Temporal Fluctuations and Poroelasticity Can Generate Chaotic Advection in Natural Groundwater Systems

Although steady, isotropic Darcy flows are inherently laminar and nonmixing in the absence of diffusion, it is well understood that transient forcing via engineered pumping schemes can induce rapid, chaotic mixing flows in groundwater. In this study we explore the propensity for such mixing to arise...

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Bibliographic Details
Published in:Water resources research 2019-04, Vol.55 (4), p.3347-3374
Main Authors: Trefry, M. G., Lester, D. R., Metcalfe, G., Wu, J.
Format: Article
Language:English
Subjects:
Advection
Aquifers
Chaos
Darcy flow
Diffusion pumps
Groundwater
Groundwater flow
Heterogeneity
Kinetics
Lagrangian
Laminar flow
poroelastic
Poroelasticity
Reaction kinetics
Residence time
Segregation
tidal
Transport
Transport phenomena
Variation
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Summary:Although steady, isotropic Darcy flows are inherently laminar and nonmixing in the absence of diffusion, it is well understood that transient forcing via engineered pumping schemes can induce rapid, chaotic mixing flows in groundwater. In this study we explore the propensity for such mixing to arise in natural groundwater systems subject to cyclical forcings, for example, tidal or seasonal influences. Using a conventional linear groundwater flow model subject to tidal forcing, we show that under certain conditions these flows generate Lagrangian transport and mixing phenomena (chaotic advection) near the tidal boundary. We show that aquifer heterogeneity, storativity, and forcing magnitude cause reversals in flow direction over the forcing cycle which, in turn, generate coherent Lagrangian structures and chaos. These features significantly augment fluid mixing and transport, leading to anomalous residence time distributions, flow segregation, and the potential for profoundly altered reaction kinetics. We define the dimensionless parameter groups which govern this phenomenon and explore these groups in connection with a set of well‐characterized tidal systems. The potential for Lagrangian chaos to be present near discharge boundaries must be recognized and assessed in field studies. Key Points Time periodic Darcy flows in heterogeneous compressible aquifers can generate chaotic Lagrangian dynamics Widespread occurrence of coherent Lagrangian structures is controlled by key parameter groups and results from common physical processes Such structures fundamentally change our view of flow, transport, mixing, and reaction in groundwater discharge systems
ISSN:0043-1397
1944-7973
DOI:10.1029/2018WR023864