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The Impact of Water Abstraction Reform:
Public Water Supply Operations
Final R eport WT0964/WT0995
Produced: May 2014
The Impact of Water Abstraction Reform: Public Water Supply Operations
Final Report WT0964/WT0995
Produced: May 2014
A report of research carried out by HR Wallingford, on behalf of the Department for Environment, Farming and Rural Affairs
Research contractor: HR Wallingford
Publishing organisation Department for Environment, Food and Rural Affairs Flood Risk Management Division, Nobel House, 17 Smith Square London SW1P 3JR
© Crown copyright (Defra); 2014
Copyright in the typographical arrangement and design rests with the Crown. This publication (excluding the logo) may be reproduced free of charge in any format or medium provided that it is reproduced accurately and not used in a misleading context. The material must be acknowledged as Crown copyright with the title and source of the publication specified. The views expressed in this document are not necessarily those of Defra. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance on views contained herein.
The Impact of Abstraction Reform Public water supply operations
MAR5044-RT001-R02-00 May 2014
The Impact of Abstraction Reform Public water supply operations
Document information
Document permissions Unrestricted Project number MAR5044 Project name The Impact of Abstraction Reform Report title Public water supply operations Report number RT001 Release number R02-00 Report date May 2014 Client Risk Solutions Client representative Helen Wilkinson Project manager Darren Lumbroso Project director Steven Wade
Document history
Date Release Prepared Approved Authorised Notes 07 May 2014 02-00 DML SDW SDW Updated to change title only 22 Jun 2013 01-00 DML SDW SDW Water supply source locations have been redacted or anonymised in line with Defra guidance
Document authorisation
Prepared Approved Authorised
© HR Wallingford Ltd
This report has been prepared for HR Wallingford’s client and not for any other person. Only our client should rely upon the contents of this report and any methods or results which are contained within it and then only for the purposes for which the report was originally prepared. We accept no liability for any loss or damage suffered by any person who has relied on the contents of this report, other than our client.
This report may contain material or information obtained from other people. We accept no liability for any loss or damage suffered by any person, including our client, as a result of any error or inaccuracy in third party material or information which is included within this report.
To the extent that this report contains information or material which is the output of general research it should not be relied upon by any person, including our client, for a specific purpose. If you are not HR Wallingford’s client and you wish to use the information or material in this report for a specific purpose, you should contact us for advice.
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The Impact of Abstraction Reform Public water supply operations
Contents
No table of contents entries found. 1. Introduction ______1 1.1. Understanding key terms ...... 1 1.1.1. Water Resources Management Plan (WRMP) terms ...... 1 1.1.2. Water resources infrastructure and operational terms ...... 3 2. The Stour ______4 2.1. Introduction ...... 4 2.2. Normal operations ...... 6 2.3. Reconciling the demand for water from sources in the Stour ...... 7 2.4. Drought operations ...... 10 3. The Hampshire Avon ______11 3.1. Introduction ...... 11 3.2. Normal operations ...... 16 3.3. Water demand ...... 16 3.4. Water supply ...... 18 4. The Usk ______19 4.1. Introduction ...... 19 4.2. Water availability challenges ...... 21 4.3. Licensing policies ...... 21 4.4. Water abstractions ...... 22 4.5. Water balance, current water sources and discharges ...... 25 5. The Dee ______26 5.1. Introduction ...... 26 5.2. River Dee regulation system ...... 29 5.2.1. Background ...... 29 5.2.2. Control points ...... 29 5.2.3. Designated abstractors ...... 30 5.2.4. Operation of reservoirs ...... 34 5.2.5. Water transfers internal to the catchment ...... 35 5.2.6. Demand reduction measures ...... 38 6. The Tees ______41 6.1. Introduction ...... 41 6.2. Public water supply resource ...... 42 6.3. Demand ...... 43 6.4. Supplies ...... 43 6.5. Operational behaviour ...... 45 6.6. Transfers ...... 45 6.7. Drought ...... 45 6.8. Discharges ...... 46
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7. The Cam and Ely Ouse ______46 7.1. Introduction ...... 46 7.2. Transfers ...... 49 7.2.1. Raw water transfers from the catchment ...... 49 7.2.2. Normal operations ...... 50 7.2.3. Drought operations ...... 52 7.2.4. Effluent Returns ...... 53 8. The Trent and Derwent ______53 8.1. Introduction ...... 53 8.2. Normal operations ...... 55 8.2.1. Major reservoirs ...... 55 8.2.2. Surface waters ...... 58 8.2.3. Groundwater ...... 58 8.2.4. Transfers ...... 58 8.2.5. Reconciling the demand for water from sources in the Trent ...... 58 8.3. Drought operations ...... 59 8.4. Effluent returns ...... 63 9. References ______64
Appendices ______65
A. The Stour B. River Tees and Associated Tees resources operating rules and model set up C. The Cam and Ely Ouse – Additional information
Figures Figure 2.1: The Stour CAMS area and water companies ...... 5 Figure 2.2: Schematic diagram of the River Stour catchment ...... 8 Figure 2.3: Estimated demand profile for the Stour ...... 9 Figure 2.4: Groundwater trigger thresholds for Duckpit Farm borehole...... 10 Figure 2.5: Cumulative recharge drought trigger assessment from the Boughton rainfall gauging station ...... 11 Figure 3.1: Hampshire Avon CAMS area ...... 13 Figure 3.2: Licensed abstractions in the Hampshire Avon CAMS area...... 14 Figure 3.3: Hampshire Avon schematic diagram ...... 15 Figure 3.4: PWS water demand profile met by sources in the Hampshire Avon ...... 17 Figure 3.5: Factors for Bashford Lake and Ibsey Intake ...... 17 Figure 4.1: Usk CAMS area ...... 20 Figure 4.2: South East Wales Conjunctive Use Scheme (SEWCUS) ...... 23 Figure 4.3: Location of abstraction licences in the Usk ...... 24 Figure 4.4: Schematic diagram of the Usk catchment ...... 25 Figure 5.1: Overview of the Dee CAMS area ...... 27 Figure 5.2: Location of Water Resource Zones, PWS groundwater and surface water licences ...... 28 Figure 5.3: System Conservation Rule Curves for the River Dee Regulation scheme ...... 31
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Figure 5.4: Location of major PWS abstraction locations in the Dee CAMS area ...... 33 Figure 5.5: Dee Regulation Scheme decision flow chart ...... 37 Figure 6.1: Major urban areas in the Tees CAMS area ...... 42 Figure 6.2: Schematic diagram of the Tees public water supply system ...... 43 Figure 6.3: Cow Green control curves ...... 46 Figure 7.1: Cm and Ely Ouse CAMS area ...... 48 Figure 7.2: Water companies covering the Cam and Ely Ouse CAMS area ...... 49 Figure 7.3: Annual licensed quantity and PWS abstractions for the CAMS and Ely Ouse ...... 52 Figure 8.1: The Trent catchment, water companies and water resources zones ...... 54 Figure 8.2: Severn Trent’s Water Distribution Grid ...... 55 Figure 8.3: Reservoir volumes and behaviour between 1990 and 2009 ...... 57 Figure 8.4: An estimate of the demand on Trent sources plus headroom ...... 59 Figure 8.5: Derwent Valley reservoirs drought control lines ...... 60 Figure 8.6: Figure 8.6: Drought trigger curves for the Blithfield reservoir, managed by South Staffs Water ...... 61 Figure 8.7: Trigger thresholds and associated responses for Blithfield and Clywedog Reservoir ...... 62
Tables Table 3.1: Estimated percentage of the Dry Year Annual Average Demand (DYAA) that is met by the Hampshire Avon ...... 16 Table 3.2: River flow conditions for the Hampshire Avon ...... 18 Table 5.1: System Conservation Rule Curves for the River Dee Regulation scheme in m3 days ...... 32 Table 5.2: Indicative authorised maximum daily abstractions of designated abstractors ...... 32 Table 5.3: Characteristics of the major reservoirs in the Dee CAMS area ...... 34 Table 5.4: Dee system “Safe yield” Allocation ...... 36 Table 5.5: Dee system “Safe yield” Allocation ...... 38 Table 5.6: Stage 1 Demand reduction measures and net reduction on regulation release requirement ...... 38 Table 5.7: Stage 1 maximum abstraction allocation ...... 39 Table 5.8: Stage 2 Demand reduction measures and net reduction on regulation release requirement ...... 39 Table 5.9: Stage 2 maximum abstraction allocation ...... 40 Table 6.1: Normal year and Dry year Deployable Outputs for Northumbrian Water ...... 44 Table 7.1: Estimated Public Water Supply demand for the relevant water resources zones and Cam and Ely catchment ...... 51 Table 8.1: PWS Reservoirs relevant for the Trent and Derwent modelling ...... 56 Table 8.2: East Midlands drought zone management options, Derwent Valley Reservoirs ...... 60 Table 8.3: Actions and associated estimated water savings ...... 62 Table 8.4: Important operation triggers in terms of percentage volume for the major reservoir groups ...... 63
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1. Introduction
The Government has made a commitment to reform the regulatory regime for water abstraction. Risk Solutions is leading a major project supported by Defra and the Environment Agency to model the behaviour of Public Water Supply (PWS) and non-Public Water Supply (PWS) abstractors. An important part of the policy development process is to test the costs, benefits and risks of alternative policy options against the current regime, particularly looking at trading between abstractors. The overall goal is to examine how well the alternative policy options perform under different climate change and socio-economic scenarios between 2025 and 2050, balancing supply and demand at least cost whilst protecting the environment. The modelling work is focussed on seven detailed catchment level case studies, which will inform a wider impact assessment for the whole of England and Wales including: Stour Tees Cam and Ely Ouse Dee Usk Hampshire Avon Trent and Derwent this comprises the following Catchment Abstraction Management Strategy (CAMS) catchments: Staffordshire Trent Valley Tame, Anker and Mease Dove Derbyshire Derwent Soar Lower Trent and Erewash. This report provides a summary of the information required to assist Risk Solutions in formulating the Public Water Supply model components of each case study catchment. This first chapter provides definitions of key terms. The remaining seven chapters provide information for each case study catchment.
1.1. Understanding key terms
It is important that certain key terms are clearly defined in order to avoid any confusion. This section provides definitions of these terms.
1.1.1. Water Resources Management Plan (WRMP) terms
Every five years, water companies in England and Wales, in consultation with the Environment Agency, produce Water Resources Management Plans (WRMPs) where they lay out the actions they will take in order to maintain security of water supply over the next 25 years or more. These WRMPs form an important part of the water companies’ business plan submission to Ofwat for the five yearly Periodic Review. The definitions of the terms below are those used in the WRMPs.
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The level of service that a company identifies as part of its WRMP should be the minimum that it plans to deliver every year. Delivering high levels of service on this basis can be expensive. Each company should consider whether it can deliver a given level of service more efficiently by taking a flexible approach, bringing forward investment or increasing operating expenditure (for example, to reduce leakage) when the risk of exceptionally dry weather becomes a reality. A company‘s WRMP needs not identify how a company would achieve this, but it should explain the company‘s broad strategy for responding to changing conditions. This should include links to its drought plan and actions such as drought permits and orders. Catchment A water catchment is an area of land through which water from any form of precipitation (such as rain, or snow melt) drains into a body of water (such as a river, lake, reservoir, or an aquifer). Catchment Abstraction Management Strategy (CAMS) The Environment Agency’s programme of assessing and classifying the abstraction status of surface water catchments. Deployable Outputs (DO) The Deployable Output (DO) of a source is defined as the output as constrained by the abstraction licence, water quality, environmental impacts, treatment capacity, pumping plant or pipework capacity, or the borehole/aquifer properties. Drought plan Statutory plans produced by the appointed water companies that detail the actions each would take to manage the supply of water in a drought. Each Environment Agency Region has drought plans in place that set out how they plan for and manage drought. Dry year The ‘dry year’ is a period of low rainfall and unconstrained demand which can only just be met by available supplies. It, is the basis of a company‘s WRMP. A water company should carry out final planning forecasts under the dry year forecast. The dry year forecast is normally developed from base year figures and the company should explain any assumptions or adjustments it has made due to weather patterns experienced that year. Dry Year Annual Average The Dry Year Annual Average is the annual average value of demand, deployable output or some other quantity over the course of a “dry year”. Hands Off Flow (HOF) conditions Many abstraction licences contain conditions where the licence holder has to reduce or stop abstracting water once the river has dropped to a certain level or flow. These are known as hands off flow conditions and protect other river users and the environment. The hands off flow is the flow below which an abstraction licence holder cannot abstract water from a watercourse. Headroom Headroom is the term used to refer to the margin between supply and demand. The target headroom is the minimum buffer that a prudent water company should allow between supply (including raw water imports and excluding raw water exports) and demand to cater for specified uncertainties (except for those due to outages) in the overall supply/demand balance.
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Levels of service Specific measures of services to consumers with regards to water supply these are issues related to low pressure, supply interruptions and restrictions on water use. Licensed versus actual abstraction The licensed abstraction is the maximum amount of water that can be abstracted, within various constraints, from licences within a CAMS area. The actual abstraction is the actual quantity of water abstracted. This is equal to or generally less than the licensed abstraction quantity. Most individual abstraction records are reported to the Environment Agency each year. Naturalised flow Naturalised flow is the flow in a river in the absence of abstractions and discharges, i.e. the flow that would exist without any exist in a river without any anthropogenic interventions. Supply/demand balance The balance between the volume of water available in an appointed water company’s area and the volume supplied to meet consumer demand. Any imbalance between supply and demand can be met through enhancing existing resources or demand management strategies. Water Resource Zone The largest possible zone in which all water resources, including external transfers, can be shared. Hence, it is the zone in which all customers experience the same probability of supply failure from a resource shortfall.
