As Scarborough Borough Council explained, there was also a residual landslide risk, with significant problems associated with major first time failures caused by renewed cliff foot erosion, expansion of shallow landslides, extreme groundwater levels, slope drainage failures and major reactivation of pre-existing failures.

Finding the best solution to defend the coast at Scarborough was not straightforward, however, because of the considerable age of some of the existing coast protection structures (these being 18th to early 20th century structures with limited residual life), because of overtopping, the landslide risk, and the potential for loss of structures and loss of protection, The resulting threat to public safety and protected assets (estimated at approximately £100m) was considerable.

Among the priority objectives determined by the Council for the coastline in question - East Pier, Castle Headland and The Holms - were that the coastal protection provided be structurally sound, and have a design life of at least 50 years. Minimising ongoing maintenance of the coast protection structures was also an important goal, as was limiting overtopping to reduce storm damage and impact of storm events on the Harbour, whilst meeting environmental objectives in the Marine Drive and the Holms areas.

One of the major challenges was presented by the East Pier, an ancient, Grade II Listed Structure (built circa 1732 with parts pre-dating this). The pier consists of a rubble-filled dressed masonry structure founded on rubble rock bund. The seawall masonry was in poor condition with remaining residual life low, and the apron was deteriorating, with extensive rehabilitation required. Overtopping of the pier has led to regular wave disturbance in the Outer Harbour and hazard to users of the East Pier and Outer Harbour.

Among the options for the East Pier were to do nothing, do the minimum (that is, minimum maintenance), re-build it on its existing line, construct a new seawall seaward, or an offshore breakwater.

The Council determined that the viable options for the East Pier included a rock armoured revetment with the rock revetment at 1:4 slope, armoured with 9-18 tonne rock (to cope with the aggressive wave climate).

This would cover and protect the existing bund, meet design life criteria, and reduce overtopping significantly, but there would still be a need for significant future maintenance, construction would not be easy, and the structure would be highly visible.

Another option was an Accropode armoured revetment at 1:5 slope with 6.3m and 9m cubed accropodes, with the toe of new structure on existing bund, with the toe detail addressing erosion problems.

This solution would also meet design life criteria, would require minimal future maintenance, overtopping would be significantly reduced, and the construction problems would be less than with rock armour.

Moreover, this solution would provide a less visible structure than rock revetment.

On Castle Headland the problems included the fact that there was regular and costly damage to the infrastructure of Marine Drive, with the concrete in the seawall deteriorating and extensive rehabilitation required.

There was also some erosion at toe of wall, and increased overtopping of the sea wall was causing regular road closures (more than 35 per annum).

Viable options for Castle Headland and The Holms included a rock armoured revetment with strengthening of existing wall and construction of new rock bund, and a wave wall constructed to reduce overtopping. This solution would meet design life criteria, have minimal future maintenance requirements at The Holms (but not at Castle Headland), but, again, would present significant construction problems along Castle Headland, and would be a highly visible structure along Castle Headland.

The Accropode armoured revetment solution was also considered for this section of the work, the option comprising rehabilitation of existing wall and construction of new Accropode armoured bund, and a wave wall to reduce overtopping.

This solution would meet design life criteria, minimize future maintenance requirements, and have a steeper slope than rock schemes thus providing better hydraulic stability.

Accropodes are interlocking concrete armour units. They are more efficient than rock for the revetment armour because they interlock, and thus a lighter unit can be used for given wave conditions. This allows steeper slopes to be used for revetment design, and Accropodes also have a greater percentage of voids and for given wave conditions overtopping is less.

Accropodes may have a stronger visual impact than rock armour, but this is significantly offset by the smaller profile of an accropode armoured bund, the smaller volume of material, lower intrusion into inshore waters (navigation, fisheries and foreshore), the smaller size of the individual units, lower overall capital costs, greater stability and lower maintenance costs.

The Council determined that the provision of an Accropode revetment with a 1m high wave return wall would allow for overtopping to be reduced significantly, thus significantly reducing the risk of damage to Marine Drive and greatly enhancing the safety of its users.

Overall, it was decided that the Accropode option offered a number of significant advantages, including reduced visual impact and minimum foreshore cover, stability and reduced maintenance, easier constructability, and lower overall construction costs (around £26m).

The scheme received approval from DEFRA who awarded 75 per cent Grant Aid. Tendering began by advertising in the European Journal, which attracted interest from companies all over Europe. This was eventually reduced down to five companies, who were invited to tender for the job.

In March 2002 the contract was awarded to Edmund Nuttall Ltd, the contract being run from their North East office which is based in Newcastle.

Edmund Nuttall started work on site in April. High-Point Rendel has been involved with the scheme from the early days of preparing the Scarborough Coastal Defence Strategy, through detailed design and now has a team of five engineers and inspectors on site to supervise the construction works.

Rock armour stone is being imported from Norway and the concrete Accropode armour units are being pre-cast in Sunderland and brought to site by barge.

Work in the North Bay is progressing well and to date 630m (out of a total of 700m) of rock revetment and 350m (out of a total of 1,400m) of Accropode revetment have been placed.

Work continued into the winter period, beyond the planned end-of-summer shutdown date of the end of September, to catch up on delays due to unexpected ground conditions and noise constraints that effectively put a stop to planned 24-hour working.

Some work is continuing through winter but will start up again in earnest in March/April this year when construction of the revetment continues around the Castle Headland and the East Pier at Scarborough Harbour.

Throughout the course of the works, regular 'Liaison Group' meetings have been held with residents and businesses to keep them informed of progress and programme and these have been well received by the local community.