Coastal Defence Flashcards
Why do we need coastal defences?
- preventing coastal erosion - reduces loss of housing or cost of insurance
- creation of a beach
- prevent too much
What are the approaches for coastal management?
- Hold the line
- Advance the line
- Managed realignment
- Do nothing
Hold the line
Maintain the existing defences
Draw a diagram of holding the line
N/a
Advance the line
Build new coastal defences further out towards the sea than the existing line of defence
Draw a diagram of advance the line
N/a
Managed realignment
Allow the shoreline to move but manage the retreat so it causes the least damage
Draw a diagram of managed realignment
N/a
Do nothing
Build no defences but deal with erosion and flooding as it happens
Draw a diagram of do nothing
N/a
What is coastal engineering?
Coastal engineering is a type of management where strategies are put in place to protect areas from the effect of coastal erosion, transportation and deposition. Coastal engineering strategies can be categorised as being either ‘hard’ or ‘soft’.
Hard engineering
A management technique, protecting coasts by absorbing the energy of waves, preventing erosion and flooding. These are expensive and highly-visibly man-made (eg. sea wall).
Soft engineering
A method of working with nature, being ecological, less expensive, more long-term and visibly appealing.
Two types of sea defences:
- soft engineering
- hard engineering
Hard engineering types
- (recurved) sea wall - breaks wave energy
- steps - absorbs wave energy
- rock armour - stops abrasion or hydraulic action, in a slope
- riprap - disorganised limestone or granite boulders, chaotic and random
- groynes - traps sediment
- gabions - low cost wire cages with rocks inside
Soft Engineering Types
- sand dunes - compressed sand
- wetlands - natural
- beach
- beach nourishment - build beach higher with new sand
Sea walls
Vertical or near vertical masonry or concrete walls. Can incorporate wave-return profiles. Examples are in Hornsea.
Advantages:
- effective at protecting the base of a cliff
- sea walls usually have promenades so people can wall along them
Disadvantages:
- waves are still powerful and can break down and erode the sea wall
- expensive - approx. £2000 per metre
Draw a sea wall shape
N/a
Revetments
Sloping structure of either solid (South Withernsea) or open rock armour (Easington) structure
Solid:
Advantages:
- massive or made of concrete, reducing flooding
- used to reflect waves rather than resist them, long-term
- cheaper (relatively)
Disadvantages:
- still costly (initial cost)
- does not cope well with very strong waves
- requires space
- can be unattractive
Open:
Advantages:
- cheaper than a sea wall
- low maintenance
- useful for fishing
Disadvantages:
- look different to local geology, as the rock is imported from other areas
- rocks are expensive to transport
Draw the solid revetments
N/a
Draw an open (rock armour) revetment
N/a
Splash walls
Used as secondary defences to control the effects of overtopping or flooding. Examples are in Bridlington.
Advantages:
- low maintenance
- can be aesthetic
- extra protective defence against extreme weather or rising sea levels
Disadvantages:
- limited effectiveness for extreme waves
- can cause wave reflection to the base of the cliff
Draw a splash wall
N/a
Groynes
Groynes help to build up and maintain beach levels by intercepting the longshore movement of sand. Examples are in Hornsea
Advantages:
- builds a beach for tourism
- traps sediment carried by longshore drift
Disadvantages:
- trapping sediment starves beaches further down the coast, increasing rates of erosion elsewhere
- unattractive
