Hydrogeophysical Investigation for Groundwater Development in the Crystalline Terrain of Ohaganyi Area of Lokoja, North-Central, Nigeria

doi:10.21203/rs.3.rs-4690498/v1

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Hydrogeophysical Investigation for Groundwater Development in the Crystalline Terrain of Ohaganyi Area of Lokoja, North-Central, Nigeria

https://doi.org/10.21203/rs.3.rs-4690498/v1

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Hydrogeophysical investigation of Ohagainyi area of Lokoja was undertaken to understand the local geology, ground water conditions and the prospect of groundwater development in the survey area. In this study, 2D Electrical Resistivity Profiling was carried out using electrical resistivity measurements methods. Wenner electrode configuration was employed to determine the hydrogeological characteristics of the survey area. Consequently, Five Vertical Electrical Sounding (VES) points were selected based on the 2D Profiling results employing the Schlumberger electrode configuration with maximum half-current electrode spread ranging from 70 m to 100 m; the half-potential electrode spread range from 0.3 m to 5 m. Four layers were identified by the VES: topsoil, weathered, fractured, and the fresh bedrock. The weathered/fractured geologic units are the two aquifer types that were identified from the VES results. The H-type curve demonstrates that the resistivity of the first layer is higher than that of the second layer and lower than that of the third layer (ρ1 > ρ2 < ρ3s). The first layer is made up of clay and laterite. The weathered basement aquifer formed the second layer with thickness ranges of 0.69 m − 6.12 m. and the resistivity range of 3.84 Ώm − 35.17 Ώm. The fractured aquiferous layer underlain the (WB) zone with thickness range of 8.44 m – 50.7m and resistivity values ranges from 429.6 Ώm -21726.6 Ώm. If the density of the fractures in the fractured column is high, the groundwater yield from this type of aquifer could be high. The final layer is the fresh basement, which has resistivity values ranging from 16.22 Ώm to 41790.1 Ώm.

geophysical methods

hydrogeology

basement terrain

deep fractures

aquifers

groundwater development

The study was conducted within sublets of Lokoja; which is a developing settlement with increasing demand for clean and portable water for domestic needs, agricultural and industrial purposes. The Kogi State Government plan on stimulating economic growth, industrialization and other form of development lead to opening of new settlements including Ohagainyi Crescent. This area is underlain by Basement crystalline rocks. The area is drained by seasonal eastward flowing arm of Meme River with few streamlets and emptying into river Niger (Onugba et al., 2017, Ngozi-Chika et al. 2021, Ngozi-Chika, et al. 2022). Thus, if nothing is done, the area will be face with water shortage and crisis as in Ganaja and other parts of Lokoja.

Generally, the Kogi State government water supply scheme (Greater Water Lokoja Project) in parts of Lokoja metropolis does not extend to this new settlement of Ohagainyi. In the places covered by Greater Water Lokoja Project, the scheme has been inadequate for the nearby residents who ultimately depend largely on the Niger and Benue River waters to augment; even with glaring attendant health concerns that could arise from the pollution of the river waters as enumerated by Ngozi-Chika et al. (2016). The study showed that the quality of surface and ground water in parts of Lokoja are continuously polluted, notably from the random waste disposal practice by nearby resident, open defecation of faeces and excreter directly to the rivers or their close proximity. Further, incessant and indiscriminate dumping of refuse into the river channels, perennial flood waters with resultant huge amount of wastes, septic entities and gasoline constituents, washing and pouring of kind of dirts into the river waters. All of these are sources of contamination deteriorating water resource, aesthetics and the sanity of the area. Thus, the water is not safe for human health. Given all the aberrations to the surface river waters, is an urgent need for groundwater development.

Groundwater is one of the most important natural resources and its occurrence depends primarily on geology, geomorphology/weathering and rainfall. The interplay of these factors give rises to complex hydrogeologic environments with countless variations in the quantity, quality, and ease of access and renewability of groundwater resources. Development of the resource therefore depends on the accurate understanding of the hydrogeology. There is great risk inherent in proceeding with large increases in groundwater use without an adequate understanding of the resources (Dada et al., 2020, Cobbing and Davis, 2008). Thus, the need for evaluation of groundwater potential in Ohaganyi layout for Groundwater Development.

1.1 Geological setting

Ohagainyi and environ is a new-layout crescent, located on the corridor of Ganaja-Otuokiti bypass in Lokoja. This survey area is covered by Lokoja Topo-Sheet 247 SW in central Nigeria as shown in Fig. 1, and lies between latitude 7^o 43’N – 7^o 45’N and longitude 6^o 42’E – 6^o 44’E within the Crystalline Basement Rocks. The area of Lokoja and environs is generally underlain by Precambrian crystalline rocks comprising migmatites, gneiss, quartzites with granite and pegmatite intrusives, along with quartz veins, overlain by unconformably Upper Cretaceous clastic sedimentary rocks occurring in places (Obaje, 2009, Omada et al., 2009, Dada et al., 2011_a).

