Comparison of genesis and geostatistical methods for characterizing the heterogeneity of alluvial media: Groundwater flow and transport simulations

We describe a new method for generating the sediment heterogeneity of alluvial deposits, based on a genesis model which mimics some of the hydraulic rules by which meandering or braided streams deposit or erode sediments. The new model is described and compared with other approaches, and is then applied to a 5.4×1.4 km2 reach of the Aube River, upstream of Paris. The model is based on data obtained from a single cross-section of the alluvial plain, with 44 auger-holes along the 1.4 km stretch of the plain. As the model describes the sediment facies, we assign to each facies an assumed hydraulic conductivity. Flow and transport simulations are then made, with the commonly used code MODFLOW. In order to compare the results with simulations based on other descriptions of heterogeneous media, we then use classical geostatistical tools (indicator simulations) to generate alternative images of the same medium, based on the same initial data, and the same assumptions on the hydraulic conductivity of each facies. Finally, an equivalent uniform medium (obtained through permeability upscaling) is also generated. Comparing these three approaches on the basis of the flow and transport results, we show the intrinsic capacity of the new model to generate more realistic flow and transport processes in heterogeneous alluvial media, where permeability barriers and buried channels dominate the spatial distribution of heterogeneities.