Introduction - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 39

1.9 Data Used for Quantitative Study on Landslide

In the present work, atmospheric data was collected for Kurseong Tea Research
Centre (Darjiling), day wise rainfall data was collected from the Selim Hill and
Shiviter Tea Estate, historical landslide records and others relevant information
were obtained from research articles (Starkel 1972 ; Basu and Starkel 1985; Basu
and Ghatwar 1988 ; Basu and Maiti 2001 ; Basu and Sarkar 2003; Maiti 2007 ;
Ghosh 2009b), news papers (Ananda Bazar Patrika-10/09/06, 14/06/2007, 16/07/
2007 and 18/07/2007, Telegraph-04/08/2007, Statesman-August, 2006) and Geo-
logical Survey of India Technical Report, Topographical Map from Survey of India
(SOI) and Satellite data from NRSA and District Census of Darjiling for the year
1981, 1991 and 2001 and District Gazetteers Malley).

Mountain Risk Engineering Handbook provided information about population
growth, geology, soil, natural vegetation. Dow Hill Reserve Forest Of

' of Darjiling (LSS O '

ce (Kurs-

eong), Soil Conservation Of ce (Kurseong) provided

information relating to land use and land cover and rainfall data. Satellite image
(IIRS P6/Sensor-LISS-III, Path-107, Row-052, date 18 March 2010), Modi

ce and Agricultural Of

ed
SRTM (Shuttle Radar Topographic Mission) data with scene size 10 latitude and 10
longitude (date 5 April 2008) and Google Earth Image (1 Sept. 2010) were also
used in the study. Various thematic data layers were generated using ERDAS
Imagine 8.5, Arc View and Arc GIS Software.

1.10 Existing Literature on Landslide Inducing Parameters

Among numerous literatures on slope stability, the following are of worth men-
tioning. These are grouped into four subheadings according to their major line of
contribution. The balance condition between shear strength and shear stress are
completely governed by both natural and man-made circumstances. The elements
that affect slope stability and landslides are numerous and varied, and interact in
complex and often subtle ways (Varnes 1984 ). Siddle and Ochiai (2006) summa-
rized and reviewed and divided natural factors influencing landslide into

ve major
groups: seismicity; strength, chemistry and mineralogy of soil; geology; geomor-
phology and hydrology.
Geological parameters play a pivotal role in landsliding. Siddle ( 1991 ) pointed
out that there exists an association between slope instability and different types of
regolith materials. Weathering alters the mechanical, mineralogic and hydrologic
properties of the regolith and hence acts as an important factor of slope instability in
many settings. Unstable bedding sequences are another important geological
attributes for landslide incidents. This situation occurs when mass movement on
bedding planes is triggered by either the increase in pore water pressures at the
interface between two different alternative strata, or the weakening of strength of
the clay deposit by water in ltration through the overlaying regolith layer.