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(north, south and western part) is attributed with minimum soil depth. Due to steep
slope and active soil erosion process, the marginal area is associated with close slip
plane below the slope surface due to which soil layers get saturated very easily and
causes landslide. Tindharia, Gayabari Upper, Sepoydhura Upslope, Upper Pag-
lajhora, Mahanadi, Shiviter, Gitingia are falling in the marginal minimum soil depth
area of the Shivkhola watershed. On the other hand, Shivkhola R.F., and both sides
of the main river is characterized by maximum soil depth with low intensity of
landslide phenomena. It can be inferred that shallow seated slope instability is
intimately related with minimum soil depth with steep slope.
In dry condition, around 15 sq km of the watershed is attributed by moderate to
very low landslide susceptibility and only 5 sq km is characterized with high to very
high landslide susceptibility with high frequency ratio. Under semi-saturated con-
dition 0.88 sq km area is attributed with high landslide susceptibility. The area of
high and very high landslide susceptibility has been increased in saturated soil
condition and around 2.5 sq km area is registering high landslide susceptibility with
high frequency ratio. For dry and semi-saturated condition, the area under high and
very high landslide susceptibility is 5.36 and 8.5 sq km respectively and the area
under low to very low landslide susceptibility is around 9 and 5 sq km Under
saturated soil condition small area (3.5 %) is experienced with low landslide
susceptibility having frequency ratio of 0.00. Around 14 sq km out of total area
(21 sq km) of the Watershed is being characterized by moderate to very high
landslide susceptibility. Under saturated condition, around 6 sq km areas show the
moderate landslide susceptibility with frequency ratio value of 0.39. Upper and
Lower Paglajhora, Tindharia, Shiviter and Nurbong are the places where landslide
susceptibility ranges from high to very high. Lower middle section and few places
of extreme south are characterized by moderate to very low landslide susceptibility
(Table
6.4
) under all soil saturated condition.
6.5.3.1 Stability Analysis Under Dry Condition
The slope stability map (Fig.
6.5
) under dry condition reveals that only 1.58 % area
of the watershed is experienced with very high landslide susceptibility where the
chance of landslide phenomena is also very high according to the derived frequency
ratio value (21.09). High landslide susceptibility is being found in 24.88 % area in
the watershed. Maximum area of the Shivkhola watershed (30.25 %) is characterized
by moderate landslide susceptibility where the frequency of landslide is 20.835.
More than 40 % area of the Shivkhola watershed falls under the low to very low
landslide susceptibility with frequency ratio value of 0.27 and 0.00 respectively.
6.5.3.2 Stability Analysis Under Semi-saturated Condition
Under semi-saturated condition the value of safety factor varies from 0.158 to 2.58
and 4.38 % area is under very high landslide susceptibility that is around 2.50 %
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