A comparison of numerical and Lu modeling of water flow and heat transport with laboratory experiments

Reservoirs are considered to result in significant changes to river water temperature. Discharge of deep water has a large impact on aquatic ecosystems downstream of dam and on both river banks. A laboratory sand tank test investigation was conducted to simulate water flow and thermal dynamics in the riparian zone. The sand temperature (ST) data generated were used to validate and compare HYDRUS-2D, a physically based numerical model, with Lu et al.’s (Soil Sci Soc Am J 71(1):8–14, 2007) soil thermal conductivity model under different water temperature, hydraulic head and radiation temperature conditions. The Richards model and the heat conduction model were coupled through the Horton thermal conductivity model and the Lu et al. (Soil Sci Soc Am J 71(1):8–14, 2007) model, respectively. The results demonstrated the success of model coupling and its application for investigating water flow and thermal dynamics in the riparian zone. The Lu et al. (Soil Sci Soc Am J 71(1):8–14, 2007) model based on COMSOL and the Horton thermal conductivity model based on HYDRUS each had their own advantages. Global analysis showed that the Lu et al. (Soil Sci Soc Am J 71(1):8–14, 2007) model was better able to simulate the riparian zone temperature field under the investigated experimental conditions. The sensitivity analysis results showed that the parameters n_v, T and H had a considerable influence on the temperature field in the model, of which n_v was the most sensitive, whereas the parameters k_s, α, θ_s, and θ_r were relatively less sensitive to the temperature field.