Devon and Cornwall Area

Monthly water situation report Devon and Cornwall Area

Summary – August 2021 Devon and Cornwall received 56 mm of rainfall in August, which is 66% of the Long Term Average rainfall (LTA) and ‘below normal’ for the time of year. Most catchments received ‘below normal’ rainfall this month. Monthly mean river flows were mostly ‘normal’ for the time of year. Soil moisture deficit increased. Groundwater levels remained healthy overall, and reservoir storage decreased as is normal for this time of year.

Rainfall Devon and Cornwall received 56 mm of rainfall in August, which is 66% of the LTA rainfall and ‘below normal’ for the time of year. All rainfall catchments across the area had ‘below normal’ rainfall apart from the Otter, Sid, Axe and Lim catchment, which was ‘normal’ for the time of year. There were rainfall events around 5-9 August and 20-21 August.

Rainfall maps and graph Rainfall catchments map

Soil Moisture Deficit Soil moisture deficit (SMD) for Devon and Cornwall increased to 50 mm at the end of the month, close to the LTA of 52 mm. At the end of the month, soils were wetter than average for the time of year in the east of the area, and drier than average in the west of the area, reflecting the higher rainfall in the east.

SMD graph and map

River Flows Monthly mean flows were ‘normal’ for the time of year everywhere except the Otter at Dotton and the Kenwyn at Truro, where flows were ‘above normal’ for the time of year. Daily mean flows generally receded through the month, responding slightly to the rainfall around 7 August and 21 August. At the end of August daily mean flows were nearly all ‘normal’ with only the Hayle at St Erth and the Torridge at Torrington recording ‘below normal’ flows.

River flow map and graphs

Groundwater Levels The indicator groundwater sites ranged from ‘normal’ to ‘above normal’ for this time of year. Groundwater levels receded very slightly this month, but overall levels remained stable. Please note that there is missing data for Woodbury Common 2 this month.

Groundwater map and graphs

Reservoir Storage Total reservoir storage decreased from 86% at the end of July to 80% at the end of August. Storage at Wimbleball decreased to 81%, Colliford decreased to 69% and Roadford decreased to 84%. This is as expected at this time of year.

Reservoir graphs

Glossary

Author: Hydrology Devon, Cornwall and the Isles of Scilly Contact details: 020302 52532

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. © Environment Agency 2021

Rainfall

Figure 1.1: Total rainfall for hydrological areas across Devon and Cornwall for the current month (up to August), 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 5km 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. Crown copyright. All rights reserved. Environment Agency, 100026380, 2021.

www.gov.uk/environment-agency © Environment Agency 2021

Above 100% LTA rainfall Below 100% LTA rainfall 1-Month Period for Devon and Cornwall

250%

200%

150%

100%

50% Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jun-20 Jul-20 Dec-20 Jan-21 Feb-21 Mar-21 Apr-21 May-21 Jun-21 Jul-21 0% Sep-19 Oct-19 Nov-19 Aug-20 Sep-20 Oct-20 Nov-20 Aug-21

Figure 1.2: Monthly rainfall totals as a percentage of the 1961 – 1990 long term average. Final HadUK data based on the Met Office 5km 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. Crown copyright. All rights reserved. Environment Agency, 100026380, 2021.

Soil Moisture Deficit

Less than historic minimum Greater than historic maximum ..... 1961-1990 long term average ── Latest data ── 2020

100

Soil moisture deficit(mm) 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).

www.gov.uk/environment-agency © Environment Agency 2021

Month-end Soil Moisture Deficit (mm)

Figure 2.2: Soil moisture deficits for week ending 31 August 2021. MORECS data for real land use (Source: Met Office © Crown Copyright, 2021). Crown copyright. All rights reserved. Environment Agency, 100026380, 2021.

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, 100026380, 2021.

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

ST ERTH, River Hayle TRURO, River Kenwyn Ranking used data from 03/01/1968 to 31/12/2017 Ranking used data from 31/10/1968 to 31/12/2017 8 3 August mean flow August mean flow .3 cumecs 7 .1 cumecs 76% LTA 3 113% LTA

2 5

4 2

3 1

Daily Mean Flow (cumecs) Daily Mean Flow (cumecs) 1 1

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 31-Aug-21 31-Oct-21

www.gov.uk/environment-agency © Environment Agency 2021

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

GWILLS, River Gannel BODMIN DUNMERE, River Camel Ranking used data from 01/12/1969 to 31/12/2017 Ranking used data from 01/01/1965 to 31/12/2017 6 40 August mean flow August mean flow .2 cumecs 1.2 cumecs 95% LTA 35 72% LTA 5

4 25

3 20

15 2

Daily Mean Flow (cumecs) 1 Daily Mean Flow (cumecs) 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 31-Aug-21 31-Oct-21

