Electrical geophysical evaluation of susceptibility to flooding in University of Nigeria, Nsukka main campus and its environs, Southeastern Nigeria

Abstract

Flooding occurs when rainfall exceeds the absorption capacity of soil and causes significant environmental consequences. In this study, electrical resistivity techniques were employed to assess the flood susceptibility of the study area by examining variations in electrical properties. Prior to flooding, Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT) profiles were conducted to determine the variations in resistivity within subsurface lithologies exposed to the injected current. The injected current penetrated the subsurface units characterised by resistivity ranging from 190.5 Ω·m to 6,775.7 Ω·m, 42.3 Ω·m to 7,297.4 Ω·m, and 320.2 Ω·m to 24,433.3 Ω·m in the first, second and third layers, respectively. These layers were identified as lateritic topsoil, medium-coarse brownish grained sand, and coarse pebbly blackish sand, respectively. The calculated reflection coefficients between layers 1, 2, and 3 reveal alternation in layers with values ranging from −0.04 to 0.66 and 0.36 to 0.95 for k1 and k2, respectively. The transverse resistivity, longitudinal resistivity and anisotropy ranged from 243.59 Ω·m to 24,115.42 Ω·m, 199.61 Ω·m to 14,950.76 Ω·m, and 1.02 to 2.14. Models derived from the ERT profiles reveal variations in resistivity, pinpointing areas of low resistivity which correspond to waterlogged and impermeable layers. The result of this study underscores the importance of integrated resistivity techniques in the study of floods, as it provides valuable insights into flood behaviour, and subsurface dynamics.

Keywords

• anisotropy
• vertical electrical sounding
• electrical resistivity tomography
• geoelectric layer
• permeability