Geoscience Reference
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the integration of remote sensing and GIS for groundwater potential zones
is more effective in hard rock terrain but less effective in alluvium environ-
ment. Krishnamurthy
et al.
9
have demonstrated the capabilities of remote
sensing and GIS for demarcation of different groundwater potential zones,
especially in diverse geological set up.
Various thematic maps such as geological, geomorphological, lineament,
drainage density, and slope maps have been considered to delineate ground-
water potential zones in a semi-arid zone hard rock granitic aquifer using
GIS. Each of these thematic maps has been assigned suitable weightage
factor. These thematic maps were then integrated using GIS based model
to delineate groundwater potential zones.
In order to characterize these various zones detailed hydrogeological
data were collected during the field investigation viz. well yield, water level
and groundwater quality. These data were analyzed with respect to each
zone to characterize them.
1.1.
Study area
The study area (200 sq. km), a typical watershed in hard rock terrain
(Fig. 1), lies in Nalgonda District of Andhra Pradesh State (India). Physiog-
raphy of the area exhibits three distinct features (i) hilly terrains covering
mainly northern and north-western part of the basin, (ii) mid-slope region
with moderate undulating terrain, and (iii) relatively flat region with gentle
slope covering larger part of the basin. The area receives an average annual
rainfall (1993-2003) of about 806 mm. The surface runoff goes to river
Kongal. There are several tanks across these drainages, however many of
these remain dry.
1.2.
Geology
The basin is underlained by Archaean rocks, which have suffered consider-
able degree of tectonic disturbances. The northwestern edge and northern
part are occupied by such hills of hard crystalline massive granites. The
southern fringe area is occupied with Kankar (calcium concentrate) covered
with clay. These two geological units are most unfavorable from groundwa-
ter point of view. Remaining part of the area is covered with granite and
gneisses. These are highly weathered, jointed, fractured and faulted, which
forms potential groundwater zones. There are strips of alluvium deposits
seen along the stream course, which could also be potential groundwater
zones.
