Geoscientific assessment of Kemanji Dam site using Kemanji and Semon river, Kaiama area, Kwara state, North-Central Nigeria

Abstract

Proposed Dam site is located in Kemanji.Its axis is approximately 994m in length situated across Kemanji and Semon river.The study aims to investigate the sub-soil profile for a water tight reservoir condition that will be sustainable during the dry season for irrigation of farmland.Geotechnical field work entailed boring trial/test pits in the area along the proposed dam axis.The lithological facies were 3 groups of Brownish silty clayey sand, Brownish mottled silty clay and Light brownish soil/lateritic concretions.The average Maximum Dry Density compacted was 1814.61 kg/m3 and optimum moisture content (OMC) of 41.83%.The natural moisture content varied between 2.81-7.61%,while the bulk density varied between 1200-1922.10kg/m3.The liquid limit and plastic index ranges from 30-39% and 2.6-8.5% respectively.The specific gravity ranges between 2.75-2.85.The average Maximum Dry Density compacted is 1814.61kg/m3 and optimum moisture content of 41.83%.VES revealed thickness from 0.81-4.94m, weathered/fractured basement layer of 3-10.01 m and fresh/hard basement layer rock which is infinitely thick.The resistivity values revealed a range of 14.0-3522 Ωm.Investigated area of Kemanji is suitable to construct a dam due to Geologic materials of sandy top soil, weathered and fresh basement rocks readily available in the area.For the dam to be water tight, excavation must be done to about 12meters depth for its foundational footing to rest on fresh basement rocks.This will reduce seepage to minimal level, especially during the dry season when the reservoir water will be needed mostly.