Extreme sea level events in the coastal waters of western Estonia

Extraordinarily low and high sea level events are analysed on the basis o f historical data and their mechanisms o f occurrence are studied with the 1 km grid size 2D hydrodynamic model in the two almost tideless semi-enclosed sub-basins of the Baltic Sea, the Gulf of Riga and the Vainameri. The sea level is modelled with realistic meteorological forcing and comparison data from 1999 and 2001. Resonance properties o f the sub-basins are studied and their possible role in the formation o f extraordinary sea level events is discussed. While the extremely low levels ( —1.23 m below the mean sea level) in the Estonian coastal waters do not generally originate locally, the high levels (up to 2.53 m above the mean as measured in the Pärnu Bay) are short term and local. They occur in combination with several forcing and morphometrical factors and are localised in the shallow and narrow bays exposed to the direction of the strongest possible storm winds, SW and W. Model simulations show that extremely high and low sea levels in some small bays of western Estonia can exceed the corresponding values in the Pärnu Bay