Thames Water WRMP19 Resource Options

Fine Screening Report Update

April 2017

Thames Water Utilities Ltd

Thames Water WRMP19 Resource Options

356236 WCD WAM 40 A PiMS/356236/Documents 30 August 2016 Fine Screening Report Update Thames Water WRMP19 Resource Options Fine Screening Report Update April 2017

Thames Water Utilities Ltd

Clearwater Court, Vastern Rd, Reading, West Berkshire, RG1 8DB

Mott MacDonald, 22 Station Road, Cambridge CB1 2JD, United Kingdom +44 (0)1223 463500 +44 (0)1223 461007 www.mottmac.com T F W

Thames Water WRMP19 Resource Options Fine Screening Report Update

Issue and revision record

Revision Date Originator Checker Approver Description 01 29 September 2016 Ania Bujnowicz Wendy Kilmurray Bill Hume Smith Draft for stakeholder comment Bill Hume Smith

02 21 April 2017 Jamie Radford Wendy Kilmurray Bill Hume Smith Updated draft for stakeholder Ania Bujnowicz Bill Hume Smith comment Robert MacDonald Victoria Price Bill Hume Smith

03 25 April 2017 Jamie Radford Wendy Kilmurray Bill Hume Smith Updated Tables 3.2, 3.3, 5.14 and Figure 3.4

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Contents

Chapter Title Page

Executive Summary i

1 Introduction 1 1.1 Background ______1 1.2 Structure of report______2 1.3 Stakeholder engagement ______2

2 Statement of need 4 2.1 Requirement for a Water Resources Management Plan ______3 2.2 The TW Water Resource Zones ______3 2.3 The supply-demand balance situation ______4 2.4 London Water Resources Zone ______6 2.5 Requirements for new resource options ______7

3 Approach to fine screening and option appraisal of water resources 9 3.1 Overview of four-phased approach ______9 3.2 Developments in the fine screening approach between Phase 1 and Phase 2 ______12 3.3 Generic list of options ______12 3.4 Feasibility assessments ______12 3.5 Cross-option studies ______13 3.5.1 Water treatment cross option study ______14 3.5.2 Treatment of Water to be Discharged to the Environment ______14 3.5.3 Network reinforcement cross option study ______15 3.5.4 Raw water system cross option study ______16 3.5.5 Operational philosophy ______17 3.5.6 System Strategy ______18 3.6 Fine screening ______18 3.6.1 Environment & social dimension ______19 3.6.2 Cost dimension ______20 3.6.3 Promotability dimension ______29 3.6.4 Flexibility dimension ______31 3.6.5 Deliverability dimension ______34 3.6.6 Resilience dimension ______35 3.6.7 Screening decisions ______39 3.6.8 Back-checking process ______39

4 Generic screening of water resource management options 40 4.1 Generic option screening ______40

5 London WRZ water resource options 42 5.1 Resource option types ______42 5.2 Feasibility report findings ______42 5.2.1 Water reuse ______42 5.2.2 New reservoirs ______45

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5.2.3 Raw water transfers ______50 5.2.4 Desalination ______53 5.2.5 Direct river abstraction ______54 5.2.6 Aquifer recharge ______56 5.2.7 Aquifer storage and recovery ______57 5.2.8 Groundwater development ______57 5.2.9 Removal of Deployable Output constraints ______59 5.2.10 Catchment management ______59 5.3 Exclusivities/Interdependencies ______61 5.4 Fine screening assessment ______61 5.4.1 Scenario analysis ______63 5.4.2 Rejection reasoning ______65 5.5 Next steps for water resource options passing fine screening ______68 5.5.1 Deephams reuse ______68 5.5.2 Beckton reuse ______68 5.5.3 Severn-Thames Transfer ______69 5.5.4 Abingdon reservoir ______69 5.5.5 Teddington direct river abstraction ______69 5.5.6 Beckton desalination ______70 5.5.7 Crossness desalination ______70 5.5.8 Groundwater options ______70 5.5.9 Catchment management options ______71

6 SWOX WRZ resource options 72 6.1 Resource option types ______72 6.2 Feasibility Report findings ______72 6.2.1 New reservoirs ______72 6.2.2 Raw water transfers ______72 6.2.3 Direct river abstraction ______72 6.2.4 Aquifer recharge ______73 6.2.5 Groundwater development ______74 6.2.6 Removal of Deployable Output constraints ______75 6.2.7 Catchment management ______75 6.2.8 Internal inter-zonal transfers ______76 6.2.9 Inter-company transfers ______77 6.3 Exclusivities/Interdependencies ______78 6.4 Fine screening assessment ______78 6.4.1 Rejection reasoning ______80 6.5 Next steps for water resource options passing fine screening ______80 6.5.1 Groundwater development ______80 6.5.2 Catchment management options ______80 6.5.3 Inter-company transfer options ______80

7 SWA WRZ resource options 81 7.1 Resource option types ______81 7.2 Feasibility report findings ______81 7.2.1 Aquifer storage and recovery ______81 7.2.2 Groundwater development ______81 7.2.3 Removal of Deployable Output constraints ______82 7.2.4 Internal inter-zonal transfers ______83 7.3 Exclusivities/Interdependencies ______84 7.4 Fine screening assessment ______84

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7.5 Next steps for water resource options passing fine screening ______86 7.5.1 Groundwater options ______86

8 Henley WRZ resource options 87 8.1 Water resource option types ______87 8.2 Feasibility Report findings ______87 8.2.1 Groundwater development ______87 8.2.2 Catchment management ______87 8.3 Fine screening assessment ______88

9 Guildford WRZ resource options 89 9.1 Water resource option types ______89 9.2 Feasibility Report findings ______89 9.2.1 Aquifer storage and recovery ______89 9.2.2 Groundwater development ______89 9.2.3 Removal of Deployable Output constraints ______90 9.2.4 Inter-company water transfers ______91 9.3 Exclusivities/Interdependencies ______91 9.4 Fine screening assessment ______91 9.5 Next steps for water resource options passing fine screening ______94 9.5.1 Groundwater options ______94 9.5.2 Inter-company transfer options ______94

10 Kennet Valley WRZ resource options 95 10.1 Water resource option types ______95 10.2 Feasibility Report findings ______95 10.2.1 Groundwater development ______95 10.2.2 Removal of Deployable Output constraints ______96 10.2.3 Catchment management ______97 10.2.4 Internal inter-zonal transfers ______97 10.3 Exclusivities/Interdependencies ______97 10.4 Fine screening assessment ______98 10.5 Next steps for options passing fine screening ______100 10.5.1 Groundwater options ______100 10.5.2 Catchment management options ______100

11 Conclusions 101 11.1 Screening summary ______101 11.2 Constrained list ______103 11.3 Next steps ______106

Appendices 107 Appendix A. Treatment technology selection ______108 A.1 Beckton Re-use ______109 A.2 Deephams Re-use ______110 A.3 Mogden Re-use ______110 A.4 Lower Lee (Direct Potable Supply) ______111 A.5 Lower River Lee DRA (Transfer to Lee Valley Reservoirs) ______112 A.6 Teddington Direct River Abstraction ______113 Appendix B. London WRZ fine screening tables ______114 Appendix C. SWOX WRZ fine screening tables ______126

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Appendix D. SWA WRZ fine screening tables ______131 Appendix E. Henley WRZ fine screening tables ______135 Appendix F. Guildford WRZ fine screening tables ______137 Appendix G. Kennet Valley WRZ fine screening tables ______140 Appendix H. Optimism bias & uncertainty ______144 Appendix I. Stochastic analysis of Upper Thames Reservoir ______146 Appendix J. Stochastic analysis of Unsupported Severn-Thames Transfer ______160

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Executive Summary

Introduction

This report describes the updated fine screening of water resource options to produce a Constrained List of options for the WRMP19 that has been carried out following the initial fine screening assessment undertaken in the previous Phase 1 and Phase 1A assessments. The Phase 1 and Phase 1A work identified the need for a number of investigations to be carried out to better inform the water resource decision making process. In Phase 2 these investigations have been undertaken and incorporated into a set of feasibility assessments for each resource option type and into a number of cross-option studies (see Figure S.1). The feasibility methodology employed is consistent with that used in other similar recent feasibility studies carried out by Thames Water for the Thames Tideway scheme and for the Deephams sewage treatment works upgrade. The approach also aligns with methods of site selection and feasibility assessments that are now widely applied by other organisations for major infrastructure schemes.

Figure S.1: Overview of reporting and documentation

Methodology reports

WRMP19 rejection register list of of list Screening

methodology

options

appraisal

report for report

Advanced Advanced programme programme

WRMP14 Programme

investigations

constrained list constrained Screening report Screening

options Constrained

Conceptual design design Conceptual Preferred programme Preferred 3rd party options Option feasibility Environmental performance reports New options Resilience assessments Option investigation Cross option investment needs Bottom up risk and updated cost needs

Phase 1 Phase 2 Phase 3

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As can be seen in Figure S.1, the information gathered from the feasibility studies feeds into the fine screening report which, in turn leads to the drawing up of the Constrained List of options that will inform the WRMP19 programme appraisal.

Fine screening summary A summary of the fine screening status of those options identified on the Feasible List from the feasibility reports can be found in Table S.1.

Constrained List

A summary assessment of the Constrained List water resource options is provided in Table S.2 for the London Water Resources Zone (WRZ) and in Table S.3 for the other five Thames Water WRZs.

The Constrained List breaks large scale options into separate system elements (see examples in Figure S.2). The reason for undertaking this exercise is that one system element (e.g. water treatment works) could be linked to a number of different resource elements and the phasing of these is likely to be different. The information is yet to become available to enable a choice to be made as regards the optimal phasing of these different system elements – which will be done as part of programme appraisal.

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Table S.1: Fine screening summary for specific water resource options

Size Band (Ml/d)

25 75 125 175 225 275 Option 0 Comment London WRZ Reuse - Beckton See section 5.5.2 for next steps Reuse - Mogden See section 5.4.2.1 for rejection reasoning Reuse - Deephams See section 5.5.1 for next steps Reuse - Crossness See section 5.4.2.3 for rejection reasoning Reuse - Mogden South Sew er See section 5.4.2.2 for rejection reasoning RWT - STT Deerhurst See section 5.5.3 for next steps New Reservoir - Abingdon See section 5.5.4 for next steps New Reservoir - Chinnor See section 5.4.2.4 for rejection reasoning New Reservoir - Marsh Gibbon See section 5.4.2.4 for rejection reasoning DRA - Teddington See section 5.5.5 for next steps Desalination - Beckton See section 5.5.6 for next steps Desalination - Crossness (unblended) See section 5.4.2.5 for rejection reasoning Desalination - Crossness (blended) See section 5.5.7 for next steps AR/ASR - Kidbrooke (SLARS1) See section 5.5.8 for next steps AR Merton (SLARS3) See section 5.5.8 for next steps AR Streatham (SLARS2) See section 5.5.8 for next steps ASR South East London (Addington) See section 5.5.8 for next steps ASR Thames Valley/Thames Central See section 5.5.8 for next steps GW - Addington See section 5.5.8 for next steps GW - London confined Chalk (north) See section 5.5.8 for next steps GW - Southfleet/Greenhithe (new WTW) See section 5.5.8 for next steps GW - Merton recomissioning See section 5.5.8 for next steps Licence Trade - GW North London See section 5.5.8 for next steps CM - Southfleet See section 5.5.9 for next steps CM - Green Street Green See section 5.5.9 for next steps CM - North Orpington See section 5.5.9 for next steps CM - Low er River Thames See section 5.5.9 for next steps CM - Low er River Lee See section 5.5.9 for next steps Swindon and Oxfordshire (SWOX) WRZ RWT - STT Deerhurst See section 5.5.3 for next steps New Reservoir - Abingdon See section 5.5.4 for next steps New Reservoir - Chinnor See section 6.4.1.1 for rejection reasoning New Reservoir - Marsh Gibbon See section 6.4.1.1 for rejection reasoning DRA Culham Further consideration of DO impact on London and mutual exclusivity w ith Abingdon GW - Moulsford See section 6.5.1 for next steps Ashton Keynes borehole pumps See section 6.5.1 for next steps IZT - Kennet Valley to SWOX Progress to conceptual design - Deployable Output maximised if Mortimore option developed IZT - Henley to SWOX Progress to conceptual design (mutually exclusive w ith IZT Henley to SWA) CM - Ashdow n Park See section 6.5.2 for next steps CM - Upper Sw ell See section 6.4.1.2 for rejection reasoning CM - Marlborough See section 6.5.2 for next steps Slough, Wycombe & Aylesbury (SWA) WRZ GW - Datchet Datchet main replacement See section 7.5.1 for next steps - options are partially interdependent Eton removal of constraints to DO IZT - Henley to SWA Progress to conceptual design (mutually exclusive w ith IZT Henley to SWOX) Henley WRZ CM - Sheeplands Progress to conceptual design Guildford WRZ Dapdune licence disaggregation Dapdune removal of constraints to DO See section 9.5.1 for next steps - options are partially interdependent Ladymead WTW Kennet Valley (KV) WRZ GW - Mortimer recommissioning See section 10.5.1 for next steps East Woodhay borehole pumps See section 10.5.1 for next steps CM - Playhatch See section 10.5.2 for next steps Key Screened out at fine screening Passes fine screening onto Constrained List Note: Assessment of the internal inter-zonal transfer options w ill be review ed after the April 2017 update of the Supply/Demand Forecast.

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Figure S.2: Separating options into system elements

Resource Conveyance Raw water Treatment Treated water system system

London raw Water water storage Reuse WTW London Reuse Ring Main plant

Desal Desalination plant London Ring Main

London raw New water storage WTW London Reservoir Ring Main

River regulation

Severn- London raw Thames water storage WTW London Transfer Ring Main

For options included on the Constrained List in Table S.1 the following next steps are undertaken in Phase 3: 1. the completion of conceptual design reports, building on and updating those contained in the dossiers of information prepared for WRMP14, where these exist 2. the undertaking of Strategic Environmental Assessment 3. the updating of cost estimates of conceptual designs 4. the undertaking of bottom-up assessments of risk 5. the use of the above information to inform cost, deliverability and environmental metrics to inform programme appraisal

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Table S.2: Constrained List for London WRZ

Option Resource Element Conveyance Element Raw Treatment Element Network Element Type Location Nominal Location Nominal Water System Location Nominal Capacity Capacity Capacity Ml/d Ml/d Ml/d

Water reuse Deephams 60 Deephams to See raw water system East London 60 See network reinforcement matrix - Thames-Lee Tunnel reinforcement matrix - Treatment section 3.5.3 Extension section 3.5.4 Beckton 3*100 Beckton to Lockwood 800 100*3 2*150 shaft

Raw Water Vyrnwy 180 Deerhurst to 300/400/500 See matrix Kempton 100*3 See network reinforcement matrix - Transfer Mythe 15 Culham section 3.5.3

Desalination Beckton (blended) 150 N/A N/A N/A See matrix, plus Beckton to Coppermills Crossness (blended) 3*100 As above plus Beckton to Crossness

New Abingdon 75Mm3 153 N/A See raw water system Kempton 300 See network reinforcement matrix - Reservoir Abingdon 100Mm3 204 reinforcement matrix - 150 section 3.5.3 Abingdon 125Mm3 247 section 3.5.4 100 Abingdon 150Mm3 287 Abingdon 30+ approx 90Mm3 59+179 Abingdon 70+ approx 50Mm3 145+93

Direct River Teddington Weir (Mogden effluent transfer) 300 Teddington to 300 See matrix Kempton / 100 See network reinforcement matrix - Abstraction Thames-Lee tunnel East London 200 section 3.5.3 shaft

Aquifer AR/SLARS - Kidbrooke (SLARS1) 7 N/A N/A N/A N/A Recharge AR Merton (SLARS3) 5 AR Streatham (SLARS2) 4

Aquifer ASR South East London (Addington) 3 N/A N/A N/A N/A Storage and ASR Thames Valley/Thames Central 3 Recovery

Groundwater GW - Addington 1 N/A N/A N/A N/A GW - London Confined Chalk (north) 2 GW - Southfleet/Greenhithe (new WTW) 8 Merton recommissioning 2 North London Licence Trading/Transfer 2

Catchment Southfleet (Groundwater) 0.2 N/A N/A N/A N/A management Green Street Green (Groundwater) 0.3 North Orpington (Groundwater) 0.4 Lower River Thames 2 Lower River Lee 1

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Table S.3: Constrained List for Thames Valley WRZ Option Resource Element Conveyance Element Treatment Element Network Element Type Location Nominal Location Nominal Location Nominal Location Nominal Capacity Capacity Capacity Capacity Ml/d Ml/d Ml/d Ml/d Raw Vyrnwy 20 Deerhurst to 300 Radcot WTW 24 See network blueprint outputs Water Culham 400 Transfer 500

New Abingdon 75Mm3 20 N/A Abingdon WTW 24 See network blueprint outputs Reservoir Abingdon 100Mm3 20 Abingdon 125Mm3 20 Abingdon 150Mm3 20 Abingdon 30+ approx 90Mm3 20 Abingdon 70+ approx 50Mm3 20 Groundwater GW - Moulsford 1 3.5 (ADPW) N/A N/A N/A

Removal of constraints to Ashton Keynes borehole pumps 1.6 (ADPW) N/A DO

Swindon Oxfordshire & Inter-zonal GW - Mortimer disused source Kennet Valley to SWOX 12.8 transfers 8.3 Henley to SWOX 2.5

Ashdown Park 0.3 N/A N/A N/A Catchment management Marlborough 0.2 Groundwater GW - Datchet N/A N/A N/A

Removal of constraints to Datchet main replacement 8.7 (ADPW) N/A N/A N/A SWA DO Eton removal of constraints to DO Inter-zonal transfers Henley to SWA 4.1 N/A N/A

Sheeplands (Groundwater) 0.3 N/A N/A N/A Catchment management Henley Groundwater Dapdune licence disaggregation N/A N/A N/A Removal of constraints to Dapdune removal of constraints to DO 7.8 (ADPW) N/A N/A N/A DO Ladymead WTW Guildford Groundwater GW - Mortimer disused source (recommission) 4.5 (ADPW) N/A N/A N/A

Removal of constraints to East Woodhay borehole pumps 2.1 N/A N/A N/A DO (ADPW) Catchment management Playhatch 0.4 N/A N/A N/A Valley Kennet

Assessment of the internal inter-zonal transfer options will be reviewed after the April 2017 update of the Supply/Demand Forecast.

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1 Introduction

This section provides an introduction to the purpose of this Fine Screening Report and its structure.

1.1 Background

As a statutory undertaker, Thames Water (TW) has an obligation under section 37 of the Water Industry Act 1991 to develop and maintain an efficient and economical system of water supply. The company is required to produce, every five years, a Water Resources Management Plan (WRMP), setting out how it plans to maintain the balance between supply and demand for water over a 25 year period. TW’s current WRMP was published in 2014 and covers the period 2105-2040 (‘WRMP14’).

In 2019 an updated plan will be submitted to the Secretary of State for approval, covering the period 2020- 2045 (‘WRMP19’). The Environment Agency has published Water Resources Planning Guidelines that would apply for WRMP19. The guidelines state that the WRMP must take a long term view, setting a planning period that is appropriate to the risks of your company, but which covers at least the statutory minimum period of 25 years. WRMPs are subject to strategic environmental assessment (SEA) under the Environmental Assessment of Plans and programmes Regulations 2004.

Ensuring the long term security and resilience of drinking water supplies for its customers is thus an important focus of TW’s work. Particular challenges in this respect include projected population growth in TW’s area, particularly in Greater London but also in Swindon and Oxfordshire, and climate change, which brings increased risk of drought. Much of Thames Water’s region is already classified by the Environment Agency as ‘seriously water stressed’.

TW is implementing a range of measures to maintain water resources, including an active programme of leakage detection and reduction and programmes to encourage the efficient use of water. In 2010 the company opened the UK’s first large desalination plant at Beckton in east London in order to reinforce water supply, particularly at times of drought. However, these initiatives will not, on their own, address the projected shortfall in potable water supplies in the long term. For many years there has been an acknowledgement that new water supply infrastructure will also have to be provided on a large scale. To this end, TW has been evaluating a range of technical options, in consultation with stakeholders.

A four phase programme has been developed to reduce uncertainties and update information regarding possible water resource options that might be included in the next WRMP in 2019 (WRMP19). Mott MacDonald, working in partnership with Cascade Consulting, completed Phase 1 of this work programme; the investigations and findings were described in two reports published in May 20151 and November 20152 covering the screening of large3 and small resource options respectively. The objective of Phase 1 was to review the resource options to be carried forward from the WRMP14 constrained list, including reviewing

1 Development of large scale water resource options. Option screening report. May 2015. 2 Development of small scale water resource options. Option screening report. November 2015. 3 Large options were defined as those with a Deployable Output above 50Ml/d 1 356236/WCD/WAM/40/03 25 April 2017 Sharepoint/356236/Documents/BA14

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any rejected options, to identify potential new options and to better inform the Phase 2 fine screening assessments by focusing on uncertainties and risks that were material to water resource option selection.

This report, accordingly, updates the Phase 1 screening reports to take account of the Phase 2 programme of investigations. The report assesses all water resource option sizes identified in the two separate reports that were issued in Phase 1. This report also includes consideration of groundwater, catchment management and inter-zonal transfer options that were not included in the Phase 1 reports.

The scope of the report includes assessment of water resource options to increase supplies. Demand management options (e.g. metering, leakage reduction and water efficiency) are covered in a separate screening report.

1.2 Structure of report

The report is structured as follows:  Chapter 1: sets out the purpose of the report and background;  Chapter 2: provides an introduction to the current water resources availability in the Thames Water WRZs.;  Chapter 3: sets out the approach to screening and appraisal being followed, including any changes in approach adopted since the Phase 1 work;  Chapter 4: describes the review of generic option types that has fed into the specific option development;  Chapters 5 to 10: describe the feasibility assessment and fine screening assessment for each Water Resources Zone (WRZ) in turn; and  Chapter 11: concludes by summarising the screening and the resulting Constrained List.

1.3 Stakeholder engagement

The Phase 1 resource option screening reports on small and large options were shared with stakeholders and published on Thames Water’s website. The reports were presented to the water resources Stakeholder Technical Group on 26 March 2015 (for large options) and on 13 July 2015 for small options. Comments received from stakeholders were either directly addressed in revised reports or incorporated into the Phase 2 investigation programme.

Technical stakeholder meetings to provide updates on progress with the Phase 2 investigations were held on 6 November 2015, and on 6 May 2016. Following issue of the updated fine screening report in September 2016 a further technical stakeholder group meeting was held on 6 October 2016 following which stakeholders were invited to provide feedback in writing. The response to the comments was discussed at a technical stakeholder group meeting on 7 February 2017.

The documentation issued to stakeholders, meeting agenda, meeting minutes and meeting presentations have all been posted in a document library on Thames Water’s website4. A log of stakeholder comments that have been received has been prepared together with a summary of the consideration that has been given to the comments and the response. This comment log has been shared with stakeholders alongside this report.

4 See: https://corporate.thameswater.co.uk/about-us/our-strategies-and-plans/water-resources/document-library 2 356236/WCD/WAM/40/03 25 April 2017 Sharepoint/356236/Documents/BA14

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Feedback is invited on this report in writing to [email protected] by 12 May 2017. Key findings from the report will also be presented to stakeholders at the forthcoming Technical Stakeholder Meeting on 28 April 2017.

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2 Statement of need

This section provides a brief introduction to the requirements for a water resource management plan, Thames Water’s water supply-demand position and relevant considerations in developing water resources.

2.1 Requirement for a Water Resources Management Plan

Water companies in England or Wales are legally required to produce a water resources management plan (WRMP) under Section 37A-37D of the Water Industry Act 1991, that sets out how each company intends to maintain the balance between water supply and demand. The plan must take a long term view, setting a planning period that is appropriate to address the water demand and supply risks to be managed by the company. Guidance on the contents of WRMPs is provided in the Water Resources Planning Guideline published by the Environment Agency and Natural Resources Wales5.

2.2 The TW Water Resource Zones

The TW water supply area is divided into six Water Resources Zones (WRZ)s: London, Swindon and Oxfordshire (SWOX), Henley, Kennet Valley (KV), Slough, Wycombe and Aylesbury (SWA), and Guildford. A geographic overview of these WRZs can be found below in Figure 2.1. TW’s WRZs outside London are collectively referred to in this report as the Thames Valley WRZs.

5 Environment Agency and Natural Resources Wales, Final Water Resources Planning Guidelines (May 2016) 4 356236/WCD/WAM/40/03 25 April 2017 Sharepoint/356236/Documents/BA14

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Figure 2.1: TW Water Resource Zones

Source: Thames Water (Figure A1, Appendix A, Final Draft Drought Plan March 2013)

2.3 The supply-demand balance situation

TW’s WRMP14 for the period 2015 to 2040 identified a large and increasing baseline supply demand deficit in the London WRZ and baseline deficits in the mid-long term in the Swindon and Oxfordshire (SWOX), Slough, Wycombe and Aylesbury (SWA) and Guildford zones. The Henley and Kennet Valley zones remained in surplus throughout the 25 year planning period. The forecast deficit in London was driven by a combination of population growth and climate change impacts. These also drove the SWOX deficit but with the addition of sustainability reductions6, which are reductions in licensed abstraction for environmental benefits. Deficits for SWOX, SWA and Guildford were forecast in the Average Day Peak Week scenario (ADPW)7. For SWOX deficits were also forecast in the Dry Year Annual Average scenario (DYAA)8, but of smaller magnitude than the ADPW deficit. For London the deficit was forecast in the Dry Year Annual Average scenario only.

For the 2019 WRMP the Water Resources Planning Guideline requires that the planning period should be appropriate to the risks to be managed by the water company, but should cover at least the statutory minimum period of 25 years. Thames Water has applied the problem characterisation step of the UKWIR decision making process guidance and concluded that the scale and complexity of the water demand supply problem for the London and SWOX WRZs justify developing the plan using a longer planning period

6 Thames Water (2014) Chapter 6: Final Water Resources Management Plan. 7 Average Day Peak Week (ADPW) is one seventh of total demand or deployable output in the peak week in any 12 month accounting period (ADPW). 8 Dry Year Annual Average (DYAA) is the annual average value of demand, deployable output or some other quantity over the course of a dry year.

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of potentially up to 80 years to 2100, but that for the other Thames Valley WRZs planning over a 25 year planning horizon will be sufficient.

TW has work ongoing to develop updated demand forecasts for inclusion in the WRMP19. Whilst this has still to be finalised a draft assessment is presented in Table 2.1. This forecasts:  London WRZ DYAA deficit of 833Ml/d by 2100  SWOX WRZ ADPW deficit of 52Ml/d by 2100  SWA WRZ ADPW deficit of 14Ml/d by 2045  Kennet Valley WRZ ADPW surplus of 5Ml/d by 2045  Guildford WRZ ADPW deficit of 10Ml/d by 2045  Henley WRZ ADPW surplus of 2Ml/d by 2045

For the purposes of fine screening a nominal deficit of 800Ml/d in the London WRZ has been adopted for WRMP19. Recognising that a significant proportion of the future deficit will be addressed through demand management and leakage reduction, 800Ml/d is considered to be a reasonable assessment of the likely deficit to be met from resource options so as to ensure that sufficient resource options are carried through onto the Constrained List for programme appraisal. As well as allowing for the examination of a longer planning period of up to 80 years, this will facilitate the potential provision of water resource options to other companies in the south east (Affinity Water, Southern Water, South East Water and Sutton & East Surrey Water). Affinity Water has requested Thames Water to include for up to 100Ml/d of raw water supply from the River Thames as part of its planning process. South East Water has also identified a potential requirement for additional raw water from the River Thames at Bray of up to 40Ml/d. Southern Water also has a significant potential requirement in its Hampshire supply area.

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Table 2.1: Supply-Demand Balance position for WRMP19

Volume (Ml/d) WRZ Item 2019/20 2024/25 2029/30 2034/35 2039/40 2044/45 2059/60 2099/00 Demand 2018 2074 2141 2201 2256 2299 2531 2622 London Headroom 127 159 181 174 168 152 152 152 (DYAA) WAFU 2183 2151 2091 2074 2042 2033 2008 1941 Balance 39 -81 -232 -302 -382 -418 -676 -833 Demand 319 327 337 346 354 361 367 368 SWOX Headroom 18 20 22 22 21 22 22 22 (DYCP) WAFU 354 353 346 345 345 344 343 338 Balance 18 5 -13 -22 -30 -39 -46 -52 Demand 167 171 177 183 189 196 216 258 SWA Headroom 7 8 8 8 8 8 8 8 (DYCP) WAFU 192 192 190 190 190 190 190 189 Balance 19 14 5 -2 -7 -14 -35 -77 Demand 118 120 124 127 131 134 142 154 Kennet Headroom 7 6 11 10 9 9 9 9 Valley WAFU 153 151 150 149 148 148 146 142 (DYCP) Balance 28 25 15 11 9 5 -4 -21 Demand 62 64 66 68 70 72 75 81 Guildford Headroom 3 4 3 4 4 3 3 3 (DYCP) WAFU 68 68 68 68 68 65 65 65 Balance 2 0 -2 -4 -6 -10 -14 -19 Demand 19 19 20 21 22 22 23 24 Henley Headroom 1 1 1 1 1 1 1 1 (DYCP) WAFU 25 25 25 25 25 25 25 25 Balance 6 5 4 4 3 2 2 1 Source: TW Supply/Demand Forecast (April 2017 version)

2.4 London Water Resources Zone

A geographic overview of the London WRZ can be found in Figure 2.2 below. The London WRZ is supplied primarily (80%) from the River Thames and River Lee via storage reservoirs. The quantities of water that can be abstracted from the River Thames depend on the relationship between the quantities stored in the reservoirs, the need to ensure a residual freshwater flow in the River Thames over Teddington weir, and the time of year. This relationship is governed by the formal operating agreement between Thames Water and the Environment Agency (EA) under Section 20 of the Water Resources Act 1991, called the Lower Thames Operating Agreement (LTOA).

The remainder of supply is made up of groundwater abstractions, particularly from the chalk aquifer. In addition, the Thames Gateway desalination plant at Beckton can abstract and treat brackish estuarine water from the Thames Estuary.

Treated water is conveyed to an integrated distribution system, a key feature of which is the Thames Water London Ring Main which runs underneath central London and provides flexibility by connecting the Thames and Lee water supply systems. The Thames–Lee tunnel also connects the two systems for the

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purposes of raw water supply. There are various bulk supply imports and exports to and from the London WRZ, with the principal exports relating to bulk supplies to Essex and Suffolk Water and Affinity Water.

2.5 Requirements for new resource options

To identify water resource options for addressing the forecast supply-demand deficits a set of feasible option types has been identified (see Section 4 of this report). Feasibility reports for each of these option types have then been prepared to identify feasible specific options. Specific feasible options of each type (the Feasible List) have been brought together in this Fine Screening Report to populate the Constrained List of options that is to be carried forward to programme appraisal. A number of factors are required to be taken into account in selecting the long term best value water resource options. These include:  the likely significant effects of the option on the environment (both positive and negative);  the value for customers delivered by the option in terms of cost effectiveness and other factors relating to customer preferences;  the flexibility of the option to accommodate changes in requirements;  the promotability of the option including whether requisite planning, licensing and other relevant regulatory consents are likely to be obtained;  the deliverability risks associated with the option both during construction and operation; and  the resilience of the option to drought, climate change and other hazards.

These factors have been taken into account in informing the basis of the fine screening criteria used in this report in drawing up the Constrained List options.

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Map: Existing sources Thames Water WRMP19 Resource Options Fine Screening Report Update

Figure 2.2: Principal features of the Thames Water London Water Resources Zone

King George V

Chingf ord South Deephams WTW STW William Girling

Banbury

Hornsey WTW Lee Valley Reserv oirs Stoke Newington Coppermills WTW Riv er Lee Riv er Roding

Barrow Hill Abbey Mills PS New Beckton STW & Riv erside Riv er Gateway STW Head Desalination Plant Wray sbury Riv er, Riv er Colne & Colne Brook Holland Park Park Crossness Riv er Brent Av enue Lane STW Windsor Kew Park GS Datchet Sunny meads Barnes Thames Barrier PS Intake Queen Longreach STW Datchet Mother Mogden Battersea Rav ensbourne Intake STW Riv er Richmond Wray sbury Old Half -Tide Brixton Honor Oak Staines Windsor Wray sbury King Sluice Nth Weir Intake George VI Staines Kempton Bev erley South Park Teddington Ashf ord Brook Staines PS WTW Weir Egham Bell Common Streatham Raw water storage Intake Hampton Merton Weir Staines WTW WTW Thames Water Intakes GS Littleton Kingston GS Queen Walton Intake, Molesey Penton Hook PS Riv er Mary PS & WTW Weirs Thames Water Pumping Stations Weir Laleham Hampton Ray nes Wandle Gauging Stations Intake Sunbury Intake Park Chertsey Riv er Ash Hogsmill Beddington Affinity Intakes Weirs Bessborough STW Intake Knight Island STW London Ring Main Chertsey Queen Barn Weir Walton Elizabeth II Surbiton London Ring Main Shaft GS intake Shepperton Hogsmill Sewage treatment works Weirs Walton Riv er Water treatment works Intake

Riv er Wey

Riv er Mole

Source: Thames Water/Mott MacDonald/Cascade

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3 Approach to fine screening and option appraisal of water resources

This section provides an overview of the four phase approach to development of new water resources for the Thames Water WRZs. It then focuses in more detail on the fine screening stage leading the compilation of the Constrained List of options, which is the focus of Phase 2.

3.1 Overview of four-phased approach A phased approach to developing water resource options for WRMP19 has been undertaken so that effort on reducing uncertainties is focused on the issues that will influence option screening decisions. An overview of the four-phase approach to reviewing and assessing options in the preparation of WRMP19 is shown in Figure 3.1. In each phase a broadly-based range of evaluation criteria have been applied to inform screening decisions, as described in the Feasibility Report methodology and section 3.6 of this report. The four phases comprise:  Phase 1 – Option review and screening: The objective of Phase 1 was to review the options carried forward and to better target Phase 2 option assessments by focusing on uncertainties and risks that were fundamentally material to option selection.  Phase 2 – Detailed investigations: In Phase 2, targeted detailed investigations have been undertaken to enable a clear explanation of how specific options have been identified and to reduce uncertainties concerning the identification of the best value options. The investigations undertaken in Phase 1 were considered in a series of feasibility reports and cross-option studies including: – Raw Water Transfer Feasibility report – Groundwater Feasibility Report – New Reservoirs Feasibility Report – Water Reuse Feasibility Report – Desalination Feasibility Report – Direct River Abstraction Feasibility Report – Catchment Management Feasibility Report – Inter-zonal Transfer Feasibility Report – Water Treatment Cross-option Study – Network Reinforcement Cross-option Study – Raw Water System Cross-option Study – Third Party Options Report

As these investigations were completed the fine screening process was re-applied to continually improve understanding and reduce, as far as possible, uncertainties associated with the feasibility of the options. The output of the Fine Screening Report is the Constrained List of options that proceed to conceptual design and programme appraisal in Phase 3.  Phase 3 – Programme appraisal: In Phase 3, conceptual design reports are prepared for options on the Constrained List, costs are updated and bottom-up risk assessments are developed. Options on the Constrained List are subject to programme appraisal to determine the best value

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programme of solutions to ensure that supply balances demand, taking account of future scenarios.  Phase 4 – Scheme selection, outline design and planning: Subject to confirmation of the preferred programme following consultation, Phase 4 involves progressing the selected water resource options through to outline design for submission as applications for planning permission or a development consent order.

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Figure 3.1: A phased approach to reviewing and assessing options

WRMP19 Rejection Register

Conceptual Design, Feasibility assessments for updated cost & risk Generic Generic Scheme selection each option type to reduce and SEA options screening (including Leading edge uncertainty and inform list decision making decisions EBSD Modelling methodologies)

WRMP14 Confirm planning Investigation Options problem Outline design Requirements

WRSE/EA Planning Supply and demand WRMP19 Fine Screening OJEU forecasts

Others WRMP19 Constrained List

Phase 1 Phase 2 Phase 3 Phase 4 Stakeholder Engage on appraisal criteria and Phase 1 Engage on detailed studies & Engage on WRMP19 & Government engagement option screening impact on option set preferred programme Review & Decision

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The preparation of the WRMP 19 is time sensitive. It is necessary that by the time Phase 4 is being progressed in 2018/19 all screening decisions have evidential justification based on the available information concerning the feasibility of the options and their likely significant impacts at that time (not the earlier date when the screening decision was first made). As new information becomes available this will require back-checking to ensure that previous decisions regarding the feasibility of options remain well founded.

The focus of this report is on Phase 2. The following sections describe each of the stages of Phase 2 in more detail.

3.2 Developments in the fine screening approach between Phase 1 and Phase 2

There have been several developments in the fine screening approach since publication of the Phase 1 fine screening report. These changes are summarised below:  The Phase 1 report included a coarse screening stage for options based upon the screening criteria used at WRMP14. In Phase 2 a set of feasibility reports have been prepared to identify specific options for each generic water resource option type carried forward from the initial generic screening of option types. The feasibility reports include specific options identified at WRMP14, options proposed by third parties and new options identified. These options are then subject to a three-stage screening process to identify the best specific options of each type to be carried forward to this Fine Screening Report which evaluates the efficacy of options between types. The feasibility reports therefore supersede the coarse screening stage that was included in the Phase 1 screening report.  The change in the water resource planning horizon from 25 to 80 years for London and SWOX, and the consequential increase in the scale of water resource deficits has necessitated a change in the approach to the screening of options on the grounds of cost. In Phase 1 the cost benchmark was set based upon the least cost large scale option, but this is no longer appropriate with a larger water resource planning deficit that will require development of multiple new large scale water resources and so an alternative approach has been developed that is set out in Section 3.6.2.  In Phase 1 small and large water resource options were assessed in separate reports but in Phase 2 the fine screening for small and large options is being combined into a single fine screening report.

3.3 Generic list of options

The starting point for water resource option development is the generic list of option types (e.g. reservoirs, water transfers) referenced in the Water Resources Planning Tools report9. The list has been reviewed to identify option types that have potential for providing feasible specific options for the Thames Water supply area. This is discussed further in Section 4 of this report.

3.4 Feasibility assessments

For the option types that have passed the generic screening exercise, as listed in Section 3.1, feasibility assessments have been conducted. These have identified specific options for each of the generic option types in the list. Three stages have then been undertaken in the feasibility screening reports for these specific options:

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 Stage 1: options are screened against absolute constraints (pass/fail).  Stage 2: the performance of the options is compared qualitatively against a number of criteria that enable differentiation between options of that type.  Stage 3: the performance of the options is assessed in further detail (e.g. including costing).

Further detail relating to the criteria used at each stage of the feasibility assessment can be found within each of the feasibility reports.

Options are carried forward from stage 3 of the feasibility assessment into the Feasible List for further fine screening where:  the option is not compromised by any absolute or key constraints; and  if there is mutual exclusivity between options then only the best performing option will be carried forward, provided that this assessment can reasonably be made based upon the information available at the feasibility assessment stage; and  if the total estimated Deployable Output of resources for a given type in a WRZ exceeds the indicative deficit for the WRZ over the planning horizon10 then only the best performing options are carried forward to the Feasible List, provided that this assessment can reasonably be made based upon the information available at the feasibility assessment stage.

3.5 Cross-option studies

The cross option studies address the investment requirements and operating philosophy of individual system elements. Figure 3.2 illustrates how these system elements combine to provide an individual water resources option.

Figure 3.2: Separation of options into system elements

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The Phase 1 reports identified the need to take account of network reinforcement and water treatment costs when comparing options. Further work has been undertaken to consider requirements for reinforcement of the raw water system and the treatment of water for discharge back into the environment (for reuse and transfer options).

3.5.1 Water treatment cross option study

Work is ongoing by Thames Water to review the resilience of treatment capability in the London WRZ. However, following preliminary findings it has been concluded that new water resource options for London will require additional treatment capacity (except in the case of desalination which produces potable water). A cross-option study has been undertaken to find sites for additional treatment. Two sites have been identified in London:  Kempton WTW for additional resources from the west (e.g. Upper Thames Reservoir, Severn- Thames Transfer, Mogden reuse)  Coppermills WTW for additional resources from the East (e.g. Beckton and Deephams reuse) – this would entail redevelopment of the existing works as there is no further space on the existing site. Alternative sites to Coppermills in east London are also being investigated.

These additional treatment requirements have been included in the costings in this report for options that augment raw water resources for the London WRZ.

3.5.2 Treatment of Water to be Discharged to the Environment

Raw water transfers, water re-use and some direct river abstraction options involve discharges to the environment. These discharges may require treatment to achieve a quality that does not adversely affect the receiving water bodies. Modelling of water quality using available water quality data has been undertaken to assess the required product water quality based on the requirements of the receiving waters that discharges are being made to. For most scenarios two alternative treatment schemes have been identified:  Scheme 1 is intended to be comprehensive and addresses all parameters considered, across all prioritisations and flows; while  Scheme 2 is more selective, addressing just those parameters that are considered to be high priority.

A summary of the findings from this work can be found in Appendix A.

3.5.2.1 Water reuse treatment technology

A key question to be addressed is the level of water treatment required to enable water reuse. It is assumed that planned water re-use would be indirect (i.e. that sewage would be subject to advanced treatment, conveyed upstream and discharged into the environment before being re-abstracted through existing intakes for further water treatment and supply). The technologies included in the feasibility reports were those selected at WRMP14:  For untreated “black water” options: advanced primary + aeration + membrane bio-reactor + granular activated carbon  For sewage treatment works final effluent water options: microfiltration + reverse osmosis + advanced oxidation process

Modelling of water quality has been undertaken to prevent material deterioration in the receiving water (see further details in Appendix A).

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3.5.2.2 Review of risk from parameters of emerging concern

Thames Water manages risks to drinking water through the Drinking Water Safety Plan process (DWSP) which is continually evolving. Of particular concern is the increased risk to water wholesomeness from human transmitted disease (e.g. viruses and pathogens) and chemicals of emerging concern (e.g. pharmaceuticals and personal care products). These risks cannot be controlled by source control measures such as those used for industrial discharges. Thames Water is also cognisant that the means of quantifying virus and pathogens risks is an emerging science and one that it is supporting through its reuse research programme, that is expected to generate changes to Thames Water’s future approaches and enhancements to the Drinking Water Safety Plan process. Thames Water is committed to increasing the resources available to its DWSP team to implement improved monitoring based on the insights obtained from its research. This will no doubt in turn drive innovation in the field of cost effective control measures.

Thames Water proposes a precautionary but adaptive, approach to implementing planned water reuse that will also provide information on the effectiveness of measures to control risks of emerging concern. This precautionary-adaptive approach involves initially implementing an intensive process (including reverse osmosis - a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from drinking water) as a precaution, that can subsequently be adapted to follow any of three future pathways: 1. The plant is effective and water quality results demonstrate that the processes are suitable for direct potable reuse plant through the addition of a chemical conditioning system 2. The plant is effective and water quality results demonstrate that the processes are all needed, but concerns remain around direct reuse and so the plant continues as an indirect reuse scheme 3. The plant is effective and water quality results and associated pilot trials demonstrate that a lower energy indirect reuse system is feasible (e.g. excluding reverse osmosis).

Building upon previous and ongoing pilot trials, it is considered that there would be benefit from applying this precautionary-adaptive approach initially on a small-medium scale reuse plant so that the learning can be maximised before deploying a large scale water reuse programme.

3.5.3 Network reinforcement cross option study

A cross-option study11 has been undertaken to identify network reinforcement requirements for London. The report identified six interventions that could be required, including two extensions to the Thames Water Ring Main (TWRM), with the necessary reinforcements dependent on whether the additional water resource is treated in East or West London. The network reinforcement requirements identified are: 1. Replace New River Head Pump 4 2. Replace Barrow Hill Pump 6 3. TWRM extension - Hampton to Battersea 4. TWRM level controlled by new header tank at Coppermills WTW 5. TWRM extension - Coppermills to Honor Oak 6. Resolve issues with supply to Surbiton during TWRM outage

The matrix in Figure 3.3 shows which of these reinforcements are required for different combinations of new treatment capacity – depending upon whether the additional water resource is available for treatment to the east or the west of the existing TWRM. It can be seen that initially no reinforcement may be required.

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For the purpose of costing water resource options in this fine screening report, only the network reinforcements that involve an extension to the TWRM (denoted 3 and 5 here) are considered to have material impact. The estimated costs for these TWRM extensions have been proportionally allocated to water resource options assuming a notional ring main extension capacity of 800Ml/d.

Figure 3.3: Network reinforcement requirements for additional water resources treated in East or West London

East (Ml/d) 0 100 200 300 400 500 600 700 800 0 - - 5 4,5 4,5 4,5 4,5 1,4,5 1,4,5 100 1 1 3,4,5 3,4,5 3,4,5 3,4,5 4,5 1,4,5

200 1,3 1,3 3,4 3,4,5 3,4,5 3,4,5 3,4,5

300 1,3 1,3 1,3,4 3,4,5 3,4,5 3,4,5 (Ml/d) 400 1,3 1,3 1,3,5 3,4,5 3,4,5 500 1,3,5,6 1,3,5,6 1,3,5 1,3,5

West 600 1,2,3,5,6 1,3,5,6 1,3,5,6 700 1,2,3,5,6 1,2,3,5,6 800 1,2,3,5,6

3.5.4 Raw water system cross option study

A cross-option study12 has been undertaken to identify reinforcements required to the raw water system (between the point of abstraction and the WTW inlet) for the different water resource options. This is of particular relevance for options that augment resources in the River Thames or the River Lee (including new reservoir options, raw water transfers, effluent reuse and some direct river abstraction options). The study used currently available models of the raw water system for the River Thames abstractions and River Lee abstractions. Further work will be required at the programme appraisal stage to confirm the exact thresholds that trigger the different system reinforcements.

The report identified ten interventions that might be required, the most significant including an extension to the Thames Lee Tunnel (TLT), a second Spine Tunnel and additional conveyance from Queen Mary Reservoir to Kempton WTW. The necessary reinforcements are again dependent on the water resource options selected and whether they enter the raw water system in East or West London. The raw water system reinforcements, divided between East and West London, are:

East London 1. King George V Reservoir intake capacity increase 2. Chingford South (above Chingford Mill) intake capacity increase 3. TLT extension from Lockwood PS to King George V Reservoir intake 4. TLT upgrade to remove existing constraints to maximise transfer capacity (not shown in table) 5. Additional conveyance from King George V Reservoir to break tank 6. Second Spine Tunnel from break tank to Reservoir 5 upstream of Coppermills WTW

West London 7. Datchet intake capacity increase with transfer to Queen Mother and Wraysbury Reservoirs 8. Littleton intake capacity increase with transfer to Queen Mary 9. Surbiton intake capacity increase with transfer to Walton inlet channel, required for Teddington DRA option only (not shown in table)

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10. Additional conveyance from Queen Mary Reservoir to Kempton WTW

The matrix in Figure 3.4 shows which of these reinforcements are required depending upon the additional water resource added to the East and West London raw water systems. It can be seen that initially no reinforcement may be required.

Figure 3.4: Raw water system reinforcement requirements for additional water resources in East or West London Additional Raw Water Resource in East (Ml/d) 0 100 200 300 400 500 600 700 800

0 - 3 1,3,5 1-3,5,6 1-3, 5, 6 1-3, 5, 6 1-3, 5, 6 1-3, 5, 6 1-3, 5, 6 100 - 3 1,3,5 1-3,5,6 1-3, 5, 6 1-3, 5, 6 1-3, 5, 6 1-3, 5, 6

(Ml/d) 3 1,3,5 1-3,5,6 1-3, 5,6 1-3, 5, 6 1-3, 5, 6

200 300 3 1,3,5 1-3,5,6 1-3, 5, 6 1-3, 5, 6

West 400 7 3,7 1,3,5,7 1-3,5-7 1-3, 5-7

in in 500 7/8,10 3,7/8,10 1,3,5,7/8,10 1-3,5-7/8,10 600 7/8,10 3, 7/8,10 1,3,5,7/8,10

700 7/8,10 3, 7/8,10

AdditionalRaw Water

Resource 800 7/8,10

3.5.5 Operational philosophy

A cross-option study has also been undertaken to provide an operational philosophy for new water resource options, to support minimum and maximum utilisation scenarios and contribute to developing robust operating cost estimates for all major option types (desalination, wastewater reuse, raw water transfers and reservoirs).

The study has considered the impacts of different operational modes on the different water resource options being considered under the WRMP19 programme. This work has identified that there are essentially four possible operational modes for the options under consideration (although not all modes are applicable to all options). These operational modes are:  Full Operation – Normal scheme operation between the minimum operational condition and full rated Deployable Output (DO)  Hot Standby – Under this mode the facility would be held at (typically) the minimum operational condition with most / all facilities available. The scheme could be returned to full operation in a very short time (such as a day)  Cold Standby - Under this mode the facility would be in a partial shutdown condition with only some facilities available. The scheme could be returned to normal operation in a moderate time (say a few days / weeks)  Care and Maintenance – Under this mode the facilities are essentially shutdown, with only a minimal amount of equipment operational (heating, lighting, etc). Returning the scheme to service could be an extended and complex process similar to commissioning the scheme from new, though it may be simpler.

The study has developed a description of each option and the operational modes that are applicable. Based on these descriptions the estimates of the potential operating costs have been developed and a high level qualitative risk assessment has been produced.

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3.5.6 System Strategy

A system strategy is required to identify dependencies that need to be taken into account during programme appraisal. This strategy draws together the cross option studies and considers alternative combinations of resource options and their implications for system design and operation. It also accounts for how the new resource options would operate in conjunction with the existing supply system (from resource to water distribution) and with other new options.

3.6 Fine screening

The options that pass Stage 3 of the feasibility assessments form the “Feasible List”. These options are then subjected to a further ‘fine screening’ stage to produce the “Constrained List” of options for further development before programme appraisal. The fine screening brings together all resource option types and compares them using a consistent set of criteria. Where options are rejected an explanation is provided in the report and they will also be compiled in a Rejection Register.

The fine screening process will compare options within each WRZ. The fine screening approach taken combines quantitative analysis of costs with qualitative analysis of other relevant dimensions. A set of six dimensions were developed for fine screening during Phase 1 of the project – these are shown in Figure 3.5 which illustrates the different stages in the project lifecycle that the dimensions relate to

Figure 3.5: Mapping of six fine screening dimensions to project lifecycle

Time

Option Development Construction Operation

Environment & Social ✔ ✔

Cost ✔ ✔

Promotability ✔

Deliverability ✔

Flexibility ✔ Commissioning ✔

Resilience granted permission Planning ✔

All options that pass the generic screening process have been assessed against these dimensions to identify potential benefits/opportunities as well as the dis-benefit/risks of each option. The assessment against each dimension is categorised and visualised in a summary matrix using the categories shown in Table 3.1. For any one dimension more than one symbol may be needed to capture the nature of the risks and benefits. For example, under the environmental and social dimension some options (e.g. Cotswold Canals transfer) may include material dis-benefit during the construction stage, but material benefits during the operational phase.

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Table 3.1: Dimension category definitions Symbol Meaning Definition ◉ Substantial benefit/opportunity The option has substantial benefits/opportunities either individually or cumulatively. ◎ Material benefit/opportunity The option has some material benefits/opportunities. ○ Neutral The option does not have significant residual effects. ◑(r) Material dis-benefit/risk The option has some material residual dis-benefits/risks, either individually or cumulatively ●(r) Substantial dis-benefit/risk The option has substantial residual dis-benefits/risks, either individually or cumulatively

A superscript ‘(r)’ next to the symbol would highlight that a dis-benefit/risk could potentially be reduced to ‘neutral’ by additional development of mitigation measures during detailed design.

Definitions for each of the six fine screening dimensions were developed in Phase 1 and these are set out below.

3.6.1 Environment & social dimension

3.6.1.1 Dimension description

Environment & Social: The WRMP falls within the scope of the Strategic Environmental Assessment (SEA) Directive, the Water Framework Directive (WFD) and the Habitats Regulations. Evidence compiled to support the SEA appraisal, Habitats Regulations Assessment (HRA), and WFD Assessment is used to inform indicators of likely environmental effects as part of the Fine Screening process.  The SEA process promotes consideration of a wide range of both beneficial and adverse environmental and social effects in assessing a wide range of alternative options to support the development of the WRMP and helps identify potential cumulative effects with other plans and programmes. The SEA is also informed by the HRA and WFD assessment.  The HRA process assesses whether any options may have ‘likely significant effects’ on one or more European sites (Special Area of Conservation; Special Protection Area or Ramsar sites)  The assessment of effects on water body status and achievement of WFD objectives is also undertaken as required by the WFD and the EA Water Resources Planning Guideline (WRPG).

