USING NUMERICAL MODELING TO QUANTIFY THE ERROR ASSOCIATED WITH VIOLATING THREE COMMON ASSUMPTIONS OF USING HEAT AS A TRACER

In order to use temperature as a tracer to quantify groundwater-surface water interactions, many assumptions and simplifications must be made. These simplifications include assuming that the subsurface is homogenous, the temperature front is propagating through the subsurface at a constant rate perpendicular to the subsurface, and water flows through the subsurface solely in the vertical domain. A suite of numerical model realizations were created using COMSOL Multiphysics, a finite element analytical solver, to investigate the error associated with violating each of these assumptions under typical field conditions. The model represents a fully coupled surface water-groundwater domain with realistic bedforms that induce hyporheic flow. The groundwater domain can be modified to include various realistic heterogeneous subsurface configurations as well. By quantifying the error of violating each assumption, the validity of the use of heat as a tracer in certain conditions can be evaluated as well as the determination of the optimal placement of sensors in the field.