‘How and why do sediment roundness and sediment size differ between the west and east of Criccieth beach?’
...wn the beach – they get smaller and rounded. This is because the pebbles are being eroded for a longer period. As the sediment is transported by traction and saltation the process of attrition erodes it. Attrition is when sediment in the sea smashes against other sediment/pebbles breaking them down. Step 2: Development of a Strategy: The primary data that I am going to collect will be the pebble roundness, and the percentage of round and very round pebbles recorded from the west and east of the beach. This will be measured using a Power’s Chart which is qualitative or subjective data. I will also measure the pebble size; using the b axis of each pebble sample from the west and east of the beach. This is quantitative data. My sampling strategy will be to have six groups. A stratified sample of pebbles will be collected from the foreshore where the pebbles are subjected to daily coastal processes. At each end of the beach each member of the group will sample 25 pebbles. These results will then be collated later at the study centre. This amount of samples being collected is good because there is a sufficient amount of data to consider the results reliable. The secondary data will be an Ordnance Survey Map. This will be used to select sites for data collection and to assist in the construction of an annotated sketch map of the area. Also I am going to get data collected from other groups. The risk assessment is that the access to the beach is dangerous at high tide and as data is to be collected in the foreshore region, care must be taken. To minimise the risks we will collect the data early in the morning when the tide is not high. I will need to refer to the tide table to see when the tide is low. I will record my data on pre-prepared sheets and tables. Each group is going to calculate the mean percentage of rounded and very rounded pebbles. The differences in pebble roundness between the west and eastern ends of the beach will be shown using pie charts. The Mann Whitney test will be used to investigate whether the two sample sets are significantly different. The data on pebble size will be plotted between the two data sets described using the median and inter-quartile range. Step 3: Data collection, recording organisation and representation: I selected randomly from the foreshore zone along the eastern and western ends of the beach. The samples were chosen from the foreshore because this is in the zone of daily wave action so therefore the pebbles will have been eroded by attrition. The technique I used to select the pebbles at random was the ‘big-toe technique’. I moved without looking and wherever I stopped I collected data on the pebble under my big toe. Each person in the six groups collected 25 samples in the east and 25 samples on the west. The total sample for the roundness of the pebbles was 550. The total sample size for the size was 150. The b axis (essentially the width of the pebble) was measured for each pebble and roundness was calculated according to the Powers Chart. The reason I measured the b-axis was because it eliminates the anomalies. I am sampling roundness and size of pebbles. This will help me link the data back to the question. In order to represent the pebble roundness I will calculate the overall percentage of round and very round for my data’s group. Then I will draw also two pie charts for my group’s data. One will illustrate the Powers data for roundness collected form the West and the other will show that from the East. I will also do a Mann-Whitney calculation for everyone’s round and very round pebbles. In order to represent the pebble size I will draw a dispersion graph to show the 25 b axis results that I have collected. This will be done using just my data and not all the data from my group. I will then calculate the median and IQ range of my data and then add them to my graph. The Mann-Whitney test allows me to answer the question because it tells me the differences in the size and roundness of the pebbles. (see graphs) Step 4: Analysis, Interpretation and Evaluation: The differences in pebble roundness between the west and east data sets are that the West has a larger number of angular pebbles than rounded ones; whereas the East has a larger number of rounded pebbles than angular pebbles. Using the pie chart, 57% of the pebbles in the east are angular (not-rounded), and in the west 45% of the pebbles are angular. Statistically; using the Mann-Whitney test, there is no statistical difference, at the 95% level, between the two data sets (as the critical value of U for a sample size of n1=6 and n2=6, is 7. The computed U value for the roundness of pebbles is 13). However, although the difference is not huge but the results collected are substantial enough to say there are more rounded pebbles in the East than the West of the beach. The reason for this variation in pebble size is because of Long Shore Drift and attrition. The pebbles on the East are rounder because they have been eroded more; and so therefore become more round. They erode because of Long shore drift and are transported along to the east of the beach. Also the rounder pebbles roll (traction) more easily than angular pebbles. The differences in pebble size are that the pebbles in the East are smaller than those pebbles in the West. This can be shown by the fact that the median pebble size in the west was 5...