The approved option from the Scarborough Coastal Defence Strategy is a rock revetment in front of the existing sea wall, with a wave return wall, and cliff stabilisation. The options being considered are explained below. As part of the approval process we also have to look at the options of doing nothing and just maintaining what we already have, to provide a comparison to the options we are considering.
The option from the Strategy is for a rock revetment in front of the seawall and a wave return wall on top of the seawall. These parts of the scheme will reduce the amount of waves which overtop the seawall onto the promenade to a safe level for pedestrians. The revetment will also prevent the seawall from being undercut at its toe which would result in its collapse, and protect it from damage from direct wave attack.
The height of the wave return wall depends on the size of the rock revetment; the wider the rock revetment the lower the wave return wall needed. We have considered a range of revetment sizes to find the best balance between wall height and revetment size.
We have also considered a concrete stepped revetment to provide an alternative possible appearance for the scheme. The concrete stepped revetment would not be as good at absorbing the wave energy as a rock revetment. Therefore the wave return wall on top of the seawall would need to be at the highest acceptable level (1.4m) and the revetment would extend further out onto the beach. The concrete stepped revetment option would be more expensive than a rock revetment and would require more maintenance once constructed.
In order to stabilise the cliff a pile array would be installed behind the Spa buildings, going through all the softer clay material and down to the harder stable bedrock. These would not be visible above ground once installed. Horizontal drainage would be installed in the cliff to control the flow of water through the slope. This would stop any large deep-seated landslips.
The smaller surface slips would be dealt with through either:
- Large scale soil nailing and installation of a mesh covering across the surface of the cliff; or
- Construction of a series of low level walls, similar to those that are currently present in the South Cliff Gardens, and reducing the steepness of the slope between the walls.
Do Minimum (Ongoing Maintenance of Existing Defences)
Maintenance of the seawall and cliffs would continue, but no new coastal defences would be constructed.
This option would not deal with the wave overtopping issue. It would continue as now at 300 times the recommended safe limits for pedestrians, placing people, vehicles and buildings at risk of injury, death and damage.
Maintenance of the seawall would deal with small amounts of damage from wave attack. However it would not be able to deal with larger problems such as undercutting of the toe which could lead to large collapses of the seawall. As the condition of the seawall gets worse over time due to continued wave attack the amount of money spent on maintenance would increase.
Maintenance of the cliffs would be able to deal with the small surface slips which occur, however these can be expensive to repair, the most recent repairs to a surface slip cost in the region of £170k. Maintenance would not be enough to prevent a large scale deep-seated landslip occurring which has the potential to destroy the Spa buildings.
No further maintenance would be carried out on the seawall or cliff. This would result in failure of the seawall and large scale landsliding of the cliff, with the destruction of the Spa and cliff top properties.
This is not an option being considered by Scarborough Borough Council. This is worst case scenario against which we have to compare all the other options in order to build up a business case.