Landslide Mitigation - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 250

Garubathan formation and Reyang formation are very much attributed with
weaknesses planes and associated land slide phenomena which are common in the
right hand side of the main Shivkhola River and are to be brought under such
management technique to minimize the slope failure. The potential dissection and
roughness of the topography is very high in the north, north-east, east, south and
south-east facing escarpment slope of Lower Paglajhora, Mahanadi, Shiviter,
Gayabari Up-slope and Tindharia through which the Hill Cart Road and Railway
Line is passing. At all those places slope is attributed with high positive curvature
that invites immediate drainage concentration and makes the places detrimental to
slope failure. The extreme lower segment of the slope is registered with high
negative curvature caused by active toe erosion of the main river that also invites
drainage concentration. The places of more dissection and the roughness should be
avoided for the establishment of new settlement and further construction to reduce
the landslide hazard risk. Besides, the diversion of drainage lines just above the
potentially active slided area and cementation by developing concrete steps along
the drainage lines can reduce the concentration of both surface and sub-surface
drainage water and reduce the pore-water pressure. The more convexity of the slope
could also be reduced modifying the topography up to the threshold slope angle of
24

°

that can control more drainage concentration and make the slope more stable.
The extreme middle and lower most part of the basin is characterized by cut and ll

terrace where slope stability is very high due to less slope steepness. Sub-water-
shed-II is more susceptible for slope instability as most of it lies on steeper slope
and is followed by sub-watershed-III and I.
The study envisages that the middle most part of a particular slope facet is more
prone to failure due to easy and maximum drainage concentration. The extreme
marginal part of the basin is registered with low landslide potentiality because of the
less drainage concentration. The areas lying in the mid-central part of the slope
segment in Lower Paglajhora, Tindharia, Gayabari and Shiviter are dominated by
moderate level of drainage density indicating the more saturation excess surface
water which is an indicator of potential erosion and instability. All the rst order

tributaries are characterized by head-ward extension and branching which produces
sharpened interfluves and make the slope steeper beyond threshold slope angle. The
central part of the watershed shows the maximum concentration of drainage but due
to gentle slope gradient the propensity to slope failure is less. Watershed-III is more
prone to slope instability as it possesses higher drainage and deserves more
attention for management. In watershed-III nearly 92 % of the basin area posses the
lower value of Constant of Channel Maintenance and it means higher drainage
density and is thus detrimental to the slope and soil stability.
The upslope contributing area increases toward the main tributaries where the
concentration of channels and accumulation of water promotes more excess
moisture and instability of slope and soil. The large numbers of drainage concen-
tration at Lower Paglajhora, Shiviter, 14 Miles Bustee and Gayabari have made the
places more susceptible to soil erosion and slope failure. The places of landslip
induced by drainage concentration should be brought under the measures of catch
water concrete drains and installations of horizontal pipe with

filters to extract