A PowerPoint about storm surges and how it affects the weather. A brief case study about storm surges in the North Sea and Bangladesh are also included.

1. Storm SurgersStorm Surgers

2. Weather – The BasicsWeather – The Basics
DepressionsDepressions
 Low pressure systems (often below 1000mb)Low pressure systems (often below 1000mb)
 Represented on weather map with closed isobars andRepresented on weather map with closed isobars and
decreasingdecreasing pressure towards the centrepressure towards the centre
 Move across the UK from west to eastMove across the UK from west to east
 Isobars are close together, indicating a steep pressureIsobars are close together, indicating a steep pressure
gradient. This can cause strong windsgradient. This can cause strong winds

3. Weather – The BasicsWeather – The Basics
AnticyclonesAnticyclones
 High pressure systemsHigh pressure systems
 Closed isobars with pressureClosed isobars with pressure increasingincreasing towards thetowards the
centrecentre
 They move slowly and can remain stationary forThey move slowly and can remain stationary for
days/weeksdays/weeks
 Isobars are far apart so there is little pressure differenceIsobars are far apart so there is little pressure difference
(light/no winds).(light/no winds).

4. Storms – The BasicsStorms – The Basics
 Air covers the surface of our planet and has mass, thatAir covers the surface of our planet and has mass, that
is, it has weight and volume, and it can be made tois, it has weight and volume, and it can be made to
move.move.
 Our atmosphere is dynamic, and it's temperatureOur atmosphere is dynamic, and it's temperature
constantly changes in response to rotation of the planet,constantly changes in response to rotation of the planet,
changes in seasons and earth's orbit around the sun.changes in seasons and earth's orbit around the sun.
 Hot air is less dense than cold air, and when hot andHot air is less dense than cold air, and when hot and
cold air collide, the hot air is forced to rise over thecold air collide, the hot air is forced to rise over the
colder air.colder air.
 Cold air is typically dryer than warm air and originatesCold air is typically dryer than warm air and originates
from the poles. Warm air comes from the tropics/equatorfrom the poles. Warm air comes from the tropics/equator
(where there is more evaporation).(where there is more evaporation).

5. Storms – The BasicsStorms – The Basics
 Whenever cold dry air moves away from the poles, itWhenever cold dry air moves away from the poles, it
eventually encounters warm wet air moving away from theeventually encounters warm wet air moving away from the
equator.equator.
 The warm wet air is forced up and over the cold air. When theThe warm wet air is forced up and over the cold air. When the
warm air is forced up, it causes surface air pressure to drop.warm air is forced up, it causes surface air pressure to drop.
 Cold air rushes in to fill the area of lower air pressure, whichCold air rushes in to fill the area of lower air pressure, which
causes more warm air to be displaced upward, and more coldcauses more warm air to be displaced upward, and more cold
air moves in, forcing more warm air upward, and a cycle startsair moves in, forcing more warm air upward, and a cycle starts
to develop.to develop.
 Also, factor-in that the earth rotates from west to east,Also, factor-in that the earth rotates from west to east,
dragging the atmosphere with it. The low-pressure area startsdragging the atmosphere with it. The low-pressure area starts
to rotate, and all this moving air creates wind, and lots of it.to rotate, and all this moving air creates wind, and lots of it.
 So a storm forms in response to an extreme difference in airSo a storm forms in response to an extreme difference in air
pressure, driven by the movement of cold and warm air.pressure, driven by the movement of cold and warm air.
 Eventually either the cold or warm air dissipates, andEventually either the cold or warm air dissipates, and
equilibrium becomes re-established and calm, less-windyequilibrium becomes re-established and calm, less-windy
weather prevails.weather prevails.
 A storm can last as short as a few days to over a week.A storm can last as short as a few days to over a week.

