Hydrogeophysical characterization and recharge potential of three Wadi basins along the Red Sea Margin, Northeastern Desert, Egypt

In the arid Red Sea margin setting, episodic Wadi runoff is a primary mechanism for groundwater recharge; its effectiveness depends on surface morphology, structural fabric, and subsurface architecture. This study assessed groundwater potential and recharge dynamics in Wadi Ramliya, Wadi Umm Alda, and Wadi Hamad in Northeastern Egypt by integrating morphometric, geophysical, hydrochemical, and meteorological datasets to prioritize sites for managed aquifer recharge and reconnaissance drilling. High-resolution Digital Elevation models (DEMs) and multi-azimuth hillshades were used to map topographic zoning and structural trends, while morphometric analysis quantified drainage metrics. Flood-event hazard mapping was developed by integrating the Suez rain gauge station as a reference, satellite-based rainfall from the CHIRPS dataset, and data on DEM, slope, drainage density, land-use/land-cover, and road distance. Twenty-eight Vertical Electrical Soundings (VES) were used to constrain a six-layer geoelectric model, and Archie-based transforms (ρw = 2.85 Ω.m) were applied to the estimated formation factors and porosities. Water quality was classified using hydrochemical data from the JICA-5 borehole, while land magnetic surveys, utilizing Total magnetic intensity (TMI), Reduced to the Pole (RTP), and analytic signal filters, delineated basement structural highs and depocenters to guide structural targeting. DEM/hillshade analysis delineated four topographic zones (17.5-1,292 m) and showed dominant NW-SE and NE-SW trends that control drainage orientation. Morphometric indices highlight contrasting basin behavior; Wadi Hamad (A = 46.8 km²) exhibits the highest drainage density (D_d = 1.79 km km⁻²), relief ratio (R_r=31.3), and bifurcation ratio (R_b=3.0), consistent with steep, structurally guided, flash-prone headwaters. By contrast, Wadi Ramliya (A = 452.6 km²) and Wadi Umm Alda (A = 377.4 km²) act primarily as transit and depositional basins. The VES interpretation yielded three principal curve types (QH, HK, and QQ), with QH dominating the dataset. It resolves a hydraulically significant Middle Miocene calcareous-sandstone aquifer at 77-122 m (with resistivity of 12-23 Ω.m). Archie-derived formation factors (F = 4.2-8.2) imply porosities of 35-49% (mean ≈ 40.6%); resistivity-based saturation remained low (illustrative S_w= 5.6%). JICA-5 chemistry classified the deeper layer (layer-6) as slightly brackish (TDS = 2,447 mg L⁻¹). Magnetic depth estimates and analytic-signal mapping identified shallow structural highs and deeper depocenters that correlated with depositional fans and VES targets. Flood-hazard mapping identified low-slope fan toes and coastal plain cells as high-priority recharge locations, which coincide with favorable geophysical signatures. Integrated data indicate that managed recharge pilots at alluvial fan toes and targeted reconnaissance drilling at lineament intersections are the highest-priority field actions; these should be accompanied by downhole logging, pumping tests, water-quality monitoring, and sediment control measures.