Aquifer Systems Of Ndokwa Land Delta State, Nigeria...

IJRRAS 5 (3) December 2010 Otutu Aquifer Systems of Ndokwa Land

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AQUIFER SYSTEMS OF NDOKWA LAND DELTA STATE, NIGERIA

Oseji Julius Otutu

Department Of Physics, Delta State University, Abraka, Delta State.

Email: [email protected]

ABSTRACT

The execution of water borehole project is expensive; there is therefore the need for surface resistivity

measurements before drilling. Vertical Electrical Sounding (VES) using Schlumberger configuration is one of the

most reliable geophysical techniques and was carried out in Ndokwa land to obtain and document not only the layers

of the near surface aquifer but to determine the thickness and depth to the aquifer and hence recommend the area/s

boreholes could be drilled for potable and sustainable water supply.

A total of 569 vertical electrical soundings data were obtained from 36 locations evenly spread and spaced 2 km

apart using the Schlumberger array method. The apparent resistivity values obtained in the field were plotted against

half current electrode spacing in a log-log graph. The resulting curves were interpreted both qualitatively by

inspection and quantitatively by matching small segments of the field curves using two-layer model and their

corresponding auxiliary curves. The resistivity and thickness obtained from the partial curve matching were

improved upon by employing an iterative computer program to obtain the layer parameters. The type of curves, the

resistivity of the sediments and the knowledge of the local geology of Ndokwa land were used as guides in the

analysis and interpretation of the layer parameter in terms of probable and sustainable water supply.

In Ndokwa land, 2 – 4 layers of aquifer were identified within the third and the fourth geoelectric layers of the earth.

These layers consists of the medium to coarse grained sand formations of resistivity values ranging from 300 Ωm to

1500 Ωm with an average thickness of 35 m, Boreholes for potable and sustainable water supply is therefore

recommended at a depth of between 30 m and 45 m in Ndokwa land.

Key words: Ndokwa Land, Vertical electrical sounding, groundwater, aquifer, elevation and water table.

1. INTRODUCTION

Ndokwa Land consists of three Local Government Areas: (Ndokwa West, Ndokwa East and Ukwuani). It is in the

Southeastern region of Delta State situated in the South southern part of Nigeria and lies between latitudes 50 48

1 N

and 50 60

1 N and longitudes 6

0 08

1 E and 6

0 32

1 E. It has common boundaries in the North with Ika South and

Aniocha South Local Government Areas. Isoko South and Isoko North bound it in the South while it also has

common boundaries with Ughelli North and Ethiope East Local Government Areas and Edo State as well as River

Niger in the West and East respectively. The important rivers in the region are Niger, Ethiope, Adofi and Umu while

the Ase creek is the major creek. The political map of Ndokwa land (inset map of Nigeria) is shown in Figure 1.

2. GEOLOGY OF NDOKWA LAND

One of the greatest oil producing areas in Nigeria is the Niger Delta basin. The study area Ndokwa land is within

this zone. The Niger-Delta in this project applies to the entire 3-Dimensional bodies of continental, transitional and

marine deposits formed by sediments from Rivers Niger and Benue. The continental deposits form the land area

otherwise called the sub aerial regions. The marine deposits are the water filled region otherwise called the sub

aqueous region. While the transitional deposits forms the swampy (mangrove) regions. (Hospers. 1965); (Ejadiavwe,

1981).

The structure of the continental geologic framework directed River Niger and Benue towards the present site of the

Delta. Hence the geology of Niger-Delta, like other parts of the earth has undergone different changes right from the

tectonic setting through the paleogeographic evolution to the present day. This development of the Delta has been

dependent on the balance between the rate of sedimentation and subsidence. The balance and the resulting

sedimentary patterns appear to have been influenced by the structural configuration of tectonics of the basement.

(Evany, et al, 1979).

