The main title of the investigation is “To what extent is the rate of erosion evenly disturbed at Lulworth Cove and Durdle Door?” This main question was then split into 3 sub questions; “To what extent do wave characteristics contribute to the distribution of erosion at Durdle Door and Lulworth Cove?”, “To what extent do geological features such as faults and bedding planes (Lithology) contribute to erosion at Lulworth Cove and Durdle Door?” and finally “How and why does beach profile vary between Lulworth cove and Durdle Door?”. During the investigation relevant data was collected and they were displayed and presented on tables and graphs, thus allowing a valid conclusion to be reached.
“To what extent do wave characteristics contribute to the distribution of erosion at Durdle Door and Lulworth Cove?”
From the data collected we can establish, that in general, the type of waves present at the two investigation sites are different. The waves that have a high frequency at Durdle Door are destructive waves whereas at Lulworth Cove, the predominant wave is constructive waves. This conclusion was made due to the amount of waves counted per minute. At Durdle Door the maximum amount of waves counted were 11 therefore destructive. On the other hand at Lulworth Cove the maximum amount of waves counted were 9. The conclusion is further supported by the speed of longshore drift, which also implies the speed at which sediments move along the coastline affecting the rate of erosion at the landforms. The speed at which sediments move along both investigation points is a theoretical value as mass, friction and any other important factors are not accounted for. The approximate speed at which rocks and sediments move along Durdle Door is O.O47m/s whereas at Lulworth Cove the approximate speed is 0.041m/s. The difference is not significant however on a large scale it can cause vital change to a landform. This therefore implicates that the rate of erosion at Durdle Door exceeds the rate of erosion at Lulworth Cove, which was what I expected to find.
Geologically, the results the can be explained using geological terms. Wave refraction and geology are two important factors that contribute to the rate of erosion at both investigation points. Wave refraction reduces the wave intensity and magnitude due to the waves being concentrated at one area, which is the narrow entrance. The headlands in front of the cove absorb the majority of the wave’s energy resulting to an increase amount of constructive waves at the cove. One the other hand Durdle Door is vulnerable to all kinds of waves as there is no natural or artificial barrier in front of the landform to absorb wave energy thus rate of erosion is higher. Geology also contributes to the rate of erosion at both landforms. If the geology is at a high resistance the rate of erosion will be slow. In this case Portland limestone and Wealden beds have the same physical properties. They both contain significant amounts of faults and bedding planes which is a large contributor to the rate of erosion.
“To what extent do geological features such as faults and bedding planes (Lithology) contribute to erosion at Lulworth Cove and Durdle Door?”
It can be concluded from my finding that the presence of faults and bedding planes have a significant impact on the rate of erosion at Lulworth Cove and Durdle Door. As the geology and lithology at both investigation points is quite similar it was difficult to construct primary evidence for the sub question. Thus, secondary information and research was required obtain relevant information about the geology and lithology at the two investigation points. Landforms with completely different geology characteristics would improve the results and provide reliable results. However in this scenario Portland limestone can be views as the resistant rock and Wealden bed as the less resistant rock.
My findings conclude; depending on lithology the rate of erosion should be equal at both investigation points as the lithology present is extremely similar which implies whatever weathering process that occurs at Durdle Door should also occur at Lulworth Cove.
“How and why does beach profile vary between Lulworth cove and Durdle Door?”
In general, despite fluctuating results, we can establish that Durdle door has the steeper beach profile compared to that of Lulworth Cove. At Durdle Door the greatest height change was 33.5cm and the lowest height change was 0cm. The figure 0 was obtained due to there being no more accessible area to measure as we were met by the cliff face. At Lulworth the largest height change was 20.5cm and the lowest height change was 8cm. It can be seen by through the figures obtained that every point measured was greater at Durdle door which implies that the beach profile is steeper. This can also be supported by the wave type present at the two investigation points. At Durdle Door destructive waves was the most predominant wave. When destructive waves break at a beach they possess the characteristics of a weak swash and a powerful backwash. As a result, material is strip from the beach producing a steep beach. Evidently Lulworth Cove should portray the opposite as the most frequent wave present is constructive waves. They have a strong swash and a weak backwash which means the rate material is deposited exceeds the rate at which material is removed. Thus, overtime material builds up and the beach flattens out.
Initially, I took into consideration that sediment size contributed and had an effect on the beach profile. However sediment size was evenly distributed at both investigation points but the arrangement of sediments was different due to the types of waves present. At increasing distance from the sea at Durdle Door the average sediment size increases, whereas at Lulworth Cove the average sediment size decreases. Conclusively, the results present on the bar chart displays on average Lulworth Cove contains the larger sediments which indicates less erosion at the coast in contrast to Durdle Door.
To conclude, the main question “To what extent is the rate of erosion evenly distributed at Lulworth Cove and Durdle Door?” can be answered by starting with the most important factor which is waves. You can state that the velocity at which sediments travel at Durdle Door is greater by 0.006m/sec in contrast to Lulworth Cove. However the value is approximate as mass, friction and other factors weren’t accounted for. Some aspects such as beach profile can also determine the rate of erosion at both investigation points. Overall it can be concluded that the rate of erosion at Durdle Door exceeds that of Lulworth Cove.
