Groundwater Resource Exploration

The exploitation of groundwater resources is the only option that farmers have undertaken for increasing their water supplies to overcome the canal water scarcity and to get more control over irrigation water supplies. Tubewells can be installed in areas having good potential of ground water and where quality of water is within recommended limits for irrigation purposes. There are certain pockets of saline or brackish water both in irrigated and barani areas of Punjab where tubewells cannot be installed. In other places where water availability is not sure or is negligible, this option is again not feasible. Hence information on water bearing formations, underground soil strata, quality of water and its potential is very important prior to drill a bore. Such information can be collected by conducting a survey with resistivity meter. The resistivity meter can be used successfully upto a depth of 600 feet (Under favorable conditions more than 600 feet) to determine the water bearing formations and to differentiate between saline and fresh water aquifers. The energy audit is required to estimate the energy cost of pumping water which is contributing heavily in the overall expenditure of farmers. A Systematic Study / Energy Audit of randomly selected tubewells will be carried out on the current usage of energy

Following are the objectives of the project;

Objective

  • To identify groundwater aquifer through survey with electric resistivity meter (ERM) for sinking of tubewell
  • To make energy audit of randomly selected tubewells already operational in the province for efficient extraction of groundwater
  • To enhance agriculture productivity, income and cropping intensity through exploration of ground water

Electric Resistivity Meter (ERM)

In Electrical Resistivity Surveys, a commuted direct current is introduced into the ground viz two electrode and potential difference is measured between a second pair of electrodes. The current and potential measurements then are used to calculate apparent resistivity values.

Description / Theory of ERM

Electrical Resistivity Survey is a practical application of Ohm’s law i.e. R = K * (V/I) to study the sub-surface hydrological set up of the earth. The resistivity of any formation is mainly dependent on two factors, viz, the porosity of the formation and the salinity of the solution held in the pores. In water bearing formations the current is carried, entirely, by the dissociated ions of the salt held in solution.

 

Thus the resistivity of the formation is not characteristics of the formation itself as any one formation may have a wide range of values, depending upon its nature i.e. rock type, lithology, degree of weathering, moisture contents and the quality of water which is influenced by such factors as porosity and the amount of salts held in solution. Bearing in mind these factors, it is possible to classify the resistivity of the formation in terms of its textural and lithological character. For example, a particular formation with constant porosity will have different resistivity values depending on (a) its moisture, and (b) its salt content. The moisture content in a formation is directly proportional to the porosity of the formation, and hence, under given condition the resistivity directly may reflect porosity also.

Sufficient resistivity contrast exists between sweet and saline water. Saline water conducts electric current more quickly, and its resistivity therefore, falls sharply as compared with the geological formation holding sweet water; whereas sweet water conducts electrical current in a smaller amount, given its increased value of resistivity (conductivity of material being inversely proportional to its resistivity). From the gradient of the resistivity field curve, the quality of water in the area can therefore be inferred. Electrical resistivity survey can be used profitably for solving various groundwater problems such as:

  • To determine qualitatively the type of water bearing formation, e.g. clay, sand sandstone or gravel provided conditions are favorable and not complicated by abrupt changes in lithology.
  • To differentiate between saline and fresh water aquifers, provided the lithology of the aquifer is uniform.

Interpretation of ERM Data

The aim of geophysical interpretation of resistivity sounding data is to determine the thickness and resistivity of different horizons from a study of the vertical electrical sounding (V.E.S) field curves and to use these results for obtaining a picture of subsurface hydrogeological set up of the investigated area.
Field curves of apparent resistivity vs depth of the formation are plotted on log log paper and then these field curves are matched with the instrument curves for that particular VES and final interpretation is made. The software is also available for the interpretation.

Water Flow Meter

It is a portable ultrasonic flow meter and is used to measure discharge of pump with highest accuracy. It is mostly utilized on every type of water supply/discharge line and is the latest portable flow measurement and recording system. It can display instantaneous fluid flow rates or velocity. The flow sensors, or transducers, connected to the water flow meter are attached to the outside of the pipe being monitored and provide totally non-invasive flow measurement without disturbing the existing plant, equipment or process operation. When ultrasound is transmitted through a liquid the speed at which the sound travels is accelerated slightly when transmitted in the same direction as the liquid flow and decelerated slightly when transmitted against it. The difference in time taken by the sound to travel over the same distance but in opposite directions is therefore proportional to the flow velocity of the liquid and can be used to calculate the flow rate. The instrument will be used to measure the discharge of the tubewell from which the efficiency of the pump will be calculated.

   

EC Meter

An EC meter works by measuring the electrical conductivity of the water. Most elements other than the hydrogen and oxygen will conduct electricity to a certain degree. An EC meter will measure the EC and convert that electrical charge to an estimated TDS level. EC is measured by determining the amount of electrical charge between two sensors and greater the charge higher the EC and higher the TDS level. The EC meter will be used to test the quality of water of already installed tubewells.

 

Tachometer

It is an instrument which measures the working speed/rpm (revolutions per minute) of an engine, electric motor etc. Tachometer has been proposed to measure the working speed/rpm of an engine, electric motor.