Walton on the Naze
a) Describe and explain the natural processes operating on the Naze cliffs.
All along the exposed side of the Naze cliffs, and to a smaller extent on the managed areas, erosion is constantly taking place. These are as such:
Slumping
The Naze cliffs are made up in layers. The base off the cliffs is a thick layer of very soft but impermeable London clay. Sitting on top of this are two permeable layers. The first is the Red Crag. This is made of reddish coloured sand and shells, which are the remains of an ancient seabed from 3 million years ago. The next thinner layer is of Glacial Materials, deposited from the last ice age. Slumping occurs when it has been raining heavily. The top two permeable layers become totally saturated with water and become very heavy. The water then seeps down and reaches the impermeable London clay. Now as it cannot seep through this layer it runs out of the cliff at the intersection between the layers. This causes mini streams and fountains to be seen on the cliff. This and the weight of the material on top causes it to slip off the clay onto the beach, where the loose material is quickly taken away by normal coastal deposition. Examples of this can be seen all along the unmanaged section of the Naze.
Hydrostatic pressure (Hydraulic action)
Waves breaking onto the face of cliffs can exert large amounts of pressure. This has a huge impact on the joints and cracks in the cliff, as the pressure and speed of the waves forces air into the cracks and compresses it, followed by rapid air expansion as the wave subsides. This puts huge amounts of stress on the rocks and can cause large blocks to be pulled off the cliff, as well as smaller weathered fragments. The force of the wave can also pound the cliff. This happens when bubbles form in a breaking wave and as they hit the cliff they collapse the rock with a hammer like pressure effect.
Abrasion or Corrasion
Waves that have been breaking up the beach will have inevitably picked up beach material such as sand and shingle. As the wave hits the cliff, so does all of the material it is carrying. This rock-hitting-rock (ballistic impact) is the process of abrasion or corrasion. The amount of erosion this will make depends on the size of the sediments available, aswell as the speed and type of breaking wave.
A larger version of this is Terminal Scouring. This is when large pieces of material are driven against the cliff base by the wave, inevitable causing the cliff to be literally scoured out.
During the process of Abrasion Attrition occurs. This is when the material used in the process is broken down, and the individual parts are rounded off, finally forming the fine sand we find on beaches.
Both Hydrostatic pressure and Abrasion are most effective in storm conditions. These mechanical erosive processes will pick out the differences in rock strength, or any joints, cracks, bedding ...
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A larger version of this is Terminal Scouring. This is when large pieces of material are driven against the cliff base by the wave, inevitable causing the cliff to be literally scoured out.
During the process of Abrasion Attrition occurs. This is when the material used in the process is broken down, and the individual parts are rounded off, finally forming the fine sand we find on beaches.
Both Hydrostatic pressure and Abrasion are most effective in storm conditions. These mechanical erosive processes will pick out the differences in rock strength, or any joints, cracks, bedding planes and fault lines. This selective erosion is called differential erosion.
Corrosion
Corrosion is the chemical weathering by the dissolving of rock and sediment in saline water. It is unlikely that much of this occurs in the unmanaged section of the Naze as the material is eroded so quickly anyway. Where we might find this is in the managed section, on the Greenheart piles and on the concrete wave breaks. These are normally too resistant for the power based erosions, but could be broken down by a very slow gradual disintegration.
Water-Layer weathering
This is another form of coastal erosion that would have effect on the managed areas as, aswell as effecting the unmanaged somewhat.
This is the alternate wetting and drying of rock exposed at the coast. This combines with many other chemical weathering processes, such as hydration, oxidisation, salt crystallisation to weather the rocks. As each layer is removed, it leaves a fresh one for the same to repeat again.
Biological weathering and bioerosion
Plants and animals weather rocks by boring or abrading them, or by chemical action. Algae, lichens, sponges and molluscs bore into soft rocks and leave fine tubes and pits in the rock surface. On the Naze cliffs, in the unmanaged area it was very clear to see large holes dug by various animals in the softer permeable surface. These were by creatures such as sand martins, badgers and foxes to name but a few.
Also on the rocks on the beach it was clear to see barnacles, seaweed, mussels, lichen and algae encrusting the surface. They form some protection in basic wave conditions, but in stormy weather they may be ripped off, taking rock with them, and then used themselves in the abrasion of the rock.
b) Describe and explain the coastal management system operating between the Mabel Greville and the Tower Breakwaters.
