An enhanced runoff model with dual-permeability and discharge-dependent leakage for mining-affected catchments

Coal mining substantially alters watershed hydrology processes, yet quantitatively disentangling the dominant mechanisms within hydrological models remains challenging. Here, an enhanced Spatiotemporal Variable Source Mixed Runoff model, termed E-SVSMR, was developed to explicitly represent two key mining-induced perturbations: enhanced slope infiltration caused by mining fractures, parameterized through a soil-fissure dual-permeability system with an equivalent saturated hydraulic conductivity, and riverbed leakage, characterized by a nonlinear discharge-dependent function. The physical framework was initially validated at the hillslope scale via high-fidelity 3D variably-saturated flow modeling (COMSOL) in the Wujiayao catchment (78.7 km²). The physical basis of the framework was first evaluated at the hillslope scale in the Wujiayao catchment using high-resolution three-dimensional variably saturated flow simulations. Results demonstrate that goaf-induced fractures form preferential flow pathways and increase effective infiltration by approximately one order of magnitude. When upscaled to the Luzhuang catchment, the E-SVSMR markedly improved runoff simulation, increasing the Nash-Sutcliffe efficiency from 0.41 in the traditional SVSMR to 0.89. Continuous simulations from 1996 to 2009 indicated a cumulative mining-induced runoff loss of 1.73 × 10⁸ m³. Mechanistic decomposition of a representative storm event further suggested that enhanced slope infiltration accounted for approximately 70% of the runoff reduction, whereas riverbed leakage contributed the remaining 30%. Application to the independent Lingshi catchment further demonstrated the transferability of the model. By correcting the systematic post-1994 runoff overestimation in the baseline model, the E-SVSMR increased the Nash-Sutcliffe efficiency from -2.27 to 0.88, and successfully captured the timing and magnitude of mining-driven hydrological disturbances. Overall, the E-SVSMR provides a physically interpretable and transferable modeling framework for diagnosing mining impacts on runoff generation, with implications for flood forecasting and water-resource management in mining-affected catchments.