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DSD-INT 2018 Characterizing the drivers of coral reef hydrodynamics at the Rowley Shoals, off northwestern Australia, using Delft3D FM - Grimaldi

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Presentation by Camille Grimaldi, University of Western Australia, Australia, at the Delft3D - User Days (Day 2: Hydrodynamics), during Delft Software Days - Edition 2018. Tuesday, 13 November 2018, Delft.

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DSD-INT 2018 Characterizing the drivers of coral reef hydrodynamics at the Rowley Shoals, off northwestern Australia, using Delft3D FM - Grimaldi

  1. 1. D R I V E R S O F C O R A L R E E F H Y D R O D Y N A M I C S A T T H E R O W L E Y S H O A L S , W A U S I N G D E L F T 3 D F M Camille Grimaldi, Ryan Lowe, Rebecca Green and Jessica Benthuysen Photo- Sharyn Hickey
  2. 2. Coral reef hydrodynamics NOAA • Retention/circulation of water and material in the reef (e.g. heat, nutrient, organisms) • Flushing time and residence time • Affect most of the biological and chemical processes on the reef INTRODUCTION
  3. 3. 3rd Global-scale coral bleaching Benthuysen et al., 2018 Temperature anomaly INTRODUCTION
  4. 4. 2015/2016 - 3rd global-scale coral bleaching NOAA Northwestern Australia Coral cover and species diversity dramatically reduced (Gilmour et al., 2018) INTRODUCTION
  5. 5. Only minor (<10%) coral bleaching observed (Gilmour et al., 2018) INTRODUCTION 2015/2016 - 3rd global-scale coral bleaching Northwestern Australia
  6. 6. Atmospheric and oceanographic conditions influence the reef variability. INTRODUCTION 2015/2016 - 3rd global-scale coral bleaching Northwestern Australia
  7. 7. What drivers of hydrodynamics on reef systems? INTRODUCTION 2015/2016 - 3rd global-scale coral bleaching Northwestern Australia
  8. 8. Rowley Shoals - Pristine environment - 3 atolls (=ring-shaped coral reef including a lagoon) - Channel on the NE side INTRODUCTION Imperieuse Clerke Mermaid
  9. 9. Photo : Lady Cruises Rowley Shoals INTRODUCTION Imperieuse Clerke Mermaid
  10. 10. Mermaid Reef INTRODUCTION Mermaid reef Imperieuse Clerke Mermaid
  11. 11. Coral reef systems’ hydrodynamic drivers Lowe and Falter 2015 CONCEPTS • Waves ~ 2/3 of the world’s reefs are wave-dominated Significant wave height (Hs) >1.5 m
  12. 12. Coral reef systems’ hydrodynamic drivers INTRODUCTION OutflowInflow Top view Reef channel inflow Wave setup 1 inflow 2 outlfow 3 Forereef Reef flat Lagoon Cross section of an atoll • Waves CONCEPTS
  13. 13. ~ 1/3 of the world’s reefs are tide-dominated Coral reef systems’ hydrodynamic drivers • Tides Mean tidal range (MTR) Significant wave height (Hs) > 1 CONCEPTS Lowe and Falter 2015
  14. 14. Coral reef systems’ hydrodynamic drivers • Tides OutflowInflow Top view Reef channel inflow 1 outflow 2 Forereef Reef flat Lagoon Risingtide inflow Fallingtide Cross section of an atoll CONCEPTS
  15. 15. Global models estimates: - Mean Tidal Range = 2.4 m - Signif. Wave Height = 1.4 m (Egbert & Erofeeva, 2002; Lowe and Falter 2015) NTRODUCTION RESULTS & DISC. CONCLUSIONCONCEPTS METHODS Rowley Shoals - hydrodynamic MTR / Hs > 1 Hs ~ 1.5m CONCEPTS Influenced by both waves and tides?
  16. 16. NTRODUCTION RESULTS & DISC. CONCLUSIONCONCEPTS METHODS Waves and tides dominated atolls CONCEPTS Costa et al., 2018
