INTEGRATED GEOPHYSICAL MAPPING OF GROUNDWATER AQUIFER FOR SPATIAL DISTRIBUTION OF GROUNDWATER DEVELOPMENT IN IPERINDO AND ITS ENVIRONS, SOUTHWESTERN NIGERIA

Assessment of groundwater potential of Iperindo area, Southwestern Nigeria was conducted by mapping spatial distribution of groundwater availability within the area and consequently locating areas of groundwater reserve to serve the community and its environs. This was achieved by integrating geophysical techniques involving landsat ETM-7 satellite data, aeromagnetic data, VLF-EM and electrical resistivity methods to delineate subsurface structures, understand the direction of groundwater flow, and detect the depth to groundwater aquifer. The result of landsat and aeromagnetic revealed some lineament intersection approximately NE-SW direction and interpreted to be potential sites for groundwater development. VLF-EM revealed geologic structures of significant hydrogeological importance at depths of 40 m to 200 m. Vertical electrical sounding (VES) confirmed high groundwater prospect in the areas with estimated depth to water table between 30 m and 100 m. The integrated results of the study revealed adequate groundwater spatial distribution for effective groundwater development in the area.

Multi-Criteria Decision Making and Dempster-Shafer Model Based Delineation of Groundwater Prospect Zones From A Semi-Arid Environment

The present study illustrates the delineation of the groundwater potential zones in one of the most critical and drought affected areas under Bundelkhand region of Uttar Pradesh. Hydrological evaluations were carried out in district Mahoba using GIS tools and remote sensing data which ultimately yielded several thematic maps, such as lineament density, land use/land cover, drainage density, lithology, slope, geomorphology, wetness index (WTI), altitude and soil. CartoDEM data which have spatial resolution of 30m i.e. equivalent to one arc second were used to create digital elevation model, drainage density, altitude, WTI and slope. The thematic layers were assigned relative weightages as per their groundwater potential prospects under multi-criteria decision making (MCDM) method through analytical hierarchy process (AHP). To recognize the groundwater potential zone, weighted overlay analysis was performed using ArcMap software. Additionally, for testing of the Dempster-Shafer model, 16 borewells in high potential areas have been selected. Based on the probability of the groundwater occurrence, the belief factor was equated. Further combining the weighted layers, groundwater potential zones were obtained. The groundwater potential maps illustrate five zones having different potential in the Mahoba district. According to the AHP model the north-west side of the study area is characterized with very good potential zones whereas the north-east and south-east region constitute medium and poor groundwater potential zones respectively. It reflects that more than 50% of the area is having medium groundwater potential while 30 percent of the area falls under low potential zone. 10% of the study area falls under very good groundwater potential zones. According to the DS model, very high groundwater zones constitute only 7% and the remaining area falls under poor potential. Overall accuracy of the DS model was higher than AHP model.

Aeromagnetic and electrical resistivity mapping for groundwater development around Ilesha schist belt, southwestern Nigeria

Aeromagnetic and vertical electrical sounding around Ijano, southwestern Nigeria, was investigated for groundwater potential. Aeromagnetic dataset and vertical electrical sounding were acquired and used to investigate the study area. Oasis Montaj, Microsoft Excel and Arc GIS were used to present the results in maps, images and profiles. In order to map out the geological structures of the study area, magnetic image enhancing filters applied to the total magnetic intensity using Geosoft (Oasis Montaj) are reduction to equator, vertical derivative, total horizontal derivative and upward continuation. These filters helped define the lithological boundaries, geological structures, faults, folds and contacts. The lineament of aeromagnetic map was generated from derived field intensity gradients and solutions of Euler deconvolution carried out on the aeromagnetic data using structural index of 0.5 and 1. The processed image shows the lineaments trends majorly towards NE–SW directions. From these combined results of the study area, consistent aeromagnetic lineament map was generated showing the probable positions and trends of the suspected fractured/faulted zone as well as other basement structures. Hydro-lineament density maps based on lineament were produced from the generalized structure trends in the area. The result from the depth sounding data interpretation indicates three curve types which are H, HA and KH, where curve type H has the highest occurrence. The results from the vertical electrical sounding data revealed that the areas with the highest hydro-lineament density are good for groundwater prospect and development. The study has led to the delineation of areas where groundwater occurrences are most promising for sustainable supply, suggesting that an area with high concentrations of lineament density has a high tendency for groundwater prospecting. The results from the study show that the aeromagnetic technique is capable of extracting lineament trends in an inaccessible tropical forest.