3.6.1.2 Discussion

Strategic Environmental Assessment

For the fine screening of options, consideration has been given to the likely adverse and / or beneficial residual effects (after taking account of mitigation measures) of each option against the SEA topics (e.g. biodiversity, flora and fauna; landscape and visual amenity; water; population and human health). The effects assessment has drawn on the Feasibility Reports, which employed a range of environmental and social assessment criteria that link to the SEA topics.

The fine screening SEA appraisal also took account of the outline engineering design and outline operating philosophy.

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and reported separately in this Phase 2 Fine Screening report. Construction and operational effects were considered in the assessment,

Habitats Regulations Assessment

The Conservation of Habitats and Species Regulations 2010 (as amended - referred to hereafter as ‘the Habitats Regulations’) implement the Habitats Directive (Council Directive 92/43/EEC) in England and Wales. As a competent authority, Thames Water must ensure that its WRMP meets the requirements of the Habitats Regulations prior to implementation. If the WRMP (i.e. one or more schemes within it) may cause a likely significant effect (LSE) on one or more European sites, either alone or in-combination with other schemes, plans or projects, the WRMP must be subject to ‘appropriate assessment.’

The HRA component of the Fine Screening Report draws on the HRA screening carried out on each option within the Feasibility Reports that assessed whether the option had the potential for likely significant effects on a European site, taking account of the outline engineering design, mitigation measures and outline operating philosophy. Construction and operational effects were assessed.

Outcomes of the HRA screening also informed assessment against the SEA topic of biodiversity, flora and fauna.

Water Framework Directive Assessment

The WFD assessment for the Phase 2 Fine Screening Report draws on the assessment of options carried out for the Feasibility Reports. The WFD assessment addresses the risk of deterioration between status class13 for each relevant WFD water body element during both construction and operation. It also considers whether the option would hinder the attainment of the WFD Good status and the WFD objectives set for the waterbody.

3.6.2 Cost dimension

3.6.2.1 Dimension description Cost: Comparison of option Average Incremental Cost + carbon against a benchmark value. The comparison takes into account uncertainty ranges as well as the relative magnitude of point estimates.

3.6.2.2 Approach to costing

Calculation of AIC+carbon has been undertaken using option cost data extracted from Thames Water’s Asset Planning System (APS). APS generates profiles of fixed and variable capital, operating, and carbon costs.

The APS inputs include:  Capital cost estimates using either Thames Water’s Engineering Estimating System (EES) or bottom- up cost estimates where EES models are not available  Operating costs based upon estimates of the option’s impact on power, chemicals and labour costs  Estimates of embodied and operational carbon monetised using the traded price of carbon (for embodied carbon and for grid electricity) and the non-traded price of carbon (for non-grid operational carbon)  Assumed splits between fixed and variable costs by option type

13 Under the WFD water bodies are classified according to chemical, ecological and biological status. 21 356236/WCD/WAM/40/03 25 April 2017 Sharepoint/356236/Documents/BA14

Thames Water WRMP19 Resource Options Fine Screening Report Update

The outputs from APS have been used to generate the AIC+carbon calculation. Key assumptions made in calculating the AIC+carbon include: 1. When calculating variable costs, assumptions on utilisation need to be made. Currently zero and 100% utilisation scenarios have been used, except for the Crossness (unblended) desalination option where a minimum utilisation of 75% has been applied as it is assumed that the plant would operate continuously14. 2. The scaling factor used for the denominator in the AIC calculation is the estimated Deployable Output (DO). There is a risk that this approach could unfairly favour large options, but this has been mitigated by increasing the screening threshold for small options. In most cases the Deployable Outputs are based upon, or informed by, WARMS2 outputs using the historical drought record; the Severn-Thames Transfer Deployable Outputs are based upon stochastic analysis. 3. Costs and benefits have been discounted using the Treasury declining long term discount rate: a. 3.5% for years 0-30 of the appraisal period, b. 3.0% for years 31-75, and c. 2.5% for years 76-125 4. Financing costs have been calculated as a stream of annual costs over the life of the option, using an assumed 3.6% average cost of capital. 5. A contingency has been added to option capital costs to cover optimism bias (see Appendix H) 6. A range of uncertainty has been applied to the capital costs for each option (see Appendix H) 7. A range of uncertainty can be entered for operating costs on the costing spreadsheets, with a default figure of ±10% applied

For the purpose of comparing options using AICs it has been necessary to make assumptions around how individual option elements (i.e. resource, conveyance and treatment) combine to provide overall supply options. The assumptions made for London and the Thames Valley are shown in Table 3.2 and Table 3.3 respectively.

Costs associated with reinforcements to London’s raw water system and treated water network depend upon the combination of water resource options selected. However, the variability in these costs is not material for scenarios combining significant resources in East and West London, which is the expected outcome. The raw water system and network reinforcement costs have therefore been pro-rated based upon the ratio of option Deployable Output to 800 Ml/d. Raw water system reinforcement costs have not been included in desalination, aquifer recharge, aquifer storage and recovery, groundwater and catchment management option types, as these options do not require reinforcement to the existing raw water system. This approach is a simplification for screening purposes, and dependencies will be modelled more rigorously as part of programme appraisal.

14 Unlike other desalination options identified, the Crossness desalination option is not blended with water from other sources and so cannot be operated intermittently without causing changes in water quality that are likely to result in customer acceptability issues. 22 356236/WCD/WAM/40/03 25 April 2017 Sharepoint/356236/Documents/BA14

Thames Water WRMP19 Resource Options Fine Screening Report Update

Table 3.2: London WRZ - summary of options elements included in AIC calculation

Deployable Output (DYAA) Master Solution Name WRZ Historical (Ml/d) Stochastic (Ml/d) Resource elements Conveyance elements Water treatment elements Network costs Reuse: Beckton 380Ml/d London 336 Reuse Beckton 380 MLD Beckton to King George V intake 380 MLD Coppermills WTW 100 MLD + 100 MLD + 100 MLD + 100 MLD Yes Reuse: Beckton 300Ml/d London 268 Reuse Beckton 300 MLD Beckton to King George V intake 300 MLD Coppermills WTW 100 MLD + 100 MLD + 100 MLD Reuse: Beckton 200Ml/d London 183 Reuse Beckton 200 MLD Beckton to King George V intake 200 MLD Coppermills WTW 100 MLD + 100 MLD Reuse: Beckton 150Ml/d London 138 Reuse Beckton 150 MLD Beckton to King George V intake 200 MLD Coppermills WTW 100 MLD + 50 MLD Reuse: Beckton 100Ml/d London 95 Reuse Beckton 100 MLD Beckton to King George V intake 100 MLD Coppermills WTW 100 MLD Reuse: Beckton 50Ml/d London 49 Reuse Beckton 50 MLD Beckton to King George V intake 100 MLD Coppermills WTW 50 MLD Reuse: Mogden 200Ml/d London 180 Reuse Mogden 200 MLD Mogden to Walton 200 MLD Kempton WTW new 100 MLD + 100 MLD Yes Reuse: Mogden 150Ml/d London 137 Reuse Mogden 150 MLD Mogden to Walton 200 MLD Kempton WTW new 150 MLD Water Reuse Reuse: Mogden 100Ml/d London 94 Reuse Mogden 100 MLD Mogden to Walton 100 MLD Kempton WTW new 100 MLD Reuse: Mogden 50Ml/d London 49 Reuse Mogden 50 MLD Mogden to Walton 100 MLD Kempton WTW new 50 MLD Reuse: Deephams 60Ml/d London 58 Reuse Deephams 60 MLD Deephams to King George V intake 60 MLD Coppermills WTW 50 MLD Yes Reuse: Crossness 190Ml/d London 174 Reuse Crossness 190 MLD Crossness to King George V intake 200 MLD Coppermills WTW 100 MLD + 100 MLD Yes Reuse: Crossness 150Ml/d London 138 Reuse Crossness 150 MLD Crossness to King George V intake 200 MLD Coppermills WTW 100 MLD + 50 MLD Reuse: Crossness 100Ml/d London 95 Reuse Crossness 100 MLD Crossness to King George V intake 100 MLD Coppermills WTW 100 MLD Reuse: Crossness 50Ml/d London 49 Reuse Crossness 50 MLD Crossness to King George V intake 100 MLD Coppermills WTW 50 MLD Reuse: Mogden South Sewer 50Ml/d London 49 Reuse Mogden South Sewer 50 MLD Kempton to Walton Black Water 50 MLD Kempton WTW new 50 MLD Yes RWT: STT Deerhurst 300 Ml/d (Lon only) Vyrnwy Mythe 195 London 207 160 Vyrnwy 180 MLD (Lon only) RWT Deerhurst to Culham 300 MLD (Lon only) Kempton WTW new 100 MLD + 100 MLD Yes RWT: STT Deerhurst 400 Ml/d (Lon only) Vyrnwy Mythe 195 London 256 200 Mythe 15 MLD (Lon only) RWT Deerhurst to Culham 400 MLD (Lon only) Kempton WTW new 150 MLD + 100 MLD RWT: STT Deerhurst 500 Ml/d (Lon only) Vyrnwy Mythe 195 London 292 213 RWT Deerhurst to Culham 500 MLD (Lon only) Kempton WTW new 150 MLD + 150 MLD Raw Water Transfers RWT: STT Deerhurst 300Ml/d (2 zone Lon) Vyrnwy Mythe 195 London 197 150 RWT Deerhurst to Culham 300 MLD (Lon only) Kempton WTW new 100 MLD + 100 MLD RWT: STT Deerhurst 400Ml/d (2 zone Lon) Vyrnwy Mythe 195 London 246 190 RWT Deerhurst to Culham 400 MLD (Lon only) Kempton WTW new 150 MLD + 100 MLD RWT: STT Deerhurst 500Ml/d (2 zone Lon) Vyrnwy Mythe 195 London 282 203 RWT Deerhurst to Culham 500 MLD (Lon only) Kempton WTW new 150 MLD + 150 MLD Abingdon 150Mm3 (Lon only) London 287 282 Abingdon 150 Mm3 - 283 MLD (Lon only) N/A Kempton WTW new 150 MLD + 150 MLD Yes Abingdon 150Mm3 (2 Zone Lon) London 281 Abingdon 150 Mm3 - 274 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD + 150 MLD Abingdon 125Mm3 (Lon only) London 247 Abingdon 125 Mm3 - 252 MLD (Lon only) N/A Kempton WTW new 150 MLD + 100 MLD Abingdon 125Mm3 (2 Zone Lon) London 239 Abingdon 125 Mm3 - 242 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD + 100 MLD Abingdon 100Mm3 (Lon only) London 204 Abingdon 100 Mm3 - 201 MLD (Lon only) N/A Kempton WTW new 150 MLD + 50 MLD Abingdon 100Mm3 (2 Zone Lon) London 196 Abingdon 100 Mm3 - 191 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD + 50 MLD Abingdon 75Mm3 (Lon only) London 153 Abingdon 75 Mm3 - 151 MLD (Lon only) N/A Kempton WTW new 150 MLD Abingdon 75Mm3 (2 Zone Lon) London 144 Abingdon 75 Mm3 - 141 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD Abingdon 50Mm3 (Lon only) London 103 Abingdon 50 Mm3 - 101 MLD (Lon only) N/A Kempton WTW new 100 MLD Abingdon 50Mm3 (2 Zone Lon) London 93 Abingdon 50 Mm3 - 91 MLD (2 zone Lon) N/A Kempton WTW new 100 MLD Abingdon 30Mm3 (Lon only) London 59 Abingdon 30 Mm3 - 63 MLD (Lon only) N/A Kempton WTW new 100 MLD New Reservoir Abingdon 30Mm3 (2 Zone Lon) London 51 Abingdon 30 Mm3 - 53 MLD (2 zone Lon) N/A Kempton WTW new 100 MLD Chinnor 50Mm3 (Lon only) London 103 Chinnor 50Mm3 - 100MLD (Lon only) N/A Kempton WTW new 100 MLD Yes Chinnor 50Mm3 (2 Zone Lon) London 93 Chinnor 50Mm3 - 80MLD (2 zone Lon) N/A Kempton WTW new 100 MLD Chinnor 30Mm3 (Lon only) London 59 Chinnor 30Mm3 - 60MLD (Lon only) N/A Kempton WTW new 100 MLD Chinnor 30Mm3 (2 Zone Lon) London 51 Chinnor 30Mm3 - 50MLD (2 zone Lon) N/A Kempton WTW new 100 MLD Marsh Gibbon 75Mm3 (Lon only) London 153 Marsh Gibbon 75Mm3 - 150MLD (Lon only) N/A Kempton WTW new 150 MLD Yes Marsh Gibbon 75Mm3 (2 Zone Lon) London 144 Marsh Gibbon 75Mm3 - 135MLD (2 zone Lon) N/A Kempton WTW new 150 MLD Marsh Gibbon 50Mm3 (Lon only) London 103 Marsh Gibbon 50Mm3 - 100MLD (Lon only) N/A Kempton WTW new 100 MLD Marsh Gibbon 50Mm3 (2 Zone Lon) London 93 Marsh Gibbon 50Mm3 - 80MLD (2 zone Lon) N/A Kempton WTW new 100 MLD Marsh Gibbon 30Mm3 (Lon only) London 59 Marsh Gibbon 30Mm3 - 60MLD (Lon only) N/A Kempton WTW new 100 MLD Marsh Gibbon 30Mm3 (2 Zone Lon) London 51 Marsh Gibbon 30Mm3 - 50MLD (2 zone Lon) N/A Kempton WTW new 100 MLD River Abstraction DRA: Teddington 300 Ml/d London 268 Teddington Weir (Mogden Effluent Transfer) - 300 MLD Teddington to Thames Lee Tunnel Shaft 300 MLD Kempton WTW new 150 MLD + 150 MLD Yes Desalination: Beckton 150 Ml/d London 142 North Beckton RO 150 MLD N/A N/A (Desal provides treated water) Yes Desalination: Crossness 65 Ml/d (Unblended) London 60 South Crossness RO 65 MLD N/A N/A (Desal provides treated water) Yes Desalination Desalination: Crossness 150 Ml/d (Blended) London 138 South Crossness RO 150 MLD N/A N/A (Desal provides treated water) Yes Desalination: Crossness 300 Ml/d (Blended) London 268 South Crossness RO 300 MLD N/A N/A (Desal provides treated water) AR/ASR Kidbrooke (SLARS1) London 7 SLARS Kidbrooke (SLARS1) N/A N/A (Included in resource) Yes Aquifer Recharge AR Merton (SLARS3) London 5 AR Merton (SLARS3) N/A N/A (Included in resource) Yes AR Streatham (SLARS2) London 4 AR Streatham (SLARS2) N/A N/A (Included in resource) Yes Aquifer Storage & ASR South East London (Addington) London 3 ASR South East London (Addington) N/A N/A (Included in resource) Yes Recovery ASR Thames Valley Central London 3 ASR Thames Valley/Thames Central N/A N/A (Included in resource) Yes GW: Addington London 1 GW - Addington N/A N/A (Included in resource) Yes GW: London Confined Chalk (north) London 2 GW - London confined Chalk (north) N/A N/A (Included in resource) Yes Groundwater GW: Southfleet/Greenhithe (new WTW) London 8 GW - Southfleet/Greenhithe (new WTW) N/A N/A (Included in resource) Yes Merton Recommissioning London 2 Merton recommissioning N/A N/A (Included in resource) Yes North London Licence Trading London 2 North London Licence Trading N/A N/A (Included in resource) Yes Southfleet (Groundwater) London 0.2 Southfleet (Groundwater) N/A N/A (Included in resource) Yes Green Street Green (Groundwater) London 0.3 Green Street Green (Groundwater) N/A N/A (Included in resource) Yes Catchment North Orpington (Groundwater) N/A N/A (Included in resource) Yes management North Orpington (Groundwater) London 0.4 Lower River Thames London 2 Lower River Thames N/A N/A (Included in resource) Yes Lower River Lee London 1 Lower River Lee N/A N/A (Included in resource) Yes Note: Deployable outputs shown in italics are indicative

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Thames Water WRMP19 Resource Options Fine Screening Report Update

Table 3.3: Thames Valleys WRZs - summary of options elements included in AIC calculation

Deployable Output DYAA ADPW Network reinforcement Master Solution Name WRZ (Ml/d) (Ml/d) Resource elements Conveyance elements Water treatment elements Raw water system elements elements RWT: STT Deerhurst 300Ml/d (2 zone SWOX) Vyrnwy 180 SWOX 20 Vyrnwy 180 MLD (2 zone SWOX 24MLD) RWT Deerhurst to Culham 300 MLD (2 zone SWOX 20MLD) Radcot WTW new 24 MLD (SWOX) Included in treatment element RWT- STT Deerhurst 300Ml/d (2 zone SWOX) Vyrnwy 60 SWOX 20 Vyrnwy 60 MLD (2 zone SWOX 24MLD) RWT Deerhurst to Culham 300 MLD (2 zone SWOX 20MLD) Radcot WTW new 24 MLD (SWOX) Included in treatment element Raw Water RWT- STT Deerhurst 400Ml/d (2 zone SWOX) Vyrnwy 180 SWOX 20 Vyrnwy 180 MLD (2 zone SWOX 24MLD) RWT Deerhurst to Culham 400 MLD (2 zone SWOX 20MLD) Radcot WTW new 24 MLD (SWOX) Included in treatment element Transfer RWT- STT Deerhurst 400Ml/d (2 zone SWOX) Vyrnwy 60 SWOX 20 Vyrnwy 60 MLD (2 zone SWOX 24MLD) RWT Deerhurst to Culham 400 MLD (2 zone SWOX 20MLD) Radcot WTW new 24 MLD (SWOX) Included in treatment element RWT- STT Deerhurst 500Ml/d (2 zone SWOX) Vyrnwy 180 SWOX 20 Vyrnwy 180 MLD (2 zone SWOX 24MLD) RWT Deerhurst to Culham 500 MLD (2 zone SWOX 20MLD) Radcot WTW new 24 MLD (SWOX) Included in treatment element RWT- STT Deerhurst 500Ml/d (2 zone SWOX) Vyrnwy 60 SWOX 20 Vyrnwy 60 MLD (2 zone SWOX 24MLD) RWT Deerhurst to Culham 500 MLD (2 zone SWOX 20MLD) Radcot WTW new 24 MLD (SWOX) Included in treatment element Abingdon 150Mm3 (2 Zone SWOX) SWOX 20 Abingdon 150 Mm3 - 24 MLD (2 zone SWOX) N/A Abingdon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Abingdon 125Mm3 (2 Zone SWOX) SWOX 20 Abingdon 125 Mm3 - 24 MLD (2 zone SWOX) N/A Abingdon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Abingdon 100Mm3 (2 Zone SWOX) SWOX 20 Abingdon 100 Mm3 - 24 MLD (2 zone SWOX) N/A Abingdon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Abingdon 75Mm3 (2 Zone SWOX) SWOX 20 Abingdon 75 Mm3 - 24 MLD (2 zone SWOX) N/A Abingdon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Abingdon 50Mm3 (2 Zone SWOX) SWOX 20 Abingdon 50 Mm3 - 24 MLD (2 zone SWOX) N/A Abingdon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element New reservoir Abingdon 30Mm3 (2 Zone SWOX) SWOX 20 Abingdon 30 Mm3 - 24 MLD (2 zone SWOX) N/A Abingdon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Chinnor 50Mm3 (2 Zone SWOX) SWOX 20 Chinnor 50Mm3 - 24MLD (2 zone SWOX) N/A Chinnor WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Chinnor 30Mm3 (2 Zone SWOX) SWOX 20 Chinnor 30Mm3 - 24MLD (2 zone SWOX) N/A Chinnor WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Marsh Gibbon 75Mm3 (2 Zone SWOX) SWOX 20 Marsh Gibbon 75Mm3 - 24MLD (2 zone SWOX) N/A Marsh Gibbon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Marsh Gibbon 50Mm3 (2 Zone SWOX) SWOX 20 Marsh Gibbon 50Mm3 - 24MLD (2 zone SWOX) N/A Marsh Gibbon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Marsh Gibbon 30Mm3 (2 Zone SWOX) SWOX 20 Marsh Gibbon 30Mm3 - 24MLD (2 zone SWOX) N/A Marsh Gibbon WTW new 24 MLD (SWOX) Included in treatment element Included in treatment element Dapdune licence disaggregation Guildford 0 2.2 GW - Mortimer disused source (recommission) KV 4.5 4.5 Groundwater GW - Datchet SWA 1.6 6 GW - Moulsford 1 SWOX 2 3.5 Ashton Keynes borehole pumps SWOX 0 1.6 East Woodhay borehole pumps KV 0 2.1 Removal of Dapdune removal of constraints to DO Guildford 0 1 constraints to DO Datchet main replacement SWA 1.1 1.1 Eton removal of constraints to DO SWA 1.6 1.6 Ladymead WTW Guildford 0 4.6 Henley to SWOX 2.46 Ml/d SWOX 2.5 Internal inter- Kennet Valley to SWOX 12.81Ml/d SWOX 12.8 GW - Mortimer disused source - 4.5 MLD Included in GW element zonal transfers Kennet Valley to SWOX 8.31Ml/d SWOX 8.3 Henley to SWA 4.13Ml/d SWA 4.1 Ashdown Park SWOX 0.3 Upper Swell SWOX 0.2 Catchment management Marlborough SWOX 0.2 Sheeplands (Groundwater) Henley 0.3 Playhatch KV 0.4 Note: Deployable outputs shown in italics are indicative Assessment of the internal inter-zonal transfer options w ill be review ed after the April 2017 update of the Supply/Demand Forecast.

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

The resulting AIC ranges are shown in Figure 3.8 and Figure 3.9Error! Reference source not found. for London and the Thames Valley WRZs respectively and an explanation of the chart is provided in Figure 3.6. For each option the red marker shows the ‘most likely’ estimate based upon maximum utilisation while the green marker shows the ‘most likely’ estimate based upon minimum utilisation. The whiskers above and below these markers indicate the extent of capex and opex uncertainty assumed. The sensitivity of each option to utilisation assumptions can be seen by the distance between the red and green ‘most likely’ cost markers. Where the markers are wide apart then a significant proportion of the AIC comprises variable costs (varying by volume of water used) and where the markers are close together then most costs are fixed.

For each water resource zone a benchmark option has been selected. The benchmark option for the London WRZ has been identified by ranking options in order of increasing AIC at full utilisation and selecting as the benchmark the option that would be the least cost option remaining at the end of the planning horizon. The AIC threshold is then set at the most likely cost for the benchmark option at maximum utilisation. For the London WRZ up to 800Ml/d of resource is estimated to be needed by the end of the century. This includes potentially allowing for water supply to other water companies in the south east region. This has led to the Abingdon 75Mm3 new reservoir option being selected as the benchmark option for London, which results in a cost screening threshold for the 125-175 Ml/d band of 127p/m3.

Figure 3.6: Explanation for AIC chart and category definitions

Upper estimate (max utilisation) option

Most likely cost (max utilisation) ●

Most likely cost (min utilisation) ● ● Benchmark Lower estimate (min utilisation) ● ● Cost threshold ● ● ● ● ● ●

●

Symbol: ● ◐ ○ ◎ ◉ Substantial Material Material Substantial Meaning: Neutral disbenefit disbenefit benefit benefit

For the London WRZ there are a wide range of different sized options. However, AICs of very differently sized options are not directly comparable. To address this options have been categorised into size bands and the thresholds for other capacity bands have been adjusted to correct for two issues that arise when using AICs (at full utilisation) to compare between options of very different sizes for addressing a gradually increasing deficit profile:

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

1. Benefit adjustment - If the full capacity of the option is not required upon commissioning then a capacity based AIC will overestimate the resource benefit (denominator in the AIC calculation). This over estimate will be greater for large options than for a series of smaller options. A higher AIC threshold therefore needs to be applied to smaller options to correct for this. 2. Cost adjustment - By more closely matching the deficit profile smaller options also allow expenditure to be deferred which then reduces the discounted cost of a programme. Again, the benefits of being able to defer expenditure for smaller options are not captured in the AIC calculations which consider each option on an individual basis, with implementation starting in the first year of the planning period. A higher AIC threshold therefore also needs to be applied to small options to ensure that the advantage they offer in deferment of expenditure is captured.

The screening threshold adjustment factors to correct for these two issues have been calculated using a notional linear deficit profile increasing from zero to an indicative 800Ml/d over 80 years. This is illustrated in Figure 3.7 which shows the notional deficit profile (grey line) and how this could be addressed in, for example, 50Ml/d increments (green line) or say 300Ml/d increments (blue line). It can be seen from the chart that:  The area between the blue and the grey line is much larger than the area between the green and the grey line. The benefit adjustment factor corrects for this by dividing the NPV of benefits for any given option size by the NPV of benefits for the benchmark size.  The programme incorporating smaller water resource increments allows expenditure to be deferred. As this benefit is not captured in the calculation for individual options the cost adjustment factor is calculated by dividing the NPV of notional costs for any given size by the NPV of notional costs for the benchmark size (note that the sum of the notional costs for each given size over 80 years is assumed to be equal)

Figure 3.7: Notional deficit and option size increments 900 800 700 600 500

Ml/d 400 Notional deficit 300 50Ml/d increments 200 300Ml/d increments 100 0 0 10 20 30 40 50 60 70 80 Years

The overall benchmark adjustment factor for any given capacity band is taken as the multiplicative product of the cost adjustment factor and the benefit adjustment factor. This factor is then applied to the cost benchmark to provide the cost threshold for each capacity band which in turn informs the selection of cost assessment symbol for the option (see Figure 3.6). The effect of applying this benchmark adjustment factor is to improve the performance of small options compared with how they would otherwise perform in a direct comparison of AICs with larger options so as to correct (approximately) for the issues that arise when using AICs to compare options of different sizes.

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

For Water Resource Zones outside London a simpler approach to setting the screening threshold is adopted due to the smaller range of option capacities. The screening threshold for the Thames Valley has been set at the most likely cost (at maximum utilisation) of the least cost, large scale resource for the Thames Valley (i.e. the lower of the Abingdon Reservoir or Severn Thames Transfer options).

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Thames Water WRMP19 Resource Options Fine Screening Report Update

Figure 3.8: AIC+Carbon for options in the London WRZ

450

400 Reuse:Crossness50Ml/d

350

Reuse:Beckton50Ml/d

ChinnorZone(2 30Mm3 Lon) Chinnor(Lon 30Mm3 only)

300

MarshZone(2 30Mm3 Gibbon Lon)

RWT:STTDeerhurst Mythe Ml/d & 500 Vrynwyonly)(Lon

Marsh(Lon 30Mm3 only) Gibbon

DeerhurstMythe & 300Ml/dVrynwy(Lononly)

2 MLD 2

Kidbrooke

RWT: STTRWT:Deerhurst Mythe Ml/d & 400 Vrynwyonly) (Lon

-

DeerhurstMythe & zoneLon)Vrynwy400Ml/d(2

DeerhurstMythe & zoneLon)300Ml/dVrynwy(2

DeerhurstMythe & VrynwyLon)zone 500Ml/d(2

Reuse:Crossness100Ml/d

RWT: STTRWT:

AbingdonZone(2 30Mm3 Lon) RWT: STTRWT:

250 STTRWT:

RWT:STT

4 MLD 4

Abingdon(Lon 30Mm3 only)

-

Reuse:Deephams60Ml/d

8 MLD 8

- Reuse:Crossness190Ml/d

Reuse:Mogden 50Ml/d

Reuse:Crossness150Ml/d

MarshZone(2 50Mm3 Gibbon Lon)

ChinnorZone(2 50Mm3 Lon)

Marsh(Lon 50Mm3 only) Gibbon

Chinnor(Lon 50Mm3 only)

Reuse:Beckton150Ml/d

AIC (p/m3)

Reuse:Beckton100Ml/d

1 MLD 1

MarshZone(2 75Mm3 Gibbon Lon)

- Marsh(Lon75Mm3 Gibbononly)

200 Reuse:MogdenSewer50Ml/dSouth

1 MLD 1

Reuse:Beckton380Ml/d

-

AbingdonZone(2 Lon) 50Mm3

2 MLD 2

1 MLD 1

-

Reuse:Beckton200Ml/d

-

Reuse:Beckton300Ml/d

Reuse:Mogden100Ml/d

AR StreathamAR (SLARS2)

DesalinationMLD PlantCrossness150 SouthTreatmentRO

Reuse:Mogden150Ml/d

Desalination:Ml/d 150 Beckton

AbingdonZone(2 Lon) 100Mm3

Abingdon(Lon 50Mm3 only)

Reuse:Mogden200Ml/d

AbingdonZone(2 Lon) 75Mm3

GroundwaterLondonChalk confined (north)

AbingdonZone(2 Lon) 125Mm3

AbingdonZone(2 Lon) 150Mm3

Abingdon(Lon only) 100Mm3

Desalination:Ml/dCrossness 65

Abingdon(Lon 150Mm3 only) Abingdon(Lon 75Mm3 only)

150 Abingdon(Lon 125Mm3 only)

GroundwaterAddington

ASRSouth EastLondon (Addington) GroundwaterSouthfleet/GreenhitheWTW)(new

100 ASRThames CentralValley/Thames

DRA:Teddington Ml/d 300 GroundwaterArlaFoods Licence Trading/Transfer

50

0 0-25 25-75 75-125 125-175 175-225 225-275 >275

WAFU (Ml/d) Band

Max Utilisation Min Utilisation Benchmark

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Thames Water WRMP19 Resource Options Fine Screening Report Update

Figure 3.9: AIC+Carbon for options in the Thames Valley WRZs

700

600

500

4.5 MLD 4.5

3.5 MLD 3.5 -

400 -

Radcot 300Ml/d (2 zone300Ml/d(2 SWOX)Radcot

-

ChinnorZone(2 30Mm3 SWOX)

Hogsback)

Radcot 100Ml/d (2 zone100Ml/d(2 SWOX)Radcot

-

-

ChinnorZone(2 50Mm3 SWOX)

Moulsford 1

AIC (p/m3)

-

MarshZone(2 30Mm3 Gibbon SWOX)

MarshZone(2 50Mm3 Gibbon SWOX) MarshZone(2 75Mm3 Gibbon SWOX)

300 (noMLD 5.6

-

7.8 MLD 7.8

-

STT Deerhurst 180 SWOX)zoneVyrnwy400Ml/d (2

WESSEX to SWOX 2.9 MLD (Flaxlands)MLDWESSEX SWOX to2.9

-

STT Deerhurst 180 SWOX)zoneVyrnwy500Ml/d (2

-

AbingdonZone(2 SWOX) 30Mm3

RWT: STTRWT: Deerhurst

-

AbingdonZone(2 SWOX) 150Mm3

AbingdonZone(2 SWOX) 100Mm3

2.1 MLD 2.1

STT 60 DeerhurstSWOX) zoneVyrnwy (2400Ml/d

WESSEX to SWOX 2.9 MLD (AshtonMLDWESSEX Keynes)SWOX to2.9

AbingdonZone(2 SWOX) 125Mm3

-

Kennet Valley to SWOX 1.36 MLD Kennet SWOX1.36 toValley

RWT:STT Deerhurst 180 SWOX)zoneVyrnwy300Ml/d (2

-

AbingdonZone(2 SWOX) 50Mm3

-

2.5 MLD 2.5

RWT

STT Deerhurst 60 SWOX)zoneVyrnwy500Ml/d (2

AbingdonZone(2 75Mm3 SWOX)

-

-

-

Groundwater

RWT

RWT:STT Deerhurst

Henley to SWOX 2.46 MLD Henley SWOX2.46 to

RWT: STTRWT: Deerhurst 60 SWOX)zoneVyrnwy 300Ml/d(2

RWT

DRA:Culham Ml/d 4.5

- RWT

200 MLD Henley SWAto4.13

-

Kennet Valley to SWOX 8.31 MLD Kennet8.31 SWOXtoValley

-

Kennet Valley to SWOX 12.81 MLD 12.81 SWOXKennettoValley

SEW to GUI 5 MLD (HogsbackSEWGUItoMLD 5

-

-

disaggregaion)

InterZonalTransfer

InterZonalTransfer InterZonalTransfer

100

InterZonalTransfer

Kennet12.81Ml/dSWOXtoValley

GroundwaterdisusedMortimersource (recommission)

InterZonal Transfer

InterZonalTransfer

InterZonalTransfer DatchetEtonEnhancementWTW &

InterZonalTransfer

RC Eastborehole Woodhay pumps

RC AshtonpumpsKeynes borehole

LadymeadWTWconstraintsremovaltoDOof LadymeadconstraintsDOtoWTWremoval of 0 SWOX KV SWA Guildford Series1 Series2 Benchmark

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3.6.3 Promotability dimension

3.6.3.1 Dimension description

Promotability: The Promotability dimension considers the scheme up to the point of planning permission being granted and includes the application of professional judgement relating to:  Synergies (e.g. synergies with water resource needs of other water resource zones in the South East and synergies with third party developments)  Customer preference (e.g. in relation to wastewater reuse, including views of Customer Challenge Group);  Local acceptability (e.g. in relation to planning challenges);  Regulatory acceptability (including DWI, EA, Ofwat); and  Wider stakeholder acceptability.

3.6.3.2 Discussion

The Promotability dimension considers a range of potential issues and risks that could either singularly or cumulatively result in the option type being rejected before it has even reached the planning permission stage. Each of the six sub-dimensions is described further below.

Synergies

Assessment of synergies with other water resources zones involves consideration of the extent that an option will provide resources that could supply either other Thames Water WRZs or those of neighbouring companies. Where an option has the potential to directly support another company’s new resource requirements then this has been categorised as substantial benefit. Where an option could directly support or indirectly free up water for export to other WRZs then this has been considered as a material benefit. All other options have been categorised as neutral in terms of synergies.

Those option types where a benefit has been attributed include all reservoir options. The level of benefit would ultimately be dependent upon the geographical location of the site and the known reservoir capacity range. Options involving the canal network have been assigned a ‘material benefit’ based on synergies with the navigational needs of other canal users. Wastewater reuse options could also potentially indirectly address the needs of other water companies in the South East; but again dependent upon the capacity range for the specific scheme.

Customer preference

Customer preference considers the likely long-term view of the consumer of a water resources option. Customers’ perceptions concerning the direct impacts of water resource options such as water bills and drinking water quality are considered, alongside their perceptions of the indirect impacts, such as environmental effects. This issue is concerned with perceived rather than actual impacts. The acceptability of actual impacts is covered by other dimensions (Cost, Environmental & Social and ‘Regulatory Acceptability’ within Promotability etc.).

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Research reported by the Customer Challenge Group for Thames Water15 highlighted the following customer preferences which, if acknowledged and addressed, would develop and promote acceptability. Customers want their water and sewerage suppliers to:  conserve water;  reduce the impact of their operations on the environment, particularly on local rivers;  adopt energy-conserving technologies; and  be more active in educating consumers on the preservation of water supplies and the wider environment.

These customer preferences have been used as evidence for assigning categories to the customer preference sub-dimension. Accordingly, high energy option types such as those involving intensive treatment processes have been allocated a material dis-benefit, reducible with the inclusion of renewable energy sources, such as has been actively applied at the existing Thames Gateway desalination plant.

Wastewater reuse, has been allocated a neutral benefit/dis-benefit, as the Customer Challenge Group (CCG) specifically highlighted the customer preference that “water that has already been captured into supply should fully be used. Reuse of wastewater is preferred to massive capital expenditure on new resources such as reservoirs”. A material benefit was not considered appropriate as it is expected that there will be some customer groups that are less positive about the concept of reuse.

In light of the preferences expressed by the CCG, option types potentially involving the construction of a new reservoir have been assigned a material dis-benefit.

Local acceptability

Local acceptability and planning risks associated with water resource option types are categorised in terms of their severity and whether there is scope for them to be reduced or eliminated through e.g. stakeholder engagement. This sub-dimension highlights schemes that might give rise to strong local opposition. The views of organisations such as the Group Against Reservoir Development (GARD) and local Councils are evaluated and where pressure groups actively oppose a scheme this is noted.

Regulatory acceptability

Regulatory acceptability includes consideration of the likely positions to be adopted by the Environment Agency (EA), Drinking Water Inspectorate (DWI), Ofwat, Natural England and Historic England to the development of water resource options. The likely approval or not of abstraction licences, potential challenges to achieving regulatory water quality standards and the views of the industry economic regulator among other relevant considerations are all taken into account.

Where further research is required in order to mitigate any opposition to an option type, a reducible material risk/dis-benefit has been applied.

Wider stakeholder acceptability

Other bodies (which are not water industry regulators) may have a particular interest in the development of a water resource option type and could offer either support for or challenge the realisation of an option. Such organisations might include the Royal Society for the Protection of Birds and the Campaign to Protect Rural England (CPRE).

15 Customer Challenge Group for Thames Water: Report to Ofwat on Thames Water Business Plan. 2 December 2013. http://www.thameswater.co.uk/pr14/CCG-for-Thames-Water-report-to-Ofwat.pdf

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Experience gained in the promotion of WRMP14 has been used to assign categories to the wider stakeholder acceptability sub-dimension. It is assumed, for example, that those organisations that made representations at the Abingdon Reservoir WRMP09 public inquiry would continue to object to reservoir development and so a material irreducible dis-benefit has been ascribed to those option types potentially involving reservoir development.

Where it is considered that wider stakeholder objections could be reduced through the provision of evidence and/or engagement, the sub-dimension has been assessed to have a material, but reducible, dis- benefit.

Risks of objections from media sources, however, are considered to be irreducible dis-benefits, due to the public platform on which any such objections may be raised and difficulties in managing and challenging public dissemination of possible misinformation.

3.6.4 Flexibility dimension

3.6.4.1 Dimension description

Flexibility: Assessment of how flexible an option is to changes in requirements including in relation to:  Lead time: WRMP14 lead times will be used to inform this assessment;  Phasing: Potential for the scheme to be incrementally built and/or commissioned;  Adaptability: Whether the scheme is extendable once built; and  Ramp-up: How quickly the system can respond to changes in demand over its operational life.

3.6.4.2 Discussion

The flexibility dimension considers potential issues and risks that could either singularly or cumulatively result in a material benefit or dis-benefit in the delivery or operational flexibility of an option. Each of the four sub-dimensions is described further below.

Lead times

The Phase 1 assumptions on lead times were based upon WRMP14 information (WRP3a tables), these have been updated to take account of changes in lead times identified during the development of Phase 3 conceptual designs. The updated lead times assumed are:  Groundwater, aquifer recharge and aquifer storage and recovery options have the shortest lead times of under 5 years;  Deephams wastewater reuse and direct river abstraction are predicted to have a lead time of 5 and 6 years respectively;  Other wastewater reuse options, desalination, Severn-Thames transfers and network reinforcement options are predicted to have a lead time of 7 to 8 years; and  the Upper Thames Reservoir options are predicted to have the longest lead times of up 13 years.

An option that has a short lead time offers benefits in terms of its influence on the supply-demand balance. Options’ lead times have been assessed as being a material benefit where they are less than 5 years, neutral where they are 5 to 7 years, a material dis-benefit when 8 to 10 years and substantial dis-benefit where over 10 years. For water resource options with long lead times, the promotion of another option may be needed to address short to medium term WRZ deficits.

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Phasing

Phasing offers benefits in terms of spreading and/or deferring the capital expenditure of a water resource option. Some types of water supply assets lend themselves to phasing more than others. Options have been reviewed in light of the potential for a scheme to be incrementally built and/or commissioned. For those where economies of scale are strongest (e.g. pipeline construction at larger diameters), the benefits of phasing would be the least as phasing could involve significant additional cost; however, these need to be weighed against the benefit of deferred expenditure.

The following option type assessment can be made:  Long distance pipelines: The phasing dis-benefits of the raw water transfer options have been assessed as being material due to the influence of economies of scale. Desalination and wastewater reuse options also include long distance transfers and have been assessed as having a material dis-benefit for phasing. These options have the added difficulty of being located in a heavily urban area and they potentially require significant tunnelling where the size of the tunnel is governed not just by capacity requirements, but also other factors such as health and safety considerations.  River abstraction: Rather than being constructed and operated at the maximum available Deployable Output from the outset, river intakes could be built in phases up to the maximum Deployable Output. Phasing could therefore be possible by, for example, building the first 50% of the Deployable Output in one AMP and then the remaining capacity in a later AMP. This could be a material benefit.  Treatment options: Treatment plants would offer a material benefit in terms of phasing opportunities, as treatment streams could be built and commissioned individually.  Reservoirs: Reservoirs have been assessed as having a material dis-benefit for phasing as while provision can be made in the design for subsequent reservoir extensions this limits the potential maximum storage potential on the site due to the storage that is given up to provide the dividing embankment.  Groundwater: There are unlikely to be opportunities for phasing of the groundwater options. However, there may be benefits gained from delivering some artificial recharge or aquifer storage and recovery schemes in phases such that data from testing can be used to refine the proposed option design. This is a material benefit.

Adaptability

Adaptability is distinct from phasing in that it considers the ways in which a water resource option might be adapted in future to meet unexpected future requirements e.g. in terms of source availability and capacity; whereas phasing relates to the potential for an option to be expanded in future to meet expected future requirements.

As regards adaptability, the following option type assessment can be made:  Raw water transfers: These could potentially be linked up and connected to new sources and demand centres in future (e.g. as part of a national grid) and so do offer material adaptability benefits.  River abstraction: River intakes have limited adaptability once built as they are constrained by the available hydrological yield. As such, these options are the option type considered to be neutral in terms of adaptability.  Treatment options: There may be opportunities to adapt treatment works to increase capacity, depending on space constraints. However, the potential for adaptation of works for the treatment of water from different sources will be dependent on raw water quality and the suitability of installed treatment processes. Increasing the capacity of wastewater reuse options would be constrained by

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the availability of effluent. As such, these options are considered to be neutral in terms of adaptability. Desalination options would be the most adaptable of the treatment options types and offer a material benefit.  Reservoirs: Once built, there is the potential for the reservoir to hold water from alternative sources, thereby offering flexibility. For the purposes of assessment at the option type level, adaptability has been categorised to be a material benefit.  Groundwater: For the most part, the groundwater options are restricted by licence conditions and therefore are not able to provide significant benefits of adaptability. The groundwater options are considered to be neutral in terms of adaptability.

Ramp-up

Ramp-up assesses operational flexibility. The time from which a scheme can be activated to the time that potable water is available to go into the supply network has been estimated based on an understanding of potential water quality constraints and discussions with process engineers and hydraulic engineers. A scenario of a dry year has been employed, when a short ramp-up time offers a clear benefit. The following categorisations have been made:  Material benefit: A scheme is able to provide potable water within a week;  Neutral: A scheme is able to provide potable water within two weeks;  Material dis-benefit: A scheme is able to provide potable water within four weeks; and  Substantial dis-benefit: A scheme would not be able to provide potable water within four weeks.

The ramp-up times of the option types are summarised below in Error! Reference source not found..

Table 3.4: Assessment of option type ramp-up times

Option type or Option element Ramp-up time

Desalination – ‘hot standby’ mode (3 months per year) <1 day Desalination – ‘care and maintenance’ mode (9 months per year) 8 weeks Water reuse – ‘hot standby’ mode (3 months per year) <1 day Water reuse (MBR/GAC) – ‘care and maintenance’ mode (9 months per year) 6 weeks Water reuse (RO/AOP) – ‘care and maintenance’ mode (9 months per year) 7 weeks Direct river abstraction & partial treatment 6 weeks (abstraction & treatment elements) Direct river abstraction & partial treatment (conveyance element)16 <1 day Direct river abstraction and full treatment 6 weeks Raw water transfer (Deerhurst Pipeline) <1 week Raw water transfer (Cotswold Canal) 2 weeks Raw water reservoirs <1 day Groundwater abstraction (excluding treatment) <1 day

The operating philosophy17 has been used to inform this assessment as follows:  Desalination: Plants are operated in a ‘hot standby’ mode for three months of the year, with a ramp-up time of less than one day. However, outside this period a ‘care and maintenance’ state is used, with a ramp-up time of eight weeks. Desalination is therefore considered to offer material dis-benefit in terms of ramp-up.

16 Excludes Option 4 which discharges into the Walton WTW intake and for which standby modes would apply. 17 Described in Options operating philosophy (Utilisation) Report prepared for TW by Mott MacDonald/Cascade for issue in September 2016.

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 Reuse: Plants are operated under the same philosophy as desalination, with ramp-up times of less than one day from ‘hot standby’, and six weeks from ‘care and maintenance’ for RO/AOP. Reuse is therefore considered to offer material dis-benefit in terms of ramp-up.  Direct river abstraction: For the Teddington DRA option it is proposed that tertiary treatment will operate continuously and so ramp up of the option can be done in under a day, providing a material benefit. For options where treatment may be in Care and Maintenance for part of the year ramp uptimes would be longer.  Raw water transfer: Deerhurst pipeline will be operated in a ‘cold standby’ mode, with a ramp-up time of less than one week, offering material benefit. Cotswold Canal will have a ramp-up time of two weeks, and is therefore considered neutral in terms of ramp-up.  Reservoirs: Operated in a ‘cold standby’ mode with a ramp-up time of less than one day, offering a material benefit.  Groundwater abstraction: It is assumed that the source is already in use, resulting in a ramp-up time of less than one day, offering material benefit.

Conventional water treatment and treated water conveyance are operated in a ‘hot standby’ mode with a ramp-up time of less than one day and therefore have no impact on the assessment of option types.

3.6.5 Deliverability dimension

3.6.5.1 Dimension description

Deliverability: The Deliverability dimension evaluates the option from the planning permission stage to commissioning and operation. It includes assessment of construction, technology and other implementation risks. Both the WRMP14 Delivery and Solution Confidence Scores below will be used as part of this assessment.  Constructability: Uncertainties surrounding construction - e.g. unknown technologies, land availability, access or contamination risks;  Operability: Whether there is a track record of successfully using the technology and if it is a dependable and proven technology;  Dependencies: Dependencies on other assets, activities or third parties; and  Data confidence: Reliability and uncertainty of design data and DO assessment methodologies, etc.

3.6.5.2 Discussion

The Deliverability dimension takes into account a range of potential issues or risks that could either singularly or cumulatively result in the water resource option type failing to be delivered.

Constructability

Constructability embraces and assesses uncertainties surrounding construction, such as unknown technologies, land availability, or contamination risks. The level of risk is determined based on the historical experience of TW or, in the absence of any such experience, other known challenges.

The development of a new technology type is not a substantial risk, but should be highlighted as an area requiring consideration as to the level of risk regarding constructability. Where no recent experience or knowledge is available, this would constitute a material irreducible risk; conversely where there is some experience of the efficacy of the technology, this would be a material reducible risk.

Other examples of material constructability challenges include reservoir construction, construction constraints within designated areas, and the availability of land for development.

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Operability

Operability includes an assessment of whether there is a track record of successfully using the technology and whether it is dependable. Where it is not, this can constitute a risk. As with constructability, this can be either reducible or irreducible.

Where extensive experience of its utility has been had, an option type has been assessed as neutral against the operability sub-dimension (e.g. reservoir and direct intake operation). Conversely, a material irreducible risk has been assigned where TW has no experience of an option type. Limited experience of the technology has been categorised as a material reducible dis-benefit when either greater experience can reasonably be expected to be gained through time (e.g. desalination), or where learning could be had from analogous schemes either nationally (e.g. Ely Ouse to Essex Transfer Scheme) or overseas (e.g. desalination).

Dependencies

A water resource option may be dependent upon the involvement of other assets, activities or third parties. Internal dependencies (such as on other WRMP elements) are excluded as they will be resolved through the WRMP programme appraisal. However external dependencies, whether upon third parties or upon TW assets, for example, in the wastewater wholesale business, generate uncertainty that is assessed as a material dis-benefit.

Data confidence

It is important that there is a reasonable degree of certainty around key design data associated with specific options that are carried through into programme appraisal. Uncertainty around some design data will have limited effect on deliverability, while for other data a reasonable degree of certainty is crucial. For instance, yield certainty surrounding a desalination plant or wastewater reuse scheme is considerably higher than for a surface water source, where uncertainties are material due to being based on complex modelling data and assumptions. The employment of such assessment methodologies is, however, in keeping with industry standards. As such, where options offer a greater confidence in Deployable Output delivery than would normally be expected, a material benefit has been assigned.

3.6.6 Resilience dimension

3.6.6.1 Dimension description

Resilience: The Resilience dimension considers the likely performance of the water resource option from the operation stage continuing into the future. It will be an assessment of confidence that the option at the given cost will provide the stated deployable output, with the required water quality in the future, and include:  Vulnerability to climate change and severe drought;  Resource predictability;  Contribution to the wider system’s resilience to outage;  Vulnerability to other ‘failure modes’ (e.g. pollution events, power outages, chemicals commodity chains and terrorism); and  Vulnerability to regulatory changes (e.g. abstraction reform).

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3.6.6.2 Discussion

The protection of London’s water supply system from failures is something that the Customer Challenge Group specifically noted in consultation as being of paramount importance18. The drought of 2010-12 with its two dry winters highlighted the vulnerability of the water supply system to drought and Defra determined that the potential for water supply shortages was higher than previously appreciated. The Water White Paper19 set an action for Defra and the Environment Agency to assess options to increase future water supply resilience across all water-reliant sectors and to evaluate the social and economic impacts of the introduction of enhanced levels of resilience to mitigate the effects of water supply shortage. Key issues considered in the Phase 1 assessment of resilience included vulnerability of each proposed water resource option type to climate change and severe drought, predictability, net contribution to system outage resilience, vulnerability to other ‘failure modes’ and regulatory change. These sub-dimensions have been assessed for each option type.

It should be noted that the resilience dimension deals with events outside of normal operation.

Vulnerability of option type to climate change A climate change vulnerability assessment of all of Thames Water’s WRZs was undertaken as part of WRMP14 and showed London to be highly vulnerable20. The UK Climate Projections show a clear trend of wetter winters and drier summers by 2050 for the Thames catchment, under low, medium and high emissions scenarios21.

The use of the raw water transfers and Upper Thames Reservoir options would be driven by a requirement for water in London, which in turn depends upon the maintenance of flows in the River Thames and reservoir water levels in London.

Climate change projections suggest that summer support would be of increasing importance. Options such as water reuse, desalination, reservoir storage or supported transfers would offer substantial benefits, as they would all be able to contribute to addressing summer shortages either because they are essentially unaffected by climate change (e.g. reuse and desalination) or because they provide additional storage that would allow surplus winter rainfall to be utilised (e.g. reservoirs or transfers supported by reservoirs). dis- benefit

Vulnerability of option type to severe drought Water sources are assessed against the worst historic drought and an option’s yield is the calculated output that could be achieved during that event. Sensitivity analysis undertaken by Thames Water as a part of WRMP14 showed that there could be more extreme drought events and an increased probability of drought events in the future22. If droughts are more severe than the historical record it would reduce the forecast likelihood of the supply system meeting its level of service. Thames Water’s existing water resources primarily comprise surface water and groundwater abstractions. With the exception of the Gateway desalination plant the existing water resources are reliant upon natural

18 From Introduction to part A of the draft Water Resources Management Plan, citing ‘A Non-Essential Use Drought Order for London: Economic Impact Assessment’ (NERA, commissioned by Thames Water, April 2012) 19 Water for Life, Defra, HM Government, December 2011. 20 Thames Water Revised Draft Water Resources Management Plan 2014, Appendix U: Climate Change. 21 UK Climate Projections (2009). Mean winter and mean summer precipitation trends for the Thames basin. Downloaded from http://ukclimateprojections-ui.metoffice.gov.uk/ui/admin/login.php, accessed on 09/03/2015. 22 Thames Water Revised Draft Water Resources Management Plan 2014, Section 4: Current and Future Water Supply.

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hydrology and are potentially vulnerable to severe drought. New resources that can be considered to offer a substantial benefit to the wider resilience of the London WRZ during droughts worse than the historical record are sources that are non-reliant on natural hydrology, such as desalination. Options that are reliant on effluent (such as wastewater reuse and, to a lesser extent, Lower Lee abstraction) are considered marginally more vulnerable than desalination as it is unclear how these options would perform in an extreme drought (e.g. with severe restrictions in place); and these options also rely on existing sources to provide water for blending. Those option types reliant on natural groundwater and surface water catchment flows are most vulnerable to droughts outside of the historical record.

