Preliminary Investigation of a Proposed Dam Site along River Ome, Ago Iwoye South Western Nigeria

Soil investigation was carried out at a proposed dam site across River Ome in Ago Iwoye, southwestern Nigeria to investigate the depth to bedrock, possible geologic structures, foundation conditions of the dam axis, abutments and choice of best location for construction of dam. Six Vertical Electrical Soundings (VES) were carried along the river course and this was done using Schlumberger configuration. Evaluation of the engineering properties of the soil was carried out for twelve samples collected across the river using atterberg limit, grain size analysis, California Bearing Ratio (CBR) and compaction characteristics of the soils. The geophysical result showed three geo-electric layers; top sandy layer, clay and weathered/fresh basement. Analysis of the atterberg limit shows a dominance of inorganic clay size particles with high plasticity and moisture content while the grain sizes analysis reveals well graded gravelly clayey silty sand. The soil type classification, CBR and compaction values obtained showed some significant agreement. The values of river discharge were computed during dry and wet seasons and this showed that the magnitude of flood to be averted will pose no challenge on the selection of spillway type. The integration of these methods helped in the choice of location for the dam axis.