Forums > General Discussion   Shooting the breeze...

Winter coastal errosion.

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Created by busterwa A week ago, 10 Jun 2019
busterwa
3677 posts
10 Jun 2019 7:11PM
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Lots of complaints over here in West Aus People blaming big business for dreading big blame game... allways seems to be the same each year. Wind washes sand onto beach during summer. Winter always a combination of high tide and fronts moving forward to land bringing in large volumes of water causing super high tides . Swell often high wrapping around into areas which havent seen much movement Lucky the moon isn't out else people be having kittens.

So is high tides followed by large fronts hitting the shoreline during winter really something new? a high tide paired along with a 30-40knot storm front will do some sort of coastal damage regardless.
ps: wish channel 7 would swap the 19;30 home and away slot with channel 9`s 17;30 come dine with me show . Its heaps better.

cauncy
WA, 7229 posts
10 Jun 2019 7:31PM
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No but things are certainly on the move, 13 years ago you could only get around the point at my local on a low tide to access 20klm southbeach, weve seen plenty of erosion but some have been of our own doing here, our marina wall is a perfect catchment of swell concentration from the nwesterly storms, if you lived here it really defies logic, youd have to be a f##KTARD to design and construct it,
lancelin is getting chewed out, i passed information on from my background of sand bag defences inc geraldton but they just ferry truck after truck of fill in an attempt to halt, un retained sand washes away its a simple as that, a couple of good fronts will see lano sea rescue in the sea,
on a plus side that house you bought that your neighbour blocked your view will be gone soon and you wont have to watch wank on tv

busterwa
3677 posts
10 Jun 2019 8:19PM
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Just a bit disappointed at the media. Was like interviewing vegan to review the taste of steak.

Razzonater
1888 posts
10 Jun 2019 8:37PM
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This will be a great thread.... I have popcorn in microwave..

Took a boat up river on Saturday the water level in the river was 2 metres higher than the tide, proper storm surge. For example at e-street in front of the left bank the water level was maybe 300mm below the jetty walkway. On our higher spring tides there is still 2 metres to the walkway, the storm surge itself at Cottesloe and as seen on the news has been pushed up higher about two metres more than the tide of a metre. It has done this in the past but we haven't had four fronts in three days pass the coast for a long time.. once the fronts have gone the water will recede however will take some of the beach with it as it already has........

Coastal erosion in west oz is managed poorly,, sand bags are effective as are sand/concrete bags but we are just far to disorganised at council level to even implement anything of the sort...

Multiple curved sandbag walls similar to the hexagons on a beehive would be super effective and actually trap some of the sand as it rises up and down the coast however this would deplete sand movement in other areas....

One thing I find extremely controversial is coastal dune stabilisation,,,, we have built out the top of every single dune from mindarie to Fremantle, twenty years ago this was more Fremantle to watermans with some good loose dunes in between......

historical summer easterlies would pump tonnes and tonnes and tonnes tonnes of sand onto the beaches, this doesn't happen anymore , hence when we get any form of storm surge and the associated scalloping slop the sand gets chewed away and never replaced.....

One thing that isn't discussed is sand particle size,,, it matter far greater than people realise,, the dune sand has a very different particle size to that of the coarser beach sand, dune sand need sand to be mixed with beach sand for many reasons but all of them relate to sedimentation and settling,,, the smaller particles pack in between the coarser ones and actually make the banks stronger and more resilient to coastal drift of sand... it may seem counter productive but imagine a glass of marbles and the gaps between them, now pour in a high calcium fine product such as dune sand... it will pack and harden in there eliminating any losseness between the oversized particles.....

This is very easy to prove ,, think of the best beachies you have ever surfed in the state and now place yourself there,, as you look around in your mind there are a few very apparent things
1) no sand dune stabilisation
2) no excessive buildings and roads in the 1-2km of coast
3) no man made groynes or harbours
4) all of these places are exposed to far more swell than the Perth area yet seem to go through the high tide low tide erosion and always have sand on the beachies after storms.

(Above is personal opinion and may not reflect the views of government, greenies or other meddling forkwits)

mazdon
925 posts
10 Jun 2019 10:40PM
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The residual and surge above predicted tide is captured at Fremantle and at barrack street - and put online daily (usually)

www.transport.wa.gov.au/imarine/tidal-movement.asp











Not sure about 2m surge razz, but I wasn't there

mazdon
925 posts
10 Jun 2019 10:49PM
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I would say the beachie situation you describe is more impacted by:
1) bathymetry
2) geology (sand type available)
3) incoming energy profile
4) sources and sinks of sediment for that particular beach
And it's all inter related

while I agree with most of the other points near the end of your post, I think they are correlation rather than causation.

i submit:
a) dbah
b) superbank
c) the wedge

for your consideration sir

Razzonater
1888 posts
11 Jun 2019 7:10AM
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Good points Mazdon, and to some degree I do agree, however,

The sand for both snapper and d,bah is pumped from Letita spit, this is not natural sand movement, prior to the comps and after big storms the sand will be pumped continuously for days, this is actually a bit of a kicker to assist my philosophy.... the location the sand is pumped is comprised of river sand and coastal dune sand , all of which drifts up the coast much of it from sand dunes.

