Forecasting the water level in Venice: physical background and perspectives.

INTRODUCTION The exceptional flood of 4 November 1966, marked a milestone in the international concern for Venice, and this is also true for the efforts for the quantitative forecasting of the water level in the lagoon. Around 1970 the interest in this challenge involved many scientific centres all around the world, so that in 1972 the oceanographer W. Munk reported thirteen research institutes developing prediction techniques for Venice (Munk and Munk, 1972). The results were significant, even though the complexity of the problem does not allow, even today, the claim that a definitive solution has been found. Over the years, these research interests have been paralleled by the development of questions from an operational point of view. The historical Hydrographic Office of the Magistrato alle Acque is complemented by a service of the city of Venice, the Centre for Tides, committed to alerting the city, initially by using sirens, and, step by step, by the various modern tools of high technology, like the internet and the Short Message System (SMS). Moreover, a deeper interest has grown from the perspective of the mobile barriers, for which a long-term forecast becomes important. It is not correct to say that the need for prediction is limited to flood events. For a town like Venice, for example, the very low tides are also dangerous; one thinks of their effect in each ‘rio’ (small, internal canal), on commercial traffic and much more on the rescue boats. Many considerations force a general request for the forecasting of all water levels, including the intermediate ones (Boarto et al., 2001).