Table of Contents
Introduction
My investigation will look at several coastal processes and how they affect the beach, and the question I came up with is ‘How do coastal processes shape the beach at Porlock Bay?’ From this I devised 2 sub questions;
How does the path of transportation affect the beach’s shape?
From this investigation I aim to understand how coastlines are shaped depending on the active processes present there. The investigation will take place in Taunton, Somerset as this area is close to the coastline and has examples of coastlines; on one hand Minehead has coastal defences to prevent changes happening to the land whilst Porlock Bay, the area I have decided to investigate, has a lack of defences, meaning it’s easier to investigate processes and how changes are made specifically at the coastline. Porlock bay is a shingle beach so I wouldn’t be able to measure movement of fine particles such as sand but I will be able to look at rock sizes across the beach and how high the beach is built up over the years. A shingle beach also makes it easier to observe movement as they can be tracked if I decide to use rocks to measure processes such as longshore drift direction.
My sub questions focus on two main processes; the first question looks more at deposition of sediment whilst the second looks at longshore drift. The first sub question looks at how the movement of sediment could contribute to the shape of the beach and what direction would sediment come from, and from this we could deduce how longshore drift and deposition contribute to the shape of the beach. To investigate this, I would measure what direction longshore drift occurs in. In relation to this the second sub question aims to investigate the varying shapes along the beach and try to understand how the shape alters at different points along the beach, and from this we could theorise how different processes or events could help build up the beach. To measure this, I would look at the different pebble sizes across the beach and identify if there are any outstanding landforms such as headlands.
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This study relates back to the specification 3.1.3.1 (Coastal Systems – Coasts as Natural Systems) as it looks at changes made to the landscape, and the question itself looks at a specific area in Taunton to investigate how changes occur to coastal landscapes from the processes within the systems. The study will also help me understand how beaches are formed and can provide details on active processes at the beach.
Porlock Bay is located in Taunton, Somerset. It is situated in west England. The closest body of water is the Bristol Channel
Literature Review
The way processes affect the beach has been studied in different papers, but I wanted to focus on what processes have helped form Porlock Bay
The official Exmoor National Park website has a section dedicated to coastal management for Porlock Bay, which is split into different sub sections. The first section, called How have geomorphological processes shaped the coastal landforms at Porlock Bay, talks about the origins of Porlock Bay as a beach. It states that the shingle and pebble ridges formed after rising sea levels 6000 years ago. It also states that longshore drift carried the stones eastwards. From this we can deduce that the beach was formed mainly from transportation processes, and I will see how my findings compare to historical research.
Plymouth Coastal Observatory provides a case study of Porlock Bay and how it changed over time, particularly the storm in October 1996. This storm resulted in a high storm surge that destroyed the top of the old beach and pushed it back, which allowed a lot of the land behind it to flood.
Methodology
How Why Pros Cons
Beach profiling I will measure the profile every 20 steps and take a measurement at each berm. I will also take 50 step measurements to get a wider range of results. I will take around 6-10 measurements. The sampling type is systematic. This gives us an idea of the beaches shape and how it changes across the beach. The 20 step measurements will be done to see the consistency of the sizes across the beach whilst the 50 step measurements will be done to get a bigger range on the sizes from the starting point. This method will show how steep certain areas of the beach is and, in some cases, how high the beach can build up to. From this we can infer reasons why the beach builds up this high. This method is incredibly time consuming and will therefore need to be done straightaway. To deal with this me and a friend did the beach profiling whilst another measured pebble size at the same time. Also the length measured can be subjective; where we measured from the top of each berm someone might measure at a different point. In addition to this identifying berms is also subjective, particularly the smaller ones where it would be harder to tell where it starts and ends.
Pebble Size I measured different aspects of the size of the pebble and used Power’s Index to measure the curvature of the pebble. I also took an average from the size of the pebbles. The pebbles were measured at the top, bottom and middle sections of the beach where I conducted the profiling study. I took the measurements at berms as they show changes in water levels and would therefore show how different sizes of pebbles would build up. I will use this method to look at where bigger and smaller rocks are located so I can identify changes in size and see if there are any possible patterns in the sizes This method is useful for showing how rock size changes not only across the beach but also at different gradients of the beach. This could show which rocks are more exposed to erosion or what types of rocks are able to be built up high.
