- Why is erosion so great?
- Why is erosion so rapid?
- What evidence is there that erosion is taking place?
- What is the distance from the Naze tower to the cliff edge?
- What causes the cliffs to collapse?
- How much have the cliffs eroded each year?
- How does the nature of the coastline affect the rate of the erosion?
- What is the geology of the cliff?
- What is the height of the cliff?
- What volume of material has been eroded?
- How do the characteristics of the waves determine the rate of erosion?
- How high is the wave crest?
- How high is the wave trough?
- What is the wave frequency?
- What is the wave depth?
- What is the wavelength?
- What type of wave is it?
- What is the wave energy?
- What direction did the fetch come from?
- How does the amount of transportation affect erosion?
- What was the amount of longshore drift?
- What direction did the longshore drift come from?
- What was the height of the beach either side of the Groyne?
- Was there any evidence of suspension?
- How does the beach affect the rate of erosion?
- What is the beach gradient?
- What is the width of the beach?
- How deep is the sand?
- What are the different types of sea defences that Walton uses?
LOCATION
Walton-On-The-Naze is located in South East Essex/East Anglia. It is on the coast and very close to the North Sea, which can be very cold and very powerful. It is also not far away from Southend. Below is a map. Fig 10.
AIM: - To explain the rate of coastal erosion, and the processes and how successful they are.
The coastline.
The coastline can be seen as a system in which there are inputs, processors, and outputs. As seen below. Fig 11.
OBJECTIVES.
There are four objectives for this project, and they are: -
To examine the nature of the coastline.
To examine the types of waves that hit the coastline.
To measure the rate of transport along the coastline.
To examine the nature of the beach.
CHAPTER 2 - OBJECTIVE 1
DATA REQUIRED
Below is a list of information that I collected for this chapter.
- How much the cliff edge (from the naze tower) has eroded each year since 1996.
- Evidence that erosion is taking place.
- The geology of the cliff.
- What types of rock cliff is made up of.
- Appearance, colour, texture, hardness, and permeability.
- Influencing factors and limitations.
- Height of cliff.
- Influencing factors, limitations.
- Volume of material eroded.
- Influencing factors and limitations.
METHOD
I found about the geology of the cliff by: -
I looked carefully at the cliff to estimate the proportions of the different types of rock. From near the base I collected samples of each type of rock that appeared in the cliff and examined them carefully to identify their characteristics.
I made careful notes from what the teacher said about each of the different type of rocks and when I got back to school I carried out further research using the Internet. I used the search engine YAHOO to find information about Walton.
I used all of this information to annotate the cross-section of the cliff and to complete a table to describe the appearance, colour, texture hardness, and permeability.
The influencing factors are that the cliffs rock types are easily weathered aren’t very resistant, as clay is relatively impermeable, though crag is permeable. The water adds to the weight and also acts as a lubricant. Wildlife can effect it by pecking at it. The drainpipes in the cliff start to crack, the rocks erode easily and the clay is springy. A wave-cut platform was formed. There were also some limitations – human error is always a limitation as is easy to make mistakes. It may have been measured from a different point in the last year or so, and we could have measures at an angle rather than straight.
The cliff height: -(ordnance survey)
We used the ordinance survey map to measure the height of the cliff at the north, centre and southern sections. To draw a cross- section you take a map, mark on two points and draw a line between them. Then mark on contour lines, and join them up using curved lines. I also used trigonometry to find out the height of the cliff (see fig 12). This is were we have length of one of the sides a right angle plus another angle, and using these figures you must work out the length of the left-over side.
The influencing factors were the wave energy, the wave power, as these could erode the cliff by more or less each year. The type of rock, permeable etc. can affect it if it’s resistant then it will erode less than a weak rock. How much rainfall, e.g. weathering, and the wildlife, e.g. birds that rest on it. The limitations are the height/width of the measuring tool and how accurate it is, and human error. Below is a graph for the distance, of the top of the cliff. Fig 12.
