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stability classes based upon slope and speci
nite slope
stability model concept based on soil cohesion and root cohesion with the help of
determining the safety factor is put forwarded by De Smedt ( 2005 ).
c catchment area. The in
1.11.1 Hydrological Models and Slope Stability
The hydrologic system over the mountainous area is seldom simple and rarely exist
in steady state. The hydrologic response of a hill slope to rainfall leads to a water
table rise that is very dif
cult to predict. The amount and duration of rainfall and lag
time between the rainfall events, and water table rise may vary widely depending on
the hill slope con
guration, intensity of rainfall, initial saturation condition and the
saturated and un-saturated hydro-geologic properties of the hill slope materials
(De Bleeschauwer and De Smedt 2002 ). The hydrologic factors like daily rainfall
threshold, rainfall intensity, in
ltration were studied by Guzetti et al. ( 2007 ), and
Gabet et al. ( 2004 ) etc. The critical rainfall for initiating landslide was studied (r cr )
by Borga et al. ( 1998 ). The recurrence interval of rains of certain intensity above
threshold value was analysed using log probability law by Chow (1951, 1954) and
Schwab et al. ( 2002 ). Hydrological model incorporating the saturation excess
run-off were constructed by Beven and Kirkby ( 1979 ), O
Loughlin (1986), Moore
et al. (1988), Moore and Grayson (1991). A geomorphology based arti
'
cial neural
networks (GANNs) was put forward for estimating direct runoff over watersheds by
Zhang and Govindaraju (2003). Mishra et al. (2003) presented a modi
ed SCS-CN
Method. Saragni et al. ( 2007 ) evaluated three unit hydrograph models to predict the
surface runoff from a Canadian watershed. Recently, an integrated approach for
estimating surface run-off using Remote Sensing and GIS in the applied
field of
hydrological research is applied by Durbude et al. (2001), Ambazhagan et al.
(2005), Jasrotia and Singh (2006), Tripathi et al. (2002) and Zade et al. (2005).
SCS Curve Number was used for estimation of runoff by correlating generalized
land cover with hydrologic soil groups and data were derived from the SCS table by
Chandra et al. (1984), Ragan and Jackson ( 1980 ), Tiwari et al. (1991) etc. Sing
(1975) has pointed out Antecedent Moisture Condition (AMC) as the water content
present in the soil at a given time. The build-up of soil pore water pressure at the
contact between the soil mantle or weathered regolith and the underlying lithology
during rainstorms and the period of rapid snow melt was well recognized as the
triggering mechanism of slope failure and it was studied by Pierson (1977),
Swanston (1982), and Megahan (1983).
1.11.2 Landslide Susceptibility Zonation Models Concept
Landslide hazard zonation consists the division of an area into several zones, which
indicates progressive levels of landslide hazard. To constitute the zonation map of
slope instability it is necessary to understand triggering mechanism of landslides.
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