Research on density effects of interaction between River water-Groundwater by temperature tracer method based on sand tank test

Abstract In this study, four sets of control tests of groundwater recharge river steady flow were designed using the indoor two-dimensional sand tank model to evaluate the density effect caused by temperature change and evaluate the error of temperature tracer method in calculating groundwater velocity. The test results show that the density effect caused by temperature difference can affect the velocity and direction of groundwater flow. The calculation results of the temperature profile from the bed to the bottom of the trough show that the higher the depth, the smaller the vertical component velocity of groundwater, and the less effective the temperature tracer method is in interpreting the velocity. When the temperature gradient reaches 0.33°C/cm, local free convection has formed in the lower part of the characteristics profile, and the error of the groundwater velocity calculated by the temperature tracer method is about 200%, which is much higher than the error of Darcy’s solution 175%. The influence of density effect driven by temperature difference on the analytical results should be evaluated in the study of using temperature tracer method to estimate the exchange capacity of surface water and groundwater.