Coastal Protection Methods

Hard Engineering

Re-Curved Sea Wall are appropriate/mandatory in promenades and harbour situations as these bulkheads separate land from sea, protecting land and holding back sea, protecting low lying areas behind from flooding. Modern designs of concrete seawall absorb as well as resist wave attack, the wall, which is curved on the underside, deflect rather than reflect power of waves.
Very expensive to build (up to 1-2mil pounds/km) and maintain. May accelerate wave erosion due to downward movement of water and reflected waves can scour material at base and undermine the wall.

Gabions are metal cages of boulders which can be stacked to build walls, built into the cliff faces to protect cliff from the force of the waves; may be arranged as a mattress so that waves can percolate. They absorb wave energy, reduce erosion and are cheaper than sea walls and can be very effective were severe erosions is a problem.
Visually intrusive, metal cage may fail quickly & spill contents. If stacked, may move in strong waves.

Breakwaters are offshore structures of concrete or rocs that are built parallel to the coast, break the force of incoming waves, and deflect waves before they reach the shore. Slows longshore current flow, leading to deposition of sediment behind the breakwater.
Very expensive to construct (one million dollars/linear foot) and tend to deflect waves along new paths, which may cause scouring of foundations or erosion elsewhere.

Groynes are wooden, rock, steel barriers sited perpendicular to shore, designed to stop longshore drift and hence, act to build up and anchor beach material, protecting the base of cliffs/coast. They are effective at reducing erosion in the area they are constructed in by causing significant build up of beach material and slowing the speed of the waves as they break along the coast. Relatively low cost.
May starve areas further down the coast of material by stopping longshore drift, resulting in an increase in erosion in these areas.

Rip Rap/Rock Revetment are large boulders placed together on a beach. They are permeable and able to adapt to change, absorb wave energy and break the power of the waves. Look more natural.

Conclusion: Some hard coastal defence structures if proactively designed and built, such as offshore islands, can reduce erosion and increase habitat for fish/coastal birds, but may also modify sediment transport and damage beaches. The decision should result from a cost-benefit analysis and should be a concerted decision among the stakeholders. (Consider needs of stretch of coast)


Soft Engineering

Also consider Soft Engineering that address erosion problems while preserving the natural habitat for shoreline ecosystems, working with natural processes to enhance coastal resilience and are effective in the long run. It slows down coastal retreat but does not stop it. Require continual efforts and maintenance, can be expensive and resource intensive. Less expensive to implement, can involve loss of property or land.

Beach Nourishment is where beach material (sand) is added to coast, maintaining the beauty of the landscape, avoiding visual intrusion, but very expensive to maintain as longshore drift continues to move beach material down coast and hence regular replenishment is required. Miami Beach, USA.

Dune Regeneration is where a fragile environment needs careful management where sand dunes can be stabilised by planting marram grass, building walkways or duckboards to reduce trampling, and planting fences and brushwoods to reduce wind velocity and trap sand. Land use zoning also to keep areas from pressure and is only effective in Aeolian environments and where public access can be controlled. At Omaha Beach in New Zealand.

Mangroves grow in the intertidal zone and are salt tolerant, with a horizontal layering with the species that have adapted to being flooded with seawater growing near the water. Protect coast from erosion as prop roots, aerial roots and knee-like roots slow down incoming waves, reducing energy and encouraging deposition, these roots bind the soil and stabilise the coast. Fruits float also such that they are transported to newly deposited delta fronts where they colonise and protect newly developed coastal areas. Good for coastal ecosystem, fishery industry.
Only grows in sheltered tropical waters, mangroves take time/years to grow before they can be effective means for coastal protection. Planting exercises require cooperation of local people.
Along Malaysian coastline and Sulawesi, Indonesia.

Encouraging Growth of Coral Reefs whereby coral reefs protect beaches against coastal erosion reducing the speed of waves approaching the coast hence less erosion. Governments may ban fishing within certain protected areas, build wastewater treatment facilities in coastal settlements and plant artificial reefs for corals to grow. In Malaysia.
Success in the long run depends on cooperation of various groups of people and constant effort to reduce water pollution. Corals can only grow in clear water.


Hope this helps! (: If any problems or queries, please feel free to ask!

- debb

Labels: Geography

An otherwise carefree student at MGS, who is currently studying in secondary 4, and totally not proud to be a MUGGER! :O


I sincerely apologise for the subjects which I do not include (: The list may be found just below. Thanks!

gooodluck!