Given the potential vulnerability of surface water sources to severe drought Thames Water has commissioned stochastic analysis of future drought impacts on the yield of the Abingdon Reservoir options (see Appendix I) and on the yield of the Severn Thames Transfer options (see Appendix J). This analysis suggests that: 1. The vulnerability of the Abingdon options to severe drought may be quite limited, and it has therefore been assessed as providing material benefit. 2. In contrast, drought worse than the historical record could substantially reduce the potential yield of the unsupported Severn-Thames Transfer. Source yields informed by the stochastic analysis have therefore been used for the assessment of AICs for the Severn-Thames Transfer under the cost dimension. As the yields generated through the stochastic analysis can be considered resilient resilience to severe drought has been upgraded to a material benefit for the Severn-Thames Transfer.

Future resource predictability The predictability of the resource is also a key consideration in relation to drought planning and outage response planning. An option type with storage would provide material benefits in terms of operational predictability, which would again be a significant advantage in terms of continuity of water supply over an unsupported water transfer option type. Desalination and wastewater reuse options are predictable in terms of raw water availability, however there is a risk of long ramp-up times from a ‘care and maintenance’ state preventing the anticipated DO benefit from being realised. This is partially mitigated by using a ‘hot standby’ mode for three months of the year, therefore assessed to have neutral benefit/dis- benefit.

Net contribution to system outage resilience The provision of additional water storage in the London supply system would provide extra operational flexibility and security to deal with outages. This would be a substantial benefit of a supported water resource option type over an unsupported option type, as the availability of an unsupported supply would be highly uncertain, being strictly controlled by factors such as seasonal timing and river flows etc.

Desalination and reuse could provide resilience for planned outage events, but for unplanned outage events the benefit would be reduced due to the potential need to ramp-up the resources and the length of time required to bring them into operation if they are in a “care and maintenance” mode. Both option types are therefore considered to have material dis-benefit in terms of system outage resilience. dis-benefit

Vulnerability of option type to other failure modes As a part of work undertaken for Thames Water in 2013 on resilience gap analysis, a list of hazards was compiled based upon that provided for the UKWIR resilience project “RG06 Resilience – Making a Business Case for PR14”. These hazards were then grouped together into ‘failure modes’ for the purpose of the gap analysis so as to make the process more manageable as shown in the table below.

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Figure 3.10: List of failure modes and associated hazards Flooding Physical damage: societal Communications loss Coastal flooding Malicious damage Cyber attack Fluvial Flooding Sabotage Solar flare/Space weather Surface water flooding Security related Telecoms failures Groundwater flooding Third party interventions National strike Tsumani Civil unrest Sea level rise War Supply chain loss Aircraft Crash Chlorine - supply chain Drought Nuclear incident Materials shortages Drought Comodity prices and economic change Supply chain failure Pollution incidents Physical damage: geological Major fuel crisis Catchment / site contamination Earthquake National strike Contamination incident Landslides / subsidence Extreme reservoir pollution Reservoir or dam breach Shortage of staff Extreme river pollution Epidemic/Pandemic Physical damage: internal Civil unrest Physical damage: weather Fire / major fire Skills crisis Excessive cold & ice/snow Asset deterioration / failure National strike Prolonged hot/dry weather Lighting strike Power supply loss Denial of access to sites Storms and gales Power failure Transport disaster Power loss (extended period) Civil unrest National strike Source: Thames Water Resilience Gap Analysis Rev B, Mott MacDonald, June 2013.

These ‘failure modes’ (excluding drought, communication and staffing) have been used as the basis of a resilience review of the options type, in order to understand the range of vulnerabilities and what potential future large scale resource options might add (or not) to overall resilience:  Flooding – The review has been made on the assumption that key water resource assets are protected to a certain level of fluvial and coastal flood risk. – Fluvial flooding could halt river abstraction and reservoir refill due to water quality issues;  Pollution incidents – Pollution outages would have the greatest impact on river abstractions that were not supported by reservoir storage but this would likely be only for short periods; – Whilst raw water reservoirs are potentially vulnerable to algal blooms, measures have been included in the reservoir design to manage the water depth, provide mixing and ensure that water can be drawn off at more than one location and at different levels within the reservoir.  Physical damage – Water resource options that require a large number of complex assets to be operational (e.g. desalination, or reuse), and those where assets are geographically dispersed (e.g. canal transfers) tend to be more vulnerable to physical damage than assets that have low operational complexity (e.g. reservoirs);  Power supply loss and supply chain loss – Option types with high energy or chemical requirements would be most vulnerable to power supply loss and increasing commodity prices.

An Upper Thames Reservoir has been assessed as being resilient to the most ‘failure modes’ of all the option types. As reservoir storage already provides a considerable proportion of London’s supply, this option type is in line with the majority of the existing London WRZ sources and therefore has been assessed as having a neutral benefit/dis-benefit. The other water resource option types are all vulnerable to a number of ‘failure types’ and are therefore considered to have a material dis-benefit.

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3.6.7 Screening decisions

To arrive at the Constrained List of options from the Feasible List, fine screening decisions have been made by looking across all six dimensions. Rather than imposing rigid rules to make screening decisions, the focus is on ensuring that there is a clear and robust reasoning for each screening decision which will then be reflected in the rejection register for WRMP19. It is expected that the nature of fine screening may include: 1. Rejection of options with substantial irreducible dis-benefit/risk unless this may be offset by a substantial benefit/opportunity 2. Where there are mutually exclusive options and some are clearly less favourable than others then this would provide grounds for rejection 3. Where there are more options than could reasonably be required over the planning horizon under future scenarios, then there may be a case for rejecting the least favourable options.

The reasons for screening decisions will be recorded in the WRMP19 rejection register. Stakeholder views will be sought on the screening decisions and these decisions will be reviewed and updated in the light of stakeholder observations where necessary.

3.6.8 Back-checking process

A back-checking exercise is being undertaken to review whether, in the light of the further knowledge gained in preparation of conceptual design reports and bottom-up costs for those options on the Constrained List, and of changes in external circumstances, options dismissed earlier in the WRMP19 evaluation process afford material advantages that warrant their reconsideration. Where it is considered that new information could change a screening decision then it is important to revisit the screening to ensure that it remains valid.

This process includes:  DO consistency check – where the deployable output of a water resource option has materially changed during Phase 3, the fine screening assessment has been updated, including calculation of AIC+carbon.  Option scope check – where there has been a material change in the scope of an option as part of the Phase 3 work then the impact of this on Phase 2 screening decisions is being checked  Option-level AIC check – all Phase 2 and Phase 3 costs are being compared for water resource options passing fine screening to identify any material changes in the combination of elements that could impact on original screening decisions.

In each case, the impact of any material changes identified is being considered for all resource options and the Feasible List, this Fine Screening Report and the Constrained List will be updated accordingly.

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4 Generic screening of water resource management options

This section reports the findings of the review of generic water resource option types and provides a summary of the reasoning for option type rejections.

4.1 Generic option screening The option types considered in the generic screening are those listed in the UKWIR Water Resources Planning Tools report23. The generic options list and a summary of the results are shown in Figure 4.1. Commentary on the reasoning behind the rejection is provided in Table 4.1. In some cases (marked TBC; To Be Confirmed) further work was deemed required to obtain the information needed to inform the screening decision.

Figure 4.1: Summary of generic option type review

† screening Generic resource management options Generic Specific option identification 1 Direct river abstraction ✔ Direct river abstraction feasibility report 2 New reservoir ✔ New reservoirs feasibility report 3 Groundwater sources ✔ Groundwater feasibility report 4 Infiltration galleries ✔ Included in DRA/Desal as possible intake 5 Aquifer storage and recovery ✔ Groundwater feasibility report 6 Aquifer recharge ✔ Groundwater feasibility report 7 Desalination ✔ Desalination feasibility report 8a Bulk transfers of raw water ✔ Raw water transfer feasibility report 8b Bulk inter/intra company transfers of treated water ✔ Inter-zonal transfers study 9 Tankering of water ✖ 10 Redevelopment of existing resources TBC 11 Reuse of existing private supplies ✔ Third party options report 12 Water re-use ✔ Water reuse feasibility report 13 Imports (icebergs) ✖ 14 Rain cloud seeding ✖ 15 Tidal barrage ✖ 16 Rainwater harvesting ✖ 17 Abstraction licence trading ✔ Third party options report 18 Water quality schemes that increase DO ✔ Catchment management feasibility report 19 Catchment management schemes ✔ Catchment management feasibility report 20 Conjunctive use operation of sources ✔ Built into DOs through WARMS 21 Joint ("shared asset") resource ✔ Included in feasibility reports where applicable 22 Asset transfers ✔ Third party options report 23 Options to trade other (infrastructure) assets ✔ Third party options report † Taken from UKWIR 2012, Water Resources Planning Tools, EBSD Report, Ref 12/WR/27/6

23 UKWIR, Water Resources Planning Tools, EBSD Report, Ref. 12/WR/27/6. 2012.

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Table 4.1: Summary of options generic screening rejection Screening Scheme Key elements Comments decision 9 Tankering of water Tankering requires the development of new A proposal by Albion Water for tankering from sources in Norway and the infrastructure, including pipelines and deep water Netherlands has been considered. This concluded that while technically feasible at facilities for loading / unloading. The logistical, full utilisation (one tanker per day) it would be excessively costly; and at low utilisation Tankering by sea environmental and planning constraints at the ✖ (one tanker per week) the option remains uncompetitive with other options of a similar Thames Estuary are considerable as the estuary is size. Tankering has therefore not been developed as a water resources option, but is relatively shallow and access would be restricted. being considered by Thames Water as a potential drought plan option. 13 Imports (icebergs) Rejected on the basis that the techniques involved are not sufficiently advanced for This option would require the development of a commercial use and because of the high level of uncertainty around scheme yield. system for towing of icebergs over long distances Also, as the Thames Estuary is designated under the EA Habitats Directive, an Icebergs e.g. from the Norwegian Sea to the Thames ✖ Appropriate Assessment is likely to be required. As part of this, the company will be Estuary. required to demonstrate that there are no feasible alternative options; which is not the case. 14 Rain cloud seeding Rejected on the basis that the techniques involved are not sufficiently advanced for This option would require the development of a Rain cloud seeding commercial use and because of the high level of uncertainty that the scheme would system for wide commercial implementation. ✖ provide significant yield. 15 Tidal barrage Rejected as this option would limit the navigation of the river Thames to both private and commercial traffic resulting in disproportionate social and economic costs. It The option for the use of the Thames Barrier to would also limit the passage of aquatic life which would cause significant ecological The Thames Barrier impound fresh water. ✖ damage. The option could also result in raising the groundwater levels in the surrounding areas which could increase the incidence of flooding and cause damage to services and historic buildings in London. 16 Rainwater harvesting

Rainwater harvesting Direct collection and storage of rainwater. ✖ Rejected on the basis of limited drought resilience.

10 Redevelopment of existing resources TBC because redevelopment of reservoir storage is not possible unless sufficient Redevelopment of existing surplus resources are available to compensate for the temporary loss of storage and Changes to current system that could yield benefits resources (e.g. Staines the consequent risks to security of supply that would therefore result whilst the to the supply /demand balance. TBC Reservoir) reservoir is being redeveloped. The provision of the surplus resources would be likely to be required for several years to allow the redevelopment of existing sources.

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5 London WRZ water resource options

This section provides a summary of the feasibility reports and undertakes the fine screening assessment for the London Water Resource Zone grouped by water resource option type. Options are assessed qualitatively against the six dimensions: Cost, Environmental and Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is presented for each option type together with the screening decisions.

5.1 Resource option types

Section 5.2 summarises the feasibility report findings for each option type identified for the London WRZ, which includes:  Water reuse  New reservoirs  Raw water transfers;  Desalination;  Direct river abstraction;  Groundwater development - Aquifer recharge;  Groundwater development - Aquifer storage and recovery;  Groundwater development;  Removal of Deployable Output constraints; and  Catchment management

Section 5.3 summarises exclusivities and interdependencies between options. Section 5.4 summarises the fine screening assessment, identifying those options being screened out together with the reasons for rejection. In section 5.5 next steps for options progressing onto the Constrained List are set out. Next steps required to finalise the fine screening are described in section 5.6.

It is emphasised that this report provides only a summary of relevant considerations and that source documents should be consulted for a detailed substantiation of the technical assessments.

5.2 Feasibility report findings

5.2.1 Water reuse

The options identified in the Feasibility Report for water reuse are listed in Table 5.1 below together with a summary of the status of the options.

Table 5.1: London options identified in the feasibility report for water reuse Stage* Source Treatment Discharge DO Location Location location (Ml/d) 1 2 3 Comment Site within 380 ✔ ✔ ✔

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Stage* Source Treatment Discharge DO Location Location location (Ml/d) 1 2 3 Comment Beckton STW Beckton River Lee 300 ✔ ✔ ✔ Treatment site land - Armada Way initially - final effluent STW Diversion - considered however discounted due to proposed 200 ✔ ✔ ✔ (initially upstream of housing development. Area in the north of Beckton ✔ ✔ ✔ assessed King George 150 STW site to be used instead, although noted that V Reservoir TW have other schemes which demand land on the on Armada 100 ✔ ✔ ✔ intake STW site (desalination option, AMP7 growth). Way) 50 ✔ ✔ ✔ Abbey Mills Luxborough River Lee 300 ✔ ✔ ✖ These options have been screened out in PS - sewer Lane Diversion - preference to the Beckton STW site options for the

mining upstream of 200 ✔ ✔ ✖ following reasons: King George 150 ✔ ✔ ✖  the options are mutually exclusive - DO option V Reservoir combinations are possible intake 100 ✔ ✔ ✖  planning designations, consents and requirements are more onerous at the Abbey 50 ✔ ✔ ✖ Mills PS site  the land area available at Luxborough Lane offers less scope for expansion / additional treatment processes if required  less opportunities for biodiversity enhancement at the abstraction location  effects on heritage assets particularly at the PS site  restricted land opportunity for expansion at the Abbey Mills PS abstraction location  there is less potential to mitigate non-traffic impacts upon local properties Options are screened out in preference to Abbey Mills Lower Hall River Lee 300 ✔ ✖ PS - sewer Diversion - Luxborough Lane as follows: mining upstream of  the Beckton catchment options are mutually exclusive King George 200 ✔ ✖ V Reservoir  greater flood plain encroachment intake 150 ✔ ✖  additional major crossing and conveyance route complexity 100 ✔ ✖  nature conservation and biodiversity importance affected 50 ✔ ✖  Lower Hall site is allocated for use as flood compensation storage Crossness Site adjacent River Lee 190 ✔ ✔ ✔ Best performing of the Crossness catchment STW - final to Crossness Diversion - options. Treated raw water to be discharged into

effluent STW upstream of 150 ✔ ✔ ✔ the River Lee Diversion for treatment at a new (Crossness King George 100 ✔ ✔ ✔ treatment works in E London. Southern V Reservoir Marshes) intake 50 ✔ ✔ ✔ The two Greenwich PS options have been rejected Greenwich Lower Hall River Lee 150 ✔ ✖ PS - sewer Diversion - at Stage 2 in favour of retaining the better

mining upstream of 100 ✔ ✖ performing Millbrook Road and Wandle Valley options. The main / differentiating reasons being: King George 50 ✔ ✖ V Reservoir  the assumed limit for reuse in the Crossness intake catchment is 190Ml/d  the Crossness catchment options are mutually exclusive  other options available with shorter conveyance  visually sensitive viewpoints affected  heritage assets affected  Lower Hall site is allocated for use as flood compensation storage The two Greenwich PS options have been rejected Greenwich Hogsmill River 150 ✔ ✖ PS - sewer STW Thames - at Stage 2 over retaining the better performing

mining upstream of 100 ✔ ✖ Millbrook Road and Wandle Valley options. The main / differentiating reasons being: the Walton 50 ✔ ✖ WTW intake

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Stage* Source Treatment Discharge DO Location Location location (Ml/d) 1 2 3 Comment  the assumed limit for reuse in the Crossness catchment is 190Ml/d  other options available with shorter conveyance  visually sensitive viewpoints affected  heritage assets affected Millbrook Hogsmill River 100 ✔ ✔ ✖ These Crossness catchment options have been Road PS STW Thames - screened out in preference to the Crossness STW

(Brixton) - upstream of 50 ✔ ✔ ✖ site options for the following reasons: sewer mining the Walton  the options are mutually exclusive - DO option WTW intake combinations are possible  the AIC (average incremental cost) £/m3 for corresponding DO options is higher than Crossness STW  more impacts on visual sensitivity particularly at the PS location  less opportunities for biodiversity enhancement at the abstraction site  potential of restricted land opportunity for expansion at the Millbrook Road PS abstraction location  less potential to mitigate non-traffic impacts upon local properties The Crossness Wandle Valley PS option is Wandle Hogsmill River 17 ✔ ✔ ✖ Valley PS - STW Thames - screened out in preference to the Crossness STW sewer mining upstream of site options for the following reasons: the Walton  the options are mutually exclusive - DO option WTW intake combinations are possible  the option has similar conveyance length as Crossness STW but for lower DO availability  there is no potential to expand the option  AIC (average incremental cost) £/m3 is higher than similar comparable options Mogden STW Kempton River 200 ✔ ✔ ✔ Due to lack of available land at Mogden STW, - treated Park - Hydes Thames - treatment is located at Hydes Field (TW owned

effluent Field upstream of 150 ✔ ✔ ✔ land). Discharge of the treated raw water is into the the Walton 100 ✔ ✔ ✔ River Thames upstream of the Walton intake with WTW intake treatment at Kempton. 50 ✔ ✔ ✔ Mogden Kempton River 50 ✔ ✔ ✔ This option takes untreated sewage from the South Sewer Park - Hydes Thames - southern sewer into Mogden STW located along - sewer Field upstream of the A316, near to Hydes Field. This option is mining the Walton mutually exclusive of the Mogden STW option at WTW intake 200 Ml/d DO. Deephams - Deephams River Lee 60 ✔ ✔ ✔ Work required to confirm maximum capacity of treated STW Diversion - Deephams reuse that would be environmentally effluent / post upstream of acceptable. screening King George treatment V Reservoir stream intake 25 ✔ ✔ ✖ The 60 Ml/d option provides better value The reasons for rejecting these options are: Long Reach - Site adjacent River Lee 80 ✔ ✖ treated to STW Diversion -  significant conveyance lengths

effluent upstream of 50 ✔ ✖  conveyance complexity due to length and King George number / type of pipeline crossings options V Reservoir intake Riverside - Riverside River Lee 38 ✔ ✖ The reasons for rejecting this are: treated STW Diversion -  significant conveyance lengths effluent upstream of  conveyance complexity due to length and King George number / type of pipeline crossings options V Reservoir intake

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The post Stage 3 assessment feasible list of reuse water resource options is as follows:  Beckton STW reuse: – Development of a water reuse plant using effluent from Beckton Sewage Treatment Works (STW) on land either on the Beckton STW site, or in the vicinity. The capacity of the plant could range from 50 to 380Ml/d – Transfer of reuse water to River Lee flood channel upstream of the King George V intake, or direct to the Lee Valley reservoirs.  Crossness STW reuse: – Development of a water reuse plant using effluent from Crossness STW, on land south of the STW. The capacity of the plant could range from 50 to 190Ml/d. – Transfer of reuse water to River Lee flood channel upstream of the King George V intake, or direct to the Lee Valley reservoirs.  Deephams STW reuse: – Development of a water reuse plant at Deephams STW with a capacity of up to 60Ml/d. – Transfer of reuse water to River Lee flood channel upstream of the King George V intake, or direct to the Lee Valley reservoirs.  Mogden STW reuse: – Development of a water reuse plant at Hydes Field (located south east of Kempton) using effluent transferred from Mogden STW. The capacity of the plant could range from 50 to 200Ml/d. – Transfer of reuse water to River Thames upstream of the Walton intake.  Kempton South Sewer (black water): – Development of a water reuse plant at Hydes Field (located south east of Kempton) using sewage from the Mogden South Sewer intercepted at Kempton. The capacity of the plant is 50Ml/d. – Transfer of reuse water to River Thames upstream of the Walton intake.

Further explanation of the on reasons for the rejection of reuse options is set out in the relevant Feasibility Report and will be summarised in the Option Rejection Register.

5.2.2 New reservoirs

The water resource options identified in the Feasibility Report for new reservoirs are listed in Table 5.2 below together with a summary of the status of the options. The land areas covered by the potential reservoir sites ranged from approximately 200 hectares to almost 1,500 hectares. Due to this wide range of land area, the Feasibility Report defines land area “size bands”. This is to allow the comparison of similarly sized sites at the later stages of the assessment. Following a review of the range of site sizes identified in previous studies it was determined that the size bands would be:  Band A: 200 – 399 hectares;  Band B: 400 – 699 hectares;  Band C: 700 hectares or larger.

The potential reservoir sites considered are shown on a map in Figure 5.1.

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Figure 5.1: Potential reservoir sites

Table 5.2: London options identified in the Feasibility Report for new reservoirs Stage Comment Size 1 2 3 Element band Rejected due to poor performance across many criteria Site 1 – A ✔ ✖ including statutory heritage designation and loss of residential Minety dwellings Site 2 - Leigh Rejected due to poor performance across many criteria A ✔ ✖ including presence of a Wiltshire Wildlife Trust nature reserve

Site 3 - Rejected due to statutory heritage designation and birdstrike C ✖ Cricklade risk

Site 4 - Rejected due to built development (housing) A ✖ Swindon Site 5 – Broad Rejected due to poor performance across many criteria C ✔ ✖ Blunsdon including presence of Ancient Woodland Rejected due to poor performance across many criteria Site 6 - B ✔ ✖ including distance from intake / outfall point and loss of Highworth agricultural land

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Stage Comment Size 1 2 3 Element band Site 7 - Rejected due to poor performance in criteria including planning A ✔ ✔ ✖ Wanborough (housing) and flood risk Rejected due to poor performance across many criteria Site 8 - C ✔ ✖ including distance from intake / outfall point and proximity to an Bishopstone Area of Outstanding Natural Beauty Site 9 - Rejected due to statutory heritage designation B ✖ Lechlade Site 10 - Rejected due to poor performance across many criteria B ✔ ✖ Shrivenham including presence of Ancient Woodland Site 11 – Rejected due to poor performance across many criteria A ✔ ✖ Clanfield including access and loss of agricultural land Site 12 - Rejected due to poor performance across many criteria C ✔ ✖ Faringdon including presence of Ancient Woodland Site 13 - Rejected due to insufficient clay thickness B ✖ Uffington Site 14 – Rejected due to poor performance across many criteria B ✔ ✖ Brize Norton including presence of Ancient Woodland Site 15 - Rejected due to poor performance across many criteria B ✔ ✖ Bampton including flood risk and loss of agricultural land Site 16 - Rejected due to poor performance across many criteria B ✔ ✖ Witney including flood risk, loss of agricultural land and heritage Site 17 – Rejected due to poor performance across many criteria Stanford in B ✔ ✖ including access and loss of residential properties the Vale Site 18 - Rejected due to poor performance across many criteria B ✔ ✖ Longworth including presence of Ancient Woodland Site 19 – Rejected due to poor performance across many criteria A ✔ ✖ South Leigh including presence of Ancient Woodland Site 20 – Rejected due to insufficient clay thickness B ✖ West Hanney Site 21 – Rejected due to poor performance across many criteria Stanton A ✔ ✖ including flood risk and recreation Harcourt Site 22 - C ✔ ✔ ✔ Abingdon Site 23 - Rejected due to poor performance across many criteria B ✔ ✖ Wantage including presence of Ancient Woodland Site 24 - Rejected due to statutory nature conservation designations B ✖ Kidlington Site 25 - Rejected due to poor performance across many criteria A ✔ ✖ Oxford including of Ancient Woodland and recreation Site 26 - Rejected due to poor performance across many criteria A ✔ ✖ Didcot including presence of Area of Outstanding Natural Beauty Site 27 - Rejected due to statutory nature conservation and heritage C ✖ Beckley designations Site 28 – Rejected due to statutory heritage designation Brightwell B ✖ cum Sotwell Site 29 - Rejected due to insufficient clay thickness A ✖ Ambrosden Site 30 – Rejected due to poor performance across many criteria Drayton St A ✔ ✖ including numbers of adjacent local residents and loss of Leonard agricultural land

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Stage Comment Size 1 2 3 Element band Site 31 - Rejected due to statutory nature conservation designations B ✖ Wheatley Rejected due to statutory heritage designation and birdstrike Site 32 – B ✖ risk Benson

Site 33 – Rejected due to poor performance across many criteria B ✔ ✖ Chalgrove including construction traffic and topographical variation Site 34 - Rejected due to insufficient clay thickness B ✖ ✖ Bicester Site 35 – Rejected due to poor performance across many criteria Chalgrove B ✔ ✖ including construction traffic and heritage Airport Site 36 – C ✔ ✔ ✔ Marsh Gibbon Site 37 - Rejected due to landscape, construction complexity and B ✔ ✔ ✖ Ludgershall impact on the floodplain Site 38 – Rejected due to poor performance across many criteria Great A ✔ ✖ including presence of Ancient Woodland Haseley Site 39 - Rejected due to poor performance across many criteria B ✔ ✖ Quainton including presence of Ancient Woodland Site 40 - Rejected due to insufficient storage capacity A ✔ ✔ ✖ Postcombe Site 41 - B ✔ ✔ ✔ Chinnor Site 42 – Rejected due to construction complexity, landscape and views A ✔ ✔ ✖ Haddenham Site 43 - Rejected due to planning, views and construction complexity B ✔ ✔ ✖ Aylesbury Site 44 - Rejected due to statutory heritage designation B ✖ Stone Site 45 - Rejected due to insufficient clay thickness A ✖ Whitchurch Rejected due to statutory heritage designation and insufficient Site 46 - clay thickness B ✖ Stewkley

Site 47 - Rejected due to birdstrike risk and insufficient clay thickness B ✖ Bierton

Rejected due to insufficient clay thickness Site 48 - A ✖ Wingrave

Site 49 - Rejected due to poor performance across many criteria A ✔ ✖ Cheddington including heritage and distance from intake / outfall point Rejected due to poor performance across many criteria Site 50 - B ✔ ✖ including presence of Area of Outstanding Natural Beauty and Kintbury Ancient Woodland Site 51 - Rejected due to built development (military establishment) A ✖ Burghfield Site 52 – Rejected due to poor performance across many criteria B ✔ ✖ Beech Hill including presence of Ancient Woodland Site 53 - Rejected due to statutory heritage designation A ✖ Wokingham

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Stage Comment Size 1 2 3 Element band Site 54 - Rejected due to insufficient storage capacity A ✔ ✔ ✖ Bracknell Site 55 - Rejected due to insufficient clay thickness A ✖ Maidenhead

The assessment of the sites that passed through to Stage 3 addressed a range of property, planning and engineering criteria. The assessment undertaken to the end of stage 2 identified Site 22 - Abingdon as the best performing site against these criteria across all reservoir capacities from 30Mm3 – 150Mm3.

Although the conclusion of the staged assessment approach was that Site 22 – Abingdon was the best performing site overall, consideration was given to the next best performing site(s) and where appropriate these were also identified to be taken through to the fine screening stage for further appraisal.

At the larger reservoir capacity options (125Mm3 and 150Mm3), Abingdon was the only available site option. Two potential options were considered at a 100Mm3 reservoir capacity; however, the difference between the overall assessment performance of Site 22 - Abingdon and Site 36 - Marsh Gibbon at this capacity was such that only Abingdon was considered suitable to be taken through to the fine screening stage.

At some of the smaller reservoir capacity options, the difference in performance between Site 22 – Abingdon, Site 36 – Marsh Gibbon and Site 41 – Chinnor was less. In consequence, at a reservoir capacity of 75Mm3 the next best performing site, which was Site 36 – Marsh Gibbon, was also taken forward to the fine screening stage.

The next best performing sites at both 30Mm3 and 50Mm3 reservoir capacities were Site 36 – Marsh Gibbon and Site 41 – Chinnor. As there was limited difference in the performance of these two sites at these reservoir capacities, both these sites were taken forward to the fine screening stage for consideration.

Consideration of different reservoir capacities ranging from 30 Mm3 to 150 Mm3 provides flexibility in terms of reservoir options that could potentially be included in the WRMP19 option appraisal process. To retain this flexibility, an initial review as to the feasibility of a phased development of a reservoir at the Abingdon site has also been undertaken. This exercise identified the possibility of the Abingdon site being developed in two phases, including a 30Mm3 + 120Mm3 option as well as a 75Mm3 option + 75Mm3 option. Consideration of both single and phased reservoir development at the Abingdon site will therefore be taken forward to the fine screening stage.

The preferred options to be taken forward to the fine screening stage are therefore:  30Mm3 – Site 22 Abingdon, Site 36 Marsh Gibbon, Site 41 Chinnor  50Mm3 – Site 22 Abingdon, Site 36 Marsh Gibbon, Site 41 Chinnor  75Mm3 – Site 22 Abingdon, Site 36 Marsh Gibbon  100Mm3 – Site 22 Abingdon  125Mm3 – Site 22 Abingdon  150Mm3 – Site 22 Abingdon  30Mm3 + 120Mm3 – Site 22 Abingdon  75Mm3 + 75Mm3 – Site 22 Abingdon

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Further explanation of the reasons for rejection of reservoir options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

Further development of the phased reservoir options at the Conceptual Design stage has refined the embankment profiles and borrow pit shapes as constrained by site specific geological conditions which has led to changes in the capacities of the phases and to a reduction in total storage volume.

5.2.3 Raw water transfers

For raw water transfers the resource element and conveyance elements have been considered separately in the Feasibility Reports. The elements considered are listed in Tables 5.3 and 55.4 below together with a summary of their status.

Table 5.3: London options identified in the Feasibility Report for raw water transfers (resource elements) Stage Comment Capacity

Element (Ml/d) 1 2 3 Kielder Reservoir Not ✔ ✖ Rejected because its associated conveyance elements fail defined Stage 2 screening. These conveyance elements (existing canals and a new pipeline) are considered the only realistic ones.

South-East Wales Resource Awaiting This option is on hold pending information from Welsh Water (Including Great Spring) Information and confirmation of Natural Resources Wales and Welsh Government view. The option replaces the historical Columbus options.

CRT supporting Oxford Canal Awaiting ✔ ✔ TBC Some further information received and option being Information developed, but further information required from CRT to establish option feasibility.

Minworth STW effluent and 88 ✔ ✔ Awaiting Insufficient information received to establish viability of pipe to the River Avon Info. scheme. Severn Trent Water scoping out further work required to obtain information needed to confirm feasibility.

Minworth STW and 88 ✖ Severn Trent have not offered Minworth effluent for canal conveyance through existing transfer as consider river transfer more cost effective. canal network

Expansion of Draycote 25 ✔ ✔ Awaiting Insufficient information received to establish viability of Reservoir and an abstraction Info. scheme. Severn Trent Water scoping out further work from the River Avon required to obtain information needed to confirm feasibility.

Mythe WTW unused part of 15 ✔ ✔ ✔ Details of licence transfer conditions need to be confirmed licence

Netheridge STW effluent 15 ✔ ✔ ✖ Cotswold Canal conveyance rejected therefore Netheridge resource discharging into Gloucester & Sharpness Canal is also rejected.

Lake Vyrnwy 180 ✔ ✔ ✔

Craig Goch Reservoir Not ✖ Failed on National/ International Nature Conservation expansion defined designations.

River Severn (unsupported) Not ✔ ✔ ✔ Screened out at Stage 4 (validation) of feasibility study as not defined cost effective in comparison with supported STT. However an element of unsupported flow will be included in the partially supported STT options.

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Stage Comment Capacity Element (Ml/d) 1 2 3 Longdon Marsh reservoir to Reservoir ✔ ✖ Rejected because of comparatively poor performance against support River Severn volume other resource/ support elements on several criteria, including abstraction 50/89/125 estimated land acquisition cost, flood plain encroachment, Mm3 impact on residential dwellings and archaeology and the historic environment.

Use of a new Thames n/a ✖ Rejected due to negligible DO benefit of a combined reservoir (as in reservoir transfer/reservoir option when compared with two separate report, if successfully options. This is based upon the pattern of historical droughts promoted) to support River in the Thames catchment that have not historically required Severn abstraction and the STT to refill. transfer

Use of Farmoor Reservoir to n/a ✖ As above, Thames Water have assessed that there would be support River Severn minimal DO benefit associated with a combined abstraction and transfer transfer/reservoir option. There could be ecological benefits from transferring part of the STT flow to Farmoor so as to allow more River Thames water to be left in the river at low flows. However, this would also incur additional cost. Expected to be rejected as more complex and costly than direct transfer.

Table 5.4: London options identified in the feasibility report for raw water transfers (conveyance elements)

Stage Capacity Element (Ml/d) 1 2 3 Comment

South-East Wales resource Awaiting This conveyance will be provided in conjunction conveyance (previously known as Information with any Welsh Water resource. On hold awaiting Columbus) confirmation on the Welsh Water resource.

Oxford Canal – Thames (for London 15 n/a ✔ ✔p Provisionally passed pending further engineering WRZ only) review

Oxford Canal - Farmoor Reservoir 15 (SWOX) n/a ✔ ✔p Provisionally passed pending further engineering (SWOX) review TBC (LON)

Canal transfer Minworth STW to Isis 100 n/a ✖ Severn Trent have not offered Minworth effluent Lock for canal transfer as consider river transfer more cost effective.

Pipeline from Kielder Reservoir Up to 300 to n/a ✖ Rejected because of comparatively poor LON; performance against other conveyances on several criteria including total pipeline conveyance 40 Ml/d to length, pumping head, construction complexity SWOX and operational complexity.

Canals from Kielder Reservoir 45 n/a ✖ Rejection reasons include: The Water UK study concluded that the water from Kielder Reservoir is likely to be required by neighbouring areas; and the operational complexity associated with this conveyance is disproportionate to the limited DO benefit that could be achieved.

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Stage Capacity Element (Ml/d) 1 2 3 Comment

Pipeline Deerhurst to Culham for 100 100 n/a ✖ Rejected because the Deerhurst to Lechlade Ml/d transfer pipeline route for the same capacity is significantly shorter route and had similar performance for other criteria.

Pipeline Deerhurst to Culham for 300 - 500 n/a ✔ ✔ 300/400/500 Ml/d transfer

Pipeline Deerhurst to Culham for 600 600 n/a ✔ ✖ Rejected due to less promotable compared with Ml/d transfer other options due to environmental effects and cost.

Pipeline Deerhurst to Lechlade for 100 n/a ✔ ✖P Provisionally rejected in comparison with larger 100 Ml/d transfer transfers on basis of cost and adequate capacity given projected deficits.

Cotswold Canal 100 Ml/d 100 n/a ✔ ✖ Rejected as it is mutually exclusive of the Deerhurst pipeline conveyances and was concluded to be overall less feasible than the latter. Performed worse on the key criteria of Water resources and water quality, normalised cost, constructability and operability.

Cotswold Canal 300 Ml/d 300 n/a ✔ ✖ Rejected as it is mutually exclusive of the Deerhurst pipeline conveyances and was concluded to be overall less feasible than the latter. Performed worse on the key criteria of Water resources and water quality, normalised cost, constructability and operability.

Note: ✔p / ✖P denotes options provisionally passed / rejected.

During the validation stage, the raw water transfer resource and conveyance options assessed separately in stages 1 to 3 were assessed in combination. The potential combinations are given in Table 5.5 below.

Table 5.5: Raw Water Transfer Combined Options

Resource Capacity Feasible Resource(s)/Support(s) Conveyance Comments zones (Ml/d) List? Welsh Water: South-East South-East Wales TBC TBC Insufficient No information provided, therefore Wales resource (Incl. Great conveyance info cannot progress Spring) provided Oxford Canal options Oxford Canal to London and 15 TBC Option is currently being developed Farmoor Reservoir SWOX and assessed Unsupported River Severn Deerhurst pipeline 100-500 X Rejected at validation stage of feasibility report on cost grounds given low stochastic reliable yield for unsupported transfers Minworth STW effluent, CRT Canal transfer London, 88+15 X Severn Trent have not offered abstraction Minworth STW to SWOX or both Minworth effluent for canal transfer Isis Lock as consider river transfer more cost effective. This option will be rejected at Stage 1 and will not appear in the Validation section of the final report.

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Resource Capacity Feasible Resource(s)/Support(s) Conveyance Comments zones (Ml/d) List? Combinations of Deerhurst to London, 100 XP Provisionally rejected at validation Unsupported River Severn Lechlade SWOX stage of feasibility report on cost water and support from or both grounds Mythe, Lake Vyrnwy Deerhurst to 300/400/500

Culham ✔ Combinations of Deerhurst to London, 100 Insufficient Awaiting updated information from Unsupported River Severn Lechlade SWOX info Severn Trent Water for support from water and support from or both provided Minworth WTW and Draycote Mythe, Lake Vyrnwy, Deerhurst to Reservoir Minworth STW and Culham 300/400/500 Draycote Reservoir Minworth STW, Draycote Cotswold Canal London, ~300 X Cotswold Canal will be rejected at Reservoir, Mythe, SWOX Stage 3 and will not appear in the Netheridge STW and Lake or both Validation section of the final report. Vyrnwy resources

Work to finalise the Feasibility Report is ongoing and the above table will be updated once the work is complete. Pending finalisation of the Feasibility Report only the Deerhurst pipeline option has been carried forward to fine screening. A brief description of this option is provided below.  Severn-Thames Transfer (Deerhurst to Culham pipeline) with capacity of 300, 400 or 500 Ml/d – Redeployment of Lake Vyrnwy from United Utilities to support flows in the River Severn (180Ml/d) and development of replacement resource by United Utilities as required – Transfer of 15Ml/d of Severn Trent Water Mythe licence to support flows in the River Severn – A transfer pipeline of raw water from the River Severn at Deerhurst, via a new pipeline, for discharge at Culham and reabstraction at existing TW intakes downstream.

Further explanation on reasons for rejection of raw water transfer in combination options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

5.2.4 Desalination

The options identified in the feasibility report for desalination are listed in Table 5.6 below together with a summary of the status of the options.

Table 5.6: London options identified in the feasibility report for desalination Stage Distribution DO Ref. Plant Location Location (Ml/d) 1 2 3 Comment Treatment site land - Armada Way initially considered however discounted due to proposed Coppermills housing development. Areas of Beckton STW site 1a Beckton STW WTW 150 ✔ ✔ ✔ to be used instead, although noted that TW have (blended) other schemes which demand land on the STW site (water reuse, AMP7 growth) as well as potential safeguarding for a river crossing. Source – Option considered abstraction from the Coppermills River Thames and return of brine reject stream to

1b River Lee WTW 150 ✔ ✖ River Lee. (blended) Rejected at Stage 2 due to constraints on land availability. Honor Oak 2a Manor Rd, Erith 150 ✔ ✖ Rejected at Stage 2 due to length of conveyance. (blended)

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Stage Distribution DO Ref. Plant Location Location (Ml/d) 1 2 3 Comment Distribution location – Honor Oak considered, but 2b(i) 150 ✔ ✔ ✖ Coppermills WTW preferable due to greater capacity for blending treated water. Crossness (Honor Oak) – (Erith Southern Coppermills 300 option rejected at Stage 3 due to Grazing WTW environmental sensitivity of potential site and size of site would reduce potential for on-site Marshes) (blended) 2b(ii) 300 ✔ ✔ ✖ environmental mitigation.

150 option rejected as less environmental impact at Waldrist Way site, but should be revisited if this site proves unavailable.

2c(i) (Honor Oak) – 150 ✔ ✔ ✖ Screened out as site is deemed unviable due to Tripcock Ness, Coppermills large planned residential development (outline Thamesmead WTW planning permission granted) and other land being 2c(ii) (blended) 300 ✔ ✔ ✖ designated Metropolitan Open Land.

Crossness Coppermills (Thamesmead WTW Alternative site to Tripcock Ness. Site is Industrial 2d (blended) 300 ✔ ✔ ✔ designated in Local Plan for business use in three Estate phases (outline planning permission granted). Extension – Waldrist Way) Crossness Northumberland Distribution location – Northumberland Heath 3a (Erith Southern Heath 65 ✔ ✔ ✔ service reservoir for direct-supply to Riverside Marshes) (unblended) WRZ

Following the Stage 3 assessment the following desalination water resource options have been identified as being feasible:  Desalination plant located at Beckton STW: – Development of a 150 Ml/d desalination plant located on Beckton STW, or another site in the vicinity, using brackish estuarine water from the River Thames as its feedwater. – Transfer of treated water to Coppermills WTW for blending.  Desalination plant located at Crossness (Thamesmead Industrial Estate Extension – Waldrist Way): – Development of up to a 300Ml/d desalination plant located south of Crossness, using brackish estuarine water from the River Thames as its feedwater. – Transfer of treated water to Coppermills WTW for blending.  Desalination plant located south of Crossness STW for direct supply to Northumberland Heath service reservoir: – Development of a 65 Ml/d desalination plant located to the south of Crossness STW, using brackish estuarine water from the River Thames as its feedwater. – Transfer of treated water to Northumberland Heath service reservoir for direct-supply of Riverside Zone.

Further explanation of reasons for rejection of desalination water resource options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

5.2.5 Direct river abstraction

The options identified in the Feasibility Report for direct river abstraction are listed in Table 5.7 below together with a summary of the status of the options.

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Table 5.7: London options identified in the feasibility report for direct river abstraction Stage Comment

Option Sub-option Capacity / DO 1 2 3 Lower Lee Surface 1a) Abstraction at Three 35Ml/d – 55Ml/d DO benefit assessed with/ Water abstraction Mills Lock, transfer flow to without Hoddeston transfer Lockwood shaft and treat at ✔ ✔ ✖ operating. Provisionally Coppermills WTW from rejected on basis of high AIC where it is put into supply. Lower Lee Surface 1b) Abstraction at Three 150 Ml/d Land not available for bank

Water abstraction Mills Lock, treat flows and ✔ ✖ side storage required to put into supply. mitigate quality risk Teddington Weir 3a) Transfer 300Ml/d from 300 Ml/d (Mogden effluent Mogden to Teddington. New transfer) intake upstream of ✔ ✔ ✔ Teddington Weir with direct transfer to Thames Lee Tunnel. Teddington Weir 3b) New intake and 300 Ml/d High construction (Mogden effluent upstream of Teddington weir complexities. Cost ✔ ✔ ✖ transfer incl. and transfer to Queen comparison higher when Storage) Mother reservoir for storage. compared to 3a. Teddington Weir 3c) New intake and 300 Ml/d Land available not sufficient (Mogden effluent treatment works upstream of for full treatment site. ✔ ✖ transfer incl. Teddington Weir at Canbury Ownership of land issues. treatment) Gardens for direct supply. Mogden effluent 4) Increase existing 300 Ml/d Area availability on site transfer to abstraction upstream at ✔ ✖ insufficient. Teddington Weir Surbiton. Beckton effluent 5a) No treatment and 300 Ml/d The proximity to abstraction transfer transfer to Thames Lee ✖ means high length of Tunnel conveyance and associated cost compared with Beckton effluent 5d) Partial Treatment and 300 Ml/d ✖ equivalent Mogden option transfer transfer to reservoir Beckton effluent 5c) Full treatment transfer to 300 Ml/d ✖ transfer supply network Lower River Roding 6) Lower River Roding 17.3 Ml/d Not resilient during drought abstraction for direct supply conditions. to potable network or ✖ transfer to Lee Valley Reservoirs River Mardyke 7) River Mardyke 3.7 Ml/d Not resilient during drought ✖ conditions. River Rom/Beam 8) River Rom/Beam 7.2 Ml/d Not resilient during drought abstraction for direct supply ✖ conditions. to potable network River Ingrebourne 9) River Ingrebourne 4.2 Ml/d Not resilient during drought abstraction for direct supply ✖ conditions. to potable network

Following the Stage 3 assessment the following direct river abstraction option has been identified as feasible for the London WRZ:  Option 3a - Transfer of 300Ml/d from Mogden STW to upstream of Teddington Weir, enabling additional abstraction further upstream. New intake upstream of Teddington weir connecting into the existing Thames Lee Tunnel.

Further explanation of reasons for rejection of direct river abstraction options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

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5.2.6 Aquifer recharge

The aquifer recharge water resource options identified in the Groundwater Feasibility Report are listed in Table 5.8 below together with a summary of the status of the options.

Table 5.8: London options identified in the feasibility report for aquifer recharge DO (Ml/d) Stage* Comment

Option Average Peak 1 2 3 Eltham Green site removed from the option (with consequential reduction in yield) to allow progression of scheme through Stage 2. EA AR/SLARS approved as non- consumptive with Kidbrooke 7.0 8.1 ✔ ✔ ✔ recommendations for consented test pumping to (SLARS1) assess the risk of sub-surface flooding. Requires agreement with the EA on operating principal as part of SLARS. Drilling and test pumping of a new abstraction borehole will be required at the Byegrove Road AR Merton 5.0 6.0 ✔ ✔ ✔ site to confirm yield and water quality. (SLARS3) Requires agreement with the EA on operating principal as part of SLARS. Definition of operating strategy required. Requires AR Streatham 4.0 4.5 ✔ ✔ ✔ agreement with the EA on operating principal as (SLARS2) part of SLARS. Option not assessed as WARMS2 modelling AR - HARS - - indicated that there was no Deployable Output (Hornsey) benefit for this option

* DO benefit is the WARMS2 modelled DO benefit for the average values and peak source yield for the peak values.

Following the Stage 3 assessment the following aquifer recharge options have been identified as being feasible:  SLARS/AR Kidbrooke (SLARS1): – Component of the larger SLARS project based on the development of boreholes for recharge/abstraction purposes in the confined Chalk. The scheme comprises the upgrade of the existing borehole at the Rochester Way site and another at the Bromley Reservoir site. – Development of two existing boreholes for recharge and abstraction in the confined chalk at Kidbrooke – The scheme also includes construction of a new WTW  AR – Merton (SLARS) – The proposed works at Merton Abbey include redevelopment of the existing 1.5 m diameter borehole and provision of a new abstraction pump. A new connection will provide recharge water while abstracted raw water will be routed to the existing WTW which is currently limited to a maximum flow of 5 Ml/d, though the full design capacity is 8 Ml/d; – The proposed works at Byegrove Road include a new recharge borehole and two additional observation boreholes, network connection to provide recharge water, equipping the borehole with an abstraction pump rated at 4.5 Ml/d and pumping of the abstracted water to the new Merton Abbey WTW via a new 1.1 km main.  AR Streatham (SLARS) – Component of the larger SLARS project based on the upgrade of an existing borehole plus the construction of a new AR borehole. Water for recharge will be abstracted from the River Thames in west London during periods of low demand, treated to drinking water standards and supplied through the existing mains network. The scheme also includes works on the WTW at Streatham to service these two boreholes.

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5.2.7 Aquifer storage and recovery

The aquifer storage and recovery water resource options identified in the Groundwater Feasibility Report are listed in Table 5.9 below together with a summary of the status of the options.

Table 5.9: London options identified in the feasibility report for aquifer storage and recovery DO* (Ml/d) Stage* Option Average Peak 1 2 3 Comment Yield and quality will be confirmed following drilling and ASR South East London test pumping. Impact of scheme on nearby 3.0 5.0 ✔ ✔ ✔ (Addington) abstractions and the River Eden needs to be confirmed. Agreement to abstract from the River Thames during wet periods needs to be confirmed with the EA. The ASR Thames yield and quality of water abstracted from the proposed 3.0 5.0 ✔ ✔ ✔ Valley/Thames Central boreholes at Ashford cannot be confirmed until drilling and test pumping of the proposed new boreholes has taken place.

* DO benefit is the WARMS2 modelled DO benefit for the average values and peak source yield for the peak values.

Both options have been carried forward from the Feasibility Report to the fine screening stage.  ASR South East London Addington – Scheme comprises the upgrade of one existing borehole and installation of four new operational ASR boreholes in the confined Lower Greensand aquifer at the TW Addington site. – Recharge of up to 5Ml/d will take place using water from the treated water network during the winter months. – Abstraction from the ASR boreholes at up to 5Ml/d will be treated at a new Addington WTW during the summer, as required.  ASR Thames Valley/Thames Central – Scheme comprises the installation of five new operational ASR boreholes in the confined Lower Greensand aquifer at the TW Ashford WTW site. – Recharge of up to 5Ml/d will take place using water from Ashford WTW during the winter months. – Abstraction from the ASR boreholes at up to 5Ml/d will be treated at the existing Ashford WTW during the summer, as required.

5.2.8 Groundwater development

The groundwater development water resource options identified in the Groundwater Feasibility Report are listed in Table 5.10 below together with a summary of the status of the options.

Table 5.10: London options identified in the feasibility report for groundwater development DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment Requires agreement with current owner over North London licence trading. TW to decide whether to Licence Trading/ 2.0 2.3 ✔ ✔ ✔ progress this option. Further investigations into Transfer the condition of the borehole are also required. The Environment Agency will not support the proposed licence disaggregation due to 3.3 2.9 ✖ GW – Epsom concerns about the impact of the increased abstraction on flows in the River Hogsmill. Option failed due to uncertainties about the Shortlands 4.2 1.0 ✔ ✖ impacts of the proposed increase in abstraction

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DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment on groundwater levels in the Chalk aquifer, flows in the River Ravensbourne, the deployable output of other nearby Thames Water abstractions and stability of the Thanet Sands Formation. GW - London Drilling and test pumping of a new abstraction confined Chalk 2.0 2.0 ✔ ✔ ✔ borehole will ultimately be required at the site (north) to confirm yield and water quality. Further liaison with the EA to understand what GW - they would require to grant this licence Southfleet/Greenhithe 8.0 9.0 ✔ ✔ ✔ disaggregation. Test pumping and monitoring (new WTW) may be required. Drilling and test pumping of a new abstraction borehole will ultimately be required at the site GW – Addington 1.0 1.5 ✔ ✔ ✔ to confirm yield, water quality, impacts on third parties and impact on surface water features A review of data from the British Geological Survey, Environment Agency and Essex and Suffolk Water indicate that there is unlikely to London confined 0.5 0.5 ✔ ✖ be sufficient yield within the identified area to Chalk (north-east) provide any deployable output benefit for the London water resource zone or to justify further investigation of this option. Merton 2.3 8.0 ✔ ✔ ✔ recommissioning

* For options that passed Stage 3 the DO is the WARMS2 modelled DO benefit for the average values and peak source yield for the peak values. For those options that failed at any of the three stages the figures shown are yields as WARMS2 modelling has not been undertaken for the options.

The options to be taken forward to the fine screening stage are therefore:  North London licence trading/transfer – Current owner operates two boreholes at a site in north London. TW is interesting in utilising the available water within the existing licence. – Contractual agreement between TW and current owner is required. – Buy in from the Environment Agency is also needed and currently under discussion.  GW – Addington – The construction of new abstraction borehole located on the site of the existing WTW to be operated within existing licence limits. – Water abstracted from the borehole will be treated at the existing WTW.  GW – London confined Chalk (north) – The scheme is a new unlicensed and unproven groundwater development scheme and will require drilling of a new abstraction borehole and test pumping to support the application for a new abstraction licence. – The target most likely deployable output of the scheme is 2.0 Ml/d (average & peak); and – Abstracted water will be treated at a new on site water treatment works (WTW), processes will include superchlorination, dechlorination and reverse osmosis.  GW – Southfleet/Greenhithe (new WTW) – This scheme is for the disaggregation of group licence to allow increased abstraction from the chalk aquifer. – Redevelopment of two boreholes (previously owned by Empire Paper Mills) for abstraction as part of the scheme. – Provision of a new WTW at the Southfleet EPM borehole – Connection pipeline from the Greenhithe EPM Borehole to the new WTW

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– Treated water pipeline from the WTW to the existing network  Merton recommissioning – The option involves the recommissioning of the WTW at Merton Abbey, including an upgrade to the pressure sand filters, provision of coagulation and flocculation, removal of the existing GAC plant and provision of a booster pumping station. – The target most likely deployable output benefit of the option is 2.3 Ml/d average and 8.0 Ml/d peak.

5.2.9 Removal of Deployable Output constraints

The options for removal of Deployable Output constraints identified in the Groundwater Feasibility Report are listed in Table 5.11 below together with a summary of the status of the options.

Table 5.11: London options identified in the feasibility report for removal of deployable output constraints DO Stage* (Ml/d) Option 1 2 3 Comment Option not assessed as it is being delivered and therefore the additional RC - Green St Green - deployable output will be included in the baseline.

No removal of DO constraints water resource options have been carried forward from the Feasibility Report.

5.2.10 Catchment management

The options identified in the feasibility report for catchment management are listed in the table below together with a summary of the status of the options.

