Jacek Tylkowski

Abstract The work described here has sought to identify the variable hydro-meteorological conditions (across hydrological years 2009–2014) determining cliff-erosion dynamics along the coast of Poland’s Wolin Island. Daily data from the tide-gauge station in Świnoujście allowed for the presentation of variability in sea level, with data obtained from the Institute of Meteorology and Water Management. Also presented are annual, semi-annual and monthly characterisations of elements of the weather capable of exerting the greatest erosive impact on cliffs, i.e. precipitation and snow cover, as well as thermal and anemometric conditions. The daily meteorological data derived from the author’s own measurements, from the meteorological station in Biała Góra situated on the Wolin cliff top. The potential erosive hydro-meteorological conditions were set against annual measurements of cliff-top recession rates, the research into this involving geodetic RTK GPS measurements on 5 test sections representing different morpholithological conditions. The hydrological years 2009-2014 experienced very significant hydro-meteorological events potentially favouring the occurrence of erosion processes (mass movements and aeolian erosion). The occurrence of potentially erosive hydro-meteorological events is referenced against cliff-top recession rates. In particular, this study presents the geomorphological effects of two extreme hydro-meteorological occurrences. i.e. Hurricane Xavier of December 2013 (maximum sea level 612 cm) and a two-hour extreme (74mm) precipitation event occurring in August 2014 year. The specific nature of the cause-effect relationship between hydro-meteorological conditions and cliff erosion on the cliff coast of Wolin Island is also described, though these results are also capable of being applied to other cliff sections of the Southern Baltic coastal zone. The relationships between hydro-meteorological conditions and coastal erosion are not seen to be directly proportional, but are non-linear. It is not always the extreme storm surges and high levels of precipitation that generate extreme erosion along the shore. Rather, the dynamics of cliff-edge erosion are found to be determined by a number of other determinants obscuring the simple relation-ship between hydro-meteorological conditions and intensity of erosion. The most important factors influencing the dynamics of coastal erosion are morphological conditions, slope aspect vis-à-vis approaching waves, qualitative and quantitative conditions of sediment on beaches and in the shallows, the dynamics and frequency of extreme hydro-meteorological events in the preceding period, and human activity relating to hydrotechnical installations. Given the current upward trend for sea level and the increasing frequency of extreme hydro-meteorological events, the Southern Baltic coastal zone is expected to be subject to intensified cliff erosion in the near future. In this context, the results presented here might also gain wider application in studying other parts of the Baltic coastal zone with a morainic cliff coastline, especially along the stretch between Estonia and Germany.

Jacek Tylkowski

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