Investigate the dominant Coastal processes acting on Porlock bay and also consider suitable management strategies for Porlock bay
* To investigate the dominant Coastal processes acting on Porlock bay.
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* To consider suitable management strategies for Porlock bay.
This is an Investigation into the Coastal processes occurring in Porlock Bay, Exmoor National Park.
Porlock bay is a bay that has two points, which are Gore Point and Hurlstone Point. These two points were built because there was soft rock in between two hard rocks so it became a bay. This is a famous area for the tourists that go on holiday there because it is quiet and has beautiful natural scenery. It is also famous because of its geographical processes. This bay also has farmland growing on it.
Hurlstone point is at the West of Porlock Beach and is in the position of the end of Long Shore Drift. Therefore Hurlstone point had more rounded rocks. Hurlstone Point also has a cliff stopping the Long shore drift so that’s why it might have more shingle on this point because the cliff (fig 1) acts as a natural barrier that blocks the rocks so they build up.
(A map of the 2 points is provided on the next page)
Gore Point is in the east of Porlock Beach and is in the position where LSD starts because the winds refracting and creating waves that hit at Gore point in a West direction. Because Attrition wouldn’t be able to start its process, the rocks here are angular and sub-rounded. This place also has a groin that is man made.
These are pictures of the 2 points on the next page:
Photos of Hurlstone and Gore Point
Coastal processes involves a lot of things, like what influences Coastal processes like:
Geology is the type of Earth you are investigating for example there is hard rock which is more resistant and soft rock which is more vulnerable to coastal erosions.
(Fig 2, 3, 4)
Wave Action is the type of wave that is hitting the coast. It could either be a destructive wave or a constructive wave which is:
* Destructive = When there is a weak Swash and a strong Backwash, removes material for the beach. These waves are only built up on rare occasions
* Constructive = When there is a strong Swash and a weak Backwash, Builds up beach material.
Swash is when the wave collapses into the beach and backwash is when the wave goes back into the sea. Swash carries lots of materials onto the beach such as rocks, sand or dirt building beach material while back swash is when the waves removes beach material as it goes back into the sea. (Fig 5)
This is basically long shore drift.
Long Shore Drift
Long shore is happening in porlock bay because the prevailing winds blows the waves towards england, the waves then hit the south west coast of England. These waves then refract and the waves then go towards Porlock bay where long shore drift occurs.
Longshore drift is the process by which the action of waves moves material along a beach or coastline. The direction of the waves is controlled by the ‘FETCH’ this is the distance or area that allows the wind to blow across the surface of the sea to create the waves.
The diagram below shows the effect of longshore drift on the direction of material movement. As you already know the wind does not come from the same direction all the time, but what does happen is that the wind tends to have a dominant direction which it blows in most of the time.
* (1) shows the direction of the Swash (this is the direction that the wave wash up the beach).
* (2) Shows the direction of the Backwash (this is the direction of the wave that washes down the beach).
* (3) demonstrates the overall direction of the movement of beach material)
Why is this important ?
Longshore drift supplies material to beaches along a coastline, making sure that the beaches are not eroded away by the action of the waves. It is possible to trap the material by the use of Groynes. These are ‘arms’ of wood that are built out to sea that trap the longshore drift to make the beaches wider.
The reason for doing this (widening the beach) is to force the waves to break on the beach and not at the base of the cliff which would cause the cliff to collapse and recide.
Sub-aerial is when the whether acts on the coasts to speed-up or slowdown the rate of erosion. This process often ends up in slumping. Such as: (Fig 7, 8)
Human activity is also known to speed-up or slow-down coastal erosions. A few examples are:
* Builing on top of cliffs
There also a few other protection strategies that I will explain later on in my investigation.
The Coast is eroded in a number of natural processes that slowly break up the coast.
These 6 processes are:
Coastal Erosion Processes
1. Hydraulic Pressure: When Parcels of air trapped and compresses in joints in the rock. Pressure weakens rocks.
2. Wave pounding: When waves physically remove material. (Fig 9)
3. Attrition: When Rocks are broken down into smaller and more rounder pieces, particularly if they are rolled onto each other.
