Explanation Of Profile 2, Newhaven West
This cliff is made of sandstone at the top and the rest is chalk. So as sandstone is a soft rock the angle of the dip is less steep than at Peacehaven. Also we know that clay is present as there is evidence of slipping and sliding and these only occur when clay is there. Also there are a lot of joints, faults and bedding planes which could result in hydraulic action happening as we saw in the first profile but this is an inactive cliff so there won’t be any examples of erosion happening here, as the cliff face is being buried by debris and weathering and mass movement will dominate. Furthermore at the top of the cliff there is physical weathering happening, which could account for the undercut in the cliff and why there are rock falls at the bottom of the cliff. Also as in the first one there is salt spray, an example of chemical weathering, and at the bottom some vegetation, an example of biological weathering.
Explanation Of Profile 3, Newhaven East
This profile is much like that of Newhaven West. They are both made up of chalk, sandstone and clay, although there is considerably more clay. They are both inactive cliffs so no examples of erosion will take place here. They both have faults, joints, bedding planes and lines of weakness. They both have the same examples of physical, chemical and biological weathering. They both have rock falls and slipping and sliding. Although one major difference is the angle of dip. At Newhaven East the angle is much less vertical which could be to blame for the slumping, although it could be because of the soft sandstone at the bottom.
Explanation Of Profile 4, Rottingdean
This cliff is very different to the others. It is completely made out of white chalk, thus containing a small amount of clay. Also it has a cliff defence at the bottom probably to stop slumping and sliding and slipping. Although it has some similarities to the other three. It has plenty of faults, joints, bedding planes and lines of weakness. It has chemical weathering, from the salt spray and rainwater getting into the joints etc, biological weathering, from the vegetation on the cliff, and physical weathering, from freeze thaw action, acting upon the cliff, which could account for the small number of rock falls on the bottom. It is an inactive cliff, although it is protected by the wall and the man made path.
Data and Calculations
Map 3
Map 4
We can also use this information to estimate the average land lost per year: _
Problems of estimating the future rate of erosion and the problem of using an average figure
One problem when trying to predict the future rate of erosion is human intervention. Man could invent a machine to slow down or stop erosion and would therefore make the predicted figures inaccurate. Also due to global warming we could have bigger and more violent storms that would then result in a quicker rate of erosion.
The problem of using an average figure is that one-year the sea could be eroding an area of very hard rock, e.g. granite, and would therefore be slow. Whereas during another year the sea is eroding some very soft rock, e.g. clay, the rate of erosion will be much quicker.
The problem of cliff retreat
The main problem of cliff retreat is how it affects the houses nearby. Houses near an eroding cliff with no protection are very hard to get insurance on. Furthermore the price of the house will depreciate and the owners will gradually lose more and more money. Also any roads near the eroding cliff could fall in, for example the A259, and if major roads like this fall in, commuters will have to take another local road and that will eventually become extremely congested. Also all the gas and sewage pipes and electricity wires would have to be dismantled and put somewhere else before they fall into the sea.
Solutions To Cliff Retreat
Groins
Groins help to slow down the effects of long shore drift and build up material at the bottom of the cliff and protecting it from further erosion. Groins are built perpendicular to the shore and are usually 50 – 200 metres apart. Normally they are made of tropical hardwoods, which are more resistant to erosion and marine borers; many are now made of large rocks, concrete or steel. The wooden groins have rotted easily so a new design was needed, and new boulder groins are now built, as they look far more natural.
Groins are relatively cheap, wooden groins cost about £6000 each. However the “zig-zag” effect is caused by long shore drift, building up sediments either side of the groins. This means the beach requires regular annual servicing, with bulldozers levelling out the shingle once again and this costs a lot making these groins not particularly cost effective. Moreover groins usually have an adverse effect on the currents and this can endanger swimmers. The groins themselves get very slippery and can become a hazard, which means more work is needed to put up sufficient warning signs on the groins. These signs look out of place on an already unattractive and unnatural eyesore. Much like seawalls a groins effect of trapping shingle means there is further erosion down the coast because it is less protected. Many tourists will come to beaches and the only help groins provide is as a windbreak.
Revetment
A revetment is a sloping structure that breaks and absorbs the wave energy. It is a cheaper alternative when the cost of a sea wall cannot be justified. They trap material behind to protect the base of the protected cliff. The old types of revetments are made out of wood and are fixed by posts into the beach with wooden slats. Concrete and stone revetments are sometimes built, and these allow added permeability. Revetments are relatively cheap (about £1000 – £1200) but in heavy storms, as their height does not give total protection, letting material over and through it, they will break and eventually collapse. Because of this, revetments, especially wooden ones, need to be repaired or replaced over time. Moreover they are unnatural and unappealing to tourists.
Sea Walls
A sea wall is another way of protecting a cliff. This construction normally consists of a concrete wall that runs parallel to the cliff deflecting the wave energy. Over time though these structures needed constant maintenance because of the hydraulic action acting upon it. As a result of this new versions of the sea wall were made including a “bull nose” sea wall. This type of sea wall is now the most popular because of its effectiveness. The curved bull nose deflects the waves energy and spreads the impact. This bull nose also stops water getting over the top and stopping possible salt-water erosion.
These sea walls create a nice sea walk for tourists and locals and so don’t destroy the beauty of the sea. Although a big disadvantage of sea walls is the expense. One metre of sea wall costs between £2000 and £5000. They also need frequent maintenance adding to the expense. Furthermore they are environmentally unfriendly as they disrupt the natural ecosystem of the animals living in that area.
Beach Nourishment
This uses several methods of protecting or replenishing beaches where natural systems have failed. Sand or shingle may be placed directly on the beach to build it up. Sediment is sometimes also placed in the nearby area, to make sure that sand is available when needed. This method is more attractive than other methods and the most natural. But it also costs a lot of money and has to be repeated over and over again. Also it is not necessarily hugely effective as the sediment that is taken from the seabed can make the sea deeper, so the waves get bigger and therefore wave action erodes the beach more quickly.
Gabions
These are a short-term solution to this major problem. They are very cheap, usually costing about £350. They are metal cages filled with rocks. Although they are susceptible to rust and damage in bad weather, they are a very effective, cheap, short-term solution.
Breakwaters
These are very effective especially on wide beaches and allow some of the shore drifts to continue. However they have to be built deep in the water and are hence fairly expensive. Recent improvements are oil drums and old tyres floating parallel to the shore. This is much cheaper and an effective wave energy absorber and a useful way of recycling.
Different views of solutions to cliff retreat
People who live near to an unprotected area of cliff retreat will be very interested in any possible solution to the problem. However people who live further inland may not want the council to spend considerable amounts of money on cliff protection. Additionally people who live further up the coast will probably be adverse to these ideas as it is possible that they may experience an increased rate of erosion near where they live.