A methodology for simulating perched conditions in multilayer aquifer systems with 2D variably saturated flow

Abstract

Simulatingflow through multilayer aquifer systems is essential for groundwater management applications such evaluating natural recharge, assessing managed aquifer recharge (MAR), the characterization of surface water–groundwater interactions, and groundwater pollution risk analysis. However, dealing with flow through variably saturated porous media with perched water tables is a difficult task. Usual codes for groundwater flow modeling such as MODFLOW, TOUGH2, and FEFLOW require tedious procedures based on simplified assumptions and approximations. This paper presents a simple approach to simulate two‐dimensional flow through perched aquifers and aquitards in deep vadose zones by combining the Dirichlet and Neumann boundary conditions that may apply to any code simulating unsaturated flow. The proposed approach is illustrated with the unsaturated flow code VS2DTI. The main strengths of the proposed methodology are (a) variably saturated flow in the multilayer system is solved using Richards’ equation, taking into account the lateral flow that sustains observed water levels in perched aquifers and variations in recharge; (b) a Dirichlet‐type boundary condition at the top perched water table is substituted by a Neumann‐type boundary condition, allowing for the representation of any disturbance (e.g., infiltration from ponds, pumping from wells, etc.), regardless of duration and intensity; and (c) the impact of the disturbance is evaluated by comparing the responses of the undisturbed and the disturbed systems. The versatility of this methodology is applied to a MAR case study of a deep aquifer in a sedimentary basin where aquitards limit its feasibility.

Modelling regional effects of artificial groundwater recharge in a multilayer aquifer characterized by perched water tables

“…The figure represents the extent to which groundwater level increase is detected at its maximum extension (5 years into the simulation period). as well as with previously developed multilayer unsaturated zone models (Aguilera et al, 2019;Aguilera et al, 2021;Valle et al, 2018).…”

“…Gauging was performed at different points along the stream course to evaluate the spatial distribution of flooded areas, as well as to measure flow rates. This provided much‐needed data for an ungauged stream that typically runs dry, as well as key information for the development of unsaturated zone models (Aguilera et al, 2019; Aguilera et al, 2021; Valle et al, 2018). Furthermore, the effects on shallow groundwater levels were recorded in 14 monitoring wells.…”

“…Conceptual model of vertical groundwater flow in the study area (modified from Aguilera et al, 2021). …”

“…The multilayer aquifer has been modelled in the past by means of the VS2DI code (Hsieh et al, 2000). The available models provide an estimate as to the travel time of artificial recharge from the surface to the regional saturated zone (Aguilera et al, 2019; Aguilera et al, 2021; Valle et al, 2018). However, because this approach consists of 2D vertical profiles, it can neither be used to quantify regional‐scale effects nor to evaluate the impact of artificial recharge on surface water bodies.…”

Erratum to: A methodology for simulating perched conditions in multilayer aquifer systems with 2D variably saturated flow

“…The original publication of Aguilera et al. (2021) contained incorrect numbering in the methodological approach on pp. 4–5.…”