4. Corrasion/Abbrasion: Wearing away of cliffs by rock/sand etc being hurled against them by waves.
5. Sub-aerial: an example is when the rain erodes the cliffs.
6. Solution: dissolving of limestone by acidic water.
I hypothesise that the shingle ridge at Hurlstone Point will be larger than the shingle ridge in Gore point because Hurlstone Point has a natural barrier, which is the cliff, preventing the pebbles from moving with the long shore drift. The pebbles in Gore point will be more angular than the pebbles in Hurlstone Point because attrition and abrasion hasn’t taken place yet therefore the pebbles at Hurlstone Point will be more rounder because attrition and abrasion has taken place. I also hypothesise that the pebble size will be bigger at Gore point and the pebbles at Hurlstone Point will be smaller because attrition/abrasion hasn’t occurred in Gore point because long shore drift hasn’t started yet and long shore has ended at Hurlstone point therefore Hurlstone having smaller pebbbles
As there were dangers whilst carrying out our fieldwork we had to take the necessary precautions.
The first precaution was when we were measuring the beach we weren’t aloud to go near the sea as the tides may sweep one the pupils in.
To add support to your ankles we were made to use wellington boots to walk on the shingle ridge as you could twist and hurt your ankle with normal foot ware
When we were in Porlock Bay we were prohibited from throwing pebbles as the pebbles could ship and fly into someone’s eye.
To test our hypothesis we had to collect data as a group for the beach transect and as a class for pebble shape and size.
At the two extreme ends of the bay (Gorepoint & Hurlstone point), the length and the angle of each and every facet will be taken. The slope angle and distance of each facet will be determined using a Clinometer (Fig 10) and a Tape-measure (Fig 11). At the regular intervals along length of transect a stone will be sampled, the longer side will be measured using a Pebbleometer (Fig 12). The shape was then be determined using a Powers index. 30 stones were measured systematically.
How we did it
* We visited Gore point first, we examined the groin and had a little look at the facets.
* We then got to using the equipment to collect our data. (photos of these equipment is provided on the next page). The equipment we used were, the pebbleometer, clinometer and the tape measure. We also used a powers index, which defined what type of rock we are analysing.
* The pebbleometer is a tool that measures the length of the rocks. It looks like a vice with a ruler stuck on it. The clinometer is used to measure the angles of the facets, it has an eye piece where you look through and aim at where you want it to be. To use this tool you have to find someone of the same height so you can focus on him or her to get the angle. The tape measure was used to measure the length of each facet.
* So we got started by measuring the 1st facet from the back of the shingle ridge. We laid out the tape measure on the start of a facet then it rolled it on to the end of the facet.
* We then recorded the result.
* After measuring each facet like this we measured each angle by going to the start of the facet then focusing on your partner with the clinometer that is the same height as you and took the reading that is inside the clinometer (Fig 13). Then we recorded the angle.
* We then laid out the tape measure from the beginning of the shingle ridge to the end. We then systematically took a stone at each 3 metres.
* When we picked up the stone we immediately measured the taller side. We then recorded the results.
I used this strategy because it was the most easily to use, it was time efficient and it was accurate too. This Strategy gave us all the information we needed for our coursework.
Pebble Shape at Gore Point
Pebble Shape at Hurlstone Point
Pebble Size at Gore Point
Pebble Size at Hurlstone Point
Discussion and Analysis
In this section I will discuss and analyse the graphs that I have created.
I will start with the Bar graph that shows the Pebble size in Gore Point and Hurlstone point. We can see from this graph that 5.0-7.4cm sized pebbles were most common with 78 pebbles in Hurlstone Point and 20+ sized pebbles were least common with 0 pebbles. At Gore Point we found that 10.0-12.4sm sized pebbles were most common and 0-2.4cm sized pebbles were least common. (Fig 16)
The reason for these results is all to do with Attrition and Abrasion. Attrition hadn’t taken place at Gore Point because that is where the process starts by the North Sea Winds refracting and attacking the Headland, therefore there are bigger pebbles in Gore Point. But because of Long Shore Drift Hurlstone Point has smaller pebbles because the Pebbles were rubbed against each other, therefore chipping the Pebbles into smaller pieces. Abrasion also takes of making the pebbles smaller because the Pebbles get slammed or hurled at the headland also breaking it into smaller pieces.
