Landslide Mitigation - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 251

sub-surface water that can resist seepage and reduce pore-water pressure and bring
stability to the slope and soil.
Land use and land cover plays a signi

cant role in the Shivkhola Watershed as it
influences surface run-off, slope material saturation, potential retention of rainfall
and pore-water pressure. Since 1950, rapid rate of deforestation and clearing of
forest cover in connection to the expansion of settlement, establishment of
communication lines and ful llment of the socio-economic demand of the local

people have aggravated the problems of soil loss and slope failure. The establish-
ment of settlement and communication lines and transformation to flat surface
invites the concentration of drainage water and make steep back wall very much
critical to slope failure. In Shivkhola Watershed, degraded forest rank

first in terms
of triggering land use factor of slope instability and that is followed by settlement,
road, open forest, tea garden, mixed forest, jungle, dense forest, bare surface and
agricultural land. The major landslide sites Lower Paglajhora is associated with
degraded forest and road contributing area (RCA); Tindharia with communication
lines and settlement concentration; 14 Miles Bustee with RCA; and Shiviter with
haphazard concentration of settlement, degraded forest and open forest. Spatially,
the sub-watershed-I, III, IV and VI are dominated by degraded forest, settlement
and road and tea garden. To keep the slope safe from slope failure, the human
intervention over steep escarpment slope should be stopped at any cost. Not only
that the places characterized by degraded forest, open forest and bare surface will
have to be brought under effective afforestation and plantation programme and that
would be monitored by the local inhabitants. A strict Government rules against the
illegal modi cation of slope and clearance of forest cover must be imposed for the

healthy growth of vegetation that can maintain the stability of soil and slope.
The dense forest, down slope jungle, mixed forest, tea garden, and open forest
area are characterized by fair to good hydrological condition with the curve number
(CN) value of 75 that shows maximum retention and minimum run-off as well as
lower rate of soil loss. On the other hand settlement, road, bare surface, upslope
degraded forest are attributed with the Curve Number (CN) of more than 76 which
is an indicator of minimum retention and maximum run-off and soil erosion. The
derived instability rank based on CN, retention, run-off, and landslide potentiality
suggests that Sub-watershed VI, I and III have to be paid more attention for a proper
management of land, water and soil as these three are characterized by maximum
run-off and high susceptibility to slope failure. To manage the land, water and soil
in all these three sub-watersheds a well accepted land use planning should be
launched immediately by introducing several afforestations programme with active
community participation. The people of landslide prone area should also be
restricted from constructional works during the moisture period i.e. June-
September.
The most landslide prone area, the Shivkhola watershed of Kurseong Sub-div-
ition of Darjiling Himalaya registers the continuous growth of household and
population. This continuously adds huge population pressure on the existing land
and soil resources. The growth rate of household during the period of 1981

1991

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and 1991 2001 are 75 and 169 % respectively where as the growth rate of

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