The Rf value of the study area indicates that
basins are sub-circular and elongated in shape.
16.6.2.5 Circulatory Ratio (Rc)
The circulatory ratio is mainly concerned with
the length and frequency of streams, geological
structure, land use/land cover, climate, relief and
slope of the basin. A circulatory ratio is the ratio
of the area of the circle having the same circumference as the perimeter of the basin (Miller
1953). The Rc values of the study area vary from
0.24 to 0.49. The Rc values of Spiti, Tsarap Chu
and Parechu river basin are 0.49, 0.24 and 0.28,
respectively. The Rc value of Spiti river basin
indicates that it is sub-circular in shape, while the
Rc value of Tsarap Chu and Parechu basins
indicate that it is elongated in shape. The Rc
values of the study area are given in Table 16.3.
A circular basin appears to be more efficient in
the discharge of runoff than that of an elongated
basin (Singh and Singh 1997).
16.6.2.6 Elongation Ratio (Re)
Elongation ratio is the ratio of diameter of a
circle of the same area as the drainage basin and
the maximum length of the basin (Schumm
1956). The values of elongation ratio generally
vary from 0.6 to 1.0 over a wide variety of climatic condition and geologic types. The elongation ratio value near to 1 indicates region of
very low relief, whereas values between 0.6 and
0.8 are generally associated with strong relief and
steep ground slope (Strahler 1964). The Re values of study area vary from 0.51 to 0.70. The Rc
values of Spiti, Tsarap Chu and Parechu are 0.51,
0.60 and 0.70 indicating high relief and steep
slope.
16.6.2.7 Length of Overland Flow (Lg)
The length of overland flow is the length of water
over the ground surface before it gets concentrated into definite stream channel (Horton 1945).
The Lg values of Spiti, Tsarap Chu and Parechu
are 2.16, 1.57 and 1.96 km. The length of overland flow is approximately equal to the half of
the reciprocal of drainage density. This factor is
related inversely to the average slope of the
channel and is quiet synonymous with the length
of sheet flow to a large degree.
16.6.3 Relief Aspects
The elevation difference between the highest and
lowest point on the valley floor of the region is
known as relief. The relief measurement includes
perimeter, basin length, relative relief and relief
ratio. The values of the perimeter, basin length,
total relief and relief ratio of all the three basins
are given in Table 16.4.
16.6.3.1 Total Relief
Total relief is the difference between the maximum and minimum elevations in the basin. The
maximum height of the Spiti basin is 6600 m and
the lowest is 2995 m. Therefore, the total relief
of the basin is 3605 m. The maximum height of
the Tsarap Chu basin is 6153 m and the lowest is
4216 m. Thus, the total relief of the basin is
1937 m. The maximum height of the Parechu
basin is 6600 m and the lowest is 4479 m.
Therefore, the total relief of the basin is 2121 m.
16.6.3.2 Basin Length (L)
Basin length is the longest length of the basin,
from the catchment to the point of confluence.
The length of the Spiti, Tsarap Chu and Parechu
basins are 118, 52 and 55 km, respectively.
16.6.3.3 Relief Ratio (Rh)
The relief ratio is the ratio of maximum relief to
the horizontal distance of the basin parallel to the
principal drainage line is termed as relief ratio.
“Relief ratio measures the overall steepness of a
drainage basin and is an indicator of the intensity
of erosion process operating on the slope of the
basin” (Schumm 1956). The relief ratio normally
decreases with the increasing area and size of
sub-basin of a given drainage basin (Gottschalk
1964). The values of relief ratio (Rh) of the study
area vary from 0.30 to 0.38 indicating high relief
and steep slope (Table 16.4).
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A. Husain and P. Kumar
basins are sub-circular and elongated in shape.
16.6.2.5 Circulatory Ratio (Rc)
The circulatory ratio is mainly concerned with
the length and frequency of streams, geological
structure, land use/land cover, climate, relief and
slope of the basin. A circulatory ratio is the ratio
of the area of the circle having the same circumference as the perimeter of the basin (Miller
1953). The Rc values of the study area vary from
0.24 to 0.49. The Rc values of Spiti, Tsarap Chu
and Parechu river basin are 0.49, 0.24 and 0.28,
respectively. The Rc value of Spiti river basin
indicates that it is sub-circular in shape, while the
Rc value of Tsarap Chu and Parechu basins
indicate that it is elongated in shape. The Rc
values of the study area are given in Table 16.3.
A circular basin appears to be more efficient in
the discharge of runoff than that of an elongated
basin (Singh and Singh 1997).
16.6.2.6 Elongation Ratio (Re)
Elongation ratio is the ratio of diameter of a
circle of the same area as the drainage basin and
the maximum length of the basin (Schumm
1956). The values of elongation ratio generally
vary from 0.6 to 1.0 over a wide variety of climatic condition and geologic types. The elongation ratio value near to 1 indicates region of
very low relief, whereas values between 0.6 and
0.8 are generally associated with strong relief and
steep ground slope (Strahler 1964). The Re values of study area vary from 0.51 to 0.70. The Rc
values of Spiti, Tsarap Chu and Parechu are 0.51,
0.60 and 0.70 indicating high relief and steep
slope.
16.6.2.7 Length of Overland Flow (Lg)
The length of overland flow is the length of water
over the ground surface before it gets concentrated into definite stream channel (Horton 1945).
The Lg values of Spiti, Tsarap Chu and Parechu
are 2.16, 1.57 and 1.96 km. The length of overland flow is approximately equal to the half of
the reciprocal of drainage density. This factor is
related inversely to the average slope of the
channel and is quiet synonymous with the length
of sheet flow to a large degree.
16.6.3 Relief Aspects
The elevation difference between the highest and
lowest point on the valley floor of the region is
known as relief. The relief measurement includes
perimeter, basin length, relative relief and relief
ratio. The values of the perimeter, basin length,
total relief and relief ratio of all the three basins
are given in Table 16.4.
16.6.3.1 Total Relief
Total relief is the difference between the maximum and minimum elevations in the basin. The
maximum height of the Spiti basin is 6600 m and
the lowest is 2995 m. Therefore, the total relief
of the basin is 3605 m. The maximum height of
the Tsarap Chu basin is 6153 m and the lowest is
4216 m. Thus, the total relief of the basin is
1937 m. The maximum height of the Parechu
basin is 6600 m and the lowest is 4479 m.
Therefore, the total relief of the basin is 2121 m.
16.6.3.2 Basin Length (L)
Basin length is the longest length of the basin,
from the catchment to the point of confluence.
The length of the Spiti, Tsarap Chu and Parechu
basins are 118, 52 and 55 km, respectively.
16.6.3.3 Relief Ratio (Rh)
The relief ratio is the ratio of maximum relief to
the horizontal distance of the basin parallel to the
principal drainage line is termed as relief ratio.
“Relief ratio measures the overall steepness of a
drainage basin and is an indicator of the intensity
of erosion process operating on the slope of the
basin” (Schumm 1956). The relief ratio normally
decreases with the increasing area and size of
sub-basin of a given drainage basin (Gottschalk
1964). The values of relief ratio (Rh) of the study
area vary from 0.30 to 0.38 indicating high relief
and steep slope (Table 16.4).
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A. Husain and P. Kumar