Geology Reference
In-Depth Information
Hydrogeology
Mostly horizontal fractures were prominent but vertical fractures are also
contributing as a conduit for groundwater flow. Permeability in the fissured
layer is greater than the laminated layer. In general the horizontal permeability
is greater than the vertical permeability. Groundwater occurs mostly in
fractured zone with water table varying between 11 and 20 m below ground
level. The groundwater is mostly tapped by means of bore-wells in the
fractured rock and the yield ranges between 1000-5000 gph (Subrahmanyam
et al., 2000). High yields of some of the bore-wells are due to encountering
of water bearing fractures at depths. Four sets of joints were mapped. The
most prominent joint set strikes in N-S direction based on rose diagram plot.
The strike varies between N10° E to N10° W. The joints are either vertical
or dip very steeply towards west with angles 70° to 75°. The second set of
joints strikes E-W with steep dips. The strike of this joint set varies between
N80°W and N80°E. The third set of joints strike NE-SW direction with
steep dips of 60°-75° towards SE. The fourth set of joints is more or less
parallel to the surface of the topography. All these joints and its system help
in the percolation of rainwater from the surface to the groundwater table.
They also help to act as conduits for the transmission of groundwater. There
are two sets of dykes and the strike of the first set is 90°-110° and the second
set strikes 50° to 60°. There are joints and fractures in the dykes also but the
surfaces are curved. These fracture also act as conduits for the transmission
of surface water to the groundwater. The area is also traversed by lineaments,
identified through the study of aerial photographs and land-sat imageries.
The high yielding wells are aligned along these lineaments.
1-D Variogram of Water Level in Time
In the present study using the water level data from 25 experimental
observation wells, the 1-D variogram analysis using Ahmed (1995, 2001)
was carried out individually for each well to obtain the water level variability
in time. The variogram was calculated and fitted with the theoretical variogram
for all the monitoring wells (IFP's).
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