JAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002
RESULTS AND DISCUSSION
Various thematic maps suh as soil, slope, geology and
hydrogeomorphology, etc. were prepared visually, whereas,
landuse map was prepared digitally. The details of the various
themes is as follows:
Slope:
The slope is a vital parameter from land utilization point of
view. Slope determination is important for land irrigability and
land capability assessment. It has also important bearing on
flow of the run off, soil loss, vegetation growth and finally
optimal land utilization. Slope map of Ghaggar Watershed was
prepared using 1:50,000 scale topographical map of survey of
India on VAX - 11/780 System with the help of Digital Terrain
Model Software. The contours were digitized at 20 meter
interval for Piedmont and alluvial region and 40 meter for hilly
and mountainous region. These intervals were chosen keeping
in view the map scale and the spatial seperatability of the
contours in the digital data base. The random distributive point
showing isolated peaks or valleys were also digitized and were
useful for interpolation of height. The slope programme of the
DTM was used for computation of gradient of height values at
different pixel positions and the direction of the gradient
(aspect). The slope values were grouped into ten classes viz.
nearly level, very gently sloping, gently sloping, moderately
sloping, strongly sloping, moderately steep, moderately steep to
steep sloping, steep sloping, very steep sloping, very very steep
sloping with the finite difference method. Arial estimate of
various slope classes were computed by estimating total
number of pixels falling in each class.
DIGITAL ELEVATION MODEL (DEM):
Although DEMs were originally developed for modeling relief,
they are also used to model the continuous variation of any
other attribute Z over a two dimensional surface better known
as digital terrain model (DTM).
The DEM for the Gaggar Watershed was generated using the
digitized contour information. It is useful for three dimensional
display of land forms, for statistical analysis and comparison of
different kinds of terrain; for computing slope maps, aspect
maps and slope profiles that can be used to prepare shaded
relief maps, assist geomorphological studies or estimate erosion
and run off, as a background for displaying thematic
information or for combining relief data with thematic
information such as soils, land use or vegetation; by replacing
altitude with any other continuously varying attributes etc. The
output was generated with a tilt of 40, no rotation and
exaggeration factor of 3.
Geology, Geomorphology and Hydrogeomorphology:
Geology:
Geologically, the study area consists of lithologies of Tertiary
and Quarternary periods. The Tertiaries are classified into two
groups of formations: (1) the Subathus belonging to the lower
Tertiary (Eocene) and forming the high ridges in the northern-
most part of the watershed and (2) the Siwaliks which form the
low relief foot hills and belonging to the upper T ertiary
(Miocene-Pleistocene). Both these formations trend NW-SE.
The Quarternary formations consists of the alluvium and
666
colluvium occurring along the foot of the hills and extending
further down merging with the Indo-Gangetic alluvium.
Subathus
They are the oldest tertiary sequence exposed in Himalayas. In
the study area they consist of olive green and purple shales with
intercalated sandstone beds and limestone. They form the NW-
SE trending Morni ridge which form the north eastern boundary
of the watershed.
Siwaliks
The Siwalik formations consist of fresh water sediments
belonging to the upper Tertiary period. These formations are
divided into Lower, Middle and Upper Siwaliks.
Geomorphology:
Geomorphologically the area is broadly divided into three units,
viz. structural hills, piedmont zone and fluvial zone.
Structural Hills
When the underlying geological structure have a strong bearing
on the present form of the hills, they are called structural hills.
The NW-SE alignment of the ridges, hills and valleys in the
study area indicates that they are strongly controlled by the
strike of the formations. They are further grouped as:
Structural hills of high relief in Subathus
These high hills range in heights from 600-1200m and are
formed in alternate bands of quartzite and shale in the NE part
of the area. The landforms developed are strike ridges and
valleys and escarpments.
Structural hills of low relief in Siwaliks
Due to the variations in the compactness and lithology of the
upper, middle and lower Siwalik formations, they have been
subjected to varying degree of erosion and dissection. The
structural hills of Siwaliks can be broadly grouped into two
distinct units, on the basis of erosion, dissection and vegetation
cover i.e. less dissected hills in Lower Siwaliks and highly
dissected hills in Middle and Upper Siwaliks.
Piedmont Zone
The gently sloping vast plain of coarse to fine alluvial and
colluvial deposits form the piedmont zone which extend from
the foot of the Siwalik hills downwards. The torrential streams
descending from the hills deposit their load of assorted
sediments in the form of fans which coalesce to build the
piedmont zone. On the basis of differences in slope and
elevation, the piedmont zone is divided into upper and lower
piedmonts in the area.
The upper piedmont is a narrow zone with gentle slope at the
foot of the hills and is composed of subrounded cobbles,
pebbles, gravels, sand and clay. The drainage show braided
pattern.
The lower piedmont is the downward extension of the
piedmont zone and is composed of finer materials like gravel,
silt and clay. The drainages exhibit braiding in this zone.
Alluvial Plain
The wide alluvial plain is formed by fluvial material carried by
dangari river and its tributaries. It consists of sand, silt and clay
and is under intense cultivation.
Other fluvial landforms
In addition, the streams have built landforms like flood plains,
sand bars, terraces etc.
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