GEOELECTRICAL AND HYDROGEOCHEMICAL ASSESSMENT OF GROUNDWATER OF EHA-AMUFU AND ENVIRON ENUGU STATE SOUTHEASTERN NIGERIA

ABSTRACT

An integrated geological, geoelectrical and hydrogeochemical investigations were carried out in Eha-amufu to determine the extent and the distribution of saline zone. Hydrochemical characteristic of the groundwater in Eha-amufu was investigated.  Eha-amufu area is underlain by Nkporo Formation and Awgu Formation. Both are of low permeability Formation. Twenty seven (27) Vertical Electrical Sounding (VES) were occupied at different locations within the study area, employing the Schlumberger electrode configuration with a maximum electrode separation of 600m. The VES data were modeled with the IP12win software. The result of the VES revealed that the study area is characterized by 3 to 6 geoelectrical layers, and are predominantly of QH and H curve type. Static water Levels (SWL) of the hand dug well were measured and the result used to generate hydraulic head map. The static water level ranges from 3.0m to 15.0m. Aquifer Protective Capacity (APC) parameters were used to classify the aquifer as moderately good to poor aquifer. Hydrochemical analysis of the groundwater samples collected from ten (10) hand dug well in the study area reveal that weathering is the major process that controls the groundwater chemistry and the water type is Calcium – Chloride. Water quality of Eha-Amufu its environ is not good for drinking based on World Health Organization Guideline for drinking water, but this can serve the  purposes of  irrigation.

CHAPTER ONE

INTRODUCTION

1.1       STUDY BACKGROUND

The study area is comprised of Eha-Amufu and its environs. This is located within the Benue Trough of Nigeria.  Benue Trough of Nigeria is one of the most prominent geologic features in West Africa. It extends over a length of 800km trending NNE – SSW from the Niger Delta to South- West of lake Chad basin and ranges in width from 130 to 250km. Due to its large regional extent, studies in the Trough are often divided geographically into Upper, Middle and Lower region (Fig 1). The depocenters of the Lower Benue Trough comprise the area around Anambra basin, Nkalagu, Eha-Amufu and Abakaliki while those of the Middle Benue Trough comprise the area around Makurdi through Yandev. In the Upper Benue Trough the depocenter comprise Gombe, Nafada (in the Gongola arm) and Bambam, Jessus Lakun and Numan in the Yola arm.

Occurrences of saline groundwater as spring, pond, or in dug wells and boreholes are common in parts of the Trough. Prominent outcrops (which commonly support local salt industries) are found in the Lower and Middle Benue Trough. The saline groundwater in the Lower and Middle Benue Trough are frequently associated with tectonic elements such as intrusive and mineralized vein (Uma 1998). The presence of saline groundwater constitutes a serious hydrogeological problem, which is the commonest of all the pollutants in freshwater (Adeoti et al, 2010). Therefore, understanding the zones of salinity is essential for the proper management of the groundwater in Eha-Amufu and its environs.

Fig. 1: Geologic Map of Nigeria showing Lower, Middle and Upper Benue Troughs.           (Modified after Obaje 2009).

1.2       STATEMENT OF THE PROBLEM

Eha-Amufu and its environs is dotted with numerous hand dug wells some of which are non prolific, while many dry up during dry season. These have caused inadequate water supply in the area. During rainy season, the situation may be less due to dilution of the salt concentration by infiltration of rain water. But during dry season the inhabitant of Eha-Amufu community trek great distance in search of fresh water for consumption. The water from these wells is characterized with a salty taste. The salty taste emanates from the constituents of the lithology (Offodile 1976). It is against this background, that this research work is necessitated, which is geared towards delineating the zone of fresh and saline water.

1.3       AIM AND OBJECTIVES

This research work is aimed at delineating the lateral and vertical interface of fresh water and saline water in Eha-Amufu and its environs. To achieve the aim of this research work the following are the objectives.

1. To delineate saline/ brackish and fresh water zone in the study area.
2. To investigate the geochemical properties of the groundwater and determine the suitability of the water for various purposes.
3. To attempt an establishment of the origin of the salt in the groundwater.

1.4       THE LOCATION AND ACCESSIBILITY 

The study area lies within the Anambra Basin in the Western part of the Lower Benue Trough of Nigeria. It is located within latitude 6° 37” and 6° 45” longitudes 7° 40” and 7° 50” and politically situated in South Eastern part of Enugu State. The area is accessible by a network of major and minor roads as well as footpaths. The major road is Obollo-Nkalagu express road connecting Eha-Amufu and Nkalagu. Eha-Amufu is bounded by several communities such as Ikem, Nkalagu in Enugu state and Orakaram in Benue State.

Fig. 2: Accessibility map of the study area. (Modified after Google Earth 2013)

1.5       CLIMATE, VEGETATION AND SOIL

1.5.1    CLIMATE                

The climate of the study area falls within wet and dry (Aw) climate of the Koppen classification. The area experiences seven months of effective rainfall, normally from April to October and five months of dry season (November – March). During the rainy season, the total annual rainfall ranges from 2000mm to 2500mm (Phil-Eze, 2001).

