THE IMPACT OF SEA-LEVEL RISE ON THE LONDON-PENZANCE RAILWAY LINE By DAVID A. DAWSON A thesis submitted to the University of Plymouth in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY Department of Geography School of Geography, Earth & Environmental Sciences In collaboration with: Great Western Research, Network Rail, and Devon and Cornwall County Councils FEBRUARY 2012 i COPYRIGHT STATEMENT This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the author’s prior consent. ii ABSTRACT DAVID ANDREW DAWSON THE IMPACT OF SEA-LEVEL RISE ON THE LONDON-PENZANCE RAILWAY LINE The coastal section of the London to Penzance railway line (Dawlish-Teignmouth) lies very close to sea level and has been susceptible to frequent closure during high seas and storm events. As the main railway connection for the southwest of England to the rest of Great Britain, it is a vital transport link for the Devon and Cornwall economy. Current understanding of future sea-level rise in the region is compromised by a lack of reliable geological data on which to establish accurate future sea-level projections. Furthermore, the impacts – in engineering and economic terms – of potential sea-level change on the long-term functioning of the main railway are unclear, and future policy making and planning are compromised by a similar gap in scientific knowledge. The central aim of this thesis is to establish the extent to which future sea-level changes will impact upon the Southwest‟s main railway line. This aim carries three objectives: (1) to establish accurate sea-level trends over the last 4000 years (late Holocene) in order to validate geophysical models used in current future sea-level projections in the southwest of England; (2) to establish the likely impacts of future sea- level change on the functioning of the Dawlish-Teignmouth railway line; and (3) to integrate climate and socio-economic futures (scenarios) in an internally consistent manner for future use in regional policy debates. In addressing these objectives, we estimate that during the last 2000 years the coast of south Devon has subsided at a rate of ~1.1 mm/yr, generating a relative sea-level rise of ~0.9 mm/yr. The geophysical model (used to determine regional sea-level projections) underestimates the geologically estimated coastal subsidence rate by only 17%, which would generate an additional sea-level rise, compared to predicted values, of 0.014 m by 2100. Based on an empirical trend between increases in sea-level changes and rail functioning during the last 40 years, the corrected sea-level projections provide input for establishing future days with line restrictions due to overtopping on the Southwest Mainline. Impacts to both the Southwest economy (e.g., rail users) and the infrastructure owners have been determined, and integrating these forecasts with socio-economic scenarios (SES) has highlighted the important interaction between climate and socio- economic trends and future vulnerability. In a worst case scenario (e.g., high emissions), rail services are predicted to be disrupted (on average) for around 35% of the winter by 2060. By this stage, the cost of these disruptions will have exceeded the capital needed for constructing a new alternative inland route. iii Contents Page Title Page i Copyright Statement ii Abstract iii List of Contents v List of Figures ix List of Tables xi List of Abbreviations xiii Acknowledgements xv Author‟s Declaration xvi Dedication xvii iv List of Contents Page CHAPTER ONE INTRODUCTION 1.1 Introduction 1 1.2 Applied geography and climate change 3 1.3 Aim and objectives 1.3.1 Objective 1: establishing new late Holocene sea-level data 8 1.3.2 Objective 2: establishing future line impacts 12 1.3.3 Objective 3: integrating climate and socio-economic futures 14 1.4 Scope of the study 16 CHAPTER TWO RISING SEA LEVELS, SCIENCE AND SOCIETY 2.1 Introduction 17 2.2 Palaeo sea-level studies 18 2.3 Obtaining relative sea-level data 22 2.3.1 Lithology-based approaches 24 2.3.2 Quantitative techniques 25 2.3.3 Numerical modelling of relative sea-level change 27 2.4 Holocene sea-level change in the United Kingdom 28 2.4.1 Sea-level records in the Southwest 32 2.4.2 Late Holocene sea-level records in Southwest England 35 2.5 Application of sea-level data 39 2.5.1 Implication for coastal flooding 42 2.6 Management of UK coasts 43 2.7 Critical infrastructure 49 2.7.1 Critical transport infrastructure 51 2.7.2 Scenario approaches to climate impact assessment 58 2.8 Chapter synopsis 61 CHAPTER THREE A INTEGRATED METHODOLOGICAL APPROACH 3.1 Introduction 65 3.2 Sea-level reconstruction 67 v 3.2.1 Site selection and saltmarsh sediments as palaeo sea-level indicators 67 3.2.2 