The Volume of material eroded –
I worked out the volume of material eroded by finding out how far the cliff had eroded in the last year and then multiplied it by the height to get amount of material eroded. The cliff had eroded by 4m. The results will be shown in data presentation. In one year the width of the cliff face has eroded by only 1m.
The influencing factors were the weather over previous years, whether the waves were constructive or destructive, and which wave was most commonly occurring. This is because destructive waves take the material away, whilst constructive waves push the material back up. The limitations were the accuracy of measuring (human error) and where you measure it from as the height could vary a lot.
DATA PRESENTATION
On the next page is a diagram of the different types of rocks. Fig 13.
Now is a table to show the different characteristics of the different types of rocks. Fig 14.
Below are some more cross-sections to show the height of the cliff at different points, e.g. sideways and face on.
Jubilee beach, northern section of the cliff. Fig 15.
(Sideways to cliff.)
The Pillbox, centre section of the cliff. Fig 16.
(Sideways to cliff.)
Sea wall, northern section of the cliff. Fig 17.
(Sideways to cliff.)
Below is a graph to show the volume of material eroded. Fig 18, 19.
These were the results.
0
S End Centre N End
ANALYSIS
The softer the rocks they are less resistant to erosion because they cant withstand the power of the waves etc., as they are weaker. So more rock is taken away than a stronger rock would. This means that the less protection there is for the cliffs because of its nature. The harder the rock the longer it will take to erode. London clay was the most resistant rock type of the three, and it erodes slower than red crag and boulder clay.
The cliff height can affect it as the lower the cliffs the less slumped material there is to protect it. So the higher the cliffs there is more material to protect it. The waves undercut the cliffs and this means there is nothing to support it and the top of it falls down, where it then acts as protection slowing the rate of erosion down as the waves first have to erode it.
The volume of material eroded. This can be affected b wave frequency, wave type, and wave energy. The more material eroded the better the protection for the base of the cliff, so the opposite applies for the lesser volume of material eroded. This is clearly an indication that the coastline is changing all the time. This proves that the waves and weather are making it move back. The sea defences are also stopping the erosion, e.g. sea wall. This sea defence is very strong and will remain in that position for a very long time and hen it gets destroyed/eroded the cliffs will be attacked by the waves and tide once more. These are very expensive sea defences and do their job well.
So as the cliffs are made up of clay, slumping is very likely to occur, and this causes erosion. The top two rock types are permeable which means they let water through and this adds to the weight and also acts as a lubricant, and n turn encourages movement. We walk quite close to the cliff edge and this can cause it to crumble or knock it out of place.
Another reason why the nature of the coastline keeps changing is because of slumping. There is also a diagram for sliding. Fig 20, 21.
Slumping occurs when, the coherence is lost because of saturation, and the rock body moves along a slide plane reaching a flow like state at the toe. They can frequently be seen in clays, when the angle of rest is too steep for saturated conditions.
CHAPTER 3 – OBJECTIVE 2
DATA REQUIRED
Here is a list of information that I had to collect: -
- Wave energy
- Wave crest
- Wave trough
- Wave height
- Wave frequency
- Wave length
- Water depth
- Wave type
- Fetch
METHOD
I measured the wave crest and wave trough by standing in the water and measured the two different types of the waves by using a metre rule. We took five recordings of each and then took an average, so if one or two results were wrong we had enough to correct it. To find the wave height I had to do: the wave crest – the wave trough.
To measure the wave frequency we had to take a point, a rock for example, and counted for a period of 1 minute, how many waves hit that point in the specified time. We counted for a minute because we thought that would be a fair enough period to record our results. Below is a diagram of how we did this. Fig 22.
To find the water depth we had to take our results about the wave crest and trough, and find halfway between them. There were two ways of finding the wavelength, and these were
Wave height = crest-trough
Water depth (1/2 way crest + trough) = trough ½ wave height
Wave length = 3.1 x 60 x water depth
Wave frequency.
