EFFECTS OF THERMAL VARIATION ON FLOW DYNAMICS IN THE HYPORHEIC ZONE

Heat is a naturally occurring and cost-effective tracer to study groundwater flow to, from, and throughout the subsurface. Often used for the quantification groundwater discharge, heat has been used to identify gaining and losing portions of streams and in determining flow parameters such as hydraulic conductivity (K) or velocity. Connecting ground and surface reservoirs is an area known as the hyporheic zone (HZ) where waters from both reservoirs interact. The flux of water throughout the HZ is controlled by stream bedforms, sinuosity, surface water velocity, local water table, seasonality, and sediment K. K is being dependent on both the viscosity and density of water, and it is well established that temperature influences both variables. In most studies, these changes have been neglected because of the limited effect either has on K. However, these variations are important to understand because an increase in K will result in an increase in groundwater velocity, having implications relating to residence time and subsurface nutrient processing. To better understand how water temperature effects flow dynamics in the HZ, multiple two-dimensional models will be created using the USGS software VS2DHI to map flow under both warm and cool thermal conditions. Data were collected from a series of varying temperature hydrologic flume trials where the effects of hyporheic flow altering variables like sinuosity, surface water velocity and volume, and bed-forms were controlled. We expect that K in the HZ will be greater under warm conditions and lower under cool conditions which will modify the depth of surface water penetration, and preliminary modeling indicates a faster speed of frontal movement under warm conditions than cold. Understanding these changes could help prepare us for future urban expansion, climate change, and other possibilities that could modify surface and ground water temperatures.