Table 5.12: London options identified in the feasibility report for catchment management DO Stage* Comment (Ml/d) Option 1 2 3 Bean Wellfield (Groundwater) 0.1 ✔ ✔ ✖ Low likelihood of success for the potential benefit

Brantwood Rd (Groundwater) <0.1 ✔ ✔ ✖ Low likelihood of success for the potential benefit

Nonsuch (Groundwater) <0.1 ✔ ✔ ✖ Low likelihood of success for the potential benefit

Low likelihood of success for the potential benefit Wilmington (Groundwater) 0.2 ✔ ✔ ✖

Southfleet (Groundwater) 0.2 ✔ ✔ ✔

Green Street Green 0.3 ✔ ✔ ✔ (Groundwater)

North Orpington (Groundwater) 0.4 ✔ ✔ ✔

Lower River Thames 1.5 ✔ ✔ ✔

Lower River Lee 1.0 ✔ ✔ ✔

The options to be taken forward to the fine screening stage are therefore:

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 Southfleet (groundwater source) – Measures to address rising nitrate levels in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.2 Ml/d  Green Street Green (groundwater source) – Measures to address rising nitrate levels in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.3 Ml/d  North Orpington (groundwater source) – Measures to address adverse water quality risks due to agricultural activity in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.4 Ml/d  Lower River Thames (surface water sources) – Measures to address adverse water quality risks due to pesticide runoff in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 1.5 Ml/d  Lower River Lee (surface water sources) – Measures to address adverse water quality risks due to pesticide runoff in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 1.0 Ml/d

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5.3 Exclusivities/Interdependencies

A number of options have been identified that are mutually exclusive of one another. Where there are mutually exclusive options and some are clearly less favourable than others then this would provide grounds for rejection. A summary of mutual exclusivities and interdependencies between options is provided in Table 5.13.

Table 5.13: Exclusivities and interdependencies Option type Exclusivities/Interdependencies Water reuse  The Kempton black water option is mutually exclusive of the Mogden water reuse option  Both Kempton black water and Mogden reuse options are separately mutually exclusive of Teddington direct river abstraction (Mogden effluent transfer) New reservoirs Reservoirs of different sizes are mutually exclusive on the same site. Phased reservoir options will be developed at Conceptual Design stage. Raw water transfers Deerhurst pipeline options of different sizes are mutually exclusive of each other. Desalination There is a potential limiting factor on desalination water supply capacities due to possible increased salinity levels in a given reach of the Thames Tideway. A precautionary approach to the environmental assessment has, therefore, been adopted that has resulted in a limit of 300 Ml/d of additional desalination water capacity in any single reach of the River Thames. Subject to further analysis (i.e. estuarine modelling) it is expected that a higher level may be shown to be acceptable. Direct river abstraction See water reuse Aquifer recharge  The AR options may all be delivered independently. However, they are all part of SLARS and, therefore, the proposed operating strategy reflects this interdependence.  AR Merton is dependent on the delivery of the Merton recommissioning option. ASR ASR South East London (Addington) is dependent on the delivery of the upgraded WTW proposed for the GW – Addington option Groundwater development None Removal of constraints to None DO Catchment management None

5.4 Fine screening assessment

The previous sections identified the water resource options that have been carried forward from the Feasibility Reports. Each of these options has been assessed against the six dimensions and associated sub-dimensions set out in Section 3 of this report. The assessment for each option type is set out, with commentary, in Appendix B and summarised in Table 5.14 below. It can be seen from the table that the following options have been rejected at fine screening:  Beckton reuse (50Ml/d)  Mogden, Kempton and Crossness reuse  Crossness desalination (unblended)  The 30Mm3 and 50 Mm3 single phase reservoir options (<125Ml/d) at Abingdon  Marsh Gibbon and Chinnor reservoirs

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Table 5.14 Water resource element screening summary – London WRZ Aquifer Severn-Thames Aquifer Water reuse Desalination River Regulation Reservoir DRA storage & Groundwater development Catchment Management Transfer recharge

recovery

Deerhurst to ss Culham pipeline Marsh

Beckton Abingdon Chinnor Kidbrooke

Gibbon Merton Chalk

195 Ml/d support Merton

Central

Mogden

Thames

Beckton

(SLARS1) (SLARS2) (SLARS3)

Deephams

AR AR

Crossness Crossne

Streatham Southfleet

Addington Addington

Southfleet/ Southfleet/

SE London London SE

Greenhithe

(unblended)

from (Vyrnwy Teddington

Lower River River Lower

North London North

(Groundwater) (Groundwater) (Groundwater)

Thames Valley Valley Thames

Mogden S Sewer S Mogden

Licence Trading Licence Lower River Lee River Lower

and Mythe) Orpington North

London Confined Confined London recommissioning

AR/ASR AR/ASR

Green Street Green Green Street Green

Crossness (blended) Crossness

50- 50- 150- 125- 75- 75- 300 400 500 60 50 100-380 50 150 65 <125 >225 <75 <75 300 7 4 5 3 3 2 8 2 2 0.2 0.3 0.4 1.5 1.0 200 190 300 225 174 174 1 Ml/d Sub-dimension Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d

Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Phased

Env & Social SEA ○◑ ○◑ ○◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◎◑ ○◑ ○○ ○ ○○ ○○ ○◑r ○○ ○◑ ○◑r ◎○ ◎○ ◎○ ◎○ ◎○ HRA ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ WFD ◑r ◑r ◑ ◑r ○ ○ ◑r ○ ○ ○ ○ ○ ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ○ ○ ○ ◑r ○ ◑r ○ ◑r ○ ○ ○ ○ ○ ○ Cumulative effects ○ ◑r ◑r ◑ ◑ ◑ ◑ ○ ◑ ◑ ◑ ◑ ○ ◑r ◑r ◑r ○ ◑r ○ ○ ◑ ○ ○ ○ ○ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ Cost ● ○ ○ ○ ○ ◑ ○◑● ○ ◎ ○ ○ ◉ ○ ○◑ ◑ ○◑ ◑ ◑ ◑ ◑ ◉ ○ ◉ TBC ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◑ Promotability Synergies ◉ ◉ ◉ ○ ○ ◎ ○◎ ○ ◎○ ◎ ◎ ◎ ◎ ◉ ◉ ◉ ◎ ◉ ◎ ◉ ◎ ○ ○ ○ ○ ○ ○ ◎ ○ ○ ○ ○ ○ ○ ○ ○ Customer preference ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ◑r ● ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◎ ◎ ◎ ◎ ◎ Local acceptability ◑r ◑r ◑r ○ ◑r ◑r ○ ○ ◑r ◑ ◑ ◑ ● ● ● ● ● ● ● ● ◑ ○ ◑r ◑r ○ ◑r ○ ○ ◑r ○ ○ ○ ○ ○ ○ ○ Regulatory acceptability ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◎ ◑r ○ ◑r ◉ ◉ ◉ ◉ ◉ Wider stakeholder acceptability ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑r ○ ◑r ○ ○ ○ ○ ○ ○ ○ ◑r ◉ ◉ ◉ ◉ ◉ Flexibility Lead time ○ ○ ○ ○ ○ ◑ ○◑ ○ ○◑ ○ ○ ◎ ● ● ● ● ● ● ● ● ○ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ○ ○ ○ ○ Phasing ◑ ◑ ◑ ○ ◑ ◑ ◑ ○ ◑ ◑ ◑ ○ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○ ◑ ○ ○ ○ ○ ◑ ○ ○ ◎ ◎ ◎ ◎ ◎ Adaptability ◎ ◎ ◉ ○ ○ ○ ○ ○ ○ ◎ ◎ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◉ ◉ ◉ ◉ ◉ Ramp-up ◎ ◎ ◎ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ○ ○ ○ ○ ◎ ◎ ○ ◎ ◎ ◑ ◑ ◑ ◑ ◑ Deliverability Constructability ○ ○ ○ ○ ◑r ◑r ○ ○ ◑r ◑r ◑r ○ ◑ ◑ ◑ ◑ ●r ●r ●r ●r ◑r ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ◑ ◑ ◑ ◑ ◑ Operability ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ● ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑ ◑r ◑r ○ ○ ○ ○ ◑r ◑r ◑r ◑r ◑r ◑r Dependencies ◑ ◑ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ◑ ◑ ◑ ◑ ◑ Data confidence ◑r ◑r ◑r ○ ○ ○ ○ ○ ○ ◑r ◑r ◑r ○ ○ ○ ○ ◑r ◑r ◑r ◑r ○ ◑r ○ ○ ◑r ◑r ○ ◑r ○ ◑r ◑r ◑ ◑ ◑ ◑ ◑ Resilience Climate change ◎ ◎ ◎ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◎ ◎ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◉ ◉ ◉ ◉ ◉ ◑ ◎ ◑ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Severe drought ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◑ ◑ ◑ ◑ ◑ ◑ ◎ ◑ ◑r ○ ○ ○ ○ ○ ○ ◑ ◑ ◑ ◑ ◑ Resource predictability ◑ ◑ ● ○ ○ ○ ○ ○ ○ ○ ○ ○ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◎ ◎ ◎ ◎ ◎ ○ ◎ ○ ◎ ◑r System outage ◑ ◑ ● ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ● ◎ ◉ ◉ ◉ ◎ ◉ ◎ ◉ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Other ‘failure modes’ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○ ○ ◑ ○ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ○ ○ ○ ○ ○ Screening decision     ✖  ✖ ✖ ✖   ✖ ✖    ✖ ✖ ✖ ✖                

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5.4.1 Scenario analysis

In undertaking the fine screening of potential WRMP19 water resource options a simple scenario analysis has been conducted that identifies combinations of water supply options that could meet the nominal 800Ml/d deficit. Seven scenarios have been identified that would allow for and accommodate any two of the following events occurring:  Teddington Weir (Mogden effluent transfer) direct river abstraction option is unavailable (e.g. because adverse navigation impacts are found to be significant)  Severn Thames Transfer option is unavailable (e.g. due to insurmountable concerns regarding invasive species transfer)  Water reuse options are unavailable (e.g. due to public acceptability)  New reservoir option is unavailable (e.g. due to failure to secure planning consent)

The water resource options that feature in the scenario analysis have been selected broadly on the basis of least cost, taking account of the assessed need for a delivery solution that can supply SWOX (either the STT or Abingdon reservoir) early in the planning period, but also recognising that a large resource option is likely to be required for the London WRZ before the Abingdon reservoir option came on stream due to its expected lead time. Options that have been screened out for reasons other than cost (Lower Lee DRA and the unblended Crossness Desalination option) have been excluded from the scenario analysis. The results of the analysis are presented in Figure 5.2. The purpose of this “What If” analysis is to ensure that sufficient options are included on the Constrained List to best account for and accommodate key future risks that could adversely affect the programme. The analysis is not in any way intended to pre-judge the programme appraisal work, for which sophisticated evaluation and visualisation tools have been developed by Thames Water.

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Figure 5.2: “What If” analysis to support fine screening

Indicative order of option selection

Scenario 1st 2nd 3rd 4th 5th 6th

Reuse

Reservoir

New New

STT

DRA Teddington Option GW / Catchm't Mgmt Teddington DRA Reuse Deephams Abingdon 75 Mm3 STT 500 Desal Beckton 150 1 ✔ ✔ ✔ ✔ DO 40 268 58 153 213 142 Cumulative DO 40 308 366 519 732 874 Option GW / Catchm't Mgmt Reuse Deephams Desal Beckton 150 Abingdon 150 Mm3 Desal Crossness 150 Reuse Beckton 150 2 ✖ ✖ ✔ ✔ DO 40 58 142 287 138 138 Cumulative DO 40 98 240 527 665 803 Option GW / Catchm't Mgmt Reuse Deephams STT 500 Desal Beckton 150 Desal Crossness 150 Reuse Beckton 300 3 ✖ ✔ ✖ ✔ DO 40 58 213 138 138 268 Cumulative DO 40 98 311 449 587 855 Option GW / Catchm't Mgmt STT 500 Abingdon 150 Mm3 Desal Beckton 150 Desal Crossness 150 4 ✖ ✔ ✔ ✖ DO 40 213 287 138 138 Cumulative DO 40 253 540 678 816 Option GW / Catchm't Mgmt Teddington DRA Reuse Deephams Desal Beckton 150 Desal Crossness 150 Reuse Beckton 300 5 ✔ ✖ ✖ ✔ DO 40 268 58 138 138 138 Cumulative DO 40 308 366 504 642 780 Option GW / Catchm't Mgmt Teddington DRA Abingdon 150 Mm3 Desal Beckton 150 Desal Crossness 150 6 ✔ ✖ ✔ ✖ DO 40 268 287 138 138 Cumulative DO 40 308 595 733 871 Option GW / Catchm't Mgmt Teddington DRA STT 500 Desal Beckton 150 Desal Crossness 150 7 ✔ ✔ ✖ ✖ DO 40 268 213 138 138 Cumulative DO 40 308 521 659 797 The impact of increasing salinity in the Thames Estuary during severe drought may limit the total deployment of desalination and reuse options, potentially impacting scenario 3.

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5.4.2 Rejection reasoning

The reasons for rejecting water resource options at the fine screening stage are summarised below.

5.4.2.1 Mogden water reuse

Mogden water reuse is screened out at the fine screening stage on the ground that it is mutually exclusive of the Teddington Direct River Abstraction option that is dependent on Mogden effluent to substitute the flows abstracted at Teddington. The Teddington DRA option performs significantly better than Mogden reuse against the cost dimension. The Mogden reuse option performs better on constructability, but this material risk is considered likely to be reducible with further development of the Teddington DRA option. If obstacles were to arise that prevented Teddington DRA from proceeding, then Mogden reuse should be reviewed. As regards potential adverse impacts on navigation of the Thames Tideway, this possibility, if any, would affect the integrity of both the Teddington DRA option and the Mogden reuse option equally.

5.4.2.2 Kempton reuse

The Kempton reuse option is a black water reuse option that intercepts sewage from the South Sewer into Mogden. As with the Mogden reuse option, it is mutually exclusive of the Teddington DRA option, which performs significantly better than Kempton reuse against the cost dimension.

5.4.2.3 Crossness reuse

Deephams Sewage Treatment Works has been identified as the optimum potential site for a first water reuse plant for London. The main reason for this is that the other reuse options require substantial water conveyance infrastructure that would be a sunk cost if Thames Water were to decide at a later date either not to expand water reuse further (for example because innovation in desalination technologies made desalination more competitive), or if a Deephams plant were to demonstrate that direct reuse is acceptable in terms of drinking water safety.

The capacity of reuse at the Deephams site is limited to approximately 60Ml/d and Beckton has been identified as the next best site to follow on for any subsequent large scale development of water reuse. It is envisaged that indirect reuse at Beckton would require the construction of a conveyance tunnel from Beckton to King George V Reservoir, while direct reuse would require a tunnel from Beckton to Coppermills WTW for blending. The water conveyance distance whether to King George V Reservoir or to Coppermills WTW is greater from Crossness than it is from Beckton.

Crossness reuse has been rejected on the basis that there are more water reuse options than could reasonably be required over the planning horizon and it is the least favourable reuse option measured against the cost dimension on the Feasible List. The scenario analysis in section 5.4.1 does not envisage any circumstances where Deephams, Beckton and Crossness reuse could all be required.

A further factor in the assessment is the poor performance of water reuse against the flexibility dimension and, in particular, it offers material dis-benefits against the ramp-up sub-dimension. A ramp-up time of eight weeks is estimated for water reuse using Reverse Osmosis from a ‘care and maintenance’ state, which would be employed for nine months of the year. The long ramp up time would substantially reduce the benefit of the reuse options if ramp-up were not commenced early enough to make the option available when required, or if ramp-up took longer than expected.

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Associated with the limitations imposed by ramp-up time and their consequential implications for the availability, or not, of water supply, both desalination and water reuse have been assessed as offering material dis-benefits against the following resilience sub-dimensions:  System outage: The ramp up times required for bringing a reuse water supply on-stream mean that when the reuse resource is in a ‘care and maintenance’ state it can provide limited benefit in dealing with unplanned outage events when they occur.

 Other failure modes: Thames Water’s experience at the Gateway Desalination plant has demonstrated that Reverse Osmosis technology, which is also currently proposed for water reuse, can be unreliable in operation and also subject to ramp-up delays.

Thames Water has confirmed that it considers that the cumulative effect of exposure to these resilience risks would be unacceptable if all desalination and reuse options at both Beckton and Crossness were developed using Reverse Osmosis technology.

Under prolonged low River Thames flows there is pattern of saline ingress up the Thames Tideway until flushed out by high river flows. This is a normal seasonal estuarine process. The operation of a water reuse scheme when required can be expected to coincide with these low flow periods and exacerbate this normal pattern leading to a noticeable change in the salinity regime of the middle Tideway after a period of c.100 days continuous operation. The extent of this risk is dependent on the scale of the reuse schemes and the sensitivity of environmental receptors, including estuarine ecology, both to changes in saline ranges and risk of changed patterns of fine sediment deposition within the estuary. A singular reuse scheme would associate with moderate risks to the estuary (where the baseline is already modified by the Gateway desalination plant) and multiple reuse schemes in the middle Tideway may increase this risk to major. This is subject to further consideration of potentially sensitive receptors in the middle Tideway.

On these cumulative grounds the Crossness reuse option has not, therefore, been carried forward to the Constrained List.

5.4.2.4 New reservoirs at Chinnor and Marsh Gibbon

Three sites for new reservoir development were included on the Feasible List at Abingdon (up to 150 Mm3), Chinnor (up to 50 Mm3) and Marsh Gibbon (up to 75 Mm3). The fine screening assessment of these options has found that the Marsh Gibbon and Chinnor sites perform less well than the Abingdon site across the environment & social, cost and deliverability dimensions.

The Marsh Gibbon and Chinnor sites (up to 50 Mm3) and the Marsh Gibbon site (up to 75 Mm3) perform less well than the Abingdon site in respect of their comparative environmental performance. The Marsh Gibbon site performs less well than both of the other two sites in landscape terms due to the loss of characteristic ridge and furrow field patterns. The Chinnor site performs less well than both of the other sites in respect of its impact on visual amenity. Lastly, both the Chinnor and the Marsh Gibbon sites perform less well than the Abingdon site in respect of significant adverse effects on recreational facilities with both sites adversely impacting on national trails.

The main reasons for the higher costs associated with the Chinnor and Marsh Gibbon sites compared with the equivalent Abingdon options are:  The requirement for substantially longer water intake pipelines to the reservoirs (3km, 19km and 32km for Abingdon, Chinnor and Marsh Gibbon respectively);

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 More costly and extensive infrastructure to convey flows from emergency drawdowns to the River Thames from Chinnor and Marsh Gibbon compared with Abingdon. By reason of the much greater distance of Chinnor and Marsh Gibbon from the River Thames, the water must either be conveyed in new pipelines / channels or be first attenuated in a flood storage basin prior to discharge into existing small local watercourses.  Lower earthworks quantities for Abingdon than for the Chinnor and Marsh Gibbon sites due to the Chinnor site and, more particularly, the Marsh Gibbon site, being more physically constrained. In addition the Chinnor site is more steeply sloping than the other two sites.

An assessment has also been conducted to compare the costs of phased reservoir development at the Abingdon site against development of an equivalent volume of storage at multiple sites. The following combinations were considered:  50 Mm3 at Abingdon, 50 Mm3 at Chinnor and 30 Mm3 at Marsh Gibbon  50 Mm3 at Abingdon, 30 Mm3 at Chinnor and 50 Mm3 at Marsh Gibbon  Abingdon first phase of 80 Mm3 followed by second phase of 42 Mm³

The assessment concluded that phased development on multiple sites would be approximately 50% more costly than phased development on an individual site. The costs for phased development at Abingdon are substantially lower as not only are the costs for development at the other sites more costly (as set out above) but also there is a significant amount of infrastructure that need not be duplicated in successive phases where development is undertaken on a single site including intake, river-reservoir conveyance (tunnel and pumping station) and material handling facilities such as railway sidings, work sites and stockpiling areas. Furthermore, some infrastructure such as floodzone reprovisioning, service and watercourse diversions and habitat creation can be more effectively completed within Phase 1 of a dual phase site, compared to completion on numerous occasions or sites.

Once the potential for reservoir development at Abingdon site had been fully utilised, consideration could then be given to further reservoir development at the Chinnor and Marsh Gibbon sites. However, the “what-if” analysis conducted in this report suggests that other resource types (notably desalination and reuse) are expected to be more cost effective than further reservoir development at Chinnor and/or Marsh Gibbon.

The Marsh Gibbon and Chinnor reservoir sites also perform less well than Abingdon as regards Deliverability against the constructability sub-dimension. Additional enabling infrastructure would be required for Marsh Gibbon and / or Chinnor due to their respective locations remote from the abstraction location and remote from a suitable watercourse for the discharge of water during emergency drawdown.

5.4.2.5 Desalination at Crossness (unblended) with direct supply to Northumberland Heath A desalination water resource option at Crossness was developed that would continuously supply Northumberland Heath service reservoir with desalinated water. The option was further developed as it required only relatively short water conveyance infrastructure compared to the options for blending at Coppermills WTW; and by operating continuously, it would not have led to a change in water quality (and triggered consequential customer complaints) that would be associated normally with an unblended option that is operated intermittently (e.g. as a drought scheme). However, the option has been fine screened out due to its substantial dis-benefits when tested against the promotability, deliverability and resilience dimensions, as shown in assessment Table B.5 in Appendix B.

The grounds for dismissing the option are summarised below:  Desalination plant outage events would result in changes in water quality as the supply would need to revert to water supplied from the ring main via Honor Oak. TW’s experience is that these changes in water quality would lead to a significant increase in customer water quality complaints.

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This is a substantial disbenefit associated with the customer acceptability sub-dimension of promotability.  Operation of the Crossness plant without water for blending would mean that the full capacity of the plant may not generally be utilised, as the Crossness plant is less suitable than conventional water resources for supplying other zones (due to the impact of changing water quality). The assumed Deployable Output is based upon forecast annual average demand on Northumberland Heath in 2070 of 65Ml/d, but the current average demand on Northumberland Heath is only 50Ml/d meaning that up to 15Ml/d may be unutilised in the short-medium term. This is a substantial disbenefit when assessed against the operability sub-dimension of deliverability.  Desalination resources contribute less to system resilience than surface water resources which can be treated at alternative conventional WTW in the event of a treatment outage. Furthermore, for the unblended Crossness desalination option, the works could not be used to support outage at another works without a change in water quality and the resolution of likely consequential customer complaints. This is a substantial disbenefit measured against the system outage sub- dimension of resilience.

5.5 Next steps for water resource options passing fine screening

5.5.1 Deephams reuse

Deephams Sewage Treatment Works has been identified as the preferred site for initial development of a water reuse supply for London. A plant capacity of up to 60Ml/d is assumed. Further work is required to confirm the maximum capacity of reuse that is acceptable. The treatment processes proposed include Ultrafiltration membranes, Reverse Osmosis and Advanced Oxidation Processes for treatment of Deephams final effluent. At feasibility stage a discharge location at the intake of King George V was proposed to maximise retention time. Two alternatives for conveyance to the intake of King George V reservoir are envisaged at the conceptual design stage: 1. Pipeline from Deephams to the King George V intake for Deephams reuse flows only 2. Discharge from the Deephams reuse option into the proposed Thames Lee Tunnel extension that would run from Lockwood Shaft, past the Deephams site, to the King George V intake.

5.5.2 Beckton reuse

Three scenarios are envisaged for the Beckton water reuse option: 1. Development as an indirect reuse option using treatment processes including Reverse Osmosis; 2. Development as an indirect reuse option using a lower level of treatment; and 3. Development as a direct reuse option using treatment processes including Reverse Osmosis

The conceptual design of the option is being prepared on the basis of the first scenario above, recognising that the second and third scenarios may offer future opportunities. For the indirect reuse scenarios it is assumed that conveyance of the raw water would be to Lockwood shaft from where it would be forwarded to the intake of King George V reservoir through the proposed Thames-Lee Tunnel extension. Discharge at the inlet to the King George V reservoir maximises dilution and retention time, but the capability to discharge directly into the King George V reservoir should also be provided. Consideration will be given, in the alignment of the conveyance at the conceptual design stage, to the potential need to discharge via Coppermills WTW if direct reuse were to be considered acceptable in future.

Whilst land has been identified for the reuse plant on the Beckton STW site, Thames Water is now concerned that it may conflict with spatial requirements for the expansion of the sewage treatment works. Further work is being undertaken to identify a potential alternative site.

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5.5.3 Severn-Thames Transfer

It is proposed that 300, 400 and 500Ml/d Severn-Thames Transfer options should be developed at the conceptual design stage including a pipeline transfer from Deerhurst on the River Severn to Culham on the River Thames supported by:  15 Ml/d of Mythe licence transfer;  180 Ml/d of Vyrnwy releases;

Investigations also need to be completed to confirm the magnitude of natural environmental losses that are likely to occur as part of the transfer process.

5.5.4 Abingdon reservoir

The “What If” scenario analysis indicates that there are potential future scenarios where a large reservoir option might be required, if other options are prevented from progressing. However, development of a small reservoir on the site would potentially “sterilise” the site preventing a large reservoir from being constructed at a later date. It is therefore recommended that if small reservoirs are required then they should be designed so as to allow future expansion. The following reservoir options are proposed for development at the conceptual design stage.  Abingdon Reservoir single phase 75Mm3  Abingdon Reservoir single phase 100Mm3  Abingdon Reservoir single phase 125Mm3  Abingdon Reservoir single phase 150Mm3  Abingdon Reservoir two phase: 30Mm3 first phase followed by approximately 90Mm3 second phase  Abingdon Reservoir two phase: 70Mm3 first phase followed by approximately 50Mm3 second phase

The sizes proposed for the two phase options differ from those assumed at feasibility stage (see section 5.2.2) as further work has since been done taking account of more refined embankment profiles, borrow pit shapes and site specific geological conditions. The result of this work is that due to the dividing embankment profile and geological conditions the maximum reservoir volume that can be achieved on the Abingdon site for a phased option is approximately 120Mm3.

The following small single-phase reservoir sizes are screened out on the grounds that their development would prevent a large reservoir from being developed on the site.  Abingdon Reservoir single phase 30Mm3  Abingdon Reservoir single phase 50Mm3

Should a small reservoir be required (e.g. to supply the SWOX WRZ) then the first 30 Mm3 phase of the two phase 30Mm3 + 90 Mm3 would be more appropriate as it would not preclude subsequent expansion to supply London WRZ.

5.5.5 Teddington direct river abstraction

Direct river abstraction at Teddington, supported by the transfer of Mogden effluent, has passed the fine screening. It is proposed that the tertiary treatment at Mogden would operate continuously, giving the option a fast ramp-up time and providing environmental benefit at times when the transfer to Teddington is not operating. Work is ongoing to demonstrate the extent of any navigational impact on the Thames Tideway from reduced flows downstream of the Mogden discharge at Isleworth Ait and the environmental impacts.

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Whilst land has been identified for the treatment plant on the Mogden STW site Thames Water now consider that it may conflict with requirements for expansion of the sewage treatment works. Further work is being undertaken to identify a potential alternative site.

5.5.6 Beckton desalination

The option for development of a second 150Ml/d desalination plant at Beckton has passed the fine screening. It is proposed that the plant would operate at reduced output between May and June each year and would be in a “care and maintenance” mode for the remainder of the year if its water supply was not required. The option includes a tunnel conveyance from Beckton to Coppermills WTW for blending of desalinated water at Coppermills WTW. A potential opportunity associated with the option is that the tunnel could also be used to convey water from the existing Gateway desalination plant to Coppermills WTW which would improve blending and address concerns around change of water quality when the Gateway plant is operated at full capacity.

Whilst land has been identified for the desalination plant on the Beckton STW site Thames Water now consider that it may conflict with requirements for expansion of the sewage treatment works and proposed Thames crossing. Further work is being undertaken to identify a potential alternative site.

5.5.7 Crossness desalination

Land availability for an alternative treatment site on the north bank of the Thames estuary is expected to constrain future development of desalination. It is therefore proposed to develop up to 300Ml/d of additional treatment at the Thamesmead Industrial Estate Extension Site on the south bank of the Thames estuary, south of the Crossness STW. The site has outline planning permission for a three phase business park development.

There is a potential limiting factor on desalination capacities due to possible increased salinity levels in a given reach of the Tideway. A precautionary approach to the environmental assessment has been adopted that has resulted in a limit of 300 Ml/d of additional desalination capacity in any single reach of the River Thames, but subject to further analysis (i.e. estuarine modelling) it is expected that higher levels may be acceptable.

5.5.8 Groundwater options

The proposed next steps for those groundwater options passing fine screening are shown in Table 5.15.

Table 5.15: Proposed future work Option Proposed future work AR/ASR  SLARS operating strategy needs to be agreed with the Environment Agency to obtain their support Kidbrooke for the option. (SLARS1) AR Merton  SLARS operating strategy needs to be agreed with the Environment Agency to obtain their support (SLARS3) for the option.  Drilling and test pumping of the proposed Byegrove Road borehole to confirm the borehole yield, water quality and feasible recharge rate. AR Streatham  SLARS operating strategy needs to be agreed with the Environment Agency to obtain their support (SLARS2) for the option.  Given that the connection point for both abstraction and recharge for this option will be to the existing old 42 inch main, it is recommended that network modelling should be conducted in the framework of the Network Blueprint work package.

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Option Proposed future work  Drilling and test pumping of the proposed new borehole to confirm the source yield and feasible recharge rate. ASR South East  Access arrangements should be made to the existing on site borehole to assess headworks London condition and to allow monitoring of groundwater levels. (Addington)  Yield testing of the existing borehole is required to confirm aquifer properties and water quality in the confined LGS at this site.  Network modelling work should also be carried out to provide further information on whether the existing pumps are able to operate at their maximum efficiency. ASR Thames  Drilling and test pumping of a borehole to confirm the groundwater levels, borehole yield, water Valley/Thames quality and feasible recharge rate. Central GW – Addington  Drilling and test pumping of the proposed borehole to confirm the borehole yield and water quality.  It will be necessary to confirm whether land is available for purchase for the proposed boreholes. GW - Southfleet/  Test pumping to confirm abstraction rate and water quality from the boreholes. Greenhithe (new Confirm whether land is available for purchase for the new water treatment works at Southfleet. WTW) GW - London  Drilling and test pumping of the proposed borehole to confirm the borehole yield and, water quality. confined Chalk This information should be used to refine the design of the proposed WTW. (north)  It will be necessary to confirm whether land is available for purchase for the proposed WTW. North London  A discussion of the proposed licence trade needs to take place between the current owner and TW. Licence Trading This will be used to confirm the cost of the option.  An assessment of the borehole condition and headworks is also required.

5.5.9 Catchment management options The proposed next steps for the catchment management options is to develop the conceptual design reports to refine the costs and further develop the key components of the options.

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6 SWOX WRZ resource options

This section provides a summary of the feasibility reports and the fine screening of water resource options assessment for the Swindon and Oxfordshire (SWOX) Water Resource Zone grouped by option type. Options are assessed qualitatively against the six dimensions: Cost, Environmental and Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is presented for each option type together with the screening decisions.

6.1 Resource option types

The resource option types identified for the SWOX WRZ comprise:  New reservoirs  Raw water transfers;  Groundwater development - Aquifer recharge;  Groundwater development;  Direct river abstraction;  Removal of Deployable Output constraints;  Catchment management; and  Inter-zonal transfers.

6.2 Feasibility Report findings

6.2.1 New reservoirs

The new reservoir options have the potential to supply both London and SWOX. The options are therefore linked and so have been assessed together at feasibility stage. The options identified in the New Reservoir Feasibility Report are set out in Section 5.2.2.

6.2.2 Raw water transfers

The raw water transfer options have the potential to supply both London and SWOX. The options are therefore linked and so have been assessed together at feasibility stage. The options identified in the Raw Water Transfers Feasibility Report are set out in Section 5.2.3.

6.2.3 Direct river abstraction

The options identified in the Feasibility Report for direct river abstraction are listed in Table 6.1 below together with a summary of the status of the options.

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Table 6.1: SWOX options identified in the feasibility report for direct river abstraction Stage

Option Sub-option Capacity / DO 1 2 3 Comment River Thames 2a) Abstraction at 4.5 Ml/d ✖ The option has been rejected due Culham abstraction Culham transfer to to: Insufficient flow/ Abstraction Farmoor Reservoir licence restrictions and potential via a new pumping impact on downstream main abstractors. The benefit to SWOX produces equal detriment to London and zero net benefit. River Thames 2b) Abstraction at 4.5 Ml/d ✔ ✔ ✖ The option provides 6 Ml/d benefit Culham abstraction Culham, treatment for SWOX, but this is substantially and direct supply to offset by a 4Ml/d DO reduction for SWOX. London. Based upon the 2Ml/d net benefit the option becomes excessively costly and is rejected at Stage 3.

No options have been carried forward to the Feasible List.

6.2.4 Aquifer recharge

The aquifer recharge options identified in the groundwater feasibility report are listed in Table 6.2 below together with a summary of the status of the options.

Table 6.2: SWOX options identified in the feasibility report for aquifer recharge DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The option has been rejected due to concerns about:  Increased groundwater flooding at Latton; AR – Cricklade 3.1 10.0 ✔ ✖  Requirements for very high recharge pressures; and  Impacts on the Ampney Brook, River Churn and the River Coln during periods of abstraction.

Further explanation of reasons for rejection of water resource options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

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6.2.5 Groundwater development

The groundwater development options identified in the groundwater feasibility report are listed in Table 6.3 below together with a summary of the status of the options.

Table 6.3: SWOX options identified in the feasibility report for groundwater development DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The Environment Agency will not support an Woods Farm increase in abstraction licence at this location due licence 3.0 3.5 ✖ to concerns over the impact of the abstraction on increase the River Thames. This option is mutually exclusive of the Moulsford 1 option, which has been carried forward to the fine screening stage. The Moulsford option performs GW - South better on cost and there is also a risk of the South 2.0 3.5 ✔ ✔ ✔ Stoke 1 Stoke option derogating existing TW groundwater sources. Therefore, the South Stoke 1 option cannot was rejected at the validation stage (stage 4). The Environment Agency will not support a new GW - South licence in this location due to concerns over the Stoke 2 (with 5.0 10.0 ✖ potential deterioration of the Chiltern Scarp treatment) groundwater body and impacts on flows in the River Thames. This option is mutually exclusive of the South Stoke GW - 2.0 3.5 ✔ ✔ ✔ 1 option and has been carried forward to the fine Moulsford 1 screening stage. The Environment Agency will not support a new GW - licence in this location due to concerns over the Moulsford 2 5.0 7.5 ✖ potential deterioration of the Chiltern Scarp (with groundwater body and impacts on flows in the River treatment) Thames. Option not assessed as the deployable output Bibury source - - benefit has been delivered and incorporated into enhancement the baseline. The option has failed due to potential for a low yield River Marden 0.5 0.5 ✔ ✖ from the boreholes, concerns about water quality and the costs to investigate the yield. The Environment Agency concerns regarding the potential impacts of a groundwater abstraction on surface water means that any new abstraction licence would be subject to a HOF condition or may not be supported Cotswold Edge 1.0 1.0 ✖ There is also concern about the resilience of the aquifer to drought and uncertain thickness and structurally complex geology mean that the potential yield and success of a groundwater or artificial recharge/aquifer storage and recovery option is considered to be high risk.

As the South Stoke and Moulsford options are mutually exclusive only the Moulsford option has been taken forward to the fine screening stage. The option comprises:  Moulsford 1 Groundwater Scheme – Construction of one new abstraction boreholes on agricultural land in the unconfined Chalk adjacent to the existing Moulsford (Cow Lane) operational reservoir site. Water abstracted from the boreholes will be treated at the existing Cleeve water treatment works (WTW), with 0.6 km run to

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waste pipeline to the River Thames; and 1.5 km raw water pipeline between the boreholes and the WTW, which will pass beneath the River Thames. – This scheme would provide a likely DO benefit of 2 Ml/d average and 3.5 Ml/d peak.

Further explanation on reasons for rejection of groundwater options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

6.2.6 Removal of Deployable Output constraints

The options for removal of DO constraints identified in the groundwater feasibility report are listed in Table 6.4 below together with a summary of the status of the options.

Table 6.4: SWOX options identified in the feasibility report for removal of DO constraints DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The assessment of this option suggests that there could be potential issues with lowering pumps due to borehole verticality and water quality Ashton Keynes 0.0 1.6 ✔ ✔ ✔ impacts. Defining the feasibility and borehole pumps potential impacts associated with lowering the pumps in all five boreholes would require a significant amount of intrusive testing. Option failed since the cost to complete the investigation compared Witheridge Hill 0.6 0.6 ✔ ✖ with the potential deployable output borehole pumps benefit is too high.

The preferred removal of DO constraints option to be taken forward to the fine screening stage is therefore:  Ashton Keynes borehole pumps – Installation of new borehole pumps at a lower level than the current pumps to increase both average and peak source DO; – This option would provide a likely DO benefit of 0.0 Ml/d average and 1.6 Ml/d peak.

Further explanation on reasons for rejection of removal of DO constraints options is set out in the relevant Feasibility Report and will be summarised in the option Rejection Register.

6.2.7 Catchment management

The options identified in the Feasibility Report for catchment management are listed in Table 6.5 below together with a summary of the status of the options.

Table 6.5: SWOX options identified in the feasibility report for catchment management DO Stage* (Ml/d) Option 1 2 3 Comment Blockley <0.1 ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) Ml/d deployable benefit to be gained Childrey Warren 0.2 Ml/d ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) deployable benefit to be gained Dovedale <0.1 ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) Ml/d deployable benefit to be gained

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DO Stage* (Ml/d) Option 1 2 3 Comment Gatehampton 1.0 Ml/d ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) deployable benefit to be gained Lower Swell <0.1 ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) Ml/d deployable benefit to be gained Manor Road 0.2 Ml/d ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) deployable benefit to be gained Ashdown Park 0.3 ✔ ✔ ✔ (Groundwater) Upper Swell 0.2 ✔ ✔ ✔ (Groundwater) Marlborough 0.2 ✔ ✔ ✔ (Groundwater)

The options to be taken forward to the fine screening stage are therefore:  Ashdown Park (groundwater source) – Measures to address adverse water quality risks due to rising nitrate levels in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.3 Ml/d  Upper Swell (groundwater source) – Measures to address adverse water quality risks due to agricultural activity in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.2 Ml/d  Marlborough (groundwater source) – Measures to address adverse water quality risks due to agricultural activity in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.2 Ml/d

6.2.8 Internal inter-zonal transfers

The options identified in the feasibility report for inter-zonal transfers are listed in Table 6.6 below together with a summary of the status of the options.

Table 6.6: SWOX options identified in the feasibility report for inter-zonal transfer of treated water Stage Comment

Option Sub-option Capacity / DO 1 2 3 SWA to Transfer water from Not defined SWA is forecasted to be in deficit at the SWOX Hambleden WTW to end of the planning horizon and the Long Crendon SR or proposed GW source developments are ✖ Nettlebed SR in the South East corner, mostly eligible for an intercompany water transfer to South East Water Henley to New Farm SR to 2.5 Ml/d Mutually exclusive of Henley to SWA SWOX Nettlebed service ✔ ✔ ✔ (Sheeplands WTW to Hambleden reservoir WTW) Henley to New Farm SR to 4.1 Ml/d The option requires significant network SWOX Nettlebed service reinforcement upstream and large reservoir conveyance to ensure availability of ✔ ✖ water at New Farm SR (transferring water from Sheeplands to Harpsden WTW and constructing new storage and

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Stage Comment

Option Sub-option Capacity / DO 1 2 3 new pumps along the route). The 2.46 Ml/d variant is preferred. Kennet Valley Pangbourne WTW to 1.4 Ml/d AIC is twice the value of the larger ✔ ✔ ✖ to SWOX Cleeve WTW variants for same transfer Kennet Valley Pangbourne WTW to 8.3 Ml/d ✔ ✔ ✔ to SWOX Cleeve WTW Kennet Valley Pangbourne WTW to 12.8 Ml/d ✔ ✔ ✔ to SWOX Cleeve WTW Kennet Valley Pangbourne WTW to 16.9 Ml/d Long conveyance length (>20 km in to SWOX Cleeve WTW total), significant pumping head and construction complexity (many road crossings and routing in built-up areas). Additionally, major network ✔ ✖ reinforcements required upstream to ensure water availability at Pangbourne WTW and the option is dependent on the implementation of Henley to Kennet Valley transfer

Assessment of the internal inter-zonal transfer options will be reviewed after the April 2017 update of the Supply/Demand Forecast.

A brief description of the options that are currently expected to be carried forward from the feasibility report is provided below.  Kennet Valley to SWOX (CON-TWT-KEN-8.31-SWX-CLV): – Transfer 8.3 Ml/d treated water from Pangbourne WTW (Kennet Valley) to Cleeve WTW (SWOX) – Some reinforcements upstream to ensure water availability at Pangbourne WTW (new pump in Fobney WTW and reinforcement of the pipeline running from Fobney WTW to Tilehurst SR). The reinforcement of the Fobney to Tilehurst link aims to relieve water stress at Pangbourne WTW and therefore ensure greater water availability at the starting point of the transfer.  Kennet Valley to SWOX (CON-TWT-KEN-12.81-SWX-CLV): – Transfer 12.8 Ml/d treated water from Pangbourne WTW (Kennet Valley) to Cleeve WTW (SWOX) – The option assumes a new resource at Mortimer (Groundwater peak abstraction 4.5 Ml/d) which transfers water to Early SR and in turn relieves water stress at Pangbourne WTW  Henley to SWOX (CON-TWT-HEN-2.46-SWOX-NET): – Transfer 2.5 Ml/d from New Farm SR to Nettlebed SR.

6.2.9 Inter-company transfers

The options identified in the Feasibility Report for inter-zonal transfers are listed in Table 6.7 below together with a summary of the status of the options.

Table 6.7: SWOX options identified in the feasibility report for inter-company transfer of treated water Stage Comment

Option Sub-option Capacity / DO 1 2 3 Wessex to Charlton WTW to 2.9 Ml/d Option rejected due to the long SWOX Minety SR and from conveyance length ✔ ✖ there to Blusdon SR in South Swindon Wessex to Charlton WTW to 2.9 Ml/d Mutually exclusive to Flaxlands SWOX Minety SR and from option, which is preferred due to SR there to Asthon Keynes ✔ ✔ ✖ end point, rather than WTW end WTW in South point. Swindon

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Stage Comment

Option Sub-option Capacity / DO 1 2 3 Wessex to Charlton WTW to 2.9 Ml/d Awaiting information on bulk supply SWOX Minety SR and from Awaiting charge ✔ ✔ there to Flaxlands SR Info. in South Swindon

6.3 Exclusivities/Interdependencies

The Moulsford, South Stoke and Woods Farm schemes all carry some degree of interdependence and cannot all be delivered together due to resource availability. As the Woods Farm option has failed at Stage 1 of the feasibility screening, only one of South Stoke and Moulsford options can be progressed. Moulsford has been chosen over South Stoke at the validation stage of the feasibility screening as the AIC value is lower and there is a risk that an abstraction at South Stoke will derogate from other TW groundwater abstractions in the vicinity.

The Henley to SWOX inter-zonal transfer option is mutually exclusive of the Henley to SWA inter-zonal transfer option.

The 12.8 Ml/d interzonal transfer option from Kennet Valley to SWOX is dependent on the Mortimer 4.5 Ml/d groundwater option in Kennet Valley going ahead.

6.4 Fine screening assessment

Each of the feasible options described above has been assessed against the six dimensions and associated sub-dimensions set out in Section 3 of this report. The assessment for each option type is set out, with commentary, in Appendix C and summarised in Table 6.8 below24.

Given the scale of the deficit forecast for SWOX it is important to recognise that the small options alone would not be sufficient to meet it. It is therefore important that the Constrained List includes large water resource options that could supply SWOX. The screening decisions for raw water transfer transfers and new reservoir water resource options reflect those for the London WRZ.

24 Assessment of the internal inter-zonal transfer options will be reviewed after the April 2017 update of the Supply/Demand Forecast.

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Table 6.8: Water resource element screening summary – SWOX WRZ Dimension / Sub-dimension Severn-Thames Removal of Transfer Internal inter-zonal River Regulation Reservoir Groundwater DO Catchment Management transfer Deerhurst to Culham constraints pipeline

Ashdown Upper Marlborough

to to 195 Ml/d support Park Swell

from (Vyrnwy and Abingdon Marsh Gibbon Chinnor Moulsford 1

SWOX SWOX

Kennet Ashton Ashton

Mythe) Keynes

Valley to Valley

Henley

125- 75- 300 400 500 <125 >225 <75 75-174 <75 225 174 2.0 Ml/d 1.6 Ml/d 2.5 Ml/d 12.8 Ml/d 0.3Ml/d 0.2 Ml/d 0.2 Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d

Ml/d Phased Ml/d Env & Social SEA ○◑ ○◑ ○◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ○◑ ○○ ○◑ ○◑ ◎○ ◎○ ◎○

HRA ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ WFD ◑r ◑r ◑ ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ○ ○ ○ ○ ○ ○ r r r r r r Cumulative effects ○ ◑ ◑ ○ ◑ ◑ ◑ ○ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ Cost

◎ ◎ ◎ ○ ○◑ ◑ ○◑ ◑ ◑ ◑ ◑ ◉ ◉ ◉ ◉ ◉ ● ◉ Promotability Synergies ◉ ◉ ◉ ◎ ◉ ◉ ◉ ◎ ◉ ◎ ◉ ○ ○ ○ ◎ ○ ○ ○ r r Customer acceptability ○ ○ ○ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○ ◑ ◑ ◎ ◎ ◎ r r r r r r Local acceptability ◑ ◑ ◑ ● ● ● ● ● ● ● ● ◑ ○ ◑ ◑ ○ ○ ○ r Regulatory acceptability ◑r ◑r ◑r ○ ○ ○ ○ ○ ○ ○ ○ ◑ ◑r ◑r ◑r ◉ ◉ ◉ Wider stakeholder acceptability ◑r ◑r ◑r ◑r ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○ ◎ ○ ◉ ◉ ◉ Flexibility Lead time ○ ○ ○ ● ● ● ● ● ● ● ● ◎ ◎ ◎ ◎ ○ ○ ○ Phasing ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○ ◑ ○ ◎ ◎ ◎ Adaptability ◎ ◎ ◉ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ○ ◎ ◎ ◉ ◉ ◉ Ramp-up ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◑ ◑ ◑ Deliverability r r r r Constructability ○ ○ ○ ◑ ◑ ◑ ◑ ● ● ● ● ○ ○ ○ ○ ◑ ◑ ◑ Operability ◑r ◑r ◑r ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ◑r ◑r ◑r ◑r Dependencies ◑ ◑ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑ ◑ ◑ r r r r r r r r r r r Data confidence ◑ ◑ ◑ ○ ○ ○ ○ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ Resilience Climate change ◎ ◎ ◎ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◑ ◑ ○ ○ ◎ ◎ ◎ Severe drought ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◑ ◑ ◎ ○ ○ ○ ○ Resource predictability ◑ ◑ ● ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ○ ○ ◎ ◎ ◑ ◑ ◑ System outage ◑ ◑ ● ◎ ◉ ◉ ◉ ◎ ◉ ◎ ◉ ○ ○ ◎ ◎ ○ ○ ○ Other ‘failure modes’ ◑ ◑ ◑ ○ ○ ○ ◑ ○ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ Screening decision    ✖    ✖ ✖ ✖ ✖      ✖ 

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6.4.1 Rejection reasoning

6.4.1.1 New reservoirs at Chinnor and Marsh Gibbon

Three sites for new reservoir development were included on the Feasible List at Abingdon (up to 150 Mm3), Chinnor (up to 50 Mm3) and Marsh Gibbon (up to 75 Mm3). The fine screening assessment of these options has found that the Marsh Gibbon and Chinnor sites perform less well than the Abingdon site across the environment & social, cost and deliverability dimensions. Further information on the rejection reasoning for the Marsh Gibbon and Chinnor sites can be found in Section 5.4.2.4.

The following small Abingdon single-phase reservoir sizes are screened out on the grounds that their development would prevent a large reservoir from being developed on the site.  Abingdon Reservoir single phase 30Mm3  Abingdon Reservoir single phase 50Mm3

Should a small reservoir be required (e.g. to supply the SWOX WRZ) then the first 30 Mm3 phase of the two phase 30Mm3 + 90 Mm3 would be more appropriate as it would not preclude subsequent expansion to supply London WRZ.

6.4.1.2 Catchment management option for Upper Swell

This option has been screened out at the fine screening stage as the costs required to deliver the small deployable output benefit show a substantial disbenefit.

6.5 Next steps for water resource options passing fine screening

6.5.1 Groundwater development

The proposed next steps for those groundwater options passing fine screening are shown in Table 6.9.

Table 6.9: Proposed future work Option Proposed future work GW - Moulsford 1 Drilling and test pumping of the proposed borehole to confirm the borehole yield and water quality. Ashton Keynes Use results from operational tests to obtain a hydrogeological deepest advisable pumping water level borehole pumps and reassess the current DO curve at the source.

6.5.2 Catchment management options The proposed next steps for the Ashdown Park and Marlborough catchment management options is to develop the conceptual design reports to refine the costs and further develop the key components of the options.

6.5.3 Inter-company transfer options

Allowance has been made for the cost of Wessex Water network reinforcements to facilitate the Minety- Flaxlands transfer, but this needs to be confirmed with Wessex Water. Bulk supply charges by Wessex Water have still to be identified. This needs to be addressed before the inter-company transfers can be considered on the same basis as other water resource options.

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7 SWA WRZ resource options

This section provides a summary of the feasibility reports and fine screening assessment for the Slough, Wycombe and Aylesbury (SWA) Water Resource Zone grouped by water resource option type. Options are assessed qualitatively against the six dimensions: Cost, Environmental and Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is presented for each option type together with the screening decisions.

7.1 Resource option types

The resource option types identified for the Slough, Wycombe and Aylesbury WRZ comprise:  Aquifer storage and recovery;  Groundwater development;  Release of Deployable Output constraints; and  Inter-zonal transfers.

7.2 Feasibility report findings

7.2.1 Aquifer storage and recovery

The aquifer storage and recovery options identified in the Groundwater Feasibility Report are listed in Table 7.1 below together with a summary of the status of the options.

Table 7.1: SWA options identified in the feasibility report for aquifer storage and recovery DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment Option failed as investigations indicated that the Hampden Bottom- Lower Greensand aquifer, which was proposed 3.0 7.5 ✔ ✖ Wendover as the target aquifer for ASR, was thin or missing at the identified site.

No options have been carried forward to the Feasible List.

7.2.2 Groundwater development

The groundwater development options identified in the Groundwater Feasibility Report are listed in Table 7.2 below together with a summary of the status of the options.

Table 7.2: SWA options identified in the feasibility report for groundwater development DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment

GW – Datchet 1.6 55.7 ✔ ✔ ✔

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DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The EA will not support an abstraction licence at this location, which is in a Poor Remenham 10.0 10.0 ✖ status groundwater body.

The EA will not support an abstraction licence at this location, which is in the GW – West 10.0 15.0 ✖ South West Chilterns Poor status Marlow groundwater body and due to impacts of the abstraction on the River Thames. The EA will not support an increase in the abstraction licence at this location as the abstraction is from the South West Bourne End 0.0 9.3 ✖ Chilterns groundwater body, which has a (Marlow East) Poor status and abstraction would be at the expense of flows in the River Thames. The EA will not support an increase in abstraction licence at this location as the abstraction is from the South West Medmenham 2.7 0.0 ✖ Chilterns groundwater body, which has a Poor status and abstraction would be at the expense of flows in the River Thames. The EA will not support an increase in abstraction licence at this location due to Taplow 15.9 5.1 ✖ concerns about the impacts on the Maidenhead Chalk groundwater body and flows in the River Thames.

A brief description of the groundwater development options that have been carried forward to the fine screening stage is provided below.  Groundwater Datchet – Redevelopment of two existing boreholes. The scheme also includes upgrade of an existing WTW. No licence change would be required. – The DO benefit to SWA WRZ would be 6.0 Ml/d peak and 1.6 Ml/d average.

7.2.3 Removal of Deployable Output constraints

The options for removal of DO constraints identified in the groundwater feasibility report are listed in Table 7.3 together with a summary of the status of the options.

