Analysis of Options for Tidal Power Development in the Severn Estuary

DECC ANALYSIS OF OPTIONS FOR TIDAL POWER DEVELOPMENT IN THE SEVERN ESTUARY -

INTERIM OPTIONS ANALYSIS REPORT

VOLUME 1

December 2008

Prepared by Prepared for Parsons Brinckerhoff Ltd DECC in association with 1 Victoria Street Black & Veatch Ltd London Queen Victoria House SW1 0ET Redland Hill Redland Bristol BS6 6US CONTENTS Page

EXECUTIVE SUMMARY IV

SECTION 1 1

INTRODUCTION 1

SECTION 2 6

ASSESSMENT FRAMEWORK 6 2.1 Overview of Process 8 2.2 Fair Basis Evaluation 8 2.3 Assessment Framework 9 2.4 Assessment Framework Spreadsheet 13

SECTION 3 15

LONG LIST OF PROPOSALS 15 3.1 Identification of Potential Options 16 3.2 Proposals taken from the SDC research 16 3.3 Responses to the Call for Evidence 18 3.4 Other Strategically Selected Proposals 21 3.5 Long-Listed Proposals 22 3.6 Tidal Lagoon Concept 24 3.7 Initial Screening 25

SECTION 4 32

COMPARISON OF ENERGY OUTPUT 32 4.1 Estimation of Energy Output 33 4.2 Comparison with Call for Proposal Submissions 41 4.3 Tidal Fence 43 4.4 Optimisation of Energy 46

SECTION 5 48

ENVIRONMENTAL, SOCIAL, ECONOMIC AND REGIONAL CONSIDERATIONS 48 5.1 Introduction 50 5.2 Qualitative environmental review of long-list options 52 5.3 Environmental Issues Relevant for All Options 52 5.4 Modes of Operation 84 5.5 Mitigation and compensation issues 85 5.6 Ecosystem goods and services 86 5.7 Conclusion 86

Final i December 2008 SECTION 6 87

CIVIL, MECHANICAL AND ELECTRICAL ENGINEERING CONSIDERATIONS 87 6.1 Civil Engineering 88 6.2 Lagoon Construction 93 6.3 Tidal Fence Construction 99 6.4 Tidal Reef Construction 99 6.5 Navigation Issues 100 6.6 Adaptability for Sea Level Rise 104 6.7 Turbines and Generating Equipment 105 6.8 Grid Connection and Reinforcement 112

SECTION 7 119

ESTIMATED FIRST YEAR OF OPERATION 119 7.1 Overview 120 7.2 Innovation Risks 121 7.3 Construction Programmes and Estimated First Year of Operation 122

SECTION 8 125

SCHEME COST AND COST OF ENERGY 125 8.1 Pre-Construction Cost Estimates 126 8.2 Barrage and Lagoon Civil Engineering Cost Estimates 127 8.3 Barrage and Lagoon Mechanical and Electrical Cost Estimates 128 8.4 Tidal Fence Civil, Mechanical and Electrical Cost Estimate 129 8.5 Tidal Reef Civil, Mechanical and Electrical Cost Estimate 129 8.6 Grid Reinforcement 131 8.7 Compensatory Habitat 131 8.8 Ancillary Works Costs 132 8.9 Cost per Unit Energy 137 8.10 Risk Assessment 143

SECTION 9 149

ASSESSMENT SCREENING 149 9.1 Application of the Assessment Framework 150 9.2 Summary of Analysis 151

SECTION 10 162

CONCLUSIONS 162 10.1 Conclusions 164 10.2 Overall Summary 166

Final ii December 2008 APPENDIX A 171

FINANCIAL ANALYSIS DATA 171

VOLUME 2

APPENDIX B ASSESSMENT FRAMEWORK MODEL OUTPUTS

APPENDIX C LOCATION PLANS FOR OPTIONS

Final iii December 2008 EXECUTIVE SUMMARY

Final iv December 2008 EXECUTIVE SUMMARY

Objectives and Context The Government has set ambitious targets to reduce carbon emissions by 80% by 2050 and increase renewable energy. The draft EU Renewable Energy Directive will require 15% of the UK’s energy to come from renewable sources in 2020. Both, alongside the goals of energy diversity and security, will require significant investment in low carbon energy sources including many different forms of renewable electricity which may have to account for around 32% of the UK’s electricity mix by 2020. It is in this context that generation of electricity from the tidal range of the Severn is again being examined to assess how it may contribute to the UK’s renewable energy strategy. The Severn Estuary has the second or third largest tidal range in the world and is the most significant tidal range resource in the UK by some distance. In addition, the Severn represents one of the largest single project potential contributors of low carbon energy with the largest options being capable of contributing up to 7% of the UK’s total electricity demand.

The objective of this report is to analyse, from a technical perspective, potential tidal range power options in the Severn Estuary to inform Government in developing a draft short-list of options. Government will also take account of non-technical issues which could impact on the overall feasibility of an option. The assessment to form the short-listed options has been undertaken having regard to the identification of options that are able to:

x generate electricity from the renewable tidal range resource of the Severn Estuary in ways that will have an acceptable overall impact on the environment and economy both locally and nationally, will meet our statutory obligations and provide benefit to the UK

x deliver a strategically significant supply of renewable electricity, which is affordable and represents value for money compared to other sources of supply in the context of the UK's commitments under the forthcoming EU Renewable Energy Directive and Climate Change Act and our goal to deliver a secure supply of low-carbon electricity.

Other studies undertaken by the Government are considering related technical issues such as grid reinforcement and financing / procurement options.

Assessment of Options A common set of principles and associated assumptions has been applied to the analysis of each option to enable a “fair basis” assessment of costs (the application of common assumptions and principles across all options). As a result, the information contained in this report is of sufficient accuracy as is necessary for differentiating between options.

The options studied by this report are summarised in the table ES1 at the end of this summary. This provides an executive summary for each of the options studied. Figures quoted are based on a discount rate of 8% and exclude the costs of providing compensatory habitat or grid reinforcement. Inclusion of compensatory habitat costs increases the capital costs by between 6% and 20% for larger barrage options and typically between 10% and 35%

Final v December 2008 for the other options (dependent upon replacement ratios). In addition, the relative differences between the larger barrage options and the other, smaller options become smaller and, in some cases are reversed. This is because the loss of inter-tidal areas as a percentage of energy yield is smaller for the larger options. It should, however, be noted that the fair basis assessment of loss of inter-tidal areas, which is based on Admiralty Chart data, is an indicator and may over or under-estimate areas of loss when compared with outputs from detailed analyses which take account of hydrodynamic effects upstream and downstream of each option. If a decision is taken by Government to proceed to the next stage of this study, such analyses will be undertaken for all options selected by Government to be on the short- list. As a comparison the SDC report "Turning the Tide" estimated losses of inter-tidal habitat of up to 14,500 hectare (ha) on a Spring tide for a Cardiff-Weston barrage and up to 5,500 ha for an English Stones barrage rather than the 20,000 ha and 5,000 ha respectively determined by the fair basis methodologies used in this report. Subsequent analyses, using complex hydrodynamic models, will be critical in providing more definitive estimates of inter-tidal habitat loss, as well as addressing a key issue for all options, specifically, how they would affect the geomorphological response of the estuary.

Conclusions Engineering The study has evaluated the engineering performance and requirements of all options. Tidal Barrages have been assessed on the basis of the same recommendations made in previous studies updated to suit present day requirements. Engineering for tidal barrages is well understood and the main issues relate to the selection of gates and turbine types to maximise power generation whilst adequately mitigating environmental effects. Tidal lagoons involve similar engineering components as barrages although, due to the longer lengths of wall construction required to form an impoundment, different forms of wall construction have been proposed to reduce costs by comparison with a conventional rock armoured embankment. These, more innovative, forms of wall construction involve greater risk in terms of engineering design, estimation of costs and durability. Embryonic technologies such as the tidal fence and the tidal reef present the greatest engineering challenges and this is likely to be reflected in increased development times to reduce the risks associated with such technologies.

Energy Yields and Carbon Dioxide Savings The larger barrage options (B1 to B3) have the potential to contribute the most significant reductions in carbon dioxide emissions with the ability to generate renewable energy accounting for between 4.5 and 7% of the UK’s electricity requirements. All other options are smaller in output contributing up to 1% of the UK’s electricity requirements but with the advantage that the electricity they produce during the late night / early morning tides is more likely to be fully utilised. In terms of contributing to the UK’s climate change targets of 80% reduction by 2050, those technologies that are already deployed in projects around the world can be implemented in the short term and thus be capable of making a greater contribution to the offsetting of carbon emissions compared with less developed technologies such as those used in the tidal fence and tidal reef proposals.

Costs The lowest cost per unit energy is achieved by smaller barrages located at the point where the tidal range is greatest. Larger tidal barrages are between 24 and 34% more expensive on

Final vi December 2008 a cost per unit basis, whilst land connected tidal lagoons have similar energy costs to large barrages but smaller output. Offshore lagoons represent the most expensive option. Embryonic technologies such as the tidal fence and the tidal reef are more difficult to predict in terms of cost but even allowing for a significant reduction in costs compared with current demonstration projects, the tidal fence option is more than double the unit cost of the lowest cost option (B4 the Shoots Barrage).

In terms of affordability, all options represent significant construction projects in their own right with the larger barrage options costing upwards of £18bn and the smaller options costing up to £5bn although those with the lowest cost per energy are between £1.8bn and £3bn. Costs of compensatory habitats would be additional and there would also need to be investment to reinforcing the national grid although similar investments would be required for other renewables if no Severn tidal power option was pursued. Combinations of options, such as a Barrage and a Tidal Lagoon could also be considered.

Impacts on Habitats All options would impact inter-tidal habitats including offshore lagoons. Although an offshore lagoon does not directly lead to loss of inter-tidal habitats, resultant changes in tidal currents and geomorphology will affect adjacent habitats. Following appropriate assessment which involves consideration of alternatives, and subject to the requirements of the Habitat regulations, should a decision be taken to proceed on the basis of the over-riding public interest, compensatory measures would be required including habitat compensation for lost intertidal habitat. Not all compensation would necessarily be located in the Severn. For this report, these costs have been assessed in headline terms only using a range of possible replacement ratios and an indicative cost per ha.

Environmental Effects Climate change is already affecting the Severn Estuary and any environmental effects have to be seen in the light of this changing baseline. The most significant environmental effects of a scheme will be those relating to the geomorphological response of the estuary to any tidal power structure, loss of inter-tidal habitat, changes to habitats including feeding grounds available to birds, salt marsh and sedimentation, effects on fish and changes in water quality. For some of the smaller options, whilst the effects will continue to be significant, the scale of impact may be smaller (for example availability of feeding grounds for birds). Other effects include changes to water quality and turbidity. Fish behaviour will be changed by all options and where fish navigate upstream or downstream through turbines, significant mortality rates will be experienced.

Social, Economic and Regional Effects The construction of any tidal power project in the Severn will result in significant employment opportunities both during and after construction. There is also potential for jobs to be lost from industries whose operations are compromised by a Severn tidal power development. Impacts during construction will require careful management but will result in benefits for local service industries.

Transportation links have not been considered by this study as there is no policy at present to increase the number of transportation links across the Severn. The activities of

Final vii December 2008 commercial ports will be affected by tidal barrages in particular and will entail navigation through an additional set of ship locks (increasing transit times) and modification of existing facilities to accommodate changed water levels. A potential benefit for impacted ports will be increased high water standing times and a significant increase in low water level. Non barrage options will impact ports in different ways – tidal reefs and tidal fences will present challenges in time of entry / exit through their navigation provision because of the increased tidal currents that will prevail. Tidal lagoons may have less impact on ports although changes to dredging regimes may result from all options. The numbers of ports impacted differs depending upon the location of options

The extent of flood benefits and impacts remains uncertain from a Severn tidal power scheme. Whilst flood defence should be enhanced (by protecting communities located upstream of a barrage or the Bridgwater Bay land connected lagoon from storm surges and sea level rise), this would only be effective if mitigation of adverse effects is achieved (for example submerged tide locked land drainage outfalls) so that existing standards of flood protection are maintained. Other regional effects include impacts on fisheries.

Summary Tidal barrage options offer the greatest degree of certainty in relation to energy yields, costs, timescales and technology. Tidal lagoons use similar turbines and generating equipment but involve less traditional forms of construction for the lagoon walls. Whilst, in engineering terms, there are examples of tidal power barrages in existence (La Rance, France and Anapolis Royal, Canada and Sihwa, South Korea – under construction) there are, as yet no tidal lagoons. Both tidal barrages and tidal lagoons will result in significant changes to the Severn Estuary although the real extent and nature of these changes is dependent upon the location of the specific option.

More embryonic technologies have potential (albeit unproven) benefits but will also result in significant changes to the Severn Estuary. As they are located in the outer part of the estuary, the extent of these changes, although smaller at any one location than an equivalent barrage, will extend through a greater area. In addition, their development cycle (no examples of tidal fences or tidal reefs currently exist) will delay implementation on the Severn with the consequent impact in contributing to the Government’s energy and carbon reduction targets. As this is a specific objective of the Government’s Feasibility Study, this suggests that embryonic technologies will be less able to meet the Government’s required timescales compared with tidal barrages and lagoons. However, for the purposes of this report, where adequate data are available on which to assess energy yields and costs, assessment of embryonic technologies has been analysed assuming that they and the other options follow similar timescales for planning, designing and achieving consents to enable costs to be compared on an equivalent basis.

Consideration of options operating in conjunction with each other may also be relevant, and the combination of one or more lagoons with a barrage located upstream will also be considered in Phase 2 if the decision is taken to proceed.

Generation of power using the tidal range from the Severn is technically feasible and preliminary costs have been determined for each option. All options considered have

Final viii December 2008 impacts and benefits relating to the environment, social, economic and regional effects. The scale of these impacts and benefits varies across options and further work is needed to quantify and assess these to determine the extent of benefits and technical and financial feasibility of mitigation and compensation. The purpose of this report is to differentiate between options and provide a high level indication of their respective benefits and impacts. In accordance with current normal practice, a precautionary approach has generally been adopted for identifying potential environmental impacts. In subsequent stages, after confirmation of a short-list of feasible options, more detailed work will be undertaken to assess significant benefits and impacts to a level commensurate with the strategic nature of this study.

Final ix December 2008 Table ES1- Executive Summary for Each of the Options

Option Option Name Key Conclusions

B1 Outer Barrage from x Largest producer of energy (25TWh/a) but with highest capital cost (£29bn); Minehead to Aberthaw x Cost of energy is 13.94p/kWh excluding compensatory habitat costs ; x Largest environmental impact footprint, and will result in reduction of water levels and tidal range, loss of inter-tidal habitats and impacts on bird and fish populations in the Severn; Benefits include protection from effects of storm surges, sea level rise and reduced turbidity; x Severn Ports upstream will be affected, primarily Barry, Bristol, Cardiff, Newport and Sharpness.

B2 Middle Barrage from x Longest barrage option - based on the B3 option but with additional embankment Hinkley to Lavernock extending the barrage to Hinkley Point - Energy output of 19TWh/a; Point (Shawater concept) x Although the capital cost is less (£22bn), the cost of energy is similar to Option B1 at 13.96p/kWh; x Environmental effects are similar to those for B1 as this option seeks to provide similar flood defence benefits by crossing Bridgwater Bay; x Severn Ports upstream will be affected, primarily Bristol, Cardiff, Newport and Sharpness.

B3 Middle Barrage from x Most studied of any of the options and reported on in Energy Paper 57; Brean Down to x Annual energy output of 17TWh and a capital cost of £18bn; Lavernock Point x The cost of energy is the best of all the “large” options at 12.94p/kWh excluding (commonly known as compensatory habitat costs ; the Cardiff to Weston x Environmental impacts are potentially significant, as with other large barrage options, and Barrage) will result in reduction of water levels and tidal range, loss of inter-tidal habitats and impacts on bird and fish populations in the Severn; Benefits include protection from effects of storm surges, sea level rise and reduced turbidity.

Final x December 2008 Option Option Name Key Conclusions

x Severn Ports upstream will be affected, primarily Bristol, Cardiff, Newport and Sharpness.

B4 Inner Barrage (Shoots x Significantly smaller than the large barrage options, this option is located just downstream Barrage) of the Second Severn Crossing co-incident with the highest tidal range in the Severn; x Generates 2.77TWh per year at a capital cost of £2.6bn and achieves the lowest cost per unit energy at 10.4p/kWh; x Environmental impacts are similar in type (although not necessarily scale) to other barrage options although there is an increased risk of sedimentation; x This option does not impact the Ports of Bristol or the ABP Ports on the Welsh coast.

B5 Beachley Barrage x Located upstream of the Wye, smallest barrage option studied (£1.8bn) and has similar characteristics to Option B4; x Annual energy output is 1.59TWh/a, 57% of Option B4 whilst the cost per energy is 12.58p/kWh; x Similar environmental effects as Option B4 except that the Wye is not impounded and sedimentation risk is higher; x This option affects ports in the Gloucester Harbour Trustees administered waters.

F1 Tidal Fence Proposals x Initially, proposed between Cardiff and Weston but a more feasible alignment was submitted by Severn subsequently considered between Minehead and Aberthaw; Tidal Fence Group x Annual energy output of 3.3TWh is achievable at a cost of £6.3bn. Cost of energy is more than double the lowest cost option at 22.72p/kWh; x Assumes future development costs will reduce significantly from the current demonstration project costs for tidal stream technology. This implies a significant period of further development and experience before large scale implementation could be achieved. Unlikely that a decision to proceed with a tidal fence could be made in the short-term; x It does offer the possibility of less significant environmental effects than barrage options

Final xi December 2008 Option Option Name Key Conclusions

although the area affected is as large as the biggest barrage option.

L2 Tidal Enclosure on the x Land connected lagoon located on the relatively high Welsh Grounds just downstream of Welsh Grounds the Shoots Barrage (B4); proposed by Fleming x It has an annual energy output (2.3TWh/a) achieved at a cost of £3.1bn. Cost per unit Energy energy is 15.46p/kWh and is thus more expensive than the larger barrage options, although development alongside B4 would reduce energy cost. Additional energy output could be achieved from the Welsh Grounds if the materials used in construction were excavated from within the basin to achieve greater live storage. This would marginally increase energy yield and thus reduce the cost of energy; x Land connected lagoons, like barrages, result in loss of inter-tidal habitats because of the significant reduction in tidal range within the impounded area. Other environmental effects are similar to smaller barrages except that impacts on fish and navigation are expected to be less because they do not form a barrier across the estuary.

L3 Tidal Lagoon Concept x Various land connected and offshore lagoon configurations have been studied using (which has been different forms of lagoon wall construction; subsequently modelled x As lagoon costs are influenced by the length and depth of wall forming the impounded as four land-connected basin, innovative methods of wall construction are required and the lowest cost option, lagoons and three (apart from the wall design proposed by Fleming Group for Option L2) comprises a offshore lagoons based geotextile solution using material dredged from the estuary and protected by rock armour on various general (externally) and revetment (internally); submissions received x Aside from the L2 Welsh Grounds proposal, Bridgwater Bay offers the most cost effective from the Call for lagoon option with a higher energy yield (2.64TWh/a) and slightly reduced capital costs Evidence) than L2 giving a cost per kWh of 13.02p/kWh. x An offshore lagoon, located below the low water contour (and reduced impact on habitats), has been modelled to produce a similar energy output using the same forms of construction. Because of the much deeper wall construction required, it is more expensive with a capital

Final xii December 2008 Option Option Name Key Conclusions

cost of £5.8bn for almost the same energy output of 2.6TWh/a as the £3bn Bridgwater Bay land connected option. This is also reflected in the cost of energy which is more than double the land connected lagoon alternative.

R1 Tidal Reef proposed by x Entirely new concept that has continued to evolve during the study period. Evans Engineering. x Studied and reported on to a level commensurate with the information available but the assessment has not been able to provide as definitive estimates as other options on which to develop reliable cost base and energy yields. Outline estimates provide a capital cost of £18.1bn with an energy yield of 13TWh/a with a preliminary estimated cost of energy of 20.30p/kWh. x Development period would be greater than other options and require demonstration projects to test the concept – this would take between 10 and 15 years if tidal stream technology is taken as a benchmark.

U1 Severn Lakes (promoted x Originally included because one of its objectives is to produce power using the tidal range by Gareth Woodham) of the Severn. x The cost of constructing a 1km wide causeway 16km in length would be significantly more than a conventional tidal barrage and clearly requires additional investment streams to justify its cost. On the basis of the information within the public domain, this is also recognised by the proposer who envisages other revenue streams from land, recreational and other energy developments as part of this scheme. x This study is only examining potential options from an energy perspective. For this reason this option is not considered specifically by the Study. x Should tidal power development from the Severn form part of Government’s future energy policy, a privately proposed option such as Severn Lakes could be considered in the future.

Final xiii December 2008 SECTION 1

INTRODUCTION

Final 1 December 2008 1 INTRODUCTION

The objective of this report is to analyse potential tidal range power options in the Severn Estuary and confirm quantitative and qualitative data to enable Government to recommend a draft short-list of options that have the technical potential to form the reasonable alternatives for the Strategic Environmental Assessment (SEA). The draft short-list will be finalised following examination by Government of non- technical issues which could impact on the overall feasibility of an option and public consultation. The assessment to form the short-listed options has been undertaken having regard to the identification of options that are able to:

A common set of principles and associated assumptions have been applied to the analysis of each option to enable a fair basis assessment across all options. As a result, the information contained in this report is only of sufficient accuracy as is necessary for the comparison of options. The accuracy of the data also reflects the limited understanding of some of the projects and technologies. Cost assessments used in this report are therefore based on sources common to all options and direct comparison with previously published cost data for some options is not appropriate due to the differences in assumptions required to apply a fair basis approach across all options.

The short-listed options will be worked up in subsequent phases of this study in order to develop a more detailed assessment of cost and energy yield, including modifying option configurations to achieve the optimal results having regard to construction/operating costs, value of energy produced and environmental/regional impacts.

Final 2 December 2008 Objectives The Government has launched a Feasibility Study to consider whether the Government could support a project which exploits the major energy generation potential of the tidal range of the Severn Estuary, and if so, on what terms. The Terms of Reference of the Feasibility Study were published on 22 January 2008.

The Severn Estuary has the most significant tidal range resource in the UK1. The tidal stream resource in the Severn Estuary is not nationally significant (only 4% of the potential of UK waters2). As such, the Feasibility Study scope considers all tidal range technologies, but not tidal stream technologies unless in combination with tidal range.

In recognition of the importance of the natural environment of the Severn Estuary, the feasibility study has commissioned a Strategic Environmental Assessment which will assess a plan whose purpose is:

In order to define the plan for the strategic environmental assessment, the Government seeks to identify a short list of potential tidal power schemes on the Severn from the long list that has been drawn up following a call for proposals issued in May 2008. The final decision on whether to support a Severn tidal power project will take into account the feasibility and cost of other non-Severn based options to meet our renewable energy objectives and goals on low-carbon electricity and carbon reductions.

This report covers the analysis of the candidate projects that form the long list and the process that has been used to appraise to inform selection of a draft short list of options that have the technical ability to meet the objectives of the plan. Wider issues

1 Sustainable Development Commission “Turning the Tide” Report published in October 2007 http://www.sd- commission.org.uk/publications/downloads/Tidal_Power_in_the_UK_Oct07.pdf]

2 http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK1-Tidal_resource_assessment.pdf.

Final 3 December 2008 such as affordability for the public purse will be considered by Government outside of this study prior to finalising the draft short-list for public consultation.

Report Structure This report is structured as follows:

Assessment Framework Section 2 describes the assessment screening method used to derive the short list; Identified Potential Options Section 3 describes all the potential development options identified and presents a long list of options assessed in this report; Section 4 provides an estimate of the energy output of the long listed options; Section 5 provides an analysis of the environmental effects of the long listed options; Section 6 provides an appraisal of the civil, mechanical and electrical engineering components of each long listed option; Programme and Fair Basis Cost Analysis Section 7 provides an estimate of the earliest feasible year for first energy production for each long list option; Section 8 provides an estimate of construction cost and the cost of energy for each long listed option; Application of the Assessment Framework Section 9 presents the assessment screening method worksheets and their subsequent analysis, including the comparison to plan objectives; Section 10 presents conclusions and a summary of the options. Appendices A Cost Assumptions and Analyses B Assessment Framework Outputs C Location Plans

Methodologies The methodologies used in the initial analyses are intended to enable the comparison of options on a fair basis to inform the selection of the draft short list of options with the technical ability to meet the plan objectives. Results from previous studies on some options have been used to provide the baseline data for comparison as it was not practical nor indeed necessary to study all options to the same level of detail as is available in previous studies. However, where possible, methods have been adopted which apply a common set of principles to the analysis of each option and all costs have been developed to a first quarter 2008 base. Appendix A provides further detail on this.

Final 4 December 2008 Although the core information contained in this report has been developed with sufficient accuracy to enable comparison of options on a fair basis, the resulting costs do not necessarily reflect the anticipated out-turn cost for a specific option. This is to prevent one option being disadvantaged by comparison with another if the latter has the benefit of more accurate data being available. An example would be the determination of loss of inter-tidal habitats – whilst more accurate data are available for some of the previously studied barrage options, in order that the same data source is used for all options, areas have been derived from Admiralty Charts when comparing options. More accurate estimates will be produced following detailed modelling studies using the most up to date bathymetric models of the Estuary during subsequent stages of the study. As a consequence, cost data from this phase of the study is indicative and comparative and should not be used on an absolute basis without first confirming that the data are appropriate. Similarly, levelised cost data has been used to derive cost of energy on a per kWh basis. The levelised costs are calculated by discounting the stream of generation costs over the lifetime of the asset (120 years) and dividing this value by the amount of electricity generated over this period to calculate the price at which the generator would have to sell the electricity generated in order to break even over the period. Calculating levelised costs over the lifetime of the asset illustrates the cost of generation if the lifetime of the asset is the same as the financial lifetime of the project. If the financial lifetime of the project is shorter than this, the levelised costs would be higher than those shown here but would exclude the residual value of the asset beyond the financing period of the project. A disadvantage of net present value calculations when applied to long life renewable energy projects is that, because of the high initial capital cost compared with the early revenue yields, revenues from energy beyond 40 years or so add very little calculated value except at very low discount rates. As this report is comparing different options with similar characteristics, the use of net present value analysis to produce levelised costs for comparison purposes is reasonable and fair. However, using such costs to compare tidal energy with other forms of generation requires careful application both because of the less accurate nature of fair basis assumptions and the long project lifespan. Comparison of different types of generation projects is therefore best undertaken using project life carbon dioxide emission savings in addition to the more conventional means of financial assessment.

Final 5 December 2008 SECTION 2

ASSESSMENT FRAMEWORK

Final 6 December 2008 2 ASSESSMENT FRAMEWORK FOR INITIAL APPRAISAL OF OPTIONS

The assessment framework comprises a number of actions. It is an appraisal of all proposals against the objectives contained in this report and outside of it and an assessment of whether any issues exist that would prevent an individual or all proposals coming forward. This includes cost of energy, affordability (how a project may be financed and what position the Government will want to take) and risk of delivery. This will lead to a draft short-list of proposals that will form the reasonable alternatives for the SEA subject to public consultation.

The aim, in this report, is to provide sufficient information to identify proposals that have the technical capability to meet the plan objectives. Each proposal is assessed against key criteria within the objectives: x Volume of energy x Cost of energy x Amount of Carbon savings x Timing x Cost x Compensatory habitat required x Assessment of environmental and regional impact

This can be broken into three areas;

a. scientific, technical and/or commercial credibility b. quantitative (energy yield, carbon reduction, cost etc.) c. qualitative (impact on environment, region etc.)

The high level qualitative assessment is important to ensure that proposals that may have additional benefits either in terms of the environment or economy are not missed. It provides a high level assessment of issues that help inform on a proposal’s ability to meet the EU legislation. Outside of this report, wider questions will be asked as to whether there are issues beyond technical capability which may negatively impact on a proposal’s overall feasibility. For example a low confidence on the technology will attract greater levels of risks in terms of deliverability, costs and financing.

The short-listing process is a pre-cursor to the SEA. It will help define the plan the SEA will assess and help define the list of feasible options that meet the objectives of the plan to utilise the tidal range of the Severn Estuary

Final 7 December 2008 2.1 Overview of Process Identification of options for the generation of tidal power using the tidal range of the Severn has been undertaken using inputs from three sources: x Call for Proposals, issued as part of the Call for Evidence issued on 12 May 2008. The Call for Evidence invited interested parties to submit (a) evidence based proposals for development which will generate electricity from the tidal range of the Severn Estuary, and (b) other information, which either exists or is under development, which could potentially contribute to the evidence base for the assessment of schemes and the SEA. x The options studied by the Sustainable Development Commission in ‘Turning The Tide’ x Other strategic options which were not covered by proposals in i) and ii) above.

The core component of the methodology for evaluation of options proposed for tidal power generation in the Severn Estuary is a high level screening process comparing options on the information available and the objectives of the plan. Groups of options which could operate in combination with each other have also been considered although the analyses have been undertaken on an project by project basis. The outputs from the initial screening process have been revisited further as more detailed information from proposals has been determined following analysis and the development of the environmental, social, regional and economic data and analysis. Recommendations on the proposals to include in the draft Short List that have the technical capability of meeting the objectives and are considered feasible will then be made by officials to Ministers in the autumn. A do nothing option is included but is not covered specifically by this report. The shortlisting process is a pre-cursor to the SEA. It will help define the plan the SEA will assess and help define the list of feasible options that meet the objectives of the plan to utilise the tidal range of the Severn Estuary.

2.2 Fair Basis Evaluation In order that options are not disadvantaged by differing levels of previous research and study into their feasibility, a methodology has been adopted to evaluate the cost and energy production on a “fair” basis. In essence, this involves applying a consistent set of cost rates and assumptions across all options. The cost estimates have been produced by an independent firm of cost consultants working on engineering data that has either been prepared or reviewed as part of this study.

Final 8 December 2008 Energy yield estimates have been prepared on a similar basis using a parametric approach supplemented by 0-D and 1-D modelling3. Estimates of losses of inter-tidal habitats have been taken from Admiralty Charts with the same cost rate applied to all options for the compensation of lost habitats. Construction and operation assumptions are also consistently applied. Where different assumptions apply because of scale issues, these are clearly stated. It is important to note that in some cases (for example estimates of loss of inter-tidal areas), fair basis assumptions may differ from those of more detailed studies undertaken on specific options. Using the latter data on one option when it could not be applied to all options could place that option at an unfair disadvantage. There are also some options which have unique components (for example a Tidal Fence) and in these circumstances, cost estimates have been developed which are consistent with the above principles.

The fair basis assessments of planning, construction and operation costs, together with the energy yields and the project timeline all contribute to a discounted cash flow model that calculates costs in terms of pence per kWh for each option using different discount rates. The project timeline is taken to the full project life although for anything but the lowest discount rates, the net present values calculated by the discounted cash flow model have negligible impact for energy and costs incurred after 35 to 50 years. This may be an issue in comparing unit costs with other forms of generation but is of no relevance in differentiating between options which have similar characteristics – namely high capital costs but low running costs. For similar reasons, the cost of decommissioning is not taken into account because it has been assumed that all options have similar operational lives of 120 years (with regular replacement of equipment during this period). Discounting decommissioning costs back over 120 years has a negligible (in terms of differentiating between options) effect on the cost per unit.

2.3 Assessment Framework The assessment framework comprises a number of actions which, bar the first, have been applied iteratively over the period July to November 2008 with the aim to identify which proposals could, taken individually, be feasibly built. This involves a technical assessment of each of the options. The first step of the assessment process in this report is applied to all options identified through the three sources above. It has the objective of identifying those options which do not meet the objectives of the plan as: x they are not within the Severn Estuary; or

3 0-D modelling estimates energy yield from the head generated at the turbines and the volume of flow through the turbines. It does not model the tidal range along the estuary and is limited to modelling a single basin. 1-D modelling estimates energy by modelling the tidal range and flow along the estuary. It can be used to model combinations of options and multiple basins and models the effects of schemes on the tidal range.

Final 9 December 2008 x they lack scientific, technical or commercial credibility for the purposes of the plan. An example might be a new technology that has never been tested, even at a small scale, and that may not give investors confidence in committing money to the project; another example is where the electricity output cannot be guaranteed. Proposals that do not pass through this stage are not considered further. There may be proposals that are marginal on these issues and in particular may represent other benefits – as such they may be included in the further analysis in this report on the understanding that risks surrounding their ability to deliver and confidences around costs and time are likely to be larger than other options. The next stage is an iterative assessment to provide the information as to whether the proposals have the technical ability to meet the objectives of the plan in terms of the quantitative (energy yield, carbon reduction, cost etc.) and qualitative (impact on environment, region etc.) data available with sensitivity testing included.

The quantitative assessment provides the data required to “inform broad comparison” for the quantifiable data listed in the Call for Evidence4. It looks at each proposal on a basis of the cost and amount of energy they are likely to produce, their financial feasibility, timescales for power generation, degree of technical risk, and their potential contribution to the UK’s commitments under the forthcoming EU Renewable Energy Directive and Climate Change Act and goal to deliver a secure supply of low-carbon electricity. This is the primary criterion of the assessment and aims to help identify those which are significantly more favourable as an energy project. In addition, other quantitative data such as timeframes, CO2 outputs and capital cost are included here5. The criteria are not set in absolute terms or thresholds but instead reflect the merits of each option with the aim of establishing whether the individual proposal could be taken forward and be developed to meet the plan objectives. Optimism bias is not included in the technical comparison of options but risk and contingency allowances of 15% are included. The qualitative assessment provides the “interim appraisal on a qualitative basis” and “This initial appraisal will also act as a precursor to, and will inform, the full strategic assessment of short-listed options to be undertaken within the SEA process6.” It aims to identify projects which may be marginal in terms of the energy criterion but which appear, on the information currently available, to be relatively attractive when environmental, grid compatibility and regional economic and construction impact, or lack of, are considered. Proposals that do not perform well on firstly the quantitative and then also on the qualitative screen will not be considered further subject to

4 http://www.pbworld.co.uk/index.php?doc=627

5 Carbon emissions were initially included as an environment criterion but as they can be quantified they have been included within the quantitative action for assessment purposes

6 Italicised text represents extracts from the Call for Evidence

Final 10 December 2008 sensitivity testing. It is not the intention to use any results from the qualitative analysis to screen out proposals that meet the quantitative objectives at this stage, particularly as more work is being undertaken to determine environmental impacts. The factors that are considered in the high level qualitative assessment build on the list outlined in the Call for Evidence and are informed by the SEA Directive;

i) Environment:

Surface, Marine and Ground Water Quality Soils Historic Environment Land and Seascape Resource Efficiency and Waste Hydrodynamics (including tides), Geomorphology and Sedimentation Climatic Factors (Embedded Carbon (e.g. carbon emitted during construction) Changes to Sources (e.g. low carbon generation), Changes to Sinks (e.g. sedimentation)) Habitats, biodiversity, fauna & flora (Effects on Designated Sites, Wider Effects to Habitats and Biodiversity, Birds, Fish, Other (e.g. mammals and molluscs) Ability to be compliant with EU environmental legislation

ii)) Economic /Social /Regional

Material Assets: Flooding and Land Drainage Fisheries Ports and Commercial Shipping Construction (e.g. Supply Chain pressures, sourcing of materials etc) Other (e.g. dredging and marine aggregates)

Population and Health: Tourism and Leisure Construction Impacts Other (e.g. ancillary benefits, global benefits of reduced GHG emissions etc)

The process for evaluating each of these issues uses a qualitative scale against which assessments are graded. A crucial element to note is that at this screening stage, the information available may not be able to inform a judgment as to the impact of a proposal, this will be noted within the assessment framework by a ? category. This helps identify areas where information is not available in sufficient detail so that in can be examined within the SEA framework.

Final 11 December 2008 Scale Definition

++ The proposal may have a major positive effect in relation to assessment criterion.

+ The proposal may have a positive effect in relation to assessment criterion.

0 The proposal is unlikely to have any effect in relation to assessment criterion.

- The proposal may have a negative effect in relation to assessment criterion.

-- The proposal may have a major negative effect in relation to assessment criterion.

? The proposal may have both positive and negative effects in relation to assessment criterion and the balance cannot be determined at this stage.

A model has been developed to apply the assessment framework and the results of this assessment are described in Section 9 and the model outputs are included in Appendix B. The assessment for each option has been taken against a common baseline. The assessment itself has been determined by issue area experts and subject to peer review. Whilst it would be desirable to assess against a baseline that accurately represented the changes in the estuary that are likely to take place over the next hundred years, the reality is that qualitative assessment is more readily undertaken against the baseline conditions that exist today. However, the impact of climate change and how it may affect today's baseline conditions and the subsequent evaluation of the option for each of the criteria has been considered by the issue area experts in their application of the qualitative assessment. It is recognised that at this stage that more detailed analysis will be included in the SEA framework and any subsequent environmental impact assessment (EIA). The assessment contributes to identifying areas that will merit further study within the SEA framework for short-listed options. Sensitivity tests on proposals which have been compared on ebb-only generation have also been performed to assess whether a different configuration or combination with other proposals would allow for a proposal to reach the short list. Other sensitivities for all proposals that come through the initial sift include discount rates, robustness of data on energy yield and costs and the commercial risk. At this point, further qualitative and quantitative assessment may be performed as part of the iterative assessment framework adopted. The final step of the assessment is performed outside this report, and determines whether it is reasonable to take proposals forward to the short list of options for public consultation. This step will include the outputs of this report and factor in

Final 12 December 2008 other wider issues that may impact on the feasibility of an option – such as the ability to provide sufficient compensatory habitat, ability of project to be financed and value for money. There is no pre-determined number of proposals that will come forward on to the short list. 2.4 Assessment Framework Spreadsheet Concept The assessment model itself has been designed as a series of integrated Excel Spreadsheets which follow the principles of the flow chart in Figure 2.1. The model comprises the following spreadsheets 0. Summary 1. Initial Screening 2. Quantitative (primarily energy and cost) 3. Environmental 4. Economic / Social / Regional The Assessment Framework outputs have also been reviewed using sensitivity tests on the following: a. Different compensatory habitat ratios b. Increases in capital cost estimates (+10%) c. Reduction in energy yields (-10%) d. Application of discount Rates e. Potential Combinations, Pumping and Two Way Generation The model outputs are summarised in Section 9 of this Report with the associated spreadsheets being incorporated in Appendix B to this report.

Final 13 December 2008

SECTION 3

LONG LIST OF PROPOSALS

Final 15 December 2008 3 LONG LIST OF PROPOSALS

Identification of options for the generation of tidal power using the tidal range of the Severn has been undertaken using inputs from three sources: x Call for Proposals, issued as part of the Call for Evidence on 12 May 2008. The Call for Proposals invited interested parties to submit evidence-based proposals for development which will generate electricity from the tidal range of the Severn Estuary. x The options studied by the Sustainable Development Commission in ‘Turning The Tide’ x Other strategic options which were not covered by proposals in i) and ii) above. This section describes the process used to identify and review the options for inclusion on the long-list, and the summary details for each of the options included on the long-list.

3.1 Identification of Potential Options An initial objective of the study was to assess the potential tidal power candidate projects in the Study Area. This was initially undertaken by reference to previous studies – particularly the studies published as Energy Papers (EP46 (Bondi) and EP57 (STPG/ETSU)) in the 1980’s and the more recent report on tidal power in the UK by the Sustainable Development Commission (Turning the Tide – October 2007). These reports covered both tidal barrage and tidal lagoon locations. A Call for Proposals was also launched to identify if there were any further proposals being considered by organisations. This provided a number of additional specific proposals, including variants on previous barrage proposals, a Tidal Fence, a specific design for a tidal lagoon on the Welsh Grounds, a conceptual design for a tidal reef, some general locations for offshore tidal lagoons and proposals for alternative wall designs to be used with tidal lagoons. Finally a strategic overview was undertaken to see if there were any options not previously studied or not identified within the Call for Proposals, which could potentially meet study objectives with different characteristics to those options already proposed. This resulted in the addition of a proposed barrage at Beachley to assess the effects on energy generation if the Wye was not impounded.

3.2 Proposals taken from the SDC research

The SDC’s research in 2007 identified a number of schemes for barrage and non- barrage options for developing power from the tidal range in the Severn Estuary as listed below7.

7 Sustainable Development Commission “Turning the Tide” Report published in October 2007 http://www.sd- commission.org.uk/publications/downloads/Tidal_Power_in_the_UK_Oct07.pdf]

Final 16 December 2008 (i) Barrage Proposals

Cardiff-Weston scheme: often known as the main ‘Severn Barrage’ proposal, this would run from Lavernock Point, west of Cardiff, to Brean Down, south- west of Weston-Super-Mare

Cardiff-Weston Scheme with second basin: similar to the Cardiff-Weston scheme above, but with a second basin on the seaward side, thus enabling utilisation of nearly the full estuary resource and also providing some flood protection benefits to the Somerset Levels

Minehead-Aberthaw scheme: often referred to as the ‘Outer Barrage’, this alignment would make maximum use of the Severn Estuary tidal resource, and is one of the longest barrage proposal because of its downstream location

Dawson continuous power scheme: a barrage in the outer estuary from Minehead (as the Minehead to Aberthaw barrage above), but with an embankment extending to Brean Down, thus creating a second basin and enabling greater availability of power over the tidal cycle

English Stones or Shoots scheme: the currently proposed alignment would run close to the two Severn Crossings and has been designed to facilitate a high- speed rail link to replace the aging Severn Tunnel

Hooker scheme: similar to above but with a second basin to seaward, enabling out of phase operation on both the ebb and flood tides

Severn Lake scheme: a 1 km wide causeway adopting a similar alignment to the Cardiff-Weston scheme, designed to allow the construction of a number of additional features, including a wave farm on the seaward side, and four marinas

Shaw two-basin energy storage scheme: similar to the above, but with deep-set pump turbines to enable out of phase operation .

The barrage proposals can be divided into single basin and twin basin schemes. Twin basin schemes would enable the delivery of power to the grid more frequently than a single basin scheme operating only on the ebb tide. All the twin basin schemes incorporate a barrage which would occupy a similar alignment to one of the equivalent single basin schemes. Conversely, all single basin schemes could in theory be varied to include secondary basins.

Final 17 December 2008 Single basin schemes which are relatively less economic than other single basin schemes will not become relatively more economic with the addition of a secondary basin. This is because, as highlighted in the SDC’s research 8, studies have consistently shown that schemes requiring long lengths of embankment result in relatively high unit costs of energy than equivalent schemes with embankment lengths kept to a minimum.

The long-listing of barrage proposals has therefore only considered single basin schemes to differentiate between options; the appraisal of short listed schemes will then consider variations in the operating regime, including the addition of secondary basins. This is necessary because the variations in operating regime may have important implications in terms of the delivery of power to the grid, value of energy and environmental effects.

(ii) Land Connected and Offshore Impoundment Proposals

o Russell Lagoons: two land-bordered tidal lagoons on the Welsh coast, on the Peterstone Flats and Welsh Grounds, and one land-bordered tidal lagoon on the English coast on the English Grounds

o Swansea Bay Lagoon: a smaller (in comparison to the Russell Lagoons) offshore tidal lagoon but not located within the proposed study area; as such this option may be promoted independently of any strategic tidal power development in the Severn.

3.3 Responses to the Call for Evidence

Call for Proposals Submissions Table 3.1 below lists the proposals that have been submitted in response to the Call for Proposals. Proposal Name Proposer(s) and/or Brief Description Associations/Status

Tidal Fleming Group A variant on the Russell Welsh Grounds Impoundent on lagoon comprising an infilled precast the Welsh concrete wall solution to enclose the Grounds lagoon.

New Build Tidal Rubicon Marine New build tidal lagoons and the creation

8 Sustainable Development Commission “Research Report 3 - Severn Barrage Proposals” published in September 2007 http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf

Final 18 December 2008 Proposal Name Proposer(s) and/or Brief Description Associations/Status

Lagoons of high tidal flow channels.

Outer Barrage The Burnham and Minehead to Aberthaw scheme as Somerset Levels described in 3.1 above but with a view to Sea Flood Study maximising variation in water levels to Group minimise loss of inter-tidal habitats

Severn Barrage to Tom Shaw A barrage crossing between Lavernock Hinkley and (Shawater) Point and Hinkley Point (via Steep Brean Holm). The additional enclosed water area would increase the annual generating potential of the project by up to 10% depending on the exact alignment chosen for the barrage. The plan also shows provision for traffic (road and rail) to continue by viaduct to the coastline south of Weston-super-Mare. The barrage link to Hinkley Point would offer a third outlet for the electrical connection of the project. This is the longest barrage proposal.

Severn Tidal Reef Evans Engineering A barrage that would include fixed flow turbines operating on a very low constant head difference maintained by floating caissons or movable ‘crest gates’. Minehead to Aberthaw suggested as the optimal alignment.

Tidal Fence Severn Tidal Fence A barrier constructed over part of the Proposal Group Cardiff to Weston alignment, with open sections in the ship canal and at the coastal fringes, incorporating tidal stream turbines to capture energy during both the ebb and flood tides.

Tidal Lagoons Tidal Electric A schedule of various tidal lagoons both Limited (TEL) and within and beyond the estuary submitted BCP. by TEL and the offshore Swansea Bay Lagoon submitted by BCP. The TEL submission did not include specific

Final 19 December 2008 Proposal Name Proposer(s) and/or Brief Description Associations/Status

designs but suggested the use of multiple cells within the lagoon to increase the availability of energy. The Russell lagoons sites have been used to assess land connected tidal lagoons and an offshore lagoon close to Bridgwater Bay has been used in this study to assess offshore proposals

Tidal Power Mr Frank Barriers built across the estuary with Development in Goldsmith valving at the base to provide controlled the Severn water flow through turbine or paddle Estuary driven generators. Valve controls would limit the water differential to 1m at the barrier. No specific location referenced.

