Increasing risks – Coastal
flooding
•Describe and explain the causes of sea
level rise.
•Describe, explain and evaluate the impact
of rising sea levels on London and the
Thames estuary.
•Understand that rising sea levels are
increasing the risks of erosion and
flooding in coastal areas
Starter
What is it’s
purpose?
What would
happen if it
failed?
Watch movie clip
from ‘The Flood’
http://www.youtube.com/w
atch?v=aUWlmED6m5s
Causes of sea level
rise
Ref Oxford
p204-205 on
blog
Sea Level Rise
Since 1880 sea level has risen by
approximately 17cm.
Causes of Sea level rise
Global warming has led to rising sea levels
for several reasons.
1. Rising atmospheric temperatures have
caused increased melting of ice caps
and glaciers resulting in an increase in
water in the oceans and seas.
2. As the atmosphere warms, so too does
the sea with the result that it
increases in volume due to thermal
expansion.
Sea level
• Sea level is the relative position of the
sea as it comes into contact with the
land.
• Its position will fluctuate if the amount
of water in the oceans increase or
decreases, or if the land rises or falls
relative to the sea
Eustatic change
• Changes in the amount of water are called
eustatic changes.
• Global changes in the volume of the oceans is
caused by melting of ice sheets at the end of
a glacial period or the freezing (and
therefore storage) of water in ice sheets
during a glacial period.
• When water is locked up as snow & ice there
is less liquid so sea level fall
• However, when ice melts the water turns to
liquid and sea level rises. This forms Rias ad
Fjords.
Isostatic change
• Involves local changes. It is caused by a change in
the level of the land. Eg 2004 Indonesian earthquake
lifted the land by 6m in areas of SE Asia.
• Ice on land is very heavy and during a glacial period,
land may actually sink relative to the sea. The
movement of the land is an isostatic change.
• When ice melts (after an ice age) the weight is
removed, the land slowly rises and recovers causing a
relative fall in sea level
Isostatic change in the UK
• In the UK there have been 2 main
isostatic changes since the last ice age:
• In Scotland and the North the land is
rising most after the ice retreated and
allowed the land to readjust .
• In the South East it is sinking most as
rivers pour sediment into the Thames
estuary. The weight of the sediment
causes the crust to sink, so sea level
there appears to rise.
Isostatic change in the UK
• Over the past 18000 years, the rising
global volume of ocean water as the ice
melted (eustatic), together with
localised isostatic changes, has
generally produced an increasing mean
sea level of about 0.1-0.2mm per year in
the past 100 years.
Storm Surges
• Surges are caused mainly by the action of
higher wind energy on the surface of the sea.
• When there is a depression (low atmospheric
pressure) as pressure decreases by one
millibar, sea level rises by one centimetre.
• When air pressure is high, sea level falls
correspondingly.
• Around the UK, the effect of a strong wind
coupled with very low pressure can be to raise
sea level in eastern England more than two
metres.
• The Bay of Bengal by Bangladesh also
experiences hurricanes (low pressure)
which can cause surges resulting in
damage far inland.
• The Environment Agency in the UK is
responsible for flood warning. They try
to give 2 hours notice of a possible
event.
• By 2080 sea levels in SE England could
be 26-86 cm above current level….the
chances of another storm surge like in
1953 are increasing!
Impacts of major flood
London
The UK as
a whole?
What were the causes and effects of the UK
Storm Surge in 1953?
• Occurred 31 Jan and 1 Feb 1953
• Combination of weather and tidal condition
caused an extreme storm surge
• 300 people died in the UK and 1800 in the
Netherlands
1. Watch the video and make notes
2. Use pg 187 Pearson and pg 234-235 Philip Allan
3. and use
http://webarchive.nationalarchives.gov.uk/20070108123
845/http://www.metoffice.gov.uk/education/secon
dary/students/flood.html
Thames Gateway
•
•
An area expected to be affected by rising sea levels is land
around the Thames estuary called the Thames Gateway
This is the area downstream from the Thames barrier and has
NO protection
•
1.
2.
3.
It is an area of BIG development:
160 000 new homes
Retail, university and night life venues
Banking and finance industry (20% UK
GDP)
4. Transport – Airport, surface and
underground rail networks (see map on
next slide)
5. 1.25 million+ at risk
Is this wise for London? For the UK?
Ref Oxford p.206207 on blog
Phillip Allan p237
Thames Gateway – complete a
detailed table
Costs
Social
Economic
Environmental
Benefits
Social
Economic
Environmental
Tsunamis
•To be aware of the havoc that tsunamis
can cause along the coast
•Grasp the scale and impacts of coastal
flooding
Starter
What is the difference between a
tsunami and a storm surge?
