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The mainland of Italy reaches out a finger towards Venice, and the gap is spanned by the Ponte della Libertà (Bridge of Liberty). Otherwise, the coast’s ominous profile cast in reflection across the Venetian lagoon is that of industrial developments at Mestre and Porto Marghera. These have grown around the ageless waters of the Brenta Naviglio, which flow peacefully into the lagoon at Malcontenta. The modern Tessera Airport and the prettified Jesolo beach huts betray the affluence of tourism.


The Veneto

This area comprises mainly the vast alluvial Po Delta and its tributaries which are overlooked in the north by the Venetian Pre-Alps, and further north again in the Cadore district by the western massifs of the Dolomites. The highly-eroded limestone massif of the Dolomites extends across the Veneto and Trentino-Alto Adige. The Cadores is an agricultural region growing wheat, maize, mulberry bushes, olives, fruit trees and vines. The industrial sector includes oil refineries, smelting works and chemical plants which are concentrated in the vicinity of Venice at Mestre-Marghera, as well as a large production of hydroelectric energy in the valleys of the Pre-Alps. The latter supplies the textile industry.

The landscape is punctuated by two small volcanic groups, the Berici Mountains south of Vicenza and the Euganean Hills near Padua. The slopes of these blackish heights support vines and peach orchards, and there are several hot springs.

In the Po Delta and that of the Adige lie impoverished and desolate areas, subject to flooding. Following reclamation certain areas are farmed on an industrial scale for wheat and sugar beet. The coastline takes the form of lagoons ( lagune ) separated from the sea by spits of sand pierced by gaps ( porti ). It is one of these lagoons that both provides and threatens the survival of Venice.


The Venetian Lagoon

The Venetian Lagoon extends over an area of 550sq km/213sq mi, making it the largest in Italy. It was formed at the end of the Ice Age by the convergence of flooded rivers, swollen by melted snow from the Alps and Apennines.

Today it provides a natural and complex habitat to wetland flora and fauna between the Cavallino coast to the northeast and the Lido and Chioggia to the southwest. Water levels are maintained by the sea: its tides constitute both an ever-present threat to the delicate make-up of the Venetian Lagoon while also providing its regular safeguard from stagnation. The sea merges with the canals’ fresh water through three channels ( bocche di porto ) by the Lido, at Chioggia and Malamocco, where dikes were installed during the 19C and 20C.

An age-old problem

In the 12C, Europe enjoyed a long period of mild weather followed by a noticeable rise in temperature; then came torrential rains that caused high tides and flooding. The River Brenta broke its banks and water flooded a large part of the lagoon, depositing silt, mud and detritus. Malaria broke out. The Republic of Venice tried to defend itself by placing palisades along the coast, diverting the course of the rivers and building great dikes, but the lagoon continued to pose a threat. Over the ensuing centuries (15C–17C), major drainage programmes were implemented that affected the River Brenta, River Piave, River Livenza and River Sile. In 1896 the operation aimed at diverting the waters of the Brenta was finally completed, channelling them into the mouth of the Bacchiglione. Despite these measures, as water levels continue to rise and fall, the sand deposited in the lagoon by the rivers is buffeted back inland by the sea and the wind. Thus the sandbanks are formed and strengthened. All the while, caught between marine erosion and the rebuilding action of the rivers, the fate of Venice itself is at stake: after more than 1 000 years of existence, the city is slowly sinking.

The Venetian Lagoon can be likened to a sophisticated system that has achieved a subtle balance between excessive sedimentation (leading to the emergence of “new” land) and erosion (in which the deposits carried by the sea and rivers are so scarce that a stretch of lagoon can turn into a stretch of sea). This is precisely the risk currently threatening the lagoon. About one quarter of the lagoon surface is rendered unnavigable by the existence of sandbanks or barene . Their importance is huge: they encourage the proliferation of a great many animal and vegetal species while attracting sediments that might otherwise be scattered in the water, contributing to reducing the swell.

About 4 000ha/15sq mi are taken up by the large inhabited islands and smaller, deserted ones, leaving another 40 000ha/155sq mi occupied by water.

Anyone surprised at seeing how shallow a Venetian canal may be when drained of its water (from an average of 1–2m/3–7ft to a maximum depth of 8–10m/26–33ft) will understand why the seabed of the open lagoon is often exposed at low tide. Despite this lack of depth, which gives the lagoon its millpond appearance, a complex network of crisscrossed channels maintains currents and easy movement. Navigable areas are marked by lone wooden posts or groups of poles roped together, known as bricole . The deepest channels are those nearest the mouths of the ports, and as the distance from the sea increases, these rivulets become shallower and narrower ( ghebi ), dwindling across the sandbanks before disappearing into chiari , basins where salt water and rainwater mingle.

