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Abstract

Time series of 2.9-17.5 years length, measured at 18 tide gauge stations, spread along the Adriatic Sea, were analysed to determine characteristics and periods of prevailing sea level oscillations during extreme sea level events. All series were sampled with a 1-min time step. Sea level extremes were separately extracted from residual time series and from high-frequency (T < 2 h) time series. Properties of both types of extremes were evaluated. It was shown that tide gauge stations can be classified within one of three groups. Group 1 stations are characterized by the dominant contribution of the low-frequency oscillations to extremes. These stations are commonly placed along the open coast. Their spectrum has no significant peaks and often assumes a white-noise form at the highest frequencies. Extremes of Group 2 stations are occasionally dominated by high-frequency signal. Spectra of these stations is polychromatic (i.e., with several distinct peaks). These stations are found at coastlines along gently sloping bottoms, or within bays and harbours protected from incoming long ocean waves by nearby islands. Finally, Group 3 stations are characterized by high contribution of the HF oscillations to extremes. These stations are mostly placed in high resonant bays or harbours. Spectra of Group 3 stations is monochromatic, i.e., there is one dominant period at which sea-level oscillations occur. Depending on which group does a tide-gauge station belong to, it might be essential to assess both low and high-frequency sea level component to estimate total hazard level.