This message is in reply to Y. Srinivasa Rao's message at
http://in.groups.yahoo.com/group/gwrm/message/21 on "Groundwater
study - Electrical resistivity methods - Theoretical master curves -
Curve matching software".

The subsurface structure at any given point at the surface (by way
of finding true resistivity and thickness of horizontal geological
layers) could be determined fairly accurately by matching field
curves of electrode spacing and apparent resistivity obtained by
Wenner/Schlumberger method with any of the available albums of
master curves.

Curve matching used to be performed in the past by matching the
field curve drawn on a transparent logarithmic graph paper with one
or other of a master curve chosen from an album. Very often the
exact match between the field curve and the appropriate master curve
could be obtained only by appropriate manipulation of field curve. I
could however have access to an album of master curves when I
attended a UNESCO-sponsored course, seminar and tour in the Moscow
State University during 1978. I shall be happy to share the album
with Srinivasa Rao or any other participant of this group finding
use with it.

Most commercial firms have now access to sophisticated curve
matching software programmes which allow for accurate interpretation
of resistivity data and thereby avoid subjective errors. In view of
their high commercial value, these software programmes are not made
available in the internet on free basis.

I have been using electrical resistivity methods in conjunction with
other exploration methods since 1968 as a part of a training
programme to students and less-educated youth for locating
particularly pipeline-like fractures carrying artesian/ confined
groundwater within hard rocks of south India. As curve matching
methods are cumbersome, costly, time-consuming and prone for
subjective errors, I found it extremely convenient to make use of an
adaptation of an inverse slope method to obtain thickness and true
resistivity of horizontal geological formations just by using a
pocket calculator and thereby avoid preparation of any field curve
and curve matching. The methodology has been so simplified that it
could be taught even to less-educated people to become successful
barefoot geologists/geophysicists. Many water diviners who make use
of gadgets such as twig, coconut and pendulum in locating
groundwater found it advantageous to practise these scientific
methods also to achieve a higher success rate. The cost of
exploration could be made sufficiently low by the prospector
visiting the field with the equipment almost alone by training the
local people to assist him in the survey.

This understanding of the subsurface structure is useful not only in
the exploration of minerals, oil & natural gas and groundwater but
also in geotechnical engineering, watershed management and
artificial groundwater recharge. This knowledge is particularly
helpful to those engaged in watershed management works to identify
sites best suited for artificial recharge of groundwater through
maximising infiltration from those best suited for rainwater
harvesting for domestic use/ drinking/ irrigation by maximising
surface runoff. It is worthwhile for NGOs engaged in such works to
procure the necessary equipment besides training their staff to take
up such surveys.

I shall be happy to impart training to NGOs/ individuals who can
come and stay at Tirupati for some time in electrical resistivity
and other scientific exploration methods, which I have developed
during the past 37 years.

You can contact me at:
Dr. R. Jagadiswara Rao
Former Professor of Geology, Sri Venkateswara University &
Chairman, Rayalaseema Vikas Parishad (RVP)
63A, 2nd Cross West, Vidyanagar
Tirupati, AP 517502, India
Telephone: +91-877-2249433
Mobile: +91-94401-84012
Email: jagadiswara@..., rvp_org80@...