Lyme Regis Environmental Improvements Phase IV Preliminary Design Stage Coast Protection Options

West Dorset District Council Engineering Consultancy Services Framework (Lyme Regis And Adjoining Areas) Lyme Regis Environmental Improvements Phase IV Preliminary Design Stage Coast Protection Options March 2007 002652/R/001-Rev3

CONTROL SHEET MF0923/1 ISSUE 03 Client: Assignment: Topic: West Dorset District Council Engineering Consultancy Services Framework (Lyme Regis and Adjoining Areas) Lyme Regis Environmental Improvements Phase IV Preliminary Design Stage Coast Protection Options Document Number: 002652/R/001-Rev 3 This report has been prepared by High-Point Rendel and West Dorset District Council. Assignment Director: Assignment Manager: Team Members: Sub-Consultants: West Dorset District Council: Dr. A R Clark D S Fort T H F Leung P L Martin R Milsom M Mo C Reed Prof. D Brunsden Prof. E Bromhead A Bracegirdle G Davis Environs Partnership Ecological Planning & Research (EPR) G Allen N Baker R Clarke H Middleton Record of Status and Approval 3 Consultation Issue for Consultees Draft comments 2 Second Issue for WDDC Draft comments 1 Draft Issue for WDDC comments 0 First Draft Original For Internal Review ISSUE NO. Status Description of Amendments THFL / RM 29/03/07 THFL / RM 9/03/07 THFL / RM 4/12/06 THFL / RM 27/11/06 Prepared by. Sign & Date DSF 29/03/07 DSF 9/03/07 DSF 4/12/06 DSF 27/11/06 Ass. Mgr. Sign & Date ARC 29/03/07 - ARC 4/12/06 - Ass. Dir. Sign & Date High-Point Rendel Tel +44 (0) 207 654 0400 61 Southwark Street Fax +44 (0) 207 654 0401 London SE1 1SA www.highpointrendel.com United Kingdom

West Dorset District Council Engineering Consultancy Services Framework (Lyme Regis And Adjoining Areas) Lyme Regis Environmental Improvements Phase IV Preliminary Design Stage Coast Protection Options CONTENTS Page EXECUTIVE SUMMARY 1 INTRODUCTION & TERMS OF REFERENCE 1-1 2 OBJECTIVES AND CONSTRAINTS 2-1 2.1 Objectives 2-1 2.2 Constraints 2-1 3 FORESHORE PROTECTION OPTIONS 3-1 3.1 DESCRIPTION OF THE SITE 3-1 3.1.1 Seawall 3-2 3.1.2 Foreshore 3-4 3.1.3 Foreshore Groynes 3-5 3.1.4 Environmental Designations 3-7 3.1.5 Brief History of Erosion and Coastal Protection 3-7 3.1.6 Foreshore Geology 3-8 3.2 STUDIES & INVESTIGATIONS 3-9 3.2.1 Coastal Processes Studies (HPR, 1999b) 3-9 3.2.2 Conceptual Design Report (HPR, 2000b) 3-9 3.2.3 Structural Surveys of the Seawall 3-10 3.2.4 HR Wallingford Town Beach & East Cliff Outline scheme design and physical modelling (2003) 3-11 3.2.5 Nearshore & Bathymetric Surveys 3-12 3.2.6 EPR Intertidal Ecological Survey (2006) 3-12 3.2.7 Environs Landscape Conceptual Designs Report (2001) 3-13 3.2.8 Environs: Landscape and Visual Baseline Report (2007) 3-13 3.3 CONDITION OF EXISTING SEAWALL & RESIDUAL LIFE 3-13 3.3.1 Previous Structural Surveys of the Seawall 3-13 3.3.2 Current Condition 3-15 3.3.3 Constructional Details 3-18 3.3.4 Residual Life 3-18 3.4 DESIGN PHILOSOPHY AND PARAMETERS 3-19 3.4.1 Purpose of the Coastal Protection 3-19 3.4.2 Design Life 3-19 3.4.3 Wave Regime 3-20 3.4.4 Sea Level Rise & Climate Change 3-20 3.4.5 Foreshore Lowering 3-21 3.5 FORESHORE PROTECTION OPTIONS 3-22 3.5.1 Introduction 3-22 3.5.2 Do Nothing 3-22 3.5.3 Minimum intervention and maintenance 3-22 3.5.4 Hold the Line Schemes 3-23 3.5.5 Advance the Line Schemes 3-30 N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - MainText 002652_R_001 Rev3.doc i

N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - MainText 002652_R_001 Rev3.doc 3.5.6 Existing Groynes 3-32 3.5.7 Alternative Coastal Protection Options 3-33 3.5.8 Lateral Extent of Works and Coastal Protection 3-35 3.5.9 Coastal Processes 3-39 3.5.10 Public Safety Considerations 3-39 3.5.11 Public Access Considerations 3-40 4 SLOPE STABILISATION OPTIONS 4-1 4.1 DESCRIPTION OF THE SITE 4-1 4.1.1 Location and Geography 4-1 4.1.2 Lower Slopes: Church Cliff and East Cliff 4-1 4.1.3 Middle Coastal Slopes: Charmouth Road car park, Football Ground and Allotments 4-2 4.1.4 Upper Coastal Slopes: The Meadows and Timber Hill 4-2 4.1.5 Adjacent Spittles and Black Ven Area 4-2 4.1.6 Geology and Geomorphology 4-3 4.1.7 Environmental Designations 4-3 4.2 STUDIES AND INVESTIGATIONS 4-4 4.2.1 Introduction 4-4 4.2.2 Topographic Surveys 4-4 4.2.3 Ground Investigation 4-4 4.2.4 Landslide Monitoring 4-5 4.2.5 Geomorphology and Ground Behaviour Studies 4-5 4.2.6 Geological Studies 4-6 4.2.7 Landslide Recession Scenarios 4-6 4.2.8 Conceptual Design Report (HPR, 2000b) 4-6 4.2.9 EPR Ecological Survey (2006) 4-7 4.2.10 Environs Landscape Conceptual Design (2001) 4-10 4.2.11 Environs: Landscape and Visual Baseline Report (2007) 4-10 4.3 THE LANDSLIDING PROBLEM 4-10 4.4 DESIGN PHILOSOPHY AND PARAMETERS 4-12 4.4.1 Design Life 4-12 4.4.2 Ground Models 4-12 4.4.3 Design Approach 4-13 4.4.4 Climate Change Considerations 4-16 4.4.5 Design Parameters 4-17 4.5 SLOPE MANAGEMENT OPTIONS 4-17 4.5.1 Introduction 4-17 4.5.2 Do nothing 4-17 4.5.3 Minimum intervention and maintenance 4-18 4.5.4 Area Specific Scheme Options 4-18 4.5.5 Lateral Extent of Works 4-22 4.5.6 Public Access Considerations 4-24 5 SCHEME OPTION COSTS 5-1 6 PREFERRED SOLUTION 6-1 6.1 FORESHORE ELEMENTS 6-1 6.2 SLOPE STABILISATION 6-1 6.2.1 Lower Coastal Slopes: East Cliff and Church Cliff 6-1 6.2.2 Middle Coastal Slopes: Charmouth Road car park, Football Ground and Allotments 6-3 6.2.3 Upper Coastal Slopes: The Meadows and Timber Hill 6-3 6.2.4 Unprotected sea cliff below Allotments West and Allotments East 6-3 6.2.5 Landscape Restoration and Environmental Mitigation 6-4 6.3 THe Preferred scheme 6-4 6.4 PHASING OF WORKS 6-5 6.4.1 Seawall Works Considerations 6-5 ii

6.4.2 Slope Stabilisation Works Considerations 6-5 6.4.3 Coast Protection Scheme 6-6 6.5 DESIGNERS RISK ASSESSMENT AND RISK REGISTER 6-6 7 RECOMMENDED FURTHER MONITORING, INVESTIGATIONS & STUDIES 7-1 7.1 FORESHORE 7-1 7.1.1 Further Studies 7-1 7.1.2 Seawall construction 7-2 7.1.3 Seawall Condition 7-2 7.1.4 Groundwater Conditions 7-2 7.1.5 Soil Conditions Local to Seawall 7-2 7.1.6 Foreshore Topography & Bathymetry 7-3 7.1.7 Future Wave Climate & Sea Level 7-3 7.1.8 Coastal Processes 7-3 7.1.9 Hydraulic Design 7-3 7.2 SLOPE STABILISATION 7-3 8 SUMMARY & CONCLUSIONS 8-1 9 REFERENCES 9-1 9.1 Reports: 9-1 9.2 Publications 9-2 9.3 Archival Records 9-2 N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - MainText 002652_R_001 Rev3.doc iii

APPENDICES A WDDC Drawing LREI61\023 Church Cliff and East Cliff Seawall History B Levis & Duvivier Drawings of Existing Seawall: 1342A/23 Church Cliffs, St Michael s Church Seawall Plans, Sections & Elevation of Sea Wall (Nov 1964) 1342A/26 Church Cliffs, St Michael s Church Seawall Elevations & Details of Groynes (Nov 1964) 1342A/31/1 East Cliff Sea Defences Typical Groyne Elevations & Details (June 1967) 1342A/32 East Cliff Sea Defences Sea Wall Apron and Cliff Revetment (June 1967) 1342A/34 East Cliff Sea Defences Cross Sections of Apron at North End of 1957 Wall (Oct 1967) C Seawall Crack Width and Inclination Monitoring D Survey Levels Comparison 1995-2006 E WDDC Drawings: LREI79\026 - Cliff Top Recession LREI79\027 - Cliff Toe Recession PH4\PD\004 - Foreshore Contours and Sections F Foreshore Changes Close to Existing Seawall G Coast Protection Options: First Stage Type Selection Based on Seawall Design, Thomas & Hall, CIRIA, 1992, Characteristics of various wall types, Tables 5.3 to 5.6 H Coast Protection Options: Second Stage Type Selection I Plan of Principal Landslide Areas J Landslide Site Characteristics K Coastal Slope Stabilisation Generic Options L Area Specific Coastal Slope Stabilisation Scheme Options M Preferred Options N Ground Model Sections O Cost Estimates P Designer s Risk Assessment Q Risk Register R Glossary of Terms S Schematic Construction Sequence N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - MainText 002652_R_001 Rev3.doc iv

DRAWING LIST Drawing No. Originator Drawing Title Appendix 1432A/23 LD Church Cliffs St Michael s Church Sea Appendix B Wall. Plans, Sections & Elevation of Sea Wall 1432A/26 LD Church Cliffs St Michael s Church Sea Appendix B Wall. Elevations & Details of Groynes 1432A/31/I LD East Cliff Sea Defences. Typical Groyne Appendix B Elevations & Details 1432A/32 LD East Cliff Sea Defences. Sea Wall Apron Appendix B and Cliff Revetment 1432A/34 LD East Cliff Sea Defences. Cross Section of Appendix B Apron at North End of 1957 Wall LREI61\023 WDDC Church Cliff and East Cliff Seawall History Appendix A PH4\PD\004 WDDC/HPR Foreshore Contours and Sections Appendix E PH4\PD\201 WDDC/HPR Key to Ground Model Sections Appendix N PH4\PD\202 WDDC/HPR Ground Model Section 2 Appendix N PH4\PD\203 WDDC/HPR Ground Model Sections 10 & 11 Appendix N PH4\PD\204 WDDC/HPR Ground Model Section 12 Appendix N PH4\PD\205 WDDC/HPR Ground Model Sections 13 & 14 Appendix N PH4\PD\206 WDDC/HPR Ground Model Sections 15 & 16 Appendix N PH4\PD\207 WDDC/HPR Ground Model Sections 17, 17a & 18 Appendix N PH4\PD\208 WDDC/HPR Ground Model Sections 19 & 20 Appendix N PH4\PD\209 WDDC/HPR Ground Model Sections 21 & 22 Appendix N PH4\PD\210 WDDC/HPR Plan of Principal Landslide Areas Appendix I PH4\PD\218 WDDC/HPR Cliff Top Recession Appendix E PH4\PD\219 WDDC/HPR Cliff Toe Recession Appendix E PH4\PD\224 WDDC/HPR Ground Model Section Location Plan Appendix N PH4\PD\401 WDDC/HPR Lower Coastal Slopes. Hold the Line Appendix M Option PH4\PD\402 WDDC/HPR Lower Coastal Slopes. Advance the Line Appendix M Option PH4\PD\403 WDDC/HPR Lower Coastal Slopes. Hybrid Option Appendix M PH4\PD\404 WDDC/HPR Upper & Middle Coastal Slopes Appendix M PH4\PD\405 WDDC/HPR Lateral Extent Appendix M LD = Levis & Duvivier HPR = High-Point Rendel WDDC = West Dorset District Council N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - MainText 002652_R_001 Rev3.doc v

EXECUTIVE SUMMARY 1. Lyme Regis is situated on one of the most unstable and actively eroding stretches of coastline in the UK. Over the centuries, various coast defence structures have been constructed to protect the town and adjacent areas from the sea and to provide increased stability. These structures have been under constant threat due to storm attack, foreshore lowering and landslide activity. 2. Large parts of the developed town have been constructed on pre-existing coastal landslip systems, many of which are still undergoing movement, and which over time cause damage to properties and infrastructure due to the cumulative effects of the ground movement. Occasionally rapid landslide events take place which may be a threat to public safety and destroy property and infrastructure assets including the existing coastal defence in a relatively short period. 3. These problems are particularly relevant to the Phase IV study area located immediately to the east of the town. This area comprises the lower coastal slopes at Church Cliff and East Cliff extending eastwards to the adjacent Spittles area which is part of the Black Ven landslip system, the middle coastal slopes occupied by housing, Charmouth Road car park, football ground and allotment area, and the upper coastal slopes including the Meadows and Timber Hill. The study area is bounded to the west by the Charmouth Road which provides an important access route to Lyme Regis from the east. 4. West Dorset District Council (WDDC) commissioned High-Point Rendel (HPR) in April 2006 to undertake the preliminary design stage of the Lyme Regis Environmental Improvements Scheme Phase IV Church Cliff and East Cliff. This is to provide consultancy services to consider options by which the coastal erosion and slope stabilisation risks can be effectively managed. This review has considered options ranging from do-nothing through to minimum maintenance and to full coast protection including foreshore works and slope stabilisation measures. 5. The viability of undertaking Do nothing and Minimum intervention and maintenance approaches has been assessed, and scheme options have been developed to provide various engineering alternatives for the Hold the Line and Advance the Line solutions for evaluation and selection. The development of these scheme options has largely been based on the typical engineering options documented in literature and those from previous HPR projects, with due considerations of the site-specific characteristics and constraints. Following the option development, the options have been filtered and discussed within the design team and with Consultees to identify the preferred scheme. 6. In addition, the significance of the lateral extent of the coastal protection works on the stability and continuing erosion of the existing unprotected sea cliff and the property and infrastructure has been discussed in the Report, and recommendations have been made on the lateral extent of the works. The Report also raises and discusses a number of technical issues that require further research and consideration in the later stage of the project development. 7. The Options Report gives recommendations for the preferred scheme which is the Hold the Line solution and includes the construction of a new seawall in front of the existing seawall, a rock armour revetment along a 60m length of the unprotected sea cliff east of the existing seawall, and associated slope 0-1

stabilisation works comprising slope strengthening and drainage measures mainly within the lower and middle coastal slopes. This preferred option is seen to offer the best balance between cost, engineering and environmental impact. 8. The study area lies within a number of local, national and international environmental designations including AONB, SSSI, SAC, GCR and World Heritage Site. Some of the coastal slopes are owned by National Trust and the foreshore is open to public access. It is important that the effect of any proposed works on these important environmental designations are mitigated as far as possible. In addition public safety should be maintained and preferably improved. 9. The preferred mitigation restoration strategy, for both ecological and landscape perspectives, is to allow natural colonisation of the engineered slopes wherever possible. 10. The preliminary estimate of construction costs of the various scheme options, including both the foreshore and slope stabilisation works, range from 11.2M to 15.8M. In addition a further cost of 1M to 1.4M should be added if the extension of works covering the unprotected sea cliff beyond the eastern end of the seawall is included. These costs, which exclude design, contract procurement, supervision, environmental mitigation costs etc, will be refined during Stage G Updating construction costs for the feasible options and preparing cost benefit analysis calculations of this study. 11. Phasing of the construction of any proposed works is also one of the key considerations in this Options Study. Based on technical considerations alone it is preferable for the proposed works to be constructed in a single phase. However, there may be reasons why a phased construction approach may be preferred, e.g. available funding stream. The recommendations on phasing of works have been made on the basis of the existing seawall condition and the probability of pronounced failures of various coastal slope areas. Should a phased approach be adopted it is recommended that the coast protection works for both the existing seawall and the unprotected sea cliff beyond the eastern end of existing seawall should be carried out in the first phase. This would be followed by the stabilisation works at East Cliff and above the unprotected section of sea cliff, then the stabilisation works at Church Cliff, then the drainage works in the middle coastal slopes and finally the drainage works in the upper coastal slopes if needed. 12. Following the issue and subsequent discussion of the findings of this Options Study and associated studies and investigations the objective is for the coastal authority West Dorset District Council to select a preferred scheme that can be considered in more detail during the preliminary design stage of the study. 002652_R_001_rev3 WORKING COPY\Text\Options Report - MainText 002652_R_001 Rev3.doc 0-2

1 INTRODUCTION & TERMS OF REFERENCE Lyme Regis is situated on one of the most unstable and actively eroding stretches of coastline in the UK. Over the centuries, various coast defence structures have been constructed to protect the town and adjacent areas from the sea and to provide increased stability. These structures have been under constant threat due to storm attack, foreshore lowering and landslide activity. Large parts of the developed town have been constructed on pre-existing coastal landslip systems, many of which are still undergoing movement, and which over time cause damage to properties and infrastructure due to the cumulative effects of the ground movement. Occasionally rapid landslide events take place which may be a threat to public safety and destroy properties and infrastructure assets in a relatively short period. These problems are particularly relevant to the Phase IV study area located immediately to the east of the town. This area comprises the lower coastal slopes at Church Cliff and East Cliff extending eastwards to the adjacent Spittles area which is part of the Black Ven landslip system, the middle coastal slopes occupied by housing, Charmouth Road car park, football ground and allotment area, and the upper coastal slopes including the Meadows and Timber Hill (Figure 1.1). The study area is bounded to the west by the Charmouth Road which provides an important access route to Lyme Regis from the east. West Dorset District Council (WDDC) commissioned High-Point Rendel (HPR) in April 2006, (WDDC letter ref. GCA/Lrei61, dated 27 th April 2006), to undertake the preliminary design stage of the Lyme Regis Environmental Improvements Scheme Phase IV Church Cliff and East Cliff. This is to provide consultancy services to consider options by which the coastal erosion and slope stabilisation risks can be effectively managed. This review has considered options ranging from do-nothing through to minimum maintenance and to full coast protection including foreshore works and slope stabilisation measures. In delivering this study West Dorset District Council have divided the commission into a number of Stages as follows: Stage A Reviewing and validating existing data provided by the Employer Stage B Making recommendations for additional surveys, investigations, monitoring and instrumentation Stage C Undertaking landslide and stability analysis Stage D Outline design of the slope stabilisation and coast protection works Stage E Preliminary design of the preferred solutions Stage F Undertaking the Environmental Impact Assessment for the purposes of Planning Approval Stage G Updating construction costs for the feasible options and preparing cost benefit analysis calculations Stage H Preparation and submission of planning application, drawings and documentation Stage I Preparation of Engineer s Report for design and construction funding approval 1-1

Crown copyright. All rights reserved. 100024307. 2010 Figure 1.1 Location Plan \\Hpr-lon-file01\assign_ldn\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 issued 02-04- 07\Text\Options Report - MainText 002652_R_001 Rev3.doc 1-2

This Options Report is the deliverable of Stage D in which outline coast protection options addressing both coastal/foreshore erosion and slope instability have been developed. The outline coast protection schemes have been considered with the objective of protecting / improving the seawall and arresting landslide regression / progression in the unstable coastal slopes as a consequence of coastal erosion such that infrastructure and property are safeguarded. Due consideration of future climate change effects will also be necessary. It is recognised that a coast protection scheme is essential to protect the coastline and to prevent the existing sea cliff and coastal slopes from receding and affecting properties and infrastructure within the Phase IV study area including Charmouth Road. In developing these options a meeting was held between WDDC, HPR and the specialist sub-consultants on 13 th November 2006 to discuss the approach of options assessment and to present the slope stabilisation works options. A draft of this Options Report was issued to WDDC on 6 th December 2006. Subsequently, the options for foreshore works and slope stabilisation works, together with the findings in ecological, landscape and geological studies, were presented to Consultees, including the representatives from Natural England and Dorset County Council, on 17 th January 2007. Following this consultation meeting, WDDC, HPR and the specialist sub-consultants further discussed the options in a meeting on 12 th February 2007. This Options Report includes a review of the available outline solutions for the engineering including an assessment of technical merit, buildability, maintenance and cost. This report recommends a preferred scheme to be carried forward through to preliminary design (Stage E). The critical environmental impacts and mitigations have been considered, and are included in the Options Report to facilitate the selection and development of a preferred scheme. The proposed solution(s) will be circulated to Consultees for comment, and will be presented to the public for consultation. A meeting will be held to discuss the merits of the options and the preferred solution. The preferred solution will be further developed for the purposes of preparation of an Environmental Impact Assessment (Stage F), the submission of a planning application (Stage H), and the undertaking of an appropriate cost benefit analysis (Stage G). In developing the slope stabilisation works options, the Urgent Advanced Stabilisation works carried out at East Cliff and Church Cliff in 2003/2004 have also been considered and incorporated in principle into the options. The Urgent Advanced Stabilisation works were completed in 2004 to stabilise, in the short term, parts of Church Cliff and East Cliff to protect the residential properties at Church Cliff and the groundwater collection and discharge system at East Cliff. The Urgent Advanced Stabilisation works comprised at each site two rows of piles, restrained laterally by either a series of ties or cross beams. The details of the design were reported by High-Point Rendel (HPR, 2003a). 1-3