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Table 7.3: SWA options identified in the feasibility report for release of DO constraints DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment Once the pump is replaced in ABH9 at Datchet and the borehole is brought back into supply, the replaced main can be tested in order to remove the network RC - Datchet Main constraint. 1.1 1.1 ✔ ✔ ✔ Replacement It is assumed that the main will require further testing to ensure that it can cope with pressures required to transfer the maximum peak licence quantity of 31.4 Ml/d from Datchet and Eton. It is not considered to be cost-effective to deliver the potential volume benefit without an increase in licence. However, the EA RC - Hampden 0.0 0.8 ✖ will not support an increase in licence at this Disinfection Upgrade location due to concerns about the impacts of the abstraction on headwater flows in the River Misbourne. If the removal of constraints – Datchet main replacement option cannot be delivered, the Eton removal of 1.6 1.6 ✔ ✔ ✔ full potential of the Eton removal of constraints to DO constraints to deployable output option cannot be realised.

A brief description of the removal of DO constraints options that have been carried forward to the fine screening report is provided below.  RC - Datchet Main Replacement – A main in the Slough, Wycombe and Aylesbury water resource zone that was susceptible to bursting was replaced with a ductile iron main to enable higher pressures to be achieved. Such an increase will require sign-off of a risk assessment and the monitoring of operating pressures – The DO benefit to SWA WRZ would be 1.1 Ml/d average and peak.  Eton removal of constraints to DO – Replacement of the existing membrane treatment plant, which has a capacity of 6.7 Ml/d, with a new plant capable of treating 8.7 Ml/d, which is the licensed abstraction quantity at Eton. – The DO benefit to SWA WRZ would be 1.6 Ml/d average and peak allowing for process losses.

7.2.4 Internal inter-zonal transfers

The options identified in the Feasibility Report for inter-zonal transfers are listed in Table 7.4 below together with a summary of the status of the options.

Table 7.4: SWA options identified in the feasibility report for internal inter-zonal transfer of treated water Stage Comment

Option Sub-option Capacity / DO 1 2 3 SWOX to Rejected on the basis that SWOX is SWA ✖ forecasted to be in deficit throughout the whole planning horizon Henley to Transfer water from 4.13 Ml/d Mutually exclusive of Henley to SWOX SWA Sheeplands WTW to ✔ ✔ ✔ (CON-TWT-HEN-2.46-SWX-NET). Hambleden WTW

Assessment of the internal inter-zonal transfer options will be reviewed after the April 2017 update of the Supply/Demand Forecast.

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A brief description of the internal inter-zonal transfer option that has been carried forward to the fine screening report is provided below.  Henley to SWA (CON-TWT-HEN-4.13-SWA-HAM): – Transfer 4.13 Ml/d from Sheeplands WTW to Hambleden WTW

7.3 Exclusivities/Interdependencies

GW – Datchet and Eton removal of constraints to DO are reliant on the delivery of the RC – Datchet main replacement option to realise their DO benefits. The combined total DO benefit for all three options is 9.3 Ml/d. All three options should be delivered together.

The Henley to SWA internal inter-zonal transfer option is mutually exclusive of the Henley to SWOX option.

7.4 Fine screening assessment

Each of the feasible water resource options described above has been assessed against the six dimensions and associated sub-dimensions set out in Section 3 of this report. The assessment for each option type is set out, with commentary, in Appendix D and summarised in Table 7.5 below. All four options carried forward from the feasibility stage have passed the fine screening stage and are included in the Constrained List.

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Table 7.5: Water resource element screening summary – SWA WRZ Dimension / Sub-dimension Groundwater Removal of DO constraints Internal Inter-zonal development transfers

Datchet Main Datchet Eton Henley to SWA Replacement 1.6 Ml/d 1.1 Ml/d 1.6 Ml/d 4.13 Ml/d Environmental & Social r SEA ○◑ ○○ ○○ ○◑ HRA ○ ○ ○ ○ WFD ◑r ○ ○ ○ Cumulative effects ○ ○ ○ ○ Cost

◉ ◉ ◉ ◉ Promotability Synergies ○ ○ ○ ○ r Customer acceptability ○ ○ ○ ◑ Local acceptability ○ ○ ◑r ◑r Regulatory acceptability ◑r ◑r ◑r ◑r r Wider stakeholder acceptability ◑ ○ ○ ◎ Flexibility Lead time ◎ ◎ ◎ ◎ r Phasing ○ ○ ○ ◑ Adaptability ○ ○ ○ ◎ Ramp-up ◎ ◎ ◎ ◎ Deliverability Constructability ○ ○ ○ ○ Operability ◑r ◑r ○ ◑r Dependencies ○ ○ ○ ○ r r r Data confidence ◑ ◑ ○ ◑ Resilience Climate change ◑ ○ ○ ○ r Severe drought ◑ ○ ○ ◎ Resource predictability ○ ○ ○ ◎ System outage ○ ○ ○ ◎ Other ‘failure modes’ ○ ○ ○ ○

Screening decision

   

Assessment of the internal inter-zonal transfer options will be reviewed after the April 2017 update of the Supply/Demand Forecast.

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7.5 Next steps for water resource options passing fine screening

7.5.1 Groundwater options

The proposed next steps for those groundwater options passing fine screening are shown in Table 7.6.

Table 7.6: Proposed future work Option Proposed future work GW – Datchet Take manual water level measurements in all boreholes during rest periods and during pumping. Calibrate and/or replace the water level transducers in each borehole. Calibrate and/or replace the individual flow meters Check low level pump cut-off setting and relocate if necessary. Carry out test pumping of ABH9 and ABH5/6. RC – Datchet Investigate the extent of the main replacement in order to identify exactly what has been replaced and main whether more of the main would need to be replaced and tested prior to increasing flow in the main replacement above the current constrained flow. Confirm whether further risk assessments and testing would be required to allow for transferring the potential peak DO of 31.4 Ml/d from Datchet and Eton. Eton removal of No future work is required prior to delivery of the proposed option. constraints to DO

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8 Henley WRZ resource options

This section provides a summary of the feasibility reports and fine screening assessment for the Henley Water Resource Zone grouped by water resource option type. Options are assessed qualitatively against the six dimensions: Cost, Environmental and Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is presented for each option type together with the screening decisions.

8.1 Water resource option types

The resource option types identified for the Henley WRZ comprise:  Groundwater development; and  Catchment management.

It should be noted that the WRMP14 supply-demand review concluded that Henley would be in surplus until 2040

8.2 Feasibility Report findings

8.2.1 Groundwater development

The options identified in the feasibility report for groundwater development are listed in Table 8.1 together with a summary of the status of the options.

Table 8.1: Henley options identified in the feasibility report for groundwater development DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The EA will not support the disaggregation of the licence due to impacts on the River Thames Sheeplands licence and River Loddon and the 8.5 13.3 ✖ disaggregation Maidenhead Chalk (Good status, at risk) and South West Chilterns (Poor status) groundwater bodies.

No groundwater development options have been carried forward to fine screening for the Henley WRZ.

8.2.2 Catchment management

The options identified in the feasibility report for catchment management are listed in Table 8.2 below together with a summary of the status of the options.

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Table 8.2: Henley options identified in the feasibility report for catchment management DO Stage* (Ml/d) Option 1 2 3 Comment Sheeplands 0.3 ✔ ✔ ✔ (Groundwater)

The option to be taken forward to the fine screening stage is therefore:  Sheeplands (groundwater source) – Measures to address adverse water quality risks due to rising nitrate and pesticide levels in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.3 Ml/d

8.3 Fine screening assessment

The catchment management option at Sheeplands has been assessed against the six dimensions and associated sub-dimensions set out in Section 3 of this report. The assessment is set out, with commentary, in Appendix E. The option has been carried forward from the feasibility stage, has passed the fine screening stage and is included in the Constrained List.

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9 Guildford WRZ resource options

This section provides a summary of the feasibility reports and fine screening assessment for the Guildford Water Resource Zone grouped by water resource option type. Options are assessed qualitatively against the six dimensions: Cost, Environmental and Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is presented for each option type together with the screening decisions.

9.1 Water resource option types

The water resource option types identified for the Guildford WRZ comprise:  Aquifer storage and recovery;  Groundwater development;  Removal of Deployable Output constraints; and  Inter-company transfers

9.2 Feasibility Report findings

9.2.1 Aquifer storage and recovery

The aquifer storage and recovery options identified in the groundwater feasibility report are listed in Table 9.1 below together with a summary of the status of the options.

Table 9.1: Guildford options identified in the feasibility report for aquifer storage and recovery DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment A number of risks have been highlighted concerning the option, primarily due to the ASR - Guildford 1.5 4.5 ✔ ✖ purchase of land, impacts on a local nature (Abbotswood) reserve and the location of the site in the floodplain.

No aquifer storage and recovery options have been carried forward to fine screening for the Guildford WRZ.

9.2.2 Groundwater development

The groundwater development options identified in the groundwater feasibility report are listed in Table 9.2 together with a summary of the status of the options.

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Table 9.2: Guildford options identified in the feasibility report for groundwater development DO (Ml/d) Stage* Comment

Option Average Peak 1 2 3 The EA will not support an increase in licence at this location due to concerns over the impact of the Mousehill & 1.55 0.18 ✖ abstraction on the River Ock. It is not considered to Rodborough Rehab be cost-effective to deliver the potential volume benefit without an increase in licence EA would support disaggregation of licence for peak abstraction but would expect the annual average to remain the same as the current aggregated volumes. Dapdune Licence 0 2.2 ✔ ✔ ✔ Disaggregation The delivery of this option is dependent on the delivery of the Ladymead WTW and Dapdune removal of constraints options.

The option to be taken forward to the fine screening stage is therefore:  Dapdune licence disaggregation – Disaggregation of the Dapdune, Ladymead and Millmead licence to increase DO. – This scheme would provide a likely benefit of 0.0 Ml/d average and 2.2 Ml/d peak.

9.2.3 Removal of Deployable Output constraints

The options for removal of DO constraints identified in the groundwater feasibility report are listed in Table 9.3 together with a summary of the status of the options.

Table 9.3: Guildford options identified in the Feasibility Report for removal of DO constraints DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment Investigations show that DO is constrained by the licence, not pump RC - Ladymead borehole - - capacity so the resultant DO increase pumps has been incorporated into the baseline. Capacity of the forwarding pumps and onward network needs confirmation through operational testing and some Ladymead WTW removal of network modelling. 0.0 4.6 ✔ ✔ ✔ constraints to DO The delivery of this option is dependent on the delivery of the Dapdune licence disaggregation and Dapdune removal of constraints options. The option has failed due to uncertainties in water availability and potential yield, the low resilience of the RC - Sturt Road Spring 0.25 0.25 ✔ ✖ potential increase in deployable output Capture and the cost benefit of further investigation to reduce these uncertainties. The delivery of this option is dependent Dapdune removal of on the delivery of the Ladymead WTW 0.0 1.0 ✔ ✔ ✔ constraints to DO and Dapdune licence disaggregation options.

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A brief description of the removal of DO constraints options that are currently expected to be carried forward from the Feasibility Report is provided below.  Dapdune removal of constraints to DO – This scheme involves liaison with the EA to confirm the details of the licence disaggregation. – The scheme would increase only the peak source DO, by a most likely 1.0 Ml/d, and provide additional resources to the Guilford WRZ.  Ladymead WTW removal of constraints to DO – This scheme involves increasing the high lift pump capacity at the WTW to allow water from the Ladymead and Dapdune groundwater sources to be added to the network. – The scheme would increase the peak and average source DO by a most likely 4.6 Ml/d, and provide additional resources to the Guilford WRZ.

9.2.4 Inter-company water transfers

The options identified in the Feasibility Report for inter-company water transfers are listed in Table 9.4 together with a summary of the status of the options.

Table 9.4: Guildford options identified in the feasibility report for inter-company transfer of treated water Stage Comment

Option Sub-option Capacity / DO 1 2 3 SEW to Surrey Hills SR (SEW) 5 Ml/d Large conveyance length (>20km) Guildford to Hogsback SR (TW- ✔ ✖ and major construction complexity in Guildford) comparison with alternative. SEW to Surrey Hills SR (SEW) 10 Ml/d Large conveyance length (>20km) Guildford to Hogsback SR (TW- ✔ ✖ and major construction complexity in Guildford) comparison with alternative. SEW to Hogsback SR (SEW) 5 Ml/d Small pipe size increase only Guildford to Mount SR (TW- needed (from 300mm to 350mm) to Guildford) deliver 10Ml/d, but length ✔ ✔ ✖ unchanged. 10Ml/d provides future resource resilience, and operational connectivity benefits. SEW to Hogsback SR (SEW) 10 Ml/d Awaiting information on bulk supply Awaiting Guildford to Mount SR (TW- ✔ ✔ charge Guildford) Info.

9.3 Exclusivities/Interdependencies

Dapdune and Ladymead operate under an aggregate licence. Therefore, changes in abstraction from one must be considered in terms of operation of both sources. The Ladymead WTW removal of constraints, Dapdune licence disaggregation and Dapdune removal of constraints to DO can provide a combined total additional groundwater source deployable output of 7.8 Ml/d to the Guildford WRZ in the average day peak week (ADPW), but provide no dry year annual average benefit (DYAA). This DO benefit is the total DO benefit to the Guildford WRZ assuming that all three Dapdune and Ladymead options are delivered:  Ladymead WTW removal of constraints;  Dapdune licence disaggregation; and  Dapdune removal of constraints.

9.4 Fine screening assessment

Each of the feasible options described above has been assessed against the six dimensions and associated sub-dimensions set out in Section 3 of this report. The assessment for each option type is set out, with commentary, in Appendix F and summarised in Table 9.5 table below.

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Table 9.5: Water resource element screening summary – Guildford WRZ Dimension / Sub-dimension Groundwater Removal of DO constraints development

Dapdune licence Dapdune Ladymead WTW disaggregation

2.2 Ml/d 1 Ml/d 4.6 Ml/d Environmental & Social r SEA ○◑ ○○ ○○ HRA ○ ○ ○ WFD ◑r ○ ○ Cumulative effects ◑r ○ ○ Cost ◉ ◉ ◉ Promotability Synergies ○ ○ ○ Customer acceptability ○ ○ ○ Local acceptability ○ ○ ○ r r r Regulatory acceptability ◑ ◑ ◑ Wider stakeholder acceptability ○ ○ ○ Flexibility Lead time ◎ ◎ ◎ Phasing ○ ◎ ○ Adaptability ○ ○ ○ Ramp-up ◎ ◎ ◎ Deliverability Constructability ○ ○ ○ Operability ○ ◎ ◎ Dependencies ○ ○ ○ Data confidence ○ ◎ ◎ Resilience Climate change ○ ○ ○ Severe drought ○ ○ ○ Resource predictability ○ ○ ○ System outage ◎ ◎ ◎ Other ‘failure modes’ ○ ○ ○ Screening decision   

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9.5 Next steps for water resource options passing fine screening

9.5.1 Groundwater options

The proposed next steps for those groundwater options passing fine screening are shown in Table 9.6.

Table 9.6: Proposed future work Option Proposed future work Dapdune licence No further work is proposed for this option. disaggregation Dapdune removal Following the results of the rapid gravity filter trials, review whether an upgrade of the disinfection of constraints to process at Ladymead WTW could negate the need for filtration. DO Test pump both boreholes in unison to define the maximum capacity of the existing pumps, the effects on water levels in the boreholes and water quality. Ladymead WTW Network modelling work should be carried out to provide further information on whether the existing removal of output main is capable of transferring the increased DO. constraints to DO

9.5.2 Inter-company transfer options

The costs do not currently include for South East Water network reinforcements or bulk supply charges. This needs to be addressed before the transfers can be considered on the same basis as other water resource options.

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10 Kennet Valley WRZ resource options

This section provides a summary of the feasibility reports and fine screening assessment for the Kennet Valley (KV) Water Resource Zone grouped by water resource option type. Options are assessed qualitatively against the six dimensions: Cost, Environmental and Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is presented for each option type together with the screening decisions.

10.1 Water resource option types

The resource option types identified for Kennet Valley WRZ comprise:  Groundwater development;  Removal of Deployable Output constraints;  Catchment management; and  Inter-zonal transfers

10.2 Feasibility Report findings

10.2.1 Groundwater development

The options identified in the Feasibility Report for groundwater development are listed in Table 10.1 together with a summary of the status of the options.

Table 10.1: Kennet Valley options identified in the feasibility report for groundwater development DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The EA would not support an abstraction licence at this location due to concerns about impacts on the South West Chilterns groundwater body, GW – Purley 10.0 15.0 ✖ which has Poor status. Any abstraction licence would have a hands off flow condition applied. Consequently, the deployable output benefit of the option would be 0 Ml/d. The EA have stated that they would not support an abstraction licence at this location due to concerns about impacts on the South West Chilterns groundwater body, which has Poor GW - Mapledurham 10.0 15.0 ✖ status. Any abstraction licence would have a hands off flow condition applied. Consequently, the deployable output benefit of the option would be 0 Ml/d.

GW – Mortimer disused source (recommission) GW - Mortimer and Mortimer (transfer peak licence from disused source 4.5 4.5 ✔ ✔ ✔ Arborfield), which failed at Stage 2, are mutually (recommission) exclusive.

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DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment A reassessment of the source deployable output diagram indicates that it will not be possible to GW - Mortimer achieve a deployable output of more than (transfer peak 4.5 6.8 ✔ ✖ 5.0 Ml/d, which is less than the licence transfer licence from quantity. Therefore, the option fails as the site Arborfield) may not be hydrogeologically suitable for the proposed option. The EA will not support the proposed increase in abstraction licence as the abstraction would be GW – Hungerford 2.8 1.4 ✖ from a Poor status groundwater body and there are concerns about the impact on flows in the River Kennet. The EA will not support an abstraction licence at this location due to concerns about the impact of GW - Playhatch 2.2 1.3 ✖ the abstraction on flows in the River Thames and (increased licence) because the site is within the South West Chilterns, Poor status groundwater body.

A brief description of the option that has been carried forward from the feasibility report is provided below.  Mortimer disused source (recommission) – Refurbishment of two disused confined chalk abstraction boreholes located on-site at the existing, but disused Mortimer water treatment works (WTW). Water abstracted from the boreholes will be treated at the disused WTW which will be upgraded for ammonia and iron removal and recommissioned. – This scheme would provide a likely benefit of 4.5 Ml/d.

10.2.2 Removal of Deployable Output constraints

The options identified in the feasibility report for removal of deployable output constraints are listed in Table 10.2 together with a summary of the status of the options.

Table 10.2: Kennet Valley options identified in the feasibility report for removal of DO constraints DO (Ml/d) Stage* Option Average Peak 1 2 3 Comment The solutions proposed for increasing deployable output at this source are based on East Woodhay 0.0 2.1 ✔ ✔ ✔ a number of assumptions and these will need borehole pumps to be investigated and confirmed if the options are to be progressed further.

A brief description of the option that is currently expected to be carried forward from the Feasibility Report is provided below.  East Woodhay – This option comprises upgrading the pumps and pump control in the existing licensed, operational abstraction boreholes at East Woodhay, to allow the borehole pumps to be run together. It includes a treatment upgrade at East Woodhay Water Treatment Works (WTW). – This scheme would provide a likely benefit of 2.1 Ml/d (peak). No changes to average DO are proposed (constrained by aggregate licence).

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10.2.3 Catchment management

The options identified in the Feasibility Report for catchment management are listed in Table 10.3 together with a summary of the status of the options.

Table 10.3: Kennet Valley options identified in the feasibility report for catchment management DO Stage* (Ml/d) Option 1 2 3 Comment Fognam Down 0.2 Ml/d ✖ Low likelihood of success relative to the ✔ ✔ (Groundwater) potential benefit to be gained Speen (Groundwater) 0.2 Ml/d Low likelihood of success relative to the ✔ ✔ ✖ potential benefit to be gained Playhatch 0.4 ✔ ✔ ✔ (Groundwater)

The options to be taken forward to the fine screening stage are therefore:  Playhatch (groundwater source) – Measures to address adverse water quality risks due to rising pesticide levels in the source catchment thereby reducing drinking water quality constraints to increase deployable output by approximately 0.4 Ml/d

10.2.4 Internal inter-zonal transfers

The options identified in the feasibility report for inter-zonal transfers are listed in Table 10.4 together with a summary of the status of the options.

Table 10.4: Kennet Valley options identified in the feasibility report for internal inter-zonal transfer of treated water Stage Comment

Option Sub-option Capacity / DO 1 2 3 SWA to Rejected on the basis that SWA is Kennet Valley forecasted to be in deficit at the end of the planning horizon and the proposed ✖ GW source developments are in the South East corner, mostly eligible for an intercompany water transfer to South East Water Henley to Sheeplands WTW to 4.13 Ml/d The option is only for increasing the Kennet Valley Early SR ✔ ✖ export potential but given the large construction complexity it was rejected

Assessment of the internal inter-zonal transfer options will be reviewed after the April 2017 update of the Supply/Demand Forecast

No internal inter-zonal transfer options have been carried forward from the Feasibility Report for the Kennet Valley WRZ

10.3 Exclusivities/Interdependencies

The SWOX WRZ inter-zonal transfer from Kennet Valley is partially dependent on development of the Kennet Valley option for recommissioning the disused Mortimer source.

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10.4 Fine screening assessment

Each of the feasible water resource options described above has been assessed against the six dimensions and associated sub-dimensions set out in Section 3 of this report. The assessment for each option type is set out, with commentary, in Appendix G and summarised in Table 10.5.

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Table 10.5: Water resource element screening summary – Kennet Valley WRZ Dimension / Sub-dimension Other Removal of DO Catchment

Groundwater constraints Management

ing

Playhatch

Mortimer 1 Mortimer

East East Woodhay recommission

4.5 Ml/d 2.1 Ml/d 0.4 Ml/d Env & Social r SEA ○◑ ○○ ◎○ ○ HRA ○ ○ r ○ WFD ◑ ○ r r Cumulative effects ◑ ◑ ○ Cost

◉ ◉ ◉ Promotability Synergies ○ ○ ○ Customer acceptability ○ ○ ◎ r ○ Local acceptability ◑ ○ r r Regulatory acceptability ◑ ◑ ◉ Wider stakeholder acceptability ○ ○ ◉ Flexibility Lead time ◎ ◎ ○ Phasing ○ ○ ◎ Adaptability ○ ○ ◉ Ramp-up ◎ ◎ ◑ Deliverability Constructability ○ ○ ◑ r r Operability ◑ ◎ ◑ Dependencies ○ ○ ◑ Data confidence ◑r ◑r ◑ Resilience Climate change ○ ○ ◎ Severe drought ○ ○ ○ Resource predictability ○ ○ ◑ System outage ○ ○ ○ Other ‘failure modes’ ○ ○ ○ Screening decision   

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10.5 Next steps for options passing fine screening

10.5.1 Groundwater options

The proposed next steps for those groundwater options passing fine screening are shown in Table 10.6.

Table 10.6: Proposed future work Option Proposed future work GW - Mortimer Confirm that the Environment Agency will support the proposed option. disused source Test pumping and sampling of the boreholes to confirm the proposed yield and water quality. (recommission) Check the condition of the transfer main, booster pumps and WTW to understand if rehabilitation will be required. Flood risk assessment of WTW site East Woodhay Validate assumptions used in formulating the pump control and operation options. borehole pumps Investigate treatment capacity of the existing WTW infrastructure.

10.5.2 Catchment management options

The proposed next steps for the Playhatch catchment management option is to develop the conceptual design report to refine the costs and further develop the key components of the option.

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11 Conclusions

This section provides a summary of the water resource screening decisions that have been made to enable the drawing up of the Constrained List, together with a summary of next steps.

11.1 Screening summary

A summary of the progression of water resource option types through the screening stages is provided in Table 11.1. A summary of the reasons for screening out of options will be set out in the Rejection Register. For those options that progressed to fine screening from the feasibility stage a summary of option status is provided in Table 11.2.

Table 11.1: Summary of option types considered at each stage of the screening process

†

screening Feasibility report Fine screening Generic resource management options Generic Specific option identification Feasible list Constrained list 1 Direct river abstraction ✔ Direct river abstraction feasibility report ✔ ✔ 2 New reservoir ✔ New reservoirs feasibility report ✔ ✔ 3 Groundwater sources ✔ Groundwater feasibility report ✔ ✔ 4 Infiltration galleries ✔ Included in DRA/Desal as possible intake n/a 5 Aquifer storage and recovery ✔ Groundwater feasibility report ✔ ✔ 6 Aquifer recharge ✔ Groundwater feasibility report ✔ ✔ 7 Desalination ✔ Desalination feasibility report ✔ ✔ 8a Bulk transfers of raw water ✔ Raw water transfer feasibility report ✔ ✔ 8b Bulk inter/intra company transfers of treated water ✔ Inter-zonal transfers study ✔ ✔ 9 Tankering of water ✖ 10 Redevelopment of existing resources TBC 11 Reuse of existing private supplies ✔ Third party options report ✖ 12 Water re-use ✔ Water reuse feasibility report ✔ ✔ 13 Imports (icebergs) ✖ 14 Rain cloud seeding ✖ 15 Tidal barrage ✖ 16 Rainwater harvesting ✖ 17 Abstraction licence trading ✔ Third party options report ✔ ✔ 18 Water quality schemes that increase DO ✔ Catchment management feasibility report ✖ 19 Catchment management schemes ✔ Catchment management feasibility report ✔ ✔ 20 Conjunctive use operation of sources ✔ Built into DOs through WARMS n/a 21 Joint ("shared asset") resource ✔ Included in feasibility reports where applicable n/a 22 Asset transfers ✔ Third party options report ✖ 23 Options to trade other (infrastructure) assets ✔ Third party options report ✖ † Taken from UKWIR 2012, Water Resources Planning Tools, EBSD Report, Ref 12/WR/27/6

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Table 11.2: Fine screening summary for specific options

Size Band (Ml/d)

25 75 125 175 225 275 Option 0 Comment London WRZ Reuse - Beckton See section 5.5.2 for next steps Reuse - Mogden See section 5.4.2.1 for rejection reasoning Reuse - Deephams See section 5.5.1 for next steps Reuse - Crossness See section 5.4.2.3 for rejection reasoning Reuse - Mogden South Sew er See section 5.4.2.2 for rejection reasoning RWT - STT Deerhurst See section 5.5.3 for next steps New Reservoir - Abingdon See section 5.5.4 for next steps New Reservoir - Chinnor See section 5.4.2.4 for rejection reasoning New Reservoir - Marsh Gibbon See section 5.4.2.4 for rejection reasoning DRA - Teddington See section 5.5.5 for next steps Desalination - Beckton See section 5.5.6 for next steps Desalination - Crossness (unblended) See section 5.4.2.5 for rejection reasoning Desalination - Crossness (blended) See section 5.5.7 for next steps AR/ASR - Kidbrooke (SLARS1) See section 5.5.8 for next steps AR Merton (SLARS3) See section 5.5.8 for next steps AR Streatham (SLARS2) See section 5.5.8 for next steps ASR South East London (Addington) See section 5.5.8 for next steps ASR Thames Valley/Thames Central See section 5.5.8 for next steps GW - Addington See section 5.5.8 for next steps GW - London confined Chalk (north) See section 5.5.8 for next steps GW - Southfleet/Greenhithe (new WTW) See section 5.5.8 for next steps GW - Merton recomissioning See section 5.5.8 for next steps Licence Trade - GW North London See section 5.5.8 for next steps CM - Southfleet See section 5.5.9 for next steps CM - Green Street Green See section 5.5.9 for next steps CM - North Orpington See section 5.5.9 for next steps CM - Low er River Thames See section 5.5.9 for next steps CM - Low er River Lee See section 5.5.9 for next steps Swindon and Oxfordshire (SWOX) WRZ RWT - STT Deerhurst See section 5.5.3 for next steps New Reservoir - Abingdon See section 5.5.4 for next steps New Reservoir - Chinnor See section 6.4.1.1 for rejection reasoning New Reservoir - Marsh Gibbon See section 6.4.1.1 for rejection reasoning DRA Culham Further consideration of DO impact on London and mutual exclusivity w ith Abingdon GW - Moulsford See section 6.5.1 for next steps Ashton Keynes borehole pumps See section 6.5.1 for next steps IZT - Kennet Valley to SWOX Progress to conceptual design - Deployable Output maximised if Mortimore option developed IZT - Henley to SWOX Progress to conceptual design (mutually exclusive w ith IZT Henley to SWA) CM - Ashdow n Park See section 6.5.2 for next steps CM - Upper Sw ell See section 6.4.1.2 for rejection reasoning CM - Marlborough See section 6.5.2 for next steps Slough, Wycombe & Aylesbury (SWA) WRZ GW - Datchet Datchet main replacement See section 7.5.1 for next steps - options are partially interdependent Eton removal of constraints to DO IZT - Henley to SWA Progress to conceptual design (mutually exclusive w ith IZT Henley to SWOX) Henley WRZ CM - Sheeplands Progress to conceptual design Guildford WRZ Dapdune licence disaggregation Dapdune removal of constraints to DO See section 9.5.1 for next steps - options are partially interdependent Ladymead WTW Kennet Valley (KV) WRZ GW - Mortimer recommissioning See section 10.5.1 for next steps East Woodhay borehole pumps See section 10.5.1 for next steps CM - Playhatch See section 10.5.2 for next steps Key Screened out at fine screening Passes fine screening onto Constrained List Note: Assessment of the internal inter-zonal transfer options w ill be review ed after the April 2017 update of the Supply/Demand Forecast.

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11.2 Constrained list For the purpose of fine screening, independent specific options of different sizes have been developed. For programme appraisal it is proposed that elements of some options will be phased. A summary of the options included on the Constrained List is provided in Table 11.3

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Table 11.3: Constrained List for London WRZ Option Resource Element Conveyance Element Raw Treatment Element Network Element Type Location Nominal Location Nominal Water System Location Nominal Capacity Capacity Capacity Ml/d Ml/d Ml/d

Water reuse Deephams 60 Deephams to See raw water system East London 60 See network reinforcement matrix - Thames-Lee Tunnel reinforcement matrix - Treatment section 3.5.3 Extension section 3.5.4 Beckton 3*100 Beckton to Lockwood 800 100*3 2*150 shaft

Raw Water Vyrnwy 180 Deerhurst to 300/400/500 See matrix Kempton 100*3 See network reinforcement matrix - Transfer Mythe 15 Culham section 3.5.3

Desalination Beckton (blended) 150 N/A N/A N/A See matrix, plus Beckton to Coppermills Crossness (blended) 3*100 As above plus Beckton to Crossness

New Abingdon 75Mm3 153 N/A See raw water system Kempton 300 See network reinforcement matrix - Reservoir Abingdon 100Mm3 204 reinforcement matrix - 150 section 3.5.3 Abingdon 125Mm3 247 section 3.5.4 100 Abingdon 150Mm3 287 Abingdon 30+ approx 90Mm3 59+179 Abingdon 70+ approx 50Mm3 145+93

Direct River Teddington Weir (Mogden effluent transfer) 300 Teddington to 300 See matrix Kempton / 100 See network reinforcement matrix - Abstraction Thames-Lee tunnel East London 200 section 3.5.3 shaft

Aquifer AR/SLARS - Kidbrooke (SLARS1) 7 N/A N/A N/A N/A Recharge AR Merton (SLARS3) 5 AR Streatham (SLARS2) 4

Aquifer ASR South East London (Addington) 3 N/A N/A N/A N/A Storage and ASR Thames Valley/Thames Central 3 Recovery

Groundwater GW - Addington 1 N/A N/A N/A N/A GW - London Confined Chalk (north) 2 GW - Southfleet/Greenhithe (new WTW) 8 Merton recommissioning 2 North London Licence Trading/Transfer 2

Catchment Southfleet (Groundwater) 0.2 N/A N/A N/A N/A management Green Street Green (Groundwater) 0.3 North Orpington (Groundwater) 0.4 Lower River Thames 2 Lower River Lee 1

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Table 11.4: Constrained List for Thames Valley WRZs Option Resource Element Conveyance Element Treatment Element Network Element Type Location Nominal Location Nominal Location Nominal Location Nominal Capacity Capacity Capacity Capacity Ml/d Ml/d Ml/d Ml/d

Raw Vyrnwy 20 Deerhurst to 300 Radcot WTW 24 See network blueprint outputs Water Culham 400 Transfer 500

New Abingdon 75Mm3 20 N/A Abingdon WTW 24 See network blueprint outputs Reservoir Abingdon 100Mm3 20 Abingdon 125Mm3 20 Abingdon 150Mm3 20 Abingdon 30+ approx 90Mm3 20 Abingdon 70+ approx 50Mm3 20

Groundwater GW - Moulsford 1 3.5 (ADPW) N/A N/A N/A

Removal of constraints to Ashton Keynes borehole pumps 1.6 (ADPW) N/A

DO Swindon Oxfordshire & Inter-zonal GW - Mortimer disused source Kennet Valley to SWOX 12.8 transfers 8.3 Henley to SWOX 2.5

Ashdown Park 0.3 N/A N/A N/A Catchment management Marlborough 0.2

Groundwater GW - Datchet N/A N/A N/A

Removal of constraints to Datchet main replacement 8.7 (ADPW) N/A N/A N/A

SWA DO Eton removal of constraints to DO

Inter-zonal transfers Henley to SWA 4.1 N/A N/A

Sheeplands (Groundwater) 0.3 N/A N/A N/A

Catchment management Henley

Groundwater Dapdune licence disaggregation N/A N/A N/A

Removal of constraints to Dapdune removal of constraints to DO 7.8 (ADPW) N/A N/A N/A

DO Ladymead WTW Guildford

Groundwater GW - Mortimer disused source (recommission) 4.5 (ADPW) N/A N/A N/A

Removal of constraints to East Woodhay borehole pumps 2.1 N/A N/A N/A DO (ADPW)

Catchment management Playhatch 0.4 N/A N/A N/A Kennet Valley Kennet

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11.3 Next steps

Further work is required in a number of areas to finalise the WRMP19 Constrained List of water resource options including:  Complete back checking around the impact on screening decisions (including on costs and understanding of environmental impacts) of new information that arises during the course of Phase 3 work including conceptual design, updating of cost and risk assessments and Strategic Environmental Assessment.  Further information is expected in relation to third party options for raw water transfers from Severn Trent Water, United Utilities, the Canal and River Trust and in relation to treated water transfers from Wessex Water and South East Water

For options included on the Constrained List the following activities have been undertaken: 1. Complete conceptual design reports, building on and updating WRMP14 dossiers where these exist 2. Undertake next stages of the Strategic Environmental Assessment, Habitats Regulations Assessment and Water Framework Directive assessment on the Constrained List options 3. Update cost estimates for conceptual design 4. Undertake bottom-up assessment of risk 5. Use the above information to inform cost, deliverability and environmental metrics to feed into programme appraisal

In addition to the general next steps associated with options on the Constrained List, there are also a number of key next steps to address uncertainties associated with specific options: a. Progress negotiations and reach agreement in principle on terms for bulk supply agreements (particularly for Severn-Thames Transfer resources) b. Confirm process, timescales and nature of changes needed to River Severn regulation c. Undertake hydro-dynamic modelling for Teddington DRA option to confirm discharge location and extent of navigational impacts to inform engagement with Port of London Authority and Environment Agency. d. Depending on the results of the WRMP19 programme appraisal process, Thames Water will determine whether further work is required to better understand the magnitude, extent and duration of effects from reduction of freshwater inputs on the Thames Middle Tideway.

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Appendices

Appendix A. Treatment technology selection ______110 Appendix B. London WRZ fine screening tables ______114 Appendix C. SWOX WRZ fine screening tables ______126 Appendix D. SWA WRZ fine screening tables ______131 Appendix E. Henley WRZ fine screening tables ______135 Appendix F. Guildford WRZ fine screening tables ______137 Appendix G. Kennet Valley WRZ fine screening tables ______140 Appendix H. Optimism bias & uncertainty ______144 Appendix I. Stochastic analysis of Upper Thames Reservoir ______146 Appendix J. Stochastic analysis of Unsupported Severn-Thames Transfer ______160

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Appendix A. Treatment technology selection

Two different treatment scenarios have been identified. These are direct treatment for the production of potable water and treatment of water for subsequent discharge back to the environment, such as for raw water transfer or water reuse.

With the direct production of potable water Thames Water is responsible for ensuring that it supplies wholesome water and that the water is in full compliance with all the PCV values. To achieve this, Thames Water prepare a drinking water safety plan (DWSP) which identifies the risks to wholesomeness and mitigation measures (including treatment processes) to address the risks and ensure compliance with the requirements.

With pre-treatment of discharges back to the environment the drivers are different, and include:  Invasive Non-Native Species (INNS) – Any transfer needs to consider the risk of spreading invasive non-native species, such as zebra mussels within the watercourses. If necessary suitable risk mitigation measures need to be put in place.  Water Framework Directive – Good Status / No Deterioration – Any discharge to the aquatic environment should ensure that there is no deterioration in the water quality and should not prevent the watercourse from achieving Good Status.  No Increase in Drinking Water Safety Plan Risk – Any discharge could potentially impact on the risks identified within the DWSP of any downstream water abstractions (owned by Thames or a third party). To this end discharges should not lead to an increase in risk, as this could potentially require the introduction of additional mitigation measures within each of the impacted DWSPs.

For discharges to the environment, in order to select the appropriate treatment technology and treatment scheme it is necessary to understand the quality of the source water to be treated and the required product water quality to be achieved. To assess the likely treatment standards that would have to be achieved a water quality modelling exercise has been undertaken, using the available water quality data, to assess the required product water quality based on the requirements of the receiving waters that discharges are being made to. This modelling exercise assessed a large number of parameters, identifying the required discharge concentrations that needed to be achieved, and prioritising the parameters based on their potential impact on the receiving water. This prioritisation was:  High Priority – >50% of PCV value (where defined) >10% of Environmental Quality Standard (where defined)  Medium Priority – <50% of PCV value (where defined)  Low Priority – No PCV defined No EQS defined or modelled downstream quality < 10% of EQS

For the production of potable water the situation is relatively simple as the required treated water standards are fixed (at least for those parameters with defined PCV values) and the appropriate technologies to achieve those standards are well established and accepted. In order to arrive at a suitable treatment scheme it is necessary to assess the available raw water quality data and identify the appropriate treatment technology for that application and consider the risks identified within the drinking water safety plan and develop suitable and acceptable risk mitigation measures. Where suitable risk mitigation measures cannot be identified, the source couldn’t safely be used for public supply.

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The following sections present a summary of the treatment technology assessment that has been carried out for various schemes.

The following schemes have been considered:  Water Re-use: Beckton Re-use Deephams Re-use Mogden Re-use  Raw Water Transfer River Severn transfer to River Thames  Direct River Abstraction Lower River Lee DRA (direct potable supply) Lower River Lee DRA (transfer to Lee Valley Reservoirs) Teddington DRA

A.1 Beckton Re-use

The following table summarises the conclusion of the analysis for the Beckton Re-use to River Lee Division Channel option.

50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 300 Ml/d 380 Ml/d UF+RO+AOP High       Medium       Low       Fe+NSF+O3/GAC+IX High (1) (1) (1) Medium Low

Note: UF+RO+AOP Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process Fe+NSF+O3/GAC+IX Ferric + Nitrifying Sand Filter + Ozone / GAC + Ion Exchange (1) Except for Phosphate and zinc

Two treatment schemes have been considered. The first scheme utilises Reverse Osmosis and advanced oxidation, while the second scheme utilises sand filtration, ozone and GAC adsorption and nitrate removal.

As can be seen from the table, the first treatment scheme is comprehensive and addresses all parameters, across all prioritisations and flows. The second scheme is more selective, treating just those parameters that are considered to be high priority. This is only effective up to discharge flows of 150 Ml/d. Above this flow this treatment scheme would not be effective and Scheme 1 would be required.

It should be noted, that unlike other expansions, such as a water treatment works, where the product water quality is constant and expansions can just duplicate existing treatment trains, in this application the treatment standard becomes more stringent as the discharge flow increases. This effectively means that if treatment Scheme 2 were adopted, to increase the capacity from 150 Ml/d to 200 Ml/d would mean that the Scheme 2 treatment process would have to be abandoned and replaced with a 200 Ml/d treatment plant based on the Scheme 1 technologies.

It is considered that treatment Scheme 1 provides more flexibility in terms of future treatment capacity and is better able to treat a wide range of parameters, beyond the limited list identified as high priority parameters treated by Scheme 2, and as such Scheme 1 has been adopted as the preferred technology for the development of a re-use scheme utilising effluent from the Beckton STP.

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A.2 Deephams Re-use

The capacity of the Deephams Re-use scheme is limited by the impact the scheme could have on the downstream water body, because of reduced flows. As such it is understood that the Environment Agency would be unwilling to accept a scheme with a capacity greater than 60 Ml/d

The following table presents the anticipated performance of the two treatment schemes (same as considered for Beckton re-use above) over a range of flows.

25 Ml/d 35 Ml/d 50 Ml/d 60 Ml/d 80 Ml/d 100 Ml/d UF+RO+AOP High       Medium       Low       Fe+NSF+O3/GAC+IX High (1) (1) (1) (1) (1) (1) Medium  Low 

Note: UF+RO+AOP Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process Fe+NSF+O3/GAC+IX Ferric + Nitrifying Sand Filter + Ozone / GAC + Ion Exchange (1) Except for Phosphate

As can be seen both schemes would treat the High priority parameters, while Scheme 1 will also treat the Medium and Low parameters

Selection of Scheme 1 would allow a comparable treatment scheme to be adopted at both Beckton and Deephams, rather than having different processes at each site, and potentially would allow Deephams to be developed and operated, providing full-scale operational experience in advance of the development of a larger Beckton re-use scheme. In addition Scheme 1 would treat many other parameters because of the more general nature of the RO / AOP treatment processes.

A.3 Mogden Re-use

Under this option, unlike the effluent transfer option above, the effluent will ultimately (following mixing and blending with river water) be abstracted for further treatment to produce potable water. As such the full list of parameters is considered. The table below presents the assessment of the treatment schemes.

50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 250 Ml/d 300 Ml/d UF+RO+AOP High       Medium       Low       Fe+NSF+IX High (1) (1) (1) (1) (1) (1) Medium  Low 

Note: UF+RO+AOP Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process Fe+NSF+IX Ferric + Nitrifying Sand Filter + Ion Exchange (1) Except for Phosphate

As with the Beckton and Deephams Options, Scheme 2 is suitable for treatment of the high priority parameters but not the Low and Medium Priority parameters, whereas Scheme 1 is suitable for all parameters considered, across all flows. As such Scheme 1 is considered the preferred treatment scheme.

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A.4 Lower Lee (Direct Potable Supply)

As discussed in the introduction, in order to develop a treatment scheme for a direct supply option it is necessary to do the following:  Identify a treatment scheme to achieve “wholesome water” and compliance with PCV standards for potable water  Consider the risks identified within the DWSP and determine whether adequate and sufficient mitigation measures can be put in place.

The treatment of river water from the Lower Lee and transfer to the Lee Valley Reservoirs is discussed in the following section and identifies the preferred treatment scheme as:  Ferric coagulation  Dissolved Air Flotation  Rapid Gravity Filtration  Ion Exchange

For the direct supply option the following additional treatment stages would be required to achieve full compliance with the required drinking water standards:  Ozone / GAC adsorption (for pesticide control)  Chlorination, de-chlorination, amination, and orthophosphate dosing  Chlorine contact tank

A number of risks have been identified within the River Lee catchment that need to be assessed. The main risks are:  High proportion of Deephams Final Effluent in the Lower River Lee – At times of low flow in the River Lee the discharge from Deephams Sewage Works contributes a significant proportion of the river flow. This could be further compounded if there should be an operational issue at Deephams leading to poor quality effluent being discharged into the river, or stormwater being discharged, leading to reduced river water quality.  Pollution from Contaminated Land – It is well documented that there are number of sites with significant contamination, such as the Olympic Park. Some remediation work has been undertaken but some contamination still exists within the catchment. Scenarios exist whereby contamination could pass into the river, for example by dewatering activities or from low river levels reversing the normal hydraulic gradient leading to groundwater seeping into the river.

The primary mitigation of these risks would be to close the intake and shut the plant down, and this could be linked to upstream triggers, such as overflow from the storm tanks at Deephams, or low river level through the Olympic Park. However, not all pollution events would have an obvious physical cause and this could lead to contaminated raw water entering the plant and potentially not being adequately treated, as the treatment process might not be appropriate or not configured to treat these pollutants, and the polluted water could pass undetected into the potable water.

Arsenic has been identified as a specific pollutant of concern as extremely high levels have been detected within contaminated groundwater and surface water in the catchment (in the order of 18,000 µg/l in groundwater and 900 µg/l in surface water) compared to a PCV in drinking water of 10 µg/l. While treatment processes, such as adsorption systems (ferric hydroxide, activated alumina, bone char or ion exchange resins) could be used, and in fact an ion exchange system has been proposed for the removal of nitrate, it is not considered practical to operate such systems, without being able to monitor the ongoing performance, as arsenic would not normally be present in the raw water at significant concentrations. To provide a suitable treatment process, that could achieve the required level of performance, with unknown influent concentration is therefore not considered to be practical. Further, arsenic is just one potential

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pollutant that could occur. Clearly these risks are hard to manage and mitigate with a potentially very high impact for a direct potable supply option such as this.

A.5 Lower River Lee DRA (Transfer to Lee Valley Reservoirs)

Under this option, water would be abstracted from the Lower River Lee around Three Mills Lock, treated and transferred to the Lee Valley Reservoirs and discharged to the River Lee Diversion Channel (or direct into one of the reservoirs).

The following table presents two treatment schemes, Scheme 1, which is comprehensive and treats all parameters, while Scheme 2 treats the high priority parameters.

50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 250 Ml/d 300 Ml/d Scheme 1 - UF+RO High       Medium       Low       Scheme 2 - Fe+DAF+RGF+IX High (1) (1) (1) (1) (1) (1) Medium  Low 

Note: Fe+DAF+RGF+IX Ferric + Dissolved Air Flotation + Rapid Gravity Filters + Ion Exchange UF+RO Ultrafiltration membrane + Reverse Osmosis Membrane

(1) Except for Phosphate and ammonia

The total number of parameters of medium and low concern for the River Lee scheme is relatively low (6) compared to Beckton (19). These parameters are summarised below.

Estimated Target Quality Current River Water Quality Medium Priority Boron 165 178 Sodium 87 96 Chloride as Cl 120 123

Low Priority Potassium 16 18

Nitrite as NO2 0.349 1.493 Simazine 0.023 0.029

Generally the river water quality for these parameters is close to the estimated target quality, and well below the associated PCV value. For this option it is considered that Treatment Scheme 2 is appropriate.

As discussed in the previous section on a Direct Potable Supply scheme from the Lower River Lee, there are significant DWSP risks in the catchment that are hard to adequately mitigate with a direct supply option. However, with an indirect option where the treated water is transferred to a raw water reservoir for further treatment, additional mitigation measures could be implemented. These could include:  Shutting the plant down in the event of a concern about raw water quality  Physical sampling of the treated water to ensure compliance, in addition to continuous online monitoring

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 Discharge of the treated water into a discrete reservoir, where the quality can be regularly physically tested to ensure compliance with target values  Blending of the treated water with other raw water sources to ensure low levels are achieved.

With the implementation of the above mitigation measures it is considered that the pollution risks can be satisfactorily mitigated.

A.6 Teddington Direct River Abstraction

The Mogden Effluent Transfer scheme is different from the other re-use schemes considered in that the treated effluent is not abstracted and subsequently used for potable water. As such the list of parameters considered in the analysis has been reduced to include only those parameters that are of environmental concern. The preferred treatment process is presented below and is considered to be ferric addition for phosphate control and a nitrifying sand filter for ammonia and suspended solids and particulate material removal.

50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 250 Ml/d 300 Ml/d Fe+NSF High (1) (1) (1) (1) (1) (1) Medium Low

Note: Fe+NSF Ferric + Nitrifying Sand Filter (1) Further consideration is need as to the level of performance that could be relably achieved with respect to phosphate and ammonia.

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Appendix B. London WRZ fine screening tables

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Table B.1: London WRZ – Supported raw water transfer options screening assessment: Deerhurst Pipeline 195 Ml/d support (Vyrnwy

and Mythe)

300 400 500 Sub-dimension Ml/d Ml/d Ml/d Comments Env & Social  Benefits to reliability of water supplies through use of supported river transfers, with increased resilience to climate change through use of upstream reservoir storage to support the transfer flows. Water treatment prior to discharge to the River Thames required for managing risks associated with water quality and control of invasive, non-native species. SEA ○◑ ○◑ ○◑  Material dis-benefit from the use of moderate to significant amounts of materials in construction and power and chemical use for conveyance infrastructure and water treatment when in operation. Some temporary pipeline construction effects, mitigated through careful design of the pipeline route.

HRA ○ ○ ○  No likely significant effects on Severn Estuary European Marine Site due to supported flows and hands-off flow conditions.

r r  Risks to WFD objectives (including invasive species risks) in River Thames will be mitigated through water treatment of the River Severn WFD ◑ ◑ ◑ transfers. Impacts on WFD objectives relating to the river support to River Severn can be mitigated.  Potential cumulative effects with discharges from the larger reservoir options for Abingdon and Marsh Gibbon on the flow regime in River Cumulative effects ○ ◑r ◑r Thames for 400 and 500 Ml/d Severn to Thames transfer options. These may be capable of mitigation through careful management of the cumulative operational regime and/or in-river management measures. Cost ○ ○ ○  Updated costs awaited from UU and Severn Trent. Costs also need to be updated following back checking. Promotability ◉ ◉ ◉  All supported transfer options >300 Ml/d offer the potential for synergies through ability to supply water to other WRZs besides London and to Synergies other companies in the South East.

Customer ○ ○ ○  No material customer preference concerns identified. acceptability ◑r ◑r ◑r  All options require planning permission or DCO and there might be a requirement to actively alleviate local flood risk concerns. These are Local acceptability considered to be material but reducible dis-benefits.  There would be regulatory support for transfers for reasons of allocative efficiency. EA concerns over water quality and ecology impacts of a basin to basin transfer need to be addressed through inclusion of appropriate mitigation. New abstraction licences and discharge permits would Regulatory ◑r ◑r ◑r be required, as would changes to the regime for River Severn regulation. While the regime for regulation of the River Severn has been amended acceptability previously, it is not certain that the changes needed can be secured, or that they can be obtained without negatively impacting upon the effectiveness of the solution.

Wider stakeholder ◑r ◑r ◑r  Environmental representative groups may have concerns which would need to be managed through the provision of information / evidence and acceptability engagement. Flexibility

Lead time ○ ○ ○  The lead time of the STT options is estimated to be 7 years - assessed as neutral benefit.

◑ ◑ ◑  Pipelines exhibit strong economies of scale, making phasing less economic - considered a material dis-benefit. There is however significant Phasing potential for phasing the introduction of the support elements  Bulk water transfers could potentially be linked up and connected to new sources and demand centres in future, offering adaptability benefits. It Adaptability ◎ ◎ ◉ is considered that the 500 Ml/d transfer option provides a substantial adaptability benefit as it has the potential to open up more resource options in future (e.g. from Wales).

Ramp-up ◎ ◎ ◎  The option ramp-up times are estimated to be within one week, but where supported by Vyrnwy and Mythe only. Deliverability

Constructability ○ ○ ○  Pipelines are a well-known and developed technology, with neutral benefit/dis-benefit.  Although pipelines are a well-known and developed technology, all options have a material dis-benefit due to the complexities associated with r r r Operability ◑ ◑ ◑ national-scale water transfer schemes. This is considered reducible as operational experience could be drawn from existing schemes such as the Ely Ouse to Essex Transfer Scheme and the Trent Witham Ancholme Scheme.

Dependencies ◑ ◑ ◑  All transfer options would be dependent on support from other water companies - a material dis-benefit. ◑r ◑r ◑r  There are significant modelling complexities and uncertainties associated with inter-basin transfer schemes such as the STT options - a material Data confidence dis-benefit. These uncertainties are all likely to be reducible with further research and investigation. Resilience  Supported transfers contribute to addressing summer water shortages by providing additional storage that allows surplus winter rainfall to be ◎ ◎ ◎ utilised. While the unsupported element is potentially more vulnerable to dryer summers, the stochastic analysis of future drought risks Climate change undertaken has indicated that the yield of an unsupported transfer is not sensitive to climate change. These options are partially supported therefore assessed as a material benefit. ◎ ◎ ◎  Stochastic analysis of future drought risks has been used to assess AICs for the Severn-Thames Transfer and, as such, resilience to severe Severe drought drought is assessed as a material benefit.

Resource ◑ ◑ ●  The transfer options contain a significant element of unsupported transfer. The availability of the unsupported element is difficult to predict. This predictability has been identified as a substantial dis-benefit for the 500Ml/d transfer where more than half of the transfer capacity is unsupported.

