3.10 Managing coastal erosion and flooding Flashcards
What is hard engineering?
This involves building structures along the coast e.g. sea walls, groynes and revetments. It aims to stop physical processes all together or alter them to protect the coast
What is soft engineering?
An approach designed to work with natural processes in the coastal system in order to manage it (but not necessarily to prevent erosion)
What are groynes?
Timber fences built at 90 degrees to the coast
What is the purpose of groynes?
To prevent longshore drift of sediment and encourage deposition, building a wider, higher beach
What are the advantages of groynes?
-The built up beach increases tourist potential and protects the land behind it
-groynes work with the natural processes to build up the beach
-not too expensive
What are the disadvantages of groynes
-groynes starve beaches further along the coast of fresh sediment , because they interrupt longshore drift- terminal groyne syndrome. This often leads to increased erosion elsewhere
-groynes are unnatural and rock groynes can be very unattractive
What are the costs of groynes?
£5000 to £10,000 each (at 200m intervals)
What is the purpose of a sea wall?
a physical barrier against erosion
they often also act as flood barriers
designed to dissipate rather than reflect energy
What are the advantages of a sea wall?
-effective prevention of erosion
-often have a promenade for people to walk along
What are the disadvantages of a sea wall?
-Older ones reflect wave energy rather than absorb it
-can look intrusive and unnatural
-expensive to build and maintain
What is the cost of a sea wall?
£6,000 a metre
What is the purpose of a rip rap (rock amour)
They break up and dissipate wave energy
they are often used at the base of sea walls to prevent them from undercutting and scour
What are the advantages of a rip rap?
-relatively cheap and easy to construct and maintain
-often used for fishing or sun bathing
What are the disadvantages of a rip rap?
-rocks are usually from somewhere else, so they don’t fit in with the local geology and look out of place
-can be very intrusive
-rocks can be dangerous for people climbing over them
What is the cost of a rip rap?
£100,000 to £300,000 for 100m
What are revetments?
Sloping wooden, concrete or rock structures- placed at the foot of a cliff or the top of a beach. They break up the wave’s energy
What is the purpose of revetments?
to absorb wave energy and reduce swash distance by encouraging infiltration
-reduce erosion on dune faces and mud banks
Advantages of revetments
Relatively inexpensive
Disadvantages of revetments
intrusive and unnatural looking
need for high level of maintenance
What is the cost of revetments?
Up to £4500 a metre
What is an offshore breakwater?
a partly submerged rock barrier designed to break up the waves before they reach the coast
What’s the purpose of an offshore breakwater
they force waves to break offshore rather than at the coast , reducing wave energy and erosive force
What’s the advantage of an offshore breakwater?
an effective permeable barrier
What’s the disadvantages of an offshore breakwater?
-visually unappealing
-potential navigation hazard
What is beach nourishment?
its artificially replacing sediment on the beach
What’s the purpose of beach nourishment?
-replaces sediment lost by erosion
-enlarges the beach, so it dissipates wave energy and reduces wave erosion
-increase the amenity value of beaches by adding fresh sand
What are the advantages of beach nourishment
-relatively cheap
-looks natural
-increases tourist potential by making the beach bigger
What are the disadvantages of beach nourishment?
Needs constant maintenance because of erosion and longshore drift
What’s the cost of beach nourishment?
£300,000 for 100m
What is cliff regrading and drainage?
Cliff regrading reduces the the angle of the cliff to help stabilise it
Drainage removes water to prevent landslides and slumping
How does cliff regrading and drainage work?
- slope stabilization by planting vegetation through a tough, flexible geo-textile membrane to keep the soil in place. Regrading cuts the cliff slope back to a more stable angle
- In cliff drainage pipes channel groundwater out of the cliff, reducing pore water pressure
- rock armor or revetment at the toe of the cliff- rock bolts anchor the armor and the rock within the cliff
What are the advantages of cliff regrading and drainage?
-can work on clay or loose rock
-cost effective
What are the disadvantages of cliff regrading and drainage?
effectively causes the cliff to retreat
drained cliffs can dry out and lead to collapse
What is dune stabilization and what’s its purpose?
Marram grass can be planted to stabilise dunes
Areas can be fenced off to keep people out of the newly planted dunes
Absorbs wave energy to protect low lying coastal areas
What’s the advantage of dune stabilisation?
-Maintains a natural coastal environment
-provides wildlife habitats
-cheap and sustainable
What are the disadvantages of dune stabilisation?
-time consuming to plant marram grass
-overgrazing
-people may respond negatively to being kept off of certain areas
-storm surges breach dune systems
What is the cost of dune stabilisation?
£200-£2000 for 100m
What’s the purpose of marsh creation?
Allows low lying areas to be flooded by the sea
-The land becomes a salt marsh
What are the benefits of a salt marsh?
-Creates an important habitat
-relatively cheap as it often involves reverting land to its original state
