Coastal erosion

Our coastal regions continue to experience erosion, threatening property, structures, and natural resources to an unbelievable extent. Scientists predict that erosion will increase in the not too distant future because of climate change and rise in sea levels. It is estimated that a 2 percent rise in sea temperature can raise the speed of winds by 10 percent. Global warming is expected to raise sea levels by melting glaciers and ice sheets and by warming the upper ocean, causing it to expand and accelerate erosion, inundation, and the loss of beaches and wetlands. As a result this would

• threaten aquifers
• allow salt water to penetrate farther inland in wetlands and upstream in rivers.
• lead to higher storm surges which would subject the area to flooding from coastal storms and placing more land in the path of wave-driven erosion.
• cause greater harm to small islands, deltaic regions, coastal wetlands, and developed sandy shores.

More Human than Natural Activities

Human activities contribute much more to coastal erosion than natural activities. In the natural process material that rivers transport from the catchment area replenish the sand and gravel taken away by waves and currents. Refer to Sand-Sharing Systems Of Beaches, Dunes And Offshore [1]. But these natural processes have been disturbed by rapid developments along the coast and upstream. Millions of tonns of sands that replenish the coasts are being used for construction.

When coastal communities construct marine protection structures and breakwaters as barriers along the coast, they help reduce coastal erosion in that area only. But these structures tend to interfere with the natural transport of sand and cause coastal erosion further down the coast. See Issues Addressed [2] highlighting country-wise human activities which lead to coastal erosion.

With more and more communities settling along the coastline and contributing to global warming, it is necessary that they get actively involved in coastal management.

Altering the Natural Process

Some of the ways by which human intervention alters the natural process are:

• dredging of tidal entrances [3]

• Construction of harbors in nearshore waters [4]

• constriction of groins and jetties [5]

• Hardening of shorelines with seawalls and revetments [6]

• construction of sediment-trapping upland dams [7]

• beach nourishment [8]

Natural Factors Influencing Erosion

• The sand sources and sinks

• Changes in the relative sea level

• Geological characteristics of the shore

• Sand size, density and shape

• Sand-sharing systems of beaches, dunes and off-shore bars

• Effect of waves, currents, tides and wind

• Bathymetry of the off-shore sea bottom

Other beach erosion factors:

• Effects of human impact, such as construction of artificial structures, mining of beach sand, offshore dredging, or building of dams or rivers.

• Loss of sediment offshore, onshore, alongshore and by attrition.

• Reduction in sediment supply due to deceleration cliff erosion.

• Reduction in sediment supply from the sea floor.

• Increased storminess in coastal areas or changes in angle of wave approach.

• Increase in beach saturation due to a higher water table or increased precipitation

See Coastal features created by erosion [9] for pictures, illustrations and description on how erosion creates different shapes along the coastline

Short-Term and Long-Term Erosion

Short-term coastal erosion is dynamic coastline changes taking place on all beaches and do not result in permanent retreat of the coastline. Coastal erosion is the long term (20 years or more) landward movement of the coastline.

Though coastal erosion takes place because of coastal processes and their interaction with land, it is possible that the process gets initiated by human activity. Human activities such as poor land use methods also contribute to coastal erosion.

Coastal communities face enormous problems as a result of coastal erosion and frequently lose valuable property.

Protection Against Erosion

Increase in population and more buildings have changed natural coastal areas. More and more building come up by draining wetlands, marshes, and swamps, leading to increased pollution. Plant and animals disappear and may face extinction. Beaches, dunes, and barrier islands may disappear. For safeguard, humans create structures for protection against the erosive effects of the wave action.

They are as follows:

• Seawall – These are solid structures parallel to and along the beach where it meets the water. These are made to diminish storm wave’s effects on the shore. However, the seawall intensifies erosion at either end of the wall where the beach is not protected. Eventually the seawall gets damaged as the beach surrounding it disappears.

• Breakwater – is another type of a solid structure parallel to the beach but is placed offshore. This is done to prevent large waves between the breakwater and shoreline. But in spite of this deposition increases around the breakwater and eventually starves the beach of sediment.

• Groin - A short solid structure built perpendicular to the beach outward into the water to prevent the long shore current from taking sediment from the immediate beach area.

• Jetty - This is a groin built along the side of a river or harbor entrance. This is done to keep a swift current through this confined area in order to prevent the deposition of sand in the channel.

• Upstream Dams - Used as flood prevention, development of irrigation and hydro-electric power.

Sustainable and Natural Repairs

With ‘bio-engineering’ and ‘soft landscaping’, water erosion can be fixed using sustainably produced materials and native plant species. This would also give a natural appearance, blending it with the surroundings.

Willow Spiling:

Flexible, live, growing structures can be made using woven living willow which will resist and deflect water flows. Bankings and vegetation will re-grow naturally and bind themselves, thus preventing further erosion.

Pre-made panels and shutters

These can also be supplied and fitted with minimal on-site work.

Mattings and fabrics

Mattings can be made of organic, natural materials or from man made geotextiles. They provide longevity, strength and a plant friendly environment, for use in more aggressive erosion locations, and allowing vegetation and roots to establish securely.

References

[10]
[11]
[12]
[13]
[14]
[15]
[16]