Purpose of investigation:
To test the theory of sorting. This suggests that the further up the beach, the larger the pebbles. This is due to constructive waves having a large swash, meaning they have the energy to carry large sediment up the beach.
The energy then percolates down into the beach meaning it only has a weak backwash and can only carry the smaller sediment back down, progressively depositing it down the beach so the largest is at the top and the smallest is at the bottom.
Methods used:
Selecting pebbles: To select pebbles, we used a tape measure to mark every 2 metres down the beach from the vegetation line. This ensured the results were spread evenly down the beach. At every 2 metre point, we placed a quadrat down and used a random number generator to select 5 pebbles from each sample point. For example if the number generator said 3 and then 7, we would select a pebble from the 3rd row up and 7th column along.
This ensures an unbiased sample.
Measuring pebbles: To measure the pebbles once we selected them, we used a calliper. This is a piece of measuring equipment which allows you to measure the length of an object, usually pebbles. We measured each of the 5 pebbles we had previously selected and recorded our results in a table. This piece of equipment was fairly good as it was designed to measure pebbles, which is what we needed to do. However, the callipers we were using were fairly bad quality and kept getting jammed, making them unreliable. Also, we only measured the A-axis
(longest side) of each pebble so even if a pebble was long and very thin, it would have been recorded as ‘larger’ than a slightly shorter but much wider pebble, which is incorrect. A better method to have used would be to record the volume by seeing how much they displace water. This would clearly identify the bigger from the smaller, however we did not have enough time to do this.
Data presentation:
Scatter graph: To present our data we used a scatter graph. In order to do that we worked out an average pebble size for each of the samples and plotted them. Distance from vegetation line was along the y axis and average pebble size was along the x axis. A scatter graph was the most justifiable data presentation method because once you’ve drawn a line of best fit in, you can clearly see whether there is a positive, negative or no correlation at all.
This also lets you observe the anomalies.
Analysis:
Spearman’s rank: In order to analyse our data we used the spearman’s rank coefficient. This is where you complete an equation and you come out with a number between 1 and -1. If the number is close to 1, it means there is a clear positive correlation, if it is close to -1 there is a clear negative correlation and if it is close to 0 there is no correlation at all. Once the number came out, we plotted it in the spearman’s rank coefficient graph to see how significant our result was. Our coefficient was 0.64, meaning a fairly strong positive correlation however a few anomalies. Once plotted onto the graph, it came out that our result was 95% significant meaning our investigation could be concluded to a 95% significance level that the results are reliable.
Results: Our results proved the theory of sorting to be correct as the average pebble size at 24 metres from the shore was 5.28cm and average pebble size at 2 metres from the shore was 2.54cm, a clear decrease as you reach the shore. Most of our results followed this pattern apart from a large anomaly at 12 metres from the shore where average pebble size was 5.60. This is explained by the berm at 11 metres from the shore which is caused by deposition from low energy waves. This means larger sediment may have been deposited here which affects the results. General:
Improvements: If I were to do this investigation again, I would measure the volume of the pebbles instead of the a-axis. This would be a more accurate strategy. Also, I would do more than one transect along the beach because our results only show one cross section of the beach. If we did transects along the beach it would give us a better resolution and a clearer correlation. Also, I would carry out the investigation at different times of the year to see if there are any different patterns and if sorting theory is demonstrated all year round in different weather conditions. Also, I would ensure we went at low tide as this gives a bigger sample space as there is more beach to measure so we could get more results. This further improves resolution.
Advantages of location: This was a good location because it was a pebble beach, the 1 condition required for sorting theory to be tested. Also, it had mobile phone reception meaning if there were any accidents, it was possible to call for help. Another advantage is that it was easily accessible, we were able to be driven fairly close, and then there was a footpath along the cliff and down onto the beach. This is also good if there was an accident because it is a short distance to the main road and there is a clear path to get there. It was also a very safe beach with no falling rocks or hazards.

Disadvantages of location: However, there was a footpath along the top of the beach meaning as people walked along it they were displacing the pebbles, meaning they were in a different arrangement and potentially affecting results. Safety precautions: there were very few safety precautions to consider. Some parts of the beach were steep so we had to be cautious not to slip as the pebbles were fairly unstable. Also we had to make sure not to go out into the water as the currents may have been quite strong.
Conclusion: In conclusion, the hypothesis: ‘Pebbles on the beach are smaller the closer to the sea’ has been proved correct. The results we collected showed a clear positive correlation for the transect we were testing and using Spearman’s rank, is it correct to say that our results are 95% significant. However there are some factors that could have made the results more reliable such as repetitions using different transects, and visiting at different times of day for variation. Considering the time we had for the investigation, I feel that it was successful as we managed to support our hypothesis with our results.
Limitations: One limitation is that we visited when the tide was in meaning the length of our transect was quite short, not representing the whole beach. Also, time was a major limitation. We only had a couple of hours to collect our results so even if the weather conditions were bad or the tide was in, we had to carry out the investigation anyway. Another limitation is that we visited in late October, in the Autumn, and there had been storms the week before. This means that it is likely that during this period, destructive waves were dominant which means the sediment would have been eroded from the beach and the waves would have dragged some of the larger sediment back down the beach in the strong backwash. This will have altered the arrangement formed from the constructive waves which may explain the anomalies we discovered.