The geology and Geomorphology of the Niger delta have been described in detail by various authors (Allen, 1965;

Merki, 1970; Akpokodje, 1979 and 1987; Assez 1970 and 1976; Avbovbo, 1970; Oomkens, 1974; Burke, 1972;

Rement, 1965 and Short and Stauble, 1967). The formation of the present day Niger delta started during early

mailto:[email protected]


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Palaeocene and it resulted mainly from the build-up of fine-grained sediments eroded and transported by River

Niger and its tributaries (Efeotor and Akpokodje 1990).

The sub-surface geology of the Niger Delta consists of three Lithostratigraphic units (Akata, Agbada and Benin

formations), which are in turn overlain by various types of Quaternary deposits. The Quaternary deposit of Ndokwa

land consists mainly of Coastal Plain Sands, Sombreiro – Warri deltaic Plain deposits invaded by mangrove,

wooded back Swamps Fresh water Swamp and Meander belts. The important rivers in the region are Rivers Niger,

Ethiope, Adofi and Umu while the Ase creek is the major creek. However many ponds and streams are found within

the area. The Map of Ndokwa land showing the geologic formation, important towns and Assess roads are shown in

figure 2.

3. METHODOLOGY AND DATA ACQUISITION

Electrical resistivity method using Vertical Electrical Sounding (Schlumberger array) is adopted in this

investigation. Zohdy, 1974; Zohdy et al 1974 and 1993; Ekine and Osobonye 1996; Overneeren 1989; Etu-Efeotor

and Akpokodje 1990; Etu-Efeotor et al 1989; Okolie et al 2005; Oseji et al 2005 and Osemeikhian and Asokhia

1994 gave detailed account of the use of this method.

The basic method employed in this work, is the surface resistivity sounding. In this method, current is introduced

artificially into the earth through a pair of electrode pinned to the ground (current electrode) and the resulting

potential difference due to the current is measured through another pair of electrode (potential electrode) that is also

pinned to the ground, any subsurface variation in conductivity alters the current flow; which in turn affects the

distribution of electric potential at the surface (Chukwurah, 1992; Efeotor, 1981; Dobrin, 1960; 1976; 1988 and

Parasins, 1966; 1972 and 1986).

A total of 36 stations spaced 2.00 km apart were established and surveyed for 569 vertical electrical soundings using

a method whereby readings were taken automatically and the results were averaged continuously with an ABEM

SAS 300 terrameter and a maximum half current electrode spacing of 316 m since it is a near surface investigation.

The depths to water level in the hand-dug wells close to the VES stations were measured directly with a meter tape

and recorded.


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The apparent resistivity values were plotted against half the current electrode spacing on a log-log graph. The curves

obtained were interpreted both qualitatively by inspection and quantitatively by matching small segments of the field

curves using two-layer model and their corresponding auxiliary curves. The resistivity’s and thickness obtained from

the partial curve matching were improved upon by employing an iterative computer program to obtain the layers

parameter (resistivity, thickness and depth). The numerous layers that were generated by the computer shall be

grouped into relevant geologic depth intervals called geoelectric sections. The type of curves (Selemo et al, 1995),

the resistivity of the sediments (Oyedele, 2001) and the knowledge of the local geology were used as guides in the

interpretation and analysis of the geoelectric parameters in terms of probable, potable and sustainable water supply.

FIGURE 2: MAP OF NDOKWA LAND SHOWING THE GEOLOGIC FORMATION, IMPORTANT TOWNS

AND ASSESS ROADS.


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4. QUALITATIVE INTERPRETATION

The interpretation of the field data began with qualitative process of plotting of the data on a log-log graph and

inspection of the resistivity field curves to ensure data reliability. Manual interpretations employing the use of

master curves were adopted in the field to gain first hand idea of existing layering configuration and the type of

curves as shown in table 1.

TABLE 1: QUALITATIVE ANALYSIS OF THE CURVE TYPES IN NDOKWA LAND.