6. Storms – The BasicsStorms – The Basics
 The greater the difference in air pressure between twoThe greater the difference in air pressure between two
competing systems, the greater the wind.competing systems, the greater the wind.
 The greater the surface area covered by low pressure,The greater the surface area covered by low pressure,
the greater the size of the area of wind will be.the greater the size of the area of wind will be.
 The deeper or lower the pressure, the stronger theThe deeper or lower the pressure, the stronger the
storm, the stronger the wind, and the greater thestorm, the stronger the wind, and the greater the
probability for surf to be generated.probability for surf to be generated.
 The larger the area of low pressure, the larger the fetchThe larger the area of low pressure, the larger the fetch
or ocean surface that will be affected by the resultingor ocean surface that will be affected by the resulting
wind.wind.

7. Storm SurgesStorm Surges
 Strom surges occur when weather conditions createStrom surges occur when weather conditions create
strong winds (large fetch), which in turn produce higherstrong winds (large fetch), which in turn produce higher
water levels than you would normally get at high tidewater levels than you would normally get at high tide
(basically the wind blowing across the surface off the sea(basically the wind blowing across the surface off the sea
causes water to pile up to a level higher than normal).causes water to pile up to a level higher than normal).
 The North Sea and The Bay of Bengal are two areasThe North Sea and The Bay of Bengal are two areas
where these conditions can occur because they are bothwhere these conditions can occur because they are both
narrow areas of sea.narrow areas of sea.
 Strong winds drive waves ahead of the storm, whichStrong winds drive waves ahead of the storm, which
builds up the water levels in areas where there is abuilds up the water levels in areas where there is a
limited space for the water to go.limited space for the water to go.

8. North Sea Storm Surge (1953)North Sea Storm Surge (1953)
CausesCauses
 Deep Atlantic depression (low pressure) came overDeep Atlantic depression (low pressure) came over
Scotland and continued to worsen. Strong gales (32-42Scotland and continued to worsen. Strong gales (32-42
knots). Pressure of 970mbs.knots). Pressure of 970mbs.
 A rapid fall in pressure could be responsible for a rise inA rapid fall in pressure could be responsible for a rise in
the surface of the sea of about 0.5mthe surface of the sea of about 0.5m
 An anticyclone (high pressure) lay west of Britain. TheAn anticyclone (high pressure) lay west of Britain. The
steep pressure gradient (difference between low andsteep pressure gradient (difference between low and
high pressure system) caused strong winds to movehigh pressure system) caused strong winds to move
south across the North Sea. (The anti-clockwisesouth across the North Sea. (The anti-clockwise
movement of the low system sucked down air from themovement of the low system sucked down air from the
North, which created these gales).North, which created these gales).
 Large fetch from the North. Storm waves over 6m highLarge fetch from the North. Storm waves over 6m high
 All at the same time as high spring tides and riversAll at the same time as high spring tides and rivers
discharging into the sea with large volume of water (duedischarging into the sea with large volume of water (due
to floods)to floods)

9. North Sea Storm Surge (1953)North Sea Storm Surge (1953)
EffectsEffects
 Lots of extra water in the North Sea.Lots of extra water in the North Sea.
 Sea defences breached in south east England and theSea defences breached in south east England and the
NetherlandsNetherlands
 Thousands of hectares of low-lying land floodedThousands of hectares of low-lying land flooded
 Damage to property, communication systems and farmDamage to property, communication systems and farm
landland
 250 people drowned in England compared to 1800 in the250 people drowned in England compared to 1800 in the
Netherlands.Netherlands.
 More damage in the Netherlands.More damage in the Netherlands.
 Both countries responded with coastal managementBoth countries responded with coastal management
schemes.schemes.
 Countries affected included the UK, Netherlands,Countries affected included the UK, Netherlands,
Belgium, Denmark & France.Belgium, Denmark & France.

