Chesil Beach Investigation

Hypothesis 1. The size of the pebbles will get BIGGER as you move to the LANDWARD side of Chesil Beach.

Hypothesis 2. The slope angle will INCREASE as you move to the LANDWARD side.

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Hypothesis 3. The pebble size at the western end of Chesil Beach (Abbotsbury) will be BIGGER than the eastern end (Fortuneswell).

Our aim when we got to Chesil Beach was to: –

1. Look for a change in the size of the pebbles along our transect and,

2. To look for a change in the slope angle along our transect.

To achieve these aims we inserted two ranging rods, five metres apart from each other with the tape measure, along our transect (making sure that the top of the aluminium spike, where it meets the rod, was at ground level). We decided to put them 5 metres a part, as going to Chesil Beach before to carry out an initial inspection; from this initial inspection we also decided that we should measure the pebble size every metre. We then aligned the gun clinometer, which is a device used to measure slope angles, with the bottom of the top marker on the foresight rod. We aimed the clinometer whilst making sure the sights were in line, at the bottom of the top marker on the backsight, we repeated this process to verify that no mistakes had occurred while obtaining the slope angle.

When the two ranging rods are in place we also measure the size of the pebbles. We measure a pebble every metre along our transect with a ruler. We measure the length, width and depth of each pebble in millimetres. Once the results have been recorded in our data tables, we move from the seaward side to the landward side of our transect by another five metre; and repeat the procedure of measuring the slope angle with the gun clinometer and the pebble size with the ruler.

Once we reach the landward side of Chesil Beach, we calculated the average size index at each site (every 5 metres) at Abbotsbury. To do this we added the length, width and depth of each pebble then divided the sum by 3 to get the average pebble size for each of the pebbles, we then added these 5 totals for each site and divide by 5. When this has been accomplished we then calculated the average size index for the whole of Chesil Beach at the Abbotsbury end. To attain this we added together the average size index of each site and divided that total by the amount of sites we counted (in our case 21).

We chose to use a transect to display our data because a transect is a tool for displaying characteristics along a line, drawn to present the alternating morphology along the beach. Furthermore it is the most appropriate method of showing these form of data.

When we carried out the data obtaining stage of this investigation it was not the first time we had visited Chesil Beach. We had visited Chesil Beach previously to carry out an initial inspection, this involved deciding how often we should measure the slope angle and how often we should measure the pebble sizes.

After this initial inspection we concluded that we should measure the slope angle every 5 metres. The reasoning behind this is that if we measured every 1 or 1/2 a metre it would be difficult to detect variations, as the slope angle does not change that much over 1/2 a metre; furthermore it would be too arduous and time consuming. The point of this exercise was to generate a general outline of the slope profile, not an impeccable interpretation of the beach profile. Also if we surveyed the slope angle every 50 metres we would fail to notice the subtle variations in the slope profile and as Chesil Beach is only approximately 100 metres wide we would produce a triangular shape for our profile. Along with the above if we measured to this degree we would increase the margin of error as in more instance the summit of Chesil Beach may obscure the backsight from the line of sight, preventing us from measuring accurately.

We concluded, in addition to the above, that we should measure the pebble size every 1 metre, because if we measured every 5 metres insufficient quantities of data will be collected, impeding us from acquiring a credible average. Furthermore subtle alterations in pebble size could be neglected. Also this data set is not large enough to allow us to discover trends in pebble size, this inhibited us from deducing well-founded and sound conclusions. Moreover, if we measured the pebble size every 5 centimetres, it would be too time-consuming and laborious; also in some instances the pebbles could be near enough 5 centimetres preventing us from noticing differences. In addition to this, the sizes of the pebbles do not change that dramatically over 5 centimetres.

The sort of data collection described above is recognized as systematic sampling. This is a procedure in which the sample is recorded at a predetermined interval, in our case every 5 and 1 metre. The reason why we chose to use this method is because it has a number of significant advantages, for example, it’s easy to use and allows us to relate sections of the beach to other sections. Furthermore it is invariable, so if one of the stones that needed to be measured was dirty or muddy we still had to measure it, instead of picking a cleaner stone.

But along with advantages come disadvantages; systemic sampling may pick up some queer irregularities, for example, if at every point that you were measuring the stones there was an exceptionally large pebble, this would persuade you to fabricate peculiar findings and conclusions. Also this system is dogmatic, meaning that it is biased and that certain pebbles do not have the same likelihood of being selected; for example, in this investigation every site was a metre long, so pebbles in the middle (50cm) of each site had a 0% likelihood of being selected.

Another technique of gathering data is by random sampling. As the name suggests, this is when you pick up any stones on the beach in no particular order, whilst following your chosen transect. This method has many advantages over systematic sampling; it is non-biased as every pebble has the same probability of being picked. Furthermore there is also less possibility of drawing an impropriety in your data set as there is a miniscule chance of there being a disproportionate pebble. But as with any data gathering process there will always be disadvantages; this process lacks structure, if you were using systematic sampling you could explain how and when and why you are going to measure, but with random sampling all you can see is that you will pick and measure the pebbles in any order.

This is dangerous as it may put across the sense that your work is disorganised and that you have not put any thought into your data collection. Furthermore it is harder to plot data using random sampling because if you used systematic sampling you could say that you will measure the pebbles every metre and this means that when you plot a graph/chart your axis will have regular intervals. But if you use random sampling the axis could go like this 0.3, 2.76, 50.65. Some people argue that random sampling is time consuming, others say it’s not.

It could be seen as time consuming as you will have to measure where you are selecting your pebbles every single time you select them, and this measurement will not always be a round number. But it could also be seen as quicker compared to other ways as you can pick the pebbles from anywhere and not bother about measuring every metre or so. Another negative point is that it’s subjective, this means that when a person is trying to pick random pebbles with no logic, their preferences tend to emerge and even though the person is trying to pick randomly it won’t be seen random by a neutral observer.

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