Identifying Stagnation Zones and Reverse Flow Caused by River‐Aquifer Interaction: An Approach Based on Polynomial Chaos Expansions

Fluctuating stream stages and peak‐flow events can significantly influence the interactions between streams and aquifers and modify the hydraulic gradient, the flux exchange and the subsurface flow paths. As a result, stagnation zones and reverse flow may appear in different parts of an aquifer and...

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Bibliographic Details
Published in:Water resources research 2021-12, Vol.57 (12), p.n/a
Main Authors: Merchán‐Rivera, P., Wohlmuth, B., Chiogna, G.
Format: Article
Language:English
Subjects:
Aquifers
Boundary conditions
Chaos
Confluence
Creeks & streams
Flow paths
Groundwater
Groundwater flow
Hydraulic gradient
Mathematical models
Nonlinear dynamics
Nonlinear systems
Numerical models
Nutrients
Pollutants
Pollution dispersion
polynomial chaos expansions
Polynomials
probability maps
Probability theory
Residence time
reverse flow
Reversed flow
Rivers
Solutes
Spectral methods
Stagnation
stagnation points
Storm seepage
Streams
Subsurface flow
surface water‐groundwater interaction
Uncertainty
uncertainty quantification
Water flow
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Summary:Fluctuating stream stages and peak‐flow events can significantly influence the interactions between streams and aquifers and modify the hydraulic gradient, the flux exchange and the subsurface flow paths. As a result, stagnation zones and reverse flow may appear in different parts of an aquifer and at different times. These features of the flow field play a relevant role in the transport, transformation, and residence time of solutes, pollutants, and nutrients in the subsurface. However, their identification using numerical models is complex not only because of highly nonlinear dynamics, but also due to significant uncertainties in the model input data which propagate into the quantities of interest. In this work, we use an approach based on polynomial chaos expansions to map the probability of occurrence of stagnation zones and reverse flow during a flood event. We quantify the propagation of uncertainty into the groundwater flow field due to the applied river boundary conditions. Then, we evaluate the responses of the posterior probabilities in an element‐wise fashion using a set of flow classification criteria and kernel density estimations. The proposed methodology is flexible because it employs a nonintrusive pseudo‐spectral technique and, consequently, it can be applied straightforwardly in preexisting models. The regions near the confluence of two streams in the studied area are prone to present transient stagnation and reverse flow. Key Points The probability of occurrence of stagnation zones and reverse flow is computed based on the uncertainty caused by river boundary conditions Polynomial chaos expansions are used in an element‐wise fashion for quantifying the propagation of uncertainty The regions near the confluence of two streams are very dynamic and prone to the presence of stagnation points and reverse flow
ISSN:0043-1397
1944-7973
DOI:10.1029/2021WR029824