Investigating the performance of coastalecosystems for hazard mitigationSam Hettiarachchi         H.J.S.FernandoS.P.Samara...
Hazard Impact- Tsunami Hazard
Satellite                    Images                   Impact of the tsunami on the                   coastline.           ...
IndianOcean Earthquake – Tsunami 2004
Indian OceanEarthquake – Tsunami        2004
IndianOcean Earthquake –  Tsunami 2004
Erosion and Deposition caused by tsunami waves                            CrestTrough                           Long waves...
Tsunami – Erosion and Deposition
Measured currents offshore of Colombo                              80                                                     ...
Sediment Transport by the 2004 tsunami at Sri Lanka             Ongoing Study (Tohoku University)             Sounding sur...
Sand Dunes February 2002                   Dunes                   River entrancesNatural featuresSand Dunes
Sand Dunes and their destructionOvertopping                               January 2005                              Vicini...
Natural featuresCoastal Vegetation
Destruction of vegetation in Sri Lanka              Mangrove destruction in Banda Aceh--              Dr.Subandano
Natural features of the neashoreCoral Reefs
Coral reefs are severelyaffected and damagedby the debris and sandtransported during theinland and shorewardmovement of th...
Natural Methods for MitigationCoral Reefs & Sand BarsSand DunesCoastal Vegetation and Mangrove ForestsHybrid SolutionsComb...
Coral ReefsSubmerged natural breakwaters  Hi                                                    H                         ...
Small submerged depth (h)                                Significant length (L)Coral ReefsKenyan Coastline –From J. Tychsen
The influence of Wave Reflection from Maldive Islands                                                   Reflection of wave...
Investigating the impactof coral reefs and theinfluence of gaps
Coral Reefs
Gaps created by fishermento manoeuvre boats
Theoretical Considerations        Wave Parameters (U0 , λ, a)                             U0        Reef Parameters (M, P,...
The velocity in the gap at a location (x, y, z) is given by U G = f {[ P, M , L, H ], [ω ], [ H 0 ], [ x, y, z ], [U 0 , a...
On dimensional grounds equation (1) can be written as                 L H x y z ω a λ U G = f 1  P, M , ,  , , , , ,  ,...
ωWhen the gap is absent       =0                           Hand this is equivalent to the condition far away from the gap ...
a      zIn the experiments the dependence on    P,    and     are investigated                                           H...
Schematic diagram of the experimental set-up                     (all values are in cm s)      86 cm                 W    ...
Simulation of Coral Reefs in 2D Physical Modelling Representation of high dense (20% porosity) and       low dense (50% po...
Collaborative ResearchArizona State University / University of Moratuwa(May/June 2005 and Nov/Dec 2006)                   ...
Representation of high dense (20% porosity) and      low dense (50% porosity) structures                                  ...
University of Arizona
1                                                         1        0.75                                                   ...
1                                                                     1        0.75                                       ...
1                                                        1        0.75                                                    ...
1                                         0.75                                          0.5                               ...
1                                                               1        0.75                                             ...
Case Study------ Great Train Tragedy at Hikkaduwa
Hikkaduwa Case Study Key areas of investgation (i) Discontinuity in the Continental Shelf-       Edge waves (ii) Coral Min...
(ii) Coral Mining     Illegal coral mining has created a     defenseless “low resistance path”Ilegal Coral mining over the...
Heavy Coral MiningMild negative slope
KERRY           SHIEH©2005From Dr.D Subandano
Is it role of vegetation ?            Tsunami Heights =3-4mFrom Dr. Danny Hilman Natawijaya         West NIAS - SIRAMBU
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Investigating the performance of coastal ecosystems for hazard mitigation

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Sam.S.L HETTIARACHCHI1, Saman. P SAMARAWICKRAMA1, Harsha RATNASOORIYA1, Joe FERNANDO2

1University of Moratuwa, Sri Lanka, Democratic Socialist Republic of; 2Universiy of Notre Dam, USA

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Investigating the performance of coastal ecosystems for hazard mitigation

