International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 Internc
area there are 9 flows of traps of which the first seven vegetation is supported in the absence of hard laterite )
flows are not weathered and still they appear as basaltic exposure hither and thither.
in composition, whereas the 8" and 9" flow has been
completely weathered and altered to laterites. Thus In the area the valleys are formed due to removal of
laterites occur as cap rocks over basalts and form flat hard crust of laterite consisting of )
plateaus and tablelands at elevation range from 600 to detrital/concretionary laterite. These concretionary
660 asl. Laterites have a typical reddish brown colour. detrital Jaterites rest over lithomargic clay. )
They have cavities often filled with yellowish to reddish
clayey material. A zone of lithomargic clay marks the In the area dugwells and borewells are tapping the }
contact between the traps and the laterites. The groundwater. In the plateau regions, the edges are not
lithomarge is siliceous and exhibit brown to brownish favourable for groundwater exploitation. Interior parts
green colour with soapy touch. It is slightly hard to of the plateau can give moderate yields from the |
break. It is locally called as "Sapa Murram" weathered zones. Such parts are suitable for deep /
Venkatramna (1991). In the study area the different dugwells/borewells/tubewells. Fault/fractures zones |
stratification types of laterites are as given below. act as potential areas for groundwater harvest.
|
Table- | GEOPHYSICAL SURVEY THROUGH
Geological succession in the study area VERTICAL ELECTRICAL SOUNDINGS (VES): \
The inverse slope vertical electrical resistivity (VES) /
method as suggested by Sankarnaryan & Ramanuja |
Vesicular laterites 3 to 8 meters Chary (1967) is used to investigate the nature of sub- |
Pisolitic Laterites 2 to 7 meters surface formation by studying the variations in their |
Compact and Massive Laterites 5 to 15 meters electrical properties. This method assumes [
SRR SE SS eR considerable importance in the field of ground water |
Lithomarge exploration because of its ease of operation, low cost |
eren E RAPID EE and its capability to distinguish between the saline and
Basalts (Deccan traps) fresh water zone. This method was tested widely in
India, using it in different geological situations. It was
Apart from the geology as discussed in the study area found to give good results correlating well with |
three types of geomorphic units are identified Plateau, borehole data. This method is simple and gives |
Escarpment and filled in valley. In the lateritic terrain, resistivities and depths directly from the plot of the \
plateaus are hard and compact at surface grading into field data on a linear graph. In the present study more |
clayey at depths. These are flat uplands capped by hard than 100 VES data are collected. Resistivity in the |
crust of laterite grading downwards into lithomargic study area varies from 25Qm to 900Qm and this has |
been correlated by the borehole data. At Buchinihalli
borehole point no.1the depth of drilling was upto 50 |
BoreHole Locations meters the water bearing zone was between 28-32 /
a eee ET EEE |
meters, the top weathered morram 4-14 meters showed |
a resistivity of 85Qm, the semi-weathered zone gave |
resistivity of around 129Qm and the deeper levels the
resistivity increases when the massive basalt is struck. |
The value is as high as 837Qm as seen in point no.2
near Burdipad. However these wells are yielding |
water as high as 400 to 600lpm. because of good |
weathered zone. Another well near the basalt laterite
contact bore point no.3 showed resistivity value of |
46Qm between 20-60 meters and 372Qm between 72
to 84 meters. The litho-log for this well showed the |
occurrence of redbole of 4 meters thickness at a depth |
of 72 meters and the yield was 400 to 800lpm.
However in contrast to the above the well at Ranjole |
south of Zaheerabad bore hole point no.5, this has a
weathered profile of about 20 meters with a average |
resistivity of 260Qm suddenly the resistivity beyond
20 meters is high where the basalt is struck, and when
1o mneen frr
BIDAR
9
^ «Sham shilpur
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| Had
20% Rejanfar Chelepati
PP \Malkapur — *-— a7
72 Kiishnapur
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x 16 {rame "Hapati
6° °7 HotiB /3|* jp 14 9 —
+17, Kd 1 gae. -—
*U s. | HotiKhugd — Maur /
LE 24 Gurajgeal
= 15 Picfaiy
és
Legend drilling was done the well went dry. Yet another well |
E BoUundary at point no.7 at Kasimpur which is at the basalt-laterite
ES Roads : : : : ros à = > |
Fig - 3 EX River contact gave no yields with resistivity values of |
Borewell point 710Qm and 1522Qm. Borewell at point no. 8 yielded
around 600lpm. For this bore point the geophysical
data gave the following values 89Qm till 18meters and
194Qm till 35 meters, the litholog indicated massive
basalt after this depth where the resistivity is high.
This bore point was selected along the lineament and
was successful (Fig-4) ^ Wells drilled at point
12,13,14,15 and 16 which are well within the laterites
clays and deeply weathered bedrock/saprolite.
The scarp region may be considered a sub-unit of plateau
portion having a thin soil cover, is contiguous patch seen
in the south-eastern part adjacent to valley. Dense scrub
788 |
