Using a Coupled Surface water/ Groundwater Model to Study Heat as a Tracer in Three Dimensions

Abstract:

Heat as a tracer has proven to be an effective method for quantifying groundwater - surface water interactions. However, there remains a lack of controlled, experimental data to assess fundamental aspects of heat transport in porous media. There may be a disconnect between field and model-based studies, because: 1) model results have yet to be tested against data from controlled laboratory experiments, and 2) there are often too many variables in field studies to be thoroughly modeled without simplification. This study is comprised of a three-dimensional transient numerical model of heat flow through a porous media coupled with steady state fluid flow using COMSOL Multiphysics. Pressure and temperature outputs are compared to data measured in a laboratory flume. The 3D model enables exploration of the effects of oblique flow paths through a stream bed and/or banks with a (stream) surface water upper boundary on diurnal temperature records. By imposing known flow or temperature gradients in any direction, we can analyze the effects of these diverse gradients on the veracity of current heat as a tracer methods (which assume unidirectional flow) as well as develop valid error statistics for these methods in the presence of non-vertical flow.