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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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Presentation Transcript
slide1

Coasts

Longshore Drift

lesson objectives
Lesson Objectives
  • To recognise the impact of longshore drift on the coastline.
slide4

http://www.youtube.com/watch?v=U9EhVa4MmEs&feature=player_embeddedhttp://www.youtube.com/watch?v=U9EhVa4MmEs&feature=player_embedded

longshore drift
Longshore drift

The movement of material along the coast in the direction of the prevailing winds

slide6

Benefits of Longshore Drift :

  • Builds up wider beaches at coastal resorts with groynes so more people can use the beach
  • Provides more beach material further along the coast to help protect coastline from erosion

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

longshore drift1
Longshore Drift

Draw a diagram showing the process of

Longshore Drift.

Make sure to include all the labels.

homework exam question
Homework: Exam Question

Have a go at answering this exam

question from June 2011 Past Paper.

slide12

Expect full and accurate definition for max marks (e.g.

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)

slide13

Coasts

Beaches, spits and bars

lesson objectives1
Lesson Objectives
  • To be able to describe and explain the formation of beaches, spits and bars.
formation of a beach
Formation of a beach
  • Beaches are formed by constructive waves, often in bays where the waves have less energy due to gently sloping land, and as a result deposit material.
slide17

Coasts : Features of Deposition: Spits

12

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.

  • SPIT: A linear beach that extends from the shore across a river estuary or along the coast – but doesn’t join on to any other feature. It is recurved at its end depending on which is the most powerful current.
  • e.g Spurn Head, E. Yorkshire

Is this a

SPIT

TOMBOLA or

BAR ?

Possible Questions :

Describe and explain the formation of a coastal feature of deposition.

slide18

Coasts : Features of Deposition / Evolution of Spurn Head, E. Yorkshire – A SPIT

14

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.

A

C

North Sea Current

D

River Humber Current

B

E

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

slide19

Thin neck of spit

Likely breach

Spurn Lighthouse

Deposited river silt (mud)

Direction of the North Sea current

Spurn Lifeboat station

Recent Deposition

Turbulence where 2 currents meet

Direction of the River Humber current

Coasts : Features of Deposition / Features of the spit at Spurn Head

15

slide20

Coasts : Features of Deposition / Issues of coastal protection of a Spit

16

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 :

Longshore Drift

Deposition feature

Spit

Estuary

  • Issues if the spit is allowed to be eroded away:
  • The 7 homes of Britain’s only full-time lifeboat crew of the Humber lifeboat are located at the southern end. They would have to be relocated – possible to Grimsby if the spit eroded away – meaning a longer journey time into ships in distress in the N. Sea
  • The Humber pilots are based there too – they go out to ships entering the Humber estuary – one of the busiest in Britain – to guide ships around the shifting and dangerous sand-banks of the estuary.
  • The spit is an important route for migrating birds from the continent which, in spring, use the spit to guide them into Britain, and in autumn on their flights south for the winter.
  • The Spit is managed by the Yorkshire Wildlife Trust and is a vital habitat for many plants & insects
  • Issues if the spit is protected from further erosion
  • The costs of protecting the entire length of the spit would be huge.
  • The Victorian attempts to keep the spit in one position have increased its current problems as the Holderness coast to the north continues to erode westwards – leaving the spit more exposed to NE winds and waves.
  • The erosion of material from the spit provides important material to help protect the beaches south of the Humber in Lincolnshire and even the Netherlands. Stopping the erosion and movement of this material from Spurn would cause faster erosion elsewhere.

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?

slide21

Things you could include…..

  • Direction of longshore drift
  • Arrows to show swash and backwash
  • Area of calm water behind spit
  • Saltmarsh
  • Vegetation on spit
  • Hooked end because of
  • wind changes
slide24

Coasts : Features of Deposition: Bar

13

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?