Table 3.1 Summary of Call for Proposals Submissions

Pre- Screening of the Call for Evidence Submissions

The following proposals were conceptual proposals which were not location specific or were specified for locations outside of the area covered by the Feasibility Terms of Reference. As a consequence, they were considered as information (under the Call for Information) that could potentially be used in the optimisation and/or more detailed study rather than as specific proposals:

x New Build Tidal Lagoons submitted by Rubicon Marine (this covered a new embankment construction method using shipbuilding techniques and will be reviewed as an alternative form of construction for lagoon proposals x In response to the Call for Information, Halcyon Marine Hydroelectric submitted proposals for a pile supported/modular barrier construction to be applied to the impoundment of lagoon basins. In the submission, Halcyon presented a lagoon alignment between Minehead and Hinkley Point, noting that this was just one possibility among many which could include larger or smaller lagoons, either offshore or connected to land. This form will be reviewed as an alternative form of construction for lagoon proposals. x Tidal Power Development in the Severn Estuary proposals submitted by Mr F Goldsmith (this proposed a combination of different operating equipment/modes and new construction concepts) x Swansea Bay Tidal Lagoon – this is outside the study area and any conclusion reached by this study is unlikely to impact proposals to develop a tidal lagoon

Final 20 December 2008 in Swansea Bay. However, the information and research undertaken by the Swansea Bay promoters may be relevant to similar concepts within the study area.

All other submissions have been brought forward to a long-list, reviewed and their details are summarised in this report together with detailed independent analysis of their design, costs and energy yields with the exception of those that are have been screened out during the initial stage of the Assessment Framework.

3.4 Other Strategically Selected Proposals

Beachley Barrage

Previous studies of the Severn have considered alignments throughout the Estuary but other than a causeway proposal in the 19th century, there have been few, if any, studies of proposals upstream of English Stones, the location of the Shoots Barrage. The Shoots proposal adopts a position which coincides with the highest tidal range in the Estuary and as a result has been reported to operate more efficiently with a lower cost of energy than other barrages. A barrage further upstream would however, have potentially fewer environmental effects, including less of an effect on the estuary habitats and would not act as a barrier to the River Wye. To enable a review of these relative benefits and disbenefits, a barrage alignment has been added to the long list upstream of the Shoots Barrage at Beachley Head, by the original Severn Bridge, where the estuary naturally narrows. This alignment also enables a review of the merits of barrage construction landward of the Wye. A more optimum alignment of a barrage landward of the Shoots Barrage could be determined if the Beachley Barrage is selected for the shortlist.

Other Strategic Proposals

Other potential strategic proposals are the optimal arrangement of twin basin and / or combination of options based on maximising the value of energy by allowing generation of more energy during periods of higher demand and less energy at night. Although the cost per kWh is likely to be higher and/or the total amount of energy produced is less, if the timing of generation can produce an enhancement to energy value, such arrangements could offer a better return than ebb only or single basin options. These strategic options will be examined in detail following determination of the short list of options. Although single basin ebb-only generation options do not produce the highest energy values, nevertheless, adapting such options to two way flow or two basin operation will generate better returns on investment compared with the same adaptation applied to less economic ebb only generation options. The adoption of ebb only generation for the purposes of initial assessment therefore remains the most effective means of assessing all options

Final 21 December 2008 initially with optimisation of energy value studies being undertaken subsequently on the short-listed options.

3.5 Long-Listed Proposals

The long list of proposals is as set out in Table 3.2 below and their alignments illustrated in Figure 3.1.

Option No Option Name

B1 Outer Barrage from Minehead to Aberthaw

B2 Middle Barrage from Hinkley to Lavernock Point

B3 Middle Barrage from Brean Down to Lavernock Point (commonly known as the Cardiff to Weston Barrage)

B4 Inner Barrage (Shoots Barrage)

B5 Beachley Barrage

F1 Tidal Fence Proposal (see 3.7 below)

L2 Lagoon Enclosure on the Welsh Grounds (Fleming Lagoon)

L3 Tidal Lagoon Concept (see 3.6 below)

R1 Tidal Reef (see 3.7 below)

U1 Severn Lake Scheme (see 3.7 below)

Table 3.2 Long Listed Proposals

Final 22 December 2008 Figure 3.1 Location Of Options

Final 23 December 2008 Tidal Lagoon Concept

The tidal lagoon concept can be applied to a number of locations using different forms of construction to impound the lagoon basin. These forms of construction would include those submitted by TEL, the Fleming Group, Rubicon and Halcyon, together with traditional forms of marine embankment and/or construction of similar form to barrage construction as applied in the designs available for the B3 and B4 barrages.

The lagoon concept can be either a completely artificial offshore enclosure (hereinafter termed an offshore lagoon) or an enclosure formed by an artificial barrier constructed into the estuary from two points on the shoreline (hereinafter termed a land connected lagoon).

For the purpose of this study, the tidal lagoon concept has been applied to the land connected Russell lagoon alignments in order to update the early Bondi work (1981) and recent SDC study.

In addition, the tidal lagoon concept has been applied to Bridgwater Bay as both a land connected and offshore lagoon form. Bridgwater Bay has been selected for a number of strategic reasons:

x It was listed as having the highest energy generating potential of all lagoons in the TEL submission, x It enables consideration of the specific environmental effects of impoundment of Bridgwater Bay, and x It enables consideration of the compatibility of a lagoon seaward of all barrages, except B1 Outer Barrage, and the F1 tidal fence.

It should be noted the lagoon concept has been applied to these locations in order to consider a representative sample of lagoon schemes, to update previous work on the Russell Lagoons and to build upon the previous studies undertaken for the Swansea Bay lagoon scheme. Studying the concept at these locations provides an improved understanding of performance of the lagoon concept, in terms of its energy yield, together with the relative performance characteristics of different forms of construction. The lagoon concept has required appraisal at specific locations based on specific construction forms and operating regimes to inform the analysis of options and to further understand the technical feasibility of different configurations.

Final 24 December 2008 Lagoon Location Impounded Installed Capacity Area (km2) (MW)

Bridgwater Bay 91 1360

English Grounds 40 760 (Russell Lagoon)

Welsh Grounds 72 1360 (Russell Lagoon)

Peterstone Flats 72 1120 (Russell Lagoon)

Table 3.3 Long Listed Lagoon Proposals

3.6 Initial Screening

The initial screening stage of the Assessment Framework is designed to evaluate the credibility of options in relative risk terms so that detailed assessment is not undertaken on those options which, in technology or financial risk terms, are unlikely to be developed sufficiently to mitigate those risks within the implementation period envisaged by the Feasibility Study. The implementation period commences with the necessary design, planning and environmental impact assessments proceeding soon after the conclusion of the Feasibility Study providing that the Study concludes that tidal power generation from the Severn is feasible in economic and environmental terms and that these conclusions are endorsed by the Government.

It therefore follows that proof of concept for any proposal in its use of technology has to have been established for the Feasibility Study to correctly evaluate its economic credentials. As all proposals for the Severn represent some of the largest tidal power projects in the world, it is also logical that they do not offer opportunities for pilot or prototyping. Those submissions which require some form of pilot or prototype application, to increase confidence in the proof of technological concept and reduce financial and/or technology risks, may therefore be screened out at the initial assessment phase on the basis that pilot or prototype trials will, in themselves, take many years before conclusions can be reached. However the options that potentially fall into this category are innovative and have exploitable advantages that may be applicable to tidal power generation in this country and internationally in future years if proof of concept can be satisfactorily demonstrated to reduce the technological and financial risks typically associated with emerging technologies.

Final 25 December 2008 The main proposal that potentially falls into this category comprises a completely new technology concept based on a tidal reef with turbines that generate using a constant two metre head differential over the tidal cycle except as the tide transitions from the ebb to flood and vice versa (the Severn Tidal Reef).

A second proposal that is based on new technology that would require more research and possible pilot testing is the Severn Tidal Fence. This utilises tidal stream technology configured to provide increased resistance (by virtue of the structure supporting the turbines and proximity of adjacent turbines) to concentrate and increase flow velocities through the turbines driven, in part by the tidal range.

Both these options are more “permeable” than conventional tidal range technology as used in a barrage or a lagoon and thus offer less loss of inter-tidal areas as their impact on the natural tidal range is reduced. However, the technologies and associated energy yields in both cases are not well established.

A third option, Severn Lakes (U1) is different from the above options in that it doesn’t rely as much on new tidal range technology, but nonetheless is a candidate for exclusion following initial screening because its current shape and form cannot be sustained solely by exploiting tidal range energy. Severn Lakes is a mixed development proposal involving the construction of a 1km wide causeway with different forms of energy generation and other forms of development. The construction of such a large causeway clearly requires other forms of income to support its business case by comparison with a tidal barrage in the same location.

Further detail is provided below:

Severn Tidal Reef

The concept includes fixed flow turbines operating on a two metre constant head difference. In the words of the proposer, “The Reef is a complex engineering concept that is underpinned by established engineering designs and technology.”

The Reef is essentially a structure extending between Minehead and Aberthaw comprising embankments, caissons and piled structural walls. A large number of relatively low capacity turbines are located in siphon modules mounted on the structure. The objective is to maintain a constant 2 metre head between upstream and downstream levels and generate electrical power using this head. This results in a longer period of generation but with reduced electrical output by comparison with a conventional tidal barrage. If achievable, this also has the advantage of reducing the loss of inter-tidal areas. There is claimed to be a reduction in fish mortality rates by comparison with a

Final 26 December 2008 conventional barrage. Figure 3.2 is an artist’s impression of the tidal reef provided by the proposer.

Figure 3.2 Artist’s impression of the Tidal Reef (courtesy of Evans Engineering)

Several different types and layout of turbine have been considered by the proposer in various technical submissions. Originally a system of floating turbine modules into place during construction and removing them to a dry-dock for maintenance was considered but subsequently replaced by a fixed design that is set higher out of the water and uses a siphon arrangement to stop and start the turbines. These would be constructed as modules, each housing two turbines and capable of being rotated through 90 degrees to allow increased water passage and cleaning of screens. The turbines themselves are based on low specific speed mixed-flow turbines of a type used extensively in the early days of hydropower engineering using a vertical shaft arrangement.

The proposer is also assuming that the deep water navigation gates, each weighing around 15,000 tons each and made of reinforced concrete, include turbines. The use of rotating turbine modules, navigation gates incorporating turbines and the requirement to impound the estuary to create the head differential provides an indication of the magnitude of this option and the development challenges.

In energy yield terms, the reef would operate on both the ebb and flood tides. The head attained at the reef would be controlled by the rate of flow through the reef and the head differential across the turbines. No evidence is available to support costing

Final 27 December 2008 or derivation of energy yield, indicating the very early stage of development of this proposal.

The original proposal suggests the use of 1000 no. 10m diameter, 5MW, turbines, giving an annual power output of 20 TWh/year, for a constant head of 2m. An analysis of the tide curve for Ilfracombe indicates that a 2m head could, in theory deliver approximately 13 TWh/year. The proposer has subsequently also revisited potential yield and is now indicating an energy yield between 11 and 14TWh per annum delivered for a capital cost between £10bn and £15bn. However, the predominant risks are associated with the cost of construction and the application of the technology, as no specific design information has accompanied the proposal. It has therefore been more difficult to model this option financially on the same terms as the others. The development work in relation to the rotating turbine modules and development of the siphon is however the major challenge and, if the development timeframe for tidal stream technology (itself based on established wind generation technology) is taken as a benchmark, the development timeframe could be between 10 and 15 years. Consequently, this option will be less able to contribute to the Government’s climate change targets than other equivalent tidal range options. Nevertheless, this option has been reviewed and analysed using fair basis assumptions to assess how well, in relative terms such an option performs by comparison with existing forms of tidal power. Such an approach has involved development of some design and costing assumptions given the lack of technical data available for this option.

RSPB commissioned an independent report, published in November 2008, to review the feasibility of the Tidal Reef proposal. This report has been considered by the Parsons Brinckerhoff consortium so that it can be taken into account in the appraisal of the reef. The report (produced by Atkins Ltd) focuses on three key issues: turbine technology, power output and cost estimates. These are discussed below.

Turbine Technology

The Atkins report reviewed the Armstrong Evans reef concept and, because it was concluded that it contains too many unknowns for a like for like comparison with a barrage, the turbine caissons are vulnerable to effects of wave loading and the shallow turbines likely to suffer from cavitation effects. Therefore Atkins took a different approach and varied the Armstrong Evans concept. This variation has adopted the same core principle as Armstrong Evans that the reef generates power using a controlled constant 2 metre differential head during the ebb and flood tides. This variation takes the form of a line of concrete caissons housing a new concept of submerged bi-directional very low head hydro turbine, which at present are not known to be in development. The report makes reference to a prototype very low head 410kW uni-directional hydro turbine installed at Millau, France, but this is not considered a relevant analogue as developing bi-directional turbines of this form,

Final 28 December 2008 scaled up from 0.4MW to 5MW for application in a tidal power development would require a fundamental change in the turbine concept. The report also makes reference to the potential use of tidal stream technology which would cause the Tidal Reef to behave more similarly to a Tidal Fence. This concept would require the upscaling of tidal stream technology from its current 1.2MW level to 5MW which would be a significant extrapolation of existing technology and not considered feasible. This has been discussed in relation to the Tidal Fence in Section 4.3. The Atkins report did not address the issue of how the constant 2 metre head would be controlled.

Power Output

The RSPB report estimates that the power output of the scheme is 20TWh/yr (if it is able to generate on the ebb and flood tides). This estimate assumes the availability of very low head bi-directional turbines for which there is no existing technology (as referred to above). This estimate also assumes that the 2 metre head differential is available at all times, however a review of the tidal range at Ilfracombe indicates that the 2 metre tidal range is only available from between one third and half the time and therefore the energy yield would be 10 to 15TWh/yr, which supports the Evans Engineering’s revised estimated output of 11 to 14TWh/yr. This study has taken a 13TWh/yr estimate as a median.

Cost Estimate

The RSPB consideration of capital cost has focussed primarily on the cost of the reef caisson structures and has identified opportunities to reduce the caisson cost compared to barrage caissons using the Cardiff to Weston barrage caissons as a benchmark. These opportunities include reducing the volume of concrete required on account of the smaller differential head, by simplifying the caisson design, by seating the caissons on inflatable grout mattresses and improving caissons installation techniques. Atkins estimates that if a reef were deployed on the Cardiff to Weston line, these measures could result in an overall £2bn saving in caisson construction compared to the equivalent barrage caisson cost reported in the SDC Research Report 3, £1bn of which is due to the reduced head differential. Apart from the head differential, the cost saving opportunities are not unique to the Tidal Reef and can be applied across the short list of options. Within this study, all caisson costs have been estimated on a fair basis (as described in section 8) and opportunities to improve the cost efficiency are due to be considered in Phase 2.

The £1bn reduction in caisson cost arising from the reduced head differential represents a 40% reduction in the SDC caisson cost. The reef caisson cost estimate in this study has also taken into account the effect of the reduced differential head and, applying assumptions which are favourable to the reef, a 55% saving on the outer barrage caissons have been taken for the Tidal Reef constructed on the outer line.

Final 29 December 2008 The Atkins report concludes that the tidal reef turbine cost will be similar to the Cardiff to Weston barrage turbine cost if constructed on the Cardiff to Weston line. A discussion on reef turbine costs is included in Section 8.5

Severn Tidal Fence

The Severn Tidal Fence concept has been developed in more depth than the Tidal Reef option and the first proposal envisaged an alignment between Cardiff and Weston. It is an extrapolation of an embryonic technology and has been developed to outline design stage including preliminary assessments of costs and energy yield. This option has therefore been reviewed on the basis of the information provided, verified where possible by other sources of data and knowledge. The submission by the proposer acknowledges that a number of their conclusions are subject to further research. Their methodology applies wind engineering techniques for turbine design to tidal stream applications with adjustment applied to reflect the increased marine vs wind application costs for the sub-marine plant. The original proposal (shown in Figure 3.3 overleaf) has been assessed in modified format using smaller 1MW turbines than those envisaged in the original submission. In addition, a further alignment between Minehead and Aberthaw has been proposed utilising 800 nr 1.6MW turbines. This does not have the development disadvantages of the initial proposal although 1.6MW turbines represent a 25% increase in capacity by comparison with the largest existing operating unit. This alternate option still has a number of risk factors associated with it, including cost of turbine units, and the effects on sedimentation (arising from the high rate of change in currents at the fence). Of more concern is the general acknowledgement that currents in the Severn estuary are generally lower than desirable for tidal stream generation except in the main navigation channels. Although a fence created by an array of turbines will increase velocities, the extent to which this is possible and the variability of velocities throughout the estuarine cross section and at different states of the tide, are not known and the assumptions made by the proposer may thus be optimistic. These issues are discussed in more detail in Section 6 of the report. As tidal stream technology is currently at demonstration project stage, this option has passed through the initial screen but it should be recognised that, although for the purposes of fair basis comparison the tidal fence has been assessed on the basis that construction started in 2014 in common with the other options, in reality, the tidal fence would be unlikely to be sufficiently developed by 2014 to permit commercial deployment of a 1280MW installation. Consequently, this option may be less able to contribute to the Government’s climate change targets than other equivalent tidal range options. However, it has been analysed using the fair basis approach to determine its’ relative performance against other forms of tidal power. Figure 3.3 shows an artist’s impression of the tidal fence provided by the proposer.

Final 30 December 2008 Figure 3.3 Artist’s impression of the Severn Tidal Fence (courtesy of Severn Tidal Fence Group (STFG) Tidal)

Severn Lakes (U1) The Severn Lakes concept was originally included because one of its objectives is to produce power using the tidal range of the Severn. Tidal power is part of the business plan which also relies on many other economic drivers to substantiate the cost of building a 1km wide causeway across the Severn, including development land, marinas, landfill and other renewable energy technologies. This is acknowledged by the proposer. The information relating to this option comes from the proposer’s web site and provides details of the general conceptual details. It is understood that specific design elements are being worked on but are not available for consideration by this study. The construction of a wide causeway could not result in a lower cost of energy compared to an equivalent barrage because of the increased civil engineering works required. Therefore, for the scheme to be justifiable on commercial grounds, the value of the mixed development would need to offset the opportunity cost of the increase in energy cost.

As this study is only examining potential options from an energy perspective this option will not considered specifically by the Study. However, should tidal power development from the Severn form part of Government’s future energy policy, a privately proposed option such as Severn Lakes could be considered in the future. For this reason, this report will reference information relevant to Severn Lakes for information.

Final 31 December 2008 SECTION 4

COMPARISON OF ENERGY OUTPUT

Final 32 December 2008 4 COMPARISON OF ENERGY OUTPUT

A comparison of the energy output has been undertaken on the schemes identified within the long-list and analysed to provide a fair basis of comparison.

Energy yields have initially been calculated statistically using the detailed information contained in Energy Papers 46 and 57 and applying the principles of this information to all long-list options based on the available characteristics of the impoundments. The energy yield modelling has been updated to take account of recent improvements in turbine and generator efficiency. Reviews of previous studies have then been verified and amended as appropriate using preliminary 1-D modelling incorporating the latest bathymetric data from the Severn. This has produced largely similar results to the statistical approach although there are some options where the bathymetry has influenced a change in the energy yield. Results from both methods are provided in this section and the preliminary 1-D energy outputs have been carried forward to the financial analysis.

For the purposes of the initial evaluation, energy yields have been calculated on the basis of ebb only generation (except the F1 Tidal Fence and R1 Tidal Reef which are configured only to operate in ebb and flood generation mode) as this has been demonstrated to achieve the most favourable cost per unit energy (see Section 3.2). Recent improvements in turbine design have not overcome the historic technical limitations on ebb and flood generation efficiency that make this option less attractive economically. Optimising the most cost effective schemes to achieve the most favourable energy value will be undertaken on short-listed options as the optimisation methodologies can be applied equally to all options.

4.1 Estimation of Energy Output Previous energy yield estimates, available for some long listed schemes from published reports, have been collated and reviewed as a benchmark for the comparison. This includes modelling work undertaken for EP46 by the Severn Barrage Committee (the Bondi schemes) and later by STPG between 1985 and 1990 on the then favoured schemes, much of which has been reported in EP57. These later studies on energy yield are the most accurate available. Energy predictions in the submissions in response to the Call for Proposals have also been reviewed.

Based on a reinterpretation of past estimates, the predicted annual energy, where available, for the long-list schemes have been plotted to provide a relationship between impounded area (applied in conjunction with average depth to provide an impounded volume) and annual energy yield. Impounded areas and average depths have been estimated initially from Admiralty Charts for consistency across all

Final 33 December 2008 options. Points have been plotted in Figure 4.1 distinguishing between those derived for the Bondi schemes and the post-Bondi work.

Other factors apart from impounded area that have a significant effect on annual energy output include: x The number and diameter of turbines and the electrical capacity of the attached generators. . x The tidal range at the site. Within the Severn Estuary and Bristol Channel, tidal range increases up estuary and so the larger schemes which are located further west in the lower estuary experience a lower tidal range. This factor is taken into account implicitly within Figure 4.1 as the size of the majority of schemes used to establish the relationship is related to their location within the estuary. However, if a small scheme is located further west in an area of lower tidal range, this method of energy assessment is likely to overestimate annual energy output. For example, a lagoon at Bridgwater Bay is likely to have a smaller energy output because of the lower tidal range in that area than a lagoon of similar area on the English or Welsh grounds.

Nevertheless, the data provided gives an acceptable and robust first assessment of the relative potential of the schemes. At this stage, no attempt has been made to optimise the various schemes to identify the lowest unit cost of energy for each alignment by varying the number of turbines, installed capacity and sluice area.

10000

P = 0.0398 * A ^ 0.97

1000

100 Impounded area (km2) Impounded

10 Energy from Bondi Energy post Bondi Best fit line

1 0.1 1.0 10.0 100.0 Average annual energy output (TWh) Figure 4.1 – Correlation between energy yield and impounded area

Final 34 December 2008 STPG’s most recent estimates for the Cardiff-Weston barrage increased significantly over the Bondi 1981 estimate for this site and so the best fit line included in Figure 4.1 is based on the post-Bondi results to reflect the increased energy output that has been reported post-Bondi. The results quoted in Table 4.1 for the current study are either based on reported previous work or derived from the best fit line. The notes column in Table 4.1 indicates the source of these estimates.

The current study energy output for the Minehead to Aberthaw (Outer) Barrage is assessed as 30% greater than the Bondi estimate in line with the improvement reported for the Cardiff Weston line by STPG. The installed capacity for the Outer Barrage has also been increased from 12GW to 14.8GW to achieve this. The best fit line extrapolation of Figure 4.1 predicts a higher annual energy output for the outer line that we consider unlikely to be realised in practice because of declining tidal ranges in the outer estuary.

In estimating the design annual energy output and the output with outages, the following adjustments have been made to the current study energy estimates of Table 4.1:

x The energy output has been adjusted to reflect the increased efficiency of modern turbines and generation plant. Following assessment of current plant specifications, it is concluded that a constant efficiency majoration of +1.5% can be safely applied to historic data to reflect what could be expected from modern day design and manufacture techniques. Further, an efficiency of 97.5% for the generators (electrical power out = 0.975 x power on turbine shaft) has been taken for all machines. All previous studies used a generator efficiency of 95% so there is a further +2.5% gain compared with previous work. All historic energy predictions have been increased by +4.0% to give the design annual energy output column in Table 4.1. x Annual energy yield estimates have been reduced to account for outage (typically 10% of turbines not available at any one time which). Studies by STPG found that this outage rate corresponded to 95% of maximum energy capture for barrages but would correspond to 10% for tidal fence options. x The energy yield figures have also been verified, where practicable, by 0-D and 1-D modelling9. In particular, all lagoon options, where changes in energy yield are highly sensitive to basin capacity , have been confirmed using preliminary 1-D modelling undertaken towards the end of this

9 0-D modelling estimates energy yield from the head generated at the turbines and the volume of flow through the turbines. It does not model the tidal range along the estuary and is limited to modelling a single basin. 1-D modelling estimates energy by modelling the tidal range and flow along the estuary. It can be used to model combinations of options and multiple basins and models the effects of schemes on the tidal range.

Final 35 December 2008 component of the study and using the latest available bathymetry for the Severn.

The energy output for short listed schemes will also be estimated in more detail based on the application of 1-D modelling. During that stage, an assessment will be made of the effect on energy yield of alternative operating systems, including ebb and flood generation, flood pumping and the use of a secondary basin. The possibilities of generating continuous power will also be investigated. For example, combinations such as 1) the Cardiff-Weston barrage and a Bridgwater Bay lagoon and 2) the Shoots barrage and Welsh Grounds lagoon could be investigated. These variations are considered to be refinements to options (should they be short listed), intended to optimise their performance in terms of energy value, implications of grid connection and environmental effects. This refinement is based on the premise that the more advantageous single basin ebb only schemes will provide the more advantageous opportunities for such optimisation (as discussed in Section 3.2). Therefore, all energy outputs shown in Table 4.1 are for ebb-only generation, except the tidal reef and tidal fence options.

For options with no published energy yield estimates, impounded areas have been estimated from Admiralty Chart data to derive energy yields from the energy yield and impounded area relationship. Following development of a 1-D model during the study, these initial estimates have been subsequently reviewed using the latest bathymetric data available.

Figure 4.2 – Comparison of Bathymetric Profiles at Inner and Beachley Barrages

It should be noted, however, that the Beachley Barrage site is in the upper, narrow, portion of the Severn estuary. The installed capacity is limited by the number of turbines that can be fitted into deep water at this site and the reduced head of water that can be generated. This is illustrated by Figure 4.2 which show a comparison of the bathymetric profiles of the estuary channel. Within the width of the channel at Beachley, it would be possible to incorporate eight 25 MW Straflo turbines compared

Final 36 December 2008 to thirty 30 MW Straflo turbines in the Shoots barrage. Furthermore, the channel depth at the Beachley Barrage would be 14m shallower than at the Inner Barrage. Taking both factors into account, a compromise solution has been adopted which involves some 6m depth of dredging to accommodate 50 no. 5m diameter turbines each rated at 12.5MW. Annual energy output from the Beachley Barrage has therefore been reduced compared with the value suggested by Figure 4.1 and a figure of 1.59TWh annual yield has been determined using 1-D modelling with the turbine configuration described above. A summary of the preliminary 1-D modelling outputs for Beachley Barrage and tidal lagoon options (those options where the modelled output differs from the statistical assessment) is shown in Table 4.1:

Lagoon Installe Nr Turbine Rotor Nr Sluic Annua Annual d Tur Size Dia Sluices e l Energy Capacit bine (MW) (5m) Area Energy with 5% y s (m2) (TWh) outages B5 625 50 12.5 5 26 150 1.67 1.59 Beachley Barrage L2/L3b 1360 108 12.5 5 41 150 2.43 2.31 Welsh Grounds L3a English 760 60 12.5 5 25 150 1.48 1.41 Grounds L3c 1120 90 12.5 5 33 150 2.45 2.33 Peterstone Flats L3d 1360 108 12.5 5 41 150 2.78 2.64 Bridgwater Bay L3e(i) 1360 108 12.5 5 41 150 2.74 2.60 91km2 offshore lagoon L3e(ii) 760 60 12.5 5 25 150 1.39 1.32 50km2 offshore lagoon Table 4.1 Preliminary 1-D modelling results

Table 4.2, overleaf, shows the estimated energy yields based on the analyses described in this section for all options. This includes initial assessment, for information purposes, for option U1 although it has been screened out.

Final 37 December 2008 Option Source Annual energy Number of Total Annual Impounded Notes output from turbines and capacity energy area (km2) previous work diameter (MW) output (TWh) (m) (TWh) B1 Outer Barrage Current study 25.6 370 x 9m 14800 25.3 1060 EP 46 uprated due to increase of Bondi (1981) 19.7 300 x 9m 12000 installed capacity B2 Lavernock to Current Study 19.5 - - 19.3 595 Energy output estimated from Hinkley Point Power/Area correlation (sum of B3 and L3 Bridgwater Bay) B3 Lavernock to Current study 17 216 x 9m 8640 16.8 504 Based on STPG work Brean Down STPG (1989– 17 216 x 9m 8640 90) Bondi (1981) 12.9 160 x 9m 7200 480 B4 Inner Current study 2.77 30 x 7.6m 1050 2.77 85 Based on STPG work and PB (2006) 2.75 30 x 7.6m 1050 verified using 0-D modelling STPG (1986) 2.7 – 2.8 36 972 B5 Beachley Current study 1.67 50 x 5m 625 1.59 57 Energy output estimated using 1-D modelling as number of turbines limited F1a Tidal Fence Current study 0.7 - 0.7 N/A Based on independent STFG (2008) 3.5 256nr assessment of energy yield for Cardiff Weston using tidal stream technologies F1b Tidal Fence Current study 3.3 - 3.3 N/A Based on STFG’s revised STFG (2008) 3.5 800nr proposals for Minehead to Aberthaw

Final 38 December 2008 Option Source Annual energy Number of Total Annual Impounded Notes output from turbines and capacity energy area (km2) previous work diameter (MW) output (TWh) (m) (TWh) L2 Fleming 1-D - 1360 2.31 82 Energy output estimated from Lagoon & L3b Statistical 2.6 1500 80 Power/Area correlation and Welsh Grounds Proposer: 3.2 amended using 1-D modelling. (Russell Lagoon) Additional output may be achieved if existing basin is excavated to provide wall fill. L3a English 1-D 60 x 5m 760 1.41 50 Energy output estimated from Grounds (Russell Statistical 1.48 Power/Area correlation and Lagoon) amended using 1D modelling L3c Peterstone 1-D 108 x 5m 1120 2.33 76 Energy output estimated from Flats (Russell Statistical 2.12 Power/Area correlation and Lagoon) amended using 1-D modelling L3d Bridgwater 1-D 90 x 5m 1360 2.64 89 Energy output estimated from Bay (land Statistical 2.44 Power/Area correlation and connected) amended using 1-D modelling L3e1 Bridgwater 1-D 108 x 5m 1360 2.6 91 Energy output estimated from Bay 91sq km Statistical 2.45 1900 Power/Area correlation and Offshore Lagoon Tidal Electric 9.15 amended using 1-D modelling Limited

L3e2 Bridgwater 1-D 108 x 5m 760 1.32 50 Energy output estimated from Bay 50 sq km Statistical 1.35 Power/Area correlation and Offshore Lagoon amended using 1-D modelling

Final 39 December 2008 Option Source Annual energy Number of Total Annual Impounded Notes output from turbines and capacity energy area (km2) previous work diameter (MW) output (TWh) (m) (TWh) R1 Tidal Reef Current Study 13 - 5000 13 N/A independent assessment using Armstrong 11 - 14 data from Armstrong Evans Evans (2008) submission U1 Severn Lakes Current study 15.4 - - 15.0 464 Energy output estimated from Power/Area correlation

Table 4.2 Estimated Energy Yields

Final 40 December 2008 4.2 Comparison with Call for Proposal Submissions The comparison in Tables 4.2 and 4.3 below shows the differences between annual energy yields based on the power/area relationship and the energy yields quoted in the Call for Proposals submissions.

Call for Proposals Option Option Name Annual output submissions estimated by current No study (TWh) Annual Source output (TWh) B1 Outer Barrage 25.3 24 Burnham & from Minehead to Somerset Aberthaw Levels

B2 Middle Barrage 19.32 22 Shawater from Hinkley to Lavernock Point (Severn Barrage to Hinkley and Brean)

B3 Middle Barrage 16.80 Not submitted from Brean Down to Lavernock Point (Cardiff to Weston Barrage)

B4 Inner Barrage 2.77 Not submitted (Shoots Barrage)

B5 Beachley Barrage 1.59 Not submitted

Table 4.2 – Comparison of Energy Yields Estimated and Quoted in Submissions (Barrages)

Final 41 December 2008 Call for Proposals Option Option Name Annual output submissions estimated by No power/area Annual Source relationship (TWh) output (TWh) L2 Lagoon Enclosure on 2.31 3.2 Fleming the Welsh Grounds (Fleming Lagoon)

L3a English Grounds 1.41 - Not (Russell Lagoon) submitted

L3b Welsh Grounds 2.31 - Not (Russell Lagoon) submitted

L3c Peterstone Flats 2.33 - Not (Cardiff-Newport submitted Russell Lagoon)

L3d Bridgwater Bay (land 2.64 - Not connected lagoon) submitted

L3e(i) Bridgwater Bay 2.6 9.15 TEL (offshore lagoon)

Table 4.3 – Comparison of Energy Yields Estimated and Quoted in Submissions (Lagoons)

The analysis shows that the preliminary 1-D modelling gives a smaller energy yield to that quoted by the Fleming Group for the Welsh Grounds lagoon.

The TEL estimate for the L3e Bridgwater Bay (offshore) lagoon is higher than that estimated for this study. Preliminary 1-D modelling has been used to develop the energy estimate based on an assumed location and alignment for an offshore lagoon with an impoundment area of 90sq km. Details of TEL’s alignment of a 91km2 Bridgwater Bay offshore lagoon was made available at a late stage in the study period, and the configuration and operation of a Bridgwater Bay offshore lagoon, including the use of multiple cells within the lagoons, were not available during the study period. The alignment of the TEL lagoon is different to the alignment of the 91km2 L3e(i) lagoon shown in Figure L3e. However, the impounded area and the tidal range are equivalent and therefore the energy estimated for the L3e(i) lagoon is expected to be equivalent to the energy yield of the TEL Bridgwater Bay lagoon. At the time of writing, dialogue is ongoing with TEL with the aim of reconciling the

Final 42 December 2008 difference between the two estimates. Energy calculations in support of TEL’s Bridgewater Bay estimated have not been made available and this study adopts the 2.6TWh/year output which has been estimated using the fair basis principles to enable comparison between schemes.

It is understood that the turbine and generator configuration of the L2 lagoon is preliminary and subject to ongoing design development by the Fleming Group. Analysis of the turbine and generator configuration assumed in the Bondi studies have also been found to require further design development (refer to section 6.3). Updated details of the configuration and operation of these lagoons are required to inform more refined modelling work.

Pending the availability of more refined energy modelling results, energy estimates from the power/area relationship (verified by the earlier EP57 studies and/or preliminary 1-D models) have been used for the options screening. However, these estimates will be enhanced for short-listed options through the subsequent 1-D and 2- D modelling which takes greater account of the ‘live’ storage volume in the impounded basin and related hydrodynamic effects.

4.3 Tidal Fence The tidal fence option (which is recognised as an indicative option but for the purposes of this report has been studied for the Cardiff to Weston and Minehead to Aberthaw alignments proposed by STFG) does not lend itself to direct comparison against energy estimates previously prepared for barrage schemes. This is because it uses tidal stream technology to capture the kinetic energy of the flow through the fence resulting from the effect it would have as a barrier to the tidal flow on the landward side.

The formula used for conventional tidal stream energy schemes is as follows: 0.5 u U u AuV 3

Assuming: x Density = 1025kg/m3 x Area = 147 turbines of diameter 18m (deep water) plus 109 turbines of diameter 12m (shallow water). x A velocity variation through the year based on the maximum spring tide velocity of 8 knots (4m/s) in tidal fence report and during neap tide 4 knots (2m/s). x No outage is considered in this calculation, as it is often not included in tidal stream calculations.

Final 43 December 2008 Table 4.4 below uses the velocity distribution and power distribution developed from Severn tidal curves to calculate the likely power output for 18m and 12 m rotor diameters for the Cardiff Weston Tidal Fence alignment.

Output Data Output Data 12m Value Units 18m Value Units Rotor diameter 12 m Rotor diameter 18 m Number of Number of rotors 109 / rotors 147 / Rated Power Rated Power Output 458 kW Output 1031 kW Load factor 41% % Load factor 41% %

TOTAL Annual TOTAL Annual energy per rotor energy per rotor (12m) 1636 MWh/y (18m) 3680 MWh/y TOTAL energy TOTAL energy 109 turbines of 147 turbines of 12m 178 GWh/y 18m 541 GWh/y

Table 4.4 Energy from Tidal Stream Turbines

Final 44 December 2008 A total annual energy of 719 GWh/year for the Cardiff Weston Fence alignment is therefore achieved. This is well below the 3.5TWh/year quoted by the proposer. The immediate reason for this is that the rated power of the turbines are around 1MW, rather than the 5MW originally quoted If the same site conditions are taken (i.e. Vmsp=4m/s), and the calculations are repeated with 256 turbines rated at 5MW, the annual energy production would effectively be around 4.5TWh/y, as shown in Table 4.5 below.

Output Data 5MW Value Units Rotor diameter x M Number of rotors 256 / Rated Power Output 5000 kW Load factor 41% % Mean power extracted per farm 525 GW TOTAL Annual energy per device 17958 MWh/y TOTAL energy 256 turbines of 5MW 4597 GWh/y Table 4.5 – 5MW Turbine Calculations

However, a device of 5MW could not be built at this location, using conventional tidal stream turbines. To reach a 5MW rated power at the given location (assuming Vmsp=4m/s, i.e. Vrated=65%*Vmsp=2.6m/s), the capture area of the device needs to be 1234m2. This could mean that the device has an equivalent diameter of 40m. Ignoring the engineering feasibility of this, the proposed devices are already, at 18m and 12m, at their maximum size for this location.

Conclusions for the Cardiff Weston alignment are therefore that:

x The final answer is very sensitive to a number of parameters, particularly: o Turbine diameter and o Rated rotor efficiency. Care must be taken not to be overly optimistic about the improving efficiency of stream turbines. x The rated power output required in each turbine is only 1 MW, rather than the larger 5 MW suggested by the fence promoters.

The above calculations do not invalidate the proposer’s approach, as they state that the technology used will need to be an advance on current turbine designs. It does, however, suggest that the turbines to be used will not be like a low-density tidal stream designs, but will somewhere between a tidal stream turbine and a more conventional tidal barrage turbine. A more conventional turbine arrangement would not, however, have the claimed environmental advantages of the tidal fence.

Final 45 December 2008 The proposal also included an estimate of the aggregate energy generated by a combination of the tidal fence and the Inner (Shoots) Barrage. This estimate shows how this combination would deliver power to the grid more consistently than either solution alone. This would occur because the fence generates maximum energy at around mid-tide whilst a barrage (operating in ebb generation mode) generates the majority of its power between mid tide and low water.

If the tidal fence is to be used with a barrage or other scheme, the energy extracted by the fence must be relatively small, or else the kinetic energy removed by the turbines will be converted to loss in potential energy upstream. STFG have estimated that the tidal range for a Cardiff Weston alignment would be reduced by 13% although with the revised energy outputs computed above, this is more likely to be 5%.

The proposer has also submitted proposals for a tidal fence located between Minehead and Aberthaw. This utilises 1.6MW turbines and produces a minimum of 3.3TWh per annum. It also has a relativly small effect on tidal range with a reduction of possibly only 5% or a reduction in high water level of between 2.5% if the 5% reduction in tidal range is verified in subsequent hydrodynamic modelling. This is because the tidal fence is taking out a much lower proportion of energy at this estuary location.

4.4 Optimisation of Energy As stated above, a number of options can be operated in combination and/or use different operational modes to enhance the value of energy generated. During subsequent stages of this study, an assessment will be made of the effect on energy yield of alternative operating systems, including ebb and flood generation, flood pumping and the use of additional basins. This is based on the premise that the more advantageous single basin ebb only schemes will provide the more advantageous opportunities for such optimisation (As discussed in Section 3.2). Therefore, all energy outputs shown in Table 4.1 are for ebb-only generation whilst Table 4.6 overleaf summarises the main opportunities for enhancing energy value.

Final 46 December 2008 Option Option Name “Core” Operating Compatibility Compatibility Ref. Operating Mode with Second with Other Mode Potential Basin Proposals

B1 Minehead to Ebb Pump + No No Aberthaw Barrage Ebb & Flood

B2 Hinckley Point to Ebb Pump + Yes No Lavernock Point Ebb & Barrage Flood

B3 Brean Down to Ebb Pump + Yes Yes – L3d, L3e Lavernock Point Ebb & Barrage Flood

B4 Shoots Barrage Ebb Yes Yes – F1, L2, L3

B5 Beachley Barrage Ebb Yes Yes – F1, L2, L3

F1a Tidal Fence - Brean Ebb and No Yes –B4, B5, Down to Lavernock Flood L2, L3 Point

F1b Tidal Fence – Ebb and No Yes –B3, B4, Minehead to Flood B5, L2, L3 Aberthaw

L2 Russell Lagoon - Ebb Pump Yes Yes – F1, B4, Fleming Energy B5, L3

L3 Tidal Lagoons Ebb Pump + Yes Yes – F1, B4, (Generic) Ebb & B5, L2 Flood

R1 Tidal Reef Ebb and No No Flood

U1 Severn Lakes Ebb Pump + Yes Yes – L3d, L3e Ebb & Flood Table 4.6 Energy Value Enhancement Opportunities

Final 47 December 2008 SECTION 5

ENVIRONMENTAL, SOCIAL, ECONOMIC AND REGIONAL CONSIDERATIONS

Final 48 December 2008 5 ENVIRONMENTAL, SOCIAL, ECONOMIC AND REGIONAL CONSIDERATIONS

Environmental, Social, Economic and Regional Considerations have been assessed for a range of topics including: x Climatic Factors x Hydrodynamics and Geomorphology x Habitats, biodiversity, flora and fauna x Marine Water Quality x Soils, groundwater and freshwater x Historic Environment x Landscape/ Seascape x Resource Efficiency and Waste x Material Assets x Population and Health.

All options present a wide range of potential issues that require significant resource and time (given the long life cycles of certain species) to understand adequately; and any qualitative review of options at this stage (prior to the detailed SEA) can only provide a preliminary assessment. This section of the report has therefore been prepared using a precautionary approach.

The effect of many of the options would be to reduce the tidal range within the estuary, resulting in some loss of inter-tidal area, although this may be reduced through mode of operation and/or lagoon configuration. The effects of all options on the morphology of the Severn Estuary are uncertain and subject to divergent hypotheses, but until further investigation it must be assumed that many of these changes are likely to be to the significant detriment of inter-tidal habitats. All options are likely to adversely affect fish passage and survival within the estuary, but current understanding is that the impacts would be generally more significant for barrage options.

All options therefore pose potentially high levels of risk to designated habitats and species, particularly, but not only, migratory fish and waterbirds. These risks require careful consideration having regard to the Habitats and Birds Directives and the requirements for effective mitigation and compensation packages.

There is also a need for greater understanding of other potential risks such as for land and seascape, and the historic environment. Options also have the potential to affect the water quality status of the Severn Estuary and need consideration having regard to the objectives of the Water Framework Directive, and the issue of discharge licences under Review of Consents currently underway.

A wide range of other effects to the natural and human environment are also likely, regardless of the option pursued.

Final 49 December 2008 5.1 Introduction This section provides an initial qualitative environmental review of the long-list options identified in Section 3 of this Report. Generally, it has been prepared with the precautionary principle in mind, in common with normal practice for considering environmental effects. If a risk has been identified that tidal power options might cause severe or irreversible harm to society or to the environment, and in the absence of a scientific consensus that harm would not ensue, the assumption has been made that such a risk exists. Application of the precautionary principle is not necessarily an indication of the severity or likelihood of effects. The precautionary approach has, of itself, to identify the worst scenario that could reasonably be identified. Such an approach provides assurance that potential environmental impacts are clearly identified enabling them to be studied in more detail and, as appropriate, suitable mitigation and compensation measures to be considered. However, further study may well show that some concerns are less severe than envisaged and also that, in some cases, mitigation measures can be identified that will reduce the scale of the effects of a scheme.

This section is included to highlight specific environmental, socio-economic and regional issues in relation to the options on the long-list. It is not intended to be definitive or absolute and its data are drawn from the initial work being undertaken to scope the Strategic Environmental Assessment. However, it does serve to set into a non-engineering context the effects that may arise from each of the options and summarises the basis of the qualitative analysis used in the assessment framework.

This review concentrates on key qualitative criteria identified within the long-list option assessment process, i.e. effects on: x Climatic Factors x Hydrodynamics and Geomorphology x Habitats, biodiversity, flora and fauna x Marine Water Quality x Soils, groundwater and freshwater x Landscape/ Seascape x Historic Environment x Resource Efficiency and Waste x Material Assets x Population and Health (including recreation and amenities).

Environmental legislation applies to many of these categories, and risks of failure in compliance with such legislation will be drawn-out in the relevant sections below.

Any major project of this nature will be likely to have a wide range of potential environmental effects, and these are not all extensively described here. An environmental assessment of options will be conducted within the SEA process. This will follow from selection of the short-list of options. The intent of this review of the long-list options is to focus on the relative risks of options in the key areas listed above, to inform the identification of a short-list of options for more detailed Final 50 December 2008 assessment. However, it must be noted that for some areas of study, e.g. fish, there is not yet a sound evidence base. By focussing on these key areas, some topic areas will be covered in much greater detail than others.

Coming at an early stage of options appraisal, inevitably this review uses an expert- based, but nonetheless incomplete, understanding of the potential issues. The options will be considered collectively (as a group) where the impacts are similar in scale and type. The effects will therefore be considered under the following headings: x Relevant for All Options; x Minehead to Aberthaw Barrage (B1), Hinkley Point to Lavernock Point Barrage (B2), and Brean Down to Lavernock Point Barrage (B3); x Shoots Barrage (B4) and Beachley Barrage (B5); x Russell (Fleming) Lagoon (L2) and Generic Tidal Lagoons (L3); x Tidal Fence (F1); x Tidal Reef (R1); and x Severn Lakes (U1).

As explained elsewhere in this document, it has been assumed for the purposes of this review that the options would operate under an ebb-generation only mode of operation (with the exception of the F1 Tidal Fence and R1 Tidal Reef). Although option U1 has been screened out (see Section 3), information is provided in this section on those options for information purposes.

