Coastal Defences And Erosion (1st Term) Flashcards
(21 cards)
Constructive waves?
Depository waves; strong swash and weak backwash
Destructive waves?
Storm conditions, long fetch; weak swash and a strong backwash
D. Hydraulic action?
Air trapped in cracks in rocks and caves is suddenly compressed by breaking waves, increasing pressure on the rocks and widening the crack.
D. Corrosion?
Weak acids in the water dissolve the rocks
D. Attrition?
Particles carried by the waves are reduced in size as they collide with rock and each other
D. Abrasion?
The sandpapering effect of pebbles grinding I’ve a rocky platform
D. Traction?
Large particles roll along the beach and sea bed
D. Suspension?
Small particles float in the water
D. Solution?
Dissolved particles float in the water
D. Saltation?
Small particles bounce along the beach and sea bed
Concordant coastline?
Rock layers perpendicular to the coast
Discordant coastline?
Rock layers parallel to the coast
D. Hard engineering?
Most expensive, often unsustainable and biggest impact on the landscape or environment .
D. Soft engineering?
Least expensive, sustainable and smallest impact on environment and landscape
What is beach replenishment?
- Evaluate
Sand is added to the beach to replace the sand lost, which absorbs the waves energy and protects the cliffs.
- regular replacement, upkeep
- S.E.
- looks natural
- £3-10 per m
What are dunes?
- Evaluate the coastal defence they offer
Natural defence, bound together by plant roots and Couch grass
- £200 per m
- natural appearance
- create new habitat
- S.E.
What is Off shore breakwater?
- Evaluate the coastal defence they offer
Large pieces of concrete or cement just of the coast - parallel to the beach which force the waves to break, absorbing their energy.
- £300 per m
- damage to sea floor
- ugly
- reduce erosion, doesn’t directly protect the cliffs
- H.E.
What are Groynes?
- Evaluate the coastal defence they offer
Placed at 90 degrees to the beach to stop sand being moved by longshoremen drift.
- £1200 per m
- cause erosion down coast
- ugly
- starve other beaches of sand - erosion
- H.E.
What are Sea Walls?
- Evaluate the coastal defence they offer
Concrete walls built to protect towns, absorb waves energy - curved side to reflect waves back to sea
- £5000+
- long lifespan
- strong backwash which erodes bottom of wall
- H.E.
What is Managed Retreat?
- Evaluate the coastal defence they offer
Doesn’t stop erosion, allows some coastal areas to erode and flood naturally.
- creates new habitat
- wetland
- S.E.
What are Gabions?
- Evaluate the coastal defence they offer
Steel mesh cages filled with rocks to absorb waves energy, placed at bottom of the cliffs.
- £400 per m
- ugly
- sharp
- requires replacement 10 years
- H.E.
