Archive for Centro Maree

I have often mentioned that predictions of high water in Venice turn out to be as accurate as weather predictions anywhere else.  Sometimes even less accurate, given how sensitive the whole lagoon situation is to all sorts of factors, including wind.

The reality of acqua alta at a modest level is that it doesn't uniformly cover many streets. Here you see people going from dry to wet, then it will be back to dry again.

The reality of acqua alta at a modest level is that it doesn't uniformly cover many streets. Here you see people going from dry to wet, then it will be back to dry again.

The last week or so has undoubtedly been rather trying for the dauntless Paolo Canestrelli, director of the Tide Center. Because while the Gazzettino, rightly or wrongly, published a series of articles that sounded fairly alarmist: “Feast of the Salute with your hipboots,” “Feast of the Salute with no walkways,” “F of the S at 120 cm [four feet] of high water,” and so on, it didn’t turn out quite that way.

These stories were irksome for a few reasons, none of which had to do with whether or not I had to put on my hipboots.

First, the area around the basilica of the Salute is much higher than the Piazza San Marco, therefore a tide prediction which sounds drastic in one place won’t be nearly so much so in another.

As you see here in via Garibaldi. The board as walkway is a great idea but only if it's long enough.

As you see here in via Garibaldi. The board as walkway is a great idea but only if it's long enough.

Second, so far this autumn few forecasts have turned out as given.  The 120 cm repeatedly predicted for Sunday morning? We got 103 [3 feet].

The tide did finally manage to pull itself up to 122 cm, but that was at 12:10 Sunday night, when probably there  weren’t many people or taxis or barges around to be inconvenienced.

A few nights later, the sirens sounded with two additional tones, signaling the probable arrival of 120-130 cm [4-5 feet] of water.  Two tones means that we will have some water about halfway up the street outside our door. But in the end, our canal did no more than kiss the edge of the fondamenta. The fact that there was virtually no wind also helped.

Regardless of the height or non-height of the eventual water, articles dramatize that the city has “water on the ground” without specifying the depth — sometimes it can be two inches, but the term “high water” is usually used by the media to sound as if the levees have broken. And these articles never mention how much of Venice has water, making it sound as if the entire city were going under. Someone might be sufficiently original as to publish a story that says “Two tones means that  up to 29 per cent of the city is under water,” but I have yet to see one that says “71 per cent of the city is bone dry.”

I realize that drama is entertaining, but why dramatize it at all?  It’s not dramatic.  It’s temporarily slightly tiresome, at a very low level on the Zwingle Slightly Tiresome Index.  I’d rate it a 2, the same as hanging out the laundry.

This would qualify as a true annoyance. For some reason this delivery-person was put ashore at the wrong place, and now his way forward is completely blocked by the walkways. He must be thinking all sorts of thoughts just now.

This would qualify as a true annoyance. For some reason this delivery-person was put ashore at an ill-advised spot near San Marco, and now his way forward is completely blocked by the walkways. (They spread out in a long T-shape beyond the edge of this picture.) He has obviously recognized that his only option is to wait till the workmen make a break in the barrier, which will be soon, considering how far down the tide has already fallen.


Now let me turn a sympathetic eye on the indomitable Canestrelli at the Tide Center.  Because no matter what prediction he gives — predictions which are always made according to information which has been scientifically gathered, even if journalists then recast them to sound like the last act of “Gotterdammerung” — people revile him. This is either because the prediction turned out to be accurate, and inconvenient, or because it wasn’t accurate, in which case people throw another armload of brickbats at him.

This is regrettable because the Center has just recently created a new mathematical model which has attained notably higher precision — an accomplishment for which Canestrelli was recently awarded a prize by the Italian government.  No rude remarks, thank you.

But nature resists our assumptions, as Canestrelli is the first to admit. “Look at the disastrous rainfall on the Veneto on November 1,” he told the Gazzettino on November 11; “it turned out to be ten times more than what was predicted.   Unfortunately, even with progress, there is still a wide margin of error.”

In the case of the high water on November 10, he explained that  “On Thursday our models didn’t predict anything over 100 cm. Only in the early morning [Friday, November 10] did we see indications that it might be higher, so we activated the sirens to warn it might reach 110 cm.  We then raised the forecast to 115 cm.  But unfortunately high water, like other weather phenomena, is very hard to predict even if you’re continually monitoring it.”

That particular series of unpredicted events was caused by a number of factors which aren’t taken into account in the simplistic popular impression of the Tide Center’s skills.  “Even though the weather was improving,” Canestrelli continued, “there was the return of a seiche wave in the Adriatic” [the public, including me, isn’t very good at keeping track of the seiche waves out there], “a significant rise in the barometric pressure, and a drop in the wind.

“This was a very strange situation in that the increase in pressure didn’t blunt the tide; in my 30 years here I’ve only seen that happen once or twice. The problem is that the pressure, in spite of the increase of 10 millibars, remained at an extremely low level rarely seen in our latitudes.”

