coastal erosion and its control
DESCRIPTION
Erosion is when wind, water, and ice take sediments away.Erosion on coasts by wind and water.Water is major agent of erosion.About 21% of all erosion in done by coastal erosion.TRANSCRIPT
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AUTHOR: PARTHA DAS SHARMA, E.mail: [email protected], Website: http://saferenvironment.wordpress.com
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COASTAL EROSION1. Coastal Processes.
2. Coastal Land forms
3. Impacts and Hazards on Coasts.
4. Prevention Methods used.
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Coastal Erosiono Erosion is when wind, water, and ice take
sediments away.
o Erosion on coasts by wind and water.
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o Erosion on coasts by wind and water.
o Water is major agent of erosion.
o About 21% of all erosion in done by coastal erosion.
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Coastal Processes o Currents and Waves.
o Swash and Backwash of waves.
o Tides and Tidal Currents.
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o Rip Currents.
o Long Shore drift.
o Hurricanes and Tsunami.
o Abrasion & Attrition.
o Corrosion (Salutation).
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Waves and Currentso A wave is a disturbance
that propagates through space and time.
o Current is a continuous
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o Current is a continuous flow of water in a particular direction.
o Both contains characteristics of Crest and Trough.
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Swash and Back washo Swash is the water
that washes up on shore after an incoming wave has broken.
o Also called as constructive current.
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o Also called as constructive current.
o Backwash current is a seaward current that results from the receding swash.
o Also called destructive current.
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Swash and Back wash
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Tides and Tidal currentso Tidal bulge combine with
daily earth’s rotation creates broad system of waves.
o Cause by the gravitational action.
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action.
o Mainly because of moon and sun.
o Incoming tides and out going tides.
o Neap and Lunar tides.
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Rip Currentso Fast, narrow surface
currents.
o Flow seaward at nearly
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o Flow seaward at nearly right angles to shore.
o Mainly in surfing zone.
o Move back to sea by narrow paths.
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Long Shore Drifto The movement of
sediments along a beach or shore by currents.
Having a particular
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o Having a particular direction.
o Mainly cause by Long shore currents.
o Swash and Backwash are major Phenomena.
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Hurricane and Tsunami
Hurricaneo A tropical cyclonic storm
with winds having speed >120km/hour.
o Mostly hit in late summers and fall.
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and fall.
Tsunamio A short period disturbance
create by submarine earth quake or volcanic vent.
o The waves more than 100feet, might possibly rise.
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Abrasion & Attrition(Corrasion)
Abrasion.Abrasion.o The waves pick up the
sediment & hurl it against the cliffs (uses the sediment as ammunition).
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ammunition).
AttritionAttritiono As the sediment is
hurled against the cliff, bits are chipped off, the sediment gets smaller & rounder
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Corrosion (Salutation)
o Salt & other chemicals in sea water attack & dissolve the cliffs.
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dissolve the cliffs.
o The cliffs mainly of limestone and calcium rich are mainly effected.
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Coastal Land Forms.o Headlands and Bay Mouth Bars.o Barrier islands and Barrier Reef.o Atolls and Reef Flats.o Fore shore and Back shore.o Berms and Spits.
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o Berms and Spits.o Cliffs, Crack or Inlet.o Caves and Arches.o Stack and Stump.o Wave Cut Platformo Tombolos
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Headlands and Bay mouth Bars.
Headlandso A headland is an area of
land adjacent to water on three sides.
o Where the rock is hard a Headland is left
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o Where the rock is hard a Headland is left outstanding.
Bay mouth barso A shallow bar, extends
partially or completely across the mouth of bay.
o Where there is softer rock erosion carves out a bay.
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Barrier Island and Barrier Reef
Barrier Islando Elongate ridges of sand
and gravel parallel to coasts, forms at long shallow shelf.
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o Separated from mainland by shallow lagoon.
Barrier Reefo Coral reef that parallel to
shore.o Separated by open water.
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Atolls and Reef Flats.
Atollo A ring shaped coral
reef, encloses a lagoon.o Grows upward from
submerged volcanic peak.
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submerged volcanic peak.
Reef Flatso A platform of coral
fragments and sands.o Exposed only in low
tidal zone.
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Fore Shore and Back Shore.
o Fore shore is the shore between low and high tide lines.o This area continuously attacked by currents and waves. o Back shore is the inner portion of the shore that is land
ward having gentle sloping.o It is only attacked by waves during high tides and in
severe storms.
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severe storms.
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Berms and Spits
Bermso Horizontal portion of a
beach whose edge abruptly slopes seaward.
o Located in Back shore zone.
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o Located in Back shore zone.
Spitso A narrow strip of land,
usually of sand.o Whose one end attached
with mainland and ends in water.
