Cottesloe Pier proposal 2016 - potential for sand aggregation study & new waves

Noel's picture
Noel started the topic in Friday, 15 Apr 2016 at 4:18pm

the WA Environmantal Protection Authority is seeking public comment regarding a proposal for a pier structure to be built off the end of the existing rock groyne at Cottesloe, for a restaurant etc.

https://consultation.epa.wa.gov.au/seven-day-comment-on-referrals/cottes... comments close 20th April 2016.
Media article - http://www.perthnow.com.au/news/western-australia/15m-cottesloe-pier-pro...

I downloaded the plan document from the website: figures part 1, and using google earth as a reference it appears that the planned footprint of the structure appears to extend approx 70 metres off the end of the existing rock groyne.
Given that this is a pier structure built on pylons I dont expect that this sort of structure has been built in an active surf zone in Australia in recent years, certainly not a public swimming beach. Its not clear to me which direction the prevailing near shore sand drift goes in that exact location but typically in WA its from south to north. But getting to the business end I expect there might be a wave bonus for local surfers if the usual sand aggregation occurs in the pylon area, in which case the cottesloe groyne will be effectively extended by 70 metres, or more.

I know friday afternoon is a bad time to float a new forum topic but does anyone have an beliefs on how this might pan out?
cheers.

thermalben's picture
thermalben's picture
thermalben commented Friday, 15 Apr 2016 at 4:28pm

Well, if the proposal is for 2106 then we've got ninety years to properly validate all of the modelling.

(sorry! couldn't resist).

Thanks for the heads up - I'll read the docs over the weekend. Love to hear some input from other users too.

Noel's picture
Noel's picture
Noel commented Friday, 15 Apr 2016 at 4:37pm

thermalben wrote:

Well, if the proposal is for 2106 then we've got ninety years to properly validate all of the modelling.

(sorry! couldn't resist).

.

haha... well it is WA after all.... title now fixed.

Clam's picture
Clam's picture
Clam commented Wednesday, 13 Dec 2017 at 6:55pm

How did this plan turn out,
Any updates ?
The previous two Cottesloe jetties got demolished by big swells during the last century .
https://cottesloehistory.wordpress.com/2014/08/07/cottesloe-jetty/

1. "Not many people realise that there were in fact, two jetties at Cottesloe! The photograph, snapped by Town Clerk, N. F. Haynes was taken at the opening of the Diving Jetty on 7 January, 1922."

2. "According to the Civic Centre News (V.6, No.5, Feb. 1957 p.1) the diving jetty, although greatly appreciated, was swept away by a storm four months after it was completed."

https://cottesloehistory.wordpress.com/

Noel's picture
Noel's picture
Noel commented Monday, 1 Oct 2018 at 9:41pm

Here's a report for those who get excited about these sorts of things:
http://cottpier.com.au/wp-content/uploads/2018/09/Wave-FINAL-301320-1419...
from: http://cottpier.com.au/
In their own words its a 'brief study' into the site bathymetry and swell, however, the glaring omission in my mind is the lack of any discussion around the implications once the pier support array starts to aggregate sand and become a 'soft' groyne.
Anyway, you dont need much data to bamboozle the typical City Councillor in these parts.
Anyone got any thoughts on this?

Noel's picture
Noel's picture
Noel commented Monday, 1 Oct 2018 at 9:51pm

my money is on this being stage 1 of a subsidised groyne extension.
So they build the structure, it starts getting hammered, closed to the public because of 'unforseen' high swell activity, sand build-up, leading to public outcry and 'oh woe is me' by the developers and the City of Cottesloe and the Stage Govt are pressured in to kicking in big bucks and override all normal due care and diligence and build a protective groyne around the 'highly valued' tourism asset.

And the result is a quasi marina by stealth.

Thats my reading of the tea leaves.

mikehunt207's picture
mikehunt207's picture
mikehunt207 commented Monday, 1 Oct 2018 at 11:52pm

Some very interesting pics of WA,s coastline , the country town of Perth.
Mudurup rocks has pumped out a few surfers since those photos were taken.

Jamyardy's picture
Jamyardy's picture
Jamyardy commented Monday, 1 Oct 2018 at 11:59pm

Hillarys Two hey Noel !

I don't see how this proposed structure would benefit waves at all Nth of it, it too far out in the deep (~5m depth).

Noel's picture
Noel's picture
Noel commented Tuesday, 2 Oct 2018 at 8:17am

My point is that its likely that it wont stay that depth for much longer. Piers are famous for silting up.

Jamyardy's picture
Jamyardy's picture
Jamyardy commented Tuesday, 2 Oct 2018 at 9:18am

I'm no expert on the subject, but I was watching the Huntington pier there a few years ago, it appeared to be deeper the closer you got to the piers themselves, waves were breaking on the beach sand bar long before they crashed into the pier. It seemed to be a deeper channel along either side of the pier where the waves wouldn't break (2-3ft swell), probably about as big as Cott would get in the bigger winter swells. Now if it was a groyne of rocks it would be a different story. Maybe science says otherwise.

