Perth-Scarborough artificial reef/superbank

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PedroStanley started the topic in Thursday, 5 Dec 2013 at 11:53pm

The WA State Government are looking for ideas for Scarborough in Perth. Scarborough is all about surfing and what better way to celebrate Scarbs than an artificial reef or super bank right out the front? A well designed one that works.

Get on the website and tell the WA State Government its time they listened to Perth surfers!

Clam's picture
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Clam commented Sunday, 27 Aug 2017 at 8:00am

Hey Blowin ,do you like that curly hair of Jake Patos ? Thanks for the link to Luke Whylies interview , that is a gnarly story.

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Clam commented Sunday, 27 Aug 2017 at 8:07am

Ben said; "but essentially the recorded direction would be a mixture of swells bending around the northern side of Rott, plus some swell energy pushing in from the southern side."

Yep thanks ben , for the next 5 months im interested in seeing the direction average more south west .
That will complete a year long of monitoring of cott buoy .
It will be very interesting if the direction still remains in the wnw quadrant in spring/summer although i presume it will tend more wsw soon .
Since January its averaged more wnw than wsw, from my visual observations only .

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Blowin commented Sunday, 27 Aug 2017 at 8:11am

I dare say Jake Patto was dreaming of feeling the wind blowing through that same mop only a couple of hours ago.

Good story regards a near death up North. Let's hope that's as close as either of us come to experiencing it ourselves.

On another note - Looks like you've copped shed loads of rain in the back half of winter this year. Who knows , that much rain might have really had an impact on certain catchments that take a bit of fresh to create good sandbanks where they meet the ocean ?

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Clam commented Monday, 28 Aug 2017 at 8:55am
Jamyardy's picture
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Jamyardy commented Sunday, 3 Sep 2017 at 6:24am

It's interesting how Mandurah swells average more west than Cott swells. The average swell direction for calendar 2016 at the WA buoys are listed below. Above 8 seconds constitutes swell. Sea direction is typically 10 to 20 degrees or more further south on all buoys. Sourced from the DOT.

Cott : 254
Rotto : 250
Mandurah : 261
Jurien : 232
Naturaliste : 238
Albany : 215
Esperance : 222

thermalben's picture
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thermalben commented Sunday, 3 Sep 2017 at 8:17am

Swell waves defined as anything over 8 seconds?

Just goes to show how much more clarification is needed from the agencies producing this data. The definition of "swell" waves have elsewhere been reference as above 11 seconds, and sometimes 14 seconds, depending on region.

For example, at the School of Ocean and Earth Science at the University of Hawai‘i, they state:

"The persistent trades generate limited fetch trade wind swell ... peak periods of 9 sec".
"Strong Kona storms generate ... periods of 8-11 sec.. and can cause extensive damage to south and west facing shores".
"Hawai‘i receives north Pacific swell with ... peak periods of 14-18 sec".
"South swell occur in summer months and reach Hawai‘i with .. peak periods of 14-22 sec".

Point being, 8 seconds equals wind waves in Hawaii, yet it's defined as swell waves in West Oz.

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Jamyardy commented Sunday, 3 Sep 2017 at 8:53am

Point taken Ben. Other than cyclones does the East coast of Aus ever get swells with those definitions ?

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thermalben commented Sunday, 3 Sep 2017 at 10:26am

Yep, southerly groundswells frequently clock in above 14 seconds knows though size is usually heavily diluted away from exposed swell magnets. Every year we usually see a couple of long period easterly groundswells too between 12-16 seconds. Plus a half a dozen (or more) SE swells between 12-14 seconds.

Cyclone swells are rare and don't necessarily display very long periods.. if they do it's common that it'll be a small percentage of the overall mix. But we had a great NNE cyclone swell earlier this year that produced lovely waves at a handful of exposed north facing spots (points) in SE Qld. The Noosa surfcam vid on our Facebook page was from this swell.