Tides

Tidal changes occur every six hours, fluctuating between two high points per day. Low atmospheric pressure and the sirocco and bora winds are known to accentuate high tide, whereas high atmospheric pressure and northwesterly winds tend to bring on a low tide. In this case, some of the rivers may dry up. Sea water is thereby drawn into the lagoon through the three ports, flushing “new” water in and “old” water out, assisted by a current from the rivers on the opposite side. Parts affected by these tides are therefore known as the “living” lagoon, whereas sections little affected by this lifeline are referred to as the “dead” lagoon. These outlying parts tend towards marsh, channelled with canals, ghebi between fishing banks and diked lakes built by and for the fishing industry.

The health of the lagoon is totally dependent upon the influx of “new” water brought by the tides. However, the inflow of fresh water provided by the rivers that once maintained saline levels has been greatly reduced as the rivers have progressively been diverted. This diversion has also reduced the strength of current across the lagoon and allowed vast quantities of polluting material to be deposited.

In the 20C the problem was exacerbated by the growth of industrial sites around Mestre and Porto Maghera and the accommodation of petrol tankers, with obvious implications on the environment of the lagoon. The reduction in oxygenated water flowing through the canals of Venice is gradually eroding the ability of plant and marine life to survive. Only those organisms with short life cycles have had time to adapt, and so quantities of macroalgae ( ulva rigida ) and insects (mosquitoes and the like) have increased at a fantastic rate.

The tide along the coasts can fluctuate wildly; for it to be classified as tidal flooding, its level has to reach or exceed 1.10m/3ft 6in. The last such occurrence happened on 4 November 1966 when consequences were felt way beyond the shores of Venice: the Arno overflowed in Florence, with tragic results. That year an alarming prediction said that Venice might possibly disappear. Fortunately, radical action against further subsidence, including the closure of artesian wells on the mainland (1975), has proved the prophecy false.

Similar crises of this kind are documented as far back as 589. Contemporary personal accounts are terrifying. Paolo Diacono (c.720–799) wrote of the first flood tide: “non in terra neque in aqua sumus viventes” (neither on earth nor in water were we alive). Records from 1410 state that “almost one thousand people coming from the fair at Mestre and other places drowned”.

Since the 17C the water level of the Venetian Lagoon has dropped by 60cm/24in. In past centuries, once every five years, the tide would rise above the damp-proof foundations made of Istrian stone that were built to protect the houses against salt deposits. Nowadays, in the lower areas, these foundations are immersed in water more than 40 times in a single year and the buildings can do very little to stall the degradation process.

Venice, victim of the tides

On 4 November 1966 the mareograph at Punta della Salute registered an exceptionally high tide of 1.94m/6ft. Medium to high tides usually reach a level of around 70cm/28in, flooding the Piazza San Marco and, with a further 30cm/12in, even narrow alley streets would be inundated. Between December and February the city can be the scene of very low tides indeed, estimated at less than 90cm/36in.

At the end of the 18C, when the first part of the Riva degli Schiavoni promenade was completed, Venetian magistrates ordered that the letter “C” be engraved on the city houses and their foundations. The letter was to indicate the average level of the highest-known tides. However, today it is difficult to spot these inscriptions since most of them are located under the level of the sea.


Venice in Peril

Flooding

The Centro Previsioni e Segnalazioni Maree provides warnings of impending danger and information on forecasts and tide tables. Tidal flooding tends to occur between April and September, and forecast warnings are issued about 48 hours in advance. Details are published in the Gazzettino and posted up on the landing stages of the vaporettos. Should the level threaten to exceed 1.10m/3ft 7in, 16 sirens sound five times for 10 seconds each time, three or four hours in advance of the high point.

Should high tide not exceed 1.20m/ 3ft 11in, the AMAV (Azienda Multiservizio Ambientale Venezia) sees to the laying of footbridges along prescribed routes. However, if the water level goes above this limit, then footbridges can become dangerous because they start to float. In the case of tidal flooding, the AMAV is unable to maintain its principal function (rubbish collection), because its boats are no longer able to pass under the bridges. It is therefore made responsible for laying down emergency footbridges. Meanwhile, the Venetian Municipality requests the population to just hang on to their household waste! In the UK, Venice in Peril (The British Committee for the Preservation of Venice) can help with forecasts and the latest news, 020 7736 6891, www.veniceinperil.org.