Technically one could say there was still acqua alta at the Piazza San Marco but it has obviously begun to subside.

Technically one could say there was still acqua alta at the Piazza San Marco but it has obviously begun to subside.

All this gives the tiniest indication of how many different and mutating factors affect the height of the tide and the accuracy of the forecasts.  Now let’s move on to another element which is much easier to grasp: Money and manpower.

“What can we do?” he asks more or less rhetorically.  “Few departments are as indispensible as the Tide Center, but we risk sinking to the bottom.

True, just on the other side of the walkways, there is still water in the Piazza. Evidently the person with the big bag isn't too worried about its contents, or about waiting ten minutes.But it is not spectacularly high, and obviously it's on it way out.

True, just on the other side of the walkways there is still water in the Piazza. Evidently the person with the big bag isn't too worried about its contents, or about waiting ten minutes. It's obviously on its way out.

“For 2010, the budget is for one million euros.  But 46,000 euros are for operating costs, and another 500,000 — allocated, but so far never actually seen — are earmarked for the maintenance of the equipment.

“How can we keep going with funding like this?  The money that remains is all we have to give to the personnel, who are on call 24 hours a day.

“How can it be that a department which is crucial to the well-being of an entire city isn’t regarded as the apple of the eye of the emergency services? There was a time when we had all the interest we needed to guarantee efficiency and accuracy. Now times have changed.

At 9:20 this shop in the Piazza San Marco had water on its floor, an event for which, judging by the paving, it has been well prepared.  The shop is supposed to open in ten minutes and you can see how agitated the owner and staff are.

At 9:20 this shop in the Piazza San Marco had water on its floor, an event for which, judging by the paving, it has been well prepared. The shop is supposed to open in ten minutes and you can see how agitated the owner and staff are. They're not even here yet.

“Furthermore,” Canestrelli goes on, “we risk reaching the limit of our capacity. Up until last year the Center had 17 employees; now we have 13 and those include people in administration and motor-launch drivers. This leaves very few who are involved in the forecast service.  With this level of personnel, during the high-water season of October till May, we can’t monitor the situation 24 hours a day.”

And a note that is drowned-out in the chaotic chorus of who needs to know how high the water’s going to be is from the so-called ecological workers. Not so much for collecting the trash, which they overlook on high-water days, but because they have to know — in advance, please — whether they’re going to need to muster the troops to set up the passarelle, or temporary walkways.  Preferably before the water is above the ankles.

The clever thing to do, it would seem to me, would be for the Tide Center to estimate the tide toward the higher end of the scale.  Just to be on the safe side.  I was very proud of myself for coming up with this clever and amusing idea.

Then Canestrelli told the Gazzettino that that’s  pretty much what they’re doing.

So all this being said, let us dial down the volume on the wails preceding the next expected high tide. It may turn out to be a little — or somewhat — or a lot — different than you thought it was going to be.  I suggest you buy a pair of boots and get on with your life.

Categories : Nature, Problems, Water
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Nov
10

Acqua alta update

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Watching the various weather signs yesterday morning as closely as a jungle tracker (or desert tracker, or suburban mother looking for a parking place at the mall), I realized fairly early that the Warnings which I was following were turning out to have been perhaps slightly excessive.

Caution is a superb thing and we should all have more of it, except for when we shouldn’t, I mean. But I have the sensation — and so does Lino — that a certain amount of exaggeration has crept into the whole business of predicting acqua alta. Why?

This is what water announced by the siren plus one tone looked like at 11:30 outside our house. The tide was just about ready to turn.

This is what water announced by the siren plus one tone looked like at 11:30 outside our house. The tide was just about ready to turn.

One reason, and I’m just hypothesizing here, could be that the people in the Tide Center (particularly its battle-hardened director, Paolo Canestrelli, who would feel perfectly at home with Field Marshal Montgomery) are up to here with the shrieking imprecations from people inconvenienced by a change in the situation from the earlier prediction to the reality suddenly underfoot.

As I have already noted, the weather picture can change.  Get over it.

Another reason — here, let me move that firing-range target to the side and stand there in its place — could be the relentless need for the many forces involved in the MOSE project to instill public dread of water on the ground.  Even brief articles in the Gazzettino which mention a (not “the,” but “a”) possibility of high water the following day don’t bear down too hard on the word “possibility.” They like the effect the words “acqua alta” have on people, if put in a way that makes it sound as if you need to head for the storm cellar.

Acqua alta is always very clear.

Acqua alta is always very clear.

In any case, just remember that any article that you may read that implies, or even says, that “Venice was flooded” is a bit excessive.  We didn’t get any water on our ground and we’re in Venice.  Is San Marco’s high water better than ours?  Prettier?  Wetter?

