Acqua alta: reviewing the basics II
Here are two elements of high water which aren’t usually — perhaps not ever — mentioned, much less interpreted, in the typical story, the kind that likes using emotional words like “invade.” ( As in, “The water invaded the city.” Stormed the battlements. Conquered the kingdom, wrought havoc, death and destruction, setting towns to the torch and sending everyone into slavery. You know, the usual high-water scenario.) Where was I.
One is what the numbers actually mean. Venice does not float like a lily-pad at sea level. The lowest area in the city, the Piazza San Marco, is already 80 cm above the water’s surface when the water is at mean sea-level. Therefore any height that’s reported isn’t as high as it sounds if we were just standing on a street somewhere, measuring upwards from our feet, because the starting number isn’t zero.
Example: 110 cm converts to three and a half feet, which sounds scary. But someone standing in the Piazza San Marco will have water reaching up only 30 cm from their feet, or roughly just below their knees (11 inches). Someone elsewhere in the city might well not have it even that high. Or at all. Because of Point Number Two.
Point Number Two: Headlines blaring “VENICE IS FLOODED” imply that the entire city, all three square miles of it, is going under for the third time. In fact, a tide up to 110 cm will dampen 14 percent of the city. Not a huge percentage, I think one must admit. Up at 140 cm (the relatively rare Code Red, “exceptional high water”), it covers almost 50 percent of the city, which is more impressive, except that the frequency of a tide this high is fairly low — five times in the ten years between 2000 and 2010. And still, one isn’t referring to every square inch of Venice. Amost half of the city is still high and dry.
For all of Venice to be flooded, the tide would have to rise well beyond 200 cm (the epochal acqua alta of November 4, 1966 reached 194 cm). The city’s tide office doesn’t estimate above 200 cm, at which level 86 percent of the city would be underwater. I don’t say that would be entertaining, but it would be so rare that I’d suggest saving the doomsday vocabulary for it, and not waste the drama on more mundane tidal events.
Our little hovel is safe up to the three-tone level. At four tones, it’s time to take the tarps off the lifeboats. We discovered that last December 1 at about 9:15, when the water reached the four-tone level and began to slide under our front door. Then I discovered it was also coming through a fissure in the wall under the kitchen sink, as well as up through a fissure in the stone flooring. That was more exciting than almost anything I can remember. So please don’t suppose that my viewpoint is the result of my not having to worry about water under the bed. I just want to recalibrate the popular perception of this phenomenon. Obnoxious. Not catastrophic.
We have a calendar, on sale at any newsstand, which traces the predicted tide levels each day of the year. But those are only estimates based on what’s normal. For more timely updates, I check the data on the city’s Tide Center website. You can also sign up to be alerted of the rising tide via text message (SMS) on your cell phone.
All these advisories are what make it really hard for me to feel sincerely sorry for anyone who might find that water had caused any damage to goods or appliances. It’s not like it comes like a thief in the night.
I leave you with the key phrase which ought to simplify the whole business if you’re here long enough to need to know it: Hip waders. Just do it.
Acqua alta: reviewing the basics I
Let’s start with the most basic fact of all: Venice is sitting in the middle of a tidal lagoon. This means surrounded by water that rises and falls. I don’t mean to keep harping on this, because I know it sounds really dumb, but not much dumber than all those stories that get published and broadcast that make it sound as if water on the ground here were stranger and more upsetting than four sharks singing “Shine On, Harvest Moon.”
How high the water will rise might vary from the official prediction based on a few factors, but when it’s looking imminent I’ve definitely got at least one eye on the barometer, the wind sock (on the computer) and the moon. Wait, that makes three eyes. Well, you know what I mean.
Data on the tides began to be recorded regularly after an exceptional high water in 1867 (153 cm above average sea level). In 1908 various monitoring stations were installed to more precisely measure the height of the tides, and in 1914 the pertinent data on the barometric pressure and the direction and force of the wind were added.
For events longer ago, historians can only turn to various chronicles and accounts in which the quantities aren’t always easy to assess. As in: “The water rose high enough to ruin the wells.” A flooded well would, in my view, be much more distressing than some water on the floor, seeing as the supply of fresh H2O in Venice was not infinite.
