Construction of hydrostratigraphic grid models of the Northwest German Basin for the estimation of subglacial erosion during past and future glaciations

The shallow subsurface of the North German Basin consists of unconsolidated Quaternary sediments. During the Elsterian glaciation subglacial tunnel valleys were deeply incised below the ice sheets. These tunnel valleys commonly range in depths between 100-400 m, but may reach depths of more than 500 meters. Given that the BGE is focusing on depths of 300 to 1500 meters for high-level radioactive waste repository sites, the potential for future subglacial erosion must be considered to ensure the long-term safety of a selected site.

We develop hydrostratigraphic 3D reservoir grid models of the Northwest German Basin as input for numerical hydraulic subglacial erosion modelling to assess tunnel valley formation during future glaciations. These hydrostratigraphic 3D reservoir grid models are constructed with different resolutions. All models cover Permian to Cenozoic sediments and have a depth of 2000 m. They are constructed with a layered-structural-model, voxel-grid-models approach. To construct the layered structural model, we used existing stratigraphic 3D models (GTA3D, TUNB3D-NI) and additional borehole data. The reservoir grids are constructed as hydrostratigraphic grids, integrating constant permeability values based on hydrogeological properties of the stratigraphic units. This approach allowed fast and successful construction of large grid models (up to 40,000 km² in size) despite the heterogeneous database.

By implementing grid models with different resolutions in the numerical erosion model, we will test the impact of grid size on the outcome of the erosion modelling. The results will help in the process of site selection and long-term safety assessment for potential repository sites.