If you have any interest in the damage water can seriously do to people, places and things, don’t get fixated on Venice, but look at other areas of the Veneto such as Vicenza and Verona, and even in Tuscany, over the past few days. Torrential rains, bursting riverbanks, highways and roads blocked and even broken by racing water, mudslides obliterating houses and the helpless people within them (like the mother and her two-year-old son whose bodies were dug out of their mud-filled house, still clinging to each other) — these are events involving water which deserve more publicity than they get.

Actually, “mudslide” is too innocuous a word for what happened in Tuscany after days of rain. Essentially a huge chunk of melting mountain just broke off and fell on this family’s house.  Just like that.  No warning sirens, no time to do anything except die.  There are many families who have lost everything.  Some people have drowned.

Parts of the Veneto have now been declared disaster areas.  Venice was not on the list.

Categories : Nature, Problems, Water
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Nov
09

Waiting for acqua alta

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I’m sitting here at 7:30 waiting to see what the water is going to do.

This is not the first time this fall that water has come ashore (as it probably will), but it’s the first time I’m taking it slightly more seriously — and by “seriously” I don’t mean I’m pulling the tarps off the lifeboats preparing to abandon ship, so to speak; I mean that I believe that the official prediction may be close to accurate.  That alone would be worth writing about.

The accuracy is interesting only for the same reasons that any weather prediction is interesting — Did they get it right? And does this mean I should take future predictions really seriously?

There are several indications that they may be onto something this morning, most of which do not require their intervention because I have the tools at hand to understand and evaluate the probabilities all by my big-girl self.

On an ideal day, the hand would be pointing in the opposite direction.

On an ideal day, the hand would be pointing in the opposite direction.

First, the barometric pressure.  It has been impressively low for the last 12 hours, if not more. Low pressure means high water, a rule so simple even I can remember it.

Checking the barometer is one of the first useful things to do, and this is what impressive low pressure looks like.  Note that whoever put those generic terms on the instrument’s face (“fair,” “change,” “rain”) didn’t consider putting “impressive high water” in the lower right-hand space. But that’s okay, because depending on where you live they would more usefully have had to put “monsoon,” “tropical cyclone” and other events not likely to occur here.  So never mind.

Second, the wind direction. The garbin (gar-BEAN)  was blowing strongly from the southwest yesterday afternoon, which is good because it impels the water to move northeast, or out into the Adriatic where it can do whatever the heck it wants to. Then it veered around to the north — even better.

But now it has veered to a scirocco, or southeast wind, which has the opposite effect of pressing the water into the lagoon, as I rustically think of it — or at least of creating enough force to block the tide’s normal retreat.

Third, we are now on the verge of the 24-hour period of the “morto de aqua,” or “death of the water,” when the tidal variation is minimal.  This 24-hour period falls twice a month and doesn’t particularly influence the height of the high tide, but it does mean that since the tides are not especially strong, the weather is almost always unstable.  Which means don’t count on anything except some kind of unpleasant weather.  In the summer we can get huge thunderstorms during the “morto de aqua.”

If I had a shop near the Piazza San Marco and didn’t know any of the above, instead of wailing to the city about paying me for the damage or inconvenience I had suffered, I ought to be paying them for my preposterous ignorance.  Hm — that would be an entertaining project: Setting a scale of penalty payments for preposterous ignorance.  The mind absolutely sparkles at the thought.

Fourth, if you don’t know any of the above three basic facts of life in the lagoon, you can decide to depend on the city’s system of warning sirens, which sound an hour before water is expected to start rising through the drain system.  If you live more than an hour away from San Marco, of course, this system doesn’t do you much good.

Or you might go online and consult the prediction from the city’s Centro Maree, or Tide Center.

It’s interesting to see the variation between the normal tidal flux (the lower, light red line) and the real-time prediction (upper blue line).  The only problem with this tool is that its usefulness depends heavily on being updated in a timely fashion.

The forecast hasn't changed since last night, but I still don't understand why this chart wasn't on the Tide Center's website at 7:28 AM.

The forecast hasn't changed since last night, but it would have been nice to have seen it before 7:28 AM.

Really timely updates are available through the text-messaging system. However, if you have signed up with the Tide Center to get the prediction via your cell phone, you still might want to consider a fall-back position.  A few days ago the Gazzettino reported that thousands of users had indeed received the necessary warning, but only several hours too late. The city blamed the mobile phone company and its incapacity to send thousands of simultaneous text messages.  (Oh good — something even less dependable than weather predictions: cell phone efficiency).  The city has since — they say — changed companies.

I have not signed up with this service because, well, we’ve got the barometer, which is incapable of lying and doesn’t depend on any human agent whatsoever.  What a scintillating thought that is.

Update: The sirens have just sounded.  And instead of the two tones which “code orange” would require, there was only one tone, meaning the maximum ought to be a mere 110 cm (43 inches)above normal sea level, not the earlier prediction of 115 cm (45 inches).  This doesn’t mean they were wrong, it just means that something changed.  Whatever it was, I’m for it.  Two inches makes an inordinate amount of difference..

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Categories : Venetian-ness, Water
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