High tide, which is announced by the rather sinister sound of the sirens, floods the lowest-lying parts of the city not only by bursting the banks of St Mark’s Basin and the canals and rivers of the city, but also by gushing out of the drains, cracks and manhole covers in Venice’s streets and squares.

Today’s concerns

In the past, land and water were clearly separated, with the lagoon acting as a link between the two, drawing on both to produce life and movement. However, the presence of factories, farms and areas inhabited by man have gradually changed the face of the gronda , the sloped land licking at the lagoon shores. Today, the lagoon has reached a sort of “standstill”: it takes two weeks for waste material to leave the lagoon and end up in the open sea. Every year more than 1million m3 /35.3million cu ft of solid matter is lost. Erosion, the sediments lost in the water, and the rising level of the sea all contribute to lowering the lagoon depths. This phenomenon is threatening the sandbanks known as barene , which are doomed to disappear by the year 2050 if drastic action is not taken to remedy the situation.

Water fluctuations and land subsidence

Variations in the level of the water are referred to as eustatismo. In the course of the last century, this phenomenon caused the waters of Venice to rise by 8cm/3.2in. This rise has led to dire consequences, aggravated by the effects of local subsidence, causing the land to drop, representing around 15cm/6.2in for the same period. Therefore, the city of Venice has “sunk” by around 23cm/9.2in since the end of the 19C.

Erosion

Erosion is the result of a number of factors: higher water levels, subsidence, digging for artificial canals, and the swell, which slowly increases while the seabed slumps and the sandbanks dwindle.

Pollution

Finally, to crown this somewhat pessimistic picture, pollution is responsible for the destruction of phanerogamic flora, invaluable sea-water plants whose roots serve to prevent erosion and stabilise the seabed. Water pollution has also killed the algae and other marine varieties which once thrived on sandbanks and mudflats and which are no longer able to attract sediments.

Tackling the problem

The risk of losing Venice through both tides and progressive de-population is so great that the Italian State has declared the salvation of the city to be a question of “pre-eminent national interest”. The residents of Venice appear to be particularly concerned about high-to-medium tides, which cause flooding of the city. Consequently, a number of projects currently being examined or implemented are aimed at making these inhabited areas far safer. It is a highly delicate and complex situation: the town of Venice and the myriad islands are home to many buildings, monuments and works of art which cohabit in perfect harmony but, technically speaking, require different forms of intervention. On the San Marco and Tolentini islands, the stability of paved streets, bridges and houses was meticulously checked, as well as that of underground passages and sewage drains. In the lower sections, the paving has been raised (as is clearly visible on Campo San Zanipòlo) and the shores of the lagoon consolidated to cope more efficiently against tides below 100cm/40in (120cm/48in in Chioggia).

A project is under way to deal with exceptionally high tides by placing mobile barriers at the three entrances to the port. A prototype of this system, the MoSE (Experimental Electronic Module) comprises a huge mobile sluice-gate devised to regulate the movement of the tides. It was tested along the Canale di Treporti facing the Lido from 1988–1992. It is thought that the final project would need to provide 79 of these sluice-gates.

In the Experimental Centre for Hydraulic Models, at Voltabarozzo, near Padua, a simulated mock-up of the lagoon area allows studies to be carried out into projects for the harbour mouths, the safeguarding of the coastal region and of the jetties.

In the meantime, reconstruction of the coastal region of Cavallino and Pellestrina is being carried out. The coastal area has been consolidated with 2million m3/70.6 million cu ft of sand taken from the sea. These deposits were also used to reinforce sandbanks, which play a crucial role as they combat the swell and local winds while protecting the environment. In an attempt to increase their stability, these coastal dunes have been planted with ammofila , a variety of grass that thrives on sandy soil.

The north pier at Chioggia has been strengthened, 50km/31mi of canals have been dredged and the sediment obtained through this operation used to rebuild 300ha/740 acres of sandbanks.

The restoration of sandbanks is achieved by fencing off a stretch of the lagoon with wooden masts. A large canvas sheet is then fixed to the poles and laid down over the sea depths. Sediments are poured into this artificial basin as well as water, which is then filtered by the canvas.

Further operations currently under way involve cleaning up the lagoon waters, gathering the macroalgae and salvaging the smaller islands such as Lazzaretto Vecchio.