The main high-water factors are the following:
The season. If the acqua is going to be alta, it will usually be between September and April. Articles which refer to its frequency are often misleading because they use aggregate numbers which give the impression that it’s a monthly occurrence all year long. While there might be pesky clusters of high water events in winter (as happened this year), the likelihood plummets to June; it has never been recorded in July and August.
Phase of the moon. The tides are highest and lowest when the moon is full and when it’s new. Actually, the moon is the only component to this phenomenon which isn’t even the tiniest bit likely to swerve from the forecast.
Atmospheric pressure. When it’s low, the water is high. When it’s high, the water is low. If we tap on the barometer and see that it’s gone to the bottom of the scale, there’s no getting around the likelihood that the water will be high. The barometer won’t tell us how high, but we can look out the door and make a guess. A barometer is a great friend to have because it cannot tell a lie.
Wind. If the scirocco is blowing, it will definitely aggravate the situation. The scirocco is also obnoxious because it’s warm and humid (get one blowing in the summer and you’ll wonder if you took the wrong exit and ended up in Amazonia). But as it’s from the southeast, it will blow into the lagoon and — putting it very simplistically — push against the tide and prevent it from going out in a timely and efficient fashion. On the contrary, it seems to work very hard to keep all the water in the lagoon all at once. I try to avoid anthropomorphizing the natural world here, but I have to say that sometimes it seems like the wind just does it on purpose.
When a strong scirocco is blowing, I don’t hear wind so much as I do the heavy surf rolling up in close-order-drill on the Lido’s Adriatic beaches. It’s a deep, rumbling sort of roar off in the distance, impossible to mistake for anything else.
There is a warning system to alert the city that within an hour, water will be rising in the Piazza San Marco (the lowest point in the city) and, by extension, at other various low-lying areas. This information comes from a monitoring system at the mouth of the lagoon at San Nicolo, and at other points in the lagoon.
Until two years ago, the citywide warning system was a few sirens which emitted a sequence of rising wails. The first time I heard them they woke me from a deep sleep in the middle of the night — a sudden violent tone swooping upward, overlapped by another one just following it, and then by a third. Scared the hoo out of me — it was like the Three Weird Sisters in Macbeth going mad.
But what they didn’t tell you back then was how much water was going to come ashore.
Two years ago, the system was refined. Now there is only one siren-swoop, after which comes a steady tone which indicates the maximum predicted height. One tone = 110 centimeters above sea level. Two tones = 120 centimeters. Three tones = 130. And four tones = 140 and above. This is what they sound like. I can tell you they’re very effective. There may not be any way you can ultimately prevent water from coming indoors, but you cannot possibly say you had no warning.
Acqua alta: some plusses and minuses
I realize it may sound strange to refer to there being “plusses” to acqua alta. Let me just say I don’t mean “plusses” in the sense of winning a large chunk of the lottery. But there are in fact some positive aspects to it.
For instance, many Venetians have told me that acqua alta is a good thing because it washes the streets. This is true. Unfortunately, it also deposits a fine layer of silty slime. And while it does remove some of the dog poop, it also leaves detritus behind, so the general landscape isn’t much prettier than it was before the water rose. So, you know. We could go on like this, pro and con, all day.
But let me point out something that is hardly ever remarked on, in the many and varying accounts of this event: Acqua alta is actually a very good thing for the barene (the lagoon’s marshy wetland islets). If we can focus our minds briefly on something other than our own immediate convenience, it’s worth remembering that the lagoon has its own needs which are being met ever more rarely. So if it likes a good soak, I don’t see why it (by which I mean the whole ecosystem: microorganisms, plants, birds, etc.) can’t have it. Also — speaking selfishly — rowing when the water is high is magic.
Back in town, here are a few of the positive and less positive aspects of acqua alta, as I see them:
- It doesn’t last long. Acqua alta is a tidal event. Unlike your raging rivers, it has a predictable time frame. The tide comes in for six hours, and goes out for six hours. True, sometimes it doesn’t go out as much as it should, but it eventually does go out. This coming and going means that it’s really bothersome for only about two hours.
