Powerpoint on Coasts for EDEXCEL A GCSE Geography

1. Coasts
Unit 2
Thursday 22nd May 2014

2. Constructive Waves Characteristics
Destructive Waves Characteristics
Constructive and Destructive Waves
Lower
Longer
Bigger swash than backwash
Less than 10 per minute
Steeper
Shorter
Bigger backwash
than swash
More than 10 per minute
Creates a trough
offshore

3. Hydraulic Action

4. Abrasion
Caused by waves picking up stones
and hurling them at the cliff
face, wearing it away.

5. Attrition
Any material, but usually rocks and pebbles will
become rounder and smaller over time as it
collides with other rocks and pebbles.

6. Corrosion
The dissolving of rocks and
minerals by sea water.

7. Headland
Bay

8. Headlands and Bays
Is all to do with geology!
Geology = the type of rock
Soft rocks get eroded quickly
creating bays
Hard rocks erode more
slowly creating headlands

10. Cliffs are steep rock faces along the coastline, they form along
coastlines with resistant harder rocks such as chalk

11. Wave-cut platforms are rocky ledges on the beach left behind after a cliff collapses.
They become smooth over time with erosion.

12. Cliff Retreat and
Wave Cut Platforms
1) During times of high tide the
waves attack the base of
the cliff to form a wave cut
notch.
2) As time passes corrosion
and hydraulic action widen
the notch causing the cliff to
become undercut
3) Eventually the influence of
gravity becomes too great
and the cliff collapses.
4) This causes the cliff to
retreat inland.
5) The rocks left at the base of
the cliff are eroded by
corrosion and abrasion until
a smooth rocky platform is
left, called a wave cut
platform.

13. Cave, Arch, Stack, Stump

14. Weathering and Erosion
Weathering – the breaking down of rock
without any involvement of moving
forces
Erosion – the breaking down of rock by a
moving force such as a wave

15. Coastal Weathering
Freeze Thaw Solution Biological
Temperatures drop below
freezing at night and then
rise during the day
Any water held in cracks in
the rock freezes, expands
and then thaws.
This happens over and over
until pieces break off.
All rain is slightly acidic.
Polluted air can be very
acidic
When rain falls on rocks, the
acid reacts with some of the
minerals causing them to
dissolve
The roots of vegetation
grow into cracks in the rock.
This splits the rock apart.

16. Mass Movement
• Bottom of the cliff eroded by waves and
undercut
• Rainfall saturates cliff and makes it
heavier
• Water trapped between layers of rock in
the cliff acts like a lubricant
• Rocks slide down cliff in a rotational
manner
• Often happens in clay
• Rocks are weathered on the cliff face
• They break loose and fall under the influence of gravity

17. Clay
Mass Movement - slumping

18. Slumping Explained
For slumping to occur
soil must be on top of an
impermeable rock such
as clay (that is rock that
does not allow water to
soak into it.
During times of heavy
rainfall the soil above the
clay can get saturated. At
the same time waves
undercut the base of the
cliff.
A layer of water builds
up between the soil and
the clay, where it cant
sink it, lubricating it.
Under the influence of
gravity the soil slumps in
layers down the cliff.

20. Coastal Recession is affected by:
Fetch – the bigger it is, the bigger the waves will be and
the more the cliff will erode
Geology – cliff recession is faster in soft rocks such as
sand or clay, slower in hard rocks like chalk and
limestone
Coastal defences – if they protect the cliff, erosion will
be less severe and the cliff will retreat more slowly.

21. Coastal Flooding
• Thames barrier protects London
from flooding; closed during times
of high tide and severe storms.
• A series of new flood walls will
also be installed in 2012
• The Environment Agency monitors
the weather and tides 365 days a
year and sends out warnings if
coastal flooding is likely
• People in Bangladesh build their
houses on stilts to protect their
properties from flooding
• Also, the Coastal Embankment Project
has led to the building of many flood
walls, and 500 flood shelters have
been built .
• The local people are now being better
educated about what to do in a flood
and flood warning systems are being
put in place

22. Prevailing wind – the direction the wind blows from
MOST OFTEN!
In the UK our prevailing wind
direction is from the South West.
It is this that makes swash and Long
shore Drift go onto the beach at an
angle.

23. Longshore Drift (LSD)
1) The waves approach the beach at an angle (in the UK it is
45o) depending on the direction of the prevailing wind.
2) The swash goes up the beach at the same angle carrying
sediment and sand with it.
3) The backwash carries the sediment and sand back down the
beach at 90o under the influence of gravity.
4) In this way sediment and sand is transported down the
coastline.

29. Coastal Engineering
Hard engineering is anything that is man-
made, usually out of concrete or wood
Soft engineering is using anything that is already
there in the landscape to try and manage the
risk

30. Hard Engineering – Sea Wall
Pros
• Strong
• Long lasting
• Reflects the wave energy
and protects the base of the
cliff
• Cheap
Cons
• Looks ugly
• Not popular with tourists

31. Hard Engineering – Rip rap
Pros
• Strong
• Long lasting
• Absorbs wave energy and
reducing erosion
Cons
• Not always pretty
• Very expensive
• Restricts access to the beach

32. Hard Engineering – Revetments
Pros
• Absorbs wave energy and
reducing erosion
• Not too ugly
• Cheap
Cons
• Has to be replaced quite
often

33. Hard Engineering – Off-shore Reefs
Pros
• Absorbs wave energy and
builds up the beach
• Not too ugly
Cons
• Very expensive
• Unpopular with boats and
fishing vessels

34. Hard Engineering – Groynes
Pros
• Stop longshore drift and so
build up the beach
• Cheap
• Popular with tourists
Cons
• Have to be replaced quite
frequently
• Do not stop erosion

35. Soft Engineering – Beach
Replenishment
Pros
• Builds up the beach again
• Very popular in seaside resorts
• Creates a natural barrier to
erosion
Cons
• Has to be replaced quite
frequently
• Extremely expensive
• Can make erosion worse at
other places down the coast

36. Soft Engineering – Cliff Regrading
Pros
• Reduces the risk of slumping
• Looks natural
• Cheap
Cons
• Does not stop erosion
• Not guaranteed to work

37. Soft Engineering – Managed Retreat
Pros
• Doesn’t cost anything
• Very natural
Cons
• Loss of land and homes
• Have to compensate
people who loss their
land

38. Swanage
• Managed due to weaknesses in the cliff and soft
clays and the risk to houses and hotels on the
cliff.
• 90,000m3 of sand pumped onto the beach
(beach replenishment)
• 18 new groynes in 2005 to replace old timber
ones
• Cliff regrading and drainage to lower the risk of
slumping
• Cost £2.2 million in total