Monthly Water Situation Report East Anglia

Monthly water situation report East Anglia

Summary – November 2020 November was a dry month with below normal rainfall across East Anglia. The river flows at majority of the indicator sites has reported an above normal flows with below normal Soil Moisture Deficit (SMD) of 15 mm. The groundwater levels has increased at majority of the indicator sites despite the low rainfall in the area. The reservoir levels have continued to increase at majority of the sites and some of the groundwater support schemes have been able to reduced operation.

Rainfall East Anglia received below normal amount of rainfall in November making a total average rainfall of 38 mm which results in 65% of the monthly Long Term Average (LTA) for the area. The rainfall totals were fairly consistent with below normal category across all sub-catchments with the exception of Upper Bedford Ouse receiving a normal amount of rainfall and Central area Fenland receiving notably low rainfall (relative to the monthly LTA). The 12 months rainfall surplus has decreased to 659 mm.

Soil Moisture Deficit/Recharge The Soil Moisture Deficit (SMD) continue to improve across East Anglia with an average SMD of 15 mm in November. The SMD across the area is classified as below normal for the time of the year.

River Flows River flows has increased at majority of the sites in November with majority of the indicator sites reporting above normal flows. Out of the 21 indicator sites all sites are classified as normal or higher category with the River Wissey and the River Burn reporting a notably high flows.

Groundwater Levels Groundwater levels has continue to increase at majority of the indicator sites in November. Out of the 20 indicator sites all the sites has reported a normal category or higher groundwater levels with the exception of Redlands Hall in the Cam chalk which has reported below normal ground water levels.

Reservoir Storage/Water Resource Zone Stocks Reservoirs storage level has increased at majority of the indicator sites in November with all the sites reporting a normal reservoirs levels. Levels at majority of the sites remain above their normal operating curve.

Environmental Impact The Lodes-Granta groundwater support scheme has 4 out of 6 pumps operating with 1 of the pump operating 24 hours a day. The Rhee groundwater support scheme has 3 out of 8 pumps operating and there are no pumps operating at the Hiz, the Thet and the Little Ouse in November.

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 2020

Forward Look

Probabilistic ensemble projections for river flows at key sites December 2020: There is a reduced probability of exceptionally low flows at all the key sites in December and a reduced probability of notably low and below normal flows at majority of the key sites with the exception of the river Ely Ouse. March 2021: There is a reduced probability of exceptionally low flows at all the key sites with an increase probability of exceptionally high flows at the river Stiffkey and the river Ivel in March.

Probabilistic ensemble projections for groundwater levels in key aquifers March 2021: There is a reduced probability of exceptionally low and notably low groundwater levels at all the key sites with a reduced probability of below normal levels at majority of the indicator sites in March. September 2021: There is a reduced probability of exceptionally low and notably low groundwater levels at all the key sites with an increased probability of normal groundwater levels at majority of the key sites in September.

Author: Hydrology & Operations Contact details: 03708506506

Rainfall November 2020

Above average rainfall Below average rainfall

1-Month Period for East Anglia 1-Month Period for Upper Bedford Ouse

250% 300%

250% 200%

200% 150%

150%

100% 100%

50% 50%

0% 0%

Jun-20 Jun-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20

1-Month Period for Lower Bedford Ouse 1-Month Period for Central Area Fenland

250% 250%

200% 200%

150% 150%

100% 100%

50% 50%

0% 0%

Jun-20 Jun-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20

1-Month Period for Cam 1-Month Period for NW Norfolk and Wissey

250% 250%

200% 200%

150% 150%

100% 100%

50% 50%

0% 0%

Jun-20 Jun-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20

1-Month Period for Little Ouse and Lark 1-Month Period for North Norfolk

250% 250%

200% 200%

150% 150%

100% 100%

50% 50%

0% 0%

Jun-20 Jun-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20

Above average rainfall Below average rainfall

1-Month Period for Broadland Rivers 1-Month Period for East Suffolk 250% 250%

200% 200%

150% 150%

100% 100%

50% 50%

0% 0%

Jun-20 Jun-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20

1-Month Period for North Essex 1-Month Period for South Essex

300% 350%

300% 250%

250% 200%

200%

150%

100% 100%

50% 50%

0% 0%

Jun-20 Jun-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20 Dec-19 Jan-20 Feb-20 Mar-20 Apr-20 May-20 Jul-20 Aug-20 Sep-20 Oct-20 Nov-20

Monthly Rainfall Surplus/Deficit 725 700 675 650 625 600 575

mm 550 525 500 475 450 425 400 D J F M A M J J A S O N

Annual Mean 1961-90 Total for last 12 months

Soil Moisture Deficit

─── 2019-20 ─ ─ ─ 2018-19 Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data

East Anglia Ranking derived from data for the period Jan-1961 to Dec-2012 0

80 SMD SMD (mm) 100

120

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

River Flow November 2020

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

Cappenham, TOVE Willen, OUZEL Ranking derived from data for the period Feb-1962 to Dec-2017 Ranking derived from data for the period Jan-1962 to Dec-2017

