GEOLOGY AND HYDROGEOLOGY OF PART OF MAKURDI SHEET 251 SW, NORTH CENTRAL NIGERIA

ABSTRACT

An integrated  geological, geophysical  and hydrogeological studies were carried out to investigate the groundwater potential and quality in part of Makurdi, North Central Nigeria. The study area is entirely sedimentary and is dominantly fine to coarse grained sandstone with varying amounts of silt and clay. The schlumberger array was used for the geophysical investigation with a maximum AB/2 of 100m. A total of 20 Vertical Electrical Sounding (VES) stations were established. The model curve types from the electrical resistivity plot include Q, A and H curves. Three to four major lithologic units comprising the top soil (laterite, clay or loose sand) and the subsequent layers comprising of either sandstone, clayey sandstone, clay or sandy clay. The best of these units as regards to groundwater potential is the uniform sandstone unit. Isoresistivity maps at depths of 20, 30 and 50m respectively were generated and revealed that a dominant part of the study area has a very good groundwater potential at shallow depths of about 20 – 30m; while at a depth of 50m, only the North-Eastern and South-Eastern parts of the study area have a good groundwater potential. Hydrogeological data were obtained from one hundred and ten (110) hand dug wells in the study area and thirty five (35) water samples comprising ten (10) boreholes, twenty four (24) wells and four (4) river samples were collected for physic-chemical and bacteriological analysis. The depth of wells in the study area ranges from 0.71 – 8.4m with water elevation ranging from 0.3 – 8.3m and water column ranging from 0.3 – 5.5m. Most of the hand dug wells are shallow and seasonal; the boreholes however are productive all year round. Eleven (11) out of the thirty-five (35) water samples collected did not meet the Nigerian Standards for Drinking Water Quality (NSDWQ 2007) and hence not considered safe  for drinking except  after  adequate treatment.  Hydrochemical  plots  such as  Piper, Durov and Gibbs plots were used for classification of the water type and identification of the hydrochemical processes involved in the groundwater chemistry. From the Piper plot, 57.1% of the water samples belong to the Alkaline water type while 42.9% belong to the Earth Alkaline Water type. The Durov plot indicated that the basic hydrochemical process responsible for the chemistry of the groundwater is simple dissolution or mixing with subordinate hydrochemical process of reverse ion exchange of Na-Cl waters. The Gibb‟s plot indicated that the major geological process controlling the water quality or chemistry is rock weathering with influence of evaporation. Recommendations given include; hand dug wells should be constructed to a depth of at least 9m, however, in areas where the water table appears to be deeper, boreholes should be sunk and the abandoned water works project for supply of pipe-borne water should be revisited by the government. Areas where water is contaminated should adopt adequate treatment measures before consumption and if treatment tends to be too expensive; then alternative means of supply of potable water (boreholes, water tankers) should be considered.

CHAPTER ONE

1.0    INTRODUCTION

1.1       Background to the Study

Water being an elixir of life is a commodity which controls our every day to day existence. However not all available water can readily be put to use by man as the use of water by man depends a great deal on the quality and quantity of such water. The quality of water is also a function of the source from which such water is gotten. The natural dispensation of water on the earth determines to a large extent the source of water that is of most benefit to man. The ocean/sea accounts for almost about ninety-seven percent (97%) of the global water distribution, glacier accounts for two percent (2%), groundwater accounts for less than one percent (0.67%) while the remaining 0.39% goes to surface water and other sources (Gleick, 1993). From the above information; it draws to limelight the importance of groundwater as a means of supply of freshwater owing to its relatively high abundance, less proneness to contamination and natural filtration associated with its process of storage.

How fast groundwater flows is a factor dependent on; the size of pore spaces in the soil or rock, the interconnectivity of the pore spaces and often times on the topography. Groundwater may be brought to the surface naturally through a spring or can be discharged into lakes and streams. Nevertheless, groundwater can also be harnessed artificially by drilling of wells into the aquifer. The volume of groundwater in an aquifer, its extent, depth and thickness of water bearing sediments can be estimated by measuring water levels in local wells; through geophysical surveys  and by examining the geologic records from already drilled wells.

