Groundwater Exploration:

Introduction:

Groundwater is an invisible natural resource. It is available in different proportions, in different rock types, and at different depths, in the Earth’s surface layer. In the historical past, when there was no visible water flow along the rivers, people were digging small pits, collecting groundwater in the Alluvium River, waiting and seepage, for their drinking purposes and domestic needs. Similarly, for the people of the mountainous regions, natural springs provided sources of water supply.

Springs are the result of flow from any groundwater system, hilly areas or limestone areas. More than 60 percent of the global population thrives by using only groundwater resources. Groundwater has gone deep due to excessive exploitation of shallow depths in open wells. Exploring these sources of water is a challenging task for geo-scientists.

Groundwater investigation requires a thorough appreciation of the hydrology and geology of the area concerned, and a groundwater inventory needs to determine possible gains and losses affecting the subsurface reservoir.

Of particular interest are the lithology, stratigraphical sequence and geological structure, and hydrological properties of sub-surface materials.

Water table and piezometric level positions and their ups and downs are also of importance. In a major groundwater investigation, records of precipitation, temperature, air movement, evaporation, and humidity may provide necessary or useful supplementary information.

Similarly, data relating to streamflow may be of value in helping to solve the groundwater equation since seepage into or from streams constitutes a major factor in the discharge or recharge of groundwater.

The chemical and bacterial qualities of groundwater obviously require investigation.

Essentially, an assessment of groundwater resources involves the location of potential aquifers within economic drilling depths. Whether or not an aquifer will be able to supply the required amount of water depends on its thickness and spatial distribution, its porosity and
permeability, whether it is fully or partially saturated, and whether or not the quality of the water is acceptable.

Another factor that has to be considered is the pumping lift and the effect of drawdown on it. The desk study involves a consideration of the hydrological, geological, hydrogeological, and geophysical data available concerning the area in question.

Particular attention should be given to assessing the lateral and vertical extent of any potential aquifers, to their continuity and structure, to any possible variations information characteristics, and to possible areas of recharge and discharge.

Additional information pertaining to groundwater chemistry, springs discharge, surface run-off, and pumping tests, data from mine works, water sources or meteorological data should be considered. Information on vegetation cover, land use, topography and drainage pattern can sometimes prove valuable.

Aerial photographs help identify a wide range of rock and soil types and thereby identify potential aquifers. The combination of topographic and topographic data helps identify areas of groundwater recharge and discharge.

In particular, the nature and extent of external deposits provide some indication of the distribution of recharge and discharge areas. Aerial photographs allow the occurrence of springs.

Variations in water content in mud and rocks, which are not easily seen in black and white photographs, are often depicted by false color. In fact, the specific heat of water is usually two to ten times higher than most rocks, and it facilitates its detection in the ground.

In fact, the specific heat of the water can cause the aquifer to act as a heat sink that influences the temperature near the surface. Also, vegetative cover can be identified by aerial photographs and may provide some clues about the occurrence of groundwater.

In arid and semi-arid regions, in particular, the presence of bryophytes, ie, plants with high transparency and receiving water directly from the water table, indicates that the water table is close to the surface.

In contrast, xerophytes may be present in low moisture content in the soil, and their presence indicates that the water table is at considerable depths. As a result, groundwater forecast maps can sometimes be made from aerial. These can be used to help locate the test wells.

Geological mapping often forms the starting point of exploration and should identify potential aquifers such as sandstones and limestones and distinguish them from aquifers.

Superficial deposits may perform a confining function in relation to any major aquifers they overlie, or because of their lithology, they may play an important role in controlling recharge to major aquifers.

Furthermore, the geological mapping should locate igneous intrusions and major faults. Obviously, it is important during the mapping program to establish the geological structure.

Renewable resource:

Groundwater is a renewable source. Groundwater fills up after every rain. This is called rain recharge. The level of water present in the open well indicates the upper surface of the saturation zone of the porous medium.

This is called the water table. After each recharge, the water table is increased, indicating that the porous media is saturated with more water. When we discharge the water, the water level decreases. Continuous pumping of water beyond recharge will dry the wells and force the well to deepen.

The search for groundwater got increased, due to the non-availability of sources and due to the declining water tables.

Heterogeneous distribution:

Groundwater is not uniformly distributed everywhere. The occurrence of groundwater varies from structure to structure. In the typical crystalline rocky terrain, the quantitative occurrence of groundwater depends on the atmosphere and fracture zones.

The occurrence of groundwater in sedimentary terrain is highly promising. Groundwater prospecting is a thought-provoking scientific exercise in most places.

Understanding groundwater exploration methods is essential, as it is a practical decision-making method. This module highlights some of the most common methods of groundwater exploration.

Exploring groundwater:

Ground exploration is a typical work of a hydrologist or engineer. Identifying the location of its availability is a challenging task. Groundwater exploration requires a basic understanding of its place in the sub-surface geological setup.

Groundwater exploration is attempted through direct or indirect methods. Test drilling is a straightforward method for finding a resource. This is an expensive business. Not every person can go to test drilling.

Over the past two centuries, more and more techniques have been developed to explore groundwater.

They are classified into the surface and sub-surface methods.

(1). Surface methods:

Surface methods are easy to operate and implement. These require minimal facilities, such as top-sheets, maps, reports, some field measurements, and interpretation of data in laboratories.

