Effect of bioturbation–induced riverbed morphological changes on surface water-groundwater exchange in mountain rivers
Canyong Li, Linlin Li*, Wenlong Liu, Yuhao Chen, Hang Wei, Hang Li, Yufei Dong, Jiadong He
Hydrogeology Journal · 2025
Hyporheic exchange process is a key component of surface water-groundwater interactions, it facilitates the transport of solutes, nutrients, and energy, and plays a critical role in sustaining biogeochemical processes at the sediment-water interface and maintaining habitat diversity within river ecosystems. However, the effect of riverbed morphological changes driven by bioturbation remains unclear. In this study, the effect of bioturbation-induced riverbed morphology on hyporheic exchange process was investigated by the coupled model of surface water-groundwater interaction and flume experiments. The results indicated that: (ⅰ) the topographic amplitude dominates hyporheic exchange by strengthening near-bed turbulence and pressure gradients at the sediment–water interface, thereby substantially enhancing exchange flux; (ⅱ) as the topographic amplitude increases from 4 to 12 cm, the maximum surface velocity is increased by a factor of 7.6, turbulent kinetic energy is elevated from 2.41 × 10⁻⁶ to 4.43 × 10⁻⁴ m² s⁻², and the hyporheic exchange flux is increased to 1.14 × 10⁻⁶ m² s⁻¹; (ⅲ) the peak downwelling Darcy velocity in the hyporheic zone increased from 4.01×10-8 m/s to 3.99×10-7 m/s as the inlet discharge increased from 2.8×10-3 m3/s to 8.3×10-3 m3/s; (ⅳ) the relative submergence effectively integrates bedform and hydraulic controls on hyporheic exchange, with the hyporheic exchange flux increasing by approximately 14.6 times as relative submergence increased from 0.6 to 0.9. This study reveals the crucial role of bioturbation–induced topographic changes in driving hyporheic exchange and provides theoretical insights for river ecological restoration and groundwater environmental protection in mountain rivers.