Integrated Approach for the Assessment of Ihale Damsite for Reservoir Water Storage, Kogi, Nigeria

Abstract

Aim of the Study: Ihale damsite was evaluated for the purpose of constructing a dam for water storage and irrigation of farmland in the area.

Methodology: The location of the proposed dam axis lies on the Universal Transverse Mercator (UTM) coordinates 187872mE, 916118mN and 187634mE, 915603mN and to harness river Afun which is about 2.5km to Kabba-Bunu area. 10 trial/test pits for soil sampling and 2 deep borings into the basement rock were conducted on both sides of the river channel and DCP were conducted to the point of refusal. The number of blows per 10cm for the overburden soils ranges from 1 to 50 between depths of 0 – 2.0meters. DCP test involved driving a solid cone of 60⁰ into the ground, using repeated blows of a hammer with a fixed mass of 10Kg falling through a distance of 550mm having maximum diameter of 20mm.

Findings & Conclusion: Findings revealed Clayey top soil, laterite, weathered basement and fresh basement rocks were the main geologic material obtained from the area with 4 geo-electric layers recorded. Resistivity values along the dam axis ranges from 29.1 to 2857.6 Ωm which is the third layer of VES 1 and 7. This layer was inferred to be weathered basement rock. In essence; placing the dam structure on the fourth layer of fresh basement rock will be more desirable to minimize seepages and enhance the foundational footing of the structure. Geotechnical analysis revealed bulk density varied from 1320 to 2830 kg/m². Specific Gravity ranges from 2.56 to 2.76 Ga. Natural moisture content Nmc varied between 1.73 and 24.49 % with optimum dry density and dry density desirable for the support of dam construction in the area. Unit Cone Resistance (KN/m²) that varies from 95 to 520 KN/m² across the depths is desirable to support the dam area structure. Average DCP Bearing Capacity increased from 120 to 500 as depth of investigation increased from 0.5 to 2.0 m. The integrated approach has revealed the Ihale damsite is good for dam construction.