Wen et al. (2026) Analytical solutions for coupled unsaturated-saturated flow model in riparian zones: applicability and limitations

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-01-28
• Authors: Chengyan Wen, Xiuyu Liang, Hongbin Zhan, Haokun Mu, Yunqiu Zhou
• DOI: 10.1016/j.jhydrol.2026.135035

Research Groups

• State Key Laboratory of Soil Pollution Control and Safety, Southern University of Science and Technology, Shenzhen, Guangdong, China
• Guangdong-Hong Kong Joint Laboratory for Soil and Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, China
• Department of Geology and Geophysics, Texas A&M University, College Station, TX, USA

Short Summary

This study develops and evaluates analytical solutions for a coupled unsaturated-saturated flow model in riparian zones, demonstrating their high accuracy for river stage fluctuations but revealing limitations under high infiltration intensity or thick unsaturated zones.

Objective

• To develop analytical solutions for a coupled unsaturated-saturated flow model in riparian zones by linearizing the Richards equation using a perturbation approach.
• To systematically evaluate the applicability and limitations of these analytical solutions under time-varying infiltration and river stage fluctuation conditions.
• To provide a comprehensive evaluation of analytical solutions in coupled flow systems, clarify their practical limitations, and support their application as efficient tools in riparian hydrology modeling.

Study Configuration

• Spatial Scale: Representative riparian transect; sand flume experiments simulating riparian zones.
• Temporal Scale: Transient analysis of time-varying infiltration and river stage fluctuations.

Methodology and Data

• Models used:
  • Coupled unsaturated-saturated flow model based on a linearized Richards equation (using a perturbation approach).
  • Linearized numerical solutions (for validation).
  • Fully nonlinear numerical models (for evaluation and assessment of accuracy).
• Data sources:
  • Theoretical derivations.
  • Numerical simulations.
  • Sand flume experiments simulating river stage fluctuations.

Main Results

• The developed analytical solution performs well under river stage fluctuation scenarios, demonstrating high accuracy in predicting river-groundwater exchange flux.
• The applicability of the analytical solution is reduced under time-varying infiltration conditions, especially when high infiltration intensity or a thick unsaturated zone is present.
• The analytical solutions were successfully validated against linearized numerical solutions and evaluated against fully nonlinear numerical models.

Contributions

• Development of novel analytical solutions for coupled unsaturated-saturated flow in riparian zones by applying a perturbation approach to linearize the Richards equation.
• Derivation of analytical solutions for two critical natural forcing conditions: time-varying infiltration and river stage fluctuations.
• A comprehensive and systematic evaluation of the applicability and limitations of analytical solutions in coupled unsaturated-saturated flow systems.
• Practical demonstration of the analytical solution's utility through application to sand flume experiments.

Funding

Not specified in the provided text.

Citation

@article{Wen2026Analytical,
  author = {Wen, Chengyan and Liang, Xiuyu and Zhan, Hongbin and Mu, Haokun and Zhou, Yunqiu},
  title = {Analytical solutions for coupled unsaturated-saturated flow model in riparian zones: applicability and limitations},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135035},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135035}
}