Sea Level Rise and Hard and Soft Engineering Flashcards
Define Eustatic sea level change?
Everyone
A Global change in sea level resulting in a fall or rise of the volume of water in our oceans.
What are the two main causes of eustatic change?
1.Changes In Climate- Temp decrease= more ppt falls as snow, increasing the volume of water stored in glaciers
Temp Increase= freshwater glacial melt, thermal expansion.
- Tectonic movements of the Earths crust= changes the shape of ocean basins
Define Isostatic sea level change?
A Local change in sea level resulting in the fall or rise of the land relative to sea level.
What are the three main causes of Isostatic change?
- ISOSTAIC READJUSTMENT-uplift/ depressions within the Earths surface due to the accumulation or melting of ice sheets.
- Subsidence of land due to draining of groundwater stores eg: marshland drainage
- Tectonic (crustal) processes as one plate is forced under another.
Describe past sea level fluctuations?
21,000 years ago= last GLACIAL maximum, sea levels were 130 metres lower than current situation
12,000 years ago- last glacial period, slowly started to melt
4,000 years ago- fluctuations began
1930- sea levels begin to rise
What does the IPCC predict about sea levels in 2100?
Sea levels will rise by 8-6 mm each year
Currently 2mm each year
Sea Level Rise CASE STUDY?
- The Republic of Kiribati
- 33 low lying Islands within the Pacific Ocean
- Predicted many Islands will be lost within the next 50YEARS, rising by 1.2cm each year (4X GLOBAL AVERAGE.
President Tong- bought 20km of land on Fiji Islands- contaminated groundwater, cant grow crops.
“Migrate with Dignity”- help relocate in New Zealand as Kiribati’s population will become environmental refugees.
How are emergent landforms formed?
FALL in relative sea level, isostatic rebound takes place faster than eustatic sea level rise.
Raised Beaches- former wave cut platforms exposed due to rise in sea levels
Relict Cliffs, Stacks, Caves- become covered in vegetation and are gradually weathered over time
eg: NW of Scotland on Isle of Arran
How are submergent landforms formed?
RISE in relative sea level, isostatic rebound takes place slower than eustatic sea level rise.- floods land
Rias- flooded RIVER valleys, gentle, long, sloping cross sectional area.
Wide and deep at mouth-CROSS SECTION?
eg: Milford Haven in Pembrokeshire
Fjords- flooded GLACIAL valleys, straight, narrow, very steep sides. NOT deepest at the mouth= THRESHOLD
- CROSS SECTIONAL AREA?
eg: Sogne Fjord in Norway-200km long
Dalmatian Coasts- flooded valleys that run parallel to the coast (unlike fjords and rias that run parallel)
eg: The Coast of Croatia
SPATIAL AND TEMPEROL- take place globally at different locations and different speeds.
Define Coastal Management?
The protection of the coastline from increasing pressures and implications from natural processes and human activity.
What two things does coastal management look to protect homes and businesses from?
- EROSION
2. FLOODING
What are the four options when it comes to costal management?
- Hold the line- maintain defences
- Advance the line- build new coastal defences further out to sea.
- Manged Retreat/ Realignment- allow shoreline to move, but only to where it will do the least damage eg: flood farmland not houses.
- Do nothing- allow nature to take it’s course.
Define hard engineering?
The use of entirely artificial, built structures using long lasting materials eg: concrete, steel.
H- SEA WALL
A large concrete barrier that ABSORBS wave energy.
Some have recurved ends to deflect wave energy BUT this can cause strong, base eroding backwash.
+High value land protected
-expensive to build and maintain (£6000 per m), unsightly.
H- Groynes
Artificial fences built at right angles to the sea.
Trap sediment transported by LSD, widens beaches and allows increased absorbtion of wave energy.
“localised”
+relatively cheap to install and maintain
- deprive down- drift beaches of sand
H- Rip- rap
Boulders of granite and other hard rock that are placed at the base of a cliff and absorb wave energy.
+relatively cheap and look natural within coastal environment
-can move during storm events
H- Revetments
Sloping structures made out of wood/ concrete placed at the base of a cliff to absorb wave energy.
+expensive to built but relatively cheap to maintain , more natural looking than sea wall
-They create a strong back swash
H- Offshore Breakwater
Concrete blocks/ boulders deposited off the coast, force waves to BREAK sooner offshore.
+produce “buffer effect”, decrease wave energy, don’t affect beach
- very expensive, can be damaged in storm events
H- Gabions
Rock filled cages built at the base of a cliff. Absorb wave energy and reduce erosion.
+relatively cheap to install
- can be damaged in storms,
H- Tidal Barriers and Barrages
Barrier- built across river estuaries, contain floodgates that can be used to protect against flooding
Barrage- dams built across river estuaries= MAIN PURPOSE IS TO GENERATE ELECTIRICTY- water is trapped behind dam at high tide, controlled release of water generates electricity.
VERY EXPENSIVE, may disrupt sediment flow.
Define soft engineering?
Why soft engineering?
The use of natural systems and processes that are environmentally friendly to manage costal erosion and flooding.
Seen as more SUSTAINABLE by stakeholders, generally cost less than hard.
S-Beach Replenishment?
Sand and shingle are added to beaches from elsewhere- DREDGING.
This increases the width of the beach and therefore decreases wave energy.
+increased buffering, absorbs wave energy, more natural
-dredging can disrupt tourism and marine life
S- Beach Stabilisation?
Decreasing the angle/ slope of a beach and planting vegetation= wider beach= decreased wave energy.
+decreased erosion, absorbs wave energy
-cheap, natural, adds to and creates habitats.
S- Managed Retreat?
Allowing the sea/ erosional processes to breach sea defences and allowing land to flood.
Over time, vegetation will COLONISE and marshland will form.
+new habitats, very cheap, marshland absorbs w.e
-conflicts can arise over which areas should be flooded, compensation.
