Frequently Asked Questions

What are extreme sea levels?

Extreme sea levels, the rise of the ocean surface above commonly observed levels, often associated with coastal floding and erosion. Extreme sea levels occur as a result of the combined effects of a range of factors including astronomical tides, long-term sea-level variability, storm surges due to pressure and wind, and wave breaking processes.

What are tides?

Tides are long-period waves that move through the oceans driven by the gravitational forces of the moon and sun. At the coastlines tides appear as the regular rise and fall of the sea surface. Depending on where you are in Australia, there can be either one or two high and low tides per day.

What is storm surge?

Storm surge is the abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide and is caused mostly by low air pressure and storm winds pushing water onshore. The height of the storm surge at any given location depends on the orientation of coastline, the track, intensity, size, and speed of the storm and the local water depths.

What happens when I click on the coloured coastal data points on the map?

A text box will appear containing the 1 year and 100 year Average Recurrence Interval (ARI) total water levels, along with several plots and links to download hourly sea levels from the numerical model hindcast.

What is the Average Recurrence Interval (ARI)?

The ARI is used to communicate the probability of ocurrence of extreme sea levels and is defined as the average, or expected, value of the period of exceedences of a given sea level height over a given duration. It is implicit in this definition that the periods between exceedences ins generally random. In otehr words, ARI refers to the average, or expected, time (usually in years) between events where water levels rise above a given level. This is equivalent to the "return period". A common mis-interpretation is that these extreme levels will only occur once over the given time period, when in fact they can happen, once, many times, or not at all.

Do extreme sea levels on this website contain tides or just storm surge?

The sea levels on this website are Total Water Levels that include: Tide + Storm Surge + Mean Sea Level (MSL)

Does this website contain information on wave setup?

No— the water levels on this website do not consider wave effects. However, observed sea levels on exposed beaches can be much higher than levels given here due to wave breaking which causes wave-setup and runup.

Is freshwater runoff considered?

No— the water levels on this website do not consider the rise in sea level due to freshwater runoff that can be substantial in estuaries or river entrances. Some coastal population centres (and tide gauges)in Australia are influenced by both freshwater flood events and storm surges, particularly during tropical cyclones or East Coast Lows with heavy rainfall.

Do extreme sea levels on the website account for future Sea Level Rise?

No— this website contains information on present-day extreme sea levels only.

Are model time series data available?

Yes— netCDF files containing the hourly adjusted model time series (1958-2016) can be downloaded through the link on the text box that appears when you click on coastal data points. Note that available time series underestimate sea levels caused by tropical cyclones, whilst the extreme value statistics do include these effects.

A text file listing all coastal data points (ID,longitude,latitude) is available here.

Data files can also be downloaded directly by creating a url based on the data point ID, for example:

A MATLAB tool to help bulk download the netcdf data files for a selected region (defined by a bounding box or Google Earth kml polygon) is available here.

Where can I find more information about the model setup, methods, and validation?

A document summarising the website data is available here.

I need help using the website. Where can I find a userguide?

A detailed website userguide is available here.