Considering all the risk factors outlined above and the state of coastal defences, West Dorset District Council and the Environment Agency were facing a real challenge. Clearly something had to be done sooner rather than later. The Shoreline Management Policy was to maintain the line of existing defences and the conservation designations on the old piers and Pier terrace meant that many schemes were considered which did not involve alterations to the alignment of failing and costly to maintain piers. Consultants Posford Haskoning were brought in to work on the design evaluation of the options, and elements of the schemes were tested at Hydraulics Research Wallingford.

Coastal defence options

• "Do Nothing Scenario" or "managed retreat" where areas are allowed to go undefended. This is used in cases where the value of properties at risk does not justify the expense of a scheme of coastal defence. At West Bay the "Flood Risk Areas" map was used to identify which properties would be lost through coastal erosion, tidal flooding or isolation through permanent tidal flooding of all access routes leading to the area. They were valued in 2001 and a total sum was used for the cost benefit analysis.

The result of adopting the "Do Nothing Scenario" would be

• the flooding and coastal defence failures outlined above
• the damage and loss of property
• the further decline of the fishing industry
• the total loss of West Bay for recreational and amenity use.

The existing amenity benefits

A survey was undertaken in 1997 to determine the existing amenity benefits and the level of use. The results of this survey are listed below.A survey was undertaken in 1997 to determine the existing amenity benefits and the level of use. The results of this survey are listed below.

• "Do Minimum Option" involves continuing to maintain the present defences. This would eventually lead to the same failures as above. The piers have had 3 major failures between 1980 and 2002 at a cost of millions of pounds. This option would cost several times more in the long term, than a major new scheme.
  
  
• Coastal defence schemes which maintained the alignment of the old piers, formed the majority of the 14 schemes considered. They all had varying combinations of the following scheme elements:
  • Groynes at 3 points on the West Beach
  • Beach replenishment
  • Beach management plans for East and West Beaches
  • Offshore breakwaters off West Beach - surface piercing with a rock core and armour stone walls
  • Rock armour toe protection to West Cliff sea wall
  • Steel sheet piling protection to the piers
  • Rock armour extension of East Pier
  • Rock armour on outside face of West Pier
  • Rock armour arm extension of West Pier
  • Demolition and rebuilding of both piers
    
    
• A coastal defence scheme based on demolishing and rebuilding the West Pier

Diagrams of some of the options considered are shown at figures 22 -27.

The outcome of constructing and adopting each of these possible schemes was assessed and costed. Construction costs, maintenance costs, environmental impacts, and risk assessment including hazards to shipping and public safety, were considered. The construction costs had to factor in an allowance for 30% winter downtime due to weather conditions. The exposed nature of the "site" and extremely hazardous working conditions meant additional costs would arise from programming difficulties, minute by minute wave and water level changes and possible loss of completed works. Durability issues, foundation risks and wave loadings all had to be factored in to the design and materials chosen. The following "shopping list" of materials was (in tonnes):

The costs of closing the harbour during construction also had to be considered for each scheme.

The final chosen scheme is shown at figure 28.