Fig. 1.5: table showing the geology of the cliffs
Hypotheses
The main hypothesis states: beach characteristics will vary from season to season.
The supporting hypotheses state:
- Beach profile has a steeper gradient in the winter than in the summer.
- The sediment material is larger in the winter than in the summer
- There will be a positive relationship between beach height and sediment size.
- Percolation rates will be greater in the winter than in the summer.
Section 2- Methodology of Data Collection
Fieldwork Objectives
To assess variation in beach characteristics between the beach profile in the summer and winter, six transects were used to collected data from, in both the summer and winter; six were chosen to improve statistical reliability. These transects were chosen through selective sampling. The transects were all taken from the unmanaged section of shore.
Methodology
Fig 2.1: methodology table for beach profile
Fig. 2.2: methodology table showing percolation rate
Fig 2.3: methodology table showing sediment size
Section 3 & 4- Data Presentation, Analysis and Explanation
Results
The winter data was collected on the 22/02/2006 between 10:30 and 12: 30.
The summer data was collected on the 24/06/2005 between 10:30 and 12: 30. The summer data is secondary data.
Fig. 3.1: table of summer data
Fig. 3.2: table of winter data
- Beach profile has a steeper gradient in the winter than in the summer.
This statement is true as shown in the results table above, and illustrated in the line graph (figure 3.6). The winter beach has a steady incline, whilst the summer beach has a build up of sediment towards the back of the beach. Larger sediment built up in the winter support a larger angle of repose and so the beach will be steeper as stated by Clowes and Comfort’s angle of repose theory. This will only occur in the winter. In the summer wave energy is increases and the berm is saturated with water, this lubrication by water encourages the down slope movement of beach sediment. Water pressure in the pores makes the sediment buoyant reducing the angle of repose
Fig. 3.3: diagram to show how
the angle of repose is reduced.
- The sediment material is larger in the winter than in the summer.
This statement is true when analysing the bar graph (figure 3.7). In all cases the sediment size is larger in the winter than there is in the summer. Generally there is more sediment towards the berm. This trend is true for the summer. In the winter there is a great increase from 10m-15m along the transect, and then the sediment size falls at 20m along the transect. There are the most anomalies when collecting sediment size data, this was because there was clay as part of the geology, this was to be taken out, but it was difficult in some circumstances to determine what was clay and what was the sediment that needed to be collected. So in some cases the mass weighed could have also contained clay. The clay was in the place of other materials, and so when the clay was taken out there was no material in its place, and subsequently the data collected was less then predicted. This statement is true when analysing the bar graph. The angle of repose increases with sediment size, in the winter the angle of repose will be greater than in the summer.
- There will be a positive relationship between beach height and sediment size.
This is a true statement as can be seen through comparing the line graph (figure 3.6) and bar graph (figure 3.7) with one another. As the sediment size increasing going back towards the berm the beach height increases. In winter when the sediment increases in size, the beach height also increases. The theory of the angle of repose states as the angle of repose (beach gradient) increases the size of the sediment will also increase.
- Percolation rates will be greater in the winter than in the summer.
From the divided bar graph (figure 3.5) this seems like a false statement, towards the berm where there is increase sediment size the percolation rate is faster in the winter than in the summer as expected, but at the other intervals along the transects this is not true. The method used to collect this data was difficult; it was extremely easy to make mistakes. If more time was available then the results may have been more accurate. The anomalous results identified are shaded, they are abnormally low. When percolation occurs the sand grains become covered with a layer of water. Water tension increases the cohesiveness of the grains, resulting in higher angle of repose.
Fig. 3.4: diagram to show how
the angle of repose is increased
Spearman’s Rank
This statistical test is used to test the direction and strength of the relationship between two variables. There is a 95% chance that the null hypothesis will be rejected when using the Spearman’s rank.
Null hypothesis: there will be no significant relationship between sediment size and beach height.
Fig. 3.8: Scatter graph showing the relation ship between beach height and sediment size in the summer
Spearman’s rank = 1 - 6 ∑ d²
n³ - n
360
1 - = 0.714 ( to 3 d.p.)
210
The null hypothesis is rejected, the Spearman’s rank states that there is a significant relationship between beach height and sediment size. As the result is above 0.5, it shows that beach height and sediment size have a strong positive correlation. As sediment size increases so does beach height.
If the data is -1, there is a perfect negative correlation.
