Landslide Mitigation - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 253

rain in landsliding should be transmitted to the people through electronic media
which can aware the people to avoid the negative impact of slope failure.
In the Shivkhola Watershed, Tindharia Tea Garden, Lower Paglajhora (14 Miles
Bustee), Proper Paglajhora, Tindharia Proper (Rly. Stn.), Shiviter Tea Garden,
Sepoydhura T.E., Nurbong T.E., and Lower Gayabari are unstable under saturated
condition where safety factor values are lying below . At all those places

cohesion and angle of internal friction is very low. Friction angle ranges between
19

' 1 '

and cohesion varies from 0.0355 to 0.162. One dimensional (1D) slope
stability model based landslide susceptibility maps for dry, semi-saturated and
saturated condition indicates that here is a tendency of an increase in areal extension
of high to very high landslide susceptibility area in saturated soil condition. Under
saturated condition more than 50 % area are characterized by high to very high
landslide susceptibility whereas under semi-saturated condition more than 35 %
area is dominated by high landslide susceptibility. This situation demonstrates that
soil saturation and reduction of soil cohesion is the important landslide contributing
factor in the Shivkhola Watershed. To monitor the soil saturation and cohesion,
sub-surface drainage monitoring and draining of seepage water by boreholes could
be the best stabilizing factors in the existing weak lithological composition. The
application of geotextile method and introduction of

° and 26 °

first growing grasses over
fragile lithology can bring stability over steep unstable slope. Besides the con-
struction retaining walls and breast wall, jhora training through concrete structure
and cementation of cracks and weaknesses planes can bring the stability to the soil
and land.
The spatial distribution of slope instability of six individual sub-watersheds in
the Shivkhola Basin could be well explained by means of the interaction between
morphometric, geometric and hydrologic factors. The synthesis of basin geometry
such as Form Factor, Elongation ratio, Circularity Ratio, Elipticity Index, Com-
pactness Coef cient and Length of Overland Flow reveals the composite ranking in

terms drainage ef rst

priority should be given for rational management of land, water and soil in
sub-watershed-I and II, which is followed by IV, III, VI and V. It is also seen that
the sub-watershed-I and II are most vulnerable due to steep slope, high drainage
ef

ciency. On the basis of total composite index values (CIV),

ciency, friable lithological composition and more anthropogenic pressure.
Landslide susceptibility analysis based on the landslide hazard evaluation factor
rating approach (LHEF) shows that PaglaJhora, Gayabari, Tindharia, Northern and
central part of Shivitar T.E., Tindharia T.E., and Gitingia T.E. are the places of very
much susceptible to catastrophic slope failure with positive relationship between
landslide triggering factors and landslide susceptibility values. On the other hand
Analytical Hierarchy Process (AHP) based prepared landslide susceptibility map
reveals that Paglajhora, 14 Miles Bustee, Tindharia, Nurbong and Shiviter are
experiencing high to very high landslide susceptibility. But no danger of landslide
exists at the places of Gitingia, Sepoydhura, lower Gayabari, extreme mid, lower
and marginal section of the watershed and lower slope of Tindharia. The traf c,

property, and life are under threat at the places of Lower Paglajhora, Tindharia (near
railway station), Shiviter tea estate and Tindharia Tea Garden where the slope