Final 51 December 2008 5.2 Qualitative environmental review of long-list options Introduction

This review has been informed by the ongoing scoping phase of the SEA. Scoping activities include literature and data review, and a programme of technical consultations. Space here does not permit a summary of the baseline environment of the Severn Estuary, but full descriptions can be found in the Sustainable Development Commission’s ‘Turning the Tide’ reports (2007). In particular, these reports include extensive reviews of previous studies of the potential effects in relation to two of the options currently under consideration (approximating to barrage options B3 and B4). The relevant discussion therein, including the identification of the many areas of uncertainty, is not repeated here.

In the following sections, each group of options is reviewed and the main environmental effects identified. The information contained in this review will be used to guide the population of the long-list assessment criteria matrices and used to inform the selection of the short-list. For the purposes of long-list evaluation, ebb only generation modes have been used as the default (except for F1 Tidal Fence and R1 Tidal Reef which are designed to operate only in ebb and flood modes). Ebb only generation produces the highest energy outputs and exhibits the largest variations on tidal range. Some of the consequent environmental effects may be mitigated through a less extreme operational mode of ebb and flood generation where less energy is generated but it is distributed over a longer time period with an associated change in environmental effects.

The issues common to all the options under consideration are presented below, ahead of the option-specific reviews.

5.3 Environmental Issues Relevant for All Options Climatic Factors

For the purposes of this report, climatic factors are principally taken to relate to the balance of carbon (carbon emitted and carbon emissions avoided). This section does not include a wider consideration of other climatic factors, which if relevant will need to be addressed in later stages of option assessment.

Initial studies by the Sustainable Development Commission suggest that the carbon emitted during construction is equivalent to the carbon emissions saved during a 6 month to 1 year period of subsequent generation. Operationally, dredging activities may contribute to carbon dioxide emissions but these are likely to be small in relation to the savings achieved through generation. Other climatic effects (such as effects on the ability of the Severn Estuary to sequester carbon) will be tested within the overall assessment of carbon footprint, if the project proceeds to phase 2.

Final 52 December 2008 If other developments supported by a tidal-power scheme are brought into the overall cost-benefit analysis, then the impact of the consequential carbon emissions would need to be set against any benefits in phase 2.

Hydrodynamics and geomorphology

Any large-scale tidal power development within the Severn Estuary which takes a significant fraction of the energy out of the system will inevitably make significant changes to the tidal regime. It will reduce tidal energy over a wide area (both up and downstream), with consequential effects for human activities and the natural environment. Barrages in particular will modify the resonant characteristics of the estuary, reducing peak water elevations. An understanding of hydraulics and geomorphology is therefore fundamental to predicting the environmental effects of such schemes, including the effects on navigation and flood risk. A reduction in peak water level could be detrimental to shipping unless appropriately mitigated. The effect on flood risk may be positive, due to peak water level reduction, but may also be negative due to the increased durations of static water levels and any effects of geomorphological changes on flood defences. The larger barrages and the tidal reef will have a greater beneficial effect than other schemes. The extent over which the effects of peak water level reduction will be experienced will be greater than smaller schemes. The effect on peak water level of a tidal fence will extend over a similar area as a barrage constructed on a similar alignment but will cause a smaller reduction in peak water level. It is assumed that existing land drainage standards of service and navigation clearances will be maintained through mitigation and the estimated costs for this are included in the cost estimates for each of the options where relevant.

Changed tidal conditions will have a wide range of secondary effects on the physical environment of the Severn Estuary, including effects on water levels, flows, waves, estuary sediment regime and morphology, and water quality. The discussion that follows for each group of options concentrates on: water levels, geomorphology and water quality, because of their direct relevance to other interests. This does not exclude the paramount need to understand the effects on all key aspects of the physical environment of the Severn Estuary. It is possible that these effects could have impacts beyond the Severn Estuary itself and its tributaries – so called far field effects, which could lead to impact along the coast into the Bristol Channel. The proposed range of studies, which will be undertaken if the project proceeds to Phase 2, will include study of these potential far field impacts.

The presence of an impoundment to generate tidal energy within the Severn Estuary will result in accretion of sediment within the impoundment because of the lower tidal velocities within the basin. There is considerable uncertainty whether this will occur within the sub-tidal area or within the inter-tidal area. In an estuary with low wave energy but higher tidal energy, accretion is more likely to occur in the intertidal area, resulting in a convex slope from the shoreline to low water. However, in an estuary dominated by wave energy, accretion is more likely in the sub-tidal zone with a resultant concave inter-tidal profile. The Severn Estuary presently has high

Final 53 December 2008 tidal energy and relatively high wave energy. Introducing an impoundment into the estuary will reduce the tidal energy, and possibly also reduce the wave energy. The relative change to these natural forces will determine whether accretion is more likely to happen in the inter-tidal area or the sub-tidal zone. The effects will vary from location to location and for each of the options depending upon their individual characteristics. It is proposed to assess this in more detail on short-listed options using specific modelling. For the purposes of this report, it would be premature to assess which of the above scenarios will results for each option

Habitats, biodiversity, flora and fauna

Habitats

The high tidal range in the Severn Estuary creates unique physical conditions which strongly influence the composition, distribution and abundance of flora and fauna. The resulting ecological importance of the estuary is recognised through international, national and local nature conservation designations. At a European level, much of the estuary is designated as a candidate Special Area of Conservation (cSAC) under the Habitats Directive and the intertidal areas are designated as a Special Protection Area (SPA) for Birds under the Birds Directive, and as a Ramsar Site under the Ramsar Convention on Wetlands of International Importance especially as Waterfowl Habitat.

The EC Habitats Directive (92/43/EC) requires the establishment of an ecological network of important high quality conservation sites, known as Natura 2000, that enables the habitats and species identified in Annexes I and II of the Habitats Directive to be maintained or restored at a favourable conservation status in their natural range. The listed habitat types and species are usually those considered to be rare or endangered at a European level, with the overall aim of the Directive being the maintenance of biodiversity.

The Severn Estuary candidate Special Area of Conservation (cSAC) was submitted by the UK to the European Commission on 31 August 2007 because it contains the following habitat types and species that are threatened within a European context: x Estuaries x Mudflats and sandflats not covered by seawater at low tide x Atlantic salt meadows x Sandbanks which are slightly covered by sea water all the time x Reefs x Sea lamprey Petromyzon marinus x River lamprey Lampetra fluviatilis x Twaite shad Alosa fallax.

Rivers adjacent to the Severn also of importance comprise the River Tywi SAC, River Wye SAC and River Usk SAC. These sites include protection of; inter alia, Allis and

Final 54 December 2008 Twaite Shad, Sea, River and Brook Lamprey, and Atlantic Salmon (with the exception of the River Tywi SAC, where Atlantic Salmon are not a feature).

There are a large number of national nature conservation designations that occur within and adjacent to the Severn Estuary – for example there are 30 Sites of Special Scientific Interest (SSSIs) within or adjacent to the Estuary. The sites have been designated for a range of geological and biological interests. In addition to the statutory designations, there are a host of non-statutory local designations that apply to sites around the estuary.

All tidal options would reduce the tidal range within at least part of the Severn Estuary under ebb-only operation. This will result in a smaller intertidal area and the increased risk of sedimentation within impounded basins could result in bed slope reduction. This may take many years and may require specifically designed dredging programmes in initial years. Initial calculations, using a fair-basis approach for all options, have been made of the change in intertidal area at Spring tide that would arise from this alteration to the tidal range using data sources that can be applied equally to all options and without taking account of any off-setting effects such as increased sedimentation.

The intertidal area as exists today is taken as the area above 0m (Admiralty chart datum), i.e. the maximum area of the Severn Estuary that can be exposed by the lowest astronomical tide.

This approach gives an overestimate of the intertidal area compared to estimates based, for example, on mean low water; and this conservative approach has been used because of the need to use a common data source across all options to preserve the fair-basis evaluation. At the time of these estimations only Admiralty chart data was available for all option locations.

The intertidal area for each option is based on ebb only generation assuming a simplified horizontal water surface and an approximate tidal range upstream of a barrage or within an impounded lagoon. This is a simplification which may underestimate or overestimate the loss of intertidal area.

The estimates do not allow for the change in tidal range causing a change in intertidal area downstream of a barrage or outside an impounded lagoon where inter-tidal area losses could be a significant proportion of the overall inter-tidal area lost depending on the size, shape and location of the scheme.

Virtually all the intertidal area upstream of Option B2 is designated cSAC and SPA. However, these preliminary estimates do not distinguish between designated intertidal and undesignated intertidal habitat, and the method of estimation means that the data does not closely match habitat estimates for the cSAC designation.

Final 55 December 2008 These calculations are recognised to be simplistic because of the coarseness of the Admiralty chart data and the necessity to adopt simplifying assumptions at this stage of the study. The inter-tidal loss areas calculated are only intended to enable a relative comparison of options and not an absolute assessment of the effects of any option. Subsequent stages of this study will utilise more accurate estuary bed data and water level modelling to refine these estimates. The data used at this stage are summarised in Table 5.1.

The effect of tidal fences on the tidal range stated in Table 5.1 has been based on an estimate of its impact on flow speeds and a corresponding reduction in tidal range. The accuracy of these estimates is uncertain as more detailed research is required into the effects of the fence on high and low water levels in the vicinity of the fence and further upstream and downstream. This further research would also need to address uncertainties in the effect of the fence on patterns of erosion and sediment deposition which will also impact on the inter-tidal habitat. In any future research, the estimates of inter-tidal loss will remain theoretical as there are no analogues to draw upon where fence construction has been employed at a full scale. Therefore, the estimates must be considered precautionary. An upper bound estimate could be equivalent to a barrage of similar energy yield which for F1b could incur an inter-tidal loss of around 5,000 to 6,000ha.

These preliminary estimates of changes in intertidal area are of importance to considerations of compliance with the requirements of the Habitats Directive, and of the attainment and maintenance of ‘good ecological status’ under the Water Framework Directive.

Important ecosystem services are known to be associated with intertidal habitats. These include CO2 sequestration, nutrient stripping and PM10 absorption. Intertidal habitat losses on the scale proposed by the tidal power options are likely to have negative impacts on these estuary services, and will be considered alongside the SEA in the next phase of assessment.

Option Estimated upstream intertidal area (ha)* Without option With option Loss B1 Minehead to Aberthaw 31,500 3,500 28,000 Barrage B2 Hinkley Point to Lavernock 29,400 3,400 26,000 Point Barrage B3 Brean Down to Lavernock 22,500 2,500 20,000 Point Barrage B4 Shoots Barrage 5,100 100 5,000 B5 Beachley Barrage 3,560 60 3,500 F1a Tidal Fence between Cardiff 22,500 20,500 2,000 and Minehead F1b Tidal Fence between 31,500 28,700 2,800 Final 56 December 2008 Option Estimated upstream intertidal area (ha)* Without option With option Loss Minehead and Aberthaw L3 Bridgwater Bay Lagoon (land- 6,400 900 5,500 connected) L3 Peterstone Lagoon 3,000 300 2,700 L2/ Russell (Fleming) Lagoon 6,947 540 6,500 3 (Welsh Grounds) L3 Russell Lagoon (English 2,200 200 2,000 Grounds) R1 Tidal Reef Unquantified due to insufficient data U1 Severn Lakes Scheme Unquantified due to insufficient data – possibly similar to B3 Table 5.1 Preliminary and Precautionary Intertidal Loss Assessments *Note: All estimates are preliminary and precautionary.

This preliminary assessment focuses on the loss of upstream intertidal owing to changes in tidal range. There are many other important effects on habitats that may arise, for example through the direct footprint of schemes, effects on water quality, sedimentation and erosion of foreshores etc. These effects are not yet well understood for each option. Hence, whilst there is good broad-scale information for the distribution of many estuarine features, a meaningful assessment of the effects upon these is not possible until better information on the physical effects of each option is available. These effects are therefore an uncertainty at this stage.

The complete range of impacts of options on the other habitats and features of the Severn Estuary cSAC/ SPA and other designated sites will need to be considered in the full assessment of options. Effects may arise both up and downstream.

Fish

Fish species which are designated features of the relevant internationally designated sites are outlined above (e.g. Allis and Twaite Shad, Sea, River and Brook Lamprey, and Atlantic Salmon). All of these species are classed as diadromous migratory species, i.e. they live in freshwater and marine environments at different stages in their lifecycles.

Key environmental changes resulting from the development of the range of proposed tidal power options that are most relevant to migratory fish, marine/estuarine fish and angling (estuarine and upstream freshwater) include:

x Alterations to migratory cues Final 57 December 2008 For fish which display natal homing behaviour, such as Atlantic salmon and shad, any changes in salinity in the estuary basin could delay migration by disrupting their ability to locate their natal rivers contained within freshwater discharge. Reduced mixing upstream however and increased surface freshwater may aid natal river identification and decrease transit time and straying upstream. Reduced turbidity in the basin may be both beneficial and detrimental with murkier water disrupting navigation and clearer water aiding predation; however impacts are uncertain.

x Disruption to route of passage

One of the prime sources of impact for fish is the presence of a tidal power project structure and the operation of its turbines. There is the potential for significant impacts on fish survival, particularly that of the migratory species, of turbine passage, shear stress, mechanical injury, pressure, cavitation, sluice passage, and any indirect impacts. These factors may be enhanced or reduced by alterations in turbine operations and possibly design but could result in local species extinction and/or loss of genetic diversity. Consideration of detailed evidence and potential mitigation (including potential fish screening and acoustic fish guidance systems) will be pursued in Phase 2 of the studies. In addition, flatfish and roundfish fry (2-10cm in length) migrate through estuaries using selective tidal stream transport. This migration is predicated on the presence of a continuous intertidal foreshore. Loss or interruption of intertidal habitat is likely to have implications for this migration pattern.

x Habitat Changes

All options, by reducing the tidal range within at least part of the estuary, will result in a smaller intertidal area and will impact on fish. This may affect the habitat for juvenile and adult fish both upstream (landward) and downstream (seaward) of the project. The Severn Estuary, as well as being a migratory pathway is also important in its own right as an important fish nursery ground.

x Water Quality

There are a number of potential effects of a tidal power project on water quality including potential changes to salinity, temperature, suspended sediments, dissolved oxygen and contaminants that could affect fish and their movements.

x Angling

Final 58 December 2008 Potential impacts on fish as a resource will potentially affect the freshwater fisheries of the rivers which flow into the Estuary; and sea angling and marine commercial fisheries in the Severn Estuary.

All the options are likely to have a negative effect on migratory fish. The severity of the impact will be dependent on the specifics of the design, for example the type of turbine deployed, operating regime and use of screening / baffles etc to deter fish from encountering turbines. These factors collectively are likely to be as relevant as the geographical location of the option, to the overall impacts upon fish.

There is currently low confidence in the effectiveness of measures available to mitigate these effects.

Birds

The EC Birds Directive (79/409/EEC) requires all member states to identify areas to be given special protection for the rare or vulnerable species listed in Annex 1 of the Directive (Article 4.1), for regularly occurring migratory species (Article 4.2) and for the protection of wetlands, especially wetlands of international importance. These areas are known as Special Protection Areas (SPAs).

The Severn Estuary SPA qualifies under Article 4.1 of the EU Birds Directive by supporting internationally important populations of regularly occurring Annex I species. It also qualifies under Article 4.2 of the EU Birds Directive in that it supports: x Internationally important populations of 18 regularly occurring migratory species; and x an internationally important assemblage of waterfowl (over 20,000 birds).

Sub-features of the SPA, which support these bird species, include: x Intertidal mudflats and sandflats; x Saltmarsh; and x Shingle and rocky shore.

Under the 1972 Ramsar Convention on Wetlands of International Importance, it is a requirement of signatory states to protect wetland sites of international importance, including those that are important waterfowl habitats. The Severn Estuary qualifies as a Ramsar Site through meeting a number of the qualifying criteria, as outlined below: x Criterion 1 - due to its immense tidal range x Criterion 3 - due to its unusual estuarine communities, reduced diversity and high productivity x Criterion 4 - as it is particularly important for the run of migratory fish between the sea and rivers via the estuary x Criterion 5 - bird assemblages of international importance x Criterion 6 - bird species/ populations occurring at levels of international importance

Final 59 December 2008 x Criterion 8 – the fish population of the whole estuarine and river system is one of the most diverse in Britain with over 110 species recorded.

There are also a large number of national and non-statutory designations applicable to birds species, for example BAP and species listed under section 42 of the Natural Environment and Rural Communities Act 2006. The list includes herring gull which use the estuary both in winter and summer, and wintering passerines which feed on the salt marsh, such as twite, skylark and linnet and breeding lapwing.

In most cases, the physical changes of relevance to birds are broadly generic to the barrage and lagoon options being considered. However, the magnitude of the changes associated with each option will vary depending on their scale and the option’s location relative to the distribution of key species. Most of the changes will primarily affect estuarine wintering waterbirds, although predominantly freshwater species and other groups such as gulls that are also included among the designated features may additionally be affected by some of the issues identified.

Other marine ecology

Planktonic communities reflect the prevailing physical conditions in the Severn Estuary. Phytoplankton growth within the estuary is limited by the high turbidity in the water column and significant growth only occurs towards the outer Bristol Channel. Zooplankton within the estuary is dominated by detrital grazers, supplemented by meroplanktonic species entering the estuary by larval transport.

Macroalgal assemblages within the estuary exhibit the reduced diversity associated with estuarine environments. Zonation is truncated with no macroalgae occurring subtidally because of the high turbidity of the overlying water.

A variety of epibenthic species occur in the estuary. In particular, there are seasonally large populations of the brown shrimp Crangon crangon in the estuary and mysids such as Schistomysis spiritus in the inner estuary.

There is little information on the distribution and abundance of cephalopods in the estuary and Bristol Channel although most of the commonly occurring species are known to occur.

The highly turbid waters of the estuary are not significantly used by marine mammals. While significant numbers of harbour porpoise are seasonally present to the west of Worms Head, there are few records for marine mammal in the estuary.

All the likely tidal power development options are likely to cause significant changes to the prevailing physical regime in the estuary once constructed. These changes are likely to affect the distribution and abundance of marine ecological receptors. In particular, predicted reductions in tidal range upstream of tidal power developments would reduce the extent of intertidal areas and reduce inundation of saltmarsh.

Final 60 December 2008 Changes in erosion and deposition patterns within the estuary could also significantly affect the quality of existing habitat features. Reductions in salinity upstream of a tidal power development would affect the distribution and abundance of species. Changes in turbidity and flushing rate could affect primary productivity in the estuary and change the composition of zooplankton.

Given the high sensitivity of many of the marine ecological receptors and the potentially large environmental changes that could be introduced by tidal power development, potentially significant risks are likely for most of the receptors for all the tidal power development options considered.

Water quality

The EC Water Framework Directive (WFD) (2000/60/EC) establishes a framework for the management and protection of Europe’s water resources. The WFD has two key objectives for all water bodies: x To prevent deterioration of the status of all surface water and groundwater bodies; and x To protect, enhance and restore all bodies of surface and groundwater with the aim of achieving good status in all surface water and good ground water status by 2015.

The Severn Estuary is naturally a highly turbid estuary due to its physical shape, tidal regime and flow rates and the availability of fine sediment for resuspension. There are a wide range of direct and indirect discharges into the Severn Estuary, but it is currently classified as being of good quality in the upper estuary and fair quality in the middle and lower estuary. Sediment concentrations of contaminants such as metals, PAHs and PCBs are relatively uniform around the Severn Estuary and the Bristol Channel. This reflects the strong tidal mixing and fluid mud transport which disperse contaminants from their source.

The potential water quality impacts are, to some extent, generic for all of the tidal power options. This is because all of the options are likely to affect the prevailing hydrodynamic regime, which, in turn significantly influences the main physical, chemical and biological processes influencing water quality. Changes to the hydrodynamic regime have the potential to:

x Change initial dilution and dispersion characteristics around outfalls and discharges resulting in local changes in the concentrations of contaminants and pathogens in the water column; x Modify the salinity regime resulting in changes in the behaviour of adsorbed contaminants; x Increase the potential for salinity (density driven) stratification resulting in changes in the behaviour of adsorbed contaminants and biological availability and influencing dissolved oxygen concentrations and nutrient cycling;

Final 61 December 2008 x Modify flushing characteristics in the main estuary and tributary estuaries resulting in changes in residence times of contaminants and pathogens; x Modify suspended sediment concentrations, sediment transport patterns and processes with consequences for dissolved oxygen concentrations and the transport, fate and behaviour of sediment-associated contaminants; x Change flushing time and light attenuation, affecting primary productivity and thus alter nutrient cycling within and export from the main estuary and tributary estuaries and export from the Severn Estuary; x Changes in light attenuation may have consequential effects on bacterial concentrations; x Change physical processes and nutrient cycling, altering carbon cycling within the main estuary and tributary estuaries and export from the Severn Estuary; x Change sediment properties and dynamics, affecting the potential for colonization and sediment water interchanges.

Soils, groundwater and freshwater

The Severn Estuary is bordered by a complex sequence of geologically recent deposits, most of which are water-bearing and in hydraulic continuity with the surface water system, particularly on the low-lying land of the Somerset and Gwent Levels. These deposits contain a large number of services, including drains, culverts and sewers. They form the foundation for an extensive system of tidal defence embankments, and contain building foundations and basements. They also contain areas of landfill and historic waste disposal.

The recent deposits are underlain by folded and fractured bedrock which emerges at ground surface on both sides of the coast, forms two islands in the estuary (Flat Holm and Steep Holm, both of which are designated as SSSIs) and is exposed extensively sub-tidally. The Severn railway tunnel runs within these bedrock deposits. Several groundwater sources used for the Public Water Supply emerge from the Carboniferous Limestone and have Source Protection Zones that abut the coastline.

Because of the complexity of the geology, the Severn Estuary contains many sites of geological and geomorphological interest, several of which are designated as SSSIs. Several regionally important geological sites (RIGS) are also present.

Land drainage is dominated by the Severn Estuary itself, seven main sub-tributaries and a network of multiple drains on the lower levels, many of which are tide-locked for part of the tidal cycle. The low-lying land supports important habitats, some of which are designated. Terrestrial surface water quality is complicated by the hydrodynamics and geomorphology of the Severn Estuary.

At this early stage of assessment, the potentially significant effects are considered to be similar for each option:

Final 62 December 2008 x Altered water quality (including sediment and salinity) caused by altered flow and sedimentation regimes within the impoundment, and the consequential effects on freshwater fisheries, shellfisheries , and biodiversity; x Altered terrestrial groundwater regimes, with increased groundwater elevations adjacent to impounded water and the consequential effects on adjacent land drainage (less capacity), soils (fertility, quality, diversity and access to agricultural machinery), trees and sites of water-dependent nature conservation importance; x Reduced groundwater quality as a result of increased saline or brackish intrusion or the mobilisation of contaminants from natural or anthropogenic sources (such as landfills or other contaminated sites) affecting groundwater or freshwater sources used for the Public Water Supply; x Increased groundwater elevations affecting the integrity of buildings (foundations, dampness in basements etc.) and subterranean infrastructure, including the Severn railway tunnel and other culverts, pipes etc. as well possibly affecting the stability of sea defences due to increased pore fluid pressure; and x An increased rate of decay or reduced access to designated sites of geological and geomorphological importance as a result of altered tidal regimes within the impounded basin.

Historic Environment

The historic environment of the Severn Estuary consists of both natural and built components and is one of the most significant in the UK. It consists of internationally, nationally, regionally and locally important sites. The Severn Estuary’s features are located along its coast-line (including prehistoric and Roman features); its waters hold features reflecting its maritime heritage dating from the Bronze Age, and its associated levels and hills offers a rich and varied archaeological landscape. The potential of the Severn Estuary is not however limited to, or even fully represented by, the number of nationally designated sites, but also includes a vast number of non- designated sites and finds, and has a high potential for the discovery of new finds.

At this early stage, the significance of effects to the historic environment varies little between the options; the historic environment is irreplaceable, and it is sensitive to change. As many of the effects of the development will be irreversible and the magnitude could affect the entire estuary, changes are potentially significant.

On the Welsh side of the Severn Estuary, the Gwent Levels have been designated an Area of Special Interest, and are included in the Register of landscapes of historic interest in Wales. In the draft Heritage Protection Bill which is likely to become law in 2010, it will be a statutory duty for developers and consenting bodies to consider historic landscapes.

Final 63 December 2008 Within each of the options there are a number of other designated sites on both sides of the estuary. However, future assessment should not be confined to designated sites, as the potential for discoveries outside these areas may be high.

The potentially significant issues regarding the effects of development include direct, indirect and secondary effects. Direct effects include direct damage to structures, features, deposits, artefacts, and the disturbance of relationships between these and their wider surroundings. Indirect effects reach beyond the footprint of the development, including changes to hydrodynamics, coastline, tidal movement, sedimentation, erosion, water level and water quality. Secondary effects result from development activities such as access roads and anchorages for construction vessels. Impact on the historic landscape and access to the historic environment are also significant.

Landscape and Seascape

Landscape is deemed to include townscape and can be considered to be an area or tract of land, which can be of any extent or scale. Landscape results from the interaction of both natural processes and human influences. These determine the form and appearance of the landscape and affect the way we experience it. Seascape can be defined as the coastal landscape and adjoining areas of open water, including views from land to sea, from sea to land and along the coastline, and the effect on landscape at the confluence of sea and land.

Large developments within the Severn Estuary will be visible over long distances due to the open, flat character of the estuary and the raised, undulating topography of the coastline. The necessary transmission infrastructure such as additional power lines will also have implications for the landscape and need assessment. However much depends on public perceptions and the zone of visual influence in relation to receptors. These aspects therefore require further investigation to be able to distinguish between options on the basis of risk to the sea and landscape.

Effects on the ‘marine landscape’; i.e. the dominant seabed, coastal and water column features are not directly considered at this stage, although its components are considered in the relevant sections of this assessment.

Resource Efficiency and Waste

Tidal range technologies require considerable use of natural resources during construction although there are some minor mitigation opportunities such as use of re-cycled materials during construction (for example aggregates and fuel ash in concrete). However, during operation, tidal range technologies are a significant producer of energy without consuming significant natural resources or producing waste. Further information relating to the impact of resource efficiency and waste will be undertaken as part of the Phase 2 study.

Final 64 December 2008 Material assets

Flood risk

As all options under consideration would change the tidal regime, particularly upstream of a structure, they may consequently affect flood risk and land drainage. Whilst large barrage options (and to a lesser extent smaller barrages) have benefits in providing protection from storm surges and sea level rise, there are also a number of impacts that require mitigation as well as some uncertainties. These are itemised below: x Changes in the tidal regime may have flood risk implications for the maintenance of some flood defences, resulting in greater expenditure modifying or maintaining assets. This is partly dependent on the nature of the estuary’s geomorphological response, that is currently uncertain; x All options will cause a reduction in the tidal range, including a reduction in peak water level, and the extent and magnitude of the reduction will depend on the structure and the mode of operation. The more significant reduction in tidal range will occur within the impounded basin of barrages and lagoons where there will be an increase in low water levels and a potential reduction in the peak water levels; x Whilst the reduction in peak water levels will be beneficial in flood risk terms there may also be some detrimental effects caused by increased erosion at the base of tidal defences and saltmarsh; x There is likely to be a change in the wave climate upstream of a tidal power structure. The reduced fetch resulting from a barrage will reduce wave heights but the amount of reduction and the potential beneficial effects are uncertain and require further research. x A larger barrage may prevent waves generated in the south west approaches from propagating upstream. This would be a flood risk benefit; x Barrage options, by providing a structure across the Severn that can be readily adapted to protect against future sea level rise, provide a means of protecting upstream communities from the impacts of storm surges and sea level rise. DEFRA's current estimate of sea level rise for the South West and South Wales is approximately 1m by 2100 and continuing to rise thereafter. This will increase flood risk severely for infrastructure and populated areas at risk from tidal flooding and to protect the upstream communities would require significant expenditure. Such expenditure would need to be considered against other flood defence priorities. x The increased low water levels will restrict the free drainage of some outfalls and levels that discharge / drain into the tidal estuary and will thus require modification to enable pumped discharge (currently included within option cost estimates);

Final 65 December 2008 Navigation

The Severn Estuary is home to a number of commercial ports including significant facilities at Bristol, Cardiff, Newport and Sharpness/Gloucester. The largest port, the Port of Bristol comprises both Avonmouth and Royal Portbury docks. The ports and the services they support are an important part of the local and regional economy, and are responsible for handling around 5% of Great Britain’s trade.

All of the major ports within the Severn Estuary currently rely on locking into their respective docks and each carefully plan ship movements according to available draughts as a direct consequence of the extremely large tidal range and advertised high waters. The operation of the ports requires regular survey and dredging of navigation channels.

All of the options are considered likely to affect navigation within the Severn Estuary in terms of where and when the activity takes place. The issues considered to be potentially significant to the ports are:

x The direct and immediate effect of any barrage option proposed is to provide a direct barrier to navigation. This will require the addition of locks, with sufficient redundancy, to allow vessels to traverse the two different water levels; x Reduction of spring tide levels which will decrease the access window that vessels with large draughts will have to access the ports, unless mitigated by associated reduction in the lock cill levels; x Increase in low tide level which will increase the access windows that vessels have to access the ports and provide flexibility to ports in managing vessel movements. Some marine structures will however be permanently immersed; x Reduction in salinity will increase the draft requirements for vessels (ships sit lower in fresh water than sea water because it is less dense), although this is not considered significant to Sharpness/Gloucester; x Long term effects on seabed geomorphology and sediment distribution are uncertain, potentially affecting dredging requirements; x Any physical works on the Severn Estuary near navigation routes will affect currents and will also represent a potential navigation hazard. x Reduced tidal currents and wave climate coupled with the higher low water level will change sailing and leisure conditions in the estuary upstream of any barrage.

Society and Economy

Many of the potential changes to the community and socio-economic environment resulting from tidal power options are broadly similar in nature, but would vary in magnitude according to the scale of the proposed scheme.

Final 66 December 2008 Such generic changes that are considered likely to occur arise from the substantial construction phase for most tidal power schemes. These include: x Employment opportunities during the construction and operation phase and competition for labour and loss of skilled labour in local businesses; x Population migration in response to the construction phase, resulting socio- cultural changes and pressure on existing housing stock and services; x Health effects through changes in noise and air quality emissions, principally during construction; post construction minor odour changes may be noticed from the changed tidal regime; x Effect of such substantial proposals on existing, proposed and committed developments and the future use of land; x Regional economic effects including the opportunity for regeneration and new development.

Tourism is an important economic activity in the region with over 7.5m tourist visits generating an income of over £1bn p.a. A wide range of recreational activities occur on or near the Severn Estuary, including: sailing, boating, windsurfing, canoeing, surfing, bore surfing, sand surfing, bathing, diving, wildfowling, bird watching and fishing. The presence of tidal power structures could benefit some of these activities (eg sailing, boating and windsurfing) whilst pose significant issues for others, for example by creating visual impact issues, altering bird distributions and affecting recreational angling opportunities. These latter issues are discussed in other relevant sections.

Amenity and recreational changes will also take place. The construction of a tidal power project will provide opportunities for enhancement of some recreational uses. These range from interest during the construction phase, through to managed activities resulting from the less aggressive tidal range upstream of a barrage, such as sailing and other water sports. Opportunities arising from tidal lagoons include use of the lagoons for sailing and other water sports although these would require specific access arrangements which may have to be provided at additional cost. These may in turn result in environmental impacts that would need to be considered and managed.

Barrages may reduce or eliminate the Severn Bore phenomenon. It is unclear at this stage whether a bore could be preserved by not generating from the barrage and allowing water levels to recover to their natural levels and flows at the time of a predicted Bore. Depending on the measures required, this may entail a significant cost in terms of lost energy yield.

Effects on certain other issues with a socio-economic bearing, namely fishing, flood risk and navigation, are discussed in the relevant sections.

Minehead to Aberthaw Barrage (B1), Hinkley Point to Lavernock Point Barrage (B2), and Brean Down to Lavernock Point Barrage (B3)

Final 67 December 2008 Hydrodynamics and Geomorphology Hydrodynamics Hydrodynamic modelling undertaken as part of the EP57 studies confirm that the tidal regime upstream will be modified, quoting the top water level being suppressed by approximately 10% both upstream and immediately downstream of the barrage and the total tidal range being reduced by approximately 50%.

These studies also suggest that downstream of a large barrage there would be a reduction in high water and raising of low water, resulting in a net reduction in tidal range. Model studies for EP46 calculated a reduction in mean tidal range of 20% for the B1 alignment and 14% for the B3 alignment. The modelling for EP57 calculated a slightly smaller reduction in mean tidal range just seaward of the B3 barrage. This effect diminishes with distance, but the modelling for EP46 predicted a reduction in mean tidal range of 15cm for the B1 barrage and 5cm for the B3 barrage at Morte Point.

Geomorphology The nature of potential geomorphological responses (both up and downstream) to enclosure by a barrage is uncertain and needs further assessment.

It has been postulated in discussions with statutory nature conservation agencies that, upstream, erosion of the upper foreshore by wind-generated waves, and the ongoing erosion of the upper-intertidal may be exacerbated. This is because, with a barrage in place, there remains the potential for south-westerly wind-driven waves; and the exposure-time of the upper foreshore to such waves would be increased. Overall this would lead to a further reduction in intertidal habitat through erosion of soft sediments. This hypothesis could also have significant consequences for flood risk management and for other coastal habitats. It is widely recognised that intertidal habitat fronting sea defences absorbs wave energy and protects built structures.

Conversely, studies of the Cardiff-Weston scheme in the 1980s have concluded that the upper intertidal / saltmarsh would stabilise and possibly increase in extent owing to a reduction in these erosive processes. This converse hypothesis is also supported by conventional engineering assumptions which would recognise the wind fetch in the basin as a different entity to the fetch downstream of the barrage (with the barrage absorbing energy from the downstream fetch).

Other geomorphological responses that may arise include the risk of reduced sand transport rates and possible ingress of fines impacting on a large proportion of the Sabellaria spp. reefs that are a feature of the Severn Estuary cSAC. The enclosed estuary would be likely to undergo morphological change, with accumulation of fines in the deepest areas: Bristol Deep, Newport Deep etc., which are presently scoured after neap tides.

Final 68 December 2008 The geomorphological response of the Severn Estuary to a tidal power scheme is fundamental to understanding its wider effects on the natural and human environment, including many designated features. There are currently divergent schools of thought on the likely nature of the geomorphological response. As an important area of uncertainty, it must be investigated further before the impacts of such schemes can be understood.

Sedimentation The Severn Estuary’s sediment budget, in comparison to the size of the enclosed basin for these barrages, is not believed to be adequate for the estuary to establish a state of dynamic equilibrium for centuries. The risk of sedimentation significantly affecting the operation of these barrages is therefore generally considered to be low if there is no major requirement to maintain new channels to facilitate navigation (during construction or operation). If there is such a need then sedimentation may be a significant issue, albeit one which is likely to be manageable at a cost and associated environmental impact.

Habitats, biodiversity, flora and fauna Habitats These options may result in a substantial reduction in intertidal area upstream of the barrages. Without mitigation, which itself has a low confidence of being even partially effective, the majority of existing saltmarsh habitat would be lost (because of the reduction in high water levels). A smaller extent of new saltmarsh may be expected to develop seaward of the existing marshes but previous studies have shown that the net loss is likely to be significant. The extent of intertidal mudflat and sandflat habitat would also significantly reduce as a result of the reduction in tidal range. The majority of these habitats are within the Severn Estuary cSAC/SPA and Ramsar site, and the River Usk and River Wye SACs. Additional areas of undesignated intertidal habitat would also fall within the enclosed basin of the B1 and B2 barrages and be similarly adversely affected.

Intertidal habitat loss would primarily be caused by the reduced tidal range, leading to lower-intertidal areas becoming sub-tidal, and upper intertidal areas no longer being exposed to inundation. The intertidal that remains within the barrage basin will also have a reduced duration of exposure due to the holding of standing water in the basin.

In absolute terms these options have the greatest impact on the designated area of intertidal habitat through the change in tidal range, and are therefore likely to have the greatest risks in this regard. The direct loss of existing habitat due to the footprint of these barrages, may also be the greatest for any of the options currently proposed.

Final 69 December 2008 There are two contrasting schools of thought about the biological productivity of the remaining intertidal areas. One, that draws upon the tidal power scheme at La Rance (Brittany, France), a rocky estuary with a different morphology to the Severn, suggests that mudflats will increase in stability and their productivity will thereby be enhanced. The other draws upon the tidal barrage on the Eastern Schelde (southwestern Netherlands), which has more of a similar morphology to the Severn (although a very different tidal range), and suggests that foreshores will continue to erode and will become less biologically productive. It should be noted, when citing analogues, that conditions in estuaries vary, particularly in terms of tidal range, sediment sources and configurations of structures. However, these contradictory hypotheses are fundamental to any final conclusion about habitat changes in the long term and require further investigation before any firm conclusions can be reached.

Further it is important to note that even if there were an increase in productivity it should not be concluded that this would necessarily be a nature conservation benefit. The Severn Estuary is designated for its very particular habitats and communities, which have developed due to the unique physical conditions and as a representative of an extreme of estuarine habitat within the United Kingdom.

For the purpose of this stage of option assessment, it is assumed that the relative impact of habitat loss will be in proportion to the area loss due to tidal range change. These options therefore have the greatest risks in this regard.

Birds

It has been noted above that these options present a very large reduction in the area and exposure period of the intertidal habitat. Certain areas of the estuary are used intensively for waterbird feeding and roosting, although information is needed to better understand their distributions. There is, therefore, potential for significant impacts upon water birds. Those birds feeding or breeding in the saltmarsh areas, which may be subject to erosion, are especially vulnerable to the expected changes in tidal range.

Previous studies in the 1980s for the Cardiff-Weston scheme suggested that, in relation to bird interests, the reduction in intertidal area and exposure would be offset by an improvement in the biological productivity of the remaining intertidal. This was considered to be driven by an improvement in foreshore stability and reduction in water turbidity. This finding is under question given the contradictory hypotheses relating to foreshore response described above. Conclusions on the biological productivity of the remaining habitat and its ability to support birds cannot therefore be drawn at this stage. Until this question is investigated and resolved, it is assumed at this stage that the scale of loss of waterbird habitat is in proportion to the intertidal area lost through the change in tidal range.

Final 70 December 2008 A particular feature of the B1 option is that, being located furthest seaward; it offers little opportunity for birds displaced by the barrage to exploit other local intertidal areas for feeding.

By the scale of effect upon tidal range and habitats, these options and B1 in particular, are currently considered to have the greatest risks with regard to impacts on birds. However, much will depend on further investigations of the effects on the quality (as well as quantity) of remaining habitat.

Fish

The protection of several fish species within the Severn, Usk, Wye and Tywi under the Habitats Directive has been discussed above. Other rivers that may be adversely affected include the Rivers Ely, Taff (both already impounded by the Cardiff Bay Barrage), Rhymney, Ebbw and Avon.

For the reasons described above, there are therefore risks of potentially significant effects from a large barrage on important fish such as shad species, lamprey, salmon, eel, sea trout, sturgeon and estuarine fish species due to factors such as changes to migration cues, water quality, habitat, disruption to route of passage including turbine passage. This will have an associated effect upon the angling/ fish activities these support.

Marine Water Quality

By enclosing much, if not all, of the Severn Estuary these barrages will have an effect on water quality: reduced currents may for example lead to reduced turbidity and increased light penetration. There may however also be adverse effects on water quality parameters. Impact on the attainment of WFD objectives will therefore require assessment.

The differences between options are likely to be reflected in the spatial extent and magnitude of the changes in water quality factors. Being the largest schemes, these hold the greatest risks of an adverse effect or the largest benefit if water quality improves..

Historic Environment

The main effects will arise from construction, although geomorphological response may also lead to exposure or loss of features. Archaeological assessment is likely to be limited to the dryland margin. In these areas archaeological sites are quite visible and can be protected by modifications in design or mitigated through comprehensive archaeological excavation. On the Welsh side, the intertidal areas are quite short and are understood to have less archaeological potential.

Final 71 December 2008 Any assessment of the marine archaeological potential is very difficult and undertaking any mitigation almost impossible.

Landscape and seascape

A large barrage could have the following effect on the receiving landscape and seascape: x Changes to the character of the shoreline associated with changes in land use and infrastructure including link roads, power lines and on-shore built development; x Visual effect on views of the Severn Estuary from parts of the Glamorgan and Exmoor Heritage Coasts, Exmoor National Park, the Wye Valley, Quantock Hills and Mendip Hills AONBs and the Gwent Levels Historic Landscape (the different options will have different impacts from different locations); x Indirect effect of reduction in tidal range, loss of salt marshes and changes to water clarity due to reduced turbidity; x The extent of the intertidal zone visible at low water level would be much reduced; x Indirect effect arising from a reduction in the dynamic character of the Estuary including the loss of the Severn Bore phenomenon; x Loss of tranquillity during the construction phase; and x Requirement for significant grid reinforcement through additional transmission lines.

Material Assets

Flood Management

The effects of a large barrage on flood risk are uncertain but more likely to be positive if the required mitigation works to offset any flood defence impacts are satisfactorily undertaken. Predictions are wholly dependent upon the model of geomorphological response that is determined to be most applicable. If, as has been postulated in previous studies, foreshores will accrete, then the stability of defences should be unaffected. If as an alternative hypothesis suggests, the foreshore will erode, then the protection this provides to the defences will be reduced and the stability and effectiveness of existing flood defences will be potentially compromised. This may trigger the need for additional investment to secure flood defences are in a stable position. Increased sedimentation and reduction in wave energy upstream of a barrage appear to suggest upstream flood defences should benefit but reflected wave energy may not benefit downstream defences.

Flood risk benefits could arise if adverse impacts (such as required changes to tidal outfalls to maintain existing standards of protection) are satisfactorily mitigated.

Final 72 December 2008 However, hydrodynamic and geomorphological changes may also have negative implications.

A large barrage may have flood defence benefits in protecting communities and agricultural land within the tidal flood plain upstream of the barrage from the effects of sea level rise and storm surges. Barrages landing at Minehead (B1) and Hinkley Point (B2) may protect the low lying areas of Somerset from tidal flooding as well as the Wentlooge and Caldicot Levels (collectively known as the Gwent Levels) and Avonmouth, which would also be protected by B3.

Any attenuation of surge tides would have a direct benefit by both a reduction of damages on tidal events that overtop defences and also due to avoiding or delaying expenditure to keep pace with sea level rise. This could be a significant benefit for the barrage options, but is not expected to be significant for lagoon options.

The wave climate would be changed upstream of a power generating structure, with barrage options having the bigger effect. The changes have the potential to bring both flood risk benefits and increase risks, depending on the location, type of structure and operating mode. This applies both to the risk of wave overtopping and erosive effects.

The reduced tidal range, particularly affecting the level of low tides, will impact on some land drainage and surface water outfalls into the estuary. The effect will be dependent on the type of power generating structure, the mode of operation as well as the location and characteristics of the outfalls. Some will suffer from a reduced period of free discharge and ‘tide lock’ with a corresponding increase in flood risk unless mitigating measures are introduced. These mitigation requirements have been included in the cost assessments for options within this report on the basis that the standard of service offered by existing flood defence assets should not be compromised.

The changed tidal regime could result in a reduction in the exposure of some outfalls, which may reduce the time available to undertake maintenance work. This may also lead to siltation in some channels and pipework.

The changed tidal regime and wave climate may be a benefit in some locations, but create risks in others.

Navigation

These barrages will affect the operation of the Ports of Cardiff and Newport, the Port of Bristol and Sharpness Docks. Effects will include increased time to navigate through locks required to enable the passage of vessels through the barrage.

Final 73 December 2008 Navigation will be affected by changes in water levels. The reduction in water level at high spring tide will affect those vessels which can only gain access to ports in these high tides. There will be a reduction in tidal range which will increase the access window for all shallower draught vessels into all of the ports within the estuary. Changes in salinity will increase the available draught required by vessels as they will sit lower in water with lower levels of salinity although this is less likely to be an issue for ports in the upper part of the Severn Estuary. Depending on the morphological response to a scheme, channels and other navigational areas might become more prone to siltation. Morphological changes may therefore change existing dredging and maintenance regimes.

The increase in low water levels will result in the permanent immersion of marine structures in the whole of the Severn Estuary which were previously uncovered at low water and could be maintained during these times. However, it will also allow greater flexibility in marshalling vessels within the estuary.

Further consideration of navigation issues is included in section 6.2, including proposed mitigation of the above effects.

Final 74 December 2008 Shoots Barrage (B4) and Beachley Barrage (B5)

Hydrodynamics and Geomorphology Hydrodynamics The hydrodynamic effects of barrages located this far upstream show a relatively small reduction in top water level upstream of the barrage and the total tidal range being reduced by approximately 50%. The downstream tidal regime will be slightly influenced with the tidal range reduced (high water slightly lower and low water higher by up to 1m) over a seaward distance of some 20km.

Geomorphology The nature of potential geomorphological responses (both up and downstream) to enclosure by a small barrage is uncertain and needs further assessment.

These options are smaller but they are located in a more dynamic part of the estuary. Construction impacts have the potential to be significant and far reaching, with subsequent requirements for long term maintenance dredging activities to facilitate navigation.

Sedimentation

The estuary’s sediment budget, in comparison to the size of the enclosed basin for these barrages, is relatively large, and therefore there is a potential risk of sedimentation affecting their operation. Maintenance dredging to maintain the tidal prism and navigation may be required during construction and operation, with associated environmental impact. The design of these options uses a large number of high level sluices to manage this risk, but nonetheless the risks are greater for these options relative to the larger impoundments of barrages further downstream. In addition, the fluvial sediment load is a larger proportion relative to the impounded basin volume.

