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Civil Engineering along the coast -environmental problems and solutions

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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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slide1

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,

storm surge barriers

Non-structural measures- sand dunes, beach nourishment,

bio-shields (mangroves, coral reefs)

Closure

slide2

Introduction

  • 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
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

tsunami
Tsunami

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.

slide5
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.

coastal erosion by breaking waves and associated currents
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

slide7

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

slide8

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

groins)

slide9

Revetments -- protection from erosion

Bulkheads -- basically for slope stability

slide10

Groins

- 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

slide11

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

bio shields
Bio-shields
  • Mangroves
  • Coral reefs
  • Sea grass
  • Sea weeds
  • Animal habitats
  • Marine parks
  • Marine sanctuaries
mangroves
Mangroves
  • 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: www.deh.gov.au/.../ protect/images/mangroves.jpg)

coral reefs natural barriers against erosion and storm surge
Coral Reefs-natural barriers against erosion and storm surge

(Source:mbgnet.m

obot.org/salt/

coral/faq.htm)

  • 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

slide15

destruction - outbreak of reef-destroying animals,

storms,

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

oil spill control
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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