Geoscience Reference
In-Depth Information
diversity of forms and the complexity of interrelationships. The practical rele-
vance of landslide can be recognized only by the systematic and thorough study
of geomorphic attributes such as relief, geology, and soil. A detailed and inte-
grated investigation of the geological structure of the area, the petrographical and
physical properties of the rocks and the local hydro-geological conditions with
changing slope of the Shivkhola watershed will help to prepare the corrective and
preventive measures in a reasonable scheme. The Shivkhola Watershed provides a
wide range of elevation from 2,040 m in north-west to 300 m in south-east. The
middle section of both north facing slope and south facing slope is attributed with
sudden and abrupt steepness. Geologically, the study area owns seven major
lithological units with varying degree of resistance and intensity of landslide
phenomena. The development of drainage network in the Shivkhola watershed is
the outcome of elevation and slope which are the ubiquitous elements of land-
scape, the structure and tectonic history of the area, and the existing humid
climate. There is continuous branching and headward extension as well as the
sharpening of the interfluves area caused by the present drainage network within
the basin. The soil up to the depth of 1.5 m is heavily disintegrated and
decomposed in the study area. The existence of
finer to large size soil-rock
composition has aggravated the problem of soil erosion and soil slip in the
Shivkhola Watershed. Besides the size of the soil particles, the mineralogical
composition of the soil changes all the physical and chemical properties within
the soil. The amount of sand, silt and clay; porosity, water holding capacity and
bulk density; cohesion; and saturated depth of the soil are some of the signi
cant
properties which continuously changing the actual nature of the soil-rock prop-
erties of the hill slope causing slope failure.
The study of various geomorphic attributes and their interrelations generally
offers a concrete accounts and evidences on the morphological characteristics and
landscape evolution. The analysis of relief, lithology, dissection, ruggedness,
topographic index, slope, aspect and curvature in relation to slope instability will
contribute an impression about the degree of importance and dimension of indi-
vidual geomorphic attribute. Landslide potentiality was estimated incorporating
landslide inventory map (Fig.
2.1
) for all the geomorphic attributes by determining
class/ranges wise Landslide Potentiality Index Value (LPIV) of each factor by
means of a ratio (Eq.
2.1
) between the number of cells/pixels disturbed by land-
slides and the total number of cells/pixels for that speci
c class. More details of
these procedures were obtained in other studies (Vieira et al.
1998
; Guimaraes et al.
1999
). Topographic Index (TI) Value was calculated in consultation with slope and
upslope contributing area. The effectiveness of all these parameters were being
influenced by hydrologic conditions and other atmospheric processes. Anderson
and Burt (
1978
) presented the role of topography in controlling through flow
generation and related landslips. GIS tools were applied for the identi
cation of
topographic settings conducive to landslide occurrences by Gao (
1993
). Various
geomorphic models were being introduced for understanding slope instability by
Beven and Kirkby (
1979
), Ahnert (
1987
), Montgomery et al. (
1994
), and Dietrich
et al. (
1998
). Cruz (
2000
) studied in detail the role of geomorphic processes on
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