Geography Independent Investigation
“To what extent is the rate of erosion equally distributed at Durdle Door and Lulworth Cove?”
Coastal landforms can be views as the most dynamic structure on earth and hence most catastrophic. The rate in which coastal landforms change can occur significantly faster than others. At one area of land there can be erosion in one season and deposition in another. The majority of changes along the coasts are accomplished by waves, which can be either constructive (slow rate of erosion) or destructive (fast rate of erosion). Weathering plays a vital role in the formation of Landforms. This process is stated to be of natural events which break down pieces of rocks to give the coastline its shape. These natural events include wind or rain, freeze thaw and salt crystallisation which have minimal effects on the landforms at a short period of time whereas colossal hazards/ events such as hurricanes and storms can have a dramatic effect of the erosion rate at landforms. May, (1971), remarked that the most substantial losses occurred in winter where rainfall and winds were at their peak. In coastal areas such as Dorset, which is concordant, immense winds and waves of long fetches break off soft or less resistant material and rocks which leaves the more resistant rocks exposed therefore channelling the formation on landforms demonstrated at the Cliffs of Moher, County Clare, Ireland. The definition of a concordant coast is when coastline has alternating layers of hard rock and soft rock that run parallel to the coast. The soft rock in usually protected from erosion as the hard rock acts as a protective barrier. Landforms such as Coves can be formed if the hard rock has been ruptured through therefore leaving the soft rock exposed to erosion (e.g. Lulworth Cove).
Furthermore, previous coastal studies carried out by Johonnessen et al (1982) concluded that heat of salts on salt crystallisation was possibly the main erosive mechanism above high tide on sunny, south facing sandstone landforms for example east cliff in Dorset. The average surface reading of NaCl are 27ppm (De Wolf, 2001). This study was constructed in Brighton therefore results will approximately be similar in Dorset.
Many studies have been carried out to investigate what factors which put certain landforms at risk of rapid erosion. A variation of landform response occurs according to material strength. Hard rock coasts erode very slowly due to the constraining factors of material strength and rock mechanics (ALLISON, 1989). Therefore the more resistant rock landforms should remain essentially stable when erosional processes act upon them. In contrast, soft rock landforms are subject to additional weakening by weathering and degradation by mass movement; these processes are likely to operate more rapidly in the wetter, warmer climate predicted for regions such as Southern England due to global warming (Department of the Environment, 1991). Conclusively the landforms present in the south of England are more susceptible to erosional/ weathering processes. (Richard and Lorriman, 1987) pointed out that taller landforms erode more rapidly because they generate higher shear stresses and suffer larger landslides, however they also yields more sediment per unit of recession. Whilst reading the article on BBC news ‘UK storms: Extreme weather caused years of erosion’ (21 February 2014) an interesting fact caught my attention which stated “more than 3m of the cliff at Birling Gap has been lost to the sea this year”. This is where I felt that a wider range of studies can be beneficial to investigate the reasons why this unpredictable event occurred, and also encouraging more people to undergo investigations to arrive at reliable conclusion.
Locations for Study
West bay is a small coastal harbour settlement and resort situated on the English Channel coast in Dorset, England. It is approximately 1.5 miles (2.4km) south of Bridport in West Dorset. Coordinates are 50.7116?N 2.763750?W. The coast of West Bay is also part of the Jurassic Coast, which is a World Heritage site which stretches for 98 miles which includes most of the Dorset coastline. West Bay is surrounded by an Area of Outstanding Natural Beauty which is an organisation whose aims are to conserve and enhance the natural beauty of the landscapes around the UK.
Durdle Door is a costal landform (arch) on the south of Dorset. It is a natural limestone/chalk arch. It is situated on the Jurassic coast near Lulworth in Dorset, England. Coordinates are 50?37’16N 2?16’36W. The development of the area around Durdle door and landform itself is directly related to the geology of the area, which comprises of alternating resistant and less resistant rock parallel to the shoreline also known as a concordant coastline.
I have chosen these two locations as they show several significant differences such as geology, coastal landforms, wave speed etc., which will allow me to compare and contrast and determine which factors are the most significant which contribute to erosion.
The title of my investigation is “To what extent is the rate of erosion equally distributed at Durdle Door and Lulworth Cove.”