1.1.2. Water resources infrastructure and operational terms
Bulk supplies Supplies of water traded between individual appointed water companies. These supplies are often traded under long-term contracts and on non-standard terms. Under certain circumstances, we have the power to determine the terms of bulk supply trades. Conjunctive use schemes Conjunctive use is the coordinated management of surface water and groundwater supplies to maximize the yield of the overall water resource. Demand management Attempting to defer the need to invest in new resources to meet increases in demand by using water more efficiently. Demand management strategies include: selective metering; appropriate tariff structures; leakage reduction; and the promotion of water efficiency. Effluent Treated wastewater discharged into a river or the sea. Groundwater abstraction Groundwater abstraction is the process of taking water from an aquifer, either on a temporary or permanent basis. Groundwater augmentation schemes Some watercourses in England and Wales are under increasing pressure from abstraction of water. In some catchments public water supply companies augment flows in rivers by pumping water into them from groundwater sources. This report covers the schemes in the case study catchment s operated by public water supply companies but not those managed by the Environment Agency.
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Normal conditions, drought conditions and emergency plans Under normal conditions, each water company aims to meet demand at minimum costs and subject to any licence constraints. With respect to droughts water undertakers in England and Wales have a statutory requirement to prepare and maintain drought plans. A drought plan usually sets out the short-term operational steps a company will take before, during and after a drought. The Water Industry Act 1991 defines a drought plan as “a plan for how the water undertaker will continue, during a period of drought, to discharge its duties to supply adequate quantities of wholesome water, with as little recourse as reasonably possible to drought orders or drought permits”. This report covers the “rules” that public water supply companies follows under “normal conditions” as defined by the WRMPs and “drought conditions” as covered by the Drought Plans. This report does not cover the “rules” that public water companies follow in order to provide water alternative supplies of water in emergency situations. Reservoirs and natural lakes Reservoir is a body of water used for the storage and regulation of water. The water is usually impounded by artificial structure such as dam. A natural lake will not have a structure such as a dam or weir artificially maintaining water levels in it. Return flows Return flows are the part of the water withdrawn for an agricultural, industrial or domestic purpose that returns to the groundwater or surface water in the same catchment as where it was abstracted. This water can potentially be withdrawn and used again. In the case study catchments this water is generally returned to watercourses via sewage treatment works and hence is often referred to as effluent flows. Service reservoir This is a tank containing drinking water that is usually sited within or near to a water distribution system. It is usually used as a reserve (for example, in cases where the supply from a water treatment works to the distribution system fails). It evens out distribution system demand on the supply. 2. The Stour 2.1. Introduction
There are three Public Water Supply (PWS) companies, Southern Water, South East Water (SEW) and Affinity Water that abstract from the Stour catchment. These are shown in Figure 2.1. The water balance is currently marginal with almost all abstraction from groundwater sources. The Catchment Abstraction Management Strategy (CAMS) process indicates there are limited resources and suggests that no summer abstraction is possible (Environment Agency, 2003). South East Water’s, Chalk sources are only constrained by licences so are simple to model but the catchment is complicated owing to the internal and external transfers, which connect the Stour to zones across the South East. The situation in 2025 will depend on whether the relevant zones are supported from outside or whether a major reservoir or other local options, such as increasing the capacity of effluent reuse and surface water abstraction, have been developed. A simplified schematic diagram was developed for the internal modelling team and an initial catchment estimate of the PWS supply-demand balance was completed, based on the available data. The schematic diagram, shown in Figure 2.2, includes one future reservoir option, which is included in South East Water’s draft plan because this will need to be modelled properly to understand impacts.
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Southern Water are considering supply side options in the lower catchment (effluent re-use) to increase the yield to up to 20 Ml/day and this scheme is already included in the Water Resources in the South East (WRSE) plan to 10 Ml/day. They also have a small scheme planned to recover process losses at one water treatment works. All options that should be considered in the Agent Based Model (ABM) will be included in the Price Review 2009 (PR09) planning spread sheets (held by London Economics) and any updates in the form of draft plans for the Price Review 2014. The reservoir option has a volume of 2,815 Ml with a winter abstraction of 20 Ml/day in the lower Stour. It is anticipated that abstraction will also be limited to 50% of the flow above the Q95 (i.e. the flow which is exceeded 95% of the time). The yield for the option is 9 Ml/day but the water treatment works have been designed to supply the dry year critical period Deployable Output assumed to be 1.5 times the average yield i.e. 13.5 Ml/day. The reservoir will also need to release 1.28 Ml/day back in to the Sarre Penn to maintain low flows.
Figure 2.1: The Stour CAMS area and water companies Source: HR Wallingford, 2013
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The Impact of Abstraction Reform Public water supply operations
2.2. Normal operations
Under normal conditions, each water company aims to meet demand at minimum costs and subject to any licence constraints. Therefore local groundwater resources will be used first, followed by more expensive local sources and imports from other water resource zones. Most Chalk sources are constrained by licence and therefore can be abstracted up to the licence limit and Lower Greensand sources are hydrologically constrained so cannot be abstracted greater than their defined Deployable Outputs (DO). Therefore the following logic for PWS agents and order of abstraction is suggested: Establish the PWS demand for each time step. Check the groundwater storage or level conditions in the Chalk and Lower Green Sand units. If the levels are in the normal range then the PWS demand in each time step can be met by: SEW PWS agent abstracting from the Chalk up to the licence limits South East Water abstracts from the Lower Green Sand up to the reported DO (constrained by hydrological conditions) Southern Water and Affinity Water abstract water up to their published Minimum Deployable Outputs for groundwater sources1 Southern Water abstracts up to 3.44 Ml/day from the lower Stour (effectively an effluent recycling scheme but water will be more expensive to treat than groundwater) Any shortfalls are dealt with by internal or boundary transfers in to the zone up to a defined limit (based on the WRMPs in 2025), which is around 12 Ml/day. If the groundwater levels have declined below a drought trigger demand may be reduced by 5% (hosepipe bans) and an additional 3% Non-Essential Use (NEU) bans to help manage supplies. If groundwater levels decline further then there are some additional abstractions that may be allowed of approximately 18 Ml/day, if drought permits are issued (based on company drought plans). It should be noted that this introduces simplifying assumptions, such as: Chalk groundwater sources can provide PWS supplies across the whole catchment (i.e. no network constraints). If a catchment balance is attempted, rather than water company resource zone balances, it will assume that companies share water (existing or planned long term bulk supplies, imports and exports) when needed. The existing PR09 WRMPs suggest that the supply-demand balance is tight but there should be sufficient water available in 2025. If a new reservoir is in the model at the start or during the simulation it needs to be coded into the model. While a gross simplification would be that it could provide 9 Ml/day, the reservoir should be modelled using a mass balance with abstractions from the Stour, inflows from the Sarre Penn and the appropriate hands off and compensation flows. Further details are provided in Appendix A.
1 These data are available from WRP table 5 provided to LE by the Environment Agency
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2.3. Reconciling the demand for water from sources in the Stour
The catchment boundary dissects multiple water resource zones and there are significant imports to the basins so it is difficult to reconcile the catchment supply-demand balance based on published data. The location of individual sources and the distribution of population can be used to weight elements of the supply- demand balance and estimate the demand placed on key abstractions in the Stour. An example is shown in Figure 2.3 that estimates a Dry Year Demand of 129 Ml/day for use in the basin and applies a profile to this demand to reflect changes throughout the year. It assumes that some imports would be required to meet demand.
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sea
ENV
sea
o o
Demands
T
20Ml/d pumps
to to Effluent Effluent
KT to FD 4 Ml/d Affinity
Gauging station
Demands
Gutter
SWS Plucks Plucks SWS
C
MRF 145 145 MRF Ml/d
?
Wingham
C
HoF
Effluent Dour
Little Stour Little
SWS Demands SWS
20 Ml/d pumps, pumps, 20Ml/d by limited
13.5
–
River
?
9Ml/d
–
SEW 2Ml/d SEW
Broad Oak Reservoir Reservoir Oak Broad Option DO Ml/d
Effluent to Stour to Effluent
Ashford & & Ashford
Canterbury
SEW Demands SEW
C
Horton
Penn
Stour
Sarre
Groundwater abstraction
Great Great
G
Stour Great Upper
East Stour East
Environment demand Environment
Surface water Surface abstraction
RZ6
0.1 Ml/d 0.1 RZ8 SEW
SEW SEW
4 Ml/d Ml/d 4 export
to Kent Thanet Kent to
SWS Import KM KM Import SWS
Boundary conditions
baseline and future baseline future and Need imports and for exports runs
PWS demand PWS
Raw water water Raw reservoir
Figure 2.2: Schematic diagram of the River Stour catchment
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The Impact of Abstraction Reform Public water supply operations
Estimate of a monthly production profile for PWS abstraction in the Stour basin
Dry Year Annual Average conditions in 2025 (no Broad Oak)
DYAA production profile for Stour basin
250.0
200.0
150.0
100.0 Water abstraction Ml/d abstractionWater
50.0
0.0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Month SEW Chalk SWS GW SWS Plucks Gutter Affinity
SEW LGS Imports Demand
Groundwater levels Significant recharge Demands rise and GW levels lowered lower but should tops up GW but GW sources pumped but demand begins sustain an MDO demand is low during harder to decline under normal the winter conditions Catchment may need supporting from imports
Figure 2.3: Estimated demand profile for the Stour Source: Water company published Water Resources Management Plans and consultation
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2.4. Drought operations
All three companies operate drought plans that determine the level of restrictions for different frequency of drought conditions. Various triggers have been developed related to groundwater levels or long term recharge, These are shown in Figures 2.4 and 2.5. These could be used in the modelling to trigger various actions including demand restrictions.
Figure 2.4: Groundwater trigger thresholds for Duckpit Farm borehole. Notes: Sourced from SEW Drought Plan (2011). Decisions on drought status are made by comparing actual groundwater levels to the historical minima and proportions of the long term average (LTA) level.
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Figure 2.5: Cumulative recharge drought trigger assessment from the Boughton rainfall gauging station
Notes: Sourced from SEW Drought Plan (2011). A measure of cumulative recharge is made using a calculation of Soil Moisture Deficit (SMD) rather than using rainfall data directly 3. The Hampshire Avon 3.1. Introduction
The main water companies in the Hampshire Avon CAMS area are Wessex Water and Sembcorp Bournemouth Water, although the catchment boundary also dissects Cholderton and District’s Water’s supply area and the edges of Southern Water and Thames Water supply areas. According to the CAMS documents, PWS makes up approximately 89% of the consumptive abstraction in the catchment, the river is regarded as ‘over abstracted’ or ‘over licenced’ and all four groundwater units have been classified as having ‘no water available’ (Environment Agency, 2006). Water abstracted from the catchment supplies the towns of Bournemouth, Christchurch and Salisbury, as well as a number of smaller towns such as Amesbury and Fordingbridge. The Hampshire Avon is an important resource that serves populations that are outside of the catchment boundary but within Bournemouth and Wessex Water (East and North) water resources zones. Although this a predominantly a Chalk catchment, more than 30% of the public water supply in this catchment is sourced from surface water sources in the lower reaches of the River Avon as shown in Figure 3.1. Important water resources features in the basin include Hands Off Flow (HOF) conditions applied to groundwater as well as surface water sources and arrangements for “stream support” where water is abstracted from groundwater to maintain surface water streams. The ecological value of the River Avon is very high and there are concerns regarding the impact of abstraction on the natural environment in some areas. As such Habitat’s Directive Review of Consents (RoCs) is already affecting licence conditions and
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Water Framework Directive (WFD) may have a significant impact in future. The distribution of licences in the Hampshire Avon CAMS area is shown in Figure 3.2. In the 2009 WRMP, the main water companies in operation in this area determined that they can manage their supply and demand with a small surplus to 2025 and as a result did not anticipate any significant infrastructure developments. The area imports around 6 Ml/day of potable water from Veolia, Southern, Bournemouth and other Wessex’s zones. Sembcorp Bournemouth Water export over 42 Ml/day to the Fawley Refinery, just outside the catchment. The catchment experiences significant peaks in demand during the summer months as the result of tourism. A schematic diagram of the Hampshire Avon is shown in Figure 3.3.
