VERTICAL AND LONGITUDINAL DIFFERENCES OF HEAT TRANSMISSION BETWEEN HOT AND COLD WATER PULSES IN A HYDRAULIC CHANNEL

The mixing of surface water and groundwater in the hyporheic zone influences the temperature of stream water and underlying sediments. This change in temperature is important to biological processes as well as the physical and chemical conditions of the system. To investigate the thermal fluctuations of water in the hyporheic zone, a study was conducted to analyze the variations in temperature propagation between hot and cold water runs in a flume of unconsolidated sand. Multiple trials were completed by adding either ice or hot water to a reservoir which was then run through the approximately 4.5 meter long channel. Temperature data were collected every five seconds using 28 equally spaced loggers until the system returned to equilibrium. The minimum and maximum temperatures were used to determine an average temperature change at each measuring location, and several statistical analysis tools, as well as a contour mapping program, were used to examine the differences between cold and heat pulse data. Hot and cold trials were found to behave similarly both vertically and longitudinally at all locations except the shallowest point of measurement, which was 28 centimeters above the base of the flume. This is most likely due to advection being the primary process of heat transport at the top of the flume, while conduction is the primary driver at greater depths. The results of this ongoing study will help in the understanding of the important groundwater/surface water mixing zone in streams.