- It’s fairly tranquil. Inexorable, I grant you. Anyone who hasn’t watched the water rising near one’s front door (as we have) hasn’t fully grasped the fundamental meaning of “Time and tide wait for no man.” But the typical reports of high water in Venice make it sound as if Niagara Falls is pouring through your living-room window (CNN once referred to the “Adriatic bursting its banks.” Banks? Bursting? Are we suddenly in Holland?), when in reality it’s more like the bathtub slowly overflowing. Water in both cases, I agree, but not really the same.
- It is predictable. True, raging rivers are also predictable, but some of the factors influencing acqua alta, such as the direction of the wind, can change. In addition, we get plenty of warning. If you don’t want to wait for the sirens to blare, just look at the barometer. (You do have a barometer, don’t you?) The lower the pressure, the higher the water. Check the sky: Full or new moon? There will be more pronounced highs and lows. Wind from the southeast? Not good; it will prevent (or slow) the regular retreat of the tide. We want a southwest wind (garbin) or better yet, northeast (bora). Those will settle acqua alta’s hash.
I’ll tell you what’s really annoying about acqua alta, apart from the distraught articles that keep getting published. It’s not that you have to put on boots for a few hours. It’s that:
- When the tide goes out, it leaves all kinds of detritus
This is a modest example of a street not long after the tide has gone out. Clumps of eelgrass and bits of reeds are unavoidable and even not so ugly. It's the other stuff, pieces of plastic and styrofoam and general junk littering every wet street that are ugly. Unavoidable, fine. But there is no telling when, if ever, someone is going to sweep it up. all over the sidewalks. Stuff that was just floating gently comes to rest on whatever pavement was just below it when the last inch retreated. Also, if anyone puts out a plastic bag of garbage the night before (yes, despite the warning sirens — dumb, I agree), that bag will be floating around the street and either settle on the pavement somewhere or drift out to sea. Neither case is highly desirable, though obviously the second is worse.
- The garbage-people will be extremely slow in collecting the trash and/or — make that just “or,” they can’t seem to do both in the same day, even when the sun is shining — sweeping away the detritus, which means the streets look more or less like a slum. The garbage-people are slow because … I’ve tried to understand this… It may be because they are already so desperately overworked that high water adds an insuperable burden (you’re believing this, yes?), and because they are otherwise urgently and industriously occupied in setting up or taking down the temporary walkways over the high water (sometimes yes, mostly no). But they seem to get a special pass on their normal work when the acqua is even moderately alta. I can’t explain it, except to compare it to the mysterious sore throat which a kid who doesn’t want to go to school suddenly develops when it rains or snows.
- Transport gets all scrambled up,
not only for taxis and barges but also some vaporettos and/or motoscafos. They have to change their normal routes because the high water prevents them from passing under certain bridges. There are alternatives by which they resolve this temporary dilemma, but it adds inconvenience to your own trajectory. As for heavy work boats and taxis, they either have to pick another route from A to B, or wait for the tide to turn. Tiresome, true, but hardly the stuff of calamity. - Your front door swells. If you have been so unfortunate as to have even an inch of water come inside (and for many people, this just means it has reached the edge of a staircase leading up to their apartment, not the apartment itself), and your front door is made of wood, it will soak up the water and then want to stick. It will take a while to dry out. Like, maybe weeks. You may end up having to sand it down some. Irritating. Not disastrous.
not only for taxis and barges but also some vaporettos and/or motoscafos. They have to change their normal routes because the high water prevents them from passing under certain bridges. There are alternatives by which they resolve this temporary dilemma, but it adds inconvenience to your own trajectory. As for heavy work boats and taxis, they either have to pick another route from A to B, or wait for the tide to turn. Tiresome, true, but hardly the stuff of calamity.
I think if you’re going to live here you need to accept the fact that you’re sitting in the middle of a tidal lagoon. If that creates really too many problems, it might be good for you to consider moving. At least to the second floor, or maybe across the bridge to the mainland. No more worries about the tide coming ashore over there. All you have to deal with there, even as nearby as Mestre, are rivers and rain and totally inadequate storm drains. Which leads to flooded basements full of water that actually has little or no natural urge to recede. Fun.
