Development of a three-dimensional hydrogeological model for the island of Norderney (Germany) using GemPy

Abstract

Geological information is required to parameterize hydrogeological properties in groundwater flow models. Our aim was to provide a hydrogeological model for the island of Norderney, Northwest Germany and the surrounding Wadden Sea for this purpose. The model focuses on Holocene, Pleistocene and Pliocene deposits which are the most relevant to groundwater flow in and around the island's freshwater lens. For these geological units, borehole data was available that allowed us to distinguish between sediments acting as aquifers and aquitards. Conceptual units were derived that comprise the most common stratigraphic and petrographic features into discrete entities. The borehole data was supplemented by maps of the pre-Holocene surface as well as data from an existing stratigraphic model for deeper geological units. The model was developed and created using the open-source geological modelling software GemPy. The resulting model contains major hydrogeological units that can be assumed continuous over a larger extent of the model area based on the available data. From the deeper geology, a possible range of locations of the aquifer base below Norderney was extracted. By integrating borehole data, existing geological models and geological interpretations available in the literature, this dataset complements the so far mainly cross-sectional and partial descriptions of the hydrogeology below Norderney.