There were 4 main stages to undergo completion of the investigation; “To what extent is the rate of erosion evenly distributed at Durdle Door and Lulworth Cove?” The stages included introduction, planning/method, data presentation and conclusion. Evidently, each stage had both positives and negatives aspects in attempting to fully answering the main investigation question.
The introduction stage was carried out to ensure that a relevant and worthwhile investigation could be conducted that allowed a wide variety of results to be collected and analysed to ensure that a valid conclusion could be drawn. The introduction section contained a vast amount of positives. The background research/reading conducted provided the necessary knowledge of understanding the significant factors that contributed to rapid erosions at coastlines and to ensure the results I gathered were geologically correct. The Location of study section provided precise information on the destination of the investigation, which allowed secondary research to be carried out such as wind speed and weather forecast on the particular day.
The planning stage was also carried out to ensure that my investigation question was effective and that the means of gathering results were reasonable and assessable. The breakdown of the main investigation question allowed me to assess the question in depth to ensure it was fully answered. The risk assessment that was carried out reduced the risks of injuries as we possessed the knowledge of the potential accidents that could occur when data was being collected out in the field. For example tripping and clipping was a risk which was resolved by wearing sensible footwear. A recording sheet was constructed to allow neat and tidy data collecting, which also reduced the time spent understanding and figuring out which data represented what method. The recording sheet also allowed data presentation to be reasonably easier as we could distinguish what type of graph would be suitable to the chosen data. Finally, gathering and understanding how the equipment’s and methods function allowed effective and accurate data collection. However some of the equipment enabled some recording to be inaccurate. For example the 1 metre string between the two ranging poles was not fully stretched which means the distance from the sea may have been less than we expected. To obtain better and accurate results a metre stick could have been places between the two ranging poles to ensure the string was fully stretched to 1 metre.
The data collection stage provided both positive and negative points whilst collecting data. The investigation was constructed in reasonable amount of time that enabled us to obtain relevant results, however for my investigation question the area chosen was too small/compact to show great contrast. Wind speed, geology and other factors were quite similar which means only a hand full of factors could be analysed. However a large quantity of successful data was collected which indicated my investigation was worthwhile and successful as I could identify areas of contrast between the two investigation points. To obtain approximate sediment speed the longshore drift values were required to calculate a velocity which represented the speed rocks and minerals moves along the sea bed. How hard the sediments hit the landforms depend on how fast they are travelling. Therefore a greater speed equals a more vicious impact. Finally, the wave count to distinguish if constructive waves or destructive waves were the most frequent waves had its limitations. The area of investigation was densely populated at the time which means it was difficult to distinguish actual waves from ripples. Preventing this could involve underdoing the investing at a different time of the year that doesn’t attract a vast quantity of individuals.
Data presentation showed a lot of positives. A bar graph was constructed to show the average sediment size at increasing distance from the sea. The graph contained two bars on the same distance, blue representing Lulworth Cove and red representing Durdle Door. This data presenting technique was advantageous it was quite easy to compare the sediment size between the two investigation points. Also construction of bar graphs is easy and provides the sufficient data comparison. By including the two investigation points in one bar graph significant differences can be identified, thus aiding in answering segments of the main question.
Line graphs were used to show the cumulative height change on beach profile at increasing distance from the sea. The two lines showed variation between Lulworth Cove and Durdle Door. The two sets of lines allowed multiple data two be analysed. The line graph was an effective method in that, the data collected was quantitative which means a large range of data could be plotted at once and the values were continuous. Unfortunately, the technique was time consuming as plotting some points required a large amount of concentration to avoid plotting in the wrong area. Theoretical values may have been plotted due to exact values being difficult to deduce due to the scale size.
Tables and lists were made to hold data neatly and show comparison between the two types of data collected. Initially this method of presenting data was very effective as it was very easy to understand and information was really easy to compare however there are some complications with this sampling technique. It was not effective when finding or determining trends and correlations. If more time was spent constructing the investigation more values could have being obtained for wave frequency which means the data would be more representative and a suitable graph could have been drawn, therefore a more accurate conclusion.
Finally, annotated photographs were used to show the visual contrast between the two sites. It provides a general overview on the surroundings and what the environment was like on that day. This technique can be viewed as advantageous as it provides excellent visual representation of the sites and they can support the data collected to some aspects. One the other hand, they do provide some negative points. Individuals are keener to annotate the most attractive areas on the photograph and leave out the least attractive aspects which can also provide important information. The reliability and accuracy of secondary photographs is not always guaranteed, which provides irrelevant information and may lead to incapability’s of understanding results.
They data collected provided evidence for conclusions to be reached on each of the sub questions. The relevancy of the conclusions was at a high as they were drawn directly from the data collected. These conclusions provided explanations for each of the sub questions which made answering the main question easier. However, some flaw were identified which may set some minor draw backs. Some data collected were not 100% accurate meaning the conclusions drawn weren’t 100% reliable. For instance, distinguishing between waves and ripples was difficult as the investigation sites were densely populated. Results were collected and inaccurate conclusion may have been drawn. The quality of the conclusions can also be viewed as inadequate standards as they were based upon data collected from one day and a certain time of the day. Undergoing data collected for a large period of time would improve the conclusions drastically.
Overall, the entire investigation contained a vast amount of positives and negative which may provide opportunities for other researchers to improve and gain a better understanding of the subject matter coastline erosion.