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Jamyardy commented Sunday, 3 Sep 2017 at 11:36am

OK thanks heaps for the rundown Ben. Where do they delimit swell from seas, with swell buoys in other states, is it 11 seconds ? All I know is in WA they use 8 seconds, but I don't know why. Cheers.

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Clam commented Sunday, 3 Sep 2017 at 12:50pm

"It's interesting how Mandurah swells average more west than Cott swells. The average swell direction for calendar 2016 at the WA buoys are listed below. Above 8 seconds constitutes swell. Sea direction is typically 10 to 20 degrees or more further south on all buoys. Sourced from the DOT."
Cott : 254
Rotto : 250
Mandurah : 261
Jurien : 232
Naturaliste : 238
Albany : 215
Esperance : 222
-----------------------------------------------------
Hi Jamyardy, can you provide a link or directions where to find this info please?
I disagree with the stats and believe that cott averages more norwest than the mandurah buoy .
Interesting info to learn about nonetheless . Thanks

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thermalben commented Sunday, 3 Sep 2017 at 12:51pm

Buoy output isn't split into sea and swell states anywhere else in Australia other than WA. Everywhere else outputs classic oceanographical values such as Tp, Tz, Hmax, Hsig etc. I've been meaning to write to an article on this for ages (hi Clam!) and I'll try to get on to it soon. 

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Clam commented Sunday, 3 Sep 2017 at 2:25pm

Hi ben , cool sure thing , re article soon .
Im still studying the WA -SA- TAS buoys and look forward to further investigations .

Ps is there a link to jamyardys DoT directional averages ? Or can i find it myself on the DoT website ?

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Jamyardy commented Sunday, 3 Sep 2017 at 2:45pm

Hi Ben, WA does Hs(m), Tp(s), T1(s), and Dir (deg) for both swell and sea, however for the combined, which I assume is the same as the other states they only provide Hs(m), Tp(s), T1(s) but not Dir(deg).

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Jamyardy commented Sunday, 3 Sep 2017 at 2:56pm

Hi Clam, I hear ya, I have spent a little bit of time around the cott and Mandurah buoys and I know where they are, and it doesn't make sense to me either as to why Mandurah would show more west than Cott. All I can think of is the bathymetry in those areas may have an impact. Also I know as you move up the West coast the winds tend a little more easterly, but I don't know if that has a significant bearing on the swell direction (and obviously it does not have an impact on the Jurien buoy, however many outer refs block swell in that area. The only error I see is that, as you are probably aware from time to time buoys go on the blink anywhere from a few hours to a few days, and depending on the swells/directions etc on those days it would have an impact on averages, but I would not imagine to a large degree.

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Jamyardy commented Sunday, 3 Sep 2017 at 3:15pm

OK I just checked 2015 calendar year in case 2016 was an odd year. Cott buoy average direction was 246 degrees and Mandurah was 261 degrees. DOT recommends you verify their stats with alternate sources, however this is the output from their buoys. The Cott buoy is in 17m of water and the Mandurah buoy is in 30m of water. I think I read somewhere, probably on here that water bends/refracts quicker in deeper water ???

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Clam commented Sunday, 3 Sep 2017 at 4:10pm

Thanks jamyardy , yes its the bathymetry that makes mandurah average west rather than sw .
Presumably the continental shelf off the cape redirects the angle
Did you read the wandres pdf link yet ?

Rottnest Island will be partly responsible for the reason cott doesnt rate number 1 , in my opinion .
I can assure you that rottnest outdoes mandurah from my observations and the (man) direction defaults to w-wnw .
Cottesloe direction is a much wider scope .
http://www.transport.wa.gov.au/imarine/cottesloe-tide-and-wave.asp

Check the mandurah buoy now .
The direction is usually stable, whereas cott has a much wider scope .

http://www.transport.wa.gov.au/imarine/mandurah-tide-and-wave.asp

"Sea direction is typically 10 to 20 degrees or more further south on all buoys. Sourced from the DOT."
Can you please provide a link for this?

