Reflective waves in the surf zone

thermalben's picture
thermalben started the topic in Saturday, 9 Jun 2018 at 7:49am

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 8:02am

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.

morg's picture
morg's picture
morg commented Saturday, 9 Jun 2018 at 8:47am

Newy point definitely gets them at certain times. They tend to throw unsuspecting SUP riders off too.

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 9:07am

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.

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Saturday, 9 Jun 2018 at 10:14am

Could it be from a boat?

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 10:27am

That’s a possibility, but there appears to be a lot more waves than what a standard boat wake would produce.

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 10:32am

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

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Saturday, 9 Jun 2018 at 10:38am

Check the top left of the kirra footage from around 3.50.

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Saturday, 9 Jun 2018 at 10:41am

Does look more like wind swell to me though.

John Eyre's picture
John Eyre's picture
John Eyre commented Saturday, 9 Jun 2018 at 11:33am

Mysterious......

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 1:35pm

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.

Craig's picture
Craig's picture
Craig commented Saturday, 9 Jun 2018 at 3:22pm

Weird, looks like boat/ski wake to me.. but again too many close spaced ripples.

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Saturday, 9 Jun 2018 at 3:29pm

3 skis going back and forth though. Sometimes against each other. could do it.

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 4:24pm

But.. if the skis were going back and forth, there’s no way that the swell lines would be so perfectly spaced apart.

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Saturday, 9 Jun 2018 at 5:19pm

They wouldn't catch up to each other and arrange themselves?

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 5:24pm

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.

lostdoggy's picture
lostdoggy's picture
lostdoggy commented Saturday, 9 Jun 2018 at 5:33pm

Final suggestion. haha
A humpback whale breaching.

thermalben's picture
thermalben's picture
thermalben commented Saturday, 9 Jun 2018 at 5:39pm

Saw four of ‘em today so I suppose that’s a possibility!

Jamyardy's picture
Jamyardy's picture
Jamyardy commented Saturday, 9 Jun 2018 at 10:28pm

Primary/secondary swell refracting on the sea floor ?

thermalben's picture
thermalben's picture
thermalben commented Sunday, 10 Jun 2018 at 6:11am

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).



gcuts's picture
gcuts's picture
gcuts commented Sunday, 10 Jun 2018 at 9:52am

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.

thermalben's picture
thermalben's picture
thermalben commented Sunday, 10 Jun 2018 at 10:15am

Bugger. You’re right. 2:05 mark here:

https://www.swellnet.com/surfcams/snapper-rocks/replays#/2018-06-09/139209

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.

thermalben's picture
thermalben's picture
thermalben commented Sunday, 10 Jun 2018 at 1:34pm

By a complete stroke of luck, a boat sauntered into view at our Trigs (South Oz) surfcam just then - allowing me to take some snaps on the surfcam. This shows the boat wake from an ideal angle. Nothing like what was seen at Snapper!

udo's picture
udo's picture
udo commented Sunday, 10 Jun 2018 at 1:41pm

oily 2 stroke trail ?

thermalben's picture
thermalben's picture
thermalben commented Friday, 15 Jun 2018 at 7:26am

Random snap from our Coolum surfcam shows some interesting features - is reflected wave energy off the sandbank leading to the formation of a quasi-standing wave in its lee?