Coasts Longshore Drift . Lesson Objectives. To recognise the impact of longshore drift on the coastline. How did the beach ball end up here?. http://www.youtube.com/watch?v=U9EhVa4MmEs&feature=player_embedded. Longshore drift.
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The movement of material along the coast in the direction of the prevailing winds
Waves approach at an angle to the shore
Beach material is Higher on the side of the groyne facing the prevailing wind and waves
Eroded material (chalk pebbles from Flamborough head) are found down the coast where the natural cliff material is Boulder Clay
Beach is Wider on the side of the groyne facing the approaching waves
Draw a diagram showing the process of
Make sure to include all the labels.
Have a go at answering this exam
question from June 2011 Past Paper.
the movement of material (1) parallel to coast (1)
by/because of ...(1)). Partial statements conveying
idea of material moving of sediment worthy of 1 mark.
Direction – accept eastwards, easterly, east, northeast or west-to-east (1). Accept - in direction of
prevailing wind (1).
Reason – credit any valid Figure 2a/b observation e.g.
build-up of deposition on west side of Cobb(1); more
beach on west side of groynes(1)... Accept likely
fieldwork finding that beach height lower on east side
of groynes(1); prevailing wind (if not offered
previously unless qualified/developed)
Beaches, spits and bars
As cliff and beach material is transported along a coast by Longshore Drift, if the flow is interrupted or slowed down, the material is DEPOSITED to form a range of Features of Deposition.
A SPIT is unable to extend right across an estuary due to the force of the river current finding a route out to the sea.
It is RECURVED at the end in the direction of the strongest of the two currents. In Spurn Head’s case, the North Sea current is more powerful than the River Humber current, so the spit curves in towards the estuary.
Is this a
Possible Questions :
Describe and explain the formation of a coastal feature of deposition.
Coasts : Features of Deposition / Evolution of Spurn Head, E. Yorkshire – A SPIT
A : Sea erodes the coast and Longshore Drift transports material down the coast
B : The North Sea and R. Humber currents meet, slow down & deposit their material. The N.Sea current is stronger so the recurved spit bends in to the Humber channel.
North Sea Current
River Humber Current
C : As the Spit head grows southwards, erosion still takes place up-coast
D : The neck of the spit has more erosion than deposition – so gets thinner
E : The sea breaks through the neck, the spit head is an island and is eroded away
Deposited river silt (mud)
Direction of the North Sea current
Spurn Lifeboat station
Turbulence where 2 currents meet
Direction of the River Humber current
Coasts : Features of Deposition / Features of the spit at Spurn Head
Coasts : Features of Deposition / Issues of coastal protection of a Spit
The thin neck of Spurn Head is only a few metres wide. Victorian coastal engineers tried to stop the spit eroding away at its thinnest point over a hundred years ago, but their wooden groynes have now collapsed and are no longer effective. The issue is whether to protect the spit from further erosion, or let the sea carry out its operations, and erode it away.
Key Terms :
Example / Case-Study :
Spurn Head, E. Yorkshire (Spit)
Possible Questions :
Why are there disagreements about whether to protect coasts from further erosion?
What are the issues surrounding the management of sensitive coastal environments?
A BAR is a spit which extends across a bay and reaches the shore on the other side. The water which is cut off becomes a salt-water LAGOON of still water. Eventually, over time the lagoon fills in with wind-blown sand, sediment, reeds and other vegetation and becomes a marsh.
This is SLAPTON LEY in Dorset.
Possible Questions :
What is the difference between a Bar and a Spit?
Are these permanent or temporary features of coastal deposition?