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Figure 3.1: Hampshire Avon CAMS area Source: Environment Agency, 2006
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Figure 3.2: Licensed abstractions in the Hampshire Avon CAMS area Source: Environment Agency, 2006
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The Impact of Abstraction Reform
Public water supply operations
–
Tidworth
~5Ml/d ~5Ml/d recent actual
discharge
~5Ml/d ~5Ml/d recent actual
abstraction
Bournemouth Water Water Bournemouth
~3Ml/d ~3Ml/d recent
actual discharge
~5Ml/d ~5Ml/d recent
actualdischarge
~25Ml/d ~25Ml/d recent actual
abstraction
Ashley Heath Ashley
River to 15Ml/d sea, River Avon
recent recent discharge actual
Ringwood and Ringwood
Sembcorp
Deployable output sites outputDeployable sites C, ~156Ml/d D andG
A
P
4
~35Ml/d ~35Ml/d recent actualabstraction
and Devizes and
A P
2 River Avon
1
P
A
Pewsey
Christchurch
3
P
A
Salisbury
Ebble
~20Ml/d ~20Ml/d recent
actualdischarge
~10Ml/d ~10Ml/d recent actual
abstraction
River
~5Ml/d ~5Ml/d recent actual
discharge
Refinery
~2Ml/d ~2Ml/d recent actual
abstraction
Fawley
Groundwater
abstraction
42Ml/d export to export 42Ml/d
Deployable
–
Gauging
station
Warminster
~1Ml/d ~1Ml/d recent
actualdischarge
Environment demand Environment
Wessex Water Water Wessex
output East WRZ ~55Ml/d outputWRZ East
Surface water Surface
abstraction
~25Ml/d ~25Ml/d recent actual
abstraction
Shaftesbury
Effluent
other companiesother
~135Ml/d ~135Ml/d recent actual
abstraction
6Ml/d import from variousfrom import6Ml/d
River
Raw water water Raw
reservoir PWS demand PWS
Figure 3.3: Hampshire Avon schematic diagram
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3.2. Normal operations
There are more than 70 sources listed in the WRMPs for Bournemouth Water (Hale, Bournemouth Water Resource Zones), Wessex Water (East and North Water Resource Zones) and Cholderton Water Resource Zones that overlay the catchment. Around half of these sources are inside the Hampshire Avon CAMS area. Each water company operates its sources to meet both local demands (inside the catchment) and broader water resources zone demands. Table 3.1 shows estimates of the percentage of the Dry Year Annual Average Demand (DYAA) that is met for each Water Resource Zone by the Hampshire Avon catchment. Table 3.1: Estimated percentage of the Dry Year Annual Average Demand (DYAA) that is met by the Hampshire Avon Dry Year Annual Average Demand Demand meet by Hampshire Water Resources Zone (Ml/day) Avon
Bournemouth Water (Hale) 9.72 100%
Bournemouth Water (Bournemouth) 113.15 70%
Wessex Water (East) 46.59 85%
Wessex Water (North) 139.18 30%
Cholderton 2.70 100%
DYAA Demand Estimate 311.34 Source: Bournemouth Water, 2012, Wessex Water, 2013 The sources are constrained by hydrological conditions (e.g. physically there is no water available or the discharge is below Hands Off Flows), licence conditions or, in a few cases, infrastructure constraints. From a modelling perspective the key hydrological constraints relate to HOFs for groundwater sources and the need for groundwater sources to provide “stream support”. Wessex Water’s operations are clearly set out in their operational procedures and examples for key sites are summarised in this report. Some of the licensed abstractions are linked so that a maximum daily or annual abstraction limits is imposed on sets of licences. Bournemouth Water’s sources are regarded as “exceptionally reliable even during dry years”. (Bournemouth Water, 2012). Once these constraints are captured it can be assumed that sources have equal priority as most are drawn from the same Chalk aquifer and there is no evidence available to suggest that some sources are given priority over others.
3.3. Water demand
The Water Resource Zone demands are shown in Table 3.1 and a profile for public water supply has been estimated from the CAMS ledger returns data for Knapp Mill abstraction. CAMS demand profiles may not be the most accurate data available (Environment Agency, 2013.) but our modelling is being compared to AMEC’s national work on abstraction reform option, which uses the same demand profiles so these are reasonable starting point. The water demand profile for the water demand met by sources in the Hampshire Avon is shown in Figure 3.4.
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200
190
180
170 Monthly PWS THR
Avon Ml/d Monthly PWS Demand 160
150 DYAA DYAA Demandmet by sources thein
140 1 2 3 4 5 6 7 8 9 10 11 12
Figure 3.4: PWS water demand profile met by sources in the Hampshire Avon
This is based on a demand profile for PWS; however, the CAMS ledger suggests some different abstraction profiles for some sources, such as Blashford Lakes and river intake which are shown in Figure 3.5. We have no information available on the size of Blashford Lakes and the natural filling processes, which will be from groundwater and surface water sources.
3.03.00
2.52.50
2.02.00
FactorFactor Ibsey for Intake Ibsey intake 1.50 1.5 FactorFactor Blashford for Blashford Lakes Lakes PWSPWS Ratio ratio
1.0Monthlydemand factor 1.00 Monthly demand factor demand Monthly
0.50.50
0.00.00 Jan1 Feb2 Mar3 Apr4 May5 Jun6 Jul7 Aug8 Sep9 Oct10 Nov11 Dec12
Figure 3.5: Factors for Bashford Lake and Ibsey Intake
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3.4. Water supply
In the Bournemouth Water Resource Zone the treated water at the main abstraction point is divided into two supply streams: a potable supply to domestic and commercial customers; and a bulk industrial supply to the Fawley oil refinery. The latter is regarded as an export for the purposes of the WRMP. At Matchams the source is a run-of-river abstraction from the River Avon. The average daily abstraction licence is for 63.6 Ml/day. It has been assumed that both these are constrained by licence conditions but it should be noted that Wessex Water’s licences have constraints that are linked to other abstractions. In the Wessex Water Zone Wessex the water sources are constrained by licence, infrastructure or hydrology. The main constraints are summarised in Table 3.2 based on details from Wessex Water’s Operations Handbook. Individual river flow conditions and stream supports are described by site in the Handbook. Table 3.2: River flow conditions for the Hampshire Avon
Annual Two- River flow Stream Annual licence licence thirds conditions support Site ID Site code (Ml/year) constraint rule conditions 17157 AM SS 2.5 12005 BH 1.114 322.77 12007 BC 1.15 620 ● 2.30 12010 BRI 12010 3000 ● 30 12012 B1 2.1 1120 ● 4.1 12013 B2 1.591 499.161 12017 BD 18.0 3300 ● 12020 B3 0.763 278.766 12029 C1 2.27 827 12030 C2 13.0 2072 ● 12032 C3 14.0 4000 ● 12041 D1 12.0 4300 12042 D2 6.546 330 ● ●
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Annual Two- River flow Stream Annual licence licence thirds conditions support Site ID Site code (Ml/year) constraint rule conditions 12050 D3 6.55 1800 (12135– GAC) 12055 FB 7.0 2550 12057 F1 2.073 758.727 12063 H1 15 3300 ● 12501 KD 10 1500 ● 12074 LB 4.546 1000.139 ● 12082 M1 9.092 3318.645 12089 NT 6.546 2396 ● 12105 SS 4 1022.87 12106 S1 2.273 831.934 12109 S2 2.182 796.474 12117 USB 11.4 3820 12117 USS 10 1410 ● 12132 W1 1.647 603.254
Source names are not shown in accordance with Defra guidance on sensitive information. 4. The Usk 4.1. Introduction
The USK CAMS area is located in South-East Wales. It covers an area of some 1,169 km2 and encompasses the River Usk and its tributaries, but not the Usk Estuary. A map of the catchment is provided at Figure 4.1. The River Usk is a sandstone river of considerable ecological diversity and is important for many nationally and internationally important species. The catchment is forecast to be in deficit owing to the Environment Agency Wales’ review of environmental requirements under the EU Habitat’s Directive. Under the Environment Agency Wales’ Habitats Directive Review of Consents (HD RoC), abstraction licences that could not be concluded as having ‘no adverse impact’ will have to be changed through introduction of cut back rates or hand-off-flows. New licence applications will be subject to a HOF in line with HD RoC findings. This will have an impact on water availability so that there is unlikely to be any surplus of water available in a
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“dry year” in the Usk for new abstraction applications. Other challenges to water availability include increased demand for water (increasing population) and climate change. The majority of water, (98%) abstracted is from surface water sources. There are approximately 410 abstraction licences in the CAMS area and about half of these are for agricultural purposes.
Figure 4.1: Usk CAMS area Source: Environment Agency Wales, 2007 The Usk CAMS area is an important farming region. Very little other industry exists within the catchment, the largest industrial site being a combustion plant at Glascoed. Industrial pressures and their demands for water within the catchment are therefore minimal. Angling takes place throughout the catchment. The River Usk is the most important salmon fishery and probably the best brown trout fishery in Wales. It is also one of the top five salmon rivers in England and Wales. Recreation and tourism is a great asset within the Usk catchment and an important contributor to the area’s local economy. The area also has an intense, diverse and important archaeological and heritage history with a number of water related Scheduled Ancient Monuments and Parks and Gardens. The Monmouthshire and Brecon Canal (completed in 1777) is itself a heritage feature.
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The River Usk at 121 km long is one of the largest rivers in Wales. Its headwaters and some of its tributaries are impounded by the Usk, Crai, Talybont and Grwyne Fawr reservoirs in the upper catchment. Llandegfedd Reservoir, located on the Sor Brook in the lower catchment, is a storage reservoir for water pumped from the lower River Usk. The catchment is long and narrow with the Usk running through its centre. The tributaries are short. At Brecon some of the River Usk’s flow is abstracted to supply the Monmouthshire and Brecon Canal, which runs parallel to the river until the flood plain widens at Abergavenny. Here the canal veers to the south west, while the river continues its course south easterly via Usk town towards the centre of Newport where it discharges into the Usk Estuary. Two of the River Usk’s tributaries, the Sor Brook and Malpas Brook, also flow directly into the Usk Estuary. Over most of the area, the groundwater contributions to river flows are modest, emanating from the Old Red Sandstone, the Coal Measures or from sands and gravels along the river channels. As a result, river flows fluctuate dramatically with changes in rainfall. Groundwater is, however, an important local contributor in the Clydach catchment. The karstic carboniferous limestone underlying this tributary is a major aquifer.
4.2. Water availability challenges
The Usk is an important resource for Dŵr Cymru Welsh Water (DCWW), particularly as part of the South East Wales Conjunctive Use System ‘SEWCUS’ water resources zone, which supplies Cardiff shown in Figure 4.2. The main challenges for water availability in the catchment are environmental . Both The main water resource zones in the catchment are forecast to be in deficit due to a number of drivers such as population growth, climate change and WEAW’s review of environmental requirements under the EU Habitat’s Directive. New abstraction licence options are being considered for the lower Usk to meet environmental objectives. A range of supply and demand-side options are being considered to close the supply-demand deficit. The anticipated changes could have a is will have a major impact on water availability for public water supply in the Usk and the SEWCUS zone so that there is unlikely to be any surplus of water available in a “dry year”.
4.3. Licensing policies
The CAMS sets out the following strategy. All new licences or significant variations are time limited. With the exception of abstractions found to be impacting on the River Usk Special Areas of Conservation (SAC), there is a presumption that new licences will be granted and time limited licences will be renewed if: Environmental sustainability is not in question; There is a continued justification of need for the water; The water is used efficiently. In cases where an abstraction is found to be impacting on the River Usk SAC there is no presumption of renewal. At the time of the CAMS (2007) four of the catchment’s Welsh Water licensed abstractions and one licence exempt Canal and River Trust abstraction could not be shown to have ‘no adverse effect’ on the integrity of the River Usk SAC. A number of options concerning the operation and conditions/constraints of these abstractions have been identified and discussed with both Welsh Water and the Canals and Rivers Trust. These licence changes include a number of key flows thresholds and proportional shares of the volume of water available and hands off flow.
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A general exemption has been given from the need for abstractions to be licensed in a number of 'exempt areas'. The Environment Agency Wales is planning to remove the 'exempt areas' when the relevant section of the Water Act 2003 is enacted.
4.4. Water abstractions
There were on average, over the WRGIS data extract period, about 412 licences issued for abstraction in the catchment. Surface water is the dominant source. Less than 2% of water abstracted is from ground sources. Although approximately 50% of the licences within the catchment have been issued for general agricultural purposes, these represent less than 1% of the total daily volume available for abstraction. The largest abstractor by volume is DCWW for public water supply, at approximately 85% of actual abstractions. The Usk catchment is a key strategic resource for supplying water to much of South East Wales and an extensive conjunctive system of water infrastructure transfers has been developed to distribute this water. DCWW operate these abstractions and transfers under the South East Wales Conjunctive Use Scheme (SEWCUS).
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Figure 4.2: South East Wales Conjunctive Use Scheme (SEWCUS)
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Figure 4.3: Location of abstraction licences in the Usk Source: Environment Agency, 2007
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The next largest use (at approximately 3%) is a licence exempt Canal and River Trust (previously British Waterways) abstraction to supply the Monmouthshire and Brecon Canal for navigation purposes. The remaining water is abstracted for commerce/industry, domestic use, spray irrigation, horticultural watering, lake/pond maintenance, fish farming and hydropower generation purposes.
4.5. Water balance, current water sources and discharges
The schematic diagram in Figure 4.4 shows the main features of PWS operations in the Usk catchment itself. The main supply for PWS is from surface water reservoirs. There are four main reservoirs in use, the Usk, Crai and Talybont in the headwaters, which provide supplies to Towy and Nant Lydach, and the larger Llandegfedd reservoir, a pumped storage scheme, that supplies the city of Newport and parts of Cardiff. There is a groundwater abstraction for PWS in the Brecon WRZ area that provide local supplies. There are small discharges in the upper and mid Usk and then larger discharges into the estuary at Newport. Analysis of Dry Weather Flows (DWF) from wastewater treatment works suggests that around 15 to 20 Ml/day of treated water is discharged into the river upstream of CAMS assessment points.
Figure 4.4: Schematic diagram of the Usk catchment
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5. The Dee 5.1. Introduction
The main water companies in the River Dee Catchment Abstraction Management Strategy Area (CAMS) area are: Welsh Water - Dwr Cymru; United Utilities; Dee Valley Water. The total catchment area of the River Dee up to Chester Weir, the tidal limit, is approximately 1,817 km2. The CAMS area covers the full extent of the river catchments that feed into the Dee Estuary. The main urban areas, Chester and Wrexham, of the Dee CAMS area are located in the east of the catchment. The total population of the CAMS area is around 420,000 people. Figure 5.1 shows a map of the Dee CAMS area. There are some 30 PWS licences with significant abstractions in the Dee CAMS area. The location of these PWS licences and the Water Resource Zones is shown in Figure 5.2. In 2009 PWS abstracted a total of 197,042 Ml of water, which accounted for approximately 93% of all the water abstracted in the Dee CAMS area. Of the water abstracted by PWS companies in 2009 only around 1% was taken from groundwater sources. The River Dee is managed by Natural Resources Wales (formerly the Environment Agency Wales) through a regulation scheme. PWS surface water abstractions from the River Dee are governed by the River Dee General Directions which set out rules for abstraction during drought conditions and are approved by the statutory Dee Consultative Committee. If storage in the River Dee regulation reservoirs falls to the drought action trigger level, a meeting of the Committee will take place to discuss the introduction of drought alleviation measures as enshrined in the Dee General Directions. To conserve water supplies and ensure efficiency of operation, the PWS companies provide a weekly abstraction forecast to Natural Resources Wales to assist in calculating the required releases from the reservoirs and Llyn Tegid (Bala Lake). The River Dee Regulation system is described below.
