Author Topic: Beach - a hypothesis  (Read 9295 times)

Offline Jimbo

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Beach - a hypothesis
« on: October 17, 2015, 01:30:27 AM »
A distinguished local who cannot be named said to me that he/she thought that the extreme narrowing of the beach at the Havana/Mango point was a result of construction work there - extensions to Mango and Delfino Blu.

I could not see how this could happen, but many of us remember the wide beach there, the football pitch below Havana, even the cabana on the beach. The beach is not (to my recollection) significantly narrower anywhere else, and was almost visibly widening at the other ends this autumn.

So I've been pondering this. Why would the tides attack this sector more than the others? Variations in the tidal drift could perhaps do it, and that was the theory presented to me. But we would expect those to be random and on average cause a small coming and going. What we are seeing is consistent erosion in one "hot spot." What mechanism could consistently produce this effect?

The beach, as we all know, at Agios Stefanos is very flat, with a low tidal range. Low points on the land side of the beach will be more vulnerable to inundation.  Even a 0.5 centimeter lowering of a region could cause more aggressive tidal influx and hence more erosion.

Concrete weighs a lot. The geology there is sandstone. I'm not a geologist, but I can imagine that sandstone may be subject to compression. Is it possible that several tons of concrete close to the beach could be lowering the beach level just enough to permit attack?

If anybody knows a geologist or structural engineer, please pose this question. Meanwhile, I will send it to New Scientist - that's a free way of getting expert advice.

Should this theory be correct, that sector of the beach will not recover. It may be rubbish, of course. But there has to be a rational explanation.





Offline Gillywoo

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Re: Beach - a hypothesis
« Reply #1 on: October 17, 2015, 06:45:45 PM »
Sounds very plausible to me!

We stood on the steps above the Havana Bar, watching the waves rolling in and out.

Large rocks have now been placed on the sand in this area - I think they were placed there last winter.

When you watched the waves, as they hit the rocks they became distorted and ebbed at an angle instead of flowing back and forth. So no doubt the sand below was being pulled away in a different direction to the rest of the beach.

I wonder if this may also be an added reason?

Offline Lesley

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Re: Beach - a hypothesis
« Reply #2 on: October 17, 2015, 07:13:06 PM »
Or another subject is the new harbour responsible??????

Offline Jimbo

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Re: Beach - a hypothesis
« Reply #3 on: October 18, 2015, 02:31:21 AM »
I've hear the "new harbour" argument, but I don't see how that could affect the small zone in front of Havana/Mango. It would be interesting to hear a reasoned analysis.



Offline abbo

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Re: Beach - a hypothesis
« Reply #4 on: October 18, 2015, 01:32:12 PM »
hmm, i've stood there too a few times this year mulling over it. the thing that fascinates me is the drop in height over, say, 5 years. the Havana was never that "high" then. The football pitch was maybe 2 feet up, its dropped 5/6 feet.

There has to be a cause, the building work seems a logical cause given the pinpoint area, but why is bemusing. Logically you'd think any erosion would be at the Manthos end, but that end was in good nick this year.


Offline Jimbo

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Re: Beach - a hypothesis
« Reply #5 on: October 18, 2015, 04:54:25 PM »
There hasn't been much building at the southern end of the beach for years. What is there is way back from the beach, and not very heavy construction apart from Nafsika, which has been there a very long time.

Construction higher up - like Vicky - is almost certainly on a reasonable chunk of sandstone. The central zone is lower and marshy. Athina is set well back, so not likely to influence the beach.

Beaches at the nudist end onward and at Waves end have ebbed and flowed in quite a natural way. The situation in the centre is of steady erosion. It's like a target. It shows no signs of natural repair.

A swimming pool full of water can weigh over 1,000 tons. That's a lot of pressure on an unstable substrate!



Offline Dupnica

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Re: Beach - a hypothesis
« Reply #6 on: October 18, 2015, 10:07:39 PM »
 I have been puzzling over this for some time.When you look at the aerial photos from a few years ago you'll see a couple of rows of sunbeds at the water's edge and behind them a very wide expanse of sand.How could things have changed so dramatically in just a year?
 I don't believe it has occurred naturally by tides or storms or even the dreaded Longshore Drift.