Wave type
Constructive – less than 10 per minute, builds beaches
Destructive – more than 13 per minute- erodes beaches
Wave energy (strength of wave) = 740 x H² x L
To record the results for the fetch, we had to watch the direction that the waves came from; I could also use a compass for the
The influencing factors were the wind speed and the wind direction, whilst the limitations were the fetch may change course due to the rocks in the way and the power and speed of the wind, plus the prevailing winds. human reaction speed. I think that other limitations could be the different seasons had we visited in the spring etc.
The limitations were that whilst recording there was lots of waves coming in and we couldn’t get enough time to measure the troughs etc.
DATA PRESENTATION
Below is a diagram showing each part of the wave and its measurements etc. Fig 23.
Now is a table of all our results for each method. Fig 24
(Above is the table continued.)?
Other results that I collected were as follows.
Wind direction- South East fetch- 120 kms.
Prevailing wind- South West fetch- ? Kms.
Strongest wind- North East fetch- 1008 kms. (Although it would be 640 kms if it hits Denmark.)
Below are a number of bar charts to show the information. Fig 25-26.
ANALYSIS
All of the information of the different parts of the wave has something to do with erosion, and I will explain this now. This is why erosion occurs and how it varies depending on these different influencing factors.
The wave energy is a large factor that causes erosion because the more energy it has the more power it has and it can all be concentrated on a large surface area. So the more energy the wave has the more erosion there is likely to be.
Another factor is that of the speed that the wave is travelling at. The winds and fetch are the main culprits of this as they blow hard onto the waves, which gather speed and hit the cliff with a lot of power.
Then the water depth can be a problem, as the higher it is the more area it has to aim at and it can hit the cliff at different places instead of one small place. It can also encourage mass movement.
The type of wave is a great influencing factor on this subject because depending on which one it is, it can either build a beach or destroy it. For example a destructive wave takes away part of the cliff in its backwash, while a constructive wave pushes material up the beach with its sash. (See page 2 figures 2 and 3). All of the evidence shows that the waves are constructive beach building.
The wavelength can also vary it as for the same reason as the water depth, it can concentrate on a larger surface than a thin and not so long wave would do.
The wave height is another influencing factor because it can also concentrate on larger areas of the cliff face etc. rather than just at the bottom and can sometimes lead to longshore drift. This means that the higher it is the more energy will be focused on the cliff eroding sections and transporting them along the beach.
The wave frequency can also effect it as the more waves there are in a certain time the more erosion there will be. If there are a lot of waves one of after the other then the rocks will get weakened and cracks will appear.
The wave crest and trough also effect it because of the same reason as the wave height.
The sea and its water themselves area very important factor as the hydraulic pressure push shingle etc. against the cliff face, and the gradient of the beach changes due to shingle turning into sand.
CHAPTER 4 – OBJECTIVE 3
DATA REQUIRED
Here is a list of information that I had to collect: -
- the amount of longshore drift
- the direction of longshore drift
- the height of the beach either side of the groyne
- any evidence of suspension
METHOD
Longshore drift- the greater amount of movement along the beach the greater amount of eroded material that will be moved away exposing the cliff to further attack.
I measured the amount of longshore drift by putting a cork in the water and recording how long t took for it to reach the second ranging pole we had stuck in the bottom of the ground, which were two metres away from each-other.
The influencing factors were the fetch, wind speed and the wind direction, also how strong the waves were and how much energy they had. The limitations were human error. Below is a diagram of our method. Fig 27.
Longshore drift- Groyne
We dropped a tape measure down both sides and recorded the result. It would’ve gone further although the tide wasn’t in.
The influencing factors were how much and how frequent the longshore drift was and the winds effects on wave type, and energy (cork). The cork was sometimes stuck or impeded by seaweed and other things during the experiment.
The limitations were human error and error with the apparatus, and not being to travel out into the sea as far as possible to get good results. Below is a diagram. Fig 28.
DATA PRESENTATION
To show the method used for the cork experiment I will use a cross between a horizontal bar graph and a pyramid graph to show whether movement was from the north or the south. Below is a table to show my results. Fig 30, 31. Some of our information was borrowed from other groups, ours is highlighted.
Below is a diagram to show the information about the distance from either side of the groyne, e.g. north or south. Fig 32.
