To Test if Longshore Drift is Taking Place Along Deal Beach on the Day of Our Visit
- Length: 1086 words (3.1 double-spaced pages)
- Rating: Excellent
For this aim, we measured the wave angle. To do this, I laid a
protractor on the floor, and watched for about 5 minutes in which
direction the waves were travelling. I would look down on the
protractor, and note down the angle of the waves. I then worked out
the average angle.
We had to do measure the wave angle because it would show us in which
direction the longshore drift (if any) was taking place, therefore
resulting back to the title of the aim.
Wave Angle = 150º
Wave Direction = South East
Wind Speed (mph)
On the day of the visit, the weather conditions were probably the
worst conditions of the week. There was rain early on in the morning
and when we arrived, so we had to wait in the minibus for the rain to
stop. It did, and so we could carry out our investigation. The
temperature was 59 º, so not very warm. The cloud cover was about 80%,
so not much sunshine at all.
To measure the wind speed, I used an instrument called Anemometer
(fig.3). I basically held this instrument up in the air, and the wind
would blow onto its fan, and it would measure the speed for me. To
measure the wind direction, I held my handkerchief up in the air, and
recorded using a compass, the direction the handkerchief was facing,
and went to the opposite of that because that would be the direction
the wind was coming from.
Anemometer. (What I used to measure the wind speed)
As you can clearly see from my results, the wave direction and wind
direction are exactly the same. This is correct because as we know,
the wave direction is affected by the wind direction.
The purpose of the aim is to see whether Longshore Drift is taking
place on the day of our visit and if so, in what direction.
Longshore drift is the movement of material along the shore by wave
Diagram of Longshore Drift
Longshore drift happens when waves moves towards the coast at an
angle. The swash (waves moving up the beach) carries material up and
along the beach. The backwash carries material back down the beach at
right angles. This is the result of gravity. This process slowly moves
material along the beach.
Longshore drift provides a link between erosion and deposition.
Material in one place is eroded, transported then deposited elsewhere.
Longshore Drift moves material along a coastline. Where there is an
obstruction or the power of the waves is reduced the material is
deposited. Where rivers or estuaries meet the sea deposition often
occurs. The sediment which is deposited usually builds up over the
years to form a long ridge of material (usually sand or shingle). Such
a ridge is called a spit. Spurn Head on the Holderness Coast is an
example of this feature. The general direction of longshore drift
around the coasts of the British Isles is controlled by the direction
of the dominant wind. Prevailing westerly winds cause the drift from
the west to east along the Channel coast and south to north along the
west coast. The east coast is protected by land from the prevailing
south-westerly winds. However, winds from the north cause longshore
drift movement from north to south on the east coast. Northerly winds
(winds from the north) have crossed a long stretch of open sea so
that, although they do not blow as frequently as the westerly winds,
they have the greatest influence overall. Longshore drift is important
in the formation of all landforms of coastal deposition.
First we measured any longshore drift taking place on the surface of
the water by floating a piece of driftwood in the sea surface. We put
a ranging pole beside the water's edge at the point opposite where we
threw our floating piece of wood (about 30cm x 30cm x 3cm) into the
sea. The wood wasn't too high because then it sticks out of the water
and would be caught by the wind. Wind aiding the movement of the wood
would not be a true reflection of surface longshore drift.
After each minute we plotted the distance it had travelled along the
shore in the sea by using measuring tape from the ranging pole along
the beach. We needed to assess before we laid out our measuring tape,
in which direction the longshore drift was taking place so we knew
which side of the ranging pole to lay out our tape.
To measure any longshore drift on the sea bed on the day of our visit,
we threw our 30 coloured pebbles into the swash of the wave by the
shore. We marked the point with a
ranging pole on the beach. After 5 minute intervals we measured the
distance they travelled from the ranging pole.
This fieldwork method was chosen as it seemed to be the easiest and
most practical way to collect our data on longshore drift.
My group was the group right next to the pier. We found that the pier
affected the angle of which the waves approached the beach, which
interrupted longshore drift.
Most of our pebbles disappeared because the backwash was too strong
because the waves were destructive (see aim1 table and graph) because
the wind that day was at an average of 6.4mph.
The stones collected could have been too large or too small and
angular to roll along the seabed. Selecting the correct place within
the swash to get maximum movement was difficult.
Finally, the plank of wood could have been too tall (caught by the
wind and so did not truly measure Longshore Drift as it was wind
Wind Speed (mph)
By looking at the limitation section I wrote about earlier, as we were
right next to the pier, our results for the seabed and surface
longshore drift were incorrect, so we used somebody else's results.
Surface Longshore Drift
Time in minutes
Distance Driftwood Travelled (cm)
Seabed Longshore Drift
Time in minutes
Distance Pebbles moved (cm)
By looking at all the results I collected for wind speed, it is clear
to see that there was an average of about 6.4. As we were by the pier,
I had to use somebody else's results, for the surface and seabed
longshore drift. For the seabed longshore drift (pebbles) there is a
clear increase of about 7 or 8 cm every 5 minutes. The results for the
surface longshore drift show a much wider range of results.
I can conclude from my results that it is clear to see that longshore
drift is taking place and we did manage to find the direction of the
wind and the longshore drift. The wind was affective on the day of our
visit, because it did direct the waves in the same direction of
itself, as the results of the wind and wave direction showed.
Relation to hypothesis
After concluding my results, I found that on the day of our visit,
longshore drift was taking place, and the direction of which was south
easterly. My hypothesis is 'to see if Deal is being shaped more due to
the process of L.D (if we found L.D present on our visit) or by human
activity on the beach'. My results do show that the beach is being
shaped by longshore drift because longshore drift was taking place on
the day of our visit.