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

• It is an area of BIG development: 1. 160 000 new homes 2. Retail, university and night life venues 3. 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.206 207 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 asteroid or volcanic eruption meteoroid , a sub marine rockslide, or, more rarely, by an 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

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!

Case Study

For Revision – summary card

Location Why Vulnerable?

Social Impacts Economic Impacts Environmental Impacts Duration Lessons Learnt?

Rapid Coastal Erosion – Holderness Rising Sea Levels – Storm surges – Thames Barrier Localised Effects – Asian Tsunami

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)