  17. 17. Numerical simulations vs In situ observations METHODS
  18. 18. RESULTS & DISC. CONCLUSIONCONCEPTS METHODS Numerical simulations - Delft3D Flexible Mesh METHODS • Spatially-complex bathymetry • Influence of range of hydrodyanmic processes • Interest in temperature and water quality applications Challenges Delft3D Flexible Mesh • Flexible Mesh Grid • Coupling D-Flow FM and D-Waves • Residence time, heat exchanges, water quality, etc
  19. 19. RESULTS & DISC. CONCLUSIONCONCEPTS METHODS D-Flow FM – Preliminary simulations Input parameters METHODS
  20. 20. RESULTS & DISC. CONCLUSIONCONCEPTS METHODS Input parameters • Flexible Mesh Grid Inside reef: 50x50m Outside reef 100x100m D-Flow FM – Preliminary simulations METHODS
  21. 21. RESULTS & DISC. CONCLUSIONCONCEPTS METHODS Input parameters • LiDAR Bathymetry 30m resolution Triangular interpolation D-Flow FM – Preliminary simulations METHODS
  22. 22. RESULTS & DISC. CONCLUSIONCONCEPTS METHODS Input parameters • Boundary conditions Tidal constituents TPXO 8.0 D-Flow FM – Preliminary simulations METHODS
  23. 23. RESULTS & DISC. CONCLUSIONCONCEPTS METHODS D-Flow FM – Preliminary simulations METHODS
  24. 24. Nov. 2017 - October 2018 : FULL year of in situ observations In situ observations AWAC retrieval METHODS
  25. 25. Open Ocean Channel Lagoon Reef flat Current sensors In situ observations Water levels and current speed and directions at 4 key locations METHODS Pressure sensors Water levels and significant wave height across the reef
  26. 26. PRELIMINARY RESULTS Water levels – Numerical simulations
  27. 27. Water levels – Numerical simulations PRELIMINARY RESULTS
  28. 28. Effect of atoll morphology Water levels – in situ observations PRELIMINARY RESULTS
  29. 29. INTRODUCTION Water levels – Numerical simulations vs observations PRELIMINARY RESULTS
  30. 30. Currents - numerical modeling Channel Lagoon Reef flat INTRODUCTION PRELIMINARY ESULTS
  31. 31. Currents - numerical modeling PRELIMINARY RESULTS
  32. 32. CONCLUSIONCONCEPTS METHODS RESULTS Currents - In situ observations vs Numerical simulations 10 days 4 days Completely tidally driven PRELIMINARY RESULTS
  33. 33. DISCUSSION CONCLUSIONCONCEPTS METHODS Potential wave forcing DISCUSSION
  34. 34. Mermaid reef Potential wave forcing DISCUSSION Wave influence on the Western Side
  35. 35. Hs from the western side Potential wave forcing DISCUSSION
  36. 36. Conclusions and next steps - Good agreement for water level between model and observations - Good agreement for current between model and observations in the channel - Tides are not enough to explain the entire hydrodynamics - Mermaid reef influenced by both waves and tides Mermaid reef Tides Waves CONCLUSION
  37. 37. Conclusions and next steps Next steps : - Drivers of reef hydrodynamics : - Incorporate D-Waves - Couple D-Flow FM and D-Waves - Determine residence time - Test different grids and sensitivity analysis - Regionnal hydrodynamics - Temperature variability simulations - Water quality (carbonate chemistry) simulations CONCLUSION
  38. 38. Aknowledgements - Ryan Lowe, Rebecca Green, Jessica Benthuysen and Carlin Bowyer - University of Western Australia, Center of Excellence for Coral reef studies and Australian Institute of Marine Science - Deltares CONCLUSION
  39. 39. Questions? CONCLUSION

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