Geomorphic Threshold and Landslide - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 160

5.4 Conclusion

Threshold slope angle for two major landslide locations i.e. Tindharia and Pag-
lajhora varies from 21 . Large parts of Tindharia, Gayabari, 14 Miles Bustee,

Lower Paglajhora and Shiviter are facing the slope angle of more than average
threshold slope angle and shows absolute instability. It is also examined that more
than 60 % area of the Shivkhola Waterhsed is beyond the threshold slope angle.
The calculated critical rainfall at Tindharia and Lower Paglajhora are 105.88 and
88.93 mm/day respectively. 120.7 mm daily rainfall can occur at a recurrence
interval of 1.4 years following Gumbel ( 1954 ) and 128.507 mm daily rain has a
recurrence interval of 2 years with 50 % probability following Chow ( 1951 , 1954 ).
That means there is every possibility for the generation of geomorphic threshold for
initiation of slide due to hydrologic factor in Shivkhola watershed. Antecedent
Cumulative rainfall induced landslide analysis shows that the continuous and
uniform rate of minimum amount of rainfall (approx. less than 80 mm/day) for few
consecutive days can cross the geomorphic threshold and can introduce slope
instability condition. On the other hand, one or two day

° to 26 °

s heavy showers that are
more than 200 mm/day rain may cause devastating slope failure in the Shivkhola
Watershed. Critical slope height with 48

'

steepness may range from 5.89 to
7.80 m. Special care should be taken to reduce the height of back wall along the
main road to that of 6.00 m of less. The Interaction between physical and
anthropogenic processes leads to the initiation of geomorphic threshold that leads to
slope failure reducing the slope through internal feedback mechanism and may
proceed towards the new state of equilibrium (Fig. 5.6 ).

53 °

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