Geology Reference
In-Depth Information
LINEAMENT STUDY
In the hard rock areas, the movement and occurrences of groundwater depends
mainly on the secondary porosity and permeability resulting from folding,
faulting, fracturing etc. The most obvious structural features that are important
from the groundwater point of view are the lineaments. The lineaments are
linear or curvilinear feature pattern and play a vital role, particularly in
geomorphic and structural analysis. The lineaments like joints, fractures etc.,
developing generally due to tectonic stress and strain, provide important clue
on surface features and are responsible for infiltration of surface run off into
sub-surface and also for movement and storage of groundwater (Subba Rao
et al., 2001). Photolineaments generally represent the surface traces of fractures
in bedrocks, projected more or less vertically upwards to the erosion surface
by various mechanisms (Srinivasan, 1988). A systematic mapping effort
needs to be conducted to perform the lineament trace analysis. By visually
interpreting the satellite imageries, the lineaments of the study area are
picked up and traced on the basis of tonal, textural, soil tonal, vegetation,
topographic and drainage linearities, curvilinearities and rectilinearities
(Lillesand, 1989; Drury, 1990; Gupta, 1991).
The remote sensing data, which offer synoptic view of large area, helps
in understanding and mapping the lineaments both on regional and local
scale. The lineament analysis of the area from remotely sensed data provide
important information on subsurface fractures that may control the movement
and storage of groundwater. To determine the lineament density in the study
area, the total study area is subdivided in a number of grids of dimension 1
km × 1 km. Density of the lineaments of a single grid is obtained from the
values of the total length of the lineaments in a single grid (
L
). Calculation
of the density of the lineaments in the area involves the ratio of
&
L
to
A
. By
calculating the value of &
L
/
A
for each grid and locating the value at the
centre of that grid, the density of the lineaments of the study area is calculated.
These values are joined by isolines to prepare a lineament density map using
GIS software.
The main advantages in using remote sensing techniques for groundwater
exploration are: quick and less expensive way of getting information on the
occurrence of groundwater, aids to select promising areas for further
groundwater exploration thus reducing field work and provides information
on prospects in one map.
&
WEIGHTED INDEX OVERLAY ANALYSIS (WIOA)
It is a simple and straightforward method for a combined analysis of multi-
class maps. The efficacy of this method lies in that the human judgement can
be incorporated in the analysis. A weight represents the relative importance
of a parameter vis-à-vis the objective. WIOA method takes into consideration
the relative importance of the parameters and the classes belonging to each
