101 CHAPTER 4 Topographic Analysis 4.1 Digital Elevation Model (DEM) in topographic analysis The term digital elevation model or DEM is frequently used to refer to any raster representation of continuous elevation of a topographic surface with a common datum. Burrough (1986) has defined DEM as any digital representation of continuous variation of relief over place. With increased popularity of GIS technology and availability of DEMs the potential of using DEMs in studies of surface process has been widely recognized (Wharton, 1994). DEM has been utilized as one of the core databases in many GIS application practices. DEM not only provides the description about three-dimensional surface and data foundation for impressive three-dimensional visualisation of geographical data, but also sets the foundation for deriving other surface morphological parameters such as slope, aspect, curvature, slope profile and catchment areas. Among all the morphological parameters, slope and aspect have been arguably the most frequently utilised in GIS applications. DEMs are data files that contain elevation of a terrain over a specified area, usually at a fixed grid interval over the surface of earth. The individual between each of grid points will always be referenced to some geographical co-ordinate system. DEM is used for extracting the terrain information and determining the terrain attributes such as elevation, slope aspect etc to delineate drainage networks and watershed boundaries. New methods and algorithms have been developed to automate the procedure to terrain characterization (Hogg et al., 1993; Guth 1995; Desmet and Govers, 1996). It also helps to geological and geomorphological mapping In addition; DEMs have been incorporated in distributed hydrologic models (Garrote and Bras, 1995).
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101
CHAPTER 4
Topographic Analysis
4.1 Digital Elevation Model (DEM) in topographic analysis
The term digital elevation model or DEM is frequently used to refer to any raster
representation of continuous elevation of a topographic surface with a common
datum. Burrough (1986) has defined DEM as any digital representation of continuous
variation of relief over place. With increased popularity of GIS technology and
availability of DEMs the potential of using DEMs in studies of surface process has
been widely recognized (Wharton, 1994). DEM has been utilized as one of the core
databases in many GIS application practices. DEM not only provides the description
about three-dimensional surface and data foundation for impressive three-dimensional
visualisation of geographical data, but also sets the foundation for deriving other
surface morphological parameters such as slope, aspect, curvature, slope profile and
catchment areas. Among all the morphological parameters, slope and aspect have
been arguably the most frequently utilised in GIS applications.
DEMs are data files that contain elevation of a terrain over a specified area, usually at
a fixed grid interval over the surface of earth. The individual between each of grid
points will always be referenced to some geographical co-ordinate system. DEM is
used for extracting the terrain information and determining the terrain attributes such
as elevation, slope aspect etc to delineate drainage networks and watershed
boundaries. New methods and algorithms have been developed to automate the
procedure to terrain characterization (Hogg et al., 1993; Guth 1995; Desmet and
Govers, 1996). It also helps to geological and geomorphological mapping In addition;
DEMs have been incorporated in distributed hydrologic models (Garrote and Bras,
1995).
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Shuttle Radar Topography Mission (SRTM) is lunched on 11th February, 2000 and
available in public domain is a useful elevation model data source for regional
landscape analysis even with its coarse spatial resolution (pixel size ~90m). SRTM 3-
arc second DEM is the result of a collaborative effort by the National Aeronautics and
Space Administration (NASA), the National Imagery and Mapping Agency (NIMA),
the German space agency and Italian space agency (van Zyl 2001, Rabus et al. 2003;
Foni and Seal 2004).
In the present study, the SRTM data for whole Jia Bharali River was clipped (Figure,
4.1) and brought in to GIS environment for further analysis maintaining same datum
and projection (WGS-1984, UTM Zone-46) as in the satellite data. The SRTM DEM
has been downloaded from the Global Land Cover Facility (GLCF) Web site of the
Maryland State University.
Figure 4.1: SRTM DEM of the Jia Bharali River Catchment
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From the SRTM DEM an elevation map is prepared in Arc-Info by reclassifying the
DEM into eleven zones of elevation differences (Figure, 4.3). The maximum
elevation is more than 6000 in the Indo-Tibet boarder while the minimum elevation is
less than 100m. The minimum elevation of the area is less than 68m near the
confluence of Jia Bharali with Brahamaputra River. More than 83% of the total area
lies above the 500m elevation value and almost 17% of total area lies within the 500m
contour. Thus the upper part of the 500m elevation divided into seven divisions with
an interval of 1000m. Below the 500m upto the 200m demarcated as one zone and
after 200m three divisions is made with 50m elevation interval upto 100. (Table 4.1)
Table 4.1: Table showing the distribution of area within different elevation class
Figure 4.2: Bar diagram showing area distribution within different elevation
This NNE-SSW fault divides the basin centrally and it accumulates the stress, which
may cause the numerous earthquakes in the central part of the basin (Seismic Atlas of
NE). East of this fault, the fan-shaped structure with smooth mountain front convex
toward south.
Profile EF and GH are made diagonally in the middle part of the basin. From these
profile it is clearly observable the different geomorphic surface. The alluvial plain,
piedmont zone, fluvial terrace, dissected older alluvium and the Siwaliks hill. From
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KL, EF and GH profile it is observed that the hills, north of MBT, the hills of the
western side are highly dissected than the hills of eastern side, which may be due to
horse-tail geometry of the fault system (Duarah et. al., 2004). RS profile is made
along the foothills. In this profile the different geomorphic surface, Rangapara
surface, fluvial terrace near Naduar and Seijosa are prominent. The older alluvium
and the piedmont zone have a dissected surface. The alluvial fan topography is well
exposed in the profile.
Figure 4.10: Topographic profile along AB, across the basin in N-S direction shows
the gradual increase in elevation from south to north.
Figure 4.11: Topographic profile along AC, across the basin in N-S direction in the
same line with AB. Kameng is flowing through MBT
Figure 4.12: Topographic profile along IJ, across the basin in N-S direction in the
western part of the Kameng River
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Figure 4.13: Topographic profile along OP in N-S direction in the eastern part of
the Kameng River. Valleys represent the position of different stream.
Figure 4.14: Topographic profile along MN in N-S direction in the western part of
the Kameng River across Lesser Himalayan and Sub Himalayan part. The profile represents the high dissection in the area comparing to the profile OP. The height and distance ratio shows more incision in MN profile
Figure 4.15: Topographic profile along EF in diagonally the basin. Alluvial plain,
HFT, Siwalik Hills, Gondwana is well representing. The Jia Bharali is following through the piedmont zone and Siwalik through a structural valley.
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Figure 4.16: Topographic profile along GH diagonal to the basin in NW-SE
direction, represents the high elevation in the western part and high dissection in between MBT and MCT
Figure 4.17: Topographic profile along KL in E-W direction represents the high
elevation in the western part compare to the eastern part. Kameng is flowing with a lower elevation
.
Figure 4.18: Topographic profile along RS in E-W direction in the foothill region. The profile represents the Older Alluvium and alluvial fan deposits of the piedmont zone