Analysis of tide measurements in a Sicilian harbour

Designing of ports and coastal protection works as well as planning of coastal human activities require knowledge of tidal oscillations. The latter vary noticeably from site to site and present an “astronomic” component, which is roughly periodic, and a “meteorological” component which is usually considered as random. In this paper, the tidal oscillations observed in a Sicilian harbour in the period 1999-2009 are analysed statistically, in order to recognize a probability distribution which allows one to predict the highest tidal levels. First, the measurements are used to obtain, for each year, the astronomic tide by the harmonic analysis by the software package T_TIDE. The difference between the observed tide and the astronomic tide, indicated as “noise”, is imputed to meteorological factors and treated by a statistical approach. The noise imputable to sea storms moving onshore is divided from that imputable to storms moving offshore. Several probability distributions are then considered for each noise and it is established that each noise closely follows the Weibull extreme value distribution better than other distributions.