Surface methods of groundwater exploration include:

a. Esoteric Methods
b. Geomorphologic methods
c. Geological & structural Methods
d. Soil and Micro-Biological Methods
e. Remote Sensing Techniques
f. Surface Geophysical Methods

(2). Subsurface methods:

This methods of groundwater exploration include test drilling and borehole geophysical logging techniques. When compared to surface methods, sub-surface methods are very expensive.

These are done for large-scale investigative government-level projects to find the results of the surface surveys. Sub-surface methods are very precise methods because they provide indirect observations of features in the form of bore-hole lithology into core models and geological measurements of structural properties.

(a). Esoteric methods:

Esoteric methods are primitive methods. These are the oldest water partitioning methods practiced by ancient people for many centuries. They are also called water-dosing. People believed that groundwater flow would induce some major currents above the surface. When the wet plant twig is moved over such zones, it also turns the twig.

Wet twigs of trees, husked coconuts, watches, and other materials are used as dosing materials. The person who handles the twig has some provocative character and therefore it does not apply to everyone who tries to divine water. All these methods have been practiced since the 17th century.

There are no scientific explanations available for these methods. The probability of success is just a coin-throwing experiment. These methods are known as water divining.

(b). Water Witching:

Water witch bore-well is a traditional method adopted by people to find places. The forked stick is called a water witch to find the source of the water. While this method has no scientific justification for the method, water witches diligently practice art wherever they can to persuade people about its potential value.

Generally, this method involves holding the forked stick in both hands and walking over the local area until the butt end is attracted to the bottom-up surface. It is surprising that the idea of ​​supernatural powers has such a constant fascination for people to use, despite its limitations.

(c). Geomorphological Methods:

Surface drainage is subordinate to topography. It is dominated by basement rocks. Most often, groundwater flows coincide with surface drainage. Streams and water bodies can be controlled by some underlying structures. Junctions of streams on the lower slopes are promising areas for groundwater. Geomorphologies originate from several geological processes.

Some of them are likely to contain relatively permeable seams. Modern alluvial terraces, floodplains, stratified valley filling in abandoned channels, glacier outflow, and moraine deposits are good forms of groundwater. Alluvial fans, beach lines, partially drift valleys, sand dunes, moisture depressions, and marshy environments are great places.

(d). Geological Methods:

The geological investigation begins with the collection, analysis, and interpretation of hydrology of existing topographic maps, aerial photographs, geological maps and records, and other related documents.

This should be supplemented, when possible, by geologic field reconnaissance and by evaluation of available hydrologic data on streamflow and springs, well yields, groundwater recharge, discharge, and levels, and water quality.

In some places, drainage can be completely controlled by the presence of small and major structures, such as joints, defects, and lines. These zones are good and potential zones for groundwater exploration. These are groundwater flow paths.

(f). Structural methods:

Contact points is in between permeable water-bearing strata overlying relatively impermeable strata usually along the sides of valleys that cut across the interface between different strata are suitable locations for groundwater.

Hills, valleys, and springs at or near the base of native scarps are indicators of groundwater occurrence on the hillsides. Dykes are good barriers to arresting groundwater flow.

Analyzing the location of the dykes and their dip and strike helps to select potential groundwater potential zones on the upstream side.

(g). Geophysical methods:

Exploring groundwater by the method of geophysics is called groundwater geophysics. Geophysical research is conducted on the Earth’s surface to explore groundwater resources by observing certain physical parameters such as density, velocity, conductivity, etc.
Resistance, magnetic, electromagnetic, and radioactive phenomena.

Geophysical methods involve the measurement of signals by natural or induced phenomena of physical properties of the sub-surface structure. Methods of terrestrial physics detect variations or anomalies of physical properties within the Earth’s crust.

Density, magnetism, elasticity, and electrical resistivity are commonly measured properties. The purpose of the quest is to find indirect indicators and to identify potential zones of exploitation.

The main geological methods that can be used to solve some of the hydrological problems are electricity, earthquake, gravity and magnetic methods.

(3). Gravity Method:

This is a widely used geological method for determining mineral resources and groundwater in sedimentary terrain.

Gravimeters are used in this method to measure the density differences on the Earth’s surface, which indicate the underlying geological structures. This method is expensive and because the variations in the water content on the surface surface involve measurable differences in the specific gravity of the surface, the gravity method has little application to groundwater expectancy.

Under special geological conditions such as a large burial valley, the total configuration of aquifers can be determined by gravity differences.

(4). Magnetic Method:

The magnetic method allows the detection of Earth’s magnetic fields, which can be measured and mapped. Magnetometers are instruments used to measure magnetic fields and differences.

Since magnetic contrast is rarely associated with the occurrence of groundwater, this method has little relevance for exploring groundwater. Indirect information for groundwater studies, such as the presence of dykes that form the aquifer boundaries or the limits of basaltic flow, can be obtained by this method.

(5). Seismic Method:

Seismic modes are two types of seismic refraction and reflection methods. The seismic refraction method involves the creation of a small shock on the surface of the earth under the influence of heavy equipment or a small explosive charge and measuring the time required to travel the known sound, or shock, at a distance known to the wave.

Earthquake waves follow the laws of propagation similar to light rays and can be reflected or refracted at the interface where the velocity changes. Seismic reflection methods provide information on geologic formation thousands of meters below the surface, but seismic refraction methods of interest in groundwater studies go only 100 meters deep.

The travel time of an earthquake wave depends on the medium through which it passes. Velocities are high in solid igneous rocks and in non-consolidated materials. Based on these instructions, it is possible to delineate the sub-surface zones of fractures, cracks, defects, and lines.

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