Additionally as displayed in the below photo it can be seen that on the southern side of tweed river there is limited coastal development for several kilometres so I don't think that you can utilise snapper and d,bah as a normal coastal situation as it has been heavily tampered by man..
The fact 99% of the sand that is pumped there is from non developed coast and how the banks there are quite resilient to storms probably only adds further weight to my point?

not so sure about the wedge set up you are referring to Mandurah? California but neither of these places in my opinion are considered a "a class beachies" they are both refracted waves off breakwalls and again man made,,

I am more picturing myself standing on a beach down south or up north looking at dunes,,,,



Your storm surge points do hold a lot of validity and as can be seen on your supplied chart it is the predicted surge, this is where it gets tricky and I don't really know how it happens but....below pic is Claremont jetty from sat night, whilst a terrible photo this boat on a normal night would be sitting at least a metre below the jetty, (on a high tide) there is at least a metre above to the gunwhales also you can see the jetty is wet this is from the water underneath slapping up.
at least two metres of storm surge....I actually had to do a calculation to get under the first bridge in the river coming upstream. My calc with the surge and tide as displayed in the chart left me with 3.8 metres above my roof, in reality it was no more than 1.2-1.5 this is why I was so perplexed that not one website had any info in regards to the "actual"




Ian K
NSW, 2841 posts
11 Jun 2019 10:46AM
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I'm trying to figure out what's going on at South beach. Fremantle, well just south of the Cockburn Council high risers. Noticed a truck or two dumping sand there in september on top of a wide ledge of sand about 3-4 metres above the water level. No vegetation on this ledge of sand as there would be if it had accumulated by wind over many years. Surely it wasn't all brought in by truck?

Any way it's gone.

16th April 2019 - half of what was there in September had gone.
Yesterday it's almost back to the vegetation line.

Anyway just curious. Can't see any geophysical process that might pile sand here quickly enough that it's not vegetated. If it was all trucked in surely they would have known it would be gone first storm?

Ian K
NSW, 2841 posts
11 Jun 2019 2:10PM
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Bumped into a local this morning who tells me that the sand was in fact all trucked in. It's dredged out of the pleasure boat harbour 2km to the south at great expense and consumption of fossil fuel. second time they've done it. So it's not a natural event, not a misguided attempt to reverse the effects of rising sea level. Just a convenient way of disposing of excess fill.

Mark _australia
WA, 19208 posts
11 Jun 2019 12:37PM
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^^^ Don't think it is rising sea levels necessarily at that location.
It was caused by the construction of the development just to the south about 15yrs ago that stuffed it up. I was a part of writing WWA's opposition to it as the sand flow change would ruin Crazy Waves for us (and it did) and now its also screwing up the shoreline.

$$$ is far more important and "public consultation" is a tick box then do whatever you were going to do anyway.

Foghorn
WA, 147 posts
11 Jun 2019 12:59PM
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Crystals beach at pt peron was ruined a decade ago by boat ramp developement and dredging there. What they take out simply washes back in to the boat launching area.Not rising sea levels to blame but dumb ass Rockingham council .

jbshack
WA, 6820 posts
11 Jun 2019 2:21PM
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I wonder how the locals will like the idea of a offshore rock wall built at Cottesloe to protect the club house..As mentioned on the news story..

JoeMc
WA, 92 posts
12 Jun 2019 2:39PM
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Darkslides across the beach are causing the loss of a lot of sand!

Underoath
QLD, 2340 posts
12 Jun 2019 5:42PM
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I destroyed Noosa doing that!

Buster fin
WA, 1902 posts
12 Jun 2019 4:19PM
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Select to expand quote
JoeMc said..
Darkslides across the beach are causing the loss of a lot of sand!


Say whodey howdy what now?

quikdrawMcgraw
1111 posts
12 Jun 2019 6:42PM
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It comes and goes

cauncy
WA, 7229 posts
12 Jun 2019 10:19PM
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Tide and time waits for no man
the wind and swell sculpts our coast

Mark _australia
WA, 19208 posts
13 Jun 2019 1:41AM
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Select to expand quote
cauncy said..
Tide and time waits for no man
the wind and swell sculpts our coast


So rich men with their big dollars
Come with a development plan



(I see a whole poem thread.....)


lotofwind
NSW, 5054 posts
13 Jun 2019 11:02PM
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hmmmmmm, so WA is eroding away and getting smaller,
Seems there is a positive to global warming and rising sea levels.

But seriously though, the rising sea levels are causing more erosion problems, well derrr, some small low islands around the world have already gone under and locals have had to relocate. So yes, rising sea levels are making a big impacted, as well as development.



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Forums > General Discussion   Shooting the breeze...


"Winter coastal errosion." started by busterwa