Geo-Electric Assessment of Kali Failed Dam Project Aliero, North Western Nigeria

Abstract

An integrated geophysical investigation using very low frequency electro-magnetic (VLF-EM) and electrical resistivity methods using (VES) technique has been carried out for investigation of possible causes of dam failure in Kali, Aliero Northwestern Nigeria. A total of Three 3 (VLF-EM) traverses and Ten 10 vertical electrical soundings (VES) techniques have been carried out to identify the fracture zones, seepage and possible threat that lead to the collapse of the dam. The interpretation of VLF-EM data is carried out qualitatively using Fraser and Karous-Hjelt filters and the interpretation of sounding data is done using IPI2 win software. VLF-EM data signifies the exact fracture zones founded on higher values of relative current density that coincide to the subsurface fracture. The survey was conducted on an interval of 10 m interval along traverses at South-North direction ranging from 620 - 640 m in length. The plot of filtered real and filtered imaginary identified noticeable fracture zone close to the surface which was later further delineated by (VES) technique. VES soundings were carried out at locations of prominent VLF anomalies presumably typical of basement fracture using AB/2 of 80 m. Results interpreted show layers thickness and their corresponding resistivity, top soil (0.5 m to 3.45 m, 51.9 Ωm to 318 Ωm), underlain by clay to confined clay (4.56 m to 54 m, 7.88 Ωm to 60.2 Ωm) which is underlain by fractured/fresh basement (5.76 m to 73.9 m, 40.3 Ωm to 197 Ωm). The overburden materials underlain are far away to subsurface (bed rock) in most of the area to support the dam. The clay materials which could serve as conduit, exist within the shallow overburden which was not excavated during the construction. Therefore it was concluded that the dam cannot retain its strength to oppose the dam against collapse.