This method takes a lot of time to do and can feel mundane as you repeat the same procedure. In addition to this the differing rock sizes won’t guarantee that you can find similar sized rocks along different sections; the measurements taken depend entirely on which rocks are used for measurements.
Longshore Drift Test I will lay out a measuring tape and throw an orange into the ocean, tracking how long it takes to reach a distance of 10 metres This enables me to see the direction of longshore drift and work out the prevailing wave direction. The method is easy to carry out and requires little equipment. The use of an orange is also good for the local environment as using artificial products like corkscrews could disrupt the ecosystem, for example if a sea bird mistakes it for food it could choke to death The biggest issue is that the conditions will be very unpredictable; on a calm day you will get better results as opposed to a stormy day, so results will depend entirely on the weather. In addition to this once you throw the oranges you won’t be able to get the oranges back, which can be seen as littering and locals may complain about the test.
Photo analysis I will take photos of different areas and will use these to present different aspects of the coastline This helps to identify any outstanding landforms and help identify active processes at the coastline. By taking photos instead of doing sketches the features are kept the same so I won’t miss any aspects that could be important. It is also to draw comparisons between different images Features that become identified are subjective as some people would be able to name features other people would’ve missed. Lighting conditions are also crucial in making features visible.
Secondary Data
Sediment Cell Type I will find out which sediment cell Porlock Bay is located at This may help me to understand what processes occur at Porlock Bay as it might give information as to what occurs at the general area If I find information on what processes occur at the beach then it would help me answer my investigation much more easily and give me an idea of the processes that help shape the beach It’s highly likely I won’t find information on processes and I may be forced to filter through a lot of information to actually find something, which is incredibly time consuming
Risk Assessment
Issue What Issue Does This Pose? How Can This Be Dealt With?
Weather Conditions Ideally we would want to go out when the weather conditions are good, however the forecast predicts that we would run into rainy weather, which could affect data collection We will have to wear waterproof clothes to make sure that we don’t get wet. Making sure the data collection is done under cover is also important as recording data during rain would be incredibly difficult
Walking Porlock Bay is a shingle beach which means it can be painful to walk on if you don’t have appropriate footwear. In addition to this, to actually reach Porlock Bay there is a lot of walking to do uphill and downhill which can be very tiring Making sure to have footwear such as wellington boots or hiking boots would be required to help give comfort; I believe that wearing wellington boots would be the better option as the weather is predicted to be bad so wearing these would be a far better option than risking getting a lot of water in your shoes
Dangerous Terrain In addition to the long walks, the terrain itself could be very dangerous and you could slip and fall, which is particularly dangerous when going up and down steep hills Wearing shoes with strong grips will be very important to help traverse the terrain. In addition to this you have to be careful when walking, so you shouldn’t run, especially along the beach and on the hills
Data Analysis
Rock Size & Power’s Index
This chart shows the average rock size in Porlock Bay at different sites, starting from Hurlstone Point and going westwards; the measurements were taken at every 50 steps except for the last bar which was taken 200 steps away from site 8 to get a larger range and see how an area further away matches up with the general pattern. And there is a pattern; the further away we went from Hurlstone Point the bigger the average rock size until site 6 where the sizes start to decline. Site 9 followed the initial trend of increasing sizes and has the highest average, which could suggest that sites 7 and 8 are anomalies and the rock size increases past site 8. Site 2 is also an anomaly as the average rock size suddenly increases before decreasing again. Measuring rock size poses some issues as it comes down to which rocks we decide to measure as every rock would have a different measurement. To combat this, we could measure different rocks at each section (top, middle and bottom) and make an average of each section before creating an overall average. However, in exchange for more accurate data, this makes the method even more time consuming than it seemed at first. Overall, the pattern follows how I thought it would go; I theorised the smaller rocks to be built up against the headland as smaller rocks are easier to deposit and easier to carry in currents, so they would be the first to be placed. However, this isn’t to say that this is the definite reason for how my data turned out as there are a lot of deciding factors to take into consideration such as how sudden increases in sea levels (e.g. during storm surges) can carry different sized sediment upwards. Additionally, the rocks that we chose to measure could be a coincidence as no two rocks would be completely alike, so if we measured different rocks in the same sites we could’ve easily found different results.
