Application of Modflow-Based Seawat Code for Seawater Intrusion Forecasting into the Upper Pliocene Coastal Aquifer in the Ca Mau Peninsula, Southern Vietnam

Abstract

To identify the extent of seawater intrusion into the Upper Pliocene aquifer on the Ca Mau Peninsula, southern Vietnam, the groundwater flow and solute transport model are applied. A total of five observation wells evenly distributed throughout the study area are applied to build a groundwater flow model using the MODFLOW-based SEAWAT code from 2000 to 2015. The groundwater flow model calibrates by a trial and error approach of two parameters: hydraulic conductivity and sink/source rate. Then, the seawater intrusion simulation model for the next 16 years runs with the same initial conditions as 2015. The groundwater flow model result showed that the freshwater area with the Chloride concentration of 250 mg/L only existed from 2000 to 2003 with a displacement range of 400 m/year in the study area. After 2003, this freshwater area no longer existed and was replaced by a 500 mg/L value with a displacement range of 410 m/year. The simulation model of seawater prediction shows that, by 2031, the lowest Chloride concentration might be 2000 mg/L. An average displacement range of this value from 2016 to 2031 reaches an average level of 439 m/year.