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Figure 5.1: Overview of the Dee CAMS area Source: Environment Agency, 2008
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Groundwater abstraction licences abstraction Groundwater Surface water abstraction licences abstractionwater Surface
Figure 5.2: Location of Water Resource Zones, PWS groundwater and surface water licences
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5.2. River Dee regulation system
The River Dee regulation scheme is a system of flow balancing and quality management along the River Dee managed by the Natural Resources Wales, formerly the Environment Agency Wales.
5.2.1. Background
To a large extent, water flow in the Dee and certain of its tributaries, is regulated under a set of rules called the Dee General Directions, a requirement of the Dee and Clwyd River Authority Act 1973. These comprise: “Normal General Directions” which are employed during times of “normal” flows; and Drought General Directions which are specified to define the principles and detail under which the prescribed flows and abstractions must be reduced in a drought, more severe than the design drought. These rules are introduced when the total storage of Llyn Celyn and Llyn Brenig reservoirs fall below the seasonal “System Conservation Rule Curve” (SCRC), which are shown in Figure 5.3 and the numbers relating to these curves are given in Table 5.1. The flows in the Dee are controlled by the River Dee regulation scheme which comprises a system of flow balancing along the River Dee. There are four major lakes/reservoirs in the upstream part of the Dee CAMS area: 1. Llyn Tegid (Bala lake); 2. Celyn Reservoir; 3. Brenig Reservoir; 4. Alwen Reservoir – this is used primarily as a water supply reservoir for Welsh Water - Dwr Cymru. The River Dee Regulation Scheme utilises the storage in Celyn reservoir, Brenig reservoir, and Llyn Tegid to ensure that up to 733 Ml/day can be abstracted in the lower reaches of the Dee for public water supply. In terms of a hierarchy the use of the water from the reservoirs, the release of water is as follows: 1. Llyn Tegid (Bala lake); 2. Celyn Reservoir; 3. Brenig Reservoir. Llyn Tegid is controlled to hold a” buffer” of 0 to 20 m3days of water. Once it holds more than this it will “spill”.
5.2.2. Control points
There are two key control points on the Dee as follows: 1. Chester Weir is a control point for the River Dee Regulation Scheme. The Dee Regulation Scheme aims to maintain a minimum of 362.9 Ml/day (4.2 m3/s) under “Normal General Directions” at Chester Weir. The Chester Weir residual flow is calculated based on flows measured at the Chester Suspension Bridge ultrasonic flow gauge, minus the abstractions taken by United Utilities from the Chester Weir intake. 2. Manley Hall gauging station is also a control point. It is our understanding that the Dee regulation Scheme aims to maintain around 10.2 m3/s (881 Ml/day) at this point.
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5.2.3. Designated abstractors
The designated abstractors as far as the River Dee regulation system are: Welsh Water - Dwr Cymru; United Utilities; Dee Valley Water; The Rivers and Canals Trust. The indicative authorised daily abstractions of the designated abstractors are given in Table 5.2.
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System storage (m3 days) excluding Llyn Tegid
Figure 5.3: System Conservation Rule Curves for the River Dee Regulation scheme Source: Environment Agency Wales, 2013
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Table 5.1: System Conservation Rule Curves for the River Dee Regulation scheme in m3 days Storage required for full yield Stage 1 (1535 cumec SCRC: Drought days) with including SCRC: General current 119 cumec Current Direction 30 day control days spill licensed (DGD) Stage 2 Implement storage Month curves release abstractors Curve DGD Curve Stage 3 reserve Jan 1421 1240 1121 1021 921 - 318 Feb 1490 1309 1190 1090 990 - 318 Mar 1529 1348 1229 1129 1029 - 318 Apr 1547 1366 1247 1147 1047 - 318 May 1531 1350 1231 1131 1031 827 318 June 1474 1293 1174 1074 974 770 318 July 1364 1183 1064 964 864 660 318 Aug 1249 1068 949 849 749 545 318 Sep 1134 953 834 734 634 430 318 Oct 1022 841 722 622 522 318 318 Nov 1115 934 815 715 615 411 318 Dec 1303 1122 1003 903 803 - 318
Source: Environment Agency Wales, 2013 Table 5.2: Indicative authorised maximum daily abstractions of designated abstractors
Maximum daily quantity abstracted Number of abstraction Abstractors Ml/day m3/s points
Dwr Cymru – Welsh Water*# 48.0 0.555 1
United Utilities# 709.2 8.208 5
Dee Valley*# 81.5 0.943 2
Canal and Rivers Trust 28.3 0.328 1
Sub-totals 867.0 10.034 9
Off-peak abstraction
Dee Valley* 6.8 0.079
Totals 873.8 10.113 Note: * This indicates that daily peak factors are included. # This indicates that this is subject to joint conditions with more than one licence. Off-peak abstraction is defined as abstraction that is allowed without need for regulation. These values are indicative only and the appropriate licence condition should be referred to. The locations of these abstraction points and the two main control points are shown Figure 5.4.
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3
1
2
1
WelshWater
Cymru
Dwr
Locations of important points ofpoints importantof Locations
abstractions for the Dee Regulation Regulation Dee forthe abstractions
Scheme
1. United Utilities United 1.
2. Dee Valley WaterValley Dee 2.
3.
4. Canals and Rivers Rivers and TrustCanals 4.
Manley Hall Manley
gauging station
2
Chester Chester Weir
gauging station
1
The The is above
only used used onlywhen
the canal is shutthe canalis
for for maintenance
4+1
abstracts
1
United Utilities
from the from canal
Brenig
Llyn
Reservoir
3
Lake)
Tegid
Alwen
Bala
Celyn
Llyn
Reservoir
(
Llyn
Reservoir
Surface water APs water Surface
Groundwater licencesGroundwater
Llyn
Reservoir Surface water licences licenceswater Surface
Figure 5.4: Location of major PWS abstraction locations in the Dee CAMS area Source: Environment Agency, 2007
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5.2.4. Operation of reservoirs
This section details the operation of the major reservoirs in the Dee CAMS area, that is: Llyn Tegid (Bala lake); Celyn Reservoir; Brenig Reservoir; Alwen Reservoir. Water is released from the Llyn Celyn Reservoir into the River Tryweryn which flows into the River Dee. The majority of the water passes through a small hydro-electricity plant to generate electricity. There are three hydropower licences. The catchment of the Llyn Brenig reservoir is very significantly “over-reservoired”. This means that the reservoir cannot normally fill from its own catchment within one annual hydrological cycle. When the reservoir level is drawn down, it can take several years for it to completely re-fill again. Llyn Brenig Reservoir is therefore only used during drought conditions when the capacity of Llyn Celyn and Llyn Tegid Reservoirs are no longer predicted to be capable of maintaining the flow in the River Dee. Lyn Tegid (Bala Lake) is a natural lake that now forms part of the River Dee regulation system and the level at its outflow is automatically controlled. Alwen Reservoir is used as a direct source for public water supply. It is not part of the Dee regulation system. Table 5.3 provides the main reservoir characteristics of the main reservoirs in the upper reaches of the Dee catchment. Table 5.3: Characteristics of the major reservoirs in the Dee CAMS area
Reservoir name Height of dam Total storage Estimated usable Estimated (m) volume (Ml) storage volume surface area at (Ml) full supply level (km2)
Llyn Celyn 58 73,965 71,000 1.32
Llyn Brenig 50 61,500 60,000 1.5
Alwen 30 14,564 13,000 1.5
Lyn Tegid (Bala Lake) Not applicable 18,000 18,000 1.6
Reservoir compensation flows and levels The following are the statutory compensation flows for the four large reservoirs in detailed above. Llyn Celyn Reservoir compensation flow The Llyn Celyn reservoir downstream statutory minimum compensation flows are as follows: 1 October to 31 March 0.368 m3/s (31.8 Ml/day) 1 April to 30 September 0.737 m3/s (63.7 Ml/day). Llyn Brenig and Alwen Reservoirs compensation flows The combined minimum statutory downstream compensation flows from Brenig and Alwen Reservoirs are as follows: 1 October to 31 March 0.158 m3/s (13.6 Ml/day) 1 April to 30 September 0.289 m3/s (25.0 Ml/day).
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The above are subject to a very minimum downstream release of 0.053 m3/s (4.5 Ml/day) from each reservoir. There are specific rules for the minimum compensation flows from the Alwen and Llyn Brenig reservoirs individually. These are as follows: Alwen Reservoir must have a minimum downstream compensation flow as follows: 1 October to 31 March 0.079 m3/s (6.8 Ml/day) 1 April to 30 September 0.157 m3/s (13.6 Ml/day). Llyn Brenig Reservoir must have a minimum downstream compensation flow as follows: 1 October to 31 March 0.079 m3/s (6.8 Ml/day) 1 April to 30 September 0.132 m3/s (11.4 Ml/day). The maximum water retention levels for Llyn Celyn Reservoir are between 1 m and 3 m below the dam spillway level. If the water levels in Llyn Celyn Reservoir exceed these values a maximum controlled discharges of 16.0 m3/s from Llyn Celyn is mandatory. Llyn Tegid (Bala Lake) compensation flow This has an “unofficial” compensation flow of 2.5 m3/s (216 Ml/day) below Bala Sluices. Conjunctive use of Alwen Reservoir and Llyn Brenig compensation waters To maximise the water resources of Alwen and Llyn Brenig Reservoirs the compensation waters are used conjunctively based on the following principles: 1. Alwen Reservoir is generally filled each winter and allow to spill, so it can help the refill of Llyn Brenig Reservoir (if required) by releasing extra compensation water to match a reduction from Llyn Brenig. 2. When Llyn Brenig releases exceed the “normal” compensation water (see above), summer compensation water from Alwen Reservoir can be reduced accordingly. 3. When Dee System Storage is below the 'System Conservation Rule Curve' (SCRC), shown in Figure 2.1, Alwen Reservoir compensation water discharges must at least equal the statutory minimum requirement i.e. 1 October to 31 March 0.079 m3/s (6.8 Ml/day) and 1 April to 30 September 0.157 m3/s (13.6 Ml/day). In general Llyn Brenig Reservoir is used to “help” Alwen Reservoir during dry summers and Alwen helps Llyn Brenig reservoir during the winter refill after a drought.
5.2.5. Water transfers internal to the catchment
At a small amount of water (0.16 Ml/day) is exported from the Alwen Dee Water Resource Zone to Dee Valley Water in the lower part of the Dee system which enables them to supply domestic properties in that area. The flow chart in Figure 5.4 shows Dee Regulation rules work. At times of “unsupported” river flow (i.e. when the river is not said to be “supported” by releases from the reservoirs), and at times when the total storage of Llyn Celyn and Llyn Brenig plots above the “System Safe Yield Line” (SSYL-Green Line) shown in Figure 5.3, abstractors may abstract within the constraints of existing licences. At times when the river is “supported” by reservoir releases and when the total storage of Llyn Celyn and Llyn Brenig plots between the SSYL and the “System Conservation Rule Curve” (SCRC-Solid Black Line), shown in Figure 5.3, abstractors must restrict their abstraction to the agreed “Safe Yield Allocations” as detailed in Table 5.4. It should be noted that at the “Safe Yield” the design residual flow remains at 362.9
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Ml/day (4.2 m3/s) at Chester weir. This reflects the requirement to protect fisheries in the lower Dee and estuary and to restrict saline intrusion at Chester. At times of “unsupported” river flow (i.e. when the river is not said to be “supported” by releases from the reservoirs), and at times when the total storage of Llyn Celyn and Llyn Brenig plots above the “System Safe Yield Line” (SSYL-Green Line) shown in Figure 5.3, abstractors may abstract within the constraints of existing licences. At times when the river is “supported” by reservoir releases and when the total storage of Llyn Celyn and Llyn Brenig plots between the SSYL and the “System Conservation Rule Curve” (SCRC-Solid Black Line), shown in Figure 5.3, abstractors must restrict their abstraction to the agreed “Safe Yield Allocations” as detailed in Table 5.4. It should be noted that at the “Safe Yield” the design residual flow remains at 362.9 Ml/day (4.2 m3/s) at Chester weir. This reflects the requirement to protect fisheries in the lower Dee and estuary and to restrict saline intrusion at Chester. Table 5.4: Dee system “Safe yield” Allocation Authorised abstraction Ratio of Abstractor Safe yield allocation (Ml/day) (Ml/day) authorized abstraction to Gross Net Gross Net the safe yield
United Utilities 632.6 628.0 709.2 704.6 89.1%
Welsh Water - 30.25 24.2 34.0 27.2 89.1% Dwr Cymru
Dee Valley 70.3** 36.6 78* 41.1 89.1%
Canal and 28.3 28.3 28.3 28.3 100.0% Rivers Trust Total 761.45 717.1 846.9 801.1 Notes: *The revised Dee Valley Gross total is based on: Chester revised total of 32.5 Ml/day (gross/net -1.6 Ml/day) Varied permanent Twll licence including transfer of safe yield from Minera source 37.5 Ml/day (2.5Ml/d net 0 transfer of existing licence) New time limited Twll licence for 8Ml/day (net +1.6Ml/day) ** The revised Dee Valley “Safe Yield” Gross total is based on: Chester supply zone 28.8 Ml/day (-1.5Ml/day) Wrexham Supply Zone 41.5 Ml/day (including TFR 2.5 Ml/day from Minera) The “safe yield” allocation of 717.1 Ml/day (net abstraction) is based on a regulation demand of 12.5 m3/day (1080 Ml/day), with a residual flow component of 4.2 m3/day (362.9 Ml/day).The difference between the net and gross abstraction gives amount of water returned to the River Dee.