2 OBJECTIVES AND CONSTRAINTS 2.1 OBJECTIVES The objective at this stage of the preliminary design is to develop a preferred scheme or a shortlist of solution(s) to the coastal instability problem, including detailed consideration of the inter-relationship between the technical requirements of the scheme, and the landscape, ecological and environmental issues. Two outline scheme options have been developed, namely: 1) Hold the Line option that enables the coastal slopes to be stabilised without significant change to the current topography. 2) Advance the Line option that requires construction of buttress seawards of the coastal slopes to provide lateral support to the unstable slopes. A hybrid option, using these two scheme options for different parts of the coastal slopes, is also considered, namely the Bay and Buttress option. In addition, the feasibility of phasing the works over a period has been considered. The Lyme Bay and South Devon Shoreline Management Plan (prepared by Posford Duvivier, 1998) gives the Preferred Strategic Option for the Cobb Gate to Harbour and East Cliff area of Lyme Regis (Coastal Process Unit CPU 3 and Management Unit MU 6) as Hold the Line. Seawall options supporting these schemes are derived, described and discussed. 2.2 CONSTRAINTS The constraints to the development of the project are broadly classified into physical, environmental, programme and cost, and they are explained below. Some of these constraints are identified as potential, and will require confirmation by WDDC and others. Physical Constraints 1. The coastal slopes are within developed areas with high-density housing, a church (St Michael s Church) and its graveyard, and are close to one of the two main vehicular access routes Charmouth Road to the Lyme Regis town. 2. There are listed buildings, including St Michael s Church, at the top of Church Cliff. 3. The coastal slopes are within areas with restricted construction access. Environmental Constraints 4. The whole area is in the Dorset Area of Outstanding Natural Beauty (AONB). 5. The foreshore is open to public access and public safety should be maintained and improved. 6. Large parts of the coastal slopes, partly owned by the National Trust, are designated as West Dorset Coast Sites of Special Scientific Interest (SSSI), a Special Area of Conservation (SAC) and a World Heritage Site. 7. The World Heritage Site status is attributed both to the natural beauty of the area and the slopes exceptional geology relating to the Jurassic period apparent in the coastal cliffs and foreshore. 2-1

8. The area covering the coastal slopes and the Spittles is designated as West Dorset Heritage Coast. 9. There is a wide range of undercliff habitats and diverse insect fauna. 10. The site is a selected Geological Conservation Review (GCR) site GCR No. 916 under GCR Block Jurassic-Cretaceous Reptilia. The GCR sites were selected to form the basis of statutory geological and geomorphological site conservation in Britain. Programme Constraints 11. The urgency of works is indicated by the timescale of coastal recession and impact of landsliding on infrastructure in the updated Landslide Recession Study (HPR, 2007a). 12. There is currently no scheduled date for implementation and completion of the stabilisation works. 13. The duration of any stabilisation works will be dependent on various factors. The conceptual design report (HPR, 2000b) indicates a preliminary construction period of 12 to 24 months, including both foreshore and slope stabilisation works. 14. Planning permission and a possible inquiry could possibly have a significant impact on the programme. 15. Ecological clearance in advance of any proposed construction works could be critical in implementation of the works. Cost Constraints 16. The May 2005 Project Appraisal Report to DEFRA (WDDC, 2005) gave a benefit of 40M in property value plus infrastructure and associated benefits. This benefit value will be updated as part of this Preliminary Design Study. The coast protection scheme will be developed to ensure a high ratio of benefit to cost as economics justification. 17. The construction cost of the coast protection works is estimated in this Options Report (Section 5), and will be further reviewed in the development of the Preliminary Design. 18. WDDC is planning to obtain funding from the Department of Environmental, Food and Rural Affairs (DEFRA). This will be preceded by undertaking cost benefit analyses calculations to establish the beneficial cost of the proposed scheme. The application is also required to meet the financial and risk criteria in compliance with DEFRA s requirements. 2-2

3 FORESHORE PROTECTION OPTIONS 3.1 DESCRIPTION OF THE SITE The seawall, groynes and foreshore, are described in the following sections. Seawall sections and Groynes are referenced as shown in Figure 3.1. Figure 3.1 Foreshore Key Plan \\Hpr-lon-file01\assign_ldn\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 issued 02-04- 07\Text\Options Report - MainText 002652_R_001 Rev3.doc 3-1

3.1.1 Seawall A full description of the seawall based on visual inspection is contained in the 2006 Brody Forbes Partnership report referred to below; it is not attempted to duplicate the detailed observations of that report here. Table 3.1.1 Summary of Seawall Dimensions: Church Cliff East Cliff Approximate length 87 metres 299 metres Approximate top level Approximate beach level at toe of wall Varies 6 to 6.9 metres above Ordnance Datum Varies 1.3 to 3 metres above Ordnance Datum Varies 5.3 to 6 metres above Ordnance Datum Varies 1.5 to 3.4 metres above Ordnance Datum Church Cliff Seawall The section of seawall between Church Jetty and groyne 4 was constructed in 1910 of mass concrete and refaced with concrete in the 1960s. The top of the wall is returned to form a curved wave return. At the toe of the wall a concrete apron was formed to prevent local foreshore erosion. A drawing dated 1964 by Lewis & Duvivier (Appendix B, Drawing 1432A/23) appears consistent with the existing structure and shows the refacing to be of 12 inches (305mm) thickness with a single layer of mesh reinforcement centrally placed. It is noted that for a section of about 12m length between groynes 3 & 4 the front face is formed at a shallower angle than the adjoining sections; Lewis & Duvivier indicate that the original wall was at a similar inclination here; the reason for this feature is unclear. A masonry faced wall of varying height, approximately 2 metres, with mass concrete backing (see Appendix B, Drawing 1432A/32) was built along the top of the concrete seawall about 1969. This appears to protect the cliff face directly above the wall from erosion. Figure 3.1.1a Church Cliff Seawall Typical Section 3-2

East Cliff Seawall The section of seawall between groynes 4 and 19 (see Appendix B, Drawing LREI61/023) was first constructed in 1957 of mass concrete. Sloping concrete aprons were added in 1969 to protect the toe of the most vulnerable sections of the wall. Drawings dated 1967 by Lewis & Duvivier (Appendix B, Drawings 1432A/32 & 34) show details of a heavy concrete apron to the front of the wall, from west of groyne 8 to west of groyne 13 and east of groyne 16 to the east termination, which is keyed into a trench cut in the foreshore to a depth of approximately 4 feet (1200mm) possibly to increase the resistance of the wall to sliding and/or foreshore erosion. These drawings appear consistent with the existing. Figure 3.1.1b East Cliff Seawall - Typical Section Figure 3.1.1c Existing Wall at East Cliff (Diagrammatic) 3-3

East End At the east end of the East Cliff seawall the wall is returned at a right angle inland for a distance of approximately 4 metres and was clearly originally terminated at the rock face of the cliff line. Here the cliff line appears to have receded leaving debris at the termination of the wall. Armour stone protection placed here in 1998 is reported to have been 200 tonne of 3 tonne stone. Figure 3.1.1d East Cliff Seawall - East End - View 1 Figure 3.1.1e East Cliff Seawall - East End - View 2 3.1.2 Foreshore The foreshore in front of Church Cliff and East Cliff seawalls consists of near level limestone ledges with some overlying shingle. Cobbles and boulders are present over some but not all lengths of the seawall. The coverage of the limestone ledges diminish at the east end of the East Cliff seawall and beyond this end a sandy beach extends virtually to the cliff bottom. 3-4

Figure 3.1.2a View of Foreshore from Church Jetty Figure 3.1.2b Breach in Groyne 17 3.1.3 Foreshore Groynes A total of 17 Groynes have been constructed on the foreshore forward of the seawall (see Figure 3.1 and Appendix A, Drawing LRE161/023), the westernmost (1-4) in the 1960s but replacing earlier structures, the eastern ones (5-17) in 1969. An upper section of most groynes has been breached in recent years to aid personal escape at high tides. Quoting CIRIA s Guide on the uses of groynes in coastal engineering Groynes are shore protection structures which are used to control the natural movement of beach material. This is done principally by altering the natural orientation of the beach line and intercepting wave-induced alongshore currents. It is not known if the groyne field was ever supplied with beach material artificially, or whether it was intended that sediment would accumulate between the groynes 3-5

naturally. In any case, the groyne field has been largely ineffective at either trapping or holding a beach. A detailed survey of the groynes was carried out by Graham Garner and Partners in 1996 (See References). The groynes will clearly have deteriorated in the intervening period but remain essentially the same, excepting that, while in 1996 some of the removable groynes timbering near the seawall (originally intended to allow constructional plant access) remained in place they have now been removed to allow pedestrian escape on rising tides. Drawings dated 1964 & 1967 by Lewis & Duvivier (Appendix B, Drawings 1432A/23 & 1432A/31/1) of groynes 1 to 4 and groynes 5 to 17 respectively are consistent with those observed by Graham Garner and Partners and now existing except for deterioration and timberwork loss. 3.1.3.1 Groynes 1 to 4 The outer lengths of these groynes are constructed of steel sheet piling between steel box piles, those sections nearer the cliff were topped with timbering now mostly lost. A section where removable timbering extended to a lower level to form a plant access bay connects to a concrete section nearest the seawall. As described above most of the timbers in the plant bay are removed and the steps over the concrete section are so badly eroded as to be virtually unusable. See Lewis & Duvivier Appendix B, Drawing 1432A/23. Figure 3.1.3.1 Groyne 4 (Typical for groynes 1 to 4) 3.1.3.2 Groynes 5 to 17 These groynes comprise a concrete base with, on the more landward parts vertical steel posts formed of steel bulls head rails originally supporting horizontal timber planking, now generally lost. Removable timbering originally connected the main part of the groyne to a concrete section nearest the seawall forming a plant access bay. As at groynes 1 to 4, most of the timbers in the plant bay are removed and the steps over the concrete section are so badly eroded as to be virtually unusable. See Lewis 3-6

& Duvivier Appendix B, Drawing 1432A/31/1. Some step-irons have been installed to provide a route over the eroded steps but these are now heavily corroded. Figure 3.1.3.2 Groynes 8 & 9 (Typical for groynes 5 to 17) 3.1.4 Environmental Designations The Phase IV foreshore area falls under several environmental designations with the whole area being in the Dorset Area of Outstanding Natural Beauty (AONB) and defined as Heritage Coast. The foreshore area is under the European designation for the Sidmouth to West Bay Special Area of Conservation (SAC) for the qualifying reason of there being an annual vegetation of the drift line, although this Annex 1 habitat is not present in the study area being considered. This area along the foreshore has several Geological Conservation Review sites (GCR s) which have been identified by the Joint Nature Conservation Committee and fall under the protection of the Sites of Special Scientific Interest (SSSI) network and legislation. The GCR s have led to the area being designated as England s First Natural World Heritage site, mainly due to the degree of Jurassic and Cretaceous marine fossils found along the coast. The Lyme Regis Undercliff is a National Nature Reserve (NNR), because of the combination of rare flora and fauna and the geologic formations on show. The foreshore of the Cobb Gate and Church Cliff falls within the UK Biodiversity Action Plan (UK BAP) for the occurrence of the Honeycomb Worm (Sabellaria alveolata) reef communities which are relatively scarce within the UK. 3.1.5 Brief History of Erosion and Coastal Protection The development of the coast protection structures at Church Cliff and East Cliff is indicated on Appendix A, Drawing LREI61/023. Prior to 1910 the cliff was unprotected. However, the Church Cliff Jetty (or its predecessors) is thought to be of considerable antiquity. It was in existence before 1723, and possible much earlier, 3-7

as part of a system of defences which protected the nucleus of the town of Lyme Regis around the mouth of the River Lim. This might account for the presence of the Church Cliff headland, which would have behaved as a protected strong point, whilst the coastline to the east continued to retreat through coastal erosion and landslipping. The retreat of the top of Church Cliff has been estimated from old maps to have been between 10 and 25 metres between 1841 and 1888, depending on location, giving a rate of retreat of between 0.2m and 0.5m per year. Erosion seems to have occurred at a faster rate earlier in the 19th century, with about 1 yard a year being lost between 1800 and 1829 (ref. Lyell C. 1832. Principles of Geology. 2nd Ed.) The rate of erosion at East Cliff was up to 0.55m per year in the period 1841-1888. Cliff recession is likely to have been accelerated by quarrying of the limestone ledges in the cliffs and foreshore, which was a major industry in Lyme Regis from the 1820 s to the time of the First World War. Quarrying took place along the whole of the Blue Lias outcrop, from the Church Cliffs headland to Black Ven, and the operations even involved the use of explosives. Up to 5m of cliff top retreat occurred at Church Cliff between 1888 and 1960, with this much lower rate reflecting the construction of the Church Cliff seawall in 1910 and the cessation of sea quarrying at about the same time. The rate of erosion at East Cliff during the same period was up to 0.35m per year. There is a local tradition in the town of the former existence, centuries ago, of a large headland, with houses on it, at the position of the present-day Broad Ledge. This idea is supported by the fact that there exist several old engravings from the 18th century which indicate a considerable hill seaward of the Church. The original sea wall at Church Cliff was constructed in 1910, together with rubblefilled drains which extend up the cliff and into the churchyard. Groynes were added at sometime between 1910 and 1928. There was a major refurbishment of the Church Cliff seawall in the 1960 s, which included the provision of the present slipway and masonry splash wall. The adjoining East Cliff seawall was constructed in 1957. Problems with erosion of the foreshore soon after its completion led to the addition of the concrete aprons and groyne field in 1969. In 1998, a pile of rock armour was added to the end of the East Cliff wall in an attempt to reduce the rate of outflanking as a result of progressive erosion of the Blue Lias cliff. Historical recession of the cliff top and toe is illustrated on Appendix E Drawings PH4\PD\218 & 219. 3.1.6 Foreshore Geology The foreshore ledges in the East Cliff study area are composed of the interbedded limestones and mudstones of the Blue Lias. In front of Church Cliff the beds are nearly horizontal, however the general dip of the strata is a few degrees towards the south-east in a broad syncline which may be seen at low tide. The foreshore ledges 3-8

are cut by several minor faults with throws of no more than a few metres. Thin patches of sand and shingle beach are present close to the sea wall and a boulder ramp is present below the unprotected cliff to the east of the seawall. 3.2 STUDIES & INVESTIGATIONS Relevant previous studies and investigations include the following: 3.2.1 Coastal Processes Studies (HPR, 1999b) This report concluded, in connection with the Church Cliff and East Cliff foreshore: The East Cliff area is a remnant of a once more extensive periglacial slope which formed the southern flank of Timber Hill, between Lyme Regis and Charmouth (the Black Ven-Spittles East Cliff landslide complex). These relict slopes were covered with landslide debris and head deposits, probably formed during past phases of slope instability. As sea level rose after the last glaciation, marine erosion at the cliff foot removed the periglacial debris slopes, created the near vertical seacliffs and led to the progressive reactivation of the relict landslide systems. In time, the entire preexisting landslide system will have been reactivated. During the last century, there was a phase of accelerated seacliff erosion along the Church Cliff and East Cliff frontage, probably as a result of quarrying of limestone ledges on the foreshore and in the seacliffs. This led to the construction of the Church Cliff seawall in 1910 11. The effect of seawall construction has been to promote the development of a small bay on the adjacent unprotected cliffline which, in time, would outflank the defence structure and destabilise the unstable landslide slopes above. Thus, there was a need to extend the defences further eastwards to protect an increasing length of cliffline. However, a similar bay has been developing to the east of this new section of seawall, once again creating pressure extend the defence line. The integrity of the seawalls on this section is an important factor in controlling the instability problems experienced at East Cliff, the consequences of seawall failure are discussed in High-Point Rendel (1999b) [Landslide Regression Scenarios. Phase IV]. The direction of net longshore drift in front of Church Cliff and East Cliff is given to be eastwards with a potential transport (sand and shingle) of around 5000m³/year although very little material is derived from the protected cliffs themselves. This longshore drift was demonstrated by the fate of 3000 tonnes of distinctive red Budleigh Salterton pebbles placed on Church Cliff beach in July 1995 a substantial amount of which had by October 1998 reached between Black Ven and the western rock groyne at Charmouth. 3.2.2 Conceptual Design Report (HPR, 2000b) The objectives of this report was to prepare a range of optional designs to address the coast protection and slope instability problems at Lyme Regis [Church and East Cliffs], with budget costs and time scales for implementation. 3-9

The report considered: General strategy Work to the foreshore Work to the sea wall Work to the sea cliffs Work to the lower, intermediate and higher slopes at East Cliff A Strengthening and Drainage Solution and a Slope Buttress Solution were compared. 3.2.3 Structural Surveys of the Seawall 3.2.3.1 Hutchinson (1984) This report is not available; however, the observations are included in the 1996 report below. 3.2.3.2 Graham Garner & Partners (1996) This report includes photographic and diagrammatic records of the seawalls and groynes. The diagrammatic records are overlaid with the 1984 observations. 3.2.3.3 WDDC - Crack Monitoring (1999) Monitoring of crack widths in the Seawall was initiated by WDDC in July 1983. This report reviewed the movements at 5 cracks over the subsequent 15 year period. It found that little movement had occurred over this period. 3.2.3.4 Brody Forbes Partnership (2006) This report includes photographic and diagrammatic records of the seawalls. The diagrammatic records are overlaid with the 1984 & 1996 observations. The groynes are not considered in this report. 3.2.3.5 WDDC On-Going Structural Monitoring (To-Date) WDDC has in 2006 resumed monitoring wall crack widths at two of the locations reported in 1999, and at several new locations. Inclination measurements on the wall are also being taken to determine if any tilting is occurring. Initial results of these measurements are given graphically in Appendix D. While it is too early to draw any significant conclusions from the new monitoring an initial view would appear to indicate the conclusions of the 1999 report remain valid. 3-10

Figure 3.2.3.5a Crack Monitoring Figure 3.2.3.5b Inclination Monitoring 3.2.4 HR Wallingford Town Beach & East Cliff Outline scheme design and physical modelling (2003) Three schemes were examined with the use of physical modelling; these schemes were: 1. Strengthening and Drainage, i.e. Hold the Line 2. Slope Buttress, i.e. Advance the Line - scheme 3 in this report 3. Bay and Buttress, i.e. Hybrid Option The conclusions of this report were: The physical modelling has assessed the performance of outline conceptual schemes for the East Cliff frontage. The decision on the particular scheme to be adopted at each cliff will be determined by geotechnical and environmental considerations. However, the physical modelling has shown that: Incorporating a shingle beach in to the Bay and Buttress scheme is feasible but will require beach control structures, notably the stub breakwater and timber groynes, to retain the beach. Overtopping along the frontage can be reduced with a beach and / or rock revetment. This will also considerably reduce wave reflections, which may slow the rate of breakup of the foreshore rock ledges. The downdrift effects experienced at the northern end of the coastal defences can be reduced significantly with a slight re-orientation of the revetment at the northern end. It is suggested that a 2-D physical model be conducted during detailed design to fully optimise the rock revetment profile to meet armour stability and overtopping requirements. 3-11

3.2.5 Nearshore & Bathymetric Surveys 1987 1995 2005/6 Topographic surveys were carried out at the three above dates. The primary purpose of these surveys was in connection with onshore landslip monitoring but these have been examined with respect to foreshore changes. The 1987 survey plots available appear to have some ambiguity with regard to foreshore contours and their use would raise some doubts. The level changes between the 1995 and 2005/6 surveys are illustrated by isopleths in Appendix C. This shows significant changes in shingle beach thickness close to the wall, while the foreshore level changes further from the wall are less. The exposed foreshore limestone ledges off the more easterly end of the wall appears to have reduced in level although due to differences in survey techniques the exact amount of such lowering is difficult to ascertain. Nearshore and offshore bathymetric data used by HR Wallingford for their physical modelling (2003) was surveyed in 1996/7. 3.2.6 EPR Intertidal Ecological Survey (2006) This ecological survey focuses on the offshore reefs from Broad Ledge to East Cliff. The main environmental interest found by Ecological Planning & Research (EPR) is the Sabellaria alveolata (Honeycomb worm) reef communities. This is of importance due to the area providing a significant contribution to the UK s overall resource. These reef communities form a UK Biodiversity Action Plan (BAP) priority habitat and are classed as being scarce according to the Marine Nature Conservation Review (MNCR). EPR were concerned that this habitat may be affected by the vegetation stripping on the slope and the removal of sea defences, during construction, of the proposed works. This would be due to an increase in the sediment supply from works on the slope, which may have significant effects upon the extent of the intertidal biotope communities. Therefore, any loose soil will have to be managed and controlled during the development. After completion of the proposed works, the changes in the sediment supply and also wave energies due to certain sea wall options and removal of groynes may have an impact. This is because the Sabellaria alveolata communities are only found in areas of strong to moderate wave action. Also the increased access may cause further adverse effects due to increased visitor numbers and other associated problems. In order to avoid any future problems the quality of the habitat must be maintained in accordance to the UK BAP. But it must be noted that coastal processes will increase the zone of influence beyond the immediate works zone and that the Sabellaria alveolata reef communities are dynamic and generally recover quickly from detrimental impacts. 3-12

Coastal stabilisation to be carried out in Phase IV has the potential to result in negative impacts and needs to be managed and or mitigated, especially if there are to be barge moorings in the area of the reef communities during construction. 3.2.7 Environs Landscape Conceptual Designs Report (2001) This report was prepared for the conceptual design of the coastal protection measures in terms of landscape, amenity and nature conservation for the Phase IV area. It considered the slope reinforcement and buttress options contained within the HPR Conceptual Design Report (HPR, 2000b) and suggested a Bay and Buttress scheme. This hybrid scheme, however, was purely based on landscape proposals and at the time the engineering viability of the option had not been assessed. 3.2.8 Environs: Landscape and Visual Baseline Report (2007) As part of the current Phase IV Preliminary Design Studies, Environs Partnership have carried out a review of the landscape baseline which includes landscape character areas and public access considerations. The report concludes with some mitigation design strategy recommendations. All new works will include environmental restoration works integrating both ecological and landscape mitigation considerations. 3.3 CONDITION OF EXISTING SEAWALL & RESIDUAL LIFE 3.3.1 Previous Structural Surveys of the Seawall The 2006 Structural/Condition Survey by Brody Forbes Partnership incorporates the findings of the 1984 Hutchinson and the 1996 Graham Garner & Partners and can be seen as a definitive summary of the wall condition up to 2006. It is not intended that this report duplicates these previous surveys but that it reviews the findings in the light of all available information and with respect to the aims of Phase IV. For convenience the conclusions of previous reports on the condition of the seawall are reproduced below: Hutchinson (1984) Text not available Graham Garner & Partners (1996) This investigation has revealed that the sea walls in front of Church Cliff and East Cliff has suffered further deterioration since surveyed in 1984. This can be summarised as follows. 1 Erosion of the toe of the wall due to wave scour has continued since the previous study, and now forms significant undercutting in places. 2 The overhang of the upper sections of wall over the lower particularly between groynes 8 and 12 has increased significantly. 3 New vertical cracks have formed at apparently random intervals along the whole length of the wall, and some existing cracks have increased in width although not to the extent anticipated by Professor Hutchinson in 1984. 3-13

