Cyclone Wave Inundation Models for Apataki, Arutua, Kauehi, Manihi and Rangiroa Atolls, French Polynesia SPC Applied Geoscience and Technology Division (SOPAC) September 2013 Hervé Damlamian, Jens Kruger, Maleli Turagabeci & Salesh Kumar SPC SOPAC TECHNICAL REPORT (PR176) Ocean and Islands Programme © Copyright Secretariat of the Pacific Community (SPC), 2013 All rights for commercial / for profile reproduction for translation, in any form, reserved. SPC authorises the partial reproduction or translation of this material for scientific, educational or research purposes, provided that SPC and the source document are properly acknowledged. Permission to reproduce the document and/or translate in whole, in any form, whether for commercial / for profit or non-profit purposes, must be requested in writing. Original SPC artwork may not be altered or separately published without permission. SPC Applied Geoscience and Technology Division (SOPAC) Private Mail Bag GPO Suva Fiji Islands Telephone: (679) 338 1377 Fax: (679) 337 0040 E-mail: [email protected] Web site: http://www.sopac.org SPC Applied Geoscience and Technology Division (SOPAC) Cyclone Wave Inundation Models for Apataki, Arutua, Kauehi, Manihi and Rangiroa Atolls, French Polynesia SPC SOPAC TECHNICAL REPORT (PR176) Hervé Damlamian, Jens Kruger, Maleli Turagabeci & Salesh Kumar September 2013 Ocean and Islands Programme DISCLAIMER While care has been taken in the collection, analysis, and compilation of the data, it is supplied on the condition that the Secretariat of Pacific Community Applied Geoscience and Technology Division (SOPAC) shall not be liable for any loss or injury whatsoever arising from the use of the data. IMPORtaNT NOTICE This document has been produced with the financial assistance of the European Union through the Supporting Disaster Risk Reduction in Pacific Overseas Countries and Territories, 9th European Development Fund – C Envelope. The contents of this document are the sole responsibility of the Secretariat of the Pacific Community and can under no circumstances be regarded as reflecting the position of the European Union. The SPC Applied Geoscience and Technology (SOPAC) Division undertook the work in collaboration with ‘Service de I’Urbanisme’ of French Polynesia TABLE OF CONTENTS ACKNOWLEDGEMENTS........................................................................................................................ 2 EXECUTIVE SUMMARY.......................................................................................................................... 3 1 INTRODUCTION.............................................................................................................................. 4 2 METHODOLOGY.............................................................................................................................. 6 2.1 Physical processes......................................................................................................................................................... 6 2.2 Characteristic cyclone sea state.................................................................................................................................... 7 2.3 Oceanographic data collection...................................................................................................................................... 8 2.4 XBeach model................................................................................................................................................................ 9 3 CALIBRATION.................................................................................................................................. 11 3.1 Sensitivity analysis........................................................................................................................................................... 11 3.2 Calibration....................................................................................................................................................................... 12 3.3 Other modelling considerations........................................................................................................................................ 13 4 RESULTS.......................................................................................................................................... 20 4.1 Rangiroa.......................................................................................................................................................................... 21 4.2 Apataki............................................................................................................................................................................ 29 4.3 Kauehi............................................................................................................................................................................. 33 4.4 Manihi.............................................................................................................................................................................. 37 4.5 Arutua.............................................................................................................................................................................. 42 5 CONCLUSION.................................................................................................................................. 49 6 REFERENCES.................................................................................................................................. 51 7 APPENDICES................................................................................................................................... 52 APPENDIX A: 3D COMPUTATIONAL DOMAIN........................................................................................................................ 52 APPENDIX B: MODEL RESULT PLOTS................................................................................................................................... 55 1 Cyclone Wave Inundation Models for Apataki, Arutua, Kauehi, Manihi and Rangiroa Atolls, French Polynesia ACKNOWLEDGEMENTS The success of this study is due to the assistance of a number of individuals from the Government of French Polynesia, especially Emilie Nowak and Emmanuel des Garets. We also acknowledge the guidance received from Scott Stephens, National Institute of Water and Atmospheric Research, New Zealand, and Dano Roelvink, United Nations Educational, Scientific and Cultural Organization Institute for Water Education, the Netherlands. 2 SPC SOPAC TECHNICAL REPORT (PR176) Cyclone Wave Inundation Models for Apataki, Arutua, Kauehi, Manihi and Rangiroa Atolls, French Polynesia EXECUTIVE SUMMARY This study is a component of a larger project aimed at assessing the storm surge hazard in the Tuamotu Archipelago of French Polynesia and at providing information that would aid the inclusion of this hazard into future development plans and risk prevention solutions. This study used forcing conditions generated by a 12 m wave impacting on the atolls of Apataki, Arutua, Kauehi, Manihi and Rangiroa at high tide. The inundation was computed using the XBeach hydrodynamic model. Such a wave correlates to about a 50 year return interval that has a 2 per cent chance of occurring in any one year. Prior to applying the above input parameters, the XBeach model was initially set up and calibrated based on baseline and observational data collected in the field from June to December 2011. This report covers the results of the two- dimensional cyclone wave model of the five targeted sites set up under this study. A companion report of the fieldwork component, including details on the oceanographic data collected and used in the calibrations, is available, as is a report on the bathymetry survey for Rangiroa. Model results were mapped into four risk categories of weak, intermediate, strong and very strong. All modelled sites that were adjacent to the ocean showed very strong risk to extreme cyclone-generated significant wave heights of 12 m. Lagoon sides that were mapped as having intermediate to weak levels of risk should be considered with caution, because inundation could also come from the lagoon side through storm surge, which was not investigated in this study. We found that the model results to be very sensitive to wave direction. It is noted that the effects of variable incident wave directions that deviate from the perpendicular could result in higher risk in some areas, especially near a pass or hoa. SPC SOPAC TECHNICAL REPORT (PR176) SPC SOPAC TECHNICAL REPORT (PR176) 3 Cyclone Wave Inundation Models for Apataki, Arutua, Kauehi, Manihi and Rangiroa Atolls, French Polynesia 1 INTRODUCTION Following the impact of Cyclone Alan on the Society Islands in 1998, the Government of French Polynesia requested the systematic study and mapping of natural hazards in all of the island groups (through the ARAI Programme1). This project received 3.7 million euros in funding and was implemented by the Bureau de Recherches Géologiques et Minières (the French Geological Society) from 2002–2006. The natural hazards examined included tsunamis, floods, landslides, ocean swell waves and earthquakes. Given ARAI’s findings, the Government of French Polynesia decided to introduce the systematic use of risk prevention plans known as PPR or plan de prévention des risques. The PPR is a document produced by the Government of French Polynesia with the goal of regulating