Modelling of glacial melt water erosion of the overburden of a HLW over 1 million years

The site selection procedure in Germany is searching for a site with the best possible safety for a repository for high-level waste (HLW). The integrity of the overburden is crucial in the assessment of the best possible safety (StandAG §23 (5), para.3). Beyond the safe inclusion in the selected host rock for a HLW repository, a sufficient stability of the overlaying overburden horizons must be ensured. Erosion by glaciation induced processes are but one of the potential threats to the stability of these overburden horizons. The research project presented here is funded by BASE under the grant number FKZ 4721F10401.
Within the research project “Evaluation of methods and models to predict the protective function of the overburden in Germany over the period of 1 Ma” (MeMoDeck) a framework to assess the risks introduced by glacial erosion that are to be expected within 1 million years was developed. As an indication of this, the erosion processes, prevailing during the Pleistocene, have been analysed with respect to the extent of the erosion depth introduced by them. The largest depths are attained to incisions by subglacial meltwater transport in the form of tunnel valleys. 
The authors employed a combined modelling approach, which includes a three-dimensional deterministic numerical modelling of the tunnel valley genesis with FLAC3D and a multivariate probabilistic modelling with GoldSim to account for the remarkable uncertainties over 1 Ma. The uncertainties result from the lack of data with respect to hydraulic conditions during the melting of the ice sheet and the variability of the erosion resistance of the geological horizons of the overburden, which overlies the respective host rock. 
The authors determine the depth of a prospective tunnel valley by a simulation at well-constrained geological and melt water conditions by the deterministic FLAC3D model.
The results from the deterministic modelling with Flac3D are the basis of the simulation within the probabilistic model with GoldSim, which relaxes the modelling constraints towards melt water and geological properties using statistical distribution functions for these quantities.
The results of the modelling will be presented and the most influential parameters towards the final depths of the overburden incisions will be discussed.