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Efects of anisotropic changes on the conductivity of sedimentary aquifers, southeastern Niger Delta, Nigeria

George N. J., Bassey N. E., Ekanem A. M., Thomas J. E.

Acta Geophysica

2020

Vol. 68, no. 6

1833--1843

Sundry soils/rocks are characterized by electrical properties with clearly or obscurely expressed anisotropies. These anisotropic efects may be low, moderate or high depending on the coefcient of anisotropy (λ). The vertical electrical sounding technique employing Schlumberger electrode confguration and lithological information from boreholes were deployed to characterize the lithological diversity in homogeneous and anisotropic geologic units that serve as aquifer systems and their overlaying layers in the coastal region of Akwa Ibom State. Based on the λ, the assessed volume of sedimentary formation is classifed into low anisotropy λ<1.2 , moderate anisotropy (1.2 < λ ≤ 1.3) and high anisotropy (λ > 1.3) with alluvium (64.3%), inter-bedded shale and sandstone (14.3%) and shale and slate (21.3%). The estimated percentage of respective compositional coverage indicates that alluvium is dominant, while the blended inter-bedded shale and sandstone as well as the shale and slate are minor geologic units in the Benin Formation. Inferred index of spread of alluvium indicates that the homogeneous and anisotropic units assessed are intrinsic/microscopic in nature as identifed by the impressed current that passed through geologic system. The results showcased that the plot between the strike-dependent resistivity ( ρθ ) at arbitrary chosen strike and geometric mean resistivity ( ρm ) can be used as a yardstick for inferring the degree of consistency of geologic compositions in homogeneous and anisotropic media. Both the quantitative (graphic) and qualitative (contour) results portend the thin possibility of having anisotropy free geologic units. The finding proposes that ground resistivity measurements and interpretations of geologic structures should be constrained by borehole information in order to frm up the intended plans for obtaining clearer, defendable and well-resolved subsurface structures.

Zarys warunków hydrogeologicznych rejonu Falent

Fic M., Dziedziczak Robert

Woda-Środowisko-Obszary Wiejskie

2003

T. 3, z. spec. (6)

9--17

W pracy przedstawiono zarys warunków hydrogeologicznych w rejonie Falent. Głównym poziomem wodonośnym na tym terenie jest, lokalnie odkryty oraz międzyglinowy, poziom plejstoceński. Jego płytkie występowanie od 0 do 50 m p.p.t. - i zadowalające parametry wydajności uzyskiwane ze studzien sprawiają, że na omawianym terenie jest to główny poziom eksploatacyjny (GPU). Drugoplanowe znaczenie w lokalnym zaopatrzeniu w wodę ma trzeciorzędowy poziom oligoceński. Głębokość występowania najpłytszej warstwy wodonośnej oraz uwarunkowania hydrogeologiczne sprawiają, że istnieje tu ścisły kontakt hydrauliczny między wodami podziemnymi i powierzchniowymi.

The purpose of this paper was to present hydrological conditions of the neighbourhood of Falenty and part of the Raszynka's river basin. The main aquifers in described region are located in partly uncovered Pleistocene sediment situated between two clay layers. This aquifer is the main quaternary water-bearing horizon because of the shallow depth of groundwater (0–50 m) and appropriate discharge parameters. Tertiary Oligocene aquifer is not as import ant for water supply as the Pleistocene one. The hydraulic connection between groundwater and surface water is secured by depth of the shallowest aquifer and many other hydrological factors.