4 Rotation of the end of the wall at groyne 17 has continued. This now appears to be at least partially due to seasonal expansion of the wall itself. 5 Lack of provision for seasonal expansion and contraction of the wall along its length due to temperature and moisture changes is thought to have contributed significantly to the deterioration of the condition of the wall. WDDC - Crack monitoring (1999) 1 There has been little change in the width of the near-vertical cracks in the East Cliff sea wall over the past 15 years. 2 This indicates that the deterioration of the wall is more likely to have been caused by expansion and contraction of concrete than the effects of earth pressure or landsliding, as the latter would have been expected to have led to a more rapid progressive deterioration. Brody Forbes Partnership (2006) 1 Rock erosion at the foot of the wall was highlighted in the report of 1996. This current survey indicates that this erosion is continuing at a significant rate. Were the beach levels higher, then the erosion would of course be substantially less, but it is interesting to note that beach levels in the Hutchinson survey of 1984 are not that dissimilar to the levels noted by ourselves. It is quite probable, therefore, that the status quo is a low beach level which allows erosion to take place at the foot of the wall. 2 Not highlighted in 1996 but present now, at least in one place, is erosion actually underneath the base of the wall, which if left unattended could lead to the wall's collapse. We recommend, therefore, as a first priority that the wall/rock layer interface is investigated for the full length of the wall. 3 If original construction drawings are not available, the stability of the wall should be established by survey techniques and then calculation to assess how much total lateral restraint (against forward sliding) is required and an assessment made of how much lateral resistance can be provided by the surviving layers of lias rock. 4 The erosion of concrete at the base of the wall is leading to loss of mass and as the wall is designed as a gravity wall, this, if taken to excess, could compromise stability. It is therefore important that the wall mass is retained by suitable repairs. In the longer term consideration should be given to additional protective measures to stop any further erosion in the future. 5 The actual increase in crack sizes between 1996 and now, generally speaking, is very small, which suggests that disruption due to thermal expansive effects is actually diminishing as time goes on. There is evidence, however, of expansive movement in places leading to greater overhangs of higher sections of wall over lower. An assessment of the wall stability could also include any compromise on stability with the overhang. A prediction could be made for the maximum permissible overhang. It would then be possible to predict how much overhang can be tolerated before something needs to be done. Of course, this would require a presumption of atmospheric temperature range which if anything is going to become more extreme. 6 Part of the analysis, too, could test what sort of earth slopes behind will be tolerable before instability sets in. With constant land slipping, the weight of material behind the wall will fluctuate markedly and could exceed design loads. Having said that, however, there have been several slips between 1996 and the present time, some of which have been major. 3-14

However, it would appear that the wall has remained stable at all times, a testament to its design. 7 The return wall at the north eastern end is almost in a terminal state and extensive rock armouring could be considered to protect this end of the construction. It is interesting to note that the existing cliff face has probably eroded by 10-15m since 1957 when the wall was built. 8 Finally, as noted in detail above, there are some cracks which are inexorably increasing in width. There also appears to be some forward movement of the additional section of wall placed at the top. We recommend that these are monitored accurately to establish a pattern and rate of movement. There is a range of other minor works of repair and weep hole installation, which should be carried out in due course. 3.3.2 Current Condition The current wall condition has not significantly changed since the Brody Forbes Partnership survey of January 2006. Observations on the major areas of concern are made below. 3.3.2.1 Wall Cracking Cracking is clearly evident at all sections of the wall. The cracks occur both vertically and horizontally and are generally, but not always, at construction joints in the wall. It is suggested in the previous reports that these cracks are due to thermal effects; this is concurred with. No expansion/contraction joints were made in the wall construction and it is thus no surprise that cracking has occurred. This cracking is likely to have been caused by the initial thermal shrinkage of the concrete after construction (the hydration of cement is an exothermic process, generating heat; as the concrete cools it contracts), by seasonal variations in temperature. Other possible contributory mechanisms to crack enlargement might be wave generated hydraulic pressure, ice expansion, or salt crystallisation. The vertical cracks, if stable and well spaced, are in themselves of no concern structurally but may be possible points of vulnerability to erosion. Some of the horizontal cracks show a forward movement of the upper section of the wall in relation to the lower section. This is practically evident on the curved sections of the wall with an overlap of approximately 60mm occurring near groyne 12. That the overhang is most apparent on the curved wall sections may reinforce the view that this is due to longitudinal thermal movements forcing the wall outwards rather than soil or water pressure from behind although monitoring of wall movement has not yet ruled out that ground movement might be contributory. 3-15

Figure 3.3.2.1a Vertical and horizontal cracking following construction joints in the concrete (near groyne 7) Figure 3.3.2.1b Horizontal crack showing overlapping top section 3.3.2.2 Wall Erosion The face of the wall in several sections has been severely abraded by the action of wave borne shingle. This action is at its worst near the west side of the groynes and has lead to erosion of up to around 300mm. Figure 3.3.2.2 Heavy erosion near Groyne 4. Here the concrete facing installed in the mid-1960s here been eroded by nearly 300mm exposing and allowing the corrosion of steel reinforcement. 3.3.2.3 Wall Drainage Weepholes have been built into the seawall at a number of locations, general 2 or 3 occurring between each pair of groynes. Weepholes are commonly provided in such walls to prevent the build-up of hydrostatic pressure behind the wall. Only a minority of these weepholes showed signs of activity at the time of visit (November 2006) whereas, at a number of locations, seepage of water was apparent from cracks and joints in the wall. While it cannot be certain in all cases that this seepage was due to groundwater rather than tidal water it appears likely that many of the weepholes are blocked or otherwise ineffective and that groundwater is escaping through the cracks. 3-16

Figure 3.3.2.3a Weephole showing signs of seepage Figure 3.3.2.3b Seepage through construction joints Figure 3.3.2.3c Weephole apparently blocked or otherwise inactive Figure 3.3.2.3d Seepage through horizontal construction joint and diagonal joints caused by bad concreting practice 3.3.2.4 Beach Erosion Movement of shingle and boulders on the beach and erosion of the foreshore limestone ledges is apparent from visual inspection and comparison of survey data. This has been recognised in the past and concrete aprons have been constructed along vulnerable sections of the wall; some of these aprons are now becoming damaged or undermined by further foreshore erosion. It might be noted that gradual erosion of the foreshore out from the wall will allow larger waves the reach the wall location; thereby escalating the rate of erosion at the wall toe and to the face of the wall concrete. 3-17

Figure 3.3.2.4 Erosion of limestone ledge near groyne 16 3.3.3 Constructional Details Construction details of the original seawall constructions are not available, the only drawings traced relating to the refacing and strengthening works carried out in the 1960s (see Appendix B). If it is intended to retain these walls in their current condition, or as repaired in the future as the primary sea wall or as a structural component of a new sea wall it would be necessary to ascertain their construction (see Section 7). 3.3.4 Residual Life Accurate determination of residual life is not possible with the presently available data. Foreshore erosion and consequent undermining of the seawall structure will not be linear but will occur in separated sudden events; thus any calculated life expectance would be a contentious prediction. It is however clear that, unchecked, wall and foreshore erosion would eventually lead to structural failure. A failure may be without prior warning and likely to occur during storm conditions. Once collapse had occurred the cliff behind could be rapidly eroded before remedial works could be implemented. The original design life for the structures, if this was ever considered, is unknown; however it is likely that at the time of the major works in the 1950s to 1960s, a life expectancy of 50 years might have been considered. It is now approximately 50 years from the East Cliff seawall original construction and approximately 40 years since any significant works have been carried out on the seawall structures. It would thus be realistic to anticipate that the seawall is reaching a stage where extensive remedial works or rebuild will become necessary in the near future. 3-18

Table 3.3.4 Age of Foreshore Structures Church Cliff Seawall Church Cliff Groynes East Cliff Seawall East Cliff Groynes Original Build (approximate date) 1910 1964 (Total replacement of earlier structures) 1957 Additional or Remedial Works (approximate date) Extensive refacing and concrete apron installation mid 1960s Approximate Age Original wall 96 years New works 40 years - 42 years Concrete apron installation 1969 49 years (apron 37 years) 1967-39 years It is suggested that if it is necessary to define a residual life period for assessment a notional 10 years is assumed although failure could occur before should significant storm events occur. 3.4 DESIGN PHILOSOPHY AND PARAMETERS 3.4.1 Purpose of the Coastal Protection The coastal protection is required to perform the following primary functions: To prevent erosion of the base of Church Cliff and East Cliff which would be detrimental to the stability of those cliffs To prevent wave overtopping from reaching the surface of Church Cliff and East Cliff and causing erosion In addition to these primary functions, the coastal protection may also be required to provide the following secondary functions: Provide access along the foot of the cliff for safety and emergency reason including pedestrian escape on rising tides Provide access for plant, men and materials for maintenance Enhance the amenity value of the area Protect the existing landscape 3.4.2 Design Life For the purposes of this report the target design life for the Church Cliff and East Cliff seawall is taken as 60 years from the implementation of Phase IV. 3-19

3.4.3 Wave Regime HR Wallingford report EX4621, March 2003 used the following wave climate for physical modelling: Table 3.4.3 Wave Conditions used in the Physical Model (2003) Offshore Wave Direction South Southeast Joint Return Period (Years) Water level return period (Years) Still water Level (m OD) Wave height return period (Years) Offshore Significan t wave height, Hs (m) Offshore Mean Wave Period, Tm (s) 10 0.1 2.35 3 4.61 7.7 50 20 3.14 0.14 2.92 6.1 100 100 3.52 0.18 3.08 6.3 10 0.1 2.35 3 4.19 7.3 50 20 3.14 0.14 2.47 5.6 100 100 3.52 0.18 2.63 5.8 The above values were chosen to assess the performance of the then proposed schemes under present day conditions and therefore do not include for potential future sea level rise. 3.4.4 Sea Level Rise & Climate Change Current tidal levels at Lyme Regis based on Admiralty Tide Tables are: Table 3.4.4a Tidal Levels Metres above Admiralty Chart Datum Metres above Ordnance Datum LAT MLWS MLWN MSL MHWN MHWS HAT -0.02 +0.60 +1.60 +2.30 +3.00 +4.20 +4.64-2.37-1.75-0.75-0.05 +0.65 +1.85 +2.29 These levels do not allow for storm surges. DEFRA Flood and Coastal Defence Appraisal Guidance, October 2006 gives regional net sea level rise allowances and extreme wave height change for SW England as: 3-20

Table 3.4.4b Net Sea Level Rise Allowance and Extreme Wave Height Change 1990-2025 2025-2055 2055-2085 2085-2115 Relative Sea-level rise (mm/yr) 3.5 8.0 11.5 14.5 Extreme wave height (Hs; % change from current conditions) +5% +5% +10% +10% Assuming a 60 year design life from 2010 this would imply a 0.535 metre net sea level rise above the 1990 baseline level or 0.475 metres above the end 2006 level. With regard to future sea level rise, it should be noted that the HR Wallingford report of 2003 was based on current sea levels. The report stated: The aim of the model studies was to assess the relative performance of each of the proposed schemes relative to the existing layout under present day conditions. The influence of potential future sea level rise has therefore not been included in the extreme water levels used, i.e. all water levels described are those considered to be applicable to the present day. Assuming the proposed coast defence scheme has a design life of 60 years, a sea level rise of 0.25m (5mm/year) would result in the 1:200 year condition in the year 2050 having a return period of around 1 in 50. 3.4.5 Foreshore Lowering Any seawall design at Church Cliff and East Cliff should accommodate foreshore lowering. The previous survey records have been examined to ascertain the current rate of foreshore lowering. The 1985 survey is difficult to interpret due to ambiguity in the foreshore contours shown on the available plot. The 1995 and 2005/6 surveys appear to show useful information but the structural surveys of 1984, 1995 and 2005/6 have yielded the most useful information in showing the beach level close to seawall. Appendix E Drawing PH4\PD\004 shows beach sections derived from the 1995, 2005/6 and, where possible, 1987 surveys. Observations on the foreshore level changes are tabulated in Appendix F. Level changes at Church Cliff seawall and the western sections of East Cliff seawall show both rises and falls between 1984 and 2005/6, presumable due to shingle movement and possibly artificial beach replenishment. It is not possible to determine a long term trend but it is clear that the situation should be monitored. Here the depth of shingle, cobbles, etc. is possibly protecting the underlying limestone ledges although in places causing erosion of the seawall. From groyne 8 to groyne 12 it is unclear from the structural survey records if the foreshore is lowering at a significant rate. Observation of the interface between the apron concrete and the foreshore appears to confirm, at least local to the apron, that significant lowering has not occurred here. However the apparent lowering indicated by the 1995 2005/6 level survey comparison might be interpreted as showing that the foreshore limestone ledges are progressively eroding back towards the seawall. 3-21

Further east, beyond groyne 12, the foreshore appears to be lowering at a nonlinear rate possibly averaging about 0.5m per decade. It must however be recognised that a future rate of foreshore lowering may be greater that the current rate due to sea level rise, increased water depth and increased storminess. 3.5 FORESHORE PROTECTION OPTIONS 3.5.1 Introduction In order to address the primary functions described in section 3.4.1 above three foreshore management options have been considered: Do nothing Minimum intervention and maintenance: Scheme Options The development of these options is described below together with their projected efficacy and implications. Other options that may be available to protect the shoreline include: Beach enhancement including the use of beach nourishment and groynes Offshore breakwaters preventing wave attack to the shoreline These latter options are perceived as having unacceptable effect on the environment and are not further considered in this report. Furthermore without effective groynes continuous artificial beach nourishment would be necessary due to the longshore drift. The Lyme Bay and South Devon Shoreline Management Plan (prepared by Posford Duvivier, 1998) gives the Preferred Strategic Option for the Cobb Gate to Harbour and East Cliff area of Lyme Regis (Coastal Process Unit CPU 3 and Management Unit MU 6) as Hold the Line. 3.5.2 Do Nothing A Do Nothing approach would leave the wall liable to damage and collapse due to the continuance of the currently deteriorative and destabilising mechanisms, principally the erosion of the beach/foreshore in front of the wall causing undermining of the wall itself and erosion of the wall concrete causing structural failure. Such an event would be without warning and likely to occur during storm conditions. Once collapse occurred the cliff behind would be eroded as it could not be assumed that mobilization and execution of remedial works could be achieved in time to prevent cliff damage. It is thus considered that a Do Nothing approach is not viable. 3.5.3 Minimum intervention and maintenance If the seawall currently meets all functional requirements a minimum intervention and maintenance approach may be acceptable. Such a minimum intervention and 3-22

maintenance regime must address the currently deteriorative and destabilising mechanisms: Table 3.5.3 Seawall deteriorative and destabilising mechanisms Problem Solutions Comments Wall Cracking Do nothing May be viable, drainage to rear should be improved to prevent seepage Superficial sealing Liable to damage and erosion in marine environment. May be forced out under hydrostatic pressure if ground water drainage to rear is not improved. May be eroded by wave action Grout injection Capable of sealing cracks Wall Erosion Do nothing Not viable, wall will continue to erode Concrete Patch Repair Preferably bonded to existing wall with marine grade stainless steel reinforcement Wall Drainage Do nothing May be viable but subject to calculation of wall stability after investigations of wall construction Reactivate existing weepholes and core additional holes Without knowledge of backfill material (if any) it cannot be ascertained if this will be effective in reducing hydrostatic pressure other than local to each hole Beach Erosion Do nothing Not viable, foreshore will continue to erode Concrete Apron (local areas where necessary) Rock armour apron (local areas where necessary) and undermine wall Repair and installation of new concrete apron and toe to wall will provide interim solution. Future repair will be necessary as beach erodes Installation of rock armour apron to wall will provide interim solution. Future maintenance may be necessary May interfere with pedestrian access and tidal escape along beach Such minimum intervention and subsequent maintenance would be the least obviously necessary works comprising local concrete repairs, local filling of holes in foreshore, cleaning drainage holes, and possibly partly sealing cracks leaving drainage provision. This would be confined to superficially visible and determinable defects without undertaking extensive investigation such as borings, etc. The hazards of this approach are that there would remain a high risk that repairs do not cover all the damage and the risk of future failures would be high. The minimum intervention and maintenance option, however, does not address the current public safety concerns relating to the foreshore. In view of the ongoing maintenance burden, risk of failure and safety issues this option is not considered to be sustainable in the medium to long term. 3.5.4 Hold the Line Schemes Significant seawall schemes can comprise a variety of seawall types. A range of potential seawall types is listed in CIRIA Report Seawall Design, R S Thomas & B 3-23

Hall, 1992, and these are reproduced in Appendix F. However not all these seawall types are suitable for the Church Cliff and East Cliff locations and it is only by applying selective criteria to the various types that a final selection of appropriate wall type can be made. The CIRIA publication proposes a variety of possible criteria which might be adopted. These include range of wave climate, hydraulic performance, visual aspect, ease of access to shore, maintenance, permeability to groundwater, flexibility and durability. The report proposes using only those criteria which are deemed essential in relation to the particular location, i.e. at Church Cliff and East Cliff. The various criteria are reviewed in detail in Table 3.5.4a below. Table 3.5.4a CIRIA Criteria Relevance CIRIA criteria Relevance to Church Cliff and East Cliff Range of wave climate Essential - Church Cliff and East Cliff are subject to aggressive wave attack Hydraulic performance This relates to whether waves will be reflected, dissipated or overtop the wall. While this is of relevance alleviating measures can be taken and this is not considered a reason for selection/rejection of seawall type at this stage Visual aspects This not considered a reason for selection/rejection at this stage but it is recognised that this will be a significant criteria in the final choice. Ease of access to shore While access is of concern difficulties involved may generally be overcome, thus this not considered a reason for selection/rejection at this stage Maintenance Essential - A low maintenance solution is required Permeability to groundwater If necessary drainage can be incorporated. Not an essential criteria Flexibility As the wall will be founded on competent strata and is located below potential slip planes this is not an essential requirement for seawall type. However, as demonstrated by cracking of the existing seawall some provision of movements joints, to allow for thermal movements and potential ground movements, should be allowed. Durability (assuming good Essential A minimum design life of 60 years is to be materials) considered Examination in Appendix G of the CIRIA wall types in the light of the above criteria has produced a short list, Table 3.5.4b below, of suitable types for use at Church Cliff and East Cliff; it should however be noted that a number of hybrid walls using these component types are possible and may form the better options. 3-24

Table 3.5.4b Summary of Wall Types Meeting Essential Criteria Type of slope protection Rock armour Random placed concrete armour units Stepped concrete slopes Smooth concrete slopes Mass concrete gravity wall Masonry gravity walls Steel sheet piles Advantages Disadvantages Comments Durable Low Maintenance Good wave dissipation Durable Low Maintenance Good wave dissipation Durable Low Maintenance (if well detailed) Safe for public access Durable Low Maintenance Durable Low Maintenance Safe public access may be provided along top Durable Low Maintenance Good appearance Safe public access may be provided along top _ Not ideal for public access due to deep voids between rocks Requires filter layer or solid barrier to prevent loss of materials from behind Not ideal for public access due to deep voids between units Regular, clearly man-made units visually intrusive on wild coast and in Lyme Regis town Requires filter layer or solid barrier to prevent loss of materials from behind Harsh and urbanising appearance, out of character with wild coast and Lyme Regis Phase I Wide footprint effects foreshore ecology Harsh and urbanising appearance, out of character with wild coast and Lyme Regis Phase I Wide footprint effects foreshore ecology Wave run-up Urbanising appearance but similar to existing situation High cost Urbanising appearance, but in keeping with Lyme Regis Phase I promenade Worst aesthetic appearance, totally out of character with wild coast and town Liable to corrosion May be used in front of existing or new solid wall in hybrid solution to reinforce wall and/or to prevent scour at wall base Appearance closest to natural coastline but not in keeping with local cliffs. Least intrusive on wild coast May be used in front of existing or new solid wall in hybrid solution to reinforce wall May be used as an apron in front of main wall to prevent scour at wall base May be used as an apron in front of main wall to prevent scour at wall base A concrete or rock armour apron may be used in front of a gravity wall to prevent scour at wall base As mass concrete gravity wall but better appearance Masonry facing may be used on a mass concrete wall to give a lower cost option May be used as toe protection to main wall 3-25

Of the above technically feasible further elimination of type has been carried out on the following basis: Random placed concrete armour units serve essentially the same function as rock armour. As rock armour is considered visually more appropriate for this application the concrete units are eliminated. Stepped and smooth concrete slopes have a wide footprint and do not have the good wave dissipation characteristics of rock armour slopes, in fact the smooth slopes are particularly liable to wave run-up. These are therefore eliminated as principle structural forms although it is recognised that they may have use at foreshore protection at a vertical wall toe. Masonry gravity walls are essentially similar to mass concrete gravity walls but of higher cost. These are thus eliminated from further consideration but it is noted that a concrete wall may be masonry faced if required. Steel sheet piling is eliminated as inappropriate to this site but may be considered for scour protection at a wall base. Thus, taking the visual requirements and these technical considerations into account, a final short list of principle wall construction types is derived: Rock Armour Revetment Mass Concrete Gravity Wall Hybrids of the above Based on these wall construction methods scheme options have been devised and are reviewed in Appendix H. These schemes, listed below, are described in the following section. Hold the Line Scheme 1 Hold the Line Scheme 2 Hold the Line Scheme 3 Hold the Line Scheme 4 Hold the Line Scheme 5 Rock armour revetment to front of existing wall Refacing of existing concrete seawall Granular fill and drainage to rear Provision of wall-top access route Protective apron to front Refacing of existing concrete seawall Granular fill and drainage to rear Provision of wall-top access route Rock armour revetment to front New front wall Provision of wider access route over possible Protective apron to front New front wall Provision of wider access route over possible Rock armour revetment to front All schemes will be provided with access steps or ramps at the eastern end. For schemes where a wall top access route is provided steps at, at least one, preferably two intermediate locations along the sea wall allowing access to this route can be provided. 3-26

