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Civil Engineering along the coast -environmental problems and solutions PowerPoint PPT Presentation

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Civil Engineering along the coast -environmental problems and solutions. Dr. M. C. Deo IIT Bombay. Contents Introduction - types of problems, damage Structural measures - dykes, sea walls, bulkheads, revetments, groins,

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Civil Engineering along the coast

-environmental problems and solutions

Dr. M. C. Deo

IIT Bombay


Introduction - types of problems, damage

Structural measures - dykes, sea walls, bulkheads, revetments, groins,

storm surge barriers

Non-structural measures- sand dunes, beach nourishment,

bio-shields (mangroves, coral reefs)


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  • Indian coastline (~7500 km)

  • vulnerable to hazards

    normal wind, waves,

    tides, currents,

    sediment movement

    extreme cyclones,

    storm surges, (~6 / yr)

    tsunami, (1, 2/century)

    oil spills,…

  • Impact depends on: -Density of population, (25 %  within 50 km)

    -Design of structures and quality of construction,

  • -Environment (presence of mangrove forests,..)

Cyclones storm surges l.jpg

Cyclones & Storm surges

  • tropical cyclone a rotating wind

    (low pressure disturbance

    generally with heavy rainfall)

  • As cyclone approaches coastal area,

    strong on-shore winds create water current circulation,

    together with lowering of pressures

     rise of several meters in sea level

    (Storm surge)

     flooding large areas of the coast

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Primary : Earthquake

  • Cause

    Secondary : Landslides, volcanic activities

    Wave ht. @ shore : 20m or more

    Time of oscillation

    Tsunami: 30 to 60 min

    Wind generated gravity waves: 3 to 20 sec

    Tides: 12 or 24 hr

Warning system:

Occurrence of the tsunami-generating earthquake

can be recorded on seismographs

and communicated via satellites to the warning center,

where computer-based models calculate tsunami heights and travel times.

This could be verified by a series of wave rider buoys and accordingly

tsunami warning can be issued.

Such warning systems exist in Pacific countries including the U.S. and Canada

since 1964.

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  • Damage due to water coming from the sea:

    - Associated hydrostatic, hydrodynamic forces,

    - Impact of objects being carried by the attacking water mass,

    - High speed currents, overtopping,

    - Resulting flooding and current induced erosion.

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Coastal Erosion - by breaking waves and associated currents

Oil Spills

caused by accidents involving

tankers, barges, pipelines,

storage facilities

can harm marine life, which in turn can harm human beings through food

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Structural measures for hazards reduction

  • Sea Dykes

  • Protect low-lying areas against flooding

  • Mound of sand and clay – sloping towards sea to reduce wave run up

  • Slope surface armored with grass, asphalt, stones, or concrete slabs

Shore protection manual, 1984, Coastal Engineering Manual, 2003

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Sea walls

Sloping faced (armored with concrete slabs

or armor units)

Parallel to shoreline

Vertical faced (concrete or stone filled)

Problem --

toe erosion

(use with


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Revetments -- protection from erosion

Bulkheads -- basically for slope stability

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- Fixed or adjustable

- High or low height

- Permeable or impermeable

Walls Perpendicular to shoreline; rubble mound or sheet piles

Updrift  accretion

Downdrift  erosion

 saw-tooth shoreline

Storm surge barriers A series of movable gates (sliding or rotating)

that prevent water intrusion in low lying areas

- open – normally; but closed – in storm surges

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Non-structural measures

--Building sand dunes and growing vegetation around them

--Artificial beach nourishment – removal of sand from one place and

and transportation to some other place

upstream where erosion feared

--Providing bio-shields

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  • Mangroves

  • Coral reefs

  • Sea grass

  • Sea weeds

  • Animal habitats

  • Marine parks

  • Marine sanctuaries

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  • Located in inter-tidal regions, can grow in saline water and in sheltered places like creeks and estuaries

  • Act as buffer against storm surges arrest erosion, trap sediments, harbor fish

  • But certain species are sensitive to excessive sedimentation, stagnation, oil spills

In recent Gujarat and Orissa cyclones,

presence of mangrove buffers  less destruction

(Source: protect/images/mangroves.jpg)

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Coral Reefs-natural barriers against erosion and storm surge



  • corals  slow growing colonies of animals

    - growth rate = 1, 10 cm / yr.

    - occur in shallow tropical areas

    - sea water should be clean, clear and warm - provide habitat for a large variety of animals and plants

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destruction - outbreak of reef-destroying animals,


depletion of essential symbiotants

chemical pollution,

mechanical damage,

nutrient or sediment loading

  • necessary to quantify the

    protection the bio-shields provide

    and determine limits beyond which

    they are not so effective

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Oil spill control

  • Mechanical Containment

    • Booms and barriers >

    • Skimmers

    • Sorbents (oil collecting sponges)

  • Chemical and Biological dispersants

    -- disintegrate oil

    -- Used in conjunction with mechanical means

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