Introduction - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 38

geo-technical parameters 1-D Slope stability model was used to prepare land-
slide susceptibility maps under dry, semi-saturated and saturated condition.

The range of cohesion and friction angle of different soil was adopted from
Foundation of Engineering Geology (Waltham 2002 ) for the analysis of slope
stability. Similarly, saturated soil density of rock was adopted from the

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eld
experiences done by Deoja et al. (Mountain Risk Engineering Handbook 1991 )
and Speci c Yield from Basic Ground-water Hydrology (Ralph C. Heath).

The values of the Safety factors were calculated dividing the value of shear
stress

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by the value of Shear strength

s ¼ r 1 r 3
2

sin 2 a ðÞ ¼ r n tan u þ C .

The angle that fractures ( ʱ ) should theoretically make with the greatest principal

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axis is:

a ¼ 45 u= 2 : ð 1 : 7 Þ

Landslide susceptibility map of the Shivkhola watershed was prepared using
remotely-sensed data,

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field surveys and GIS tools applying Analytical Hierarchy
Approach (AHA)/Decision Support System after Saaty ( 1990 , 1994 ), Saaty and
Vargas ( 2001 ) and Yang et al. (2006). In this method, landslide susceptibility
index (LSI) value for each pixel was computed by summation of each factor s

weight multiplied by class weight (or rating) of each referred factor which is
expressed as under:

'

X

n

LSI ¼ ð W i R i Þ ð 1 : 8 Þ

i¼1

where, R i and W i are class weight (rating value) and factor weight.

Accuracy assessment of landslide hazard map was being performed after
Congalton ( 1991 ).

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Landslide hazard risk map of the Shivkhola Watershed was made with the help
of following equation.

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Risk ¼ Hazard Exposure : ð 1 : 9 Þ

Risk exposure was calculated as a combination of three data layers i.e. weighted
land use/land cover, road contributing area and settlement density.

Management proposal to mitigate landslide and also to avoid the landslide was
constructed following Royster (1979), Collison and Bhandari (1988), Valdiya
( 1987 ), Carrara et al. ( 1995 ), Pla (1997), Montgomery et al. ( 1989 ) and Howell
( 2001 ).

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