  1. 1. Investigating the performance of coastalecosystems for hazard mitigationSam Hettiarachchi H.J.S.FernandoS.P.Samarawickrama University of Notre DameA.H. R. Ratnasooriya IndianaUniversity of Moratuwa USASri Lanka
  2. 2. Hazard Impact- Tsunami Hazard
  3. 3. Satellite Images Impact of the tsunami on the coastline. (South west coast of Sri Lanka) IndianOcean Earthquake – Tsunami 2004
  4. 4. IndianOcean Earthquake – Tsunami 2004
  5. 5. Indian OceanEarthquake – Tsunami 2004
  6. 6. IndianOcean Earthquake – Tsunami 2004
  7. 7. Erosion and Deposition caused by tsunami waves CrestTrough Long waves of high amplitude High velocity profile from surface to sea bed
  8. 8. Tsunami – Erosion and Deposition
  9. 9. Measured currents offshore of Colombo 80 Current Speed 70Velocity Magnitude (cm/s) 60 50 2.5 km/hour Tsunami 40 30 20 10 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 360 315 270 Current Direction (deg) 225 180 135 90 45 Current Direction 0 24-Dec 25-Dec 26-Dec 27-Dec 28-Dec 29-Dec Time
  10. 10. Sediment Transport by the 2004 tsunami at Sri Lanka Ongoing Study (Tohoku University) Sounding surveys were conducted before (December 2004) and after (December
  11. 11. Sand Dunes February 2002 Dunes River entrancesNatural featuresSand Dunes
  12. 12. Sand Dunes and their destructionOvertopping January 2005 Vicinity of opening for rivers
  13. 13. Natural featuresCoastal Vegetation
  14. 14. Destruction of vegetation in Sri Lanka Mangrove destruction in Banda Aceh-- Dr.Subandano
  15. 15. Natural features of the neashoreCoral Reefs
  16. 16. Coral reefs are severelyaffected and damagedby the debris and sandtransported during theinland and shorewardmovement of thetsunami waves. From Prof. H.Fernando
  17. 17. Natural Methods for MitigationCoral Reefs & Sand BarsSand DunesCoastal Vegetation and Mangrove ForestsHybrid SolutionsCombination of Natural /Artificial Methods
  18. 18. Coral ReefsSubmerged natural breakwaters Hi H t h τb ub Submerged depth (h) d Coral Reefs – act as submerged natural breakwaters L Length (L)
  19. 19. Small submerged depth (h) Significant length (L)Coral ReefsKenyan Coastline –From J. Tychsen
  20. 20. The influence of Wave Reflection from Maldive Islands Reflection of waves Sri Lanka Maldive Islands
  21. 21. Investigating the impactof coral reefs and theinfluence of gaps
  22. 22. Coral Reefs
  23. 23. Gaps created by fishermento manoeuvre boats
  24. 24. Theoretical Considerations Wave Parameters (U0 , λ, a) U0 Reef Parameters (M, P, L, H) Reef Gap (ω) Depth of water (H0)Location (x, y, z) UC UG UC UG Gap M z P x y H ω L Wave Parameters Uo , λ, a
  25. 25. The velocity in the gap at a location (x, y, z) is given by U G = f {[ P, M , L, H ], [ω ], [ H 0 ], [ x, y, z ], [U 0 , a, λ ]} reef parameters gap location wave parametersReef Parameters: Height H, Length L, Porosity P and other hydrodynamic andphysical characteristics of the ridge represented by the dimensionless parameter M.Gap in the reef ωDepth of water at the location is H0Oncoming wave parameters: Velocity amplitude U0, the Wave length λ andWave amplitude a.
  26. 26. On dimensional grounds equation (1) can be written as  L H x y z ω a λ U G = f 1  P, M , , , , , , , ,   × H H0 L H H H H0 H0  (2)Since the interest here is the velocity just at the lee edge of the reef or x = 1 and the velocity distribution at the centerline ( y = 0) L  L H z ω a λ U G = f 2 P, M , , , , , ,  (3)  H H0 H H H0 H0 
