Comparing the Usefulness of 1D, 2D, 3D Transient and 1D Steady-State Heat-Flow Simulations in Determining Riverbed Hydraulic Conductivity at Sites of Induced Infiltration

Determining riverbed hydraulic conductivity is important when modeling groundwater / surface-water interactions at sites of induced infiltration.  Of the many techniques available for determining riverbed hydraulic conductivity, heat-flow modeling has become an increasingly important tool.  There are many approaches to simulating heat flow ranging from relatively simple, 1D steady-state models to complex, 3D transient models.  This study examines the question of the necessity and advantages associated with more complex models versus simpler approaches. At sites of induced infiltration, where horizontal gradients might be strong, a 2D or 3D approach might seem advantageous, but it is unclear whether the extra complexity and effort yields significantly different and more accurate results. 

Heat flow was simulated to estimate riverbed hydraulic conductivity at three sites of induced infiltration adjacent to the Great Miami River in southwest Ohio.  Three approaches were compared: 1D steady-state, 1D, 2D and 3D transient simulations. Preliminary results indicated that where strong downward gradients existed, 1D and 2D transient modeling performed equally well. The 1D transient model did not perform as well at sites with strong horizontal flow and weak downward gradients. The 1D transient approach produced results that showed similar trends to the 2D transient models in predicting short-term temporal changes of riverbed conductivity, but the absolute estimates were sometimes dissimilar. The 1D steady-state approach sometimes produced very similar results to the 2D transient models, but at other times it over-predicted riverbed conductivity. While the reasons for these observations are still under investigation, it is clear that 2D models are more appropriate in many circumstances for predicting hydraulic conductivity at sites of induced filtration. The 3D approach is expected to produce more accurate results and is still under investigation.