Geoelectrical Investigation of a Proposed Dam Site in a Sedimentary Terrain: Case Study of Aba River at Amapu-Ideobia, Akanu Ngwa Southeastern Nigeria
- 1 Department of Geosciences, Federal University of Technology, Owerri, Nigeria
- 2 Department of Geosciences, Federal University of Technology, Owerri, Nigeria
- 3 Department of Geosciences, Federal University of Technology, Owerri, Nigeria
- 4 Department of Geosciences, Federal University of Technology, Owerri, Nigeria
- 5 Department of Geosciences, Federal University of Technology, Owerri, Nigeria
- 6 Department of Physics, Federal University of Technology, Owerri, Nigeria
- 7 Department of Geosciences, Federal University of Technology, Owerri, 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 th is study is to determine the downward and lateral trends of the rock layers or units along and near the propose d 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 range d from 216 to 519 Ohm-m. The second layer (lateritic matter) ha d 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 range d 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 underline d 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 w ould be of deleterious effect were observed in all the VES points down to about 40 m. However, it was observed that the axial length ha d 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.
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