Groundwater exploration is the investigation of underground formations to understand the hydrologic cycle, know the groundwater quality, and identify the nature, number and type of aquifers. … Surface geophysical method is one of the ground water survey investigation methods.
The use of geophysics for both groundwater resource mapping and for water quality evaluations has increased over the years in large part due to the rapid advances in microprocessors and associated numerical modeling solutions.
ERT Survey Method application for ground water survey exploration.
The Wenner array consists of four collinear, equally spaced electrodes. The outer two electrodes are typically the current (source) electrodes and the inner two electrodes are the potential (receiver) electrodes. The array spacing expands about the array midpoint while maintaining an equivalent spacing between each electrode. The advantages of the Wenner array are that the apparent resistivity is easily calculated in the field and the instrument sensitivity is not as crucial as with other array geometries. Relatively small current magnitudes are needed to produce measurable potential differences. The disadvantages are that for each sounding, all of the electrodes have to be moved to a new position. In order to image deep into the earth, it is necessary to use longer current cables; handling the cables and electrodes between each measurement can be cumbersome, especially in difficult terrain. The Wenner array is also very sensitive to near surface in homogeneities which may skew deeper electrical responses. The Wenner array is a labor-intensive survey because of the cable lengths required and the movement of the electrodes during the survey. Substantial lengths of cable energized with current at high voltage present a safety hazard.
The Schlumberger array consists of four collinear electrodes. The outer two electrodes are current (source) electrodes and the inner two electrodes are the potential (receiver) electrodes. The potential electrodes are installed at the center of the electrode array with a small separation, typically less than one fifth of the spacing between the current electrodes. The current electrodes are increased to a greater separation during the survey while the potential electrodes remain in the same position until the observed voltage becomes too small to measure. Typically, expanding the current electrodes occurs roughly six times per decade. The advantages of the Schlumberger array are that fewer electrodes need to be moved for each sounding and the cable length for the potential electrodes is shorter. Schlumberger soundings generally have better resolution, greater probing depth, and less time-consuming field deployment than the Wenner array. The disadvantages are that long current electrode cables are required, the recording instrument needs to be very sensitive, and the array may be difficult or confusing to coordinate amongst the field crew. Substantial lengths of cable energized with current at high voltage present a safety hazard. The Schlumberger array is a labor-intensive survey because of the cable lengths required and the movement of the electrodes during the survey.
OBJECTIVES OF THE SURVEY
1- To investigate the aquifer characteristics, thickness, layer wise soil type, ground water quality (by conductivity value) and water table depth using VES survey technique.
2- To determine the geoelectric and hydrogeologic characteristic of the aquifer present in the study area.
3- Detecting and mapping water saturated layer in various type of shallow as well as deep aquifer.
Adequate groundwater exploration can be considered as one of the primary components of the groundwater management practices. The assessment of the aquifer potential both on the basis of quality and quantity is of utmost importance. ERT survey can be used as an initial step for assessing the aquifer potential to promote the sustainable groundwater usage.
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