6.0 9.0 8.0 5.0 7.0 4.0 6.0 5.0 3.0 4.0

2.0 3.0

Flow (cumecs)Flow (cumecs)Flow 2.0 1.0 1.0 0.0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

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

Burnt Mill, RHEE Roxton, GREAT OUSE Ranking derived from data for the period Oct-1962 to Dec-2017 Ranking derived from data for the period Oct-1972 to Dec-2017

7 50 6

5 40

4 30 3

20 Flow (cumecs)Flow Flow (cumecs)Flow 2 10 1

0 0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Blunham, IVEL Offord (Gross Flows), GREAT OUSE Ranking derived from data for the period Aug-1959 to Dec-2017 Ranking derived from data for the period Jan-1972 to Dec-2017

12 70 10 60

8 50

6 40 30

4 Flow (cumecs)Flow Flow (cumecs)Flow 20 2 10

0 0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Dernford, CAM Temple, LARK Ranking derived from data for the period Feb-1949 to Dec-2017 Ranking derived from data for the period Nov-1960 to Dec-2017

5.0 5.0 4.5 4.5 4.0 4.0 3.5 3.5 3.0 3.0 2.5 2.5

2.0 2.0 Flow (cumecs)Flow Flow (cumecs)Flow 1.5 1.5 1.0 1.0 0.5 0.5 0.0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Abbey Heath, LITTLE OUSE Northwold Total, WISSEY Ranking derived from data for the period Jun-1968 to Dec-2017 Ranking derived from data for the period Jul-1983 to Dec-2012

8.0 16 7.0 14 6.0 12 5.0 10 8 4.0

6 3.0

Flow (cumecs)Flow (cumecs)Flow 4 2.0 2 1.0 0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Denver, ELY OUSE Marham, NAR Ranking derived from data for the period Nov-1971 to Dec-2017 Ranking derived from data for the period Apr-1982 to Dec-2017

3.0

50 2.5

40 2.0

30 1.5

20 1.0

Flow (cumecs)Flow (cumecs)Flow

10 0.5

0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Heacham, HEACHAM Colney, YARE Ranking derived from data for the period Nov-1965 to Dec-2017 Ranking derived from data for the period Jan-1970 to Dec-2017

1.0 8.0 0.9 7.0 0.8 6.0 0.7 0.6 5.0 0.5 4.0 0.4

3.0 Flow (cumecs)Flow Flow (cumecs)Flow 0.3 2.0 0.2 0.1 1.0 0.0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Ingworth, BURE Burnham Overy, BURN Ranking derived from data for the period Jan-1970 to Dec-2017 Ranking derived from data for the period Jan-1970 to Dec-2017

3.0 1.4

2.5 1.2

1.0 2.0 0.8 1.5 0.6

1.0 Flow (cumecs)Flow Flow (cumecs)Flow 0.4

0.5 0.2

0.0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Swanton Morley Total, WENSUM Needham Weir Total, WAVENEY (LOWER) Ranking derived from data for the period Jan-1970 to Dec-2017 Ranking derived from data for the period Jan-1970 to Dec-2017

10 9 10.0 8 7 8.0 6 6.0 5 4

4.0 Flow (cumecs)Flow Flow (cumecs)Flow 3 2 2.0 1 0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Bramford, GIPPING Lexden, COLNE Ranking derived from data for the period Jan-1970 to Dec-2017 Ranking derived from data for the period Jan-1970 to Dec-2017

10.0 7.0 9.0 6.0 8.0 7.0 5.0

6.0 4.0 5.0

4.0 3.0 Flow (cumecs)Flow Flow (cumecs)Flow 3.0 2.0 2.0 1.0 1.0 0.0 0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Springfield, CHELMER Ranking derived from data for the period Jan-1970 to Dec-2017

6.0

5.0

4.0

3.0

2.0 Flow (cumecs)Flow

1.0

0.0 Feb-20 Apr-20 Jun-20 Aug-20 Oct-20 Dec-20

Groundwater Levels November 2020

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

Fringford - GREAT OOLITE Bath Spring, Charlton - IVEL CHALK Ranking derived from data for the period Sep-1980 to Dec-2017 Ranking derived from data for the period Mar-1993 to Dec-2017

99 72

98 71

97 70

96 69

95 68

Level (mAOD) Level Level (mAOD) Level

94 67

93 66 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

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

Biggleswade - IVEL SANDSTONE Therfield Rectory - N HERTS CHALK Ranking derived from data for the period Mar-1968 to Dec-2017 Ranking derived from data for the period Jan-1883 to Dec-2017

100 27.4

27.1 95 26.8 90 26.5

26.2 85

25.9 80

Level (mAOD) Level (mAOD) Level 25.6 75 25.3 25.0 70 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

Redlands Hall, Ickleton - CAM CHALK Linton - CAM CHALK Ranking derived from data for the period Aug-1963 to Dec-2017 Ranking derived from data for the period Jan-1980 to Dec-2017