Groundwater is a cryptical nature‟s treasure. Its exploitation has continued to remain a crucial issue due to its mostly unalloyed nature and relative abundance. Though there are other sources of water which includes streams, rivers, ponds, just to mention a few; none is as hygienic as groundwater. This is due to the excellent natural microbiological quality and generally adequate chemical quality groundwater possess for most uses (Macdonald et al., 2002). Therefore, to  untangle  the mystery of  groundwater,  a detailed  geophysical and hydro-geological  understanding  of  the  aquifer  types  and  their  spatial  location  are paramount in order to characterize the hydrogeological zones in an area.

Makurdi is basically a sedimentary environment (Geological Survey of Nigeria, 1994) and groundwater in the sedimentary environment is usually contained in the porous and permeable  formation  (Offodile,  2002).  Consequently,  such  geologic  setting  requires  a critical understanding of the hydrogeology and integration of geophysical data types to effectively characterize the hydro-geologic zones and to enhance successful identification of well locations (Omosuyi, Adegoke and Adelusi 2008).

Although electrical resistivity method has been used immensely for hydro-geologic investigations Ajayi and Hassan (1990); Olaleye (2005) and Alile et al. (2008), the use of other supplementary approach such as well data acquisition and other groundwater inventories were also used to complement and further aid the hydrogeological characterization of the study area.

In this study, geophysical and hydrogeological mapping of some selected areas in Makurdi L.G.A of Benue State was carried out using Electrical Resistivity prospecting technique along with hydrogeological and hydrochemical analysis of groundwater inventories. This was done with a view to investigating the groundwater potential, groundwater quality and most  importantly  recommend  the  most  prolific  aquifer  type(s)  capable  of  providing adequate and good quality water for the people of the area.

1.2       Statement of the Research Problem

Makurdi (the study area) basically depends on groundwater as the major source of water for the populace. With the exception of the few living around the province of the River Benue, all other areas depend on groundwater for its sustenance. The government is making effort to supply pipe borne water by constructing a new waterworks which however is yet to be completed and as such, a dominant fraction of the populace depend on groundwater which is not readily available both in quantity and quality.

Groundwater in the study area is harnessed through hand-dug wells and boreholes with a dominance of hand dug wells as this is cheaper to construct. However, this have not been able to solve the water supply problem as most of the wells dry up during the dry season (seasonal wells). This seasonal nature of the wells may be due to the fact that the wells are not dug to reach the water table or depletion of the water table as a result of excessive dependency (overuse) on the groundwater. This is however subject to verification from this research work. Furthermore, groundwater is vulnerable to pollution from domestic, municipal, industrial and agricultural activities; the groundwater in the study area is not an exclusion from these tendencies of pollution. Therefore, this study is carried out with a view of investigating the potential as well as quality of the groundwater of the study area. This would aid in tendering solution to the water scarcity/shortage in the study area and also reveal the safety health-wise and otherwise associated with the usage of groundwater in the study area.

Tentatively, this study would attempt to answer the following research questions:

i.   What constitutes the geology of the study area (Makurdi)?

ii.  What is the groundwater potential of the study area?

iii. What are the factors that determine the groundwater potential and what techniques can be used to determine them?

iv. Can  electrical  resistivity  geophysical  method  and  hydrogeological  inventory technique prove useful in the determination of the factors affecting groundwater potential of the study area?

v.   What is the quality of the groundwater in the study area?

vi. If water is polluted, what is the possible cause and what is the possible remediation?

vii. What is the feasible solution to the provision of portable water in the study area?

1.3       Justification for the Research

The provision of clean water and sanitation is goal number six (6) amongst the strategic goals of the Sustainable Development Goals (SDGs) set by the United Nations General Assembly in 2015. The importance of potable water to the overall wellbeing of man need not be overemphasized as economic improvement and productivity can only be achieved when  man is  healthy.  Groundwater is  a resource that  can  become contaminated  from anthropogenic sources including during its development as a result of which its quality cannot be undermined. The availability of water is one factor but its safety for a particular usage is  another important factor  which  cannot  be ignored. This  research therefore is focused  on  generation  of  reliable  data  on  the  groundwater  potential  and  groundwater quality of the study area.

