Cliff erosion in East Sussex - the processes, problems and solutions.

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Index

Introduction                                                                                    page 3

Summary of Coastal Erosion and Weathering                               page 4

Rottingdean                                                                                    page 5

Peacehaven                                                                                     page 7

Newhaven West                                                                              page 9

Newhaven East                                                                               page 11

Cliff Retreat rates                                                                            page 13

Problems of Cliff Retreat                                                                page17

Solutions for Coastal Erosion                                                         page 19

Cost Benefit Analysis                                                                     page 23

Questionnaire                                                                                  page 24

Questionnaire Results                                                                     page 25

Questionnaire Analysis                                                                  page 26

My solutions for the sites                                                               page 27

Lewes District Council’s plans                                                       page 28

Reference page                                                                               page 31

Introduction

We went to Rottingdean, Peacehaven and Newhaven to look some examples of cliffs. All these places are located in Sussex, to the east of Brighton on the south coast. These maps show the location of these places:-


The aims of this project are to find out how and why the cliffs are being eroded and weathered. Then to discuss what can be done and the best method to prevent or slow down these actions, which are causing coastal retreat.

On the fieldwork afternoon we visited the cliffs and sketched the cliff profiles in rough, we also took photos so that we could look at them later. We labelled the profiles to show what was happening to the cliffs. We then noted down the coastal protection schemes already in action, eg sea wall, nothing, groynes etc.

To collect the questionnaire data I first made a suitable questionnaire which I then handed out to people living in the local area to fill in. Once I had all the data I needed, I represented it so that I could see people’s opinions.

I noted down problems when I visited the cliffs, which I later looked up to confirm what I had seen. I researched on the internet to see if there were any other problems. At the same time I looked at the solutions to these problems, so that I could discuss the management methods which should be employed to prevent or slow down cliff retreat in East Sussex.

 

         

Summary of the Processes of Erosion and Weathering

Coastal Erosion:-

  • Corrasion- the wearing away of cliffs by large waves hurling beach material against              them.
  • Attrition- is when waves cause rocks and boulders on the beach to collide with each other and break up into smaller pieces.
  • Corrosion/solution- is when salts or other acids in sea water slowly dissolve a cliff. Eg salt spray.
  • Hydraulic action- is the force of waves trapping and compressing air in cracks, thus cracking pieces of rock away from the cliff.  

Coastal Weathering:-

           …it is the break down of rocks where they, it doesn’t involve movement. It comes in three main forms:-

  • Physical- freeze-thaw, where water seeps into cracks, freezes and expands by 9% thus enlarging the crack and weakening the rock/cliff.
  • Chemical- salt spray and limestone solution. The salt will eat into soft rock such as chalk. Limestone solution is caused by carbonic acid, which occurs naturally in rain water. It reacts chemically with rocks, such as limestone, which contain calcium carbonate.
  • Biological- roots grow into rocks and crack them. Also birds create nest and in doing so they make holes in cliffs.

Wave Action

        When waves break on the coastline, their energy is converted into a constructive or destructive force. This depends upon the steepness of the coastline, the height and fetch of the waves and the wave frequency.

        Constructive waves have a strong swash, and because their backwash seeps into the beach, material is left on the beach. Whereas, destructive waves have a weak swash and there strong backwash stays on the surface so little or no material left on beach, yet transported along the coast by long-shore drift.

An active cliff is where erosion is still happening and there is a steep cliff face.

An inactive cliff is where erosion has stopped and weathering is eroding the face to a less steep gradient.

        

  Cliff Profiles

Rottingdean:-

Rottingdean is an inactive cliff because a coastal path and a sea wall have been built here. The cliff used to be active; this can be seen by the wave-cut platform primarily at low-tide, until man built a sea wall and placed an artificial beach there to protect the cliff. However, although the base of the cliff is protected from the sea, the top is still vulnerable to weathering. This can be seen by holes forming at the top of the cliff, this could be one of many things. It could be salt weathering, where salt crystals (from sea spray) form in the air spaces in the rock, and then over a period of time they grow cracking the rock; or it could be the action of acid rain (solution/corrosion) causing the cliff to dissolve at the top. There are also other forms of weathering. Biological weathering is obvious from the growth of vegetation on the cliff face and the top of the cliff, where the roots of plants grow into the rocks causing it to crack. Also there are bird holes which are created by birds trying to make a habitat. Also the chalk is clean in some places yet stained (by surface run-off of the clay) in others which show that bits have broken off; this is possibly from freeze thaw, which is where water seeps into the cracks already present, expanding as it freezes by 9% causing bits of rock to break off. This causes the cliff to have an undulating surface.  

This cliff was also “scraped” back, when the coastal path and sea wall was built, so that it was at a less steep angle so that it was more stable. On the fieldwork afternoon I took the approximate cliff angle to be around 80° as the base is protected yet the top is being weathered back.

There is only a very fine layer of soil at the top bearing little vegetation (low grasses); however there are a few plants on the cliff face because it is an inactive cliff, adding to the process of biological weathering.

There are also flint layers and signs of horizontal bedding in on the cliff face that shows that it was built up in layers then metamorphosed into the present day chalk, which is a soft rock. The flint, which was created millions of years ago, is a  sign of changing sea temperatures and thus climate change, because flint is the remains of sponges (which prefer warmer sea temperatures) that have died and the silicon in them has compressed and formed flint. This shows that there were forces acting on the rocks which also explain the faults and joints (vertical lines of weakness) present.

Peacehaven:-

This was the only active cliff that we visited. Luckily when we did visit it, it was low-tide, so we were able to see everything that was happening. We saw the wave-cut platform extend out to sea; showing us how far the cliff has moved over time. There was debris at the very foot of the cliff, which tells us that erosion and mass movement have taken place. The debris of chalk boulders had been rounded off so we know that they have been there a while whilst being eroded. The base of the cliff has also been eroded by similar processes such as- abrasion, attrition, hydraulic action and solution.  I could not see any signs of biological weathering; however I am sure that both freeze-thaw and chemical weathering were taken place, because once again there was an undulating surface.

Join now!

There was also a wave cut notch and a chalk overhang visible created by under-cutting at the base of the cliff; both features displayed signs of weaknesses because I could see cracks. All the cracks would be enlarged by hydraulic action mainly.

The brown stains on the cliff were caused by the clay at the top of the cliff being washed by surface run-off. This clay is being weathered also, visible because of a difference between the cliff angle and the angle of the clay. There is only about 30cm of clay soil at the top, with very little ...

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