Starter: Mind-map all the different things people use coast lines for. What are Coasts used for?
Some coastlines are under threat of erosion causing cliffs to retreat and beach material to be lost. Others are at risk from coastal flooding . In many cases the decision has been made to try and reduce the erosion to protect the coastline. This is called COASTAL MANAGEMENT. Coastal Management = The attempt by people to maintain the natural features of the coast for their own advantage
Types of Coastal Management HARD ENGINEERING Hard engineering options tend to be expensive and short-term options. They may also have a high impact on the landscape or environment. SOFT ENGINEERING Soft engineering options are often less expensive than hard engineering options. They are usually also more long-term and sustainable , with less impact on the environment.
GROYNES – Wooden/concrete barriers built at right angles to the beach.
One of the most frequently used protection types used to stabilize the coast.
They are help build up beach material by preventing longshore drift.
Groynes build up beaches at a small scale & are cheaper than sea walls.
Groynes can reduce the amount of sediment downcoast, which may have an effect on areas elsewhere (as these areas might get starved of material and their beaches get smaller).
They also have a short lifespan.
Vertical or sloping structures, built along the shoreline in an attempt to stop erosion
Can be constructed from any type of material- e.g. from sand-filled bags to reinforced concrete structures.
Often controversial as they are ugly and can be destroyed eventually.
Waves scour at the bases of the walls & eventually undermine them, causing failure. As a result, seawalls only provide temporary protection before needing replacement.
They are expensive .
The object of defence work is to dissipate wave energy (beaches do this very well) whereas sea walls have the opposite effect- walls concentrate wave energy and reflects it back at the sea .
The wall receives maximum impact which weakens the structure.
Often situated away from the cliffs and attempt to reduce the energy of the waves before they reach the cliffs/ coastline
Designed to allow sediment to pass through them , which means that longshore drift is not hindered .
The structures absorb the energy of the waves before they reach the cliffs. This method prevents wave scour.
They are also very cheap , but they do need to be replaced quite often & can be regarded as ugly.
Large boulders that work in a similar way to seawalls, but they are permeable structures.
They are able to dissipate wave energy by absorbing the impact of the waves.
Rip-rap structures do not suffer from the wave scour that afflict the seawalls.
Clearly, masses of boulders are much cheaper than sea walls & are longer lasting .
However, they are pretty unappealing to the eye & can reduce the recreational value of the beach.
They can also act as groynes & can prevent downdrift movement of sediment.
Rock Armour (Rip-Rap)
The principle of gabions is similar to the Rip-rap method of protection (i.e. dissipation of wave energy etc).
However, gabions use smaller rocks and are encased in a wire mesh ; this means that local beach material could be used, which enables the structures to blend in more with its surroundings.
Potential problems arise when the wire mesh breaks ( risk of injury ) and one could also argue that they are pretty ugly .
Gabions may not last for a long period of time (5-10 years)
Replacement of sand/pebbles on eroding beaches.
The best example is the nourishment of beaches at Miami Beach where 17.7 million m³ of sediment was dredged & moved to the beach to provide an area for recreation & also to protect the expensive properties that were found in the location.
The problem with beach nourishment is that one severe storm event may remove vast amounts of the expensive sediment.
Sand dunes and cliffs are a natural sea defence .
They dissipate wave energy and protect the area behind from flooding .
They are stabilised by fences or by planting grasses to hold the sand and rocks together.
This is cheap and effective but easily damaged by people if not maintained.
MANAGED RETREAT/ COASTAL REALIGNMENT
This is where in certain areas, the sea is allowed to reclaim (flood) the land that was once covered by the sea.
This often means that farmland is lost , but the pressure of floods are reduced because it creates salt marshes that can be flooded and can absorb the energy.
A natural and long-term sustainable solution.
Does require compensation for land that is lost.
Cheaper in the long term as structures not having to be maintained
Sea levels rising- can’t expect to keep position of the current coastline
Will produce wetland, which would have huge wildlife potential
Salt marshes absorb tidal/wave energy and reduce the impact of flooding
Only giving back what naturally belongs to the sea
Farmland and livelihoods lost
People’s homes will be sacrificed
Coastal realignment, but for how long? Where do you draw the boundary? Can you keep retreating?
Cost of compensation will be extremely high
Can’t be adopted in built-up areas
Some farmers unwilling to sell their land
MANAGED RETREAT/ COASTAL REALIGNMENT
Sea Wall Do nothing – managed retreat Beach Renourishment Groynes Cliff reshaping Beach Renourishment Rock Armour
Method How does it work? Advantages Disadvantages Groynes Sea Wall Revetments Rock Armour Gabions Beach renourishment Beach reshaping Managed Retreat