Offshore Wind Farms, Waves and Beaches

This article is a modified version of one that appeared in the November 2023 issue of The Illawarra Flame magazine.

Backstory: there’s a proposal to put a large wind farm offshore of the Illawarra coastline in NSW (which is where I live) and it’s become quite a controversial issue. You can read more about the proposal here. Below is what I wrote about how the wind farm might impact local surf conditions and beaches:

Official rendition of the wind turbines 10 km from shore. Bit light perhaps?

I’ve been getting a lot of questions lately about the impacts that the proposed offshore wind farm will have on our surf and beaches. There’s a lot of information about the issue floating around out there (pun intended) and while it’s good to ask these questions, the good news it that the windfarms will have absolutely no impact on our surf, or on our beaches.

‘Wave climate’ describes the characteristics of waves for a region. Ours is dominated by swell waves that are formed by wind hundreds and thousands of kilometers away. ‘Swell’ is defined as waves with wave periods – the time it takes successive wave crests to pass the same point – of between 8 and 20 seconds and or swell comes from the south-east, east and north-east directions.  Swell waves can propagate thousands of kilometers without losing their energy, until they hit shallow water and the coast. Swell is what gives us good surf.

If the turbines are floating structures, they’ll either go up and down with the swell, or the swell waves will simply wrap around and quickly reform thanks to the process of wave diffraction. It wouldn’t matter if the turbines were only 1 km offshore, there would still be no impact on the swell reaching our beaches.

We also get wind waves, which are locally generated waves caused by strong wind and these have periods of between 3 to 8 seconds. Most of our wind waves are associated with the strong north-easters we get in the summer and by storms – usually not the best surfing conditions. There has been some research done in Europe and Canada on the downwind impacts of windfarms on locally generated waves and it’s all been shown to be minimal. These are also completely different wave climates to ours. As far as I’m aware, no research has been done on the impact on swell waves, mostly because there’s not many examples of windfarms on swell-dominated coasts, but to be honest, there doesn’t need to be – we already understand swell wave behaviour extremely well.

Our beaches are dynamic features that constantly adjust with changing wave conditions. If the turbines aren’t going to affect the waves, they’re not going to affect the beaches. There’s also a concept called ‘depth of closure’ which is the furthest offshore distance that the seabed is altered by wave action. At most, even during the most severe east coast cyclones, ours is probably about a kilometer offshore, which is nowhere near where the closest wind turbines will be.

So at least we don’t have to worry about what the windfarms (if they happen!) will do to our surf and beaches! What we should be worrying about is what climate change will do to them with rising sea levels and potentially more damaging storms. Then we’ll see major impacts and the news won’t be so good.