The rivers Niger, Benue, Kaduna, and Meme generally drain Lokoja and its environs. The average annual humidity is approximately 70% (Meteorological Department, Federal Ministry of Aviation, 2007). Aquifers in this sub-region are recharged directly by precipitation, but they can also be recharged through infiltration from the rivers Niger, Benue, and Meme. Groundwater availability in crystalline rocks in the sub-region is highly dependent on the degree of weathering and fracturing of the rocks, as well as the interconnectivity of the fracture. Hand-dug wells, boreholes, and springs are the most common methods of groundwater abstraction.

The area of Ohagainyi is underlain by migmatites, older granite and porphyritic granite. The migmatites are foliated and lineated while cross-cutting quartzo-feldspathic veins are common in the granite and porphyritic granite. Joints and fractures are common in the survey area. The groundwater availability in crystalline rocks in the area is greatly dependent on the degree of weathering and fracturing of the rocks and the interconnectivity of the fractures.

The vegetation is the Tropical Forest-Savannah with mixture of trees, shrubs and grasses. Ohagainyi and its environs have the peculiar climate of equal long dry season (November to April) and rainy season (May to October) of Central Nigeria. The mean annual rainfall ranges from 1250 to 1500mm and 70% occur during the months of July – August; the mean temperature is put at about 26.1^oC (97^oF) Iloeje (1981).

Ground truthing was undertaking to understand the geology and structures of study area. The geophysical properties of water-bearing zones (electrical resistivity, seismic velocity, average density, etc.) depend, among other factors, on the degree of fracturing, the mode of water occurrence and the dissolved salts (UNESCO, 1984). Two (2) D Electrical Resistivity Profiling was carried out using electrical resistivity measurements methods to understand the local geology and ground water conditions and more particularly to elucidate on the prospect of groundwater development in the area. 2D ER Profiling was first undertaken using the Werner electrode configuration to understand the hydrogeological characteristics within the crystalline basement of the survey area. This is because when profiling precedes electrical sounding in the basement environment, it gives a better picture of structural features and hydrogeological characteristics of the groundwater system (Onugba et al., 2017, Obihan et al., 2021). Based on the 2D profiling results, five points were selected for VES, employing the Schlumberger electrode configuration with maximum half-current electrode spread ranging from 70 m to 100 m; the half-potential electrode spread range from 0.3 m to 5 m. The Mini-Res Resistivity Metre was used for all the electrical resistivity measurements. Data quality was relatively good. IX2-D (Interpex) and RES2DINV (2D Resistivity and IP Inversion) software for computer modelling. The

Summary of geophysical information to assist location and drilling of productive boreholes in the survey area is presented in Table 1

Table 1

Summary of Vertical Electrical Sounding (VES) Results and Analysis
NS	Layer’s Average Resistivity (Ωm)				Layer’s Thickness (m)			Total Depth to Basement (m)
NS	1	2	3	4	1	2	3	Total Depth to Basement (m)
VES 1	464.50	32.65	429.60	41790.1	0.94	6.12	50.70	57.70
VES 2	309.5	33.21	9542.9	16.84	0.95	4.23	8.50	13.68
VES 3	309.8	27.72	9508.5	16.87	0.59	3.83	8.44	12.87
VES 4	300.9	35.17	21726.6	16.61	1.25	4.62	14.56	20.44
VES 5	371.4	3.84	18340.7	16.22	0.70	0.69	9.79	11.18
Average values	351.22	26.52	11909.66	8371.33	0.87	3.90	18.40	23.17
Range values	309.5–464.50	3.84 – 35.17	429.60 – 21726.6	16.22 – 41790.1	0.59 – 0.94	0.69 – 6.12	8.44 – 50.70	11.18 – 20.44

Table 2

Summary of Geophysical Information to Assist Drilling of Salem Campus (Onugba et al., 2017)
WATER BEARING UNITS		REMARK	RECOMMENDED BOREHOLE DEPTH
1^ST Aquifer	2nd Aquifer	REMARK	RECOMMENDED BOREHOLE DEPTH
4–10m	20–30m	Low yield	not recommended
6–11m	-	Poor yield	not recommended
7–15m	30–52m	Good yield	55m
7–10m	15–32m	Moderate yield	45–50m
4–12m	24–40m	Moderate yield	45–50m
6–10m	16–25m, 45-65m	Moderate yield	70m
7–10m	15–25m, 30 − 52m	Moderate yield	55 - 60m
7–10m	15–25m, 30 − 65m	Moderate yield	70m
7–11m	17–30m, 40 − 65m	Good yield	70m
6–10m	16–50m	Good yield	55 -60m
7–11m	14–40m, 43 − 65m	Good yield	70m

