Influence of conceptual model uncertainty on contaminant transport forecasting in braided river aquifers

• Data paucity can be balanced by the use of analog data in hydrogeological modeling.
• Reasonable contaminant transport predictions can be achieved using analog data.
• The plume speed is weakly correlated to the equivalent permeability.
• The type of geological structures influences strongly the plume behavior.
• The initial conditions are determinant for the plume evolution.

SummaryHydrogeologist are commonly confronted to field data scarcity. An interesting way to compensate this data paucity, is to use analog data. Then the questions of prediction accuracy and uncertainty assessment when using analog data shall be raised. These questions are investigated in the current paper in the case of contaminant transport forecasting in braided river aquifers. In using analog data from the literature, multiple unconditional geological realizations are produced following different geological conceptual models (Multi-Gaussian, Object-based, Pseudo-Genetic). These petrophysical realizations are tested in a contaminant transport problem based on the MADE-II tracer experiment dataset. The simulations show that reasonable contaminant transport predictions can be achieved using analog data. The initial concentration conditions and location regarding the conductivity heterogeneity field have a stronger influence on the plume behavior than the resulting equivalent permeability. The results also underline the necessity to include a wide variety of geological conceptual models and not to restrain parameter space exploration within each concept as long as no field data allows for conceptual model or parameter value falsification.