Geophysical insights into aquifer characteristics of the Tanakpur area in Champawat district, Uttarakhand, India

DELINEATION OF QUATERNARY AQUIFER USING VERTICAL ELECTRICAL SOUNDING (VES) IN OGBIA AREA, BAYELSA STATE, NIGERIA

Electrical resistivity method using the schlumberger configuration were employed to delineate the quaternary aquifer in Ogbia area of Bayelsa State, Nigeria. The aim of this research is to determine the viability of the aquifer for borehole drilling. 10 VES points were carried out in Ogbia Area. They were interpreted by the use of IP12Win software. The interpreted VES data revealed 4-5 delineated layers of silty-clay, clay, clayey sand, sandy-clay, fine to coarse sand. Five sounding curve types were identified in the study area and they are of the KA, HA, QH, AK, and HKH types. The 4-layer geo-electric section were dominant compare to the 5-layer. The first aquifers were delineated at average depth of 24m and 34m with thicknesses ranging from 9.2m to 26.5m and resistivity ranging from310 to 8254Ωm while the 2nd aquifer were delineated at average depth of 37m to 43m with thicknesses ranging from 19.2m to 27m and resistivity values ranging from 740 to 9086Ωm. The second aquifer in the area are more reliable as sources of groundwater because they are less vulnerable to infiltration of surface contaminants and as well as possess better indices for higher groundwater yield due to their texture and greater thickness when compare to the first aquifer.

PATTERN OF ELECTRICAL RESISTIVITY IN REGOLITH AQUIFER AND THEIR IMPLICATION FOR GROUNDWATER MANAGEMENT IN ILORIN METROPOLIS, NIGERIA

Groundwater development in basement complex terrains is largely dependent on the occurrence and characteristics of the regolith aquifer, making geophysical investigation a vital precursor to borehole siting. This paper examines the pattern of electrical resistivity in the regolith aquifer of Ilorin metropolis, Kwara State, Nigeria. Forty (40) Vertical Electrical Sounding (VES) points were established across the study area to delineate subsurface lithological layers, determine resistivity patterns, and estimate weathering depth. The resistivity data were processed and interpreted using computer iteration techniques, while an aquifer potential index was used to evaluate groundwater potential. The findings reveal a geo-electric sequence of five lithological layers, comprising topsoil, lateritic layer, clayey soil, weathered basement, and fresh basement, with resistivity curve types identified as H, K, A, and Q. The regolith aquifer, represented by the weathered basement, recorded resistivity values ranging from 3.57Ωm to 297Ωm, while weathering depth varied from 3.30 m to 31.28 m, with both parameters showing higher values in the south-western and north-eastern parts of the study area. Analysis indicated that 45% of the study area exhibited optimum weathering and groundwater potential, whereas correlation analysis revealed a weak inverse relationship (r = -0.361) between regolith resistivity and aquifer potential, suggesting that resistivity alone is insufficient predictor of groundwater yield. The study concludes that the regolith aquifer constitutes the principal groundwater reservoir in the study area. Recommendations include the adoption of pre-drilling geophysical surveys as a mandatory practice and the prioritization of boreholes in zones identified with optimum aquifer potential.

Application of Geoelectric and Hydrogeological Methods in Delineation of Aquifer Potential and Protective Capacity in Parts of Asaba Metropolis, Niger Delta Region of Nigeria