This graph shows the number of different rock shapes found along a stretch of beach. My results say that at the bottom and middle of the beach there were mostly sub-rounded rocks (3 and 4 rocks respectively), whilst at the top of the beach there is a large amount of sub angular rocks (5 rocks). The trend makes sense as the rocks closer to the bottom of the beach will have been more exposed to erosion by particles in the water and other rocks hitting against each other (this process is called abrasion) whilst the rocks at the top of the beach would’ve been less rounded due to not being exposed to water erosion. However, I theorised that the rocks closer to the water would be much more rounded than the ones in the middle, which is the complete opposite in my data sample. I thought it would be this way as the rocks in the middle are further away from the water and therefore would be exposed less to erosion, however the data says otherwise. All the data collected in this sample will contribute to the outcomes; as mentioned with the pebble size analysis the shape of the rocks found will differ greatly between rocks, more so when it comes to the actual shape as there aren’t any averages drawn. In addition to this Power’s index is a more subjective method of data collection; despite having a visual scale the class given to each rocks depends on what each person sees it as, for example where one person can see a rock as sub-rounded another person can see the same rock as well rounded. In addition to this, on the way to the site we walked across the beach and I noticed that there appeared to be a lot of rounded rocks at the very top of the beach so the sample I collected would differ greatly had I collected data from a different site. This means that the results found entirely depend on the rocks measured; the data could have easily followed my hypothesis if I was more careful in selecting the rocks, but this would likely not reflect the actual rocks there. To improve the collection, I could’ve selected a few different rocks at each point, see which shape pops up the most, and then add this to the data, but this again has the issue of the sample varying across the beach.
Orange/Corkscrew Test
This table comes from the orange test where you throw an orange or cork into the ocean to see the direction and speed of longshore drift. At the beginning of the test we had 5 oranges but we could only record 3; the 1st orange we tested was thrown too far out, which wouldn’t have been a problem had it moved a significant amount at a visible distance, but instead it drifted away out of sight. The 4th orange was broken on our way to the site so this wouldn’t have provided a good result. Nevertheless, we still threw the broken orange into the ocean. The result of this was that the orange split into several pieces and we didn’t know where to measure from. Apart from this we managed to work out some results and drew an average of about 46.8 seconds. Then I worked out the velocity of longshore drift and found it to be around 0.21m/s.
The location marked with a cross is the approximate area from which I conducted the orange peel study, with the arrows showing the directions that the oranges moved in. The varying lengths of lines represent the time taken for each of the measured oranges to travel, decreasing with each orange. Aside from the various issues with the oranges themselves there are a lot of other factors that could’ve hampered the investigation. To begin with, the day we went out was quite stormy which affects the way the waves moved. The first orange was a prime example of this as it took far longer than all the other oranges to move, and this was because the tide kept changing directions which led to the orange continuously following it as well until it finally began moving leftwards. In addition to this the test itself left1905000may not be 100% reliable as we had to make an estimate as to when the oranges would cross the 10-metre mark, so it may have been shorter or longer. To counter this one person stood at each end of the mark whilst one person in the middle threw the orange.
Photo Analysis
left279178900left65849500This landform is Hurlstone Point, an example of a headland which has formed from erosion of hard rock. The different grooves between the rocks show how erosion crack the rocks up ask miss what erosion type this is. The erosion makes the rocks appear very onion like and almost like it has different sections. The Headland also appears to have formed a cave at the front judging by how the rocks behind it are arranged, but it’s hard to tell without getting a closer look, which unfortunately wasn’t possible as its too dangerous.
The above image is a picture of Bossington Beach after the tide receded. The tides are weaker and at this point the weather has died down a bit but was still rainy. The beach is far more visible and reveals a groyne that was previously submerged. The berms are also much higher at low tides.
