Spatial and temporal dynamics of water flow and solute transport in a heterogeneous glacial till: The application of high-resolution profiles of δ18O and δ2H in pore waters

The heterogeneity and dynamic of water flow and solute transport processes were investigated in the upper 6 m of a surficial, glacial till in southern Saskatchewan, Canada. Continuous core samples from three vertical sites located over a maximum spatial distance of 65 m were collected and analyzed for particle size distribution, porosity, and water content. High-resolution (0.2 m) profiles of δ18O and δ2H in pore waters were also measured for the three sites on a seasonal basis. Depth profiles of all measured parameters indicate highly heterogeneous structures in the upper 6 m. In two coreholes, depleted water isotopes measured at different depths below ground (0.7 and 3 m) were in the range of winter precipitation values, suggesting preferential flow of meltwater in spring accompanied by a rising water table. A one-dimensional equilibrium flow and transport model failed to simulate the isotope-depth distributions with depleted winter values, and could not reproduce the measured values even when accounting for vertical, preferential flow. A conceptual model was created, based on the consistency of all measured data and assuming preferential lateral flow as the controlling flow and transport mechanism after snowmelt. In the model, water from surface runoff (after snowmelt) drains into an ephemeral depression that crosses the study site. As this water infiltrates, it forms a water table mound that slowly propagates away from the depression. As the water table propagates outwards, dynamic vertical flow processes result in net upward and downward fluxes.