Monthly water situation report Wessex Area Summary – August 2021 Wessex received ‘below normal’ rainfall overall in August, at 74% LTA (50 mm); though, this was split between higher rainfall across north Wessex and lower rainfall in the south. Two main periods of rainfall occurred over 1 – 9 August and 19 – 21 August, at 71% and 22% of the month’s total, respectively. The period between these events was largely dry, as was the last week of August. The soil moisture deficit fluctuated in response to the changing wet and dry conditions. The deficit steadily increased at the end of August, ending the month on 76 mm, which is lower than the LTA (81 mm) but higher than the deficit this time last year (72 mm). Monthly mean river flows were largely ‘normal’ or ‘above normal’. Daily mean flows increased in response to the main periods of rainfall, to then recede with the dry end to the month. The majority of reporting sites ended August with ‘normal’ river flows. Groundwater levels decreased at all reporting sites, with end of month levels ranging from ‘notably high’ to ‘normal’. Despite groundwater levels falling, all reporting sites were classed the same as July bar Chantry (monitoring the Old Red Sandstone), which decreased from ‘above normal’ to ‘normal’ . Total reservoir storage decreased to 79% for Wessex Water and to 66% for Bristol Water. Rainfall Wessex received 50 mm of rainfall in August (74% LTA), which is ‘below normal’ for the time of year. Rainfall totals were highest in north Wessex where catchments largely received ‘normal’ rainfall, and lower towards the south and west, where catchments received ‘below normal’ rainfall. The Axe in north Wessex had the highest rainfall total (76 mm, 96% LTA), which was over double of that received in the Lower Dorset Stour and River Crane (35 mm, 59% LTA) and Poole Harbour and Purbeck (35 mm, 60% LTA) in the south. There were two main periods of rainfall: 1 – 9 August, when 71% of the month’s rain fell, and 19 – 21 August, when 22% of the month’s rain fell. The period between these rainfall events, along with the last week of August, was largely dry. The 12 month cumulative rainfall totals are ‘above normal’ in the south and west Wessex catchments, whilst the majority of northern catchments are ‘normal’, reflecting the spatial distribution of rainfall received since August 2020. Cumulative rainfall since the start of the water year (October 2020) remains high at 116% LTA. Rainfall map and graph Soil Moisture Deficit The soil moisture deficit decreased during the start of the month, following the rainfall and peaking at 52 mm on 10 August. The deficit increased slightly during the drier period that followed, before decreasing once again following the rainfall over 19 – 21 August. The dry end to August led to the deficit increasing steadily, ending the month on 76 mm, which is lower than the LTA (81 mm) but higher than the deficit this time last year (72 mm). SMD graph and maps River Flows Monthly mean flows were ‘normal’ or ‘above normal’ at all reporting sites bar Piddle (Baggs Mill) which had ‘notably high’ flows at 124% LTA. Daily mean flows increased in response to the two main periods of rainfall over 1 – 9 August and 19 – 21 August, with the majority of reporting sites reaching ‘above normal’ or higher flows during these periods. The dry end to August led to a recession in flows, with the majority of reporting sites ending the month with ‘normal’ flows for the time of year. River flow map and graphs All data are provisional and may be subject to rev ision. 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 Groundwater Levels Groundwater levels steadily decreased throughout August at all reporting sites bar Chantry (monitoring the Old Red Sandstone), which had a small period of increased groundwater levels as a result of the rainfall received. Groundwater levels ended the month lower than they started at all reporting sites. Month end levels ranged from ‘notably high’ to ‘normal’, with all reporting sites remaining within the same classification bands as July apart from Chantry, which decreased from ‘above normal’ to ‘normal’. Groundwater map and graphs Reservoir Storage Total reservoir storage decreased throughout August, with Wessex Water ending the month on 79% and Bristol Water ending the month on 66%, which are both higher than the total storage this time last year. Reservoir graphs Flood Warnings and Alerts Flood Warnings Flood Alerts Area Fluvial Coastal Groundwater Fluvial Coastal Groundwater North Wessex 0 0 0 0 1 0 South Wessex 0 0 0 0 0 0 Sites Providing Stream Support River Site Gauge End of Month Status