Transport processes in porous media are controlled by the characteristics of the flow field which are determined by the porous material properties and the boundary conditions of the system. This work provides experimental evidence of the relation between mixing and flow field topology in porous media at the continuum scale. The setup consists of a homogeneously packed quasi-two-dimensional flow-through chamber in which transient flow conditions, dynamically controlled by two external reservoirs, impact the transport of a dissolved tracer. The experiments were performed at two different flow velocities, corresponding to P茅clet numbers of 191 and 565, respectively. The model-based interpretation of the experimental results shows that high values of the effective Okubo-Weiss parameter, driven by the changes of the boundary conditions, lead to high rates of increase of the Shannon entropy of the tracer distribution and, thus, to enhanced mixing. The comparison between a hydrodynamic dispersion model and an equivalent pore diffusion model demonstrates that despite the spatial and temporal variability in the hydrodynamic dispersion coefficients, the Shannon entropy remains almost unchanged because it is controlled by the Okubo-Weiss parameter. Overall, our work demonstrates that under highly transient boundary conditions, mixing dynamics in homogeneous porous media can also display complex patterns and is controlled by the flow topology.
<p>This presentation aims at covering different and interdisciplinary research aspects focusing on hydropeaking, highlighting in particular which temporal scales are relevant at different spatial scales. We will present how the impact of hydropeaking at the catchment scale changed in the past decades due to changes in legislation and the energy market and the role of hydropeaking in the context of energy complementarity. We will then focus on the effects of sudden river stage fluctuations at the reach scale and their impact on surface water-groundwater interaction and eventually on energy and mass transfer processes, considering seasonal, weekly and sub-daily time scales. Finally, laboratory scale investigations will show the effects of hydropeaking on solute mixing in porous aquifers. The environmental impact of hydropeaking on the ecosystem calls for effective mitigation strategies and policies to find a sustainable compromise between energy production and ecosystem preservation which are capable of tackling processes occurring at multiple spatial and temporal scales.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations鈥揷itations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.