Abstract:
Wave conditions and local atmospheric pressure were recorded during a 6 month and 20-day deployment at two sites in Mount Maunganui, New Zealand between May 21st and December 11th, 2019. Three pressure sensors were deployed to capture wave motions at both Moturiki Island off the main beach and within the Port of Tauranga, as well as a local record of atmospheric pressure. Instruments recorded continuously at 2 Hz for the duration of this study, giving a large high frequency dataset for both Moturiki Island off the main beach, and within the Port of Tauranga. From this raw data, long period wave events with a height of 0.1 m or greater were identified by long period filtering. This process extracted ten events of interest, ranging from 0.1 to 0.19 m in magnitude. The potential mechanisms responsible for these motions were investigated using local atmospheric data recorded during the deployment and offshore wave data from the Pukehina offshore directional wave buoy deployed by Bay of Plenty Regional Council. From this, it was established that nine of the identified events were closely linked to a decrease in local atmospheric pressure and an increase in significant offshore wave height. Both mechanisms appear to be strong indicators for the presence of a long period oscillation, however the long period (> 20 minutes) of these motions indicates that they are of an atmospheric origin rather than swell-induced infragravity events. These oscillations fall within the accepted period range of meteotsunami events identified in other research, despite their relatively low magnitude. This supports the assertion that this data can potentially be used for the development of a tool for the prediction of long period wave events at the coastline at Mount Maunganui, with the methods implemented suitable for further studies at additional sites. The one oscillation not linked to either of these mechanisms occurred on June 16th 2019 shortly after a M7.0 earthquake was reported near the Kermadec Islands, and is believed to be small (0.1 m crest to trough) tsunami signal from this event. This highlights the potential hazard posed to the Bay of Plenty by tectonic activity in this area, and the need for an effective plan to manage the risk associated with this.