16.6.1.5 Bifurcation Ratio (Rb)
The ratio of the number of stream segments of
given orders to the number of segments of next
higher order is known as bifurcation ratio
(Schumn 1956). Bifurcation ratio for different
basins of the study area for different stream
orders has been calculated (Table 16.2). The Rb
values are not the same from one order to next
order and they range from 1.63 to 2.26. The
difference in Rb values depends on the geological development of the drainage basin. “The
lower value of Rb indicates that the basin has
suffered less structural disturbances and the
drainage pattern is not distorted” (Strahler 1964).
The mean bifurcation ratio, which is the average
of bifurcation ratios of all orders, varies from
1.37 to 1.61, indicating that the area is not much
influenced by the geological structure and
undisturbed drainage pattern.
16.6.1.6 Stream Length Ratio (RL)
Stream length ratio is defined as the ratio of the
mean length of the one order to the next lower
order of the stream segments. The stream length
ratio between the streams of different orders of
the study area shows change in each basin. This
change may be attributed to variation in slope
and topography (Vittala et al. 2004). The RL
values have been presented in Table 16.2.
16.6.2 Aerial Aspects
The aerial aspects include drainage density,
drainage texture, stream frequency, form factor,
circularity ratio, elongation ratio and length of
overland flow. The results of aerial aspects are
given in Table 16.3.
16.6.2.1 Drainage Density (D)
The drainage density is a ratio of the total length
of the stream of all orders and drainage. It indicates the closeness of spacing of channels (Horton 1932). All factors related to drainage density
are also related to the climate, surface roughness
and runoff in the area. High rainfall results in
more runoff with more drainage lines, whereas
runoff is reduced at places where subsurface is
permeable and vegetation covers increase the
infiltration capacity. The drainage density of the
study area is low and varies from 0.92 to 1.27 per
km
2 , indicating that the area has highly permeable soil and low vegetation cover. The drainage
densities of all three basins have been given in
Table 16.3.
16.6.2.2 Drainage Texture (Rt)
Drainage texture is a ratio of the total number of
stream segments of all orders and perimeter of
the basin (Horton 1945). It is an important concept of geomorphology which means the relative
spacing of drainage lines. Drainage lines are
numerous over impermeable areas than permeable areas. There are five different types of
drainage texture that have been classified based
on drainage density (Smith 1950). The drainage
density less than 2 indicates very coarse, between
2 and 4 are related to coarse, between 4 and 6 is
moderate, between 6 and 8 is fine, and greater
than 8 is very fine drainage texture. The value of
drainage texture ratio of the study area varies
from 5.17 to 17.51 (Table 16.3), which indicates
moderate to very fine drainage texture.
16.6.2.3 Stream Frequency (Fs)
The total number of stream segments of all order
per unit area is known as stream frequency
(Horton 1932). The Fs value of the study area is
presented in Table 16.3. The value of Fs varies
from 1.19 to 1.33. The value of drainage density
shows a positive relation with the stream frequency suggesting that the number of stream
increases with increasing drainage density.
16.6.2.4 Form Factor (Rf)
Form factor can be defined as the ratio of the area
of the basin and square of basin length. The form
factor value varies from 0 to 1, where 0 indicates
highly elongated basin and 1 is perfectly circular
basin. The value of form factor more than 0.78
indicates perfectly circular basin. The smaller the
value of form factor, more elongated will be the
basin (Horton 1932). The Rf value of the study
area varies from 0.21 to 0.38. The Rf values in
Spiti, Tsarap Chu and Parechu river basins are
0.38, 0.28 and 0.21, respectively (Table 16.3).
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221
The ratio of the number of stream segments of
given orders to the number of segments of next
higher order is known as bifurcation ratio
(Schumn 1956). Bifurcation ratio for different
basins of the study area for different stream
orders has been calculated (Table 16.2). The Rb
values are not the same from one order to next
order and they range from 1.63 to 2.26. The
difference in Rb values depends on the geological development of the drainage basin. “The
lower value of Rb indicates that the basin has
suffered less structural disturbances and the
drainage pattern is not distorted” (Strahler 1964).
The mean bifurcation ratio, which is the average
of bifurcation ratios of all orders, varies from
1.37 to 1.61, indicating that the area is not much
influenced by the geological structure and
undisturbed drainage pattern.
16.6.1.6 Stream Length Ratio (RL)
Stream length ratio is defined as the ratio of the
mean length of the one order to the next lower
order of the stream segments. The stream length
ratio between the streams of different orders of
the study area shows change in each basin. This
change may be attributed to variation in slope
and topography (Vittala et al. 2004). The RL
values have been presented in Table 16.2.
16.6.2 Aerial Aspects
The aerial aspects include drainage density,
drainage texture, stream frequency, form factor,
circularity ratio, elongation ratio and length of
overland flow. The results of aerial aspects are
given in Table 16.3.
16.6.2.1 Drainage Density (D)
The drainage density is a ratio of the total length
of the stream of all orders and drainage. It indicates the closeness of spacing of channels (Horton 1932). All factors related to drainage density
are also related to the climate, surface roughness
and runoff in the area. High rainfall results in
more runoff with more drainage lines, whereas
runoff is reduced at places where subsurface is
permeable and vegetation covers increase the
infiltration capacity. The drainage density of the
study area is low and varies from 0.92 to 1.27 per
km
2 , indicating that the area has highly permeable soil and low vegetation cover. The drainage
densities of all three basins have been given in
Table 16.3.
16.6.2.2 Drainage Texture (Rt)
Drainage texture is a ratio of the total number of
stream segments of all orders and perimeter of
the basin (Horton 1945). It is an important concept of geomorphology which means the relative
spacing of drainage lines. Drainage lines are
numerous over impermeable areas than permeable areas. There are five different types of
drainage texture that have been classified based
on drainage density (Smith 1950). The drainage
density less than 2 indicates very coarse, between
2 and 4 are related to coarse, between 4 and 6 is
moderate, between 6 and 8 is fine, and greater
than 8 is very fine drainage texture. The value of
drainage texture ratio of the study area varies
from 5.17 to 17.51 (Table 16.3), which indicates
moderate to very fine drainage texture.
16.6.2.3 Stream Frequency (Fs)
The total number of stream segments of all order
per unit area is known as stream frequency
(Horton 1932). The Fs value of the study area is
presented in Table 16.3. The value of Fs varies
from 1.19 to 1.33. The value of drainage density
shows a positive relation with the stream frequency suggesting that the number of stream
increases with increasing drainage density.
16.6.2.4 Form Factor (Rf)
Form factor can be defined as the ratio of the area
of the basin and square of basin length. The form
factor value varies from 0 to 1, where 0 indicates
highly elongated basin and 1 is perfectly circular
basin. The value of form factor more than 0.78
indicates perfectly circular basin. The smaller the
value of form factor, more elongated will be the
basin (Horton 1932). The Rf value of the study
area varies from 0.21 to 0.38. The Rf values in
Spiti, Tsarap Chu and Parechu river basins are
0.38, 0.28 and 0.21, respectively (Table 16.3).
16 Remote Sensing and GIS-Based Morphometric Analysis …
221