Befitting its location not far from the Alps and at the lower end of the monumental Po Valley, the Laguna Veneta, and therefore the City and Republic of Venice, were formed by, and inextricably impacted by the major rivers that drain such a vast area.
The rivers that now flow, used to flow, and wanted to flow into the Lagoon include the Piave, Sile, Zero, Dese, Marzenego, Muson, Brenta, Bacchilione, Adige and the mighty Po itself.
The Dese qualifies as a minor stream, even as now combined with the Zero before entering the Lagoon, however the Piave, Brenta, Bacchilione and Adige have large annual flows and sometimes monumental seasonal flood flows that could and did dramatically affect the Lagoon and Venice itself. They would be of concern to inhabitants in any area of the world. Of course the Po is one of the great rivers of Europe. Although I have not found evidence of a historic flood incursion into the Lagoon by it, the Po‘s impacts certainly drove its lower valley residents and Ravenna itself to push it toward their sometimes unloved neighbor, Venice.
At the same time, in their flat lower reaches, they allowed navigation for transport of goods and people from the productive terra firma to communities in the Lagoon, and trade goods from there to a broad area of the mainland, all of which allowed Venice to become the focus of the region.
A World of Water
This vast network of rivers arrived at the seaside lowlands and formed broad marshes and lagoons for along the entire northern and northwestern reaches of the Adriatic. The marshes and channels were a very effective barrier to north-south transportation for many kilometers inland from the sea, and greatly hindered invasions from over the Alps. The great exceptions led to the relocation of a major segment of the population of many mainland towns to new communities within the protective arms of the Venetian Lagoon and others along that difficult coast.
Introducing the Rivers
- Piave: 220 km long, with a drainage basin of 4,126 sq.km., a major stream out of the Alps that formerly entered the Adriatic Sea at Porto di Piave Vecchia at the near the current northeast corner of the Lagoon. The Republic relocated the lower reach of the river out of the Lagoon to its current mouth at Cortellazzo, just north of Lido di Jesolo. The lower reach of the Piave now interacts via a major channel parallel to the seashore with yet the next river north, the Livenza. About 120 “river kilometers” upstream, the Piave flows through the middle of Belluno.
- Sile: 95 km long, with a drainage basin originating far above Treviso. The Sile channel was relocated to Portegrandi in the northwest reach of the Lagoon, routed into the then unused Piave riverbed to flow around the north end, then south along the littoral to exit into the Sea at Porto di Piave Vecchia, the old mouth of the Piave River!
- Zero: A fairly small stream that entered the Lagoon very close to the Dese, and now is joined with it a little upstream.
- Dese: km long, with a drainage basin of 90 sq.km., and the “token” river still allowed to flow into the Lagoon. It enters the Lagoon north of Marco Polo Airport, northwest of Torcello. Its major tributary is now the Zero river.
- Marzenego: A small drainage located in the general vicinity of Mestre, and now caught up into the channels that also divert the Brenta.
- Muson: Another small drainage, between the Marzenego and Brenta, also now absorbed into the diversion system.
- Brenta: 174 km long, with a drainage basin of 2,300 sq.km., the fifth longest river in Italy. In the 16th Century, the Republic first relocated this major stream to the south from an original Lagoon entry south of Mestre. Over the centuries, its flow was adjusted to the southeast from a point just east of Padova, and its mouth into the Lagoon relocated southward several times all the way into the 18th Century. The works finally routed the river around the south end of the Lagoon and out to the Mare Adriatico just south of Chioggia. When the Brenta had entered the Lagoon near Marghera, many believe that its main channel to the sea ran through what we now call the Grand Canal (or was it the Canale Giudecca – or both??) and then exiting through a historically much larger gap in the littoral islands just north of Lido di Venezia. The river is the central focus of Bassano del Grappa, about 50km upstream from Padova.
- Bacchiglione: 118 km long, with a source in the Alps, like the Brenta and Piave. Also rerouted around the southern end of the lagoon to join the newly built channel of the Brenta River, sharing its exit to the sea south of Chioggia. It also flows through Padova in an old channel of the Brenta (which was also diverted away from Padova!) and is reinforced by the Tesina and Orolo rivers in the vicinity of Vicenza.
- Adige: 410 km long, with a drainage basin of 12,100 sq.km., the river of Verona. Rising far to the north in the Alps, the Adige flows through Trento and Roverto above Verona. Whether or not the Adige had a long-lasting mouth into the southern area of the Lagoon, its final routing (to date!) was into the narrow area between Chioggia and the Po that is now also occupied by the Brenta and Bacchiglione.
- Po: 650 km long, with a drainage basin of 74,000 sq.km. The longest river in Italy. The active delta at the Adriatic Sea is the result of a constructed diversion of the river by Venice in 1604, done to prevent the river from continuing to move northward and eventually into the Lagoon, which would have had dire results for Venice. That diversion was necessitated by an eleventh century diversion of the Po that reached upstream above Ferrara (more than 50 km from the coast at that time) to keep the river from inundating Ravenna (almost 50 km south of the current Lagoon limits) during major flood years!
A very instructive interactive map “Evolution of the Lagoon between 1300 and 1900” is available on line at http://www.salve.it/uk/eco/default.htm , on the site “SAL.VE” to share “activities for the safeguarding of Venice and its lagoon”, presented by the Ministry of Infrastructure and Transport of the Venice Water Authority.
A vast array of old channels, irrigation canals and overflow channels create an enormous network for the control and utilization of water across the eastern Veneto. What the rivers did by themselves since their creation has been wrestled into a tentative management system that has eliminated their vital washing of the Lagoon, nutrient replacement, and siltation that redefined the meaning of land and water there many, many times.
At the same time, the siltation has been greatly reduced, along with erosion and catastrophic flood effects within the Lagoon. No one “wins” these epic wars between man and nature, only a few battles that may last a few years or many centuries.
Your national Corps of Engineers or Reclamation Authority has nothing on their Venetian predecessors!