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Jamyardy commented Monday, 4 Sep 2017 at 4:25am

Hi Clam,

OK I gleaned through parts of the Wandres report. It is very interesting, it's long and some sections are out of my league. A couple of points to note in that report are :
Page 3 : states previous studies found the mean wave period off the inner Perth shelf to be 8.8s, and in the prevailing summer breeze, less than 8s. This may explain why DOT uses 8 sec to differentiate seas from swells. They probably don't want to call the freo doc a swell.
Page 11 : Offshore waves generally approached the shelf between 200 and 230 Degrees (summer/winter variability exceeded these boundaries). "During all seasons as the waves refracted across the shelf the direction changed towards a westerly angle (250 - 280 degrees), perpendicular to the contour lines of the sea bed."
What interested me here was "perpendicular to the contour lines of the sea bed". Now if you look at Fig 1. on page 3 (Bathymetry of the study region), the contours of the shelf offshore at Mandurah are roughly WWNW, and the contours pretty much at Rotto going north change to the WWSW. The report indicates that the offshore swells hit the shelf and want to run perpendicular to it's contours, so it appears very plausible that the Mandurah buoy will have more westerly directed swell than Cott/Rotto would.

OK just checked the buoys, almost identical direction for Mand/Cott, more south at Rotto.

For each buoy below I have put the average seas direction for the same period (calendar 2016) to the right of the average swell direction. Data source is the DOT. Treat it like a govt library, a source of info, it can be done.

Cott : 254 244
Rotto : 250 233
Mandurah : 261 243
Jurien : 232 221
Naturaliste : 238 220
Albany : 215 191
Esperance : 222 204

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Clam commented Monday, 4 Sep 2017 at 1:02pm

Jamyardy "OK just checked the buoys, almost identical direction for Mand/Cott, more south at Rotto."

Hi Jamyardy, good work you found the vital info already about swells perpendicular approach etc .

Although the arrow direction maybe the same on compass at moment ,its the the dot graph that is so much different . ( see 3 day history ) Mandurah is perfectly stable but cott is showing a very wide range .
Cott as usual is recieving more nw than mandurah !

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Jamyardy commented Monday, 4 Sep 2017 at 12:20pm

Cott certainly has more variation on the dot graph by a long shot. I reckon that Cott has more red dots below the West line than above the West line. Mandurah for the last couple of days has been pretty much on the West line. My guess for Cott is that it is picking up Swell from the South and the North of Rotto, hence it's variation in swell directions. Dunno for sure.

As for the perpendicular swell flow, and given the shelf bearings are different offshore of Mandurah and Cott, I would consider that the explanation as to why Mandurah see more West in swells than Cott, over extended periods.

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Optimist commented Wednesday, 18 Oct 2017 at 6:49am

In my travels, I have come across some great surf spots that simply had old pipes running a long way out to sea and spaced quite a few metres apart and not very big in diameter.The sand was always usually there at these spots as the sand got caught while it drifted across the surf zone and the best ones of course faced toward the predominant swell direction. Seems simple and very cheap to me and if you did them out of concrete with some holes in them , the sea critters would have a new home and the fishos could hit it when its flat.

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amb commented Wednesday, 18 Oct 2017 at 9:23am

What diameter pipes we talking?

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Optimist commented Wednesday, 18 Oct 2017 at 4:23pm

AMB...Just a few hundred mm... a quick way to start a bank would be to join long lengths of poly pipe together capped on the ends to float. Plumbers pipes are usually 6 metres each. 10 of those and you have a 60metre sand trap .Float the lengthy snaking beast out to the spot and leave a good gap from shore to allow crossflow inshore current..Take a bunch of besser blocks or anything to attach to sink it. There's plenty of rock over there as scrap. Attach the weights and knock off the caps...A few hundred bucks and a bunch of mates towing it out and you have a sand trap which can be as long as you like...Put them all along that stretch in perth and make lots of banks that extend out to sea...Might be a cheap fun way to try something and see what happens....

