Lyme Regis Environmental Improvements Strategy Plan
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WEST DORSET DISTRICT COUNCIL, ENGINEERING DIVISION LYME REGIS ENVIRONMENTAL IMPROVEMENTS STRATEGY PLAN LYME REGIS ENVIRONMENTAL IMPROVEMENTS STRATEGY PLAN August 2002 WEST DORSET DISTRICT COUNCIL, ENGINEERING DIVISION CONTENTS LYME REGIS ENVIRONMENTAL IMPROVEMENTS STRATEGY PLAN Subsection. Figures and Tables. 1 Introduction 1.1 Background. 1.1 Interrelationships between studies. 1.2 The Lyme Regis Environmental Improvements. 1.3 Objectives of the Strategy Plan. 1.4 Study framework. 2 Definition of the Problems 2.1 Boundaries. 2.1 Location plan. 2.2 Interconnection between study areas. 2.2 Summary of coastal protection problems. 2.3 Time frame. 2.4 Summary of the problems. 3 Generic Objectives 3.1 Shoreline Management Plan. 3.1 Summary of recommended generic actions. 3.2 Recommended generic objectives. 3.3 Alternative philosophies. 4 Coastal Protection Options Phases II & V 4.1 Description of options. 4.1 Conceptual design elements. 4.2 Preferred options. 4.2 Coast protection benefits. 5 Coastal Protection Options Phase IV 5.1 Description of options. 5.1 Conceptual design elements. 5.2 Appraisal. 5.2 Coastal protection benefits. 5.3 Preferred option. 6 Programme 6.1 Principles. 6.1 Programme chart. 6.2 Sub -phasing of Phase II. 7 Cost Benefit Analysis 7.1 General. 7.1 Summary of estimated costs, benefits and benefit/cost ratios. 7.2 Sensitivity. 7.3 Additional benefits. 8 Summary References Appendices: A Rejected Scheme Options B Data Sources for Cost Benefit Analysis: C Property Benefit Location Plans D Present Value Property Benefits E Harbour Benefits F Sensitivity Analysis WEST DORSET DISTRICT COUNCIL, ENGINEERING DIVISION 1.0 INTRODUCTION LYME REGIS ENVIRONMENTAL IMPROVEMENTS STRATEGY PLAN 1.1 Background 1.3 Objectives of the Strategy Plan Lyme Regis is an ancient coastal town situated in Lyme Bay on the south coast of Britain. It The purpose of this Strategy Plan is essentially to bring together the findings of the is both a popular residential area and a major holiday resort, with a summer population of Preliminary Studies, including early work on the conceptual design of engineering schemes, approximately 14,000. Lyme Regis is famous for its unique harbour structure, the Cobb, in order to establish an action plan for improving the coast protection situation at Lyme which is the oldest working breakwater of its type in the country. The town's economy relies Regis in the long term. The principal objectives of the report are: heavily upon tourists who are attracted by the harbour, the beaches and the spectacular coastal scenery. 1) to review the coast protection problems facing Lyme Regis; The historical development of the town has been strongly influenced by coastal erosion and 2) to consider coast protection policy objectives; landslipping. Over the centuries the coastline has been protected against marine erosion by the construction of a series of sea walls, jetties and other defences of various forms. These 3) to determine preferred coast protection management objectives including, where defences have been repaired and replaced in a piecemeal fashion in response to storm appropriate, engineering scheme options; damage and general decay so that today the town is protected by a variable complex of ageing structures. 4) to develop a programme for implementation of the management options. Although the town has been partly protected from the direct erosive action of the sea, large areas of it have been constructed on ancient coastal landslides which periodically become reactivated resulting in disruption and damage to property. 1.4 Study Framework 1.2 The Lyme Regis Environmental Improvements The data used to develop the Strategy Plan have come from the Preliminary Studies carried out by West Dorset District Council and its consultants in the period 1996 - 2000. A In the early 1990's West Dorset District Council initiated the Lyme Regis Environmental summary of the methodology and findings of the studies is given in the Preliminary Studies Improvements with the aim of safeguarding the integrity of the coastal areas of Lyme Regis Summary Report prepared by WDDC (August 2000). The Summary Report is a in the long term. The initial emphasis was upon the implementation of a new coast companion volume to this Strategy Plan and it is recommended that the two reports should protection scheme for the central part of the town adjacent to the River Lim, the existing 250 be read in conjunction. year old sea walls at which were approaching the point of failure. Slope stabilisation scheme options were developed in the reports entitled 'Conceptual The construction work for this first phase, which comprises a new sea wall and rock armour Management Strategy and Scheme Options