Marine biology and surf Science

[ralphy]

Hey guys well firstly being from WA i dont have intimate knowledge of the coastline over there, other than from my readings and from the 2 times ive being over there. So here goes.

Firstly the southern Goldy points get there sand from the southern rivers like the Tweed which pump out a fair bit of sediment. This available sediment combined with the dominant S/SE winds and current help push the sediment up and around the points, and deposit them out along those perfect banks that make up the super bank. So as long as those rivers keep flowing and those SE lows keep forming and pushing up along the coast, the Goldy points will always have banks. (Climate change, reduction in rainfall, removal of sediment from the river etc could all have an affect on this over time but i will talk about that another time.)

As for the beaches up around Surfers, well thats a different thing altogether. The whole Gold Coast is pretty much an island of sand (Pacific on the east, Canals and rivers on the West) so is a very dynamic area that is constantly changing and moving around under the affects of waves, currents and wind.

Before development, the Gold Coast would have shown a very different coastline each day. Beaches would have moved a great deal more than they do today. In a general beach cycle, sediment is cycled from onshore (beach/dunes) to offshore (banks) and back again. So back then there would have been a great deal more movement in sand from the beaches into the ocean and vice-versa.

Since development, the amount of sediment available to the beach cycle has reduced a great deal. Compared with what there would have been prior to development, there is really "no" sediment for the beach to cycle. So there has been a reduction in the amount of sand available to make sand banks, hence why there may appear to be less quality surf banks. As the development increases along that bit of coast, the sediment available to the beaches will only reduce more (unless there is beach nourishment, which is a fix of the symptoms, not the cause).

The high rises along the Goldy have also have changed the local winds. For example, when i was there in April, the wind was fresh out of the South. When i went for a walk through Surfers i noticed that the flags along some of the roads were showing the wind blowing direct West, while a bit further down the road another showed it blowing from the East. This just shows that the buildings have caused the winds to move around in between them. This may have an affect on the position and quality of sand banks adjacent to high rises. A southerly wind is one that should be moving around the sediment & shaping the banks, but if at certain parts along the beach, the wind is blowing in a Westerly direction then the banks may not be shifted around.

Cal, I hope that answers your question a bit. It would be very interesting to have conducted a study into local wind patterns before development and compare them with local wind patterns now.

[captain6230]

can u answer a question for me? how come everywhere else has pumping barrels and my local has 2 foot closeouts?

however on a more serious note however, how come some waves break on amazingly shallow reef where others have a more deep water set up going yet there similar size? i regularly surf a wave that i wont name but breaks onto ridiculously shallow coral yet the beach break next to it and a little closer to shore is deeper and the waves are the same size?

[Cal]

Awesome! Thanks Ralphy. Gets you thinking about how good it would have been 100 years ago or more?

Climate change well thats another big issue hey....

[doclach]

Brilliant stuff Ralphy - that woulda taken a while to write - so goodonya.

the thing I don;t understand is the wind thing... never really got to ask anyone b4 and have always wondered... I get that it will cause surface waves and little deeper, but can wind coming off, say the Goldy foreshore, cause water movement deep enough to affect sand bottom (sediment) movement close enough in to affect shorebreak patterns?

Will take my turn after Caps' question (ya second one Cap - not da first one ya funny bastard).

[ralphy]

Ok Cap, pretty complicated answer but ill give it a try.

Firstly i will get all physics on ya. Waves as they approach the shoreline will start to grow in amplitude (height), once they get to a depth about 1 half of the wavelength (length of the wave, period has an affect on this). The wave will break when it reaches a water depth that is approx 1.3x wave height.
Well i got that bit of background out the way.

Now to answer your question Cap, i am going to have to take a few guesses & make some assumptions, please correct me if im wrong.

Say for example the beach you are talking about is an East facing beach with headlands at either end. The beach break is at the northern end and the reefy is at the southern end. Given a typical SE swell, the breaks to the northern end will always have "bigger" waves as the swell can penetrate into the bay without much affect from the headlands. The breaks at the southern end (the reef) will only receive smaller waves as the headland at the southern end will act upon the swell, refracting (bending) the swell around towards the reef, hence reducing its size.
Refraction of swell and the affects of headlands etc probably has the most affect upon swell size.

Another reason for the reduction in swell size could be due to the bottom contours. For example, the beachy may have fairly deep water offshore from it, allowing the swell to maintain its power as it moves towards the beach. The reef on the other hand may have shallower water offshore from it, hence causing a reduction in the power of the swell as it "feels" the sea floor more when heading towards the reef.

Any offshore trenches, holes in reefs etc can also act to make the swell bigger in some parts than in others. These deepwater trenches can act as swell amplifiers, as the swell can move through these parts without "touching" the sea floor.

