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Electrical Resistivity Method: Success Rates?

I have undertaken a of geophysical survey using electrical resistivity method for finding borewell points in my farm plot. My farm is located 10km from Denkanikota (Hosur, Tamilnadu).  I would like to know from the experts about the success rate (or dependability) of this method. Kindly let me know the pros and cons of the same.

Ponnu Subramanian

ponswetha@gmail.com

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1.

Dear Ponnu Subramanian,

Electrical Resistivity survey gives the resistance of different depth /layers/fracture. Further, it depends on the person, how he collects data, interpreting and correlating with the terrain.
The recommendation is based on resistivity data and understating of the geological setting and other well inventories.
Normally, the success rate more than 80 percent. And also, it will help us to decide whether we have to drill or not, by which it will avoid the loss of money.

Regards,

C.Vijayakumar
Hydrogeologist

2.

Dear Ponnu Subramanian,

Electrical Resistivity method is a common practiced method for locating ground water fracture zones underneath a rocky area. It is done by two methods. First, one is called profiling through which one can detect whether the site selected by a geologist after studying the rock types of the area is on a potential fracture zone. Then VES i.e Vertical Electrical Sounding is conducted to get an idea about the depth and type of fracture zones. But all these methods success depend on the interpretation capacity of a Geophysicist well versed with the area.

However no body can predict how much water you will get from a fracture zone or a bore well. Another fact to be remembered is that "for predicting a deep fracture of 100 meter depth, a spread of around 200 to 300m is required". Thus you are best person to judge the Firm you are employing for the same.

With Regards

Nirad Chandra Nayak
Scientist
Central Ground Water Board
Bhubaneswar-Orissa

3. Help needed with method to analyse resistivity data

Dear Sir

Can you please mail me the method of analysis of resistivity meter readings. And also the method of interrelations.

Kindly contact me at my e mail address- dayageol@gmail.com

4.

Dear Subramanian,

The success rate of electrical resistivity method depends upon many factors. However if you conduct more number(4 to 5 per hactare in an Hard rock Area) of Vertical Electrical Soundings and and get it interpreted by an experienced Hydrogeophysicist/Hydrogeologist in that area, the success rate is definitely very high.

5.

Dear Sir,

If the area under study is sufficiently big and if electrical resistivity survey is conducted following stipulated procedures one can get reasonably good results.
To locate potential subsurface fractures one has to conduct resistivity profiling.This helps in narrowing down / focusing on couple of sites for resistivity soundings.

If there is a near by well,borewell the technical expert has to first take sounding near that spot to get a reasonable idea regarding the range of resistivities at different depths as resistivity values do change from one region to the other(even within hard rock terrain).Such a preliminary assessment would help in better analysis of resistivity data.It is also essential to have perpendicular sounding, at the recommended site, to ascertain that the identified potential zone is present at the same depth and resistivities noted earlier do repeat.

This narrows down the ambiguity.quantification of water is rather subjective.The scientist/technical expert usually uses his acquired knowledge in analysing the quantum of water from the derived resistivity-thickness-depth details.

Since you may be interested in having borewells for either irrigation or for industry etc it is always advisable to have indepth hydrogeological investigations prior to resistivity surveys.

So, in nutshell the scientific technique will not fail if the technique is properly used.
Regards

Dr.P.R.Reddy
Emeritus Scientist
N.G.R.I,Hyd-500606

6.

Dear Ponnu Subramanian,

Resistivity survey can be useful to decipher the sub-surface formation and can indicate about the design of well construction and quality of ground water. The most important is the method of the survey and the interpretation. Most of the people interpret by inverse method which is tentative.

However, interpretation by Shulmberger method is most recommended. It is more important that the person undertaking the survey is qualified and not just an eye wash.

Thanks

D. Chakraborty
Scientist
Central Ground Water Authority (CGWA)
New Delhi

7.

Dear Ponnu Subramanian,

Resistivity survey for location of feasible bore well sites is an indirect method of determining the sub-surface information. It all depends upon then experience of the specialist (Hydrogeologist) who is conducting the investigations and if he conducts the investigations systematically the success rate is good. If the investigations are conducted systematically the success rate is 90 to 95 %. There are several other methods but still resistivity survey holds good till today.

With regards

S.A.Hirudia Raj
Consultant
Water Resources

8.

Dear Ponnu Subramanian,

You have asked a very good question.

A simple answer is that in Tamil Nadu, we are just about 30 years behind the use of technology and tools. But in the contrast, the public is more aware that the use of groundwater and we stand first in the exploitation and usage.

What I meant to say is we use the equipments, which adopt obsolete technologies and obsolete methodologies in location sites for good yielding bore wells in Hard rock and soft rock regions, especially in Tamil Nadu.

The reason for this is in we do not have any institute in Tamil Nadu that teaches Geophysics as Master Degree. No Geophysicist is coming out from Tamil Nadu. We produce many Geologist who take up the water divining as their profession.

If we deeply analyze, for ground water location in general, any student should study the Darcy’s Law, the Flow equations and Digital Modeling.

In addition to reading and remembering these laws. The student should also derive these fundamental equations on own and will be able to solve problems.

Our geologists who come out of the universities the just glance through these aspects and they never study it or derive it because it is not in their curriculum and they are not capable of deriving these equations and laws.