ANALYSIS
Both of the graphs on the previous page show that the cork’s movement was to the north and not the south. Both of the techniques give roughly the same result, as the direction the cork went was shown as the same on both of them. So the beach tends to build up on the north side and so this is the way that the longshore drift moves. The longshore drift comes in around 320 degrees. As you can see from my diagram the height of the beach on the north side is always larger than that of the south side of the sea wall. When the south side is 95 cm, the north is 126, when the south is 138 and 124 cm the north is 170 and 190 cm, and when the south is 102 cm the north is 204 cm. The four differences in height between the north and south are, starting from bottom, 31 cm, 32cm, 66 cm, and 102 cm. The groynes were 2.4 m high, and are used to stop longshore drift and stop sand. They were in good condition which means it was working, and if they were in bad condition then the sand and longshore drift could perhaps get past the groynes and be more in the south rather than the north. This all shows that the rate of erosion is high, and the cliffs etc. are getting smaller.
My contradictions are that the groynes are rather old, and may be broken slightly, holes in them etc. which can let material through, and settle on the south side of the groynes and not on the north which is what you would think is most likely. We could have had inaccurate results from the fact that we didn’t place the equipment (poles) in the same height above the sand.
CHAPTER 5 – OBJECTIVE 4
DATA REQUIRED
- The beach gradient
- The width of the beach
- The depth of the sand
METHOD
The gradient and width- the steeper and the wider the beach the greater the wave energy that will be used travelling up the beach and so less energy there is to erode the cliff.
We placed the ranging poles 5 metres apart from the sea edge, and at each one we recorded the angle to the top of the next one using the klinometre and dug down. We then measured how deep it was till we reached sand with a metre rule. The influencing factors were erosion, the weather, the situation of the wave-cut platform and sea defences. The limitations were human error. Below is a diagram of our method. Fig 33.
The beach depth-the deeper the beach material the less backwash that will take place and therefore less material will be transported out to sea. The beach also absorbs the impact of the waves.
We stuck the metre rule in the beach, and measured how far it went down. We then dug a hole in the beach at 5 metre intervals until we found London clay. The influencing factors were how many waves and the wave energy, as well as the weather and erosion, sea defences and wave-cut platforms and high or low tide. The limitations were the rule was too small, and that we couldn’t go out very far. We didn’t have any negative readings as such. We did the measurements in that way to get them as accurate as possible, and as we thought that would be a fair interval. The only problems that we faced were that we couldn’t walk any further, as things were in the way, and that it was hard to get a reading if the rule was too small. The equipment was fairly accurate.
DATA PRESENTATION
Below are my results in a table, showing the section of the transect, the angle and depth of the sand. For the beach depth, my results were as follows. Fig 34. The total beach width we found out to be 65metres long.fig 35 is a graph.
ANALYSIS
The slope profile of the beach shows (fig 35) that as the width of the beach increases and the angle gets higher to the next ranging pole.
From the side view, I can see that the shape of the beach is relatively flat, due to London clay being at the bottom of the cliff so not much erosion has taken place and continues to get steeper as it reaches the cliff.
There has been a lot of backwash because as there isn’t much sand on there and energy is concentrated on destroying the beach rather than building it.
The graph proves, that the steeper the beach the less erosion as the waves need a lot of energy, to get up the slope, which leaves less energy to attack the beach.
The depth of the beach, there is mainly London clay on the top of the sand and the waves are mostly moving the London clay back, rather than eroding it.
The beach width means that there are more waves and longer/ larger waves needed to erode the beach when it is longer, so the smaller the beach length the more erosion and quicker.
With wider beaches it takes the waves and erosion longer to erode the beach or to take place.
My own results do not indicate much about the probable amount of erosion as they don’t support the theory of deeper sand means weak waves and energy is then absorbed by the waves.
CHAPTER 6
Reasons why erosion is so great at Walton on the Naze: -
The rate of erosion is so great at Walton because, the softer the rocks the less resistant they are to erosion. This was explained in my first objective where the picture and table of the types of rocks are.
