Geoscience Reference
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channel order, it being the lowest for the
first- order channels. The law of stream
length applied in the present study revealed that the mean length of the channel
segments of each of the successive orders of the shiv-khola watershed formed
approximately a direct geometric series. A plot of logarithms of mean stream
lengths against their respective order showed the positive exponential form of
relationship between stream order and mean stream length of the different sub-basin
of the siva-khola watershed. The length of the overland
flow is the length of no
channel flow from the basin perimeter to the nearest channel. It is an important
independent variable affecting the quantity of water required to exceed a certain
threshold of erosion. Horton (
1945
) and Schumm (
1956
) noted that the length of
overland flow approximately equals half the reciprocal of drainage density. When
the rainfall intensity exceeds soil in
fl
ltration capacity, the excess water flows over
the land surface as overland flow.
According to Gregory and Wallings (
1973
) the form factor is the governing
factor of the water courses which enter the main streams. Form factor has been
introduced by Horton (
1932
) that shows the shape of the basin.
Form Factor de
ned as the ratio of the basin area to the square of the basin
length using the following equation:
Rf =
Au
L
2
b
ð
3
:
10
Þ
where,
A
u
Basin area (km
2
)
L
b
Basin length (km).
If the basin is wider, the form factor will be comparatively higher, and conse-
quently much narrower basins have low form factor values (Gregory and Wallings
1973
). The calculated values of form factor of the six sub-basin for the shiv-khola
watershed are 0.12, 0.40, 0.45, 0.36, 0.25 and 0.52 respectively which reveals the
sub-basin-I and sub-basin-V are more elongated than other basins and that is why
the erosional activities become prominent within the two sub-basin. The circularity
index, (Rc) is expressed as the shape of the basin that was used by Miller (
1953
).
The circularity ratio is dimensionless, whose values vary from 0 to 1. The circu-
larity ratio obtained from the ratio of the basin area (Au) to the area of a circle (Ac)
having equal perimeter as the perimeter of the drainage basin.
Rc =
Au
Ac
ð
3
:
11
Þ
where,
Au Area of the basin
Ac
Area of the circle with same perimeter as the basin.
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