Estimation of porosity and specific yield were carried out from Vertical Electrical Sounding (VES) measurements in Anambra State, Southeastern Nigeria. The study area lies within longitudes 060 38I 00IIE and 0070 15I 00IIE and latitudes 050 42I 00IIN and 0060 45I 00IIN with an area extent of about 4844sqkm (1870sqmi), underlain by formations within two geological basins. It falls within the Anambra River Basin. The dominant aquifer is the Nanka Sands with Ameki Formation, Ebenebe Sandstone and Amenyi Sands as sandy lenses. A total of four hundred and fifty-two (452) VES was carried out in over one hundred and seven towns (107) within the study area, employing the Schlumberger array configuration. Layer resistivities, thicknesses and depths were obtained using the computer program INTERPEX. Lithological inference from layer resistivity shows dominantly sand/sandstones with moderate shaley facies. The 2D regional maps for Iso-resistivity, Isopach, depth, formation resistivity factor (F), groundwater resistivity, porosity and specific yield were constructed. Iso-resistivity 2D map shows high layer resistivities within the central part of the study area, with corresponding appreciable thicknesses. These are possible potential groundwater zones. Based on the groundwater resistivity, values range from 350?m to 800?m for fresh water and 50?m to 250?m for non-fresh areas, possibly iron water. Formation resistivity factor F is variable and dimensionless. F ranges from 2 to 40. Porosity ranges from 10% to 30% within the sandy Formations and 35% to about 60% within the shale/clay Formations. Specific yield is variable in the study area with values ranging from 5% to 90%. The constructed 2D regional maps can serve as a useful guide for groundwater exploration, development and management.
Keywords: VES, Porosity, Groundwater resistivity, Specific yield, Regional map