VES LOCATION CURVE TYPE RMS % ERROR

1 MAJOR ROAD IN ABOH HAA 2.10

2 MAJOR ROAD IN OKPAI-OLUCHI AAK 2.60

3 IGBUKU HAA 1.70

4 ASHAKA AK 1.36

5 BENEKU HA 2.39

6 UMUSEDELI KA 1.65

7 UMUSETI HK 1.76

8 OBIOGWA UMUSAM KA 1.20

9 2ND OWESSEI ST.UMUSADEGE KH 2.01

10 OSEJI ESTATE UMUSADEGE AK 1.05

11 UGILIAMAI HA 1.73

12 ONUGA KHQ 2.19

13 AMOJI QH 1.52

14 EWESHI ONICHA-UKWUANI HA 2.56

15 OKPALA-UKU ONICHA UKWUANI HA 2.95

16 OSEJI COMPD, IKE-ONICHA KHA 1.37

17 OGUME ROAD IKE-ONICHA KHA 2.18

18 OBIOGWA OGBE-OGUME KHA 1.32

19 UTUE-OGUME AA 1.88

20 OBODOUGWA OGUME HA 1.89

21 EBENDO HA 1.96

22 OBODOETI HA 1.76

23 OBIOGO HA 1.87

24 ETEVIE, EMU-UNO HA 1.79

25 IKOSA, EMU-UNO HA 2.22

26 WIRE ROAD OBIARUKU KA 1.37

27 GHANA QUARTERS, HA 3.46

28 OBINOMBA AA 2.41

29 UMUKWATA K 1.88

30 ADONISHAKA, EBEDEI HKQ 1.36

31 UMUTU MIXED SEC. SCHOOL A 3.70

32 MICHELIN ROAD UMUTU HA 1.41

33 OGBEOLE OGUME AKH 4.24

34 AMAI/OGUME ROAD, OGUME AKHK 4.41

35 OGBE-ODOLU, OGBE OGUME AK 2.81

36 OGUME GRAM. SCHOOL HAK 3.34

5. QUANTITATIVE INTERPRETATIONS.

Quantitative interpretation of the vertical electrical sounding field curves were interpreted using partial curve

matching (Zohdy et al 1974). The resistivity and thickness obtained from the partial curve matching were improved

upon by employing an automatic iterative computer program. The number of layers were modified based on the

inflation points and were modeled in a step function. Samples of type curves HAA, AAK, AK, HA, HK, KA, KH,

KHQ, QH, KHA, AA, K, HKQ, A, AKA, AKHK and HAK are shown in figures 3-20.


319

The type of curves (Selemo et al, 1995), the resistivity of the sediments (Oyedele, 2001) and the knowledge of the

local geology were used as guides in the interpretation and analysis of the geoelectric parameters in terms of

probable, potable and sustainable water supply (Tables 2 and 3).

These depths were correlated with that obtained from direct measurements of the water level in the hand-dug wells

using Pearson correlation coefficient (Table 4). The result was confirmed using the SPSS computer program (Table

5).

The 0.836 obtained reveal that there is significant difference between the depths to water level measured in the

hand-dug wells and that obtained from the VES interpretation. Hence the interpretation is valid and reliable.

Consequently, 2 – 4 layers of aquifer were identified in Ndokwa land (Table 6 and 7), These layers consists of the

medium to coarse grained sand formations of resistivity values ranging from 300 Ωm to 1500 Ωm with an average

thickness of 35 m, Boreholes for potable and sustainable water supply is therefore recommended at a depth of

between 30m and 45m in Ndokwa land.