The fight to save Venice

In 1966, the year in which record water levels were registered in Venice, UNESCO stressed the urgency of the fight to save this beautiful city and her lagoon. A number of organisations and committees, both public and private, were set up to salvage and restore Venice’s cultural heritage, namely the Ufficio per la Salvaguardia di Venezia .

The Head of the Monuments and Fine Arts Department is involved in the technical aspects of this undertaking and UNESCO oversees the allocation of funds raised by several private committees. Every year millions of euros are spent on rescue operations aimed at preserving the architectural, historical and artistic treasures of the city, as well as on scholarships for artisans and research. Each of these committees is directly concerned with a specific project on a regular basis. Among the many foreign organisations dedicated to saving Venice, the most important are The Venice in Peril Fund (Great Britain, www. veniceinperil.org/), Save Venice (United States, www.savevenice.org, Comité Français pour la Sauvegarde de Venise (France, www.cfsvenise.org).

Life forms

The lagoon comprises a vast and rich habitat for fauna and flora, part of which may even be glimpsed from the vaporetto between Venice and Burano or from a car driving through the section enclosed by the Cavallino coast. The best way, however, to appreciate the extent of vegetation and animal life thriving in this “watery plain” is to explore the sandbanks by boat.

The waters of the lagoon vary in salt concentration depending on their proximity to the river outlets, where the water is almost fresh. In the middle they tend to be brackish; near the ports, where the tides inject sea water, they are far saltier. At the same time, areas around the river deltas tend to be muddy, whereas by the port mouths the lagoon bed is sandy.

Fauna

At the lower end of the food chain, different types of molluscs breed successfully on the wooden piles or bricole .

The principal category is undoubtedly that of the fish kingdom , which has defined the very character of the lagoon, with its distinctive collection in shoals around sandbanks, and the interaction of human beings with this environment as they seek to exploit such rich resources.

Crab and shrimp are central to the fishing industry and to Venetian cuisine. From a boat it soon becomes obvious where the fishing banks are situated as these attract various species of aquatic birds: wild duck (mallard and teal), tens of thousands of coots, herons and marsh harriers. Besides the common sparrows, swallows and blackbirds, the Venetian Lagoon is visited by special migratory birds, often with highly coloured plumage.

It is perhaps their beauty, strangeness and cleverness that is most fascinating: the black-whiskered bearded tit clings to the reeds; the reed warbler builds a floating nest between four reeds, which rises and falls with the tide; the kingfisher dives acrobatically and the moorhen nods her head in time to the rhythm of her strokes; little grebe pop out of the water only to dive quickly and silently below the surface again and emerge where least expected.

The very rich bird life of the lagoon also includes the cormorant, the inevitable sea-gull, the sea swallow, whose whirling wings and V-shaped tail allow it to swoop effortlessly time and again, and the little egret, recognisable by its elegant carriage and startlingly white feathers with which women adorned themselves at the beginning of the 20C. Even more beautiful is the black-winged stilt, whose sombre wings contrast with its white body and the red of its long legs; its thin, distinguished beak adds a touch of refinement.

Elegance seems to be a trait shared by all the birds of the lagoon, among which the mute swan must reign supreme.

There are numerous marsh harriers and hen harriers among the birds of prey.

Among the mammals, the rodent provides a somewhat harmful presence. The rat, the so-called pantagena , is at home anywhere, on the city squares as well as in rubbish dumps and attics.

Flora

The sandbanks are abundantly cloaked in vegetation: glasswort, sea lavender and asters turn the mounds first green, then red, then blue, then grey. Rooted in the water are various reeds and rushes with long stalks and spiky flowers. On the beaches grow convolvulus with shiny dark-green leaves and pink flowers, and sea rocket with its violet blooms.

On the first dunes of shifting sands grows couch grass, a perennial member of the grass family. Farther back, tufts of coarse grass sprout among the spurges, with their long stalks of small lancet-like leaves and flowers with yellowish bracts. Tall bushy gramineae ( erianthus ravennae ) are also widely found.

Shrubs and trees grow beyond the dunes: along the Romea highway, south of Chioggia, between Santa Anna and Cavanella d’Adige, is the Bosco Nordio (Nordio Wood) of evergreen oaks. Even the market gardens form part of the vegetation of the lagoon, especially in the south at Chioggia, where red chicory ( radicchio )is grown, highly prized but not as famous as the radicchio of Treviso.

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