Preprints
https://doi.org/10.5194/hess-2021-634
https://doi.org/10.5194/hess-2021-634
 
18 Jan 2022
18 Jan 2022
Status: this discussion paper is a preprint. It has been under review for the journal Hydrology and Earth System Sciences (HESS). The manuscript was not accepted for further review after discussion.

Effects of the dynamic effective porosity on watertable fluctuations and seawater intrusion in coastal unconfined aquifers

Zhaoyang Luo1,2, Jun Kong1,3, Lili Yao4, Chunhui Lu1, Ling Li5,6, and David Andrew Barry2 Zhaoyang Luo et al.
  • 1State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, China
  • 2Ecological Engineering Laboratory (ECOL), Environmental Engineering Institute (IIE), Faculty of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
  • 3Key Laboratory of Coastal Disaster and Protection (Ministry of Education), Hohai University, Nanjing, China
  • 4Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, USA
  • 5School of Engineering, Westlake University, Hangzhou, China
  • 6School of Civil Engineering, The University of Queensland, Brisbane, Australia

Abstract. Watertable fluctuations and seawater intrusion are characteristic features of coastal unconfined aquifers. The dynamic effective porosity due to watertable fluctuations is analyzed and then a modified (empirical) expression is proposed for the dynamic effective porosity based on a dimensionless parameter related to the watertable fluctuation frequency. After validation with both experimental data and numerical simulations, the new expression is implemented in existing Boussinesq equations and a numerical model, allowing for examination of the effects of the dynamic effective porosity on watertable fluctuations and seawater intrusion in coastal unconfined aquifers, respectively. Results show that the Boussinesq equation accounting for the vertical flow in the saturated zone and dynamic effective porosity can accurately predict experimental dispersion relations (that all existing theories fail to predict), highlighting the importance of the dynamic effective porosity in modeling watertable fluctuations in coastal unconfined aquifers. This in turn confirms the utility of the real-valued expression of the dynamic effective porosity. An outcome is that the phase lag between the total moisture (above the watertable) and watertable height measured in laboratory experiments using vertical soil columns (1D systems) can be ignored when predicting watertable fluctuations in coastal unconfined aquifers (2D systems). A dynamic effective porosity that is, by comparison, smaller than the soil porosity leads to a reduction in vertical water exchange between the saturated and vadose zones and hence watertable waves can propagate further landward. The dynamic effective porosity further plays a critical role in simulations of seawater intrusion, since it predicts a more landward seawater-freshwater interface and a higher position of the upper saline plume.

Zhaoyang Luo et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • AC1: 'Comment on hess-2021-634', Zhaoyang Luo, 26 Feb 2022
  • RC1: 'Comment on hess-2021-634', Anonymous Referee #1, 18 Mar 2022
    • AC2: 'Reply on RC1', Zhaoyang Luo, 18 Mar 2022
  • RC2: 'Comment on hess-2021-634', Anonymous Referee #2, 05 Jun 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • AC1: 'Comment on hess-2021-634', Zhaoyang Luo, 26 Feb 2022
  • RC1: 'Comment on hess-2021-634', Anonymous Referee #1, 18 Mar 2022
    • AC2: 'Reply on RC1', Zhaoyang Luo, 18 Mar 2022
  • RC2: 'Comment on hess-2021-634', Anonymous Referee #2, 05 Jun 2022

Zhaoyang Luo et al.

Zhaoyang Luo et al.

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Short summary
Watertable fluctuations and seawater intrusion are characteristic features of coastal unconfined aquifers. A modified expression is first proposed for the dynamic effective porosity due to watertable fluctuations. Then, the new expression is implemented in existing Boussinesq equations and a numerical model, allowing for examination of the effects of the dynamic effective porosity on watertable fluctuations and seawater intrusion in coastal unconfined aquifers, respectively.