Water Situation Report Wessex Area

Monthly water situation report Wessex Area

Summary – November 2020 Wessex received ‘normal’ rainfall in November at 84% LTA (71 mm). There were multiple bands of rain throughout November; the most notable event occurred on the 14 November, when 23% of the month’s rain fell. The last week of November was generally dry. The soil moisture deficit gradually decreased throughout November, ending the month on 7 mm, which is higher than the deficit this time last year, but lower than the LTA. When compared to the start of the month, groundwater levels at the end of November had increased at the majority of reporting sites. Rising groundwater levels in the Chalk supported the groundwater dominated rivers in the south, with the majority of south Wessex reporting sites experiencing ‘above normal’ monthly mean river flows, whilst the surface water dominated rivers in the north had largely ‘normal’ monthly mean flows. Daily mean flows generally peaked around 14-16 November in response to the main rainfall event. The dry end to November caused a recession in flows, with all bar two reporting sites ending the month with ‘normal’ daily mean flows. Total reservoir storage increased, with Wessex Water and Bristol Water ending November with 84% and 83%, respectively.

Rainfall Wessex received 71 mm of rainfall in November (84% LTA), which is ‘normal’ for the time of year. All hydrological areas received ‘normal’ rainfall bar the Axe (69% LTA; 61 mm) and West Somerset Streams (71% LTA; 79 mm), which had ‘below normal’ rainfall. The highest rainfall accumulations (for the time of year) were generally in the east and south. There were multiple bands of rain throughout November; the most notable rainfall event occurred in the middle of the month, with 23% of the month’s rain falling on the 14 November. The last week of November was generally dry.

The 3 month cumulative rainfall is similarly ‘normal’ for the majority of hydrological catchments. In contrast, 12 month cumulative rainfall is largely ‘above normal’ or higher across Wessex, which reflects the heavy rainfall received at the end of 2019, and in February and October 2020. The cumulative rainfall since the start of the water year (October 2020) has decreased, but remains high at 142% LTA.

Rainfall map and graph

Soil Moisture Deficit The soil moisture deficit continued to gradually decrease throughout November in response to the rainfall received. At the end of the month, the deficit was 7 mm, which is higher than the deficit this time last year (0.1 mm), but lower than the LTA (18 mm).

SMD graph and maps

River Flows Monthly mean flows were ‘normal’ or ‘above normal’ at all reporting sites bar Sydling Water (Sydling St Nicholas), which flows were ‘notably high’ at 157% LTA. Groundwater dominated rivers in the south were supported by the ‘normal’ or higher groundwater levels in the Chalk, with the majority experiencing ‘above normal’ monthly mean flows, whilst the surface water dominated rivers in the north had largely ‘normal’ flows.

Daily river flows fluctuated throughout the month in response to the bands of rainfall. The main rainfall event led to peak flows generally occurring around 14-16 November, with many of the responsive surface water dominated rivers in the north peaking at ‘exceptionally high’ flows, whilst the majority of the less responsive groundwater dominated rivers in the south, only reached ‘notably high’. The dry end to November led to a recession in flows, with all bar two reporting sites ending the month with ‘normal’ daily mean flows.

River flow map and graphs

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 2020

Groundwater Levels When compared to the start of the month, groundwater levels at the end of November had increased at all reporting sites bar the responsive Chantry borehole (monitoring the Old Red Sandstone). On the Chalk, rising groundwater led to Ashton Farm and Woodyates reaching ‘above normal’ levels for the time of year, though levels at Tilshead remained ‘normal’. At the start of the month, groundwater levels at Kingston Russell Road (also monitoring the Chalk) were ‘above normal’, and whilst there was an increase in groundwater throughout November at this reporting site, by the end of the month these levels were ‘normal’ for the time of year.

Groundwater map and graphs

Reservoir Storage Reservoir levels increased throughout November. At the end of the month, total storage for Wessex Water was 84% and for Bristol Water was 83%, which are both lower than this time last year.

