Assessing the effects of long-term landscape evolution on the overburden of deep repository sites: application to northern Switzerland

The safety assessment of radioactive waste repositories requires scenarios and forecasts of the erosional, climatic, and tectonic future evolution. One of the major challenges in the assessment of long-term landscape evolution for safety is that the relevant processes, models and model parameters are subject to a range of significant uncertainties. Assessments should provide the full range of conceivable developments using the best available scientific knowledge. Here, we present an assessment framework for future erosion with a rigorous uncertainty management. The approach anticipates erosion from fluvial, hillslope, and glacial processes over a timescale of 105-106 years. Uncertainties are addressed in a hybrid way, using probabilistic methods in combination with a scenario approach, whereby the chosen scenarios cover a wide range of possibilities. A protocol was followed to derive model parameter uncertainties that respect individual estimates of experts. The entire process is accompanied by a sensitivity analysis. We used the workflow to assess erosion in Northern Switzerland over the next million years. The results serve as input to site a deep geological repository for nuclear waste in Switzerland and to demonstrate its long-term safety.