The area the Council of the Naze decided to manage was between what is now the Mabel Greville Breakwater and the Tower Breakwater. They did this to protect the valuable housing land.
Sea wall
The main way they did this was to build a large sea wall all the way along between the two breakwaters. This is quite a complex, and yet expensive, sea wall, but it is very effective. There is a diagram on the following page.
The main part of the sea wall is made of concrete blocks that go up in a three step formation. Each step was about a meter in length. The purpose of this is to dissipate most of the wave energy before it goes anywhere else. This then leads up to the flat concrete slab revetment. This was about three meters long. The purpose of this was to again dissipate wave energy, and it also prevents terminal scouring. This then led upto the slanted wave return wall. This was slanted towards the sea so that any waves that did reach that far with any force would be turned back out to sea, and not onto the land. Beneath the Revetment and the wave return wall is a fill in of london clay. But beneath that at the level of the beach as it meets the sea wall is a sand sheet drain layer, to ensure the sea wall does not become too waterlogged and fall apart from the inside. The weight of all of this protection is very great, and to stop it all falling into the sea a timber breastwork was put in made of Greenheart piles. Greenheart is a wood from the Amazon that is very resistant to salt water and to rotting. There are beams running horizontally against the concrete blocks, and also vertically, thrust deep into the beach to keep it all in place.
Breakwaters and rip rap
The breakwaters (Mabel Greville and Tower) have a large purpose aswell. There aim is to break the waves further off shore, so they loose there energy before they reach the shore and so make less damage to the cliffs. Also due to there size and build, the breakwaters act as large groynes.
At Tower breakwater, on the unmanaged side the council has recently put in large amounts of rip rap in the form of large boulders. This was to protect the unmanaged side as the waves were cutting right into where the breakwater is, and if left unprotected, the waves could of cut right round the breakwater, defeating the point.
Groynes
The groynes (and as aforementioned the breakwaters) act in preventing Long shore drift occurring. This is when the waves move material along the beach. Without any of these most of the beach material here would be washed away leaving quite a barren beach. As it is the groynes and the breakwaters form six separate smaller beaches, of rather high quality for the area.
Drainage and Vegetation
Up in the cliff, a herring bone drainage system has been put in to help drain the water off the cliff face. This prevents slumping. This is also a non visual protection unlike the other very visual protection schemes. Aswell as drainage, the vegetation all along the cliff helps hold it together and again prevent slumping. This of course attracts wildlife, some of whom burrow holes, which is in turn detrimental to the sustaining of the headland.
Steps
Finally, for an access and safety purpose steps have been put in on the cliff face and on the sea walls between the groynes. On the cliffs the steps and paths are always going at an angle and change direction. This reduces the amount of erosion that walkers would otherwise have on the area. This does however produce quite an eyesaw, of a strange zig zagging path on the cliff. There are also steps towards the Mabel Greville breakwater above the sea wall for use by the beach hut owners, and these also act as an extra protection from the sea.
c) Do you think the scheme has been successful?
Before we see whether it was successful we really need to look at whether it was really needed in the first place.
In favour of the protection we can firstly look at the Social and Human factors.
Firstly there are large amounts of people living just up from the cliff. If the cliff was allowed to recess by itself the houses would not stand for long. Also the area is seen as an area of beauty and has many visitors, especially dog walkers and families who enjoy the area. On the negative side the sea walls are very large and unsightly, and produce quite an eyesaw, and people may not want to see this ever time they open there curtains.
In terms of environmental factors, without protection much land, vegetation and wildlife habitat would be lost to the sea. But on the other hand this is what is supposed to be happening, and putting in sea walls is going against nature.
With the economic factors, it is obviously very expensive to put in, but if it is done well (like it is) it will last for a considerable amount of time, and should be worth the money. On the negative side, again the protection does cost a huge amount, and the council could put this into better use somewhere else, and could easily move the people to better housing away from the cliff danger and buy off any owned land and leave it for the sea.
In terms of the political reasons it is more to do with the views of the local Tendring District Council. The view most of them had was that there was a problem and it should be fixed. The main problem was where the huge funds needed would come from.
For how successful the project has been we only have to look at what it has achieved. Since the protection has been installed the cliff has not retreated at all. This is obviously a very effective solution and so is successful. Also the groynes have helped to build up the beach and retain a pleasant atmosphere.
WALTON ON THE NAZE F IELD STUDY
PHIL HIETT 12C