◑ ◑ ●  Availability of the unsupported transfer element is less predictable and is therefore of limited use when planning system outage mitigation. This System outage has been identified as a substantial dis-benefit for the 500Ml/d transfer where more than half of the transfer capacity is unsupported. ◑ ◑ ◑  There are material risks of power outages and physical damage on long distance transfers. The STT options would also be vulnerable to Other ‘failure modes’ pollution events in the River Severn (as well as in the River Thames) and to hazards impacting third party suppliers of support options. Screening decision

  

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Table B.2: London WRZ – Water reuse options screening assessment

Beckton Mogden Crossness

Kempton Deephams

50 100- 200- 50 100- 200 50 50 100- 60 0190 Ml/d 150 380 Ml/d 150 Ml/d Ml/d Ml/d 150 Ml/d Ml/d Sub-dimension Ml/d Ml/d Ml/d Ml/d Comments Env & Social  Reuse increases climate change resilience and avoids additional pressures on freshwater SEA ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ resources. Material dis-benefit associated with significant amounts of materials for construction and power and chemicals for operation with consequent carbon emission implications. ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○  Tunnelling and/or pipeline routes will avoid conveyance impacts on any European designated HRA sites.  WFD effects of treated effluent on receiving waterbodies can be mitigated through robust WFD ◑r ○ ○ ○ ◑r ◑r ◑r ○ ○ ○ ○ treatment processes. WFD risks to Lower Lee (Deephams) and upper Thames Tideway (Mogden) due to reduced effluent flow returns to these watercourses would need to be mitigated.  Potential cumulative effects identified in relation to increased salinity from multiple reuse, direct Cumulative effects ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ◑ ◑ ◑ river abstraction and/or desalination schemes that affect flows in the Thames Tideway pending further investigation of receptors that may be adversely affected by such cumulative effects Cost  The small Beckton and Crossness options perform poorly due to the long conveyance infrastructure required and low deployable outputs. The larger options perform poorly as the ○ ◑ ○◑ ◑● ○ ○ ○ ◎ ● ◑ ◑ screening thresholds reduce more rapidly at the larger sizes than the reduction in unit cost due to economies of scale. Crossness performs worst for comparable option sizes. Promotability  Synergy opportunities offer material benefits at higher capacities. There is the potential to Synergies ○ ○ ◎ ◎ ○ ◎ ◎ ○ ○ ◎ ◎ increase the synergy for the Mogden and Kempton options by extending the discharge further upstream (Staines) to allow direct supply to Affinity intakes.

Customer ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○  No material customer preference concerns identified. acceptability ○ ◑r ◑r ◑r ○ ○ ○ ○ ◑r ◑r ◑r  All options apart from Deephams, Kempton and Mogden involve lengthy conveyances in excess Local acceptability of 10km. The potential to cause disruption could materially affect local acceptability.

Regulatory ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r  Material environmental regulatory acceptability issues need to be addressed but these are acceptability considered likely to be reducible.  Concerns about potential net flow impacts on the Rivers Thames and Lee may give rise to Wider stakeholder ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r objections from river users and environmental groups, but these are expected to be reducible acceptability once evidence of the extent of likely impacts is available. Flexibility  Deephams’ lead time is estimated to be only 5 years, due to the relatively low DO and the shorter Lead time ○ ○ ◑ ◑ ○ ◑ ◑ ○ ○ ◑ ◑ conveyance routes. Options with higher DO potentially require tunnelling for water conveyance which significantly increases their expected lead time. ○ ◑ ◑ ◑ ◑ ◑ ◑ ○ ◑ ◑ ◑  Options apart from Deephams and Kempton involve lengthy conveyances that do not lend Phasing themselves to phasing, particularly in congested urban areas.

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○  Future capacity increases are constrained by the availability of effluent. As such, these options Adaptability are considered to have a neutral benefit/dis-benefit.  All RO options (treatment of final effluent) could be ramped-up in under 1 day from ‘hot standby’ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ mode, but take 8 weeks from a ‘care and maintenance’ state. The risk of a long ramp up time Ramp-up reduces the benefit of the scheme if ramp-up has not commenced early enough to make the supply option available when required, or if ramp-up takes longer than expected. Deliverability  Options with longer conveyance infrastructure pose greater risk to constructability, which is ○ ◑r ◑r ◑r ○ ○ ○ ○ ◑r ◑r ◑r considered a material but reducible dis-benefit. Water reuse would involve a new use of industry Constructability standard technology. Hence smaller capacity plants as a first option would be beneficial in terms of constructability.  TW have been operating the Gateway desalination plant for 6 years, which includes UF and RO. ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r ◑r RO technology is complex and requires skilled operators. Experience at Gateway has also Operability shown that intermittent operation of RO plant can be challenging. A material dis-benefit has been assigned accordingly.

Dependencies ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○  No material dependencies identified.  Yield certainty assessed as neutral benefit/dis-benefit. While there is uncertainty around how Data confidence ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ effluent volumes will change in a severe drought, a conservative approach has been adopted for assessing available effluent volumes. Resilience ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉  Water reuse options are not expected to be affected by climate change impacts resulting in Climate change wetter winters and drier summers ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎  All water reuse options are assessed to have a material benefit for resilience to severe drought Severe drought as the resource should be available in all but extreme (level 4 restrictions) drought scenarios.  The resource for reuse is predictable, however there is a risk of long ramp-up times preventing Resource ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ the anticipated DO benefit from being realised. This is partially mitigated by using a ‘hot standby’ predictability mode for three months of the year, therefore assessed to have neutral benefit/dis-benefit. ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑  The 8 week ramp up time from a ‘care and maintenance’ state limits the utility of the resource to System outage support unplanned outage events if it is not in supply, providing material dis-benefit. Other ‘failure modes’ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑  Reuse is energy intensive and is particularly vulnerable to asset failure and power failure.

Screening decision  ✖ ✖ ✖ ✖ ✖ ✖ ✖  Refer to section 5.4.2 for the rejection reasoning for the Mogden, Kempton and Crossness reuse  ✖   options.

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Table B.3: London WRZ – New reservoir options screening assessment Marsh Chinnor

Abingdon Reservoir Gibbon Reservoir

Reservoir

125- <125 >225 <75 75-174 <75 75-174 225 Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d

Sub-dimension Ml/d Phased Comments Env & Social  Substantial beneficial effects include provision of significant additional storage for water resources resilience, opportunity for recreational resource provision and opportunity for biodiversity enhancement. Material dis-benefits include loss of a small number of properties and agricultural land, with effects on landscape and visual amenity mitigated to an extent through landscaping.  Adverse effects from prolonged construction period can be mitigated through best practice construction methods, screening of construction works, traffic management controls and measures to minimise temporary effects on recreational facilities.  The Marsh Gibbon and Chinnor sites (up to 50 Mm3) and the Marsh Gibbon site (up to 75 Mm3) perform less well than the Abingdon site in respect of their comparative environmental performance, although the environmental effects of all three reservoir sites are within the material dis-benefit assessment category. The SEA ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ Marsh Gibbon site performs less well than both the Abingdon and Chinnor sites in landscape terms due to the loss of characteristic ridge and furrow patterns. The Chinnor site performs less well than both Abingdon and Marsh Gibbon sites in respect of its impact on visual amenity. Both Marsh Gibbon and Chinnor perform less well than the Abingdon site in respect of adverse impacts on recreational facilities with both sites impinging on national trails.  The phased option at Abingdon will likely have a greater material dis-benefit than the other Abingdon options due to the extended construction period being repeated for each of the two phases; however, the magnitude of this impact will depend on how much time elapses between each phase – if the phases are close together in time, a substantial dis-benefit would arise; if the phases are many decades apart, the construction effects are assessed as a material dis-benefit.

HRA ○ ○ ○ ○ ○ ○ ○ ○  Options will not lead to likely significant effects on any European designated sites.

r r r r r r r r  Options involve some loss or diversion of watercourses, with material dis-benefit to WFD objectives. These are WFD ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑ reducible through careful design and mitigation measures. ○ ◑r ◑r ◑r ○ ◑r ○ ○  Potential cumulative effects of discharges from the larger reservoir options for Abingdon and Marsh Gibbon on the flow regime in River Thames alongside the 400 and 500 Ml/d supported Severn to Thames transfer options. Cumulative effects These may be mitigatable through careful management of the cumulative operational regime and/or in-river management measures. Cost The two zone options are more cost effective than single zone options as the SWOX resource also benefits London ○ ○◑ ◑ ○◑ ◑ ◑ ◑ ◑ through effluent returns to the River Thames. The larger options perform poorly as the screening thresholds fall more rapidly at the larger sizes than the reduction in unit cost. Promotability The potential for synergies through supplying other WRZs (both belonging to TW and other companies) exists for Synergies ◎ ◉ ◉ ◉ ◎ ◉ ◎ ◉ all river regulation reservoir options but would be greater with larger capacity reservoirs as larger schemes provide greater potential for supplying other WRZs or water companies.

Customer ◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑  Assigned material dis-benefit on the basis of WRMP14 research reported by the Customer Challenge Group acceptability which concluded that reuse was preferred to capital intensive options such as reservoirs.  There is some strong local opposition to the Abingdon reservoir and a Group Against Reservoir Development Local acceptability ● ● ● ● ● ● ● ● (GARD) has been established. GARD opposes both small and large reservoirs at the Abingdon site. Similar local opposition is possible at other sites which is a substantial dis-benefit.

Regulatory ○ ○ ○ ○ ○ ○ ○ ○  No material regulatory acceptability concerns identified. acceptability

Wider stakeholder ◑r ◑ ◑ ◑ ◑ ◑ ◑ ◑  Assigned material irreducible dis-benefit on the basis of representations made at the Abingdon Reservoir acceptability WRMP09 public inquiry. Flexibility Lead time ● ● ● ● ● ● ● ●  All options are predicted to have a lead time of up to 13 years, considered substantial dis-benefit.

◑ ◑ ◑ ◑ ◑ ◑ ◑ ◑  Phasing is assessed as a material dis-benefit as it limits the potential maximum storage potential on the site due Phasing to the storage that is given up to provide the dividing embankment. ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎  Once built, there is the potential for the reservoir to hold water from alternative sources, thereby offering material Adaptability benefit in terms of adaptability.

Ramp-up ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎  Ramp-up into supply requires less than one day, offering material benefit. Deliverability Geotechnical risks around construction on the Abingdon site are reduced by the existence of previous geotechnical investigations. Uncertainty remains around geotechnical risks associated with the Marsh Gibbon and Chinnor sites, but these are potentially reducible with further investigation. The Marsh Gibbon and Chinnor sites also face Constructability r r r r ◑ ◑ ◑ ◑ ● ● ● ● additional constructability challenges associated with the substantially longer intake pipelines and more complex emergency drawdown arrangements required compared with those needed for the Abingdon site which is more proximate to the River Thames.  Thames Water has extensive experience of operating raw water reservoirs on the River Thames. Although the Operability ○ ○ ○ ○ ○ ○ ○ ○ existing reservoirs are not used for river regulation, operation of a new Upper Thames reservoir is considered to be well within TW’s established operational capabilities.

Dependencies ○ ○ ○ ○ ○ ○ ○ ○  No material dependencies identified. ○ ○ ○ ○ ◑r ◑r ◑r ◑r  Geological risk is greater for Marsh Gibbon and Chinnor reservoirs due to the lack of ground investigations, which Data confidence are available for the Abingdon site. Resilience ◉ ◉ ◉ ◉ ◉ ◉ ◉ The resource benefits of large reservoir options should not be significantly diminished as a result of climate change Climate change ◉ scenarios resulting in increasingly wetter winters and drier summers.  Stochastic analysis of resilience of reservoir storage to future droughts indicates that the reduction in Deployable Severe drought ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Output associated with future droughts is not significantly less than the Deployable Output based upon historical droughts. Therefore assessed as material benefit.  Reservoir options perform very well in terms of predictability compared with other option types. In particular the Resource ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ramp-up time for reservoirs is short and there is low risk that the supply is not available when required. predictability Furthermore, if ramp-up is delayed the resource is not lost, but it is stored and there is the possibility of releasing larger volumes to compensate if needed. ◎ ◉ ◉ ◉ ◎ ◉ ◎ ◉  Large reservoirs offer a substantial benefit in terms of resilience to system outage in that water can be called System outage upon rapidly to augment resources through any of the west London intakes and treatment works.

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Marsh Chinnor

Abingdon Reservoir Gibbon Reservoir

Reservoir

125- <125 >225 <75 75-174 <75 75-174 225 Ml/d Ml/d Ml/d Ml/d Ml/d Ml/d

Sub-dimension Ml/d Phased Comments  Reservoirs are more resilient than other option types to other failure modes, particularly electrical/ ○ ○ ○ ◑ ○ ◑ ○ ○ mechanical/process failure. Managing water quality in the reservoir is a risk, but mitigation measures have been Other ‘failure modes’ provided for (including provision for mixing and multiple draw off locations/depths), therefore assessed as neutral benefit/dis-benefit.

Screening decision  Refer to section 5.4.2 for rejection reasoning for Marsh Gibbon and Chinnor reservoirs. ✖    ✖ ✖ ✖ ✖  The Abingdon option <125Ml/d is rejected due to mutual exclusivity with larger options on the same site, including phased construction.

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Table B.4: London WRZ – Direct river abstraction options screening assessment

Teddington

300 Sub-dimension Ml/d Comments Env & Social  Material beneficial effect due to additional climate change resilience and avoiding additional pressures on freshwater resources by making use of river flow support from sewage treatment works. The option also optimises the use of existing infrastructure. SEA ◎◑  Adverse effects from the use of materials in construction and power and chemicals for treatment of effluent or poor quality river water when in operation. It may have some adverse effects on navigation at low flows in Upper Thames Tideway (this is currently being assessed through modelling work).

HRA ○  No likely significant effects on designated European sites, with tunnelling and/or careful pipeline routeing to avoid any impacts on sites.

WFD ◑r  Impact on WFD water quality objectives is a material dis-benefit, reducible through design of discharge location and extent of effluent treatment. ◑  Potential cumulative effects identified in relation to increased salinity from multiple reuse, direct river abstraction and/or desalination schemes Cumulative effects that affect flows in the Thames Tideway pending further investigation of receptors that may be affected by such cumulative effects. Cost ◉  Substantial benefit against the cost dimension. Promotability Synergies ◎  Options could indirectly benefit other companies by freeing water from existing licences that could be traded.

Customer acceptability ○  No material customer preference concerns identified.

Local acceptability ◑  Planning permission required for a new outfall and new intake upstream of Teddington weir.  Abstraction licence required and change to discharge consent for Mogden effluent transfer. Regulatory r ◑  Tertiary treatment required for Mogden effluent to meet EA consent conditions to discharge to semi-tidal reach. Potential EA concerns over acceptability environmental impacts of reducing flow downstream of Isleworth Ait on SSSI need to be addressed through appropriate mitigation.

Wider stakeholder ◑r  Port of London Authority agreement needed, but this risk is considered reducible through demonstration by ongoing modelling work. acceptability Flexibility Lead time ○  The option is predicted to have a lead time of 6 years, but there are uncertainties regarding planning, environmental and construction timings. ◑  The river intake and treatment component of the option could be phased, however phasing is likely to be less economic due to requirement for Phasing pipeline/tunnel infrastructure, amounting to a material dis-benefit.

Adaptability ○  River intakes considered to have limited adaptability as they are constrained by the hydrological yield of the rivers. ◎  Tertiary treatment at Mogden is assumed to operate continuously, therefore the Teddington DRA option should be available for ramp up within a Ramp-up week. Deliverability r Constructability ◑  Land availability is a particular concern.

Operability ○  No material operability concerns identified

Dependencies ○  Abstraction from the Lower Lee expected to require a licence from the Canal and River Trust.

Data confidence ○  Assessed as neutral benefit/dis-benefit. Resilience Climate change ◎  The option is dependent on transfer of effluent from Mogden treatment works, which has been estimated conservatively. ◎  In extreme drought a drought permit could be sought to reduce Teddington Target Flows, allowing Mogden tertiary treated effluent to be Severe drought abstracted into the raw water system.

Resource predictability ◎  The option provides good predictability as flow predominately determined by effluent discharges.  The water abstracted at Teddington is discharged into the Thames Lee tunnel and ultimately treated in East London. Outage at Coppermills System outage ◑ would significantly reduce treatment capacity, but this risk is reducible as options for developing east London treatment at alternative sites are being explored.

Other ‘failure modes’ ○  Vulnerability is similar to that of existing abstractions on the River Thames in west London, providing neutral benefit/disbenefit.

Screening decision  

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Table B.5: London WRZ – Desalination option screening assessment

Beckton Crossness (Blended) Crossness (Unblended)

150 150-300 65 Sub-dimension Ml/d Ml/d Ml/d Comments Env & Social ◎◑ ◎◑ ◎◑  All options provide material benefit by enabling climate change resilience and avoiding additional pressure on freshwater SEA resources. Adverse effects from the use of materials in construction and chemicals and power for treatment when in operation are a material dis-benefit, with consequential carbon emission effects  Tunnelling and/or pipeline routes will avoid conveyance impacts on sensitive terrestrial features, preventing any significant HRA ○ ○ ○ effects on any European designated sites.

WFD ○ ○ ○  WFD water quality and ecology risks from brine discharges will be mitigated through design and location of the discharge. ◑ ◑ ◑  Potential cumulative effects identified in relation to increased salinity from multiple reuse, direct river abstraction and/or Cumulative effects desalination schemes that affect flows in the Thames Tideway pending further investigation of receptors that may be affected by such cumulative effects. Cost Unblended option performs better on cost as it excludes the cost of a tunnel to convey desalinated water to Coppermills for ○ ○ ◉ blending. Promotability Synergies ◎ ◎ ◎  Could potentially indirectly support other water companies in the South East, but with a reduced DO for London.  Opposition from customers to high energy schemes is assessed as a material dis-benefit, reducible through inclusion of renewable energy sources, such as at Gateway desalination plant. r r Customer acceptability ◑ ◑ ●  The unblended Crossness option (with direct supply to Northumberland Heath Service Reservoir) is a substantial dis-benefit due to the risk of customer complaints caused by outages of the desalination plant. This risk is significantly lower for the other options where desalinated water would be blended with water from Coppermills Water Treatment Works. ◑ ◑ ◑  All three options require tunnelling or directional drilling. This will require intermediate shafts with the potential to cause Local acceptability disruption and materially impact local acceptability, especially through heavily urbanised areas.

Regulatory acceptability ○ ○ ○  No material regulatory acceptability concerns identified.

Wider stakeholder ◑r ◑r ◑r  Possible objection from conservationists is a material dis-benefit. Reducible with further evidence and engagement. acceptability Flexibility  The large desalination options have an estimated lead-time of 7 years, which is a neutral benefit/dis-benefit. Lead time ○ ○ ◎  The unblended Crossness option is expected to have a lead time under five years, which is assessed as a material benefit.  Treatment options can be implemented incrementally at low cost; however phasing is often less economic because of Phasing ◑ ◑ ○ significant upfront cost for long distance conveyance. This is assessed as a material dis-benefit for Beckton and Crossness (blended) options which include a transfer tunnel. ◎ ◎ ○  Transfer tunnel from new Beckton desalination plant provides opportunities to transfer water from the existing Beckton Adaptability Gateway plant and/or from part of the future expansion of the London ringmain.  The ramp-up time for RO technology desalination is estimated at less than 1 day from ‘hot standby’ mode, used for three Ramp-up ◑ ◑ ○ months of the year, but 8 weeks from the ‘care and maintenance’ state used at other times. Crossness (unblended) desalination plant assumed to be in service all the time and so ramp up time has neutral benefit/dis-benefit. Deliverability  TW have experience of constructing a desalination plant. The Beckton and Crossness (blended) sites have constraints; the r Constructability ◑ ◑r ○ Crossness (unblended) site has fewer constraints. The majority of constructability challenges relate to conveyance, providing material dis-benefit that is reducible through further option development.  TW has been operating the Beckton Gateway plant for 6 years. Desalination technology is complex and requires skilled operators, and its use is assessed as a material but reducible dis-benefit. Operability ◑r ◑r ●  Operation of the Crossness (unblended) plant without water for blending means that the full capacity of the plant may not generally be utilised, making it less flexible to supply other zones (due to the impact on changing water quality).

Dependencies ○ ○ ○  There would be limited dependencies on third parties. There are competing TW schemes for the available land at Beckton.  During a prolonged drought the saline interface progresses up the Thames Tideway. There is therefore uncertainty around Data confidence ◑r ◑r ◑r the range of salinities that should be considered so as to ensure that the desalination plant can operate both in a normal year and under severe drought conditions. Resilience ◎ ◎ ◎  Raw water availability for the option would not be vulnerable to climate change. However, in severe drought, increasing Climate change salinity could impact on plant availability/output (see comment on severe drought). ◎ ◎ ◎  Raw water availability for the option would not be vulnerable to severe drought as it is non-reliant on natural hydrology. However, in a prolonged drought salinity is expected to increase as the saline interface moves upstream. If salinity were to Severe drought increase beyond the design envelope for the desalination plant then the deployable output benefit could be substantially reduced.  The resource is predictable, however there is a risk of long ramp-up times preventing the anticipated DO benefit from being Resource predictability ○ ○ ○ realised. This is partially mitigated by using a ‘hot standby’ mode for three months of the year, therefore assessed as neutral.  The 8 week ramp up time from a ‘care and maintenance’ state limits the utility of all desalination resources to support unplanned outage events if not already in supply, providing material dis-benefit.  The unblended Crossness option (with direct supply to Northumberland Heath Service Reservoir) provides substantial dis- System outage ◑ ◑ ● benefit as it could not be used to support unplanned outage events without a change in water quality and the resolution of associated customer complaints. This risk is significantly lower for the other options where desalinated water would be blended with water from Coppermills WTW  Desalination involves complex treatment processes which increases its vulnerability to failure, is vulnerable to power ◑ ◑ ◑ outages (mitigated by own power generation), has a high dependency on the chemical supply chain and would be Other ‘failure modes’ vulnerable to coastal flooding but mitigation is already provided from the existing flood defences. Pollution incident from shipping would impact water quality.

Screening decision    ✖  Refer to section 5.4.2 for rejection reasoning for the Crossness (Unblended) option

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

Table B.6: London WRZ – Aquifer recharge options screening assessment

SLARS SLARS

Kidbrooke Streatham Merton AR/ 7 4 5 Sub-dimension Ml/d Ml/d Ml/d Comments Env & Social  No significant beneficial effects. Some minor beneficial effects (but small volume of water) with respect to improved resilience to the likely effects of climate change by increasing water storage capacity and allowing the storage of water during times of surplus for re-abstraction SEA ○◑ ○○ ○○ during times of high demand.  Minor adverse effects from the use of materials in construction and power and chemicals for treatment when in operation. Some option specific, temporary adverse construction effects with respect to SLARS Kidbrooke.

HRA ○ ○ ○  No likely significant effects on any European designated sites.

WFD ○ ○ ○  WFD risks to groundwater bodies will be mitigated through careful design and operation of the schemes.

Cumulative effects ○ ○ ○ No material cumulative effects identified Cost ○ ◉ TBC  Merton costs are to be confirmed Promotability Synergies ○ ○ ○  Due to the small scheme sizes of the AR options, there are no opportunities for synergies.

Customer preference ○ ○ ○  No material customer acceptability concerns associated with these options.  New WTWs would be required at all sites, which would have short-lived and not significant impacts on local residents, and are assessed therefore as neutral. New boreholes would need to be drilled for the SLARS option, but with no lasting effects on local residents. Disruption Local acceptability ○ ◑r ◑r during construction of the pipeline for the Merton option is considered a material but reducible dis-benefit.  Construction at Streatham is in a residential area and the proposed works are anticipated to be of concern to local residents. This may be managed through engagement and is therefore considered to be a material if reducible dis-benefit.  Licensing is a key issue for these options. The EA have indicated that they would be prepared to licence an AR scheme but this is not guaranteed. The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse Regulatory ◑r ◑r ◑r impact on the environment, including Merton and Streatham as category 2 items. The Kidbrooke options are located in an area categorised as acceptability “no water available for licensing”. The SLARS option also requires a new winter abstraction licence from the River Thames. All options have therefore been assessed as providing material reducible dis-benefit.

Wider stakeholder ○ ◑r ○  The WTWs would be located on TW-owned land. Previously granted planning permission would allow the Kidbrooke options to be built. The acceptability proximity of the Streatham site to a Network Rail railway line provides a material but reducible dis-benefit. Flexibility ○ ◎ ◎  The lead time for all these options has been assessed as being under 5 years, providing material benefit, with the exception of SLARS Lead time Kidbrooke owing to the length of pipeline needed crossing key services.  There are limited opportunities for phasing or adaptability, due to the nature of the schemes. Boreholes could be constructed incrementally but ○ ○ ◑ with the result of delayed DO delivery and a likely increase in costs. There is potential opportunity if both Kidbrooke options are selected to Phasing phase construction of the WTW as required, but not at the individual option level. The Merton option is assessed as a material dis-benefit due to the long distance urban pipeline included in the scheme.  AR schemes could be adapted to use different recharge water in the future (e.g. treated sewage effluent), but with significant uncertainties Adaptability ○ ○ ○ around practicalities and acceptability. Any option to increasing the capacity of the schemes would be highly dependent on the hydrogeological recovery rates of the sites. All AR options are therefore assessed as neutral benefit/dis-benefit.

Ramp-up ○ ○ ○  Based on operational experience, the ramp-up times during a drought would be under two weeks – a neutral benefit/dis-benefit. Deliverability  There are no constructability risks highlighted. Both river intakes (to provide the recharge water) and AR are known technologies that TW have Constructability ○ ○ ○ constructed and currently utilise as a part of their existing supply systems. The options have therefore all been assessed a neutral for constructability.  River intakes and AR are known technologies currently utilised by TW, and are therefore assessed as neutral. Operation of the Merton AR ○ ○ ◑ scheme requires shut-down of the WTWs during recharge, with specific associated design features and operational procedures. This has been Operability assessed as a material dis-benefit. Potential network constraints may limit water availability for recharge in the SLARS Kidbrooke option, therefore assessed as neutral.

Dependencies ○ ○ ○  There are no third-party dependencies for these options.  Yield certainty of AR schemes requires significant testing. Where this has already been undertaken, the options are assessed as a neutral benefit/dis-benefit. SLARS Kidbrooke has a material risk of not achieving the planned DO benefit to the WRZ. This is considered likely to be ◑r ○ ○ reducible as investigation and testing is yet to be completed for one of its component sites. Merton requires drilling and test pumping of a new Data confidence borehole at the Byegrove Road site to confirm yield and water quality, however it is a major aquifer and conditions are not expected to markedly differ from other sites. Further investigation is required to confirm the ability of the network to provide the required volume to the AR- Kidbrooke site. Resilience  The AR schemes do not depend on naturally occurring groundwater levels and therefore provide a greater level of resilience than conventional Climate change ◉ ◉ ◉ groundwater schemes. AR abstraction would not be impacted by climate change (when defined as wetter winters and drier summers) and would provide additional storage for the capture of surplus winter water – a substantial benefit.  SLARS schemes could be vulnerable to severe multi-season droughts diminishing the volumes available for aquifer recharge during winter Severe drought ◑ ◑ ◑ months, which is assessed as a material dis-benefit. Although more resilient than a direct river abstraction, surplus water from the treated water network may also not be available during severe winter droughts, which is assessed as a material dis-benefit.

Resource ◎ ◎ ◎  The AR schemes provide a predictable resource, assessed as a material benefit. predictability ○ ○ ○  Although all schemes provide additional water resources for London that can be ramped up at relatively short notice, the options are assessed System outage as a neutral benefit/dis-benefit due to their small sizes ○ ○ ○  The schemes are similarly vulnerable to other ‘failure modes’ as existing groundwater abstraction sites in the London WRZ and therefore Other ‘failure modes’ amount to a neutral benefit/dis-benefit.

Screening decision   

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

Table B.7: London WRZ – Aquifer storage and recovery options screening assessment

Addington Valley Thames Central London SE 3 3 Sub-dimension Ml/d Ml/d Comments Env & Social  No significant beneficial effects. Some minor beneficial effects associated with improved resilience to the likely effects of climate change by increasing water storage capacity and allowing the storage of water during times of surplus for re-abstraction during times of high demand. SEA ○○ ○○  Minor adverse effects during construction (after mitigation) and minor use of new materials during construction, and power and chemicals during operation. Some minor adverse effects on the water environment during operation.

HRA ○ ○  No likely significant effects on any European designated sites.

◑r  SE London Addington is assessed as a material dis-benefit due to minor adverse WFD effects on baseflow of surface waters (tributaries of the River WFD ○ Eden and the upper River Darent), that are reducible through careful design and operational control.  Thames Valley Central option is assessed as a potential material dis-benefit due to the cumulative effects with other options that share the same Cumulative effects ○ ◑ water resource (River Thames) as the source of recharge water (for example AR Kidbrooke). Cost  ◉ ◉ Recent testing at Horton Kirby has shown that a greater DO may be available from fewer boreholes than considered in the WRMP14 option. Promotability Synergies ○ ○  Due to the small scheme sizes of the ASR options, there are no opportunities for synergies.

Customer preference ○ ○  No material customer preference concerns have been identified associated with these options.  New boreholes would need to be drilled at the sites, but their construction would be particularly short-lived with no lasting effects on local residents, therefore assessed as neutral benefit/dis-benefit. Local acceptability ○ ◑r  Thames Valley Central option may require construction of a 1 km sewer, which is assessed as a material but reducible dis-benefit to local residents from impacts during the construction period. Further investigation is required to confirm that this sewer will be needed to deliver the option.  Licensing is a material risk for both options, but considered reducible through engagement with the EA. The EA have recently issued TW with a list of Regulatory ◑r ◑r groundwater sources that they consider have the potential to have an adverse impact on the environment, including the Addington groundwater acceptability source as a category 2 item, which may affect the viability of the ASR scheme.

Wider stakeholder ○ ○  The WTWs would be located on TW-owned land. No material wider stakeholder acceptability concerns have been identified associated with these acceptability options Flexibility Lead time ◎ ◎  The lead time for all these options has been assessed as being under 5 years, assessed as a material benefit.

Phasing ○ ○  There are limited opportunities for phasing due to the nature of the schemes.  ASR schemes could be adapted to use different recharge water in the future (e.g. treated sewage effluent), but with significant uncertainties around Adaptability ○ ○ practicalities and acceptability. Any option to increasing the capacity of the schemes would be highly dependent on the hydrogeological recovery rates of the sites. All ASR options are therefore assessed as neutral benefit/dis-benefit. ○ ○  Based on operational experience, the ramp-up times of these options during a drought would be under two weeks – assessed as a neutral benefit/dis- Ramp-up benefit. Deliverability Constructability ○ ○  There are no constructability risks highlighted and this is a well-known technology to TW. It has therefore been assessed as neutral. ◑r ◑r  Groundwater conditions at the Addington and Thames Valley sites are described as artesian. This could require boosting mains pressure to ensure Operability recharge into the aquifer at certain times of the year, and is assessed as a material but reducible dis-benefit.

Dependencies ○ ○  There are no third-party dependencies for these options. r r Data confidence ◑ ◑  Yield certainty of ASR schemes requires significant testing and is assessed, therefore, as a material, but reducible, dis-benefit. Resilience  The ASR schemes do not depend on naturally occurring groundwater levels and therefore provide a greater level of resilience than conventional Climate change ◉ ◉ groundwater schemes. ASR abstraction would not be impacted by climate change (when defined as wetter winters and drier summers) and would provide additional storage for the capture of surplus winter water – a substantial benefit.  Thames Valley Central relies on river flows during winter months to make use of surplus water. Although more resilient than a direct river abstraction, Severe drought ◑ ◑ surplus water from the treated water network may also not be available during severe winter droughts, assessed as a material dis-benefit.  SE London Addington ASR relies upon conventional groundwater sources sensitive to severe drought, assessed as a material dis-benefit.

Resource ◎ ◎  The ASR schemes provide a predictable resource, assessed as a material benefit. predictability

System outage ○ ○  Although both schemes provide additional storage for London, it is considered a neutral benefit/dis-benefit due to their small sizes ○ ○  The schemes are similarly vulnerable to other ‘failure modes’ as existing groundwater abstraction sites in the London WRZ and therefore offer neutral Other ‘failure modes’ benefit/dis-benefit.

Screening decision

 

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

Table B.8: London WRZ – Groundwater development options screening assessment

London London Chalk Confined Southfleet/ Greenhithe Merton recommissionin g London North Trading Licence Addington 1 2 8 2 2 Sub-dimension Ml/d Ml/d Ml/d Ml/d Ml/d Comments Env & Social  No material beneficial effects beyond the associated water resource yield benefit. Some minor adverse effects associated with power and chemical use during operation.  The Addington abstraction would have potential hydrogeological and hydrological effects due to the abstraction on nearby springs with subsequent effects on surface water flows and ecology. This is assessed as a material dis-benefit, reducible through further investigation, test pumping and monitoring with regard to potential effects on identified surface water features.  The London confined Chalk abstraction has no interaction with surface waters and there is potential for making best use of available groundwater resources, plus delivery of minor local benefits associated with rising groundwater levels. r r SEA ○◑ ○○ ○◑ ○◑  The Southfleet/Greenhithe option is in an area of Paleolithic and paleoanthropological interest therefore potential effects on cultural heritage could arise from construction of the scheme. Dialogue with Historic England is required. The abstraction has potential hydrogeological and hydrological effects in relation to groundwater quantity and potential for saline intrusion. The catchment context is, however, that large scale historical Chalk quarry dewatering has reduced significantly and there is a water resource available.  The North London Licence Trading option is on an existing industrial abstraction site from a confined aquifer so the abstraction impact is likely to be low, with no material adverse or beneficial effects. Construction related impacts of the required conveyance pipeline are assessed as a material but reducible dis-benefit.

HRA ○ ○ ○ ○  No likely significant effects on any European designated sites.  Addington provides a material risk of deterioration of WFD Epsom North Downs Chalk groundwater waterbody, which is reducible through careful design and operation of the scheme. r r WFD ◑ ○ ◑ ○  Southfleet/Greenhithe abstraction has potential hydrogeological and hydrological effects due to the abstraction in relation to groundwater quantity and potential for saline intrusion. The catchment context is, however, that large scale historical Chalk quarry dewatering has reduced significantly and there is a water resource available.

Cumulative effects ○ ○ ○ ○  No cumulative effects anticipated assuming licence trading removes any risk of derogation of the existing abstractor.

Cost ◉ ◉ ◉ ◉  All options provide substantial benefit, primarily due to low capital costs. Promotability  Due to the small size of these schemes, there are no opportunities for synergies, except for the London confined Chalk option Synergies ○ ◎ ○ ○ ○ which offers material benefit to the Old Oak & Park Royal Development Corporation integrated water management plan. customer preference

Customer ○ ○ ○ ○ ○  No material customer preference concerns have been identified associated with these options. preference  The Addington option involves construction of a new WTW on the existing TW site which would have short-lived and not significant impacts on local residents, and is therefore assessed as neutral.

r  London Confined Chalk involves construction in an industrial area – assessed as neutral Local acceptability ○ ○ ◑ ○ ○  Southfleet/Greenhithe includes construction of a 3km pipeline through an urban area – a material, but reducible, dis-benefit.  Merton recommissioning involves construction in a mixed residential and industrial area on an existing TW site. Impacts will be short lived, therefore this is assessed as neutral.  Regulatory acceptability is a key issue as where licence changes are required they could meet with challenges.  Addington provides material dis-benefit as the CAMS status is “no water available” and although the scheme only requires maximisation of an existing licence, there is a nearby abstraction that the EA are concerned may be affected by the proposed work. This dis-benefit is reducible through engagement with the EA.  The London confined Chalk abstraction has potential for making best use of available groundwater resources, plus delivery of minor local benefits associated with rising groundwater levels, and is assessed as a material benefit  The CAMS status for Southfleet/Greenhithe is “over-licensed”, assessed as a material dis-benefit. This is considered reducible based on comments received from the EA. The North London Licence Trading option requires agreement and arrangement of payment to the current owner and is dependent upon this. Therefore, this represents a material risk, but this can be reduced by Regulatory r r r ◑ ◎ ◑ ○ ◑ putting a suitable arrangement in place. Initial comments received from the EA indicate that they would not rule the option out at acceptability this stage. Regulatory acceptability is therefore assessed as material, but reducible dis-benefit. The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on the environment. This has implications for regulatory acceptance. Addington and Southfleet/Greenhithe appear on this list as category 2 items. Initial comments received from the EA on the North London Licence Trading option indicate that they would not rule the option out at this stage. It is therefore assessed as being a material but reducible dis-benefit.  Merton recommissioning is a within licence increase in DO, therefore it is assessed as a neutral benefit/dis-benefit.  The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on the environment. This has implications for regulatory acceptance. Addington and Southfleet/Greenhithe appear on this list as category 2 items.  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be reduced through engagement and are assessed as neutral benefit/dis-benefit. Wider stakeholder ○ ○ ○ ○ ◑r acceptability  The North London Licence Trading option requires agreement and payment to the current owner, providing reducible material dis- benefit. Flexibility Lead time ◎ ◎ ◎ ◎ ◎  The lead time for these options has been assessed as being under 5 years, assessed as a material benefit.

○ ○ ◑ ○ ○  There are no opportunities for phasing due to the nature of the schemes, assessed as a neutral benefit/dis-benefit. Phasing Southfleet/Greenhithe includes a 3km pipeline through an urban area which is assessed as a material dis-benefit for phasing. ○ ○ ○ ○ ○  There are no opportunities for adaptability due to the nature of the schemes. Any increase in capacity would be outside of the Adaptability existing licence and therefore cannot be assumed. All options are assessed accordingly as having neutral benefit/dis-benefit.  All options except Southfleet/Greenhithe have a ramp-up time during a drought of under one week, assessed as material benefit. Ramp-up ◎ ◎ ○ ◎ ◎  Southfleet/Greenhithe has a ramp-up time of under two weeks, assessed as a neutral benefit/dis-benefit. Deliverability  No significant constructability risks have been identified and this is a well-known technology to TW, and assessed as a neutral benefit/dis-benefit. Constructability ○ ○ ○ ○ ◑r  North London Licence Trading requires a new pipeline under the A406 by pipe jacking, assessed as a material, but reducible, dis- benefit.

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Fine Screening Report Update

 No significant operability risks have been identified and this is a well-known technology to TW - as such it has been assessed as a neutral benefit/dis-benefit Operability ○ ○ ○ ○ ◑r  The North London Licence Trading option requires an arrangement with the current owner for operation of the scheme, assessed as a material, but reducible, dis-benefit. ○ ○ ○ ○ ◑r  The North London Licence Trading option relies upon reaching an agreement with the third party current owner, assessed as a Dependencies material, but reducible, dis-benefit.  The yield certainty of these schemes aligns with the industry standards.  Further test pumping will be required for the London Confined Chalk option to quantify the DO, confirm groundwater quality and confirm the level of treatment required, and is assessed as a material, but reducible, dis-benefit. r r r Data confidence ○ ◑ ○ ◑ ◑  The data and physical state of the North London Licence Trading borehole is reported to be poor, and is assessed as a material, but reducible, dis-benefit.  There is some uncertainty regarding the potential DO of the Merton recommissioning option at peak licensed rates. This is a material dis-benefit, which is reducible following testing of the source. Resilience  Merton, London Confined Chalk and North London Licence Trading abstract from the London Confined Chalk aquifer which is broadly resilient to changes in recharge patterns.  Climate change analysis was undertaken at these sites as part of the WRMP14 investigations, on which basis they are assessed Climate change ◑ ◎ ◑ ◎ ◎ as a material benefit. Southfleet/Greenhithe is assessed as a material dis-benefit due to its hydrogeological setting in the unconfined Chalk. Addington is also an unconfined source and therefore less resilient to changes in recharge patterns, which is a material dis-benefit.  Options reliant on natural groundwater or surface water catchment flows are the most vulnerable to droughts outside of the historical record. Options located in the confined Chalk are considered at relatively low risk of impact, and so are assessed as having neutral benefit/dis-benefit. The London confined Chalk option would be particularly resilient, and is assessed as a material Severe drought ◑ ◎ ◑ ◑r ○ benefit. Southfleet/Greenhithe and Addington are both assessed as having material dis-benefit due to their hydrogeological setting in the unconfined Chalk.  Historical data from the Merton source indicate that it may not be able to deliver the peak DO during a drought period. This is a material dis-benefit, which is potentially reducible through testing following recommissioning.  The London Confined Chalk groundwater options would offer a material benefit in terms of the predictability of the resource.  Southfleet/Greenhithe and Addington are unconfined sources with reduced predictability as groundwater levels are more variable, Resource ○ ◎ ○ ◎ ◑r and are assessed as having neutral benefit/dis-benefit. predictability  The North London Licence Trading option may be adversely affected by the resource requirements of its current owner, and it is therefore assessed as having material dis-benefit, that is reducible through putting an appropriate agreement in place. ○ ○ ○ ○ ○  The groundwater options would not add operational flexibility for system outage, and are assessed as having neutral benefit/dis- System outage benefit.  The options are similarly vulnerable to other ‘failure modes’ as existing groundwater abstraction sites in the London WRZ and Other ‘failure ○ ○ ○ ○ ◑r therefore offer neutral benefits/dis-benefits. North London Licence Trading may be more vulnerable because TW is not in direct modes’ control of the site, and is assessed as a material, but reducible dis-benefit. Screening decision       

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Thames Water WRMP19 Resource Options

Fine Screening Report Update

Table B.9: London WRZ – Catchment management options screening assessment

(Groundwater) Street Green Green (Groundwater)

Southfleet

North Orpington Orpington North (Groundwater) River Lower Thames Lee River Lower 0.2 0.3 0.4 1.5 1.0 Sub-dimension Ml/d Ml/d Ml/d Ml/d Ml/d Comments Env & Social  Material beneficial effects on the local terrestrial and water environment through catchment land improvements over time. SEA ◎○ ◎○ ◎○ ◎○ ◎○  Negligible adverse effects identified.

HRA ○ ○ ○ ○ ○ No likely significant effects on any European designated sites

WFD ○ ○ ○ ○ ○ No material adverse or beneficial effects on WFD water bodies No material adverse or beneficial cumulative effects identified Cumulative effects ○ ○ ○ ○ ○ Cost With the exception of the Lower Lee option, the options are assessed as having substantial benefit. The Lower Lee option is ◉ ◉ ◉ ◉ ◎ assessed as having material benefit Promotability ○ ○  Potential minor synergies with the Lower Lee direct river abstraction scheme for the Lower Lee option. Limited synergies Synergies ○ ○ ○ relating to the other options. ◎ ◎ ◎ ◎ ◎  Material benefit to customer preference likely to be associated with these options due to improvements to local environment as Customer preference well as addressing water quality risks

Local acceptability ○ ○ ○ ○ ○  Subject to engagement with local landowners and agreement on approach, no material risks anticipated

Regulatory ◉ ◉ ◉ ◉ ◉  Substantial material benefit to regulatory acceptability as options align with policy objectives of Defra acceptability

Wider stakeholder ◉ ◉ ◉ ◉ ◉  Substantial material benefit to wider stakeholder acceptability as options align with feedback received from stakeholders during acceptability screening and feasibility report consultations Flexibility  The lead time for these options has been assessed as being more than 5 years before any benefits are likely to be realised in ○ ○ ○ ○ ○ Lead time terms of deployable output.

◎ ◎ ◎ ◎ ◎  Some material benefit from opportunities for scaling up the activities over time in response to learning from initial Phasing implementation in targeted areas

Adaptability ◉ ◉ ◉ ◉ ◉  Substantial benefit from adaptability to changing circumstances due to operational nature of the options

Ramp-up ◑ ◑ ◑ ◑ ◑  Material dis-benefit to ramp-up / ramp-down capability. Deliverability ◑ ◑  Some material dis-benefit due to challenges in agreeing specific measures with landowners and implementation of the right Constructability ◑ ◑ ◑ measures in the right settings  Some material dis-benefit due to challenges in maintaining the land management improvements with landowners and adapting Operability ◑r ◑r ◑r ◑r ◑r measures to reflect monitoring findings over time. Dis-benefit reducible through careful structuring of agreements and flexibility to adapt to emerging monitoring evidence.

◑ ◑ ◑ ◑ ◑  Some material dis-benefit due to dependencies on other co-funding provision, landowner agreements and land management Dependencies activities outside the control of Thames Water ◑ ◑ ◑ ◑ ◑  Some material dis-benefit due to uncertainties over implementation costs, availability of co-funding and the benefit to water Data confidence quality that will arise as a result of implementation. Resilience  Some material benefit by improving the resilience of sources by addressing water quality risks that may deteriorate due to ◎ ◎ ◎ ◎ ◎ Climate change climate change without land management interventions

Severe drought ○ ○ ○ ○ ○  Resilient to severe drought but very low additional volume of reliable supply provided  Some material dis-benefit as the resource benefit is not predictable and will be dependent on a variety of factors for the Resource ◑ ◑ ◑ ◑ ◑ predictability deployable output benefit to be confirmed ○ ○ ○ ○ ○  The options would not add any material operational flexibility for system outage and have therefore been assessed as having System outage neutral benefit/dis-benefit. ○ ○ ○ ○ ○  The options would not add any material benefits to addressing other ‘failure modes’ and have therefore been assessed as Other ‘failure modes’ having neutral benefit/dis-benefit. Screening decision     

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Appendix C. SWOX WRZ fine screening tables

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Table C.1: SWOX WRZ – Groundwater development options screening assessment

1 Moulsford 2.0 Sub-dimension Ml/d Comments Env & Social  No beneficial effects beyond the associated water resource yield benefit. SEA ○◑  Pipeline construction in an AONB and close to some SSSIs and heritage sites provides material dis-benefit, with impacts mitigated as far as possible through best practice construction methods and careful routing.

HRA ○  No likely significant effects on any designated European sites. ◑r  Moulsford 1 abstraction is from the Chilterns unconfined Chalk aquifer. There is a potential risk to WFD water body status that can be mitigated through WFD appropriate engagement with the Environment Agency.

○  Some potential for minor cumulative effects on water resources with respect to other schemes that draw on the same or connected resources of this part Cumulative effects of the River Thames, but assessed as neutral benefit/dis-benefit. Cost ◉ The option provides substantial benefit, primarily due to low capital cost. Promotability Synergies ○  Due to the small size of the option there are no opportunities for synergies.

Customer preference ○  No material customer preference concerns have been identified associated with this option. ◑r  The option involves 2.1 km of new pipeline (raw, treated and/or washout). This would be a material but reducible dis-benefit to local residents due to Local acceptability impacts during the construction period and planning permission will be required.  Regulatory acceptability is a key issue. The proposed abstraction is in a water body classified as ‘No Water Available’. Transfer of the Childrey Warren Regulatory ◑r licence to Moulsford is expected to be accepted by the Environment Agency. However, the Environment Agency may fail to issue a licence or impose a acceptability flow constraint which could reduce DO benefit.

Wider stakeholder ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be mitigated acceptability through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility Lead time ◎  The lead time for this option has been assessed as being under 5 years - assessed as a material benefit.

Phasing ○  There are no opportunities for phasing due to the nature of the scheme - assessed as a neutral benefit/dis-benefit

Adaptability ○  There are no opportunities for adaptability due to the nature of the scheme - assessed as a neutral benefit/dis-benefit

Ramp-up ◎  The ramp-up time during a drought is under one week - assessed as a material benefit Deliverability ○  The option is unlicensed and unproven but a conventional groundwater development in a well understood major aquifer, therefore assessed as neutral Constructability benefit/dis-benefit.

Operability ○  No material operability risks have been identified and this is a well-known technology to TW, therefore assessed as neutral benefit/dis-benefit.

Dependencies ○  No material third-party dependencies have been identified for these options, therefore assessed as neutral benefit/dis-benefit. ◑r  There are risks associated with borehole yield, water quality and abstraction licence changes. These material dis-benefits are all reducible through drilling Data confidence and test pumping pilot boreholes. Resilience  The resource benefit could be diminished as a result of increasingly wetter winters and drier summers, particularly as the source is in the unconfined Climate change ◑ Chalk, which responds more rapidly to changes in recharge. Moulsford 1, as a Thames-side source, is considered more resilient to climate change due to buffering of water levels by surface water interaction. The option is assessed as having material dis-benefit. ◑  Options reliant on natural groundwater or surface water catchment flows are the most vulnerable to droughts outside of the historical record, providing Severe drought material dis-benefit. The proximity of the River Thames will buffer groundwater levels during a severe drought.

Resource ○  Moulsford 1 is an unconfined source - assessed as a neutral benefit/dis-benefit. predictability

System outage ○  This option would not add to the operational flexibility of the SWOX supply system to outage ○  The scheme is similarly vulnerable to other ‘failure modes’, as existing groundwater abstraction sites in the SWOX WRZ and therefore offers neutral Other ‘failure modes’ benefit/dis-benefit.

Screening decision 

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Table C.2: SWOX WRZ – Removal of DO constraint option screening assessment

borehole borehole pumps Keynes Ashton 1.6 Sub-dimension Ml/d Comments Env & Social  No material benefit beyond the associated water resource yield and the use of existing infrastructure. No material adverse effects. SEA ○○  Option is of small scale with negligible effects on the environment.

HRA ○  No likely significant effects on any designated European sites.

WFD ○  No likely adverse effects on WFD objectives.

Cumulative effects ○  No material cumulative effects identified. Cost ◉ Option provides substantial benefit as no construction required. Promotability Synergies ○  Due to the small size of the option, there are no opportunities for synergies.

Customer preference ○  No material customer preference concerns have been identified associated with this option.

Local acceptability ○  No construction works are planned as part of this option therefore no local acceptability issues are expected.  The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on the environment, Regulatory ◑r which includes Ashton Keynes as both a category 1 and category 2 item. This has implications for regulatory acceptance. However, as the option acceptability comprises an increase in DO within the licence this is considered a reducible material dis-benefit.

Wider stakeholder ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be mitigated acceptability through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility Lead time ◎  The lead time for this option has been assessed as being under 5 years - assessed as a material benefit.

Phasing ○  There are no opportunities for phasing as the option involves lowering pumps in the boreholes - assessed as a neutral benefit/dis-benefit.

Adaptability ○  There are no opportunities for adaptability due to the nature of the option - assessed as a neutral benefit/dis-benefit

Ramp-up ◎  The ramp-up time during a drought is under one week - assessed as a material benefit Deliverability Constructability ○  No construction is proposed as part of this option - assessed as a neutral benefit/dis-benefit. ○  A change is proposed to the operation of the source which should increase the potential yield of the source. However, this will also affect the resilience of Operability the source. The proposed changes are therefore assessed to have an overall neutral benefit/dis-benefit.

Dependencies ○  No material third-party dependencies have been identified for this option.  There is significant uncertainty that the pump lowering will result in the stated DO increases, due to potential adverse water quality impact such as r increased turbidity due to proximity of lowered pumps to the base of the boreholes and increased pumping rates; and uncertainty around the sensitivity of Data confidence ◑ the source to low water levels. This provides a material dis-benefit, reducible through test pumping or logging of the boreholes.  Uncertainty around the ability to lower pumps to the required depth due to possible issues with borehole verticality Resilience ◑  The resource benefit could be diminished as a result of increasingly wetter winters and drier summers reducing raw water availability. The deployable Climate change output shows that there is a significant decrease in borehole efficiency with decreasing water levels - assessed as a material dis-benefit.  Options reliant on natural groundwater or surface water catchment flows are the most vulnerable to droughts outside the historical record. The option Severe drought ◑ improves the resilience of the existing Deployable Output by lowering the borehole pumps. However, the boreholes’ poor performance at low groundwater levels is an indication that the increased deployable output may not be resilient to severe drought - assessed as a material dis-benefit.

Resource ○  This option offers no material benefit/dis-benefit to the predictability of resource. predictability

System outage ○  This option would not increase the operational flexibility of the SWOX supply system to outage - assessed as a neutral benefit/dis-benefit ○  The scheme is similarly vulnerable to other ‘failure modes’, as existing groundwater abstraction sites in the SWOX WRZ and therefore offers neutral Other ‘failure modes’ benefit/dis-benefit. Screening decision 

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Table C.3: SWOX WRZ – Catchment management options screening assessment

(Groundwater) Swell Upper (Groundwater)

Park Ashdown

Marlborough Marlborough (Groundwater) 0.3 0.2 0.2 Sub-dimension Ml/d Ml/d Ml/d Comments Env & Social ◎○ ◎○ ◎○  Material beneficial effects on the local terrestrial and water environment through catchment land improvements over time. SEA  Negligible adverse effects identified.

