Coupled modeling of hyporheic exchange and nutrient transport with log jam-induced riverbed deformation

Hyporheic exchange is a fundamental process governing surface water–groundwater interactions, plays a critical role in regulating nutrient cycling, energy fluxes, and ecological dynamics. In this study, the impacts of log jams on riverbed deformation and the enhancement of hyporheic exchange were investigated using a proposed coupled model of surface water–groundwater interaction. Under log elevations ranging from 2 to 11 cm and flow discharges from 0.005 to 0.016 m3/s, the results revealed significant morphological and hydrodynamic changes. Lower log elevations intensified scouring, increasing scour pit depths from 1.29 to 3.19 cm and downstream deposition areas by 72%, while the hyporheic flux increased by 40%. At the highest flow discharge of 0.016 m3/s, the total hyporheic exchange flux reached 1.45 times that under 0.010 m3/s, driven by the enlargement of active exchange domains. Log-induced morphological forcing governed the spatial extent and transport efficiency of solute migration, with broader scour–deposition structures facilitating deeper and more distributed subsurface delivery. These hydrodynamic alterations enhanced oxygen availability and prolonged solute retention, thereby increasing physical and chemical gradient diversity that supports the formation of ecologically functional hyporheic habitats. The findings provide valuable insights and practical guidance for river ecological restoration and water resource management in alluvial channels, highlighting the importance of log jam-induced hydrodynamic processes in shaping aquatic ecosystems.