Heat as a tracer to monitor water flow in heterogeneous sand box: experiment and numerical modeling

Heat as a tracer has been widely used to investigate water flow and exchange patterns in soil and aquifer in the past few decades. A laboratory experiment with a heterogeneous sand box was carried out under steady-state condition to verify the capability of heat as tracer to reflect the flow process of water and to estimate the corresponding parameters of the two dimensional flow field. A series of measured temperature data at different locations of the sand box were utilized for curves fitting by HYDRUS software. The optimized parameters both for water flow and heat transport were obtained consequently. The results showed that heat as an environmental friendly tracer, is capable to visualize the flow patterns of water in two dimensional flow region. Despite the apparent match between water flow and heat transport, a significant discrepancy was presented between measured and simulated water flux density. The bias between simulated and measured value was because of no compensating for heat loss in the numerical model. Two methods based on thermal equilibrium and heat loss were then proposed to improve the accuracy of simulation. Both methods proved a better capability in estimating water flux density. The relative errors for water flux density between measured and estimated is improved from approximately 19% to 2%.