Approximate delineation of groundwater yield capacity and vulnerability via secondary geo-electric indices and rock-water interaction hydrodynamic coefficients in a coastal environment

Electrical geophysical method in 1-D case was used to investigate the penetration of current into the subsurface of 45 vertical electrical sounding (VES) points in the study area located within in southeastern part of Nigeria. The primary aim was to assess the groundwater yield potential index (GWYPI) and to characterize the readily available potential aquifer system in terms of vulnerability and coefficients of hydrodynamics. Resistivity meter was used to acquire VES data while WINRESIST software programme was used to estimate the primary geo-electric indices (PGI). The GPI results were used to compute the secondary geo-electric indices (SGI) used in estimating GWYPI and protective capacity (PC). Cored samples closer to the VES points were also analyzed in the laboratory and correlated with the subsurface parameters to determine the aquifer hydrodynamic parameters. At a mean depth of 114.6 m within the gamut of 39.5-290.9 m, the bulk resistivity spread between 26.3 to 3688.7 Ωm with an average of 1049.047Ωm. The thickness spread from 22.6 to 273.3m with a mean of 97.69m. The various indices realized are suggestive of the fact that the probable water repository is sustainable and vulnerable. The subsurface showed proportionally nine (9) characteristic curves, which are: (HA (1.9%), HK (13.3%), H (28.9%), KH (4.4%), AK (4.4%), K (31.1%), Q (1.9%), KQ (1.9%) and A (11.1%). The estimated anisotropy varied from 0.85 to 1.00 with a mean of 0.872. This gamut of anisotropy reflects models for groundwater yield indices and categorizes aquifers as low yield, moderate yield, high yield and very high yield. The PC was classed as poor (44.4%), weak (20.0%), moderate (28.8%) and good (6.7%) with high and moderate yield indices and good PC found near only VES 18, 27 and 28 locations. The hydrodynamic coefficients indicate that the magnitudes and distributions of pore fluid in the aquifer hydraulic units within the geologic unit are sustainable and transmissible during water-rock/soil interaction.