  27. 27. ωWhen the gap is absent =0 Hand this is equivalent to the condition far away from the gap where the effects of thegap are hardly felt. Therefore the lee-side velocity far away from the gap (or that inthe absence of the gap) can be written as  L H z a λ U C = f 3  P, M , , , , ,  (4)  H H0 H H0 H0 Since the present experiments are designed to demonstrate the possibility of largevelocity amplifications and their dependence on the porosity of the barrier L H λM, , and were kept Thus (3) and (4) yields: H H0 H0 constant. ∆U U G − U C  a z = = π  P, ,  (5) UC UC  H0 H 
  28. 28. a zIn the experiments the dependence on P, and are investigated H0 HPorosity P = 20% and 50%Amplitude a = 20, 30 and 40 cm for H0=30 cmMeasurements at z = 5, 10, 15, 20 cm for H=20 cm∆U U G − U C  a z = = π  P, , UC UC  H0 H  U0 UC UG
  29. 29. Schematic diagram of the experimental set-up (all values are in cm s) 86 cm W 60 cm 30 cm 20 cm ADV Positions 26 cm (a) Plan view (b) Elevation
  30. 30. Simulation of Coral Reefs in 2D Physical Modelling Representation of high dense (20% porosity) and low dense (50% porosity) structures
  31. 31. Collaborative ResearchArizona State University / University of Moratuwa(May/June 2005 and Nov/Dec 2006) PIV method Large flume studies ADV method Simulated reefs
  32. 32. Representation of high dense (20% porosity) and low dense (50% porosity) structures Gap
  33. 33. University of Arizona
  34. 34. 1 1 0.75 0.75 0.5Z/H 0 0.5 Z/H 0 0.25 0.25 0 0 0 0.5 1 1.5 2 0 0.5 1 1.5 2 U/U0,surface U/Uo,surface (a) 50% porosity (b) 20% porosity Normalized Velocity as a function of normalized height 2a = 10cm U0 Velocity without the reef = 0.4Hz UC Velocity behind the reef UG Velocity in the reef gap
  35. 35. 1 1 0.75 0.75 0.5 0.5 Z/H 0Z/H 0 0.25 0.25 0 0 0 0.5 1 1.5 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 U/U0,surface porosity (a) 50% (b) 20% porosity U/U0,surface Figure 11: Normalized Velocity as a function of normalized height 2€ = 20cm, (a) 50% porosity (b) 20% porosity Normalized Velocity as a function of= normalized height 2a = 20cm 0.4Hz U0 Velocity without the reef UC Velocity behind the reef UG Velocity in the reef gap
  36. 36. 1 1 0.75 0.75 0.5 0.5 Z/H 0Z/H 0 0.25 0.25 0 0 0 0.5 1 1.5 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 U/U0,surface U/U0,surface (a) 50% porosity (b) 20% porosity Normalized Velocity as a function of normalized height 2a = 30cm U0 Velocity without the reef UC Velocity behind the reef UG Velocity in the reef gap
  37. 37. 1 0.75 0.5 Z/H 0 0.25 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 U/U 0,surface 20% porosityU0 Velocity without the reefUC Velocity behind the reefUG Velocity in the reef gap
  38. 38. 1 1 0.75 0.75 0.5 0.5 Z/H 0Z/H 0 0.25 0.25 0 0 0 0.5 1 1.5 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 U/U0,surface U/U0,surface (a) 50% porosity (b) 20% porosity Normalized Velocity as a function of normalized height 2a = 30cm U0 Velocity without the reef UC Velocity behind the reef UG Velocity in the reef gap
  39. 39. Case Study------ Great Train Tragedy at Hikkaduwa
  40. 40. Hikkaduwa Case Study Key areas of investgation (i) Discontinuity in the Continental Shelf- Edge waves (ii) Coral Mining (iii) Negative Slope
  41. 41. (ii) Coral Mining Illegal coral mining has created a defenseless “low resistance path”Ilegal Coral mining over thelast few decades Presence of Corals and Rocks
  42. 42. Heavy Coral MiningMild negative slope
  43. 43. KERRY SHIEH©2005From Dr.D Subandano
  44. 44. Is it role of vegetation ? Tsunami Heights =3-4mFrom Dr. Danny Hilman Natawijaya West NIAS - SIRAMBU

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