10. Storm Surges in BangladeshStorm Surges in Bangladesh
 Events in 1970, 1985 & 1991.Events in 1970, 1985 & 1991.
CausesCauses
 High winds (due to a cyclone forming to the south)High winds (due to a cyclone forming to the south)
pushed water northwards.pushed water northwards.
 The Bay of Bengal is narrow, so struggled to contain theThe Bay of Bengal is narrow, so struggled to contain the
extra water.extra water.

11. Causes of CyclonesCauses of Cyclones
 Low pressure systems that develop in the tropics.Low pressure systems that develop in the tropics.
 Surface heating causes warm air to be drawn into it in aSurface heating causes warm air to be drawn into it in a
spiralling manner.spiralling manner.
 The sea needs to be over 27`C = maintain rising currentsThe sea needs to be over 27`C = maintain rising currents

12. Storm Surges in BangladeshStorm Surges in Bangladesh
EffectsEffects
 10m waves hit densely populated coastline.10m waves hit densely populated coastline.
 Storm surge travelled several km inland destroyingStorm surge travelled several km inland destroying
everything (poorly constructed buildings so easily swepteverything (poorly constructed buildings so easily swept
away).away).
 Densely populated so 300,000 deaths in 1970.Densely populated so 300,000 deaths in 1970.
 Salt water contaminates soil – country relies onSalt water contaminates soil – country relies on
agriculture – subsistence life style. Leaves manyagriculture – subsistence life style. Leaves many
dependent on aiddependent on aid
ResponsesResponses
 Attempts to protect areas with embankments andAttempts to protect areas with embankments and
mangrove plantations to act as buffers. Some success,mangrove plantations to act as buffers. Some success,
but little money for large scale management schemes.but little money for large scale management schemes.
 Problem will only worsen with global warmingProblem will only worsen with global warming

13. Sediment CellsSediment Cells
 Coastal sediment comes from a variety of places: seaCoastal sediment comes from a variety of places: sea
bed, beaches, cliffs, river channels and estuaries.bed, beaches, cliffs, river channels and estuaries.
 Some believe that sediment movement occur in distinctSome believe that sediment movement occur in distinct
areas (or cells). These are closed systems with balancedareas (or cells). These are closed systems with balanced
inputs and outputs.inputs and outputs.
 There are 11 cells in England and Wales.There are 11 cells in England and Wales.

http://jncc.defra.gov.uk/pdf/gcrdb/v28chap1.pdfhttp://jncc.defra.gov.uk/pdf/gcrdb/v28chap1.pdf
 They are separated by headlands or stretches of deepThey are separated by headlands or stretches of deep
water.water.
 In reality, sediment could easily move cells e.g. around aIn reality, sediment could easily move cells e.g. around a
headland.headland.

14. UK sediment cellsUK sediment cells

15. High & Low Energy CoastlinesHigh & Low Energy Coastlines
High EnergyHigh Energy
 Wave power is strong forWave power is strong for
most of the year e.g. westmost of the year e.g. west
coast of British Isles. Thecoast of British Isles. The
prevailing wind isprevailing wind is
westerly and they facewesterly and they face
the direction of thethe direction of the
longest fetch.longest fetch.
 Distribution of theseDistribution of these
coastlines is controlled bycoastlines is controlled by
climate and the directionclimate and the direction
they face.they face.
 Strong winds are moreStrong winds are more
frequent in areas wherefrequent in areas where
there is a cool temperatethere is a cool temperate
western maritime climatewestern maritime climate
 High wavesHigh waves
Low EnergyLow Energy
 These can be found whenThese can be found when
the coastline changesthe coastline changes
direction and when theredirection and when there
are few strong winds.are few strong winds.
 Estuaries, inlets andEstuaries, inlets and
sheltered bays occursheltered bays occur
where wave heights arewhere wave heights are
lower.lower.
 Waves spread outwardsWaves spread outwards
and energy is dissipatedand energy is dissipated
leading to depositionleading to deposition
 Enclosed sea areas alsoEnclosed sea areas also
have low energy e.g.have low energy e.g.
Baltic SeaBaltic Sea