Ryszard Hoc, Andrzej Sadurski, Zenon Wiśniowski Geologos 24, 3 (2018): 207–216 DOI: 10.2478/logos-2018-0021 A groundwater flow model for the Wolin Island area, including glaciotectonic deformation Ryszard Hoc1*, Andrzej Sadurski2, Zenon Wiśniowski1 1Pomeranian Branch of Polish Geological Institute – National Research Institute, Wieniawskiego 20, 71-130 Szczecin, Poland 2Nicholaus Copernicus University Faculty of Earth Sciences, Lwowska 1, 87-100 Toruń, Poland *corresponding author, e-mail:
[email protected] Abstract During the construction of mathematical models for mapping hydrogeological conditions it is necessary to apply sim- plifications, both in the geological structure and in hydrogeological parameters used. The present note discusses prob- lems surrounding the mapping of glaciotectonic disturbances that occur in the northern part of Wolin Island (northwest Poland). For this part of the island, a direct outflow of groundwater towards the Baltic Sea basin has been determined on the basis of geophysical survey results. An important feature in the hydrogeological conditions here is the isolation of groundwater from both the Baltic Sea and Szczecin Lagoon by clay with a Cretaceous xenolith. Such a geologi- cal structure explains the presence of perched water at considerable heights in zones close to the cliffs, without any significant hydraulic connection with surrounding reservoirs. Hydrogeological conditions of Wolin Island have been modelled using the Visual MODFLOW package v.4.2. In the vertical section, these conditions can be simplified to one aquifer (Pleistocene-Holocene), in which two aquifers can be distinguished. In a large part of the island, these remain in mutual hydraulic contact: layer I – upper, with an unconfined aquifer, and layer II – lower, with a confined aquifer, locally an unconfined one.