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amb commented Thursday, 19 Oct 2017 at 8:40am

Intersting, can think of a few isolated beach breaks you could do this. The places you have seen this done in your travels, were the pipes for creating banks or other purposes?.

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Clam commented Thursday, 26 Oct 2017 at 6:20pm

https://www.scribd.com/document/361976870/Scarborough-Reef-Feasibility-F...

Quoted: "the wave direction was found to be very close to due west (Figure 3-6).
The reef was aligned to the mean swell direction (272°)
derived over the annual wave climate."
-----------------------------------------------------

Jamyardy,
Can you provide a link for your information about the average directions please? ( again )
Ive searched the dotr site and asked a oceanographer about your info....
Can you share your source, a link ?

Jamyardy quoted;
"The report indicates that the offshore swells hit the shelf and want to run perpendicular to it's contours, so it appears very plausible that the Mandurah buoy will have more westerly directed swell than Cott/Rotto would..
For each buoy below I have put the average seas direction for the same period (calendar 2016) to the right of the average swell direction.
Data source is the DOT. Treat it like a govt library, a source of info, it can be done."
Cott : 254 244
Rotto : 250 233
Mandurah : 261 243
Jurien : 232 221
Naturaliste : 238. 220
Albany : 215 191
Esperance : 222 204

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Jamyardy commented Friday, 27 Oct 2017 at 1:24pm

Hi Clam,

The DOT sent me a spreadsheet with the buoy readings for every hour of every operational day, over 8,000 line items. I garned it for personal use only, one of the conditions is that it can't be passed on, or used for commercial purposes etc. I produced the average directions only, on here for discussion purposes, that's all. They do say you should verify the data with independent sources, but I don't know who else has buoys with data in WA.

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Clam commented Saturday, 28 Oct 2017 at 11:36pm

Thanks jamyardy .
Mandurah direction is stable, but cott has a way bigger scope .
Maybe that is the reason your average direction calculation , was distorted by that anomaly.

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Clam commented Friday, 8 Dec 2017 at 1:04pm

Amazing results so far ,
Im now in the 11th month of research monitoring the Cottesloe swell buoy.
Even now in December with howling seabreeze the swell direction still comes in west-north-west .
See the directional graph history for last few days .
Pity i cant post a screen save of this data.
Ps could anyone help with posting a frame?
Ben , Craig , guys please ?

https://www.transport.wa.gov.au/imarine/cottesloe-tide-and-wave.asp

And the swell was really quite south on the rest of the south-west coast

https://www.transport.wa.gov.au/imarine/comparative-swells-data.asp

https://www.transport.wa.gov.au/imarine/naturaliste-tide-and-wave.asp

http://www.srosurf.com/allwabuoy.html

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foamie commented Friday, 8 Dec 2017 at 6:17pm

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Clam commented Friday, 8 Dec 2017 at 6:46pm

Thanks foamie your a champ .
Hows those spikes, from the seabreeze in the arvos ?
Even still, the swell direction still comes around the Rottnest Island and refracts in .
Thats remarkable , and it was obviously a south type swell , by the sizes of the statewide buoy trends ; re. south coast

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foamie commented Saturday, 9 Dec 2017 at 2:09am

No problems Clam.
Yeah those spikes have been showing up recently - I've actually been out on a few of them. I don't know much about the cause/ effect/ accuracy of swell and seas data however I can say it seems they are just large wind waves breaking or coming from the south. Super weak waves but the current pushes you from Brighton to Trigg in about 15 minutes!

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foamie commented Saturday, 9 Dec 2017 at 5:30am

Oh and yes. I see your point regarding swell direction.

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Clam commented Saturday, 9 Dec 2017 at 5:50am

If it was ever going to turn pure sw ,
re: swell coming south side of Rottnest only it would be about this time of year,
When that counter current flows northward .
So even whilst all the odds are stacked against it, it doesnt seem to stop this due to the bathymetry surrounding rottnest island .