Collaborative Research: Role of Interfacial Turbulence in Hyporheic Exchange and Fine Particle Dynamics

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It is essential to improve understanding of interactions between surface water flows and underlying porewaters in order to advance our ability to assess connectivity in aquatic ecosystems, evaluate the propagation of carbon, nutrients, and contaminants through river networks, and predict the net effects of human modification of watersheds. Previous NSF-supported research found that hydrodynamic interactions caused rapid exchange between rivers and underlying porewater, along with ongoing deposition and resuspension of fine particles. These processes are expected to substantially influence downstream migration of solutes and particles in river networks. Unfortunately, very little information is available on the hydrodynamic mechanisms that control this behavior because it has been extremely difficult to directly measure solute and particle dynamics in porewaters. The objectives of the current project are to improve fundamental understanding of hydrodynamic interactions between freestream flows and porewaters, and to use the information gained to transform conceptual and quantitative models for solute and particle dynamics in rivers. The project will use an array of new flow visualization technologies to obtain direct observations of fluid exchange between rivers and streambeds, and the associated fluxes of solutes and fine suspended particles. The results will be used to identify the main fluid flow processes responsible for solute and particle transport across porous environmental interfaces. This work will yield improved models for the surface-subsurface flow continuum, as well as new probabilistic models for downstream solute and particle transport. The project will contribute to the broader education of students and the public by incorporating project results into major outreach efforts at Northwestern University and the University of Illinois. Focus will be on helping K-12 students and neighborhood communities to understand how river processes influence water quality, human health, and natural ecosystems. The PIs will also work with several university student groups to develop a new program involving regular on-campus activities and mentoring for students from populations underrepresented in the sciences. Overall, the project will engage ~1,500 K-12 students and adults citizens each year (~4,500 over the lifetime of the project) in laboratory activities and discussions of the significance of hydrological processes to sustainability.The major scientific contributions of this work will be an improved characterization of fundamental mechanisms of flow coupling between rivers and riverbeds, and new models for the migration of dissolved and suspended materials in rivers. Such models are essential to enable the prediction of large-scale, long-term dynamics required for sustainable management of river systems. The project will characterize important components of interfacial flux currently missing from solute transport models, and provide critical new observations of fine particle deposition and resuspension. This information is needed to address pressing problems in freshwater systems, including contaminant interactions with sediments, protection of ecological diversity within rivers, nutrient retention and carbon processing in rivers, and waterborne disease transmission. The models developed in this project can be used to evaluate the factors that produce high risks of transmission of contaminants and waterborne diseases, and thereby improve management of watersheds to minimize these risks. The project will also contribute to longer-term sustainability of drinking water resources and aquatic ecosystems by improving our capability to predict long-term biogeochemical and ecological dynamics in rivers.