Sand Banks

Nick Bone's picture
Nick Bone started the topic in Thursday, 14 May 2015 at 8:04am

A very general question which probably has alot viable answers but im just wondering how sand banks actually form up at beachbreaks? What are some contributing factors that lead to bank development?

Specifically, I live on the Mornington Peninsula and at one end we havr Gunnamatta which gets better quality and more consistent sand banks whereas down the other end at Portsea it struggles to form any decent banks.

Is it to do with the bathymetry from beach to beach? Is it the way the coast faces to swell direction. The Peninsula faces pretty much straight on to predominant swells but Gunna and Portsea are angled differently ever so slightly. Is it to do with the minor rock formations on the shoreline which may direct sand flow?

Any insight on this matter would be muchly appreciated! I understand there probably a definitive answer but i would love to hear any theories etc. on it!

Cheers!!

VICLB's picture
VICLB's picture
VICLB Wednesday, 20 May 2015 at 11:58am
southey wrote:

Vic lb your proving yourself the right royal wanker . Nobody likes a self righteous tosser . And it doesn't matter where u live your still a tosser . In the times I enjoyed that region , people didn't tolerate " tossers " like u ...
People just reminded you to be a little more discreet , and you go and shit in their direction . No wonder I don't frequent the water there anymore , because even " new locals " like you are dickheads . Way to shit in your own nest . All I hope is that some " Ol' school " no nonsense guys read this work out who you are and fade you on your rice bubble at every opportunity at all these low key spots you keep talking up as " your playground " , your not impressing any one , loud mouths aren't legends . Best you keep your act local .
PS , I have a fair idea who you are , and if I'm wrong then pretty sure goofy does .

thumbs up!

Craig's picture
Craig's picture
Craig Wednesday, 20 May 2015 at 12:31pm
Nick Bone wrote:

A one Mr. Alex Zadnik may have got wave of the day during one of the sessions.

Yeah, we heard about it alright, sounds like it was pumping!

alexz's picture
alexz's picture
alexz Wednesday, 20 May 2015 at 12:44pm

Thanks for pumping up my tyres Nick! From memory you got a pretty good one on the Sunday. I was pretty happy with my score on the Saturday.

I'd say you're on the money with the orientation of Gunna versus Portsea impacting on bank quality, along with the overall shape of the beach. Gunna is a little more curved and broken up with rock sections that probably facilitates the formation of gutters more readily, and the orientation (more west facing) probably means SW swells don't hit quite as straight on.. Portsea's beach is pretty straight from LB's through to Sphinx, plus faces due SW for the most part. Also different offshore set ups, which probably contributes as well.

All in all a number of factors probably play a role.

Might see you back out there this weekend...

Nick Bone wrote:
thermalben wrote:
Nick Bone wrote:

But now it seems Portsea is stuck on groundhog day with sandbars parallel to shore with the occasionallllllllll corner.

Six weeks ago Portsea had unreal banks, that were perfectly visible on our surfcam (see image below). Was like this for about a week if I recall correctly.

Yeah Ben, it got a good right. But it lasted about a week before getting real straight again. Not to mention how long that took to take shape haha.

After two weeks of howling onshores and macking swells, there were some good waves around the peninsula too this weekend just past. A one Mr. Alex Zadnik may have got wave of the day during one of the sessions.

mitchvg's picture
mitchvg's picture
mitchvg Thursday, 21 May 2015 at 9:51am

No one else thinks the gradient out to deeper waters has much to do with it? I haven't looked any closer than the 20m contours and google sattelite images, but it looks deeper out off Gunnas. As it does at wooly; not sure about the others but (liptrap, etc)

Nick Bone's picture
Nick Bone's picture
Nick Bone Thursday, 21 May 2015 at 12:07pm

Im not too sure mitch. Of all the people ive chatted too about it, a majority share of the blame always seems to go the plant out of the dunes. The last 5-7 years have been pretty pathetic at Portsea. I hope that its not that the beach is rooted but rather in a cycle phase (wishful thinking).

