December 2021 (ROTM#156) Stockton Beach, NSW Australia

Rips are pretty important features along beaches, although I may be a little biased in that regard. But it’s true. Aside from being a huge hazard to bathers and swimmers, they can also cause significant beach erosion, particularly channelized rip currents, which can stay in the same place for days, weeks and even months.

 When this happens, the rip tends to erode out a pronounced ‘bowl’ along the beach – a megacusp in coastal geomorphology speak. It’s another visual clue about how to spot rips, but it’s also a sign of localised erosion, which wouldn’t normally be a problem unless that bowl is eating further back into the beach and starts encroaching on structures.

 This picture is courtesy of Dr Mitch Harley of the UNSW Water Research Laboratory (and proud member of the UNSW Beach Safety Research Group!) and his taken from his Twitter feed @DocHarleyMD. Mitch runs an amazing citizen science program called CoastSnap where people can take pictures of their favourite beach from the same location over time and Mitch does some nifty image processing to map out how the shoreline is changing over time in response to changing waves and tides. This is an example of the CoastSnap station at Stockton Beach, which is just north of Newcastle, NSW. Stockton has a long history of erosion problems, well…as long as the training wall keeping the Hunter River mouth open has been in place, which is starving the beach of its normal sand supply.

 This picture shows some of localised erosion caused at the base of the seawall (which is what happens at the base of seawalls) that was constructed to stabilise the shoreline due to the now chronic erosion problem on the beach. As you can see, the rip bowl is getting pretty close to it, which would enhance the erosion. As for the rip? There’s a nice red arrow showing you exactly where it is!

The problem with using arrows is that they sometimes hide the rip