My hypothesis stated that the pebble size at Gore point will be bigger than in Hurlstone Point because attrition hasn’t had a chance to take place and my results agree with this.
The Pie Charts shows the pebble shape at Gore Point and Hurlstone Point. We can see from the Pie chart that Sub Rounded pebbles were the most common at Gore Point with 30% of the pebbles and the least common type of pebble was the Very angular Pebbles with only 6% of the pebbles. But at Hurlstone Point the most common pebble is Very Rounded with 54% and the least common is the Very Angular pebbles with 0% of pebbles. (Fig 14, 15)
The reason for this is also because of attrition and abrasion. At Gore Point attrition and abrasion hasn’t had the chance to take place there fore there are more angular pebbles at Gore Point because attrition rolls the pebbles onto each other, this chips away rough edges of the pebbles and the same for abrasion, when it hits the headland it chips away rough edges. Therefore the pebbles at Hurlstone point are more rounded, because attrition and abrasion has take place through long shore drift and wave action.
My Hypothesis stated that the pebbles at Hurlstone Point will be rounder because of attrition and abrasion taking place so my results agrees with my hypothesis.
In this drawing of the beach it shows the sizes of the sizes of the Shingle Ridges of the beaches at Hurlstone Point and Gore Point. We can see from this drawing of the beach that the shingle ridge at gore point is smaller than the shingle Ridge at Hurlstone Point. The maximum Height of the Gore Point shingle ridge is 3.5m and the Width is 39m while the shingle ridge at Hurlstone Point has the maximum height of 13m and has the width of 106m.
The reason for this is because Longshore drift is carrying the pebbles away from the shingle ridge in Gore Point therefore the shingle is very small in comparison to the shingle ridge in Hurlstone Point. The reason for the large shingle ridge in Hurlstone is because there is a natural barrier or groin stopping any more long shore drift. So the pebbles have built up at the headland at Hurlstone Point which has been increasing through out the years and now is very large.
My Hypothesis stated that the pebbles would be more at Hurlstone Point because of the natural barrier that stops the stones from moving in long shore drift so this agrees with the results that I’ve found.
There are ways of maintaining any loss of land when land needs to be preserved. The government decides whether the land is to be protected or to be left for nature to do its course. The government decides if land is kept or not by means of money. If the land that may well be destroyed through coastal processes is more expensive than it is to build a coastal defence then the government will consider defending the land. For an example say if there was a road or house that was close to the coast which is getting eroded, the government will calculate the coast of how much they would need for the compensation or for the relaying of that road and depending on how much money that is they would act in either protecting the land or leaving it.
The ways the land could be protected are:
* Concrete Sea Wall
* Artificial beach / beach replenishment
* Boulders Rip/Rap
A groyne is a coastal protection tool that looks like a wooden fence made out of wood.
Groynes are very useful at Porlock Bay because it keeps in the material before it accumulates at Hurlstone Point. A good thing about having groynes in general is that it is very cheap to build an the government has this alternative. Also having a groyne at Porlock weir is useful because it keeps the harbour channel free so importing and exporting would be easier. A bad thing about it is that this erodes quite quickly so new groins have to be built. (Fig 17)
Concrete Sea Wall
This is one of the most effective processes and it lasts for a longer time period than a normal groyne. Another good thing about the Concrete Sea wall in the National Park is that it has a curve that facing the sea. So when the sea level gets high and waves smash into it, it absorbs some of the energy because the waves are reflected because of swash and backwash doesn’t occur. It provides easy access but it is very expensive and it does spoil the view, which causes fewer tourists to visit at places where this is built. (Fig 18)
Artficial Replenishment /
Artificial replenishment is going to be things like sand that has been sent from abroad or even pebbles. The positive factors about artificial replenishment is that the national park has a suited position for it and this is the coast. This would attract a lot more tourists especially in hot seasons. tourists like beaches because they look very attractive. Also as a defence it is very effective because it absorbs the energy from the waves so swash and backwash would occur so waves become harmless. The bad thing about having an artificial beach is that the material needs to come from somewhere else and also transportation and machinery which would cost a lot of money so the government doesn’t choose this option because it is so expensive.