Evaluation of Topsoil Competence, Aquifer Types, Groundwater Prospect and Flow Pattern using Geoelectric Characterization for Part of Ogbomoso, Nigeria

Part of Ogbomoso Southwestern Nigeria was assessed using electrical resistivity method with a view to obtaining the subsurface geoelectric parameters (resistivities and thicknesses), categorizes the topsoil into different competence zones and evaluates the aquifer types, groundwater prospect and flow pattern. Fifty-four Vertical Electrical Sounding (VES) data were quantitatively interpreted using the partial curve matching technique to obtain the preliminary layer parameters which were further refined through 1-D forward modelling WinResist software package. The resulting final layer parameters were used to generate 2D geoelectric sections, isopach and isoresistivity maps and subsequently used to categorize the study area into different topsoil Competence, Aquifer types and Groundwater Potential zones. Static water levels of hand-dug wells in the area were used to generate the groundwater flow pattern. Four subsurface geoelectric layers were delineated. These were the topsoil, laterite, weathered/partly weathered layer (main aquifer) and fractured/fresh bedrock. The resistivities and thicknesses of the layers were 76-1858, 649-2021, 17-880 and 260-33385 Ωm and 0.4-4, 0.7-1.9 and 1.9-25.2 m respectively. The groundwater flow pattern in the area was NE-SW. The study concluded that incompetent to highly competent topsoil, weathered bedrock (main) aquifer unit/partly weathered/fractured bedrock aquifer and generally low groundwater potential with NE-SW flow direction underlay the study area.

Preprocessing approaches in machine learning-based groundwater potential mapping: an application to the Koulikoro and Bamako regions, Mali

Groundwater is crucial for domestic supplies in the Sahel, where the strategic importance of aquifers can only be expected to increase in the coming years due to climate change. Groundwater potential mapping is gaining recognition as a valuable tool to underpin water management practices in the region, and hence, to improve water access. This paper presents a machine learning method to map groundwater potential and illustrates it through an application to two regions of Mali. A set of explanatory variables for the presence of groundwater is developed first. Several scaling methods (standardization, normalization, maximum absolute value and min-max scaling) are used to avoid the pitfalls associated with the reclassification of explanatory variables. A number of supervised learning classifiers is then trained and tested on a large borehole database (n = 3,345) in order to find meaningful correlations between the presence or absence of groundwater and the explanatory variables. This process identifies noisy, collinear and counterproductive variables and excludes them from the input dataset. Tree-based algorithms, including the AdaBoost, Gradient Boosting, Random Forest, Decision Tree and Extra Trees classifiers were found to outperform other algorithms on a consistent basis (accuracy > 0.85), whereas maximum absolute value and standardization proved the most efficient methods to scale explanatory variables. Borehole flow rate data is used to calibrate the results beyond standard machine learning metrics, thus adding robustness to the predictions. The southern part of the study area was identified as the better groundwater prospect, which is consistent with the geological and climatic setting. From a methodological standpoint, the outcomes lead to three major conclusions: (1) because there is no aprioristic way to know which algorithm will work better on a given dataset, we advocate the use of a large number of machine learning classifiers, out of which the best are subsequently picked for ensembling; (2) standard machine learning metrics may be of limited value when appraising map outcomes, and should be complemented with hydrogeological indicators whenever possible; and (3) the scaling of the variables helps to minimize bias arising from expert judgement and maintains robust predictive capabilities.

Hydrogeophysical investigation for the aquifers in part of Ilorin, Central Nigeria: Implication on groundwater prospect

Hydrogeophysical study involving the use of Vertical Electrical Sounding (VES) was carried out in part of the basement complex rocks of Ilorin, central Nigeria, with the aim of determining its geoelectric parameters and groundwater potential. A total of thirty (30) VES were carried out using Schlumberger electrode configuration, with half electrode separation (AB/2) varying from 1m to 100m. Information on the subsurface lithologies, overburden thickness and aquiferous layers were obtained from the different VES locations in the study area. From the quantitative interpretations of the data collected, using the method of curve matching with the Orellana-Mooney master curves and 1-D forward modeling with WinResist 1.0 version software, three to five lithologic units were identified in the study. These include: the topsoil, sandy/lateritic clay/laterite, the weathered basement, the fractured basement and the fresh bedrock which are predominantly of the ‘KH’ curve type (30%), followed by ‘H’ type (26.7%), other type curves include ‘QH’ (16.7%), ‘HKH’, ‘HA’ and ‘A’ (6.7% each) and KQ and KQH (3.3% each). The weathered layer and the fractured basement constitute the main aquifer units. The aquifers are of generally low resistivity values (mostly below 100 Ω-m). The depths to dry bedrock at the chosen VES locations vary from 2.7 to 62.7 m with a mean value of 13.02 m in the study area. The geoelectrical interpretations of data obtained in these areas have permitted the delineation of the study area into low and moderate groundwater potential zones. This study is expected to assist in future planning for groundwater resources. Keywords: Hydrogeophysical, Basement Complex, Groundwater, Electrical Soundings, Weathered, Fractured

