Press Release - 4th September 2007

West Beach gets some temporary protection but the hole remains

Chichester District Council Executive Board agreed at their meeting of 4th September 2007 to do a temporary repair of the broken sections of sea wall at Clayton Road Selsey, caused by a partial collapse of the sea wall in March 2007.

We welcomed this decision by the Council. SOS had been urging the Council to shore up the existing emergency repairs to the sea wall, in advance of the coming winter.

Originally the Council had rejected this idea. It had suggested a programme of monitoring the damaged wall, and then reacting to any further collapse. This was partly because it had hoped government money would be forthcoming to rebuild the wall in full.

A few days before the Executive Board met, news came that there would be no government money for the wall rebuild, in this financial year. We redoubled our lobbying efforts and, to its credit, the Council very sensibly reviewed its position. It agreed to the placing of boulders (a “revetment”) along the beach in front of the damaged wall, to give it protection against wave damage.

The Council got on with the work quickly. A shipload of boulders, from France, was dropped by barge on the beach at high tide. During the next few low tides, mechanical excavators were used to manoeuvre the rocks into position. About 100m of seafront was given protection in this way, which is hoped will last for 5 years or more.

This has been a cost effective way of protecting some of Selsey’s most vulnerable bit of urban coast. It’s much cheaper to protect the sea wall using a revetment, than have to rebuild the wall following a collapse.

We have over 8km of sea wall and shingle defences on the Manhood Peninsula. SOS believes that revetments could be a great way to protect & prolong the life of these defences, by starting with the most exposed sections of shoreline and gradually extending the protected zone.

Why did the sea wall collapse?

When the wall was designed, it was assumed that the shingle in front of it (on the beach) would be “topped up” when needed. This was never done, and over time the shingle has been washing away. Once this process started, it escalated. As the beach gets lower, the depth of water in front of the wall at high tide is deeper. This means the waves hitting the wall are bigger, as they rebound they stir up more sediment, which is carried away in the tide, and the beach levels drop further.

Eventually the beach level gets so low that the wall’s foundations are exposed, and it simply slides or falls onto the beach, because it has been undermined. This is what happened at Clayton Road in March 2007. No matter how big the wall, if you undermine its foundations, it will collapse.

How does a revetment work?

The revetment takes all the energy out of the waves, before they hit the wall. The revetment is a mix of solid boulders, and gaps between the boulders, so doesn’t act like a solid sea wall. It disperses the waves’ energy, the water doesn’t rebound (as it does when it hits a solid wall), so less sediment is stirred up and carried away by the tide.

This means the beach level should remain fairly constant, or even build up. When this happens, it appears the revetment is “sinking” into the beach, but actually the beach is rising around the boulders! An example of this took place on the beach near Hillfield Road over the past few years.