These schemes are more fully described below. The scheme sketches are diagrammatic only. 3.5.4.1 Hold the Line Scheme 1: Rock Armour Revetment to Existing Seawall Figure 3.5.4.1 Hold the Line Scheme 1 A rock armour revetment would be placed to the front of the existing seawall. This would both provide additional support to the wall and give protection to the wall and immediate foreshore by dispersing the wave energy, thus reducing any risk of failure. It would not provide any additional wall top access and would reduce foreshore access thus potentially aggravating public safety problems. The integrity of the existing seawall may be improved by repairs prior to placement of the rock armour. 3.5.4.2 Hold the Line Scheme 2: Seawall Reconstruction/Refacing Figure 3.5.4.2 Hold the Line Scheme 2 A thick concrete refacing of the existing seawall provides structural homogeny, designed movement joints at, say 25m centres, will be formed in the facing and cut through the existing wall to allow for thermal and other movements and prevent crack formation. Drainage to material behind the existing wall will be improved thus relieving any hydrostatic pressure. This type of seawall will not reduce reflected wave 3-27

energy and without beach protection the foreshore is likely to continue to erode and lower. To prevent this endangering the wall a rock apron is laid in front of the refaced wall to prevent local foreshore erosion to the toe of the wall; this will also reduce erosion to the wall face. A rock apron has been chosen in lieu of the concrete apron used in front of sections of the existing seawall as its flexibility will allow for a degree of foreshore erosion and would be easier maintained; the rock apron also has better wave absorption characteristics. A concrete apron has been used with some success at Church Cliff where it is protected by a steel sheet piling toe but this piling is subject to corrosion. A disadvantage however is that this will cover some of the foreshore and limit public access at the foot of the seawall. Concrete refacing of the wall will also allow the crest level to be raised, if necessary, with the top of the wall incorporating an improved wave return wall detail, to prevent overtopping with future sea level rise and allow improved wall top access. The works outlined would provide much increased confidence that all existing damage had been covered and risk of forecast future damage reduced. However a latent residual risk of damage would still remain which could be further reduced by a new wall. 3.5.4.3 Hold the Line Scheme 3: Seawall Reconstruction/Refacing with Rock Armour Revetment Figure 3.5.4.3 Hold the Line Scheme 3 This scheme is similar to the Hold the Line Scheme 2 above except that a rock armour revetment is used in front of the wall. The armoured revetment in front of the existing repaired wall is an improvement over an concrete or rock apron in that it improves the stability of the wall, reduces wave impact forces on the wall and thus further reduces any risk of failure. Also the improved wave absorption of this scheme will reduce reflected waves and thus lessen foreshore erosion. This has been shown to part wall height, further armour height would be unnecessary for wall stability and would further restrict public access on the foreshore. 3-28

3.5.4.4 Hold the Line Scheme 4: New Wall Figure 3.5.4.4 Hold the Line Scheme 4 A new concrete wall will be constructed in front of the existing wall; it will be provided with designed movement joints at, say 25m centres thus preventing crack formation. The new wall will effectively relieve the existing seawall of its functional requirements. Drainage to material behind the existing wall will be improved but may not necessitate such extensive measures as the above Hold the Line schemes 2 or 3. As in Scheme 2 a rock apron is laid in front of the new wall to prevent local foreshore erosion to the toe of the wall; this will also reduce erosion to the wall face. The new seawall may, if necessary, have a higher crest level than the existing to prevent overtopping with future sea level rise. Improved wall top access may be provided by means for a concrete slab between the new and existing walls, this could allow for emergency vehicle access. A new seawall ensures that a fully known and designed as fit for purpose structure is provided without any of the indeterminates that that may be associated with reuse of the existing structure. 3.5.4.5 Hold the Line Scheme 5: New Wall with Rock Armour Revetment Figure 3.5.4.5 Hold the Line Scheme 5 3-29

This scheme is similar to the Hold the Line - Scheme 4 above except that a rock armour revetment is used in front of the wall. The armoured revetment in front of the new seawall is an improvement over a concrete or rock apron in that it improves the stability, reduces wave impact forces on the wall and thus further reduces any risk of failure. Also the improved wave absorption of this scheme will reduce reflected waves and thus lessen foreshore erosion. 3.5.5 Advance the Line Schemes In these schemes fill buttressing the seacliff will be placed forward of the existing seawall and must be protected from wave attack by a new forward seawall or other means. Choice of seawall is governed by largely similar parameters to those for a Hold the Line seawall. It is only envisaged that an Advance the Line slope buttress solution would be applicable if this technique is required to increase the stability of the cliff face above and behind the wall. The following schemes are considered in this report: Advance the Line Scheme 1 Advance the Line Scheme 2 Advance the Line Scheme 3 New forward wall Gravity wall construction with protective apron to front Wide promenade behind wall New forward wall Gravity wall construction with rock armour revetment to front Wide promenade behind wall New forward wall Rock armour bund construction Wide promenade behind wall All schemes will be provided with access stairs or ramps at the eastern end and at least one intermediate location These schemes are more fully described below. The scheme sketches are diagrammatic only. 3-30

3.5.5.1 Advance the Line Scheme 1 Figure 3.5.5.1 Advance the Line Scheme 1 A new concrete wall will be constructed significantly forward of the existing wall; it will be provided with designed movement joints at, say 25m centres thus preventing crack formation. Graded fill will be installed behind the wall buttressing the cliff face above; this is further discussed elsewhere in this report. A rock apron may be laid in front of the new wall to prevent local foreshore erosion to the toe of the wall; this would also reduce erosion to the wall face. The new seawall may, if necessary, have a higher crest level than the existing to prevent overtopping with future sea level rise. Improved wall top access may be provided by means for a concrete slab or roadway behind the new seawalls, this could allow for emergency vehicle access. A new seawall ensures that a fully known and designed as fit for purpose structure is provided without any of the indeterminates that that may be associated with reuse of the existing structure. 3.5.5.2 Advance the Line Scheme 2 Figure 3.5.5.2 Scheme 2 3-31

This scheme is similar to the above except that a rock armour revetment is used in front of the wall in place of an apron. The armoured revetment in front of the existing repaired wall is an improvement over an apron in that it improves the stability, reduces wave impact forces on the wall and thus further reduces any risk of failure. 3.5.5.3 Advance the Line Scheme 3 Figure 3.5.5.3 Advance the Line Scheme 3 This scheme is similar to the above except that a rock armour revetment is used in place of the wall and may thus provide a lower cost option. 3.5.6 Existing Groynes Options for the foreshore groynes must be considered in connection with the seawall options. The basic options for the groynes are: Removal Retention as existing i.e. Do Nothing Repair and maintenance Replacement Further study would appear to be required to determine if, in the environment of the chosen seawall scheme, the groynes have beneficial, neutral or adverse effect on the coastal protection. Beneficial effects of the groynes would appear to be the protection of loose foreshore material, where this exists, against longshore drift. Adverse effects of the groynes would appear to be the erosion of the seawall face and foreshore limestone ledges that is taking place close to the western face of the groynes. Removal of the groyne locally to the seawall may alleviate the latter effects but promote longshore drift. 3-32

HR Wallingford s report of 2003, see Section 3.2.5 above, considered that groynes should be an integral part of the overall scheme if a shingle beach is included. It is noted that the existing groynes have proved largely ineffectual in preventing longshore drift; this may be at least partially due to their deteriorated condition and the removal of the timbering at the plant access points for public safety reasons. 3.5.7 Alternative Coastal Protection Options 3.5.7.1 Bay & Buttress Solution A landscape conceptual hybrid solution, or Bay and Buttress solution, was developed by Environs in 2001 and presented in the Conceptual Landscape Design Report (Environs, 2001). The conceptual landscape solution comprised creating a bay at Church Cliff by slope strengthening / drainage works and construction of a buttress for stabilisation of East Cliff. The details of the strengthening / drainage works and slope buttress works were based on the recommendations provided in the Conceptual Design Report (HPR, 2000b). This geometry was one of the options tested by HR Wallingford (see Section 3.5.7.2 HR Wallingford, 2003). At that time however the slope works were purely conceptual and had not been subject to geotechnical design. The physical model comprised: A short masonry breakwater extension (13m from the corner of Gunn Cliff) fronted by rock armour; A new seawall directly in front of the existing seawall with a crest elevation of +5mOD along the bay section; Shingle nourishment along the bay section extending from a level of +5mOD at the seawall and a straight beach slope of 1:7; Four timber groynes (3 no. 30m in length and the fourth 32m long) at a slope of 1:7; Rock revetment protecting the buttress section of the defences; A terminal groyne 32m in length along the eastern flank. The conclusions of the HR Wallingford report on the Bay and Buttress option were: Incorporating a shingle beach in to the Bay and Buttress scheme is feasible but will require beach control structures, notably the stub breakwater and timber groynes, to retain the beach, together with episodic beach maintenance especially after storms. Overtopping along the frontage can be reduced with a beach and / or rock revetment. This will also considerably reduce wave reflections, which may slow the rate of breakup of the foreshore rock ledges. It is suggested that a 2-D physical model be conducted during detailed design to fully optimise the rock revetment profile to meet armour stability and overtopping requirements The required buttress geometry is discussed further in Section 4.5.4.2. 3-33

3.5.7.2 Beach Nourishment A primary form of coast protection for consideration is beach nourishment. This was used very successfully for the Lyme Regis Town Beach Phase II area where the former depleted sand and shingle beaches were re-nourished and beach holding structures comprising two masonry jetties and two extended and realigned rock breakwaters were constructed. The configuration of the beach holding structures, i.e. length and orientation were designed using numerical and physical modelling techniques by H R Wallingford (2003). For the Town Beach alternative structures including new groyne systems were also shown to be feasible. The Phase IV area in front of Church and East Cliffs is however not directly comparable. A groyne field comprising a total of 17 groynes has been in place on the foreshore since at least the mid 1960s below Church Cliff and 1969 below East Cliff (see Section 3.1.3). It is understood that this foreshore area has never been artificially recharged and a sound beach has not naturally formed between the groynes. The direction of net longshore drift in front of Church Cliff and East Cliff is given to be eastwards with a potential transport (sand and shingle) of around 5000m³/year although very little material is derived from the protected cliffs themselves (see Section 3.2.1). The inclusion of beach holding structures such as groynes, breakwaters etc would therefore unlikely to be successful in accumulating natural drift material. Consideration however could be given to importing suitable beach material, (likely to be coarse shingle size material rather than sand), which together with new beach holding structures could potentially be designed to form a stable beach. The HR Wallingford 2003 report stated.it is considered that, despite there being potential for longshore transport, it is not too significant an issue, with beach levels capable of being maintained with episodic beach maintenance activities (likely to be required following storms). HR Wallingford s report of 2003, examined stub breakwaters at Gun Cliff and the east end of the East Cliff seawall. The report stated that The stub breakwater at Gun Cliff is required to help stabilise the beach along the southern section of the East Cliff frontage by acting as headland and controlling the way that waves diffract around the end of the headland and on to the beach Regarding the position at eastern end of the existing seawall and while investigating a Bay and Buttress solution the HR Wallingford 2003 report stated The stub extension to the eastern end of the revetment had less influence in protecting the cliff immediately downdrift of the end of the existing wall. However, there was no indication that the beach that will be held behind the stub extension would be eroded leaving the cliff vulnerable to further wave attack. Should this beach nourishment option be considered further, extensive numerical and physical beach / hydraulic modelling would be required to confirm both its effectiveness and its effect on coastal processes, however given the current wave regime it is likely that the replenished beach and holding structures would need to be of large extent and would be unlikely to be acceptable on ecological grounds. 3-34

3.5.7.3 Offshore Breakwaters and Submerged Reefs Offshore breakwaters and submerged reefs are also sometimes considered as a method by which wave energy at a seawall can be reduced. However these have been discounted at this stage on both technical and ecological grounds since the impact on the stability of the existing seawalls is likely to be small. Submerged reefs may also present a hazard to shipping. 3.5.8 Lateral Extent of Works and Coastal Protection At present it is considered that the eastern limit of foreshore works would be that of the existing seawall but with a possible short rock armour breakwater extension to protect the seacliff toe in the immediate vicinity of the seawall termination. While investigating a Bay and Buttress solution the HR Wallingford 2003 report stated The stub extension to the eastern end of the revetment had less influence in protecting the cliff immediately downdrift of the end of the existing wall. However, there was no indication that the beach that will be held behind the stub extension would be eroded leaving the cliff vulnerable to further wave attack. It must be recognised that the cliff beyond the present eastern limit of the seawall is currently subject to erosion leaving the slopes behind liable to future instability. The future protection, or otherwise, of these cliffs must be addressed. Protection to the sea cliff below the Allotments West and Allotments East landslip areas would require an extension of approximate 60m length. Options for coastal protection east of the existing seawall include; Eastwards extension of seawall construction Rock armour protection to cliff toe Conventional nearshore breakwater Reef breakwater The first two of these options entail direct protection of the cliff toe while the latter two options shield it from wave attack and are generally consistent in approach with the stub breakwater included in the above HR Wallingford investigations. If foreshore works could not be provided along this unprotected sea cliff for geological interest or environmental reasons, it would be required to undertake works on the coastal slopes to prevent the continued sea cliff retreat from reactivating potential landslides upslope. This is discussed in detail in Section 4.5.5. 3-35

3.5.8.1 Eastwards extension of seawall construction Figure 3.5.8.1 Eastwards extension of seawall construction A seawall of similar form to the existing Church Cliff and East Cliff seawalls could be constructed to extend the coastal protection further to the east. It would be necessary that the wall was constructed a sufficient distance from the cliff foot to allow safe excavation for its foundation. This option may be considered unacceptable as it may be seen as an intrusive extension of urbanisation into currently natural cliff foot area. 3.5.8.2 Rock armour protection to cliff toe Figure 3.5.8.2a Rock armour protection to cliff toe A rock armour protection to the cliff toe would be less urbanising than a vertical wall but require a large footprint (see figure 3.5.8.2a).. The width of the armouring would reduce access along the beach at high tides although deposition of fine beach material may occur along the toe of the rock armouring due to the rocks absorbing wave energy thereby improving access. A pathway could be provided along crest if improved alongshore access is necessary but would require an increased 3-36

construction width; such a pathway should be set away from the cliff toe to avoid danger from falling debris (see figure 3.5.8.2b). Figure 3.5.8.2b Rock armour protection to cliff toe with access at crest 3.5.8.3 Conventional nearshore breakwater Figure 3.5.8.3 Conventional nearshore breakwater A nearshore breakwater, running parallel or at an diagonal to the cliff foot, would shelter the cliff from wave action without obstructing pedestrian access along the foreshore. This option would however be visually obtrusive as the crest height will obstruct views seaward from the foreshore, it may also be a hazard to boats. The effectiveness would be dependant on crest height but a higher crest would be visually more obtrusive and more costly. The final crest height and location would be dependent on hydraulic design and testing. 3-37

3.5.8.4 Reef breakwater Figure 3.5.8.4a Reef breakwater A nearshore reef type breakwater, running parallel or at an diagonal to the cliff foot, would also provide shelter to the cliff foot without obstruction to pedestrian access along the foreshore. As the crest height can be at high water level, or possibly lower although this could be hazardous to boats, and the mound may be designed to be reshaped by wave action this type is less intrusive than a conventional breakwater, has lower materials requirements and would have less footprint area. As a reef breakwater is entirely constructed from armour stone without core material it is more resistant to damage and may be allowed to reform under wave attack. It is however more permeable to waves; this factor together with reduced crest height and increased overtopping prevents it from being as effective as a conventional breakwater but it will substantially reduce the wave climate at the cliff toe. This zone of more benign conditions may encourage beach retention/formation. The final crest height and location would be dependent on hydraulic design and testing. Reef breakwaters appear to have been successfully used, and have promoted beach accretion, further west along the coast off The Esplanade at Sidmouth. 3-38

Figure 3.5.8.4b Tentative locations for a reef breakwater related to landslide locations 3.5.9 Coastal Processes It is important that any proposed coast protection works do not adversely effect the coastal processes of adjacent areas including Lyme Regis Town Beach area (Phase II) and the area to the east. Both sediment supply from the Church Cliff and East Cliff slopes and the predominate net sediment transport from the west to the east is relatively insignificant (see Section 3.2.1), this is also demonstrated by the lack of beach material in front of the existing seawall and between the groynes. The Hold the Line options are therefore unlikely to have any adverse effect on coastal processes, similarly the Advance the Line options as described above are considered to have minor influence on coastal processes. 3.5.10 Public Safety Considerations The foreshore between East Cliff, Lyme Regis and Charmouth is much favoured by walkers all year round. This walk can only be undertaken safely at lower tides and in favourable sea conditions. The route does tend to become safer nearer Charmouth to the east as parts of the sea wall below East Cliff at Lyme Regis can become flooded and impassable, not long after some low tides have turned. This is despite the beach on either side still being seemingly accessible. It is therefore always advisable in the current circumstances to pass this point on the sea wall at around the time of any low tide. The East Beach also contains 17 groynes extending out from the sea wall. The concrete steps over these groynes have been eroded away in many locations making them unusable. Sections of the groyne timbers were removed in the mid/late 1990's at the sea wall end as they had previously proved to present an additional hazard in that they had, on occasions, blocked a safe passage to walkers 3-39

with reported instances of people becoming trapped between the groynes and having to be rescued. The area that causes the most concern is between groynes 8 and 11 as the incoming tide can result in a 'pinch point' at this location. There are corroded step irons/ladders attached to the sea wall in a few locations, but these are generally hazardous to use. These rise to the top of the sea wall but mudslide deposits and debris now rests directly on top of the sea wall hindering any escape. The beach below the sea wall is also very slippery in places mainly along a steep concrete apron section between groynes 8 and 11 where the tide rises quickly and this provides an additional hazard when trying to pass. The cliffs along this stretch of beach are also prone to falls and mudsliding whereupon debris and mudflows can spill onto the beach and this can prevent access along the beach, leading to the risk of being cut off by the rising tide. It is not always possible or even advisable to climb over the mudslides as these can present their own dangers of becoming trapped in the soft mud. Any seawall/groyne system for Church Cliff and East Cliff should be designed with the view to preventing the hazards referred to above and avoiding loss of life and unnecessary call out of emergency services being caused by persons being trapped by rising tides. Sufficient accesses over/across groynes and to a seawall top escape path should be provided to mitigate such risk. It should be noted that such access features are needed where attrition by shingle motion under wave conditions is greatest and that careful detailing is necessary to minimise such damage. 3.5.11 Public Access Considerations In view of the severe potential risks imposed on the public described in section 3.5.10 above it is considered that an important objective of any new works would be the improvement of access to increase safety. Such considerations include: Access routes may be: Access along top of seawall Access along beach Access between beach and seawall Public access may be provided for the following classes of traffic: Pedestrians Wheelchair & pushchair Emergency vehicle Road-train or other passenger carrying vehicle Maintenance vehicles In addition consideration may be given to: Vehicle turning area Vehicle waiting/parking areas (authorised vehicles only) Amenity buildings (shelters, conveniences, kiosks, etc.) 3-40

The scheme options described in the preceding section illustrate how improved access along the top of the wall can be readily achieved by the incorporation of an access path. Access along the beach is tidal and options which result in encroachment onto the existing foreshore will potentially reduce the available access time between suitable tides. Currently access between the beach and seawall is poor and unsafe. Opportunities exist therefore to improve such access by including emergency steps and/or ramps in front of the seawall (see also section 4.5.6). 3-41

4 SLOPE STABILISATION OPTIONS 4.1 DESCRIPTION OF THE SITE 4.1.1 Location and Geography The location of the Phase IV study area is shown in Figure 1.1 and an aerial photo of the coastal slopes is shown in Figure 4.1. The coastal slopes that are the subject of this study extend over a length of about 500m from the east of Church Cliff Jetty eastwards to the Spittles landslide system. The inland boundary of the study area extends from the existing seawall, described in the previous Chapter, inland to Timber Hill a distance of about 700m. The Phase IV study area can be divided into the areas described below. For the purposes of the Phase IV study the coastal slopes have been further divided into areas of different landslide characteristics (see Appendix I: Drawing PH4\PD\210). Charmouth Road Car park Spittles Lane Football ground Timber Hill Meadows to The Spittles East Cliff Allotments to Church Cliff Blue Lias Cliffs existing defences mudslides landslide debris to Black Ven Figure 4.1 Aerial Photo of Coastal Slopes 4.1.2 Lower Slopes: Church Cliff and East Cliff These lower coastal slopes comprising relatively steep and unstable slopes include two main areas, known as Church Cliff and East Cliff, the toe of which is protected by an existing seawall. Church Cliff is about 200m in length and is located directly east of Church Cliff Jetty and to the west of East Cliff. Church Cliff is about 23m high, and the coastal slope above the 6 to 7m high vertical seawall is typically at an approximately average gradient of 20 to 25 to the horizontal rising to a crest elevation of about 24mOD. St 4-1

Michael s Church and its graveyard, and residential buildings are located inland of the crest of Church Cliff. East of Church Cliff, East Cliff is 24 to 35m high and extends inland by about 150m from the seawall. Above the sea cliff behind the seawall, the slope comprises two benches formed by landsliding. The approximate average gradient of the two-bench slope is 10 to 15 to the horizontal. The crest of the lower coastal slope is at an elevation of about 24 to 37mOD. At East Cliff Lane, there was an old gas works in an area that has now been lost due to landslide instability. 4.1.3 Middle Coastal Slopes: Charmouth Road car park, Football Ground and Allotments Inland from the lower coastal slopes, and extending north for a distance of about 180m, the middle coastal slopes are largely developed with properties above Church Cliff, and the Charmouth Road public car park, amenity area (including the football ground and allotments), and infrastructure. The area is bounded by Charmouth Road to the west and the Spittles landslide system to the east. Charmouth Road is the only main access route into the town of Lyme Regis from the east, and to the west of the road the land slopes down into the valley of the River Lim. The middle coastal slopes gently rise from the crest of Church Cliff and East Cliff at elevations of about 24 to 37mOD, to 60mOD along Spittles Lane located immediately to the north of the football ground. These developed slopes have been partly modified by man to create level areas for the car park and football areas and the natural drainage has also been extensively modified. To the immediate east of the car park and allotment gardens lies an old disused landfill site, believed to have been closed in the 1970s. 4.1.4 Upper Coastal Slopes: The Meadows and Timber Hill The Meadows and Timber Hill extend northwards from Spittles Lane and are largely undeveloped comprising pasture/grazing land and wetland areas with Timber Hill comprising a wooded area. The area is bounded by Charmouth Road to the west and the Spittles landslide system to the east. The area rises from an elevation of approx. 60mOD at the Spittles Lane to 120 to130mod at the Old Charmouth Road located at the foot of Timber Hill. There are multiple breaks of slopes and terraces within the Meadows, and the average gradient is about 5 to 7 to the horizontal. Inland of Old Charmouth Road is a wooded steep rear scarp forming Timber Hill, and to the north of the rear scarp is a heavily wooded area and a golf course. 4.1.5 Adjacent Spittles and Black Ven Area The Spittles and Black Ven complexes are one of the largest and most active coastal landslide systems in the UK. The complexes form the eastern margins of the Phase IV area, and extend from Lyme Regis in the west through to Charmouth in the east. The complexes consist of a series of terraced cliffs. The back scarp of the landslip is steep and extends to the north of the line of the former Old Charmouth Road. 4-2

