ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata
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Ocean and coastal extreme waves (4m), 2008
These data estimate the occurence of extreme wave events in coastal and oceanic waters for 2008, particularly for wave events where significant wave height exceeds a threshold of 4 metres and for a period of at least 12 hours. Significant wave height is defined as four times the square root of the variance of sea surface elevation due to wave motion.
The data have been commissioned from NIWA in order to quantify the occurrence of extreme wave events in New Zealand on an annual basis. However, it is apparent that NIWA's primary reason for collecting these data is to develop as accurate a picture as possible of what is happening at present with extreme waves. I.e. while it is possible to compare data over time to create a longer-term series of data on extreme waves - data are not completely comparable over time because the resolution of data has increased over time (allowing more and more accuracy of data over time - but reducing long-term comparability).
NIWA has advised that international data maybe available that provides a longer time series of extreme wave events (at lower resolution). Further work is needed to look into this.
This index was generated using NIWA’s operational wave forecasting model NZWAVE-12 (Gorman, 2016). This model has a 12-kilometre resolution and models wave heights. The model was created using: • wind from NIWA’s NZLAM-12 weather forecast model • swell from NIWA’s global wave forecast model
We use a duration threshold of 12 hours as it allows semi-diurnal tides to cover their full low water to high water range. This means that there was both a high tide (when overtopping and damage to coastal infrastructure, for example, is most likely) and a low tide during an event.
Gorman, R (2016). Extreme wave indices for New Zealand coastal and oceanic waters. NIWA Client Report HAM2016-014 prepared for the Ministry for the Environment.