Geoelectric Investigation of Groundwater Potential Using Vertical Electrical Sounding at the Male Student Hostel Isa Kaita College of Education Dutsinma, Katsina State, Nigeria
CHAPTER ONE
Aim and Objectives of the Survey
The aim is to use the Electrical Resistivity Techniques to investigate the groundwater potential at the male student hostel of Isa kaita College of Education Dutsin-ma, Katsina State. The objectives are as follow
- To determine the thickness and resistivity of the topsoil
- To determine the depth and thickness of the aquifer
- To determine the variation of the depth to the basement
- To determine areas suitable for borehole construction
- To produce contour maps of the thickness of Aquifer, resistivity of top soil and the Depth to fresh basement.
CHAPTER TWO
LITERATURE REVIEW
Review of Previous work
In northern Nigeria, a good number of geophysical surveys on groundwater have been conducted.
Geoelectrical investigation of groundwater potential was carried out in Dawakin Tofa LGA of Kano State. Here, over forty Vertical Electrical Soundings were carried out. Dynamic water level from open wells was also collected and was used as a guide for the selection of the electrode spread distance. The schlumberger array with a maximum electrode spread of 100 m was employed in all the points. Results from the sounding data indicates that the area is generally underlain by five geoelectric or geologic sections which include Lateritic top soil or Lateritic sand, Silty sand or Sandy clay, Weathered basement or Clayed sand, Fractured basement and Fresh basement. Based on the result obtained the fractured and the weathered basement makes the aquiferous zone within the study area. The resistivity of these zones varies from 7.3 Ωm to 772 Ωm with an average value 178 Ωm, while the thickness varies from a value of 1.66 m to 28 m with an average value of 14.33 m. Depth to this zone varies from 5 m to 31 m with an average value of 16 m. The study also recommended the use of 80 m minimum electrode spread for future electrical survey to be used in the study area (Abubakar and Auwal, 2012).
In Kongo Campus, A.B.U. Zaria, Zaria LGA of Kaduna State, a geophysical investigation of groundwater potential using the same Resistivity Method was done by Afuwai. In his research, the interpretation of 12 Schlumberger Vertical Electrical Sounding (VES) data was carried out. This was an attempt to investigate the groundwater potential and the geologic characteristics of aquifers of the area. Terrameter Signal Averaging System (SAS) model 300 was the instrument used. The schlumberger electrode configuration was used in the data acquisition. The field procedure consists of expanding AB
(distance between current electrodes) while MN (distance between potential electrodes) was fixed. This process yielded a rapidly decreasing potential difference across MN, which eventually exceeds the measuring capacity of the instrument; therefore a larger value for MN was taken to continue with the survey. The VES curves were interpreted using IPI2Win resistivity computer software. The survey area was found to be dominated by mainly four layers, namely: Topsoil, Weathered basement, fractured basement and Fresh basement. The results of the interpreted VES data showed that the saturated groundwater bearing layer (aquifer) lie within the weathered and fractured basement of the predominantly four-layered geoelectric structure. The thickness of the aquifer varied from 3 m- 25 m with an average of 15m. VES points 4, 5, 8 and 12 were found to be suitable for groundwater exploitation either by dug well or borehole (Afuwai et al., 2014). Again, in an attempt to determine the variation in the depth of overburden at different VES points at Samaru College of Agriculture, A.B.U. Zaria, Sabongari LGA of Kaduna State, Nigeria, Afuwai still employed resistivity method. The interpretation of 32 Schlumberger VES data was carried out. This investigated groundwater potential and the geologic characteristics of the overburden of the area. Terrameter Signal Averaging System (SAS) model 300 was the instrument used. The Schlumberger electrode configuration was used in the data acquisition. The field procedure consists of expanding AB (distance between current electrodes) while MN (distance between potential electrodes) was fixed. This process yields a rapidly decreasing potential difference across MN, which eventually exceeds the measuring capacity of the instrument; therefore a larger value for MN was taken to continue with the survey. The VES curves were interpreted using IPI2Win resistivity computer software. The survey area is dominated by mainly four layers, namely: Overburden, Weathered basement, fractured basement and Fresh basement. The overburden consists of lateritic, clay and fadama loam. The results of the interpreted VES data showed that the overburden thickness varies from 1.3 m to 5.2 m, with an average of 3.1 m. The lowest overburden depth was at VES 20 where the depth to basement was as low as 6 m. A map was produced by contouring all the overburden depths at each VES point at an interval of 0.5 m. The map shows the variation of the topsoil depth from one place to another within the survey Area which is an indication of the in homogenuity of the subsurface structures. The thickness of the aquifer varied from 1-35m with an average of 18m (Afuwai, 2013).
