Geoscience Reference
In-Depth Information
occurrences phenomena (Dutta
1966
). Since 1968, the Shivkhola watershed of
Darjiling Himalaya faced 128 approachable landslide events, of which 76 events
were identi
ed as reactivated (not 70 m away from old slided area) and 52 as fresh
events (70 m away from the old slided area) (Appendix D, Table D.1). The
considered landslide events took place in 16 years and out of which 12 years were
recognized as the major landslide years. All the landslide events occurred during the
monsoon period being triggered by continuous and heavy showers. Rainfall on all
the major landslide events date was more than the critical rainfall calculated after
Borga et al. (
1998
). Most of the landslide events occurred in the lithological unit of
Darjeeling Gneiss, Daling, Damuda and Siwalik.
In the present study of landslide hazard risk mapping in Shivkhola Watershed of
Darjiling Himalaya prioritized class ranking value (PCRV) and prioritized factors
rating value (PFRV) for each thematic data layers and their consistency checking
was accomplished through pair-wise comparison matrix as described by Saaty
(
1980
,
1990
,
1994
), and Saaty and Vargas (
2001
). Landslide hazard risk map was
made integrating landslide susceptibility map and landslide risk exposure map on
ARC GIS platform to identify the spatial distribution of potential risk prone area.
In the Shivkhola Watershed, Lower Paglajhora, Tindharia, Shiviter and Maha-
nadi are the major and prominent landslide location sites where settlement,
communication lines, and tea garden area are being affected severely. Since 1968,
Paglajhora alone has had 10 landslide events, all in the above mentioned landslide
event years. The majority of these landslides was dangerous as in most of the events
Hill Cart Road (NH-55) was affected and the communication line between Siliguri
and Darjiling was completely interrupted, from days to month. Paglajhora sinking
zone faced massive slope failures in 1998, 2002, 2005 and 2011 which indicates
that the occurrence of landslides in the region is ongoing. This poses a tremendous
threat to upslope settlement and Hill Cart Road (life line between Siliguri and
Darjiling Town). The landslide events at Tindharia also used to cut-off the Hill Cart
Road and brought tremendous threat to tourists, upslope settlements and tea
gardens. In Shiviter, around 8 acres of land were destroyed by the destructive slope
failure in the past 10 years. The physiographic con
guration (arcuate) that provide a
favourable condition for producing hydrostatic pressure, proximity to Main Central
Thrust (MCT) and Main Boundary thrust (MBT), intensely fractured and sheared
bed rock, toe cutting and headward erosion of debris covered slope by fast flowing
tributaries, immense pressure over the fragile slope materials by man-made concrete
structure, moderate to steep slope gradient, improper drainage and accumulation of
highly anisotropic materials with a great thickness and low shearing resistance have
made these landslide locations in the Shivkhola watershed most unstable in char-
acter. The main purpose of the present study is to prepare landslide susceptibility
map and landslide hazard risk map applying RS and GIS semi-quantitative
approach and to compare risk dominated part of Paglajhora, Tindharia, and Shiviter
with the prepared risk map by incorporating landslide inventory statistics and
frequency ratio (FR) analysis.
Search WWH ::
Custom Search