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DSD-INT 2019 Coral Restoration for Coastal Hazard Risk Reduction - Roelvink

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Presentation by Floor Roelvink, Deltares, at the Delft3D and XBeach User Day: Coastal morphodynamics, during Delft Software Days - Edition 2019. Wednesday, 13 November 2019, Delft.

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DSD-INT 2019 Coral Restoration for Coastal Hazard Risk Reduction - Roelvink

  1. 1. Coral Restoration for Coastal Hazard Risk Reduction Floortje Roelvink A.R. van Dongeren C.D. Storlazzi S.G. Pearson M.F.S. Tissier A.J.H.M. Reniers
  2. 2. Coral Restoration for Coastal Hazard Risk Reduction Cluster analysis of reef bathymetric profiles XBeach non- hydrostatic The effect of coral restoration on wave transformation over various reef morphologies and the resulting runup
  3. 3. Deltares–CoralRestoration 3 Content Conceptual modelXBeach modellingProfile ClassificationMethodIntroduction Conclusion
  4. 4. 4 Introduction Functions of a reef • Ecological value • Economic value • Shoreline protection Threat to the shoreline protection function • Coral Degradation • Sea level rise Before After What to do to protect the vulnerable reef lined coasts? Coral Restoration? Deltares–CoralRestoration
  5. 5. Objective • Large knowledge gap on effect of restoration • Operational constraints & limited funds ask for efficient coral restorations ➢ What are the hydrodynamic effects of coral restorations? ➢ Which reef morphologies are worth restoration efforts? ➢ Where along the cross-shore is restoration most efficient in reducing the runup? 5 Deltares–CoralRestoration
  6. 6. Method • Classification reef morphologies using a cluster algorithm • Reef geometry control on nearshore hydrodynamics using XBeach non-hydrostatic • Effects of coral restoration on reef hydrodynamics and coastal hazards using XBeach non-hydrostatic • Aggregration results in Conceptual model 6 Deltares–CoralRestoration
  7. 7. 7 Classification Reef Morphologies • 30.000 reef profiles • Depth measurements at 2 m interval, between -30 and + 20 m • Locations: Hawaii, Florida, Guam, Puerto Rico, US Virgin Islands, American Samoa, and the Northern Mariana Islands • Cluster algorithm • Testing of different Cluster Variables and Clustering techniques Deltares–CoralRestoration
  8. 8. 8 Classification Reef Morphologies • Clustering Techniques • K-means algorithm • Gaussian Mixture Model • Maximum Dissimilarity Algorithm • Clustering variables Deltares–CoralRestoration
  9. 9. 9 Classification Reef Morphologies Deltares–CoralRestoration • Evaluation of methods on performance in grouping into geometrically distinct profiles with relatively high frequency of occurrence • Best results with k-means algorithm and depth at regular cross-shore intervals
  10. 10. 10 XBeach model setup • XBeach non-hydrostatic • Validated for reef lined coasts (e.g. Quataert (2015), Pomeroy (2012)) • Short-wave resolving • 1D • Fast, efficient, easy to setup • Wave driven circulation not captured • Coral restoration modeled as an impermeable bed level elevation with enhanced friction • First indication of the effect of coral restorations • Effects such as in-canopy flow not taken into account, possibly overestimating setup and reflection Deltares–CoralRestoration
  11. 11. 11 XBeach model setup • No calibration • Relative effect of different restoration configurations Deltares–CoralRestoration
  12. 12. 12 XBeach model setup • Input conditions Hydrodynamic forcing Profile parameters Restoration parameters Water level [m] Wave height [m] Wave steepness [-] Slope [-] Width [m] Height [m] Width [m] 0.5 2 0.01 0.025 100 0.25 5 1 4 0.05 0.1 250 1.25 10 2 6 0.5 25 3 4 Deltares–CoralRestoration
  13. 13. 13 XBeach results • Reef geometry control • Steep slope (narrow surfzone) -> large setup and IG wave generation • Reef flat width and submergence determine beach toe short wave heights • Convex and typical fringing profile sheltered from waves by reef flat in contrast to straight and three-slope profile Deltares–CoralRestoration
  14. 14. 14 XBeach results • Effect of coral restoration • +/- 15.000 model runs • At steep interface of restoration, waves are reflected • Across restoration, short and IG waves are dissipated, setup across restoration • Reduction of short wave heights decreases setup near the shore due to smaller radiation stress gradients • Diminished transfer of energy from short waves to infragravity waves. Deltares–CoralRestoration
  15. 15. 15 XBeach results • Effect of coral restoration • Location determines effect on hydrodynamic processes • Restoration potential distinctly different across different reef morphologies • Typical fringing reef profile 0-10 % reduction • Convex profile 0-10 % reduction • Straight profile up to 20 % reduction • Three-slope profile up to 40 % reduction Deltares–CoralRestoration
  16. 16. 16 Conceptual model aggregration • Large variety of stakeholders involved with coral restoration • Aggregation results into simple model could be highly beneficial • Pinpoint where restoration efforts are most efficient • Conceptual model synthesis Deltares–CoralRestoration
  17. 17. 17 Conclusion Take home • There is potential for coral restoration! • First guideline on how to optimize the effect of coral restoration • Promising example of green infrastructure • XBeach simulations as input for empirical parametrization • Possibility for simple reef hydrodynamic model Not there yet • 1D schematization • Schematization of restoration • Limited variation forcing conditions, profile parameters etc • Include restoration in conceptual model • Validation conceptual model So much to do and learn! • Ecological aspects of coral restoration • Calibration and validation of restoration schematization (field and lab experiments) • Convert knowledge into simple tool for stakeholders working with coral restoration Deltares–CoralRestoration
  18. 18. • Thank you very much for your attention! Questions? floortje.roevink@deltares.nl

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