Geoelectrical Investigation of a Proposed Dam Site in a Sedimentary Terrain: Case Study of Aba River at Amapu-Ideobia, Akanu Ngwa Southeastern Nigeria

Abstract

The geoelectrical investigation of the proposed Aba River dam at Amapu-Ideobia, Akanu Ngwa Southeastern Nigeria has been carried out. The objective of this study is to determine the downward and lateral trends of the rock layers or units along and near the proposed dam axis and deduce the possible structures that may enhance workable design of the dam. ABEM Terrameter SAS 4000 model was used and the symmetrical Schlumberger configuration was adopted. Twelve (12) Vertical Electrical Sounding stations were located and fully occupied along the dam axis. Preliminary input data from the field were fed into Zohdy software to generate real resistivities and depths to geoelectric layers. Five geoelectric layers were interpreted as Loamy Top soil, Alluvial matter, Pebble bed, Sandy lateritic and Gravely sand. Layer 1 (the top loamy soil) was encountered in VES 1, 2, 3, 4, 5, 9, 10, 11 and 12 locations with maximum thickness of 1.5 m in VES 3 and 4. Resistivity values ranged from 216 to 519 Ohm-m. The second layer (lateritic matter) had a maximum lower depth of 5 m in VES 3 and 4 points. This was not encountered in VES 6 point being replaced by alluvium. Resistivity values ranged from 101 to 6190 Ohm-m. Layer 3 was interpreted as a restricted pebble bed which occurred only at VES 6, 7 and 8 locations flanking the river course with thickness of about 3.5 m and resistivity values range of 182 -415 Ohm-m. The fourth layer was modeled as the alluvial matter and restricted to the river course (VES 6,7, 8) locations with base at between 12.5 m in VES 8 and 8 m in VES 6. The last modeled layer (Layer 5) was composed of gravely sandstone that underlined the whole study area apart from the restricted pebble bed at the NE crestal portion (VES 12). No structures like fractures, lineaments and faults that would be of deleterious effect were observed in all the VES points down to about 40 m. However, it was observed that the axial length had overriding sandy matter with high porosity and potentially rife for great infiltration; a condition that could facilitate seepage around the reservoir portion of the dam.

Field‐Controlled Electrical Switch with Liquid Metal

“…Here, σ is the solution conductivity, and ℓ ij for i ∈ A , B and j ∈ M , N represent the distances between the outer electrodes (A, B) and an intermediate pair of points (M, N), as marked in Figure b. This approach is adapted from techniques in geophysics to interpret vertical electrical sounding data (also used for measuring resistivity of semiconductor germanium). With Equation , one can predict the required current to achieve the necessary potential drop ΔΦ for a specific level of bipolar redox.…”

Application of geological and geo-electric methods in the assessment of corrosivity, competence, and vulnerability of soils around Southeastern Nigeria

“…It is predominantly a farming area, with almost 80% of its population as peasants and petty traders. They mostly trade in finished farm products (Ibeneme et al, 2013). The soils are fertile during the rainy season, which is an added advantage, and mostly dry and damp during the harvest season.…”