TABLE 2: RESISTIVITIES AND DEPTHS OF THE FIRST WATER BEARING FORMATION FROM THE

VES INTERPRETATION

S/N

VES LOCATION RESISTIVITY OF THE FIRST WATER

BEARING FORMATION IN THE VES

INTERPRETATION

“Ωm”

DEPTH TO THE FIRST WATER BEARING

FORMATION FROM THE VES

INTERPRETATION “M”

1 MAJOR ROAD IN ABOH 140.00 4.15

2 MAJOR ROAD IN

OKPAI-OLUCHI

76.00 0.71

3 IGBUKU 83.44 8.10

4 ASHAKA 359.00 7.74

5 BENEKU 185.00 7.93

6 UMUSEDELI BY AGIP

PETROL STATION

513.00 3.80

7 OPPOSITE ONEFELI’S

COMPD, UMUSETI

177.00 3.63

8 OBIOGWA UMUSAM 265.47 4.87

9 2ND OWESSEI

ST.UMUSADEGE

66.60 2.61

10 OSEJI ESTATE

UMUSADEGE

1360.40 2.60

11 UGILIAMAI 993.00 0.56

12 ONUGA 271.00 4.21

13 AMOJI 294.82 5.83

14 ADOH PRI. SCH.

EWESHI/IKE-ONICHA

268.00 2.28

15 OKPALA-UKU ONICHA-

UKWUANI

24.70 3.10

16 OSEJI COMPD, IKE-

ONICHA

106.20 4.02


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TABLE 3: RESISTIVITIES AND DEPTHS OF THE FIRST WATER BEARING FORMATION FROM THE VES INTERPRETATION

S/N VES LOCATION RESISTIVITY OF THE FIRST WATER

BEARING FORMATION IN THE VES

INTERPRETATION“Ωm”

DEPTH TO THE FIRST WATER

BEARING FORMATION FROM THE

VES INTERPRETATION “M”

