Coastal Management in PorlockBay

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Coastal Management in Porlock Bay

Aims

Aim 1:

To find out if beach material is moved across Porlock Bay by longshore drift.

Aim 2:

To find out which type of sea defense is best for Porlock bay.

If L.S.D. (long shore drift) were taking place I would expect to find:

a) Deposition at one end of the bay and against any abstractions such as groynes.

b) An increase in pebble roundness in the direction of long shore drift. The process of attrition will erode the pebbles.

c) A decrease of pebble size in the direction of long shore drift, again attrition is involved.

d) Undercutting (active erosion of the cliffs at one end of the bay).

Method (data collection)

If Long Shore Drift were taking place, I would expect to find:

* Deposition of pebbles on one side of any obstruction. This obstruction could be a headland or an artificial barrier such as a groyne.

* A decrease in pebble size in the direction of long shore drift.

* An increase in pebble roundness in the direction of long shore drift.

I visited the two extreme ends of the beach, Gore point at the west and Hurl stone point at the east, at each end I measured:

* The shape of the beach known as the beach profile, using a tape measurer and a clinometer. A clinometer measures the angle of a slope.

* The size and shape of a sample of pebbles. These pebbles were picked out randomly. We took 100 pebbles from each end and measured their length using a ruler and used the shape chart to decide what shape the pebbles were.

First we had gone to gore point to study the area. There we saw a lot of sub angular rocks, so we set up a beach profile experiment.

Then after that we had gone to hurl stone point. There we saw a lot a lot of rounded pebbles, so we then again set up a beach profile experiment.

Introduction

We went on a Geography field trip with our class to Crowcombe in Somerset. Our class along with Mr Hopping went for three days and two nights, and stayed at the Youth Hostel. I studied and investigated Coasts. Which to be a bit more specific was interaction between sea and land. The general weather conditions were sunny with showery intervals.

There are five types of erosion as well as the four types of transport but first I will talk about the types of erosions. There are five different types, and they are corrosion or you could say abrasion, scouring, hydraulic action, solution and attrition.

Corrosion/abrasion is where the breaking waves scoop up stones and rocks fragments and hurl these at cliffs. This has the effect of chipping away at the rock, eventually breaking pieces off.

Scouring is waves that break at the base of a cliff swirl and remove loose rock with the strong current.

Hydraulic action is the pressure exerted by breaking waves and traps and compresses air in cracks. The intense pressure forces open the cracks further so weakening the rock.

Solution is where some rocks have a chemical composition which salt water can dissolve. In chalk and limestone, the calcium carbonate is dissolved, so weakening the rock.

Attrition is when the waves swirl rock fragments about and as they collide they wear down.

The process of longshore drift is when longshore drift is at work when waves break at an angle to the beach. The swash runs up the beach at an angle. However, the backwash flows straight back due to the beach's slope. This process of longshore drift also provides the link between the wearing down and building up of the coastline. The movement of material builds up to form distinctive features including spits, tombolo, beaches and bars.

There are the four different types of transport, which are Solution, Suspension, Saltation, and Traction. Solution is where the salts and minerals are dissolved from the rocks. Then we have suspension, which are finer materials that can be carried in suspension by waves. Saltation is the material, which is just too heavy to be carried in suspension, and that will be bounced along. We finally have traction, and this is heavier material that is rolled along the seabed by the strongest waves.

Formation of Porlock Bay

00,000BP

Bristol Channel

Sandstone Clay Limestone

resistance rock soft rock resistance rock

The rock types are important in explaining how Porlock Bay was formed.

Bristol Channel

Porlock Bay

Sandstone Clay Limestone

Resistance rock soft rock resistance rock

Rocks such as Sandstone and Limestone are resistant to erosion. These rocks will form headlands and cliffs. Soft rocks such as Clay are easily eroded and will form wide beaches called Bays.

Porlock Bay is a 4km wide pebble beach, which is placed in the North-west Somerset, in southwest England. Porlock Bay faces the Atlantic Ocean. When gales blow along the coastline they usually blow from northwest. Porlock Bay faces north.

The coast in this area is generally formed by cliff fronting hills, which rise steeply to 400 meters on Exmoor. At Porlock the hills are set back from the coast between Gore Point to the West and Hurlstone Point to the East, a distance of 5 kilometres. Between these points Porlock Bay has formed a shingle ridge to the landward edge, which has provided some protection to the property at Porlock Weir and Porlock Marsh.
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Porlock Marsh is a strip of low-lying farmland behind Porlock Bay. Porlock Marsh is less than 10m above sea level. As a result Porlock Marsh floods at some high tides. The submarine forest, which is present at Porlock Marsh, shows that the sea level has risen in the past.

On 28th October 1996 the remains of the Hurricane Lily reached the British Isles and the storms that ensued gave rise to high tides and strong winds, which caused sea water to break through the shingle ridge. Four houses the Ship Inn and three cottages were flooded and ...

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