Thesis Abstract

Abstract
Groundwater is a vital resource for various human activities such as drinking water supply, agriculture, and industrial processes. Detecting and mapping groundwater resources are essential for sustainable water management. Resistivity methods have proven to be effective in characterizing subsurface structures and locating groundwater sources. This research project focuses on the application of resistivity methods to detect horizontal and vertical discontinuities in the electrical properties of the ground for groundwater detection. The project involves the use of resistivity surveys to investigate subsurface geology and hydrogeological conditions. Horizontal discontinuities, such as faults and fractures, can affect the flow of groundwater and create barriers to its movement. Vertical discontinuities, such as changes in lithology or stratigraphy, can also impact groundwater flow and storage. By analyzing the resistivity data collected from the surveys, the project aims to identify these discontinuities and their influence on groundwater occurrence and movement. The research methodology includes field data collection using resistivity instruments, data processing and interpretation, and mapping of subsurface structures. The resistivity surveys are conducted using techniques such as electrical resistivity tomography (ERT) and vertical electrical sounding (VES) to capture variations in subsurface resistivity. Data processing involves inversion algorithms to create resistivity models of the subsurface, which are then interpreted to identify potential groundwater-bearing structures. The project also integrates geological information such as lithology, structure, and hydrogeological properties to enhance the interpretation of the resistivity data. By combining resistivity results with geological knowledge, the research aims to provide a comprehensive understanding of the subsurface conditions influencing groundwater occurrence. The project's outcomes include maps and cross-sections illustrating the distribution of subsurface structures and their impact on groundwater resources. Overall, this research project contributes to the field of groundwater exploration by utilizing resistivity methods to detect horizontal and vertical discontinuities in the electrical properties of the ground. The findings are valuable for water resource management, environmental assessment, and land-use planning. By enhancing our understanding of subsurface structures affecting groundwater flow, the project supports sustainable development and utilization of groundwater resources.

Thesis Overview

The resistivity method is used in the study of the horizontal and vertical discontinuities in the electrical properties of the ground and also in the detection of three dimensional bodies of anomalous electrical conductivity. In the study of ground water movement in obubra area, the the resistivity method commonly employed are the electrical resistivity method. Electrical resistivity method is one of the most useful techniques in groundwater geophysical exploration, because the resistivity of rocks is sensitive to its ionic content (Alile, et al., 2011). The method allows a quantitative result to be obtained by using a controlled source of specific dimensions. Records show that the depths of aquifers differ from place to place because of variation in geo-thermal and geo-structural occurrence (Okwueze, 1996). Therefore, the need to study the area for groundwater potential especially in terms of determining the flow direction is a prerequisite for portable ground water exploration and exploitation in this area.

1.1     Location And Geology Of The Area

The study area lies between latitudes 50 15′ and 60 15′N and longitudes 70 45′ and 80 45′E. It is located within the sub-equatorial climatic region of Nigeria with a total annual rainfall of more than 300 to 400cm. Temperature ranged from 250C to 280C. The area experiences two seasons, these are the wet season which lasts from April to September with a peak in June and July while the dry seasons lasts from October to March (Iloeje,1991).

The study area is underlain by two major lithologic units: Crystalline basement and Cretaceous sediments. The crystalline basement rocks occupy the extreme south of the study area. Also, there are intermediate rocks scatteredin patches around Obubra, Iyamayong, Iyamitet, Ikom, Nkpani and Usumutong. The Cretaceous sediments cover about 90% of the study area. Asu River Group is the basal and oldest recorded sediment in the study area. It is dominated by bluish gray/black to olivine brown shale and sandy shale, fine – grained micaceouscalcareous sandstone and siltstone with limestone lenses. The shale is often carbonaceous and pyritic which indicates that the sediments were deposited under a poorly oxygenated shallow water environment of restricted circulation, an indication of low energy environment (Petters et al., 1987). In general, Southern Obubra lies within the Cross River plain and the clastic beds in the study area can be ascribed to the Ezillo Formation. The Ezillo Formation comprises mostly dark gray shales with fine sandstone and siltstone intercalations in the lower part, and an upper unit that is highly bioturbated, fine medium sandstone, similar to the sandstone of the Amaseri Formation. The Ezillo Formation between Appiapum and Ikom was deposited in a deltaic coastal plain, in brackish marshes and inter-distributary bays (Barth, et al., 1995). A major river (Cross River) exists in the study area into which minor streams empty their loads. The elevation of the study area ranged from 14 to 170m above sea level. The relief is characterized by undulations running at undefined direction and variably demarcating the very lowland areas from moderate relief landmarks. The occurrence of the low plains is occasionally broken by inselbergs of granite and basalts in the southern portion of the study area. In the sediment filled portions, the low plains are occasionally broken by flat -topped hills of sandstone ridges and igneous intrusive with highly ferroginized sandstones with gravels resulting from uplifts. The area is drained by the Cross River with major tributaries like, Udip, Ukong, Lakpoi, Okwo, and Okpon rivers. These rivers form a network of dendritic drainage system