RESTORMEL, River Fowey GUNNISLAKE, River Tamar Ranking used data from 31/03/1961 to 31/12/2017 Ranking used data from 25/06/1956 to 31/12/2017 70 300 August mean flow August mean flow 1.4 cumecs 5.1 cumecs 60 65% LTA 250 60% LTA

50 200

40 150 30

100 20

Daily Mean Flow (cumecs) Daily Mean Flow (cumecs) 50 10

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 31-Aug-21 31-Oct-21

TORRINGTON, River Torridge UMBERLEIGH, River Taw Ranking used data from 31/07/1960 to 31/12/2017 Ranking used data from 30/09/1958 to 31/12/2017 180 180 August mean flow August mean flow 160 2.3 cumecs 160 4.7 cumecs 44% LTA 80% LTA 140 140

120 120

100 100

80 80

60 60

40 40 Daily Mean Flow (cumecs) Daily Mean Flow (cumecs) 20 20

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 31-Aug-21 31-Oct-21

BELLEVER, East Dart River AUSTINS BRIDGE, River Dart Ranking used data from 31/03/1964 to 31/12/2017 Ranking used data from 30/09/1958 to 31/12/2017 25 200 August mean flow August mean flow .7 cumecs 180 5.0 cumecs 104% LTA 102% LTA 20 160

140

15 120

100

10 80

5 40 Daily Mean Flow (cumecs) Daily Mean Flow (cumecs) 20

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 31-Aug-21 31-Oct-21

www.gov.uk/environment-agency © Environment Agency 2021

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

CHUDLEIGH BRIDGE, River Teign THORVERTON, River Exe Ranking used data from 17/02/1990 to 31/12/2017 Ranking used data from 30/04/1956 to 31/12/2017

70 160 August mean flow August mean flow 1.2 cumecs 140 6.4 cumecs 60 82% LTA 102% LTA

120 50

100 40 80 30 60

20 40 Daily Mean Flow (cumecs) Daily Mean Flow (cumecs) 10 20

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 31-Aug-21 31-Oct-21

DOTTON, River Otter WHITFORD, River Axe Ranking used data from 30/09/1962 to 31/12/2017 Ranking used data from 06/11/1964 to 31/12/2017 35 90 August mean flow August mean flow 1.8 cumecs 80 2.3 cumecs 30 115% LTA 96% LTA 70 25 60

20 50

15 40

30 10 20

Daily Mean Flow (cumecs) 5 Daily Mean Flow (cumecs) 10

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 31-Aug-21 31-Oct-21

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

www.gov.uk/environment-agency © Environment Agency 2021

Groundwater Levels

Figure 4.1: Groundwater levels for indicator sites at the end of August 2021, classed relative to an analysis of respective historic August levels (Source: Environment Agency). Geological map reproduced with permission from UK Groundwater Forum, BGS © NERC. Note: groundwater levels are reported at different times during the month and therefore may not be fully representative of levels at the month end. Crown copyright. All rights reserved. Environment Agency, 100026380, 2021.

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data WOODLEYS NO1 WOODBURY COMMON NO2 Ranking derived from data for the period Jan-1966 to Dec-2017 Ranking derived from data for the period Nov-1967 to Dec-2017

34 103

34 103 102 33 102 33 101 32 101

32 100

Level (mAOD) Level (mAOD) Level 100 31 99 31 99 30 98 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21

www.gov.uk/environment-agency © Environment Agency 2021

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data BUSSELS NO7A WHITLANDS Ranking derived from data for the period Nov-1971 to Dec-2017 Ranking derived from data for the period Sep-1984 to Dec-2017

26 89

25 88

24 87 Level (mAOD) Level Level (mAOD) Level

24 87

23 86 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21

BRANSCOMBE LANE WINNARDS PERCH B.H. Ranking derived from data for the period May-1987 to Dec-2017 Ranking derived from data for the period Jan-2002 to Dec-2017

22 134

21 133 20 132 19

18 131

17 130 Level (mAOD) Level (mAOD) Level 16 129 15

14 128 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21

COLEFORD PRODUCTION Ranking derived from data for the period Jan-1998 to Dec-2017

95 Level (mAOD) Level

93 Nov-18 Mar-19 Jul-19 Nov-19 Mar-20 Jul-20 Nov-20 Mar-21 Jul-21

Figure 4.2: Indicator groundwater level sites for major aquifers. End of month groundwater levels compared to analysis of historic end month levels (Source: Environment Agency, 2021).

Reservoir Stocks

── 2021 ── 2020 ── 1995 ..... 100% live capacity South West Water - Colliford South West Water - Roadford

100 100

80 80

60 60

40 40 Percentage of live capacity Percentage of live capacity 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 South West Water - Wimbleball South West Water - Total Reservoir Storage

100 100

80 80

60 60

40 40 Percentage of live capacity Percentage of live capacity 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 Devon and Cornwall (Source: South West Water).

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

Rainfall Catchments