 4 3 3 2 2 2 1 Daily FlowMean (cumecs) Daily Daily FlowMean (cumecs) Daily 1 1 0 0 31-Oct-19 31-Dec-19 29-Feb-20 30-Apr-20 30-Jun-20 31-Aug-20 31-Oct-19 31-Dec-19 29-Feb-20 30-Apr-20 30-Jun-20 31-Aug-20 RIVER THAMES AT FARMOOR (NATURALISED) Ranking used data from 01/10/1992 to 31/12/2017 80 70 60 50 40 30 20 Daily FlowMean (cumecs) Daily 10 0 31-Oct-19 31-Dec-19 29-Feb-20 30-Apr-20 30-Jun-20 31-Aug-20 Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data www.gov.uk/environment-agency © Environment Agency 2021 Thames – Page 2 Monthly total rainfall (mm) Long term average rainfall (mm) North Downs Hampshire - Rainfall Wey Greensand - Rainfall 250 250 200 200 150 150 100 100 Rainfall (mm) Rainfall (mm) Rainfall 50 50 0 0 Sep-20 Sep-20 Oct-20 Oct-20 Nov-20 Nov-20 Dec-20 Dec-20 Jan-21 Jan-21 Feb-21 Feb-21 Mar-21 Mar-21 Apr-21 Apr-21 May-21 May-21 Jun-21 Jun-21 Jul-21 Jul-21 Aug-21 Aug-21 North Downs Hampshire - Effective Rainfall Wey Greensand - Effective Rainfall 140 140 120 120 100 100 80 80 60 60 40 40 Effective (mm) Effective Rainfall Effective (mm) Effective Rainfall 20 20 0 0 Sep-20 Sep-20 Oct-20 Oct-20 Nov-20 Nov-20 Dec-20 Dec-20 Jan-21 Jan-21 Feb-21 Feb-21 Mar-21 Mar-21 Apr-21 Apr-21 May-21 May-21 Jun-21 Jun-21 Jul-21 Jul-21 Aug-21 Aug-21 RIVER WEY AT TILFORD RIVER LODDON AT SHEEPBRIDGE Ranking used data from 01/01/1973 to 31/12/2017 Ranking used data from 01/10/1965 to 31/12/2017 30 14 12 25 10 20 8 15 6 10 4 Daily FlowMean (cumecs) Daily Daily FlowMean (cumecs) Daily 5 2 0 0 31-Oct-19 31-Dec-19 29-Feb-20 30-Apr-20 30-Jun-20 31-Aug-20 31-Oct-19 31-Dec-19 29-Feb-20 30-Apr-20 30-Jun-20 31-Aug-20 RIVER THAMES AT KINGSTON (NATURALISED) Ranking used data from 01/01/1951 to 31/12/2017 450 400 350 300 250 200 150 100 Daily FlowMean (cumecs) Daily 50 0 31-Oct-19 31-Dec-19 29-Feb-20 30-Apr-20 30-Jun-20 31-Aug-20 Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data www.gov.uk/environment-agency © Environment Agency 2021 Hertfordshire and North London Monthly total rainfall (mm) Long term average rainfall (mm) Chilterns East Colne - Rainfall Lee Chalk - Rainfall 200 180 180 160 160 140 140 120 120 100 100 80 80 60 60 Rainfall (mm) Rainfall (mm) Rainfall 40 40 20 20 0 0 Sep-20 Sep-20 Oct-20 Oct-20 Nov-20 Nov-20 Dec-20 Dec-20 Jan-21 Jan-21 Feb-21 Feb-21 Mar-21 Mar-21 Apr-21 Apr-21 May-21 May-21 Jun-21 Jun-21 Jul-21 Jul-21 Aug-21 Aug-21 Chilterns East Colne - Effective Rainfall Lee Chalk - Effective Rainfall 120 100 90 100 80 70 80 60 60 50 40 40 30 20 Effective (mm) Effective Rainfall Effective (mm) Effective Rainfall 20 10 0 0 Sep-20 Sep-20 Oct-20 Oct-20 Nov-20