Sea defences


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About sea defences

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Sea defences

  1. 1. What Are They?
  2. 2. Sea Defense or Costal protection are defenses thatstop erosion, flooding, silting up of harbors etc.Walls, breakwaters and other measures designed toprevent coastal erosion.
  3. 3. SEAWALLSSeawalls are durable structures designed to protect the coast against erosion andflooding by the sea. They are sometimes additionally used for amenity purposesor to protect reclaimed land from erosion. Because of the potential for scouring atthe toe (bottom) of the structure, seawalls are often used together with somesystem of beach control such as groynes or a nourished beach
  4. 4. Gabions are wire baskets filled with stone, cobbles or small rocks. They can beplaced as either a vertical wall or as as a sloping revetment, where theirpermeability helps to limit wave run-up and overtopping. Gabions are mostcommonly used to stabilise shorelines against erosion, or as earth retainingwalls.
  5. 5. Revetments are simply described as an earth embankment corecovered by a protective surface layer. A revetment may beeither rigid or flexible, depending on the material from whichthe protective surface layer is constructed. The main types ofrevetment construction used for coastal defences are RockArmor, Concrete Blocks (often inter-connected), Gabions or byway of Earth Reinforcing Geotextiles.
  6. 6. Groynes are beach control structures designed to reduce the loss (or rate of loss) of beachmaterial due to long shore drift. Groynes are narrow structures usually built at right angles tothe shoreline, most commonly built using timber planking between timber piles, howevergroynes can also be built from rock and concrete. Across the partnership area there areseveral examples of different types of groynes, the Hayling Island Southern frontage has over60 groynes, mostly of timber construction, with rock groynes found at the Eastern end of thebeach. Groynes can also be found to the east of Gilkicker Point, Gosport.
  7. 7. Also known as riprap, rock armour is large rocks piled or placed at the foot ofdunes or cliffs with native stones of the beach. This is generally used in areasprone to erosion to absorb the wave energy and hold beach material. Althougheffective, this solution is unpopular due to the fact that it is unsightly.Also, longshore drift is not hindered. Rock armour has a limited lifespan, it is noteffective in storm conditions, and it reduces the recreational value of a beach.The cost is around £3000 per metre, depending on the type of rocks used.
  8. 8. Enormous concrete blocks and natural boulders are sunk offshore to alter wave direction and tofilter the energy of waves and tides. The waves break further offshore and therefore reduce theirerosive power. This leads to wider beaches, which absorb the reduced wave energy, protectingcliff and settlements behind. The Dolos which was invented by a South African engineer in EastLondon has replaced the use of enormous concrete blocks because the dolos is much moreresistant to wave action and requires less concrete to produce a superior result. Similar concreteobjects like the Dolos are the A-jack, Akmon, Xbloc and the Tetrapod, Accropode