Oceanographic assessment Rangiroa, Kauehi, Arutua, Apataki and Manihi, French Polynesia Aseri Baleilevuka ... [et al.]

Également en français : "Étude océanographique : Rangiroa, Kauehi, Arutua, Apataki et Manihi, Polynésie française"

Includes bibliographical references (p. 29)

"The Applied Geoscience and Technology Division of the Secretariat of the Pacific Community carried out an oceanographic survey on five atolls — Apataki, Arutua, Kauehi, Manihi and Rangiroa — in the Tuamotu Archipelago of French Polynesia from July to December 2011. The objective of the survey was to study storm surge hazard and to include this hazard into future development plans. This report details the deployment of oceanographic instruments to measure current velocities, surface water parameters and water elevation. These oceanographic data improve our understanding of atoll hydrodynamics. The emphasis of the study was on Rangiroa Lagoon and wave transformation on the atoll’s outer rim to support cyclone wave inundation modelling. Current velocities (speed and direction of water flow) were measured in situ using three Nortek acoustic doppler current profilers, or Aquadopps (AQDs), and two Nortek acoustic wave and current meters (AWACs) at Rangiroa and one AQD at each of the other four atolls. Data from the AQD in the Tiputa channel show that the flow of water is tidally influenced, with a dominant flow out of the lagoon towards the northeast at an average speed of 1.5 meters per second (m/s). A maximum speed of about 4.6 m/s was observed on a single occasion and coincided with the higher incident offshore swell wave event that occurred on 27 August 2011. Other current profilers recorded average speeds of less than 0.3 m/s, with their maximum speed corresponding to the offshore wave event in August, with the exception of the AQD on the Avatoru reef flat. Surface wave parameters and water elevation were measured in situ using eight RBR tide and wave recorders (TWRs), pressure sensors, in Rangiroa and three TWRs for each of the other four atolls. The TWRs deployed at Rangiroa recorded maximum water levels during the extreme offshore wave event on 27 August. The exceptions were the TWRs on the Tivaru reef slope and the ones on the Avatoru reef crest and shore. These TWRs are on the northern part of the atoll, and were protected by islets from incident swell waves. The AQDs and TWRs deployed at Apataki, Arutua, Kauehi and Manihi atolls recorded no swell events because the earliest deployment was at Kauehi in November 2011. Average speeds observed by the AQDs were 0.2 m/s or less, with the TWRs recording wave heights between 0.1 m and 0.9 m."