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Civil Engineering along the coast -environmental problems and solutions

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

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  1. 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

  2. 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,..)

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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)

  9. Revetments -- protection from erosion Bulkheads -- basically for slope stability

  10. 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

  11. 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

  12. Bio-shields • Mangroves • Coral reefs • Sea grass • Sea weeds • Animal habitats • Marine parks • Marine sanctuaries

  13. 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)

  14. 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

  15. 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

  16. 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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