In his poem entitled “Lines written amongst the Euganean Hills”
(1818) Shelley wrote of “Ocean’s nursling Venice”, and went on
prophetically: “Sea-girt city, thou hast been/Ocean’s child and then
his queen/Now is come a darker day/And thou soon must be his prey.”
The
sea is indeed preying on Venice. In Science for August 25, Albert Ammerman and
Charles McClennan of Colgate University, New York, discuss tidal events that
are giving rise to intense anxiety regarding the future of the city of the Doges.
In 1981 a scheme was put forward, involving the construction of 79 mobile flood
gates at the three outlets to the lagoon which surrounds the city. Since then
dire warnings of global warming and higher tides have suggested that even such
a barrage of gates would need to be closed so frequently that there would be
a serious impact on the ecological systems of the lagoon.
In November, 1966, there occurred a tide that peaked at 1.94m above the standard
mean sea level established back in 1897. On that occasion some of the art and
architecture of Venice suffered substantial loss. It was forecast that winds
from the south-east could assist in producing storm surges reaching well beyond
normal limits. During the past century, relative sea levels rose by some 23cm,
an effect intensified by construction of an industrial complex at neighbouring
Porto Marghera.
The most recent plan proposes raising the 79 gates into position whenever the
tide reaches the level of 100cm above the 1897 standard. At present this occurs
seven times every year on average, but it is estimated that in a bad year as
many as 150 gate closings would be necessary to offset a 30cm rise in relative
sea level. Tidal events are seasonal, with two thirds of the floodings occurring
between October and January. Offsetting this would seriously limit the water
circulation essential for living creatures in the lagoon. There is a conflict
between scientists and public policy makers, since the augmentation of tides
in Venice will continue for the next two centuries or more, and the mobile flood
gate system will then have long ceased to give protection. Planning the city’s
future promises many headaches and heartaches.