Coastal Erosion And Its Control

AUTHOR: PARTHA DAS SHARMA, E.mail: [email protected], Website: http://saferenvironment.wordpress.com

COASTAL EROSION1. Coastal Processes.

2. Coastal Land forms

3. Impacts and Hazards on Coasts.

4. Prevention Methods used.

Coastal Erosiono Erosion is when wind, water, and ice take

sediments away.

o Erosion on coasts by wind and water.

http://saferenvironment.wordpress.com

3

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.

Coastal Processes o Currents and Waves.

o Swash and Backwash of waves.

o Tides and Tidal Currents.


4

o Rip Currents.

o Long Shore drift.

o Hurricanes and Tsunami.

o Abrasion & Attrition.

o Corrosion (Salutation).

Waves and Currentso A wave is a disturbance

that propagates through space and time.

o Current is a continuous


5

o Current is a continuous flow of water in a particular direction.

o Both contains characteristics of Crest and Trough.

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.


6

o Also called as constructive current.

o Backwash current is a seaward current that results from the receding swash.

o Also called destructive current.

Swash and Back wash


7

Tides and Tidal currentso Tidal bulge combine with

daily earth’s rotation creates broad system of waves.

o Cause by the gravitational action.


8

action.

o Mainly because of moon and sun.

o Incoming tides and out going tides.

o Neap and Lunar tides.

Rip Currentso Fast, narrow surface

currents.

o Flow seaward at nearly


9

o Flow seaward at nearly right angles to shore.

o Mainly in surfing zone.

o Move back to sea by narrow paths.

Long Shore Drifto The movement of

sediments along a beach or shore by currents.

Having a particular


10

o Having a particular direction.

o Mainly cause by Long shore currents.

o Swash and Backwash are major Phenomena.

Hurricane and Tsunami

Hurricaneo A tropical cyclonic storm

with winds having speed >120km/hour.

o Mostly hit in late summers and fall.


11

and fall.

Tsunamio A short period disturbance

create by submarine earth quake or volcanic vent.

o The waves more than 100feet, might possibly rise.

Abrasion & Attrition(Corrasion)

Abrasion.Abrasion.o The waves pick up the

sediment & hurl it against the cliffs (uses the sediment as ammunition).


12

ammunition).

AttritionAttritiono As the sediment is

hurled against the cliff, bits are chipped off, the sediment gets smaller & rounder

Corrosion (Salutation)

o Salt & other chemicals in sea water attack & dissolve the cliffs.


13

dissolve the cliffs.

o The cliffs mainly of limestone and calcium rich are mainly effected.

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.


14

o Berms and Spits.o Cliffs, Crack or Inlet.o Caves and Arches.o Stack and Stump.o Wave Cut Platformo Tombolos

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


15

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.

Barrier Island and Barrier Reef

Barrier Islando Elongate ridges of sand

and gravel parallel to coasts, forms at long shallow shelf.


16

o Separated from mainland by shallow lagoon.

Barrier Reefo Coral reef that parallel to

shore.o Separated by open water.

Atolls and Reef Flats.

Atollo A ring shaped coral

reef, encloses a lagoon.o Grows upward from

submerged volcanic peak.


17

submerged volcanic peak.

Reef Flatso A platform of coral

fragments and sands.o Exposed only in low

tidal zone.

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.


18

severe storms.

Berms and Spits

Bermso Horizontal portion of a

beach whose edge abruptly slopes seaward.

o Located in Back shore zone.


19

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.

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


20

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

Caves and Arches.

o The inlets with time further opened due to action of currents


21

action of currents and waves form Caves.

o The hole broken through the rock makes an arch

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.


22

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

Wave cut Platform

o The cliff above the wave cut notch eventually collapses leaving the cliff further back.


23

back.

o Repeat this process & a wave cut platform is left at the cliff foot, indicating retreat

Tombolos

o Derived from an Italian word means"long chain of rocks “.

o It is a deposition


24

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.

Impacts and Hazards on Coasts

o Plate Tectonic Impacts. Due to the movement and collision of Plates.


25

o Human made impacts.Due to Man made artificial structure and human activity.

Plate Tectonic Impacts

oDivergent/Convergent plate boundaries possess steep continental shelves

o Passive Continental Margins-


26

o Passive Continental Margins-have broad continental shelves and have beaches with spit

o Island Arcs can protect coastlines oAllows deltas to form

Human Impacts on Coastline

o Retention walls, groins, and Revetments all cause large bulk deposition of sediment somewhere.

o Other areas lose beach sand


27

o Other areas lose beach sando Development destroys vital shoreline vegetation

o Water and petroleum pumping cause subsidence

Hazards Related to Coasts

o Mass wasting.

o Danger to Urbanization.


28

o Danger to Marine life.

o Permanent Changes in Topography.

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


29

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

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.


30

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.

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


31

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.

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.


32

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.

Prevention Methods Used.

o Structural Measures.


33

o Non-Structural Measures

o Bio Shield Methods

Structural Measures.

o Sea walls.o Groins.


34

o Groins.o Jetties.o Bulkheadso Revetments.

Sea wallsIn order to stop high tides


35

GroinsIt is oriented perpendicular to shore


36

JettiesOn the both side of inlets


37

RevetmentsStop the erosion


38

Bulk HeadsThey also used for steep slope stability


39

Non Structural Measures

o Building sand dunes and growing vegetation around them.


40

o Artificial beach nourishment

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


41

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.

Bio Shields


42

• Mangroves• Coral reefs• Sea grass• Sea weeds• Animal habitats• Marine parks• Marine sanctuaries

Coastal Erosion And Its Control

Education

wash http

fore shore

shore bycurrents

smaller rounder http

backwash of waves

open water

sea water attack

mouth of bay