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Cliffs, Crack or inlet
o A cliff is a steep, often vertical, rock outcrop along a coast.
o The waves erode the rock through processes such as hydraulic action and
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as hydraulic action and corrosion.
o Wave attack picks out cracks, joints & weaknesses in the cliff.
o With time these weaknesses are widened, to form inlets or Goes
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Caves and Arches.
o The inlets with time further opened due to action of currents
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action of currents and waves form Caves.
o The hole broken through the rock makes an arch
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Stack and Stump.
o A pillar of rock surrounded by sea is left as a stack.
o Pressure is put on the arch roof until it collapses.
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collapses.
o Waves undercut the base of the stack until only a rock stump is left.
o Stump then disappears later on due to wave attacks
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Wave cut Platform
o The cliff above the wave cut notch eventually collapses leaving the cliff further back.
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back.
o Repeat this process & a wave cut platform is left at the cliff foot, indicating retreat
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Tombolos
o Derived from an Italian word means"long chain of rocks “.
o It is a deposition
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o It is a deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar.
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Impacts and Hazards on Coasts
o Plate Tectonic Impacts. Due to the movement and collision of Plates.
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o Human made impacts.Due to Man made artificial structure and human activity.
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Plate Tectonic Impacts
oDivergent/Convergent plate boundaries possess steep continental shelves
o Passive Continental Margins-
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o Passive Continental Margins-have broad continental shelves and have beaches with spit
o Island Arcs can protect coastlines oAllows deltas to form
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Human Impacts on Coastline
o Retention walls, groins, and Revetments all cause large bulk deposition of sediment somewhere.
o Other areas lose beach sand
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o Other areas lose beach sando Development destroys vital shoreline vegetation
o Water and petroleum pumping cause subsidence
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Hazards Related to Coasts
o Mass wasting.
o Danger to Urbanization.
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o Danger to Marine life.
o Permanent Changes in Topography.
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Mass Wasting.
1. Include mainly land slide.o Land slide causes the sediments to erode in a large bulk.o Triggered due to hurricanes, Tsunamis.o Results are heavy loss of property.
2. Process of Rock fall.o When a hard cliff is under cut by waves the bulk of rocks fall
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o When a hard cliff is under cut by waves the bulk of rocks fall under the influence of gravity.
o The Speed of fall might exceeds about 500km/hour.o Cause structures to subside and heavy turbulence in water.o Triggered coastal floods.
3. Toppling.o Rotation of a mass of rock, debris, or earth outward from a steep
slope face is called Toppling.o Toppling also produce turbidity and might also destroy structures
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Danger to Urbanization
o Heavy loss of property taken place every year.
o Loss of life also taken place.
o Oil spillage during extreme storms may also cause various diseases.
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o Sea water intrusions with drinking water bodies also a major hazard
o Different under ground structures might become exposed and become collapsed.
o The Most Effected urban countries of world is Holland and Japan.
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Danger to Marine life.
o The marine life specially the shelf marine life heavily suffer.
o Due to continuous erosion the shelf life heavily buried inside and become extinct,
o Oil spillage near shore destroy the coral
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o Oil spillage near shore destroy the coral reefs and other biodiversities.
o The production rate also disturbed as the eco system changes with coastal processes.
o Every year about 24-29% of all marine life near coast effected by various coastal factors.
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Permanent Changes in Topography
o The continuous erosion move the shelf further landward.
o The artificial constructed structure don’t control the rate of sediments.
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o The artificial constructed structure don’t control the rate of sediments.
o A large bulk of sediments erodes from one side and deposited at some other side, disturbing Isostacy.
o The artificial structures restrict the natural land forms.
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Prevention Methods Used.
o Structural Measures.
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o Non-Structural Measures
o Bio Shield Methods
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Structural Measures.
o Sea walls.o Groins.
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o Groins.o Jetties.o Bulkheadso Revetments.
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Sea wallsIn order to stop high tides
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GroinsIt is oriented perpendicular to shore
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JettiesOn the both side of inlets
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RevetmentsStop the erosion
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Bulk HeadsThey also used for steep slope stability
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Non Structural Measures
o Building sand dunes and growing vegetation around them.
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o Artificial beach nourishment
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Coastal Dunes
o Vegetation, wind-flow and sand transportation are all inter-dependant in the coastal dune environment.
o Air movement and not water movement form the coastal dune, unlike most coastal features, and is therefore
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dune, unlike most coastal features, and is therefore quite unique.
o The coastal dune is characterised by an interaction between sand transport by the wind and vegetation cover.
o Under both natural and human induced circumstances the dune can become unstable, and this can lead to coastal erosion.
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Bio Shields
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• Mangroves• Coral reefs• Sea grass• Sea weeds• Animal habitats• Marine parks• Marine sanctuaries