[ralphy]

Doc, the main affect that the high rises could have would be to reduce/change the direction of the bank making winds. These are predominantly the S/SE that blow up the coastline.
For most banks to form/move around, a S/SE wind needs to blow strongly for a fair time (a day for example). The affect that the closely packed high rises could have would be to reduce the strength/direction of these winds along certain parts of the beach, hence reducing the affect on the surface of the ocean and in turn reducing the movement of the sediment by waves/currents.

[doclach]

Cheers Ralphy - i didn;t realise the wind was that critical to the banks.
will be interesting to see what has happened t the banks here at my breaks in sydney after the storm swells they were just sorting some nice stuff before - luckily my fave reef doen't blow around too much

[ralphy]

Further to the climate change stuff, yeh its a pretty big issue that will probably have the greatest affect upon the surf in the future.

Myself, i would like to say is that that climate change is not caused by humans and is just a natural occurance that has been happening since the beginning of time (scientifically proven). What we have done may have an affect upon the speed at which it happens but it is all natural and is going to happen no matter what we do. The media has taken on the whole "end of the world" thing & blown the whole thing up and is scaring people. So there you go, you can stop worrying about something that is going to happen no matter what we do

So take QLD for an example. If in the future, rainfall is reduced, like is pretty much occuring throughout the southern parts of Oz, then this could have a dramatic affect on the quality of the surf. Your points are made up of the sediment that is bought down by the southern rivers. If rainfall were to reduce, hence river flow reduce, there is going to be a great loss to the amount of sediment that is available to those points.
Take away the sand pumping and this probably would be happening during El Nino years, when there is a lack of rainfall. You would have to go chase up locals who surfed the points before they started pumping to determine if this was the case.

[doclach]

Yer, climate change is a thing. One of my friends flies to Europe regularly to participate in UNEP talks (United Nation Environmental Program) talks. Is pretty big stuff. Insurance companies, interestingly , are having to make major policy shifts to accommodate climatic shifts - cos they have billions of dollars invested in complex situations which many, many actuaries are busy trying to sort from their end of numeric understanding gained from the science data. Lot to it.

With man, I sometimes wonderif the fiddling of sandbanks is ever reversible. Look at a recent posting in the Courier Mail, it starts with [quote]Gold Coast surfers launch website www.kirrapoint.org on Friday to broaden the campaign to fix what was once Queensland's best surf break.
They believe its demise because of sand dredging could be losing the economy millions of dollars from the surf tourism market.[/quote-yer, never mind the locals. Full story is at:
http://www.news.com.au/couriermail/story/0,23739,23862793-3102,00.html

Ralphy, do ya reckon that even with the dough and resources they hope to raise - do ya reckon, theoretically, that man can restore such a natural 'freak' break that nature took years to build and effectively they just pumped away?

[ralphy]

If they stop pumping and let nature take its course then yeh Kirra should return to what it was like. Nature always works in equilibrium, so it will always do what is needed to get back to that equilibrium, which before our involvement was cracking Kirra and no superbank. But the trade off is that the Superbank will not be so super anymore. It will take a few years for nature to run its course too, so while Kirra will be steadily improving, the superbank will be steadily degrading, hence causing more crowding etc.
So it depends on what the people really want??? Do they want a more consistent and longer break that can accomodate more people (attract tourists $$$$) or do they want 2 less consistent/shorter but higher quality waves???

[doclach]

yer, good stuff Ralphy, you are an insightful man. I just wonder though when equilibrium has been so far thrown out - will there be a new equilibrium for nature? Mebbe, just mebbe - if they change it again there could be no superbank and no mega Kirra. Is the funny thing of messing around with complex stuff - like water flows, winds and channels - stuff which on paper can look so simple... but ulimately... isnt eh?

[captain6230]

ralphy u are amazing.....
haha thanks for that mate uv explained alot

[ralphy]

No worries Cap, hope it helped.

Thats the exact reason i said "should" Doc, as once the equilibrium is changed there may always be another different equilibrium, like you have said. More than likely it will return to something resembling what it was but it could also go the opposite way and leave the Goldy with two rubbish waves. I think they may have to let go of the dream of having Kirra like it was 20/30 years ago, yeh they might get it back to something similar but there is a very big chance that it may not ever get back to what it was.

Changing the natural environment is like smoking cigarettes, its relatively cheap and easy to do, but the results can sometimes be very expensive & extremely difficult, if not impossible to fix.

[JONNO313]

AHHHHHH personallyh. I would want hi quality and consitant waves with less ppl. but we cant have everything. HMMM Superbank is good but so many ppl. its only good wen its big enough that not everyone goes out. Is a long ride but even then has a huge sweep. Quality wave sounds like the go.

[JonoIsMad.com]

south straddie on a 6ft light offshore day

with not a single person out and you would have me made........

ralphy that was a good read....so well informed on this riptide forum these days