Stream functions and equivalent freshwater heads for modeling regional flow of variable‐density groundwater: 2. Application and implications for modeling strategy

Stream functions and equivalent freshwater heads are used to simulate steady state flow of variable-density groundwater in a regional, cross-sectional flow model through the Palo Duro Basin, Texas, where fluid densities vary between 1.0 and 1.15 g/cm3. Centroid-consistent velocities computed from the stream function solution allow a more precise interpretation of local flow patterns in cross-sectional models than those from the head solution. Effects of significant fluid density variation on the regional groundwater flow pattern are studied by comparing simulation results that incorporate spatially varying, time-invariant densities with those that assume uniform density. Modeling shows that the regional groundwater flow pattern in the Palo Duro Basin is not significantly affected by variations in fluid densities, indicating that the topographically driven flow component dominates buoyancy forces associated with dense brines. An exception is near the eastern boundary where high fluid densities cause stronger downward flow. However, simulated equivalent freshwater heads in the variable-density model differ significantly from simulated heads in the freshwater density model, which is important for model calibration. In addition to the well-known problems of hydraulic parameter and boundary condition uncertainties, modeling strategies for regional flow systems require consideration of uncertainties associated with fluid density and evaluation of equivalent freshwater head data.