Abstract:A metal mining area located in Hunan Province was selected as the research subject with the aim of comprehensively investigating the characteristics of soil surface runoff migration in typical mining areas. Specifically, lead-zinc polymetallic tailings were identified as the primary pollution source for this study. To achieve a thorough exploration of the horizontal migration of cadmium (Cd) and lead (Pb) in the soil of the typical metal mining area, a combination of indoor simulation rainfall experiments and numerical simulations was carried out. In the indoor simulation rainfall experiments, a series of different conditions were set up. For the indoor experiments, various rainfall intensities and soil slopes were considered as key factors. The rainfall intensities range from 40 mm/h to 120 mm/h, and the soil slopes varies from 5° to 25°. During the experiments, the soil samples were collected from the metal mining area in Hunan Province, and the lead-zinc polymetallic tailings were evenly distributed on the soil surface to mimic the actual pollution situation. For the numerical simulations, the HYDRUS-2D model was employed. The model parameters were optimized through a single - parameter sensitivity analysis and parameter inversion process. In the single - parameter sensitivity analysis, different parameters related to soil properties, such as saturated hydraulic conductivity, were adjusted to observe their impacts on the model output. The results reveal several important findings. Firstly, it is clearly demonstrated that both rainfall intensity and soil slope have significant influences on soil erosion and the total amount of surface runoff. Through statistical analysis, it is found that the influence of rainfall intensity, with a correlation coefficient of 0.737, is remarkably higher than that of the soil slope, which has a correlation coefficient of 0.649. Regarding the migration of Cd and Pb, it is determined that they mainly migrate in particulate form within the soil. When the rainfall intensity increases from 40 mm/h to 120 mm/h, the surface runoff migration amounts of Cd and Pb increase by 142.61 μg and 22 399.75 μg respectively. This represents increases of 354.8% for Cd and 438.1% for Pb. Similarly, when the soil slope increases from 5° to 25°, the migration amounts of Cd and Pb increase by 87.60 μg and 9 133.45 μg respectively, with corresponding increases of 191.9% for Cd and 78.2% for Pb. Secondly, the optimized HYDRUS-2D model was used to simulate and analyze the horizontal migration of Cd and Pb in the mining area soil. A comparison was made between the horizontal migration experiment results simulated by the optimized model and the measured data obtained from the indoor experiments. The statistical analysis shows that the average coefficient of determination (R2) is 0.63, and the average root mean square error (RMSE) is 0.527. These results indicate that the HYDRUS-2D model has a relatively high accuracy in simulating the horizontal migration of heavy metals in the mining area soil. In conclusion, this study successfully investigates the characteristics of soil surface runoff migration and the horizontal migration of Cd and Pb in a typical metal mining area through the combination of indoor simulation rainfall experiments and numerical simulations using the HYDRUS-2D model. The findings of this study provide valuable data and insights into the behavior of heavy metals in mining area soils. The model developed in this study can serve as a reliable tool for predicting the horizontal migration of heavy metals in similar mining area soils, which can potentially assist in the development of effective strategies for soil pollution control and environmental protection in metal mining areas. However, further research can be conducted to explore the long-term effects of heavy metal migration in different types of mining area soils under various environmental conditions.