Abstract
A three-dimensional variable-density finite element model was developed to study the combined effects of overabstraction and seawater intrusion in the Pingtung Plain coastal aquifer system in Taiwan. The model was generated in different layers to represent the three aquifers and two aquitards. Twenty-five multilayer pumping wells were assigned to abstract the groundwater, in addition to 95 observation wells to monitor the groundwater level. The analysis was carried out for a period of 8 years (2008–2015 inclusive). Hydraulic head, soil permeability, and precipitation were assigned as input data together with the pumping records in different layers of the aquifer. The developed numerical model was calibrated against the observed head archives and the calibrated model was used to predict the inland encroachment of seawater in different layers of the aquifer. The effects of pumping rate, sea-level rise, and relocation of wells on seawater intrusion were examined. The results show that all layers of the aquifer system are affected by seawater intrusion; however, the lengths of inland encroachment in the top and bottom aquifers are greater compared with the middle layer. This is the first large-scale finite-element model of the Pingtung Plain, which can be used by decision-makers for sustainable management of groundwater resources and cognizance of seawater intrusion in coastal aquifers.
Highlights
Developing industrial, agricultural and tourism activities together with human settlements in coastal areas has led to overexploitation of aquifers, increasing seawater intrusion (SWI) and decreasing groundwater quality
The transverse dispersivity was calculated as 10% of this value as 7 m based on the FEFLOW parameter’s definition which is in good agreement with the literature (Bear et al 1999; Sherif et al 2012; Huang and Chiu 2018)
The simulated mass concentration results from the steady-state run showed that the aquifer system underwent seawater intrusion throughout the whole depth, but horizontal encroachment in the middle and left side of the plain was highlighted more than the right side, which is in good agreement with the encroachment pattern reported in a recent study (Huang and Chiu 2018)
Summary
Developing industrial, agricultural and tourism activities together with human settlements in coastal areas has led to overexploitation of aquifers, increasing seawater intrusion (SWI) and decreasing groundwater quality. The encroachment of saltwater at different layers of the multilayer aquifer system in the Pingtung Plain in Taiwan, is simulated in 3D using FEFLOW, considering the density-dependent flow and solute transport in the aquifer.
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