17 OGUME ROAD IKE-ONICHA 22.50 4.35

18 OBIOGWA OGBE-OGUME 194.51 5.94

19 UTUE-OGUME 350.00 5.81

20 OBODOUGWA OGUME 105.00 6.40

21 EBENDO 187.82 1.77

22 OBODOETI 148.05 2.60

23 OBIOGO 223.00 3.10

24 ETEVIE, EMU-UNO 301.32 2.57

25 IKOSA, EMU-UNO 174.30 2.02

26 WIRE ROAD OBIARUKU 171.16 5.10

27 GHANA QUARTERS, 56.50 3.75

28 OBINOMBA 234.90 11.25

29 UMUKWATA 701.40 6.73

30 ADONISHAKA, EBEDEI 435.00 8.23

31 UMUTU MIXED SEC. SCHOOL 587.10 8.24

32 MICHELIN ROAD UMUTU 232.00 5.58

33 OGBEOLE OGUME 1121.40 3.68

34 AMAI/OGUME ROAD, OGUME CONSTRUCTION OF ROAD (7904.00) 2.98

35 OGBE-ODOLU, OGBE OGUME 569.00 3.60

36 OGUME GRAM. SCHOOL 493.00 2.12

TABLE 4: DATA FOR PEARSON’S CORRELATION COEFFICIENT

S/N VAR001 “X” VAR002 “Y” X2 Y2 XY

1 4.15 3.66 17.223 13.396 15.189

2 0.71 1..56 0.504 2.434 1.108

3 8.10 9.14 65.610 83.540 74.034

4 7.74 8.23 59.908 67.733 63.700

5 7.93 7.62 62.885 58.064 60.427

6 3.80 3.20 14.440 10.240 12.160

7 3.63 3.66 13.177 13.396 13.286

8 4.87 4.57 23.717 20.885 22.256

9 2.61 3.66 6.812 13.396 9.553

10 2.60 3.66 6.760 13.396 9.516

11 0.56 5.49 0.314 30.140 3.074

12 4.21 5.49 17.724 30.140 23.113

13 5.83 4.57 33.989 20.885 26.643

14 2.28 3.66 5.198 13.396 8.345

15 3.10 3.66 9.610 13.396 11.346

16 4.02 3.66 16.160 13.396 14.713

17 4.35 3.66 18.923 13.396 15.921

18 5.94 6.10 35.284 37.210 36.234

19 5.81 6.10 33.756 37.210 35.441

20 6.40 5.49 40.960 30.140 35.136

21 1.77 5.79 3.133 33.524 10.248

22 2.60 4.58 6.760 20.976 11.908

23 3.10 5.49 9.610 30.140 17.019

24 2.57 4.58 6.605 20.976 11.771

25 2.02 3.05 4.080 9.303 6.161

26 5.10 5.20 26.010 27.040 26.520

27 3.75 4.25 14.063 18.063 15.938

28 11.25 12.36 126.563 152.770 139.050


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29 6.73 5.49 45.293 30.140 36.948

30 8.23 9.00 67.733 81.00 74.070

31 8.24 9.00 67.898 81.00 74.160

32 5.58 7.62 31.136 58.064 42.520

33 3.68 3.66 13.542 13.396 13.469

34 2.98 5.49 8.880 30.140 16.360

35 3.60 4.58 12.960 20.976 16.488

36 2.12 3.49 4.494 12.280 7.399

2222 YYnXXn

YXXYn

Where n =36

X = 161.96

Y = 190.47

2X = 931.714

2Y = 1175.477

XY = 1011.224

Therefore

2247.190.477.11753696.161714.93136

47.19096.161224.101136

352.6038663.7310

543.5555

( ) = 44144356

543.5555

( ) = 1219.6644

543.5555 ( ) = 0.836

SPSS CORRELATION USING COMPUTER PROGRAM

TABLE 5: CORRELATION OF THE DEPTHS OBTAINED AT THE FIRST WATER BEARING FORMATION

FROM THE VES INTERPRETATION WITH THAT MEASURED IN THE HAND-DUG WELLS

Correlations

1.000 .836**

. .000

36 36

.836** 1.000

.000 .

36 36

Pearson Correlation

Sig. (2-tailed)

N

Pearson Correlation

Sig. (2-tailed)

N

VAR00001

VAR00002

VAR00001 VAR00002

Correlation is signif icant at the 0.01 level (2-tailed).**.