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Is Dee System Yes Abstraction is constrained by Storage licence conditions only in Zone 1?
No
Is Dee System Yes Maximum abstraction is “safe yield Storage allocation” – See Table 5.4 in Zone 2?
No
Has Dee System Storage Yes fallen below or is likely to fall below the SCRC ?
No Maximum abstraction is “Stage 1 allocation”. The “prescribed flow” Is Dee System Yes regulation is suspended and the releases Storage calculated as detailed in this report in Zone 3?
No
Maximum abstraction is “Stage 2 Is Dee System Yes allocation” – see details in the report Storage in Zone 4?
No
Is Dee System Yes Implement Stage 3 action plan Storage – see details in the report in Zone 5?
Figure 5.5: Dee Regulation Scheme decision flow chart Source: Environment Agency Wales, 2013
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When the regulation method changes to 'Natural' residual flow the net abstractions attributed to various abstractors will be as shown in Table 5.5. Table 5.5: Dee system “Safe yield” Allocation Abstractor Method of abstraction
Rivers and Canal Trust 100% of forecast requirement Dee Valley (Wrexham Supply Zone) 5% of forecast requirement from Dee less 0.95 Ml/day additional augmentation release from Talwrn borehole. This allows for effluent returns from all Wrexham Supply Zone sources. Dee Valley (Chester Supply Zone) 20% of forecast requirement from Dee Dwr Cymru - Welsh Water 20% of forecast requirement from Dee United Utilities 100% of forecast requirement from Dee less 0.05 m3/s wash water return Source: Environment Agency Wales, 2013
5.2.6. Demand reduction measures This section details the demand reduction measures that are implemented at Stages 1, 2 and 3 shown in Figure 5.3. Stage 1 drought reduction measures The general principle of operation of 'Stage 1' Drought General Directions is that any reduction in residual flow over Chester Weir (i.e. below 4.2 m3/s) should be matched by an equivalent reduction in net abstraction by designated abstractors. Table 5.6 presents the Stage 1 demand reduction measures for the main abstractors and Table 5.7 presents the Stage 1 maximum abstraction allocations. Table 5.6: Stage 1 Demand reduction measures and net reduction on regulation release requirement Net reduction on Revised proposal for method “safe yield” release of reducing release requirement, Abstractor requirement Ml/day Canals and Rivers Trust None Nil Dee Valley Water (Wrexham Additional river augmentation 0.2 Ml/day (minimum) Supply Zone) from Talwrn Borehole (0.2 Ml/day minimum) Dee Valley Water (Chester Recycling of process water at 0.2 Ml/day (minimum) Supply Zone) Boughton Water Treatment Works - Additional 1 Ml/day Dwr Cymru - Welsh Water Use of Bretton boreholes or other 0.2 Ml/day (minimum) alternative sources (minimum 1 Ml/day into supply) United Utilities Use of alternative sources. 29.4 Ml/day (minimum) Total 30.0 Ml/day Source: Environment Agency, 2013
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Table 5.7: Stage 1 maximum abstraction allocation Abstractor Stage 1 maximum allocation (Ml/day) Gross Net United Utilities 603.2 598.6 Dwr Cymru – Welsh Water 29.25 24.0 Dee Valley 69.3* 36.2 Canals and Rivers Trust 28.3 28.3 Total 730.05 687.1 Note: * Based on Chester Supply Zone 27.8 Ml/day Source: Environment Agency, 2013 Stage 2 drought reduction measures When usable water conservation storage in the three regulating reservoirs falls to below the Stage 1 implementation line (Blue Line) as shown in Figure 5.3, the implementation of Drought General Directions (DGD) “Stage 2” drought reduction measures are likely to occur. The Stage 2 implementation line (Red Line in Figure 5.3) represents the 100 days output under Stage 1 from the 1 September. This line is 200 m3 days below the SCRC. The requirement to reduce abstraction under Stage 2 follows the same principles as for Stage 1. The target is to reduce net abstraction by a further 30 Ml/day below the Stage 1 allocation. The Stage 2 demand reduction measures are given in Table 5.8. Table 5.8: Stage 2 Demand reduction measures and net reduction on regulation release requirement Net reduction on “safe yield” release Revised proposal for method of requirement, Abstractor reducing release requirement Ml/day Canals and Rivers Trust None Nil Dee Valley Water (Wrexham Use of other sources including river 0.2 Ml/day (minimum) Supply Zone) augmentation from Talwrn Borehole (0.4 Ml/day minimum) or a reduced demand through a hosepipe ban and non-essential use ban. Dee Valley Water (Chester Reduce demand by 1 Ml/day by any 0.2 Ml/day (minimum) Supply Zone) means possible. Increase river augmentation from Talwrn Borehole to 0.9 Ml/day and reduce demand by 0.5 Ml/day or reduced demand through hosepipe ban and non- essential use ban. Dwr Cymru - Welsh Water Use of Bretton boreholes or other 0.2 Ml/day (minimum) alternative sources (minimum of 2 Ml/day into supply), or reduced demand through h/pipe ban and non-essential use ban.
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Net reduction on “safe yield” release Revised proposal for method of requirement, Abstractor reducing release requirement Ml/day
United Utilities Use of alternative sources to save a 29.4 Ml/day (minimum) minimum of 29.4 Ml/day on average or reduced demand through hosepipe ban and non-essential use ban.
Total 30.0 Ml/day Source: Environment Agency, 2013 The target maximum net and gross abstraction rates for the designated abstractors, under Stage 2 DGD are also given in Table 5.9. In order to deliver the resource savings identified, abstractors must ensure that the target maximum abstraction rates are delivered within two days of crossing the Stage 2 implementation line (Red Line as shown in Figure 5.3). Table 5.9: Stage 2 maximum abstraction allocation Abstractor Stage 2 maximum allocation (Ml/day) Gross Net
United Utilities 573.8 569.2
Dwr Cymru – Welsh Water 28.25 23.8
Dee Valley 68.8* 35.8
Canals and Rivers Trust 28.3 28.3
Total 699.15 657.1 Note: * Based on Chester Supply Zone 27.8 Ml/day Source: Environment Agency, 2013 Stage 2 drought measures are only expected to occur with a frequency of around 1 in every 40 years, on average. Under Stage 2 Drought General Directions, the river would be regulated as follows: 1. All designated abstractors should: a. Reduce net abstractions in accordance with Table 5.9; b. Abstractors can achieve and must maintain these reductions by any appropriate measures available to them; c. If the abstractor fails to meet the required reduction within 7 days of the storage falling below the Stage 2 implementation line, or fails to maintain the required reduction, the abstractor must immediately introduce a hosepipe ban (this is seasonally dependent) and make an application for a drought order to ban non-essential water use. 2. River regulation would be as follows: a. Cease to discharge 0.3 m3/s which is the assumed reservoirs inflow as part of the regulation releases from the dams; b. Carefully review the need for additional releases for Chester Weir residual flows during high tides;
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c. Apply for drought order to reduce summer compensation water at Llyn Celyn to winter level, when the river is unsupported; d. Allow discharge from Llyn Tegid reservoir to fall below 2.5 m3/s to conserve Llyn Tegid reservoir storage; e. Use Section 57 powers to restrict spray irrigation abstractions to 50% of the licence entitlement. This will be seasonally dependent. Stage 3 drought reduction measures Under the Drought Contingency Planning Guidelines (1999), issued by the Environment Agency, a further stage of drought action has been proposed. The trigger line for such actions has not been crossed in any of the historical drought sequences modelled for the Dee System by the Environment Agency. If the system storage was to fall below this line, during the regulation season, then it is highly likely that the storage reserve would be required before the end of September. If system storage were to approach this line, despite implementation of all measures under Stages 1 and 2, then the Dee Consultative Committee would meet to discuss available options. The options would be subject to the prevailing conditions and time of year, but would focus on extending existing storage reserves to the end of the regulation season (end of October). Stage 3 drought measures could include the following: 1. All designated abstractors: a. introducing a hosepipe ban (seasonally dependent); b. making an application for a drought order to ban non-essential water use; c. making every effort to reduce demand on the Dee System by use of alternative resources. 2. River regulation: a. Reduce support to Shropshire Union Canal (Canals and Rivers Trust to reduce abstraction). The Canals and River Trust and United Utilities would liaise to ensure that any flow reduction does not result in an unacceptable deterioration in raw water quality at Hurleston. b. A Section 57 order would be implement i.e. there would be total ban on spray irrigation. This would be seasonally dependent. 6. The Tees 6.1. Introduction
Northumbrian Water is the main water company operating in the Tees River Basin. Other companies in this area are Anglian Water, Yorkshire Water and United Utilities. Approximately 95% of the PWS comes from surface water sources. The Tees is located in the south of the much larger Kielder Water Resources Zone area that includes the Kielder Reservoir. This is a regional transfer system designed to allow water from Kielder Reservoir to be released into the Rivers Tyne, Derwent, Wear and Tees. Although the scheme was originally expected to meet industrial demand in the Tees, this did not materialise and the transfers to the Tees are rarely used; instead the scheme provides additional security of supply, which means that local supplies can be used with the confidence that Kielder can provide back-up supplies if local resources were ever under severe pressure. (Note: that Kielder reservoir holds sufficient water to supply the whole of Northumbria for one year). Figure 6.1 shows the location of the major watercourses and urban areas in the Tees CAMS area.
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Figure 6.1: Major urban areas in the Tees CAMS area Source: Environment Agency, 2007 Northumbrian Water operates within healthy headroom and forecasts that this will continue up until 2025. The areas of this catchment that have been assessed in the CAMS indicate that there is currently water available. Northumbrian water operates with strict levels of service, identifying that they will consider appealing for restraint once in every 20 years in the case of a drought and will never undertake hosepipe bans, restrictions on non-essential use or rota cuts. This is due to the significant investment in surface water storage that has been made to date. There is no significant infrastructure investment planned. There are little or no constraints on sources or demand.
6.2. Public water supply resource
A simplified schematic diagram is shown in Figure 6.2. This shows the main features of the system and some data from the first round of CAMS. It should be noted that owing to declining demand this may indicate higher abstractions than currently take place. The most important resource is Cow Green, which regulates the river to meet ‘Minimum Maintained Flows’ (MMFs). Cow Green provides some flood storage, flood releases, a regulated flow for abstraction at Broken Scar, Blackwell and Lower Worsall and a minimum constant MMF of 38.64 Ml/day. There are two groups of reservoirs in parallel on tributaries, including Grassholme and Hury, that provide additional compensation flow and can also be called upon for some regulation flow if Cow Green is under significant pressure during drought. Finally the Tyne-Tees tunnel has an outlet Eggleston; the water company indicate a DO of 60 Ml/day in the planning tables but the tunnel could provide 180 Ml/day currently and there is the potential to supply three or more times this flow. There is a small amount of groundwater abstraction to meet Northumbrian Water’s demands and additional groundwater abstraction to meet Hartlepool Water’s demands. The Hartlepool Water surface water sources are no longer used and Crookfoot reservoir has been sold by Anglian Water. It should be noted that recent actual abstraction in the CAMS ledger should be ignored and reset to zero for modelling purposes.
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Reservoir AWS ~ 30 Ml/d AWS ~ 33 Ml/d Surface water
Groundwater Kielder Scheme (Occasional support) Hartlepool Water Demand Demand Flow gauge HB & MB Industrial raw water Crookfoot
(sold) River Skerne River
Cow Green River Leven Hury Grassholme 66 Ml/d 66 Ml/d Blackton Selsey NW ~ 10 Ml/d Balderhead
SUPPLY DO ~ 308 Ml/d DEMAND ~ 222 ml/d Reservoir group (take at (Kielder Zone ~ 969 (Kielder Zone ~ 694 Lartington) Ml/d) Ml/d)
Figure 6.2: Schematic diagram of the Tees public water supply system Note: The figures shown in this Figure are the recent actual abstraction in the CAMS ledger It is clear the supplies far outweigh the demand for water in the Tees catchment. The demands are a mix of industrial and household and have declined significantly over the last 12 years. This creates some challenges for reconciling recent WRMP data with old abstractions data from the CAMS ledgers. We have assumed that Broken Scar and groundwater abstractions meet public potable water supply and some potable industrial water and that the lower abstractions are raw water for industrial usage.
6.3. Demand The 2009 WRMP and tables provide data for the Kielder Zone and the recent Drought Plan provides a description of how demands have declined. For the purposes of modelling, we have assumed 2009 as a base year and estimated that the demand for potable water is approximately 222 Ml/day, around one third of the Distribution Input in the Kielder Zone. The industrial demand for raw water in Teeside in 2009 was approximately 150 Ml/day but this has already declined to around 120 Ml/day (2012/13). These figures suggest that the CAMS Ledger is already somewhat out of date as it indicates “recent actual” raw water abstraction by Northumbrian Water at Blackwall and Lower Worsall (industry) of 225 Ml/day.
6.4. Supplies The Normal Year and Dry Year Deployable Outputs are for Northumbrian Water are summarised in Table 6.1 from the WRMP. This suggests DYAA DO of 308 Ml/day for operational sources in the Tees and this could be topped up with water from the Balderhead group of reservoirs and then Tyne Tees tunnel in the event of an extreme drought.