No emotional articles about that, though. Who cares about a foot of water in somebody’s garage? Nobody — at least not until that somebody snaps a picture of a person rowing around the car or trailer.
Acqua alta: here we go again
If there’s one thing people everywhere know about Venice, it’s that sometimes those romantic canals try to barge into your house.
Rather than “flooding,” Venetians call this acqua alta, or “high water” (literally “high tide”). Or, depending on how deep it’s likely to be, sometimes they call it “acqua in terra,” or “water on the ground,” which is less dramatic and often more accurate.
I’ve got water on the brain at the moment because night before last, the warning siren sounded again. It indicated the lowest predicted level, one out of four, which was nice, and in the end we barely got any at all. With rare exceptions, acqua alta, more than being some kind of apocalyptic affliction, as it is often portrayed, is really a low-grade nuisance. If it happens often, as it has this winter, it becomes as annoying as any other uninvited guest who doesn’t realize it’s time to go home.
There are so many notions people have about high water, based on the generally inaccurate and overwrought accounts in the press, that I thought I’d review and readjust a few of them.
- It’s always happening, or likely to happen. Not really. This winter we’ve had more acqua in terra (again, not really what I’d call “alta”) more often than many other winters. On the other hand, there have been years when I haven’t put my boots on even once. Yet all kinds of claims keep being thrown around in stories written about this little phenomenon. The website of the basilica of San Marco states that water begins to flood the Piazza San Marco, just in front of the church, 250 days a year. Check my math, but that works out to 8 months. A photo caption on the National Geographic website claims that Venice has high water ten times a month. That’s crazy talk.
- It creates, or will create, really big, really bad problems.
If for some reason your kids (or somebody else's) don't have boots, high water can be somewhat demanding. Then again, why don't they just go barefoot? I've done it and I'm still alive. I’m not sure what people think those might be, but the words “acqua alta” seem to inspire a lot of hyperventilating outside Venice (and even inside Venice, mostly from merchants around the Piazza San Marco). I’m not saying that having to put the stuff in your store up on higher shelves isn’t annoying, or that having to sweep out the receding brackish water and then wash the floor with fresh water isn’t annoying. But in 9 cases out of 10, the situation doesn’t exceed the annoyance level — not much worse than having to shovel the snow out of the driveway for the fiftieth time this winter.
- It’s going to be alarmingly deep. Those fun photos of people rowing boats in the Piazza San Marco don’t ever show how deep the water actually is. (In fact, those boats can be rowed in four inches of water.) Venice isn’t flat as a griddle — the streets undulate as much as the water does, which you discover when the water comes ashore. There can be dry spots even in a wet street.
- The entire city’s drowning. The municipal tide center reports that when the tide is predicted to reach 110 cm above mean sea level, 14 percent of Venice has water on the ground. And that that might not be a depth of more than an inch or two. Fourteen percent doesn’t strike me as an immense area, and several percentages of that would always be the Piazza San Marco, the lowest point in the city.
When the water starts to rise in the Piazza San Marco, it looks like this. Sometimes it doesn't get any higher than this amount. I guess you could say Venice was flooding, but there are still plenty of dry spots left. - It’s going to hurt you, or hurt something. Not that I’ve noticed. Acqua alta is nothing like real floods. Rivers overflowing their banks in torrential rainstorms are dangerous; tsunamis are dangerous. With acqua alta, nobody dies. People survive, buildings survive, art works are fine. The water rises very gently, even politely. Despite the distraught tones in which the event is almost always reported, I still don’t understand why the mere term seems to have acquired such a menacing overtone.
If the water rises near a low sidewalk, it flows over the edge. It's even more common -- as here in the Piazza San Marco -- for it to come up through the storm drains. Naturally it also goes out the same way.
Acqua alta is not dangerous. It’s not even especially upsetting. In my experience, if it happens more than a few times, though, it can begin to seem like a two-year-old who’s gotten into the “Why?” groove. Nothing wrong with it, really, except that it gets to be irritating. The kid turns three, and spring and summer come, and all of this fades from memory.
In my next post: A few real-life aspects of acqua alta which tend to mitigate its fearsome reputation.
