Heat tracer test in a riparian zone: Laboratory experiments and numerical modelling

摘要

The use of water temperature as a tracer has been widely utilized for characterizing the dynamics of water flow and heat transport in riparian zones. By using experimental approaches, we investigated the effects of water temperature, hydraulic head, and heat radiation on water flow and thermal dynamics in riparian zones through sand tank experiments, which simulate the dynamics of water flow and heat transport in riparian zones. Water of low temperature was pumped into the sand tank, and changes of temperature at different locations of the sand tank were measured. Temperature data was examined for three different water temperatures (4.0 degrees C, 6.0 degrees C, and 9.5 degrees C), two different hydraulic heads (25 cm and 45 cm), and two different radiation temperatures (no radiation and 22 degrees C). The thermal dynamic variation pattern in different types of water temperatures, hydraulic heads, and radiation combinations, was also analyzed using a HYDRUS-2D model. The temperature sensors, located near the inlet infiltration boundary, required a shorter time to reach the steady state, because the temperature declined more rapidly near the inlet. The effect of lateral inflow on the temperature gradient was obvious. The temperature gradient in the horizontal direction gradually decreased, and the vertical temperature gradient gradually increased. In the initial stage of infiltration, the temperature gradient in the horizontal direction was larger than the temperature gradient in the vertical direction, however, as time goes on, the temperature gradient in the vertical direction was larger than the temperature gradient in the horizontal direction. In addition, the horizontal temperature gradient of the top sand layer was less affected by the water temperature. The closer the temperature observation point of the same horizontal section was to the infiltration boundary, the higher the rate of temperature difference changes. Comparison of the predicted and observed ther