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TABLE 6: LAYERS OF NEAR SURFACE AQUIFER IN NDOKWA LAND

VES

FIRST LAYER OF

AQUIFER

SECOND LAYER OF

AQUIFER

THIRD LAYER OF

AQUIFER

FOURTH LAYER OF

AQUIFER

1 T1 D1 2 T2 D2 3 T3 D3 4 T4 D4

1 339.39 26.01 12.35 504.90 38.36

2 455.05 9.41 2.96 654.00 45.68 18.01 31.00 58.09

3 565.00 18.43 17.08 950.00 35.51

4 359.00 0.61 0.70 1000 35.51

5 2054.85 23.53 13.26 1803.19 37.26

6 513.00 59.95 13.75 2907.00 37.28

7 2537.83 19.03 3.63 889.00 17.06 22.66 416.60 58.06 49.72 363.00 107.78

8 265.47 24.63 4.87 1285.02 29.50

9 132.30 21.33 6.43 726.92 29.90 27.76 347.10 37.66

10 1502.66 6.42 5.59 2800.60 56.77 12.01 1050.00 41.93 68.78 342.00 110.71

11 1497.30 23.17 7.90 8776.31 29.90 24.93 2718.10 54.83

12 271.00 11.80 4.21 1879.00 141.40 16.02 679.00 34.33 75.25 271.00 109.58

13 297.82 27.31 5.83 1923.70 18.43 33.14 807.00 51.57

14 156.55 11.48 9.20 668.85 16.66 20.68 1336.65 17.67 37.34 3348.45 55.01

15 258.29 14.13 7.00 2612.12 30.30 21.13 6370.29 77.12

16 446.00 13.24 10.42 1915.05 53.46 23.66 1410.97 77.12

17 93.66 5.31 7.23 1698.00 12.54

18 194.51 34.75 5.94 683.10 56.13 40.69 2318.36 96.82

TABLE 7: LAYERS OF NEAR SURFACE AQUIFERS IN NDOKWA LAND

VES

FIRST LAYER OF

AQUIFER

SECOND LAYER OF

AQUIFER

THIRD LAYER OF

AQUIFER

FOURTH LAYER

OF AQUIFER

1 T1 D1 2 T2 D2 3 T3 D3 4 T4 D4

19 350.00 50.30 5.81 2471.70 56.11

20 105.00 12.05 6.70 353.00 38.17 18.75 1039.00 58.06 56.92 683.00 114.98

21 235.00 38.12 12.01 638.90 50.18

22 278.00 26.01 16.21 615.30 41.22

23 711.00 12.58 12.06 3619.00 24.54

24 515.28 12.58 11.08 3125.74 96.09 23.66 903.00 117.74

25 184.68 8.53 7.85 972.84 20.37 16.38 1056.78 46.23 36.75 760.00 82.98

26 171.16 14.53 5.10 2989.00 19.66

27 56.50 6.52 3.75 645.96 16.01 10.27 3662.40 26.28

28 595.21 38.17 14.20 1643.00 52.37

29 735.00 29.91 16.27 1132.00 36.64

30 1343.00 23.71 8.23 537.00 56.13 31.94 259.00 88.06

31 587.10 15.05 8.24 976.00 18.43 17.67 764.00 36.10

32 232.00 9.95 15.53 3539.00 63.36 39.06 6041.00 78.89

33 3702.51 16.66 16.72 1302.91 17.67 33.38 4376.29 51.05

34 5103.05 17.54 12.77 62247.15 16.74 30.31 1954.00 73.62

35 1163.00 17.66 13.69 434.00 12.63 21.26 2424.45 47.43 33.89 879.00 81.32

36 4078.00 4.46 6.58 9488.00 55.32 21.50 4642.00 76.82


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6. CONCLUSION AND RECOMMENDATIONS

In Ndokwa land, 2 – 4 layers of near surface aquifer were identified within the third and the fourth geoelectric

layers. Apart from Adonishaka in Ebedei and Okpai-Oluchi in Ndokwa East Local Government Area of Ndokwa

land that seems to have local clay deposits in the second and fourth geoelectric layers, which though are very thin

and appear to create local confined conditions, the aquifer characteristics of Ndokwa land shows that they are not

confined. In the event of pollution, groundwater in Ndokwa land is easily contaminated.

Borehole for potable and sustainable water supply is therefore recommended at a depth of between 30.00 m – 45.00

m in Ndokwa land. This depth has an average thickness of 35.00 m and it coincides with the second relevant

geologic layers in Aboh and Utagba-Ogbe environs while in Ogume, Onicha-Ukwuani and Obiaruku environs, the

depth is within the fourth relevant geologic layers and in Emu and environs, it is in the fifth layer.

These layers consist of the medium-grained sand to the coarse-grained sand formations, which is the best

environment to obtain an appreciable quantity of water for sustainable groundwater development.

The research did not only pave way for a clear picture of the hydro geological knowledge of Ndokwa land in other

to create awareness on the productive and prolific aquifer for sustainable groundwater supply but act as guides to

both the Government and individuals especially those involved in groundwater development on the type of near

surface aquifers, the formation of the aquifer as well as the thickness of the aquifer and the depths boreholes could

be drilled for sustainable water supply.

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8. ABOUT THE AUTHOR

OSEJI, JULIUS OTUTU, Ph.D. is a Senior Lecturer in the Department of Physics, Delta State University, Abraka,

Nigeria. His research focus is on groundwater and environmental geophysics, with special interest in aquifer

delineation and vulnerability in sedimentary and crystalline basement terrains.

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