Habitats, biodiversity, flora and fauna Habitat These options would risk a substantial reduction in area and tidal exposure, of saltmarsh and other intertidal habitats within the Severn Estuary cSAC/SPA and Ramsar, and the Wye SAC, for much the same reasons as have been described above. The great majority of intertidal upstream of the barrages will be lost, including reedbed, saltmarsh and intertidal mud.

These options result in a smaller absolute reduction in the designated area of intertidal through the change in tidal range, and are therefore considered to pose lesser risks than larger barrages in this regard.

Final 75 December 2008 Birds

It has been noted above that these options are likely to lead to a reduction in the area and exposure period of the intertidal. Certain areas of the estuary are of more value than others for water birds; the area upstream of options B4 and B5 being less important for some species although there are exceptions. There is, therefore, potential for impacts upon waterbirds although the area affected is much less than that for the larger barrages.

Fish

These options create a physical impediment to migratory fish movements between the Outer Bristol Channel and the River Wye and Severn. Option B5 is upstream of the Wye but there is still some risk of impact (both to Wye and Usk populations) because shad, salmon and possibly lamprey may travel upstream in the Severn before entering the Wye and Usk.

There are likely to be potentially significant effects from a small barrage on shad species, lamprey, salmon, eel, sea trout, and sturgeon (but possibly less so than for large barrages in relation to estuarine fish species). This is due to factors such as changes to migration cues, water quality, habitat, and disruption to route of passage including turbine passage. This will have an associated effect upon the angling/ fish activities these support.

Although these barrages enclose fewer tributary rivers than the larger barrages they nonetheless pose the significant risk of major reductions in population of important migratory fish within several rivers, including salmon and shad in the Wye and Usk. Risks relative to lagoons are not readily discerned.

Marine Water Quality

These options will have an effect on water quality, and their impact on the attainment of WFD objectives will require assessment.

The positions of these barrages in relation to point source discharges to the estuary imply that both benefits and disadvantages for water quality could arise. For example, concentrations of cadmium might reduce landward of a barrage, because the main sources are seaward of B4. In contrast, concentrations of nickel, copper and other substances at the head of the estuary could increase, partly because there is less scope for their dispersion. There may also be less potential for a major reduction in water turbidity.

The other effects on water quality have been previously discussed. Being smaller in scale these barrages may be expected to hold a smaller risk of water quality deterioration, that is still significant. Equally, any potential improvements in water quality such as those caused by reduced tidal currents, reduced turbidity and

Final 76 December 2008 increased light penetration, will also be less significant. The smaller impoundment of the Beachley Barrage may result in increased risk of eutrophication effects caused by nutrient inputs from rivers.

Historic Environment

For these barrages the main risks come from construction across the intertidal areas. There is experience from the building of the Second Severn Crossing, where comprehensive archaeological surveys and subsequent excavations were undertaken on both the English and Welsh sides of the estuary.

The risks of impact on the dryland margins is likely to be less than for the larger barrages, but the need for new large drydocks in the intertidal area is a significant factor.

Any assessment of the marine archaeological potential within the deepwater channels is very difficult and undertaking any mitigation almost impossible.

Landscape and seascape

The potential consequences of the small barrages in terms of landscape and seascape are: x Changes to the character of the shoreline associated with changes in land use and infrastructure including link roads, power lines and on-shore built development; x Reduced intertidal visible at low tide; x Indirect effect of reduction in tidal range and changes to water clarity due to reduced turbidity; x Effect on views of the estuary from the Wye Valley, Cotswolds and Mendip Hills AONB and the Gwent Levels Historic Landscape; and x Requirement for significant grid reinforcement but not on the scale of large barrages.

Other than at close proximity to land falls, as these options are smaller they may be expected to pose less risk than the larger barrages.

Material Assets

Flood Management

The flood management issues associated with a barrage have been previously discussed. A barrage at English Stones or Beachley may have flood defence benefits in protecting communities and agricultural land within the tidal flood plain upstream – primarily the tidal flood plain of the Gloucestershire banks on the Severn.

Final 77 December 2008 In keeping with larger barrage options, the implications for flood defences have short- term and longer-term scenarios, with considerable uncertainty about the long-term morphological evolution both upstream and downstream of a barrage. These differences have more significant implications for management of the tidal basin, as an erosive regime could lead to proportionately more subtidal in-filling over the life of the barrage.

Navigation

These barrages will affect the operation of the Ports within Gloucester Harbour Trustee’s jurisdiction, the largest of which is Sharpness Docks. Effects will include increased time to navigate through locks required to enable the passage of vessels through the barrage.

Navigation will be affected by changes in water levels. The reduction in water level at high spring tide will affect those vessels which can only gain access to ports in these high tides. There will be a reduction in tidal range which will increase the access window for all shallower draught vessels into all of the ports within the estuary. Changes in salinity will increase the available draught required by vessels as they will sit lower in water with lower levels of salinity. Morphological changes will change existing dredging and maintenance regimes.

Further consideration of navigation issues is included in section 6.2 including potential mitigation works.

Russell (Fleming) Lagoon (L2) and Generic Tidal Lagoons (L3)

Hydrodynamics and Geomorphology Hydrodynamics The hydrodynamic effects will depend greatly on the design of the lagoon and whether it will drain down completely at low tide. The effects are nonetheless expected to be similar to the smaller barrages in that the main effects (a potential reduction in top water level) and reduction in tidal range are contained within the impounded basin.

Due to a reduced estuary width, there may also be a reduction in tidal range and foreshore exposure outside the lagoon impoundments. The scale of change is uncertain and needs to be explored further, but is likely to be smaller than for large barrages.

Geomorphology The nature of potential geomorphological responses to the narrowing of the estuary as a result of lagoon structures is not well-explored. It is nonetheless likely that a Final 78 December 2008 series of major lagoons would alter the estuary regime: by leading to increased current velocities they could cause extensive erosion and transportation of sediments into the inner estuary. Construction impacts will also be important with potentially significant impacts on adjacent subtidal channels.

Whilst the spatial extent of impact from lagoons may be less compared to the larger barrages, the lagoons are not obviously sited in areas which minimise their overall geomorphological impact. Only following detailed study would it be possible to optimise their effects on mobile features.

Sedimentation

The estuary’s sediment budget, in comparison to the size of the enclosed basin for each lagoon, is substantial and there is likely to be a considerable cost entailed with the management (probably through dredging) of sedimentation within the basin. Maintenance dredging might also be required to maintain navigation throughout the estuary. This would in itself have ecological and water quality impacts that would need to be assessed along with the implications for the structure’s carbon footprint and wider sustainability.

Habitats, biodiversity, flora and fauna Habitats The effects of these options on tidal range are not as readily predicted as for the barrages, but are assumed to risk a reduction (in the impoundments) in the extent of saltmarsh and other intertidal habitats within the Severn Estuary cSAC/SPA and Ramsar, and the River Usk and River Wye SACs. The area enclosed and therefore potentially affected is much smaller than for a large barrage.

Under lagoon options the tide is not likely to be truncated and the reduction in tidal prism is modest compared to the overall system. Tide propagation past the lagoons may be impacted but to a lesser degree than by construction of a barrage. The effects on tide levels and hence intertidal habitats outside the lagoons are therefore likely to be relatively minor.

The degree to which the lagoon footprint would directly enclose intertidal area, varies between land-connected lagoon options. An offshore lagoon would mainly affect sub-tidal habitats, that are nonetheless protected in some locations. Conversely, a land-connected lagoon would mainly enclose intertidal habitat. The direct loss of habitat due to the footprint of the lagoon schemes, or sedimentation management activities such as dredging, will therefore vary. Indeed, there are potential opportunities to create areas of intertidal habitat within lagoons, although this would be at the expense of reduced power generation.

Final 79 December 2008 Birds

The principal effects on waterbirds from these options would relate to the effects of a land-connected lagoon on the intertidal. As has been stated above, the area affected will be smaller than for the larger barrages. However any effect would also be influenced by the relative importance of the impounded area as intertidal foraging habitat for waterbirds. The Welsh Grounds, Bridgwater Bay and Peterstone Flats, i.e. the locations for some of the lagoons, are noted for their importance to several species of waterbirds. An offshore lagoon would have a much reduced effect on bird feeding areas. Effects of the lagoon structures on geomorphological processes such as sediment erosion and redistribution could also potentially affect the quantity and quality of remaining habitat.

Nonetheless, in comparison to the large barrage options these options may present less risk with regard to impacts on birds. Relative risks compared to smaller barrages cannot be assigned at this stage.

Fish

These optionsare likely to pose an obstruction to migratory fish movements between the Outer Bristol Channel and the Avon, Parrett, Usk, Wye and Severn.

There are therefore risks of potentially significant effects from lagoons on shad species, lamprey, salmon, eel, sea trout, and sturgeon. Land-connected lagoons in particular may interrupt the continuity of the intertidal and thereby affect movement and survival of estuarine and migratory fish species. This will have an associated effect upon the angling/ fish activities these support.

It is uncertain as to what the risks are to migratory fish in comparison to the larger barrage options, although they are still regarded as being significant. There is a poor understanding of fish movements in the estuary and the effect of the lagoons on tidal currents and geomorphological process. This makes it difficult to ascribe an assessment of impact of lagoons on fish movements per se.

Marine Water Quality

Marine water quality issues have been previously described. It is likely that the lagoons would be designed to retain a minimum amount of water compared to the tidal exchange. The majority of the water retained within each lagoon would therefore be flushed out on each tide. There is therefore unlikely to be a significant issue in relation to water quality retained within the lagoon, although this will be dependant on the nature of sediment interactions.

The lagoons would be likely to alter the tidal current regime within the estuary. Depending on the scale of lagoon development, the effect upon the estuary’s current regime and water quality status is likely to be less than in comparison to the larger

Final 80 December 2008 barrage options. As lagoons are unlikely to affect estuary currents to the same extent as large barrages, they are therefore less likely to result in reduced turbidity and increased light penetration. Nonetheless, these options may pose less risk in relation to compliance with the Water Framework Directive’s objectives, compared to barrage options.

Historic Environment

Land-connected lagoons impound the large areas of tidal mudflats in the Severn Estuary. These mudflats have produced most of the best archaeological sites of all periods with the Severn Estuary and Levels as a whole.

Given that the lagoons require embankments built with excavated foundations and will introduce turbines and sluices which will create a whole array of new channels, these types of structure may well present the greatest threat to the historic environment.

These options are capable of full archaeological assessment, though working at the limit of the tidal range is very challenging. Dryland and marine archaeological sites will probably remain largely unaffected.

Landscape and seascape

The potential consequences of land connected lagoons on the Welsh and English sides of the Severn Estuary to the landscape and seascape are:

x The lagoons would generally be located in the upper estuary adjacent to low lying areas where they would be visible from elevated vantage points including Penarth and Brean Down. The visual effect would be most prominent at low tide when the embankment would be fully exposed, and

x There may be a visual effect on the Wye Valley, Quantock hills and Mendip Hills AONBs, the Glamorgan and Exmoor Heritage Coasts, Exmoor National Park and the Gwent Levels Historic Landscape.

There is likely to be the requirement for significant grid reinforcement through new transmission lines, although on a smaller scale than for the larger barrages.

Material Assets

Flood Management Final 81 December 2008 The flood management issues have been previously described. A tidal lagoon does not provide the same level of flood defence as a barrage, but equally impacts on land drainage systems are less (for a land connected lagoon such as L2) or non existent for offshore impoundments. Land-connected lagoons offer protection to the contained shoreline. However, there may be negative impacts in terms of changing geomorphology which may in turn affect existing flood defences within the lagoon. Offshore lagoons provide no additional flood defence benefit and the increased currents between the lagoon and the foreshore may result in increased coastal erosion.

Navigation

Tidal lagoons do not impede the passage of shipping and do not require ship locks. However, changes in currents and consideration of ship impacts on marine structures do require consideration. Effects may also include changes to the existing dredging and maintenance regimes for Ports within the Estuary if tidal lagoons influence nearby navigation channels. It is assumed for the purposes of comparative assessment that the above impacts can be satisfactorily mitigated.

Tidal Fence (F1a and F1b)

In broad terms the Tidal Fence options presents similar risks to the barrage options on similar alignments (F1b and B1, F1a and B3). The issues are therefore not repeated here. Areas of potential difference are summarised below: x The accelerated currents through and around the Tidal Fence are likely to exert geomorphological changes, the nature of which is not yet explored but could be adverse for intertidal habitats locally; x The greater ease of water passage through the structure suggests that risks of changes to water quality should be reduced, but the variations in velocity across the fence suggest turbidity levels could be increased; x The area of intertidal lost owing to the altered tidal regime is likely to be smaller than for a barrage on a similar alignment. This reflects the lesser amount of energy converted, therefore having lesser impacts on habitat for birds (setting quality considerations aside); x Issues arising from the divergent hypotheses over the long-term geomorphological evolution of the Severn Estuary would apply here; x The structure has more open passages and therefore may not hinder fish passage to the same degree as barrage structures in the same location. The accelerated currents through these passages are not expected to prejudice fish movements passively on the tide. The relative risks of fish damage from the turbines adopted under this option requires further study; x The accelerated water currents through the structure requires careful consideration in relation to navigation, both in terms of safety of passage through the structure and potential for ship impact;

Final 82 December 2008 x Connections with the land and the scale of the construction infrastructure may pose less risk to the historic environment, and may mean that some archaeological assessment and mitigation is possible; x The accelerated water currents through the shipping channel will also greatly increase the potential for scour along the channel. Structures to either side of the channel will require heavy protection against erosion. Similarly, the open sections at either end of the structure will likely experience accelerated water currents which will likely lead to erosion of the intertidal areas adjacent to the Tidal Fence which would require heavy scour protection.

Although there are some possible advantages in terms of impact in comparison to the larger barrages, there is uncertainty over the Tidal Fence’s effects owing to the limited understanding and experience in the application of this type of project.

Tidal Reef (R1)

In broad terms the Tidal Reef presents similar risks to barrage option B1, adopting a similar alignment. The issues are therefore not repeated here. Areas of potential difference are summarised below: x The accelerated currents through the Tidal Reef are likely to exert geomorphological changes, the nature of which is not yet explored but could be adverse for intertidal habitats locally; x The greater ease of water passage through the structure suggests that risks of major water quality impacts should be minimal; x The area of intertidal lost owing to the altered tidal regime is likely to be smaller than for a barrage on a similar alignment., therefore having lesser impacts on habitat for birds (setting quality considerations aside); x Issues arising from the divergent hypotheses over the long-term geomorphological evolution of the Severn Estuary would apply here.

Although there are some potential advantages in terms of impact in comparison to the larger barrages, there is uncertainty over the Tidal Reef’s effects owing to the limited understanding and experience in the application of this type of project.

Severn Lakes (U1)

Severn Lakes adopts a sinuous alignment near to the barrage option B3. It is also a much wider structure, being 1km wide to accommodate the other non-tidal power related infrastructure. Whilst impacts on tidal range and geomorphology are assumed to be similar to a more typical tidal power project, it would also appear to pose greater environmental risks. Many of the issues are similar to option B3 and are therefore not repeated here. Some of the points of potential difference to option B3 are summarised below:

Final 83 December 2008 x The wider structure will result in greater footprint and consequential loss of habitat; x The introduction of multiple uses onto the structure poses risks of additional disturbance to protected bird and fish species using nearby areas (e.g. noise and lighting); x The multiple uses of the structure poses additional risks in terms of impacts upon water quality; x The much larger scale of structure suggests that impacts on the land and seascape will be greater.

This assessment does not take into account the scope for wider economic benefits (e.g. associated economic development) under this option.

5.4 Modes of Operation

For the purposes of differentiating each option, the quantitative analysis used within the Assessment Framework has focused on a “base case” for each option in terms of its operational mode. This is based on the premise that many of the options have similar opportunities for optimising energy through the use of ebb and flood generation, pump-assisted operation and/or the use of multiple basins and/or operating different options in combination. The logic used is that those options that perform best in their “base-case” mode will also offer relatively better opportunities for optimisation by comparison with options that have a higher cost of generation. The “base-case” mode is the operational mode which offers the best unit cost of electricity. Previous studies have indicated this is ebb-only generation for the tidal range technologies used in barrages and lagoons. More permeable options using the kinetic energy of the tides are more constrained in their operational modes and operate only in ebb and flood generation mode.

In environmental terms, different modes of operation have different effects and these are briefly considered below for each of the options:

Small Tidal Barrages B4 and B5

These utilise Straflo type turbines because of the physical restrictions of their locations. Straflo turbines have the benefit of requiring smaller caissons than their Bulb turbine counterparts but have the disadvantage that they are not designed to operate in reverse mode to either pump or generate on the flood tide. Because of the higher sedimentation risks associated with the smaller barrage sites, low level inflows into the basin by generating on the flood tide need to be avoided so the fact that the Straflo turbine is only able to operate one way is not necessarily disadvantageous, particularly when consideration is given to the energy outputs which are much more easily absorbed by the grid in comparison with the larger installations.

Larger Tidal Barrages and Tidal Lagoons B1, B2, B3, L2 and L3

Final 84 December 2008 These utilise Bulb turbines that can operate in flood and ebb mode and can also be used for pumping, albeit at some loss of overall efficiency. Increases in energy yield from flood pumping have been estimated in previous studies (EP57) to improve energy yields by less than 5% Flood pumping would start at high water levels and mitigate some of the loss in high water levels upstream of the barrage. Generation during both ebb and flood tides results in lower overall energy yields but a more distributed energy profile over the tidal cycle. However, ebb and flood generation results in a further reduction in total tidal range with the high water level being lower than the equivalent ebb only generation mode.

Tidal Fences F1

A tidal fence operates in both ebb and flood tide modes. The timing of generation is also different and thus operation of a tidal fence with a barrage or lagoon located further upstream is in theory possible. However, the reduction in tidal range, and in particular the reduction in high water level resulting from tidal fence generation, compromises the tidal range available from the barrage with the consequential impact on cost per unit energy.

5.5 Mitigation and compensation issues

As should be evident from the previous sections, all options present risks to internationally designated bird and fish populations and their habitats. Certain of these risks may lead to effects that cannot be fully mitigated – for example habitat loss for birds, and barriers to fish passage. To comply with the requirements of the Habitats Directive, there will therefore be a need to provide ‘compensatory measures’ under the Directive to ensure ‘coherence of the Natura 2000 network’, subject to the other tests under the Habitats Directive being satisfactorily addressed.

A high-level review of the potential for mitigation and compensation under the Habitats Directive is currently underway. This review is likely to conclude that the scale and nature of the impacts presented by schemes of this sort pose unprecedented challenges, and that based on European Habitats Directive guidance there are currently few (if any) measures available with a high degree of confidence in their effectiveness. It will therefore identify a number of requirements for additional studies to establish whether credible mitigation and compensation packages can be developed. The options having the largest quantitative impacts on intertidal areas, and presenting the greatest obstruction to fish survival and passage, are seen to pose the most risk in this area.

Guidance on providing compensatory habitat, existing practice and precedent has established that provision should be at a ratio that exceeds parity with the area of habitat lost to recognise the uncertainty and risks of establishing a habitat that maintains the ecological functions of the habitat that is lost.

Final 85 December 2008 The scale of potential compensation and its potential effect on a European site is unprecedented. This creates an additional element of uncertainty around quantifying and managing the risk.

Furthermore, it may be necessary to take measures in addition to those required by the Habitats Directive, for example in relation to other nature conservation policy and legislation, water quality, recreation, historic environment, and visual impact. These will need to be considered in more detail under Phase 2 of the Study.

5.6 Ecosystem goods and services

Estuaries and coastal habitats provide a wide variety of ‘ecosystem goods and services’ including carbon sequestration, nature conservation, flood defence, transport, treatment of water pollution, and recreational opportunities – indeed many of the issues discussed in previous sections. Work on ecosystem goods and services is not being undertaken as part of the SEA but the SEA will be able to provide data to, and be informed by, analysis of this sort that is being undertaken within a separate component of the feasibility study.

5.7 Conclusion

Predictions about the possible ecological and socio-economic impacts hinge upon an understanding of possible geomorphological response both to barrages and to lagoons. There are currently divergent schools of thought in relation to such responses, and this means that all considerations must be subject to considerable uncertainty.

All options present a wide range of potential issues that require significant research, but clearly the central focus of the investigations must concentrate upon geomorphological responses and the risks associated with the two principal theories.

Any qualitative review of options at this stage (prior to detailed SEA) is therefore made on the basis of information currently available. The extent of environmental impacts will continue to raise uncertainties until more detailed assessment is possible during the SEA scoping and assessment phases.

Final 86 December 2008 SECTION 6

CIVIL, MECHANICAL AND ELECTRICAL ENGINEERING CONSIDERATIONS

Final 87 December 2008 6 CIVIL, MECHANICAL AND ELECTRICAL ENGINEERING CONSIDERATIONS

High level reviews of the primary engineering considerations have been undertaken for each of the options. The purpose of this review is to identify any technical issues with the scheme designs which may affect their technical feasibility. Many of the schemes use similar methods and technologies, albeit applied in different locations and to different scales. Some use more novel technologies which are being demonstrated at relatively small scales but not in tidal range applications. Some technologies are at conceptual stage and have not been demonstrated at full scale.

The form of the civil, mechanical and electrical engineering technologies incorporated in each scheme is appraised and key technical risks and issues identified. These include susceptibility to varying ground conditions, adaptability for rising sea level and durability by design.

Navigation issues have focused primarily on the provision of appropriately sized locks within the barrage options.

Turbine and generating equipment proposals are also discussed. Most are largely based on conventional hydropower equipment, the exception being the tidal current turbines utilised in the Tidal Fence and the novel proposals for the Tidal Reef.

Electric grid connection and requirements for the reinforcement of the grid have been examined and grid reinforcement costs assessed at a high level.

6.1 Civil Engineering

6.1.1 Barrage Construction

Embankment Construction

B1, B2 and B3 Barrages

Available designs for barrage schemes include embankment sections based on the traditional use of materials in a marine environment. For the B3 barrage alignment, the STPG Report 1989 proposed a single embankment formed of a tipped rock control structure on the seaward side and an hydraulically placed sand fill on the impounded side contained by a series of rock mounds (“Christmas tree” construction). The exposed faces would be protected with concrete armour units (dolos) on the seaward side and armourstone on the impounded side. Dolos units are no longer widely used but alternative Accropode units would be suitable. Granular filter layers of stone would be used throughout.

Final 88 December 2008 The crest level adopted by STPG was conservatively set to protect against wave action. Sea level rise as a consequence of climate change was not allowed for in the STPG design and the crest height would need to be reviewed in line with current sea level rise predictions. It would also be reasonably straightforward to design in the facility to increase the height of the embankment in the future if sea level rise exceeds the design levels.

The design would be a robust, possibly conservative, form of embankment for B3 which could also be applied to B1 and B2. Nevertheless, some issues with the embankment design should be addressed to improve its durability. These include:

x a review of the filter layers between the sand and rock control structures which should be generously proportioned; x a review of the stability of slopes to confirm that temporary factors of safety are no lower than 1.3 for appropriate soil parameters; x a review of crest levels to provide tolerance for climate change.

There would be the potential to rationalise the embankment form for each barrage at detailed design stage where ground conditions are less challenging. The embankments for barrage B1 would be founded on more competent rock and gravel than the embankments for B3.

Being further seaward, the B1 embankments would be more exposed and could therefore require higher crest levels and heavier armouring on both the eastward and westward faces.

The ground conditions along the B2 and B3 embankments are more challenging on the English side and would likely require significant dredging of at least 2 metres. Along challenging ground conditions, ongoing consolidation and differential settlement could lead to operation and maintenance difficulties. There would also be the risk of scour at the toe of the embankment requiring scour blankets.

B4 and B5 Barrages

The original reports for B4 (MRM Partnership in association with AV Hooker – The Hooker Barrage1990) proposed an embankment built in three metre lifts, with a hydraulically placed sand fill core contained by a series of rock mounds on both sides. Both faces would be protected by rock armour. A scour blanket is provided in the section.

This is a reasonably simple embankment form which could be applied to barrages B4 and B5. Embankment construction for B4 and B5 would be less challenging than for the more seaward barrages as the inter-tidal rock outcrops and sandy sediments at B4, and the sands at B5, provide reasonably good foundations for the embankments. Also, the embankment construction would be substantially above mean low water spring tide and therefore could be constructed in the dry.

Final 89 December 2008 Some issues with this embankment design should be addressed to improve its durability. This would include:

x a review of the protection against wave action; x a review of protection against wave and current action during construction; x a review of crest levels to provide tolerance for climate change.

Key delivery risks for embankments of all barrages is the availability of large volumes of rock which could impact on the market and may require a dedicated source. Sand fill would also be dependent on the availability of dredging plant which is currently very limited in the UK. Dredging costs are sensitive to fuel costs. The larger B1, B2 and B3 barrages are more susceptible to these risks.

Caisson Construction

B1, B2 and B3 Barrages

The 1989 STPG Report "Severn Barrage Project - Volumes III A and III B - Civil Engineering" provides a comprehensive review of the Civil Engineering and Geotechnical requirements of the B3 Cardiff to Weston barrage. Although the report was written nearly 20 years ago, and construction techniques have advanced in those years, it is considered that most of the issues raised and conclusions reached are still valid today, and the report can be used as a basis for determining the viability of the B3 Cardiff to Weston barrage scheme and applying these to the B1 and B2 barrages. Similar principals could also be applied to the F1 tidal fence proposal subject to a more thorough understanding of the fence configuration. There are however some aspects of the proposals which need to be reviewed due to the passage of time, or for other reasons.

The B3 barrage would consist of a continuous line of reinforced concrete caissons stretching across the estuary and three lengths of rock-armoured embankment. There would be 175 massive caissons up to 80m square in plan and up to 45m in height. 54 of the caissons would contain turbines and 46 would contain sluice gates. The B1 and B2 barrages would require caissons of relatively similar scale but correspondingly larger numbers relative to their longer lengths.

Rock exists along the length of the B1, B2 and B3 barrages at, or close to the surface of the bed of the estuary. The surface rock is usually weathered but sound rock exists at lower levels, varying between about -20m AOD and -35m AOD along the B3 alignment. The proposal would be to expose the sound rock by dredging a trench in the weaker overlying layers of rock along the length of the barrage, and to overlay this with a mattress of crushed rock on which the caissons would be founded. The rock mattress under each caisson would grouted up immediately after that caisson has been installed.

Final 90 December 2008 The barrage structure would consist of a series of abutting cellular reinforced concrete caissons. The caissons could be constructed in dry dock, floated out to their location on the barrage, lowered onto the pre-prepared foundations and ballasted with sand for stability.

Following a high level review of the STPG caisson proposals, the following key issues have been identified which require more detailed study:

x The STPG report proposed seven dry docks to accommodate the simultaneous construction of several caissons for the B3 barrage and it is reasonable to assume similar infrastructure requirements for B1 and B2. The construction of these dry docks would be a major component of the whole barrage scheme which would depend on the viability of their construction. Further consideration of the form and location of the dry docks will be required if any of these schemes are shortlisted. This should include consideration of issues of draught required for caisson stability which will affect the size of the dry docks. Consideration should also be given to the particular requirements for deep caissons; x Several different measures are available for preventing deterioration of the caissons with varying effects on maintenance requirements and initial construction costs. Some refinement of these options should be carried out to improve certainty of caisson cost; x Consideration should be given to simplification of the caisson design without increasing caisson weight or incurring loss of facility. Recent developments in computer aided design should facilitate such refinement; x Updated consideration should be given to shipping impact forces and the opportunity to link caissons to improve resistance to impact; x Consideration is required to the effects of climate change on caisson height, including how measures might be designed in for the future adaptation of caissons to deal with sea level rise and associated increase in wave heights and storm surges.

B4 and B5 Barrages

The 1990 Report on B4 provides an overview of the caisson requirements for the B4 inner barrage. Although the report was written nearly 20 years ago, and construction techniques have advanced in those years, it is considered that most of the issues raised and conclusions reached are still valid today, and the report can be used as a basis for determining the viability of the B4 inner barrage scheme and applying these to the B5 Beachley Barrage. There are however some aspects of the proposals which need to be reviewed due to the passage of time, or for other reasons.

The main structural components of the B4 barrage are as follows:

x In-situ sluice caissons located on the Welsh rock platform founded on bedrock;

Final 91 December 2008 x Four sluice caissons placed on excavated rock foundations where the bed level is too deep for insitu construction; x 13 turbine and sluice caisson, and 2 turbine only caissons; sluices where provided are located at high level (which helps to prevents heavier sediments from being carried into the basin on the incoming tide) and the turbines are located at low level; x Two plain caissons.

Following a high level review of the original caisson proposals, the following key issues have been identified which should be the focus of more detailed studies for short listed options:

x The original report suggests that the dry dock for the caisson construction could be located in the Northwick deep anchorage upstream of the barrage. This recommendation was made before the Second Severn Crossing was built. It is considered that floating the caissons through the navigation span of the new bridge would be ill-advised. The Second Severn Crossing is designed for impact from ships up to 10,000 dwt (or 6000 dwt Class 1 ice- strengthen). The proposed caissons are likely to have 10 times the mass of 10,000 dwt vessel and as they are far more rigid than a steel ship the impact force would be of a higher order of magnitude than the impact force for which the piers of the Second Severn Crossing have been designed. An impact between a caisson and the main pier of the Second Severn Crossing would almost certainly result in the collapse of the main spans of the bridge, and, however carefully the caissons are moved, the risk of an impact is unacceptably high. The dry dock or docks for caisson construction therefore need to be located downstream of the bridge for the B4 Inner Barrage where a deep water channel exists (or can be dredged) out into the main navigation channel. x Several different measures are available for preventing deterioration of the caissons with varying effects on maintenance requirements and initial construction costs. Some refinement of these options should be carried out to improve certainty of caisson cost; x Updated consideration should be given to shipping impact forces, taking account of the shipping sizes that are permitted to pass beneath the Second Severn Crossing; x A review of the relative merits of steel and concrete caisson construction, together with a cost comparison at an appropriately high level; x Consideration is required to the effects of climate change on caisson height, including how measures might be designed in for the future adaptation of caissons to deal with sea level rise and associated increase in wave heights and storm surges and associated increase in wave heights and storm surges.

Final 92 December 2008 6.2 Lagoon Construction

L2 Fleming Lagoon Wall Construction

The wall enclosing the Fleming Lagoon consists of a typically 11 metre high by 13 metre thick double- leaf gravity wall. The core of the wall consists of "dredged material and possibly imported material such as clean construction and demolition waste products". The core is retained by two 500mm thick vertical reinforced concrete slabs. The slabs which are 6m wide are precast and monolithic over the full height of the wall (14m). The slabs on opposite sides of the core are joined by different methods depending on the ground conditions encountered. These options are described in the Table 6.1 below:

Fleming Description Example Areas of Use Wall Option 1A Twin 11m high panel Good ground conditions secured together with tie such as exposed shallow rods (no anchors) rock, fill must remain 1B Single 11m and 14m high Good to Moderate ground panels secured together conditions such as weaker with tie rod and 3m anchor exposed rock, fill must on one side (ie 14m) remain dry unless anchors are designed to provide suitable stability which may require prestressing or substitution with piles 1C Twin 14m high panels Moderate ground secured together with tie conditions such as exposed rods and 3m anchors' on weak rock, fill must remain both sides dry unless anchors are designed to provide suitable stability which may require prestressing or substitution with piles 2A Twin 11m high panel Moderate ground secured together with PC conditions braces (no anchors) 2B Single 11m and 14m high Moderate to poor ground panels secured together conditions with PC braces and 3m anchor on one side (ie 14m)

Final 93 December 2008 Fleming Description Example Areas of Use Wall Option 2C Twin 14m high panels Poor Ground Conditions secured together with PC braces and 3m anchors on both sides 3A 11m high box caisson with Poor Ground Conditions in no anchors exposed areas 3B 11m high box caisson with Poor Ground Conditions in single row of anchors exposed areas

Each of these proposed wall constructions has their own structural viability and costs. Their use would vary, dependant on the ground conditions encountered within the Welsh Grounds. Although in general the proposals are all viable, stability for the tie rod solutions are dependent on whether the fill within the wall can be kept dry or whether it will become saturated by water ingress between the precast wall units and fill. Saturation of the fill causes buoyancy uplift within the fill which reduces the stability of the structure. If it can not be guaranteed that the fill will remain dry, which in practice is implausible, the anchors would need to be designed to provide suitable stability which may require pre-stressing or substitution with piles.

Given the diversity of the methods of construction of the wall the proposed range of solutions are likely to be able to meet the requirements of the varying ground conditions within the Welsh Grounds.

Further consideration should be given to the level of sea level rise and associated increase in wave heights and storm surges which the wall construction should accommodate. As a minimum, the wall should be designed for current predicted sea level rise over the design life. However, it is also noted that unlike traditional embankment and caisson construction as proposed for the barrages, it would not be straightforward to design in the facility to increase the wall height in the future should sea level rise exceed the design level.

Further consideration is also required on how to achieve closure of the lagoon with the proposed wall panel construction. High velocities will occur through the gaps as the lagoon approaches closure and it is questionable whether the partially filled wall panels at the gaps will remain stable under these conditions. Erosion caused by the velocities through the gaps will increase the risk of instability. Therefore, at the position of closure the wall units may need to be replaced with rockfill embankments, constructed on extensive bed protection if the embankments are to be constructed on sand.

Final 94 December 2008 Other areas of concern that need to be addressed during further development of this wall concept are:

x The wall height may have to be higher than currently proposed to allow for varying ground levels and varying ground conditions x Potential failure of large section of structure if a single panel fails x Risk of damage and failure should the structure be hit by shipping vessel

Consideration will also need to given to the durability of the structure in order to meet the 120 year design life requirement, in particular the potential failure of joints.

Embankment Construction for Lagoons

Section 3 listed the submissions in response to the Call for Evidence which related to lagoons within which were a variety of forms of construction which could be applied to the L3 land connected lagoon concept. In addition, lagoons could also be constructed of traditional marine embankment or wall construction such as has been applied in the designs available for the B3 and B4 barrages. These various forms are considered below.

Traditional marine embankment construction

A traditional form of embankment, based on the barrage proposals described above, could be applied to lagoon construction. The embankment form would vary along a lagoon embankment with the varying level of exposure and varying ground conditions. Development of such a design would need to take account of similar issues to those described for the barrages. Lagoons require longer lengths of embankment per volume impounded than barrages and it is considered that the application of this form of wall would be economically unfeasible.

Halcyon Pile Supported/Modular Barrier Construction

The proposed Halcyon construction consists of a line of "mini-caissons" spanning between "support columns" at 20m centres. The concrete panels are seated on vertical piles. The support columns consist of a combination of vertical and raked piles and a fabricated structure of steel tubes through which the piles are drilled and grouted, and to which the mini-caissons are attached. The mini- caissons are elliptical in plan, 20m long and 4m wide at the thickest point. The walls of each unit are 300mm thick with a reinforced concrete base. Each 5m deep caisson would be floated out to its required location, guided into position by the support column, and sunk on top of the previous segment, ensuring that each joint is sealed. The support column structure would be also fabricated on shore and floated out to site where it would be accurately positioned. Prior to pile drilling, the tubes act as "legs" for the structure.

Final 95 December 2008 The application of this form of construction to lagoons requires further consideration of the following potential issues:

x It is anticipated that the life of the structure is only 60 years with an extension to 120 only by significant replacement of major components of the structure including a significant quantity of new structural steelwork.

x As a minimum, the wall should be designed for current predicted sea level rise and associated increase in wave heights and storm surges over the design life. However, it is also noted that unlike traditional embankment and caisson construction as proposed for the barrages, it would not be straightforward to design in the facility to increase the wall height in the future should sea level rise exceed the design level.

x Further consideration is also required of the wall detail at the positions of lagoon closure where high velocities through the gaps as the lagoon approaches closure are likely to increase pressures on the wall and could lead to erosion of the bed. x Raked piles will prove to be a hazard to vessels and will be vulnerable to damage from shipping impact and therefore require navigation routes with sufficient clearance from the structure. x Any failure to seal any joint within the structure could lead to internal stresses, in particular it will be important to seal the joint between the underside of the bottom caisson and the seabed in order that erosion beneath the structure does not occur. Halcyon's current proposal includes the use of geotextiles and rock fill to ensure this, but states that "seepage need not be entirely eliminated", this would need to be resolved, possibly including testing. x There is no vehicular access along the top of the wall and no provision for inspection, maintenance or the replacement of turbines or sluices. Therefore, all access for inspection and maintenance would be from the sea. The maintenance regime would therefore need to be appraised and allowed for in the whole life costing. x Application of the construction technology in deeper water would require piles of up to 100m length, projecting 25m in front of the wall. The feasibility of installing the large number of piles of this type needs further review. Given the engineering and maintenance difficulties with the deeper proposal, significant changes would be required in order to consider the use of this technology in these deeper areas. Subject to the outcome of such a review, the proposals are only considered suitable for shallower wall construction provided there is suitable resolution of the above issues.

Final 96 December 2008 x Consideration is required on how the concept is fitted onto the sea bed when the bed is of varying depth. x Consideration is required to the effects of downwash from large waves which could require extensive erosion protection.

Rubicon Marine Scheme

The Rubicon Marine submission proposes a structural solution to the construction of lagoons which comprises box structures fabricated using a composite of glass fibre reinforced panelling reinforced with a mesh constructed of recycled rubber coated bead hoops sourced from disused tyres. The boxes would be filled with dredged material seated on a level dredge-filled geotextile base. The boxes could be constructed from the seabed or founded on an embankment placed below water. This is an embryonic technology which would need to be subject to further research and development, including prototyping within a marine environment, prior to application in tidal energy context.

Tidal Electric Limited Geotextile Reinforced Embankment

The TEL submission is based on an embankment structure comprising of loose rock, sand and gravel with a core of fines (contained in geotextile bags) and clad with appropriately sized armourstone on the seaward side and turf reinforced matting on the basin side. It is a lower cost form of embankment than proposed for barrages and is likely to incur a different level of maintenance liability. The principal features of the TEL embankment which differentiates it from barrage embankments are its more steeply sided slope on the lagoon side, its narrow 3m crest width and lower crest height which would be low enough for the embankment inner core to be overtopped at times. There are a number of issues with the design which would need to be addressed in further development of the embankment design:

The design is susceptible to varying ground conditions and suited only to founding on rockhead. Where less competent founding conditions exist, the side slopes would need to be slacker and the embankment founded on a granular scour blanket. In the absence of site investigation data, the proportion of the embankment that would be founded on rockhead is difficult to estimate; Adequacy of the narrow crest width for anchoring of geosynthetic erosion control; Durability of the turf reinforced matting on the basin side, giving due consideration to the potential for vegetation only to become established over a narrow fringe around high tide level, which would be vulnerable to wave induced erosion; hard erosion control should be considered as a more feasible alternative;

Final 97 December 2008 Type and availability of fill for geotextile filled tube construction; Sealing of gaps between the filled geotextile tubes to provide for water retention; Anticipated design life and maintenance requirements; health and safety implications would prohibit inspection and maintenance work from the surface of the embankment and all access would be from the water; Durability during construction to prevent loss of material during high tides; The effects of climate change on embankment height, including how measures might be designed in for the future adaptation of embankments to deal with sea level rise and associated increase in wave heights and storm surges.

Taking account of the above issues, an updated version of the TEL design has been developed for the purpose of this study which could be applied to the lagoon schemes on sandy or rocky founding conditions. It is not considered appropriate to apply a reinforced embankment on a soft foundation as the embankment would be susceptible to instability. The updated version of the embankment includes a 5m wide crest width sufficient to anchor the geotextile reinforcement at the crest and suitable for access, employs slacker side slopes (1: 2.5 on the basin side and 1:2.5 on the sea side) to ensure sufficient factors of safety against instability, employs hard erosion control on the basin side, and an unreinforced scour blanket on a sandy foundation. It is understood that the TEL lagoon concept is not intended for construction in water deeper than 5 metres below chart datum and a reinforced embankment does not tend to be suited to deeper water applications. Deeper applications have been considered for the purpose of estimating the cost as lagoons of the sizes included in the long list are located in deeper water over some lengths. If an offshore lagoon concept is shortlisted, it will be necessary to review the lagoon alignment to optimise the performance of the lagoon in terms of embankment construction cost and energy yield. This optimisation can also include a further review of crest widths and side slope gradients. Further consideration is required on how to achieve closure of the lagoon with a reinforced embankment. High velocities will occur through the gaps as the lagoon approaches closure and it is questionable whether the integrity of the exposed ends of the reinforced embankment at the gaps can be preserved under these conditions. Erosion caused by the velocities through the gaps will increase the risk of instability and loss of material. Therefore, at the position of closure the reinforced embankment may need to be replaced with rockfill embankments, constructed on extensive bed protection if the embankments are to be constructed on sand. Further understanding of the alternatives to traditional marine embankment construction, and resolution of issues arising from reviews of the alternatives,

Final 98 December 2008 is required to inform estimates of the cost of lagoon construction of these forms.

L3e(i) and L3e(ii) Bridgwater Bay Offshore Lagoons

Alignment details have been made available by TEL for offshore lagoons just prior to the conclusion of the options analysis. Prior to its receipt, a review was carried out of the potential for an offshore lagoon at various locations including those listed in the TEL submission. To enable a fair comparison against other schemes and in response to the plan objective to deliver a strategically significant supply of renewable energy, the smallest lagoon considered in the review was 50km2. A limiting factor in the feasibility of each location is the principle that an offshore lagoon should avoid as far as physically possible any impact on the inter-tidal zone whilst keeping clear of the navigation routes to the commercial ports. Lagoons constructed close to the shore would effect hydrodynamic induced changes between the lagoon and the shoreline which would be likely to adversely impact habitats and coastal defences. The conclusion of the review was that Bridgwater Bay offers the optimum location for a reasonably sized offshore lagoon. For the purpose of this study, two Bridgwater Bay lagoons have been considered of 91km2 (reflecting the largest of the TEL submissions) and 50km2 (similar to the smaller land connected lagoons). A review of the TEL lagoon alignments has not changed this conclusion. Any of the forms of construction described above for the L3 land connected lagoons could be applied to the L3 offshore lagoon subject to resolution of the issues identified above.

6.3 Tidal Fence Construction

The proposed tidal stream systems would be surrounded by a duct and the ducted turbine mounted between two gravity base foundation structures. If deployed at the Cardiff to Weston location, the channel above the turbines would be blocked by modular concrete or steel flow barriers. Due to the limited design information available for the Fence, it is not possible to further appraise the civil engineering construction proposals.

6.4 Tidal Reef Construction

The main civil engineering elements of the Reef are the foundations for the modular turbine units. These would be founded on the sea bed. In comparison to barrage caissons, they would be smaller as they would be subject to a smaller two metre differential head. The foundations will house service tunnels and cable ducting. Information from Evans Engineering suggests that the foundations might be piled but gravity structures are likely to be less expensive. Due to the limited design

Final 99 December 2008 information available for the Tidal Reef, it is not possible to further appraise the civil engineering construction proposals.

6.5 Navigation Issues

Overview

The ports in the estuary and the services they support are an important part of the local and regional economy, and are responsible for handling around 3% of the UK trade. It is estimated that the Bristol and South Wales ports generate over 15,000 jobs between them. Navigation effects have the potential to hinder the commercial viability of the ports within the Severn Estuary. It is recognised therefore that one key objective of the Strategic Environmental Assessment will be to avoid significant impact on the ports and on the vessels transiting the estuary. This section considers the issues in terms of the likely effect on the construction and operation of the long listed schemes. Structures Requiring Locks Downstream of the Ports of Bristol and Cardiff Minehead to Aberthaw Barrage (B1), Hinkley Point to Lavernock Point Barrage (B2), Brean Down to Lavernock Point Barrage (B3), Severn Lakes Scheme (U1) and Tidal Reef (R1)

Proposed Shipping Transportation in the Estuary These options are downstream of many of the large ports within the Severn Estuary including Bristol, Cardiff and Newport. The construction of such a structure would change the way shipping travels both within the Estuary itself and through the barrage. The previously published proposals for the B3 barrage incorporate two lock systems. One on the northern side, close to Cardiff, would become the main shipping lane, and a smaller lock would be provided on the southern side of the barrage, designed for smaller craft. The twin locks as originally published would only have sufficient capacity to allow large ships of around 275 metres in length. Ship Sizes and Limitations Large ships of the type visiting the port facilities within the Estuary also transport goods around the world. One of the main limitations on the size of these ships is the current limitation through the Panama Canal. This bottleneck has led to the size of ship passing through here being limited to “Panamax” size. However the widening of this canal will enable a larger class ship known as the “Panamax II” to pass through and therefore will become more prominent in ship transportation. It is proposed that any barrage or similar barrier placed across the estuary includes a lock suitable to carry a Panamax II class ship. The internal measurement for this lock would need to be at least 427m long, 55 metres wide and have an available draught at all times of 18.3 metres. This compares with the available lock size at Portbury dock of 366m long and 43m wide. It is also known that Port of Bristol wish to develop a deep water port facility at Avonmouth and cater for Ultra Large Container Ships (ULCS) which have a maximum size of 381m long, 57m width and a draught of 14.5m. Port of Bristol have

Final 100 December 2008 requested that the locks are able to cater for ships up to 500m in length and 75m in width with an available draught of 18.3 metres and this has been reflected in the revised configuration and proposed costings for these potential barrage options.

Tidal Range and Depth of Water

The impoundment of the estuary would also alter the tidal range, speed of water flows, and as a result effective depth of water within the estuaries shipping lanes. A reduced tidal range will increase the available depth of water the majority of the time. An exception to this is the reduction in the available depth of water at high tide. The reduction is currently envisaged to be up to 1m for spring tides. Other risks to the long-term use of the estuary for shipping could come from the deposition of sand and silt within the channel due to the lower velocities of water within the main channel. Sufficient modelling work would have to be carried out to ensure that any barrage proposals ensure sediment build-up was within acceptable limits.

