Turbulence-Driven Clogging of Hyporheic Zones by Fine Particle Filtration

Hyporheic exchange (HE), fine particle deposition and clogging are tightly coupled processes that control ecosystem services in rivers. While HE is assumed to be induced primarily by riverbed topography, surface flow turbulence also drives significant exchange. We show that turbulence-driven HE produces large interfacial fluxes and drives long-term feedback between HE and fine suspended particles via bed clogging. Turbulence significantly increases total HE fluxes as it rapidly delivers suspended particles into porewater over the entire interface, whereas advective pumping exchange only delivers particles into focused downwelling regions on the upstream side of bedforms. While turbulence is associated with rapid fluctuations and shallow HE, it is key on longer-timescale outcomes, namely bed clogging. However, beyond the general effect of clogging in attenuating HE, turbulence-driven HE will also be important for other river-borne materials that are retained and transformed within hyporheic zones, such as nutrients and organic pollutants. Fine natural sediments like clay particles are transported in rivers and deposited in riverbeds. Clay deposition is important to river ecosystems because it controls habitat conditions within riverbeds. In this research, new computational simulations show that turbulent river flow controls clay deposition in riverbeds. These new simulations incorporate turbulence, and they are able to correctly predict patterns of clay deposits. They also predict how clay deposits clog the riverbed and reduce the exchange of water between the river and bed. These simulation capabilities are important to protect river ecosystems and to manage contaminants that interact with riverbeds, because clogging is a common process that damages river ecosystems. Turbulence accounts for a significant fraction of fine particle delivery to the hyporheic zoneTurbulent transport of fine particles contributes substantially to interfacial clogging that attenuates Hyporheic exchange (HE)A numerical model is presented that integrates interfacial turbulence, HE of suspended particles and bed clogging