The main title of the investigation is “To what extent is the rate of erosion equally distributed at Lulworth Cove and Durdle Door. This main question has been split into 3 sub questions to ensure the question is answered to its fullest. “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 “How and why does beach profile vary between Durdle Door and Lulworth Cove. During the investigation data was collected, tables and graphs were constructed which contained primary evidence to help answer the sub question. However secondary data was required to answer the sub question “To what extent do geological features such as faults and bedding planes contribute to erosion at Lulworth Cove and Durdle Door”. This is due to not having enough time and reasonable equipment to gain the correct evidence.
“To what extent do wave characteristics contribute to the distribution of erosion at Durdle Door and Lulworth Cove?”
Tables/ lists were used to represent the data for this method comparing both Lulworth Cove and Durdle Door. The wave count table displays a tally chart which shows that the wave frequency at Lulworth Cove is lower than that in Durdle Door in general. At Durdle Door we counted 11 waves in 1 minute whereas in Lulworth Cove we concluded with a figure of 9 in 1 minute. These numbers mean destructive waves are the most predominant wave at Durdle Door, due to there being more than 10 waves breaking on the shoreline in 1 minute. Constructive waves are the most frequent at Lulworth Cove as only 9 waves broke at the shoreline in 1 minute. This data therefore suggests that the rate of erosion at Durdle Door; compared to Lulworth Cove, is higher. Geographically, this implies that the beach profile at Durdle Door should be steeper. With the values obtained from the longshore drift method, an approximate speed was calculated to determine the velocity at which sediments and rocks may hit the landform. Using the formula speed = distance/time we can figure out the speed in which the buoyant object travels. In this case it was an orange. The buoyant objects represents rocks and sediments however the results gained are indefinite as other factors such as friction and mass are not accounted for. Rocks don’t float on the sea surface they roll on the sea bed (traction) which would decrease speed. Therefore the speed presented is an approximate value. 0.047m/sec is the speed in which the orange travelled at Durdle Door and 0.041m/sec was the speed of the orange at Lulworth cove. It can already be seen that the difference in sediment/wave speed between Durdle Door and Lulworth cove is 0.006m/sec which isn’t significant on a small scale. However this event occurs on a large scale therefore will have a dramatic impact. These results imply Durdle Door to be the landform with the higher rate of erosion as the speed in which rocks and sediments hit the landform (abrasion) is greater than that at Lulworth Cove.
Furthermore, while gathering the results for these two methods there were some limitations and ethical issues that were established, one being the frequency of waves to determine if the waves were constructive or destructive. As the investigation areas were densely populated the nearshore and offshore were never isolated at that time therefore distinguishing between waves and ripples was difficult. To improve the results the investigation could have been constructed at a time in the year where it was less busy. As wind speed the equal at both investigation points it had no effect on the final results. Ethical considerations that were established were to use a buoyant object that was biodegradable and not to impede the flow of individuals.
“To what extent do geological features such as faults and bedding planes (Lithology) contribute to erosion at Lulworth Cove and Durdle Door?”
Secondary evidence such as rock type was needed to configure this sub question. From the booklet given by the instructor we can see that Durdle Door consists of a rock called Portland Limestone which is extremely vulnerable to erosion and weathering processes such as freeze thaw, hydraulic action and carbonation. This is due to its physical characteristics. Limestone is commonly known to contain a drastic amount of faults and bedding planes which makes it vulnerable to erosion. Therefore it is acknowledged as a less resistant rock. On the other hand, Lulworth Cove consists of a narrow limestone entrance and Wealden Beds being the predominant rock type. Wealden Beds is known to be the less resistant rock in the scenario and its physical characteristics are similar to that of Portland Limestone however its chemical properties make it a lot weaker, therefore the rate of erosion at Lulworth Cove should exceed that of Durdle Door. Conclusively, we can establish that lithology in this aspect doesn’t have a massive contribution to the rate of erosion due to the physical properties being extremely similar and to truly discover significance the rocks need to be viewed at a microscopic scale.
While gathering information about this method the only ethical consideration that I came across was copyright. Reliable images and website on Google were used to avoid any copyright claims.
“How and why does beach profile vary between Lulworth cove and Durdle Door?”
A line graph was used to show the cumulative height change at increasing distance at a Lulworth Cove and Durdle Door. The line graph displays two colour coded lines that represent the two different investigation points. Blue being Lulworth Cove and red being Durdle Door. The graph shows that Durdle Door contains a steeper beach profile compared to Lulworth Cove. This is due to the height change at every point being significantly higher at Durdle Door. For example at 3m away from the sea Durdle Doors height change increased by 33.5cm whereas Lulworth only increased by 8cm. The greatest height change at Lulworth Cove was 20.5cm compared to that of Durdle Door which was 33.5cm. These figures show that in general Lulworth Cove has a flatter beach profile than Durdle Door. Wave type can be viewed as one of the most important factor that contributes to a variation on beach profiles and using past and present geographical knowledge the primary evidence I have collected have shown positive results. For example destructive waves provide a steeper beach, which my result evidently illustrates. Furthermore, I took to knowledge that sediment size might have an effect on the beach profile. The bar chart shows the average sediment size at increasing distance from the sea. In general, the bar graph shows at Durdle Door when you go up the beach the sediment size increasing whereas at Lulworth Cove the sediment size decreases. At initial the average sediment size was measured to be 1.2cm at Durdle Door and finishes at 2.1cm, which is a 0.9cm increase. On the other hand, at Lulworth 1.4cm was the initial and ended with ;0.1cm, which is a significant decrease in value. The results on the bar chart show on average Lulworth Cove contains the larger sediments which implies less erosion occurring. These results provide evidence that beach profile increases as wave magnitude/frequency decreases.
In addition to gathering evidence limitations and ethical considerations were established one being the average sediment size. The investigation areas were densely populated which implies throughout the whole day sediments may have been moved by individuals intentionally or purposely which will have a negative impact on the results as the sediments aren’t distributed in the natural positions. The ethical consideration was not blocking the path and view/ disturbing individuals on the beach.