Series of 1-D ER and IP traverses reveal vestige of regional geological structure

At the Basement Complex geological province of central Nigeria, in the state of Niger, just northeast of the Bida Sedimentary Basin, there is the character of non-complexity and high uniformity in the local geology over an appreciable linear spread. This appreciation makes it a standard practice to do one-dimensional vertical electrical sounding surveys in the search for groundwater resources at this area with the expectation of reliable results. This seeming “simplicity” means that intense manual labour can be invested in acquiring a large data-field at a local area of survey where resources are not readily available to do a standard two-dimensional survey of the conventional kind. This is especially significant for the proposed area of development at the Gidan Kwano Campus of the Federal University of Technology, Minna, Thus, with this awareness and the use of the ABEM Terrameter 4000 equipment, the aim of this study was to do an intense acquisition of one-dimensional electrical resistance and concomitant induced polarization programme for this proposed area of development so as to achieve the objective of garnering information about exploitable groundwater locations before structural developments cover these points up. Typical point-to-point one-dimensional tandem electrical resistance and concomitant induced polarisation surveys were completed along east-west profile lines for about 309 survey stations of the available 441 principal locations of the 4 km2 extent of the proposed new development. After due processing and interpretation of the data-field of this survey, whilst remarking that the induced polarisation data-set was used herein as quality control “refiner” only, clusters of reliable groundwater locations were observed at the southwest end of the 4 km2 areal extent of the proposed new development. It conforms to the dip of the landform and comparatively significant overburden-material thicknesses observed over there. Interestingly, in a twist of serendipity, the series of diagonal subsurface “fault-lines” that connect one promising groundwater prospect with the other, describable by a prominent northeast-southwest dip, aligns exactly with the Kazaure-Karaukarau-Kushaka-Ilesha Schist Belt. In the modern geography setting of the present time, the Kazaure-Karaukarau-Kushaka-Ilesha Schist Belt actually traverses a lengthy diagonal across the landscape of Nigeria, cutting through such Nigerian states as Jigawa, Kano, Kaduna, Niger, Kwara, Ekiti, and Osun. There is virtually no surface indicator of this once-prominent schist belt and what this study reveals is its vestigial signature

Structural Development and Geomorphic Relationship in Wadi Atyaruh, Al Jabal Al Akhdar, NE Libya

The present study has been carried out to analyze the relationship between faulting and geomorphology of the Wadi Atyaruh to reveal the effect of structures on the morphology and distribution of the different karst features. Geographical Information System (GIS) and Remote Sensing (RS) techniques were applied to investigate morphological and topographic characteristics of Wadi Atyaruh, based on ASTER Global Digital Elevation Model (ASTER GDEM) Version 3 (V3) data. Dextral strike-slip fault is the main faulting type in the valley. Conjugate faults system has been found in the study area, which reveals the orientations of the principal stresses. Wadi Atyaruh consists mainly of Dernah formations (Eocene) and Quaternary deposits. Two types of Karren have been recognized, they are Rillen karren and solution basis which are well distributed in Darnah formation. Caves are found in the Darnah formation, the passages and chambers of these caves show a phreatic bedding plane, elliptical shape, laminar profiles, and rectangular and rounded top vadose profiles. The drainage system of this valley is sub-parallel drainage pattern to dendritic drainage pattern, indicating that the area has affected by strike-slip movement (Dextral), joints and it has steep slopes. interpretation of DEM of study area indicate moderate and high relief, low run off and high infiltrations due to the nature of the fracture carbonate rock, the basin have early mature stage of erosion development. Geomorphic parameters such as hill shade, slop, aspect, area shaded and elevation maps, was produced to describe geomorphic forms and processes of the Wadi Atyaruh. The complete morphometric analysis of drainage basin indicates that the given area is having good groundwater prospect.