HRA ○ ○ ○  No likely significant effects on any European designated sites

WFD ○ ○ ○  No material adverse or beneficial effects on WFD water bodies ○ ○ ○  No material adverse or beneficial cumulative effects identified Cumulative effects

Cost  Marlborough and Ashdown Park options provide substantial benefit. ◉ ● ◉  Upper Swell option provides substantial dis-benefit Promotability Synergies ○ ○ ○  No likely synergies with other options identified ◎ ◎ ◎  Material benefit to customer preference likely to be associated with these options due to improvements to local environment as well as Customer preference addressing water quality risks

Local acceptability ○ ○ ○  Subject to engagement with local landowners and agreement on approach, no material risks anticipated ◉ ◉ ◉ Regulatory  Substantial material benefit to regulatory acceptability as options align with policy objectives of Defra acceptability

Wider stakeholder ◉ ◉ ◉  Substantial material benefit to wider stakeholder acceptability as options align with feedback received from stakeholders during screening and acceptability feasibility report consultations Flexibility ○ ○ ○  The lead time for these options has been assessed as being more than 5 years before any benefits are likely to be realised in terms of Lead time deployable output. ◎ ◎ ◎  Some material benefit from opportunities for scaling up the activities over time in response to learning from initial implementation in targeted Phasing areas

Adaptability ◉ ◉ ◉  Substantial benefit to adaptability to changing circumstances due to operational nature of the options

Ramp-up ◑ ◑ ◑  Material dis-benefit to ramp-up / ramp-down capability. Deliverability ◑ ◑ ◑  Some material dis-benefit due to challenges in agreeing specific measures with landowners and implementation of the right measures in the Constructability right settings ◑r ◑r ◑r  Some material dis-benefit due to challenges in maintaining the land management improvements with landowners and adapting measures to Operability reflect monitoring findings over time. Dis-benefit reducible through careful structuring of agreements and flexibility to adapt to emerging monitoring evidence. ◑ ◑ ◑  Some material dis-benefit due to dependencies on other co-funding provision, landowner agreements and land management activities outside Dependencies the control of Thames Water ◑ ◑ ◑  Some material dis-benefit due to uncertainties over implementation costs, availability of co-funding and the benefit to water quality that will Data confidence arise as a result of implementation. Resilience ◎ ◎ ◎  Some material benefit by improving the resilience of sources by addressing water quality risks that may deteriorate due to climate change Climate change without land management interventions

Severe drought ○ ○ ○  Resilient to severe drought but very low additional volume of reliable supply provided

Resource ◑ ◑ ◑  Some material dis-benefit as the resource benefit is not predictable and will be dependent on a variety of factors for the deployable output predictability benefit to be confirmed

System outage ○ ○ ○  The options would not add any material operational flexibility for system outage – assessed as neutral benefit/dis-benefit.

Other ‘failure modes’ ○ ○ ○  The options would not add any material benefits to addressing other ‘failure modes’ – assessed as neutral benefit/dis-benefit. Screening decision  Upper Swell option rejected due to substantial dis-benefit in relation to cost  ✖ 

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Table C.4: SWOX WRZ – Internal inter-zonal transfer options screening assessment

WOX

to to S

Henley to Kennet Valley SWOX

2.5 12.8 Sub-dimension Ml/d Ml/d Comments Env & Social  Minor beneficial effects associated with the provision of increased water resource yield to the resource zone. SEA ○◑ ○◑  Temporary adverse effects associated with pipeline construction on AONB, heritage conservation sites, public rights of way and flood risk zones 2 and 3 provide material dis-benefit, to be mitigated as far as possible through best practice construction method and route selection

HRA ○ ○ No likely significant effects on designated European sites – assessed as neutral benefit/dis-benefit.  No WFD impacts are anticipated subject to sensitive design and construction of river crossings (including crossing River Thames for Kennet WFD ○ ○ Valley to SWOX option)

Cumulative effects ○ ○  No likely cumulative effects anticipated with other water resource options. Cost ◉ ◉ Costs exclude water production costs for transferred water Promotability ○ ◎  Transfers from Kennet Valley to SWOX could facilitate cascade transfers on to SWA, should deficits in SWOX be smaller than forecast, or Synergies free up resource in Henley, which could enable the Henley to SWA transfer in place of Henley to SWOX. ◑r ◑r  Due to potential mixing of water from different sources, there is a risk of changes in water quality (e.g. taste, odour etc.) assessed as a Customer acceptability material dis-benefit to customer preference. This is reducible with appropriate treatment, but could increase costs. ◑r ◑r  The options include new pumping stations and significant lengths of new treated pipeline, likely requiring planning permission. This is Local acceptability assessed as a material but reducible dis-benefit to local residents due to impacts during the construction period.  There would be regulatory support for transfers for reasons of allocative efficiency. r r  However, the EA have concerns around the impact of some of the groundwater abstractions in Kennet Valley and Henley that may provide Regulatory acceptability ◑ ◑ the surplus resource to be transferred. However, the transfers would require an increase in abstraction within existing licences which make this risk reducible.  Wider stakeholders are also expected be supportive of sharing treated resources between zones, compared with new resource Wider stakeholder ◎ ○ development. acceptability  However increased abstraction within licence (particularly in Kennet Valley) could lead to concerns by environmental groups. Flexibility Lead time ◎ ◎  The lead time of the internal transfer options is estimated to be 4 years – assessed as a material benefit.  Long distance pipelines have significant economies of scale which reduces the benefits from phasing. The transfer from Henley is assessed as having a material dis-benefit. Phasing ◑ ○  The transfer from Kennet Valley to SWOX could be phased in that the there is potential to defer the introduction of the Mortimer groundwater scheme that is needed to deliver the full transfer volume – assessed as having a neutral benefit/dis-benefit.

Adaptability ◎ ◎  Bulk transfers could potentially be linked up and connected to new sources and demand centres in future, offering material benefit.

Ramp-up ◎ ◎  Treated water transfer ramp-up times are estimated to be less than one week, providing material benefit. Deliverability Constructability ○ ○  Pipelines are a well-known and developed technology, with neutral benefit/dis-benefit.  Pipelines offer the benefit of being a well-known and developed technology. Possible operability risks associated with water quality and Operability ◑r ◑r mixing water originating from different raw resource types are assessed as having material dis-benefit. These are reducible with suitable planning.  Henley to SWOX has no particular dependencies associated with it. Larger Kennet Valley to SWOX options are dependent on the Mortimer Dependencies ○ ○ groundwater option in Kennet Valley, but this is within TW control. Both options may require reinforcements to the existing network downstream of the transfer.  All treated bulk transfers are based upon the most recent supply/demand balance forecasts for the associated water resource zones. These Data confidence ◑r ◑r are subject to inherent uncertainty over population growth and PCC forecasts, sustainability reductions, climate change, etc. These risks are reducible with improved forecasting and as more data becomes available. Resilience ○ ○  The resource benefits of the transfers should be largely independent of climate change as it is already accounted for in the supply/demand Climate change balance forecasts that identify the available surplus for transfer – assessed as having neutral benefit/disbenefit.  Transfer from Henley assessed as material benefit as groundwater sources are predominantly Thames-side and so likely to be comparatively drought resilient Severe drought ◎ ○  Transfers from Kennet Valley assessed as neutral benefit/dis-benefit as some sources potentially subject to sustainability impact assessments in future. Also, Mortimer is assessed as neutral for drought resilience.

Resource predictability ◎ ◎  Sources supporting transfers are predominantly groundwater sources which are predictable as groundwater levels are monitored.

◎ ◎  Increasing connectivity between WRZs should increase resilience of the system by providing more potential sources of water to mitigate System outage outage events – assessed as a material benefit.

Other ‘failure modes’ ○ ○  Vulnerability to other hazards is similar in nature to those of the existing asset base – assessed as neutral benefit/dis-benefit.

Screening decision  

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Appendix D. SWA WRZ fine screening tables

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Table D.1: SWA WRZ – Groundwater development options screening assessment

Datchet Sub-dimension 1.6 Ml/d Comments Env & Social  No material beneficial effects beyond the associated water resource yield. Minor adverse effects associated with construction and operation of the SEA ○◑r scheme, including potential adverse effect on surface water (River Thames) provides material dis-benefit, reducible through inclusion of appropriate mitigation in the design of the abstraction scheme.

HRA ○  No likely significant effects on any designated European sites.  The Datchet abstraction is made from the confined aquifer but close to an area of outcrop under the River Thames which could potentially provide material r WFD ◑ dis-benefit to the surface water body (River Thames), classed as at Risk of Serious Damage. This is reducible through further investigation to determine the impact of increased abstraction on the surface water body

Cumulative effects ○  No material cumulative effects identified. Cost ◉ The option provides substantial benefit, primarily due to low capital cost. Promotability Synergies ○  Due to the small size of the option, there are no opportunities for synergies.

Customer preference ○  No material customer preference concerns have been identified associated with this option.

Local acceptability ○  The option includes WTW expansion works on TW land, which is not considered to be an issue in terms of local acceptability.  Regulatory acceptability is potentially a key issue for this option. At the present time, and in the absence of further environmental investigations at the Regulatory ◑r sites, this is considered to provide material, reducible dis-benefit. Additionally, the EA have recently issued TW with a list of groundwater sources that they acceptability consider have the potential to have an adverse impact on the environment, including Datchet as a category 2 item. However, the option comprises an increase in DO within the licence so this is considered to be a reducible material dis-benefit.

Wider stakeholder ◑r  The option requires a pump replacement in a borehole, which is adjacent to the railway. The work will require additional approval from Network Rail, acceptability which provides a material, reducible dis-benefit. Flexibility Lead time ◎  The lead time for this option has been assessed as being under 5 years, providing material benefit.

Phasing ○  There are no opportunities for phasing due to the nature of the option, providing neutral benefit/dis-benefit.

Adaptability ○  There are no opportunities for adaptability due to the nature of the option, providing neutral benefit/dis-benefit

Ramp-up ◎  The ramp-up time during a drought is under one week, providing material benefit Deliverability Constructability ○  No significant constructability risks have been identified and this is a well-known technology to TW, providing neutral benefit/dis-benefit. ◑r  There is a concern that the peak licence flow rate will not be achievable due to operational difficulties with the source and the impacts of increased Operability abstraction on groundwater levels and water quality. This provides material dis-benefit, reducible through the investigations into borehole yield at Datchet.

Dependencies ○  No material dependencies have been identified for these options. ◑r  The yield certainty of these schemes aligns with the industry standard, although further test pumping and rehabilitation will be required at Datchet to Data confidence confirm borehole performance, considered a material reducible dis-benefit. Resilience  The resource benefit could be diminished as a result of increasingly wetter winters and drier summers, particularly for sources in the inter-fluvial ◑ unconfined chalk, which responds more rapidly to changes in recharge. As Datchet is near the River Thames it is considered more resilient to climate Climate change change due to buffering of water levels by surface water interaction; however, there is uncertainty around potential water quality issues at low groundwater levels. The option is assessed as providing material dis-benefit. ◑r  Options reliant on natural groundwater or surface water catchment flows are the most vulnerable to droughts outside of the historical record, providing Severe drought material dis-benefit. This is considered reducible at Datchet through the works proposed in the scope of this option.

Resource ○  The Datchet abstraction is made from the confined aquifer but close to an area of outcrop under the River Thames, providing neutral benefit/dis-benefit. predictability

System outage ○  This option would not add to the operational flexibility of the SWA supply system to outage ○  The scheme is similarly vulnerable to other ‘failure modes’, as existing groundwater abstraction sites in the SWA WRZ and therefore offers neutral Other ‘failure modes’ benefit/dis-benefit.

Screening decision 

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Table D.2: SWA WRZ – Removal of DO constraint option screening assessment

Main

Replacement Eton Datchet Sub-dimension 1.1 Ml/d 1.6 Ml/d Comments Env & Social  No material beneficial effects beyond the associated water resource yield and the use of existing infrastructure. SEA ○○ ○○  Options are of small scale or operate within licence with negligible effects on the environment anticipated.

HRA ○ ○  No impact on any designated European sites.

WFD ○ ○  No likely adverse effects on WFD objectives.  Both options are in a surface water body classed as at risk of serious damage but assessed as unlikely to have an adverse effect on the surface Cumulative effects ○ ○ water flow regime, providing neutral benefit/dis-benefit, although ongoing liaison with the Environment Agency will be required to confirm water availability. Cost ◉ ◉ Options provide substantial benefit. Promotability Synergies ○ ○  Due to the small sizes of these options there are no opportunities for synergies.

Customer preference ○ ○  No material customer preference concerns have been identified associated with these options. ○ ◑r  The Eton removal of constraints option requires the upgrade of the membrane plant at Datchet WTW, which is considered to be a reducible Local acceptability material dis-benefit for local acceptability.  The EA has recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on the Regulatory ◑r ◑r environment, including both Datchet and Eton as category 2 items. This has implications for regulatory acceptance. However, the option acceptability comprises an increase in DO within the licence so this is considered to be a reducible material dis-benefit. Both options are in a surface water body classed as at risk of serious damage. Ongoing liaison with the EA will be required to establish water availability.

Wider stakeholder ○ ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be acceptability mitigated through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility Lead time ◎ ◎  The lead time for these options has been assessed as being under 5 years – assessed as a material benefit.

Phasing ○ ○  There are no opportunities for phasing due to the nature of the schemes – assessed as a neutral benefit/dis-benefit.

Adaptability ○ ○  There are no opportunities for adaptability due to the nature of the schemes – assessed as a neutral benefit/dis-benefit.

Ramp-up ◎ ◎  These options have a ramp-up time during a drought of under one week – assessed as a material benefit. Deliverability  No construction is proposed for the Datchet main replacement option – assessed as a neutral benefit/dis-benefit. Constructability ○ ○  No significant constructability risks have been identified for Eton and this is a well-known technology to TW – assessed as a neutral benefit/dis- benefit.  It is possible that a section of the Datchet main may be susceptible to bursting if pressures are increased, providing a material reducible dis- Operability ◑r ○ benefit that may require a further section of the main to be replaced  There are no concerns over the operability of the Eton option, providing neutral benefit/dis-benefit.

Dependencies ○ ○  No material dependencies have been identified for these options. ◑r ○  There is some uncertainty regarding the ability of the Datchet main to take the proposed increased pressures, providing material dis-benefit. This Data confidence is considered reducible through risk assessment as part of option development. Resilience ○ ○  As the options increase treatment and conveyance capacity, they are not expected to be affected by climate change, providing neutral Climate change benefit/dis-benefit. ○ ○  As the options increase treatment and conveyance capacity, they are not expected to be affected by severe drought, providing neutral Severe drought benefit/dis-benefit.

Resource ○ ○  These options will not change the resource predictability of the SWA supply system. predictability

System outage ○ ○  These options would not add operational flexibility for system outage, providing neutral benefit/dis-benefit. ○ ○  The options are similarly vulnerable to other ‘failure modes’ as existing similar infrastructure in the SWA WRZ, providing neutral benefit/dis- Other ‘failure modes’ benefit.

Screening decision  

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Table D.3: SWA WRZ – Internal inter-zonal transfer options screening assessment

SWA

to to

Henley

4.13 Sub-dimension Ml/d Comments Env & Social  Minor beneficial effects associated with the provision of increased water resource yield to the resource zone. SEA ○◑  Temporary adverse effects associated with pipeline construction on AONB, heritage and nature conservation sites and public rights of way provide material dis-benefit, which will be mitigated as far as possible through best practice construction methods and careful routing of the pipeline.

HRA ○  No likely significant effects on designated European sites.

WFD ○  No WFD impacts are anticipated subject to careful design and construction of river crossings (including River Thames)

Cumulative effects ○  No likely cumulative effects anticipated with other water resources schemes. Cost ◉ Promotability Synergies ○  Due to the small size of the option there are no opportunities for synergies. ◑r  Due to potential mixing of water from different sources, there is a risk of changes in water quality (e.g. taste, odour etc.) assessed as a material dis- Customer acceptability benefit to customer preference. This is reducible with appropriate treatment, but could increase costs. ◑r  The options include new pumping stations and significant lengths of new treated pipeline, likely requiring planning permission. This is assessed as a Local acceptability material but reducible dis-benefit to local residents due to impacts during the construction period.  There would be regulatory support for transfers for reasons of allocative efficiency. r Regulatory acceptability ◑  However, the EA have concerns around the impact of some groundwater abstractions in Henley that may provide the surplus resource to be transferred. However, the transfers would require an increase in abstraction within existing licences which make this risk reducible.

Wider stakeholder ◎  Wider stakeholders are also expected be supportive of sharing treated resources between zones, compared with new resource development acceptability Flexibility Lead time ◎  The lead time of the internal transfer options is estimated to be 4 years – assessed as a material benefit. ◑r  Long distance pipelines have significant economies of scale which reduces the benefits from phasing. The transfer from Henley is assessed as Phasing having a material dis-benefit.

Adaptability ◎  Bulk transfers could potentially be linked up and connected to new sources and demand centres in future, offering material benefit.

Ramp-up ◎  Treated water transfer ramp-up times are estimated to be less than one week, providing material benefit. Deliverability Constructability ○  Pipelines are a well-known and developed technology, with neutral benefit/dis-benefit. ◑r  Pipelines offer the benefit of being a well-known and developed technology. Possible operability risks associated with water quality and mixing water Operability originating from different raw resource types provide material dis-benefit. These are reducible with suitable planning.

Dependencies ○  Henley to SWA has no particular dependencies associated with it, but may require reinforcements to the existing network downstream of the transfer. All treated bulk transfers are based upon the most recent supply/demand balance forecasts for the associated water resource zones. These are subject Data confidence ◑r to inherent uncertainty over population growth and PCC forecasts, sustainability reductions, climate change, etc. These risks are reducible with improved forecasting methods and as more data becomes available. Resilience ○ The resource benefits of the transfers should be largely independent of climate change as it is already accounted for in the supply/demand balance Climate change forecasts that identify the available surplus for transfer – assessed as having neutral benefit/dis-benefit. ◎  Transfer from Henley assessed as material benefit as groundwater sources are predominantly Thames-side and so likely to be comparatively drought Severe drought resilient

Resource predictability ◎  Sources supporting transfers are predominantly groundwater sources which are predictable as groundwater levels are monitored. ◎  Increasing connectivity between WRZs should increase resilience of the system by providing more potential sources of water to mitigate outage System outage events – assessed as a material benefit.

Other ‘failure modes’ ○  Vulnerability to other hazards is similar in nature to those of the existing asset base – assessed as neutral benefit/dis-benefit. Screening decision 

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Appendix E. Henley WRZ fine screening tables

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Table E.1: Henley WRZ – Catchment management options screening assessment Sheeplands (Groundwater) Sub-dimension 0.3 Ml/d Comments Env & Social  Material beneficial effects on the local terrestrial and water environment through SEA ◎○ catchment land improvements over time.  Negligible adverse effects identified. HRA ○  No likely significant effects on any European designated sites WFD ○  No material adverse or beneficial effects on WFD water bodies Cumulative effects ○  No material adverse or beneficial cumulative effects identified Cost ◉  Option provides substantial benefit. Promotability Synergies ○  No likely synergies with other options identified  Material benefit to customer preference likely to be associated with these options due Customer preference ◎ to improvements to local environment as well as addressing water quality risks  Subject to engagement with local landowners and agreement on approach, no material Local acceptability ○ risks anticipated Regulatory  Substantial material benefit to regulatory acceptability as options align with policy acceptability ◉ objectives of Defra  Substantial material benefit to wider stakeholder acceptability as options align with Wider stakeholder feedback received from stakeholders during screening and feasibility report acceptability ◉ consultations Flexibility  The lead time for these options has been assessed as being more than 5 years before Lead time ○ any benefits are likely to be realised in terms of deployable output.  Some material benefit from opportunities for scaling up the activities over time in Phasing ◎ response to learning from initial implementation in targeted areas  Substantial benefit to adaptability to changing circumstances due to operational nature Adaptability ◉ of the options Ramp-up ◑  Material dis-benefit to ramp-up / ramp-down capability. Deliverability  Some material dis-benefit due to challenges in agreeing specific measures with Constructability ◑ landowners and implementation of the right measures in the right settings  Some material dis-benefit due to challenges in maintaining the land management improvements with landowners and adapting measures to reflect monitoring findings Operability r ◑ over time. Dis-benefit reducible through careful structuring of agreements and flexibility to adapt to emerging monitoring evidence.  Some material dis-benefit due to dependencies on other co-funding provision, Dependencies ◑ landowner agreements and land management activities outside the control of Thames Water  Some material dis-benefit due to uncertainties over implementation costs, availability Data confidence ◑ of co-funding and the benefit to water quality that will arise as a result of implementation. Resilience  Some material benefit by improving the resilience of sources by addressing water Climate change ◎ quality risks that may deteriorate due to climate change without land management interventions Severe drought ○  Resilient to severe drought but very low additional volume of reliable supply provided  Some material dis-benefit as the resource benefit is not predictable and will be Resource predictability ◑ dependent on a variety of factors for the deployable output benefit to be confirmed  The options would not add any material operational flexibility for system outage, System outage ○ providing neutral benefit/dis-benefit.  The options would not add any material benefits to addressing other ‘failure modes’, Other ‘failure modes’ ○ providing neutral benefit/dis-benefit. Screening decision 

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Appendix F. Guildford WRZ fine screening tables

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Table F.1: Guildford WRZ – Groundwater development options screening assessment

disaggregation licence Dapdune Sub-dimension 2.2 Ml/d Comments Env & Social

r  No beneficial effects beyond the associated water resource yield but potential for moderate adverse effects on the water environment, providing reducible SEA ○◑ material dis-benefit.

HRA ○  No impacts anticipated on designated European sites.

r  The disaggregated licence quantities at Dapdune could worsen the WFD surface water body flow compliance requirements (River Wey) at fully licensed WFD ◑ conditions. This depends upon the timing of the increased peak flows and is therefore considered a material, reducible dis-benefit

r  Cumulative adverse effects with other groundwater abstractions could provide material dis-benefit, reducible through control of abstraction licence Cumulative effects ◑ conditions. Cost ◉  No construction is proposed, providing substantial benefit. Promotability Synergies ○  Due to the small size of the option there are no opportunities for synergies.

Customer ○  No material customer preference concerns have been identified associated with this option. acceptability

Local acceptability ○  No construction is proposed and planning permission would not be required, providing neutral benefit/dis-benefit.  The annual average quantities have been limited to remain per the aggregate licence (20.5 Ml/d), as required by the EA. However, the EA have recently Regulatory ◑r issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on the environment, including Dapdune as a acceptability category 2 item. This provides material dis-benefit, reducible through further engagement with the EA.

Wider stakeholder ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be mitigated acceptability through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility Lead time ◎  The lead time for this option has been assessed as being under 5 years, providing material benefit.

Phasing ○  There are no opportunities for phasing due to the nature of the option, providing neutral benefit/dis-benefit.

Adaptability ○  There are no opportunities for adaptability due to the nature of the option, providing neutral benefit/dis-benefit

Ramp-up ◎  The ramp-up time during a drought is under one week, providing material benefit Deliverability Constructability ○  No construction work is proposed for this option, providing neutral benefit/dis-benefit.

Operability ○  No material changes to the source operation are proposed, providing neutral benefit/dis-benefit. ○  There are no third-party dependencies for these options. But delivery of the DO benefit is reliant upon delivery of the Dapdune and Ladymead WTW Dependencies removal of constraints options.

Data confidence ○  Limited uncertainty apart from that associated with inter-dependant options. Resilience ○  The resource benefit could be diminished as a result of increasingly wetter winters and drier summers, however the impact of climate change on the Climate change sources within the Dapdune group licence has been assessed as less than 10% of yield. This provides neutral benefit/dis-benefit. ○  Options reliant on natural groundwater are the most vulnerable to droughts outside of the historical record, however the impact of severe drought for the Severe drought sources within the Dapdune group licence has been assessed as less than 10% of yield. This provides neutral benefit/dis-benefit.

Resource ○  The option provides neutral benefit/dis-benefit to resource predictability. predictability

System outage ◎  As Guildford WRZ is largely reliant on groundwater for its supply, this option provides material benefit through the increase in peak licence. ○  The scheme is similarly vulnerable to other ‘failure modes’, as existing groundwater abstraction sites in the Guildford WRZ and therefore offers neutral Other ‘failure modes’ benefit/dis-benefit.

Screening decision 

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Table F.2: Guildford WRZ – Removal of DO constraint option screening assessment

Ladymead WTW Ladymead Dapdune 4.6 1 Ml/d Sub-dimension Ml/d Comments Env & Social  No material beneficial effects beyond the associated water resource yield and the use of existing infrastructure. No material adverse SEA ○○ ○○ effects, Options are of small scale or operate within licence with negligible effects on the environment. HRA ○ ○  No impact on any designated European sites. WFD ○ ○  No likely adverse effects on WFD objectives. Cumulative effects ○ ○  No material cumulative effects identified. Cost ◉ ◉ These options involve relatively minor engineering works, providing substantial benefit. Promotability Synergies ○ ○  Due to the small size of these options, there are no opportunities for synergies.

Customer ○ ○  No material customer preference concerns have been identified associated with these options. preference ○ ○  These options involve relatively minor engineering works on TW sites not requiring planning permission, assessed as a neutral Local acceptability benefit/dis-benefit.  The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on Regulatory ◑r ◑r the environment, including Ladymead and Dapdune as category 2 items. However, the options comprise an increase in DO within the acceptability licence so this is considered to be a reducible material dis-benefit.

Wider stakeholder ○ ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be acceptability mitigated through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility ◎  The lead time for these options has been assessed as being under 5 years with a ramp-up time during a drought of under one week, Lead time ◎ which are both material benefits.  At Dapdune, the GAC could be upgraded without any change to borehole pumps for a smaller increase in DO, providing material benefit. Phasing ◎ ○  There are limited opportunities for phasing at Ladymead WTW – assessed as a neutral benefit/dis-benefit.

Adaptability ○ ○  There are no opportunities for adaptability due to the nature of the schemes – assessed as a neutral benefit/dis-benefit.

Ramp-up ◎ ◎  These options have a ramp-up time during a drought of under one week – assessed as a material benefit. Deliverability Constructability ○ ○  No significant constructability risks have been identified and this is a well-known technology to TW, providing neutral benefit/dis-benefit.

Operability ◎ ◎  The proposed options will improve the operation of the Dapdune and Ladymead sources, offering a material benefit.

Dependencies ○ ○  There are no third-party dependencies for these options.

Data confidence ◎ ◎  The Dapdune and Ladymead WTW resource constraints are well understood. Resilience ○  The resource benefit could be diminished as a result of increasingly wetter winters and drier summers, however the impact of climate Climate change ○ change on each source has been assessed as less than 10% of yield – a neural benefit/dis-benefit. ○ ○  Options reliant on natural groundwater are the most vulnerable to droughts outside of the historical record, however the impact of severe Severe drought drought for each source has been assessed as less than 10% of yield - a neutral benefit/dis-benefit.

Resource ○ ○  These options offer no material benefit/dis-benefit to the predictability of resource. predictability

System outage ◎ ◎  As Guildford WRZ is largely reliant on groundwater for its supply, the removal of DO constraints is assessed as a material benefit. ○ ○  The options are similarly vulnerable to other ‘failure modes’ as existing groundwater abstraction sites in Guildford WRZ – assessed as a Other ‘failure modes’ neutral benefit/dis-benefit.

Screening decision

 

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Appendix G. Kennet Valley WRZ fine screening tables

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Table G.1: Kennet Valley WRZ – Groundwater development options screening assessment

1 1 recommissioning Mortimer Sub-dimension 4.5 Ml/d Comments Env & Social ○◑r  No material beneficial effects beyond the associated water resource yield. No material construction effects anticipated. In operation there is SEA material dis-benefit from uncertain impact on the surface water River Pang, reducible through abstraction licence conditions.

HRA ○  No likely significant effects on any designated European sites. ◑r  Confined aquifer but potential material dis-benefit from adverse effects on WFD objectives of surface water River Pang where the Chalk aquifer WFD becomes unconfined, reducible through further investigation and mitigation by abstraction licence conditions. ◑r  Potential cumulative effects on surface water River Pang with other abstractions provides material dis-benefit, reducible through further Cumulative effects investigation. Cost ◉  The option provides substantial benefit. Promotability Synergies ○  Due to the small size of the option there are no opportunities for synergies.

Customer preference ○  No material customer preference concerns have been identified associated with this option.

Local acceptability ◑r  The option involves construction of new/upgraded treatment on the existing TW site, which is considered to be a reducible material dis-benefit for local acceptability.

 Mortimer is located in the Pang CAMS area, designated as over-abstracted and the EA have concerns over the impacts of the abstraction on the ◑r River Pang. The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact Regulatory acceptability on the environment, including Mortimer as a category 2 item. However, the option comprises an increase in DO within the licence so this is considered to be a reducible material dis-benefit. ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be Wider stakeholder acceptability mitigated through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility Lead time ◎  The lead time has been assessed as being under 5 years, providing material benefit.

Phasing ○  There are no opportunities for phasing due to the nature of the scheme.

Adaptability ○  There are no opportunities for adaptability due to the nature of the scheme.

Ramp-up ◎  The ramp-up time during a drought would be under one week, providing material benefit. Deliverability Constructability ○  The option involves conventional, well established groundwater and treatment construction techniques, providing neutral benefit/dis-benefit. ◑r  Mortimer involves recommissioning disused assets, with risks and uncertainties associated with borehole yield and water quality, providing a Operability material, reducible dis-benefit.

Dependencies ○  No material dependencies have been identified for these options ◑r  Mortimer involves recommissioning disused assets, for which data confidence is low. There are risks and uncertainties associated with borehole Data confidence yield and water quality, which may impact DO benefit and the type and cost of treatment. This is a reducible material dis-benefit. Resilience  With drier summers, the availability of raw water from groundwater sources could be at risk, although the confined Chalk is considered to be Climate change ○ broadly resilient to changes in recharge patterns. The source is considered neutral with respect to the climate change resilience of TW’s supply. ○  Options reliant on natural groundwater or surface water catchment flows are the most vulnerable to droughts outside of the historical Severe drought record. Options located in the confined Chalk are considered lower risk than unconfined sources, providing neutral benefit/dis-benefit.

Resource predictability ○  This option offers no material benefit/dis-benefit to the predictability of resource.

System outage ○  This option would not add to the operational flexibility of the Kennet Valley supply system, providing neutral benefit/dis-benefit. ○  The options are similarly vulnerable to other ‘failure modes’ as existing groundwater abstraction sites in Kennet Valley WRZ, providing Other ‘failure modes’ neutral benefit/dis-benefit. Screening decision 

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Table G.2: Kennet Valley WRZ – Removal of DO constraint option screening assessment

Woodhay East Sub-dimension 2.1 Ml/d Comments Env & Social  No beneficial effects beyond the associated water resource yield and the use of existing infrastructure. Potential impact on surface water SEA ○○ features unlikely as abstraction is within existing licence conditions.

HRA ○  No likely significant effects on any designated European sites. ○  Unlikely to affect the WFD status of nearby waterbodies given confined nature of the aquifer and abstraction is within existing abstraction WFD licence conditions.  Potential for cumulative effects with other groundwater abstractions from a heavily used groundwater body providing material dis-benefit. This r Cumulative effects ◑ is reducible through further investigation of cumulative effects and can be mitigated if necessary through abstraction licence conditions and/or operating regime of the source. Cost ◉ Options provide substantial benefit. Promotability Synergies ○  Due to the small size of this option, there are no opportunities for synergies.

Customer preference ○  No material customer preference concerns have been identified associated with this option.

Local acceptability ○  The option involves relatively minor engineering works on a TW site not requiring planning permission, providing neutral benefit/dis-benefit.  The EA have recently issued TW with a list of groundwater sources that they consider have the potential to have an adverse impact on the Regulatory acceptability ◑r environment, including East Woodhay as a category 1 and category 2 item. However, the options comprise an increase in DO within the licence so this is considered to be a reducible material dis-benefit. ○  There could be challenges from environmental groups on the basis of potential impacts of increasing abstraction, however these could be Wider stakeholder acceptability mitigated through effective engagement and are assessed as neutral benefit/dis-benefit. Flexibility Lead time ◎  The lead time for these options has been assessed as being under 5 years, providing material benefit.

Phasing ○  There are no opportunities for phasing due to the nature of the schemes, providing neutral benefit/dis-benefit.

Adaptability ○  There are no opportunities for adaptability due to the nature of the schemes, providing neutral benefit/dis-benefit.

Ramp-up ◎  These options have a ramp-up time during a drought of under one week, providing material benefit. Deliverability Constructability ○  No significant constructability risks have been identified and this is a well-known technology to TW, providing neutral benefit/dis-benefit. ◎  The option provides material benefit as the pumps will have the option of operating together without the current control system and health and Operability safety issues.

Dependencies ○  There are no third-party dependencies for this option. ◑r  There is some uncertainty over borehole yield, the capacity of Enborne WTW disinfection process and possible water quality issues resulting Data confidence from lower borehole pumps due to a lack of data. This provides material dis-benefit, reducible through small scale investigations. Resilience Climate change ○  The source is not yield-constrained, providing neutral benefit/dis-benefit.

Severe drought ○  The source is not yield-constrained, providing neutral benefit/dis-benefit.

Resource predictability ○  These options offer no material benefit/dis-benefit to the predictability of resource.

System outage ○  These options would not add to the operational flexibility of the Kennet Valley supply system, providing neutral benefit/dis-benefit. ○  The options are similarly vulnerable to other ‘failure modes’ as existing groundwater abstraction sites in Kennet Valley WRZ, providing neutral Other ‘failure modes’ benefit/dis-benefit. Screening decision 

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Table G.3: Kennet Valley WRZ – Catchment management options screening assessment

(Groundwater) Playhatch Sub-dimension 0.4 Ml/d Comments Env & Social  Material beneficial effects on the local terrestrial and water environment through catchment land improvements over time. SEA ◎○  Negligible adverse effects identified.

HRA ○  No likely significant effects on any European designated sites

WFD ○  No material adverse or beneficial effects on WFD water bodies  No material adverse or beneficial cumulative effects identified Cumulative effects ○

Cost ◉  Option provides substantial benefit. Promotability Synergies ○  No likely synergies with other options identified ◎  Material benefit to customer preference likely to be associated with these options due to improvements to local environment as well as addressing Customer preference water quality risks

Local acceptability ○  Subject to engagement with local landowners and agreement on approach, no material risks anticipated

Regulatory acceptability ◉  Substantial material benefit to regulatory acceptability as options align with policy objectives of Defra

Wider stakeholder ◉  Substantial material benefit to wider stakeholder acceptability as options align with feedback received from stakeholders during screening and acceptability feasibility report consultations Flexibility ○  The lead time for these options has been assessed as being more than 5 years before any benefits are likely to be realised in terms of deployable Lead time output.

Phasing ◎  Some material benefit from opportunities for scaling up the activities over time in response to learning from initial implementation in targeted areas

Adaptability ◉  Substantial benefit to adaptability to changing circumstances due to operational nature of the options

Ramp-up ◑  Material dis-benefit to ramp-up / ramp-down capability. Deliverability ◑  Some material dis-benefit due to challenges in agreeing specific measures with landowners and implementation of the right measures in the right Constructability settings ◑r  Some material dis-benefit due to challenges in maintaining the land management improvements with landowners and adapting measures to reflect Operability monitoring findings over time. Dis-benefit reducible through careful structuring of agreements and flexibility to adapt to emerging monitoring evidence. ◑  Some material dis-benefit due to dependencies on other co-funding provision, landowner agreements and land management activities outside the Dependencies control of Thames Water ◑  Some material dis-benefit due to uncertainties over implementation costs, availability of co-funding and the benefit to water quality that will arise as a Data confidence result of implementation. Resilience ◎  Some material benefit by improving the resilience of sources by addressing water quality risks that may deteriorate due to climate change without Climate change land management interventions

Severe drought ○  Resilient to severe drought but very low additional volume of reliable supply provided ◑  Some material dis-benefit as the resource benefit is not predictable and will be dependent on a variety of factors for the deployable output benefit to Resource predictability be confirmed

System outage ○  The options would not add any material operational flexibility for system outage, providing neutral benefit/dis-benefit.

Other ‘failure modes’ ○  The options would not add any material benefits to addressing other ‘failure modes’, providing neutral benefit/dis-benefit. Screening decision 

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Appendix H. Optimism bias & uncertainty

There is a systematic tendency for project costs developed at the outline business case stage to underestimate the actual outturn cost. As a result, HM Treasury Green Book25 guidance recommends that adjustments be made to project costs to reflect ‘optimism bias’. For non-standard civil engineering projects a factor of 66% is applied. The supplementary Green Book Guidance on Optimism Bias26 provides an approach for reducing optimism bias based upon an assessment of the extent that the various contributing factors have been mitigated. For WRMP14 Thames Water adopted an approach to mitigation of optimism bias that took an assessment of the confidence grade for each option from its corporate Asset Planning System (APS) and used this to mitigate optimism bias, splitting options into three categories: High Risk, Medium Risk and Low Risk.

An assessment was also made of uncertainty which drew upon guidance from the Association for the Advancement of Cost Engineering27 (AACE). The AACE guidance provides a range of uncertainties for projects at different levels in the development process (see Table H.1 below).

Table H.1: AACE cost estimate classification matrix for process industries Estimate Level of project Accuracy range Accuracy range Preparation class definition End usage low high effort Class 5 0% to 2% Concept Screening -20% to -50% +30% to +100% 1 Class 4 1% to 15% Study or Feasibility -15% to -30% +20% to +50% 2 to 4

Class 3 10% to 40% Budget -10% to -20% +10% to +30% 3 to 10 Authorisation Class 2 30% to 70% Bid or Tender -5% to -15% +5% to +20% 4 to 20

Class 1 50% to 100% Check Estimate or -3% to -10% +3% to +15% 5 to 100 Bid/Tender

Source: AACE Recommended Practice No. 18R-97

For WRMP14 Thames Water took the mid-point of the low and high accuracy ranges from Table H.1 to provide a range of uncertainty. For options assessed as being Low Risk the Class 3 ranges were used as TW’s view was that the cost estimates it had developed for those options were at a level that would not change significantly before reaching Class 3 (Budget Authorisation). Similarly, for Medium Risk projects the Class 4 uncertainty ranges were used and for High Risk projects the Class 5 uncertainty ranges were used. This resulted in the combined optimism bias and uncertainty assumptions set out in Table H.2 below.

25 HM Treasury (2003), The Green Book, Appraisal and Evaluation in Central Government 26 HM Treasury, Supplementary Green Book Guidance – Optimism Bias 27 AACE, Cost Estimate Classification System – As Applied in Engineering, Procurement, and Construction for The Process Industries, 18R-97

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Table H.2: Optimism bias and uncertainty assumptions used at WRMP14 Low Risk Medium Risk High Risk Estimating Uncertainty -15% to +20% -22.5% to +35% -35% to +65% Optimism Bias +5% +25% +66% Estimating & Scope Uplift -10% to +25% +2.5% to +60% +31% to +131% Most Likely Point +5% +25% +66%

Source: HFA, PR14 Option Development and Uncertainty Estimating

The WRMP14 approach to optimism bias and uncertainty has been taken as the basis for adjustments made to costs in the fine screening process. However, rather than banding options into three risk bands a continuous adjustment to the capital costs has been made linked directly to the APS confidence grade and using the relationship set out in Figure H.1.

Figure H.1: Allowance for optimism bias and uncertainty used in fine screening

140%

Min 120% confidence grade = 2.05 100%

80%

60% Lower (linear) Most likely (linear) 40% Upper (linear)

20%

0% Percentage uplift for optimism bias and uncertainty

-20% 1 1.5 2 2.5 3 3.5 4 4.5 5 Confidence Grade (5 = low confidence; 1 = High confidence)

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Appendix I. Stochastic analysis of Upper Thames Reservoir

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WRMP19 Stochastic Water Resources: Stage 4 Options Appraisal

WRMP19 Options Appraisal: Appendix Document for the Upper Thames Reservoir Development

Thames Water

25 January 2017

WRMP19 Stochastic Water Resources: Stage 4 Options Appraisal Appendix Document for the Upper Thames Reservoir

Table of contents

Chapter Pages 1. Introduction 4 2. Use and Performance under Historic Droughts 5 3. What is its Expected Performance Under Future Major Droughts? 5 4. Summary of Scheme Resilience 13

Figures Figure 3-1 Analysis of the Yield-Storage Behaviour of the Drought Library A ...... 9 Figure 3-2 Analysis of the Yield-Storage Behaviour of the Drought Library B ...... 10 Figure 3-3 Analysis of the Yield-Storage Behaviour of the Drought Library C ...... 11

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WRMP19 Stochastic Water Resources: Stage 4 Options Appraisal Appendix Document for the Upper Thames Reservoir

Atkins WRMP19 Stochastic Water Resources Stage 4: Upper Thames Reservoir Scheme | Version 4.0 | 25 January 2017 | 5140905

WRMP19 Stochastic Water Resources: Stage 4 Options Appraisal Appendix Document for the Upper Thames Reservoir

1. Introduction

This document provides an overview of the nature of the yield benefit and level of drought resilience that is expected to be provided by the 150Mm3 Upper Thames Reservoir development across a range of possible future drought events. The analysis presented within this report seeks to move beyond the ‘conventional’ historically based water resources concept of ‘Deployable Output’ and examines the expected yield and resilience risks associated with a statistically representative range of different drought patterns and severities. The analysis is separated into the following sections

 Summary of Use and Performance under Historic Droughts. This section uses the information included within the historic record to provide an understanding of the scheme performance and acts as a ‘sense check’ on the more complicated analyses in the next section.  Expected performance under future major droughts. This section uses advanced, statistically based methods that are in line with the most recent UK Water Industry Research (UKWIR) methods for risk based water resources planning to evaluate the performance of the scheme under future drought events.

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2. Use and Performance under Historic Droughts

The UTR effectively provides additional storage that is filled during ‘normal’ or even reasonably ‘dry’ winters and released to support the existing London reservoirs during drought years. It is designed to fit in with the existing Lower Thames Operating Agreement, which means that the storage it provides is the same in its nature and use as the existing London reservoirs. The only significant difference in terms of fill and recession behaviour is that it will only start to fill either after the London reservoirs are already full and natural flows at Teddington Weir are high enough to satisfy London abstraction demands without reservoir releases, or flows are high enough to allow refill even when existing London storage refill is operating at full capacity. Under the driest winters of the historic droughts this means that there is limited or no refill of the UTR, so in order to achieve a specified yield benefit the scheme needs to release at that rate throughout the critical part of the drought.

The scheme is estimated to provide 287Ml/d of additional yield (Deployable Output) during the critical 1921 and 1934 drought events. This equates to approximately 520 days’ worth of recession below the relevant control curve, and demonstrates that the refill to the UTR would have been negligible during the driest winter of each of those events. The actual duration of the major droughts was slightly longer than this, as they contained short periods where the UTR would not be required to release, so in general the historic record indicates that the scheme is resilient to droughts with a critical duration of around 20 months or less. All of the major events in the 20th Century followed this type of duration, with the London reservoirs starting to recess during the April prior to the critical drought year, with limited refill availability for the UTR during the winter, and the drought finally breaking between September and December of the following year (the 1921 drought broke in January of the third year, but there was also some refill during winter 1920/21). Even the ‘long’ three year drought of 1932-34 would have provided complete and reliable refill for the London reservoirs during the winter of 1932/33, so the critical duration (i.e. the period during which the storage in the UTR would be used) of this event was still less than 20 months.

The nature of the scheme (storage with limited refill during the drought) means that the yield will tend to increase during shorter droughts and decrease during longer droughts. However, the 1932-34 drought demonstrates that the ‘duration’ is not simply a reflection of when the drier meteorological conditions start, but rather reflects the period when conditions and flows are dry enough to start challenging the storage performance of the existing London reservoirs. This relationship between intensity and duration needs to be accounted for when the resilience of the London system acting conjunctively with the UTR to different drought durations is considered.

3. What is its Expected Performance Under Future Major Droughts?

Before the benefit can be analysed, it is first necessary to define what is meant by a ‘reliable yield’ for the UTR scheme. Reliability is an often used term in risk assessment, but for water resource planning it has a specific meaning – it is the yield that the scheme can provide without affecting the existing Level of Service. If investment is planned on the basis that the yield is lower than this value, then the planned investment would actually result in a slight increase in Thames’ effective level of service. Conversely, if the yield from the scheme is assumed to be higher than this amount, it will tend to result in a decrease in Thames’ effective level of service. In statistical terms this can be referred to as the expected benefit – it is the benefit that does not change Thames Water’s underlying drought risk profile. This requires the use of advanced risk based methods, as described in the UKWIR ‘WRMP19 Risk Based Methods’ guidance.

In this case the derivation of the expected yield was carried out through a stochastic analysis of rainfall and evaporation, which used a spatially coherent weather generator which is able to emulate 20th Century

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WRMP19 Stochastic Water Resources: Stage 4 Options Appraisal Appendix Document for the Upper Thames Reservoir climatic conditions and hence generate a large number of droughts of known severities. This contained weather generation techniques that are now being widely adopted within the water industry (Southern Water, Anglian Water, Welsh Water, Severn Trent and United Utilities are all using the same technique for WRMP19, along with the Water Resources in the South East and Water Resources in the East regional groups, plus the Water UK National Long Term Water Resources Planning study). A full description of the generator, plus its validation against the 20th Century record, is contained in the ‘Thames Water WRMP19 Stochastic Methods Phase 2 & 3 Report’.

This large number of drought events was run through a simulation model of the Thames Water water supply system in order to estimate both the expected yield of the Thames-London system with and without the UTR under a range of drought severities. This involved large amounts of data and hence was not practical to run entirely within the WARMS2 modelling platform. Instead, the ‘core’ evaluation relied upon lumped sub- catchment rainfall-runoff models (in the Catchmod modelling platform) and a simplified water resource emulator (using the IRAS software platform) to generate the flows and yield responses for each drought sequence. The outputs from these were checked and validated against WARMS2 to ensure the process was sufficiently accurate for the analysis. This modelling process and the validation against WARMS2 are also fully described within the Stochastic Methods Phase 2 & 3 Report. .

For the UTR it was important to see how droughts of different durations affected the storage and performance, so the process that was used was slightly different to those described for the Severn-Trent Transfer options (with and without Lake Vyrnwy). Whilst the same modelling platforms were used, the IRAS modelling was used as a screening tool that allowed all of the generated droughts to be ranked. From this ranked data set, a set number of drought events were selected to provide a statistically representative sample of events (30 in total) that were at, or worse than, the severity of the critical 20th Century droughts. These were then run through WARMS2 to analyse the yield response of the London reservoirs with and without the support of the UTR.

The droughts that were used were the same as those described in the ‘Thames Water WRMP19 Stochastic Methods Phase 2 & 3 Report’, which were originally used to determine the yield-severity response of the London reservoir system without the UTR. There were three key advantages of this drought data set:

1. The droughts were selected to represent a good range of events from a circa 1 in 1000 year through to circa 1 in 100 year return period. They covered 1/6th of the events available within this range from the full stochastic data set, so therefore provided a good test of UTR performance across droughts of a wide range of severities.

2. The droughts had already been run through WARMS2, so their yield and relative severity was known prior to the inclusion of the UTR.

3. The droughts were selected entirely based on the estimated yield of the London reservoir system within IRAS, based on a matrix output of year versus Level 4 failure occurrence under a range of demand increments (see the Phase 2 & 3 report for further information). There was therefore no knowledge or analysis of the pattern or duration of each event; they had all been randomly selected based on their relative yield alone.

The droughts were formed into three ‘libraries’ (A-C). Each of these libraries contained a continuous 110 year time series of rainfall and PET rainfall for each of the 10 Thames sub-catchments contained in the WARMS2 model. The first 10 years of the library represented a model warm up period, and were not used in the yield analysis. Each 10 year period after that was taken as a continuous record from the full stochastically generated data set, with the critical point of the drought during year 5 of the record. The extraction of complete 10 year sequences from the full stochastic data set ensured that the time series immediately before and after the drought event were statistically valid according to the underlying probabilities of the 20th Century record, and ensured that there was no statistically inappropriate interference between drought events.

The analysis of likely yield during each event was estimated based on the storage performance of the London system with and without the UTR at the various demand levels. The conceptual evaluation framework that was used can be summarised as follows:

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 When the UTR is added to the London system, then the yield of the scheme for each drought is equal to the level of additional demand in London that can be supported without changing the minimum storage level reached during that drought under the ‘baseline’ (i.e. without the UTR) run. If the system is subject to additional demand that is higher than this yield then there will be a reduction in storage to compensate, so the minimum storage level that is reached will be lower than the ‘baseline’ run. Conversely, if the level of additional demand is lower than the yield then the minimum storage level will be higher than the ‘baseline’ run.

 By comparing the ‘baseline’ (no UTR) run against the minimum storage achieved for the system that incorporated the UTR plus additional demand set between defined upper and lower bounds, it was therefore possible to draw conclusions about the relative yield of the UTR under each drought (N.B. for Drought Library B it was found that the yield of the UTR was higher than the historically based 287Ml/d, so no lower bound run was needed).

 For those droughts where the yield was not equal to additional demand contained in the upper or lower bound runs, the actual yield of the UTR under that drought was estimated by:

o selecting the yield run that generated a minimum storage level that was closest to the ‘baseline’,

o evaluating the duration of the recession period for that drought, and

o dividing the difference in storage between the yield run and the baseline by that recession period.

o For example, if the minimum storage was 5000Ml above the baseline for a drought with a recession period of 500 days, then this implied the UTR could support an additional 10Ml/d demand beyond that allowed for in the yield run and still maintain the minimum storage reached under the baseline. The estimated yield under that drought was therefore estimated to be equal to the demand increment allowed for under that yield run (e.g. 287Ml/d), plus 10Ml/d.

 The above quantification process did not take into account the effects of demand restrictions, so it was only considered to be an estimate. However, the impacts of demand restrictions on yield are relatively small (less than 10%), so the additional uncertainty caused was not significant, particularly as it only applied to the proportion of the yield estimate associated with the difference in net storage (in the example above it would only affect the 10Ml/d differential, and not the 287Ml/d assumed in the yield run). It was found that, for some droughts, the presence of the UTR and the associated additional demand had a significant influence on the effective timing of the start of the recession and/or the timing of the minimum storage, in some cases by a year. This introduced much higher levels of uncertainties in the yields for those droughts, so, in order to reduce the estimation uncertainties, for Library A and Library C an intermediate yield run was also carried out, with the additional demand set at a reasonable level between the upper and lower bounds.

Based on the above concepts, each of the ‘drought libraries’ were therefore run through the WARMS2 simulator under the following system set up and demand conditions:

1. A baseline run, with overall demand set at the minimum London system yield achieved under each library without the UTR

2. The baseline run (1) plus an additional 287Ml/d demand with the UTR included in WARMS2 (no further runs were required for Library B, as the UTR had a yield greater than 287Ml/d under all of the droughts within the Library).

3. For Libraries A and C two further yield runs were carried out; one with demand set at the baseline value plus the minimum yield of the UTR within that library (baseline plus 220Ml/d for Library A and baseline plus 95Ml/d for Library C) and one at an intermediate level designed specifically to help

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estimate the yield benefit of the UTR under longer droughts (baseline plus 242Ml/d for Library A and baseline plus 230Ml/d for Library C).

Figure 3-1 to Figure 3-3 provide a summary output of the storage response of the London system under all of these runs, showing the absolute storage plus the differential in storage for the upper bound and (for Libraries A and C) the intermediate runs.

Table 3-1 to Table 3-3 provides a summary of the estimate of yield from the UTR under each drought, based on the storage response under each of the yield runs.

The following conclusions were drawn from those analyses:

 The yield of the UTR is expected to be robust for all droughts with a similar critical period to the major historic events. This covered the majority of the sampled drought events, so the UTR provided a yield benefit within 20% of the 287Ml/d yield calculated from the historic record for 27 out of 30 of the tested droughts.

 Some longer duration (24 to 36 month type) events were contained in the libraries, and under three of these there was insufficient winter recharge available for the UTR to offset this longer duration, so the yield of the UTR was significantly lower than the historic estimate.

 There was no noticeable trend of resilience versus severity – Library A generally contained the most severe droughts and overall the average expected yield for that library was 278Ml/d, with only one drought significantly (>20%) below the 287Ml/d historic value. The Library B droughts were then generally the next most severe, but in all cases the yield of the UTR was higher than for the historic record. Library C contained the least severe droughts, but contained 2 out of the 3 events where the yield of the UTR was significantly below the historic record.

