Geo Electrical Assessment of Groundwater Potentials of Some Parts of Orsu and Environs, South Eastern Nigeria

ABSTRACT

In a bid to determine the groundwater potential of some parts Orsu and environs, which lies within latitude N5º53.858΄ to N5º47.572΄ and longitude E7º0.847΄ to E6º56.988΄, a total of ten (10) vertical electrical soundings were carried out. The study area belongs to the Anambra basin which is one of Nigeria’s most important hydrological basins. It is overlain   by   the Miocene to recent Benin formation and   Eocene Ameki formation.Equipment such as ABEM terrameter SAS  4000, 12volts battery,  global positioning system (GPS), four electrodes, reel of cables, clip, hammer etc were used during the data acquisition   process and were processed   using   FORTRAN   2D Resistivity inversionSoftware. Moreso, Surfer 14 program was used to provide the transmissivity, hydraulicconductivity, diffusivity, and storativity maps, as the imaging pictures of the subsurfacein the form of contour maps. Results from the processed data revealed that the study areaconsist of top soil, sand, clayey sand and clay. Out of a total of 10 Vertical electricalsoundings obtained from selected locations in the study area, All VES points indicated a5-layer curve except VES 3 and VES 5 which have shown a 7-layer lithology. VES 2 and6 has shown KH curve type (i.e. ρ1 ρ3> ρ4< ρ5  characteristic), VES 4, VES 7 andVES 8 has also shown HA (i.e. ρ1> ρ2< ρ3< ρ4< ρ5  characteristic). VES 1, VES 9 and VES10  have  shown  KA, AK  &  HK   curves   respectively.   However,  from  analyses  made,greater part of the region is prolific (that is, high groundwater potential). The depth towater from VES 1 to VES 10 were estimated as 92.8m, 87.0m, 91.0m, 104.0m, 139.0m,139.93m,  214.0m, 137.0m, 67.0m,  37.0m respectively. Shallow  aquifer systems  wereencountered at areas such as: Akwakuma Okporo, Okwuruokwuo Amannachi, UmualumIsiafor Ofeahia, Umuoka Asaa, and Amaruru , while deep aquifer systems were seen atareas  such as: Afor-Iduu  Amaebu Ebenator, St.  peters, Umuezeala Amaebu, Umuhu-Okabia,   Umucheke   Omuokabia   Awo-Idemili,   Uda   Orsu-Ihiteukwa.   Areas   such   asAmannachi, Ebenator, Amaebu and Isiafor ofeahia are highly prolific and have shownhigh level of transmissivity of about 3000 to 4000m2/day and high storativity rangingfrom 0.0004 to 0.00058. These areas have also shown high rate of diffusivity with valueranging from 5500000 to 8500000, except Amaebu which have shown very low level ofdiffusivity.Keywords: Groundwater, Vertical Electrical Sounding, Transmissivity, HydraulicConductivity, Diffusivity, and Storativity

TABLE OF CONTENTS

 

Title Page                                                                                                    i

Declaration                                                                                                 ii

Certification                                                                                                         iii      

Dedication                                                                                                  iv

Acknowledgement                                                                                                v

Abstract                                                                                                      vi

Table of Contents                                                                                       vii

List of Figures                                                                                            x

List of Plates                                                                                               xi

List of Tables                                                                                              xii

 

CHAPTER ONE:   INTRODUCTION

1.1     Background Information                                                                            1

1.2     Aim and Objectives                                                                           2

1.2.1  Aim                                                                                                   2

1.2.2  Objectives                                                                                         2

1.3     Location and Accessibility                                                                2

1.4     Justification of Study                                                                        5

1.5     Climate and Vegetation                                                                     5

1.6     Geological settings of the study area                                                 6

1.6.1  Regional Geology                                                                                       6

1.6.2  Local Geology of the study area                                                                 6

1.6.2.1  Benin formation                                                                            6

1.6.2.2  Ameki formation                                                                           7

1.7     Groundwater                                                                                     9

1.8     Porosity and Permeability                                                                 10

1.8.1  Porosity                                                                                            10

1.8.2  Permeability                                                                                      11

1.9     Aquifer and Aquiclude                                                                      12

1.10   Scope and Limitations of the study                                                  13

1.11   Relief                                                                                                 14

 