Navigation Summary

In order to minimise the negative effects and maximise the positive effects of the barrage a number of issues should be incorporated in future stages of this study.

x Specification of sufficiently large locks x Study of the sediment deposition and water velocity within the Estuary x Study of the effect on the tidal range and the available water depth for the main channels and ports.

Further consultation will be undertaken with the development of the proposed shortlist schemes to further study these and other impacts of the change in regime on navigation within the Estuary.

Structures Requiring Locks Upstream of the Ports of Bristol and Cardiff Shoots Barrage (B4) and Beachley Barrage (B5)

Proposed Shipping Transportation with the Estuary

These barrages are just downstream of the Second Severn Crossing and are upstream of the main Estuary ports of Bristol, Cardiff and Newport. The ships travelling through this barrage will be travelling to/from ports in the areas such as Gloucester, Sharpness and Chepstow. It is envisaged in this barrage that a single twin lock facility would operate within the “Shoots” channel as this is the only part of the estuary with sufficient depth of water at all parts in the tide cycle to ensure that ships are able to pass through the locks. The current proposal within the Shoots Barrage envisages a large lock to allow ships of up to 200m in length, a width of 37.5m and a draught of 10.5m.

Final 101 December 2008 Ship Sizes and Limitations

Since the conception of the Shoots proposal the Second Severn Crossing (SSC) has been undertaken and this has placed limitations of the type and size of shipping passing through and upstream of this bridge. The SSC was constructed with a restriction that a braced ship of no larger than 6,500dwt (Ice Class 1AS) would pass under it. These restrictions are set out in detail within the New Severn Bridge (Restriction of Navigation) Regulations 1993 (S.I. 1993 No 190). Any collision between the bridge and a ship larger than this could cause serious damage to the bridge. As such the size of the lock facilities within the Shoots Barrage should be sized to cater for this maximum size. It is therefore recommended that the lock size be reduced from the 200m by 37.5m by 10.5m to a smaller 175m by 20m with adequate depth to allow a vessel to navigate through Sharpness Dock lock with 6.5m draft at high water.

Tidal Range and Depth of Water

The impoundment of the estuary at this point would also alter the tidal range, speed of water flows, and, as a result, effective depth of water upstream of the barrage, and have a minor effect downstream. The reduced tidal range will increase the available depth of water the majority of the time. An exception to this is the reduction in the available depth of water at high tide. Other risks to the long-term use of the estuary for shipping could come from the deposition of sand and silt within the channel due to the lower velocities of water within the main channel. Sufficient modelling work would have to be carried out to ensure that sediment build-up was within acceptable limits.

Navigation Summary

In order to minimise the negative effects and maximise the positive effects of the barrage a number of issues should be incorporated in future stages of this study. x Specification of correctly sized locks x Study of the sediment deposition and water velocity within the Estuary

Further consultation will be undertaken with the development of the proposed shortlist schemes to further study these and other impacts of the change in regime on navigation within the Estuary.

Non Barrage Options (L2 and L3 Lagoons, R1 Reef and F1 Fence Options)

F1 Fence

Tidal fence options would not block the transit of vessels. Therefore, they would not affect the tidal regime as significantly as a barrage and would be unlikely to cause significant issues from changes in salinity. However, they may still introduce issues

Final 102 December 2008 relating to current velocity and estuary morphology. These would require further detailed consideration and modelling before the severity of impact can be judged. In relation to the F1 fences, the size of the opening for the shipping channel and measures necessary for safe navigation through the opening require detailed consideration and an assessment of the risk of collision with the fence structures. Other issues vary in scale depending upon location but it is anticipated that tidal fences would be likely to have the following effects: x Reduction in tidal range and flow speeds of around 5%. This would result in reductions in the extreme tidal levels of 2.5% of the tidal range. Reductions in high tide levels have an impact on the upstream ports unless mitigated through reduction of lock sills

x Accelerated flow speed through the shipping channel would have an effect on shipping movements in the estuary. Between Cardiff and Weston, the mean spring peak flows in the shipping channels are naturally of the order of 6kts, so the predicted effects would be an increase of 2kts over the existing currents. The proposed channel in the fence, at 400m wide would represent a constriction for the largest ships to use the estuary and would probably mean that shipping movements would be exclusively upstream on the flood tide, and downstream on the ebb. In particular there may be increased travel times and constraints on scheduling for shipping to the ports of Bristol and Cardiff.

R1 Reef The Reef incorporates rotating modular turbine units that siphon the flow of water across the turbines. These rotating modules can be opened and closed to allow passage of vessels without the need for locks. Also, the Reef would not affect the tidal regime as significantly as a barrage and would be unlikely to cause significant issues from changes in salinity. However, it may still introduce issues relating to current velocity and estuary morphology especially in the region of the openings for vessel passage where accelerated flows should be expected. These would require further detailed consideration and modelling before the severity of impact can be judged.

In a similar manner to the F1 fences, the size of the opening for the shipping channel and measures necessary for safe navigation through the opening require detailed consideration and an assessment of the risk of collision with the reef structures. The Reef would also be likely to have the following effects: x Reduction in tidal range and flow speeds with a possible decrease in high water level of around one metre and a similar increase in low water level. Reductions in high tide levels have an impact on the upstream ports unless mitigated through reduction of lock sills

x Accelerated flow speed through the shipping channel would have an effect on shipping movements in the estuary. The proposed opening in the Reef would

Final 103 December 2008 represent a constriction for the largest ships to use the estuary and would probably mean that shipping movements would be exclusively upstream on the flood tide, and downstream on the ebb. In particular there may be increased travel times and constraints on scheduling for shipping to the ports of Bristol and Cardiff.

Lagoons A land connected lagoon enclosing Bridgwater Bay would require a small ship lock to enable navigation on the River Parrett.

Other land connected lagoons and the offshore lagoons have the potential to affect currents and water levels within the estuary though these effects will be much smaller than the effects of barrages, fences and the reef. Detailed modelling is required to quantify these effects.

6.6 Adaptability for Sea Level Rise

Any tidal power development scheme should be designed to tolerate sea level rise at least in line with the current guidance existing at the time of the design development. Current guidance predicts sea level rise up to one metre in the next one hundred years but predictions of much more significant sea level rise of several metres have also been put forward. For reasons of economy, it is not anticipated that a scheme would be designed to tolerate estimates of sea level rise above current guidance within the design life nor the potential for future sea level rise beyond the intended design life as the benefits may either not be realised or would not be expected to be realised for some time. Therefore, a consideration in the design of a tidal power development is how the scheme can be designed to be adaptable in the event sea level rise exceeds the level allowed for in the design.

Designs submitted for the L2 lagoon wall and the design adopted for the L3 embankment for the purpose of the cost estimates could not be adapted without modifying the entire length of wall or embankment structures so that a suitable factor of safety is maintained against instability under the increased water pressures that would occur in the event of sea level rise. Embankment structures required for barrages and assumed to be required for the tidal reef would require similar modification. In contrast, turbine caissons would be determined by the space required to accommodate the turbines, gates and ducting and can be designed to be adaptable for sea level rise without needing as onerous modifications as would be required for embankments. Sluice caissons could be designed to be adaptable for sea level rise but would require a greater level of initial structural redundancy than turbine caissons.

The tidal reef could be designed to be adaptable for sea level rise but is likely to require more onerous modifications and a greater level of initial structural redundancy than

Final 104 December 2008 other tidal schemes. This is because the turbine modules would need to be raised and the foundations would need to be designed and constructed from the outset to accommodate the increased water pressures which would occur with sea level rise. Similar but probably less onerous issues would be faced with the tidal fences.

In conclusion, barrages would be the most adaptable of all schemes in the event that sea level rise exceeds the tolerance built into the design as they have the largest proportion of turbine caissons. The larger barrages are also the schemes which provide the greater degree of flood risk benefits due to the protection they would provide against surge tides and the greater extent of the reduction in high water level which they would cause.

6.7 Turbines and Generating Equipment Barrage Proposals

A summary of the turbine configurations anticipated for each barrage option is provided in Table 6.2. It should be noted that these configurations are not necessarily optimal for maximum energy yield as no optimisation has been carried out for the purpose of this study.

Option Option Name Anticipated Commentary No turbine configuration

B1 Outer Barrage 370 x 40 MW 9m Configuration from the from Minehead dia. bulb Bondi studies (1981) to Aberthaw turbines expected to remain appropriate although turbine numbers and output has been increased in line with EP57 study conclusions for Cardiff Weston. Large number of turbines could over-stretch European and possibly worldwide manufacturing resources, with consequential constraints on delivery period and cost of supply.

B2 Middle Barrage Total capacity Similar to B3 but with from Hinkley to 9000MW additional turbines along

Final 105 December 2008 Option Option Name Anticipated Commentary No turbine configuration

Lavernock Point possibly Steepholm to Hinkley line. (Severn Barrage comprising 225 to Hinkley and x 40 MW 9m Brean) dia. bulb turbines

B3 Middle Barrage 216 x 40 MW 9m Configuration from the from Brean dia. bulb 1989-90 STPG studies Down to turbines expected to remain Lavernock Point appropriate although use of (Cardiff to double regulated bulb units Weston Barrage) rather than single regulated units (as previously proposed) may provide more overall efficiency and at least 2.5% additional energy. Good experience has been gained of double regulated bulb units at La Rance.

Final 106 December 2008 Option Option Name Anticipated Commentary No turbine configuration

B4 Inner Barrage 30 x 35MW, Configuration from 1990 (Shoots Barrage) 7.6m dia Straflo MRM report expected to turbines remain appropriate. Offers advantages over bulb turbines being more compact and providing construction cost savings. A single 20MW 7.6m dia turbine exists at Annapolis Royal which has been reported to operate well and a number of smaller units have been installed in Europe. However, use on tidal schemes is limited.

B5 Beachley 50 x 12.5MW, Configuration based on B4 Barrage 5.0m dia Straflo in the absence of previously turbines published information

Table 6.2 Barrage Turbine Configurations

Bulb turbines are proposed for the larger barrages because, although more costly than Straflo turbines, provide the opportunity for flood pumping. Also, only one known manufacurer of Straflo turbines is in existence which could constrain availability and affect cost of supply where larger numbers are required.

Final 107 December 2008 Lagoon Options

L2 Russell Lagoon Option

Information submitted by the Fleming Group indicates a nominal capacity of 1250 to 1700 MW. Turbine selection by the Fleming Group is the subject of ongoing work and it is understood that between 25 and 34 no 50MW turbines are being considered. 0-D and 1-D modelling for the purpose of this study has verified that the required capacity is likely to be towards the lower end of this range. This capacity is significantly larger than the nominal generation capacity of 945 MW originally stated at the time of the Bondi studies for the same lagoon, which had a slightly longer embankment length. This lesser capacity was based on 21 x 45 MW, 9m units per lagoon. .

It should be noted however that the turbine size is constrained by available depth. Work of the STPG after the original Bondi study resulted in the use of slightly smaller units, later modified to 40MW for technical and other reasons. An alternative arrangement of 12.5 to 25 MW units may prove to be more viable in this case. Units of this size would require a dredged channel to provide sufficient submergence to protect against cavitation effects with an average dredged depth below existing bed level of 5 to 7.5 metres depending on turbine size.

It should be noted that configurations described above are not necessarily optimal for for maximum energy yield as no optimisation has been carried out for the purpose of this study. Energy yields have been determined by 1-D modelling using the latest bathymetric model for the Severn Estuary. Additional energy output could be achieved from the Welsh Grounds if the materials used in construction were excavated from within the basin to achieve greater live storage. This is more feasible at the Welsh Grounds site than other lagoon sites because of the relatively high formation level of the impounding basin compared with the turbine axis level. This would marginally increase energy yield by up to 5%.

The configuration includes 35 to 45 sluice gates at various locations around the structure. Operation is proposed using only ebb generation because of the 0.6m reduction in head on the flood tide.

L3 Tidal Lagoon Concept

The turbine sizes for land connected lagoons will be constrained by available depth. Turbine sizes may therefore need to be reduced to between 12.5 and 25MW. A summary of L3 lagoon turbine configurations, based on energy modelling undertaken for this study is provided in table 6.3 below. Dredged depths of up to 7.5 metres below existing bed level will be required to provide sufficient submergence depending on the turbine size selected.

Final 108 December 2008 Lagoon Configuration

L3a Russell Lagoon (English Grounds) 60 x 12.5MW 5.0 m dia bulb units

L3b Russell Lagoon (Welsh Grounds) 108 x 12.5MW 5.0 m dia bulb units

L3c Russell Lagoon (Peterstone Flats) 90 x 12.5MW 5.0 m dia bulb units

L3d Russell Lagoon (Bridwater Bay) 108 x 12.5MW 5.0 m dia bulb units

L3e(i) 90km2 offshore lagoon off Bridgwater 108 x 12.5MW 5.0 m dia bulb Bay units

L3e(ii) 50km2 offshore lagoon off Bridgwater 60 x 12.5MW 5.0 m dia bulb Bay units

Table 6.3 Lagoon Turbine Configurations

It should be noted that configurations described above are not necessarily optimal for for maximum energy yield as no optimisation has been carried out for the purpose of this study.

Bulb turbines are proposed for the lagoons because, although more costly than Straflo turbines, provide the opportunity for flood pumping. Also, only one known manufacurer of Straflo turbines is in existence which could constrain availability and affect cost of supply where larger numbers are required.

Tidal Fence

The original tidal fence submission (F1a) proposed some 256 no 5 MW ducted tidal stream turbines of 18 metres diameter to deliver a power output of 3.5TWh/yr. This would represent a significant advancement in turbine output capability as current experience demonstrates that much lower power outputs are likely to be capable from these units.

For example, a similar size prototype turbine recently installed at Strangford Narrows in Northern Ireland (Seagen) is reported to produce 1.2 MW output, with the use of twin 16m diameter rotors. Further research would therefore be required to provide evidence to show that by installing a ducting arrangement, the turbine output can be increased by such large magnitudes. Although ducting may be expected to increase the specific flowrates somewhat, in practice the operation of the machine is going to be limited by blade velocity and other factors. Further analysis has been undertaken

Final 109 December 2008 (see section 4) and it is concluded that turbines of 1MW are appropriate for the Cardiff Weston alignment giving an annual energy yield of some 0.7TWh, significantly lower than the original 3.5TWh.

The proposer has also reviewed the concept and has submitted an alternate proposal (F1b) for the Minehead to Aberthaw alignment comprising 800 1.6MW units with a phased construction programme installing 100 units a year over 8 years following initial construction advance works. This proposal is more likely to achieve the claimed output of 3.5TWh although there are risks, particularly related to current velocity distributions within the channel and at different tidal states.

Further detailed work is required to establish the technical feasibility of this option and the optimum turbine ratings and resulting energy yields. There are also potential construction issues associated with housing the turbines. In particular the ducting arrangement is considered to be vulnerable to hydraulically induced fatigue and daily distortions associated with the tidal flows and pressure differentials involved, particularly affecting any welded joints. Constructionally, the ducting would most probably require to be embedded in concrete, as is done in conventional hydropower practice. In addition there are numerous construction issues for the configuration of the generators and turbines taking account of the size of the generators which would need to be considered.

The durability of the structures proposed is also a concern and full replacement costs are included in the economic assessment with an asset life of 20 years being used for the turbines, generators and all electrical equipment..

Other concerns are for the potential of scour:

x In the open, coastal, margin. x In the shipping channel.

If shortlisted, these issues will need to be considered in more detail with the full estuary 2-D model, but they are considered briefly below for the Cardiff Weston alignment (F1a).

The tidal fence assumes that velocities in the shipping channel for a spring tide will increase from 4 knots to 8 knots (2m/s to 4m/s). Neap tide velocities have also been assumed to increase from 2 knots to 4 knots (1m/s to 2m/s).

Using the July 1981 report, Severn Tidal Power – Two-dimensional water movement model study (Hydraulics Research Station, Wallingford report EX 985), to obtain observed velocities in the estuary, pre-barrage velocites, close to the line of the tidal fence, are approximately 2m/s for a spring tide and 1m/s for a neap tide. .

Final 110 December 2008 The following velocities are thus calculated through the channel for heads across the fence:

Head across fence (m) Velocity (m/s) 0.5 2.4 1.0 3.4 1.5 4.1 2.0 4.7

From the information received, it is assumed that the tidal fence proposers have, at this stage, assumed the same velocities through the turbines as through the shipping channel. This is an optimistic assumption as it is probable that velocities in the shipping channel will be higher, and the velocities in the turbines lower, due to:

x Higher velocities occurring in the deeper water areas; x The channel providing less resistance to flow on size alone; and x The turbines providing additional resistance to flow.

Navigation issues will therefore need careful review to ensure that shipping will be able to safely pass through the fence.

The other engineering issue with the fence is that of scour. Increasing the tidal velocity to 4m/s at the shipping channel will greatly increase the potential for scour along the channel. The structures to either side of the channel will have to be heavily protected by rip-rap or similar protection, that will be both large and costly.

‘Open’ areas are proposed at either end of the tidal fence structures, where flow will be able to pass between the fence and the shore. However, it is likely that the current velocity of flow parallel to the shore will be small, and the concentration of the flow will increase velocities and cause major erosion of the intertidal areas adjacent to the fence.

Tidal Reef

The tidal reef comprises 1000 x 5MW 10m diameter turbines oriented on a vertical axis and housed within a siphon module which conveys the flow across the reef via the turbines. The modules are able to be rotated 90 degrees to open the reef and increase its permeability at times when it is desired to increase the tidal range to preserve habitat and allow passage of vessels. The reef can also be closed to protect against surge tides.

The reef turbines are at concept stage and design information is very limited. Prototyping of this turbine technology is required to prove the concept before the reef could feasibly proceed to full scale deployment. A pilot scheme on a smaller scale would also help develop the concept and significantly reduce the technology risk associated with a reef at the outer estuary location. Final 111 December 2008 Procurement and Manufacturing Issues

Installation of a relatively large number of units on one site poses particular procurement issues. Sourcing options for the bulb units proposed on the various barrage and lagoon schemes is likely to be from one of the four major international turbine manufacturers capable of producing units of the required size, having suitable track record with reference of installed plants elsewhere. Very few manufacturers have produced bulb units near 9m diameter, which is considered to be at the limit of current experience. For Straflo units, likewise these would be probably sourced in a number of European locations, with final assembly at the supplier’s works in Austria and/or Germany.

Design life and maintenance issues

For the fair basis comparison, a design life of 40 years has been assumed for conventional hydropower turbines and generators, after which major refurbishment will be required. Routine maintenance of some 4-6 weeks per unit per two years can be expected, plus 1 weeks forced outage per year. Maintenance would normally be carried out on a rolling ongoing basis in an annual cycle. Maintenance costs would be relatively high at approximately 1.5 x the cost for a conventional hydro plant. A significant degree of maintenance would be necessary to carry out long-term monitoring and replacement of cathodic protection and other corrosion protection of the units. Removal and decommissioning aspects will be relatively complex, involving the removal of the main bulb units in situ and significant excavation of embedded parts.

Electrical and mechanical plant used in projects based on tidal stream technology are anticipated to have shorter asset lives and will require replacement sooner than the 40 years for conventional hydropower technology. A life of 20 years has been adopted for tidal stream technology.

6.8 Grid Connection and Reinforcement Overview

High-level estimates for the likely level of network reinforcement required to connect the generation are included in this section. The network reinforcement works are those works undertaken by and owned by National Grid, and include all the works to establish a local connection point to the transmission system, as well as wider transmission reinforcements remote from the local connection point. These works do not include the electrical systems between the generators and the connection point to the transmission system. The cost of these works is included in Section 8.

For a standard large generator National Grid would build and own a substation in the vicinity of the generating site, and would build the connection from this substation to

Final 112 December 2008 the rest of the transmission system. The generator would build and own the electrical system connecting their generators into National Grid’s substation.

It has been estimated that the peak power output of the proposed Severn Estuary tidal generation schemes lies between 0.2GW and 14.8GW. Given the magnitude of the generation capacity, a connection to the 275kV or 400kV networks, owned and operated by National Grid, is required.

400kV Network Capacity

The National Grid network in the vicinity of the Severn Estuary is below.

400kV Network 275kV Network

2008/09 Transmission System as at 31st December 2007

National Grid publishes network capacity studies in their Seven Year Statement in order to indicate the level of spare transmission capacity within each of the 17 zones that comprise their network. This information can be used to generally ascertain the level of generation that can be connected to the network before major reinforcement is required. The proposed generation would be connected into zones 13 and 17, as shown below. ”

Final 113 December 2008 2008 Generation Connection Opportunities

The studies show that the combined generation capacity available in zones 13 and 17 is up to 0.25GW. Further analysis has shown that there have been significant increases in the capacity of planned generation connections onto the National Grid networks in recent years and it is understood that two new reactors are planned at Hinkley Point for commissioning around 2017. The effect of other generating schemes on overall demand will affect the severity of the issue of grid capacity.

From the information published in the 2008 Seven Year Statement, it can be concluded that significant 400/275kV network reinforcement will be required before the Severn Estuary generation can be connected. The degree and cost of the required network reinforcement will be dependent on a number of factors, but primarily the proposed peak generation capacity.

Grid Connection and Reinforcement Requirements

400kV grid substations would be instated on the Welsh or English shore close to the generation. In the case of the barrage schemes with a peak generation capacity in excess of approximately 5GW, 275kV or 400kV substations are likely to be required on both shores to facilitate connection into both Zone 13 and Zone 17 of the National Grid network.

The detailed grid connection studies from the 1989 Department of Energy report entitled “Severn Barrage Project, Volume II” stated that for the Cardiff – Western barrage:“Approximately 370km of new 400kV line route would be required, plus 75km of line

Final 114 December 2008 rebuilt over existing 400kV routes, 150km of reconductoring to increase line capacities and 55km of uprating to 400kV of existing 275kV routes. A new 400kV substation would be built at Seven Springs and reactor coupling would be necessary at eight National Grid substations.”

A high level estimate of the grid reinforcement required by each proposal has been prepared by scaling the reinforcement detailed within the 1989 studies by the peak generating capacity of each of the long-listed schemes. National Grid would typically pay for these works, and charge the regulated cost reflective tariff to the generating company. National Grid would own the assets and earn a regulated rate of return on the investment, normally over 40 years. Although National Grid would pay for and own the transmission assets, an estimate of overall costs has been factored into the assessment process so that the various options can be compared. The grid reinforcement required is therefore estimated to be as shown in Table 6.5. The high level estimate for these works is shown in Table 6.4.

Typical 2008 equipment prices were then used when calculating the total cost. Advances in technology since 1989, such as the use of high capacity GAP conductors or HVDC systems, have not been considered at this stage. In addition, changes in generator capacity will result in step changes to the reinforcement requirement as additional new plant and circuits are required. Such step changes are not accounted for in this sliding scale approach.

Option Installed Capacity High Level Grid Reinforcement (GW) Estimate (£m) B1 14.8 3,950 B2 9 2,400 B3 8.64 2,300 B4 1.05 280 B5 0.625 167 F1a 0.256 68 F1b 1.280 189 L2 1.36 363 L3a 0.76 203 L3b 1.36 363 L3c 1.12 299 L3d 1.36 363 L3e(i) 1.36 363 L3e(ii) 0.76 203 R1 5.0 1,300 Table 6.4 High-Level Grid Reinforcement Cost Estimates (Note: Figures for all options are provisional and estimates only)

Final 115 December 2008 Option B1 B2 B3/U1 B4 B5 F1 F1b L2 L3a L3b L3c L3d L3e(i) L3e(ii) Peak Generation 14.8 9 8.64 1.05 0.625 0.256 1.28 1.36 0.76 1.36 1.12 1.36 1.36 0.76 Capacity (GW) 400kV double 2 1 1 0 0 0 0 0 0 0 0 0 0 0 busbar substations: New 400kV line 630 390 370 40 30 11 50 60 30 60 50 60 60 30 route (km): New 400kV cable 17 10 10 1 1 0 1 2 1 2 1 2 2 1 route (km): 400kV lines 130 80 75 10 10 2 10 10 10 10 10 10 10 10 rebuilt (km): 400kV lines 260 160 150 20 10 4 20 20 10 20 20 20 20 10 reconductored (km): 275kV lines 90 60 55 10 0 2 10 10 0 10 10 10 10 0 uprated to 400kV (km): Reactor coupling 14 8 8 1 1 0 1 1 1 1 1 1 1 1 installations:

Table 6.5 Grid Reinforcement Works (Note: Figures for all options are provisional and estimates only)

Final 116 December 2008 System studies have not been undertaken at this stage to assess the likely National Grid reinforcement requirements. The above estimate should therefore only be used as a high-level guideline, as the actual amount of grid reinforcement required may vary considerably, and the grid costs would be recovered through revenues. It should also be noted that no land acquisition or consenting costs have been included in the estimates above.

Equipment lifespan

The electrical equipment required for the generator connection arrangements and for grid connection has a typical life-span of 40 years although some ancillary plant equipment would likely need to be refurbished or replaced at around 20 years. Control systems are likely to require replacement after 10 to 15 years. Some cables may last an additional 20 years before replacement is required.

Further Considerations for Connection to the Transmission System

The proposed generation would impose a significant fault infeed contribution to the National Grid network. Fault level studies are essential to ensure that fault levels do not exceed switchgear ratings at existing substations.

Transient stability studies detailed in the 1989 Department of Energy report entitled “Severn Barrage Project, Volume II” indicate that for an 8GW barrage, at 60% of maximum demand and above, the system would be stable for three phase double circuit faults. For demand conditions below 60% it was necessary to restrict the barrage output. System studies are recommended to verify that the 1989 results remain valid.

The GB Security and Quality of Supply regulations state the maximum capacity of generation that can be connected via a single or double circuit. This restriction is imposed in order to maintain system frequency to within a range of 49.5Hz and 50.5Hz following a fault that results in a disconnection of generation. The requirements are entitled ‘Normal infeed loss risk’ and ‘Infrequent infeed loss risk’. These are currently under review, but are presently defined as follows:-

Normal Infeed Loss Risk: This is the level of risk of the loss of power which is covered over for the loss of a single transmission circuit or busbar. This is set at 1000MW and is to avoid a frequency deviation of greater than 0.5Hz in the long term due to a permanent outage such as a cable failure. In reference to the proposed generation this would mean that no more than 1000MW could be connected on a single generation circuit.

Infrequent Infeed Loss Risk: This is the level of risk of the loss of power which is covered over the loss of up to two circuits, both on the same double circuit line, in normal operation or the loss of one circuit at the same time as a planned outage within the transmission system. This is set at 1320MW and is to avoid a frequency

Final 117 December 2008 deviation of greater than ±0.5Hz for more than 60 seconds. In reference to the proposed generation this would mean that generation above 1320MW would need to be connected by at least 3 transmission circuits to account for an N-2 event.

If the 1000MW/1320MW limits are changed, this would have a significant impact on the design of the local grid connection works, including those between the generators and the point of connection to the transmission system.

For the large tidal generators, there may be restrictions on how quickly the output can be changed up or down. For example, National Grid normally accommodates rates of change of 40-50MW per minute.

Final 118 December 2008 SECTION 7

ESTIMATED FIRST YEAR OF OPERATION

Final 119 December 2008 7 ESTIMATED FIRST YEAR OF OPERATION

Construction programmes and the estimated first year of operation have been based on a common preconstruction programme but with varying construction times. Since the publication of Energy Paper 57, shortened construction programmes have been proposed for the Cardiff Weston Barrage and the Shoots barrage although detailed work substantiating these reductions in programme is not available. For this reason, all options have been compared on a similar basis using the work undertaken in EP57 as a baseline. However, it should be noted that achievement of faster construction programmes may be feasible and this will be reviewed in more detail during the work being undertaken to optimise the short-listed options. The opportunity for schemes to deliver energy in phases leading up to full scale power output has been taken into account.

7.1 Overview For a fair basis comparison, a common pre-construction programme has been assumed for all schemes on the basis that they are all of a scale and complexity to require the length of periods for design, environmental studies, Environmental Impact Assessment, consents and permitting as would be required for any very large scale infrastructure project. Schemes of different scales could be prepared for within similar timescales but would require different levels of resource.

The common pre-construction programme is as follows:

SEA Complete April 2010 Consultation Complete Dec 2010 Environmental Studies and EIA Complete Mid 2012 Consents, approvals, agreement and financing in place Dec 2013

Given the detailed studies behind the programme set out in the DOE Report 1989 Vol IIIA for the Cardiff to Weston Barrage, this programme is taken as a benchmark for construction timeframes. The 2002 reappraisal of the B3 Barrage (ETSU Report No T/09/00212/00/REP) concluded that the accelerated 6 year programme for the Cardiff to Weston Barrage should be adopted. Subsequent studies reported by SDC in their report “Turning the Tide” indicate a shorter construction period of 5 years for Option B3 but, for the purposes of the fair basis evaluation, the 6 year programme has been used. Overall construction programmes have been estimated at a high level based on a comparison of the principal quantities of turbines, embankments and caissons structures.

Final 120 December 2008 7.2 Innovation Risks The programme set out in 7.1 above does not take account of specific programme risks relating to innovations in the individual proposals. With the exception of F1, R1, L2 and L3, all proposals are based around relatively traditional civil engineering design and construction. The engineering innovations included in F1, L2, L3 and R1 are discussed in section 6.

Traditional methods of construction and operation for a barrage (which can equally be applied to a lagoon) have been proven by prototypes at La Rance and Annapolis Royal. Innovative solutions without such prototypes carry a higher degree of risk to investors because of higher uncertainty over such issues as construction methods and programme, suitability of materials, durability and maintenance cost, and lost energy output. It seems likely that investors will have less appetite for innovative solutions applied to a full scale development in the Severn Estuary than more traditional proven methods, particularly if the financial viability of the proposal is dependent on the effectiveness of the innovation. Therefore the Tidal Fence (F1) may require a smaller scale prototype development to enhance the conceptual evidence base and confirm likely energy yields to reduce financial and technology risk which could delay the estimated first year of production by several years. In addition, the proposed size and form of ducted turbine requires its own form of validation using a single prototype before large scale implementation such as envisaged by Option F1. It is therefore unlikely that the fence will be sufficiently developed in readiness for a 2014 construction start.

As discussed in section 3.7, the embryonic status of the reef concept is such that 10 to 15 years may be required for the development of the technology prior to full scale construction in the estuary.

The SDC Report "Turning the Tide" proposed construction of a pilot for tidal lagoons (Options L2 and L3) although the technologies involved in lagoons are similar to those in barrages, particularly in respect of turbine types and calculation of energy yield. For this reason, comprehensive trials through pilots or prototypes are not envisaged for lagoons. However, because of the longer embankment lengths required of lagoons compared with barrages, innovative embankment / wall construction techniques have been proposed for tidal lagoons to bring the unit cost of creating the impoundment structure down. The application of innovative embankment/wall construction techniques will in themselves require further research which may involve construction of small pilots. There is also the issue of sedimentation risks associated with lagoons (and smaller barrages) which are more likely to be determined by mathematical modelling than field trials. The impact of such research on timescales is difficult to estimate accurately but would be less than more fundamental proof of concept prototyping

Final 121 December 2008 7.3 Construction Programmes and Estimated First Year of Operation

Construction programmes and the phasing of power generation are set out in this section subject to the innovation risks which are discussed in 7.2 above.

Lagoon options L2 and L3 and the smaller B4 and B5 barrages would deliver full scale power in the first year of operation.

The larger barrages would deliver power in a phased manner as the installation of turbines after barrage closure is critical to the programme for delivery of full scale power.

The 6 year programme for the B3 Barrage provided for approximately 50% output shortly after barrage closure, increasing to 75% one year after closure and to 100% two years after closure. The same phasing has been assumed for barrages B1 and B2.

The full power output of the F1a fence would be achieved in two phases. Approximately one third capacity would be installed after four years from construction start with the remainder installed in the following year.

The full power output of the F1b fence would be achieved progressively over an eight year period. Based on information submitted by STFG, 100 turbines per year would be installed per year commencing three years after construction starts. An additional 100 turbines would be installed per year until the full capacity is installed.

Little design information is available on which to base a construction programme for the R1 reef. However, it seems reasonable to assume that a reef constructed over a similar alignment to the B1 barrage would take a similar length of time and an overall construction programme of 10 years has therefore been selected. The method of operation of the reef would not require its full completion prior to first energy generation although it would not be able to develop the intended 2 metre differential head over the full length of the reef until it is completed. It is assumed that turbines would be installed progressively along the reef as the structure is constructed and in the initial phases the reef would capture the energy from the tidal stream passing through the reef. It is therefore assumed that until completion of the reef structure, which could occur after 7.5 years construction, the reef delivers energy progressively at the same rate as the F1b fence. Thereafter, the reef would ramp up to full production.

Potential construction programmes and estimated first years of operation are provided in Table 7.1 below.

Final 122 December 2008 Option Option Name Period from Estimated Year Subsequent No construction of First Phasing of start to first Operation and % Power Output energy of Full Capacity production (years)

B1 Outer Barrage 7.5 years 2022 (50% ) 2023 (75%) from Minehead to 2024 (100%) Aberthaw

B2 Middle Barrage 7 2021 (50%) 2022 (75%) from Hinkley to 2023 (100%) Lavernock Point (Severn Barrage to Hinkley and Brean)

B3 Middle Barrage 6 2020 (50%) 2021 (75%) from Brean Down 2022 (100%) to Lavernock Point (Cardiff to Weston Barrage)

B4 Inner Barrage 5 2019 (100%) None (Shoots Barrage)

B5 Beachley Barrage 4 2018 (100%) None

F1a Tidal Fence 4 2018 at earliest 2019 (100%) Proposal but embryonic (Lavernock to nature of fence Brean Down likely to require alignment) trial (33%)

F1b Tidal Fence 3 2017 at earliest 12.5% added Proposal (outer but embryonic year on year alignment) nature of fence from 2018 to likely to require 2024 trial (12.5%)

L2 Lagoon Enclosure 5 2019 None on the Welsh Grounds (Fleming Lagoon)

Final 123 December 2008 Option Option Name Period from Estimated Year Subsequent No construction of First Phasing of start to first Operation and % Power Output energy of Full Capacity production (years)

L3a Russell Lagoon 4 2018 None (English Grounds)

L3b Russell Lagoon 5 2019 None (Welsh Grounds)

L3c Russell Lagoon 5 2019 None (Peterstone Flats)

L3d Russell Lagoon 5 2019 None (Bridwater Bay)

L3e(i) 90km2 offshore 6 2020 None lagoon off Bridgwater Bay

L3e(ii) 50km2 offshore 5 2019 None lagoon off Bridgwater Bay

R1 Tidal Reef 4 2018 at earliest 0.41TWh added but embryonic per year from nature of fence 2018 to 2021 likely to require when reef trial ‘closure’ is achieved. Full power then ramped up from 50% to 100% over four years. Table 7.1 Construction Programmes

Final 124 December 2008 SECTION 8

SCHEME COST AND COST OF ENERGY

Final 125 December 2008 8 SCHEME COST AND COST OF ENERGY

The estimation of cost per unit energy generated has been undertaken using a fair basis approach applied equally to all options where sufficient evidence / data exists. This entails the application of a consistent set of unit rates applied to the principal quantities for all options with additional costs covering other elements such as design, overheads, ancillary works, grid transmission costs and habitat compensation, for example.

Reasonably detailed estimates have been prepared for the B3 and B4 barrages and the unit costs for the main components of these barrages have been applied to produce high level cost estimates of the other barrages. A high level estimate has been made of the L2 lagoon proposed by Fleming Energy in their submission to the Call for Proposals. High level estimates have also been made of the costs of the L3 lagoons based on an assessment of the several forms of construction which could be applied to the impoundment with the lowest cost solution adopted for the derivation of the scheme costs. High level assessments have been prepared for Option F1 (Tidal Fence) at both the outer and Lavernock to Brean Down positions and of the R1 Tidal Reef. Insufficient data are available to estimate the costs of the U1 Severn Lakes concept.

A discounted cash flow model has been used which incorporates scheme construction costs spread over the timeline of the construction phase (Section 7) and operation, maintenance and asset replacement costs (derived from section 6) and energy yields (Section 4) spread over a 120 year design life which has been assumed for all schemes. Discount rates of 8% have been applied with sensitivity tests applied at 3.5% and 15%, to bring all values to a net present day value per kWh of energy generated. Whilst the assumed 120 year design life would not account for the potential for some schemes to remain serviceable for longer periods, in practical terms energy yields and costs beyond 50 years have little impact on net present value for the discount rates applied.

Appendix A contains a detailed breakdown of the scheme cost estimates and contains the discounted cash flow model.

8.1 Pre-Construction Cost Estimates Civil Engineering Cost Methodology

A common set of assumptions has been applied to the pre-construction cost estimates of all schemes as set out in Table 8.1 below:

Final 126 December 2008 Item Cost Assumption Project Management 0.25% of construction cost Design (up to procurement stage) 25% of total design cost (see 8.2) Site Investigation 1.25% of civil engineering construction cost Environmental Impact Assessment 0.3% of construction cost and Consents

Table 8.1 Pre-construction Cost Estimates (fair basis assumptions)

8.2 Barrage and Lagoon Civil Engineering Cost Estimates Cost Methodology

The main purpose of the civil engineering cost estimates is to provide a reasonable basis for comparison between the various long list options. The estimates presented in this section do not necessarily reflect the optimal cost assessments for specific options but are instead derived from the generalised and consistent application of cost rates across all the options.

A reasonably detailed estimate has been prepared for the B3 Barrage based on approximate quantities for the civil engineering work derived from information provided in Vols 3A and 3B of the DOE Report. Rates and prices have been assessed at 1st quarter 2008 price level. No allowance has been made for future inflation beyond this date.

For these options, principal quantities have been estimated for the following items:

Preliminaries Caissons (including casting yards, construction, installation and fit-out works) Embankments (including preparatory works, construction, and fit-out works) Navigation locks (where required) Surface Buildings Ancillary works (for example, navigation modifications, land drainage pumping stations)

Much less detailed information is available for other long list options and the estimates are therefore inherently less accurate. Estimates for other long list barrage options have therefore been based on a comparison between the overall dimensions

Final 127 December 2008 of the main civil engineering components and costs attributed in proportion to the B3 and B4 estimates as appropriate.

A high level estimate has been made of the L2 Fleming lagoon wall construction based on the principal components of the design shown in the Call for Proposals submission and following detailed review and subsequent revision by proposers of their designs. The estimate assumes that the scheme can be designed to include the lower cost forms of the wall solution (ie. forms 1A and 1B described in Section 6.1). More robust forms of wall will incur an increase in construction cost. A discussion on some issues over the technical feasibility of the lower cost wall forms is included in Section 6.1 and until these issues are resolved, the L2 cost estimate should be considered as a lower bound and treated with caution.

The cost of the L3 lagoons is highly dependent on the technology employed to construct the impoundment structure. Therefore, a high level estimate has been made of the forms of construction considered in Section 6.1 to determine which forms reflect the potential lower bound construction cost of the impoundment structures. Detail of this comparison is included in Appendix A.

8.3 Barrage and Lagoon Mechanical and Electrical Cost Estimates

Turbines and Generators

For the Bulb and Straflo turbines, cost estimates for turbines and generators have been developed by both independent review of existing turbine contracts and consultation with turbine manufacturers. These resulted in cost estimates that were within 2% of each other.

For multiple unit bulb turbines of 35 to 40 MW per unit capacity, a cost of £0.676m per MW has been applied consistently for the larger capacity barrages and lagoons. Straflo units, proposed for the B4 and B5 Barrages, are expected to be more economical at £0.611m per MW. These unit costs include delivery, installation, commissioning and contingency.

The turbine and generator costs have been based on the installed capacities estimated for this study (as set out in section 6.3).

Turbine and Sluice Gates

Gate costs have been estimated in detail for the B3 and B4 Barrages based on the available design information. These estimates have provided a cost per turbine and a cost per sluice for each different sluice gate size.

For the other barrages, an estimate has been made of the number and size of sluice gates taking account of the relative live storage volumes and, in the case of the Outer Barrage, taking account of the sluice gate sizes and numbers obtained from Bondi Final 128 December 2008 (1981). The turbine costs have allowed for the number and size of turbines that have been estimated for each barrage. For turbines and sluices, the costs per gate derived for B3 have been applied to B1 and B2 barrages and those for B4 Barrage have been applied to B5 Barrage and the L2 and L3 lagoons.

Transmission and Grid Connection

An assessment has been made of the principal components required between the generator terminals and the connections to onshore substations. A full breakdown of these costs is contained in Appendix A.

8.4 Tidal Fence Civil, Mechanical and Electrical Cost Estimate

The same principles as apply to barrages have been used to estimate the civil engineering costs of the F1a and F1b tidal fences which have been broken down into dredging and bed preparation, flow barrier construction, turbine foundation modules. An allowance has also been made for an access bridge. The detail is provided in Appendix A.

For the tidal fence turbines, research was undertaken of existing on-shore and offshore turbine/generator costs as well as reference to existing demonstration project costs. A figure of £2m per MW of installed capacity has been used in the analyses for the turbine, gearbox and generator with additional costs on a per unit basis for the cowl and installation. Although not identical, offshore wind turbine equipment offers the closest comparator although accurate costs are difficult to predict as material costs have been rising significantly since 2005. Costs of 2.23 million euros per megawatt (BTM Consult APS 2008) which equates to approximately £1.8m per MW have been reported in 2008 for offshore turbine equipment whilst earlier studies (Sustainable Development Commission Research Report 5 - Tidal Energy Case Studies, 2007) have used ranges of between £1m and £6m per MW of installed capacity for equipment and all associated costs. The 1.2MW demonstration turbine at Strangford Lough in Northern Ireland has a reported cost of £12m (all inclusive) which equates to £10m per MW. For this study, the total project cost for the F1b Tidal Fence is approximately £4m per MW which is significantly less than the Strangford Lough costs (reflecting the large scale implementation) and is the middle range of the costs bands used in the SDC Research Report.

8.5 Tidal Reef Civil, Mechanical and Electrical Cost Estimate Very little design information is available on which to estimate the cost of a tidal reef. Therefore, a very high level estimate has been prepared and the detail of this estimate is set out in Appendix A. The estimate makes a number of very broad high level assumptions and approximations. None of these is considered precautionary and the overall estimate should therefore be treated with caution as it is likely to represent an optimistic estimate given the level of design information available and the absence of

Final 129 December 2008 any prototype or analogue on which to base the estimate. The assumptions are as follows:

Embankment required as a barrier to flow in the shallower regions estuary near each shoreline will be equivalent to B1; No navigation lock as such is proposed although the reef structure will require rotating turbine modules with a longer span than elsewhere on the reef to provide a navigable opening. There will be costs associated with these elements but none is included as there is no information available to determine the quantum; Surface building costs will be the same as B1; The structures which support the turbine and siphon modules and incorporate service tunnels, cable ducts, access shafts etc and the siphon modules themselves which house the turbine generators have been broadly estimated as 45% of the caisson cost of B1. This is on the basis that for stability the structure will require 45% of the weight of the B1 structure due to the reduced head differential. This assumes that the cost per tonne of barrage and reef structural components, including precasting, transportation, positioning, placing and infilling, are the same. It also assumes that the reef structure is a gravity structure and not piled (piled strucutres would be expected to be more expensive). This is not precautionary as it does not allow for special factors such as the complexity of the movable siphons modules; Turbine generators will be akin to tidal stream turbines and therefore the same £2m per MW rate has been used as applied to the tidal fence. This allows for fabrication, installation, commissioning and for elements required to fit the turbines into the structure. A further discussion on the cost of tidal stream turbines is included in Section 8.4; Grid connection cost will be 34% of the B1 cost pro-rata’d on the basis of installed capacity; The gate cost estimate assumes 2000 gates (2 per turbine), each 10m by 4m to control flow through the siphon and to act as stoplogs for turbine access. Costs have been based on £13,000 per sq. m which is equivalent to B1 and an additional allowance of £300m for temporary bulkheads during construction.

On the above principles, the overall civil, mechanical and electrical construction cost for the tidal reef is estimated at £15.7m which equates to just over £3m per MW compared to the £4m per MW estimated for the tidal fence. As stated above, this estimate should be treated with caution due to the lack of design information and the very broad assumptions stated above, many of which look favourably on the reef. The confidence behind this estimate is the least of all schemes. It must not be concluded that the reef concept is more economical than the fence concept as a generous optimism bias should be added to allow for uncertainty. With the current level of available design information, the estimate could conceivably be at least twice the £3m per MW estimate but without the application of optimism bias, which has been omitted from the fair basis approach, there is no rationale for making such a global adjustment to the estimate.

Final 130 December 2008 8.6 Grid Reinforcement

A high level estimate of the grid reinforcement is included in Section 6. These costs have not been included in the scheme cost estimates as National Grid would typically pay for these works, and charge the regulated cost reflective tariff to the generating company.

8.7 Compensatory Habitat

Guidance on providing compensatory habitat, existing practice and precedent has established that provision should be at a ratio that may exceed 1 Ha of compensatory habitat for every 1 Ha of habitat lost (in some cases a ratio of 3:1 has been required). This recognises the uncertainty and risks of establishing a habitat that maintains the ecological functions of the habitat that is lost.

This study provides estimates of the cost of providing compensatory habitat at ratios of 3 Ha for every 1 Ha lost, and at 1Ha for every 1 Ha lost. This acts as a sensitivity analysis by offering a range of values for each option. It should be noted that this does not make any assumptions about an appropriate ratio to apply to the Severn Estuary and that some compensation ratios have exceeded a 3:1 ratio. At this stage of the assessment it should also be recognised that the basis of this estimating is simplistic based on area of inter-tidal habitat lost and takes no account of the need and likely cost of other compensatory measures that might be required. The scale of any option and its potential effect on a European site is unprecedented and could require an unprecedented level of compensation. This creates an additional element of uncertainty around quantifying and managing the risk and effectiveness of compensatory measures which has not been considered at this stage.