Based on the interpretations of the VES data, four major subunits were identified in the investigated area (Table 1 and Fig. 2). It showed that the subsurface can be characterized into four major sub units based on the electrical resistivity distribution (Fig. 2). The first unit comprised of the topsoil made up of clay and laterite, characterized by electrical resistivity distribution range of 300.9Ώm – 464.5Ώm and delineated within the depth range of 0.5m to 1.25m while the second layer is the weathered basement and the first aquifer layer with depth range from 1.39 m to 7.06 m and the resistivity range of 3.84 Ώm to 35.17 Ώm. The third region is the fractured basement and the second aquifer layer characterized by electrical resistivity range of 429.6 Ώm -21726.6 Ώm and delineated to depth range of 11.18 m to 57.77 m with average depth of about 23.2m. The fourth region is the fresh basement represented by relatively high electrical resistivity range of 16.22 Ώm – 41790.1 Ώm and delineated to an average depth of about 59m.

From the VES result, two type of aquifer were delineated, these include the weathered basement aquifer zone and fractured basement aquifer zone. The H – type curve represents a subsurface whereby the resistivity of the first layer is greater than the second layer while the resistivity of the second layer is less than the third layer (ρ1 > ρ2 < ρ3s). The weathered basement aquifer and the fractured basement zones directly overlies the weathered basement zone. The groundwater yield from the fractured basement aquifer zone could be high if the density of the fractures in the fractured column is high. Furthermore, two type of aquifer were delineated falls water bearing units reported in Onugba et al. 2017 (Table 2)

The study reveals four units: lateritic layer, weathered zone, fractured unit, and fresh basement. The two aquifer types are the weathered/fractured geologic units. The resistivity of the first layer is higher than that of the second layer, and that of the second layer is lower than that of the third layer, as indicated by the H-type curve (ρ1 > ρ2 < ρ3s). The resistivity of the first layer ranges from 300.9 Ώm to 464.5 Ώm, and its depth and thickness vary from 0.593 m to 1.25 m. The second layer is the weathered geologic unit; its thickness ranges from 0.692 m to 6.12 m, and its depth ranges from 1.39 m to 7.06 m. The range of resistivity is 3.84 Ώm − 35.17 Ώm. The third layer is made up of the fractured aquifer zone. Its resistivity values range from 429.6 Ώm to 21726.6 Ώm, its depth from 11.18 m to 57.77 m, and its thickness from 8.44 m to 50.7 m. The groundwater yield from this aquifer type may be high if the fractures in the fractured column are dense. The final layer is made up of the fresh bedrock. Resistivity values in this unit range from 16.22Ώm to 41790.1Ώm.

Aquifers in this area are recharged by precipitation as well an arm of River Meme flowing eastwards to join River Niger (a major hydrologic feature in the area) depending on the interconnectivity of the subsurface geologic structures.

Conflict of Interest

The authors declare that they have no conflict of interest.

Author Contribution

Ngozi-Chika, C.S. conceived of the presented idea and design of the work. He participated in an orientation survey, geological fieldwork, a geophysical survey, and data collection. Ngozi-Chika also participated in data analysis, interpretation, and drafting of the original manuscript, as well as further scientific contributions.Okanigbuan, P.N. participated in a geophysical survey and data collection, as well as data analysis, interpretation, scientific contributions, and the revision of the article.Ibrahim, O.I. participated in the orientation survey and geophysical survey, data collection, data analysis, data interpretation, scientific contribution, and revision of the manuscript.Adeoye, A.S. participated in a geophysical survey and data collection, as well as data analysis, interpretation, and scientific contribution, as well as the revision of the manuscript.Oyeyemi, S.T., participated in geological and geophysical surveys, data collection, as well as data analysis, interpretation, and scientific contribution, as well as the revision of the manuscript.Onugba, A. participated in a geophysical survey and data collection, as well as data analysis, interpretation, scientific contributions, and critical revision of the article.

Acknowledgement

The authors would like to express their gratitude to the host institution, Dennis Osadebay University for creating a supportive environment that allowed us to complete this work. The work has benefited from helpful critiques and remarks from anonymous reviewers as well as from a larger audience.

Data Availability

Field generated data supporting the findings of this study are available from the corresponding author on request.

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No competing interests reported.

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Hydrogeophysical Investigation for Groundwater Development in the Crystalline Terrain of Ohaganyi Area of Lokoja, North-Central, Nigeria

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Abstract

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1. Introduction

1.1 Geological setting

2. Materials and methods

3. Results and Discussion

4. Conclusion

Declarations

Conflict of Interest

Author Contribution

Acknowledgement

Data Availability

References

Additional Declarations

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