Reflective waves in the surf zone
Behind the scenes, we've been working on some coastal analytical tools over the last few years. This morning our Greenmount surfcam randomly captured what appears to be swash-based reflection through the surf zone.
The angle of the surfcam (facing E/NE, almost perpendicular to the direction of the energy) shows that the wavelength is very short. It can't be northerly windswell, which would look much more peaky and delineated - besides, upstream winds have been out of the southern quadrant for the last few days.
Instead I suspect these are reflected waves off the beach following a spell of surf beat (i.e. a set, or several sets of waves). Interestingly, you can see small scale refraction and diffraction as this energy passes through a couple of of gutters extending north from the shoreline.
Newy point definitely gets them at certain times. They tend to throw unsuspecting SUP riders off too.
I’m not talking out wedgey rebounds though (which can be surfed.. as per Knights in SA). In the lineup you may not even notice these tiny reflective waves passing underneath.
That’s a possibility, but there appears to be a lot more waves than what a standard boat wake would produce.
Wow. I just checked the Surfcam Replay, and there is no sign of a boat (and any subsequent wake) - but the lines seem to be coming from the north. Kinda trippy looking, actually.
https://www.swellnet.com/surfcams/greenmount/replays#/2018-06-09/139215
Hmmmm.. looks like couple of skis doing circle work off Kirra.. but the waves don’t look like ski wake to me - however I might be mistaken. Def not windswell I reckon.
Weird, looks like boat/ski wake to me.. but again too many close spaced ripples.
3 skis going back and forth though. Sometimes against each other. could do it.
But.. if the skis were going back and forth, there’s no way that the swell lines would be so perfectly spaced apart.
No. At a bare minimum there’d be irregular spacings. Some would overlap, and depending on the driving pattern we’d see differing responses along the length of the Superbank.
Here's another older example from the Coal Coast, overlooking Thirroul.
The key here is that it's the sun glare that makes it visible. As soon as cloud cover eliminated the glare, you couldn't see these waves at all.
And in this case, it's interesting to note that there was little regional wind either (image taken at 7:57am, Sun 13th Nov 2016) - Bellambi and Wattamolla were under 10kts at the time the image was taken, and for the preceding 12 hours too, mainly W'ly in direction (BOM obs data via Weatherzone, below).
Look at the 2 min mark and the lines are out past the peak at Snapper.
It's the wake from a vessel, jetski or boat running at fair speed, for a long distance. If a couple of jetski ran behind each other, the wake would be like this.
The the image capture later, as posted above, doesn't have the lines running as far out, which would more align with a vessel turning and so the lines are more condensed.
Can you pick up any footage from the sweep past North Cooly. The surf life saving base is there and they may have been running IRB or jetski's off the stretch of beach.
Bugger. You’re right. 2:05 mark here:
https://www.swellnet.com/surfcams/snapper-rocks/replays#/2018-06-09/139…
I’m amazed at just how much wake (i.e. how many lines of swell) was generated by a small boat. I suppose my preconception was shaped by my experience with wakeboard boats.
