Influence of the In-Stream Structure on Solute Transport in the Hyporheic Zone

The hyporheic zone (HZ) plays an important role in the river ecosystem, and hyporheic exchange and solute transport in the HZ are important ecological functions. However, the relationship between the design parameters of river structure and solute transport is still poorly understood. In this study, we combined flume experiments and numerical simulations to systematically evaluate how in-stream structures impact the solute transport depth (D(P)), hyporheic vertical exchange flux (Q), and solute flux (Qs). The results showed that the in-stream structure had a significant influence on solute transport in the HZ and could obviously increase the intensity of hyporheic exchange and promote solute transport. Model results indicated that D(P), Q, and Qs increased with the ratio of ground height to underground height of structure (H/D) and structure number (N), while Q, D(P), and Qs increased with the structural spacing (S) to begin with; then, Q remained constant, and D(P) and Qs decreased as S continued to increase. This study deepened our understanding of the influence of in-stream structural design parameters on HZ solute transport, which is helpful to provide a theoretical basis for ecological restoration projects in the river HZ.