Reservoir graphs

Flood Warnings and Alerts Flood Warnings Flood Alerts Area Fluvial Coastal Groundwater Fluvial Coastal Groundwater North Wessex 2 7 0 5 20 0 South Wessex 0 5 0 9 20 0

Sites Providing Stream Support River Site Gauge End of Month Status Tetbury Avon Tetbury Brokenborough Off Luckington Brook Luckington Fossway Off Sherston Avon Stanbridge Fossway Off Charlton Stream Charlton Crabb Mill Off Gauze Brooke Hullavington Rodbourne Off Rodbourne Brook Lower Stanton St. Quinton Startley Off Chalfield Brook South Wraxall Great Chalfield (Wessex Water) Off Chalfield Brook Little Chalfield Great Chalfield (Wessex Water) Off Semington Brook Easterton No gauge Off Horscombe Stream Tucking Mill No gauge Off River Wylye Brixton Deverill Brixton Deverill Off River Wylye Kingston Deverill Norton Bavant Off Chitterne Brook Codford Road Codford On Bourne Porton Salisbury Bourne Off River Allen Wyke Down All Hallows Off Gussage Stream Gussage All Saints Bowerswain Off Crichel Stream Long Crichel No gauge Off Pimperne Stream Pimperne No gauge Off South Winterbourne Winterbourne Abbas Winterbourne Steepleton Off Devil’s Brook Dewlish WDX Dewlish Woodsdown Cross Off River Piddle Alton Mill and Morningwell South House & Little Puddle Off 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 – 1; Restrict – 0 Dorset Cease – 1; Restrict – 1 Bristol Avon Cease – 0; Restrict – 0 Somerset Cease – 2; Restrict - 0 Glossary Author: Wessex Hydrology

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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 2020). Provisional data based on Environment Agency 1km gridded rainfall dataset derived from Environment Agency intensity rain gauges.

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Above 100% LTA rainfall Below 100% LTA rainfall 1-Month Period for Wessex

200%

150%

100%

50%

Aug-19 May-20 Dec-18 Jan-19 Feb-19 Mar-19 Apr-19 May-19 Jun-19 Jul-19 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

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 2020). Provisional data based on Environment Agency 1km gridded rainfall dataset derived from Environment Agency intensity rain gauges.

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Soil Moisture Deficit

Less than historic minimum Greater than historic maximum ..... 1961-1990 long term average ── Latest data ── 2019

100

Soil moisture deficit (mm) deficit Soilmoisture 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, 2020).

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Figure 2.2: Soil moisture deficits for week ending 29 November 2020. 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, 2020). Crown copyright. All rights reserved. Environment Agency, 100024198, 2020.

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River Flow

Figure 3.1: Monthly mean river flows at indicator sites for November 2020, expressed as a percentage of the respective long term average and classed relative to an analysis of historic November monthly means (Source: Environment Agency). Crown copyright. All rights reserved. Environment Agency, 100024198, 2020.

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 45 November mean flow November mean flow 5.539 cumecs 35 40 6.372 cumecs 130% LTA 127% LTA 35 30

30 25

25 20

20 15 15 10

10 Daily FlowMean Daily (cumecs) Daily FlowMean Daily (cumecs) 5 5

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

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Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data

Bristol Avon at Bathford Bristol Frome at Frenchay Ranking used data from 27/10/1969 to 31/12/2017 Ranking used data from 01/09/1961 to 31/12/2017

160 November mean flow November mean flow 30.814 cumecs 2.151 cumecs 20 140 120% LTA 86% LTA

120 15 100

80 10 60

Daily FlowMean Daily (cumecs) FlowMean Daily (cumecs) 20

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Upper Brue at Lovington Yeo at Pen Mill Ranking used data from 01/10/1964 to 31/12/2017 Ranking used data from 31/10/1963 to 31/12/2017

November mean flow 40 November mean flow 30 3.672 cumecs 4.707 cumecs 139% LTA 123% LTA 35 25 30

20 25

20 15

15 10

10 Daily FlowMean Daily (cumecs) Daily FlowMean Daily (cumecs) 5 5

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Isle at Ashford Mill Tone at Bishops Hull Ranking used data from 01/10/1962 to 31/12/2017 Ranking used data from 01/02/1961 to 31/12/2017 16 25 November mean flow November mean flow 1.716 cumecs 3.502 cumecs 14 92% LTA 95% LTA 20 12