The cost estimate for the offshore lagoon at Bridgwater Bay assumes that no compensatory habitat is required although it should be noted that this is not a precautionary assumption.

Compensation costs have been provisionally estimated, based on the replacement of areas of intertidal areas lost under each option through 'managed realignment'. This is a simple approach, prior to more detailed investigation, to derive costs for the compensation of the unmitigated loss of internationally designated habitats and species. In practice, managed realignment is very unlikely to be the only approach taken to deliver compensation measures, but it would almost certainly represent the great majority of the cost. The costs have been estimated at £65k per Hectare based on calculation of inter-tidal areas from the static models that are used in the fair basis assessment of proposals. This cost rate is derived from literature review of the costs of implementing managed realignment schemes to create new intertidal areas (Rupp- Armstrong et al, 2008, CIRIA, 2001) and consultation with Statutory Consultation Bodies. Whilst this rate is in the upper range for managed realignment schemes in the UK, it reflects the higher cost associated with Natura 2000 compensatory schemes and / or those where a new counter wall of significant length is required. In addition

Final 131 December 2008 to the uncertainty of likely cost per hectare, it is also likely that the static models overestimate the total area of inter-tidal areas lost and that subsequent hydrodynamic modelling will achieve a more refined estimate of total areas lost through the changed tidal regime.

8.8 Ancillary Works Costs

All options require consideration of ancillary works - works that are necessary as a consequence of the construction of a tidal power facility to mitigate the impact on day to day operation of existing assets. These are in addition to any mitigation works incorporated directly into an energy generation structure such as ship locks, fish passes etc. Such assets include:

- Modification of port facilities as a consequence of reduced high water levels and changes in vessel buoyancy - Navigational aid requirements - Pumping systems at tidal outfalls to allow land drainage discharges that would otherwise have been prevented from the reduced tidal range - Permanent works for dredging and sedimentation management - Additional flood defence protection from increased erosion due to changed water levels

At present, these costs are included as a provisional sum for each option with the size of provision, for this stage, depending upon the assessed change in water levels for each proposal. The sums are calculated on a linear scale between £400m for a large effect on the tidal range over the estuary upstream of the Outer barrage location to £10m for a small effect on the tidal range over a smaller region.

Client’s promotional costs

Client’s promotional costs, including the client’s project management, have been included in the cost estimates at a rate of 2% of the capital cost.

Exclusions

The following items have been excluded from the construction cost estimates:

x Environmental mitigation (except impacted land drainage – see 8.8 above) x Historical costs incurred on project x Land and property acquisition x Parliamentary costs and public relations x Public road or rail link across barrage (or passive provision for them) x VAT

Contingency and Optimism Bias

Final 132 December 2008 A 15% contingency has been applied to the combined net values of the civil engineering works, including gates. For the initial fair basis evaluation, optimism bias has not been applied as there has not yet been an assessment of appropriate optimism bias specific to each scheme. A consistent application of the 66% optimism bias adjustment recommended in Treasury guidance10 for non-standard civil engineering projects would not affect the selection of options to study further in Phase 2. Cost estimates should therefore not be used as an assessment of the likely out-turn project cost.

The contingency item should be regarded as a temporary provision subject to the results of a quantitative risk assessment which should be carried out at a future stage in the study. Once completed, estimates can then be reconciled with Treasury guidelines.

Construction Cost Estimates

Construction cost estimates (fair basis assumptions) are presented in Table 8.2 for each long list option before habitat compensation costs.

10 HMT Green Book Supplementary Guidance on Optimism Bias, http://www.hm- treasury.gov.uk/d/5(3).pdf

Final 133 December 2008 Option Assessed Construction Cost (excluding compensatory habitat cost) (£bn) B1 - Outer Barrage from Minehead to Aberthaw 29.0 B2 - Middle Barrage from Hinckley Point to Lavernock 21.9 Point B3 – Middle Barrage from Brean Down to Lavernock 18.3 Point (formerly Cardiff – Weston) B4 – Inner Barrage (Shoots) 2.6 B5 - Beachley Barrage 1.8 F1a – Tidal Fence (Lavernock to Brean Down) 4.4 F1b – Tidal Fence (Outer) 6.3 L2 – 2008 Russell Lagoon Option (based on Fleming 3.1 tied panel construction) L3a – Russell Lagoons English Grounds 2.6 L3b – Russell Lagoons Welsh Grounds 3.7 L3c – Russell Lagoons Peterstone Flats 3.3 L3d – Bridgwater Bay Land Connected Lagoon 3.0 L3e(i) – 90km2 offshore lagoon off Bridgwater Bay 5.8 L3e(ii) – 50km2 offshore lagoon off Bridgwater Bay 3.5 R1 – Tidal Reef 18.1 U1 – Severn Lakes Scheme Unquantified due to insufficient data

Table 8.2 Construction Cost Estimates (fair basis assumptions)

It should be noted that the fair basis assumptions have resulted in cost estimates which are higher than those previously published. This includes the estimated construction cost of the L2 2008 Russell Lagoon which differs markedly from the £2bn cost estimated referenced in the Fleming Group submission. Further dialogue has been held with Proposers to reconcile engineering issues that influence cost estimates.

A sensitivity test has been applied during the assessment of options to assess the degree to which increased ratios of habitat compensation impact the relative differences between the options. This is shown in Table 8.3 for all options.

Final 134 December 2008 Option Construction Cost Estimate Based on 1:1 ratio Based on 3:1 ratio of compensatory of compensatory habitat provided to habitat provided to habitat lost (£bn) habitat lost (£bn) B1 - Outer Barrage from Minehead 31.0 34.7 to Aberthaw B2 - Middle Barrage from Hinckley 23.5 26.9 Point to Lavernock Point B3 – Middle Barrage from Brean 19.6 22.2 Down to Lavernock Point (formerly Cardiff – Weston) B4 – Inner Barrage (Shoots) 2.9 3.5 B5 - Beachley Barrage 2.1 2.5 F1a – Tidal Fence (Lavernock to 4.5 4.8 Brean Down) F1b – Tidal Fence (Outer) 6.5 6.9 L2 – 2008 Russell Lagoon Option 3.6 4.4 (based on Fleming tied panel construction) L3a – Russell Lagoons English 2.7 3.0 Grounds L3b – Russell Lagoons Welsh 4.1 4.9 Grounds L3c – Russell Lagoons Peterstone 3.5 3.8 Flats L3d – Bridgwater Bay Land 3.4 4.1 Connected Lagoon L3e(i) – 90km2 offshore lagoon off 5.8 5.8 Bridgwater Bay L3e(ii) – 50km2 offshore lagoon off 3.5 3.5 Bridgwater Bay R1 – Reef 18.7 19.8 U1 – Severn Lakes Concept Unquantified due to insufficient data

Table 8.3 Construction Cost Estimates for Alternative Amounts of Compensatory Habitat

A summary breakdown of costs by option for all options (including habitat compensation at the 3:1 ratio) is shown in Figures 8.1 (large barrage options) and 8.2 (smaller options).

Final 135 December 2008 Summary of Construction Costs

40,000 Habitat Compensation 35,000 Contingency 30,000 Ancillary Costs 25,000 M&E Caissons 20,000 General Civil Works Cost £m 15,000 Prelims and Overheads 10,000 Site Investigation Design and Supervsion 5,000 Planning and PM - B1 B2 B3 R1 Options

Figure 8.1 Summary Breakdown of Costs for Large Barrages and Reef

Summary of Construction Costs

7,000 Habitat Compensation 6,000 Contingency 5,000 Ancillary Costs 4,000 M&E 3,000 Caissons Cost £m Cost 2,000 General Civil Works 1,000 Prelims and Overheads - Site Investigation B4 B5 F1a F1b L2 L3a L3b L3c L3d L3e(i) L3e(ii) Design and Supervsion Planning and PM Option

Figure 8.2 Summary Breakdown of Costs for Smaller Options

Final 136 December 2008 Figure 8.3 Summary Breakdown of Costs for Large Barrages as % of Total

Summary of Construction costs as % of Total Cost

100% 90% Habitat Compensation 80% Contingency 70% Ancillary Costs M&E 60% Caissons 50% General Civil Works 40% Prelims and Overheads

% of % Total Cost 30% Site Investigation 20% Design and Supervsion 10% Planning and PM 0% B4 B5 F1a F1b L2 L3a L3b L3c L3d L3e(i) L3e(ii) Options

Figure 8.4 Summary Breakdown of Costs for Smaller Options as % of Total

8.9 Cost per Unit Energy Methodology

The costs per unit energy, using a fair basis costing approach are detailed in Table 8.4. The fair basis costing approach includes a number of assumptions which are applied equally to all options. As such, the costs per unit energy are intended as indicators of energy cost differences between options not a reflection of actual cost which will be developed in more detail for short-listed options.

Final 137 December 2008 Construction costs are as detailed in section 8.1 and are inclusive of grid connection, and compensation works for land drainage and navigation. The costs are exclusive of grid reinforcement costs. The cost per unit energy in Table 8.4 are based on construction costs inclusive of high level indicative estimates for habitat compensation (using a 3:1 ratio) whilst the costs per unit energy in Table 8.5 exclude costs of habitat compensation. Costs per unit energy have been calculated taking into account construction programme (as set out in section 7.2), estimated energy output and operation and maintenance costs. Costs have been discounted at a rate of 8% and at 3.5% and 15% to assess sensitivity to discount rate. The discounted costs have been calculated over the full lifetime of the scheme up 2140. This period covers the full assumed 120 year useful life although the more robust schemes would be expected to have a useful life of at least 120 years with appropriate maintenance. The effect of discounting causes costs beyond 2140 to have a negligible impact on the assessment.

The assessment assumes that construction costs are distributed evenly over the construction period. It also assumes that where there is opportunity to do so, generation is commenced earlier than completion of construction and that output is ramped up as turbine and generating equipment is installed and comes on line, as set out in Section 7.

Operation and maintenance costs have been estimated in past studies for Cardiff to Weston and Shoots Barrages as 1.25% and 1.75% respectively. The difference represents an economy of scale and these percentages have been applied to other options based on their comparable scale. The costs include staff costs, routine minor civil mechanical and electrical maintenance, consumables, business rates, and insurances.

These allowances do not include major maintenance liabilities. For the purpose of calculating the cost of energy, all barrage and lagoon options have been assumed to have a major maintenance intervals of 40 years. The tidal fences have been assumed to have major maintenance intervals of 20 years as tidal stream technology is expected to have a 20 year design life. 20 year intervals have also been assumed for the tidal reef as the turbine generator technology is expected to be more akin to tidal stream than traditional hydropower technology. In the assessment, a major maintenance cost has been attributed to each scheme at these intervals to reflect the maintenance liability which will vary between proposals.

The major maintenance common to all proposals is the refurbishment of on- barrage/lagoon mechanical and electrical equipment which has been included in the comparison to take account of the different scales of equipment in each option. For barrages and lagoons, this has been estimated at a present day cost of 70% of the supply, installation and commissioning costs of mechanical and electrical equipment incurred every 40 years. For tidal fences, it has been estimated at a present day cost of 100% every 20 years.

Final 138 December 2008 Sedimentation represents a potentially very significant cost item which could vary significantly between options. However, the severity of sedimentation relating to each option (and therefore the cost of dredging of sediment deposits) is difficult to quantify without further analysis of the effect each option will have on the sediment regime. Sedimentation has therefore only been considered qualitatively as a key environmental effect.

Mitigation of other environmental impacts will also have implications with respect to construction and operational costs, and could potentially have an impact on energy yield. The magnitude of the construction and operational costs, and energy yield implications, depends on the magnitude of the impact which has only been considered qualitatively at this stage. Therefore, a quantitative assessment in terms of construction cost and cost of energy has not been carried out.

Maintenance costs relating to the caisson and embankment structures have been excluded on the basis that they would be designed for a 120 year design life without major maintenance and routine maintenance of these components will not differentiate the energy costs of the different options. It has been assumed that the alternative lagoon wall proposals would be designed to be sufficiently robust so as not to require major maintenance over a 120 year life. Whilst the components of the wall are not themselves innovative, the application of these components in the form proposed in a marine environment is. There are inherent risks in such an innovation which could lead to the wall carrying a greater liability than an equivalent embankment as discussed in section 6.2.

Unit Costs of Energy

The costs per unit energy for each scheme is presented in Table 8.4. The capital cost, maintenance, replacement costs and energy yields on a year by year basis are set out in Appendix A.

Option Option Name Cost of energy (p/kWh) for different discount No rates (based on 3:1 habitat compensation ratios)

8% 3.5% 15%

B1 Outer Barrage from 16.24 7.30 37.51 Minehead to Aberthaw

B2 Middle Barrage from 16.67 7.82 36.82 Hinkley to Lavernock Point (Severn Barrage to Hinkley and Brean)

Final 139 December 2008 Option Option Name Cost of energy (p/kWh) for different discount No rates (based on 3:1 habitat compensation ratios)

8% 3.5% 15%

B3 Middle Barrage from 15.29 7.39 32.35 Brean Down to Lavernock Point (Cardiff to Weston Barrage)

B4 Inner Barrage (Shoots 13.68 6.69 27.55 Barrage)

B5 Beachley Barrage 16.48 8.21 31.98

F1a Tidal Fence (Lavernock to 75.00 40.47 135.24 Brean Down)

F1b Tidal Fence (Outer) 24.20 14.33 42.75

L2 2008 Russell Lagoon 20.43 9.99 41.20 Option (based on Fleming tied panel construction) Russell Lagoons English L3a 22.22 11.35 42.71 Grounds Russell Lagoons Welsh L3b 23.01 11.27 46.31 Grounds Russell Lagoons Peterstone L3c 18.06 9.03 36.03 Flats Bridgwater Bay Land L3d 16.85 8.29 33.88 Connected Lagoon Lagoon 90km2 offshore lagoon off L3e(i) 25.90 12.86 53.29 Bridgwater Bay 50km2 offshore lagoon off L3e(ii) 29.64 15.05 58.68 Bridgwater Bay Tidal Reef R1 21.671 12.161 43.571

Note: 1. These estimates should be read in conjunction with the comparison of unit energy costs in Section 8 which notes that the R1 reef cost estimates are highly uncertain and could be at least twice the stated values Table 8.4 Unit Costs of Energy

Final 140 December 2008 Table 8.5 shows the differences in energy cost between the options excluding the provision of habitat compensation and the likely range in costs for provision of habitat compensation based on rations of 1:1 and 3:1.

Option Option Name Cost of energy (p/kWh) excluding and including No habitat compensation

8% 3.5% 15%

Habitat Compensation Excl Inc Exc Inc Exc Inc Excl – excluded Inc – Included (range)

B1 Outer Barrage from 13.94 14.70 6.42 6.72 - 31.92 33.78 - Minehead to Aberthaw -16.24 7.30 37.51

B2 Middle Barrage from 13.96 14.87 6.78 7.13 - 30.41 32.54 - Hinkley to Lavernock -16.67 7.82 36.82 Point (Severn Barrage to Hinkley and Brean)

B3 Middle Barrage from 12.94 13.72 6.46 6.77 - 27.00 28.79 - Brean Down to Lavernock -15.29 7.39 32.35 Point (Cardiff to Weston Barrage)

B4 Inner Barrage (Shoots 10.40 11.49 5.35 5.79 - 20.51 22.86 - Barrage) -13.68 6.69 27.55

B5 Beachley Barrage 12.58 13.88 6.58 7.13 - 23.91 26.60 - -16.48 8.21 31.98

F1a Tidal Fence (Lavernock to 69.40 71.68 38.00 39.04 124.30 128.70 Brean Down) -75.00 -40.47 -135.24

F1b Tidal Fence (Outer) 22.72 23.35 13.70 13.98 39.79 41.02 - -24.20 -14.33 42.75

L2 2008 Russell Lagoon 15.46 17.18 7.98 8.68 - 30.48 34.18 - Option (based on Fleming -20.43 9.99 41.20 tied panel construction)

L3a Russell Lagoons English 19.72 20.55 10.30 10.65 37.52 39.25 - Grounds -22.22 -11.35 42.71

Final 141 December 2008 Option Option Name Cost of energy (p/kWh) excluding and including No habitat compensation

8% 3.5% 15%

L3b Russell Lagoons Welsh 17.84 19.56 9.16 9.87 - 35.21 38.91 - Grounds -23.01 11.27 46.31

L3c Russell Lagoons Peterstone 15.93 16.64 8.16 8.45 - 31.46 32.99 - Flats -18.06 9.03 36.03

L3d Bridgwater Bay Land 13.02 14.30 6.73 7.25 - 25.66 28.40 - Lagoon Connected Lagoon -16.85 8.29 33.88

L3e(i) 90km2 offshore lagoon off 25.90 25.90 12.86 12.86 53.29 53.29 Bridgwater Bay

L3e(ii) 50km2 offshore lagoon off 29.64 29.64 15.05 15.05 58.68 58.68 Bridgwater Bay

R1 Tidal Reef 20.301 20.77- 11.631 11.82 40.351 41.43 - 21.671 - 43.571 12.161

Comparison of Unit Energy Costs

The comparison of energy costs shows that cost of energy generally becomes more economic between the Outer Barrage and the Inner Barrage which is consistent with the finding of earlier studies. The Beachley Barrage has been found to be less economic than the Shoots Barrage which would be a result of its lower output potential due to the limitations on turbine numbers that could be provided within the space available. Barrage B4 is the most economical of all the schemes. Barrage B5 is comparable to B3.

The comparison shows that the L3d Bridgwater Bay lagoon is the most economical of the L3 lagoons whilst L2 is more economical than all L3 lagoons except L3d in most sensitivity tests. The comparison also shows that the more economical lagoons have relatively similar costs per unit energy to the larger barrages, higher unit energy costs than the smaller barrages but lower than the tidal fence options.

Final 142 December 2008 Offshore lagoons at Bridgwater Bay are less economic than land connected lagoons on account of the additional construction required to enclose the basin. The larger offshore lagoon is the more economic of the two considered but both are the least economic of all options with the exception of the F1a fence.

The Tidal Fence F1a option proves to be significantly less economic than F1b and the least economic of all schemes. It is less economic than F1b because:

x at the outer location a turbine size of 1.6MW is feasible compared to only 1MW at the Lavernock to Brean Down location; x the civil engineering infrastructure requirements at the outer location are less onerous; and x 800 turbines can be accommodated at the outer location compared to 256 at the Lavernock to Brean Down location.

The R1 Tidal Reef has a higher estimated cost per unit energy than the barrages and the land connected lagoons but a lower unit cost than the offshore lagoons and the tidal fences. However, the estimates for the tidal reef should be treated with caution as the construction cost is based on very limited design information and a high degree of uncertainty is attached to these estimates due to the embryonic nature of the concept. Optimism bias has not been applied in the fair basis approach but it should be noted that the estimated unit costs for the R1 reef could be at least twice the quoted values.

8.10 Risk Assessment

Each option has been assessed in terms of risk. Risk has been qualitatively assessed in terms of probability (High, Medium, Low) and impact (High, Medium, Low). The technical risk assessment is a development of work carried out across the feasibility study workstreams which included risk workshops attended by the study team and invited experts, and through informed technical work carried out as part of the options analysis. The risks considered in this assessment are those technical risks that differentiate between the schemes. Non-technical risks, such as political and reputational risks, have not been considered. Environmental risks, such as risk of geomorphological change and risk of sedimentation, have been considered in Section 5 and are assessed qualitatively during the assessment screening process. Environmental risks are therefore not assessed in this section.

The risks assessment is set out in Table 8.6. An analysis of the risk assessment is set out in Table 8.7.

Final 143 December 2008 Description Mitigation Likelihood/ B1 B2 B3 B4 B5 F1a F1b L2 L3 L3 L3 R1 Consequence a - d e(i) e(ii) Designs based on ground Conduct further Likelihood M M M M M M M H H H H M investigation data may require detailed ground modification if ground conditions condition surveys encountered during construction Consequence M M M M M M M H H H H M prove more challenging than forecast introducing construction delays and increased costs The requirement to pay a royalty to Scheme choice could Likelihood L L L L L M M M M M M M use the technology employed in the be amended based on construction of the scheme. the costs of intellectual property Consequence L L L L L L L L L L L L applicable to some schemes Material availability can impact upon Alerting the supplier Likelihood M M M L L M M L L M L M overall project costs through both market to material direct cost increases and time requirements in overruns. A lack of materials will advance of Consequence H H H H H H H H H H H H stall the project and could also add a construction. premium on to material price. This is especially true for the larger scheme due to the vast quantities of materials required. Difficulties in procuring marine plant The pre-procurement Likelihood M M M L L M M L L M L M equipment due to resource of plant equipment; competition from other projects. and alerting the Competition for plant could increase market to the exact costs through the creation of a price plant requirements Consequence L L L L L L L L L L L L premium as well as delay project well in advance of completion construction

Final 144 December 2008 Description Mitigation Likelihood/ B1 B2 B3 B4 B5 F1a F1b L2 L3 L3 L3 R1 Consequence a - d e(i) e(ii) Adverse tides and weather conditions Appoint Likelihood H H H H H H H H H H H H may have an impact on construction organisations with causing delays to delivery and experience in possible damage to electrical and operating in similar mechanical equipment increasing conditions, who are Consequence L L L L L L L L L L L L costs likely to price the risk into the contract, this will ensure the project is not delayed more than necessary It is questionable whether the market The testing of the Likelihood M M M L L H H L L L L H will be able to meet the project's markets capability to demand for turbines. If the market is meet the demand unable to provide the number of level required would turbines required within the be a good indicator - timeframe available it will cause time this would also give Consequence H H H L L H H L L L L H delays to completion and potentially them market time to price premiums on the turbines. react to the forecast demand. It could also be possible to commission the turbine contract early. There will be other large scale Forward planning of Likelihood M M M L L M M L L M L M construction projects commencing at resource the same time as a Severn Tidal requirements Power project which will lead to competition for labour. This could result in labour shortages causing Consequence M M M L L M M L L M L M project delays; there is also the potential for cost escalation due to premium wages demanded by specific manpower.

Final 145 December 2008 Description Mitigation Likelihood/ B1 B2 B3 B4 B5 F1a F1b L2 L3 L3 L3 R1 Consequence a - d e(i) e(ii) There is a chance that a rise in sea Build the potential for Likelihood L L L L L L L L L L L L levels could limit the effectiveness of sea level rise into the any of the schemes. The lagoon design of each of the schemes are more susceptible to sea schemes. Consequence L L L L L L L M M M M L level rise. Once operational there is an Navigation measures Likelihood L L L L L H L L L L L H increased risk of shipping accidents provided in estuary Consequence H H H M M H H L L L L H

Delays in development of technology Use of established Likelihood L L L L L M M L L L L H cause longer than planned pre- technology construction development period prototyping of with delay to generation or possible technology and pilot Consequence L L L L L H H L L L L H cancellation testing at smaller scale Key

H = High

M = Medium

L = Low

Table 8.6 Technical Risk Assessment of Long Listed Options

Final 146 December 2008 Option Summary of Higher Risks Overall Assessment B1 - Outer Barrage from Higher risks compared to other Medium Minehead to Aberthaw schemes relate to: risk schemes B2 - Middle Barrage from Material, labour and plant Hinckley Point to availability Lavernock Point Risk of shipping accidents B3 – Middle Barrage from Brean Down to Lavernock Point (formerly Cardiff – Weston) B4 – Inner Barrage (Shoots) The only higher risks compared to Low risk B5 - Beachley Barrage other schemes is the increased risk of schemes shipping accident F1a – Tidal Fence Higher risks compared to other High risk (Lavernock to Brean Down) schemes are in: schemes F1b – Tidal Fence (Outer) Intellectual property costs Material, plant and labour availability Turbine availability Risks of shipping accidents Delay in development of technology L2 – 2008 Russell Lagoon Higher risks compared to other Medium Option (based on Fleming schemes are in: risk scheme tied panel construction) The suitability of the wall solution to prevailing ground conditions and vulnerability to variable ground conditions Intellectual property costs Potential to adapt for sea level rise not easily built into scheme design

L3a – Russell Lagoons The risk profile is similar to L2 Medium English Grounds risk schemes L3b – Russell Lagoons Welsh Grounds L3c – Russell Lagoons Peterstone Flats L3d – Bridgwater Bay Land Connected Lagoon

Final 147 December 2008 Option Summary of Higher Risks Overall Assessment L3e(i) – 90km2 offshore The risk profile is similar to L2 and Medium lagoon off Bridgwater Bay L3(a to d) but with the additional risk risk schemes of material, plant and labour availability L3e(ii) – 50km2 offshore The risk profile is similar to L2 and Medium lagoon off Bridgwater Bay L3(a to d) risk scheme R1 – Reef Higher risks compared to other High Risk schemes are in: Scheme Intellectual property costs Material, plant and labour availability Turbine availability Risks of shipping accidents Delay in development of technology U1 – Severn Lakes Concept Insufficient data on which to evaluate risk

Table 8.7 Risk Analysis

Final 148 December 2008 SECTION 9

ASSESSMENT SCREENING

Final 149 December 2008 9 ASSESSMENT SCREENING

The assessment of each option has been undertaken by issue area experts and subject to peer review. The quantitative input to the assessment is based on the consistent application of assumptions and principles which are aimed at achieving a fair comparison between options. The input is not provided in absolute terms but instead reflects the merits of each option relative to each other with the aim of establishing whether the individual proposal could be taken forward and be developed to meet the plan objectives. The assessment is summarised in the assessment screening sheets contained within this section which should be read in conjunction with the remainder of this options analysis report. The full assessment model is reproduced in Appendix B.

9.1 Application of the Assessment Framework

Quantitative Screening The assessment worksheet provides the data on which the options will be assessed quantitatively to determine those options which are significantly more favourable in terms of the cost and amount of energy they are likely to produce, their financial feasibility, timescales for power generation, degree of technical risk and their potential contribution to the UK’s commitments under the forthcoming Renewable Energy Directive and Climate Change Act and goal to deliver a secure supply of low- carbon electricity. The analysis of this data is summarised in Section 10 and the model outputs are contained within Appendix B.

Qualitative Screening All options have been assessed qualitatively in terms of their environmental, social, economic and regional effects in the assessment worksheets. Those options which have less favourable assessments from the quantitative screening but may be marginal in terms of the energy criterion have been subject to a qualitative screening to determine whether, on the information currently available, they appear to be attractive when environmental, grid compatibility, and regional economic and construction impact are considered. The analysis of this data is summarised in below and the model outputs are contained within Appendix B.

Final 150 December 2008 9.2 Summary of Analysis

To assist in the presentation of the conclusions, the options have been categorised into three groups so that options with similar characteristics are presented together. The three groups are:

x Tidal Barrages x Tidal Lagoons x Embryonic Options

The options are considered under three headings:

x Initial Screen x Quantitative Assessment x Qualitative Assessment

Final 151 December 2008 Initial Screen Severn Lakes (U1) The Severn Lakes concept was originally included because one of its objectives is to produce power using the tidal range of the Severn. Tidal power is part of the business plan which also relies on many other economic drivers to substantiate the cost of building a 1km wide causeway across the Severn, including development land, marinas, landfill and other renewable energy technologies. This is acknowledged by the proposer. The information relating to this option comes from the proposer’s web site and provides details of the general conceptual details. It is understood that specific design elements are being worked on but are not available for consideration by this study. The construction of a wide causeway could not result in a lower cost of energy compared to an equivalent barrage because of the increased civil engineering works required. Therefore, for the scheme to be justifiable on commercial grounds, the value of the mixed development would need to offset the opportunity cost of the increase in energy cost. As this study is only examining potential options from an energy perspective this option will not considered specifically by the Study. However, should tidal power development from the Severn form part of Government’s future energy policy, a privately proposed option such as Severn Lakes could be considered in the future. For this reason, this report will reference information relevant to Severn Lakes for information.

Quantitative Assessment Summary The Quantitative Assessment focuses on energy (including contribution towards the UK’s climate change goals), time and costs. The key metrics that capture the various quantitative measures are the levelised costs and annual energy output (and thus the potential reduction in carbon dioxide emissions) for each option. The levelised costs are calculated by discounting the stream of generation costs over the lifetime of the asset (120 years) and dividing this value by the amount of electricity generated over this period to calculate the price at which the generator would have to sell the electricity generated in order to break even over the period.

The tables below tabulate the annual energy yield and total carbon dioxide emissions savings over the assumed lifetime of each option. Carbon costs during construction, decommissioning and major refurbishment have been accounted for and 1MWh of energy production has been equated with 0.43t CO2 to be consistent with the Renewable Energy Strategy. Capital Cost excluding compensatory habitats and grid reinforcement costs are also given. The tables are presented for the three categories referenced above, namely tidal barrages, tidal lagoons and tidal fences.

Final 152 December 2008 The second and third tables within each category present the levelised costs for each option. These cover a period of 120 years for all options and where individual asset lives are less than this, the cost of refurbishment and/or replacement as appropriate has been included. These figures are presented excluding habitat compensation costs and including an estimate of compensatory habitat using a 3:1 replacement ration of new habitat to inter-tidal habitats lost.

Levelised costs here are calculated by discounting the stream of generation costs over the lifetime of the asset (120 years) and dividing this value by the amount of electricity generated over this period to calculate the cost per MWh of electricity generated such that the generator would break even. Calculating levelised costs over the lifetime of the asset illustrates the cost of generation if the lifetime of the asset is the same as the financial lifetime of the project. If the financial lifetime of the project is shorter than this, the levelised costs would be higher than those shown here but would exclude the residual value of the asset beyond the financing period of the project. Tidal Barrage Options

OPTION B1 B2 B3 B4 B5 Annual Energy 25.3 19.3 16.8 2.8 1.6 Yield (TWh) Lifetime CO2 emission savings 1,270 970 845 140 80 (mt) Capital Cost (£bn) 29 22 18 2.6 1.8 excluding habitats Capital Cost (£bn) with 3:1 habitat 35 27 22 3.5 2.5 compensation Table 9.1 Energy Yield, Lifetime CO2 savings and Capital Costs for Tidal Barrage Options

OPTION B1 B2 B3 B4 B5 Discount Rate Excluding Habitat Compensation (%) 3.5 6.42 6.78 6.46 5.35 6.58 8 13.94 13.96 12.94 10.40 12.58 15 31.92 30.41 27.00 20.51 23.91 Table 9.2 Levelised Costs excluding habitat compensation costs for Tidal Barrage Options

Final 153 December 2008 OPTION B1 B2 B3 B4 B5 Discount Rate 3:1 Habitat Compensation Ratio (%) 3.5 7.30 7.82 7.39 6.69 8.21 8 16.24 16.67 15.29 13.68 16.48 15 37.51 36.82 32.35 27.55 31.98 Table 9.3 Levelised Costs including habitat compensation costs at 3:1 ratio for Tidal Barrage Options The key conclusions from these tables are summarised below. For ease of comparison, capital costs quoted exclude compensatory habitats and levelised costs are presented using an 8% discount rate: x Barrage B1 (Minehead to Aberthaw) makes the greatest contribution to climate change targets (~1270mt reduced CO2 emissions over 120 years or 10mt per year) but at the greatest capital cost (£29bn); x Of the larger barrages, B3 (Cardiff to Weston) contributes significantly to climate change targets (7mt reduced CO2 emissions per year) and with the least unit cost (12.94p/kWh). x Of all tidal barrages, B4 (Shoots) has the lowest cost per kWh (10.40p/kWh)and whilst its contribution to climate change targets is still significant (1.2mt reduced CO2 emissions per year) it is significantly less than for larger barrages. x B5 (Beachley Barrage) has the lowest capital cost (£1.8bn) and would save 0.67mt CO2 emissions per year. Subject to the time taken to achieve planning consents, all large barrage options could be initiated in the next decade and be contributing to the UK’s Climate Change targets in the subsequent decade (2020 to 2030) It will be seen that, for the lower discount rate, the variation between options are relatively small. The Outer Barrage, with its greater energy output, emerges relatively strongly from this analysis, although it is likely to be subject to considerations from other work within the Feasibility Study, particularly considerations of affordability and the ability for the grid to absorb relatively large intermittent inputs of energy, particularly the low demand period at night when 50% of the energy will be produced. These are highlighted as risks for Option B3 so the scale of risk is greater for the larger B1 option. At all discount rates, B4 (Shoots) has the lowest cost per energy of all options considered by this study, including non barrage options.

Final 154 December 2008 Final 155 December 2008 Tidal Lagoon Options

OPTION L2 L3a L3b L3c L3d L3e Annual Energy 2.31 1.41 2.31 2.33 2.64 2.6 Yield (TWh) Lifetime CO2 emission savings 116 71 116 117 132 131 (mt) Capital Cost (£bn) 3.2 2.6 3.7 3.3 3.0 5.8 Capital Cost (£bn) with 3:1 habitat 4.4 3.0 4.9 3.8 4.1 5.8 compensation Table 9.4 Energy Yield, Lifetime CO2 savings and Capital Costs for Tidal Lagoon Options

OPTION L2 L3a L3b L3c L3d L3e Excluding Habitat Compensation Discount Rate (%) 3.5 7.98 10.30 9.16 8.16 6.73 12.86 8 15.46 19.72 17.84 15.93 13.02 25.90 15 30.48 37.52 35.21 31.46 25.66 53.29 Table 9.5 Levelised Costs excluding habitat compensation costs for Tidal Lagoon Options

OPTION L2 L3a L3b L3c L3d L3e Discount Rate 3:1 Habitat Compensation Ratio (%) 3.5 9.99 11.35 11.27 9.03 8.29 12.86 8 20.43 22.22 23.01 18.06 16.85 25.90 15 41.20 42.71 46.31 36.03 33.88 53.29 Table 9.6 Levelised Costs including habitat compensation costs at 3:1 ratio for Tidal Lagoon Options The key conclusions from these tables are: x Tidal lagoon options are similar in scale to the smaller barrage options (B4 and B5); x Lagoons located at Welsh Grounds (L2 and L3b) and (or off) Bridgwater Bay (L3d and L3e) plus Peterstone Flats (L3c) make the best contribution to climate change targets of all lagoons (>1mt reduced CO2 emissions per year). Although significant and comparable with the smaller barrages it is significantly less than for larger barrages.

Final 156 December 2008 x The design of lagoon proposed by the Fleming Group for Welsh Grounds (L2) and the land-connected Bridgwater Bay lagoon (L3d) using a variant of the geotextile construction proposed by Tidal Electric Limited (TEL) offer the least cost per kWh (13.0 to 15.5p/kWh) for lagoons as well as the best contribution to carbon targets. The cost per kWh is higher than the smallest barrages but of a similar order to the larger barrages. x The most expensive lagoon option is the offshore proposal (L3e). This has been modelled as a generic example of an offshore lagoon, located such that its foundations do not encroach on the inter-tidal zone. This has the benefit of having zero inter-tidal loss as a consequence of generating tidal energy. However, the depth of wall construction (by definition it has to exceed the tidal range if it is not to encroach on the inter-tidal zone) increases the cost of construction significantly, no matter what innovative forms of wall construction are used, by comparison with land connected lagoons of similar storage capacity by virtue of their shallower and therefore less expensive construction costs, albeit that wall lengths are longer. Subject to the time taken to achieve planning consents, all tidal lagoon options could be initiated in the next decade and be contributing to the UK’s Climate Change targets in the subsequent decade (2020 to 2030)

Final 157 December 2008 Embryonic Options

OPTION F1a F1b R1 Annual Energy 0.7 3.3 13 Yield (TWh) Lifetime CO2 emission savings 35 165 654 (mt) Capital Cost (£bn) 4.4 6.3 18

Table 9.7 Energy Yield, Lifetime CO2 savings and Capital Costs for Tidal Fence Options

OPTION F1a F1b R1 Discount Rate Excluding Habitat Compensation (%) 3.5 38.00 13.7 11.63 8 69.4 22.72 20.30 15 124.3 39.79 40.35 Table 9.8 Levelised Costs excluding habitat compensation costs for Tidal Fence Options

OPTION F1a F1b R1 Discount Rate 3:1 Habitat Compensation Ratio (%) 3.5 40.47 14.33 12.16 8 75.00 24.20 21.67 15 135.24 42.75 43.57 Table 9.9 Levelised Costs including habitat compensation costs at 3:1 ratio for Tidal Fence Options

The key conclusions from these tables are: x The alignment for Fence Option F1a between Cardiff and Weston is not viable and that if tidal fence technology is to be deployed in the Severn, an alignment between Minehead and Aberthaw (F1b) is preferable both in terms of contribution to carbon reduction targets and cost per kWh. x The energy output and the savings in carbon dioxide emissions from Option F1b are slightly greater than small barrages and lagoons but less than large tidal barrages.

Final 158 December 2008 x The Tidal Reef delivers significantly greater energy yields and lifetime carbon savings than tidal fences. x The cost per unit energy for all embryonic options is greater than for large barrages and significantly higher than the lowest cost option (B4).

It should be noted that the tidal fence uses tidal stream technology. At present this is still in demonstration stage with a single 1.2MW twin rotor unit commissioned within Strangford Lough within the past year. It is therefore likely that significantly more development time will be required to achieve sufficient confidence in the implementation costs and associated turbine performance before large scale deployment on the Severn could be realised. This implies that full scale generation of tidal fence technology on the Severn would lag tidal barrage and tidal lagoon options. Tidal Reef technology has not yet been developed and proposals are at concept stage only. Development of tidal reefs is therefore likely to lag behind tidal fences by as much as ten years if similar development cycles are anticipated.

Construction and Technology Risks All options involve risks. Tidal barrages represent the least risk but nevertheless weather related risks during construction increase the further downstream an option is located. Weather related risks can increase both construction timeframes and costs. Tidal lagoons, if selected as the preferred option, are likely to be constructed using a relatively innovate form of wall construction to create the tidal impoundment required. Analysis of these wall designs during this stage of the study has indicated that these designs have higher degrees of risk associated with them than more conventional (but more expensive) forms of construction. Such risks present themselves in terms of ground conditions and structural stability during construction, ability to withstand extreme surge events, ship impact and durability. More embryonic options have the additional risks of new product development cycles and the time required to attract sufficient confidence for large scale deployment.

Qualitative Assessment Summary

A key component of the assessment is the review of all options from a qualitative perspective in terms of environmental, social, economic or regional effects to

Final 159 December 2008 determine whether there are any significant issues that should either a) prevent any of the above options proceeding to the short list or b) allow other options which have less advantageous economic characteristics to proceed to the short list. A review of this indicates that all options have both positive and negative effects and that the scale of these effects differs across options. Impacts on Habitats All options would impact inter-tidal habitats including offshore lagoons. Although an offshore lagoon does not directly lead to loss of inter-tidal habitats, resultant changes in tidal currents and geomorphology will effect adjacent habitats. Following appropriate assessment which involves consideration of alternatives, and subject to the requirements of the Habitat regulations, should a decision to proceed on the basis of the over-riding public interest, compensatory measures would be required including habitat compensation for lost intertidal habitat. Not all compensation would necessarily be located in the Severn. For this report, these costs have been assessed in headline terms only using a range of possible replacement ratios and an indicative cost per ha.

Transportation links have not been considered by this study as there is no policy at present to increase the number of transportation links across the Severn. The activities of commercial ports will be affected by tidal barrages in particular and will entail navigation through an additional set of ship locks (increasing transit times) and modification of existing facilities to accommodate changed water levels. A

Final 160 December 2008 potential benefit for impacted ports will be increased high water standing times and a significant increase in low water level. Non barrage options will impact ports in different ways – tidal reefs and tidal fences will present challenges in time of entry / exit through their navigation provision because of the increased tidal currents that will prevail. Tidal lagoons may have less impact on ports although changes to dredging regimes may result from all options. The numbers of ports impacted differs depending upon the location of options

Flood defence is potentially enhanced upstream of any option which prevents sea levels being transferred upstream. This includes any option that barrages the Severn and also the Bridgwater Bay land connected lagoon, providing mitigation of adverse effects (for example submerged tide locked land drainage outfalls) is achieved so that existing standards of flood protection are maintained. These options may therefore offer improved protection from storm surges and sea level rise to communities located upstream compared with the other options.

Embryonic Technologies Tidal fence and tidal reef technology is still embryonic and there is less data available to assess environmental performance as none have yet been built. It is likely that, as these technologies present some impediment to flows though the Severn, both will have some effect on fish as they are attracted through the turbines. Geomorphology of the estuary will also change as a consequence of constructing these structures. For a tidal fence, associated benefits such as providing protection from sea level rise are not as significant as barrage options whilst the reduction in top water level impacts port operations located upstream – more ports are likely to be impacted than an equivalent output barrage options located further upstream, although the scale of impact will be less. Tidal fences have different characteristics than tidal barrages and lagoons as they utilise the kinetic energy of the tidal currents with some limited augmentation from the tidal range through the resistance to flow provided by the tidal fence. The increase in velocity profile across the fence may lead to negative effects in terms of water quality and potential erosion of the existing shoreline due to the accelerated estuary currents. On current information, for both tidal fence and tidal reef options, the loss of intertidal habitats is less than equivalent barrage structures but is likely to extend over greater lengths of the estuary shoreline (a consequence of locating tidal fence structures further downstream in the Estuary than an equivalent tidal barrage). The estimated loss of inter-tidal habitat should be considered with caution because it is based on limited information due to the absence of any precedent and the embryonic status of the concept. There is therefore a significant degree of uncertainty attached to these options.

Final 161 December 2008 SECTION 10

CONCLUSIONS

Final 162 December 2008 10 CONCLUSIONS

This section presents the overall conclusions from the analysis of options and the application of the assessment framework. This, alongside other work being undertaken as part of the Feasibility Study will be used by Government to recommend a draft short-list of options that have the technical potential to form the reasonable alternatives for the Strategic Environmental Assessment (SEA). The draft short-list will be finalised following examination by Government of non-technical issues which could impact on the overall feasibility of an option, and public consultation.

Following finalisation of a short-list, options will be worked up in more detail in order to develop a more detailed assessment of cost and energy yield, including modifying option configurations to achieve the optimal results having regard to construction/operating costs, value of energy produced and environmental/regional impacts.

Final 163 December 2008 10.1 Conclusions

The conclusions from this study have been developed following a logical process of data collection, analysis, evaluation and application of the assessment framework. The main conclusions are: x There are many options for generating tidal power from the Severn Estuary. These include both different locations and different technologies; x Contribution to reduction in carbon emissions is driven mainly by the annual energy yield and the earliest date by which energy production can be achieved. Those options that can contribute more to the Government’s Climate Change reduction targets will be the larger (energy yield) options and those that are mature in technology development terms. x The energy yields range from 0.7TWh per year to over 25TWh (7% of the UK’s electricity demand) per year depending upon the option under consideration. Construction costs range from over £1bn to circa £30bn or more if compensatory habitat costs are included; x All options, by virtue of capturing significant energy from the tidal regime, will effect, to some degree, the existing environment. In particular, the geomorphological response of the estuary and the effects of changes to the tidal range will need careful consideration as well as additional works to be undertaken to mitigate or compensate for these effects; x Other significant environmental effects include: Rate of sedimentation for tidal lagoons and the smaller tidal barrages. The impact on fish of changing currents and flow passages and the different mortality rates depending upon location, operational mode and type of turbines used. The impact on birds, particularly for those options where inter-tidal habitats that are lost account for a significant proportion of the estuary. x Not all environmental effects are necessarily negative. For example, reduced currents within impounded basins could lead to a reduction in suspended silt with the consequent improvement in turbidity and biological productivity. x Regional and social effects also comprise impacts and benefits. Negative impacts include effects on ports and fisheries. However, positive effects include employment during and after construction, and, particularly for tidal barrages and the tidal reef, enhanced protection from storm surges and sea level rise (on the basis that mitigation costs are included to modify tidal outfalls upstream of barrages and lagoons to deliver the same land drainage performance). x All schemes should be designed to accommodate predicted sea level rise in line with guidance current at the time of design development and all would be

Final 164 December 2008 adaptable if actual sea level rise exceeds predictions. Barrages would be the most adaptable of all schemes in the event that sea level rise exceeds the tolerance built into the design, as they have the largest proportion of turbine caissons. The larger barrages are also the schemes which provide the greater degree of flood risk benefits, due to the protection they would provide against surge tides and the greater extent of the reduction in high water level which they would cause. Tidal lagoons, the tidal reef and tidal fences would require onerous modifications and/or a greater degree of initial structural redundancy to adapt for sea level rise. x Costs of tidal power generation, on a per kWh basis, vary significantly depending upon the discount rate used because of the initial high capital cost. At lower discount rates, the benefit of the effectively zero fuel cost has greater significance. x Cost per unit energy for barrages and lagoons reduce as the natural tidal range increases, but increase with barrage / lagoon length and depth or if the site is physically constrained in terms of feasible turbine capacity. x Land-connected tidal lagoons are constructed in shallower waters than offshore tidal lagoons (by definition, if an offshore lagoon is not to impact inter-tidal areas, wall depths have to exceed the maximum tidal range). Although land connected lagoons generally require longer wall lengths to impound the same live storage volume, the cost per metre length of wall is significantly less than for an off-shore lagoon of the same volume because of the reduced wall depth. x It has been recognised by the SDC Report “Turning the Tide” as well as other sources, that there are more promising locations for tidal stream technology (as used in the Tidal Fence options) than the Severn. Although outside the scope for this report, nevertheless, it is relevant to note that development of a tidal fence may have a better return on investment in higher tidal current locations such as the Pentland Firth. x Tidal Fence costs are influenced by water depth and their ability to efficiently capture the kinetic energy within the constraints of the Severn. Because most of the tidal fence costs are made up of manufacturing and installation costs and involve a large number (800 for Option F1b) of individual turbines, the rate and cost of manufacture and installation is subject to change. x The Tidal Reef concept is not yet sufficiently advanced to permit reasonable assessment of energy yields / costs although an indicative analysis of the using fair basis assumptions gives a maximum 13TWh annual yield and £18bn construction costs. At an 8% discount rate, these figures produce a cost per kWh of approximately 20.3p. x Both tidal fence and tidal reef options are embryonic and require further development before large scale implementation. Tidal stream technology is at demonstration project status, with 1.2MW being tested currently. No tidal fence as proposed using this technology exists as yet. The tidal reef is at pre-design stage and exists as a concept only. If it follows a similar development path to tidal stream technology, it is likely that it will take at least ten years to pilot the technology followed by smaller scale implementation than that envisaged for the Severn. Although the programme assumptions for a tidal fence have been

Final 165 December 2008 modelled using the same start date as the more conventional tidal range projects (to enable fair comparison), the likely start date for first generation would be beyond this. Although this does not change the volume of carbon emission savings over the lifetime of the project, it will impact on the contribution this option could make to the Government’s 2050 carbon reduction target. x Costs of tidal power generation are also influenced by the construction programme and in particular the ability to generate power before the project as a whole is complete. This benefits the larger tidal barrage options where the civil engineering and grid connection works can be completed to allow generation from installed turbines ahead of all turbines being delivered and commissioned. It also benefits the modular tidal fence concept. This does not apply to the smaller barrage and tidal lagoon options, because of the smaller number of turbines which would be connected prior to first generation. x The costs involved in satisfying the requirements of the Habitats Directive are subject to detailed consideration in themselves and may be expected to increase the unit cost of energy by between 0 and 35%, depending upon the option selected and the assumptions made.

