How are these problems going to be solved?
We have looked at a number of ways of improving the sea defences and a scheme based on a beach with timber groynes came out as the best of the many alternatives we had studied. A long list of options were examined and included a new seawall in a realigned location, an open plan beach, a much larger beach controlled by groynes involving a significant beach recharge and various rock structures including both revetments and headlands.
Clearly one of the most important considerations is the economics and the large beach and groyne scheme came out on top with the best benefit/cost ratio. Nowadays the possible effects on the environment are also a critical aspect of the decision making process and the scheme we’re going ahead with also scored highly in its environmental analysis. Natural England, the Environment Agency and other national and local bodies were closely involved in the analytical process and have confirmed these findings.
Longshore drift, or ‘littoral drift’ is the movement of material along a coast by waves which approach the shore at an angle and recede directly away from it. We can interrupt this transport of shingle through the use of timber groynes. However by interrupting the flow of shingle, the shape of the coastline is changed: as shingle accumulates on one side of the groyne it is lost on the other as there is now no supply of shingle to this area.
One of the reasons for ineffective defence at Kingsdown is that the current groynes are not aligned perpendicular to the direction of longshore drift. The new groynes are being built in the correct position.
By pairing the groyne works with a supply of recycled shingle to the groyne bays, this problem is overcome.
Using this method of management, the landward advance of the sea can be halted. Beaches provide the best form of protection against wave attack as their porous structure helps dissipate the wave’s energy. Therefore by holding onto the beach at Kingsdown, the sea defences can continue to protect us against overtopping, without the fear of undermining.
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Contact
Liam Wooltorton, Canterbury City Council: Tel: 01227 862454, email liam.wooltorton@canterbury.gov.uk
or
Keith Watson, Dover District Council: Tel: 01304 872399, email keith.watson@dover.gov.uk