Although Portsea is a straight beach it has a rock formation (hueys) that runs perpendicular to shore albeit rather holey, i dont see how that during summer easterlys and winter westerlys that hueys cant act as a natural groin and catch sand on either side as per season?

The fact that i know first hand that Portsea used be to a much better beach drives me nuts that i cant understand why this occured and if its possibly for a reverse action to happen?

But i guess the answers will always just be speculation and never convlusive simply because there is so many varibles and factors that make an impact.

crip's picture
crip's picture
crip Thursday, 21 May 2015 at 12:27pm

Another possibility is the contemptible channel dredging at The Rip several years ago. This certainly would have affected tidal currents in the area, so I wonder if the effect has extended as far as Portsea Back Beach? It certainly screwed things inside the Bay. As an aside, I wonder if Quarantine was affected by the dredging?

Nick Bone's picture
Nick Bone's picture
Nick Bone Thursday, 21 May 2015 at 3:38pm

I dont think the dredging has had as much effect on the ocean side as a opposed to the bay. Portsea has had visible changes to the beach (the whole thing nearly disappearing!). There waves further down the track towards the heads that are still producing quaility waves consistently. They are sand dependent but definitely a different set up to Portsea, more of a enclosed bay which believe to be the reason behind the consistency.

As for the heads. Thats still doing its thing. Ghe only thing thats changed out there is the 80 plus people on it and i dont think the dregding had anything to do with that ;)

Craig's picture
Craig's picture
Craig Thursday, 21 May 2015 at 3:45pm

Yeah, and I hear that because of the dredging, when you have large storm swell events, erosion on the front beach at Portsea has increased. More energy entering in through the bay.

adam12's picture
adam12's picture
adam12 Thursday, 21 May 2015 at 5:23pm

Yo Craig, not really more entering thru the heads. just a deeper funnel inside the bay pointed at Portsea front beach. The digging was more inside the heads.
Yo Crip, Corsair (as it's called over the other side) didn't change, same wave.

floyd's picture
floyd's picture
floyd Friday, 22 May 2015 at 9:43am

Its a good thing the WOTD from yesterday isn't on the Mornington Peninsula coz it wouldn't be a secret and it would be named here

crip's picture
crip's picture
crip Friday, 22 May 2015 at 1:30pm

Yeah, like there are secret spots on the Peninsula!

Ok, there are spots that aren't as well known as Gunna, Rye or Portsea, but naming them or even giving them a show on WOTD is not really going to change things.

Let's face it, most of 'em are a bit of a walk in to check it out and most are fickle. Unreal when they turn on, but you have to know when, what tides, what swell, what wind and how to get in there. Don't get them right and you'd wonder what the fuss was about.

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 31 May 2017 at 5:54pm

hopefully this gets picked up again..

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 31 May 2017 at 6:04pm

http://www.ozcoasts.gov.au/conceptual_mods/beaches/ShortJCR06.pdf from freeride, about half way down theres aerial photos of 6 beaches and it has photo 'C' labelled as the Mornington Peninsula, yet im 99% sure it aint. Ill happily admit i havent exactly read the article too throughly, but i would like to know what beach Portsea would be classified as?

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 31 May 2017 at 6:04pm

i tried to read the stuff at the start but my brain is acting like a brick and not a sponge

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 31 May 2017 at 6:07pm

also, the bathymetry of Bass Strait. I dont understand how we actually get anything other than a SW swell. I mean the swell source would have to originate inside of bass strait? Any swell with semi decent period generated from out side is gonna fell the Otway Shelf and Otway depression and get focused SW??

lostdoggy's picture
lostdoggy's picture
lostdoggy Wednesday, 31 May 2017 at 6:17pm

Photo 'C' looks like Woolamai with foots in the background.
Actually I'll go ahead and say 'it is' Wooly.

Nick Bone's picture
Nick Bone's picture
Nick Bone Wednesday, 31 May 2017 at 6:30pm

haha. getting old google earth and getting the angle of the photo going blew my mind. i never realised that woolys was so thin there.

but that would go on to say that Woolmai and therefore most beaches around there and peninsula are 'rythmic bar and beach' i guess