This study evaluated aquifer potential and protective capacity in parts of Asaba Metropolis, using fifteen Vertical Electrical Soundings (VES) with the Schlumberger array. The ABEM Terrameter SAS 1000 was used and the maximum current electrode spacing (AB/2) was 300 m. Geoelectrical data were interpreted using WINRESIST and integrated with Dar-Zarrouk parameters to estimate hydraulic conductivity (K) and transmissivity (T). The subsurface comprises three to six geoelectric layers. Aquifer resistivity ranges from 156.0 Ωm to 7365.2 Ωm, aquifer thickness from 3.0 m to 33.7 m, and aquifer depth from 4.9 m to 39.8 m. Longitudinal conductance (S) varies from 0.0111 ℧ to 0.1236 ℧, indicating predominantly poor overburden protective capacity and high vulnerability to surface contamination. Hydraulic conductivity ranges from 0.095 m/day to 3.477 m/day, while transmissivity varies from 0.602 m²/day to 53.353 m²/day, with the highest values occurring in the southwestern sector, indicating the most productive aquifers. High transverse resistance, anisotropy and fracture porosity further delineate favourable groundwater-bearing zones. This study concludes that the integrated geoelectrical approach effectively identified aquifer geometry, groundwater potential and vulnerability, providing a scientific basis for borehole siting, groundwater protection and sustainable water-resource management in parts of Asaba and similar Niger Delta sedimentary terrains.

Hydrogeophysical investigation for groundwater development in the crystalline terrain of Ohagainyi area of Lokoja, North-Central, Nigeria

Hydrogeophysical assessment of groundwater and saltwater–freshwater interface in a quaternary– neogene coastal aquifer, Kilwa Kisiwani island, southeast Tanzania

This study aims to identify and explore new potential sites of groundwater resources using geophysical methods, and to demarcate the depth to the saltwater-freshwater interface. Kilwa Kisiwani Island is geologically covered mostly by Neogene and Quaternary alluvial sediments, sand and gravel. The geophysical techniques employed during the research include Vertical Electrical Sounding (VES), Electrical Resistivity Tomography (ERT), and Transient Electromagnetics (TEM). The Island has the potential for groundwater occurrences, but the layer with fresh water is shallow and thin. Out of the 18 VES sites, 2 (11%) points have shown non-potential, but the remaining 16 (89%) of the VES sites have shown potential, and drilling has been recommended depending on the hydrogeophysical characteristics of each potential VES point. Out of the 16 TEM points, 4 (25%) have shown non-potential, but the remaining 12 (75%) have shown potential, and drilling has been recommended depending on TEM point-specific hydrogeophysical characteristics. Generally, geophysical results show the presence of freshwater lenses with a thickness range between 10 and 30 meters. The recommended drilling depth ranges between 10 and 30 meters below ground surface. The depth to saltwater-freshwater interface varies between 1 and 39 meters below ground surface.

Electrical Resistivity Imaging on Limestone Formation for Aquifers Identification in Poguwatu Village, Central Sumba

Poguwatu Village in Central Sumba Regency is a dry area characterized by low rainfall and dominated by carbonate rocks, resulting in limited surface water availability and posing a persistent challenge for groundwater exploration. This study presents the first subsurface investigation using the Dipole-dipole resistivity geoelectrical method to characterize aquifer-bearing rock conducted in Poguwatu Village, West Cendana. This method has the ability to identify the conductor zone related to the saturation area where the water accumulated. Measurements were conducted along 5 survey lines, where each line has 620 m length, except Line 5 extending to 880 m, with 10 m electrode spacing. The measured data calculate in apparent resistivity value and then invert to true resistivity using least-square inversion processes. The result yielded RMS errors ranging from 17.7% to 24.8%. The inversion results identified four rock units based on resistivity values, sandy limestone saturated with saline water (< 2.0 Ωm), marl (2.0–32.0 Ωm), fractured or sandy limestone (32.0–128.0 Ωm), and compact limestone (>128.0 Ωm). A seepage with thickness ± 2 m was identified on Line 2 within the fractured/sandy limestone, bounded below by an impermeable marl. Compact limestone, with very low porosity and permeability, dominates in most of the study area and functions as an aquifuge, a finding corroborated by a dry borehole on Line 5 that failed to yield groundwater. These results indicate limited groundwater potential across Poguwatu Village, and further investigation into alternative water sources from surrounding areas is recommended for the community's water supply.