Hard Engineering Flashcards
What are sea walls?
A structure of concrete with steel reinforcements and stone deep-piled foundations. These walls are recurved with a lip closest to the coast to deflect wave energy.
What are the advantages of sea walls?
- Act as flood barriers
- Absorbs and deflects wave energy back to sea
- Recurved upper lip decreases oncoming wave power.
What are the disadvantages of sea walls?
- Expensive to build and maintain (requires regular repair)
- Quarrying at base can undermine sea wall foundations - strong backwash erodes under the wall
- Not aesthetically or visually pleasing.
What is the approximate cost of sea walls?
Up to £6 million per kilometre
What are groynes?
Wooden or stone barriers constructed perpendicular to the coastline designed to prevent the process of longshore drift in order to build up the beach width and height.
What are the advantages of groynes?
- Increases the natural barrier of beach between sea and shore
- Groynes can act as ‘wind breaks’ for visitors
- Cheap to build and repair.
What are the disadvantages of groynes?
- Can lead to an increase in erosion further down the coast (adjacent beaches have lower inputs of sand)
- They require regular maintenance and repair since most are constructed from hardwood.
What is the approximate cost of groynes?
£5000 per groyne
What are revetments?
Slanted structures built along cliffs or in front of sea walls from concrete, wood or rocks. This prevents cliff erosion as it absorbs wave energy when they break.
What are the advantages of revetments?
- Cheap to maintain and relatively low maintenance
- Impermeable revetments have a life expectancy of around 30-50 years
What are the disadvantages of revetments?
- Expensive to build
- Can make some beaches inaccessible to locals and tourists
- They create a strong backwash so erosion occurs at the base of the structure, causing structure failure
- Can disrupt natural dune processes
What is rip-rap (rock armour)?
Large rock boulders placed in front of a cliff or sea wall to absorb the energy of the waves and reduce backwash by encouraging percolation.
What are the advantages of rip-rap?
- Quick and easy to construct
- If well maintained, the structure will last for a long time
- Can be used to extend the life span of sea walls.
What are the disadvantages of rip-rap?
- Rocks have to be quarried to make the structure which can cause environmental damage
- Not aesthetically pleasing.
What is the approximate cost of rock armour/rip rap?
£1000-£3000 per metre
What are gabions?
Metal cages containing rock located at the base of a cliff to absorb and disperse wave energy and reduce erosion.
What are the advantages of gabions?
- Very quick to build and cheap to maintain
- Can last between 20-25 years
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What are the disadvantages of gabions?
- Damaged gabions can pose a risk to natural life (e.g. sea birds)
- Gabions quickly degrade on shingle beaches
- Not aesthetically pleasing to local people.
What is the approximate cost of gabions?
£110 per metre
What is cliff drainage?
Reducing pore water pressure and mass movement of material from the cliff. This prevents surface runoff and infiltration of water into the soil.
What are the advantages of cliff drainage?
- Drainage structure are hidden so aesthetic appearance is maintained
- No build up of water on impermeable areas of clay.
What are the disadvantages of cliff drainage?
- Can result in the cliff drying out causing the collapse of large rocks and degrading the cliff - increased risk of danger to wildlife.
What is the approximate cost of cliff drainage?
£1 million per 100 metres
What are off-shore breakwaters?
Large concrete boulders or blocks which can be found offshore, placed parallel or at an angle to the coastline. They act as barriers which reduce wave energy.
What are the advantages of off-shore breakwaters?
- Beaches have a natural appearance (they do not disrupt the physical landscape)
What are the disadvantages of off-shore breakwaters?
- Difficult to maintain due to location
- Less effective than other methods at preventing coastal erosion
- Can disrupt natural processes.
What is the approximate cost of off-shore breakwater?
£1000 per metre
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