SIMULATION OF STREAMWATER THERMAL LOADINGS USING A FULLY-INTEGRATED SURFACE/SUBSURFACE MODELING FRAMEWORK

Natural and anthropogenic thermal loadings to streams have significant relevance with respect to climate change, ecosystem health, and water resources management. In recent years, there has been increased field-based research directed towards the characterization of thermal transport exchange processes occurring at the surface water/groundwater interface of streams. In spite of this effort, relatively little work has been performed to simulate these exchanges and elucidate their roles in mediating surface water temperatures in a holistic watershed context where the pertinent hydrological, meteorological and surface/variably-saturated subsurface processes are simultaneously taken into account. To address this issue, the capabilities of HydroGeoSphere, a fully-integrated surface/subsurface flow and transport model, has recently been enhanced. HydroGeoSphere can simulate water flow, evapotranspiration, snow accumulation and melting, and advective-dispersive heat and solute transport over the 2D land surface and in the 3D subsurface under variably-saturated conditions. In order to demonstrate the capabilities of the enhanced model to capture thermal transport and exchange processes, a high-resolution 3D numerical simulation was performed for a highly-characterized stream segment in Ontario, Canada. It is shown that the transient model can mimic the spatio-temporal thermal patterns observed in the streambed, the surface water and the groundwater. The computed thermal regime is shown to vary markedly both spatially and temporally depending on the intensity of the groundwater discharge/recharge patterns along and across the streambed. The computational framework can be used to provide quantitative guidance towards establishing the conditions needed to maintain a balance between a healthy ecosystem and consumptive water use.