EVALUATION OF HYDRAULIC PROPERTIES AND WATER TABLE FLUCTUATION OF GBAKO AQUIFER, NIGER STATE, NIGERIA

ABSTRACT

Water table fluctuation of selected hand dug wells, and hydraulic properties were determined. The methods of investigation included water level measurements, laboratory tests and analysis. The results indicated that the water level values for 16 wells under study ranged from 6.30 – 7.10 m (Minimum) and 25.40 – 26.30 m (Maximum) during rainy season, while the average during the dry season was 7.60 – 8.90 m (Minimum) and 27.10 – 28.00 m (Maximum). The depth of the wells investigated were between 11 to 30 m, and diameter of the wells ranges between 0.8 and 1.3 m. The aquifer Hydraulic properties were determined from pumping test (recovery test) method. Results showed that transmissibility magnitude ranged from 7.48 to 26.94 m2/day. The hydraulic conductivity ranged from 1.4 to 8. 2 m/day, while specific yield average was 14.5%. The results showed that the aquifer potential of the wells in the study location is generally low which conform to the general phenomena for basement complex terrain on which Gbako drainage Basin is located. The data and results from this investigation are applicable in assessing and the management of groundwater storage, upward flux, water table configuration as well as groundwater exploration and exploitation. There was no significant differences (P>0.05) in the water level of the representative wells indicating they are located within the same geological formation.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Available groundwater information indicates that water level declines are occurring in key agricultural areas and that some aquifers are almost certainly experiencing high levels of over abstraction (Food and Agriculture Organization, 2007).Groundwater information plays an important role in development, and financing of agricultural projects and other politically sensitive decisions. Groundwater is commonly used in the developed world for drinking water supplies in large part because it is more economical than treating surface water for consumption. Göçmez (2009) claims that the use of groundwater is on the rise in the developing world as surface water becomes increasingly contaminated and scarce. With the increase in groundwater use, governments of developing countries rarely do invest in the researches necessary to quantify sustained yields within aquifers unless they experience water shortage. Effective management of groundwater is highly dependent on appropriate, reliable and up-to-date information. For the past 20 years rural communities in Nigeria have experienced an increase in groundwater exploitation as a result of rapidly diminishing and poor quality surface water with no rural community having less than two shallow hand dug wells. However these wells tend to go dry during dry season (Olaniyan and Olabode, 1998).

Changes in the depth of the groundwater table are determined by climatological factors (precipitation and evapotranspiration and their distributions), hydrological characteristics (drainage in and out flowing seepage), soil conditions (hydraulic conductivity), and storage capacity. Quantitative data on the depth, fluctuation and duration of the groundwater table are scarce for tropical West Africa (Ogban and Babalola, 2009).Veldkamp (1979) reported that the precipitation of groundwater regimes of soil characteristics can be inaccurate because great variation may occur during a year and between years, and because oxidation from incoming groundwater may obscure soil morphological features indicative of long term saturation. He therefore recommended the measurement of actual groundwater table depth to determine suitability for uses.

Recovery and pumping tests are normally carried out to explore how much ground water can be safely exploited from a well. It is now a well known fact that before groundwater resources can be managed, it must first be quantified through the estimation of aquifer hydraulic parameters. The success of it, however, depends much on how accurately the test data can be acquired and exhaustively analyzed. Good aquifer naturally corresponds to high porosity and high permeability characteristics (Egharevba, 2010).The result from properly conducted tests on an aquifer is the important tool in groundwater resources evaluation, monitoring and management. The knowledge of soil permeability or other aquifer constraints like transmissibility that relates to the rate of fluid movement in both soils and water bearing aquifer is needed for the design of surface and subsurface drainage facilities. Wells are either shallow or deep and may be dug, driven or bored. Dug wells are excavated by hand or by a variety of unspecialized excavation equipment. In the study area (Gbako Basin), most wells are used for domestic purposes, and water level observations reflect a rapid aquifer response to changes in conditions, presumably rainfall and abstraction (Shekwolo, 1990).

1.2       Statement of Problem

In the past 25 years, Gbako drainage basin has experienced an increase in groundwater exploitation by the rural population (Amadi et al., 2010). The fast growing population in the parts of the basin is connected to the high potential for agricultural production in the area which causes a serious water and population imbalance, compounding the problem of falling groundwater levels. The rapidly diminishing and poor quality surface water resource have forced the rural people of the area to install relatively inexpensive shallow hand-dug wells. However, over the years, in many areas, these wells tend to go dry during the critical dry months (January to March).

The increased exploitation of groundwater coupled with lack of information on declining water tables, extraction estimates, and aquifer properties is of great concern from a sustainability stand point. The inability to access these information, which at times is part of institutional secrecy, encourages inaction or incorrect decisions. Therefore, for a sustainable groundwater and correct decisions there is the need to study or determine water table fluctuations and aquifer properties in the study location.

1.3       Justification of the Study

Groundwater forms one of the important sources of water supplies in many areas, as it is believed to be safe and free from pathogenic bacterial and from suspended matter. The pace of groundwater withdrawal in many fertile regions is increasing due to the fast pace of population growth accompanied by agricultural and industrial development. Generous amount of money have been spent on sinking of boreholes and wells for agricultural and industrial  purposes  including  domestic  uses  but  not  properly managed  because  of  the fluctuating nature of groundwater New data bases need to be developed for relating the aquifer geometry vis-à-vis availability of groundwater especially in the part of Gbako drainage basin.The knowledge of groundwater fluctuation and the aquifer potential is imperative for groundwater management resources of the area.

1.4       Aim and Objectives

The study is largely on the investigation of water table fluctuation and the corresponding aquifer potential of some selected hand dug wells and boreholes around the Gbako drainage area. The objectives of the research work were to:

1.         Determine the seasonal fluctuation of the depth to water level of the wells in the study area.

2.        Determine    the    aquifer    hydraulic    characteristics    (hydraulic    conductivity, transmissibility and specific yield).

1.5       Scope of the study The work covered the Gbako drainage basin, a catchment of the middle-Niger (Bida) Basin North of River Niger. The study location extends from Edozhigi, Zanchita through Bida/Edokota/Emizhiru, Badeggi/Essa, and Kuchiworo/Vunchi. The geology of the area, geophysical surveys and some climatic data will be considered. The aquifer hydraulic characteristics will be evaluated using hand dug wells and selected boreholes within the study area. Due to financial and time constraints, it was not possible to dig or drill new wells, so existing wells in the study area were relied upon for the required investigation

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