Waves in Real Time

This blog originally appeared in the June 2023 issue of the Illawarra Flame magazine

You certainly don’t need to be a surfer to have a keen interest in ocean waves and while there’s a range of surf forecasting apps and websites out there predicting what wave height and direction will be, there’s not a lot of information available in real time that tells you just how big those waves really are. The exception is the NSW Coastal Data Network Program operated by the NSW Government Dept of Planning and Environment’s Manly Hydraulics Laboratory (MHL).

Following a series of damaging storms in 1974, the MHL developed a network of offshore waverider buoys to monitor wave conditions along the NSW coast that now consists of seven buoys deployed approximately 6 to 12 km offshore of Byron Bay, Coffs Harbour, Crowdy Head, Sydney, Port Kembla, Bateman’s Bay and Eden. It’s one of the best wave monitoring networks in the world.

A waverider buoy is like a big soccer ball tethered to the ocean floor that bobs, pitches and rolls at the surface with the passage of waves. In-built sensors translate this movement into wave information and an antenna transmits the data continuously to a receiving station.  All of the data collected by the waverider buoys is available in real time online at www.mhl.nsw.gov.au/Data . On the website, you can look at graphs showing wave data from all of the buoy locations at once or you can focus just on the buoy nearest you – for us that would be the Port Kembla and Sydney buoys.

The main data of interest are significant wave height (Hs), which is the average of the highest 33% of waves recorded over a given time. It’s really a measure of the biggest waves and the average yearly Hs for our coast is about 1.6 metres. Anything bigger than 2.5 metres can be considered big. The wave period (Tp) is the time between two wave crests to pass a fixed point and while typical wave periods along our coast are about 8 seconds, anything above 10 seconds represents long period swell from a distant storm. Wave direction refers to the direction that waves are coming from so a direction of 135° relative to true north represents waves coming from the southeast. One of the more interesting graphs is the directional spectrum as shown in the accompanying image. These are generated hourly and provide the Hs, Ts and show the direction that the waves are coming from and the energy (colours) associated with the waves, which is really a measure of the wave height. One good thing about these graphs is that they show if there’s waves coming from multiple directions. There’s plenty more to explore so if you are into waves, definitely go check out the website!

Directional wave spectra can be addictive (image courtesy Manly Hydraulics Laboratory)