Venice lagoon with sandbanks and ghebi
Venice Lagoon covers an area of 550 square kilometers and only 8% is made of emerged earth. It is connected with the Adriatic Sea by three outlets: Lido San Nicolò, Malamocco and Chioggia. The north, consists of the islands of Murano, Pellestrina, Burano, Torcello, Mazzorbo and Vignole; in the centre, there is Venice with San Lazzaro, San Servolo and San Clemente and, in the south, from Chioggia with a number of smaller islands.
The environment of the lagoon is formed by a series of channels that run among velme, sandbars, islands and fishing valleys. The landscape varies depending on tides entering the lagoon twice a day by flooding lower lands and by exchanging and oxygening the inside water. The average tidal excursion is about 70 centimeters.
The sandbanks are flat land covered by small channels called “ghebi” and small lakes of brackish rainwater called “ciari”. During the twentieth century, most of existing barene have been destroyed causing serious damages to the ecosystem. In the last years, an artificial rebuilt has been tried in order to allow kentish plover, oystercatchers, fraticelli, mallard, black-winged stilts and common redshanks to nest.
Fishing valleys in the Venice lagoon
The velme emerge with low tide, they are devoid of vegetation and made up of soft soils. The fishing valleys are special areas separated from the lagoon and opened up by dikes that protect the flow of the tides. Within them, there are pools of brackish water used for fish farming and hunting.
Surely, the Venice lagoon has been inhabited since prehistoric times. Some excavations have revealed the presence of villages that date back to 2000 b.C.. During the Roman period, flourishing cities on the mainland as Altino, Spina, Adria and Aquileia came into life. The first settlements in the lagoon were at Torcello, Mazzorbo and in the disappeared islands of Ammiana and Costanzico. It seems that, in Malamocco existed a thriving port that connected the trade of the Adriatic.
The real migration flow was in the fifth and sixth century b.D., when people coming from the mainland were forced by the closing in of barbarians to take refuge in safer islands of the lagoon. From this period onwards, Malamocco and Torcello began to grow up to become centres of economic, political and religious power. Around the eighth century and for a millennium, Venice became the centre of prestige and power. In the twentieth century, the construction of the chemical plant of Porto Marghera began and it brought deep changes to the landscape and to the delicate ecosystem.
Over time, human being had to struggle against the force of nature which threatened the lagoon by tides corrosion on the Adriatic coast and from alluvial deposits brought by rivers that damaged to bury it. The Government of the Serenissima has always sought to put a remedy to these problems. In 1324, started the first works to divert the River Brenta which, at the time, led in front of Venice.
Subsequently, in 1431 and 1531, new works were done in order to bring the mouth to Chioggia. Another important deviation was the one of river Sile which flowed in front of Burano, and the river Piave. Embankment works have always been done such as: the construction of the embankments “murazzi” built in 1740 with large blocks of stone from Istria.
“Mose” is still under construction that will counteract the exceptional high tide flows. Thus consists of a series of mobile dams that will be placed on the three outlets bottom and, during exceptional high tides, they will raise to hinder the adriatic water to flood Venice.