Jennie Lace 10c                                                                        Friday 21st March 2003

Eastbourne Project

  1. Introduction

My hypotheses are:

  • Longshore drift is from the Southwest.
  • Sediment size increases with distance from the shoreline.

Eastbourne is a large coastal town in East Sussex.

                                    Eastbourne

Eastbourne’s main function is tourism, but it is also a residential town.  Many retired people live there in the high numbers of houses and care homes. There are many hotels, especially on the sea front.  The reason that we chose to do our study in Eastbourne was because it has a shingle beach, which means we can measure the pebbles near and further from the coastline.  There are also groynes which, if we measure the distance from the top of them down to the beach, can help us find out from which direction longshore drift is.

There is a shingle beach in Eastbourne, and that part of coastline is at risk from coastal erosion, so some ways of slowing this erosion down have been put in place by the council.  Along the beach there are wooden groynes placed at regular intervals, which help prevent the lots of the shingle being transported along the coastline due to longshore drift.

Longshore drift is the transport of sand and pebbles along the coast by waves.  Waves often approach the coastline at an angle (which is determined by the direction of the prevailing wind).  The sand and pebbles carried by the waves roll back down the slope at right angles to the coastline, due to gravity.  These sand grains and pebbles will be transported by waves to the next point in the coastline and so on, and this results in the beach material being transported along the coastline by the action of the waves.

Here is a diagram to show how longshore drift erodes the coastline in Eastbourne.

Another way in which the council in Eastbourne tries to manage the retreat of the coastline is by replenishing the shingle which makes up the beach.  This shingle beach helps to bring money to the town because of tourists, and so is important to the town.

        Due mainly to attrition, pebbles and particles of sand are reduced in size as they collide with the rock face and one another.  They are picked up from the beach by the action of destructive waves, which have a weak swash and a strong backwash:

  These pebbles and sand particles are deposited on the beach by constructive waves with a strong swash and a weak backwash:

        My expectations are that as the pebbles get further away from the shoreline, they increase in size.  This is because the more powerful the backwash is, the heavier pebbles it will pick up, and so the further up the beach the constructive waves will deposit them.

The waves are bigger in amplitude and length if the wind is stronger, and if they have a bigger fetch.  The fetch is the distance that the wave has travelled.  This means that the waves in Eastbourne are quite large, because the prevailing wind is from the Southwest and so the waves have to travel all the way across the large Atlantic Ocean.  This results in the waves, destructive and constructive, being large, and powerful enough to transport even large bits of shingle up the beach.

        This diagram shows how the action of waves transport shingle up the beach:

        From our data collection and analysis I am hoping to prove that longshore drift in Eastbourne is from the Southwest, and that on the beach in Eastbourne, pebble size increases with distance from the shoreline.

  1. Method

We collected the data on Tuesday 18th March 2003 from three different randomly chosen groynes along the beach in Eastbourne so that we had a fair set of data and could work out various averages. For each groyne we measured the same things to compare with each other.

To work out which direction longshore drift is from on the beach, we took the vertical measurement from the beach to the top of the groyne for both sides of the groyne (updrift and downdrift) using a tape measure.

First for the updrift side of the groyne (the left if you are looking from the sea), and then the downdrift (the right if you are looking from the sea) we decided on measuring points wherever there was a break in the slope.  We measured the distances and between each of these different measuring points using a tape measure.

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Two people then stood on, for example, point 2 and 3 and each used a clinometer to measure the angle between the points to get an average measurement, and to make the measuring of the angles as accurate as possible.

The two people had to be roughly the same height to make it a fair test and we made a note of whether the slope was rising or falling.  These measurements were not so much to prove or disprove our hypotheses but so that we could draw ...

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