52 30 29 47 28

42 27 Level (mAOD) Level Level (mAOD) Level 26 37 25

32 24 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

Gog Magog, Stapleford - CAM CHALK Bury St Edmunds - UPPER LARK CHALK Ranking derived from data for the period Jan-1980 to Dec-2017 Ranking derived from data for the period May-1983 to Dec-2017

18 33

32 17 31 16 30

15 29

14 Level (mAOD) Level Level (mAOD) Level 27 13 26

12 25 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

Newmarket - SNAIL CHALK Kenninghall - LITTLE OUSE CHALK Ranking derived from data for the period Feb-1983 to Dec-2017 Ranking derived from data for the period Aug-1973 to Dec-2017

17.0 33 16.5 32 16.0 31 15.5 30 15.0 29 14.5 28

14.0 27 Level (mAOD) Level Level (mAOD) Level 13.5 26 13.0 25 12.5 24 12.0 23 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

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Breckland - WISSEY CHALK Washpit Farm, Rougham - NW NORFOLK CHALK Ranking derived from data for the period Jan-1971 to Nov-2017 Ranking derived from data for the period May-1950 to Dec-2017

29 50 49 28 48 47 27 46 26 45 44

25 Level (mAOD) Level Level (mAOD) Level 43 42 24 41 23 40 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

Bircham Newton - NW NORFOLK CHALK Castle Farm, Offton - MID SUFFOLK CHALK Ranking derived from data for the period Mar-1995 to Sep-2017 Ranking derived from data for the period Mar-1967 to Dec-2017

46 45 24.0 44 22.0 43 42 20.0 41 18.0 40

16.0 Level (mAOD) Level Level (mAOD) Level 39 38 14.0 37 36 12.0 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

Old Primary School, South Creake Hazlewood Common - SUFFOLK CRAG NW NORFOLK CHALK Ranking derived from data for the period Oct-1988 to Feb-2020 Ranking derived from data for the period Oct-1971 to Dec-2017 24 2.4 23 2.2 22 2.0 21 1.8

20 1.6 Level (mAOD) Level Level (mAOD) Level 19 1.4

18 1.2

17 1.0 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

The Spinney, Costessey - WENSUM CHALK Smeetham Hall Cottages, Bulmer - ESSEX CHALK Ranking derived from data for the period Oct-1971 to Dec-2017 Ranking derived from data for the period Jan-1964 to Dec-2017

12.0 30.0

11.5 29.0 11.0 28.0 10.5

10.0 27.0

9.5

26.0 Level (mAOD) Level Level (mAOD) Level 9.0 25.0 8.5

8.0 24.0 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

Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low ─── Latest data Hindolveston - NORFOLK CHALK Rook Hall, Braiseworth - SUFFOLK CHALK Ranking derived from data for the period Sep-1984 to Nov-2017 Ranking derived from data for the period Jan-1980 to Dec-2017

57.0 34.0

33.5 56.5 33.0 56.0 32.5

55.5 32.0

31.5

55.0 Level (mAOD) Level Level (mAOD) Level 31.0 54.5 30.5

54.0 30.0 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

Reservoir Stocks November 2020

─── 2019-2020 ─── Normal Operating Curve ─── Drought Alert Curve ── ─ 1995-1996

Grafham Alton

100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30

20 20

Percentage of live capacity live of Percentage capacity live of Percentage 10 10 0 0 Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov

─── 2019-2020 ─── Normal Operating Curve ─── Drought Alert Curve ── ─ 1995-1996

Ardleigh Abberton

100 100 90

80 80 70

60 60 50 40 40 30

20 20 n.b. from 20/01/2014 Abberton %full is based

Control curve 1 Percentage of live capacity live of Percentage Percentage of live capacity live of Percentage on increased “19m.Volume” Control curve 2 n.b. from 29/09/2014 Abberton %full is based 10 on increased “20m.Volume” 0 0 Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov

Hanningfield

100 90 80 70 60 50 40 30 20

Control curve Percentage of live capacity live of Percentage 10 0 Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov

Forward Look – River Flows

Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.

Probabilistic ensemble projections of river flows at key indicator sites in December 2020. Pie charts indicate probability, based on climatology, of the surface water flow at each site being e.g. exceptionally low for the time of year. (Source: Centre for Ecology and Hydrology, Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2020. ^ “Naturalised” flows are projected for these sites’

Probabilistic ensemble projections of river flows at key indicator sites in March 2021. Pie charts indicate probability, based on climatology, of the surface water flow at each site being e.g. exceptionally low for the time of year. (Source: Centre for Ecology and Hydrology, Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2020

Forward Look - Groundwater

Probabilistic ensemble projections of groundwater levels at key indicator sites for end of March 2021. Pie charts indicate probability, based on climatology, of the groundwater level at each site being e.g. exceptionally low for the time of year. (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2020.

Probabilistic ensemble projections of groundwater levels at key indicator sites for end of September 2021. Pie charts indicate probability, based on climatology, of the groundwater level at each site being e.g. exceptionally low for the time of year. (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2020.

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.

Flow The water passing in the river, as measured.

Groundwater The water found in an aquifer, as measured.

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).