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geography coasts help needed

On the Holderness coasts, parts of the coastline have been protected with sea walls and groynes eg Mappleton, rubble armouring eg Barmston. This results in accelerated erosion down drift (to the south).

Explain why this happens (you could draw a diagram to help you)

Can someone give me some help please. My theory is that the groynes are preventing sand/sediment moving southwards which would occur because the predominant wave directing would be north east and somehow that less sand/sediment further south causes greater levals of erosion.

thanks

Reply 1

gbp1

actually i will put this thread in study help, realized i put it in the university section

Reply 2

Nynyflower

From what I can remember it's because the big groyne at mappleton stops long shore drift beyond that point so the amount of sand, stones and sediemnt are greatly reduced on the otherside as longshore drift continues with nothing there to replace it. Beaches are a natural sea defence so the cliffs become more exposed south of the groyne, meaning they will erode faster as there is nothing to protect them :smile:

Reply 3

Nynyflower

gbp1

actually i will put this thread in study help, realized i put it in the university section

Don't worry someone'll move it for you!

Reply 4

etudiant

What you've said is basically right. The groynes further up the coast line are trapping the sediment and therefore creating 'beaches'. However, these 'beaches' are somewhat artificial as they would not have formed in such large quantities had it not have been for the groynes. Therefore when the waves meet the coast further down, they are not carrying any sediment that they can drop to create more beaches. Also, as there is a lack of a beach already there (due to the sediment being trapped prior) there is nothing to slow the waves down; thus dissipating the energy. This means that the cliff gets the full force of the wave as beaches slow the wave down, thus making them less errosive.