Experimental and Numerical Investigation on the Impact of Emergent Vegetation on the Hyporheic Exchange

Hyporheic exchange leads to the transfer of gases, solutes, and fine particles across the sediment-water interface, playing a critical role in biogeochemical cycles and pollutant transport in aquatic environments. While in-channel vegetation has been recognized to enhance hyporheic exchange, the mechanisms remain poorly understood. Here, we investigated how an emergent vegetation canopy impacts hyporheic exchange using refractive index-matched flume experiments and coupled numerical simulations. Our results show that at the same mean surface flow velocity, vegetation increases the hyporheic exchange velocity by four times compared to the non-vegetated channel. However, the hyporheic exchange velocity does not increase further with increasing vegetation density. In addition, our results show that the hyporheic exchange velocity scales with the square root of sediment permeability. Our findings provide a predictive framework for hyporheic exchange in vegetated channels with varying vegetation densities and sediment permeabilities and could guide the future design of environmental management and restoration projects using vegetation.