A dedicated field investigation programme was undertaken to reconstruct the erosion history of the siting regions over the past 1 – 2 million years as a basis for establishing future erosion scenarios (Section 6.4). In addition to characterising the depth, shape and age of glacially over­deepened troughs, the investigations sought to constrain the age of the Early to Middle Pleistocene gravel deposits for reconstructing past fluvial incision history.

The investigations involved the acquisition of high-resolution 2D reflection seismic data (Nagra 2018), data for seismic surface wave investigations (Nagra 2021) and 11 Quaternary boreholes with ~ 50 to 300 m length (Fig. 2‑2, Tab. 2‑2). The boreholes were fully cored and numerous laboratory investigations were carried out, including sediment age determinations (e.g. Mueller et al. 2024, Tomonaga et al. 2024). Surface outcrops were also studied and sampled to determine relative and absolute ages of the deposits (e.g. Grischott et al. 2020, Scheidt et al. 2023, Thew et al. 2024). Understanding of the past landscape evolution has significantly improved as a result of these investigations (e.g. Gegg et al. 2023, Buechi et al. 2024; see Sections 3.5 and 6.4.1).

Tab. 2‑2:List of Nagra’s 11 Quaternary boreholes drilled 2018 – 2020 including references to data reports

MD: Measured depth below ground level. Borehole locations are shown in Fig. 2‑2.