I. Introduction
After the disastrous flood of November 1966 in Venezia (194 cm over the average sea level) the Municipality of Venezia set up the first observation service of the high tides. In December 1979 another severe flood occurred (166 cm over the average sea level). In consequence of these events, the municipal government decided to found the CPSM - Centro Previsioni SegnalazioniMaree(Tide Forecasting and Signalling Center) - which mainly has to supply an effective alarm service regarding the occurrence of important or extraordinary high (and ebb) tides [5].