Frequency and strength of storm surges in the Oder River estuary area

The aim of the study was to estimate the frequency and strength of storm surges in the Oder River estuary area during the 1993/94–2016/17 seasons. The analyses involved water level readings recorded at gauges located in the Oder River estuary area, including the coasts of the Pomeranian Bay (Zatoka Pomorska) and the Szczecin Lagoon (Zalew Szczeciński), as well as the downstream reach of the Oder. Recognition of temporal and spatial water level variations in the region under investigation revealed significant irregularities in storm surge occurrence; periods with an increased frequency of freshets followed long periods with their scant occurrence. During the year, most of the storm events were observed between November and January. In the period discussed, the most severe and extensive storm surge in the Oder River estuary area was observed in October 2009. Very high freshets were recorded in November 1995, January 2012, and January 2017. The long-lasting and extensive high water events in the downstream reach of Oder River resulted from the progressive and prolonged increase in sea level in the Pomeranian Bay. Long-term persistence of high water levels in the Oder River estuary area were also registered when storm surges limited the outflow of the Oder River during snow-melt events, ice jams developing on the lower Oder at the same time. Finally, severe storm events were observed under the condition of the increased water volume in the Baltic Sea.