coastal hazards (cyclones-hurricanes)

7/31/2019 Coastal Hazards (Cyclones-hurricanes)

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Natural Hazard

The probability of occurrence of a

potentially damaging phenomenon within

a specified period of time and within a

given area

Coastal hazards - Definitions


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Coastal hazards - Main types

Short term:

A. Cyclone - hurricane - typhoon

B. TsunamiC. Flash flooding from river

Long term:

D. Land subsidence

E. Sea level rise

F. Coastal Erosion


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Definitions : Coastal Hazards

Cyclone An atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the

Southern Hemisphere.

Storm Surge An abnormal rise in sea level accompanying acyclone or other intense storm, and whose height is the

difference between the observed level of the sea surface and

the level that would have occurred in the absence of the

cyclone. Storm surge is usually estimated by subtracting the

normal or astronomic high tide from the observed storm tide.

Storm Tide The actual level of sea water resulting from theastronomic tide combined with the storm surge.


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Typhoons or hurricanes are tropical revolvingstorms. The are called cyclones, when they

occur in the Indian Ocean area.

It are low-pressure systems or depressions

around which the air circulates in an anti-

clockwise direction in the northern hemisphere,

but in a clockwise direction in the southern

hemisphere.

The speed of the circulating air may exceed 33

metres per second near the earths surface.

A -Hurricanes / Cyclones


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Most tropical cyclones originate between 5 and30 degrees latitude on both sides of the equator.

On average 80 cyclones are formed every year,

Two thirds of those in the northern hemisphere.

Tropical cyclones are the most devastating of all

natural phenomena. It usually effects large

areas.

It may cause river flooding, storm surge andland-sliding.



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Cyclone classification according to intensity:

Depression - Winds up to 62 km/hr

Cyclonic storm - Winds from 63-87 km/hr

Severe cyclonic - Winds from 88-118 km/hrstorm

Severe cyclonic - Winds >118 km/hr

storm of hurricane

intensity



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Number of casualties caused by some cycloneevents in Bangladesh:

1822 40.000 1961 11.500

1876 400.000 1965 31.300

1897 175.000 1970 300.000

1911 120.000 1971 11.000

1917 70.000 1985 11.100

1919 40.000 1988 5.7001958 12.000 1991 145.000

1960 11.600



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A.Hurricanes

Hurricane

for

Florida

coast


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Vertical section of a cyclone

Heat-flow clouds Air circulation

Source:

Mitigating natural Disasters

UN Publication, 1991

A - Hurricanes / Cyclones


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Horizontal section of a cyclone

EYE

Source:

Mitigating natural Disasters

UN Publication, 1991

A -Hurricane / Cyclones


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A. Cyclones

Typical

cyclone path

affecting

Bangladesh


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Example of 29 April 1991 cyclone in Chittagong,Bangladesh:

On 23 April 1991 the cyclone was first detected as adepression - wind speeds not exceeding 62 km/hr

On 25 April it intensified into a deep depression in the

evening and turned into a cyclonic storm at midnight

On 27 April it developed into a severe cyclonic stormwith wind speeds up to 115 km/hr, having 990 mb as thecentral pressure

The same day it turned into a storm with a hurricanecore with wind speeds exceeding 130 km/hr.

On 28 April it crossed Chittagong port in the morning.

The estimated pressure drop was 60 mb.



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Pressure drop of 29 April 1991 cyclone inChittagong, Bangladesh:

Pressure drop



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Pixel informationPixel information

BangladeshBangladeshPoints of landfall cyclonesPoints of landfall cyclones

Example G.I.S. data analysis from Bangladesh



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Fi ld Ph t h d i O i C l


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Field Photographs during Orissa Cyclone


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C l d i


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Hurricane Mitch

Multi-temporal

Radarsat images

30 October 1998

A - HurricanesCoastal dynamics


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Tsunami Japanese word for Harbor wave

A series of waves of extreme length and period

triggered by a sudden displacement of the sea

floor: seismic activity or volcanic eruption

The wave travels outwards in all directions from

the source area with speeds of over 500 km/hr

Still it can have a velocity of over 50 km/hr and a

height of 30 m at the coast Several waves may follow each other at intervals

of 15 - 45 minutes

B - Tsunami waves


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Waves of extreme length and period

150 km

Triggering Quake

Source: Lausch, E. - Tsunami- GEO 4/April, 1997

B - Tsunami waves


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Waves are triggered by: Seismic activity /displacement of the sea floor

Source: Lausch, E. -

Tsunami- GEO 4/April,1997

B- Tsunami waves


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Waves are triggered by volcanic eruption

B- Tsunami waves


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Urban flood disaster - 12 July 1993

Okushiri

Island

Japan

B- Tsunami waves


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Hilo town

Hawaii

- 1 April 1946

Tsunami wave

B- Tsunami waves


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House at risk, Hawaii - 9 March 1957

Oahu Island

1

2

B- Tsunami waves


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Website tropical storm tracks:

http://www.hawaii.edu/news/storm.tracks.html

Hurricane Floyd:

http://cnn.com/WEATHER/

http://www.hawaii.edu/news/storm.tracks.htmlhttp://www.hawaii.edu/news/storm.tracks.html


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Interesting websites:

NOAA:

http://www.pmel.noaa.gov/tsunami/

B- Tsunami waves

Multitemporal Changes in the Sagar Island between 1968 and 2002


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Erosion(km

2)

Accretion(km

2)

1968-1996 6.44 13.519

1996-1998 7.833 15.666

1998-1999 3.021 0.4821999-2000 0.108 17.751

2000-2002 16.598 0.001

1996-1998: Erosion trend1998-1999: Accretion trend1999-2000: Accretion trend1996-2002: Erosion is dominant

The erosion trend is likely to be

continued

-20

-15

-10

-5

0

5

10

15

20

1968-

1996

1996-

1998

1998-

1999

1999-

2000

2000-

2002

erosion

accretion

GRID Analysis for shoreline changedetection for every 10 m


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Euclidian distance Grid of 1968 Direction Grid of 1968 10 m cell shoreline arc cover o

y


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depth


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Salt affected mudflat along Gulf of Cambay


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g y

Salt water intrusion along Gulf of Cambay


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Salt water intrusion along Gulf of Cambay

Erosion/accretion along Kakinada Coast


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g

Coastal turbulence induced erosion


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Coastal turbulence induced erosion

coastal hazards (cyclones-hurricanes)

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