GraphFlow v1.0: approximating groundwater contaminant transport with graph-based methods – an application to fault scenario selection

Abstract. Groundwater contaminant transport problems remain challenging with respect to their computing requirements. This often limits the exploration of the conceptual uncertainty that is mainly related to large-scale geological features – such as faults, fractures, and stratigraphic variations – and limited characterization. Here, to facilitate geological conceptual uncertainty exploration, we develop further the use of graph representation for geological models to approximate groundwater flow and transport. We consider a faulted multi-heterogeneous-layer medium to test our approach. The existing rank correlation between the shortest path distribution from a contaminant source to the model domain outlet and the cumulative mass distribution at the outlet enables us to perform scenario selection. The scenario selection approach relies on a metric combining the Jaccard dissimilarity and the Wasserstein distance to compare binary images. Among a set combining eight alternative scenarios, where three faults can act as either a flow barrier or a preferential path, we show that the use of graph approximations allows us to retain or reject scenarios with confidence, as well as to estimate the individual probability of a fault to act as a barrier or a path. This methodology framework opens up possibilities to explore more thoroughly conceptual geological uncertainty for processes affected by flow and transport.