Recession and hysteresis effects of hyporheic zone permeability changes on baseflow in seasonal freeze-thaw mountainous areas

Baseflow is the main groundwater discharge mode from mountainous areas to rivers and is an important component of river runoff. Temperature changes in the hyporheic zone in seasonal freeze-thaw areas cause changes in its permeability, which then affect the recession of baseflow. It is critical to study underground surface water transformation processes in cold regions to explore baseflow recession and hysteresis effects caused by permeability changes in the hyporheic zone under variable temperatures. In this study, we investigated the Hanyangtun Basin in the Changbai Mountain District to determine the functional relationship between permeability and temperature in the hyporheic zone using theoretical analysis combined with laboratory saturated permeability experiments using medium-and fine-grained sand at variable temperatures. We then calculated and analyzed the recession amplitude and hysteresis time of the baseflow caused by permeability changes in the hyporheic zone of this freeze-thaw mountainous area using water temperature and reference baseflow data. The results indicate that owing to large temperature changes in the study area, the permeability of the hyporheic zone changed substantially. Lower permeability leads to the blocking of groundwater discharging to surface water, i. e., the baseflow hysteresis effect. The recession amplitude of the baseflow caused by lower permeability increased with decreasing temperatures, reaching a maximum of 41.67%. The groundwater discharge hysteresis time increased with decreasing temperature. The hysteresis effect was most obvious during the stable melting period, with a maximum hysteresis time of 16 days, while the total annual hysteresis time was 60 days. This study provides a new perspective for qualitative and quantitative studies of the relationship between groundwater and surface water in the mountainous areas that experience seasonal freeze-thaw.