River Talik Development and Its Implications for Cryo-Hydrogeological Processes and Infrastructure in Permafrost Regions on the Qinghai-Tibet Plateau

Permafrost is extensively distributed across the Qinghai-Tibet Plateau (QTP) in China and is interspersed with numerous streams, rivers, and lakes, forming a highly sensitive cryo-hydrogeological environment. Beneath these aquatic systems, permanently unfrozen zones, known as taliks, commonly develop within the permafrost and play a critical role in regulating hydraulic connectivity and water exchange between groundwater and surface water. As such, river-talik systems exert a strong influence on regional water resources, river discharge regimes, and the stability of engineering infrastructure. Nevertheless, the functioning and dynamics of river-talik systems in discontinuous permafrost regions remain complex and insufficiently understood. During the summer season, when taliks remain hydraulically connected to the riverbed, groundwater flow through taliks can sustain river baseflow, thereby influencing seasonal water availability and downstream water resources. In contrast, during winter, progressive refreezing of the riverbed disrupts this hydraulic connection, resulting in groundwater pressure accumulation within aquifers at talik constrictions. Elevated groundwater pressure may fracture the overlying ice cover, allowing supra-permafrost groundwater to discharge onto river floodplains and form extensive icings. These processes not only alter winter runoff pathways but may also inundate adjacent land and infrastructure corridors. In addition, ongoing permafrost degradation beneath riverbeds can induce differential ground settlement, which poses significant risks to bridge foundations, embankments, and other critical infrastructure in cold regions. To investigate the cryo-hydrogeological characteristics and engineering implications of a complex river-talik system in a discontinuous permafrost region of the QTP, a comprehensive field-based approach was employed, integrating continuous monitoring of ground temperature, surface temperature, and hydraulic head with electrical resistivity tomography (ERT) surveys. The presence of flowing river water enhances subsurface heat storage beneath the riverbed, substantially delaying riverbed freezing during autumn and early winter. Moreover, the formation, thickening, and lateral expansion of icings during winter provide an additional thermal buffer. Together, these processes maintain ground temperatures above 0 °C at depth throughout the year, resulting in the development of an approximately 2 m thick talik beneath the riverbed. ERT inversion results further identify both supra-permafrost taliks and taliks penetrating through the permafrost. The river talik exhibits a complex three-dimensional geometry, with cross-sectional dimensions varying along the channel and extending locally above or intermittently through the permafrost. Furthermore, the warm permafrost underlying the talik retains partial permeability, allowing limited groundwater flow within the permafrost matrix. Collectively, these characteristics give rise to intricate local-scale cryo-hydrogeological processes that strongly affect groundwater-surface water interactions, winter river dynamics, and the long-term stability of infrastructure in permafrost regions.