Geology Reference
In-Depth Information
measurements every few seconds have solved the problem to a great extent
even for highly permeable formations.
In the recent times where the hard rock aquifers have been subjected to
over exploitation, there has been a considerable decline in the water level to
a extent that the weathered portion is completely dry and the water is limited
to the fissured/fractured zone. In such situations if pumping tests are carried
out it will not represent the true aquifer parameter, as the zone of investigation
will be reduced due to further drop in water level because of pumping. In
these cases slug tests and injections tests can give a better picture of the
aquifer parameter as the zone of investigation increases because there is an
increase in water level when a slug is lowered in the bore-well during a slug
test or when water is injected in the bore-well during the course of an
injection test.
Flow meter tests when coupled with injection tests helped in determining
the conductive fissure zones within the aquifer and thus help in the
characterization of the hydraulic properties of the aquifer in the vertical
direction.
SLUG TESTS
Context
Hydraulic parameters in saturated zone of aquifer are required to be
determined for the purpose of modelling groundwater flows in Maheshwaram
watershed. In this regard slug tests were carried out in all 25 IFP wells for
the pre-monsoon period in 2002. The slug tests data were interpreted using
Bouwer & Rice method to estimate the hydraulic conductivity in the wells.
In addition, slug tests were performed on six IFP wells during 2001 and
were interpreted using de Marsily method (for transmissivity and storage
coefficient) and the same were reinterpreted using Bouwer & Rice method
to compare the results.
To have a completed data base of the hydraulic conductivities of all the
observation wells present in Maheshwaram, seven more slug tests were
carried out in the newly drilled wells by NGRI during July 2003. All the
tests were interpreted using Bouwer & Rice method.
Principle and Theory
The principle consists of analyzing the rate of water level fluctuation in the
well after a certain volume (“slug”) of water is suddenly removed/added
from/to the well. Emerging/submerging a cylinder in the water brings about
this sudden fluctuation (fall/rise) of water level. Instantaneously, it creates a
cone of depression/pression, which corresponds to pumping/injection test.
The chosen interpretation method is the one proposed by Bouwer & Rice
(1976) for slug tests in unconfined aquifers with completely or partially
penetrating wells. In addition to experiment measurements (water level
