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The high water levels are provided for a range of Average Recurrence Interval (ARI) events. Average recurrence interval is often referred to as a return period. These can be approximately converted to Annual Exceedance Probability (AEP), the probability of occurrence each year, by the following conversion table:
ARI (yr) | AEP (%) |
2 | 50 |
5 | 20 |
10 | 10 |
20 | 5 |
50 | 2 |
100 | 1 |
The high water level values (1% AEP + 1 m sea level) are used to calculate the required height of habitable floors for developments in the coastal inundation hazard zone, as per Unitary Plan rules.
High sea level values for Auckland were collected between 2013 and 2019, via four separate studies:
In 2013, Auckland Council’s Civil Defence & Emergency Management Department commissioned NIWA to calculate and model coastal-storm inundation elevations for the entire Auckland region, primarily for emergency management purposes. NIWA calculated extreme high-water level values at fixed locations across the region, focusing on the open coasts and harbour areas.
In 2016, NIWA calculated high water level values for the east coast estuaries.
In 2020, DHI calculated high water levels for the Parakai/Helensville area to the south of the Kaipara Harbour. Inundation in this area is particularly complex due to the wide, low lying coastal plains sitting above the confluence of the Kaipara river with the harbour.
Also in 2019, NIWA calculated high water levels for Great Barrier and Little Barrier for 16 sites at ARI scenarios of 1, 2, 5, 10, 20, 50 and 100 years
Details of each study and the high water level calculations are available in Technical Report 2020/024
Credit:
Data supplied by Resilient Land and Coasts, Auckland Council
Use Limitations:
Constraints– General:
The high water level values were collated from tables within Technical Report 2020/024. They are made available in GIS to improve the workflow of Regulatory development engineers, specifically in relation to the calculation of habitable floor levels. The dataset is not meant to stand alone, and users outside of Regulatory should be directed to Technical Report 2020/024.
Constraints– Legal:
There are no legal constraints in relation to this dataset.
Constraints– Security:
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