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Table 6.1: Normal year and Dry year Deployable Outputs for Northumbrian Water WRP04 dry WRMP09 dry WRP04 normal WRMP09 Source code (Ml/day) (Ml/day) (Ml/day) normal (Ml/day) WD1 106.80 118.00 108.18 118.00 G1 7.00 11.00 7.00 11.00 BRO 1.20 0.33 1.20 0.33 H1 135.00 150.00 135.00 150.00 F1 10.00 19.00 15.00 19.00 W1 45.46 42.50 45.46 42.50 SW 0.53 0.000 0.70 0.00 T1 3.20 2.62 4.00 2.62 C1 0.12 0.00 0.12 0.00 S1 0.03 0.04 0.03 0.04 S2 0.06 0.10 0.06 0.10 A1 0.02 0.03 0.02 0.03 HlG 0.03 0.00 0.03 0.00 B1 1.56 0.70 1.56 0.70 CS/C 0.01 0.06 0.01 0.06 Northern supply zone 311.02 344.39 318.37 344.39
Derwent (Mosswood water 155.00 152.00 152.00 152.00 treatment works) Wear valley water treatment works 22.00 34.00 25.00 34.00 Honeyhill water treatment works 45.00 45.00 47.54 45.00 Sunderland GWS total 43.06 44.00 45.00 44.00 L1 40.00 42.00 40.00 42.00 Central supply zone 305.06 317.00 309.54 317.00
Lartingdon 121.00 128.00 121.00 128.00 BrokenScar total 180.00 180.00 180.00 180.00 Southern Supply Zone 301.00 308.00 301.00 308.00
Kielder Resource Zone 917.08 969.39 928.91 969.39 Note: Source names are not shown in accordance with Defra guidance on sensitive information.
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6.5. Operational behaviour
The objectives for operating the Tees water resources are clearly described in the Northumbrian Water’s WRMP as follows. “Within the general framework of ensuring proper use of resources, objectives for the River Tees and the operation of local resources within the Tees catchment are: to regulate the River Tees to maintain flow rates above a prescribed minimum flow rate as measured at Broken Scar gauging station to regulate the River Tees to support at Broken Scar, Blackwell and Low Worsall and hence to support associated water resources in the Tees catchment in times of drought to provide water in emergency for flushing the River Tees, following major pollution incidents”. The principal regulating reservoir on the Tees catchment is Cow Green providing the full support required for prescribed flows and abstractions under normal conditions. In conditions of dry weather or future higher abstractions, releases may be made from Balderhead reservoir or the Tyne-Tees transfer system. As local water sources will be cheaper to use that pumping via the transfer, it should be assumed that Cow Green is used first, until there is no longer a surplus, then the Balderhead group and then the Tyne-Tees transfer system. The Northumbrian Water drought plan modelling indicates that Cow Green could maintain supplies in every drought since 1960 and that additional resources would only be needed in droughts like 1959, 1955/56 and 1941. The key data for describing operational behaviour is included in Appendix B.
6.6. Transfers
A small amount of water (0.75Ml/day) is transferred to United Utilities and Yorkshire Water from the Kielder Water Resource Zone. The drought plan discusses larger transfers to Yorkshire Water of around 40 Ml/day in drought situations. There are clearly opportunities for broader regional trading of water from the Kielder system but these may not be included in the catchment scale Agent Based Model.
6.7. Drought
The key consideration for drought is the modelling of Cow Green including some simple control rules on a monthly basis as shown in Figure 6.3.
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Figure 6.3: Cow Green control curves
There is a requirement for some flood storage (up to 5,000 Ml) and there may be substantial releases to maintain this, in addition to releases for compensation flows (fixed mount) and regulated water for abstraction downstream. The rules change as the reservoir enters the conservation zone water can be taken from the Balderhead group and if levels fall into the drought zone then a third of regulation water will come from Cow Green and the rest from the Balderhead Group and Tyne Tees tunnel. The minimum compensation flows for the environment are fixed under all circumstances unless the “dead water” zone is hit. Further information is included in Appendix B.
6.8. Discharges
The CAMS Ledger identifies 27 Sewage Treatment Works discharges with a recent actual discharge of approximately 99 Ml/day, although the largest discharge of 30 Ml/day is at Seaton Carew in the tidal Tees. Some additional discharges may go directly to the coast and therefore not be included in the CAMS Ledger. 7. The Cam and Ely Ouse 7.1. Introduction
The Cam and Ely Ouse catchment comprises an area of 3,664 km2. The main urban areas within the Cam and Ely Ouse CAMS encompass Cambridge, Royston, Saffron Walden, Newmarket, Bury St Edmunds, Ely and Swaffham. The catchment is predominantly rural and includes high-grade agricultural land. The Cam and Ely Ouse CAMS area is characterised by the East Anglian Chalklands in the south, Brecklands in the north and the South Level Fenland to the centre of the area. Groundwater is the only direct source
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(excluding transfers) of water in the catchment. Land use is predominantly arable agriculture. The CAMS area is shown in Figure 7.1. The low lying lands of the Fens are protected from inundation by the sea and fluvial floods by the Denver Complex. The Denver Sluice and the A G Wright (or Head) Sluice perform the flood defence role. In the summer months the river flows may be reduced as water is drawn off into the low-level drains via slackers for crop irrigation. In addition to natural flows, the river flows are also regulated by effluents from sewage treatment works and the discharge of industrial cooling water. Ely Ouse to Essex Transfer Scheme comprises two main elements; a transfer of surface water to Essex and the provision for groundwater to be transferred into the Little Ouse and the Thet. The transfer was developed to meet the demands of public water supply in Essex. The main scheme, The Ely Ouse to Essex Transfer, was promoted in the 1960s and was authorised by the Ely Ouse to Essex Water Act 1968. Under this scheme water is diverted at Denver from the Ely Ouse River into the Cut Off Channel and is subsequently pumped from the Cut Off Channel through a series of pipelines into Essex water courses which is then abstracted and stored in reservoirs. The transfer of water from Denver is limited by a minimum flow requirement to the Tidal River Ouse. At times of low flow there is insufficient water in the Ely Ouse to meet abstraction demand for the Ely Ouse to Essex Transfer Scheme. As a result a supplementary scheme has been developed using a series of groundwater boreholes and an additional transfer from the Little Ouse at Hockwold. The Environment Agency uses up to 26 boreholes to pump water into the Little Ouse and Thet Rivers. There are four water companies that operate in this catchment, Anglian, Cambridge and Affinity cover the majority of the catchment; Essex and Suffolk water just crosses into the catchment on the eastern side,. This is shown in Figure 7.2. Whilst the three main companies anticipate being able to meet demand without the need to develop further resources, the CAMS process indicates that parts of the catchment are over- licenced or over-abstracted. Cambridge Water anticipates being in surplus by 2025, despite population increases and climate change impacts. The different companies experience various constraints on their water sources, including hydro- geological constraints and infrastructure constraints; many sources need to be carefully managed to avoid environmental impacts. A small amount of internal transfer occurs within this catchment, between Cambridge and Anglian Water. Affinity Water’s northern resource zone as a whole, receives external and internal transfers. A simplified schematic diagram is included in based on the CAMS data is included in Appendix C.
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Figure 7.1: Cm and Ely Ouse CAMS area Source: Environment Agency, 2007
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Figure 7.2: Water companies covering the Cam and Ely Ouse CAMS area
7.2. Transfers
7.2.1. Raw water transfers from the catchment
Ely Ouse to Essex Transfer Scheme Surplus water from the Ely Ouse system is transferred to South Essex rivers. The Ely Ouse to Essex Transfer Scheme (EOETS) takes water at Denver from the Ely Ouse River (tidal boundary) and transfers it to the River Stour at Kirtling Green in South Essex. Transfer of water to the scheme at Denver is limited by a condition which requires that a minimum residual flow (MRF) is maintained to the tidal River Ouse. Transfers must cease if flows fall to that specified by the 1968 Act. The cessation condition is referred to as the ‘Denver Clause’. The flows stipulated by the Clause tie in exactly to the prescribed flows defined in Section 17 of the Act. A large part of the Denver MRF was a
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requirement to ensure the adequate dilution of discharges from King’s Lynn sewage treatment works and sugar beet factory. This may, in part, be the reason for the higher MRF between September and March. However, given that the sewage works in now greatly improved and the sugar beet factory closed, these factors no longer play a part. It is worth noting that maintenance of flow is also important in preventing siltation within the tidal Ouse. During prolonged reductions in low freshwater flows, navigation of ships to King’s Lynn becomes more difficult because of siltation in the tidal river because of a sandbank that moves opposite the dock entrance. High bed levels downstream of the Denver Sluice might persist longer if the MRF were to be reduced. A knock-on effect might be difficulty in the evacuation of flood flows. Under the 1968 Act discharge of the MRF was to be through ‘one or more gauges on an approved site or sites by some other approved method’. The MRF was therefore treated as if it were an abstraction. A licence application was made and a licence granted (4 September 1970) to allow diversion of water through the Residual Flow Sluice at times when the EOETS was in operation. Essex and Suffolk Water’s Abberton Scheme, which is due to be operational in 2014, will place an additional demand on the EOTS scheme up 100,000 Ml per annum (maximum of 455 Ml/day). The current Hands Off Flow condition at Denver Sluice is 318 Ml/day for September to February, reduced to 114 Ml/day for the period March to August. The licence variation is described here: www.eswater.co.uk/your-home/your- services/denver-licence-variation.aspx Recent presentations by Essex and Suffolk Water suggest a maximum 18 month quantity of 79,555 Ml and daily maximum of 455 Ml/day. Transfers to Essex (2008 Baseline) were between 15,800 Ml (average) and 58,000 Ml (maximum) over 18 months. Transfers were generally made in dry years with often no transfers in average or wet years2.
7.2.2. Normal operations
The water resources zones that the catchment supplies are almost entirely supplied by groundwater. As such the reported Dry Year Deployable Output provides a good estimate of the reliable outputs from these sources, although outputs could be increased by almost 30% to meet higher demands for a shorter period (weeks only, based on the Critical Period DO in the WRMP tables). In Table 7.1 the Water Resource Zone demands (distribution input) are summarised along with an estimate of the proportion of this demand met by sources in the Cam and Ely Ouse catchment. This suggests a demand of approximately 232 Ml/day, which is a marginally higher than the demand needed to serve population inside the catchment and suggests small transfers within water resource zones from inside to outside of the catchment divide.
2 See http://www.raeng.org.uk/news/releases/pdf/696_William_Robinson_presentation.pdf
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Table 7.1: Estimated Public Water Supply demand for the relevant water resources zones and Cam and Ely catchment
DY Average Met from Average WRZ Demand sources in the catchment Water Resource (Ml/day) catchment demand Zone demands (Ml/day) Comment
Anglian 99.09 85% 84.23 WRMP. Weight based Cambridgeshire on DO figures and West Suffolk
Anglian Norfolk 35.82 62% 22.21 WRMP. Weight based Rural on DO figures
Anglian Fenland 56.16 36% 20.22 WRMP. Weight based on DO figures
Veolia North 267.66 12% 31.45 Estimated weight based on area
Cambridge 77.46 100% 77.46 WRMP. Weight based on DO figures
Essex and Suffolk 6.90 12% 0.83 WRMP. Weight based Hartismere on DO figures
Total demand 543.09 231.71 Note: Demand from WRP1 and proportions estimated by identifying sources inside the catchment. There are some sources in the CAMS Ledger that are outside of the catchment divide and these have not been included. It has been is assumed that these four companies will be modelled as individual agents and that water will be abstracted from their own sources up to the licensed annual limits and not in excess of the Critical Period DOs. Anglian Water, which has the largest demand on the catchment, report high peak week factors on demand of 1.32 and that ‘dry years’ have a demand 2% to10% higher than a ‘normal year’. For modelling purposes a standard monthly profile is assumed for a Dry Year Demand with a peak month factor of 1.2 in August. Combining the demands in Table 7.1 with this profile provides an estimate of monthly demand on the PWS abstractions. This is shown in Figure 7.3. This shows that the monthly demand on the PWS abstractions is still significantly less than the annual licensed quantity of 331.4 Ml/day according to the WRMP tables. There are some small imports and exports from water resources zones of potable water reported in the company plans but these are not a significant part of the water balance. There are also some losses of DO, due to sustainability reductions recorded in the base year of the WRMPs but again the volumes are small and it is expected that these will be considered as part of the transition arrangement modelling.
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Public water supply operations Demand (Ml/day) Demand
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Annual licensed quantity PWS abstractions
Figure 7.3: Annual licensed quantity and PWS abstractions for the CAMS and Ely Ouse
7.2.3. Drought operations
As the zones are all in surplus with a reasonable freeboard between demand and licensed volumes and the predominance of groundwater sources, the zones should be reasonably resilient to drought. However, in a long drought with reduced recharge over several years’ action would be needed to maintain public water supplies. Anglian Water’s Drought Plan indicates that the following groundwater sources are sensitive to drought: Lower Links (Wooditton); Eriswell 1 & 2; Long Hill; Newmarket (Ashley Rd); Newmarket (Southfields). General assumptions can be made about the demand reductions, for example of 2% and then 5%, as groundwater levels decline. For Anglian Water, the planned sequence of supply-side measures during drought involves: i. The transfer of water from the Cut-Off channel for release as Stoke Ferry compensation to the River Wissey and the augmentation of supply from groundwater sources located at Wellington Wellfield. ii. A temporary increase to Wellington Wellfield abstraction licence (permit, appears that there is an licence of 10.96 Ml/day). The Drought Plan is not specific about the amount of water available but for (i) this will be limited by what is physically available minus the requirements for the MRF at Denver Sluice and agreed exports to Essex Water. For (ii) it would be reasonable to assume that all groundwater sources, with the exception of the
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drought sensitive sources, could provide an additional 5% output for six months, subject to granting of drought permits.
