Geoscience Reference
In-Depth Information
Chapter 5
Geomorphic Threshold and Landslide
Abstract The present study established the link between critical rainfall (c
r
),
critical slope angle (c
s
), critical height (c
h
) and landslide. The critical rainfall was
estimated incorporating geo-technical parameters such as angle of internal friction
(
), upslope contributing area (UCA), transmissivity (T), wet soil
density (p
s
), and density of water (p
w
). Cohesion (c), angle of internal friction (
u
), slope angle (
⊖
u
),
unit weight of the materials (
) were taken into account to
estimate critical slope height. The thickness of total soil (h), thickness of saturated
soil (z), wet soil density (Ps), density of water (Pw), friction angle (
γ
), and slope angle (
⊖
u
) and slope
steepness (
) were considered to derive critical slope angle. Study attempted to
calculate critical rain to slope failure and its return period. The temporal probability
of the landslide events were estimated applying Binomial and Poisson Probability
Distribution Model based on past landslide occurrences. The probability model
suggests that occurrences of major landslides with more than 90 % certainty could
be expected in every 7.5 years.
⊖
Keywords Critical slope
Critical height
Critical rainfall
Return period
Probability model
5.1 Introduction
Geomorphic threshold is signi
cant parameters in analyzing the stability condition
of particular spatial unit in a quantitative way. According to White et al. (
1996
)
the
minimum or maximum level of some quantity needed for a process to take place or
a state to change is generally de
'
. Varnes (
1978
) studied the role
of minimum intensity and duration of rainfall to cause a landslide of shallow soil
slips, debris flows, debris slides or slumps. Crozier (
1997
) opined a maximum
threshold, beyond which there is 100 % chances of occurrences of the process at
any time when the threshold value is exceeded. The most commonly investigated
threshold parameters such as critical slope, critical slope height and critical rainfall
ned as threshold
'
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