for Slope Stabilisation' for both Cobb Gate to revetment, was completed in 1995. Since then, West Dorset District Council has been Harbour and East Cliff, prepared by High Point Rendel (September 2000). Foreshore carrying out an extensive series of Preliminary Studies in order to gain an understanding of scheme options were developed in the report entitled 'Preliminary and Secondary the coast protection problems affecting the remaining areas of Lyme Regis. The Appraisal of Coast Defence Options' prepared by HR Wallingford (July 2001). Preliminary Studies have been deliberately holistic in approach, considering all of the Lyme Regis coastline (not just a series of isolated problem areas) and the whole of the physical The relevant Shoreline Management Plan for Lyme Regis is the Lyme Bay and South coastal system from the offshore submarine environment to the top of the coastal slope. Devon Shoreline Management Plan, prepared by Posford Duvivier in 1998. Thus the information obtained may be used at a strategic level in determining an integrated management policy and preparing coordinated design concepts and programming for coast The flow chart in Figure 1.1 indicates the interrelationships between the various studies protection schemes. and their outputs. WEST DORSET DISTRICT COUNCIL, ENGINEERING DIVISION FIGURE 1.1 LYME REGIS ENVIRONMENTAL IMPROVEMENTS INTERRELATIONSHIPS BETWEEN STUDIES STRATEGY PLAN Individual Preliminary Studies Preliminary Studies Summary Report (14/1) Definition of generic Shoreline Definition of problems objectives (recommended Management actions) Plan Conceptual design of stabilisation works for slopes and foreshore STRATEGY PLAN Studies Output Preferred management options and programme for implementation WEST DORSET DISTRICT COUNCIL, ENGINEERING DIVISION 2.0 DEFINITION OF THE PROBLEMS LYME REGIS ENVIRONMENTAL IMPROVEMENTS STRATEGY PLAN 2.1 Boundaries (2.2 continued) Phases II, III and V are separated physically from Phase IV by the new coast protection The area under consideration extends from Devonshire Head in the west to the Spittles in scheme for Phase I. As a result, it is considered that there is no interconnection between the east, covering the whole of the urban coastal area of Lyme Regis (Figure 2.1). Phases II, III, V and Phase IV either in terms of overlapping benefit areas or physical coastal process such as sediment transfer. The Devonshire Head boundary is defined as the westernmost limit of significant beach deposits at Lyme, at the end of Monmouth Beach. It is also, coincidently, the point at which In theory, there is some overlap of the benefit areas for the Cobb and Phases II & III. For the county boundary between Devon and Dorset crosses the foreshore and hence marks example, some of the properties to the north of the Cobb are under threat both from flooding the westernmost extent of West Dorset District Council's jurisdiction as coast protection as a result of a breach in the Cobb and landsliding from the slope behind. For the sake of authority. The eastern boundary is defined as the point furthest to the west at which simplicity, however, a simple boundary has been drawn between them as shown in Figure significant amounts of beach-forming material are issued from the highly active landslide 2.1and the conservative assumption made that there is no overlap (i.e. no one property areas of the Spittles/Black Ven landslide complex. The Preliminary Studies have shown would be under threat by both a breach in the Cobb and a landslide). that there is no significant longshore transport of beach-forming material into Lyme Regis either from the west or east. In west there is no supply. In the east the material from the Spittles and Black Ven is taken eastwards rather than westwards. Furthermore, there are 2.3 Time Frame no sources of material in between. The area within the boundaries of the Strategy Plan is therefore independent of the adjacent areas in terms of longshore sediment transport. This Strategy Plan considers coast protection in the period extending up to the next fifty years, i.e. 2002 to 2052. The inland boundary of the Strategy Plan may be defined as the crest of the coastal slope, which represents the current landward influence of the sea on landslide processes. It is envisaged that the principal coast protection schemes described in the plan would be implemented within the next ten years, i.e. before 2012. In practice, areas outside of these boundaries have received attention in the studies. For example, when considering future landslide regression scenarios and cost benefit analyses, 2.4 Summary of the Problems the study area was extended a nominal distance landward in order to allow for a hypothetical small expansion of the coastal landslide systems beyond their present The coast protection challenges facing Lyme