Understanding the Tsunami Wave

Transcription

1 The First Tsunami attack on Sri Lanka Krakatoa Island 27 th August 1883 Understanding the Tsunami Wave Generation Propagation Nearshore Transformation Shoreline Entry Inland Dissipation 1

2 Generation and Propagation of the Tsunami wave Seismological / Geo Disturbance Generation Tsunami Wave Source Initial Dissipation Propagation? Linkage between the Earthquake and Tsunami Origin 2

3 Indian Ocean Earthquake Tsunami 2004 F3 F2 F1 = 330 km F2 = 570 km F3 = 300 km F1 Displacement = 11 m Fault width = 150 km 150 km 300 km Rupture area of the December 26 th Earthquake F3 570 km F2 330 km 435 km 230 km F1 3

4 Indian Ocean Earthquake Tsunami 2004 F1 = 330 km F3 = 300 km F2 = 570 km Radar Satellite record of wave heights - Two hours after the EQ Maximum deep water wave height = 0.6 m 0.6 m Nearshore Transformation causes the damage 4

5 Deepwater Propagation Nearshore Transformation Shoreline Entry Nearshore Transformation (1) Due to reduced depth 5

6 Basic Long Wave Mechanics Wave Speed, c = gd Energy Transmitted (Power) P H 2 c 1 2 P H 2 d Energy Loss 1 E loss ( P) wave length The wave propagates with hardly any loss of energy 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 6

7 SHORELINE ENTRY OF THE WAVE Flooding - Hikkaduwa 7

8 The Tsunami Approaches as a series of waves around 30 minutes Indian Ocean Earthquake Tsunami

9 Indian Ocean Earthquake Tsunami 2004 Indian Ocean Earthquake Tsunami

10 Indian Ocean Earthquake Tsunami

11 Indian Ocean Earthquake Tsunami

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) Lateral Dispersion of wave energy around the country Diffraction 12

13 Direct waves Reflected waves Combined waves Direct & Refracted waves Refracted & Diffracted waves 13

14 Nearshore Transformation Characteristics influenced by the shape and geometry (2b) Concentration of wave energy Incoming wave rays depth contours Increase in Height/Speed and formation of Eddies Unawatuna - concentration of energy and spreading around the headland 14

15 Bay Increase of Speed & Height Bay increase of speed & height and circulation Headland concentration of energy and spreading around the headland 15

16 Proposed Development of the Port of Galle Japanese Port Consultants Assessment of the Impacts 16

17 Field Measurements that captured the event Surveys conducted by the Japanese and USA experts Monitoring, Simulation and Prediction Countermeasures against Tsunamis Field Measurements that captured the event Water level Measurements by NARA at Mutwall Fishery Harbour 3m Harbour Waves Indian Ocean Earthquake Tsunami

18 Measurements by Lanka Hydraulic Institute water level 17 Water Level (m) m Dec 23-Dec 24-Dec 25-Dec 26-Dec 27-Dec 28-Dec 29-Dec 30-Dec 31-Dec 1-Jan Tidal Period = 12.4 hours Time Tsunami period = minutes Indian Ocean Earthquake Tsunami wave speed Indian Ocean Earthquake Tsunami Velocity Magnitude (cm/s) km/hour 0 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 at 15m depth Tsunami wave speed 50 km/hour 18

19 Pressure Variation (m) am Sea wave period = 5-20 seconds pm Tsunami wave period = minutes pm pm Surveys conducted by the Japanese and USA experts Indian Ocean Earthquake Tsunami

20 East of Galle Port beach 68m road sand not flushed by tsunami attack inside of the house Hikkaduwa Fishery Harbour 65 fishery boats (inside the harbour) were damaged view 1 view 1 7m sea wharf No damage to the house Tsunami traces on the 2 nd floor 20

21 Hikkaduwa beach road washed train railway 64m leaf tarnished 188m 188m 228m Ambalangoda sea view 1 view 1 road houses view 2 view 2 railway 21

22 Nov-03 6-Nov Nov Nov Nov Nov Tsunami Wave Heights in meters m 26 th Dec 2:30 am High Water 8:30 am Low Water 2:30 pm High Water Tangalle Fishery Harbour 22

23 Incoming waves Reflected waves Combined waves Refracted and Diffracted waves Incoming & Refracted waves 23

24 9:20 9:00 8:40 Testified arrival times of the Highest Wave 5 10:10 11:05 11:30 10:00 9:50 9:40 9:20 24

25 Increase in Coastal Erosion due to the changes in the topography H d = 0.78 Depth profile before Depth profile after Interlocking concrete units Rock armoured revetments 25

26 Soft Vegetation - Hikkaduwa 7) Planned use of vegetation Coconut Plantation - Kosgoda 26

27 27 Mangrove Forest L Mangrove Forest H 1 H 2 U 1 U = g U H g U H H bu au L H i + = =

28 28

29 Coral Reefs H i H t d h τ b u b Reef act as a submerged breakwater L 29

30 Response To Tsunamis - Countermeasures against Tsunamis 1) Early Warning System & Public Warning System 2) Hazard Map for vulnerability 3) Set Back 4) Evacuation Structures Modelling promote successful evacuation from tsunami 5) Tsunami Breakwater 6) Tsunami Dike? 7) Planned use of vegetation mitigate tsunami 30

31 Planning Before 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 31

32 Risk = Probability x Damage or Consequence Damage or Consequence Severe & Widespread Moderate Tsunami High Very High Mild & Widespread/ Severe & Local Low Moderate High Land Slides Mild & Local Very Low Low Moderate Probability Low Medium High Thank you 32