Each team taking two posts, which were present horizontally on the beach for management, we proceeded to find the distance between adjacent posts with a tape measure, finding it to be roughly one hundred metres. Then we placed ranging poles at the three major gradient changes, producing an upper, middle and lower section of the beach. Then we found the middle point of each area and gathered around one hundred stones from each, simply by, without looking, placing them in the bag.
The reason why we used the poles was mainly for ease of use if we decided to continue our investigation another day. The fact that they were one hundred metres apart was a bonus which meant that there was sufficient distance between our measurements to ensure some change. From the hundred stones we selected 25 as this number would not be of too great a workload and might provide a suitable average.
Collection of Data:
We used a systematic sampling method as there are posts approximately every hundred metres along the beach; these were used as the marks where our cross-transects would be performed. This measure meant that if further study were needed it would be easy to use the same area. In the sampling of sediment size it was extremely hard to perform truly randomly so we settled for the pseudo-random effort of simply picking a handful and a pre-designated site (in the middle of our transects). The practicalities of the investigation involved keeping the tape measure low to the ground both to avoid wind moving it and to gain an accurate measurement. Meanwhile when sampling in close proximity to the sea we were careful to look out for one another in case of a wave. In order not to change the layout of the beach we had to be cautious not to tread on the shingle in our transect as it mobile. The health and safety of our investigation was not a large issue, as the day was both sunny and warm with little wind. However had it been worse conditions some attention to wearing waterproofs and staying away from the sea would have to be given.
For general impressions of Hurst Beach we used a digital camera and acquired some aerial photos to demonstrate the shape of the spit.
Analysis, evaluation and interpretation:
To address whether Hurst Beach is horizontally graded I have decided to only take the samples nearest the sea as these are the most likely to be effected by long-shore drift. To present this, this scatter graph may be useful:
There appears from sight to be a correlation between Sediment size increasing and distance along the beach increasing, however to fully determine this, a statistical test is needed: Spearman’s rank would in this case be the right one to choose.
The question of vertical sorting is very similar to horizontal grading; however in this instance I have decided to add the lower samples together and in turn do the same with the middle and upper samples then compare them:
I did this because I wanted to see whether the sediment at the bottom of the beach was on the whole smaller than at the top.
This graph though sparse shows the small sediment size of the lower sample, and although statistical analysis may be useful due to the small sample size there is not enough evidence to clearly back a correlation.
This Bar chart is here simply to show in graphical form all of the data, and the respective sizes of all of the sediment which I sampled at each pint of sampling.
Having used Spearman’s rank on the both sets of data there is no significant correlation to the geographical 95% mark of sediment size grading. I used Spearman’s rank to analysis the data because I needed to test the direction and strength of the relationship between two variables.
Presentation of a summary:
The entire investigation was fairly inaccurate; there was a fair amount of room for human error which may have distorted the results as the measurement of the volume of the sediments was done with a basic ruler using height, width and length. Other room for error exists in the relatively few samples taken, at twenty five stones for each section there are not really enough stones considering the size of the beach. Finally the pseudo random sampling technique may have skewed the results a little as, factors such as pebbles that are small falling out of the hands, and other small details add up.
To extend the investigation could be interesting one could find out the angle the waves approach the beach, and whether this angle changes throughout the year, because the angle of approach will affect long-shore drift. However the problem with this is that the spit is highly mobile and so the morphology of the beach might change during the year. Maybe personally investigating Chesil beach or other similar beaches might yield some interesting results and compare to see if human intervention is a major factor in the grading of the beach.
The results were probably not correlatory because of lack of samples; however judging by the lack of significant correlation it would be interesting to consider why – as mentioned above investigating a similar beach may provide the answers.
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