Prayag et al. (2026) Assessing infiltration dynamics using integrated hydrogeophysical monitoring in a managed aquifer recharge pond

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-03-20
• Authors: Ankita Girish Prayag, Torleif Dahlin, Kristofer Hägg, Matteo Rossi, Arnaud Watlet, Jan‐Erik Rosberg, Tina Martin
• DOI: 10.1016/j.jhydrol.2026.135338

Research Groups

• Engineering Geology, Lund University, Sweden
• Sydvatten AB, Sweden
• Luxembourg Institute of Science and Technology, Luxembourg

Short Summary

This study investigated infiltration dynamics in a Managed Aquifer Recharge (MAR) pond over eight months using an integrated hydrogeophysical monitoring system (automated Direct Current Resistivity and Induced Polarisation (DCIP), Ground Penetrating Radar (GPR), and hydrological data). It revealed subsurface heterogeneity and time-dependent infiltration pathways, including a high-permeability westward-dipping layer, and identified signs of clogging affecting lateral water spreading.

Objective

• To establish a long-term hydrogeophysical monitoring system at a pilot managed aquifer recharge (MAR) infiltration pond to investigate infiltration processes under variable inflow conditions and across different stages of pond maturation, examining the spatial and temporal variability of subsurface infiltration responses and subsurface/geological heterogeneity.

Study Configuration

• Spatial Scale:
  • Pond dimensions: approximately 80 meters (South-North) × 100 meters (West–East).
  • DCIP electrode spacing: 1 meter.
  • Total DCIP electrodes: 416 across three lines (WEP: 160 electrodes, SNP: 128 electrodes, SND: 128 electrodes).
  • GPR profile spacing: 0.60 meters.
  • Depth of investigation: DCIP up to approximately 5 meters; GPR up to approximately 3-5 meters (filter layer at ~1 meter depth).
• Temporal Scale:
  • Monitoring period: Eight months (January 2024 to September 2024).
  • DCIP data collection: Daily (results presented monthly from March to September 2024).
  • GPR measurements: Three time-steps (February 2024, April 2024, June 2024).

Methodology and Data

• Models used:
  • Direct Current Resistivity and Induced Polarisation (DCIP)
  • Ground Penetrating Radar (GPR)
  • Archie's law (for water saturation estimation)
  • pyGIMLi (Python Library for Geophysical Inversion and Modelling) for 2D unstructured mesh creation and DCIP inversions (single and time-lapse with anisotropic spatial and temporal regularization).
  • Heat equation (solved using finite element method via Crank-Nicolson approximation with pyGIMLi) for temperature correction.
• Data sources:
  • Automated multielectrode DCIP system measurements (apparent resistivity, apparent chargeability, normalized chargeability).
  • GPR surveys (170 MHz antenna, RTK GNSS for positioning).
  • Hydrological monitoring: Groundwater levels (from three observation wells), water inflow rates (measured and regulated using V-notch weirs), electrical conductivity of water at the inlet.
  • Meteorological data: Precipitation (from nearby weather station), air temperature (from nearby weather station).
  • Temperature sensors: Three installed near the pond inlet at 0.4 meters, 1.4 meters, and 2.4 meters depths.
  • Grain-size analysis (for porosity estimation).

Main Results

• DCIP results captured resistivity reductions from dry conditions (>2000 Ωm) to saturated zones (70–250 Ωm), coinciding with groundwater-level rises of up to 1.6 meters near the eastern inlet and 1.0 meter at the distal end during peak inflow (58 L/s).
• GPR revealed the lower limit of the artificial filter layer at approximately 1 meter depth and deeper reflections corresponding to the transition from vadose to saturated zones, matching groundwater levels in nearby wells.
• Both methods identified a westward-dipping layer (surface to ~2–3 meters depth; 100–50 meters along the profile), interpreted as a high-permeability layer guiding lateral infiltration.
• Decreasing GPR reflection amplitudes over time indicated increasing water content in the unsaturated zone, consistent with DCIP observations.
• DCIP inversions captured immediate subsurface responses to inflow, including localized groundwater mounding, progressive saturation, and drying during interruptions. Groundwater levels rose fastest at the inlet, more slowly at mid-distance, and minimally at the far end, reflecting inflow proximity and lateral hydraulic connectivity.
• Saturation estimations derived using Archie’s law corroborated these observations, showing moderate-to-high wetting zones, while later stages indicated signs of clogging and biofilm development.
• At the final timestep (T6), despite higher inflow, the high-saturation area near the inlet decreased, suggesting water was spreading laterally rather than increasing vertical saturation, consistent with surface clogging.
• Temperature effects on resistivity were found to be minor (approximately one order of magnitude smaller) compared to water saturation variations.

Contributions

• Demonstrated the effectiveness of long-term, integrated hydrogeophysical (DCIP, GPR, hydrological) monitoring for investigating infiltration dynamics in Managed Aquifer Recharge (MAR) ponds.
• Provided high-resolution temporal and spatial insights into infiltration and saturation changes in response to variable inflow conditions.
• Identified and characterized a site-specific high-permeability westward-dipping sedimentary layer that significantly influences lateral infiltration pathways.
• Quantified water saturation dynamics using petrophysical relationships, revealing progressive wetting, drying, and lateral spreading.
• Detected and interpreted signs of clogging and biofilm development at the pond surface, which altered hydraulic gradients and infiltration patterns.
• Established a robust and transferable integrated hydrogeophysical approach for optimizing MAR management at the field scale.

Funding

• Sweden Water Research (SWR)
• EU Interreg North Sea Region through the “Blue Transition – How to Make My Region Climate Resilient” project
• Formas - Swedish Research Council for Sustainable Development (ref. 2023-02024)
• Royal Physiographic Society of Lund (Sweden)
• Horizon Europe research and innovation programme under the Marie Skłodowska-Curie grant agreement No 101211994 (for Arnaud Watlet)

Citation

@article{Prayag2026Assessing,
  author = {Prayag, Ankita Girish and Dahlin, Torleif and Hägg, Kristofer and Rossi, Matteo and Watlet, Arnaud and Rosberg, Jan‐Erik and Martin, Tina},
  title = {Assessing infiltration dynamics using integrated hydrogeophysical monitoring in a managed aquifer recharge pond},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135338},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135338}
}