4.1.6 Geology and Geomorphology The lower part of the coastal slope at East Cliff is composed of grey-coloured clays and weak mudstones of Lower Jurassic age which contain thin beds of strong limestone. The near-vertical sea cliff is made up of the Blue Lias, comprising interbedded limestones and mudstones in about equal proportions. The Blue Lias is a relatively strong and competent unit and, whilst it is affected by coastal erosion and small rock falls, it is not prone to large landslides of the type which occur in the geological units above. The Blue Lias was once extensively quarried from the cliffs and foreshore during the 19 th and early 20 th centuries. The Blue Lias is overlain by strata known as the Shales-with-Beef and the Black Ven Marls. These units are composed mostly of clays and mudstone with only occasional beds of strong limestone. The clays and mudstones are often shaley, that is they have a tendency to split apart into thin sheets aligned parallel to bedding. The clays and mudstones may break down rapidly into soft mud on weathering and are subject to landsliding on a large scale. The position of landslides is often controlled by the presence of one of the strong limestone beds; the beds dip gently towards the sea which facilitates the seaward movement of the landslides. Landsliding at several different levels has led to the formation of the distinctive stepped morphology. Higher up on the coastal slope, the Black Ven Marls is overlain by the Belemnite Marls, a unit of light grey, relatively competent mudstone which forms a steep scarp. The top of the coastal slope is composed of the Upper Greensand of Cretaceous age. The Upper Greensand comprises fine sand with beds of strong chert, a material similar to flint. At the base of the Upper Greensand there is thought to be a thin unit of clay or fine sand known as the Gault, but this has not been identified in the East Cliff area due to the effects of large-scale landsliding which occurs in the Upper Greensand. The boundary between the Jurassic Belemnite Marls and the Cretaceous material is marked by a major ancient erosion surface, an unconformity, which forms a spring line in the cliffs and controls the base of landslipping within the Cretaceous. The whole of the coastal slope has been affected by severe climatic conditions which occurred during repeated glaciations during the Pleistocene. Whilst the Dorset coast did not have any permanent glaciers or ice sheets, the freezing and thawing of the ground led to widespread landsliding and downslope movement of weathered material, together with disturbance of geology to a depth of many metres below ground level. Hence the East Cliff area has extensive deposits of relatively weak ancient mass movement debris overlying the solid geology, which itself can be locally disturbed and weakened to a considerable depth. 4.1.7 Environmental Designations The whole area of the coastal slopes lie within the Dorset Area of Outstanding Natural Beauty (AONB) and is defined as Heritage Coast. Large parts of the coastal slopes and the Meadows are designated as West Dorset Coast Sites of Special Scientific Interest (SSSI), for its interest as an internationally important geological site and for the wide range of habitats that occur along the undercliff. 4-3

This SSSI of the study area and the fields to the north of the football ground are also designated as Sidmouth to West Bay Special Area of Conservation (SAC), which is a European-level nature conservation designation. The SAC designation relates to the vegetated seacliffs which give rise to a variety of habitats for rare and uncommon species, which are controlled by variations in geology, erosion and degree of exposure to wind and salt spray. The area covering the East Cliff, the Meadows up to the Timber Hill, and the Spittles, forms as part of the area designated as Dorset and East Devon Coast World Heritage Site. This World Heritage Site status is attributed to the natural beauty of the area and the exceptional geology of the slope relating to the Jurassic period apparent in the coastal cliffs and foreshore. The area is also designated as a selected Geological Conservation Review (GCR) site GCR site no. 916 under GCR Block Jurassic-Cretaceous Reptilia. The GCR sites, in general, form the basis of statutory geological and geomorphological site conservation in Britain. These sites display sediments, rocks, fossils, and features of the landscape that contribute to the understanding and appreciation of earth science and geological history. 4.2 STUDIES AND INVESTIGATIONS 4.2.1 Introduction This section provides a brief description of studies and investigations carried out in the area. Detailed description of previous geotechnical studies and investigations is contained in the Interpretative Geotechnical Report (HPR, 1999a) and the Addendum Interpretative Geotechnical Report (HPR, 2006). 4.2.2 Topographic Surveys Topographic surveys were carried out in 1987 and 1995, and a land-based GPS survey was carried out in 2003 for the Urgent Advanced Works. Most recently, a topographic survey was carried out in 2005/2006 by Merrett Survey Partnership covering the Phase IV study area (see Figure 1.1) including Timber Hill and the western part of the Spittles area. The survey is based on the detailed results from the Light Detection and Ranging (LIDAR) survey to the eastern part of the study area, and the conventional land-based GPS derived survey for the western part. This was surveyed at a nominal 10m grid with interpolated 0.5m interval contours. There are a few areas which have not been surveyed due to dense vegetation cover and access difficulties. 4.2.3 Ground Investigation Additional sub-surface ground investigation is being undertaken at the allotments, the Spittles and at Timber Hill Meadows to collect ground and groundwater information, specifically to locate the positions of the principal landslide-controlling marker beds and to gain information on the nature and thickness of the overlying landslide deposits. Detailed description of the ground investigation is contained in the Addendum Interpretative Geotechnical Report (HPR, 2006). Also, logging of new 4-4

geological exposures was carried out in October 2006 as part of the ground model update (HPR, 2007c). As part of the earlier Preliminary Studies, a ground investigation was carried out by Exploration Associates in 1997, and an interpretative report was prepared by HPR in 1999 (HPR, 1999a). Since the 1997 ground investigation, additional ground information has been obtained from supplementary ground investigations, namely: A ground investigation carried out in the Church Cliffs area in 2003, comprising three window sample holes to provide information for the design of the 2003-2004 Urgent Advanced Stabilisation works; Natural gamma logs from pile holes drilled during the 2003-2004 Urgent Advanced Stabilisation works, at both Church Cliff and East Cliff; Levels taken on exposed geological marker beds; and Detailed geological mapping of the cliffs and foreshore by Dr R W Gallois in 2005. This additional information has been used in the recent update of ground model sections and the stability analyses of landslides, and the findings are reported in the Addendum Interpretative Geotechnical Report (HPR, 2006) prepared as part of the current Phase IV Preliminary Design Studies. 4.2.4 Landslide Monitoring Instrumentation including ground surface markers, inclinometers and piezometers was installed in the previous ground investigations. WDDC has been monitoring the instrumentation from 1997 to date. The results of monitoring up to October 2006 were summarised in the Slope Stability Monitoring Report (WDDC, 2006) prepared as part of this Study. HPR and WDDC are working closely to review the monitoring results of the existing instrumentation. In addition, as part of the current Phase IV Preliminary Design Studies, recommendations on instrumentation have been made for design development. These recommendations are reported in the Recommendations on Instrumentation and Monitoring (HPR, 2007b) to replace the existing instrumentation that has become unserviceable due to landsliding or man-made activities and to assist with the further understanding of the landslide mechanisms and to provide more information of the extent and depth of the landslides. This recommended instrumentation for design development is currently being installed (March / April 2007). Additional instrumentation will also be installed for the detailed design if it is decided to stabilise the landslides or for use as ongoing monitoring if the do-nothing case is adopted. 4.2.5 Geomorphology and Ground Behaviour Studies A study on the geomorphology and ground behaviour was reported by High-Point Rendel (HPR, 1997). To record any major changes in geomorphology since the last study, and to identify the extent of western lateral expansion of the Spittles landslide, updated geomorphological mapping was carried out by High-Point Rendel, Professor D Brunsden and G Davis in October 2006. The updated geomorphology is presented in Addendum Geomorphology Report (HPR, 2007) prepared as part of this Study. 4-5

4.2.6 Geological Studies WDDC commissioned R Gallois to prepare geological reports on both Church Cliff/East Cliff and Monmouth Beach/Ware Cliff area (Gallois, 2005 and 2006). 4.2.7 Landslide Recession Scenarios The landslide recession scenarios were previously studied by High-Point Rendel (HPR, 2000c). Based on the additional information collected since the previous study, the landslide recession scenarios have been reviewed and reported in the Landslide Recession Scenarios (2007 update) Report (HPR, 2007a), prepared as part of this Study. 4.2.8 Conceptual Design Report (HPR, 2000b) HPR issued a conceptual design report for coastal slope stabilisation in 2000, with the objective to prepare a range of optimal generic designs to address the coast protection and slope instability problems at Lyme Regis. This included budget costs and time scales for implementation (HPR, 2000b). Two conceptual scheme options, namely the Strengthening and Drainage Solution (equivalent to Hold the Line Solution) and the Slope Buttress Solution (equivalent to Advance the Line Solution), were proposed as part of the coast management strategy to address the consequences of coastal erosion issues in developed areas where infrastructure, public safety and properties are at risk. The actions considered included monitoring, maintenance and stabilisation measures, and are listed below. The works common to both solutions are in italics. The Strengthening and Drainage Solution comprised Improving the natural drainage channels of the Meadows; Monitoring of the upper coastal slopes - The Meadows and Timber Hill; Maintaining existing drainage system along Spittles Lane; Granular counterfort drains through the Charmouth Road car park, connecting to cut-off drains along the southern edge of the car park; Grid of bored piles at close centres and granular trench drains across the main slip of East Cliff; Granular fill or reinforced earth placed against the rear and side scarp slopes of the main slip of East Cliff; Surface netting and vegetation over the sea cliff slope; Arrays of sub-horizontal drilled drains along East Cliff and Church Cliff; Ground anchors over the eastern part of Church Cliff; and New coast defence (either new seawall or new rock armour revetment). The Slope Buttress Solution comprised Improving the natural drainage channels of the Meadows; Monitoring of the upper coastal slopes - The Meadows and Timber Hill; Maintaining existing drainage system along Spittles Lane; 4-6

Granular counterfort drains through the Charmouth Road car park, connecting to cut-off drains along the southern edge of the car park; Slope buttress using imported engineered fill in front of existing coastal slopes (buttress gradient varies from 1v:2h to 1v:5h); Trench drains and drainage blanket within buttress; New coast defence (either new seawall or new rock armour revetment) seawards of the current alignment; and New walkway along the new coast defence. 4.2.9 EPR Ecological Survey (2006) 4.2.9.1 Introduction The details of the ecological survey, carried out to review and validate the 2002 EPR survey, are included in the ecological survey report (EPR, 2006). For clarity purpose, below is a summary of key points in the survey report. Before going into any detail about the individual surveys, it must be noted that the degrees of importance between the individual sections vary. One of the most important ecological aspect of the Jurassic Coast is the vegetation. This is one of the reasons for the area being designated as a Special Area of Conservation (SAC). The Lyme Regis Undercliff is also designated as a National Nature Reserve (NNR) due to the mix of vegetation and the associated habitats which it provides. Consequently, without the vegetation cover, the invertebrates, reptiles and other fauna would cease to inhabit the area. Subsequently, it must be noted that the mitigation should primarily focus on creating equivalent habitat features, including bare ground, a mosaic of vegetation from pioneer to scrub and water bodies. 4.2.9.2 Reptile Survey This investigation found that there were four main reptilian species present in the area making the survey area important due to this assemblage. The species found were: the Slow Worm (Anguis fragilis); Viviparous Lizard (Zootoca vivipara); Grass Snake (Natrix natrix); and the Adder (Vipera berus). Even though none of these species are under any individual legislative protection, they are protected under the Wildlife and Countryside Act 1981 which stipulates that they are protected from killing or injury. The majority of the reptiles recorded were found at East Cliff, but they are present throughout the survey area, mainly within hedgerows. Adders are particularly of interest for this survey because they are a short-migrating reptile species which implies that the zone of influence may go beyond the works area, and a possibility that there could be a dramatic decline in adder activities. Should vegetation stripping of the works area be required, this will result in a loss of reptile habitat, and may also result in injury and/or death to individuals trapped within the works site. Therefore the translocation of species is required in order to mitigate negative impacts upon the reptile population. 4-7

Any proposed stabilisation works may prevent any increase in suitable reptile habitat due to a reduction in future landslips, however after the completion of works the associated impact of construction and translocation should be short-term due to the abundance of slow worm, but this may not be the case for other species. The area would undergo a degree of drainage alterations which may also have adverse impacts upon the habitat and food sources of reptiles. Without mitigation this scheme could result in negative impacts to the present reptile populations. In order to protect the reptile population translocation, habitat enhancement and restoration are required. In addition, sufficient time should be allowed for the translocation from the scheme footprint to avoid any unnecessary delays. 4.2.9.3 Dormouse Survey Within the survey area suitable habitat is present. These are mainly within the hedgerows of Timber Hill Meadows and to a lesser extent within scrub on the old tip, plus some more isolated parts which proved difficult to get to and at times were inaccessible. Dormice (Musardinus avellanarius) are a European designated protected species, and fall under the Wildlife and Countryside Act 1981. This prohibits the killing, injuring or taking, as well as possession and trade. Also, places used for shelter, protection, habitation or breeding are safeguarded against any disturbance. Therefore a licence is required from Natural England (formerly DEFRA) prior to any work. The main concern for the Dormice in the area comes from the vegetation stripping as the impacts would come from habitat destruction or fragmentation if whole or parts of the hedgerows are removed. Therefore, the vegetation needs to be cleared in a sympathetic manner and under ecological supervision of an adequate party prior to any work commencement with any hedgerow containing a large proportion of Hazel to be protected as these are the most likely areas for the Dormice to be in habitation. However, any habitat loss as a result of development needs to be restored after completion which provides scope for habitat enhancement by increasing the connectivity between suitable habitat areas. Mitigation is required in order to limit any degrading impacts to Dormice habitat, mainly within the scrub on the old tip and within hedgerows. 4.2.9.4 Invertebrate Survey The instability of the area has created a mosaic of habitats for a diverse variety of invertebrates. There were a total of 354 species of invertebrates recorded. The key species being the Bee Wolf (Phinanthus triangulum), which had the status of being Nationally Endangered/Vulnerable/Rare (but no longer due to increased numbers over the last 10 years), and 18 other Nationally Notable species making the area of national importance. 4-8

However, within the survey area there were no BAP species recorded nor the two target species the Morris Wainscot Moth (Photedes morrissii) and a Mining Bee (Lasioglossum laticeps). Overall, the total number of noteworthy species recorded during all surveys to date is 2 RDB2, 4 RDB3 and 35 Nationally Notable species. During the construction phase there will be a significant destruction of habitat through the vegetation scouring and possible adverse impacts from changes in hydrology. These works will have a localised impact on the invertebrates; however, because they are mobile this should only be a short-term problem. Habitat creation opportunities should be encouraged and may need to be managed properly in order to provide long-term benefits, and these should include wetland areas, patches of vertical and horizontal bare ground in clay and sandy soils should be created in newly sown herb-rich grassland to provide a variety of nectar sources and larval host plants. 4.2.9.5 Botanical Survey Summary The area surveyed is under the designation of a SSSI due to the geological importance of the site; however there is also a diverse array of habitats present, from mature woodland to pioneer plant communities. The botanical survey conducted by EPR did not record any Red-Data-Book, Nationally Rare, Nationally Scarce or even Dorset Rare species on East/Church Cliff, however, there were 11 unimproved grassland indicator species recorded from Timber Hill Meadows along with 20 Dorset Notable species. This implies that the meadows are a high quality botanical habitat. Japanese Knotweed was found to be present on the sea cliff and within the field boundaries. It may also be found in some of the more inaccessible areas which were unable to be surveyed due to health and safety reasons. This species needs to be dealt with accordingly before any development can occur. Timber Hill Wood has been classed as not part of the SAC selection for a priority area because it does not correspond to the required 9180 Tilio-Acerion (Ash, Elm and Lime) criteria due to young and under-developed patchy areas, but it is of importance under the 1230 Vegetated Sea Cliffs of the Atlantic and Baltic Coasts. If the Church Cliffs remain stable the current patches of scrub with trees would increase in cover and would thus develop into an example of the Tilio-Acerion habitat. The study area contains four UK Biodiversity Action Plan (BAP) Habitats. These are found in the landslip area, containing Maritime Cliff and Slopes; and in the Timber Hill Meadows area where there are Ancient and/or Species Rich Hedgerows, Lowland Meadows and Purple Moor Grass and Rush Pastures. An Appropriate Assessment will have to be carried out under the Habitats Regulations, due to the works having the potential to adversely affect the integrity of the SAC. 4-9

4.2.10 Environs Landscape Conceptual Design (2001) This report was prepared to assist WDDC in the conceptual design of the coastal protection measures in terms of landscape, amenity, access and nature conservation for the East Cliff area. It considered both the HPR strengthening and drainage, and the slope buttress options, and a further hybrid bay and buttress scheme. 4.2.11 Environs: Landscape and Visual Baseline Report (2007) As part of the current Phase IV Preliminary Design Studies, Environs Partnership have carried out a review of the landscape baseline which includes landscape character areas and public access considerations. The report concludes with some mitigation design strategy recommendations. All stabilisation works will include environmental restoration works integrating both ecological and landscape mitigation considerations. Environmental restoration options will be considered in developing the preferred options. 4.3 THE LANDSLIDING PROBLEM Lyme Regis has a long history of coastal instability and landsliding, which over the past century or so has been recorded in a variety of published and unpublished reports, and other media. Some of the most significant consequences of landsliding at the coastal slopes east of the town have been listed in the Interpretative Geotechnical Report (HPR, 1999a); these include: Recession of the seacliff due to marine erosion, quarrying and landsliding, prior to construction of the seawall at East Cliff and Church Cliffs; Destruction of various buildings due to landsliding on the lower coastal slopes of East Cliff between 1903 and 1929; Landsliding in front of Cedar Cottage between 1933 and 1951; Outflanking erosion at the eastern end of the seawall; Accumulation of landslide debris on the top of the seawall; Since 1999, significant movements have occurred on the lower coastal slopes to the south of Charmouth Road car park, and in the slopes below Church Cliff Flats in 2002. Key issues relating to the problem of land instability due to marine erosion resulting from the current and previous studies are as follows:- The study area (Figure 1.1) is sub-zoned as landslide key areas as shown in Appendix I - Drg. No. PH4\PD\210, based on the type of landslide mechanisms and their characteristics. Instrumentation monitoring has confirmed that surface and sub-surface movements of the coastal slopes are widespread and ongoing. The monitoring data is summarised in Slope Stability Monitoring Report (WDDC, 2006). The landslide mechanisms are described in the Interpretative Geotechnical Report (HPR, 1999a), the Addendum Interpretative Geotechnical, the Addendum 4-10

Geomorphological and the Landslide Recession Scenario (2007 update) reports (HPR, 2006, 2007, 2007a). The key points are as follows:- o The existing seawall shows both vertical and horizontal cracks (see Section 3.3). Some of the horizontal cracks appear to suggest a forward movement of the upper section of the wall in relation to the lower section. This is considered to be principally due to the thermal action although partial cause resulting from lateral expansion of the seacliff as a result of weathering and/or stress relief, or landslides on the coastal slopes above the seawall. o The steep sea cliff above the top of seawall shows shallow failures, which are due to over-steepening of the sea cliff as a result of marine erosion prior to construction of the seawall, susceptible geology and groundwater. This is evident, for example, from the ground model Section 16 as shown on Drg No. PH4\PD\206 in Appendix N. The position of the section line is shown on Drg No. PH4\PD\224 in Appendix N. o Mudslides and translational block slides occur on the lower coastal slopes to the south of Charmouth Road car park and above the seacliff of East Cliff; these landsliding areas are designated as East Cliff Main Slip and Allotments West on Drg. No. PH4\PD\210 in Appendix I. The landslides are shown on ground model Sections 10,11,12,19 and 20 on Drg. Nos. PH4\PD\203, 204 and 208 in Appendix N. The mudslides are lithologically controlled, with the base of the mudslides typically about 2m above limestone marker beds, e.g. Grey Ledge, Fish Bed and Table Ledge. The landslide system comprises two distinct failure mechanisms. The lower one above the Grey Ledge / Fish Bed is typically a mudslide, and the upper one above the Table Ledge is typically a blockslide, i.e. a translational failure. The base level of the upper failure appears to be associated with the base of Disturbed Lias material. Based on the instrumentation monitoring, the mudslides are continuing to move forward with the potential of loading the head of sea cliff, and regression of the rear scarps. o The steep unprotected sea cliff below the Allotments West and Allotments East to the east of the existing seawall continued to retreat as a result of coastal erosion. Record shows that the sea cliff retreated by 5 to 10m in a period of 10 years (1995 to 2005). o The middle coastal slope as shown on Drg No. PH4\PD\210, extending from the Charmouth Road car park to the Meadows, consists of reactivated elongate mudslides. A ground model Section 2 through this area is shown on Drg No. PH4\PD\202 in Appendix N. The mudslide deposits are shallow and the base of the deposits are controlled by the principal limestone marker beds. This has resulted in a benched or stepped ground profile with the thickness of mudslide deposits about 5m towards the rear of each bench and thinning towards the front. o The upper slopes at Timber Hill and the upper part of the Meadows (Drg. No. PH4\PD\210) have been affected by compound landslides developed in the Cretaceous Upper Greensand stratum. Ground model Section 2 through this area is shown on Drg No. PH4/PD2/202 in Appendix N. The 4-11

basal shear surface is about 20m below the Old Charmouth Road at the unconformity with the Black Ven Marls. There is a steep back scarp to the north of Old Charmouth Road with an active break of slope. The Timber Hill area is heavily wooded, with some trees leaning backwards due to deep seated rotational landslide movement. o At the landslide key areas of Church Cliff and Church Cliff Flats (Drg No. PH4\PD\210), there are two types of landslide systems, including translational block slides and shallow slips to the face of sea cliff. Ground model sections 17, 17a and 18 in these areas are shown on Drg. No. PH4\PD\207 in Appendix N. The translational block slides are developed above Table Ledge. o From historic records, ground movements due to landsliding have been responsible for significant structural damage and loss of property. The ground movements are still on-going and spreading. If these problems are not addressed, ground movement will undoubtedly continue in the form of slow almost continuous creep of small magnitude and sporadic, more rapid, landslide events. The existing and any new coastal defences would be damaged and the residential buildings and the vital infrastructure, including Charmouth Road, could become unserviceable, and some buildings could be under an imminent danger due to landsliding. The town of Lyme Regis would be substantially affected economically by the loss or the closing down of Charmouth Road, being the only access to the town from the east. This is discussed in greater detail in the Landslide Recession Scenarios (2007 update) Report (HPR, 2007a). 4.4 DESIGN PHILOSOPHY AND PARAMETERS 4.4.1 Design Life The design life of stabilisation measures is taken as 60 years from the implementation of the Phase IV scheme. 4.4.2 Ground Models The ground model cross sections were selected to represent each main landslide area. These ground model sections are contained in the Addendum Interpretative Geotechnical Report (HPR, 2006), and are also included in Appendix N of this report together with the location plan, Drg No. PH4\PD\224. Ten ground model sections, 2, 10, 11, 12, 13, 14, 15, 16, 17 and 18, were developed in 1999 based on the geomorphological mapping information and the 1997 ground investigation, as part of the Interpretative Geotechnical Report for Phase IV East Cliff (HPR, 1999a). A further five ground model sections, 17A, 19, 20, 21 and 22, across the Church Cliff and East Cliff areas were developed during the Urgent Advanced Works in 2003. Further information on the topography and ground conditions has since been obtained, and used to update and re-interpret the ground model sections. This is discussed in greater detail in the Addendum Interpretative Geotechnical Report (HPR, 2006). 4-12

