Al-Yaqoubi et al. (2026) Modeling the fresh–saline water interface dynamics in coastal aquifers under managed aquifer recharge (MAR)

Identification

• Journal: Modeling Earth Systems and Environment
• Year: 2026
• Date: 2026-03-23
• Authors: Shahad Al-Yaqoubi, Ali Al-Maktoumi, A. R. Kacimov, Osman Abdalla
• DOI: 10.1007/s40808-026-02757-0

Research Groups

• Water Research Center, Sultan Qaboos University, Muscat, Oman
• Department of Soils, Water and Agricultural Engineering, College of Agricultural and Marine Sciences, Sultan Qaboos University, Muscat, Oman
• Department of Earth Sciences, College of Science, Sultan Qaboos University, Muscat, Oman

Short Summary

This study utilized the SEAWAT numerical model, calibrated against sand-tank experiments, to simulate and analyze saline water dynamics in a coastal unconfined aquifer under Managed Aquifer Recharge (MAR) conditions, demonstrating that MAR effectiveness is highly dependent on aquifer hydraulic conductivity, saline water density, and injection rate.

Objective

• To investigate the effect of hydraulic conductivity (K), injection rate (Qin), and saline water concentration (C) on the dynamics of the fresh-saline water interface in a coastal unconfined aquifer under Managed Aquifer Recharge (MAR) conditions using the SEAWAT numerical model.

Study Configuration

• Spatial Scale: Two-dimensional (2D) cross-sectional model representing a coastal unconfined aquifer with dimensions of 100 cm (length) by 30 cm (height). The primary grid resolution used for simulations was 0.5 cm by 0.5 cm.
• Temporal Scale: Simulations included calibration runs up to 120 minutes (2 hours) and injection scenarios with durations ranging from 4.1 minutes to 24.6 minutes, with observed water table mound persistence up to 30 minutes after injection ceased.

Methodology and Data

• Models used: SEAWAT (density-dependent numerical code for groundwater flow and solute transport), Processing MODFLOW PRO program version 8.0.31.
• Data sources: Controlled laboratory-scale sand-tank experiments (Al-Yaqoubi et al. 2021) provided detailed spatial and temporal data on hydraulic heads and salinity distributions for model calibration and validation.

Main Results

• The effectiveness of Managed Aquifer Recharge (MAR) in mitigating seawater intrusion (SWI) is strongly dependent on aquifer hydraulic conductivity, saline water density, and the total injected freshwater volume.
• In highly permeable formations, injected water disperses rapidly, leading to a smaller water table mound and reduced seaward retreat of the fresh-saline water interface. Conversely, lower hydraulic conductivity enhances water table mound buildup and improves SWI control.
• Increasing seawater concentration by 30% (from 50 g/L to 65 g/L) significantly reduced MAR effectiveness, requiring a 100% increase in injected freshwater volume to achieve a similar seaward retreat of the fresh-saline water interface.
• Lower saline water densities (e.g., 36 g/L, a 28% decrease from 50 g/L) significantly enhanced MAR effectiveness, leading to a 69% greater seaward shift of the interface compared to the base case.
• A twofold increase in the total injected freshwater volume resulted in a more than 20% reduction in the intrusion extent (e.g., 10 cm retreat for double volume vs. 8 cm for base volume at 65 g/L saline water).
• The dynamics of saline water were found to be more sensitive to the total injected volume of freshwater than to the injection rate alone, especially when the total volume was held constant.

Contributions

• Introduces a novel and hybrid methodology by fully replicating laboratory-scale sand tank experiments using a calibrated SEAWAT numerical model, bridging the gap between controlled laboratory experiments and scalable field prediction.
• Quantifies the combined influence of hydraulic conductivity, injection rate, and saline water density on fresh–saline water interface dynamics within a single, experimentally verified modeling environment, unlike previous studies that analyzed these parameters independently.
• Provides quantitative insights into the interaction of MAR design parameters and aquifer characteristics, offering guidance for optimizing MAR implementation in coastal aquifers, particularly in arid environments.
• Offers a transferable, flexible, and reliable decision-support tool for exploring a wide range of MAR design scenarios that would be impractical or impossible to investigate physically.

Funding

• Sultan Qaboos University (internal grants: IG/AGR/SWAE/19/01, CL/SQU-UAEU/AGR/25/01, DVC/RD).

Citation

@article{AlYaqoubi2026Modeling,
  author = {Al-Yaqoubi, Shahad and Al-Maktoumi, Ali and Kacimov, A. R. and Abdalla, Osman},
  title = {Modeling the fresh–saline water interface dynamics in coastal aquifers under managed aquifer recharge (MAR)},
  journal = {Modeling Earth Systems and Environment},
  year = {2026},
  doi = {10.1007/s40808-026-02757-0},
  url = {https://doi.org/10.1007/s40808-026-02757-0}
}