venice and its surroundings 37
horizontality, some land emerges, also flat. These are the barene, covered
by a particular aquatic vegetation, growing to just a few inches above the
water, and which are only covered by the highest tides. These are small
islands and archipelagos, undoubtedly formed by the alluvial deposits of
the rivers that flow into the basin, which have been gradually consoli-
dated and expanded by human work. This whole ecosystem has been and
remains the subject of incessant transformation, due to the combined
action of the sea, the rivers, and human intervention. As it stands today,
the lagoon is in fact profoundly different from what it was in the Middle
Ages or in early modern times. We must, therefore, insist on a reality:
here, the environment lives according to a specific chronology proper to
itself; it moves and changes at the will of forces that are antagonistic and
difficult for man to control. On the one hand, the sea level varies. On the
other hand, in this area, the ground collapses under the weight of river silt
deposits. And the combination of these two phenomena, subsidence and
temporary rise in sea level, may result in a danger: that of the emerged land
being flooded by water. At the base of the Adriatic, the movements of the
sea reach, in fact, a level unknown elsewhere in the Mediterranean. The
tide, which enters through the graus and rises through internal channels,
then by urban canals, sets the pace for Venetian life. It renews the water,
purifying it. It assures, in so doing, the survival of the lagoon basin.
But high tides, compounded by heavy rains and the effects of the wind,
cause veritable phenomena of temporary flooding. Aqua alta, for several
hours, invades the area, or at very least its lower parts. These exceptional
tides can attack the banks, carry away protective walls, gnaw away at the
lagoon islands, and submerge the barrier beaches that are already battered
daily by the swell, the waves, and the erosion of the sea. The Malamocco
lido was thus in the early 12th century partly submerged. The barrier beach
of Sant’Erasmo was overwhelmed, in the middle of the next century, by
a similar flood. If the coastal defense was compromised, that was a first
risk, for the sea invaded and swept away everything. Both the lagoon and
Venice disappeared. But there was another danger, that of the siltation of
rivers, which could also condemn the lagoon to decay. Silt would stop up
the lagoons, filling their depths. The lidi, already reinforced by longshore
currents and sand accumulations, threatened, if the sedimentation was
too great, to form a continuous barrier. The ports became overrun with
silt. They could be closed off more or less rapidly, isolating a pool that had
been doomed to a quick filling.
This environmental fragility allows for an immediate comprehension of
the challenges of life in the lagoon: without work, without taking actions