COASTAL EROSION MITIGATION METHODS

CONTENTS• Introduction• Coastal erosion Control• Types of controlling methods 1. Hard Structural Methods Jetties Sea walls Groins Revetments Breakwaters 2. Soft Structural Methods Beach nourishment Sand dune stabilization

INTRODUCTION• Coastal erosion is the wearing away of land or the removal of

beach or dune sediments by wave action, currents and tide . It is a dynamic and often complex process it can be cyclical with periodic episodes of coastal retreat and rebuilding.

• Beaches are eroded when they lose more sediment along shore, offshore than they receive from various sources.

• In order to prevent coastal erosion, rigid protection methods are usually used throughout the world.

• Erosion is controlled by engineering method with the help of the geology

Jetty A Jetty is any of a variety of structures used in

river, dock, and maritime works that are generally carried out in pairs from river banks, or in continuation of river channels at their outlets into deep ocean water . This is also a hard structure stabilization.• For example jetties allows boats and ships to safely enter the channel into a harbor.• Mainly, jetties are used to protect and stabilize man-made constructions such docks, piers and other maritime works.•Structure built at tidal inlet to stabilize the location of the inlet.•It permits low sand to flow across the inlet.

Kerala, kollam port

Disadvantages• It increases deposition on one side and the other side will

erode and narrow the beach.

Grays Harbor:before jetty construction

in 1900

Grays Harbor: after jetty construction

in 1999

SeawallA seawall is a hard structure constructed parallel to

the coastline that reduce the effects of strong waves and to defend the coast around a town from sea erosion.

• Investigation of the area, soil stability should be considered.• The walls can be sloping, vertical (10-15 m high) or curved to reflect wave power.• The 1/3 of the wall is made as its basement.• And also these are stepped permeable or impermeable.• These are concrete, steel sheet pile, rock or massive rigid

masonry.

Mumbai, maharastra state india

Advantages• Provide good protection to property.• May provide direct boat access to the shore.• Fair ease of repair.

Disadvantages• Must be well engineered for wave forces.• May increase erosion immediately downdrift.• Expensive to build.• Often decrease size of fronting beach.

Groins • Groins are impermeable structures that fingerlike,

perpendicularly to the shore which extend from backshore into the littoral zone.

• This type of structure is easy to construct from a variety of materials such as wood, rock or concrete, steel, bamboo

( Timber) and normally used on sandy coasts.

• The length elevation and space b/w groins should be designed on the bases of local wave energy and beach slope.

• Groins are most effective where the long shore current is predominantly in one direction.

• Groins are too long and too high tend to accelerate downdrift erosion because they trap to much of sand.

• If they are too short or too permeable the structure is inefficient because they trap too little sand.

• Sand deposition is greatly increased on the up-current side of the groin

• Meanwhile on the down-current side of the groin, sand erosion is greatly increased.

Advantages• May provide angler access to deeper waters.• May provide improved fish habitat.• Do not reduce access to beach from upland.

Disadvantages• Limit travel along beach.• may increase erosion on down drift side.

Revetments • Revetments are another type of hard structure of stone,

concrete built parallel to the sea or at the front of a beach to protect the slope against wave or current–induced erosion.

• Revetments are used in place of bulkheads in areas with moderate to severe wave energy.

• The most basic revetments consist of timber slants with a possible rock infill.

• And two other types are Rigid revetments, Flexible revetments etc.

• Waves break against the revetments, which dissipate and absorb the energy.

• The cliff base is protected by the beach material held behind the barriers, as the revetments trap some of the material.

• They may be watertight, covering the slope completely, or porous, to allow water to filter through after the wave energy has been dissipated.

In the fig. this rock rip rap revetment contains a filter layer, armor stone and toe protection to prevent undercutting by scour.

Ullal beach, Mangalore

Advantages• Result in less toe scour or depletion of fronting beach than do

seawalls.• Initial cost is usually reasonable.• Repair costs are usually reasonable because the whole

structure rarely fails at once.

Disadvantages• Decrease access to beach from upload.• May be hazardous to people walking on them. • It is not constructed in town area.

Breakwaters • Breakwaters are structures built parallel to a shoreline to

protect from the effects of weather, wave action and longshore drift .

• Breakwaters can be floating or bottom anchored. • Offshore breakwaters are usually built parallel to the shore,

but can be aligned at a slight angle to the shore to meet specific wave or bottom conditions.

• Two another types of breakwaters are Cellular steel breakwater and Rubble mound breakwater

Cellular steel breakwaters can be built and function effectively in waters up to 40 feet deep.

Rubble-mound breakwaters can be used in almost any depth of water and in almost any wave climate.

Some Indian examples of breakwaters are… Breakwater constructed (1991-94) to prevent sediment

entering the estuary in ULLAL Coast near Mangalore,Karnataka.

• North breakwater : 375 m• South breakwater : 580 m• Entrance : 500 m Mirya Bay in Maharastra also one another breakwater

Advantages• Provide sheltered swimming.• Beneficial effect may extend over a long.• May improve fish habitat.• May increase deposition, increasing beach.

Disadvantages• Subject to foundation failures.• May negatively affect the environment.• May be damaged by moving ice.• Usually very expensive to construct.• Very difficult to repair.

Beach Nourishment

• Beach nourishment is one of the most popular soft engineering techniques of coastal defense management schemes.

• Mainly, Beach Nourishment is the addition of sand and sediment to a beach to replace sand and sediment that has been eroded away.

• It involves the transport of the “nourishment material” from one area to the affected areas.

• The replacement sand is usually dredged up offshore and transported to the beach.

• Offshore sand is almost always much finer grained and muddier, therefore it erodes very quickly.

Advantages• Provide more beach for shoreline recreation.• Do not restrict access to beach.• Long stretches of beach can be protected at lower costs than

by use of human made structures.• Can have beneficial effects to downdrift shoreline as well as

immediate area

Disadvantages• Increased turbidity may impair fishing.• slowly beach sediment easily eroding by waves.• Submerged sill may be navigation hazard.

Sand dune Stabilization• Mainly, coastal sand dune are of vital importance in

providing natural protection to beaches and backshore areas from infrequent severe storms.

• Another way is Vegetation : it can be used to encourage dune growth by trapping and stabilizing blown sand.

Advantages• May create wildlife habitat.• Creates opportunity for nature study.• Blends in with natural surrounding.• Prevents flooding of inland areas.

Disadvantages• May reduce access to beach from upland.• May reduce view from upland areas.

CONCLUSION

• Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave, tidal currents, or drainage.

• The two major approaches used by human to control coastal erosion are:-

1). Hard structural stabilization 2). Soft structural stabilization• Implementations of this various methods helps to mitigate coastal

erosion though all these have some limitations.• This coastal erosion effects our environment in many ways therefore

what our society needs now from the scientific and engineering community is an accurate basis for developing long term coastal erosion stratigies.

REFERENCE• Journal of the Korean Society for Marine Environmental Engineering, Vol.

13, No. 3, pp. 216-222, August 2010• Charles R. O’Neill, Jr.(Structural Methods For Controlling Coastal Erosion),

pub:- A Cornell Cooperative Extension Publication, NewYork• Dr. Joseph Mathew, ADB Consultant Strategic Alternatives For Coastal

Protection : Multipurpose Submerged Reefs,11th Meeting of the Coastal Protection and Development Advisory Committee ,Chennai.

Web Sitehttp://www.panoramio.comhttp://en.wikipedia.org/COASTAL EROSION

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