The fifteen ground model sections cover the coastal slopes up to the eastern end of the existing seawall below the allotments. To assist in understanding the ground behaviour and the change in topography from the coastal slope area to the Spittles area, six additional ground model sections, 23 to 28, have been developed. Since little ground investigation has been undertaken on areas to the east of the coastal slopes, a walkover to identify and record marker bed exposures was carried out to assist developing these additional ground model sections. These additional cross sections are included in the Addendum Interpretative Geotechnical Report (HPR, 2006). The characteristics of landslide systems across the coastal slopes have been reviewed during the update of the ground model sections, and a plan of principal landslide areas Drg No. PH4\PD\210 (Appendix I) has been prepared to show the different landslide areas. Appendix J summarises the characteristics of each landslide system. 4.4.3 Design Approach Possible scheme options have been developed with the objective of improving the stability of the coastal slopes. The degree of improvement required is that considered necessary to protect the foreshore protection works from being damaged by landslide debris, and to arrest landslide regression / progression such that infrastructure and property are safeguarded. Back-analyses of the failure mechanisms of the various landslide key areas were carried out as part of the current Preliminary Design to estimate the water pressures that satisfy the limit equilibrium condition, i.e. the factor of safety on slope stability being equal to unity, considering the soil strength parameters provided in the 1999 Interpretative Geotechnical Report (HPR, 1999a). The back-analyses of the failure mechanisms of the key landslide areas are reported in the Addendum Interpretative Geotechnical Report (HPR, 2006) as part of this Study. The scheme options for the whole of the Phase IV Study area have been developed and evaluated through the following stages for the ultimate purpose of development of a preferred scheme. (1) Identification and compilation of a list of generic options; (2) Development of area specific scheme options for each principal landslide area on the basis of generic options; and (3) Selection of the preferred area specific scheme solution for each landslide key area for both Hold the Line and Advance the Line schemes; 4.4.3.1 Generic Options Since each principal landslide area as shown on Drg No. PH4\PD\210 in Appendix I has different characteristics, it is considered technically better to develop outline coastal slope stabilisation scheme options specific to each of these principal landslide areas. In facilitating the development of these outline scheme options specific to the landsliding areas, a list of generic slope stabilisation options has been prepared and these are shown in Appendix K. 4-13

The generic options are broadly divided into primary and secondary elements. Primary elements are designed to provide the necessary resistance to stabilise the active and potential slips. Secondary elements include stabilisation measures which are used to maintain the current level of serviceability of a slope, and remedial measures providing stabilising actions to the incipient failure planes. Secondary elements are always prescriptive, and are specified based on engineering judgement and experience. Some types of primary elements can also be specified as secondary elements. Primary elements are principally grouped into four categories: 1. Drainage measures; 2. In situ reinforcement; 3. Structural solutions; 4. Rebuild techniques. Drainage measures: Drainage measures, including cut-off drains, counterfort drains, trench drains, sub-horizontal drilled drains and deep well drains, are used primarily i) to draw down the groundwater table, or ii) to relieve pore water pressures in the soil, or iii) to intercept groundwater and/or surface runoff into the slope. Except for deep well drains with pumps, most of the proposed drainage measures are gravity systems. The provision of drainage can also reduce the likelihood of soil softening resulting from wet and dry cycles. Some of these drainage measures, including subhorizontal drilled drains and pump-operated deep wells, would require higher levels of maintenance. In-situ reinforcement: In-situ reinforcement techniques are those in which the soils are reinforced by dowel piles or soil nails. Generally, the amount of earthworks involved is minimal. Structural solutions: Structural solutions, including embedded retaining walls and other types of retaining walls, enhance overall slope stability by penetrating through the active slip surface or provide lateral support. They are generally more costly to build, but are of low maintenance and low design risk. Rebuild techniques: Rebuild techniques involve more substantial earthworks, and include shear keys, slope re-profiling, excavate and recompact, and lime/cement stabilisation. The objective is to remove the whole or part(s) of the slip mass, and to provide drainage measures by means of drainage blanket or trench drains. In most cases, some measures are required to maintain the temporary stability of the excavated slope. Secondary elements comprise slope surface protection and erosion control measures, e.g. surface netting, vegetation and sprayed concrete, and surface drainage measures. 4.4.3.2 Area Specific Scheme Options The area specific scheme options for each principal landslide area (Appendix I, Drg No. PH4\PD\210) have been developed on the basis of each of the four categories of primary stabilisation works, or their combinations. Table L1 in Appendix L shows a 4-14

summary of the different primary elements considered for each principal landslide area. The eligibility of each category of primary works, and their combinations, to each principal landslide area has been evaluated with due considerations of the technical suitability, physical constraints and health and safety. In a principal landslide area, one or more category/ies of primary works may not be appropriate in view of these factors, and therefore there may be not one area specific scheme option developed based on such category/ies of primary works. It must be noted that these options are conceptual and the details are subject to further design. The area specific scheme options for each area are summarised in a series of tables in Appendix L. Each table contains a cross-section showing the proposed works, describes the option, the primary elements adopted and their technical purposes, and comments on the various technical considerations and critical environmental impacts. Schematic construction sequences for these area specific scheme options are contained in Appendix S. 4.4.3.3 Options Selection A multi-modal analysis has been carried out to evaluate the scheme options to facilitate the selection of the preferred solution for each principal landslide area. The analysis involved assessment of considerations under two broad categories, namely the technical considerations and the critical environmental impacts. The technical considerations were qualitatively rated according to a 5-level relative merit evaluation system with equal weighting. This 5-level relative merit evaluation system has been proposed to maintain simplicity and to provide the basis for identifying the technicallypreferred solution amongst the options. The critical environmental impacts of the options for each landslide area were also evaluated. The overall merits of each scheme option have been compared and discussed to determine the preferred solution through discussion between WDDC and the design team, and consultation with others. The technical considerations are listed and briefly explained below:- T1) Buildability - This item considers the level of difficulty in constructing the scheme relating to the site specific physical conditions, including accessibility. T2) Design risk - Uncertainty in ground and groundwater conditions that could result in risk of inadequate design or failure of the scheme. The probability of occurrence of these uncertainties and risks could be reduced by additional ground investigation or pre-works construction trials. Where this is appropriate, the level of design risk after such risk mitigation is also included in the assessment. T3) Maintenance - This relates to the frequency of maintenance, and the associated maintenance works, the engineer s 4-15

inspection and constraints. T4) Cost - This is the construction cost only. Costs relating to detailed design, additional ground investigation, construction supervision and maintenance are not included. T5) Construction impacts - These include potential noise and dust generated during construction, and the intensity of traffic movement relating from the delivery of construction materials and muck shift. The critical environmental impacts are listed and briefly described below. These impacts can be reduced by modifications to the engineering solution, and the environment can be enhanced by including appropriate restoration measures, e.g. regeneration of habitat and landscape, and providing access to geological exposure. C1) Ecology - Removal or disruption of the existing habitat, and the potential for regenerating habitat in the preferred scheme C2) Geology / Geomorphology - The impact on the existing geological exposure and geomorphological features, and the potential of promoting public interest in geology and geomorphology and improving public access C3) Landscape - Removal or disruption of the existing landscape features, and the proposed restoration works to reestablish an appropriate landscape in keeping with the setting of the scheme. 4.4.4 Climate Change Considerations Climate change is envisaged to have a significant adverse effect on the stability of the coastal slopes during the design life of this coastal protection scheme. Climate changes in the UK are likely to result in higher sea level, wetter winters, drier summers and warmer temperature. All these would adversely affect the stability of the coastal slopes. The rise in sea level has already been discussed in Section 3.4.4 of this report. The significant increase in the frequency of wet years was addressed in the HPR s Landslide Recession Scenario report (2000). The report states that it is possible that what is now a 1 in 100 year rainfall total (around 520mm) could become the equivalent of a 1 in 30 year rainfall total in 25 years (annual probability = 0.03) and a 1 in 12 year rainfall total in 50 years (annual probability = 0.08). If drainage measures are not provided, it is likely that the coastal slope materials could potentially soften quicker due to the change in rainfall pattern. This factor has been addressed in the Landslide Recession Scenario (2007 update) Report (HPR, 2007a). 4-16

It is therefore recommended that the design of stabilisation measures should consider the potential for groundwater level to rise or for groundwater pressures to rise due to climate change. However, the existing groundwater conditions are very complicated because of the effect of under-drainage provided by the more permeable marker beds, and the presence of faults and debris abutting outcrops that are known to affect the drainage continuity of the marker beds. This means that it is not possible to adopt a uniform rise in groundwater level over the strata or to predict accurately such rise. For shallow active shear surfaces, it can be assumed with certainty that water level will not rise higher than ground level. For deeper-seated failures, it is necessary to consider whether groundwater level may rise above the base of the first marker beds above slip surfaces. Where drainage measures are included in the stabilisation scheme, the groundwater rise could be different from these assumptions and will be considered in each case. Further discussion on how climate change was considered in the design of Lyme Regis Environmental Improvements Phase II works is given in Fort et al (2007). 4.4.5 Design Parameters The design parameters are presented in the Addendum Interpretative Geotechnical Report (HPR, 2006). 4.5 SLOPE MANAGEMENT OPTIONS 4.5.1 Introduction The principal options considered for the development of the recommended options are: Do nothing Minimum intervention and maintenance Hold the Line solution Advance the Line solution The development of each option is described below. 4.5.2 Do nothing The Do nothing option is the basis on which the landslide recession scenarios have been considered in the Landslide Recession Scenarios (2007 update) Report (HPR, 2007a). The potential of lateral expansion of the Spittles and the Black Ven landslide complexes into the Phase IV slope area has also been considered. Monitoring of existing and new instrumentation should continue, and the data should be reviewed regularly. Trigger levels should also be determined, beyond which urgent actions should be taken. Based on the landslide recession scenarios, it is likely that there may be complete loss of the property, services and the infrastructure within the whole Phase IV Study Area within the next 30 to 50 years. Therefore, the Do nothing approach is not viable in order to protect property and infrastructure. 4-17

4.5.3 Minimum intervention and maintenance The minimum intervention and maintenance option has been considered to ensure the functionality of the existing road and slope drainage systems. These comprise: Monitoring of existing and new instrumentation; Repair existing drainage system; Clear ditches and streams; and Repair works as local slope failures develop. The integrity of the existing drainage system along the Charmouth Road should also be investigated and checked. Repair and improvement works should be carried out as necessary. These works, however, will not improve the stability of the coastal slopes, nor suppress slope recession. The properties and infrastructure would continue to be under the threat of coastal instability and therefore this approach is considered not to be an viable option to protect the property and infrastructure in the medium and long term. 4.5.4 Area Specific Scheme Options 4.5.4.1 Introduction For protection of the coastal slopes, there are basically two broad types of engineering solutions, i.e. Hold the Line and Advance the Line. Hold the Line involves improvement of the existing line of defence or construction of a new seawall, protective facing or new revetment immediately in front of the existing seawall with slope stabilisation works behind. Advance the Line involves construction of a new line of defence seawards of its present position, and placing engineering fill in the area between the existing and new lines of defence to create a buttress to support the unstable coastal slopes. A hybrid solution, involving combination of both Hold the Line and Advance the Line solutions at different locations along the lower coastal slopes, has also been considered. In all area specific scheme options, it is recommended to include the following: Establishment of a long term monitoring strategy; Investigation and checking of the integrity and adequacy of the existing drainage system along the Charmouth Road and adjacent areas, including Spittles Lane and the car park, and repair and improvement works as necessary; Improvement works to the natural drainage streams and ditches across the Timber Hill and the Meadows. All area specific scheme options have been considered with respect to technical requirements and the critical environmental impacts for the selection and finalisation of the preferred scheme. All area specific scheme options in Appendix L show the primary elements only, and secondary elements will be included in further developing the solution. 4-18

4.5.4.2 Lower Coastal Slopes: East Cliff and Church Cliff Hold the Line option Hold the Line option has been developed for each of these landslide areas (Drg No. PH4\PD\210 in Appendix I) and are summarised in a series of tables in Appendix L. The development of scheme options is explained below. These options are conceptual and the details are subject to further design (Stage E, see Section 1). East Cliff Main Slip and Allotment West East Cliff Main Slip side scarp; East Cliff Lane; Cedar Cottage; Church Cliff Flats; and Church Cliff East Cliff Main Slip and Allotment West (Section 11) The landsliding areas East Cliff Main Slip and Allotment West are located to the south and east of Charmouth Road car park respectively. The East Cliff Main Slip has a partly vegetated landslide system comprising two principal landslide benches with a steep scarp between benches at the rear and above the seawall. These landslide failure mechanisms are stratum-controlled mudslides and translational block slides on Fish Bed and approximately 2m above Table Ledge. Area specific scheme options have been developed based on all categories of primary works. The mudslides and blockslides in these areas are relatively wet, and therefore counterfort and trench drains (Drainage Measures) are considered feasible to reduce the pore water pressure in soil. The landslide benches are also generally level which allows installation of dowel piles (In-situ reinforcement) and construction of buried piled wall (Structural Solution) with lower risk of heavy plant working close to or on steep slopes. Other in-situ reinforcement such as soil nailing, however, is not technically feasible for stabilising these translational or blockslides which are undergoing near-horizontal movements. Because the landsliding areas are also close to the Charmouth Road car park, which can provide immediate access/egress for earthworks movement into and out of the landsliding area, excavate and recompact option (Rebuild Technique) is considered feasible. East Cliff Main Slip side scarp (Section 14) The steep side scarp is located to the west of the main slip area, and there are properties very close to the crest of the side scarp. There is very limited access to the crest of the side scarp. Due to the steep gradient of the scarp and the limited access, only soil nailing (In-situ Reinforcement) and earth fill buttress (Rebuild Techniques) are considered feasible. For the earth fill buttress options, piles could be required to provide structural support to avoid loading the main slip area. East Cliff Lane (Section 15) East Cliff Lane landslide area consists of a steep and densely vegetated sea cliff with some landslide benches. The area directly above the existing seawall is heavily vegetated and is known to include tipped garden waste of unknown thickness. In 4-19

view of the depth to the base of the slip and the close proximity of existing properties to the slip, it is considered not feasible to develop a scheme option relying solely on drainage measures. An excavate and recompact option (Rebuild Technique) can be made feasible with temporary support such as an embedded piled wall or soil nails to support the temporary cut face. The embedded piled wall or dowel piles (In-situ Reinforcement) can be installed through access at East Cliff Lane or East Cliff slip area. Cedar Cottage (Section 16) The principal landslide area, Cedar Cottage, consists of bowl shaped garden areas, sloping gently towards the sea with mature vegetations. The failure mechanism is believed to be circular slip directly above the Table Ledge marker horizon. The steep coastal slopes below the Table Ledge have been subjected to shallow failures. Drainage measures and rebuild techniques are considered not viable to stabilise the circular slip directly above the Table Ledge marker horizon, in view of the nature of the slippage and the close proximity of the existing properties to the slip. Implementation of rebuild technique could be difficult because of the lack of immediate road access. However, the slope above the Table Ledge is not so steep and therefore installation of anchored piled wall (Structural Solution) and dowel piles (In-situ Reinforcement) can be feasible, provided an access could be made from the adjacent East Cliff Lane landslip area. For the steep coastal slopes below the Table Ledge but above the seawall, prestressed ground anchors (Structural Solution) and soil nails (In-situ Reinforcement) are considered. Church Cliff Flats and Church Cliff (Sections 17a & 18) The two principal landslide areas - Church Cliff Flats and Church Cliff are about 100m in total length. Along the crest of these landsliding areas, there are the graveyard of St. Michael s Church and a number of residential properties. These landslide areas consist of steep highly vegetated coastal slopes. The failure mechanisms consist of shallow failures in Shales-with-Beef with some indication of stratum control on Table Ledge and/or Fish Bed. In the winter of 2002, a landslide in front of Church Cliff Flats and No 45 Church Street occurred resulting in recession of the seacliff edge. To prevent the continued coastal slope recession from endangering the stability of existing properties, Urgent Advanced Stabilisation Works were completed in 2004 to stabilise an approximately 35m length of the area. The Urgent Advanced Stabilisation Works comprised two rows of piles restrained laterally by cross-beams (Structural Solution). The details of the design were reported by High-Point Rendel (HPR, 2003a). Rebuild technique is considered not viable in view of the close proximity of the existing properties at the crest of the coastal slopes. In view of the shallow depth of the observed landslides, it is considered viable to develop options involving counterfort drains and sub-horizontal drilled drains (Drainage Measures) or soil nailing (In-situ Reinforcement). 4-20

Advance the Line option The Advance the Line option has been developed for these representative landslide areas: East Cliff Main Slip; East Cliff Lane; and Church Cliff Flats However, the option can, in principle, be adopted for all areas. In developing Advance the Line options, two types of imported fill have been considered to construct the buttress; they are cohesive fill (or clay fill) e.g. possibly from a local source, and granular fill, including sand and gravel. The use of rock fill forming steeper slopes towards the toe of the buttress has also been considered, to minimise the footprint of the slope buttress on the foreshore. All options have been found to be technically viable, and the final geometry of slope buttress will depend on the availability and cost of source fill and the environmental requirements. The approximate distance of the toe of the buttress from the existing seawall, assuming that the new sea defence will be of similar crest elevations to the existing seawall, is estimated to be: Table 4.5.1 Distance of toe of buttress from existing seawall (excluding width of coastal defence) Slope buttress toe Rock fill berm No rock fill berm Type of Fill Cohesive Fill Granular Fill Cohesive Fill Granular Fill Area East Cliff Main Slip and Allotment West (Section 11) 19m [B/11/1]# 11m [B/11/2] 51m [B/11/3] East Cliff Lane (Section 15) 17m [B/15/1] 14m [B/15/2] 50m [B/15/3] Church Cliff Flats 17m 11m 56m (Section 17a) [B/17a/1] [B/17a/2] [B/17a/3] Note: # Reference table no. in Appendix L is shown in square brackets 15m [B/11/4] 14m [B/15/4] 14m [B/17a/4] The distances of landtake on the foreshore from the existing seawall are these distances plus the width of any footpath or vehicular access, and the width of the new seawall / new coast defence structure (see Section 3). Hybrid option A landscape conceptual hybrid solution, or Bay and Buttress solution, was developed by Environs in 2001 and presented in the Preliminary Environmental Appraisal (HPR, 2003). The conceptual landscape solution comprised creating a bay at Church Cliff by slope strengthening / drainage works and construction of a buttress for stabilisation of East Cliff. The details of the strengthening / drainage works and slope buttress works were based on the recommendations provided in the Conceptual Design Report (HPR, 2000b). This geometry was one of the options tested by HR Wallingford (see Section 3.5.7.2 HR Wallingford, 2003). At that time however the slope works were purely conceptual and had not been subject to geotechnical design. 4-21

The approximate distance of landtake on the foreshore from the existing seawall at East Cliff along ground model Section 11 has been compared with that shown on the conceptual landscape design drawing in the Preliminary Environmental Appraisal (HPR, 2003). It is found that the toe of the buttress shown is similar to the outline option design if a granular fill material including a rock berm is considered. However, the toe of the buttress will be further away towards the sea for cohesive fill material (see Appendix M Drg No.PH4\PD\403). 4.5.4.3 Middle and Upper Coastal Slopes The middle coastal slopes are largely developed with properties and artificially made terraces to accommodate the football ground and Charmouth Road car park. Allotment gardens are present to the east of the football ground and Charmouth Road car park. The upper coastal slopes are largely undeveloped comprising pasture / grazing land and wetland areas. Area specific scheme options have been developed on the basis of various forms of drainage (Drainage Measures) and dowel piles (In-situ Reinforcement) to avoid works within the undeveloped land under the ownership of National Trust. A range of schemes has been considered and is presented in tables contained in Appendix L. Essentially these options comprise: Dowel piles along Old Charmouth Road; Deep drainage along Old Charmouth Road; Cut-off drainage along Spittles Lane and Charmouth Road car park; and Improvement to the natural surface drainage. 4.5.5 Lateral Extent of Works 4.5.5.1 Town Dump and The Spittles The landslide areas further east of the Phase IV study area include Town Dump and the Spittles. The Town Dump landslide area comprises an old disused landfill site above the steep sea cliff. WDDC have commissioned WPA Consultants Ltd and Bournemouth University to investigate the Town Dump area. The Spittles complex is outside the Phase IV study area as shown in Figure 1.1. The landslide complex consists of a series of terraced cliffs and was formed as a result of reactivation of relic landslide by recession of the sea cliff. This resulted in extension of landslide activity upslope towards Timber Hill and westwards towards Lyme Regis. It would however be considered not practical and economical to implement a stabilisation solution on this complex. 4.5.5.2 Allotments West and Allotments East (east of existing seawall) These landslide areas are located just above the eastern end of existing seawall and are close to the East Cliff Main Slip area. The sea cliff below part of Allotments West and the whole of Allotments East is unprotected, and sea cliff retreat has occurred due to coastal erosion. 4-22