7.2.4. Effluent Returns
According to the CAMS ledger there are 416 discharge consents owned by water companies although the majority of these are overflows rather than individual sewage treatment works. The total Dry Weather Flow is 137 Ml/day (Reference CAMS Ledger), which is fairly high compared to a public water supply demand of around 200 Ml/day, so this may include significant trade effluent inputs. The major sewage treatment works are Cambridge, Bury St Edmunds and Saffron Waldon. 8. The Trent and Derwent 8.1. Introduction
The Trent is one of England’s largest rivers with a catchment area of 10,436 km2 and main river length of approximately 275 km. There are eight major sub-catchments, the Derwent, Dove, Mease, Sow and Penk, Tame and Anker and the Soar. Each of these are covered by separate CAMS documents and ledgers. The annual rainfall is approximately 721 mm based on the period 1961 to 1990, is below average in England and Wales, and highly variable across the basin. There are two main water companies, Severn Trent Water and South Staffordshire Water that abstract surface water and groundwater from the catchment. In addition, the northern parts of the basin dissect the water supply areas of Yorkshire Water and Anglian Water as shown in Figure 8.1. However, the tidal limit of the Trent and downstream boundary of the catchment model is at North Muskham, so the Anglian Water and Yorkshire Water parts of the catchment have been excluded from this assessment. There are a large number of groundwater sources in the catchment as well as run of river and reservoirs, such as the Derwent Valley reservoirs (comprising Howden, Derwent and Ladybower), Carsington and Tittesworth operated by Severn Trent Water and Blithfield Reservoir, operated by South Staffs Water. In many supply areas these resources are used conjunctively and in several areas the constraint on DO is the capacity of the network. With large populations located in the headwaters of the catchment, water availability is limited in some areas and sewage effluents have a major impact on river flows in summer months. There is a large transfer of raw water from the Severn and Welsh Wye catchments (for example via the Elan Valley Aqueduct) to provide water supplies to the West Midlands and South Staffordshire. The resulting effluents are discharged within the Trent catchment, the largest to the River Tame from Minworth Sewage Treatment Works (STW) in north Birmingham. Water has been transferred in this manner for over a century and the resulting effluents have enhanced low flows in the Trent below the Tame confluence (Environment Agency, 2003). In Severn Trent’s supply area there is a strategic water supply grid that can transfer and balance water across different zones that provides some flexibility for dealing with periods of outage or drought shown in Figure 8.2. This is a major feature of the public water supply system and the grid supplies around 75% of all of Severn Trent’s customers. It links the Derwent Valley system in North Derbyshire to the Mythe Water Treatment Works (WTW) near Tewkesbury in Gloucestershire as well as five reservoir complexes (Ambergate in Derbyshire, Hallgates and Ragdale in Leicestershire, and Oldbury and Meriden in Warwickshire). Although the general movement is by gravity from the Derwent southwards there are pumps and boosters so that flow can be reversed.
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Despite this supply-demand deficits are anticipated in the strategic grid area due to a combination of population, climate change and reductions in abstraction due to environmental constraints by 2040 (Severn Trent Water, WRMP14 consultation notes). There are a large number designated environmental sites and water resources impacts, for example related to over licensed and potentially over-abstracted aquifers in Staffordshire and Shropshire and low flows on the Rivers Derwent and Dove. As such the Habitats Directive and Water Framework Directive may have a significant influence on the future abstraction and the public water supply balance.
Figure 8.1: The Trent catchment, water companies and water resources zones Source: Environment Agency and HR Wallingford.
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Figure 8.2: Severn Trent’s Water Distribution Grid Source: Severn Trent Water, Draft WRMP 2009
8.2. Normal operations
Both water companies aim to provide a secure water supply to customers and, under normal operating conditions, use the lowest cost sources first. In general terms the lower costs sources are groundwater and surface water sources in the north that feed the supply system by gravity. Operating control curves have been developed for all reservoirs in the Trent and the mode of operation will change during drought so that reservoir stock are not exhausted and more expensive sources are used for a period. The operating system is fairly complex and the water companies have invested significant time and effort in the development of AQUATOR water resources systems models over the last 10 years. The ABM will need to simplify operations as individual water treatments works and internal transfers are not fully represented. The following sections identify the salient features that may be parameterised in the ABM.
8.2.1. Major reservoirs
The relevant PWS reservoirs are listed in Table 8.1. Many of these are grouped as they feed a single water treatment works.
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Table 8.1: PWS Reservoirs relevant for the Trent and Derwent modelling Approx. Gross Approx. Length Volume Height Reservoirs Area (ha) (km) Ml m Comments/licence numbers Tittesworth n.c. 2 6400 30 3/28/30/124 Derwent Valley Group 46270 03/28/38/018
Howden Res 80 1.5 9000 37 Derwent Res 71 2 9470 36 The key reservoir group Ladybower Res 210 4 27800 43 Ogston Reservoir (Amber-> 81 1 6180 18 03/28/41/025 - no equivalent Derwent) record in CAMS Carsington (pumped storage 3000 3 35000 34 03/28/29/064 - abstraction from from the Derwent) Ambergate pumping station via 10 km of tunnels Dove Group 19848 Staunton Harold (a) (Source: 85 2.5 6655 26 03/28/36/147 Dove) Foremark (a) (Dove) 93 1 13193 35 03/28/36/148 Charnwood Group 5000 Group storage estimated from MM, 2008 Cropston (b) (Soar) n.c. 1 1350 03/28/57/063 Swithland (b) (Soar) n.c. 1 1350 Blackbrook (Soar) n.c. 1 2300 22 03/28/57/062 - originally developed to feed Charnwood Forest Canal Rutland (Anglian Water n.a. n.a. n.a. n.a. Outside of catchment - share of licence) licence included in Severn Trent's DO Blithfield Reservoir (Staffs 312 3 18172 16 3/28/6/41/S Trent Valley, South Staffs Water, Blithe) Nanpantan Reservoir (Soar) ? 0.25 ? ? 03/28/57/0062 Small reservoir, originally developed to supply Loughborough
Thornton Reservoir (Soar) 30 ? ? ? Source: Severn Trent Water WRMP, CAMS SWABS and Complex sheets, ICOLD database of dams for volumes and crest heights and Google maps for approximate dimensions.
Note The net reservoir volumes will be lower, dead storage is approximately 10% and emergency storage is typically set at about 20% of gross volume. The Derwent Valley reservoirs and Carsington hold the greatest volume and are therefore the key regional resources. Reservoir behaviour is shown in Figure 8.3 with reservoir drawdowns every summer and large reduction in levels during the drought of 1995.
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The Derwent Valley reservoirs are in series and fed by the Upper Derwent, Derwent reservoir direct catchment, Ladybower’s direct catchment and three catch-water’s that can be operated under normal conditions. Raw water can be exported to Yorkshire Water but the main abstraction is downstream of the reservoirs at Bamford Water Treatment Works (max output 176 Ml/d). There is a requirement for a compensation release from the reservoirs of 54 Ml/d, which increases to 72 Ml/d if the flow at Derby St Mary’s on the Derwent is below 340 Ml/d. There is a requirement to provide some flood storage in the Derwent system so levels are dropped in autumn to hold flood flows.
Figure 8.3: Reservoir volumes and behaviour between 1990 and 2009 Source: Mott Macdonald Lower Trent Study The Carsington Reservoir takes water from the River Derwent at Ambergate during winter months, pumping up to the reservoir by 10.5 km long tunnels and an aqueduct. The Ogston Reservoir also takes water from the same point and the maximum pumping volume is 220 Ml/day. The Ambergate licence has two conditions which means that: Abstraction from the Derwent must cease if flow at Derby St Marys is 340Ml/d or less. Abstraction is restricted to 15 Ml/day when flow at Derby St Marys is 680Ml/d or less. In addition the compensation flow requirements are 5.9 Ml/day from Ogston and 2.7 Ml/day from Carsington. Water from Carsington is released back into the River Dove during summer months for water abstraction and treatment further downstream. The reservoir was completed in 1991. Figure 8.3 would appear to indicate that it may have only become operational a few years later). From the CAMS ledger it appears that the daily licence is 273 Ml/day; however, it appears the constraint is therefore pump capacity, which is lower at 220 Ml/day.
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The Tittesworth Reservoir is also a strategic resource that collects water from the Churnet and Upper Hulme Springs. The maximum output is 40 Ml/day and there is a requirement for compensation flow of 14.8 Ml/day to 18 Ml/day.
8.2.2. Surface waters
There are several run-of-river surface water licences for public water supply, the largest abstraction licences are 03/28/35/005 at Egginton, 03/28/46/007 at Little Eaton and 03/28/44/006 at Church Wilne. For some sources the infrastructure constraints downstream may constrain outputs so the full licensed quantities may not be achievable.
8.2.3. Groundwater
The groundwater sources draw mainly from the Triassic Sandstones Aquifers in the English Midlands, but groundwater is also taken from smaller aquifers such as the Magnesian Limestone of Nottinghamshire (Severn Trent Water, 2009).
8.2.4. Transfers
Severn Trent Water obtains a small quantity of water (approximately 40 Ml/day) through bulk imports from neighbouring water undertakers, principally South Staffordshire Water and Anglian Water (Severn Trent Water, 2009). Whilst these volumes will be used in the East Midlands and Severn Trent Staffs Water Resources Zones, it is unclear whether they are used inside or outside the Trent basin. A major raw water import is also taken from the Elan Valley Reservoirs system which is owned by Dwr Cymru Welsh Water. This water is transferred under gravity via the Elan Aqueduct from Rhayader in Powys to Birmingham. The aqueduct has a current capacity of 345 Ml/day and all this water is treated at a large water treatment works in Birmingham. This constitutes the sole supply to the country’s second city. In a normal demand year the typical volume transferred to Birmingham is around 320 Ml/day; however, in a drier summer this quantity can increase to an average of 340 Ml/day owing to local demand increases as well as higher exports from Birmingham into the Severn Zone (Severn Trent Water, 2009). It should be noted that this is reported in the WRMP planning tables as the supply “….to Birmingham” with a DO of 340.81 Ml/day (2008/9).
8.2.5. Reconciling the demand for water from sources in the Trent
The Trent covers a large area supplying water to 5.42 million people. Its complexity and the level of transfers within zones but between catchments and between water resources zones makes it difficult to estimate the demand on sources in the basin. Based on data from water resources management plans (WRP1 and WRP5) and census population data, estimates can be made of the catchment as opposed to water resource zone supply-demand balance. The main findings from the this review are: The ABM needs to assume a fixed volume from Elan Valley to supply Birmingham (and other minor imports). A fixed volume of 335 Ml/day imported to meet PWS would be an appropriate assumption (320 Ml/day from Wales and 15 Ml/day from elsewhere). We then estimate that sources in the catchment need to provide reliable supplies of approximately 1050 Ml/day and that this could be used as a design average demand on catchment licences.
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These estimates have been developed using Dry Year Annual Average data so abstraction may be a little lower (in 9 out of 10 years) and occasionally higher (1 in every 10 years). The data should be compared with recent actual abstraction from the CAMS Ledger.
1400 Monthly PWS THR 1200 Monthly PWS Demand 1000
800
600
400 Demand on Trent sources Ml/dsources Demand onTrent 200
0 1 2 3 4 5 6 7 8 9 10 11 12 Month
Figure 8.4: An estimate of the demand on Trent sources plus headroom Source: Based on a review of WRMP data and population data to interpolate WRZ zone data to the Trent basin
8.3. Drought operations
This section describes the drought operations in the Trent and Derwent catchment. Figure 8.5 shows the Derwent Valley reservoirs drought control lines. Table 8.2 provides East Midlands drought zone management options, Derwent Valley Reservoirs. Two main sources, the River Severn Clywedog Reservoir and The Blithfield Reservoir. South Staffs Water manage these during droughts using the curves in Figure 8.6.
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Figure 8.5: Derwent Valley reservoirs drought control lines Source: Severn Trent Water Drought plan, 2012 Table 8.2: East Midlands drought zone management options, Derwent Valley Reservoirs Option name Trigger Demand saving Demand-side Consider reducing export to Derwent Valley Storage Alert line Up to 40 Ml/day off demand on Yorkshire Water Services DV Supply-side Operate system within normal Normal operation operating parameters Raise awareness in Company Any storage alert line and with EA Reduce Bamford WTW output to DV storage alert line Reduces DV output by up to 80 80 Ml/d Ml/day Consider use of Monksdale DV storage alert line Increases production by 2 Ml/day Convene Drought Action Team Any drought trigger and liaise with EA Consider increased use of Drought warning trigger unsupported river abstraction Consider use of Witches Oak Carsington drought trigger Scheme Review schedule of maintenance Drought action team Extra 30 Ml/day into Supply at major works
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Option name Trigger Demand saving Consider reopening Wing Bulk Drought action team Up to 17 Ml/day made available Supply to Whatborough Service Reservoir Consider increasing import from Any drought warning trigger Up to 70 Ml/day possibly Severn Zone available Consider use of Rothley Brook Any drought warning trigger Up to 7 Ml/day into Cropston WTW Seek Drought Permits as Drought action team Reduced compensation from DV, Required refill Carsington Return to normal operations Drought cessation trigger Source: STW Drought Plan (2010)
Figure 8.6: Figure 8.6: Drought trigger curves for the Blithfield reservoir, managed by South Staffs Water Source: SSW Drought Plan, 2007
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Figure 8.7: Trigger thresholds and associated responses for Blithfield and Clywedog Reservoir Source: SSW Drought Plan, 2007 Table 8.3: Actions and associated estimated water savings Trigger Action Estimated Water Saving Demand-side actions 1 Extra promotion of water efficiency and 3 Ml/day increased publicity campaign 1 Increased leakage detection and repair 1.5 Ml/day 3 Hosepipe and sprinkler bans 10 to 20 Ml/day 3 Enhanced pressure management 1.5 Ml/day 3 Consider bans on non-essential use Unknown Supply-side actions 1 Ensure existing sources are fully operational Maximised available deployable output 1 Increase abstraction from Hampton Loade Maximised available deployable and reduce abstraction from Seedy Mill output 1 Introduce Nethertown pump back, supported Maximised available deployable by the Trent abstraction where required output 1 Introduce nitrate treatment plants Maximised available deployable output 2 Review the potential for bulk supplies Up to 5 Ml/day between Severn Trent and South Staffs
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Trigger Action Estimated Water Saving 2/3 Apply for drought permits: River Blithe 1 to 4 Ml/day (Annual average) Hanch Tunnel 3 Ml/day (Peak week) Hampton Loade 10 to 40 Ml/day (Peak week) Source: SSW Drought Plan, 2007 Table 8.4: Important operation triggers in terms of percentage volume for the major reservoir groups
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Emergency Dead Derwent 95 100 100 100 100 100 95 90 80 80 90 95 water flood control Derwent 65 72 76 76 74 70 62 56 50 47 48 55 20 11 water drought warning trigger Carsington 65 75 78 80 75 69 60 52 48 49 53 58 15 6 and Ogden drought Warning trigger Tittesworth 72 74 76 75 73 72 68 60 50 45 55 63 28 15 drought warning Trigger South Staffs 61 65 70 65 60 55 50 48 48 48 50 56 29 water drought permit trigger Generic 66 72 75 74 71 67 60 54 49 47 52 58 23 11 trigger Source: ‘Estimated from Severn Trent Water’s and South Staff’s Drought Plans
8.4. Effluent returns
The greatest consented discharge volumes direct to the River Trent are from the sewage treatment works (STW) at Stoke Bardolph (Nottingham) and Strongford (Stoke-on-Trent). In addition, the Trent receives a large volume of treated sewage effluents indirectly from discharges made to its tributaries (Environment Agency, 2003).