In the planning stage I split this title into 3 other research question/ sub questions; (1) “To what extent do wave characteristics contribute to the distribution of erosion at Durdle Door and Lulworth Cove?”, (2) “To what extent do geological features such as faults and bedding planes (lithology) contribute to erosion at Lulworth Cove and Durdle Door?” and finally (3) “How and why does beach profile vary between Durdle Door and Lulworth Cove.
• For sub-question (1) I would expect to find as wave speed and wave frequency increases (destructive waves) the rate of erosion at the landforms will be significantly higher than coastlines with low energy for example Holderness coast. This is due Weymouth being a high energy coastline which therefore means that destructive waves will be the most foremost wave, causing the landforms to erode and recede at a higher rate. In addition I expect the area around Durdle Door to erode significantly faster than the area around Lulworth Cove, due to geology characteristic and change in wave speed.
• For sub-question (2) I expect lithology to be a major contributor to rapid erosion. Feature such as faults and bedding planes can determine whether a coastline is susceptible to erosion or firmly resistant to erosion. This therefore implies that these features also determine the shape of a coastline and what landforms can be created.
• For sub-question (3) I expect the measurements of the beach profile to be equal at both investigation points due to the prevailing wind coming from the same direction, therefore the wave frequency should also be equal. However I believe the waves at Lulworth Cove will have a lower magnitude which means the rate of deposition will exceed the rate of erosion which leads to a flatter beach profile. Furthermore there are limitations and they will be addressed in the data analysis.
Secondary information, if needed, and background research will be carried out in order for me obtain a greater understanding of the subject area. This will be executed by reading information from geography booklets supplied by the instructors which contain a wide variety of geographical literature which will help me complete my independent investigation to a high standard. All the information I obtain from secondary sources will be referenced.
In this investigation I will be involved in the collection of primary data about wave type, beach profile at the different investigation points, longshore drift/distance and the speed of longshore drift at both points. Sediment size at each landform will be collected and measured to determine if there is a correlation between sediment size and rate of erosion. Secondary data in the likes of weather forecast of that day and wind speed will be gathered and used to ensure all the variables that might provide inaccurate measurements are accounted for. This data may be gathered from the internet from website such as “Weather.com”. Specific geology landscape information will also be gathered from the internet.
Specific data will be collected and thus specific instruments of recording are required. Ranging poles will be used to measure the beach profile at both points of the investigation. The method will be executed by using the following steps. 1) Attach the string to both pole A and B at the same height and place the spirit level in the middle of the string. 2) Place pole A closest to the sea and pole B up the beach. Place a third pole C towards the top of the beach to act of as a marker.3) Line up pole A and pole B to resemble the position of pole C. 4) Ensure the string is kept tight and 1m in length. Move it up and down on pole B until the bubble in the spirit level is centred. 5) Measure the change in height from the strings starting point. The longshore drift/distance will be calculated by throwing a buoyant object into the sea and measuring the distance it travels at a given time. With this information, we can find out how fast the object moved which would be equivalent to how fast some waves hit the face of the landforms which therefore contributes to rapid erosion. To distinguish which waves were present at the landform wave counts were constructed. If there are 6-9 waves breaking on the shore in one minute then the waves are constructive. If there are 10-14 waves breaking on the shore in one minute then the waves are destructive. The sediment size will be recorded by picking out 5 sediments by a random sampling technique and using callipers to measure their size. As the majority of the data I am collecting is quantitative recording sheets will be created for each data collection method to ensure all the data is easily distributed and understandable.
(cm) Cumulative height change (cm) Distance between poles (cm) Sediment size (cm)
There are a number of ways of presenting collected data. Methods of presenting data include a line graph to show the cumulative height change at increasing distance in Lulworth Cove and Durdle Door. A bar graph could be used to show the mean sediment size at increasing distance at the two investigation points and for qualitative data radar graphs can be used. Proportional arrows could be used to show the direction and intensity of weed speeds at the different sites.
Risk assessments will be carried out throughout the whole investigation and the main risks will be identified. One of these risks could be getting lost. Avoiding this can be done by exchanging phone numbers with instructors or teachers and staying within a large group of piers. Another risk is tripping and slipping. Avoiding this involves wearing sensible and suitable footwear. And finally traffic accidents. This can be avoided by wearing a seatbelt.