Boulders rip/rap is boulders that have been broken down into rocks near the coast. They basically defend the coast against destructive waves.
In somerset there is rip rap next to the beach in the national park. The advantages of having Boulders or Rip Rap is that it looks like a natural material and also it doesn’t affect the coastal system. The negative things of having this defence is that it doesn’t fit into the environment. They are having problems maintaining it for example delivering the material causes problems and that causes fewer tourists the noise and the view of trucks unloading and constructing its apperanece. maintaining the Boulders/Rip Rap. Is very hard because these often get swept away in destructive waves. (Fig 20)
Our investigation was limited because a lot of factors which made some of our results inaccurate.
For example because of tides we were unable to measure the full size of both beaches for our beach profiles. This would affect our beach profile results and will affect our diagram in the process.
Another factor in affecting our investigation is that we could not sample the middle of Porlock Bay. This affects our investigation because we could not fully see how longshore drift has the affect on the pebble size/shape and the beach sizes.
The equipment we used may not have been accurate either, especially the clinometer as it is very easy to make mistakes over a long length that you are calculating the angle of. The tape measure also blew in the wind so the measurements may be in accurate
Also the powers index is very subjective like people may put the wrong pebbles in the wrong categories. Some people may have different opinions of what categories the pebbles go into. The powers index could also have had more categories to be more accurate and give more information.
If I were to regather information I will try and sort out these factors as much as I can.
Hypothesis 1: Beach profile
My conclusion for the beach profile is that the shingle ridge in Hurlstone Point is larger in size than the shingle ridge in Gore point. This is because the shingle Ridge has a natural barrier that stops any more long shore drift which results in the accumulation of pebbles in Hurlstone Point. The shingle ridge in Gore Point however is smaller because the pebbles get swept away in long shore drift. The pebbles move by swash and backswash which is moving across porlock bay.
My hypothesis was correct as my results of this investigation would happen in the beach profile.
“I hypothesise that the shingle ridge at Hurlstone Point will be larger than the shingle ridge in Gore point because Hurlstone Point has a natural barrier, which is the cliff, preventing the rocks from moving with the long shore drift.”
Long shore drift affects Porlock Bay by increasing the shingle ridge at Hurlstone Point and decreasing the shingle ridge at Gore Point.
Hypothesis 2: Pebbles Size
My conclusion for the Pebble Size is that the pebbles at Hurlstone Point were much smaller than the pebbles at Gore point. This is because Hurlstone point is at the stage of the end of long shore drift which means attrition and abrasion has taken place. Attrition and abrasion is when the pebbles either bump into each other or rub/roll onto each other. For this reason the pebbles are then chipped into smaller pieces.
My hypothesis was correct as my results of this investigation comply with the things that I hypothesised would happen.
“The pebbles at Gore point will be more larger because attrition hasn’t had any chance to begin its process while the rocks in Hurlstone point will be smaller because attrition chips of rough edges as the rocks knock onto each other.”
Long shore drift affects the pebble size in Porlock bay in the way that in Hurlstone Point there is smaller pebbles than there are in Gore Point. (Fig 21, 22)
Hypothesis 3: Pebble Shape
My conclusion for the Pebble Shape is that the pebble shape at Hurlstone was more proned to be rounded and in Gore Point the most common shape is sub-rounded. The reason for this is very similar to the reason in pebble size. Attrition and abrasion has taken place in Hurlstone point because it is in the process of the end of long shore drift and in Gore point it is in the beginning of long shore drift therefore more angular pebbles were found.
My hypothesis was correct as my results states that the pebbles are more rounded at Hurlstone Point than in Gore point.
“I also hypothesise that the pebble size will be bigger at Gore point and the pebbles at Hurlstone Point will be smaller because attrition/abrasion hasn’t occurred in Gore point because long shore drift hasn’t started yet and long shore has ended at Hurlstone point therefore Hurlstone having smaller pebbbles.”
Long shore drift has affected Porlock bay in the way that it made the pebbles at Hurlstone point more rounder than the pebbles at Gore Point. (Fig 21, 22)