If it falls between -1 and -0.5, there is a strong negative correlation.
If it falls between -0.5 and 0, there is a weak negative correlation.
If the data is 0, there is no correlation.
If it falls between 0 and 0.5, there is a weak positive correlation.
If it falls between 0.5 and 1, there is a strong positive correlation.
If the data is 1, there is a perfect positive correlation.
Fig. 3.9: Scatter graph showing the relation ship between
beach height and sediment size in the winter
spearman’s rank = 0.835 (to 3 d.p.) This rank shows a very strongly positive correlation between sediment size and beach height in the winter. As sediment size increases so des beach height.
Section 5 – Evaluation and Conclusion
The data collected in the winter, and the secondary data used for the summer were compared with one another so that the beach characteristics can be identified as they vary from season to season
The larger the material, the steeper the gradient of the beach. This statement was found to be true. When analysing the graphs the winter profile had the steepest gradient and when comparing this to the bar chart for sediment size it was found that in the winter the sediment size was also largest. To prove this theory further the Spearman’s rank was used, and the results found that there was a very strong positive correlation between the two variables. When this positive correlation was compared between summer and winter beaches it was found that, and the correlation is strongly positive in both cases. Clowes’ and Comfort’s theory of the angle of repose states as the sediment increases in size the angle of repose increases increasing beach gradient and therefore beach height.
When comparing the same graphs for the summer the gradient is not as steep, but this is because sediment size is smaller in the summer than in the winter. This is because in the summer high energy waves are present, so the backwash still has a lot of energy to carry the sediment down the beach. In the winter the waves carry less energy, and so the backwash does not posses the energy to carry larger sediment in the backwash; so has to deposit it on the beach creating a steep gradient made up of larger sediment. The smaller sediment can however be carried down the beach by the low energy backwash. This is why sediment at the top of the beach is usually larger than sediment at the bottom. Surfing breakers (high energy waves) present in the summer flatten beaches; they erode sediment from the beaches and transport it off shore forming a breakpoint bar. Surging breakers (low energy waves) present in the winter cause a transfer of sediment onshore, making the beach profile steep with prominent beach faces and berms.
As the sediment size is larger in the winter than in the summer percolation rates will be higher in the winter than the summer. When comparing the two bar graphs, as sediment size increases going to the back of the beach so does percolation rates. The larger sediment has bigger gaps between them for water is percolate through at a much faster rate, as larger material cannot sit together as tightly. In the summer when the beach has small sediment, the material can sit together much more tightly, and so has much smaller gaps between the sediment lengthening the percolation rate. On large sediment (winter) beaches percolation is so rapid that the swash is very short, and the backwash does not alter the nature of the beach at all leading to a build up of large sediment.
There was a time limitation when collecting the data. Data should have been collected from more transects making the results more reliable. The data could have also been collected on several different days, as the weather may have been different, the waves could have had more or less energy on different days altering slightly the characteristics of the beach. There may be slight mistakes in the data collected as it is subjective, and the anomalies may be a result of human error.
When collecting data for beach height, the spirit level was a little over 1 metre; so the change in gradient was not taken at every metre; but a little more than a metre each time.
When collecting the data for percolation rate it was difficult making sure no leaks occurred as the smaller sediment cracked as it was banked up around the piping, causing leakages. Larger material could not make a seal as efficiently around the piping so leaks occurred more readily. Water already started to infiltrate the material before the piping was full in some cases when larger material as involved so the results became slightly inaccurate.
When collecting the data for sediment analysis often there were lumps of clay in the sample which needed to be discarded but sometimes was not. In some areas it was difficult to dig to the correct depth as the sediment was too hard to dig through as it was made of solid material. Therefore sediment was collected from around the sampling area. The mass of the sediment was only collected the different shapes and sizes were not recorded; this however could be done in future studies.
The study could be developed further measuring the waves, so that their wave type could be identified. This will give explanation to the behaviour of the beach, as the energy the waves carry could be identified from this. This could not be done on this occasion, as it was a safety risk. To measure the waves’ length and amplitude the person measuring the wave needs to be in the sea.
Books
- Environment and People by Michael Witherick
- A New Introduction to Geography by David Gardner, Greg Hart and Nic Howes
- Landmark AS Geography by Robert Prosser, Michael Raw and Victoria Bishop
- Discover Physical Geography by Keith Grimwade
Websites
Word Count
2163 words