CHAPTER TWO:   LITERATURE REVIEW

2.1     Previous works                                                                                 15

2.2     Review of Geoelectric techniques                                                      16

 

CHAPTER THREE:          MATERIALS AND METHOD

3.1     Desk study                                                                                                 18     

3.2     Reconnaissance survey                                                                     18

3.3     Detailed study                                                                                   18

3.4     Field equipments                                                                               19

 

3.4.1    Global positioning system (GPS)                                                      19

3.4.2    ABEM Terrameter (SAS 4000)                                                                  19

3.4.3    Electrodes                                                                                         20

3.4.4    Cables                                                                                               20

3.4.5    Clips                                                                                                 20

3.4.6    Hammer                                                                                            21

3.4.7    Rollers                                                                                              21

3.4.8    Protective wears                                                                                21

3.4.9    Matchet                                                                                            21     

3.4.10                        Compass                                                                                          21

3.5     Field Procedures                                                                               21

3.6     Data Presentation                                                                                       23

3.7     Principles of Electrical Resistivity Method                                       24

3.8     Theory of Electrical Resistivity in rocks                                           25

3.9     Apparent resistivity                                                                          27

3.10   Observed Precautions                                                                       30

 

 

CHAPTER FOUR:  RESULT PRESENTATION AND INTERPRETATION

4.1     Data processing                                                                                32

4.2      Qualitative interpretation                                                                           36

4.2.1  Description of the various curve types                                                       36

4.3     Quantitative interpretation                                                               36

4.4     Profiles                                                                                              37

4.4.1  Profile One (A-B)                                                                              37

4.4.2  Profile Two (C-D)                                                                                       39

4.4.3  Profile Three (E-F)                                                                            41

4.5     Groundwater Potential evaluation                                                    43

 

CHAPTER FIVE:    CONCLUSION AND RECOMMENDATION

5.1     Conclusion                                                                                        48

5.2     Recommendation                                                                              50

References                                                                                                  51

Appendix I                                                                                                 56

Appendix II                                                                                                          66

 

 

 

 

 

 

LIST OF FIGURES

Figure 1.1   Location map of the study area showing VES locations                   4

Figure 1.2   Geologic map of the study area                                                        8

Figure 3.1   General four electrodes configuration for resistivity

                   measurement, consisting of a pair of current electrodes (A, B)

                   and a pair of potential electrodes (M, N) (Adapted from

                   Lowrie, 1997).                                                                         28

Figure 4.1   Correlated Geoelectric section along profile A-B                    38

Figure 4.2   Correlated Geoelectric section along profile C-D                    40

Figure 4.3   Correlated Geoelectric section along profile E-F                     42

Figure 4.4   Aquifer thickness of the VES points in the study area            43

Figure 4.5   3D Contour map of the study area showing

transmissivity variations                                                                  44

Figure 4.6   3D Contour map of the study area showing

Hydraulic conductivity variations                                           45

Figure 4.7   3D Contour map of the study area showing

Diffusivity variations                                                              46

Figure 4.8   3D Contour map of the study area showing

storativity variations                                                               47

LIST OF PLATES

Plate 3.1     ABEM Terrameter SAS 4000                                                 20

Plate 3.2     Researcher and some crew members during data

                   collection at one of the VES points.                                                  22

Plate 3.2     Data acquisition process at VES 2

                   (Okwurukwuo Amannachi, Orsu)                                                     23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LIST OF TABLES

Table 1.1    Geologic Formation Outcropping at the study area                          9

Table 1.2    Porosity and permeability of some geologic materials

                   (after Montgomery, 1990).                                                      12

Table 4.1    Vertical Electrical Sounding (VES) Summary                         33

Table 4.2    Hydrogeophysical parameters of the study area                     34

Table 4.3    Layer resistivities at different                                        35

Table 4.4    Aquifer hydraulic parameters                                                  35

Table 4.5    Qualitative interpretation of the data obtained from the

                   study area                                                                                36