The Landslide Recession Scenarios Study for East Cliff and Church Cliff (HPR, 2007a) has estimated the probability of a range of outcomes occurring as a result of predicted landslide activity over the next 100 years, and one of the scenarios considered is the complete loss of property and infrastructure as a result of the continuing recession of the unprotected sea cliff. The study has concluded that if no coastal protection works for the whole of Phase IV area were undertaken at all, there would be at least 95% chance of occurrence of the complete loss of property, infrastructure etc in East Cliff and Church Cliff within the years of concern. The study has indicated that the continuing erosion and recession of the unprotected seacliff beyond the existing seawall has a significant contribution to the potential complete loss of property, services and infrastructure within the next 100 years. Therefore, to protect the existing foreshore defence from being damaged by landslide debris and to prevent the loss of properties and infrastructure, it is necessary to also undertake coastal protection works at the coastal slopes and the sea cliff below the Allotments West and Allotments East landslip areas. The coastal protection works would therefore extend to approximately 60m from the eastern end of the existing wall. The type of coastal protection works will also depend on whether Hold the Line or Advance the Line solution is implemented in the lower coastal slopes. Advance the Line for Lower Coastal Slopes If Advance the Line solution is selected for the lower coastal slopes, it will be required to build the fill buttress around the end of the existing seawall and the outflanked sea cliff. Therefore, the unprotected sea cliff below Allotments West and Allotments East will be buttressed. Hold the Line for Lower Coastal Slopes For Hold the Line solution, the options of foreshore coast protection works east of the existing seawall are discussed in Section 3.5.8. The options of the associated slope stabilisation works primarily depend on whether foreshore works will be undertaken that might cover partly the Geological Conservation Review (GCR) site no. 916. The behaviour of the coastal slope would be different if the sea cliff east of the existing seawall continued to retreat due to coastal erosion. If no foreshore protection was provided, the sea cliff would continue to recede. Based on the observed recession rate of the unprotected sea cliff, of which recession has happened since the seawall was built in 1957, the unprotected sea cliff below the Allotments East and West is likely to recede by another 30m within the 60 years design life of coast protection works. This would also outflank the eastern end of the seawall and would likely require some structural stabilisation measures, e.g. dowel piles or piled wall, around the outflanked zone to prevent instability from developing into the East Cliff Main Slip area. On the other hand, if foreshore protection was provided, further sea cliff recession would be stopped but the coastal slope above the sea cliff would likely continue to degrade in a similar fashion to the East Cliff Main Slip. Slope stabilisation measures would thus be required to prevent the development of landslide blocks from progressively receding upslope. One of the options is installing dowel piles along the coastal slope crest of the Allotments, but shallow failures on the coastal slopes in front of the dowel piles would still occur. Debris arising from the shallow failures in the coastal slope might fell on to the foreshore that could pose risk to the people on 4-23

the shore. Alternatively, soil nailing could be employed to stabilise the whole coastal slopes below the Allotments. 4.5.6 Public Access Considerations There is currently no access from Cobb Gate through the coastal slopes to the Charmouth Road car park. The existing coastal access from Cobb Gate to the east to Charmouth is under the threat of dilapidated groynes, and is only available at times of low tide. Access considerations relating to the foreshore works are discussed in Section 3.5.11. Should an improved and safe access be provided from Church Cliff Jetty along the length of the new foreshore works to the Charmouth Road car park, the design should consider providing access to geological exposures and sea cliff to promote public awareness of the geological significance of the area. Alternatively if foreshore access improvement is not to be implemented, consideration could be given to create a new access from the eastern end of the existing seawall up to the Charmouth Road car park area to provide an escape route. This access provision will be fully developed together with the foreshore works in the Preliminary Design of the preferred solution. 4-24

5 SCHEME OPTION COSTS An estimate of construction costs for the various coast protection options presented in Sections 3.5 and 4.5 has been prepared and is detailed in Appendix O and summarised in Tables 5.1 and 5.2 below. The cost estimate of the proposed land-based coastal slope stabilisation works has been divided into the principal landslide areas (Drg. No. PH4\PD\210). The proposed foreshore coast protection works associated with the existing seawall are considered as a single element. The unit rates included in Appendix O have been based on rates obtained for similar High-Point Rendel designed schemes currently being constructed in the UK, from schemes that were recently built and from industry standard database prices. The measurement of quantities has been estimated from the details contained within the suite of option drawings in Appendix M and from the results of the outline sizing exercise. It has been observed on recent High-Point Rendel schemes that the contractor s oncost percentage to cover contractors set-up, site costs, insurance, profit, other ancillaries etc, varies between 20% and 35% for small simple schemes and high risk complex schemes respectively. Due to the early development of the scheme options and the nature of the project this cost estimate has included an on-cost percentage of 35%. At this preliminary stage there are a large number of uncertainties involved in defining the construction works which may further influence the outturn costs. These include, for example; the confined working area of the site, the limited access available to and from the site and the restraints on access routes during the period of construction and due to the complex geological nature of the site, potential identification of unknown localised ground conditions/movements and potential influence of inclement weather restricting permissible activities on site. Consequently, in addition to the above base costs and on-costs, a contingency has been made to cover the cost of additional or amended items which become apparent during the course of further development to the outline scheme options. On the basis of the nature of this site, its location and that of the surrounding environment it is considered that a contingency of 40% is appropriate to determine a realistic assessment of the likely construction costs for the works at this outline option stage. Based on the above considerations, the construction cost includes that of the preferred land-based slope stabilisation elements up to the eastern end of the existing seawall, which ranges from 8.8M for the Hold the Line scheme to 12.0M for the Advance the Line scheme, and the cost of the associated foreshore works, ranging from 2.4M to 4.1M. Therefore, the overall construction cost of the coast protection scheme up to the eastern end of the existing seawall ranges from 11.2M to 15.8M depending on the scheme selected. The construction cost could be higher if the scheme elements were different from the preferred elements considered. For example, the construction cost of constructing a buttress for the Advance the Line scheme using clay fill could be up to 2 times of the estimated cost using granular fill, because substantially more clay fill would be required. 002652_R_001_rev3 WORKING COPY\Text\Options Report - MainText 002652_R_001 Rev3.doc 5-1

The selection of the preferred solution is discussed in Section 6. The construction cost of the preferred Hold the Line solution (see Section 6) up to the end of existing seawall is about 11.7M, including New sea wall on line of the existing seawall with rock apron; Hold the Line slope stabilisation works for the lower coastal slopes; Drainage measures in the middle coastal slopes; and Deep drainage works at the upper coastal slopes (Timber Hill). It should be noted that for an eastward extension of the foreshore works beyond the existing seawall to protect the currently unprotected seacliff, an additional construction cost of 1M to 1.4M will be required for the Hold the Line scheme to provide appropriate coast protection. For the Advance the Line scheme, the additional cost for the eastward extension ranges from 2.5M to 6M depending on the type of fill to be used. The construction cost estimate presented in the above and in Tables 5.1 to 5.3 excludes: cost of any required further studies and investigations including ground investigations, ecological studies and physical modelling etc; Planning application/consent costs and possible planning inquiry; costs related to detailed design and tender document preparation; costs relating to construction procurement (e.g. scheme advertising, tender process, etc); construction supervision; CDM costs; WDDC staffing costs; any land acquisition, compensation etc that may be required; pre-works ecological surveys and ecological species translocation; cost of any licences, planning requirements, etc special landscaping etc construction and post construction monitoring; post construction maintenance/costs associated with any part of the scheme; etc. 002652_R_001_rev3 WORKING COPY\Text\Options Report - MainText 002652_R_001 Rev3.doc 5-2

Table 5.1 Summary of Preliminary Construction Cost Estimate for Coast Protection Options - Slope Stabilisation Works to the eastern end of existing seawall "Hold the Line" Scheme Scheme Cost (nearest 1000s) Site Restoration Lower Coastal Slopes Allotment West & East Cliff Main Slip East Cliff Lane & Cedar Cottage Church Cliff Flats & Church Cliff Upper and Middle Coastal Slopes Timber Hill and Timber Hill Meadows "Advance the Line" Scheme Site Restoration Lower Coastal Slopes Allotment West & East Cliff Main Slip East Cliff Lane & Cedar Cottage Church Cliff Flats & Church Cliff Upper and Middle Coastal Slopes Timber Hill and Timber Hill Meadows Hybrid Scheme Site Restoration Lower Coastal Slopes Allotment West & East Cliff Main Slip East Cliff Lane & Cedar Cottage Church Cliff Flats & Church Cliff Upper and Middle Coastal Slopes Timber Hill and Timber Hill Meadows TOTAL TOTAL TOTAL 945,000 2,221,000 2,782,000 2,156,000 661,000 8,765,000 945,000 5,014,000 3,481,000 1,938,000 661,000 12,038,000 945,000 5,014,000 2,782,000 2,156,000 661,000 11,558,000 002652_R_001_rev3 WORKING COPY\Text\Options Report - MainText 002652_R_001 Rev3.doc 5-3

Table 5.2 Summary of Preliminary Construction Cost Estimate for Coast Protection Options Foreshore Works Scheme Relative cost for 387m length of wall plus 13m return (~400m total length) Minimum Maintenance and Intervention Hold the Line Scheme 1: Rock Armour Revetment to Existing Seawall Hold the Line Scheme 2: Seawall Refacing with Apron Hold the Line Scheme 3: Seawall Refacing with Rock Armour Revetment Hold the Line Scheme 4: New Wall on Line with Apron Hold the Line Scheme 5: New Wall on Line with Rock Armour Revetment Advance the Line Scheme 1: New Wall on Advanced Line with Apron Advance the Line Scheme 2: New Wall on Advanced Line with Rock Armour Revetment Advance the Line Scheme 3: Rock Armour Revetment on Advanced Line Provisional allowance for lateral extension (assumed 60m) of coast protection works to east of existing seea wall (see section 3.5.8) 785,000 2,738,000 2,356,000 3,543,000 2,877,000 4,071,000 2,442,000 3,637,000 3,836,000 See Table 5.3 Notes: 1. Costings are indicative relative cost only 2. Minimum Maintenance and Intervention is assumed to be 1/3 the cost of the minimum "Hold the Line" option and would be assumed to be spread over a five year period 3. Additionally there should be an allowance for access and haven for maritime plant (say 80,000) 4. "Advance the Line" schemes do not include for any backfill behind the wall 5. See Section 3 for description of options 5-4

Table 5.3 Summary of Preliminary Construction Cost Estimate for "Hold the Line" Coast Protection Options - Proposed works east of the existing seawall Foreshore Works Slope Stabilisation Works Description Cost Description Cost No foreshore works: Dowel Piles 1,210,000 With foreshore works: Extension Scheme A: New Wall with Rock Armour Revetment Extension Scheme B1: Rock Armour Revetment Extension Scheme B1: Rock Armour Revetment with access Extension Scheme C: Conventional Nearshore Breakwater Extension Scheme D: Reef Breakwater 466,000 Dowel Piles 584,000 409,000 547,000 781,000 434,000 Notes: 1. Assume 60m length of defence 2. See Sections 3.5.8 and 4.5.5 for descriptions of options 5-5

6 PREFERRED SOLUTION 6.1 FORESHORE ELEMENTS The options described in Sections 3.5.2 to 3.5.5 are summarised in Appendix H. The Do Nothing option fails to address the continuing deterioration and destabilising mechanisms on the seawall and the risks associated with the wall s failure. A Minimum Intervention and Maintenance approach could delay the deterioration mechanisms and provide a greater degree of confidence, in the short term, of stability of the seawall. Risk of failure would be much reduced but a residual risk will remain. Ongoing inspection and maintenance would be necessary to ensure continuance of the status quo. The remaining reviewed schemes are all viable, the choice is dependent on cost, amenity and environmental requirements as well as any implication on the overall stability of the cliff which is discussed elsewhere in this report. A critical consideration is public safety and in particular the level of public access to be provided. A combination of schemes may be employed, for example using a slope buttress solution where necessary for cliff stability and a refacing or widening solution at other locations. The Advance the Line and hybrid solutions cost significantly more than the Hold the Line options and also have environmental disadvantages. Therefore the Hold the Line solutions are preferred; of these Hold the Line Scheme 4, i.e. new sea wall with improved wall top access appears to offer the best balance between cost, engineering and environmental impact. Whichever scheme option is selected it is important that the protection of the sea cliffs to the immediate east of the existing seawall is considered. The necessity and extent of this protection will need to be considered further during preliminary design. Subject to further studies, of the options considered in Section 3.5.8 rock armour protection along a 60m length of the unprotected cliff toe is likely to be the most appropriate solution. 6.2 SLOPE STABILISATION The options of do-nothing and minimum intervention and maintenance will not improve the stability of the coastal slopes and not suppress landslide recession. These options are not considered to be viable in the medium and long term. Therefore, scheme options to stabilise the coastal slopes are recommended. All scheme options have been considered with respect to technical requirements and the critical environmental impacts. Based on the technical requirements and merits, the preferred option for each area is described below. 6.2.1 Lower Coastal Slopes: East Cliff and Church Cliff 6.2.1.1 Hold the Line Scheme Hold the Line scheme for the lower coastal slopes comprises the following preferred options for each landslide area. Drg. PH4\PD\401 (Appendix M) indicates the proposed disposition of the preferred scheme elements in plan. 6-1

Table 6.2.1 Preferred Hold the Line Solution for Lower Coastal Slopes Landslide area Preferred primary scheme elements Reference Table in Appendix L Allotments West and Dowel piles (see Section 6.2.4) East above unprotected sea cliff East Cliff Main Slip Trench drains and counterfort drains S/11/1 and Allotments West East Cliff Main Slip Fill berm buttressing, with provisional S/14/3 Side Scarp structural support through the main area East Cliff Lane Grid of dowel piles near the slope crest, S/15/3 and soil nailing Cedar Cottage Grid of dowel piles near the slope crest, S/16/2 and soil nailing Church Cliff Flats Soil nailing S/17/2 Church Cliff Soil nailing S18/2 6.2.1.2 Advance the Line Scheme For Advance the Line scheme, the primary objective in selecting the preferred options is to minimise the encroachment upon the foreshore. In satisfying this objective, the slope buttress constructed with imported granular fill on rock fill berm is preferred. Refer to Tables B/11/2 and B/17a/2 in Appendix L. Drg. PH4\PD\402 in Appendix M indicates the proposed layout of the technically preferred Advance the Line scheme. 6.2.1.3 Hybrid Scheme It has been considered that the landtake of this hybrid scheme should be no greater than that presented in the Landscape Conceptual Design Report (Environs, 2001). A proposed layout of the Hybrid scheme has been developed, based on the preferred Hold the Line elements at Church Cliff and the geometry of granular fill buttress ( Advance the Line ) at East Cliff, considering no rock fill berm is placed at the toe. Drg. PH4\PD\403 shows the proposed layout of the technically preferred bay and buttress scheme. 6.2.1.4 Preferred Solution Table 5.1 shows that the Hold the Line scheme costs less than the Advance the Line and hybrid schemes. In addition, the Hold the Line scheme does not substantially cover the foreshore. Therefore, the preferred solution for the lower coastal slopes is Hold the Line and the preliminary layout is shown in Drg. PH4\PD\401. It is noted that the Hold the Line recommendation is also in line with the preferred strategic option given in the Lyme Bay and South Devon Shoreline Management Plan (Posford Duvivier, 1998). 6-2

6.2.2 Middle Coastal Slopes: Charmouth Road car park, Football Ground and Allotments The options considered are independent of the proposed works in the lower coastal slopes. The preferred option will be required no matter whether Hold the Line solution or Advance the Line solution is implemented for the lower coastal slopes. For the middle coastal slopes, the preferred option comprises cut-off drainage along Spittles Lane and at the rear of the Charmouth Road car park. These drainage measures are proposed to reduce groundwater flow into the existing mudslide below these areas. Drg. PH4\PD\404 in Appendix M shows the proposed layout of this solution. 6.2.3 Upper Coastal Slopes: The Meadows and Timber Hill Similar to the middle coastal slopes, the proposed works at the upper coastal slopes will be required for both Hold the Line scheme or Advance the Line scheme for the lower coastal slopes. For the upper coastal slopes, the preferred technical option comprises installing a deep drainage system along the length of Old Charmouth Road to reduce water level within the Cretaceous Upper Greensand material. Various methods are available such as deep pump wells, deep sub-soil pipe and deep trenches. Refer to Tables S/2/3 to 6 in Appendix L. Drg. PH4\PD\404 in Appendix M shows the proposed layout of the drainage. The ecological study by EPR (EPR, 2006) however indicates that drainage at the upper coastal slopes would lower groundwater in the Meadows area, which could affect vegetation, potentially the flushes in the Meadows and the associated rush pasture vegetation, a BAP priority habitat. It is also considered that the effects would still be adverse even though the groundwater level was reduced in a controllable manner to summer level only. In view of the possible ecological impacts of slope drainage measures in the upper coastal slopes, it is recommended that the proposed drainage works are deferred whilst monitoring of the existing and additional instrumentation at the upper coastal slopes continue. This information will help understanding the landslide behaviour and the seasonal groundwater level pattern. This can be reviewed together with an assessment of the performance of the proposed works undertaken in the middle and lower coastal slopes to allow further development of the deep drainage option at a later stage. 6.2.4 Unprotected sea cliff below Allotments West and Allotments East As discussed above in Section 6.2.1.4, the preferred solution for the lower coastal slopes is Hold the Line. The preferred solution for protecting the sea cliff east of the existing seawall is also Hold the Line by providing rock armour protection to the cliff toe and installing dowel piles along the top of the unprotected sea cliff below the Allotments. This will cost less than installing piles in a ring-fence layout around the potentially outflanked sea-cliff. 6-3

6.2.5 Landscape Restoration and Environmental Mitigation The preferred mitigation restoration strategy, from both ecological and landscape perspectives, is to allow natural re-colonisation of the slopes wherever possible. This would mean creating similar varied ground surface conditions to those found at present, as far as possible within the engineering constraints, and re-using site-won soils. Soil surfaces would be left open in the short term, in order to allow the kinds of complex natural plant communities that exist at present to be re-created by natural processes in the longer term. All of the options above would permit this strategy to be adopted over parts of the site, particularly towards the eastern end. For some engineering options the proposed slopes may be considered too steep resulting in surface erosion. Therefore, rapid re-vegetation or provision of erosion control measures would be required. This applies particularly towards the western end of the scheme. In these areas, restoration may necessitate seeding or planting. Where this is the case only native species will be used, taken from local seed or plant sources as far as possible. Without management, vegetation will succeed to scrub and woodland due to the dry and stable conditions being created. The type of long-term management of habitats will therefore be critical for retaining similar biodiversity interest to those currently occurring, in particular areas of bare ground, and pioneer through to scrub vegetation for supporting scarce invertebrates and reptiles. 6.3 THE PREFERRED SCHEME The preferred foreshore works and slope stabilisation elements are discussed above in Sections 6.1 and 6.2. In summary, the technically preferred coast protection solution is Hold the Line scheme and comprises: a) New sea wall on line of existing seawall with rock apron; b) Rock armour protection to the cliff toe beyond the end of existing seawall (Appendix M, Drg No. PH4\PD\405); c) Hold the Line slope stabilisation works for the lower coastal slopes (Appendix M, Drg No. PH4\PD\401); d) Dowel piles along the seaward boundary of Allotments West and Allotments East (Appendix M, Drg No. PH4\PD\405); e) Drainage measures in the middle coastal slopes (Appendix M, Drg No. PH4\PD\404); and f) Deep drainage works at the upper coastal slopes (Timber Hill) (Appendix M, Drg No. PH4\PD\404); g) Establishment of a long term monitoring strategy, investigation and checking of existing drainage system and improvement works to the natural drainage streams and ditches across Timber Hill and the Meadows; and h) Landscape restoration and environmental mitigation works. However, it is recommended to install additional instrumentation at the upper coastal slopes and continue monitoring to collect ground and groundwater information at the upper coastal slopes before deep drainage works (item f above) are developed and implemented. 6-4

6.4 PHASING OF WORKS 6.4.1 Seawall Works Considerations From a constructional point of view there are opportunities for phasing the works of the seawall if a Hold the Line solution is adopted. The residual life of the existing Church Cliff and East Cliff seawalls is difficult to predict (see Section 3.3.4), however the defence structures are currently in a poor condition and are considered to be close to the end of their originally intended design life. The probability of the seawall failing within 10 years in the do nothing scenario is considered to be high. There are a number of considerations that need to be made relating to the determination of the optimum time for improving the existing coast defence structures. These include: Foreshore works protect the toe of the seacliffs and, in order to ensure that there is a reduced risk of coastal erosion and loss of material from the lower coastal slopes that would result following loss of the sea defences, the foreshore works should be carried out with or before slope stabilisation works. Safe public access to the foreshore may be impeded by an incomplete scheme implementation. Erosive mechanisms may be promoted at the junction between any new works and the existing seawall/foreshore. On the basis of the observed seawall condition and foreshore erosion, the order for phasing the foreshore works for the Hold the Line schemes would be as follows if there might be constraints identified in constructing the whole new defence in one single phase: East Cliff Church Cliff If an Advance the Line scheme is adopted all seawall works over the length of the advanced line must be completed within a single phase. 6.4.2 Slope Stabilisation Works Considerations The proposed schemes have been developed to improve the stability of the coastal slopes and involve full engineering works. However, it is possible that during the project development, some programme and cost constraints may be identified that result in undertaking the full stabilisation measures over their entire extent is deemed to be not feasible. In this circumstance, it could be required to re-direct resources to stabilise the critical areas of coastal slopes in a phased approach matching the likelihood of slope failure, the severity of the consequences, and the knock-on effect of the slope failure. On the basis of instrumentation monitoring data and consideration of the Landslide Recession Scenarios (2007 update) Report (HPR, 2007a), the stabilisation works can be phased as follows: 6-5

