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Coastal Management

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  • Methods of protection
  • Transcript

    • 1. Coastal Management
    • 2. Starter: Mind-map all the different things people use coast lines for. What are Coasts used for?
    • 3. 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
    • 4. 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.
    • 5. HARD ENGINEERING
    • 6. 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.
    • 7.
      • 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.
      SEA WALLS
    • 8.
      • 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.
      REVETMENTS
    • 9.
      • 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)
    • 10.
      • 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)
      GABIONS
    • 11. SOFT ENGINEERING
    • 12.
      • 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.
      Beach Nourishment
    • 13. Beach reshaping.
      • 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.
    • 14. 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.
    • 15.
      • Positive
      • 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
      • Negative
      • 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
    • 16. Sea Wall Do nothing – managed retreat Beach Renourishment Groynes Cliff reshaping Beach Renourishment Rock Armour
    • 17. Method How does it work? Advantages Disadvantages Groynes Sea Wall Revetments Rock Armour Gabions Beach renourishment Beach reshaping Managed Retreat