In a research on geophysical investigation of the causes of borehole failure in the crystalline basement complex taken at Kaura LGA of Kaduna State, resistivity method was still used successfully. VES using Schlumberger array were carried out at different points along five (5) profiles. This research investigated the causes of massive borehole failure at Kaura area of Kaduna state. Terrameter SAS300 was the instruments used to acquire the data. A total of 19 boreholes were functioning, while 31 boreholes were non-functioning within the area. The investigation portrayed the possible factors which are most probably causative to borehole failures in the area which involves the design and construction, groundwater potential/hydro-geological factors, operational and maintenance factors. It was found out that it is possible for one factor to lead to the other. For example, a borehole poorly designed, constructed and completed could result in sand/clay pumping and eventually affect the rubber seals in the hand pumps or the impellers in the case of submersible pumps. The boreholes tap the weathered and fractured basement aquifers of the area with yields ranging from 2litre/min to 20litre/min. However, yields from Sandy soil aquifers were found to be extensive. The survey shows that boreholes with initial recorded yield less than 10litre/min have failed over time. The survey reveals that the areas where wells and boreholes are drilled through sandy soil and fracture zones have sustainable aquifers for groundwater exploitation, while boreholes that are constructed through clayey formation usually fail (Afuwai et al., 2014).
CHAPTER THREE
MATERIALS AND METHODS
Materials
Groundwater investigations at the Male residence (Hostel) of Isa Kaita College of Education Dutsin-ma,
Katsina State, Nigeria has been carried out, materials used for vertical electrical sounding includes the ABEM SAS 300 Terrameter and its accessories like the connecting cables, current and potential electrodes (steel rods), measuring tapes, hammer and the Global Positioning system (GPS). An enormous number of electrode spreads has been used in resistivity at various time particularly, however the electrodes are almost always in line, otherwise interpretation of result becomes difficult and then field work is complicated.
Methods used
Werner Array
Surveys of lateral variations may be made at spot or grid locations or along definite lines of traverse, a procedure sometimes called horizontal profiling. That is to say that, Horizontal Profiling, per se, means moving the array along a line of traverse, although horizontal Variations may also be investigated by individual measurements made at the points of a grid.
In horizontal profiling, a fixed electrode spacing is chosen (depends on the results of the electrical sounding) and the whole electrode array is moved along a profile after each measurement is made to determine the horizontal variation of resistivity. As shown in below figure 3.1
CHAPTER FOUR
RESULTS AND DISCUSSION
Introduction
The Werner array used for the horizontal profiling which has maximum length of 220m and minimum electrode spacing of 20m. These were obtained and presented in table (Table 4.1). Also the result for vertical electrical sounding to determine the depth of groundwater of the study area are presented in table 4.2, 4.3, 4.4,and 4.5 for VES 01,VES02, VES03 andVES04 respectively. The data was processed using IP2WIN software and contour map was produced using Surfer 10 computer software.
CHAPTER FIVE
SUMMARY, CONCLUSSION AND RECOMMENDATION
Summary
The result obtained from the Geoelectrical survey shows that the area is characterized by three layers namely the topsoil (overburden), weathered basement, fracture basement. The data of the VES curve obtained were interpreted using IPI2Win resistivity computer software. The result of the interpreted VES data revel that the water bearing layer (aquifer) lie within the weathered and fractured basement of the predominantly three layers structure. VES 01 and 03 has high potential for groundwater, however, the sitting of borehole should be done on VES 01 because it has the ability retain and sustain portable water. The resistivity of VES 01is low compare to VES 03, this shows a high conductance and from the comparison of the contour map with the VES curve, it was revel that the thickness of VES 01 is 16.2m with depth of 27m.
Conclusion
This research aimed at investigating groundwater potential at the male hostel of Isa Kaita College of Education. To achieve this, vertical electrical sounding using Schlumberger configuration was used to delineate the sub-surface geology of the study area. Four (4) stations were probed within the study area and the data obtained were interpreted using IPI2win and SURFER 10 computer software. The interpreted data indicates that the area is composed of four (3) geoelectric layers, namely; topsoil, weathered basement and fractured basement. The weathered and fractured layers constitute the aquiferous zone in all the stations. The results of the interpreted VES data showed that the male hostel of Isa Kaita College of Education contain reasonable amount of groundwater which if tapped based on geophysical report it will help to eradicate the water problem on the campus.
Recommendation
Based on the electrical resistivity survey, the research study leads to the following recommendation;
- Boreholes can be established at VES 01 and 03 at the depth of 27m and 4.33m respectively within the study area. 0.5 to 1 m depth should be also added to both depth during drilling so as to penetrate deeply into the aquifer.
- Also, a detailed pre-drilling geophysical investigation should be carry out in IKCOE and Katsina state which is part of the basement complex area of Nigeria because in order to prevent the common occurrence of borehole failure within the campus and the State at large.
- Finally, geophysical (whether taken as a core or elective) is a practical course whose success cannot be achieved without field work. I therefore recommend that a set of terrameter should be provided by the department to encourage effective study of this course.
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