Venetian tides

LadyInBed said:
They have, at great expense to the EC, installed a flood barrier around Venice. When I saw the article I thought that they could raise it to keep the water in.
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MOSE relies on buoyancy and isn't designed to keep water in where there isn't enough outside to support the barrier. And that's far from it's only point of critique :unsure:
 
I think Brits get a bit used to huge astronomical tides. Very predictable and large such that atmospheric pressure and winds don't make so much comparable difference.
Around here as I beleive in the Med you get small astronomical tides (that induced by moon ans sun) but atmospheric pressure and wind can make the same differences so are comparatively more significant. I reckon around here the 3 factors seem about similar in significance. So a high pressure system with winds blowing from inland can reduce the tide level and if these coincide with the (predicted) low tide from astronomical effects you get a very low tide. Likewise in a storm suituation usually with low atmospheric pressure when winds blow from the ocean and perhaps spring tides then you get a storm surge. ie very high tides. So yes very small astronomical tides in Med but still some significant tides due to weather. ol'will
 
We were on a day trip to Venice a while ago and the water taxi went aground, I had to laugh. I've been in Venice at Christmas and the water was knee high in St Marks Square
 
fwiw, in Volos port, last week my depth gauge showed 7.6m, yesterday noon it was down to a crazy 7.05m- Edit: checked the log this noon went even less at 6.93
I think the highest I've noticed was 7.7, so what around 65cm 75cm range.
Usually though with no fancy southerlies to fill up the whole bay and northerlies with the right moon to empty it range is 20-30cm low to high...
Now considering Pagasitikos bay is around 15nm across with a southern entry point and Volos is at the far north we doubled our typical tidal range, Adriatic which is dunno 1000nm+ with Venice at the top could easily have 5 or 6 times that :)
 
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savageseadog said:
We were on a day trip to Venice a while ago and the water taxi went aground, I had to laugh. I've been in Venice at Christmas and the water was knee high in St Marks Square
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When I was in Venice a few years ago, water was welling up through drainage gratings in St. Mark's Square as the tide rose. Duckboards were laid within the Basilica so tourists didn't get wet feet. As I remember, the flood prevention building was in progress.
 
When arriving or leaving Venice it is good to time your passage through the entrance to the lagoon. Going out against the incoming tide with a cruise ship coming into view is not a comfortable experience. The Venice charts have the tidal streams. 1m/s is almost 2 knots

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TudorSailor
 
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ghostlymoron said:
Noticed this on the BBC news website
BBC News - Low tides leave Venice canals dry
Low tides leave Venice canals dry

I didn't realise there were tides in the Adriatic. I assumed it was nearly tideless like the Mediterranean.
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Mixed semidiurnal :)
A curiosity: the civilian main importance of the height of tide is to know what perimeter of the town will flood at various particularly high HW levels (acqua alta), navigation purposes are secondary; as the whole area is prone to soil subsidence, the height of tide is given with regards to the tidal gauge located in Punta della Salute (and not LAT, which actually "moves" because of lagoon bottom subsidence): as the tidal gauge subsides together with the sea bottom of all the town, monuments, sidewalks etc, over the years the same HW value will give the same area of town flooding, whereas the actual depth of water will be higher. Could be an atypical YM exam exercise :)
 
The marina I kept my boat in in Marmaris had a couple of steps fixed to the end of one pontoon. The top step was normally a few inches below the level of the concrete yard. On occasions it could be a foot lower and sometimes a foot above the concrete, though most times it only varied by inches.
 
Around here tides are pretty small perhaps half a metre astronomic variation. However wind and atmospheric pressure can affect tides just as much. Now I club have a nice 18ft aluminium power boat for rescue with 150HP yamaha o/b on the back. It is moored in what we call a pen. In this case jetty and sea wall on front and one side and a post on the other corner. Right through summer when it gets a lot of use no problem it goes up or down about .5 metre. The 4 mooring lines plus 2 springers are attached to a middle of a chain with a heavy weight say 20kg on one end. However twice now once 3 years ago and once a month ago the boat was found sunk on the moorings. Insurance wrote off the boat but we bought it back for 500 squid fitted new motor and electrics and it went back into service. Now it is waiting determination and repair again almost certainly requiring a new engine. We are in the middle of a very wet winter and theories abound as to why it sunk. A always on bilge pump was fitted after the first sinking.
Rain certainly seems to be able to get past the sealed floor into the bilge.
My own theory is that we had exceptional high tide in fact a storm surge of low atmospheric pressure wind onto shore and waves such that the hull was held down by the mooring lines. So water entered the scuppers. Unfortunately in each case it happened at night when no one observed the conditions.
Anyway my story relates the problems of low astronomical tides that storm surge can be really quite large on population not used to it. Boaties in UK would not be surprised and quite prepared for huge tide range. ol'will An Ozzie complaining about winter weather
 
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