1

The First Tsunami attack on Sri Lanka

Krakatoa Island– 27th August 1883

Understanding the Tsunami Wave

• Generation• Propagation• Nearshore Transformation• Shoreline Entry• Inland Dissipation

2

Generation and Propagation

of the Tsunami wave

Seismological / Geo Disturbance

Tsunami Wave SourceGeneration

Initial Dissipation

Propagation

Linkage between the Earthquake

and Tsunami Origin

?

3

Indian Ocean Earthquake – Tsunami 2004

F1

F2

F3 F1 = 330 km

F2 = 570 km

F3 = 300 km

Displacement = 11 m

Fault width = 150 km

F1

F2

F3

230 k

m

435 km

330 km

300 km

570 km

150 k

m

Rupture area of the December 26th Earthquake

4

Indian Ocean Earthquake – Tsunami 2004

F2 = 570 km

F1 = 330 km F3 = 300 km

Radar Satellite record

of wave heights -

Two hours after the EQ

Maximum deep water

wave height = 0.6 m

0.6 mNearshore

Transformation causes

the damage

5

Deepwater Propagation

Nearshore Transformation

Shoreline Entry

Nearshore Transformation (1)

Due to reduced depth

6

Wave Speed,

Energy Transmitted (Power)

Basic Long Wave Mechanics

The wave propagates with hardly any loss of energy

dgc =

cHP 2∝

212 dHP ∝

( )lengthwave

PEloss1

∝Energy Loss

Deepwater Propagation

Nearshore Transformation (1)due to reduced water depth

Nearshore Transformation (2)

Coastal Processes as wave reach the shallow water (2a)

Characteristics influenced by the shape and geometry (2b)

Shoreline Entry

7

SHORELINE ENTRY OF THE WAVE

Flooding - Hikkaduwa

8

The Tsunami

Approaches as a series of waves

around 30 minutes

Indian Ocean Earthquake – Tsunami 2004

9

Indian Ocean Earthquake – Tsunami

2004

Indian Ocean Earthquake – Tsunami

2004

10

Indian Ocean Earthquake – Tsunami

2004

11

Indian Ocean Earthquake – Tsunami

2004

12

Nearshore Transformation (1) (2)

Due to reduced water depth (1)

Coastal Processes as wave reach the shallow water (2a)

Characteristics influenced by the shape and geometry (2b)

Diffraction

Lateral Dispersion of wave energy around the

country

13

Direct waves

Reflected waves

Refracted & Diffracted waves

Direct & RefractedwavesCombined waves

14

Increase in Height/Speed and formation of Eddies

Concentration of wave energy

depth contoursInc

oming

wav

e ray

s

Nearshore TransformationCharacteristics influenced by the shape and geometry (2b)

Unawatuna - concentration of energy and spreading around the headland

15

Bay – Increase of Speed & Height

Headland – concentration of energy and spreading around the headland

Bay – increase of speed & height and circulation

16

Proposed Development of the Port of GalleJapanese Port Consultants

Assessment of the Impacts

17

Field Measurements that captured the event

Surveys conducted by the Japanese and USA experts

Monitoring, Simulation and Prediction

Countermeasures against Tsunamis

Water level Measurements by NARA at Mutwall Fishery Harbour

3m

Field Measurements that captured the event

Harbour Waves

Indian Ocean Earthquake – Tsunami 2004

18

13

14

15

16

17

22-Dec 23-Dec 24-Dec 25-Dec 26-Dec 27-Dec 28-Dec 29-Dec 30-Dec 31-Dec 1-Jan

Time

Wat

er L

evel

(m)

Measurements by Lanka Hydraulic Institute

2-2.5m

water level

Indian Ocean Earthquake – Tsunami 2004

Tidal Period = 12.4 hours

Tsunami period = 20-30 minutes

0

10

20

30

40

50

60

70

80

12/26/04 0:00 12/26/04 6:00 12/26/04 12:00 12/26/04 18:00 12/27/04 0:00

Time

Velo

city

Mag

nitu

de (c

m/s

)

2.5 km/hour

at 15m depth – Tsunami wave speed – 50 km/hour

wave speedIndian Ocean Earthquake – Tsunami 2004

19

9 – 9.20 am

12 – 12.20 pm

3 – 3.20 pm

6 – 6.20 pm

Pressure Variation (m)

Sea wave period = 5-20 seconds

Tsunami wave period = 15-20 minutes

Surveys conducted by theJapanese and USA experts

Indian Ocean Earthquake – Tsunami 2004

20

East of Galle Port

road68m

inside of the house

sand not flushedby tsunami attack

beach

Hikkaduwa Fishery Harbour

7m

wharfsea

No damage to the houseTsunami traces on the 2nd floor

65 fishery boats (inside the harbour) were damaged

view 1

view 1

21

Hikkaduwa

roadbeachwashed train

railway64m

188m

188m 228m

leaf tarnished

Ambalangoda

houses

road

railway

sea

view 1

view 2 view 2

view 1

22

5

Tsunami Wave Heights

in meters

5

3 - 5

117 - 9

5 -114-94-10

2

4- 5

7 - 9

5

5

3 - 4

Tangalle Fishery Harbour

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

1-Nov-03 6-Nov-03 11-Nov-03 16-Nov-03 21-Nov-03 26-Nov-03

0.7m

26th Dec 2:30 am High Water

8:30 am Low Water

2:30 pm High Water

23

Incoming waves

Reflected waves

Refracted and Diffracted waves

Incoming & RefractedwavesCombined

waves

24

5

Testified arrival times of the Highest Wave

9:209:50

10:00

11:05

11:30

9:40

10:10

9:00

8:40

9:20

25

Depth profile before

Depth profile after

78.0=dH

Increase in Coastal Erosion due to the changes in the topography

Rock armoured revetments

Interlocking concrete units

26

Soft Vegetation

- Hikkaduwa

7) Planned use of vegetation

Coconut Plantation - Kosgoda

27

Mangrove Forest

L

Mangrove ForestH1

H2U1 U2

+−

+=∆

gUH

gUHH

22

22

2

21

12buau

LHi +=

∆=

28

29

Coral Reefs

d

h

Hi Ht

L

Reef – act as a submerged breakwater

bb uτ

30

1) Early Warning System &

Public Warning System

2) Hazard Map for vulnerability

3) Set Back

4) Evacuation Structures

5) Tsunami Breakwater

6) Tsunami Dike ?

7) Planned use of vegetation

promote successful evacuation from tsunami

mitigate tsunami

Modelling

Response To Tsunamis - Countermeasures against Tsunamis

31

PlanningBefore an extreme event

After an extreme event

Opportunity for

Damage Assessment

in the context of

Planning for Coastal Hazards

Disaster Preparedness and Mitigation Plan

Coastal Hazards

Tsunamis

32

ModerateLowVery Low

HighModerateLow

Very HighHighModerate

Low HighMedium

Mild & Local

Mild & Widespread/

Severe & Local

Severe & Widespread

Probability

Damage or Consequence

Risk = Probability x Damage or Consequence

Land Slides

Tsunami

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