1.4 The Study Area

1.4.1 Location, Extent and Accessibility

Benue State is a state within the middle belt region of Nigeria and covers a total landmass of about  34,059km2   and  is  located between  latitudes  06025’00″N  and  08008’00″N and longitudes 7047’00″E and 10000’00″E. It is named after the Benue river and was formed from the former Benue-Plateau state and some part of Kwara State in 1976. However in 1991, some parts of the then Benue state were carved out to become part of the new Kogi state. Benue state shares boundaries with six other states namely; Nassarawa State to the north, by Taraba State to the East, by Cross River and Ebonyi States to the south, Enugu State to the south-west and by Kogi State to the west (Figure 1.1). The state is populated by several ethnic groups: Idoma, Tiv, Igede, Etulo, Abakpa, Jukun, Hausa, Nyifon and Akweyan with the Tiv as the dominant ethnic group. The Tiv occupy fourteen of the twenty three local government areas while the remaining nine is occupied by dominantly the Idoma and Igede. Most of the people are farmers while the inhabitants of the river areas engage in fishing as their primary or secondary occupation. It has a population of about 4,235,641 in 2006 census. Benue State is a dominantly sedimentary environment with sediments which have undergone varying degrees of metamorphism and are underlain at variable depth by Basement Complex rocks. The sediments are dominantly sandstone but with sparse distribution of shale, siltstone, limestone and quartzite.

However the study area  in  particular is  in  the North-western  flank  of  Makurdi  Local Government Area which happens to be the capital of the state and is a monolithologic environment of indurated sandstone. Makurdi has a population density of over 380 person per km2 (Nigeria Data Portal, 2006). The study area lies between latitudes 07042’25″N and 07045’00″N  and  longitudes  8030’00″E  and  08032’30″E  covering  a  landmass  of  about 16.25km2. The topography of the study area is generally low-lying (70-250m) with dominance of undulating plains and occasional elevations of between 400m to 600m above sea level  (Offodile, 2002). The study area is  accessible by major roads, railways and footpaths.

1.4: 3D Surface relief of the study area

1.4.2    Climate

Benue state has a Tropical subhumid climate with two distinct seasons; the wet and dry season. The wet season usually commences from March/April and terminates by end of October  lasting  for  about  seven  to  eight  months.  The  dry  season  commences  from November to March/April lasting for about four to five months. Rainfall is governed by the relative movement of inter tropical convergence zone (ITCZ). It has an annual total rainfall range of 1200mm – 1500mm. Temperatures are generally very high during the day, particularly in March and April. The annual maximum temperature ranges from 33ºC to 33.96ºC   while   the   annual   minimum   ranges   from   21.58ºC   to   23.15ºC   (Nigerian Meteorological Agency Tactical Air Command Headquarters Makurdi).

1.4.3    Vegetation

The vegetation is characterized by the Guinea savannah in the eastern and northern parts with  mixed  grasses  and  trees  that  are  generally  of  average  height.  It  is  however characterized on the western and southern fringes by Tropical rain forests comprising of tall trees, oil palm trees and tall grasses.

1.4.4    Drainage

Benue state has a dendritic drainage pattern with River Benue as the dominant geographical feature and the major river into which other river tributaries discharge into. Katsina Ala river is the largest tributary, while other smaller river tributaries include the following Mkomon, Amile, Duru, Kpa, Mu, Okpokwu, Loko, Konshisha, Aya, Apa, Be, Ombi and Ogede. The flood plains are characterized by fine sands, silt and clay.

1.5       Aim and Objectives

The aim of this research work is to investigate the geological setting, the groundwater potential and quality of part of Makurdi area.

The objectives are:

i.      To reveal the subsurface stratification.

ii.      To generate a geological map of the study area.

iii.     To produce hydrogeological maps of the study area.

iv.      To determine the groundwater quality of the study area.

1.6       Scope of the Research

This research work would involve detailed geological, geophysical and hydrogeological mapping of the study area. Groundwater quality of the study area would also be assessed. The limitations of this work includes; urbanization which limited the depth of investigation during geophysical data acquisition due to limited space and ethnic, political and religious barrier during well data acquisition especially due to the high state of insecurity in the country. Secondly, the research work was carried out during the dry season, therefore data for rainy season were not obtained which would have aided seasonal comparison and proper understanding of the groundwater potential of the study area.

1.7       Organization of Study

This study would be laid out in 5 chapters. Chapter 1 presents background information on the study which includes statement of the problem, aim and objectives, justification and study area (climate, relief, drainage and vegetation). Chapter 2 discusses the literature review  and  the  geology  of  the  area.  Chapter  3  presents  the  methods  and  processes employed in conducting the research. Chapter 4 is the presentation, analysis and discussion of results and the last chapter (chapter 5) is the conclusion and recommendations.

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