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# Coastal Management in PorlockBay

Extracts from this document...

Introduction

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. ...read more.

Middle

Analysis Aim 1: To find out whether longshore drift is occurring in Porlock Bay. Hypothesis 1: Pebble length will decrease in size from west till east in the direction of longshore drift. Pebble length in the class results show that the pebbles are smaller at the west side. This is confirmed by the group results. Looking in more detail at the class results it is apparent that there are no pebbles larger than 15cm, whereas in the east 31 were larger than15cm. This suggests that the sea is moving material from Gore point to Hurlestone point. Longshore drift must be the process. As the pebbles are transported they are eroded by attrition. This is the smashing of pebbles by pebbles in rough sea areas. This gradually reduces the size of the pebbles, as they are moved from point to point. My first hypothesis is that pebble length gets smaller from Grove point to Hurlestone point and is proven correct. Hypothesis 2: The pebble roundness will increase in the percentage of the total from west to east. The class results show to be true. This is also backed up by my group results. Taking closer looks at the data.... In the west over 50% are very angular to sub-rounded while in the east 75% are rounded to sub-rounded. This backed up my group. These pebbles are from the same type and source of rock. These are located in the cliffs at the end of the beach. At that stage they are so loose, they can be picked out by hand. Observations made at the site told me they were all uneven, jagged and angular. This suggests again longshore drift is taking place. Hydraulic action has scoured out the angular pebbles during high tide storms. On their journey to Hurlestone point they have been bounced along the rocky seabed and banged into each other. This latter process- attrition takes the pebbles and bangs them together. ...read more.

Conclusion

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