What is a tsunami
• Tsunamis are caused by an underwater
earthquake, a volcanic eruption, a submarine rockslide, or, more rarely, by an
asteroid or meteoroid crashing into in
the water from space.
• Most tsunamis are caused by
underwater earthquakes, but not all
underwater earthquakes cause tsunamis
- an earthquake has to be over about
magnitude 6.75 on the Richter scale for
it to cause a tsunami.
• Tsunamis are very rare. There are roughly
six major tsunamis each century.
• About 90 percent of all tsunamis occur in
the Pacific Ocean.
• Many tsunamis could be detected before
they hit land, and the loss of life could be
minimized, with the use of modern
technology, including seismographs (which
detect earthquakes), computerized
offshore buoys that can measure changes
in wave height, and a system of sirens on
the beach to alert people of potential
tsunami danger.
The development of a tsunami
• A tsunami starts when a huge volume of
water is quickly shifted.
• After the huge volume of water has
moved, the resulting wave is very long
(the distance from crest to crest can
be hundred of miles long) but not very
tall (roughly 3 feet tall).
• The wave propagates (spreads) across
the sea in all directions; it can travel
great distances from the source at
tremendous speeds.
• Tsunamis have an extremely long
wavelength (wavelength is the distance
between the crest (top) of one wave and
the crest of the next wave) -up to
several hundred miles long. The period
(the time between two successive
waves) is also very long - about an hour
in deep water.
• In the deep sea, a tsunami's height can
be only about 1 m (3 feet) tall. Tsunamis
are often barely visible when they are in
the deep sea. This makes tsunami
detection in the deep sea very difficult.
• A tsunami can travel at well over 970
kph (600 mph) in the open ocean - as
fast as a jet flies. It can take only a
few hours for a tsunami to travel across
an entire ocean. A regular wave
(generated by the wind) travels at up to
about 90 km/hr.
• As a tsunami wave approaches the coast
(where the sea becomes shallow), the
trough (bottom) of a wave hits the
beach floor, causing the wave to slow
down, to increase in height (the
amplitude is magnified many times) and
to decrease in wavelength (the distance
from crest to crest).
• At landfall, a tsunami wave can be
hundreds of meters tall. Steeper
shorelines produce higher tsunami
waves.
• In addition to large tsunami waves that
crash onto shore, the waves push a large
amount of water onto the shore above
the regular sea level (this is called
runup). The runup can cause tremendous
damage inland and is much more common
than huge, thundering tsunami waves.
• Tsunami warning systems exist in many
places around the world. As scientists
continuously monitor seismic activity
(earthquakes), a series of buoys float
off the coast and monitor changes in
sea level. Unfortunately, since tsunamis
are not very tall in height when they are
out at sea, detection is not easy and
there are many false alarms. Sirens at
affected beaches may be activated - do
not ignore them!
• NOTE: If you see the water recede quickly
and unexpectedly from a beach (this is called
drawback), run toward higher ground or inland
-- there may be a tsunami coming.
• Also, if you are on the coast and there is an
earthquake, it may have caused a tsunami, so
run toward higher ground or inland.
• Some beaches have tsunami warning sirens -do not ignore them. The first wave in a
tsunami is often not the largest; if you
experience one abnormally-huge wave, go
inland quickly -- even bigger waves could be
coming soon.
Task outline: 2004 Indian Ocean
Tsunami
You are to produce a PowerPoint/movie etc outlining the
following:
-
Vulnerability
Causes
Scale of impact – area affected
Scale of impact – damage
Duration
Lessons learnt
You will present this to the class along with a
handout of information
Information to use
• ‘The Wave that shook the World ’
documentary notes from class (also on
blog)
• P 188 Pearson
• P 231-232 Philip Allan
• P16-19 Oxford
• Geofile 2004 Asian Tusnami (on blog)
NOTE – This will be needed for Unit 1 +2!
For Revision – summary card
Case Study
Rapid
Coastal
Erosion –
Holderness
Rising Sea
Levels –
Storm
surges –
Thames
Barrier
Localised
Effects –
Asian
Tsunami
Location
Why
Vulnerable?
Social Impacts
Economic Impacts
Environmental
Impacts
Duration
Lessons
Learnt?
Plenary
• Which do you think poses the greatest
threat in the UK – coastal erosion or
coastal flooding? 10 marks
• Give reasons!
Homework
Explain how coastal flooding presents
environment, social and economic risks
for the UK (10 marks)