I've had a look at the Beachapedia website and have discovered this--

 "Beaches are dynamic and natural.Buildings bridges and roads are static.The problem occurs when there is a static structure built on a dynamic,moving beach.
 If buildings and roads were not built close to the shore,we would not have to worry about shoreline structure or sand erosion"

 Makes you wonder how Delfino Blu and the others ever got planning permission in the first place.Guess we'll all have to wait and see what happens next.They may all crumble into the sea in a few years time.

 
 

Offline Jimbo

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Re: Beach - a hypothesis
« Reply #7 on: October 19, 2015, 12:35:04 AM »
Thanks very much for locating that. Havana Bar is quite a light structure. Delfino Blu is not, and the Mango Bar extension is even more concrete bridging the gap between the two.

We need a kindly structural engineer to advise further.

The bad news is that, if this hypothesis is true, the steady erosion of that section of the beach over the last few years is not going to go away.



Offline Jimbo

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Re: Beach - a hypothesis
« Reply #8 on: October 19, 2015, 03:50:15 PM »
I have just sent this email to the Faculty of Geology and Geoenvironment at the University of Athens:

"Kalimerasas,
 
I would be grateful for this to passed on to somebody who might be interested! Apologies for writing in English.
 
Agios Stefanos (Avliotes) in NW Kerkyra has for a very long time had a long and wide beach. But over very recent years a specific “hot spot” on the beach line has seen dramatic erosion.
 
This spot corresponds to the position of the two main beach bar/tavernas in the centre of the beach, one of which has made a substantial expansion.
 
There has been much discussion in forums of the possible causes: longshore drift, the new harbour to the south, chaotic factors arising from storms, beach sinking caused by construction etc.
 
What was a 30/40 metre beach expanse is now effectively zero (but only in this region) at high tide. This has significant impact for tourism in the village.
 
I believe that this would be a useful and interesting study for a graduate student, and might suggest what, if any, action might give a reasonable scenario of repair for what was a wide and beautiful beach.
 
Several thousand people will be pleased to hear what you may have to say!
 
Best wishes
 
Jim Hawkins"



Offline rilo57

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Re: Beach - a hypothesis
« Reply #9 on: October 19, 2015, 06:06:58 PM »
Should be interesting to see what reaction it receives...

Offline Dupnica

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Re: Beach - a hypothesis
« Reply #10 on: October 19, 2015, 08:07:43 PM »
 Top marks Jim! That will be an interesting project for someone.

 When I walked along in June and saw what had happened, my first thought was that they had dumped the excavations from the building works on the beach.  I realise now that wasn't the case,at least I hope not.

 In September it was even worse.Defino's sunbeds were almost floating and you had to paddle in the sea to get past them.

 I don't know what can be done to reverse the damage.The lovely horseshoe bay has been ruined.

Offline cambridge

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Re: Beach - a hypothesis
« Reply #11 on: October 19, 2015, 09:33:05 PM »
If the weight of the structures at Delfino Blu and the Mango Bar extension were able to have an impact upon the beach, that impact would be even more dramatic, and obvious, around and on those structures. The displacement would also produce heave elsewhere, which again on this scale would be very difficult to miss.

Don’t ask me what has created the distortion to the beach, but my monies not on the downward pressure of buildings.

Offline Dupnica

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Re: Beach - a hypothesis
« Reply #12 on: November 13, 2015, 08:00:02 PM »
 Just wondering Jimbo if you ever heard anything from the University of Athens.

Offline Jimbo

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Re: Beach - a hypothesis
« Reply #13 on: November 14, 2015, 01:44:05 PM »
Not an iota.. or alpha, beta, gamma etc.



Offline Dupnica

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Re: Beach - a hypothesis
« Reply #14 on: November 15, 2015, 01:13:51 PM »
 I guess that's the omega of that then.


 

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