Different options have different effects, depending upon the technologies used, their location and the amount of energy abstracted from the estuary. In general, the more “permeable” (the greater the unimpeded flow) options have less impact than the least permeable (such as a barrage) for any given location. However, the more “efficient” options (the greater the energy yield at a specific location) affect a smaller area of estuary compared with the less efficient but more permeable options.

10.2 Overall Summary The conclusions from the Interim Options Analysis Report will form one of the inputs into the Government’s Feasibility Study. Outside of this report, wider questions will be asked as to whether there are issues beyond technical capability which may negatively impact on a proposal’s overall feasibility. For example a low confidence on the technology will attract greater levels of risks in terms of deliverability, costs and financing. The draft short-list will be finalised following examination by Government of non-technical issues which could impact on the overall feasibility of an option. The key conclusions from the analysis of options are presented in Table 10.1 overleaf.

Final 166 December 2008 Table 10.1- Summary for Each of the Options

Option Option Name Key Conclusions

B2 Middle Barrage from x Longest barrage option - based on the B3 option but with additional embankment extending the Hinkley to Lavernock barrage to Hinkley Point - Energy output of 19TWh/a; Point (Shawater concept) x Although the capital cost is less (£22bn), the cost of energy is similar to Option B1 at 13.96p/kWh; x Environmental effects are similar to those for B1 as this option seeks to provide similar flood defence benefits by crossing Bridgwater Bay; x Severn Ports upstream will be affected, primarily Bristol, Cardiff, Newport and Sharpness.

B3 Middle Barrage from x Most studied of any of the options and reported on in Energy Paper 57; Brean Down to x Annual energy output of 17TWh and a capital cost of £18bn; Lavernock Point x The cost of energy is the best of all the “large” options at 12.94p/kWh excluding compensatory (commonly known as habitat costs ; the Cardiff to Weston x Environmental impacts are potentially significant, as with other large barrage options, and will Barrage) result in reduction of water levels and tidal range, loss of inter-tidal habitats and impacts on bird and fish populations in the Severn; Benefits include protection from effects of storm surges, sea level rise and reduced turbidity.

Final 167 December 2008 Option Option Name Key Conclusions

x Severn Ports upstream will be affected, primarily Bristol, Cardiff, Newport and Sharpness.

B4 Inner Barrage (Shoots x Significantly smaller than the large barrage options, this option is located just downstream of the Barrage) Second Severn Crossing co-incident with the highest tidal range in the Severn; x Generates 2.77TWh per year at a capital cost of £2.6bn and achieves the lowest cost per unit energy at 10.4p/kWh; x Environmental impacts are similar in type (although not necessarily scale) to other barrage options although there is an increased risk of sedimentation; x This option does not impact the Ports of Bristol or the ABP Ports on the Welsh coast.

F1 Tidal Fence Proposals x Initially, proposed between Cardiff and Weston but a more feasible alignment was subsequently submitted by STFG Tidal considered between Minehead and Aberthaw; x Annual energy output of 3.3TWh is achievable at a cost of £6.3bn. Cost of energy is more than double the lowest cost option at 22.72p/kWh; x Assumes future development costs will reduce significantly from the current demonstration project costs for tidal stream technology. This implies a significant period of further development and experience before large scale implementation could be achieved. Unlikely that a decision to proceed with a tidal fence could be made in the short-term; x It does offer the possibility of less significant environmental effects than barrage options

Final 168 December 2008 Option Option Name Key Conclusions

although the area affected is as large as the biggest barrage option.

L2 Tidal Enclosure on the x Land connected lagoon located on the relatively high Welsh Grounds just downstream of the Welsh Grounds Shoots Barrage (B4); proposed by Fleming x It has an annual energy output (2.3TWh/a) achieved at a cost of £3.1bn. Cost per unit energy is Energy 15.46p/kWh and is thus more expensive than the larger barrage options, although development alongside B4 would reduce energy cost. Additional energy output could be achieved from the Welsh Grounds if the materials used in construction were excavated from within the basin to achieve greater live storage. This would marginally increase energy yield and thus reduce the cost of energy; x Land connected lagoons, like barrages, result in loss of inter-tidal habitats because of the significant reduction in tidal range within the impounded area. Other environmental effects are similar to smaller barrages except that impacts on fish and navigation are expected to be less because they do not form a barrier across the estuary.

L3 Tidal Lagoon Concept x Various land connected and offshore lagoon configurations have been studied using different (which has been forms of lagoon wall construction; subsequently modelled x As lagoon costs are influenced by the length and depth of wall forming the impounded basin, as four land-connected innovative methods of wall construction are required and the lowest cost option, (apart from the lagoons and three wall design proposed by Fleming Group for Option L2) comprises a geotextile solution using offshore lagoons based material dredged from the estuary and protected by rock armour (externally) and revetment on various general (internally); submissions received x Aside from the L2 Welsh Grounds proposal, Bridgwater Bay offers the most cost effective lagoon from the Call for option with a higher energy yield (2.64TWh/a) and slightly reduced capital costs than L2 giving Evidence) a cost per kWh of 13.02p/kWh. x An offshore lagoon, located below the low water contour (and reduced impact on habitats), has been modelled to produce a similar energy output using the same forms of construction.

Final 169 December 2008 Option Option Name Key Conclusions

Because of the much deeper wall construction required, it is more expensive with a capital cost of £5.8bn for the same energy output of 2.6TWh/a as the £3bn Bridgwater Bay land connected option. This is also reflected in the cost of energy which is more than double the land connected lagoon alternative.

U1 Severn Lakes (promoted x Originally included because one of its objectives is to produce power using the tidal range of the by Gareth Woodham) Severn. x The cost of constructing a 1km wide causeway 16km in length would be significantly more than a conventional tidal barrage and clearly requires additional investment streams to justify its cost. On the basis of the information within the public domain, this is also recognised by the proposer who envisages other revenue streams from land, recreational and other energy developments as part of this scheme. x This study is only examining potential options from an energy perspective. For this reason this option is not considered specifically by the Study. x Should tidal power development from the Severn form part of Government’s future energy policy, a privately proposed option such as Severn Lakes could be considered in the future.

Final 170 December 2008 APPENDIX A

FINANCIAL ANALYSIS DATA

Final December 2008 APPENDIX A

FINANCIAL ANALYSIS DATA

APPENDIX A1 EXPLANATORY OVERVIEW OF COST ESTIMATES

DISCOUNTED CASH FLOW WORKSHEETS

SHEETS 1 TO 3 - NO HABITAT COMPENSATION

Sheet 1 Summary of Costs

Sheet 2 Annual Cost Flows

Sheet 3 Annual Energy Outputs

SHEETS 5 TO 8 - HABITAT COMPENSATION RATIO OF 1:1

Sheet 4 Summary of Costs

Sheet 5 Annual Cost Flows

Sheet 6 Annual Energy Outputs

SHEETS 7 TO 9 - HABITAT COMPENSATION RATIO OF 3:1

Sheet 7 Summary of Costs

Sheet 8 Annual Cost Flows

Sheet 9 Annual Energy Outputs Appendix A1 - Explanatory Overview of Cost Estimates

A1.1 OVERVIEW This appendix provides further information on the scheme cost estimates presented in Section 8. Pre-construction costs are set out in A1.2. The cost build up of the barrages, lagoons and fences are set out A1.3 to A1.4. The cost estimate of the tidal reef is set out in A1.5. Additional costs and promotional costs are contained in A1.6 and A1.7 respectively.

A1.2 PRE-CONSTRUCTION COSTS Pre-construction costs have been applied on the same basis for all schemes as follows:

Planning 0.55% of construction cost Design to procurement 25% of total design costs Site investigation 1.25% of civils cost

A1.3 CIVIL ENGINEERING COST ESTIMATES

Preliminaries and Site Overheads

For all Options these costs have been assessed at 15% of the building and civil engineering value. This is deemed to include staff & supervision, offices, welfare & messing, stores, workshops, materials testing etc; temporary power; general service plant; site transport, personnel & materials hoists etc.

Barrage and Lagoon Caisson Costs

A reasonably detailed estimate has been prepared for the B3 Barrage caissons based on approximate quantities for the civil engineering work derived from information provided in Vols 3A and 3B of the DOE Report. Temporary casting yard costs assume 4 no purpose-built basins on the Severn plus one modified existing yard remote from the Severn Estuary – probably in Scotland.

Typical measured work rates used for the caissons items are:

Structural concrete £120 per m3 Formwork (avg of any size, orientation or profile) £40 per m2 Steel bar reinforcement £1050 per tonne Ballast (sand) £15 per m3 Ballast (concrete) £110 per m3 The estimated costs include preparatory works, construction, installation and fit-out costs for the barrage caissons, summarised as follows:

B3 Barrage Caisson Estimates Casting Yards £ 96m (Including establishment and removal) Construction £ 3,868 (including preparations for tow and installation) Installation (including marine plant, dredging, temporary & permanent £ 1,037m foundations, scour protection etc) Fit-Out Works (including extra cost of fitting out deeper caissons at wet dock, £ 313 gantry cranes, attendance on and civil engineering work in connection with installation of turbines and sluice gates) Total for Caissons £ 5,315

The same approach had been taken for the B4 Barrage estimate, however the design information is less well developed and the quantities are correspondingly more uncertain. In order to achieve pricing consistency between B4 and B3, unit rates have been taken as those used for Cardiff-Weston. Temporary casting yard costs assume 1 no purpose-built basin on the Severn. Equivalent figures for B4 Barrage (including in-situ open sluices) are:

B4 Barrage Caisson Estimates Casting Yards £ 27m (Including establishment and removal) Construction £ 445 (including preparations for tow and installation) Installation (including marine plant, dredging, temporary & permanent £ 99 foundations, scour protection etc) Fit-Out Works (including extra cost of fitting out deeper caissons at wet dock, £ 37 gantry cranes, attendance on and civil engineering work in connection with installation of turbines and sluice gates) Total for Caissons £ 608 The average “all-up” cost of the caisson work for B3 and B4 (excluding open sluices) can be expressed as follows:

Average Cost B3 Barrage B4 Barrage Quantity Unit Cost Quantity Unit Cost Average cost per m3 7,512,879 m3 £ 707 / m3 665,561 m3 £ 725 m3 of caisson structural concrete (i.e. excluding concrete used as ballast or in caisson foundations) Average cost per 145 no £ 36.7m / unit 21 no £23.0 m / unit caisson (all types) Average cost per m3 24,684,090 m3 £ 215 / m3 1,499,400 m3 £ 322 / m3 of caisson volume

Rough assessments have been made of the overall volumes of each type of caisson (turbine / sluice / plain) for each option. Caisson estimates for each option are the product of the assessed volumes and the volumetric cost.

B5 barrage, L2 Fleming lagoon, L3b Welsh Grounds lagoon, L3c Peterstone Flats lagoon, and L3d Bridgwater Bay lagoon would require a dredged channel for the turbine caissons to provide sufficient submergence for the turbines. The cost of this dredging is over and above the cost of dredging included in the “all-up” caisson cost for B3 and B4. Dredging costs have been calculated using a unit rate of £63/ m3 assuming an 80:20 split between hard and weathered rock. The dredging costs as follows:

Dredged Volume Dredging Cost Scheme m3 x 1000 £ m B5 - Beachley Barrage 1,264,000 80 L2 – Fleming Lagoon on Welsh Grounds 928,800 59 L3b – Russell Lagoons Welsh Grounds 928,800 59 L3c – Russell Lagoons Peterstone Flats 160,000 10 L3d – Bridgewater Bay Lagoon 726,000 46 Caisson costs for barrage and lagoon schemes are as follows:

Caisson O/A Caisson Scheme Volume Cost Cost Basis m3 x 1000 £ m B1 - Outer Barrage from Minehead to Based on B3 40,872 8,708 Aberthaw analysis B2 –Barrage from Hinkley to Lavernock Based on B3 25,728 5,646 Point analysis B3 –Barrage from Brean Down to 24,684 5,315 B3 analysis Lavernock Point B4 – Inner Barrage 1,499 608 B4 analysis Based on B4 B5 - Beachley Barrage 1,608 601 analysis L2 – Fleming Lagoon on Welsh Based on B4 819 319 Grounds analysis Based on B4 L3a – Russell Lagoons English Grounds 630 200 analysis Based on B4 L3b – Russell Lagoons Welsh Grounds 819 319 analysis Based on B4 L3c – Russell Lagoons Peterstone Flats 1,103 360 analysis L3d – Bridgewater Bay Lagoon 1,044 377 Based on B4 analysis L3e(i) - 90km2 offshore lagoon off 1,662 535 Based on B4 Bridgwater Bay analysis L3e(ii) - 50km2 offshore lagoon off 913 294 Based on B4 Bridgwater Bay analysis

Barrage Embankment Costs

A reasonably detailed estimate has been prepared for the B3 Barrage embankments based on approximate quantities for the civil engineering work derived from information provided in Vols 3A and 3B of the DOE Report and a number of cross sections.

Rates used for supply and deposition of embankment materials are as follows:

Placed above –2mOD Placed below –2m OD (per m3) (per m3) Control structure rockfill £48 £51 Derrick stone £68 £71 Containment mounds £20 £22 Rip rap £72 £76 Filter material Type 1 £31 £33 Filter material Type 2 £43 £45 Filter material Type 3 £43 £45 Sand core Note 1 £7 £7 Armour stone (1-3 tonne) £70 £73 Rock (0.3 – 1 tonne) Note 2 £43 £46 Precast concrete armour units £580 each £610 each 1 Assumed to be sourced from dredging arisings 2 Applicable to Shoots and other options The B3 Barrage embankment cost estimate is as follows:

B3 Barrage Embankment Cost Estimate Preparatory Works £ 95m (Including rail heads, rock handling harbour, moorings and materials handling facilities on embankments, casting yard for PC armour units and provision of barge fleet) Welsh Embankment £42m (including filling and armouring) Steep Holm Embankment £116m (including dredging and disposal of underlying sediment as necessary, filling and armouring) English Embankment £199m (including dredging and disposal of underlying sediment as necessary, filling and armouring) Fit Out Works £53m (including service road, concrete service ducts between substations 1 & 2, connections to public roads each side of embankment) Total for Embankments £505m

The overall B3 embankment volume is 11,700,200 m3. This includes the volume occupied by pre-cast concrete armour units and the replacement of underlying sediment removed by dredging where required. No specific allowance has been included for filling materials punched into the seabed and it is suggested that this should be regarded as a risk item until a reliable assessment is made. The overall length of embankment works is 3,475m and the average cost is approximately £145,000 per m.

Equivalent figures for B4 Barrage have been determined as follows using the same rates for supply and deposition of embankment materials as B3:.

B4 Barrage Embankment Cost Estimate Preparatory Works £ 36m (Including rail heads, rock handling harbour, moorings and materials handling facilities on embankments and provision of barge fleet – reduced provision as compared with Cardiff Weston) Welsh Embankment £ 47m (including filling and armouring) English Embankment £ 46m (including filling and armouring) Fit Out Works £ 30m (including service road, concrete service ducts between substations only, connections to public roads each side of embankment) Total for Embankments £ 159m

The overall embankment volume is 4,433,500 m3. No specific allowance has been included for filling materials punched into the seabed and it is suggested that this should be regarded as a risk item until a reliable assessment is made. The overall length of embankment works is 4,100m and the average cost is approximately £39,000 per m.

Embankment costs for barrage options B1, B2 and B5 were estimated by calculating an average cost per metre, using the same rates as B3 and B4 applied to a number of cross sections, and applied to the embankment length. Allowances are included for Preparatory Works (rail heads, rock handling harbour etc) and Fit-Out Works(service roads, service ducts, public road connections etc). Overall lengths and average costs per metre run of embankments are as follows:

o/a Embankment Avg cost per Length (CSA Embankment cost metre run varies) B1 - Outer Barrage from Minehead 2,380 m £131,000 £ 311m to Aberthaw Note 1 B2 –Barrage from Hinkley to 12,450 m £185,000 £2,303m Lavernock Point Note 1 B3 –Barrage from Brean Down to 3,475 m £ 145,000 £ 505m Lavernock Point B4 – Inner Barrage 4,100 m £ 39,000 £ 159m B5 - Beachley Barrage Note 1 710 m £27,000 £ 19m Note: 1. Embankment quantities calculated from cross-sections at selected locations. Roughly similar estimating accuracy to Options B3 (Cardiff Weston) and B4 (Shoots) Lagoon Embankment and Wall Costs

Average construction costs per metre have been estimated for each of the embankment and wall solutions submitted in response to the Call for Proposals. These rates include plant, labour and material costs but exclude VAT, contingency, optimism bias, design and supervision, and ground investigation costs.

Construction Technology Maximum Average cost per Applicability Height (m) metre run (£/m) Geosynthetic reinforced 12.5 28,492 All L3 lagoons embankment 22.5 52,717 32.5 79,398 Halcyon piled wall 11 60,000 Shallower (applicable only to lengths of L3b Welsh Grounds lagoon and L3dBridgwater Bay lagoon Note 1 L2 tied wall panels 11 21,705 L2 Welsh 13.5 32,558 Grounds lagoon Note: 1. The Halcyon wall has not been applied to deeper applications. Refer in Section 6.1.

The comparison of unit rates shows that the geosynthetic reinforced embankments are lower cost compared to the Halcyon wall and this solution has therefore been applied for the cost estimate of all L3 lagoons.

The estimated embankment and wall costs of the L2 and L3 lagoons are as follows:

o/a Embankment/Wall Avg cost Embankment cost Length (CSA per metre varies) run L2 – Fleming Lagoon on Welsh Grounds 29,992 m £26,507 £795m

L3a – Russell Lagoons English Grounds 17,916 m £50,458 £904m

L3b – Russell Lagoons Welsh Grounds 29,992 m £37,443 £1,123m

L3c – Russell Lagoons Peterstone Flats 21,338 m £47,427 £1,012m

L3d – Bridgewater Bay Lagoon 14,590 m £43,729 £638m

L3e(i) - 90km2 offshore lagoon off 39,000 m £ 60,923 £2,376m Bridgwater Bay L3e(ii) - 50km2 offshore lagoon off 26,000 m £ 56,231 £1,462m Bridgwater Bay Tidal Fence Civil Engineering Costs

Tidal fence civil engineering costs have been developed using the same principles as apply to the barrage. However, the two fence options have different configurations and therefore different cost build ups as follows:

Component F1a F1b

Dredging and Bed Preparation for Tidal Fences £493m £616m

Dredging and Bed Preparation for the Non-Generating £164m n /a Barriers

Flow Barriers in Areas Too Shallow for Generator £299m n/a Modules

Axial Flow Turbine Foundation Modules £535m £1,672m

Shallow Water Generator Foundation Modules Included in Item 4 above

Access bridge £335m n/a

Totals £1,826m £2,288m

Navigation Locks

A reasonably detailed estimate has been prepared for the B3 Barrage navigation locks based on approximate quantities for the civil engineering work derived from information provided in Vols 3A and 3B of the DOE Report and a number of cross sections. Costs for navigation locks (excluding the lock gates which are included in the M&E section of estimate) are as follows:

B3 Barrage £m Main Navigation and Small Craft Lock Complex (towards Welsh Shore):

Rubble Mound Breakwater (west) 140 (Including dredging and disposal of underlying sediment as necessary, rock fill and armouring, concrete capping, service road and wave wall) Rubble Mound Breakwater (east) 70 (Including dredging and disposal of underlying sediment as necessary, rock fill and armouring, concrete capping, service road and wave wall) Breakwater Caissons 213 (Including preparation, construction, installation and fit-out of 16 no plain breakwater caissons) Channel Caissons 174 (Including preparation, construction, installation and fit-out of lock channel caissons) Gate Caissons 149 (Including preparation, construction, installation and fit-out of 5 no lock gate caissons) Small Craft Lock Caisson 21 (Including preparation, construction, installation and fit-out of 1 no small craft lock caisson) Landing Area 66 (including approx 1.3m m3 of fill, 30,000 m2 of apron slab, allowances for fendering and dock furniture, lock control and other buildings, flood & berth lighting, floating landing stages for small craft) Civil Engineering Work and Attendance in connection with Lock Gates 3 (for 5 no main lock gates and 2 pairs of sector gates for small craft lock) Approach Works 25 (Including lead-in structures (approx 3000m length), waiting berths, allowances for navigation aids and remote navigation lights) Bascule Bridges 25 (Including 2 no x 70m span & 1 no x 15m span bridges) Total for Main Navigation Lock Complex 886 B3 Barrage £m Small Boat Lock (towards English Shore):

Rubble Mound Breakwater 73 (Including dredging and disposal of underlying sediment as necessary, rock fill and armouring, concrete capping, service road and wave wall) Small Craft Lock Caisson 21 (Including preparation, construction, installation and fit-out of 1 no small craft lock caissons) Landing Area 1 (including apron slab, allowances for fendering and dock furniture, lock control building, flood & berth lighting, floating landing stages for small craft) Civil Engineering Work and Attendance in connection with Lock Gates Less than 1 (for 2 pairs of sector gates for small craft lock) Approach Works 17 (Including vertical screen breakwater and suspended quay structures, allowances for navigation aids and remote navigation lights) Bascule Bridges 4 (Including 1 no x 15m span bridge) Total for Small Boat Lock Complex 116

Equivalent figures for the single Navigation Lock for B4 Barrage are:

B4 Navigation Lock Complex £ m Rubble Mound Breakwater - (not required for Shoots) Small Craft Lock Caissons 29 (Including preparation, construction, installation and fit-out of 1 no small craft lock caisson) Landing Area 2 (including allowances for fendering and dock furniture, lock control, flood & berth lighting, floating landing stages for small craft) Civil Engineering Work and Attendance in connection with Lock Gates Less than 1 (for 2 pairs of sector gates for small craft lock) Approach Works 17 (Including waiting berths, allowances for navigation aids and lights) Bascule Bridges 5 (Including 1 no x 20m span bridge) Total for Main Navigation Lock Complex 53

There is little available information on the construction of the B4 navigation lock. For the purposes of pricing consistency, it has been priced as a concrete caisson similar to the Small Craft Locks in the Cardiff Weston option.

B1 and B2 Barrages are assumed to have the same lock requirements as B3 and they have been priced the same.

B5 Beachley Barrage is assumed to have the same lock requirements as B4 and has been priced the same. An allowance of £20m has been included for a small boat lock in Lagoon L3d to provide navigable access to the River Parrett. The same has been allowed for Lagoons L3e(i) and (ii) to provide access into the basin for maintenance and dredging.

No other options require navigation locks.

In summary, the navigation lock (excluding gate) costs are as follows:

Scheme Navigation Lock Cost (£m) B1 - Outer Barrage from Minehead to Aberthaw 1,002 B2 –Barrage from Hinkley to Lavernock Point 1,002 B3 –Barrage from Brean Down to Lavernock Point 1,002 B4 – Inner Barrage 53 B5 - Beachley Barrage 53 L2 – Fleming Lagoon on Welsh Grounds 0 L3a – Russell Lagoons English Grounds 0 L3b – Russell Lagoons Welsh Grounds 0 L3c – Russell Lagoons Peterstone Flats 0 L3d – Bridgewater Bay Lagoon 20 L3e(i) - 90km2 offshore lagoon off Bridgwater Bay 20 L3e(ii) - 50km2 offshore lagoon off Bridgwater Bay 20

Surface Buildings

For B3 barrage, 3 no substations are included in the proposals detailed in DOE Vols 3A / B. A notional allowance has been made for these together with other buildings which might be expected as follows. Costs are based on historical analyses of similar function buildings. These costs include architectural fit-out and normal building services:

B3 Barrage Surface Building Cost Estimate

400 kV electrical substation #1 (centre embankment) £ 13m say 1500 m2 @ £9,000 400 kV electrical substation #2 (centre embankment) £13m say 1500 m2 @ £9,000 400 kV electrical substation #3 (built on caisson in construction yard - £ 12m permanent location above turbine caisson towards Welsh shore) say 1500 m2 @ £8,000 Control Centre - assume 2 storey (centre embankment) £ 9m say 600 m2 @ £15,000 Stores £ 11m say 3600 m2 @ £3,000 Workshop £ 7m say 1800 m2 @ £4,000 Sundry other buildings £ 14m say 2250 m2 @ £6,000 Tourist centre £ 4m say 600 m2 @ £6,000 Total for Surface Buildings £ 83m Equivalent figures for the single powerhouse building indicated for B4 Barrage are as follows, equating to £40,000 per MW installed capacity:

B3 Barrage Surface Building Cost Estimate Main power house over the turbine dam £ 42m say 6000 m2 @ £7,000 (assumed that control facilities, stores , workshops, visitor centre etc will be accommodated within this building or area allowance)

Options B1 and B2 are assumed to have the same requirements as B3 (Cardiff- Weston) and have been priced the same.

The surface building requirements for schemes of similar installed capacity to B4 (ie. F1b, L2, L3b, L3c, L3d and L3e(i)) has been taken as the same as B4. Requirements for smaller schemes have been estimated at £40,000 per MW of installed capacity as for B4. A1. 4 MECHANICAL AND ELECTRICAL COSTS

Generating Equipment

Turbine and generator costs have been based on the traditional use of scaling of known plant costs using parameters of power and head, speed and machine diameter, escalated to a 2008 price level. For multiple unit bulb turbines of 35 to 40 MW per unit capacity, a cost of £0.676m per MW has been applied consistently for the larger capacity barrages and lagoons. Straflo units, proposed for the Inner and Beachley Barrages, are expected to be more economical at £0.611m per MW. These unit costs include turbines and generators, turbine control gates, contingency, delivery, installation, commissioning and contractor’s oncosts and profit. For the F1 fences, a figure of £2m per MW of installed capacity has been used in the analyses for the turbine, gearbox and generator (refer to section 8.4) .

The turbine and generator costs have been based on the installed capacities estimated for this study (as set out in section 6.3). The generating costs are therefore as follows:

Scheme Installed Capacity Turbine and Turbine and (MW) Generator Cost Generator Cost (£m/MW) (£m) B1 - Outer Barrage from Minehead 14,800 0.676 10,005 to Aberthaw B2 –Barrage from Hinkley to 9,000 0.676 6,084 Lavernock Point B3 –Barrage from Brean Down to 8,640 0.676 5,841 Lavernock Point B4 – Inner Barrage 1050 0.611 642 B5 - Beachley Barrage 625 0.611 382 F1a – Cardiff to Weston Tidal 256 2.75 704 Fence F1b – Aberthaw to Minehead Tidal 1280 2.25 2,880 Fence L2 – Fleming Lagoon on Welsh 1360 0.676 919 Grounds L3a – Russell Lagoons English 760 0.676 514 Grounds L3b – Russell Lagoons Welsh 1360 0.676 919 Grounds L3c – Russell Lagoons Peterstone 1120 0.676 757 Flats L3d – Bridgewater Bay Lagoon 1360 0.676 919 L3e(i) - 90km2 offshore lagoon 1360 0.676 919 off Bridgwater Bay L3e(ii) - 50km2 offshore lagoon 760 0.676 514 off Bridgwater Bay Gates

Turbine control gate costs are included in the unit rates applied for the turbine and generator costs.

Sluice gate and associated stoplog panel costs have been estimated for B3 and B4 barrages based on available design information. The gates for B1 and B2 barrages are assumed to be similar to B3. Sluice gates for B5 and lagoons are assumed to be similar to B4. The number of gates has been estimated for each scheme and the total cost based on the relevant cost per gate. These estimates include fabrication, delivery, installation and commissioning but exclude design fees and contingency. Gantry cranes for stoplog handling have also been included.

Temporary bulkheads for caisson floating have been estimated for B3 barrage and applied to B1 and B2.

Lock gates have similarly been estimated for B3 and B4 based on available designs. Lock gates for B1 and B2 are assumed to be similar to B3. Lock gates for B5 are assumed to be similar to the smaller lock gates required for B4. Lock gates for L3d Bridgwater Bay and L3e offshore lagoons are assumed to be similar to the small craft lock gates required for B3. Other lagoons do not include navigation locks. A summary gate costs is as follows:

Barrage Gate Cost Estimates B1 B2 B3 B4 B5

Gate Items Unit No Cost (£k) No Cost (£k) No Cost (£k) No Cost (£k) No Cost (£k) Costs (£k) 22m span Radial Sluice gate, hoist and elec controls 4,661 213 992,750 128 596,582 117 545,314 0 0 0 0 14m span Radial Sluice gate, hoist and elec controls 2,166 213 461,358 54 116,964 49 106,134 0 0 0 0 Set of 22m stoplog panels(U/S or D/S) 1,793 24 43,032 13 23,309 12 21,516 0 0 0 0 Set of 14m stoplog panels(U/S or D/S) 796 24 19,114 7 5,575 6 4,778 0 0 0 0 Set of 22m stoplog BIPs (U/S or D/S) 564 426 240,264 256 144,384 234 131,976 0 0 0 0 Set of 14m stoplog BIPs (U/S or D/S) 294 426 125,244 108 31,752 98 28,812 0 0 0 0 Gantry crane 180te capacity 1,000 12 12,000 4 4,000 3 3,000 0 0 0 0 Gantry crane 320te capacity 1,500 12 18,000 6 9,000 6 9,000 0 0 0 0 Temporary bulkheads for caisson floating 1,293 142 183,691 88 113,837 80 103,488 0 0 0 0

B3 Equivalents Temporary bulkheads 808 142 114,807 44 35,574 40 32,340 0 0 0 0 30m span Radial Sluice gate, hoist and elec controls 5,776 0 0 0 0 0 0 42 242,626 26 150,197 Set of 14m stoplog panels(U/S or D/S) 1,215 0 0 0 0 0 0 8 9,724 8 9,724 Set of 14m stoplog BIPs (U/S or D/S) 336 0 0 0 0 0 0 168 56,448 104 34,944

B4 Equivalents Gantry crane 180te capacity 1,000 0 0 0 0 0 0 2 2,000 2 2,000 Main Lock Gates - 170,000 - 170,000 - 170,000 - 45,000 - 45,000 Small Lock Gates - 4,000 - 4,000 - 4,000 - 0 - 0 Totals 2,384,260 - 1,254,977 - 1,160,358 - 355,798 - 241,865 Land Connected Lagoon Gate Cost Estimates L3a L2/L3b L3c L3d

Gate Items Unit No Cost (£k) No Cost (£k) No Cost (£k) No Cost (£k) Costs (£k) 30m span Radial Sluice gate, hoist and elec controls 5,776 25 144,420 41 236,849 33 190,634 41 236,816 Set of 14m stoplog panels(U/S or D/S) 1,215 8 9,724 16 19,448 12 14,586 16 19,448 Set of 14m stoplog BIPs (U/S or D/S) 336 100 33,600 164 55,104 132 44,352 160 53,760 Gantry crane 180te capacity 1,000 2 2,000 4 4,000 4 4,000 4 4,000 Main Lock Gates - 0 - 0 - 0 - 7,000 Totals 189,744 - 315,401 - 253,572 - 321,024 Offshore Lagoon Gate Cost Estimates L3e(i) L3e(ii)

Gate Items Unit Costs No Cost No Cost (£k) (£k) (£k) 30m span Radial Sluice gate, hoist and elec controls 5,776 40 236,816 22 127,072 Set of 14m stoplog panels(U/S or D/S) 1,215 16 19,448 9 10,935 Set of 14m stoplog BIPs (U/S or D/S) 336 160 53,760 88 29,568 Gantry crane 180te capacity 1,000 4 4,000 2 8,000 Main Lock Gates - 7,000 - 7,000 Totals 321,024 182,575

Grid Connection An assessment has been made of the principal components required between the generator terminals and the connections to onshore substations. A 15% contingency has been applied to the cost estimate for each scheme. The grid connection cost estimates are as follows: Grid Connection Cost Scheme (£m) B1 - Outer Barrage from Minehead to Aberthaw 868 B2 –Barrage from Hinkley to Lavernock Point 557 B3 –Barrage from Brean Down to Lavernock Point 500 B4 – Inner Barrage 96 B5 - Beachley Barrage 47 F1a – Cardiff to Weston Tidal Fence 217 F1b – Aberthaw to Minehead Tidal Fence 334 L2 – Fleming Lagoon on Welsh Grounds 113 L3a – Russell Lagoons English Grounds 91 L3b – Russell Lagoons Welsh Grounds 113 L3c – Russell Lagoons Peterstone Flats 95 L3d – Bridgewater Bay Lagoon 90 L3e(i) - 90km2 offshore lagoon off Bridgwater Bay 98 L3e(ii) - 50km2 offshore lagoon off Bridgwater Bay 84 A breakdown of the grid connection costs are provided below:

Large Barrage Grid Connection Cost B1 Barrage B2 Barrage B3 Barrage Breakdown Voltage Unit Cost Total Cost Total Cost Total Cost Item (kV) (£k) Quantity (£k) Quantity (£k) Quantity (£k) Offshore installation All 5000 4 20000 4 20000 4 20000 Standard Generator Disconnectors 8.6 10 1110 11100 675 6750 648 6480 Incoming SF6 Generator Breakers 8.6 200 188 37600 116 23200 108 21600 Fault Current Limiters 8.6 25 0 0 0 0 0 0 Earthing Transformer + Resistor 8.6 750 93 69750 57 42750 54 40500 Variable Frequency Starting Drives 8.6 1500 0 0 0 0 0 0 Series Reactor 8.6 500 0 0 0 0 0 0 Connection (180MW) per LV TX winding 8.6 2000 94 188000 58 116000 54 108000 Cable (35MW) per block of four 8.6 20 93 1860 57 1140 54 1080 Protection / 8 machine group 8.6 500 47 23500 29 14500 27 13500 3-Winding Transformer (360MVA) 400 / 8.6 4000 47 188000 29 116000 27 108000 350mm^2 cable (km) 400 300 36 10800 22 6600 21 6300 Disconnectors 400 35 114 3990 70 2450 66 2310 5-Switch Meshed Substation 400 10000 5 50000 3 30000 3 30000 3 x 2000mm^2 single core cable (km) 400 600 150 90000 108 64800 72 43200 Cable Joints 400 60 900 54000 600 36000 500 30000 Cable Sealing Ends 400 150 40 6000 24 3600 24 3600 Sub-totals - 754,600 - 483,790 - 434,570 Contingency at 15% 113,190 - 72,569 - 65,006 Totals - 867,790 - 556,359 - 499,756 B4 Barrage Grid Connection cost Breakdown Unit Cost Total Cost Item Voltage (kV) (£k) Quantity (£k) Offshore installation All 5000 4 20000 Standard Generator Disconnectors 8.6 10 90 900 Incoming SF6 Generator Breakers 8.6 200 16 3200 Fault Current Limiters 8.6 25 0 0 Earthing Transformer + Resistor 8.6 750 8 6000 Variable Frequency Starting Drives 8.6 1500 0 0 Series Reactor 8.6 500 0 0 Connection (360MW) per LV TX winding 8.6 2000 8 16000 Cable (40MW) per block of four 8.6 20 8 160 Protection / 8 machine group 8.6 500 4 2000 3-Winding Transformer (320MVA) 400 / 8.6 4000 4 16000 350mm^2 cable (km) 400 300 3 900 Disconnectors 400 35 12 420 4-Switch Meshed Substation 400 8000 1 8000 3 x 2000mm^2 single core cable (km) 400 600 4.1 2460 Cable Joints 400 60 100 6000 Cable Sealing Ends 400 150 8 1200 Sub-total 83,240 Contingency at 15% 12,486 Total 95,726 B5 Barrage Grid Connection Cost Breakdown F1a Tidal Fence Grid Connection Cost Breakdown Voltage Unit Cost Total Cost Total Item (kV) (£k) Quantity (£k) Unit Cost Offshore installation All 5000 1 5000 Item Voltage (kV) Cost (£k) Quantity (£k) 0.69/33kV Transformer Offshore installation All 5000 4 20000 (2.5MVA) 33/0.69 70 50 3500 0.69/33kV Transformer SF6 Breakers 33 40 100 4000 (5MVA) 33/0.69 70 256 17920 Cable (35MVA) 33 200 3 600 SF6 Breakers 33 40 24 960 400/33kV transformer Cable (35MVA) 33 200 15 3000 (120MVA) 400/33 1000 2 2000 132/33kV transformer 3-switch offshore (120MVA) 132/33 1000 12 12000 substation 400 7500 2 15000 4-switch meshed Cable (150MW) 400 300 4 1200 substation 132 2000 12 24000 Cable Joints 400 10 20 200 Cable (35MVA) 132 900 6.72 6048 Cable Sealing Ends 400 150 4 600 400/132kV transformer Protection / 4 machine (360MVA) 400/132 2000 4 8000 group 33 500 2 1000 4-switch meshed 4-switch mesh (on substation 400 10000 4 40000 shore) 400 8000 1 8000 Cable (360MW) 400 600 4 2400 Sub-total 41,100 Cable Joints 400 25 60 1500 Contingency at 15% 6,165 Cable Sealing Ends 11 150 8 1200 Total 47,265 Protection / 7 machine group 33 438 37 16187.5 6-switch mesh 400 12000 3 36000 Sub-total 189,216 Contingency at 15% 2,8382 Total 217,598 Option F1a is based on F1b costs but pro-rata’d in terms of installed capacity and structure length and estimated at £334m. Land Connected Lagoon Grid Connection Cost Breakdown L2 and L3b L3a L3c L3d Voltage Unit Cost Total Cost Total Cost Total Cost Item (kV) (£k) Quantity (£k) Quantity (£k) Quantity (£k) Quantity Total Cost (£k) Offshore installation All 5000 4 20000 4 20000 4 20000 4 20000 Standard Generator Disconnectors 8.6 10 72 720 57 570 72 720 72 720 Incoming SF6 Generator Breakers 8.6 200 12 2400 12 2400 12 2400 12 2400 Fault Current Limiters 8.6 25 0 0 0 0 0 0 0 0 Earthing Transformer + Resistor 8.6 750 6 4500 5 3750 6 4500 6 4500 Variable Frequency Starting Drives 8.6 1500 0 0 0 0 0 0 0 0 Series Reactor 8.6 500 0 0 0 0 0 0 0 0 Connection (180MW) per LV TX winding 8.6 2000 6 12000 6 12000 6 12000 6 12000 Cable (35MW) per block of four 8.6 20 6 120 5 100 6 120 6 120 Protection / 8 machine group 8.6 500 3 1500 3 1500 3 1500 3 1500 3-Winding Transformer (360MVA) 400 / 8.6 4000 3 12000 3 12000 3 12000 3 12000 350mm^2 cable (km) 400 300 3 900 3 900 3 900 3 900 Disconnectors 400 35 10 350 10 350 10 350 10 350 5-Switch Meshed Substation 400 10000 1 10000 0 0 0 0 0 0 4-Switch Meshed Substation 400 8000 0 0 1 8000 1 8000 1 8000 3 x 2000mm^2 single core cable (km) 400 600 44.55 26730 17.9 10740 21 12600 14.5 8700 Cable Joints 400 60 100 6000 100 6000 100 6000 100 6000

Cable Sealing Ends 400 150 8 1200 8 1200 8 1200 8 1200 Sub-totals - 98,420 - 79,510 - 82,290 - 78,390 Contingency at 15% - 14,763 - 11,927 - 12,344 - 11,759 Totals - 113,183 - 91,437 - 94,634 - 90,149 Offshore Lagoon Grid Connection Cost Breakdown L3e(i) L3e(ii) Voltage Unit Cost Total Total Cost Item (kV) (£k) Quantity Cost (£k) Quantity (£k) Offshore installation All 5000 4 20000 4 20000 Standard Generator Disconnectors 8.6 10 72 720 42 420 Incoming SF6 Generator Breakers 8.6 200 12 2400 8 1600 Fault Current Limiters 8.6 25 0 0 0 0 Earthing Transformer + Resistor 8.6 750 6 4500 4 3000 Variable Frequency Starting Drives 8.6 1500 0 0 0 0 Series Reactor 8.6 500 0 0 0 0 Connection (180MW) per LV TX winding 8.6 2000 6 12000 4 8000 Cable (35MW) per block of four 8.6 20 6 120 4 80 Protection / 8 machine group 8.6 500 3 1500 2 1000 3-Winding Transformer (360MVA) 400 / 8.6 4000 3 12000 2 8000 350mm^2 cable (km) 400 300 3 900 2 600 Disconnectors 400 35 10 350 8 280 5-Switch Meshed Substation 400 10000 1 10000 1 10000 3 x 2000mm^2 single core cable (km) 400 600 21.75 13050 21.75 13050 Cable Joints 400 60 100 6000 100 6000 Cable Sealing Ends 400 150 8 1200 8 1200 Sub-totals - 84,740 - 73,230 Contingency at 15% - 12,711 - 10,985 Totals - 97,451 - 84,215 A1.5 TIDAL REEF

Very little design information is available on which to estimate the cost of a tidal reef. Therefore, a very high level estimate has been prepared and the basis for this estimate is set out in the table below. The estimate makes a number of very broad high level assumptions and approximations. None of these is considered precautionary and the overall estimate should therefore be treated with caution as it is likely to represent an optimistic estimate given the level of design information available and the absence of any prototype or analogue on which to base the estimate.

