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.