Mapping the saltwater-freshwater interface by integrating electrical resistivity tomography and 3D numerical...

Area of Science:

• Hydrogeology
• Geophysics
• Environmental Science

Background:

• Seawater intrusion (SI) is a significant groundwater salinization issue in coastal areas.
• Effective methods are needed to delineate the salt-freshwater interface (SFI).
• Few studies have synergistically combined numerical modeling and electrical resistivity tomography (ERT) for SI assessment.

Purpose of the Study:

• To integrate numerical modeling and ERT to investigate SI in Longkou city, China.
• To accurately identify and characterize the SFI using a combined approach.
• To provide a tool for informed groundwater management and SI mitigation.

Main Methods:

• Collected 50 groundwater samples to measure chloride (Cl-) concentration.
• Deployed 17 survey lines for ERT data acquisition and generated inversion profiles.
• Developed a 3D numerical model for groundwater flow and solute transport with three vertical layers.

Main Results:

• Identified SFI from ERT profiles, with interfaces ranging from 1.8 km to 4.2 km offshore.
• Numerical model accurately simulated groundwater flow and Cl- concentrations (NES: 0.76/0.65, R2: 0.84/0.83).
• ERT-derived SFI was validated by numerical simulations; the shallowest layer showed the most severe SI.

Conclusions:

• The integrated numerical model and ERT methodology is effective for locating SFI in coastal zones.
• Simulated SFI showed landward shifts in the wet season and seaward shifts in the dry season.
• This approach supports better groundwater management and mitigation strategies for SI.