Coastal Defences Flashcards
What is hard engineering?
- coastal protection which has a high impact on the environment or landscape
- expensive and usually short term
What is soft engineering?
- coastal protection that has less impact on the environment
- less expensive and usually long term
What are some soft engineering techniques?
- beach nourishment/nourishment
- beach recycling/reprofiling
- managed retreat/realignment
What is managed retreat/realignment and what are its advantages and problems?
- method of allowing areas to flood up to a new line of defence inland
- salt marshes will then develop on the newly flooded areas
- disadvantages: buildings will be lost to sea
- advantages: cheaper than investing in coastal control
What is beach replenishment/nourishment and what are its advantages and problems?
- a natural defence against the sea
- can involve taking sediment that has been moved by long shore drift and replacing it to widen the beach
- e.g spraying the sediment back onto the beach by a ship
- advantages: *cheap
- forms a wide and gentle sloping beach, which is one of the best ways to reduce wave energy
- disadvantages: needs to be done constantly
What is beach recycling/reprofiling and what are its advantages and problems?
- replacing sediment that has been moved by storms
- often done through bulldozers and the sand is returned to its original position
- advantages: cheap
- disadvantages: needs to done after every storm
What are some hard engineering techniques?
- rip rap/rock armour
- tetrapod
- cliff drainage
- gabions
- groynes
- sea wall
What is cliff drainage and what are its advantages and problems?
- stabilising the cliffs through dewatering. Steel barriers and drains put into a cliff to intercept the water movement through the cliff which causes mass movement
- advantages: the cliff is stabilised and mass movement reduced
- disadvantages: can appear unsightly, costly
What is rock armour/rip rap and what are its advantages and problems?
- large boulders piled up on cliffs or beaches where erosion likely
- advantages: absorb wave energy
- disadvantages: can be undermined or moved by waves
What are sea walls and what are their advantages and problems?
- wall that deflects waves
- advantages: reduces erosion, protects against flooding, deflects waves which can wash away protective beaches and undermine the base
- disadvantages: -can be unsightly, can limit access to the beach, very expensive (£2.5 million/km)
What are groynes and what are their advantages and problems?
- wooden or steel structure places at right angles to the coast where longshore drift occurs
- advantages: -reduce the amount of sediment moved along the coast, this protects the cliff from wave attack by maintaining a beach in front of it
- disadvantages: -costs around £2000 each, can increase erosion further down the beach by stopping long shore drift and starving areas further down the coast of sediment
What are gabions and what are their advantages and problems?
- steel mesh cages containing boulders
- advantages: -costs under £1000 per metre, absorbs wave energy
- disadvantages: -unsightly (especially when used in large numbers)
What are tetrapod and what are their advantages and problems?
- they allow water to flow around than against them, and reduce displacement by allowing a random distribution of tetrapods to mutually interlock
- advantages: the shape is designed to dissipate the force of incoming waves
- disadvantages: causes more danger than the prevent because they alter ocean currents and disrupt the natural cycles of erosion and deposition that form and reshape the coast. Also is lethally dangerous to swimmers and surfers as well as shipping and recreational boaters
What is the meaning of hold the line?
-maintain the existing coastline by building defences
What is the meaning of advance the line?
-build new defences seaward of the existing defences