Item Cost Estimate (£m) Estimate Basis Preliminaries and 647 15% of civil engineering construction cost Site Overheads Embankments 311 Same as B1 on the assumption that these are required as a barrier to flow in order to achieve a head differential across the reef Navigation Locks 0 No navigation lock as such is proposed although the reef structure will require rotating siphons with a longer span than elsewhere on the reef to provide a navigable opening. There will be costs associated with these elements that are not included in this estimate but there is no information available to determine the quantum. Surface Buildings 83 Same as B1 Caissons 3,919 This includes the structures which support the turbine and siphon units and incorporate service tunnels, cable ducts, access shafts etc. This also includes the cost of the siphon units themselves which house the turbine generators. It is broadly estimated that for stability the structure will require 45% of the weight of the B1 structure due to the reduced head differential. Therefore, the overall structure cost is taken as 45% of the cost of the B1 caissons. This assumes that the cost per tonne of barrage and reef structural components, including precasting, transportation, positioning, placing and infilling, are the same. It also assumes that the reef structure is a gravity structure and not piled (piled strucutres would be expected to be more expensive). This is not precautionary as it does not allow for special factors such as the complexity of the movable siphons. Generating Plant 13,750 5000MW at £2.75m per MW. Turbine generators will be akin to tidal stream turbines. The upper bound cost per MW as applied to the tidal fence has been adopted to allow for fabrication, installation, commissioning and to allow for elements required to fit the turbines into the structure. A furhter discussion on the cost of tidal stream turbines is included in Section 6.4. Grid Connection 300 34% of the B1 cost pro-rata’d on the basis of installed capacity Gates 1,080 Allows for 2000 gates (2 per turbine), each 10m by 4m to control flow through the siphon and to act as stoplogs for turbine access. Cost based on £13,000 per sq. m which is equivalent to B1. Also allows £300m for temporary bulkheads during construction. Total Construction £20,050 Cost A1.6 ADDITIONAL ITEMS

The following costs have been applied on the same basis for all schemes:

Item Cost Basis Design and supervision (includes outline 4% of overall civil engineering and gate and detailed design and construction cost (except B1, B2, B3 and R1 which are supervision) 3.5%) plus 1.5% on value of caissons Site investigation (during outline and 0.25% of overall civil engineering cost detailed design and construction) Contingencies 15% of overall civil engineering and gate cost Contractor’s Oncosts and Profit 9.25% of overall civil engineering and gate cost

Ancillary costs

Ancillary costs are intended to cover works which are a consequence of the scheme construction and operation but which do not form part of the scheme. They primarily arise as a consequence of the effect of the scheme on the tidal range and estuary geomorphology. The costs therefore cover works required on land drainage, sea defences, permanent dredging installations, improvements to navigation and harbour works etc. The ancillary costs have been assessed in relation to the extent and severity of the potential consequences in order to inform a comparison of the relative ancillary costs between options. A detailed breakdown of these costs has not been prepared. Ancillary costs allocated to each scheme are as follows:

Scheme Ancillary Cost (£m) B1 - Outer Barrage from Minehead to Aberthaw 400 B2 –Barrage from Hinkley to Lavernock Point 350 B3 –Barrage from Brean Down to Lavernock Point 300 B4 – Inner Barrage 100 B5 - Beachley Barrage 80 F1a – Cardiff to Weston Tidal Fence 10 F1b – Aberthaw to Minehead Tidal Fence 10 L2 – Fleming Lagoon on Welsh Grounds 50 L3a – Russell Lagoons English Grounds 50 L3b – Russell Lagoons Welsh Grounds 50 L3c – Russell Lagoons Peterstone Flats 50 L3d – Bridgewater Bay Lagoon 50 L3e(i) - 90km2 offshore lagoon off Bridgwater Bay 10 L3e(ii) - 50km2 offshore lagoon off Bridgwater Bay 10 R1 – Reef from Minehead to Aberthaw 50

A1.7 PROMOTIONAL COSTS

The project promotor’s project management costs have been included as 0.5% of the overall construction cost for all schemes. Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - No Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Minehead Barrage Cardiff - Hinkley Point Cardiff - Weston Barrage Shoots Barrage Beachley Barrage Barrage

PRE-CONSTRUCTION TOTAL PLANNING 317,414,634 271,637,173 209,225,373 29,967,394 21,656,261

CONSTRUCTION Preliminaries & Site Overheads 1,515,593,727 1,355,003,993 1,035,722,544 129,272,441 104,057,312 GENERAL CIVILS Embankments 311,066,774 2,303,000,000 505,365,908 159,038,723 19,358,340 Other Civils Navigation Locks 1,001,840,886 1,001,840,886 1,001,840,886 52,733,413 52,733,413 Surface Buildings 83,100,000 83,100,000 83,100,000 42,000,000 25,000,000 TOTAL GENERAL CIVILS 1,396,007,660 3,387,940,886 1,590,306,794 253,772,136 97,091,753

CAISSONS Caissons 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659 TOTAL CAISSONS 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659

M&E Generating Plant 10,005,416,667 6,084,375,000 5,841,000,000 642,000,000 382,000,000 Grid Connection 868,000,000 557,000,000 500,000,000 96,000,000 47,000,000 Gates 2,384,000,000 1,255,000,000 1,160,000,000 356,000,000 242,000,000 TOTAL M&E 13,257,416,667 7,896,375,000 7,501,000,000 1,094,000,000 671,000,000

ADDITIONAL ITEMS Design and Supervision 425,773,346 333,580,413 271,489,685 38,808,174 31,424,546 Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 3,490,019 8,469,852 3,975,767 634,430 242,729 (eg site investigation during design & construction) Ancilliaries 400,000,000 350,000,000 300,000,000 100,000,000 80,000,000 (eg navigation and land drainage improvements) Contingencies 1,873,193,727 1,543,253,993 1,209,722,544 182,672,441 140,957,312 (15% on civil works and gates only) Contractors Oncosts and Profit 1,155,136,132 951,673,296 745,995,569 112,648,005 86,923,676 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 3,857,593,223 3,186,977,555 2,531,183,564 434,763,050 339,548,262 TOTAL CONSTRUCTION COSTS 28,734,561,795 21,471,716,504 17,972,723,069 2,519,851,763 1,812,320,986 VAT - - - - - TOTAL CONSTRUCTION COSTS (inc VAT) 28,734,561,795 21,471,716,504 17,972,723,069 2,519,851,763 1,812,320,986

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 27,949 25,697 20,240 4,946 3,514 Cost of Compensatory Habitats: - - - - - VAT - - - - -

PROMOTIONAL COSTS Client Project Management Costs 143,672,809 107,358,583 89,863,615 12,599,259 9,061,605 (Project promoter delivery costs) VAT - - - - -

TOTAL PROJECT COST 29,195,649,239 21,850,712,259 18,271,812,058 2,562,418,416 1,843,038,852 Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - No Habitat Compensation

LAGOONS Option No L2 L3a L3b L3c L3d L3e(i) L3e(ii) Option Name Welsh Grounds Lagoon - Russel Lagoon (English Russel Lagoon (Welsh Russel Lagoon Bridgwater Bay (Land 91sq.km Offshore 50sq.km Offshore Fleming Grounds) Grounds) (Peterstone Flats) Connected Lagoon) Lagoon Lagoon

PRE-CONSTRUCTION TOTAL PLANNING 41,664,432 37,829,982 51,264,760 46,941,614 38,889,710 92,442,903 56,181,699

CONSTRUCTION Preliminaries & Site Overheads 161,338,849 170,191,222 222,600,290 212,191,772 161,509,048 445,874,445 271,018,834 GENERAL CIVILS Embankments 795,000,000 904,208,147 1,123,001,931 1,012,611,816 637,726,985 2,375,496,302 1,462,392,226 Other Civils Navigation Locks 0 0 0 0 20,000,000 20,000,000 20,000,000 Surface Buildings 42,000,000 30,400,000 42,000,000 42,000,000 42,000,000 42,000,000 30,400,000 TOTAL GENERAL CIVILS 837,000,000 934,608,147 1,165,001,931 1,054,611,816 699,726,985 2,437,496,302 1,512,792,226

CAISSONS Caissons 319,000,000 200,000,000 319,000,000 360,000,000 377,000,000 535,000,000 294,000,000 TOTAL CAISSONS 319,000,000 200,000,000 319,000,000 360,000,000 377,000,000 535,000,000 294,000,000

M&E Generating Plant 919,000,000 514,000,000 919,000,000 757,000,000 919,000,000 919,000,000 514,000,000 Grid Connection 113,000,000 91,000,000 113,000,000 95,000,000 90,000,000 98,000,000 84,000,000 Gates 315,000,000 190,000,000 315,000,000 254,000,000 321,000,000 321,000,000 183,000,000 TOTAL M&E 1,347,000,000 795,000,000 1,347,000,000 1,106,000,000 1,330,000,000 1,338,000,000 781,000,000

ADDITIONAL ITEMS Design and Supervision 42,202,500 37,020,964 50,812,551 47,851,060 40,931,583 92,473,028 55,539,546

Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 2,092,500 2,336,520 2,912,505 2,636,530 1,749,317 6,093,741 3,781,981 (eg site investigation during design & construction) Ancilliaries 50,000,000 50,000,000 50,000,000 50,000,000 50,000,000 10,000,000 10,000,000 (eg navigation and land drainage improvements) Contingencies 220,650,000 198,691,222 269,850,290 250,291,772 209,659,048 494,024,445 298,468,834 (15% on civil works and gates only) Contractors Oncosts and Profit 136,067,500 122,526,254 166,407,679 154,346,593 129,289,746 304,648,408 184,055,781 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 451,012,500 410,574,960 539,983,024 505,125,955 431,629,695 907,239,622 551,846,141 TOTAL CONSTRUCTION COSTS 3,115,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201 VAT ------TOTAL CONSTRUCTION COSTS (inc VAT) 3,115,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 6,500 2,000 6,500 2,700 5,500 0 0 Cost of Compensatory Habitats: ------VAT ------

PROMOTIONAL COSTS Client Project Management Costs 15,576,757 12,551,872 17,967,926 16,189,648 14,999,329 28,318,052 17,053,286 (Project promoter delivery costs) VAT ------

TOTAL PROJECT COST 3,172,592,538 2,560,756,183 3,662,817,931 3,301,060,805 3,053,754,766 5,784,371,325 3,483,892,187 Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - No Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Minehead Aberthaw to Minehead fence Tidal fence Tidal Reef

Installed capacity (MW) 256 1280 5000 Annual Energy Output (TWh) 0.7 3.30 13 Pre Construction Period (years) 4 4 4 Construction Period (years) 5 10 10 First generation (years from start of const) 4 3 3

PRE-CONSTRUCTION TOTAL PLANNING 71,245,729 83,701,452 165,177,258

CONSTRUCTION Preliminaries & Site Overheads 377,136,000 349,518,750 647,000,000 GENERAL CIVILS Embankments 0 0 311,000,000 Other Civils 1,826,000,000 2,288,125,000 Navigation Locks 0 0 0 Surface Buildings 10,240,000 42,000,000 83,100,000 TOTAL GENERAL CIVILS 1,836,240,000 2,330,125,000 394,100,000

CAISSONS Caissons 678,000,000 - 3,919,000,000 TOTAL CAISSONS 678,000,000 - 3,919,000,000

M&E Generating Plant 512,000,000 2,560,000,000 10,000,000,000 Grid Connection 217,000,000 334,000,000 300,000,000 Gates - - 1,080,000,000 TOTAL M&E 729,000,000 2,894,000,000 11,380,000,000

ADDITIONAL ITEMS Design and Supervision 73,626,300 61,165,781 185,657,625 Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 4,590,600 5,825,313 985,250 (eg site investigation during design & construction) Ancilliaries 10,000,000 10,000,000 50,000,000 (eg navigation and land drainage improvements) Contingencies 377,136,000 349,518,750 808,965,000 (15% on civil works and gates only) Contractors Oncosts and Profit 232,567,200 215,536,563 498,861,750 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 697,920,100 642,046,406 1,544,469,625 TOTAL CONSTRUCTION COSTS 4,318,296,100 6,215,690,156 17,884,569,625 VAT - - - TOTAL CONSTRUCTION COSTS (inc VAT) 4,318,296,100 6,215,690,156 17,884,569,625

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 2,024 2,795 8,600 Cost of Compensatory Habitats: - - - VAT - - -

PROMOTIONAL COSTS Client Project Management Costs 21,591,481 31,078,451 89,422,848 (Project promoter delivery costs) VAT - - -

TOTAL PROJECT COST 4,411,133,309 6,330,470,059 18,139,169,731 Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - No Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Cardiff - Hinkley Cardiff - Weston Shoots Barrage Beachley Barrage Minehead Barrage Point Barrage Barrage

Installed capacity (MW) 14800 9000 8640 1050 625 Pre Construction Period (years) 4 4 4 4 4 Construction Period (years) 10 8 7 5 4 First generation (years from start of const) 7 7 6 5 4 Refurbishment Interval (years) 40 40 40 40 40 Refurbishment Period (years) 5 5 5 2 2 Pre-Construction Annual Cost 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 Annual Construction Costs 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,648 Annual Operation Costs 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 Annual Refurbishment Costs(inc operation costs) 1,759,940,356 1,227,567,539 1,132,262,654 268,797,406 165,415,617

YEAR 2010 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2011 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2012 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2013 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2014 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,648 2015 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,648 2016 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,648 2017 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,648 2018 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 31,715,617 2019 2,887,823,460 2,697,384,386 2,580,369,526 44,097,406 31,715,617 2020 2,887,823,460 2,697,384,386 2,737,630,853 44,097,406 31,715,617 2021 2,887,823,460 2,885,261,905 314,522,654 44,097,406 31,715,617 2022 3,067,414,472 375,755,039 314,522,654 44,097,406 31,715,617 2023 3,157,209,977 375,755,039 314,522,654 44,097,406 31,715,617 2024 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2025 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2026 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2027 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2028 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2029 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2030 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2031 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2032 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2033 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2034 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2035 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2036 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2037 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2038 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2039 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2040 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2041 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2042 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2043 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2044 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2045 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2046 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2047 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2048 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2049 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2050 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - No Habitat Compensation

LAGOONS Option No L2 L3a L3b L3c L3d L3e(i) L3e(ii) Option Name Welsh Grounds Russel Lagoon Russel Lagoon Russel Lagoon Bridgwater Bay 91sq.km Offshore 50sq.km Offshore Lagoon - Fleming (English Grounds) (Welsh Grounds) (Peterstone Flats) (Land Connected Lagoon Lagoon Lagoon)

Installed capacity (MW) 1360 760 1360 1120 1360 1360 760 Pre Construction Period (years) 4 4 4 4 4 4 4 Construction Period (years) 5 4 5 5 5 6 5 First generation (years from start of const) 5 4 5 5 5 6 5 Refurbishment Interval (years) 40 40 40 40 40 40 40 Refurbishment Period (years) 2 2 2 2 2 2 2 Pre-Construction Annual Cost 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 Annual Construction Costs 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097 Annual Operation Costs 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 Annual Refurbishment Costs(inc operation costs) 376,168,649 223,831,551 384,537,742 321,613,767 374,147,650 420,763,181 239,586,501

YEAR 2010 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2011 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2012 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2013 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2014 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097 2015 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097 2016 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097 2017 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097 2018 626,185,621 43,931,551 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097 2019 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 948,654,737 59,686,501 2020 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2021 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2022 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2023 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2024 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2025 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2026 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2027 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2028 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2029 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2030 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2031 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2032 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2033 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2034 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2035 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2036 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2037 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2038 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2039 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2040 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2041 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2042 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2043 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2044 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2045 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2046 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2047 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2048 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2049 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2050 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - No Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Aberthaw to fence Minehead Tidal fence Minehead Tidal Reef

Installed capacity (MW) 256 1280 5000 Pre Construction Period (years) 4 4 4 Construction Period (years) 5 10 10 First generation (years from start of const) 4 3 3 Refurbishment Interval (years) 20 20 20 Refurbishment Period (years) 4 8 8 Pre-Construction Annual Cost 17,811,432 20,925,363 41,294,314 Annual Construction Costs 867,977,516 624,676,861 1,797,399,247 Annual Operation Costs 75,570,182 108,774,578 312,979,968 Annual Refurbishment Costs(inc operation costs) 128,000,000 320,000,000 1,250,000,000

YEAR 2010 17,811,432 20,925,363 41,294,314 2011 17,811,432 20,925,363 41,294,314 2012 17,811,432 20,925,363 41,294,314 2013 17,811,432 20,925,363 41,294,314 2014 867,977,516 624,676,861 1,797,399,247 2015 867,977,516 624,676,861 1,797,399,247 2016 892,915,676 638,273,683 1,836,521,743 2017 918,609,538 651,870,505 1,875,644,239 2018 943,547,698 665,467,327 1,914,766,735 2019 75,570,182 679,064,150 1,953,889,232 2020 75,570,182 692,660,972 1,993,011,728 2021 75,570,182 706,257,794 2,032,134,224 2022 75,570,182 719,854,616 2,071,256,720 2023 75,570,182 733,451,438 2,110,379,216 2024 75,570,182 108,774,578 312,979,968 2025 75,570,182 108,774,578 312,979,968 2026 75,570,182 108,774,578 312,979,968 2027 75,570,182 108,774,578 312,979,968 2028 75,570,182 108,774,578 312,979,968 2029 75,570,182 108,774,578 312,979,968 2030 75,570,182 108,774,578 312,979,968 2031 75,570,182 108,774,578 312,979,968 2032 75,570,182 108,774,578 312,979,968 2033 75,570,182 108,774,578 312,979,968 2034 75,570,182 108,774,578 312,979,968 2035 184,677,636 415,177,756 1,523,857,472 2036 184,677,636 415,177,756 1,523,857,472 2037 184,677,636 415,177,756 1,523,857,472 2038 184,677,636 415,177,756 1,523,857,472 2039 75,570,182 415,177,756 1,523,857,472 2040 75,570,182 415,177,756 1,523,857,472 2041 75,570,182 415,177,756 1,523,857,472 2042 75,570,182 415,177,756 1,523,857,472 2043 75,570,182 108,774,578 312,979,968 2044 75,570,182 108,774,578 312,979,968 2045 75,570,182 108,774,578 312,979,968 2046 75,570,182 108,774,578 312,979,968 2047 75,570,182 108,774,578 312,979,968 2048 75,570,182 108,774,578 312,979,968 2049 75,570,182 108,774,578 312,979,968 2050 75,570,182 108,774,578 312,979,968 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF ENERGY YIELDS Base Case - No Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Cardiff - Hinkley Cardiff - Weston Shoots Barrage Beachley Barrage Minehead Barrage Point Barrage Barrage

Installed capacity (MW) 14800 9000 8640 1050 625 Annual Energy Output (TWh) 25.3 19.3 16.8 2.77 1.59 Pre Construction Period (years) 4 4 4 4 4 Construction Period (years) 10 8 7 5 4 First generation (years from start of const) 7 7 6 5 4 Annual Energy Yield during refurbishment 20.24 15.44 13.44 1.385 0.795 Refurbishment Interval (years) 40 40 40 40 40 Refurbishment Period (years) 5 5 5 2 2

Annual Energy yield during construction is: 6.325 4.825 4.2 0 0 Note: Overwrirtten cells are in italics

YEAR 2010 - - - - - 2011 - - - - - 2012 - - - - - 2013 - - - - - 2014 - - - - - 2015 - - - - - 2016 - - - - - 2017 - - - - - 2018 - - - - 1.59 2019 - - - 2.77 1.59 2020 - - 8.40 2.77 1.59 2021 - 9.65 12.60 2.77 1.59 2022 12.65 14.48 16.80 2.77 1.59 2023 17.39 19.30 16.80 2.77 1.59 2024 22.14 19.30 16.80 2.77 1.59 2025 25.30 19.30 16.80 2.77 1.59 2026 25.30 19.30 16.80 2.77 1.59 2027 25.30 19.30 16.80 2.77 1.59 2028 25.30 19.30 16.80 2.77 1.59 2029 25.30 19.30 16.80 2.77 1.59 2030 25.30 19.30 16.80 2.77 1.59 2031 25.30 19.30 16.80 2.77 1.59 2032 25.30 19.30 16.80 2.77 1.59 2033 25.30 19.30 16.80 2.77 1.59 2034 25.30 19.30 16.80 2.77 1.59 2035 25.30 19.30 16.80 2.77 1.59 2036 25.30 19.30 16.80 2.77 1.59 2037 25.30 19.30 16.80 2.77 1.59 2038 25.30 19.30 16.80 2.77 1.59 2039 25.30 19.30 16.80 2.77 1.59 2040 25.30 19.30 16.80 2.77 1.59 2041 25.30 19.30 16.80 2.77 1.59 2042 25.30 19.30 16.80 2.77 1.59 2043 25.30 19.30 16.80 2.77 1.59 2044 25.30 19.30 16.80 2.77 1.59 2045 25.30 19.30 16.80 2.77 1.59 2046 25.30 19.30 16.80 2.77 1.59 2047 25.30 19.30 16.80 2.77 1.59 2048 25.30 19.30 16.80 2.77 1.59 2049 25.30 19.30 16.80 2.77 1.59 2050 25.30 19.30 16.80 2.77 1.59 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF ENERGY YIELDS Base Case - No Habitat Compensation

Installed capacity (MW) 1360 760 1360 1120 1360 1360 760 Annual Energy Output (TWh) 2.31 1.41 2.31 2.33 2.64 2.6 1.32 Pre Construction Period (years) 4 4 4 4 4 4 4 Construction Period (years) 5 4 5 5 5 6 5 First generation (years from start of const) 5 4 5 5 5 6 5 Annual Energy Yield during refurbishment 1.155 0.705 1.155 1.165 1.32 1.3 0.66 Refurbishment Interval (years) 40 40 40 40 40 40 40 Refurbishment Period (years) 2 2 2 2 2 2 2

Annual Energy yield during construction is: 0 Note: Overwrirtten cells are in italics

YEAR 2010 ------2011 ------2012 ------2013 ------2014 ------2015 ------2016 ------2017 ------2018 - 1.41 - - - - - 2019 2.31 1.41 2.31 2.33 2.64 - 1.32 2020 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2021 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2022 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2023 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2024 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2025 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2026 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2027 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2028 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2029 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2030 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2031 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2032 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2033 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2034 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2035 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2036 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2037 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2038 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2039 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2040 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2041 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2042 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2043 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2044 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2045 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2046 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2047 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2048 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2049 2.31 1.41 2.31 2.33 2.64 2.60 1.32 2050 2.31 1.41 2.31 2.33 2.64 2.60 1.32 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF ENERGY YIELDS Base Case - No Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b L2 R1 Option Name Cardiff to Weston Tidal Aberthaw to Welsh Grounds Aberthaw to fence Minehead Tidal fence Lagoon - Fleming Minehead Tidal Reef

Installed capacity (MW) 256 1280 1360 5000 Annual Energy Output (TWh) 0.7 3.3 2.31 13 Pre Construction Period (years) 4 4 4 4 Construction Period (years) 5 10 5 10 First generation (years from start of const) 4 3 5 3 Annual Energy Yield during refurbishment 0.525 2.8875 1.155 11.375 Refurbishment Interval (years) 20 20 40 20 Refurbishment Period (years) 4 8 2 8

Annual Energy yield during construction is: 0.233333333 0.4125 0 0.4125 Note: Overwrirtten cells are in italics

YEAR 2010 - - - - 2011 - - - - 2012 - - - - 2013 - - - - 2014 - - - - 2015 - - - - 2016 0.23 - - - 2017 0.23 0.41 - - 2018 0.23 0.83 - 0.41 2019 0.70 1.24 2.31 0.83 2020 0.70 1.65 2.31 1.24 2021 0.70 2.06 2.31 1.65 2022 0.70 2.48 2.31 6.50 2023 0.70 2.89 2.31 8.66 2024 0.70 3.30 2.31 10.83 2025 0.70 3.30 2.31 13.00 2026 0.70 3.30 2.31 13.00 2027 0.70 3.30 2.31 13.00 2028 0.70 3.30 2.31 13.00 2029 0.70 3.30 2.31 13.00 2030 0.70 3.30 2.31 13.00 2031 0.70 3.30 2.31 13.00 2032 0.70 3.30 2.31 13.00 2033 0.70 3.30 2.31 13.00 2034 0.70 3.30 2.31 13.00 2035 0.53 2.89 2.31 13.00 2036 0.53 2.89 2.31 11.38 2037 0.53 2.89 2.31 11.38 2038 0.53 2.89 2.31 11.38 2039 0.70 2.89 2.31 11.38 2040 0.70 2.89 2.31 11.38 2041 0.70 2.89 2.31 11.38 2042 0.70 2.89 2.31 11.38 2043 0.70 3.30 2.31 11.38 2044 0.70 3.30 2.31 13.00 2045 0.70 3.30 2.31 13.00 2046 0.70 3.30 2.31 13.00 2047 0.70 3.30 2.31 13.00 2048 0.70 3.30 2.31 13.00 2049 0.70 3.30 2.31 13.00 2050 0.70 3.30 2.31 13.00 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - Ration of 1:1 Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Minehead Barrage Cardiff - Hinkley Point Cardiff - Weston Barrage Shoots Barrage Beachley Barrage Barrage

PRE-CONSTRUCTION TOTAL PLANNING 317,414,634 271,637,173 209,225,373 29,967,394 21,656,261

CAISSONS Caissons 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659 TOTAL CAISSONS 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 27,949 25,697 20,240 4,946 3,514 Cost of Compensatory Habitats: 1,816,685,000 1,670,305,000 1,315,600,000 321,490,000 228,410,000 VAT - - - - -

PROMOTIONAL COSTS Client Project Management Costs 143,672,809 107,358,583 89,863,615 12,599,259 9,061,605 (Project promoter delivery costs) VAT - - - - -

TOTAL PROJECT COST 31,012,334,239 23,521,017,259 19,587,412,058 2,883,908,416 2,071,448,852 Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - Ration of 1:1 Habitat Compensation

PRE-CONSTRUCTION TOTAL PLANNING 41,664,432 37,829,982 51,264,760 46,941,614 38,889,710 92,442,903 56,181,699

ADDITIONAL ITEMS Design and Supervision 42,202,500 37,020,964 50,812,551 47,851,060 40,931,583 92,473,028 55,539,546 Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 2,092,500 2,336,520 2,912,505 2,636,530 1,749,317 6,093,741 3,781,981 (eg site investigation during design & construction) Ancilliaries 50,000,000 50,000,000 50,000,000 50,000,000 50,000,000 10,000,000 10,000,000 (eg navigation and land drainage improvements) Contingencies 220,650,000 198,691,222 269,850,290 250,291,772 209,659,048 494,024,445 298,468,834 (15% on civil works and gates only) Contractors Oncosts and Profit 136,067,500 122,526,254 166,407,679 154,346,593 129,289,746 304,648,408 184,055,781 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 451,012,500 410,574,960 539,983,024 505,125,955 431,629,695 907,239,622 551,846,141 TOTAL CONSTRUCTION COSTS 3,115,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201 VAT ------TOTAL CONSTRUCTION COSTS (inc VAT) 3,115,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 6,500 2,000 6,500 2,700 5,500 0 0 Cost of Compensatory Habitats: 422,500,000 130,000,000 422,500,000 175,500,000 357,500,000 - - VAT ------

PROMOTIONAL COSTS Client Project Management Costs 15,576,757 12,551,872 17,967,926 16,189,648 14,999,329 28,318,052 17,053,286 (Project promoter delivery costs) VAT ------

TOTAL PROJECT COST 3,595,092,538 2,690,756,183 4,085,317,931 3,476,560,805 3,411,254,766 5,784,371,325 3,483,892,187 Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - Ration of 1:1 Habitat Compensation

TIDAL FENCE & TIDAL REEF

Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Minehead Aberthaw to Minehead fence Tidal fence Tidal Reef

PRE-CONSTRUCTION TOTAL PLANNING 71,465,729 83,921,452 165,177,258

CAISSONS Caissons 678,000,000 - 3,919,000,000 TOTAL CAISSONS 678,000,000 - 3,919,000,000

M&E Generating Plant 512,000,000 2,560,000,000 10,000,000,000 Grid Connection 217,000,000 334,000,000 300,000,000 Gates - - 1,080,000,000 TOTAL M&E 729,000,000 2,894,000,000 11,380,000,000

ADDITIONAL ITEMS Design and Supervision 73,626,300 61,165,781 185,657,625 Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 4,590,600 5,825,313 985,250 (eg site investigation during design & construction) Ancilliaries 50,000,000 50,000,000 50,000,000 (eg navigation and land drainage improvements) Contingencies 377,136,000 349,518,750 808,965,000 (15% on civil works and gates only) Contractors Oncosts and Profit 232,567,200 215,536,563 498,861,750 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 737,920,100 682,046,406 1,544,469,625 TOTAL CONSTRUCTION COSTS 4,358,296,100 6,255,690,156 17,884,569,625 VAT - - - TOTAL CONSTRUCTION COSTS (inc VAT) 4,358,296,100 6,255,690,156 17,884,569,625

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 2,024 2,795 8,600 Cost of Compensatory Habitats: 131,560,000 181,668,500 559,000,000 VAT - - -

PROMOTIONAL COSTS Client Project Management Costs 21,791,481 31,278,451 89,422,848 (Project promoter delivery costs) VAT - - -

TOTAL PROJECT COST 4,583,113,309 6,552,558,559 18,698,169,731 Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - Ration of 1:1 Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Cardiff - Hinkley Cardiff - Weston Shoots Barrage Beachley Barrage Minehead Barrage Point Barrage Barrage

Installed capacity (MW) 14800 9000 8640 1050 625 Pre Construction Period (years) 4 4 4 4 4 Construction Period (years) 10 8 7 5 4 First generation (years from start of const) 7 7 6 5 4 Refurbishment Interval (years) 40 40 40 40 40 Refurbishment Period (years) 5 5 5 2 2 Pre-Construction Annual Cost 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 Annual Construction Costs 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,148 Annual Operation Costs 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 Annual Refurbishment Costs(inc operation costs) 1,759,940,356 1,227,567,539 1,132,262,654 268,797,406 165,415,617

YEAR 2010 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2011 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2012 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2013 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2014 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,148 2015 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,148 2016 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,148 2017 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,148 2018 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 31,715,617 2019 3,069,491,960 2,906,172,511 2,768,312,383 44,097,406 31,715,617 2020 3,069,491,960 2,906,172,511 2,925,573,710 44,097,406 31,715,617 2021 3,069,491,960 3,094,050,030 314,522,654 44,097,406 31,715,617 2022 3,249,082,972 375,755,039 314,522,654 44,097,406 31,715,617 2023 3,338,878,477 375,755,039 314,522,654 44,097,406 31,715,617 2024 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2025 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2026 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2027 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2028 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2029 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2030 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2031 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2032 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2033 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2034 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2035 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2036 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2037 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2038 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2039 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2040 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2041 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2042 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2043 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2044 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2045 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2046 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2047 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2048 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2049 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2050 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 Continues to 120 years after operational start date. Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - Ration of 1:1 Habitat Compensation

LAGOONS Option No L2 L3a L3b L3c L3d L3e(i) L3e(ii) Option Name Welsh Grounds Russel Lagoon Russel Lagoon (Welsh Russel Lagoon Bridgwater Bay (Land 91sq.km Offshore 50sq.km Offshore Lagoon - Fleming (English Grounds) Grounds) (Peterstone Flats) Connected Lagoon) Lagoon Lagoon

Installed capacity (MW) 1360 760 1360 1120 1360 1360 760 Pre Construction Period (years) 4 4 4 4 4 4 4 Construction Period (years) 5 4 5 5 5 6 5 First generation (years from start of const) 5 4 5 5 5 6 5 Refurbishment Interval (years) 40 40 40 40 40 40 40 Refurbishment Period (years) 2 2 2 2 2 2 2 Pre-Construction Annual Cost 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 Annual Construction Costs 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,097 Annual Operation Costs 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 Annual Refurbishment Costs(inc operation costs) 376,168,649 223,831,551 384,537,742 321,613,767 374,147,650 420,763,181 239,586,501

YEAR 2010 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2011 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2012 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2013 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2014 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,097 2015 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,097 2016 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,097 2017 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,097 2018 710,685,621 43,931,551 806,810,634 685,923,838 674,473,011 948,654,737 685,542,097 2019 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 948,654,737 59,686,501 2020 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2021 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2022 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2023 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2024 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2025 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2026 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2027 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2028 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2029 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2030 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2031 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2032 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2033 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2034 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2035 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2036 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2037 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2038 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2039 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2040 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2041 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2042 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2043 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2044 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2045 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2046 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2047 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2048 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2049 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2050 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 Continues to 120 years after operational start date. Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - Ration of 1:1 Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Minehead Aberthaw to fence Tidal fence Minehead Tidal Reef

Installed capacity (MW) 256 1280 5000 Pre Construction Period (years) 4 4 4 Construction Period (years) 5 10 10 First generation (years from start of const) 4 3 3 Refurbishment Interval (years) 20 20 20 Refurbishment Period (years) 4 8 8 Pre-Construction Annual Cost 17,866,432 20,980,363 41,294,314 Annual Construction Costs 902,329,516 646,863,711 1,853,299,247 Annual Operation Costs 76,270,182 109,474,578 312,979,968 Annual Refurbishment Costs(inc operation costs) 128,000,000 320,000,000 1,255,000,000

YEAR 2010 17,866,432 20,980,363 41,294,314 2011 17,866,432 20,980,363 41,294,314 2012 17,866,432 20,980,363 41,294,314 2013 17,866,432 20,980,363 41,294,314 2014 902,329,516 646,863,711 1,853,299,247 2015 902,329,516 646,863,711 1,853,299,247 2016 927,498,676 660,548,033 1,892,421,743 2017 953,430,538 674,232,355 1,931,544,239 2018 978,599,698 687,916,677 1,970,666,735 2019 76,270,182 701,601,000 2,009,789,232 2020 76,270,182 715,285,322 2,048,911,728 2021 76,270,182 728,969,644 2,088,034,224 2022 76,270,182 742,653,966 2,127,156,720 2023 76,270,182 756,338,288 2,166,279,216 2024 76,270,182 109,474,578 312,979,968 2025 76,270,182 109,474,578 312,979,968 2026 76,270,182 109,474,578 312,979,968 2027 76,270,182 109,474,578 312,979,968 2028 76,270,182 109,474,578 312,979,968 2029 76,270,182 109,474,578 312,979,968 2030 76,270,182 109,474,578 312,979,968 2031 76,270,182 109,474,578 312,979,968 2032 76,270,182 109,474,578 312,979,968 2033 76,270,182 109,474,578 312,979,968 2034 76,270,182 109,474,578 312,979,968 2035 185,202,636 415,790,256 1,528,857,472 2036 185,202,636 415,790,256 1,528,857,472 2037 185,202,636 415,790,256 1,528,857,472 2038 185,202,636 415,790,256 1,528,857,472 2039 76,270,182 415,790,256 1,528,857,472 2040 76,270,182 415,790,256 1,528,857,472 2041 76,270,182 415,790,256 1,528,857,472 2042 76,270,182 415,790,256 1,528,857,472 2043 76,270,182 109,474,578 312,979,968 2044 76,270,182 109,474,578 312,979,968 2045 76,270,182 109,474,578 312,979,968 2046 76,270,182 109,474,578 312,979,968 2047 76,270,182 109,474,578 312,979,968 2048 76,270,182 109,474,578 312,979,968 2049 76,270,182 109,474,578 312,979,968 2050 76,270,182 109,474,578 312,979,968 Continues to 120 years after operational start date. Severn Tidal Power - Options Analysis

SUMMARY OF ENERGY YIELDS Base Case - Ration of 1:1 Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Cardiff - Hinkley Cardiff - Weston Shoots Barrage Beachley Barrage Minehead Barrage Point Barrage Barrage

, Annual Energy yield during construction is: 6.325 4.825 4.2 0 0 Note: Overwrirtten cells are in italics

SUMMARY OF ENERGY YIELDS Base Case - Ration of 1:1 Habitat Compensation

, Annual Energy yield during construction is: 0 Note: Overwrirtten cells are in italics

SUMMARY OF ENERGY YIELDS Base Case - Ration of 1:1 Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Aberthaw to fence Minehead Tidal Minehead Tidal Reef fence

Installed capacity (MW) 256 1280 5000 Annual Energy Output (TWh) 0.7 3.3 13 Pre Construction Period (years) 4 4 4 Construction Period (years) 5 10 10 First generation (years from start of const) 4 3 3 Annual Energy Yield during refurbishment 0.525 2.8875 11.375 Refurbishment Interval (years) 20 20 20 Refurbishment Period (years) 4 8 8

, Annual Energy yield during construction is: 0.233333333 0.4125 0.4125 Note: Overwrirtten cells are in italics

YEAR 2010 - - - 2011 - - - 2012 - - - 2013 - - - 2014 - - - 2015 - - - 2016 0.23 - - 2017 0.23 0.41 - 2018 0.23 0.83 0.41 2019 0.70 1.24 0.83 2020 0.70 1.65 1.24 2021 0.70 2.06 1.65 2022 0.70 2.48 6.50 2023 0.70 2.89 8.66 2024 0.70 3.30 10.83 2025 0.70 3.30 13.00 2026 0.70 3.30 13.00 2027 0.70 3.30 13.00 2028 0.70 3.30 13.00 2029 0.70 3.30 13.00 2030 0.70 3.30 13.00 2031 0.70 3.30 13.00 2032 0.70 3.30 13.00 2033 0.70 3.30 13.00 2034 0.70 3.30 13.00 2035 0.53 2.89 13.00 2036 0.53 2.89 11.38 2037 0.53 2.89 11.38 2038 0.53 2.89 11.38 2039 0.70 2.89 11.38 2040 0.70 2.89 11.38 2041 0.70 2.89 11.38 2042 0.70 2.89 11.38 2043 0.70 3.30 11.38 2044 0.70 3.30 13.00 2045 0.70 3.30 13.00 2046 0.70 3.30 13.00 2047 0.70 3.30 13.00 2048 0.70 3.30 13.00 2049 0.70 3.30 13.00 2050 0.70 3.30 13.00 Continues to 120 years after operational start date. Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - Ratio of 3:1 Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Minehead Barrage Cardiff - Hinkley Point Cardiff - Weston Barrage Shoots Barrage Beachley Barrage Barrage

PRE-CONSTRUCTION TOTAL PLANNING 317,414,634 271,637,173 209,225,373 29,967,394 21,656,261

CAISSONS Caissons 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659 TOTAL CAISSONS 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 27,949 25,697 20,240 4,946 3,514 Cost of Compensatory Habitats: 5,450,055,000 5,010,915,000 3,946,800,000 964,470,000 685,230,000 VAT - - - - -

PROMOTIONAL COSTS Client Project Management Costs 143,672,809 107,358,583 89,863,615 12,599,259 9,061,605 (Project promoter delivery costs) VAT - - - - -

TOTAL PROJECT COST 34,645,704,239 26,861,627,259 22,218,612,058 3,526,888,416 2,528,268,852 Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - Ratio of 3:1 Habitat Compensation

PRE-CONSTRUCTION TOTAL PLANNING 41,444,432 37,829,982 51,264,760 46,941,614 38,889,710 92,442,903 56,181,699

ADDITIONAL ITEMS Design and Supervision 42,202,500 37,020,964 50,812,551 47,851,060 40,931,583 92,473,028 55,539,546 Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 2,092,500 2,336,520 2,912,505 2,636,530 1,749,317 6,093,741 3,781,981 (eg site investigation during design & construction) Ancilliaries 10,000,000 50,000,000 50,000,000 50,000,000 50,000,000 10,000,000 10,000,000 (eg navigation and land drainage improvements) Contingencies 220,650,000 198,691,222 269,850,290 250,291,772 209,659,048 494,024,445 298,468,834 (15% on civil works and gates only) Contractors Oncosts and Profit 136,067,500 122,526,254 166,407,679 154,346,593 129,289,746 304,648,408 184,055,781 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 411,012,500 410,574,960 539,983,024 505,125,955 431,629,695 907,239,622 551,846,141 TOTAL CONSTRUCTION COSTS 3,075,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201 VAT ------TOTAL CONSTRUCTION COSTS (inc VAT) 3,075,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 6,500 2,000 6,500 2,700 5,500 0 0 Cost of Compensatory Habitats: 1,267,500,000 390,000,000 1,267,500,000 526,500,000 1,072,500,000 - - VAT ------

PROMOTIONAL COSTS Client Project Management Costs 15,376,757 12,551,872 17,967,926 16,189,648 14,999,329 28,318,052 17,053,286 (Project promoter delivery costs) VAT ------

TOTAL PROJECT COST 4,399,672,538 2,950,756,183 4,930,317,931 3,827,560,805 4,126,254,766 5,784,371,325 3,483,892,187 Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - Ratio of 3:1 Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Minehead Aberthaw to Minehead fence Tidal fence Tidal Reef

PRE-CONSTRUCTION TOTAL PLANNING 71,465,729 83,701,452 165,177,258

CAISSONS Caissons 678,000,000 - 3,919,000,000 TOTAL CAISSONS 678,000,000 - 3,919,000,000

M&E Generating Plant 512,000,000 2,560,000,000 10,000,000,000 Grid Connection 217,000,000 334,000,000 300,000,000 Gates - - 1,080,000,000 TOTAL M&E 729,000,000 2,894,000,000 11,380,000,000

ADDITIONAL ITEMS Design and Supervision 73,626,300 61,165,781 185,657,625 Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons Site Investigation 4,590,600 5,825,313 985,250 (eg site investigation during design & construction) Ancilliaries 50,000,000 10,000,000 50,000,000 (eg navigation and land drainage improvements) Contingencies 377,136,000 349,518,750 808,965,000 (15% on civil works and gates only) Contractors Oncosts and Profit 232,567,200 215,536,563 498,861,750 9.25% on civil works and gates only TOTAL ADDITIONAL ITEMS 737,920,100 642,046,406 1,544,469,625 TOTAL CONSTRUCTION COSTS 4,358,296,100 6,215,690,156 17,884,569,625 VAT - - - TOTAL CONSTRUCTION COSTS (inc VAT) 4,358,296,100 6,215,690,156 17,884,569,625

COMPENSATORY HABITATS Loss of Inter-tidal Areas: 2,024 2,795 8,600 Cost of Compensatory Habitats: 394,680,000 545,005,500 1,677,000,000 VAT - - -

PROMOTIONAL COSTS Client Project Management Costs 21,791,481 31,078,451 89,422,848 (Project promoter delivery costs) VAT - - -

TOTAL PROJECT COST 4,846,233,309 6,875,475,559 19,816,169,731 Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - Ratio of 3:1 Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Cardiff - Hinkley Cardiff - Weston Shoots Barrage Beachley Barrage Minehead Barrage Point Barrage Barrage

Installed capacity (MW) 14800 9000 8640 1050 625 Pre Construction Period (years) 4 4 4 4 4 Construction Period (years) 10 8 7 5 4 First generation (years from start of const) 7 7 6 5 4 Refurbishment Interval (years) 40 40 40 40 40 Refurbishment Period (years) 5 5 5 2 2 Pre-Construction Annual Cost 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 Annual Construction Costs 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,148 Annual Operation Costs 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 Annual Refurbishment Costs(inc operation costs) 1,759,940,356 1,227,567,539 1,132,262,654 268,797,406 165,415,617

YEAR 2010 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2011 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2012 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2013 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065 2014 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,148 2015 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,148 2016 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,148 2017 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,148 2018 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 31,715,617 2019 3,432,828,960 3,323,748,761 3,144,198,098 44,097,406 31,715,617 2020 3,432,828,960 3,323,748,761 3,301,459,425 44,097,406 31,715,617 2021 3,432,828,960 3,511,626,280 314,522,654 44,097,406 31,715,617 2022 3,612,419,972 375,755,039 314,522,654 44,097,406 31,715,617 2023 3,702,215,477 375,755,039 314,522,654 44,097,406 31,715,617 2024 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2025 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2026 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2027 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2028 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2029 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2030 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2031 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2032 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2033 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2034 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2035 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2036 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2037 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2038 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2039 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2040 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2041 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2042 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2043 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2044 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2045 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2046 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2047 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2048 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2049 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 2050 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - Ratio of 3:1 Habitat Compensation

Installed capacity (MW) 1360 760 1360 1120 1360 1360 760 Pre Construction Period (years) 4 4 4 4 4 4 4 Construction Period (years) 5 4 5 5 5 6 5 First generation (years from start of const) 5 4 5 5 5 6 5 Refurbishment Interval (years) 40 40 40 40 40 40 40 Refurbishment Period (years) 2 2 2 2 2 2 2 Pre-Construction Annual Cost 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 Annual Construction Costs 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,097 Annual Operation Costs 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 Annual Refurbishment Costs(inc operation costs) 375,468,649 223,831,551 384,537,742 321,613,767 374,147,650 420,763,181 239,586,501

YEAR 2010 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2011 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2012 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2013 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425 2014 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,097 2015 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,097 2016 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,097 2017 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,097 2018 871,645,621 43,931,551 975,810,634 756,123,838 817,473,011 948,654,737 685,542,097 2019 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 948,654,737 59,686,501 2020 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2021 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2022 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2023 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2024 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2025 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2026 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2027 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2028 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2029 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2030 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2031 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2032 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2033 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2034 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2035 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2036 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2037 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2038 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2039 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2040 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2041 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2042 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2043 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2044 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2045 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2046 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2047 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2048 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2049 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 2050 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF CASH FLOWS Base Case - Ratio of 3:1 Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Minehead Aberthaw to fence Tidal fence Minehead Tidal Reef

Installed capacity (MW) 256 1280 5000 Pre Construction Period (years) 4 4 4 Construction Period (years) 5 10 10 First generation (years from start of const) 4 3 3 Refurbishment Interval (years) 20 20 20 Refurbishment Period (years) 4 8 8 Pre-Construction Annual Cost 17,866,432 20,925,363 41,294,314 Annual Construction Costs 954,953,516 679,177,411 1,965,099,247 Annual Operation Costs 76,270,182 108,774,578 312,979,968 Annual Refurbishment Costs(inc operation costs) 128,000,000 320,000,000 1,250,000,000

YEAR 2010 17,866,432 20,925,363 41,294,314 2011 17,866,432 20,925,363 41,294,314 2012 17,866,432 20,925,363 41,294,314 2013 17,866,432 20,925,363 41,294,314 2014 954,953,516 679,177,411 1,965,099,247 2015 954,953,516 679,177,411 1,965,099,247 2016 980,122,676 692,774,233 2,004,221,743 2017 1,006,054,538 706,371,055 2,043,344,239 2018 1,031,223,698 719,967,877 2,082,466,735 2019 76,270,182 733,564,700 2,121,589,232 2020 76,270,182 747,161,522 2,160,711,728 2021 76,270,182 760,758,344 2,199,834,224 2022 76,270,182 774,355,166 2,238,956,720 2023 76,270,182 787,951,988 2,278,079,216 2024 76,270,182 108,774,578 312,979,968 2025 76,270,182 108,774,578 312,979,968 2026 76,270,182 108,774,578 312,979,968 2027 76,270,182 108,774,578 312,979,968 2028 76,270,182 108,774,578 312,979,968 2029 76,270,182 108,774,578 312,979,968 2030 76,270,182 108,774,578 312,979,968 2031 76,270,182 108,774,578 312,979,968 2032 76,270,182 108,774,578 312,979,968 2033 76,270,182 108,774,578 312,979,968 2034 76,270,182 108,774,578 312,979,968 2035 185,202,636 415,177,756 1,523,857,472 2036 185,202,636 415,177,756 1,523,857,472 2037 185,202,636 415,177,756 1,523,857,472 2038 185,202,636 415,177,756 1,523,857,472 2039 76,270,182 415,177,756 1,523,857,472 2040 76,270,182 415,177,756 1,523,857,472 2041 76,270,182 415,177,756 1,523,857,472 2042 76,270,182 415,177,756 1,523,857,472 2043 76,270,182 108,774,578 312,979,968 2044 76,270,182 108,774,578 312,979,968 2045 76,270,182 108,774,578 312,979,968 2046 76,270,182 108,774,578 312,979,968 2047 76,270,182 108,774,578 312,979,968 2048 76,270,182 108,774,578 312,979,968 2049 76,270,182 108,774,578 312,979,968 2050 76,270,182 108,774,578 312,979,968 Continues to 120 years after operational start date Severn Tidal Power - Options Analysis

SUMMARY OF ENERGY YIELDS Base Case - Ratio of 3:1 Habitat Compensation

BARRAGES Option No B1 B2 B3 B4 B5 Option Name Aberthaw - Cardiff - Hinkley Cardiff - Weston Shoots Barrage Beachley Barrage Minehead Barrage Point Barrage Barrage

Annual Energy yield during construction is: 6.325 4.825 4.2 0 0 Note: Overwrirtten cells are in italics

SUMMARY OF ENERGY YIELDS Base Case - Ratio of 3:1 Habitat Compensation

Annual Energy yield during construction is: 0 Note: Overwrirtten cells are in italics

SUMMARY OF ENERGY YIELDS Base Case - Ratio of 3:1 Habitat Compensation

TIDAL FENCE & TIDAL REEF Option No F1a F1b R1 Option Name Cardiff to Weston Tidal Aberthaw to Minehead Aberthaw to fence Tidal fence Minehead Tidal Reef

Annual Energy yield during construction is: 0.233333333 0.4125 0.4125 Note: Overwrirtten cells are in italics