Allotments East (Seacliff beyond the eastern end of existing seawall); East Cliff Main Slip; Church Cliff; Middle and Upper coastal slopes (Timber Hill and the Meadows) As discussed in Section 6.2.3, the necessity for deep drainage in the Old Charmouth Road will be reviewed when long term monitoring data is available. It must be noted that these phases may change during the development of the project should monitoring shows that movements in some areas become more significant and pronounced. 6.4.3 Coast Protection Scheme In view of the restrictions and adverse implications of phasing the works, including greater risk of a landslide event occurring, on technical considerations alone this is considered not to be the preferred option. There are however non-technical reasons that may suggest the phased sequence of coastal management / construction will be preferred, e.g. funding stream, planning restrictions, ecological / environmental reasons, etc. Should a phased approach be adopted it is recommended that the coast protection works for both the existing seawall and the unprotected sea cliff beyond the eastern end of existing seawall should be carried out in the first phase. This would be followed by the stabilisation works at East Cliff and above the unprotected section of sea cliff, then the stabilisation works at Church Cliff, then the drainage works at the middle and finally the drainage works at upper coastal slopes if needed. This recommended phasing will need to be reviewed when the monitoring data at the upper coastal slopes is available, and the funding and programme constraints are identified. For the phased approach, it is important to develop a comprehensive design that would ensure that each phase of the works can be constructed separately, can meet public access and safety requirements, will not be detrimental to the coastal management regime and also that each phase of the works will integrate with the others with the need of only minor modifications to the constructed works as each phase proceeds. 6.5 DESIGNERS RISK ASSESSMENT AND RISK REGISTER These are included in Appendices P and Q, and will be further developed during subsequent stages of the Study. 6-6

7 RECOMMENDED FURTHER MONITORING, INVESTIGATIONS & STUDIES 7.1 FORESHORE 7.1.1 Further Studies Further study will be required to verify the scheme details as part of the detailed design stage. It is necessary to demonstrate that the chosen option will meet its requirements, namely to afford protection to the toe of the cliff over the design life period without excessive maintenance and to met any other design requirements that may be specified (amenity, environmental, etc.) To this end a greater knowledge of the structure of the existing wall and loading conditions must be obtained. Aspects requiring possible further study are detailed below. Those aspects chosen to be studied will depend on the scheme or schemes to be pursued. Table 7.1.1 Further Studies required for detailed design Object of Study Option Seawall construction Seawall Condition Groundwater Conditions Soil Conditions Local to Seawall Foreshore Topography & Bathymetry Future Wave Climate & Sea Level Coastal Processes Hydraulic Design Do nothing Minimum intervention and maintenance Hold the Line Scheme 1, 2 & 3 Yes Yes Hold the Line Scheme 4 & 5 Yes (but less extensive) Yes (but less extensive) Advance the Line Scheme 1, 2 & 3 Yes Preferred No Yes Foreshore SI required on line of new seawall No No Foreshore SI required on line of new seawall Yes Yes Yes Yes Yes Yes Preferred Preferred Yes Yes Yes Yes These recommendations are described in more detail below. 7-1

7.1.2 Seawall construction Possible methods would be: Document search WDDC have carried out extensive search for detailed constructional records of the seawall. It now appears unlikely that useful details can be obtained through this route. Trial pits to the rear of the wall (to determine the rear profile) Trial pits at the toe of the wall (to determine the toe profile and foundation level) Corings through the wall (to determine the wall thickness and material quality) Breaking out short sections of the wall (to view a full section and take samples) Adaptation of ground radar techniques may be feasible to determine wall thickness, but this is not known to have been previously used in such circumstance. With any intrusive investigation method the maintenance of the slope stability must be paramount. It should however be noted that the purpose of the wall is to protect the toe of the slope and not to restrain a slip; thus excavation of a trial pit or temporary removal of a section may be feasible. 7.1.3 Seawall Condition The present crack width and inclination monitoring regime should be continued to watch for any sudden changes. It is envisaged the Phase IV will be implemented before any additional visual structural survey on the lines of the 1984, 1996 and 2006 surveys referred to in Section 2.2.5 above are necessary. A walk through to compare with the 2006 survey records on a biannual basis and/or after periods of heavy rain, severe storm or landslip events is recommended. 7.1.4 Groundwater Conditions Inspection of the seawall, as noted above, suggests that there is poor provision for groundwater drainage immediately behind the seawall. This could be investigated by: Installation of standpipes close behind the wall Measurement of hydrostatic pressure through of corings through the wall during wall construction investigations 7.1.5 Soil Conditions Local to Seawall It is not known what insitu material may have been removed at the time of construction of the seawalls and what backfill material, if any, may have been provided. Soil/backfill conditions to the immediate rear of the wall may be determined at the time of seawall construction investigation. 7-2

7.1.6 Foreshore Topography & Bathymetry Prior to detail design, confirmatory surveys should be carried out within the footprint of the proposed works to confirm both beach and bedrock levels. Depending on the coast protection solution to be adopted, confirmatory bathometric surveys of the near and offshore areas may also be required, e.g. for the purposes of further hydraulic modelling. 7.1.7 Future Wave Climate & Sea Level The future wave climate at the wall may differ from the present due to changed climatic conditions, raised sea level and changed foreshore topography. The ability of the existing seawall, or any replacement, to perform is such changed conditions should be studied. Consequences of changed wave climate may affect the beach/foreshore at the wall toe, the loading on the wall and the ability of the wall to protect the slope above from overtopping water. DEFRA have provided recommendation relating to sea level rise (see section 3.4.4). These values should be reviewed in the light of the current recommendations at the time of the detailed design and incorporated into the hydraulic design of the coast protection structure. 7.1.8 Coastal Processes Following the adoption of a design scheme coastal processes should be further reviewed (see Section 3.5.9). 7.1.9 Hydraulic Design A 2-D physical model should be conducted during detail design to optimise the seawall / rock revetment profile to meet armour stability and overtopping requirements. Any proposed cliff protection works to the east of the existing seawall will also require hydraulic testing. 7.2 SLOPE STABILISATION The extensive studies, ground investigations and monitoring being undertaken are useful in providing a basic understanding of the complex landslide systems. However, further ground investigation and instrumentation monitoring will be required in developing the detailed design of the coast protection measures. On-going monitoring of the existing instrumentation, including ground permanent markers, inclinometers and piezometers, is recommended. This is particularly important for the instrumentation in the upper coastal slopes to allow reviewing the necessity of deep drainage. A proposal on instrumentation and monitoring is presented in the Report for recommended Instrumentation and Monitoring (HPR, 2007b). Following preliminary design, recommendations for additional ground investigation and instrumentation will be made and reviewed. 7-3

8 SUMMARY & CONCLUSIONS A coast protection scheme is considered essential to protect the coastline of Lyme Regis and to prevent the existing sea cliff and coastal slopes from receding and affecting the properties and infrastructure within the Phase IV Study area including Charmouth Road. This Options Report presents the approach and the findings in identifying and appraising a range of outline coast protection options that will address the coastal defence needs at the eastern side of Lyme Regis. A range of constraints to the development of the project, covering the aspects of physical, environmental, programme and cost, has been identified. These constraints have been considered in developing the coast protection works options, and will be used and updated in developing the design. The coastal land instability problem is considered to arise from: a) Recession of the seacliff due to marine erosion, quarrying and landsliding, prior to construction of the seawall at East Cliff and Church Cliff; b) Deterioration of the existing seawall conditions due to cracking, erosion and blocked/ineffective weepholes c) Erosion of the foreshore limestone ledges, and movement of shingle and boulders on the beach; d) Outflanking erosion at the eastern end of the seawall; and e) Reactivation of pre-existing coastal landslip system as a result of seacliff erosion. In order to address these problems, coast protection works have been considered to include works on the foreshore and the coastal slopes. Three management options have been considered separately for foreshore protection and the associated slope stabilisation: Do Nothing Minimum intervention and maintenance Scheme options Foreshore Protection Works A Do Nothing approach is likely to leave the wall liable to damage and collapse due to the continuance of the currently deteriorative and destabilising mechanisms, principally the erosion of the beach/foreshore in front of the wall causing undermining of the wall itself and erosion of the wall concrete causing structural failure. The minimum intervention and maintenance approach is not considered to be sustainable in the medium to long term, in view of the ongoing maintenance burden, risk of failure and safety issues. Scheme options have been considered for both Hold the Line solution and Advance the Line solution to prevent erosion of the base of Church Cliff and East Cliff, and to prevent wave overtopping from reaching the surface of slopes above and causing erosion. These options include new rock armour revetment to the front of the existing wall, seawall reconstruction/refacing with rock apron, seawall reconstruction/refacing with rock armour revetment, new forward wall with rock apron and new forward wall with rock armour revetment. All these options are considered to be technically viable and the selection is primarily dependent on 8-1

are considered to be technically viable and the selection is primarily dependent on cost and the environmental impacts. The Hold the Line solutions are preferred and of these Hold the Line Scheme 4, i.e. new sea wall with improved wall top access appears to offer the best balance between cost, engineering and environmental impact. The protection of the sea cliffs to the immediate east of the existing seawall must be further considered during preliminary design. Initially rock armour protection to the cliff toe would appear likely to be the most appropriate solution. Slope Stabilisation Works A Do Nothing approach is not viable in the medium to long term to protect the properties and infrastructure, and might result in damage to the existing and/or proposed foreshore defence by the coastal slope landslide debris. The minimum intervention and maintenance option is also considered not to be viable in the medium to long term to improve the stability of the coastal slopes, nor suppress recession. The properties and infrastructure will still be under the threat of coastal instability. Scheme options have been considered for both Hold the Line solution and Advance the Line solution to protect the existing and new foreshore defence, and to protect the properties and infrastructure. These options have been developed on the basis of the different landslide characteristics of each landslide area and the suitability of each category of primary works for each landslide area. These scheme options range from drainage measures, in-situ reinforcement, structural support and earthworks rebuild. A preferred solution has been selected for each landslide area with the use of a multi-modal assessment method, which considers a number of technical factors and critical environmental impacts. These area-specific preferred solutions are finally combined together to give the preferred slope stabilisation solutions for the Hold the Line and Advance the Line schemes, as shown in Drawings PH4\PD\401 to 404 in Appendix M. For the preferred Hold the Line and Advance the Line schemes, preliminary estimates of the construction cost of the coastal protection scheme ranges from 11.2M to 15.8M for works up to the eastern end of the existing seawall. For the preferred coast protection scheme, the construction cost is about 11.7M, which includes deep drainage works at the upper coastal slopes. Based on the updated Landslide Recession Scenarios Study (HPR, 2007a), it is considered essential to carry out coast protection works beyond the eastern end of the existing seawall to a distance of about 60m. This requires an additional construction cost of 1M to 1.4M. The coast protection works could be implemented in phases to suit the programme and cost requirements. A number of key aspects have been considered in determining the sequence of phases: including the conditions of the existing seawall, and the timescales for occurrence of complete loss in the coastal slopes as estimated from the Landslide Recession Scenarios Study (HPR, 2007a). It is recommended that the coast protection works for both the existing seawall and the unprotected sea cliff beyond the eastern end of existing seawall should be carried out in the first phase. This would be followed by the stabilisation works at East Cliff and above the unprotected section of sea cliff, then the stabilisation works at Church Cliff, 002652_R_001_rev3 WORKING COPY\Text\Options Report - MainText 002652_R_001 Rev3.doc 8-2

9 REFERENCES 9.1 REPORTS: 1. Brody Forbes Partnership, 2006, Phase IV Structural Condition Survey of Sea Walls Church Cliff and East Cliff Sea Walls, 5114-R-001, March 2006 2. Ecological Planning & Research (EPR), 2006, Lyme Regis Environmental Improvements Phase IV, 2006 Ecological Surveys: Review, Report No. P06/41, December 2006. 3. Environs Partnership Ltd, 2001, Lyme Regis Environmental Improvements - East Cliff, Preliminary Report, Landscape Conceptual Designs, May 2001. 4. Environs Partnership Ltd, 2007, Lyme Regis Environmental Improvements, Phase IV, Landscape and Visual Baseline Report, February 2007 5. Fort, D.S., Martin, P. L., Clark, A.R. & Davis, G.M. 2007, Lyme Regis Phase II Coast Protection & Slope Stabilisation Scheme, Dorset, UK The Influence of Climate Change on Design, Proc. Int. Conf. on Landslides and Climate Change Challenges and Solutions (in press) 6. Gallois, R. 2005, Lyme Regis Environmental Improvements, Phase IV, Report on the Geology of Church Cliffs and Adjacent Areas, Lyme Regis, Dorset. Report for WDDC, 05/01, May 2005. 7. Gallois, R. 2006, Lyme Regis Environmental Improvements, Phase IV, Report on the Geology of the area between Devonshire Head and the River Lim, Lyme Regis, Dorset. Report for WDDC, June 2006. 8. Graham Garner and Partners, 1996, Lyme Regis Environmental Improvements, Phase IV, Condition Survey: Structures, 4205/3/J96, July 1996 o Part 1: Church Cliffs and East Cliff Sea Walls o Part 2: Groins 1 to 17 Condition and Photographic Record o Part 3: Church Cliffs Jetty and Retaining Wall 9. High-Point Rendel, 1997, Lyme Regis Environmental Improvements, Preliminary Studies: Geomorphology and Ground Behaviour. Report No. R/H397/1, April 1997. 10. High-Point Rendel, 1999a, Lyme Regis Environmental Improvements, Preliminary Studies, Phase IV East Cliff, Interpretative Geotechnical Report. Reports No. R/H431/2/1 and 2, May 1999. 11. High-Point Rendel, 1999b, Lyme Regis Environmental Improvements, Preliminary Studies, Phases II, III & IV Coastal Processes and Geomorphology Town Beach and East Cliff, H944/R/2, May 1999. 12. High-Point Rendel, 2000a, Conceptual Management Strategy and Preferred Scheme Elements for the Coastal Slopes: Discussion Document, Phases IV, East Cliff, 900/R/1B/01, March 2000. 13. High-Point Rendel, 2000b, Lyme Regis Environmental Improvement, Preliminary Studies, Phase IV, Conceptual Management Strategy and Scheme Options for Coastal Slope Stabilisation, Final Report, 900/R/3A/03, September 2000 14. High-Point Rendel, 2000c, Lyme Regis Environmental Improvements, Preliminary Studies, Phase IV Landslide Recession Scenarios, R/H439/2/1, July 2000 9-1

15. High-Point Rendel, 2003, Lyme Regis Environmental Improvements Phase IV (East Cliff), Preliminary Environmental Appraisal, R/1570/21/1, April 2003. 16. High-Point Rendel, 2003a, Lyme Regis Environmental Improvements, Phase IV, East Cliff/ Church Cliff, Urgent Stabilisation Works: Detailed Design Summary Report. Report No. 2139/R/01/01, November 2003 17. High-Point Rendel, 2006, Lyme Regis Environmental Improvements, Phase IV Preliminary Design Stage, Addendum Interpretative Geotechnical Report. Draft Report. Report Ref. 002652/R/003 18. High-Point Rendel, 2007, Lyme Regis Environmental Improvements, Phase IV Preliminary Design Stage, Addendum Geomorphology Report. Report Ref. 002652/R/005 19. High-Point Rendel, 2007a, Lyme Regis Environmental Improvements, Phase IV Preliminary Design Stage, Landslide Recession Scenarios (2007 update) report. Report Ref. 002652/R/002 20. High-Point Rendel, 2007b, Lyme Regis Environmental Improvements, Phase IV Preliminary Design Stage, Recommendations on Instrumentation and Monitoring. Report Ref. 002652/R/004 21. High-Point Rendel, 2007c, Lyme Regis Environmental Improvements, Phase IV Preliminary Design Stage, Exposure Logging Report (2007). Report No. 002652/R/006. 22. HR Wallingford, 2003, Town Beach & East Cliff, Lyme Regis Outline scheme design and physical modelling, Volumes 1 & 2, EX4621, March 2003. 23. Posford Duvivier, 1998. Lyme bay and South Devon Shoreline Management Plan 24. West Dorset District Council, 1999, Lyme Regis Environmental Improvements, Phase IV Preliminary Studies, Report on Crack Monitoring at East Cliff Sea Wall, 4/9, July 1999 25. West Dorset District Council, 2005, Lyme Regis Environmental Improvements, Phase IV, Project Appraisal Report, Preliminary Design Stage, May 2005 26. West Dorset District Council, 2006, Lyme Regis Coast Protection Scheme Phase IV, Slope Stability Monitoring Report No. 1 For the period 1997 2006 9.2 PUBLICATIONS 1. RS Thomas & B Hall. Seawall Design, 1992, CIRIA Butterworth-Heinemann 2. RN Bray & PFB Tatham, 1992, Old Waterfront Walls, CIRIA E & FN Spon 3. CA Fleming, 1990, Guide on the uses of groynes in coastal engineering, CIRIA Report 119 9.3 ARCHIVAL RECORDS Microfilm copies of various Lewis & Duvivier, Consulting Engineer, drawings dated 1964-68 showing proposed remedial works to Church Cliff and East Cliff seawalls (These drawings are not indicated to be as-built and although, they largely appear to reflect the existing structures, they may not accurately describe the works as constructed.) 9-2

APPENDICES A WDDC Drawing LREI61\023 Church Cliff and East Cliff Seawall History B Levis & Duviver Drawings of Existing Seawall: 1342A/23 Church Cliffs, St Michael s Church Seawall Plans, Sections & Elevation of Sea Wall (Nov 1964) 1342A/26 Church Cliffs, St Michael s Church Seawall Elevations & Details of Groynes (Nov 1964) 1342A/31/1 East Cliff Sea Defences Typical Groyne Elevations & Details (June 1967) 1342A/32 East Cliff Sea Defences Sea Wall Apron and Cliff Revetment (June 1967) 1342A/34 East Cliff Sea Defences Cross Sections of Apron at North End of 1957 Wall (Oct 1967) C Seawall Crack Width and Inclination Monitoring D Survey Levels Comparison 1995-2006 E WDDC Drawings: LREI79\218 - Cliff Top Recession LREI79\219 - Cliff Toe Recession PH4\PD\004 - Foreshore Contours and Sections F Foreshore Changes Close to Existing Seawall G Coast Protection Options: First Stage Type Selection Based on Seawall Design, Thomas & Hall, CIRIA, 1992, Characteristics of various wall types, Tables 5.3 to 5.6 H Coast Protection Options: Second Stage Type Selection I Plan of Principal Landslide Areas J Landslide Site Characteristics K Coastal Slope Stabilisation Generic Options L Area Specific Coastal Slope Stabilisation Scheme Options M Preferred Options N Ground Model Sections O Cost Estimates P Designer s Risk Assessment Q Risk Register R Glossary of Terms S Schematic Construction Sequence N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - Appendices 002652_R_001 Rev3.doc

APPENDIX A WDDC Drawing LREI61\023 Church Cliff and East Cliff Seawall History N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - Appendices 002652_R_001 Rev3.doc

APPENDIX A Technical Services Steve Woollard, Technical Services Manager, Stratton House, 58/60 High West Street, DORCHESTER, Dorset. DT1 1UZ Tel: 01305 251010 Fax: 01305 252349 Lyme Regis Environmental Improvements Preliminary Studies Church Cliff and East Cliff Seawall History This map is reproduced from the Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty's Stationery Office Crown copyright. Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings. 100024307. 2010 HM GMD July 1999 1:500 \\Lymesrv\ LymeDWG\ Lrei61 LREI61\023 E:\Coast Protection Options 002652_R_001_rev3 issued 02-04-07\Appendix A\Appendix_A 002652_R_001_rev1.doc 06/01/2010

APPENDIX B Levis & Duviver Drawings of Existing Seawall B1 1342A/23 Church Cliffs, St Michael s Church Seawall Plans, Sections & Elevation of Sea Wall (Nov 1964) B2 1342A/26 Church Cliffs, St Michael s Church Seawall Elevations & Details of Groynes (Nov 1964) B3 1342A/31/1 East Cliff Sea Defences Typical Groyne Elevations & Details (June 1967) B4 1342A/32 East Cliff Sea Defences Sea Wall Apron and Cliff Revetment (June 1967) B5 1342A/34 East Cliff Sea Defences Cross Sections of Apron at North End of 1957 Wall (Oct 1967) N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - Appendices 002652_R_001 Rev3.doc

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APPENDIX C Seawall Crack Width and Inclination Monitoring (by WDDC, 2006) N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - Appendices 002652_R_001 Rev3.doc

Seawall Crack Width and Inclination Monitoring AppendixC Seawall Crack Monitoring 1984 to 2006 Seawall Crack Monitoring 2006 140 160 135 155 130 150 Gauge Reading (millimetres) 125 120 115 110 105 100 95 90 85 80 02/1982 11/1984 08/1987 05/1990 01/1993 10/1995 07/1998 04/2001 01/2004 10/2006 07/2009 C2* (G17-2.5 left of G17) C3* (G17-7.5 left of G17) Gauge Reading (milllimetres) 145 140 135 130 125 120 115 110 105 100 01/07/2006 01/08/2006 01/09/2006 01/10/2006 01/11/2006 01/12/2006 C1 (end of sea wall) C2* (G17-2.5 left of G17) C3* (G17-7.5 left of G17) C4* (left of G10) C5 (left of G7) C6 (left of G6) C7 (right of G4) Date Date Seawall Inclination Monitoring 2006 86 84 82 80 78 76 74 72 01/07/2006 01/08/2006 01/09/2006 01/10/2006 01/11/2006 01/12/2006 Face Angle (degrees) A (end of sea wall) B (right of G11) C (left of G10) D (left of G7) E (above G3) F (left of G1) Date 002652_R_001_rev1 issued 06-12-06\Appendix C\Appendix_C 002652_R_001_rev1.doc 06/12/2006

APPENDIX D Survey Levels Comparison 1995-2006 N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - Appendices 002652_R_001 Rev3.doc

APPENDIX E WDDC Drawings E1 E2 E3 PH4\PD\218 - Cliff Top Recession PH4\PD\219 - Cliff Toe Recession PH4\PD\004 - Foreshore Contours and Sections N:\2652 - LREI Phase IV Preliminary Design\14. HPR Prepared Reports\2006 LREI Phase IV Options Report\Coast Protection Options 002652_R_001_rev3 WORKING COPY\Options Report - Appendices 002652_R_001 Rev3.doc