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9. References
Bournemouth Water (2012) Drought plan 2012, March 2012 Bournemouth Water (2012) Water Resources Management Plan Environment Agency (2003) The Stour Catchment Abstraction Management Strategy, May 2003 Environment Agency (2006) Hampshire Avon Catchment Abstraction Management Strategy, March 2006 Environment Agency (2007) The Usk Catchment Abstraction Management Strategy, March 2007 Environment Agency (2007) The Cam and Ely Ouse Catchment Abstraction Management Strategy, March 2007 Environment Agency (2008) The Tees Catchment Abstraction Management Strategy, March 2008 Environment Agency (2013) Personal communication with staff in the South-West region Wessex Water (2011) Abstraction licence compliance handbook, July 2011 Wessex Water (2008) AMP4 – Low flow investigations - Summary report 2008 Wessex Water (2013) Draft Water Resources Management Plan
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Appendices A. The Stour A.1. Modelling Broad Oak
Normally reservoirs would be modelled with a mass balance. The notes below are from some previous modelling of Broad Oak reservoir. Vt = Vt-1 + A + Qin – Qout – EVT – D Vt Volume for day t Vt-1 Volume for previous day A Pumped abstraction from the Stour. A is limited by the pump volume and Hands of Flow at the abstraction point Qin Natural inflow Qout Compensation flow EVT Surface water evaporation. Based on open water factors and PET. D Demand The flow in the Sarre Penne catchment that provides a natural inflow to the reservoir was estimated as follows:- Qin = 0.64 x Area(Sarre Penne)/Area(Horton) X Q(Horton) The factor of 0.64 was applied to reduce the average flow to the 9 Ml/d stated in the 1976 Broad Oak proposal. The compensation flow (Qout) was set at 2 Ml/d in addition to reservoir bypass/overflows. Surface water evaporation was estimated based on Penman potential evapotranspiration multiplied by an appropriate open water factor (Finch, 2003, J. CIWEM) and the exposed water surface area. Therefore EVT losses were reduced as the reservoir was drawn down. Average demand is set by the user and a standard monthly demand profile was used to increase demand in the summer months and reduce demand in the winter. A level of service “switch” can be incorporated to apply 5% reductions in demand when trigger levels are reached.
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B. River Tees and Associated Tees resources operating rules and model set up
RIVER TEES AND ASSOCIATED TEES RESOURCES 6.1 OBJECTIVES 6.1.1 Within the general framework of ensuring proper use of resources, objectives for the River Tees and the operation of local resources within the Tees catchment are: i to regulate the River Tees to maintain flow rates above a prescribed minimum flow rate as measured at Broken Scar gauging station ii to regulate the River Tees to support abstractions, especially major water supply abstractions at Broken Scar, Blackwell and Low Worsall and hence to support associated water resources in the Tees catchment in times of drought. iii to provide water in emergency for flushing the River Tees, following major pollution incidents. 6.2 RIVER REGULATION FOR PRESCRIBED FLOWS AND ABSTRACTIONS 6.2.1 Main resources and abstractions 6.2.1.1 The principal regulating reservoir on the Tees catchment is Cow Green which provides the full required support for prescribed flows and abstractions under normal conditions. In conditions of drought or future higher abstractions, releases may be made from the Lune/Balder reservoirs or the Kielder transfer system. 6.2.1.2 The outlet portal for the Tyne-Tees tunnel to the River Tees is located at Eggleston (Grid. Ref. NZ 005215). The maximum discharge capacity of the outlet valves is 10.5m3/s (907 Ml/day) but prolonged discharges exceeding the capacity of Airy Holm header pond are limited by the installed pump capacity at Riding Mill (6.25m3/s or 540 Ml/day), the current arrangement of simultaneous pump use of 2 pumps (2.08m3/s or 180 Ml/day) and by the concurrent requirement for water from the transfer tunnel to support other resources, notably on the River Wear where the average summer maximum requirement is 80Ml/day. 6.2.1.3 Water for public and raw water supply is pumped from the River Tees at Broken Scar The maximum licensed rate of abstraction is 65mgd-1 (295Mld-1) except in an emergency as defined by the abstraction licence, when abstraction up to a maximum rate of 75MGd-1 (341Mld-1) is permitted. 6.2.1.4 There is a raw water abstraction downstream from Broken Scar at Blackwell The maximum licenced abstraction is 35MG/day (159 Ml/day), except in an emergency when 45MG/day (204.5Ml/day) can be abstracted. However a further restriction is placed on the combined abstraction from Blackwell and Broken Scar which must not exceed 80MG/day (363.7 Ml/day) or 120MG/day (545.5Ml/day) in an emergency. 6.2.1.5 Regulation releases are required to support a minimum maintained flow of 1.47m3/s (28MG/day or 127 Ml/day), as prescribed by the Blackwell abstraction licence, downstream from that abstraction. Measurement in relation to the prescribed flow is taken to be the difference between the flow measured at Broken Scar gauging station and the rate of abstraction at Blackwell. Both the Undertaker and the Agency shall have access by telemetry to levels and flows measured at the gauging station and to the abstraction meter at Blackwell.
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6.2.1.6 An additional condition of the Broken Scar licence, to maintain flows above Broken Scar, is that flows should not be allowed to fall to less than 83MG/day (377.3Ml/day) above the abstraction. 6.2.1.7 There is a further abstraction of raw water at Low Worsall by the Undertaker. The maximum licensed abstraction is 59MG/day (268 Ml/day) except in an emergency as defined in the licence, when the maximum amount shall be 69MG/day (313 Ml/day). In addition, the abstraction must not exceed the difference between the observed residual flow and the prescribed residual flow below Blackwell by more than 19MG/day (86 Ml/day). This implies a minimum residual flow below Low Worsall of 9MG/day (41 Ml/day) plus inflow from the Skerne and tributaries between Broken Scar weir and Low Worsall. Measurement in relation to prescribed flow shall be the flow downstream from Blackwell as assessed above, and measurement at Low Worsall. Both the Undertaker and the Agency shall have access by telemetry to the flow rate as recorded by the abstraction flow meter at Low Worsall. 6.4 ASSOCIATED TEES WATER RESOURCES AND THEIR SUPPORT 6.4.1 Preamble 6.4.1.1 The principal objective in the design of the Kielder Scheme was to augment the water resources of the Tees basin to meet the then rapidly increasing demand for water, primarily for industrial use. Although the forecast industrial demands have not materialised, recent droughts have illustrated the advantages of a strategic regional back-up. Whilst the volume of transfer through the tunnel to the Tees has been limited to small amounts, the availability of support has enabled the cheaper local sources to be used more effectively, and to be drawn down further, without the necessity to place restrictions in water use. 6.4.1.2 The entire local resources within the Tees catchment and the water supply network which they support are under the ownership and control of the Undertaker. Table 6.3 - Reservoir capacities (Ml) and Compensation flows (Ml/day) Reservoir Gross Useable Compensation flow Capacity Capacity
Cow Green 40915 8815 38.64(8.5MGd-1)
Selset 15320 13820 -
Grassholme 6060 5760 28.48(6.26MGd-1)
Balderhead 19670 18370 -
Blackton 2110 1810 -
Hury 3900 3640 15.22(3.35MGd-1)
TOTAL 87975 82215
6.5 Control Policies 6.5.1 Day to day operation of the entire Tees system is under the control of the Undertaker. The operation of each reservoir or reservoir group depends on time of year and current reservoir storage. This is illustrated by line graphs of control zones and an equivalent tabulation of control zone boundaries at
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the beginning of each month. Control zones identify options for use and/or actions to be taken by the Undertaker or the Agency. 6.5.1 Cow Green Reservoir 6.5.1.1 Cow Green is the principal river regulating reservoir on the River Tees, and this resource is used to support abstractions from the lower Tees. River regulation demand can normally be met from Cow Green releases but are augmented when necessary by regulation from the Lune/Balder reservoirs or the Kielder transfer system. 6.5.1.2 In-river needs in the upper Tees are met by the compensation flow (Table 6.3) and by the requirement to reserve water such that at least one third of regulation releases at a given time come from Cow Green, as specified in the Tees and Cleveland Water Act 1967. That Act also requires that 1818 Ml (400MG) be reserved in the reservoir for freshet releases for fishery purposes, at a maximum additional discharge rate of 45.45Ml/day (10MG/day). 6.5.1.3 Cow Green has a flood control role during winter months with levels being drawn down to provide flood storage and hence help avoid large, uncontrollable overflows. 6.5.1.4 Control rules are shown in Figure 6.3 and Table 6.5. These have been derived using a combination of detailed flow data for 1981 to 1996, simulated inflows for 1926 to 1996 (Holm, June 1998) and operational practice. 6.5.1.5 Zones 1 - Flood Storage Zone When the level enters this zone, releases should be made to draw the level and storage down, at a maximum discharge of 500Mld, to the zone boundary and allowance made for the melting of lying snow. 2 - Surplus Zone When the reservoir storage lies in this zone, water can be released from the reservoir to fully support downstream abstractions and prescribed flows. A guidance line is shown to illustrate the drought impact of a continuous abstraction support release of 250 Ml/day during the summer months with an assumed drought which moderates by 15 November but lasts into December and no regulation support from other sources. 3 - Drought Zone In this zone no more than 200Ml/day or one third of the total regulation release can come from Cow Green. Any additional releases required to support abstractions must be made from the Lune/Balder reservoirs or the Tyne-Tees tunnel. From the end of August, releases must be managed in conjunction with Kielder transfers to ensure that the storage does not fall below the control line, thus reserving in Cow Green sufficient storage to support a maximum regulation requirements for 15 days in the event of pump or other failure at Riding Mill. 6.5.2 Lune/Balder Reservoirs 6.5.2.1 The Lune/Balder main reservoirs consist of Selset and Grassholme on the River Lune and Balderhead, Blackton and Hury on the River Balder.
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6.5.2.2 The Lune/Balder reservoirs support the demand from local Lartington and part of Teesside by direct supply through Lartington Treatment Works. Water may be available for regulation releases in support of the River Tees when the reservoir is in the surplus zone. The normal minimum draft from these reservoirs is compensation water (49 Ml/day), Lartington W.T.W. and other demands that cannot be supplied by Broken Scar W.T.W. 6.5.2.3 Instream flow needs for the Lune and Balder are met by compensation releases as shown in Table 6.3. There is significant recreational use of the reservoirs especially Grassholme and the control policy incorporates a supported summer amenity level, where possible. 6.5.2.4 Control rules are shown on Fig. 6.4 and Table 6.6. These have been derived using the detailed flow data for 1970 to 1996 and simulated inflows for 1926 to 1996. 6.5.2.5 Zones 1 - Surplus Zone When the reservoir storage lies in this zone, water is available to support demand at a rate to suit the Undertaker. River regulation releases may also be made, if the concurrent storage in Cow Green reservoir is within the conservation or drought zones. 2 - Conservation Zone If the total reservoir storage is in the first part of the zone (i) then Lartington may be supplied at a rate of 135Ml/day. As the reservoir storage drops into the lower part of the conservation zone (ii), supply to Lartington must gradually be cut back to 121 Ml/day and river regulation must cease before the drought zone is entered. 3 - Drought Zone If reservoir storages approach this line, output to Lartington must be reduced to 121Mld-1 (the maximum summer demand, assuming full capacity at Broken Scar). This line is based on the worst drought sequence at a supply rate of 121Ml/day. 4 - Emergency Zone Sufficient draught needs to be reserved for 30 days local Lartington supply (25Ml/day) and compensation (49Ml/day).
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C. The Cam and Ely Ouse – Additional information
Ely Ouse Transfer Scheme and Denver Sluice Figure G1 the downstream boundary for the ABM and its operation may be important to maintain water volumes and levels in the catchment. It is not a PWS asset and is run by the Environment Agency.
EOTS = Ely Ouse Transfer Scheme MRF = Minimum Residual Flow
Figure C.1: Cam and Ely Ouse downstream boundary
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Figure C.2: Views of Denver Sluice at the Cam and Ely Ouse downstream boundary
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Figure C.3: Schematic diagram of the Cam and Ely Ouse PWS
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