Ibrahim et al. (2026) An integrated approach to unravel the deep-shallow aquifer connectivity in the Eastern Sahara

Identification

• Journal: Scientific Reports
• Year: 2026
• Date: 2026-03-02
• Authors: Ibrahim Ahmed Ibrahim, Abotalib Z. Abotalib, Haby S. Mohamed, Mahmoud M. Senosy
• DOI: 10.1038/s41598-026-38324-x

Research Groups

• Geology Department, Faculty of Science, Assiut University, Assiut, Egypt
• Division of Geological Applications and Mineral Resources, National Authority for Remote Sensing and Space Sciences, Cairo, Egypt
• National Center for Environmental Compliance, Riyadh, Saudi Arabia

Short Summary

This study integrates remote sensing, geophysical, and isotopic data to investigate deep-shallow aquifer connectivity in the Eastern Sahara, revealing that significant vertical upwelling from the deep Nubian Aquifer System (NAS) to overlying shallow aquifers occurs along intersecting structural trends in southern and middle Egypt, with contributions ranging from 10% to 98%.

Objective

• To investigate the vertical recharge from the deep Nubian Aquifer System (NAS) toward the shallow Carbonate and Quaternary aquifers in southern Egypt.
• To better understand regional groundwater dynamics and aquifer connectivity by integrating stable isotope data, new groundwater samples, remote sensing, and geophysical methods.
• To analyze satellite images for major surface faults, process aeromagnetic data with borehole and SRTM data for deep structural features and basement depth, and determine recharge sources and mixing ratios using stable isotopes (δD, δ18O).

Study Configuration

• Spatial Scale: Eastern Sahara, Egypt, stretching from the Nile Valley to El-Kharga Oasis (30° to 33°E) and Aswan to Assiut (24.25° to 27.5°N), covering 108,477 square kilometers.
• Temporal Scale: Groundwater sampling in December 2022; remote sensing data from 2000 (SRTM) and 2017 (Landsat-8); aeromagnetic data from 1989; investigation of groundwater residence times up to 1.3 million years and recharge during Pleistocene pluvial periods.

Methodology and Data

• Models used:
  • Second-Order Tilt Derivative (STDR) filter for subsurface structure mapping.
  • Power Spectrum (PS) technique for estimating depths of magnetic sources.
  • 2D Profiling (GM-SYS modeling tool) for subsurface geological structures and basement relief.
  • Isotope mass balance calculations (using δ18O) to quantify mixing ratios between end-members.
• Data sources:
  • Remote sensing: Landsat-8 false color composite mosaic (30 m spatial resolution, 2017), Shuttle Radar Topography Mission (SRTM) images (30 m spatial resolution, 2000), high-resolution satellite imagery (ArcGIS online basemaps).
  • Geophysical: Reduced-to-pole (RTP) aeromagnetic data (1:500,000 scale, 1989, 25 nT contour interval).
  • Hydrogeological: 35 new groundwater samples (collected December 2022, from wells 45-705 m deep), previously published isotopic data [15-21].
  • Geological: Deep borehole records (18 wells reaching basement), geological maps of Egypt [37, 69], interpreted seismic data [39, 71].

Main Results

• Depths to the basement surface range from 350 meters to 4700 meters below the land surface, generally increasing from south to north.
• Major structural trends identified include E-W, NW-SE, NE-SW, ENE, NNW, and WNW.
• Surface faults and deep-seated faults show upward continuity in the southern and middle parts of the study area (south of latitude 26° 30′ N), indicating hydraulic connectivity.
• Isotope mass balance calculations reveal that the contribution of water from the deep NAS to the overlying shallow aquifers ranges from 10% to 98%.
• Significant NAS contributions (up to 98%) are observed in the southern and middle parts, particularly along intersecting NW, ENE, and NE structural trends, facilitated by a relatively thin sedimentary cover.
• The northern part of the study area (Assiut Governorate) shows no significant NAS contribution, with shallow aquifers primarily recharged by the Nile River.
• Direct evidence of deep hydraulic pressure and upwelling includes localized artesian springs and groundwater mounding phenomena.

Contributions

• Provides a comprehensive regional-scale understanding of deep-shallow aquifer connectivity in the Eastern Sahara, integrating diverse datasets (remote sensing, geophysics, stable isotopes) beyond localized case studies.
• Identifies and quantifies the critical role of specific structural features (intersecting NW, ENE, and NE fault systems, thin sedimentary cover, shear zones) as conduits for vertical groundwater upwelling from the deep NAS.
• Offers a conceptual model for groundwater flow dynamics that can guide sustainable water management and identify promising areas for groundwater exploration in the limestone plateau for agricultural development in Egypt.
• Addresses data scarcity in hyper-arid regions by demonstrating an effective integrated multi-proxy approach for hydrogeological assessment.

Funding

This work was supported by the Science, Technology and Innovation Funding Authority under Grant No. 48899, awarded to Ibrahim A. Ibrahim.

Citation

@article{Ibrahim2026integrated,
  author = {Ibrahim, Ibrahim Ahmed and Abotalib, Abotalib Z. and Mohamed, Haby S. and Senosy, Mahmoud M.},
  title = {An integrated approach to unravel the deep-shallow aquifer connectivity in the Eastern Sahara},
  journal = {Scientific Reports},
  year = {2026},
  doi = {10.1038/s41598-026-38324-x},
  url = {https://doi.org/10.1038/s41598-026-38324-x}
}