Considerations for palaeo sea-level studies 70 3.3 Site selection 73 3.3.1 Thurlestone field sites 75 3.3.2 Sampling for SLIPs 79 3.4 Laboratory methods 3.4.1 Lithology 79 3.4.2 Foraminifera analysis 80 3.4.3 Loss on ignition 80 3.4.4 AMS 14C dating 81 3.4.5 Sea-level methods synopsis 82 3.5 The impacts of future sea-level change: a semi-empirical approach 83 3.5.1 Archive and documentary analysis 86 3.5.2 Gathering archives and accounts 88 3.5.3 The Published Sources Archive (PSA) 91 3.5.4 The Frontage Management Record (FMR) 92 3.5.5 TRUST Service Data (TSD) 94 3.5.6 Sea surface and weather records 95 3.5.7 Establishing an empirical baseline 96 3.5.8 Costing the impacts 98 3.6 Integrating socio-economic futures 101 3.6.1 Developing the scenarios 103 3.7 Chapter synopsis 106 CHAPTER FOUR LATE HOLOCENE RELATIVE SEA-LEVEL CHANGES IN SOUTH DEVON 4.1 Introduction 109 4.2 Thurlestone Sands, south Devon 109 4.2.1 Litho- and biostratigraphy 111 4.2.2 Chronology 115 4.2.3 Loss on ignition 117 4.3 Paleo-environmental interpretation of Thurlestone Sands 119 4.4 Summary of field evidence 120 4.5 Deriving new late Holocene sea-level data for south Devon vi 4.5.1 Indicative meaning 121 4.5.2 Basal index points and sediment consolidation 124 4.5.3 Relative sea-level change in south Devon 126 4.5.4 Comparisons with geophysical model predictions 129 4.5.5 Rates of vertical land movement and sea-level projections 133 4.7 Chapter synopsis 138 CHAPTER FIVE THE VULNERABILITY OF THE SOUTHWEST MAINLINE 5.1 Introduction 140 5.2 Adverse weather and events 140 5.3 A record of the vulnerability of the southwest mainline 146 5.3.1 The Published Sources Archive (PSA-1846-2009) 147 5.3.2 The Frontage Management Report (FMR- 1859-2005) 152 5.3.3 TRUST Service Data (TSD-1997-2009) 158 5.3.4 Comparing the archives of rail history 161 5.4 A semi-empirical relationship of rail problems and sea-level change 168 5.5 The future of the Dawlish to Teignmouth railway line 175 5.6 Chapter synopsis 185 CHAPTER SIX COSTING THE IMPACTS OF FUTURE LINE CLOSURE 6.1 Introduction 188 6.1.1 A century and a half of regional rail problems 189 6.2 Transport and the economy 192 6.3 Costing the impacts of future rail closure 196 6.3.1 Direct costs of sea-level rise 197 6.3.2 Indirect costs of sea-level rise 203 6.3.3 Combined indirect costs of sea-level rise 211 6.3.4 Total costs of rail incidents 214 6.4 Integrating socio-economic scenarios (SES) 217 6.5 Scenarios of future rail problems 224 6.5.1 World Markets scenario 224 6.5.2 Global Sustainability scenario 227 6.5.3 National Enterprise scenario 230 vii 6.5.4 Local Stewardship scenario 232 6.5.5 The future impacts of sea-level rise 235 6.6 Connecting the science to society 243 6.7 Chapter synopsis 248 CHAPTER SEVEN CONCLUSIONS AND RECOMMENDATIONS 7.1 Introduction 252 7.2 New sea-level data for southwest England 253 7.3 The vulnerability of the southwest mainline 254 7.4 The impacts of future sea-level rise 256 7.5 Summary of investigation 260 7.6 Further research, recommendations, and reflections 263 References 274 Appendices (CD-ROM) APPENDIX A 1.1 Rail re-route study (Phillip, 2009) 1.2 Archival search terms APPENDIX B 1.1 Core analysis 1.2 Deriving late Holocene sea-level data 1.3 Validating regional sea-level projections APPENDIX C 1.1 Weather and tidal effects 1.2 Historical archive analysis 1.3 The empirical model 1.4 Projections of future days with line restrictions (DLRs) APPENDIX D 1.1 Costing the impacts of overtopping 1.2 Integrating climate change scenarios with socio-economic scenarios 1.3 The final project scenarios 1.4 Railtrack (1996) viii List of figures Page CHAPTER ONE 1.1 Location of the Dawlish-Teignmouth section of the London-Penzance railway line 2 1.2 Model predictions from UKCP09 (Lowe et al., 2009) 11 1.3 Return periods for extreme water levels and changes in sea level 13 CHAPTER TWO 2.1 United Kingdom relative land- and sea-level changes during the Holocene 29 2.2 Relative land-/ sea-level changes in mm/yr in Britain 30 2.3 Late Holocene sea-level changes estimated by geophysical models 31 2.4 Sea-level index points from Southwest England 34 2.5 Annual tide-gauge observations from the English Channel 39 2.6 Relative vertical crustal movements in Britain 41 2.7 An illustration of the coastal flood zones 44 CHAPTER THREE 3.1 Schematic diagram showing the selected sampling of sea level index points 72 3.2 Salt-marsh sites investigated for late Holocene sea-level index points 74 3.3 Estimated ages of cores sites based on geophysical models 75 3.4 South Huish marsh and investigation area, Thurlestone, south Devon 76 3.5 Foraminiferal stratigraphy at South Huish marsh 77 3.6 South Milton Ley and area investigation.