Solute Transport Modeling In An Experimental Stratigraphy

A high-resolution, multiscale hydraulic conductivity map is created based on an experimental stratigraphy. A heterogeneous model is created, incorporating the complete conductivity variation. A 14-unit hydrostratigraphic model (HSM) is also created for which an equivalent conductivity is estimated for each unit via a novel upscaling method. Under a lateral hydraulic gradient, steady-state, incompressible flow experiment is conducted in both models. Compared to the heterogeneous model prediction, HSM-predicted, global mean relative error of hydraulic head is 1.5%, that of groundwater flux is 0.77%. A conservative pulse-input line- source tracer is then simulated. In the heterogeneous model, the tracer exhibits both scale-dependency in the observed longitudinal macrodispersivity and persistent long tailing associated with anomalous, non-Fickian dispersion. Using (small) hydrodynamic dispersivities, the HSM closely predicts the tracer displacement, moments and their derivatives. In solute breakthrough, a certain degree of tailing is also predicted by the HSM which captures the large-scale, between-unit velocity variation. However, detailed plume shape is not captured, nor are the arrival and tailing of the breakthrough curves. Using macrodispersivity (both unit-specific and time- dependent), the breakthrough prediction of the HSM has improved from that using hydrodynamic dispersivities, especially in early times before encountering significant non-stationarity. However, the HSM model fails to capture the development of a steep breakthrough front and multiple peak concentrations. The plume shape is also too diffused. For all HSM simulations, the largest error occurs in a fluvial-floodplain unit where irregular trend exists and in a turbidite unit which contains preferential flow. Finally, macrodispersive displacement mapping reveals that heterogeneity-induced dispersion is correlated both in time and space, a likely result of the correlated velocity field.