The cluster effect
When comparing the current season to winters past, the years that come to mind are 2011, 2007 - when one of four succesive East Coast Lows grounded the MV Pasha Bulker at Newcastle - and 1974 when three Tasman Lows lashed the East Coast and caused enormous damage.
Different than a memorable storm, a memorable season usually involves the clustering of low pressure systems with resultant large and damaging swells, often from the east through to the north-east. You can throw the Black Nor'easter swell of 2016 into the mix, though this is an outlier as it was a lone storm and not a cluster.
So let's talk about storm clusters.
To start with, we know that the ENSO cycle - that being El Niño and La Niña - influences the East Coast wave climate more than other drivers such as the Indian Ocean Dipole (IOD) or Southern Annular Mode (SAM).
Numerous studies have looked at the wave climate off NSW, including peak wave heights and mean swell direction, during El Niño and La Niña years. Those studies found that, under La Niña conditions, on average, storm wave properties are of greater magnitude and the wave direction more easterly, while El Niño sees a reduction in storm wave properties and swells more from the south.
For instance, a study by Davies 2016 which modelled coastal storm event sequences found the frequency of storms with direction north of 120° (i.e. easterly and north-easterly events) had a mean rate of 1.7/year in El Niño years and 3.9/year in La Niña years. This matched the historical data analysed from the wave buoy off Crowdy Head.
There was also a 15% increase in the mean annual number of storms in La Niña years compared with El Nño years off the Australian East Coast.
Further to this, it wasn't the mean storm wave height that was greater during La Niña but rather the storm wave duration.
That's because clustering of storms is more likely through La Niña events, and while we haven't yet ticked all the boxes yet for the coming La Niña, we've been feeling its influence on the East Coast since late autumn.
While great for surfers who get to ride big wave boards on the reg, clustering is of great concern to coastal property holders, particularly during La Niña as storm events from the east to north-east cause the most destruction.
This is linked to the nature of sand flow. Littoral drift generally moves from south to north, so the northern ends of bays are loaded with sand, leaving southern ends with a thinner beach profile and less of a barrier to incoming storms. This means our beaches aren't setup for constant storm action and sand gouging from the east to north-east.
When back to back events hit, this creates a compounding issue and the results can currently be seen at Byron Bay, The Entrance, Wamberal, and Collaroy.
The solution to this problem is not clear, installing rock walls as defence will lead to erosion in the direct vicinity of this hard barrier, hence only moving the problem elsewhere. Instead returning the land back to council and the rate payers in the form of a natural dune system is likely the smartest approach and arguably the cheapest in the long term.
As things settle from the last two significant lows and swell events, another is starting to form in the Tasman Sea, but far enough away to not severely impact the already damaged areas.