Tetbury Avon Tetbury Brokenborough On Luckington Brook Luckington Fossway On Sherston Avon Stanbridge Fossway Off Charlton Stream Charlton Crabb Mill Off Gauze Brooke Hullavington Rodbourne On Rodbourne Brook Lower Stanton St. Quinton Startley On Chalfield Brook South Wraxall Great Chalfield (Wessex Water) On Chalfield Brook Little Chalfield Great Chalfield (Wessex Water) Off Semington Brook Easterton No gauge Off Horscombe Stream Tucking Mill No gauge On River Wylye Brixton Deverill Brixton Deverill On River Wylye Kingston Deverill Norton Bavant On Chitterne Brook Codford Road Codford On Bourne Porton Salisbury Bourne On River Allen Wyke Down All Hallows On Gussage Stream Gussage All Saints Bowerswain On Crichel Stream Long Crichel No gauge Off Pimperne Stream Pimperne No gauge On South Winterbourne Winterbourne Abbas Winterbourne Steepleton Off Devil’s Brook Dewlish WDX Dewlish Woodsdown Cross On River Piddle Alton Mill and Morningwell South House & Little Puddle On River Piddle Briantspuddle Briantspuddle Off Watergates Stream Watergates No gauge On Abstraction Licences Subject to Cease or Restrict Catchment End of Month Status Hampshire Avon Cease – 4; Restrict – 2 Dorset Cease – 2; Restrict – 3 Bristol Avon Cease – 4; Restrict – 0 Somerset Cease – 3; Restrict - 0 Glossary Author: Wessex Hydrology www.gov.uk/environment-agency © Environment Agency 2021 Rainfall Figure 1.1: Total rainfall (as a percentage) for hydrological areas across Wessex for the current month, the last three months, the last six months, and the last 12 months, classed relative to an analysis of respective historic totals. HadUK data based on the Met Office 1km gridded rainfall dataset derived from rain gauges (Source: Met Office © Crown Copyright 2021). Provisional data based on Environment Agency 1km gridded rainfall dataset derived from Environment Agency intensity rain gauges. Return to Summary www.gov.uk/environment -agency © Environment Agency 2021 Above 100% LTA rainfall Below 100% LTA rainfall 1-Month Period for Wessex 200% 150% 100% 50% 0% May-20 Feb-21 Sep-19 Oct-19 Nov-19 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 Jun-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-20 Jan-21 Mar-21 Apr-21 May-21 Jun-21 Jul-21 Aug-21 Figure 1.2: Monthly rainfall totals as a percentage of the 1961 – 1990 long term average. Produced using HadUK data based on the Met Office 1km gridded rainfall dataset derived from rain gauges (Source: Met Office © Crown Copyright 2021). Provisional data based on Environment Agency 1km gridded rainfall dataset derived from Environment Agency intensity rain gauges. Return to Summary www.gov.uk/environment -agency © Environment Agency 2021 Soil Moisture Deficit Less than historic minimum Greater than historic maximum ..... 1961-1990 long term average ── Latest data ── 2020 0 20 40 60 80 100 Soil moisture deficit (mm) Soil moisture 120 140 160 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 2.1: Latest soil moisture deficit compared to previous year, maximum, minimum, and 1961 – 1990 long term average. Weekly MORECS data for real land use (Source: Met Office © Crown Copyright, 2021). Return to Summary www.gov.uk/environment -agency © Environment Agency 2021 Figure 2.2: Soil moisture deficits for week ending 31 August 2021. Top map shows actual soil moisture deficits (mm). Bottom map shows the difference (mm) of the actual from the 1961-90 long term average soil moisture deficits. MORECS data for real land use (Source: Met Office © Crown Copyright, 2021). Crown copyright. All rights reserved. Environment Agency, 100024198, 2021. Return to Summary www.gov.uk/environment -agency © Environment Agency 2021 River Flow Figure 3.1: Monthly mean river flows at indicator sites for August 2021, expressed as a percentage of the respective long term average and classed relative to an analysis of historic August monthly means (Source: Environment Agency). Crown copyright. All rights reserved. Environment Agency, 100024198, 2021. Flows may currently be overestimated at all reporting sites, bar Knapp Mill and Bathford, so the data should be treated with caution. Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Bristol Avon at Great Somerford Somerset Frome at Tellisford Ranking used data from 16/12/1963 to 31/12/2017 Ranking used data from 01/09/1961 to 31/12/2017 35 45 August mean flow August mean flow 0.539 cumecs 1.472 cumecs 40 67% LTA 30 106% LTA 35 25 30 20 25 20 15 15 10 10 Daily FlowDaily Mean (cumecs) Daily FlowDaily Mean (cumecs) 5 5 0 0 31-Oct-20 31-Dec-20 28-Feb-21 30-Apr-21 30-Jun-21 31-Aug-21 31-Oct-21 31-Oct-20 31-Dec-20 28-Feb-21 30-Apr-21 30-Jun-21