10 15

10 6

Daily FlowMean Daily (cumecs) FlowMean Daily (cumecs) 2

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Washford at Beggearn Huish Upper Hampshire Avon at Amesbury Ranking used data from 01/01/1967 to 31/12/2017 Ranking used data from 01/02/1965 to 31/12/2017 7.0 November mean flow November mean flow 14 1.414 cumecs 3.966 cumecs 6.0 113% LTA 140% LTA 12

5.0 10

4.0 8

3.0 6

2.0 4 Daily FlowMean Daily (cumecs) Daily FlowMean Daily (cumecs) 1.0 2

0.0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

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Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data

River Wylye at South Newton Middle Hampshire Avon at East Mills Combined Ranking used data from 01/01/1967 to 31/12/2017 Ranking used data from 01/11/1965 to 31/12/2017 20 November mean flow November mean flow 60 18 3.765 cumecs 18.099 cumecs 137% LTA 136% LTA 16 50 14

12 40

10 30 8

6 20

4 Daily FlowMean Daily (cumecs) Daily FlowMean Daily (cumecs) 10 2

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Lower Hampshire Avon at Knapp Mill Middle Stour at Hammoon Ranking used data from 01/01/1975 to 31/12/2017 Ranking used data from 01/03/1968 to 31/12/2017 100 November mean flow November mean flow 100 90 20.78 cumecs 14.447 cumecs 125% LTA 146% LTA 80 80 70

60 60 50

40 40 30

20 20

Daily FlowMean Daily (cumecs) FlowMean Daily (cumecs) 10

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 31-Jan-20 31-Mar-20 31-May-20 31-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Lower Stour at Throop Piddle at Baggs Mill Ranking used data from 01/01/1973 to 31/12/2017 Ranking used data from 01/01/1964 to 31/12/2017 140 November mean flow November mean flow 20.842 cumecs 10 2.94 cumecs 120 125% LTA 133% LTA

100 8

80 6

60 4 40

2 Daily FlowMean Daily (cumecs) Daily FlowMean Daily (cumecs) 20

0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Sydling Water at Sydling St Nicholas Dorset Frome at East Stoke Combined Ranking used data from 01/12/1969 to 31/12/2017 Ranking used data from 01/10/1965 to 31/12/2017 25 November mean flow 0.8 November mean flow 0.291 cumecs 8.667 cumecs 157% LTA 128% LTA 0.7 20

0.6

0.5 15

0.4 10 0.3

0.2

Daily FlowMean Daily (cumecs) FlowMean Daily (cumecs) 0.1

0.0 0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

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Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data

Wey at Broadwey Asker at Bridport East Bridge Ranking used data from 01/09/1975 to 31/12/2017 Ranking used data from 01/03/1996 to 31/12/2017

November mean flow 5.0 November mean flow 1.4 0.307 cumecs 0.974 cumecs 120% LTA 105% LTA

1.2 4.0

1.0 3.0 0.8

0.6 2.0

0.4

1.0 Daily FlowMean Daily (cumecs) Daily FlowMean Daily (cumecs) 0.2

0.0 0.0 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21 30-Jan-20 30-Mar-20 30-May-20 30-Jul-20 30-Sep-20 30-Nov-20 31-Jan-21

Figure 3.2: Indicator river flow sites for Wessex. Daily mean flow compared to an analysis of historic daily mean flows. (Source: Environment Agency).

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Groundwater Levels

Figure 4.1: Groundwater levels for indicator sites at the end of November 2020, classed relative to an analysis of respective historic November levels (Source: Environment Agency). Geological map reproduced with permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100024198, 2020.

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Didmarton 1 Allington No2 Ranking derived from data for the period Nov-1975 to Dec-2017 Ranking derived from data for the period Oct-1974 to Dec-2017

81 99 79 94 77 89 75 84 79 73

74 71

Level (mAOD) Level Level (mAOD) Level 69 69 64 67 59 65 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20

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Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Chantry No1 Overcompton Ranking derived from data for the period Feb-1974 to Dec-2017 Ranking derived from data for the period Sep-1971 to Dec-2017

156 60

154 59

152 58 150 57

148

Level (mAOD) Level Level (mAOD) Level

146 56

144 55 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20

Tilshead Woodyates Ranking derived from data for the period Jan-1966 to Dec-2017 Ranking derived from data for the period Jan-1942 to Dec-2017

