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Just wondering. See, for eg. pettycur bay beach most of times is rough [read unsuitable for landboard] but from time to time it can be smooth as a pool table!
Has anybody got an idea what makes it rough/smooth and is there any way for how to predict it? I'm guessing it's wind-tide combination but I'm just guessing. If I would only live next to the beach I would make my own research to find it out. But I don't. So here I'm asking.
cheers
rob

I think you are spot on Rob with your thoughts. If the wind is high is makes the water rough and this in turn cuts up the sand. If there is low wind while the tide is going out then the beach will be smooth.
I guess the only way to predict it is watch the forecast and combine that with the tide going out.

o.

Yeah, that is what I was thinking, but I also though that wind direction might be the key as well, like if the wind blows along the beach waves comes back to the sea at curved angle which is a bit similar to movements that you do when polishing things. Last time I was on the beach in the morning it was smooth but wind history said it was windy during night time, but wind has ben angled at 45-60 degrees to the shore.
So my thesis is : no wind or moderate wind (waves) at angle make beach smooth while high off/onshore wind makes it rough.
Prove or fail my logic please.
If I find out some more, will update topic

www3.interscience.wiley.com/journal/1196...RETRY=1&SRETRY=0

Having read the abstract there - and by adding some fluidmechanics thoughts to it I have the following hypothesis.

Ripples are caused when there are vortexes caused by water travelling in different directions. I.E water flowing back out from the last wave will travel under the next wave, the viscosity (read stickyness) of the two sheets of passing water will tend to cause a long column of rotation in the water. A bit like a tornado on it's side. This vortex action would disturb the sand below it, causing a ripple.

Now, the extend / depth of the ripples (in my opinion) depends on a few things. One of which being the speed difference in water flows (in and out). If the sand is relatively steep, the water will flow out quickly causing powerful vortexes (or undertow, if you prefer). A strong onshore wind would push water further inshore too so you may find (if my thoughs are reasonably accurate) that a strong onshore wind with a tide going out would cause a ripply beach too because water would be pushed over the top of the outgoing tide by the wind.....

Things to maybe look for would be...

* Ripples on steeper parts of the beach
* Ripples on days where there has been a gusty/strong onshore wind ontop of an outgoing tide
* Smooth areas of beach will be like islands, raised above the ripply bits - i.e the waves coming in will flow over the top of this sand, but then fall off the sides to the lower parts, rather than backtracking. You may also find that the shape of the ripples aruond these smooth bits are curved around the outline of the smooth area, like contour lines on a map.
* Shallower gradient beaches will have smaller ripples.


I could be totally wrong with that - it's just my thoughts from picturing a beach with water going over it, taken straight off the top of my head lol so could be improved I think. Anyways - back to studying, the joys...

Actually you pictured it nicely James and I realised I've seen the process not once. As for good example- there are always ripples where a stream join the sea!
Thanks guys, I will keep an eye on winds/tides and I hope next time I'll be at pettycur bay sand will be looking exactly as predicted

Another good example . Keep us posted as to whether my thoughts have a shred of accuracy.