Geo-spatial Variability of Physiographic Parameters and Landslide Potentiality - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 63

Table 2.1 Hypsometric analysis
Elevation (m) (h)

Area above the elevation (km 2 ) (a)

a/A Cumulative a/A h/H

300 1.23 0.06 0.06 0.16

400 5.72 0.26 0.32 0.22

600 5.06 0.23 0.55 0.33

800 3.79 0.18 0.73 0.44

1,000 2.34 0.11 0.84 0.55

1,200 1.24 0.06 0.90 0.66

1,400 1.26 0.05 0.95 0.77

1,600 0.81 0.03 0.98 0.88

1,800 0.58 0.02 1.00 1.00

Total area 22.05 km 2 , H maximum elevationfriction angle ranges betweenA total area

2.2.3 Hypsometric Analysis

In the present study to develop hypsometric curve the ratio between relative height
(h/H) and relative area (a/A) were plotted on the ordinate and abscissa respectively to
recognize the stages of cycle of erosion in the Shivkhola Watershed after Strahler
( 1952 ). The hypsometric analysis of the said basin shows the distribution of area
against respective elevation zones (Table 2.1 ). The study shows that maximum basin
area lies within 400 600 m altitude and gradually the area under each successive zone

of 100 m is decreasing at a diminishing rate. The area below the curve is waiting for
erosion and so the ratio of the two represents the phase of erosion and thus the said
basin is approaching to mature stage where maximum of the areas are in sloppy
condition and no such flat surface is seen. The ridges are steep enough favouring easy
drainage and the absence of flat land is the basic hindrance in the land use and thus the
land resource cannot be used with full utility. Any attempt for reduction of slope at one
place for effective use increase the slope at other and thus introduces instability of
slope which sets instability in the other and the total system becomes instable.
Here, hypsometric integral (H.I.) has been accepted as an important morpho-
metric indicator of the stage of basin development which is the percentage of the
total volume of the basin area below the curve and thus it reveals the volume of area
unconsumed by the dynamic wheels of erosion (Strahler 1952 ). The derived
hypsometric integral value is 0.46 which depict the area is still passing through the
late youthful stage of landform development with moderate to high drainage density
which may invite havoc slope failure.

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2.2.4 Lithological Composition and Landslide Potentiality

Mallet ( 1874 ) stated that in the Darjeeling territory the “ Gondwana ” rocks are

overlain by the metamorphic rocks, which are termed as “ Darjeeling ” (mainly mica-