The under standing of the ground water flow and its close to natural behavior is very important and based on the situation only he has to evolve a tool to find out where there will be possibility of getting good underground water flow in the hard rock terrain such as yours.

Then comes the using the tool. Normally in the Indian conditions we use Resistivity methodologies. Here also these geologist glance through the methodologies. For resistivity investigation the fundamental od Ohm’s law in the potential theory and field theory is very important. Then deriving the apparent resistivity for layered year and other different models using the integral equation, numerical integration for interpretation purposes is also very important.

These aspects also they never study. We can blame the students, it the professors and universities we have to blame. Without understanding their limitations they turn themselves into professional Hydrogeologist who have never once derived the Darcy’s Equations, Flow equations, Thiess Equations, Modeling, Resistivity for layered on other earth structures and different methodologies and tolls,

Further they know very well ground water is available in Fractured and jointed medium, that is to say the occurrences very with respect to depth and space.
To search these there are many methods and all the foreign countries and few consultants in India adopt. But our so called pseudo-hydrogeologist uses blindly the so called sounding methodology that may give success or may not give success.

Under the above situation how can I say how many percent success we get in general. I can say if you get a good geophysicist who uses modern techniques, methodologies and gadgets then the success is 100 %

If you use geologist there will be 50 percent success 50 percent failure. Success in the sense what the farmer wants for pumping to save his crop during drought situation.

Now days, like heart and brain tomography. We can scan your land. Imagine we cut a vertical slice for 500 meter distance until a depth of 100 meters. Or imagine that we dig a rectangular canal of ten meter width, 100 meter depth and 500 meter distance, what ever we observe along the 500 meter wall. You can get from the resistivity imaging method. The cost of the technique on Indian condition is about Rs. 20000 for investigation about 10 acres of land. They will give to 2 dimensions or 3 dimension map of the underground pin pointing potential bore well points. This technique are very widely used in Canada, Sweden, States, U.K. Australia, Germany Brazil, China, Japan and other western counties and very rarely in India.

I honestly trust I have given clear picture, the status of art in the technique.
It is difficult to commend on the success rate when we use obsolete technologies, methods and persons. These geologists bother only for the money and they hide their limitations, fool the people and government. But, how the government gives license for them. God only can protect us from the unenlightened Government and Bureaucrats.

With best wishes,

A.Rajamohamed Ambalam
Geophysicist

9.

Dear Ponnu Subramanian,

Resistivity survey measures variations in app. resistivity of the rock formations along depth. In hard rock areas, water is likely to occur in low resistivity zone or Typically small peaked feature shown by fractured zone. The method is indirect but shows good co-relation. In order to further substantiate the resistivity survey, the geophysicist should also carry out well inventory (collecting details of the existing wells) of the area to understand how the ground water occurs and co-relate this information to infer if the low resistivity zone is indeed water bearing.

Due to over-exploitation of GW, sometimes, even the low resistivity zone (aquifer) may not yield water of desired quantity. The thumb rule is not to expect more water than your neighbor, because yield of tube wells in a particular area is likely to be more or less same as that of the closest well with same elevation. You can not expect a miracle for your well. Resistivity survey will help you to identify the best site at your land for drilling a bore well.

Best wishes.

Dr. Mihir Maitra
Consultant
Water Resource

10.

Dear Subramanian,

It may be of interest to know that the Department of Drinking Water Supply of Government of India has hired the services of National Remote Sensing Agency (NRSA) to achieve high success rate in drilling drinking water bore wells. The methodology evolved for this purpose includes interpretation of satellite images on 1:50,000 scale, field verification and preparation of groundwater prospects maps, identification of prospective groundwater zones, narrowing down target zones for follow-up electrical resistivity surveys and pinpointing well sites for drilling. The ground water prospects maps were prepared by superimposing the base, lithological, structural, geomorphological and hydrological maps.

The webpage at http://ddws.gov.in/popups/NRSA_files/slide0139.htm gives details of the NRSA work. The webpage at http://dst.gov.in/admin_finance/un-sq163.htm indicates that the wells drilled using the above methodology gave 85-90% success rate, while that at http://coe.mse.ac.in/ISRO-cove.pdf indicates that there was saving in the range of Rs. 500-800 crore by avoiding digging of unsuccessful wells through use of those maps.

Although these maps help to achieve high success rate for pinpointing sites for irrigation wells through electrical resistivity surveys, the government rules will not allow for their use by the private consultants.

Let us wait until rules are modified, so that private consultants can have access to groundwater prospects maps to obtain a similar high success rate.

Best wishes,

Dr. R. Jagadiswara Rao
Retired Professor of Geology
Sri Venkateswara University
Tirupati, AP 517502
rjagadiswara@gmail.com

Dr. R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com

11.

Dear Sir,
Have you ever tried the non scientific method of finding water, I mean water divining.
I regularly find water by this method and I have been very successful over the last 10 years.
I have not taken it up professionally and I just do it for fun and as a hobby.
If interested do contact me at guna99amu@gmail.com

12. Dear SirLast year april month

Dear Sir

Last year april month i put two bores in my land one is 180 feet another one is 285 feet but little pit water also not coming but where i put that point near (5 to 7 metter) one pump is working its coming 2 1/2 inch water . WHAT IS THE REASON ? i lost money and my life also that two points also pointed one diviner . now anybody tell me correct way of ground water diviners pls help me thanks

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