107

98 102

97 93 92

87 88

Level (mAOD) Level Level (mAOD) Level 83 77 72

78 67 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20

Kingston Russell Road Ashton Farm Ranking derived from data for the period Jan-1974 to Dec-2017 Ranking derived from data for the period Feb-1974 to Dec-2017

121 72 119 71 117 70 115 69 113 68 111 67 109

66 Level (mAOD) Level Level (mAOD) Level 107 105 65 103 64 101 63 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20 Feb-18 Jun-18 Oct-18 Feb-19 Jun-19 Oct-19 Feb-20 Jun-20 Oct-20

Figure 4.2: Indicator groundwater level sites for major aquifers. Daily groundwater levels compared to analysis of historic end month levels (Source: Environment Agency, 2020).

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Reservoir Stocks

── 2020 ── 2019 ── 1995 ── 1976 ..... 100% live capacity

Wessex Water - Clatworthy Wessex Water - Sutton Bingham

100 100

80 80

60 60

40 40 Percentage of capacity Percentage gross Percentage capacity of gross Percentage 20 20

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Wessex Water - Total Reservoir Storage (including Wimbleball) Bristol Water - Blagdon

100 100

80 80

60 60

40 40 Percentage of capacity Percentage gross Percentage of capacity Percentage gross 20 20

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Bristol Water - Chew Valley Bristol Water - Total Reservoir Storage

100 100

80 80

60 60

40 40 Percentage of capacity Percentage gross Percentage of capacity Percentage gross 20 20

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 5.1: Reservoir stocks in Wessex (Source: Wessex Water and Bristol Water).

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Glossary

Term Definition

Aquifer A geological formation able to store and transmit water.

Areal average rainfall The estimated average depth of rainfall over a defined area. Expressed in depth of water (mm).

Artesian The condition where the groundwater level is above ground surface but is prevented from rising to this level by an overlying continuous low permeability layer, such as clay.

Artesian borehole Borehole where the level of groundwater is above the top of the borehole and groundwater flows out of the borehole when unsealed.

Cumecs Cubic metres per second (m3s-1)

Effective rainfall The rainfall available to percolate into the soil or produce river flow. Expressed in depth of water (mm).

Flood Alert/Flood Warning Three levels of warnings may be issued by the Environment Agency. Flood Alerts indicate flooding is possible. Flood Warnings indicate flooding is expected. Severe Flood Warnings indicate severe flooding.

Groundwater The water found in an aquifer.

Long term average (LTA) The arithmetic mean calculated from the historic record, usually based on the period 1961-1990. However, the period used may vary by parameter being reported on (see figure captions for details).

mAOD Metres Above Ordnance Datum (mean sea level at Newlyn Cornwall).

MORECS Met Office Rainfall and Evaporation Calculation System. Met Office service providing real time calculation of evapotranspiration, soil moisture deficit and effective rainfall on a 40 x 40 km grid.

Naturalised flow River flow with the impacts of artificial influences removed. Artificial influences may include abstractions, discharges, transfers, augmentation and impoundments.

NCIC National Climate Information Centre. NCIC area monthly rainfall totals are derived using the Met Office 5 km gridded dataset, which uses rain gauge observations.

Recharge The process of increasing the water stored in the saturated zone of an aquifer. Expressed in depth of water (mm).

Reservoir gross capacity The total capacity of a reservoir.

Reservoir live capacity The capacity of the reservoir that is normally usable for storage to meet established reservoir operating requirements. This excludes any capacity not available for use (e.g. storage held back for emergency services, operating agreements or physical restrictions). May also be referred to as ‘net’ or ‘deployable’ capacity.

Soil moisture deficit (SMD) The difference between the amount of water actually in the soil and the amount of water the soil can hold. Expressed in depth of water (mm).

Categories Exceptionally high Value likely to fall within this band 5% of the time Notably high Value likely to fall within this band 8% of the time Above normal Value likely to fall within this band 15% of the time Normal Value likely to fall within this band 44% of the time Below normal Value likely to fall within this band 15% of the time Notably low Value likely to fall within this band 8% of the time

Exceptionally low Value likely to fall within this band 5% of the time

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Rainfall Catchments

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