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Figure 3-1 Analysis of the Yield-Storage Behaviour of the Drought Library A (Figures show the storage of the system when run against the 10 droughts contained in the library. The base demand run without the UTR was for 1956Ml/d. Demand with the UTR was set at 2243, 2198 and 2176 Ml/d. N.B. years are nominal for presentation only – each 10 year sequence represents an artificially generated drought event)

Analysis of Demand/Storage Behaviour of the London system with the Upper Thames Reservoir; Drought Library A 220000 210000 200000 180000 190000 180000 170000 160000 130000 150000 140000 130000 120000 80000 110000 100000 90000 80000 30000

70000 Difference Difference inStorage (Ml) 60000 Storage Storage Londonin Reservoirs (Ml) 50000 40000 -20000 30000 Storage with UTR @ 220Ml/d aditional demand Storage with UTR @ 287Ml/d additional demand 20000 Storage with UTR @ 242Ml/d additional demand Storage without UTR @ min yield for library (1956Ml/d) 10000 Storage Difference @ 287Ml/d Storage difference @ 242Ml/d

0 -70000

01 Jan 1970 Jan 01 1971 Jan 01 1972 Jan 01

31 Dec 1973 Dec 31 1974 Dec 31 1975 Dec 31 1976 Dec 30 1977 Dec 30 1978 Dec 30 1979 Dec 30 1980 Dec 29 1981 Dec 29 1982 Dec 29 1983 Dec 29 1984 Dec 28 1985 Dec 28 1986 Dec 28 1987 Dec 28 1988 Dec 27 1989 Dec 27 1990 Dec 27 1991 Dec 27 1992 Dec 26 1993 Dec 26 1994 Dec 26 1995 Dec 26 1996 Dec 25 1997 Dec 25 1998 Dec 25 1999 Dec 25 2000 Dec 24 2001 Dec 24 2002 Dec 24 2003 Dec 24 2004 Dec 23 2005 Dec 23 2006 Dec 23 2007 Dec 23 2008 Dec 22 2009 Dec 22 2010 Dec 22 2011 Dec 22 2012 Dec 21 2013 Dec 21 2014 Dec 21 2015 Dec 21 2016 Dec 20 2017 Dec 20 2018 Dec 20 2019 Dec 20 2020 Dec 19 31 Dec 1972 Dec 31

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Figure 3-2 Analysis of the Yield-Storage Behaviour of the Drought Library B

(Figures show the storage of the system when run against the 10 droughts contained in the library. The base demand run without the UTR was for 2075Ml/d. Demand with the UTR was set at 2362Ml/d. N.B. years are nominal for presentation only – each 10 year sequence represents an artificially generated drought event)

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Figure 3-3 Analysis of the Yield-Storage Behaviour of the Drought Library C

(Figures show the storage of the system when run against the 10 droughts contained in the library. The base demand run without the UTR was for 2254Ml/d. Demand with the UTR was set at 2541, 2484 and 2349 Ml/d. N.B. years are nominal for presentation only – each 10 year sequence represents an artificially generated drought event)

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Table 3-1 Summary of Yield Analysis: Drought Library A

Storage Change when Additional Estimated UTR Yield Drought Timing of Recession Demand Placed on System with UTR (Ml) (Ml/d) Number Start Finish Duration (Days) 287 242 220 Difference Est Yeild Drought 1 06/08/2024 02/11/2025 453 10000 22 309 Drought 2 Not used Minimal Diff 0 287 Drought 3 Not used Minimal Diff 0 242 Drought 4 20/06/1954 20/10/1955 487 4500 9 296 Drought 5 Not used Minimal Diff 0 220 Drought 6 Not used Approx. half way between 242 and 287 no calc 265 Drought 7 Not used Approx. half way between 242 and 287 no calc 265 Drought 8 Not used Minimal Diff 0 287 Drought 9 03/06/2004 18/11/2005 533 7000 13 300 Drought 10 29/03/2014 10/01/2015 287 7000 24 311 Average yield across all 10 droughts 278

Table 3-2 Summary of Yield Analysis: Drought Library B

Storage Change when Estimated UTR Yield Drought Timing of Recession Additional Demand Placed (Ml/d) Number on System with UTR (Ml) Start Finish Duration (Days) 287 Difference Est Yeild Drought 1 06/07/1924 07/09/1925 428 7500 18 305 Drought 2 08/03/1935 14/11/1935 251 8000 32 319 Drought 3 12/06/1944 14/11/1945 520 4000 8 295 Drought 4 09/09/1954 26/10/1955 412 3000 7 294 Drought 5 Not Used Minimal Difference 287 Drought 6 11/06/1974 06/12/1975 543 3000 6 293 Drought 7 30/05/1984 01/11/1985 520 6000 12 299 Drought 8 03/03/1995 02/11/1995 244 6000 25 312 Drought 9 Not Used Minimal diffference 287 Drought 10 08/04/1915 03/01/1916 270 7000 26 313 Average yield across all 10 droughts 300

Table 3-3 Summary of Yield Analysis: Drought Library C

Drought Timing of Recession Storage Change when Additional Demand Estimated UTR Yield Number Start Finish Duration (Days) 287 230 95 Difference Est Yeild Drought 1 Not Used Minimal Diff 95 Drought 2 23/06/1934 18/11/1935 513 4500 9 296 Drought 3 Not Used Approx. half way between 230 and 287 259 Drought 4 05/03/1954 01/12/1957 1367 5000 4 291 Drought 5 16/08/1964 06/12/1965 477 10000 21 308 Drought 6 Not Used Minimal Diff 287 Drought 7 13/04/1985 1000 4 291 Drought 8 14/08/1994 8000 17 304 Drought 9 Not Used Minimal Diff 230 Drought 10 05/07/2014 05/11/2015 488 -1000 -2 285 Average 264

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4. Summary of Scheme Resilience

The analyses methods described within this report allowed the following conclusions to be drawn about the benefits and level of resilience of the Upper Thames Reservoir (UTR):

1. The yield of the UTR is resilient for all major droughts where the critical duration is similar to that seen in the worst historic events. This resilience is demonstrated across a range of drought severities, ranging from around the 1 in 100 level right through to around the 1 in 1000 level.

2. Three out of the 30 droughts that were analysed contained longer critical durations with low enough winter recharge to significantly reduce the yield of the scheme. In other words, around 10% of the sampled droughts had a critical period that was long enough to present a resilience risk to the UTR. This means that the chance of encountering a drought that is both severe enough to test the existing London system and cause a failure of resilience in the UTR is extremely small. To put this in context Thames might expect to encounter such an event less than once every thousand years (maximum probability per annum calculated as 0.1*0.01 = 0.001). This reflects the observed nature of the climate and existing water resource system in the Thames basin. Whilst there is a reasonable chance of experiencing multiple dry winters in the catchment, the chances of experiencing 2 or more very dry winters (i.e. where there is no recharge available to the UTR) back to back, without high rainfall in any of the intermediate spring, summer or autumn periods, is very small. In water resources terms, this means the majority (around 90%) of the major drought events within the Thames catchment are expected to have a critical duration of less than 24 months (as measured between the last reliable winter/spring refill event and the point of minimum storage in the London reservoirs).

3. The average expected yield of the UTR, as measured from the 30 droughts that were tested, was slightly lower than that generated from the historic record, at 282Ml/d.

The above analysis suggests that the UTR can be considered to be resilient in terms of water resources planning, down to an extremely low frequency return period. Whilst the analysis described within this report does contain some estimations for individual events, in general it is clear that the UTR shows relatively little variability in yield across the majority of the major drought events that might be expected to occur in future.

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Appendix J. Stochastic analysis of Unsupported Severn-Thames Transfer

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WRMP19 Options Appraisal: Appendix Document for the Unsupported Severn Thames Transfer

Thames Water

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Thames Water WRMP19 Stochastic Methods Appendix Document for the Unsupported Severn Thames Transfer

Table of contents

Chapter Pages 1. Introduction 4 2. How Does the Severn-Thames Transfer Provide Yield? 5 2.1. The timing of storage recession in the London Reservoirs 5 2.2. The natural flow of water in the Severn catchment. 5 2.3. The degree of abstraction and discharge within the Severn and Avon upstream of Deerhurst. 7 3. How Would it Perform under Historic Drought Patterns? 7 4. What is its Expected Performance Under Future Major Droughts? 10 4.1. Background and Analysis Method 10 4.2. Options Testing and Results 11 5. How is it Affected by Climate Change? 14 6. What are the Risks from Other Abstractors? 15 7. Summary of Scheme Resilience 18

Figures Figure 2-1 Comparison of Seasonal Rainfall Behaviour in the Thames and Severn Catchments ...... 6 Figure 3-1 Flow Timeseries Showing Transfer Availability from the Severn at Deerhurst under Major Historical Droughts ...... 8 Figure 4-1 Illustration of the Effect of Conjunctive use on Relative Drought Severity ...... 11 Figure 4-2 Stochastic Analysis of the Net Yield Benefit of the Transfer ...... 12 Figure 5-1 Stochastic Analysis of the Net Yield Benefit of the Transfer under Climate Change ...... 14 Figure 6-1 Evaluation of the Impact of Fully Licensed Third Party Abstraction on Flows at Deerhurst .... 15 Figure 6-2 Analysis of the Net Impact of Fully Licensed Abstraction by Other Users ...... 16 Figure 6-3 Analysis of the Impact of Fully Licensed Abstraction under 2080 Climate Conditions ...... 17

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1. Introduction

This document provides an overview of the nature of the yield benefit that is gained if a transfer from the River Severn to the River Thames were to be constructed without agreements being in place with other water companies to provide support to the scheme through licence trading, the use of existing River Severn storage reservoirs, or through the construction of new storage in either the Severn or Thames catchments. The analysis is primarily focused upon the hydrological benefits that could be expected; there is no analysis of environmental or water quality consequences from the proposed transfer scheme.

Although there has been significant previous work carried out on the unsupported transfer, this has always been done based on an analysis of the droughts contained within the historic record, either through the simulation of specific events (particularly 1921-22, 1933-34, 1975-76), or through the use of artificial events that have been ‘stitched together’ from the historic record. However, such analyses are very limited and may not be adequate for examining the yield and resilience benefits that are offered by a complex scheme such as the Severn-Thames transfer, which needs to take into account the following factors:

 The amount of water that is available for transfer largely depends on the differential nature of the rainfall that occurs between the two river basins during a drought. Because the west of the country is more exposed to Atlantic frontal systems than the east, the differences in rainfall follow a complex relationship, but there are only a handful of major droughts in the historic record through which we can examine the nature of that relationship. Making sure that the spatial coherence of drought episodes is properly taken into account is particularly important.

 The presence of abstraction limits on the Severn (Hands off Flow conditions) means that there are significant periods of time where there is no water available for transfer. The amount of water that can be transferred during a drought is therefore very sensitive to both the duration and timing of that drought.

 There are a number of large existing abstractions on the Severn, and their operators vary those abstractions according to storage levels in their own reservoirs and demand from their own systems. This affects the amount of water that is available for transfer at Deerhurst (which is at the downstream end of the Severn). These abstractions are likely to vary according to future climate change and demand.

These factors create a large amount of uncertainty about the performance of the scheme when the next critical drought occurs. A detailed exploration of the performance of the scheme under, for example, the 1921 drought is of limited use for understanding the scheme performance under a major drought that might affect the Severn catchment as well as London. This report therefore seeks to explore the yield and resilience implications of these issues by using a range of analytical techniques other than the simple, historically based ‘Deployable Output’ methodology. These techniques are set out in the following sections under the following headings.

 How does the Severn-Thames Transfer provide yield? This section provides background understanding to the hydrological nature of the scheme, which underpins the analyses provided in the next sections.  How would it perform under historic drought patterns? This section uses the information included within the historic record to provide an understanding of the scheme variability and act as a ‘sense check’ on the more complicated analyses in the next section.  What is it expected performance under future major droughts? This section uses advanced, statistically based methods that are in line with the most recent UK Water Industry Research (UKWIR) methods1 to provide a risk based evaluation of scheme performance under future drought events.  How is it affected by climate change? This section applies climate change risks to the flows and hydrology analysed above.

1 See Report ‘WRMP2019 – Risk Based Planning Methods’, published by UWKIR 2016

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 What are the risks from other abstractors? This section provides an evaluation of the risks posed by other abstractors on the River Severn in the future as a result of growth, climate change and licence modifications.

2. How Does the Severn-Thames Transfer Provide Yield?

The Severn-Thames transfer would take water from the River Severn at Deerhurst and pumps it across to the River Thames. Various transfer points on the Thames have been proposed, but the choice of transfer point does not notably affect yield, so the choice of transfer points is not considered here. This report incorporates a range of pumping and pipeline capacities, from 100Ml/d through to 600Ml/d.

The unsupported transfer relies on there being water available above the Hands off Flow (HoF) constraint at Deerhurst2 when it is needed in the Thames. Obviously this availability varies across the year, but the factors that dictate the amount of water that is transferred, and hence the resulting yield under a given drought event, can be described according to the factors described below.

2.1. The timing of storage recession in the London Reservoirs The transfer would be triggered using the same, volume based, control curves that are set on the London reservoirs and are used to trigger existing strategic schemes and the progressive implementation of demand restrictions. This means it is relatively unlikely that large volumes of transfer would be called for until spring, even during a severe drought. Some transfers may be requested to aid in recharge over winter, but only under longer, 24 month drought events such as those seen in 1933-34.

2.2. The natural flow of water in the Severn catchment. The natural flow of water in the Severn catchment varies according to exact rainfall patterns for a given drought, but hydrologically can be described according to the following four periods surrounding the critical drought year:

1. Winter and early spring prior to the critical drought year (Nov-March). The Severn will almost certainly have excess water during such periods, although during widespread droughts this may be somewhat intermittent.

2. The mid to late spring of the critical drought year (April-May). The Severn will be undergoing recession, and will tend to start falling below the HoF constraint at some point towards the middle or end of the period, limiting abstraction and transfer.

3. Summer (June to August) where there is generally less transfer available due to the HoF constraints, unless temporary ‘minor spate’ flows occur in the Severn due to higher rainfall.

4. Autumn and early winter during the critical year (September to December). The timing of recharge in the two catchments becomes very important here. The Severn will often start to recover to levels that allow transfer before adequate recovery occurs in the Thames, so the unsupported transfer can provide appreciable benefit. However the duration of this very much depends on the nature of the drought. For an event such as 1976 or 1949, where the drought ends abruptly, there will only be a matter of a few weeks where the Thames reservoirs are still recessing and hence the transfer will provide benefit. On the other hand, for droughts that extend into the late autumn and winter in the Thames catchment (such as 1921 or 1934), the transfer potential from the Severn in November and December can be high.

2 The HoF refers to the amount of water that must be left in the river to protect the environment, and only flows above this could be taken by Thames Water.

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Because the availability of transfer water varies strongly according to season, the benefits from the scheme very much rely on how much a given drought relatively affects the flows that occur within the two catchments during the different times of the year. This comparative nature of flows in the two catchments is theoretically influenced by two factors:

a. Physical Catchment Characteristics. When the actual flows in both rivers are considered then the overall catchment characteristics for the Thames to Teddington are actually hydrologically very similar to the Severn catchment to Deerhurst, as shown below3. However, unlike Deerhurst where most abstraction is returned to the river before the point of measurement, the actual flows in the Thames to Teddington are notably influenced by abstraction, which serves to reduce the apparent baseflow. When the natural catchments are considered then the River Severn to Deerhurst is somewhat ‘flashier’ (i.e. responds more strongly to rainfall) than the Thames, as stated in the GARD report page 114.

i. Thames at Teddington (Kingston): total catchment area = 9948km2, base flow index = 0.63. Naturalised base flow index is circa. 0.71

ii. Severn at Deerhurst: total catchment area = 9877km2, base flow index = 0.57.

b. Meteorology. Average rainfall and the summer to winter difference in rainfall tend to be higher in the Atlantic facing west of England & Wales. This results in a different seasonal profile of rainfall in the Severn when compared with the Thames catchment (see Figure 2-1 below), particularly in the autumn period. This combines with generally lower temperatures to generate potentially greater recharge during the autumn and winter, which tends to cause a later onset of the recession in the spring and an earlier onset of recharge in the autumn.

Differences in flow are therefore influenced by both physical hydrology and meteorology. The nature of the autumn period is therefore particularly influential on the benefits from the scheme, as there is less chance of cumulative effective rainfall being low enough to maintain drought conditions right through to the end of November or December in the Severn when compared to the Thames catchment. The chance of there being continuous, reliable, beneficial transfer therefore increases as the drought persists longer into the late autumn and earlier winter.

Figure 2-1 Comparison of Seasonal Rainfall Behaviour in the Thames and Severn Catchments5

More drawn out, but less intense, drought events such as 1921 or 1934 will therefore tend to experience greater benefit than shorter, sharper events (e.g. a 1976 style event that continues into October). Of course

3 Source: National River Flow Archives – the base flow index shows how much of the total flow is made up of slower release, groundwater oriented flow. Lower BFI catchments therefore tend to absorb less of the total effective rainfall to groundwater and hence demonstrate a larger rainfall-runoff response. 4 GARD response to Thames Water’s draft Fine Screening Report on WRMP19 Resource Options GARD 31st October 2016 5 Source: Thames and Severn Trent sub-catchment rainfall data

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2.3. The degree of abstraction and discharge within the Severn and Avon upstream of Deerhurst. This can vary from year to year, but during a drought the summer abstractions tend to be maximised (due to high demand in the summer and a need to refill back to reservoir control curves). However, historically Severn Trent Water and other abstractors have taken less than their full entitlement from the Severn during the spring and autumn period. This is partly because of a lack of demand and partly because storage reservoirs are not yet below their relevant control curves, so there is no need for Severn Trent Water to maximise abstraction.

3. How Would it Perform under Historic Drought Patterns? Thames Water has carried out a conventional deployable output (DO) assessment and this indicates that the DO of the scheme is 142 Ml/d. This is defined by scheme performance during the two critical droughts of the 20th Century, namely 1921-22 and 1933-34. In order to understand the performance of the scheme under a broader range of historic drought patterns, Thames has also carried out an analysis of the amount of time that the transfer would be available when it is called upon during the droughts of the 20th Century. This was undertaken using the WARMS2 model and done by running all of the droughts through at a fixed level of demand. The full results are not replicated here, but the availability of the transfer (i.e. the proportion of days where it could provide some transfer when it is called upon) ranged from as little as 31% to as high as 68% for the significant 20th Century drought events. A summary of the percentage availability under the four most severe droughts is provided in Table 3-1 below. Table 3-1 Summary of Transfer Availability for the Major 20th Century Droughts

Critical Drought Year Percentage time that the Severn Thames Transfer would have been available if called for. 1921 56% 1934 66% 1944 63% 1976 39%

The range of availability under 20th Century droughts can be used to gain some idea of the likely range of benefits that could be expected from the scheme for that specific set of droughts. The availability figure only shows when some water was available (i.e. not necessarily the full 300 Ml/d on each day). The actual transfer availability is often much lower than 300 Ml/d, particularly during the summer period. Figure 3-1 shows how the availability varies during the summer and autumn ‘minor spates’ recorded during the four major droughts described in Table 3-1 above.

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Figure 3-1 Flow Time series Showing Transfer Availability from the Severn at Deerhurst under Major Historical Droughts

These graphs show the flows at Deerhurst, along with the upper (black dashed line) and lower (solid black line) abstraction constraints that would be placed on the transfer. Water quality related constraints would occur when the flows are above the blue line

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As well as this variability of transfer volumes, the yield is affected by the timing of the recession in the London reservoirs, plus some transfer/process losses, so estimating the scheme benefit it is not as simple as multiplying availability by transfer capacity. However, for a 300Ml/d transfer capacity pipeline, which has a net DO benefit of 142 Ml/d, this implies that for 1921 the simple calculation of [percentage availability × transfer capacity] should be multiplied by around 85% to obtain yield6. For the 1934 event this simple calculation needs to be multiplied by around 70% to calculate yield. The equivalent percentage for 1976 is unknown, but logically it will tend to be lower for such events, as transfer availability is shorter and sparser, so the number of days where the transfer is not operating at full capacity is greater as a proportion of the total number of transfer days. A lower limit of around 60% has therefore been taken as a reasonable allowance7 Although there are only a few major droughts in the 20th century, this type of information can be used to gain an understanding of the sort of range of yield benefits that might be expected from the scheme under a range of drought events. Using the upper bound of 68% availability and the lower bound of 32% availability from the historic record, multiplied by a range of 60% to 85% to translate into yield, gives a potential range of drought yield between 55 Ml/d and 175 Ml/d (to the nearest 5 Ml/d), depending on the drought. Unfortunately there are insufficient data points in the historic record to determine where in this range Thames Water might reasonably plan for during ‘design’ drought conditions. It is this ‘reasonable planning allowance’ that Thames really needs to understand to allow it to evaluate the reliable benefits of the scheme. This is discussed further and analysed within the following section.

6 Calculation as follows: 56% * 300 Ml/d = 168 Ml/d. 142 Ml/d/168 Ml/d = 0.85 (i.e. 85%) 7 This is a nominal figure – it is not relied on in the conclusions to the report, but is only used to give some guidance as to the plausibility of the stochastically analysed data shown in the next section.

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4. What is its Expected Performance Under Future Major Droughts?

4.1. Background and Analysis Method Before the benefit can be analysed, it is first necessary to define what is meant by a ‘reliable yield’. Reliability is an often used term in risk assessment, but for water resource planning it has a specific meaning – it is the yield that the scheme can provide without affecting the existing Level of Service. If investment is planned on an assumed yield that is lower than this value, then Thames would effectively over-invest in other options and hence generate a slight increase in the effective level of service. Conversely, if the yield from the scheme is assumed to be higher than this amount, then Thames would tend to under-invest in other options, resulting in a decrease in the effective level of service. In statistical terms this can be referred to as the expected benefit – it is the benefit that does not change Thames Water’s underlying drought risk profile. This requires the use of advanced risk based methods, as described in the UKWIR ‘WRMP19 Risk Based Planning’ guidance.

In this case the derivation of the expected yield was carried out through a stochastic analysis of rainfall and evaporation across the Severn and Thames basins. This process used a spatially coherent weather generator which is able to emulate 20th Century climatic conditions and hence generate a large number of droughts of known severities on a coherent basis across both catchments. This contained weather generation techniques that are now being widely adopted within the water industry (Southern Water, Anglian Water, Welsh Water, Severn Trent Water and United Utilities are all using the same technique for WRMP19, along with the Water Resources in the South East and Water Resources in the East regional groups, plus the Water UK National Long Term Water Resources Planning study8). A full description of the generator, plus its validation against the 20th Century record, is contained in the ‘Thames Water WRMP19 Stochastic Methods Phase 2 & 3 Report’.

This large number of drought events was run through a simulation model of the Thames water supply system in order to estimate both the expected yield of the Thames-London system under a range of drought severities, and evaluate the expected net impact that the River Severn transfer schemes might have under that range of drought severities. Because of the large volumes of data involved it was not practical to run this analysis entirely within the WARMS2 modelling platform. Instead, the ‘core’ evaluation relied upon lumped sub-catchment rainfall-runoff models (in the Catchmod and Kestrel-IHM modelling platforms) and a simplified water resource emulator (using the IRAS software platform) to generate the flows and yield responses for each drought sequence. The outputs from these were checked and validated against WARMS2 to ensure the process was sufficiently accurate for the analysis. This modelling process and the validation against WARMS2 are also fully described within the Stochastic Methods Phase 2 & 3 Report.

The estimation of the net expected yield impact of the scheme was relatively straight forward, however the results can be difficult to understand without understanding how the transfer scheme affects the relative severity of individual drought events. The first key point is that drought severity is a result of multiple aspects of duration, timing and intensity (see Section 2.5.1.1. of the UKWIR report). Analysis carried out for this project and Water UK demonstrated that there is a strong trade-off between drought duration and intensity – the UK climate is fairly random and the law of averages dictates that the percentage rainfall deficit reduces as the length of observation increases (for example, a single month will frequently demonstrate deficits of 75% or more, but this level of deficit has never occurred in the historic record when a period of 6 months is considered). For any water resource system the amount of storage stress that it experiences is therefore a trade-off between the intensity of the rainfall deficit and the duration over which that deficit occurs; long, multiple year droughts will tend to have periods of recharge that can more than offset the additional loss of storage caused by the increased duration. A ‘critical period’ is a commonly used concept in flood hydrology, and this can be readily applied to droughts. In Thames’ case the ‘critical period’ for drought is in the order of 15 to 24 months, with the ultimate point of storage failure occurring any time between the late summer and early winter near the end of the drought. This does not mean that longer droughts do not happen. They are indeed possible and have been observed in the historic record (e.g. 1932-34, 1942-44). However, on an

8 ‘Water Resources Long Term Planning Framework’ report published by Water UK, September 2016.

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equivalent basis, the medium term (15 to 24 month droughts) will always tend to result in a lower system yield than a longer drought with an equivalent return period. Indeed, the longer droughts in the historic record only caused a failure to refill in the London reservoirs over a single winter. Even if this critical duration is used to help define drought severity, the timing of the start and end can significantly affect drought severity. For example, 2012 was one of the driest 24 month events on record, but its timing, where it ended in April/May, meant that that it did not significantly challenge the storage of the London system. The only meaningful way to define drought severity is therefore according to yield – this wraps up all the complexities associated with duration, timing and intensities into a single value that can be compared between droughts. A drought with a system yield of 2250 Ml/d is worse than a drought of 2300 Ml/d, irrespective of timing, duration etc. This does, however add a complication into the evaluation of the Severn- Thames transfer benefit. In hydrological terms the transfer would act conjunctively with the existing Thames reservoir system. As shown previously, this means the benefit is not fixed and varies from drought to drought. A drought of a given yield and hence severity (say 1 in 100 years) may change its yield ranking relative to other droughts once the scheme has been built, which effectively changes its severity (return period). This point is best explained through example, as shown in Figure 4-1 below.

Figure 4-1 Illustration of the Effect of Conjunctive use on Relative Drought Severity

YIELD OF THE LONDON SYSTEM WITHOUT YIELD OF THE LONDON SYSTEM WITH THE THE TRANSFER TRANSFER IN PLACE

Droughts ranked in order of in orderof Droughts ranked Drought 1: 16 month event. Overall Drought 3: 20 month event. Overall system yield 2,300 Ml/d [approximately system yield 2,390 Ml/d

increasing severity increasing 1 in 100 years] [approximately 1 in 100 years]

Drought 2: 18 month event. Overall Drought 2: 18 month event. Overall system yield 2,270 Ml/d [approximately system yield 2,370 Ml/d 1 in 110 years] [approximately 1 in 110 years]

Drought 3: 20 month event. Overall Drought 1: 16 month event. Overall system yield 2,240 Ml/d [approximately system yield 2,360 Ml/d 1 in 120 years] [approximately 1 in 120 years]

This example shows three potential future droughts. Without the transfer drought 3 has the lowest yield, and its ranking relative to all other potential droughts puts it at a 1 in 120 year event. When the transfer is added, the yield increases for all three droughts, but the shortest event proportionally experiences much less benefit than the longest event. The relative ranking of the droughts therefore changes, along with their effective return period

This issue is important because any analysis that seeks to understand the ‘on average’ net benefit of the scheme needs to account for the changing order of drought severities once the scheme is built. Fortunately this complexity can be accounted for by plotting a chart of return period versus yield before and after the scheme is built, and analysing the difference between them at the desired level of severity. This chart includes a wide range of droughts and the lines on the chart inherently account for any ‘switching round’ of individual droughts that might occur.

4.2. Options Testing and Results Five versions of the IRAS model were run to analyse the scheme benefits. All versions had the same stochastic inputs and system set up, but the capacity of the pipeline between Deerhurst and the Thames was varied between 100Ml/d and 600Ml/d.

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Based on the outputs of the weather generator and system simulation referred to above, the system yield versus return period chart for all of the different pipeline capacities is shown in Figure 4-2 below. This chart shows by how much the inclusion of the various Severn-Thames transfer options affects the expected yield of the system across a wide range of return periods.

Figure 4-2 Stochastic Analysis of the Net Yield Benefit of the Transfer

To maintain reasonable run times the IRAS yield increments were only accurate to around +/- 10Ml/d, so there is some unevenness in the results, particularly at higher return periods. However, this clearly shows that the benefits of increased pipe sizes reduces dramatically above the 300Ml/d capacity. The estimated benefits from the different pipeline capacities, when considered in the 1 in 100 to 1 in 200 return period range is as shown in Table 4-1.

Table 4-1 Assessed Transfer Option Benefits

Option Approximate Benefit (Ml/d) 100Ml/d Unsupported Transfer 30 300Ml/d Unsupported Transfer 100 400Ml/d Unsupported Transfer 110 500Ml/d Unsupported Transfer 120 600Ml/d Unsupported Transfer 120-130

There is some fluctuation in benefits with increasing severity, but this is more associated with the accuracy of the model than it is any ‘real’ effect, and the benefits appear to be reasonably constant across the range of severities that were tested.

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This indicates that the net yield benefit from the 300Ml/d transfer is around 100Ml/d9 for a 1 in 100 year type event, and is actually reasonably consistent across the range of return periods tested. In terms of a ‘sense check’, this level of yield benefit is near, but slightly below, the middle of the range suggested by the historic analysis described in the previous section. It can also be seen that the current Deployable Output of the Thames-London system (2305 Ml/d) is approximately equivalent to a 1 in 100 year drought yield. Both of these results provide a high level confirmation of the reasonableness of the stochastic methods used.

The 100Ml/d is the average expected benefit for any given return period. A review of the stochastically generated droughts confirms that there is a wide range of variability for individual events. The likely range10 is between 50 Ml/d and 160 Ml/d, which is similar to that suggested by the historic record above. This is in the order of +/-50%, albeit with a slightly skewed distribution.

9 This has increased from the previously published 80-90Ml/d range as a result of an error being found in the selection of input flows for IRAS, which affected around 25% of the stochastic years in the baseline (i.e. pre-climate change runs). This did not affect the climate change inputs or results. 10 The likely range represents the 80% confidence interval (values between the 10% lowest and 90% highest modelled benefits).

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5. How is it Affected by Climate Change?

Thames Water’s analysis of the impact of climate change on the DO benefit of the scheme for the historic record indicates a loss of around 20 Ml/d when set against the full range of possible climate futures. Because of the amount of data involved, the stochastic approach only incorporated three of those climate futures, but obviously evaluated each of those futures across a wide range of drought severities. The three climate futures that were used were taken from the Thames Water WRMP14 analysis and represented the 50th, 70th and 97th percentile futures respectively (i.e. a middle, dry and very dry future). The analysis was run at the 2080 time horizon.

The results of the analysis, showing the yield-return period relationship of the Thames system with and without climate change at the 50th Percentile is shown in Figure 5-1 below. The other two scenarios produced very similar results.

Figure 5-1 Stochastic Analysis of the Net Yield Benefit of the Transfer under Climate Change

This indicates that the impact on climate change on net yield benefit from the transfer is similar to that shown by the historic record; the yield benefit of the transfer scheme under climate change is just over 80Ml/d, i.e. 20Ml/d lower than in the baseline (no climate change) scenario. This type of analysis is a very simplistic analysis of what becomes a very complex problem once climate change is introduced into the analysis of expected yield, as the situation described in Section 4 relating to the switching round of drought events also applies to climate futures. In other words, the 50th percentile climate future without the transfer is not necessarily the 50th percentile climate future once the transfer is added in. However, for the purposes of a screening assessment this analysis is sufficient to confirm the findings of Thames Water’s own historically based analysis.

This relative impact is reasonably simple to explain. Although the flows in the Severn tend to reduce during the spring to autumn period under climate change, the timing of recession and recharge in the London reservoirs also changes, so the water is called for earlier and for longer into the recharge season. The winter flows in the Severn also tend to increase under most climate change scenarios, so water is available in these earlier and later seasonal periods.

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6. What are the Risks from Other Abstractors?

Although the direct impact of climate change on river flows does not significantly affect the net yield of the scheme, the patterns of abstraction from third parties (primarily Severn Trent Water) are likely to be affected by future climate change and increasing demand. In simple terms, the transfer is located at the downstream end of the Severn catchment system, so if it is put in place without any agreements over licences or storage with the abstractors that currently use the River Severn, then the amount of water that is available will change if those abstractors change their abstraction patterns.

This risk was indirectly analysed in the recently published Water UK ‘Water Resources Long Term Planning Framework’ report. That report concluded that changes associated with reducing licences at other sources, population growth and climate change are likely to result in increased pressure on the storage systems in Severn Trent Water’s region during significant drought events, even when the medium term (2040) future is considered (see pages 138-140 of the main technical report). This, in turn, is likely to result in a fuller utilisation of the existing abstraction licences on the Severn, as these can provide an existing, readily available alternative source of water.

The analyses described in Sections 3 to 5 above incorporated abstraction by Severn Trent Water based on their estimated typical abstraction patterns under a significant drought event given the current climate, levels of demand and licences at other sources. Whilst this pattern comes close to maximising abstraction during the summer period, the abstraction in the spring and autumn periods is well below licensed volumes. Figure 6-1 below shows the impact that a change from this historically based pattern to a fully licensed scenario would have on flow rates within the lower Severn throughout the year11.

Figure 6-1 Evaluation of the Impact of Fully Licensed Third Party Abstraction on Flows at Deerhurst

This chart shows the difference between the historic (‘DO’) abstraction scenario and a scenario whereby Severn Trent Water increases abstraction up to its licence, expressed in terms of the impact on flows at Deerhurst, expressed as a monthly average. Values are negative as they reflect a reduction in flow

11 Source HR Wallingford; analysis carried out based on the information gathered during the 2016 River Severn flow modelling project

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This represents the maximum net impact that increased abstraction could have on flows in the Lower Severn, but nevertheless demonstrates the level of risk of future abstraction patterns on available flows at Deerhurst, with just over 200 Ml/d potential additional abstraction during the spring and autumn. Impacts are smaller during May, but still around 50 Ml/d. Although these numbers are large, they need to be set in the context of the much larger recession rates and ‘spate’ flows that occur in the River Severn. They will, only make a significant difference to transfer rates during those periods where flows in the Severn at Deerhurst under current abstraction patterns are in the range 1,800 Ml/d to 2,300 Ml/d. Evaluating the expected yield impact of such changes therefore requires the same sort of stochastic analysis as described previously. If these changes in abstraction patterns are introduced into the stochastic yield analysis described in Section 4, then the expected net yield of the conjunctive system changes as shown in Figure 6-2 below.

Figure 6-2 Analysis of the Net Impact of Fully Licensed Abstraction by Other Users

This shows that the risk to the reliable scheme yield from other abstractors operating within their existing licences is generally in the range 10-20Ml/d. Obviously the proportion of this risk that materialises will depend on how much changing demands, cuts to other licences and climate change increases the dependency of other water companies on the River Severn. However, the evidence provided by Water UK, and the simple logic that this is an existing resource that can be taken without affecting storage in their systems, suggests that abstraction pressures are likely to increase under future droughts.

Figure 6-3 shows the same analysis under the 2080 50th percentile climate change scenario. This indicates that, although climate change may contribute to increased abstraction in the Severn, the changes in hydrology that occur as a result of climate change do not notably increase the amount of impact that this increased abstraction has on scheme yield.

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Figure 6-3 Analysis of the Impact of Fully Licensed Abstraction under 2080 Climate Conditions

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7. Summary of Scheme Resilience

The analyses methods described within this report allow the following conclusions to be drawn about the benefits and level of resilience of an unsupported Severn-Thames transfer:

1. The scheme is very sensitive to the exact patterns and behaviour of drought across the two catchments. The likely expected (statistical average) yield benefit of the scheme is lower than suggested by a simple, historically based, Deployable Output (DO) analysis. Expected yield for the 300Ml/d capacity pipeline is around 100 Ml/d, compared with 142 Ml/d gained from Thames Water’s historically based DO analysis. This difference is simply caused by the fact that the 1921-22 and 1933-34 droughts, which act as the crucial droughts in the historically based DO analysis, happened to have drought patterns and differences in rainfall between the Severn and Thames catchments that tend to result in a more favourable estimate of scheme yield. Other drought patterns such as those seen in 1975-76 would yield much less benefit, and this is reflected when the expected conditions are analysed.

2. Although the benefits are vulnerable to drought patterns, the stochastic methods indicate that the scheme yield of 100 Ml/d is reliable across a range of drought severities, if drought severity is expressed according to total system yield. This occurs because of the conjunctive use nature of the scheme, which means droughts will tend to naturally re-order to create a smooth yield versus severity curve when the transfer is added to the system.

3. For other pipeline capacities the estimated yield benefit from the scheme is summarised below. This shows that the net benefit diminishes rapidly for pipelines greater than 300Ml/d capacity.

Option Approximate Benefit (Ml/d) 100Ml/d Unsupported Transfer 30 300Ml/d Unsupported Transfer 100 400Ml/d Unsupported Transfer 110 500Ml/d Unsupported Transfer 120 600Ml/d Unsupported Transfer 120-130

4. Both the historically based and stochastically based methods indicate that the net yield of the scheme reduces by around 20Ml/d under climate change, even though absolute flows in the Severn reduce by much more than this under climate change futures. This is because the net yield depends on the storage characteristics in the Thames-London reservoirs as well as the flows in the Severn. Lower flows and hence storage in the Thames lead to the transfer being called upon earlier in the season and for longer during a drought year than they are under the current climate. This means that the transfer is required when River Severn flows are closer to their winter maximum, so there is more opportunity for benefit from the scheme. Overall, when it comes to net yield, it appears that the lower flows associated with climate futures in the Severn are largely counter-balanced by the wider timing of need caused by lower flows in the River Thames.

5. The scheme is potentially vulnerable to third party abstractions within the Severn, and the drought abstraction patterns that would be expected under the current Severn Trent Water supply system tend to be well below their licensed capacity during the key spring and autumn periods. Risks from climate change, increasing demand and reductions in other licences are likely to increase pressure on the Severn Trent Water supply system, so there is a significant risk that abstraction will be increased towards maximum allowances in the future. Overall this places 10- 20 Ml/d of the net yield benefit at risk when future conditions (to 2040) are considered.

Overall the scheme can provide a meaningful net yield benefit when it is operated conjunctively with the Thames-London water resource system, but the above analysis indicates that this reliable yield is significantly lower than a simple historically based analysis would suggest, at around 100 Ml/d. In

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WRMP19 Options Appraisal: Appendix Document for the Lake Vyrnwy Support Scheme

Thames Water

19 April 2017

Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

Table of contents

Chapter Pages 1. Introduction 4 2. How Do Lake Vyrnwy and Severn Trent Support the USTT? 4 3. What is its Expected Performance Under Future Major Droughts? 6 4. What are the Risks from Other Abstractors? 10 5. Summary of Scheme Outputs 11

Figures Figure 2-1 Flow Time series Showing Transfer Availability from the Severn at Deerhurst under Major Historical Droughts ...... 5 Figure 3-1 Stochastic Analysis of the Net Yield Benefit of the 95Ml/d Lake Vyrnwy Transfer Scheme (plus 15Ml/d from Severn Trent) ...... 8 Figure 3-2 Stochastic Analysis of the Net Yield Benefit of the 180Ml/d Lake Vyrnwy Transfer Scheme (plus 15Ml/d from Severn Trent) ...... 8 Figure 3-3 Stochastic Analysis of the Net Yield Benefit of the 180Ml/d Lake Vyrnwy Transfer Scheme, with up to 128Ml/d available from Severn Trent ...... 9

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1. Introduction

This document provides an overview of the nature of the yield benefit that is gained if the storage contained within the Lake Vyrnwy reservoir is used to provide additional support to the Severn-Thames Transfer (STT) scheme. Potential options are also available to provide further support from Severn Trent schemes, although the reliability and environmental acceptability of these schemes is currently under investigation.

Although there has been some previous work carried out on the yield benefit from Lake Vyrnwy, this has always been done based on an analysis of the droughts contained within the historic record, with assumptions about the patterns of usage by United Utilities and Thames Water and no explicit representation of the River Severn reservoir system. This report therefore uses the same stochastic data sets referred to in the ‘WRMP19 Options Appraisal: Appendix Document for the Unsupported Severn- Thames Transfer’ (USTT) to analyse how the Lake Vyrnwy scheme might be expected to perform under different drought types, and contains analyses that explicitly model the behaviour of the Lake Vyrnwy and Clywedog reservoir systems on flows in the River Severn. The analysis is therefore separated into the following sections:

 How do Lake Vyrnwy and Severn Trent schemes support the USTT? This section provides background understanding to the hydrological nature of the scheme options, which underpins the analyses provided in the next sections.  What is its expected performance under future major droughts? This section uses advanced, statistically based methods that are in line with the most recent UK Water Industry Research (UKWIR) methods1 to provide a risk based evaluation of scheme performance under future drought events.  What are the risks from other abstractors? This section provides a qualitative assessment of the risks associated with other abstractors, in particular United Utilities and Severn Trent.

2. How Do Lake Vyrnwy and Severn Trent Support the USTT?

The ‘WRMP19 Options Appraisal: Appendix Document for the Unsupported Severn-Thames Transfer’ provides a detailed analysis of how the Severn-Thames Transfer without Lake Vyrnwy in place. Effectively the yield benefit from the scheme is limited because transfer is limited to those periods where the Thames reservoirs need the water, and water is available above the Hands off Flow (HoF) constraint at Deerhurst2. This constrains the yield to well below the transfer limit, as most summer drought periods will have very little water available for transfer, and is shown graphically in Figure 2-1 below.

The advantage of the Lake Vyrnwy scheme is that it potentially provides a large volume of storage that can be used to fill the ‘gap’ left by the availability of River Severn flows during the summer period. This ‘gap’ may only be in the order of 4-5 months, although under severe drought conditions the temporal requirement could be much longer. A storage volume the size of Lake Vyrnwy can therefore make a large difference to yield if it is only required for support during this relatively short period of time (for example, discharging at 200Ml/d over 5 months only requires 30,000Ml of available storage).

1 See Report ‘WRMP2019 – Risk Based Planning Methods’, published by UWKIR 2016 2 The HoF refers to the amount of water that must be left in the river to protect the environment, and only flows above this could be taken by Thames Water.

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Figure 2-1 Flow Time series Showing Transfer Availability from the Severn at Deerhurst under Major Historical Droughts

These graphs show the flows at Deerhurst, along with the upper (black dashed line) and lower (solid black line) abstraction constraints that would be placed on the transfer. Water quality related constraints would occur when the flows are above the blue line

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Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

Currently the physical and institutional operation of the scheme has not yet been fully developed, and this may remain unclear for some time. However, for the purposes of this analysis it was assumed that whatever water is released from Vyrnwy for Thames Water would be made available at the Deerhurst transfer point, irrespective of what intermediate releases to the Severn (particularly from Clywedog reservoir) or other abstractors are doing at the time.

The Severn Trent support could come from a number of scheme options, but currently the viability of specific options is not clear. A scenario based approach has therefore been used whereby a nominal 128Ml/d has been tested to reflect a potential upper limit scenario, and the Severn Trent inputs have been modelled on the presumption that the offered water will be available when it is required at the Deerhurst transfer. Unlike the Lake Vyrnwy support, which requires explicit modelling of the available Lake Vyrnwy reservoir storage to determine if reservoir capacity is a constraint on the scheme, the Severn Trent support components have been modelled as a simple input that is available whenever it is required. This will need to be reviewed and, if required, re-evaluated if any of the Severn Trent options are shown to be viable on a technical and environmental basis. . 3. What is its Expected Performance Under Future Major Droughts?

Before the benefits can be analysed, it is first necessary to define what is meant by a ‘reliable yield’. Reliability is an often used term in risk assessment, but for water resource planning it has a specific meaning – it is the yield that the scheme can provide without affecting the existing Level of Service. If investment is planned on an assumed yield that is lower than this value, then Thames would effectively over-invest in other options and hence generate a slight increase in the effective level of service. Conversely, if the yield from the scheme is assumed to be higher than this amount, then Thames would tend to under-invest in other options, resulting in a decrease in the effective level of service. In statistical terms this can be referred to as the expected benefit – it is the benefit that does not change Thames Water’s underlying drought risk profile. This requires the use of advanced risk based methods, as described in the UKWIR ‘WRMP19 Risk Based Planning’ guidance.

In this case the derivation of the expected yield was carried out through a stochastic analysis of rainfall and evaporation across the Severn and Thames basins. This process used a spatially coherent weather generator which is able to emulate 20th Century climatic conditions and hence generate a large number of droughts of known severities on a coherent basis across both catchments. This contained weather generation techniques that are now being widely adopted within the water industry (Southern Water, Anglian Water, Welsh Water, Severn Trent Water and United Utilities are all using the same technique for WRMP19, along with the Water Resources in the South East and Water Resources in the East regional groups, plus the Water UK National Long Term Water Resources Planning study3). A full description of the generator, plus its validation against the 20th Century record, is contained in the ‘Thames Water WRMP19 Stochastic Methods Phase 2 & 3 Report’.

This large number of drought events was run through a simulation model of the Thames water supply system in order to estimate both the expected yield of the Thames-London system under a range of drought severities, and evaluate the expected net impact that the River Severn transfer schemes might have under that range of drought severities. Because of the large volumes of data involved and the need to simulate the River Severn system, it was not practical to run this analysis within the WARMS2 modelling platform. Instead, the evaluation relied upon lumped sub-catchment rainfall-runoff models (in the Catchmod and Kestrel-IHM modelling platforms) and a simplified water resource emulator (using the IRAS software platform) to generate the flows and yield responses for each drought sequence. The ‘baseline’ outputs (i.e. without the transfer scheme or climate change) from these models were checked and validated against WARMS2 to ensure the process was sufficiently accurate for the analysis. This modelling process and the validation against WARMS2 are also fully described within the Stochastic Methods Phase 2 & 3 Report.

3 ‘Water Resources Long Term Planning Framework’ report published by Water UK, September 2016.

Atkins Lake Vyrnwy Transfer Support: Note on Option Yield | Version 5 | 19 April 2017 | 5140905

Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

The Lake Vyrnwy and Severn Trent support was added into a version of the IRAS model that incorporated all of the abstractions and discharges within the Severn catchment, as well as a representation of both the Vyrnwy and Clywedog reservoir systems and associated control curves. Abstractions and discharges from the River Avon (and its tributaries) were incorporated as fixed profiles (i.e. the Draycot reservoir was not explicitly included within the model). It was assumed that United Utilities (UU) would continue to abstract from Lake Vyrnwy according to current practice and control curves until the point at which the Severn- Thames Transfer ‘calls’ for the water, after which UU would cease abstraction and all remaining storage would be made available for the transfer. A 10% loss factor was assumed, as per previous studies (i.e. 10% of the water released from Vyrnwy would be lost to the system and would not be available at Deerhurst). The following range of schemes were tested within the model:

 A smaller scheme, using 95Ml/d support transfer capacity from Lake Vyrnwy, plus 15Ml/d from Severn Trent, with a 100Ml/d transfer capacity pipeline between Deerhurst and the Thames.  A 180Ml/d release from Lake Vyrnwy (which loses 10%, so is equivalent to 162Ml/d support at Deerhurst), with 15Ml/d support from Severn Trent and options of 300Ml/d, 400Ml/d and 600Ml/d for the Deerhurst to Thames transfer  A 180 Ml/d release from Lake Vyrnwy, with 128Ml/d support available from Severn Trent and options of 300Ml/d, 400Ml/d and 600Ml/d for the Deerhurst to Thames transfer

The estimation of the net expected yield impact of the scheme followed the same methodology as described under the USTT option appendix. Effectively the yield of the Severn-Thames-London system was analysed for all years in the stochastic record, with and without the relevant support and transfer scheme in place. The results of the analysis, showing the yield-return period relationship of the Thames system under each of the options are provided in Figure 3-1 to Figure 3-3below.

All of the schemes demonstrate resilience across a range of return periods, and provide the estimated net yield benefits as described in Table 3-1 below.

Table 3-1 Summary of Benefits from Scheme Options

Approximate Benefit (allowing for Option 10% loss from Vyrnwy) (Ml/d) 100Ml/d pipe, 95Vyrnwy, 15SVT 90-100 300Ml/d pipe, 180Vyrnwy, 15SVT 200 400Ml/d pipe, 180Vyrnwy, 15SVT 240 600Ml/d pipe, 180Vyrnwy, 15SVT 260 300Ml/d pipe, 180Vyrnwy, 128SVT 240 400Ml/d pipe, 180Vyrnwy, 128SVT 280 600Ml/d pipe, 180Vyrnwy, 128SVT 320

These results appear to be logical. Effectively the yield is dictated by the average of the rate of transfer before the flow in the Severn becomes constrained and full support is required, and the rate of transfer during the supported period. The shape of the control curve means that the transfer does not usually start for a short period once recession starts in the London reservoir, so the average rate of transfer before the full support period is effectively a percentage of the rate that would occur if the transfer operated at full capacity from the start of the recession. That percentage will depend on a complicated range of factors, but generally appears to be around 60%-70%.

Atkins Lake Vyrnwy Transfer Support: Note on Option Yield | Version 5 | 19 April 2017 | 5140905

Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

Figure 3-1 Stochastic Analysis of the Net Yield Benefit of the 95Ml/d Lake Vyrnwy Transfer Scheme (plus 15Ml/d from Severn Trent)

Figure 3-2 Stochastic Analysis of the Net Yield Benefit of the 180Ml/d Lake Vyrnwy Transfer Scheme (plus 15Ml/d from Severn Trent)

Atkins Lake Vyrnwy Transfer Support: Note on Option Yield | Version 5 | 19 April 2017 | 5140905

Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

Figure 3-3 Stochastic Analysis of the Net Yield Benefit of the 180Ml/d Lake Vyrnwy Transfer Scheme, with up to 128Ml/d available from Severn Trent

Atkins Lake Vyrnwy Transfer Support: Note on Option Yield | Version 5 | 19 April 2017 | 5140905

Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

4. What are the Risks from Other Abstractors?

Although other abstractors represent a risk for the unsupported transfer, and create some uncertainty in the yield that might be expected from that scheme, it is logically assumed that this would not affect the additional net yield benefit that is gained from the Lake Vyrnwy support, as mechanisms would be in place to ensure that all water (-10% loses) released from Vyrnwy would be available for abstraction at Deerhurst. It is not currently clear exactly how this would work given that summer abstractions above Bewdley are regulated by releases from Clywedog reservoir, which would interfere in the calculation of abstraction availability at Deerhurst. However, such issues should not be impossible to surmount, so for the purposes of this analysis it was concluded that other abstractors would not affect the net yield benefit provided by the Lake Vyrnwy storage support, but would affect the amount available from flows in the Severn, so the overall impact is likely to be the same as the unsupported transfer (i.e. up to 20Ml/d).

Atkins Lake Vyrnwy Transfer Support: Note on Option Yield | Version 5 | 19 April 2017 | 5140905

Thames Water WRMP19 Stochastic Methods Appendix Document for the Lake Vyrnwy Transfer Support

5. Summary of Scheme Outputs

The analyses described within this report allow the following conclusions to be drawn about the potential benefits and level of support gained by providing storage support from Lake Vyrnwy and Severn Trent to the Severn-Thames Transfer scheme:

 The size of pipeline is much more important than for the unsupported transfer. The addition of the support means that higher transfer rates can be maintained for a much greater proportion of the recession during a drought, so incorporating greater capacity provides a proportionally greater benefit.  In volumetric terms the Lake Vyrnwy scheme appears to provide a consistent yield across a range of droughts. The same is true for the Severn Trent element of the support, but this is directly due to the nature of the modelling (it is available at the quoted capacity whenever it is required). The Severn Trent supported scenario would therefore require further testing using a properly specified scheme to test drought resilience if any viable schemes are identified.

The quantified benefits from the options that were tested were as follows:

Option Approximate Benefit (Ml/d) 100Ml/d pipe, 95Vyrnwy, 15SVT 90-100 300Ml/d pipe, 180Vyrnwy, 15SVT 200 400Ml/d pipe, 180Vyrnwy, 15SVT 240 600Ml/d pipe, 180Vyrnwy, 15SVT 260 300Ml/d pipe, 180Vyrnwy, 128SVT 240 400Ml/d pipe, 180Vyrnwy, 128SVT 280 600Ml/d pipe, 180Vyrnwy, 128SVT 320

It should be noted that the above analysis for Lake Vyrnwy does contain a number of assumptions about the operation and control of the scheme, which are not yet certain. These would need to be reviewed and confirmed as being valid within the proposed trading agreement once this has been developed.

Atkins Lake Vyrnwy Transfer Support: Note on Option Yield | Version 5 | 19 April 2017 | 5140905