Geo-spatial Variability of Physiographic Parameters and Landslide Potentiality - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 71

Table 2.6 Slope aspect and landslide potentiality index (LPIV)
Aspect Number of

pixels (F1)

Number of landslide
affected pixels (F2)

Landslide potentiality index
(LPI) = (F2/F1 × 100)

Flat 784 24 3.06

North 3,879 665 17.14

North east 3,797 443 11.67

East 4,346 675 15.53

South east 6,290 789 12.54

South 4,556 597 13.10

South west 3,332 35 1.05

West 2,870 69 2.40

North west 3,277 76 2.32

respectively (Table 2.6 ). South west, west, northwest and middle section is attributed
as minimum number of landslide occurrences phenomena as well as landslide
potentiality index (LPIV). According to the number of pixels affected by slope failure
south east facing slope rank

first which is followed by east, north, south, north east,
north west, west, and south west. Upper halve of the watershed is dominated by south
east and south ward facing slope and lower halve is dominated by east and north ward
facing slope with LPIV >11 (Table 2.6 ). Such landslide prone facets are closely
associated with maximum slope and relief which is found at upper and lower
Paglajhora, Shiviter T.E., Gayabari Lower slope and Tindharia (Fig. 2.7 ).

2.2.8 The Surface Curvature and Landslide Potentiality

The retention of moisture in the soil depends mainly on the convexity (positive
curvature) or concavity (negative curvature) of surface. Slope curvature plays a
signi cant role in changing landform character (Gilbert 1909 ). The concave surface

holds moisture for long where the convex surface drains moisture immediately. The
curvature value represents the morphology of the topography. A positive curvature
represents the surface is upwardly convex at the pixel and a negative curvature
value represents the surface is upwardly concave at that pixel. A value of 0 indi-
cates that the surface is flat. The more positive and negative curvature value
indicates the surface is more susceptible to landslide occurrences. The reason for
this is that following heavy rainfall, a concave slope contains more water for a
longer period and saturates the soil perfectly and also reduces the cohesiveness
within soil. On the other hand a convex slope is generally more exposed to frequent
expansion and contraction processes which lead to the disintegration and decom-
position of rocks. The presence of decomposed or loosened materials along the
convex slope allows water particles to move downward, which is the triggering
mechanism of landslide phenomena.