Mining-induced land-surface reconfiguration alters runoff redistribution in a restored alpine open-pit coal mine: a remote sensing-SWAT scenario analysis

Open-pit coal mining can alter surface morphology, drainage connectivity, and runoff redistribution in alpine fragile basins, but whether ecological restoration restores basin-scale runoff or reorganizes subbasin responses remains unclear. This study used the Juhugeng District of the Muli coalfield on the Qinghai-Tibet Plateau as a case study and developed a controlled SWAT scenario framework using multi-temporal DEMs and land-use datasets for pre-mining (2006), post-mining (2014), and post-restoration (2024) land-surface conditions. All scenarios were driven by identical 2024 meteorological forcing to isolate land-surface effects. Basin-averaged runoff coefficient and runoff depth changed only slightly: mining increased them by 0.29% and 0.30%, whereas restoration reduced them by 1.01% and 1.56%. Runoff volume declined by 0.41% after mining and 2.93% after restoration, mainly due to changes in DEM-derived contributing area and drainage connectivity. Subbasin responses were more heterogeneous, and their spatial correspondence with pit lakes and engineered drainage structures suggests a decoupling between local runoff generation and downstream export. These controlled-scenario results emphasize the importance of runoff redistribution and drainage connectivity in mine restoration assessment.