Section 2: Storm surges, coastal flooding, sea level

Question 1

define storm surge

Answer 1

A rise in the normal water level along a shore resulting from reduced atmospheric pressure and strong onshore winds

Question 2

What is atmosphere pressure

Answer 2

Pressure exerted by the weight of air in the atmosphere of Earth. The force per unit area exerted on a surface by the weight of air above that surface in the atmosphere

Question 2

What is atmosphere pressure

Answer 2

Pressure exerted by the weight of air in the atmosphere of Earth. The force per unit area exerted on a surface by the weight of air above that surface in the atmosphere

Question 3

What is the atmospheric pressure at mean sea level

Answer 3

1 atmosphere

Question 4

Factors influencing how much winds piles up water levels

Answer 4

Wind strength
Wind direction
Fetch
Topography
Water depth
Coriolis force

Question 5

What happens when two layers of moving fluid are in contact

Answer 5

energy and momentum are transferred from the more rapidly moving layer to the slower layer.

Question 6

In equilibrium, what must wind stress balance

Answer 6

wind stress must balance the pressure gradient causes by the slope in the sea surface

Question 7

What is set-up

Answer 7

The rise in water level in coastal areas.
Can be caused by tides, storm surges, wave action
Influenced by shape and characteristics of the coastline and direction of the wind
Important for understanding coastal management and coastal engineering as it can help predict and mitigate the impacts of coastal flooding and erosion
Upwelling

Question 8

What is set-down

Answer 8

The fall in water level in coastal areas.
Can be caused by tides, storm surges, wave action
Influenced by shape and characteristics of the coastline and direction of the wind
Important for understanding coastal management and coastal engineering as it can help predict and mitigate the impacts of coastal flooding and erosion
Downwelling

Question 9

What are tropical cyclones

Answer 9

500-200km
Serval hours to up to half a day
Usually <200km
Compact and nearly symmetrical
November-April
Short distances and time scales

Question 10

What are extra-tropical cyclones

Answer 10

1000-500km
2-5 days
several hundred 100km
Sprawling geometry
April-August
Driven by weather front, large, longer

Question 11

Where are tropical cyclones found and not found

Answer 11

Not on the equator, tropics and deflect with Coriolis to the North or South

Question 12

How do tropical cyclones form

Answer 12

Form over large relatively warm bodies of water
Derive their energy from the evaporation of water, condenses and forms clouds etc

Question 13

How do extra-tropical cyclones form

Answer 13

‘depressions’ or ‘lows’
Fuelled by horizontal pressure contrasts
usually between 30-60o latitides

Question 14

Contrasting extra-tropical and tropical cyclone storm surges

Answer 14

tropical: very large but last less than a day
Extra-tropical: smaller but last much longer (3 days)

Question 15

Where is the largest storm surge located in the N.Hem and S.Hem

Answer 15

N.Hem: Southern side of the storm
S.Hem Northern side of the storm
Due to deflection of the wind and Coriolis

Question 16

What is a negative storm surge

Answer 16

Wind direction blows the water away from the coast, causing sea level to drop
Less chance of flooding but can strand boats

Question 17

What is a storm surge

Answer 17

An abnormal rise of water generated by storm, over and above predicted astronomical tides

Question 18

What is a storm tide

Answer 18

The water level rise due to the combination of storm surge and astronomical tide

Question 19

When would coastal flooding occur

Answer 19

Normally dry, low-lying land is flooded by sea water. Extent of flooding is reliant on elevation of inland controlled by the topography

Question 20

What is the S-P-R-C model

Answer 20

Source: The origin of the hazard (eg storm, rainfall, storm surge etc)
Pathway: Route that a hazard takes to reach receptors (eg overtopping, overflow)
Receptor: the entity that may be harmed (eg people, property)
Consequence: an impact such as economic, social, environmental damage (eg loss of life, material, environmental degradation)

Question 21

What are the different pathways in the SPRC model

Answer 21

Direct inundation: sea height exceeds the elevation of the land
Overtopping of a barrier: swell conditions, height of the wave exceeds the barrier, high velocities can cause erosion
Breaching of the barrier: broken by waves and water enters inland

Question 22

Define mean sea level

Answer 22

Average height of the sea over longer periods of time (usually month of a year)
Short term variations are filtered out

Question 23

Why are changes in mean sea level important

Answer 23

1. Inundation, flood, sea damage
2. Wetland change or loss (coastal squeeze), wildlife will attempted to retreat up shore if possible
   3.Erosion (of ‘soft coastlines’)
3. Saltwater intrusion
4. Rising water table and impeded drainage, aquifers etc

Question 24

Indirect measures of mean sea level

Answer 24

Salt marshes
Archaeology
Speleothems
Corals
Geology
Sediments (sediment cores)

Question 25

Direct measurements of mean sea level

Answer 25

Tide pole
Tide gauge (acoustic and radar) - discrete locations, 1 min-1hour
Satellites - global coverage, every 10 days

Question 26

How can saltmarshes be used to reconstruct historical sea levels

Answer 26

Zonation in saltmarshes
Dependent on degree of submersion
Testate amoebae, very hard and can survive change

Question 27

What can cause vertical land movement

Answer 27

Subsidence: groundwater withdrawal, reduced sedimentation
Uplift/rising land: sedimentation, tectonics
Subsidence and up life: Sedimentation, tectonic, groundwater with drawal

Question 28

What is Glacial Isostatic Adjustment

Answer 28

On-going movement of land once burdened by ice-age glaciers

Question 29

Why does land subside with ground water extraction

Answer 29

Total volume of sediment is reduced, sediments compact resulting in the lowering of the surface

Question 30

What is steric expansion

Answer 30

ocean warming, expansion, thermal

Question 31

What are Milankovitch cycles

Answer 31

Changes in:
Eccentricity: The shape of Earths orbit
Obliquity: Angle of the earth’s axis, tilt
Precession: direction that Earth’s spin is pointed

result in long term changes in the earth’s climate

Question 32

The climate change impacts on global mean sea level

Answer 32

Thermal expansion
Melting glaciers
Loss of ice sheets (Greenland, Antarctica)

Question 33

Why are glaciers shrinking

Answer 33

Greater-than-average- summer melting, diminished snowfall, later winters, earlier springs
Imbalance results in significant net grain in runoff versus evaporation for the ocean, sea levels rise

Question 34

What causes the loss of land bases ice

Answer 34

Meltwater from above and seawater below seeping beneath the ice sheets, effectively lubricating ice streams and causes them to quickly slide into the sea

Question 35

If all the world’s ice melted, what would be the sea level rise

Answer 35

~80m

Question 36

what is do No Active Intervention in the shoreline management plan

Answer 36

No planned investment in defence against flooding
Cost benefit analysis

Question 37

what is Hold the Line in the shoreline management plan

Answer 37

defences (hard/soft) maintained, upgraded so the shoreline position remains where it is

Question 38

what is Advance the Line in the shoreline management plan

Answer 38

New defences built seaward of existing defences
Significant reclamation of land

Question 39

What is Managed realignment in the shoreline management plan

Answer 39

Realignment of the shore (forwards or back) to control or limit movement
flood risk managed

Question 40

what is Adaptation/accommodation in the shoreline management plan

Answer 40

Flood proofing
Hazard mapping, awareness, warning and evacuation systems, land use zoning, habitat restoration