Quasi-Saturated Layer: Implications for Estimating Recharge and Groundwater Modeling.

Autor: Gonçalves RD; Center for Environmental Studies and Basin Studies Laboratory, São Paulo State University, UNESP, Rio Claro, SP 13506-900, Brazil., Teramoto EH; Center for Environmental Studies and Basin Studies Laboratory, São Paulo State University, UNESP, Rio Claro, SP 13506-900, Brazil., Engelbrecht BZ; Center for Environmental Studies and Basin Studies Laboratory, São Paulo State University, UNESP, Rio Claro, SP 13506-900, Brazil., Alfaro Soto MA; Center for Environmental Studies and Basin Studies Laboratory, São Paulo State University, UNESP, Rio Claro, SP 13506-900, Brazil., Chang HK; Department of Applied Geology, São Paulo State University, UNESP, Rio Claro, SP 13506-900, Brazil., van Genuchten MT; Center for Environmental Studies and Basin Studies Laboratory, São Paulo State University, UNESP, Rio Claro, SP 13506-900, Brazil.; Department of Nuclear Engineering, Federal University of Rio de Janeiro, COPPE, Rio de Janeiro, RJ 21941-972, Brazil.
Jazyk: angličtina
Zdroj: Ground water [Ground Water] 2020 May; Vol. 58 (3), pp. 432-440. Date of Electronic Publication: 2019 Jul 05.
DOI: 10.1111/gwat.12916
Abstrakt: This study presents an extension of the concept of "quasi-saturation" to a quasi-saturated layer, defined as the uppermost dynamic portion of the saturated zone subject to water table fluctuations. Entrapped air here may cause substantial reductions in the hydraulic conductivity (K) and fillable pore water. Air entrapment is caused by a rising water table, usually as a result of groundwater recharge. The most significant effects of entrapped air are recharge overestimation based on methods that use specific yield (S y ), such as the water table fluctuation method (WTF), and reductions in K values. These effects impact estimation of fluid flow velocities and contaminant migration rates in groundwater. In order to quantify actual groundwater recharge rates and the effects of entrapped air, numerical simulations with the FEFLOW (Version 7.0) groundwater flow model were carried out using a quasi-saturated layer for a pilot area in Rio Claro, Brazil. The calculated recharge rate represented 16% of the average precipitation over an 8-year period, approximately half of estimates using the WTF method. Air entrapment amounted to a fillable porosity of 0.07, significant lower that the value of 0.17 obtained experimentally for S y . Numerical results showed that the entrapped air volume in the quasi-saturated layer can be very significant (0.58 of the air fraction) and hence can significantly affect estimates of groundwater recharge and groundwater flow rates near the water table.
(© 2019 The Authors. Groundwater published by Wiley Periodicals, Inc. on behalf of National Ground Water Association.)
Databáze: MEDLINE
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