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Investigations on the Effectiveness of Coastal Vegetation in Tsunami Impact Mitigation
1. Investigations on the Effectiveness of Coastal Vegetation in Tsunami Impact Mitigation Dr. S.S.L.Hettiarachchi A.H.R.Ratnasooriya Dr. S.P.Samarawickrama University of Moratuwa Acknowledgements- NSF, Sri Lanka WAPMERR, Geneva PARI, Japan Geo Science, Australia University of Arizona
2. Strategic approach in developing Post tsunami mitigation and Conservation of the coastline ..for protection of lives, coastal ecosystems and infrastructure Multi Hazard Coastal Risk Assessment Framework Multi Hazard approach considers all coastal hazards, each having a frequency of occurrence and potential impact (intensity /spatial distribution) Risk= Hazard x Exposure x Vulnerability x Deficiencies in Preparedness … . towards Disaster Risk Reduction Mitigation Options
3. Assessment tsunami wave heights and inundation from field studies Galle District Information from investigations on tsunami impact 1
4. Damage profiles of housing and infrastructure (Galle City) International Cricket stadium. Damaged houses behind Gall bay. Damaged bridge. Damaged houses behind Gall bay.
5. Damage at the boundary of water bodies penetrated by the tsunami. Rail track severely affected. Damage to protection works and breakwaters in harbours
9. Promote successful evacuation from tsunamis Early Warning and Countermeasures against tsunamis Mitigate the impact of tsunami (Mitigation Options) -Early Warning System (Local and Regional) -Public Warning System -Evacuation Routes & Structures -Community Education, Maps for their benefit and Preparedness - Physical Interventions (Artificial Methods, Natural Methods and Hybrid Methods) Mitigate exposure and vulnerability to tsunami hazard -Land Use Planning -Regulatory interventions such as set back of defense line -Hazard resilient buildings and infrastructure 2
10. Promote successful evacuation from tsunamis Early Warning and Countermeasures against tsunamis Mitigate the impact of tsunami (Mitigation Options) -Early Warning System (Local and Regional) -Public Warning System -Evacuation Routes & Structures -Community Education, Maps for their benefit and Preparedness - Physical Interventions (Artificial Methods, Natural Methods and Hybrid Methods) Mitigate exposure and vulnerability to tsunami hazard -Land Use Planning -Regulatory interventions such as set back of defense line -Hazard resilient buildings and infrastructure Risk Assessment- Hazard, Exposure and Vulnerability and Capacity Hazard, Vulnerability and Risk Maps
11. Promote successful evacuation from tsunamis Early Warning and Countermeasures against tsunamis Mitigate the impact of tsunami (Mitigation Options) -Early Warning System (Local and Regional) -Public Warning System -Evacuation Routes & Structures -Community Education, Maps for their benefit and Preparedness - Physical Interventions (Artificial Methods, Natural Methods and Hybrid Methods) Mitigate exposure and vulnerability to tsunami hazard -Land Use Planning -Regulatory interventions such as set back of defense line -Hazard resilient buildings and infrastructure Risk Assessment- Hazard, Exposure and Vulnerability and Capacity Hazard, Vulnerability and Risk Maps
12. Distribution of epicentres of earthquakes greater than magnitude 5.0 for the period 1976-2000, SE Asia- Indian Ocean (UNDP) Assessment of the Tsunami Hazard and Exposure Tsunami Generation from Earthquake at a Subduction Zone 3 (1) Tsunami Hazard Source (2) Tsunami Hazard Impact on land Exposure
13. Regional Location Shoreline Geometry Location with respect to the Continental Shelf Exposure at a given location Submarine Geological features Impact of Submarine Geological features, Coastal Processes and Local Geometry on Tsunami Wave Amplification
14. Tsunami Mitigation using Artificial and Natural Methods Overall Strategic Approach 4 (1) Reduce the impacts of tsunami waves prior to reaching the shoreline (2) Protect the coastal zone thus preventing the inland movement of tsunami waves (3) Mitigate the severe impacts of tsunami waves on entry to the shoreline Energy dissipator/ Partial barrier in coastal waters Full barrier on the coastline Partial barrier on the coastline
15. Tsunami Mitigation using Artificial and Natural Methods Tsunami Breakwaters Coral Reefs and Sand Bars Revetments,Dikes (High Crest) Sand Dunes Revetments,Dikes (Low Crest) Coastal Vegetation
20. Coral reefs were severely affected and damaged by the debris and sand transported during the inland and shoreward movement of the tsunami wave. (Source-Prof. H Fernando)
21. 2.5 km/hour Current Speed Current Direction Measured MEM CURR Measured currents offshore of Colombo
22. U C U G H L M y x Wave Parameters U o , λ, a Impact of a gap in the reef Wave Parameters ( U 0 , λ, a) Reef Parameters (M, P, L, H) Reef Gap ( ) Depth of water (H 0 ) Location (x, y, z) U 0 U C U G z P
23. Collaborative Research Arizona State University / University of Moratuwa (May/June 2005 and Nov/Dec 2006) PIV method ADV method Simulated reefs Large flume studies
24. Porosity P = 20% and 50% Amplitude a = 20, 30 and 40 cm for H 0 =30 cm Measurements at z = 5, 10, 15, 20 cm for H =20 cm In the experiments the dependence on are investigated U 0 U C U G
27. (a) 50% porosity (b) 20% porosity Normalized Velocity as a function of normalized height 2a = 30cm U 0 Velocity without the reef U C Velocity behind the reef U G Velocity in the reef gap
34. L (Length) Mangrove Forest H 1 H 2 U 1 U 2 Height of mangroves (Hm) Coastal Vegetation (Mangrove Forest)- Partial Barrier Density Plant Characteristics and Resilience Porous Wave Absorber Inundation Height H 1
38. Type I Resistance provides by stem only Type II Resistance provides by stem and branch structure Type III Resistance provides by stem and aerial roots structure Type IV Resistance provides by stem, branch structure and aerial roots structure Classification of Vegetation
39. Experimental set up for small scale tests The wave in progress through vegetation Spacing s , Diameter D Uniform/Staggered grid c 2 c 1 d 1 d 2 θ L a , ( width = b ) H R Gate (Open)