The rainfall distribution of the study area varies in intensity and duration. The first minimum is in November/December, then January- February. From February, rainfall totals increase rapidly to a primary maximum in June/July. The second minimum is in August and is normally identified as the “August break”.

The intensity of rainfall in the study area is about 49mm per hour at the beginning of the season. The end of the rainy season is often marked by violent thunderstorms (Eze, 1998). The hottest months of the year are usually February to April, when the temperatures are above 27°C. Another month wherein temperature is high is in November, though this second high temperature period is short with temperature typically above 26°C. The coolest month is usually August. This is because, it is the middle of the rainy season and cloud cover is thus high with attendant lower receipt of insolution. Temperature is typically around 24°C. The mean annual temperature range of the study area is 27°C- 28°C (Monanu 1975a)

The study area is moderately humid, about 60% – 80% according to (Monanu 1975b) and Iloeje (1981).The humidity of the area increases in the wet season and decreases in the dry season.

The warm moist tropical maritime (MT) air mass which originates from the south dominates the circulation of wind in the study area. A secondary air mass is the hot dry, tropical

Fig. 3: Eastern States of Nigeria: Climatic Regions(Modified after G.E.K. Ofomata,)

STUDY AREA

4 Dry months with less than 4.9cm rainfall a month 4 Dry months, driest month having less than 2.9cm rainfall a month 3 Dry months with less than 6.0cm rainfall a month 1 to 2 Dry months less than 6.0cm rainfall month Driest month has more than  States boundary International boundary

LEGEND

10    0    10   20    30   40   50   60

20       0      20    40     60     80   100

Miles

Kilometres

SCALE

7°00N   6°00   5°00N

6°00E                              7°00                                 8°00                             9°00E

6°00E                              7°00                                 8°00                             9°00E

Nsukka

Calabar

Onitsha

Obudu

Owerri

Brass

Yenagoa

Port Harcourt

Aba

Afikpo

Ikom

Awgu

N

Eha-Amufu

Abakaliki

continental (CT) air mass, from the Sahara area. Both air masses manifest as the south-west and North-East trades respectively.

The prevailing wind in the rainy season is the South-East trade wind, while the North-East Trade wind prevails in the dry season. The North-East trade wind is locally called the “harmattan”. The harmattan wind is dry and dusty. It brings about a considerable drop in the relative humidity, making the weather highly invigorating.

Fig 2: Eastern State of Nigeria: Climatic Regions. (Modified after Ofomata, 1975)

 1.5.2   VEGETATION

Igbozurike (1975) and Anyadike (2002) have pointed out that the vegetation unit recognized in the study area is the rainforest / savannah Ectone that derive its floristic composition from three principal factors:

1. A natural transition zone between the grasslands of northern Nigerian and the lowland rainforest zone to the south.
2. Extensive cultivation
3. Consistent and rampant plant burning

Phil-Eze (2001) described the vegetation form and pattern as having a marked juxtaposition of grass, shrubs, and savannah tress and forest area in varying densities from one area to another. Tree species in the study area includes Bamboo and Iroko. The trees are of luxuriant heights and have different layers. The vegetation has undergone several alterations. Man due to land use activities has modified the vegetation of the study area such as farming, road construction and firewood procurement.

1.5.3    SOIL

1.5.3.1             LAND USE PATTERNS

Several land use patterns are in existence in the study area. Some of these are agricultural, residential and commercial land use.

1.5.3.2             AGRICULTURAL LAND USE     

Agriculture is the backbone of the economy of the area. Much subsistent farming is practiced on fragmented pieces of land around the home steads and in the outskirts of their residence called “Egu”. Obtainable in the study area is also mixed cropping of cocoyam, cassava, yam rice, and maize. Mixed cropping of different plots of lands is in abundance. Rice and vegetable farming is in the form of monocropping, especially in the swamp areas.

1.5.3.3             COMMERCIAL LAND USE

This takes the form of periodic rural markets and retail sales. The periodic market in the study area holds once in every native week (once in four days). By this method, inter-community trading is enhanced and the local produce is maximized.

1.6       TOPOGRAPHY AND DRAINAGE

The topography of the study area is generally undulating consisting of highland and lowlands. The low-lying areas with elevation less than 90m above sea level are mainly shale units. Elevation above this occurs on sandstone ridge that alternate with shale which are highly consolidated and resistant to weathering, the elevation is about 170m above sea level (Fig 4).          

The drainage system in the area is mainly controlled by River Eme, River Ngleife and River Abonyi. Both River Abonyi and River Ngleife flow westward in a long meandering fashion through, the shale. The two streams are perennial while the drainage pattern can be described as dendritic. During the rainy season, most part of the area becomes waterlogged due to impermeable nature of the shale which underlies the area.

Fig. 4:  Drainage and Physiographic map of study area

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