Coastal management on the Sussex coast between Brighton and Beachy
The management issue
The chalk cliffs between Brighton and Beachy Head are where the South Downs come to the coast. Rising sea levels following the end of the last glacial period have cut back into the dip slope of the chalk ridge. Unprotected cliffs such as Seaford Head or Seven Sisters recede at an average rate of 0.6m per year.
Although part of this stretch of coastline remains as open farmland on the cliff top, mainly east of Seaford, human settlement has continued to approach the cliff top along considerable distances between Brighton and Seaford. Within the past 100 years, some buildings have been lost to the sea, particularly at Birling Gap, while others are becoming increasingly close to the cliff edge.
Management strategies
Along this stretch of coastline, various strategies have been used involving both hard and soft engineering techniques to try to lessen the impact of coastal erosion. The earliest defences were begun in the 19th century, when the chalk cliffs between Brighton Pier and Black Rock were encased in concrete and landscaped as a response to the rapid growth of Brighton as both a residential area and holiday resort. As Brighton and its suburbs have grown, so has the need for further coastal management.
Black Rock to Rottingdean - hard engineering
Before the 1930s this stretch of coast was unprotected, but the continuing spread of Brighton eastwards along the cliff top, together with the growing importance of the main coastal road (A259), meant that some kind of management was required and a hard engineering scheme was adopted.
Between 1930 and 1933, a sea wall and promenade were built at the foot of the cliffs. The wall was made out of flint-faced concrete blocks, with the space between the wall and the cliff filled with chalk rubble from the cliff. The promenade and splash wall were then laid on top. Various groynes were then constructed at right angles to the sea wall to trap shingle, to create a defence ahead of the concrete sea wall. In 1935 the whole scheme was extended to Saltdean.
A major groyne was built at Black Rock to help build up shingle to protect a large open-air swimming pool, but it was not sufficient to fully disrupt the longshore drift of beach material from west to east. Shingle was still being made available to maintain a protective beach east of Black Rock.
In 1971 work started on the construction of Brighton Marina, which has severely disrupted longshore drift so that all the beaches to the east have become severely depleted. This has increased the exposure of the 1930s sea wall to wave attack. The problem is being made worse by cliff falls resulting from sub-aerial weathering of the cliff face. In 2001, 4,000 tonnes of material fell from cliffs close to the marina.
Further action was needed and, again, hard engineering techniques are being used:
- The 1930s sea wall is being encased in flint-faced pre-cast blocks.
- Granite boulders (rip rap) are being used in front of the sea wall to replace the protection lost through the depleted beaches.
- Promenade and splash walls are being reconstructed.
- Cliff angles are being lowered, although the scope for this is limited because the main coastal road (A259) is near the cliff edge.
- Close-mesh netting is being pegged to the cliff face to prevent loose material falling.
Seaford - soft engineering
The construction of the extended arm on the west side of the entrance to Newhaven Harbour in 1890 effectively cut off the supply of shingle by longshore drift so that Seaford, to the immediate east of Newhaven Harbour, experienced increasing erosion. Even before the construction of the harbour arm, Seaford had been experiencing serious erosion and, as early as 1836, some groynes had been constructed to help build up shingle. Also, in 1881, a major sea wall had been constructed.
However, beach levels continued to drop so that, by 1936, shingle nourishment was started to provide better protection for the sea wall. In spite of these efforts, by 1980 it was obvious that a more long- term solution was needed. Four possible solutions were considered:
- A new sea wall costing £24 million
- Interlocking pre-cast concrete wave breaks on the beach costing £16.8 million
- Beach restoration and nourishment with new groynes costing £8.4 million
- Repair the existing defences and continue to feed the beach, which eventually would still require a new sea wall, a total cost of £ 26.1 million
Option 3 – a soft engineering technique – was chosen. It was completed in 1987 and cost£9 million. It involved:
- Scraping back the existing beach to reveal the solid underlying chalk
- Putting on a foundation of small rocks
- Placing 50,000 tonnes of granite blocks, up to 15 tonnes each, in front of the old sea wall
- Adding 3 million tonnes of shingle to the height of the old sea wall and promenade. This shingle was dredged from the seabed 15km offshore
- Constructing a 160-metre-long groyne at the eastern end of the beach. This prevents any loss of shingle from the beach due to longshore drift. The gradual build-up of shingle against the groyne from the west is then redistributed back along the beach.
This solution has proved very successful at Seaford but there have been serious implications for the unprotected chalk cliffs of Seaford Head, to the immediate east of the groyne. Here, beach levels have fallen rapidly and, as a result, the rate of erosion of the unprotected chalk cliffs is clearly increasing.
The Lower Cuckmere Valley– managed re-alignment (managed retreat)
At present, the mouth of the River Cuckmere and the riverbanks adjacent to it are protected by defences, mainly earthbanks, all of which are near the end of their life and are starting to collapse. To rebuild them to a standard capable of coping with rising sea levels and an increasing frequency of storms would cost over £1 million.
The proposed solution is managed re-alignment: the sea and river would be allowed to flood the lower valley. Inter-tidal habitats are declining across the UK, particularly in the south-east, with a loss to both wildlife and natural coastal protection. The Government has international obligations to protect them and the managed re-alignment of the Cuckmere mouth will make a very positive contribution to their protection. There are arguments for and against this project as shown in the following article:
http://news.bbc.co.uk/1/hi/england/southern_counties/5165950.stm
- Hard engineering:
- the use of rigid structures such as concrete sea walls
- Longshore drift:
- the movement of material along a beach
- Shingle nourishment:
- the addition of shingle to a beach to replace material removed by the sea
- Splash walls:
- concrete or stone areas that cover the lower cliff face to prevent erosion from spray thrown up as waves hit the sea wall
- Soft engineering:
- the use of flexible material such as shingle
- Sub-aerial weathering:
- the processes by which rocks decompose or disintegrate as a result of being exposed to agents of weather, such as rain or frost
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