Kinglo et al. (2026) Are there biases in borehole databases of weathered basement aquifers affecting their reliability to estimate aquifer productivity?

Identification

• Journal: Hydrogeology Journal
• Year: 2026
• Date: 2026-01-09
• Authors: August Abdon Kinglo, Basile Hector, Clovis Galiez, Mahamadou Koita, Patrick Lachassagne, Fabrice Lawson, Jean-Michel Vouillamoz
• DOI: 10.1007/s10040-025-02991-3

Research Groups

• HSM, Univ. Montpellier, CNRS, IRD, IMT Mines Alès, Montpellier, France
• Laboratoire Eaux HydroSystèmes Et Agriculture (LEHSA), Institut International d’Ingénierie de L’Eau Et de L’Environnement (2iE), Ouagadougou, Burkina Faso
• Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, Grenoble, France
• Univ. Grenoble Alpes, CNRS, Grenoble INP, LJK, Grenoble, France
• Univ. d’Abomey-Calavi, Institut National de L’Eau (INE), Cotonou, Bénin

Short Summary

This study uses a novel numerical stochastic modeling approach to reveal systematic biases in borehole databases of weathered basement aquifers (WBAs) caused by drillers' instructions (discharge target, maximum/minimum depth). It finds that insufficient drilling depth leads to significant underestimation of aquifer productivity and fractured-layer thickness, and that traditional data processing methods fail to account for these biases.

Objective

• To systematically assess whether instructions given to water borehole drillers introduce biases into borehole databases of weathered basement aquifers (WBAs), thereby affecting their reliability for estimating aquifer productivity and fractured-layer thickness.

Study Configuration

• Spatial Scale: Conceptual model of a weathered basement aquifer (WBA) with a fractured layer thickness of 50 meters. Borehole depths considered up to 80 meters (55 meters below the saprolite base).
• Temporal Scale: Short-term behavior of WBAs, simulating the results of airlift tests performed at the end of drilling.

Methodology and Data

• Models used:
  • Numerically based, stochastic modeling approach for 10,000 synthetic Weathered Basement Aquifers (WBAs).
  • Conceptual hydrogeological model of WBA (modified from Lachassagne et al. 2021).
  • Dupuit equation (1863) for calculating instantaneous discharge of individual water-bearing fractures.
  • Model of water borehole driller's behavior incorporating instantaneous discharge target ($Q{target}$), maximum allowed borehole depth ($Z{max}$), and minimum allowed borehole depth ($Z_{min}$).
• Data sources:
  • 10,000 realizations of synthetic WBAs, parameterized based on extensive bibliographical review of fractured layer characteristics (thickness, number, depth, and hydraulic conductivity of water-bearing fractures).
  • 10,000 sets of synthetic boreholes generated by simulating driller behavior under various instructions.

Main Results

• Numerical modeling of 10,000 synthetic WBAs reveals systematic negative biases in borehole databases, leading to an underestimation of aquifer productivity and fractured-layer thickness.
• Insufficient drilling depth below the base of the saprolite (Z ≤ 35 m) causes undersampling of deeper water-bearing fractures, resulting in an underestimation of aquifer productivity and fractured-layer thickness by more than 10%.
• These biases persist across discharge targets ranging from 0.5 to 10 cubic meters per hour ($m^3/h$) and are exacerbated by shallow drilling.
• Traditional borehole-database-processing methodologies, such as the Courtois et al. (2010) approach, fail to account for driller instructions, misrepresenting the useful aquifer thickness (Lu) by up to 100%.
• The maximum allowed borehole depth ($Z{max}$) is a more significant driver of bias than the instantaneous discharge target ($Q{target}$).
• To minimize bias in database analyses, only data from boreholes drilled at least 35 meters below the base of the saprolite should be considered.

Contributions

• First systematic investigation quantifying the impact of driller instructions (discharge target, maximum/minimum depth) on biases in borehole databases for weathered basement aquifers.
• Development of a novel numerically based, stochastic modeling framework to simulate WBA short-term productivity and driller behavior, providing a tool for assessing data reliability.
• Quantification of the underestimation biases in aquifer productivity and fractured-layer thickness (e.g., >10% for shallow drilling, up to 100% for useful aquifer thickness estimation).
• Critical mathematical analysis demonstrating that existing methodologies for inferring aquifer properties from borehole databases (e.g., Courtois et al., 2010) are flawed, as their results are primarily driven by borehole density with respect to depth rather than intrinsic aquifer properties.
• Provides concrete recommendations for improving the reliability and accurate use of borehole databases, including data classification by exploration depth, archiving drilling instructions, and adopting robust indicators like specific capacity.

Funding

• French Research Institute for Development (IRD)
• French Development Agency (AFD)
• Water Cycle and Climate Change (CECC) project
• International Research Network R-ASAO (Basement Aquifers in West Africa)

Citation

@article{Kinglo2026Are,
  author = {Kinglo, August Abdon and Hector, Basile and Galiez, Clovis and Koita, Mahamadou and Lachassagne, Patrick and Lawson, Fabrice and Vouillamoz, Jean-Michel},
  title = {Are there biases in borehole databases of weathered basement aquifers affecting their reliability to estimate aquifer productivity?},
  journal = {Hydrogeology Journal},
  year = {2026},
  doi = {10.1007/s10040-025-02991-3},
  url = {https://doi.org/10.1007/s10040-025-02991-3}
}