Ray Shirlaw's picture
Ray Shirlaw's picture
Ray Shirlaw commented Tuesday, 2 Oct 2018 at 7:49pm

Ive seen it too,on some coasts(usually "Almost-Coasts"),really big rocks and even small headlands seem to create turbulence that just make a deep hole instead of creating a sand-trapping surf break. Anyone know anybody that's just got sick to fuck of no banks (ever)at their Local ,borrowed a kick arse bulldozer, and tried to make some? I'm not talking a Superbank,just something surfable. Or any smaller,accidental ones that could feasably be re-created?? Sure it wouldnt be permanent but it would beat spending 2.5 million on a Reef that didn't work.

Ray Shirlaw's picture
Ray Shirlaw's picture
Ray Shirlaw commented Wednesday, 3 Oct 2018 at 9:49am

P.s. sorry for hijacking this thread,I just thought I'd throw my2c in and try getting some answers to questions I've long been asking myself.

Jamyardy's picture
Jamyardy's picture
Jamyardy commented Wednesday, 3 Oct 2018 at 1:17pm

Hey Ray, there was a thread going a year or two ago, someone mentioned that the council at city beach I think used a wheel loader or dozer and dumped sand in near shore that created banks, only lasted a day or two before it got washed out I think. Not sure how to do a search on that.

frog's picture
frog's picture
frog commented Wednesday, 3 Oct 2018 at 8:31pm

If you bulldozed out a bank in a spot that is not where the "ocean wants it'. It will disappear remarkably quickly - matter of days. I have seen it happen where a 25 metre sand berm went overnight. But if you work with nature and bulldozed out next to a headland, groyne or on a natural kink in the beach that almost peels and where some sand tends to collect, or next to a semi permanent rip where current and rip patterns are at least a bit favourable it could hang around for quite a while. Councils and greenies won't be keen as they want straight lines and more sand on the beach not out to sea. Sneaky work on a moonless windy night with a mini exacavator might be a plan.

Frogg

Noel's picture
Noel's picture
Noel commented Saturday, 6 Oct 2018 at 11:06am

Sand transport, from south to north is the common theme on the WA coast, it actually starts down near Cape Leeuwin according to commentary I heard at coastal conferences. In one location its been measured/estimated to be in the order of about 70,000 cubic metres of sand per year, if I remember correct.
I expect that Cottelsoe is part of that flow, as evidenced by beach starvation around Port Beach.
Every jetty built on the southern end of ocean exposed westerly facing beaches in WA's history have silted up. There were jetties in places you wouldnt know about that are now long gone.

Jamyardy's picture
Jamyardy's picture
Jamyardy commented Saturday, 6 Oct 2018 at 11:49am

Hi Noel,

Maybe we are talking about two different things, I assume a jetty to something like what you see at Busso, similar framework to what they propose for that structure at Cott. A breakwall however, yeah I can see that they trap sand going up the coast for sure. You pretty close with the 70,000m3 movement, they reckon up at the cut and Mandurah they are doing 100,000 m3 of sand pumping to maintain the annual flows. I been consistently surfing up and down the WA coast for more than a couple of decades and really can;t recall a jetty in a surf zone to confirm silting, maybe they are out there or were, I just can't picture on in my head. All I know is when I stand at the waters edge and the waves lap up, I get the opposite effect of silting up, I guess somehow I liken that to a pylon in the surf.

quokka's picture
quokka's picture
quokka commented Saturday, 6 Oct 2018 at 7:40pm

Volcom ran an air comp at Scabs about 20 years ago where someone pushed some sand out using a dozer to form a small 'point'. This produced two very good A-frame banks either side of the 'point', I assume due to how it disrupted the long shore flow directing it back out to sea. Both banks were off limits due to the comp but they got cracking waves. Not sure how long the banks lasted, not very long I wouldn't reckon based on how short lived Perth banks are.
Have often thought how to get this going again these days, probably a bloody nightmare with councils and interest groups all having their say and public liability being front and centre.
If anyone out there has an idea of how to get this to happen up and down Perth's waveless beaches let me know.

Noel's picture
Noel's picture
Noel commented Saturday, 6 Oct 2018 at 10:28pm

Hey Jamyardy, you wouldnt be perhaps involved with this Cott Pier project would you? Or in the industry, consultant, perhaps... Just asking. For someone who seems so knowledgeable on WA coastal topics in past posts you are suddenly ... how can I say.. a little bit disengenuous.
Just asking for a friend.

Jamyardy's picture
Jamyardy's picture
Jamyardy commented Saturday, 6 Oct 2018 at 11:57pm

Hi Noel,

No worries asking, I have nothing to do with the Cott project, the first I heard of it was when you posted this. Mate I spent a coupe of years up in Perth back in the day (for work) never again. My life like many surfers has revolved around the ocean, and certain subjects about it interest me. If the pier silts up or not, it will have zero impact on me, just stating my thoughts/observations and what Iv'e heard, which may be inaccurate as I have very little knowledge on sand migration