Erosion is most likely to occur at the bottom of the cliff as they weren’t too high, and the rock type at the bottom was actually very soft compared to that at the top and was smooth. This is bad for the cliff as the winds were quite powerful and the waves were quite fast, and not too high, this means that this type of rock will erode easily. More resistant rocks take longer to erode than the others. If these are on top of the less resistant rocks then they will be unstable (hanging) and will given time fall off, covering the bottom of the cliff, making the rate of erosion longer. Also as lubricants enter cracks in the rocks they become heavy and the rocks below them collapse.
The lower the cliffs the less slumped material to protect it. The cliffs seemed relatively low so it will be easier to erode without a high cliff. The more volume that has been eroded the better the protection at the base of the cliff. There was a lot of eroded material protecting the cliff at the bottom so this will no doubt slows down erosion. The higher the cliff the less erosion there will be, due to the waves undercutting the cliff, which makes the head to fall down and erosion erodes that, rather than the cliff.
The higher the water the more area of the cliff it has to aim at. The type of wave, destructive destroys the waves, whilst constructive build waves. The waves were mainly constructive when we went there, and this means that they weren’t eroding the cliffs/beach. The more energy that the wave has the more powerful it is. The more waves there are the more erosion there will be. The more longshore drift, the greater amount of eroded material that will be moved away exposing the cliff to further attack. There was actually quite a lot of longshore drift.
The steeper and wider the beach the greater the wave energy that will be used travelling up the beach and so the less energy there will be to erode the cliff. This is because the angle is so steep that the waves don’t have much energy left after travelling up to the top. The fetch affects the wave. If it blows from a long way away, then it will gain energy as it moves and in turn as it reaches the cliff, its energy input is great, and the amount of erosion is very large. The beach was quite wide and wasn’t particularly steep.
The beach depth, the deeper the beach material the less backwash that will take place and therefore less material that will be transported out to sea. Also the beach absorbs the impact of the waves. At Walton the beach depth was relatively low, sometimes reaching over 30cm at the most.
Over the decades, sea defences have been introduced to Waltons’ beaches; you have already read about them in this project, for example the groynes. Sea defences are very important when It comes to erosion, for the main reason that they stop things like water and shingle from getting past, and on one side of a groyne we looked at there is a large build-up of sand and shingle. This shows that they are working, and this tries to stop longshore drift. These form a barrier in parts of the beaches, and some are broken slightly, which allows things to get through/past.
Walton-on the–Naze is situated in a poor position, right on the coast next door to the North Sea, and this is maybe the greatest reason for why it is such a target to erosion.
The weaknesses of our investigation were as follows.
The limitations.
Most of them were to do with either human error, or to the extent of the accuracy of the equipment we used for our measurements. A number of my results will not be exactly correct and some will be totally wrong because of the time limit we were given.
The weather, for example, the rain wind and sun etc. The animals that inhabit the land, e.g. birds pecking at it. Where we measured it from, for example, we changed the measuring point each year (by accident).
The size of measuring tools the number of measurements we were able to take the wave energy. Human reaction speed.
I don’t think that my work can be used to explain geographical concepts because, we didn’t have the very best in equipment as it is too expensive and that we don’t really need them because we aren’t people who look for this kind of evidence for a living.
If I were to repeat the exercise then I think that I would allow more time for the results to be taken. As it was we had to rush our experiments and record the results all inside the set time given to us. Also with more time we could have had more time to carry out more recordings for our experiments, therefore making them more accurate averages, and readings.
Perhaps we could also have used more accurate tools to get better results that were more realistic. It would be good if we could have gone back on another day to record some more results, and check them against our first ones, whilst changing if they are wrong. The waves were constructive on that day and maybe on another day the waves may have been destructive causing major changes to our recordings/ results.
Another thing that we could have done to improve the results would be to spend more time looking at the sea defences, as these are an important factor for stopping erosion. We did actually get to look at this area but again it wasn’t possible to look at for a longer period of time due to the set time. We did use a booklet to record our results but these are not included in my project as they were not necessary.
I have used a number of websites for my project and would like to thank them. Below are the websites I used.
