Natural Hazards and Earth System Science
www.nat-hazards-earth-syst-sci.net
1561-8633
1684-9981
7
5
2007
10.5194/nhess-7-523-2007
http://www.nat-hazards-earth-syst-sci.net/7/523/2007/
http://www.nat-hazards-earth-syst-sci.net/7/523/2007/nhess-7-523-2007.html
http://www.nat-hazards-earth-syst-sci.net/7/523/2007/nhess-7-523-2007.pdf
523
534
2007-09-12
Soil moisture storage and hillslope stability
A. Talebi
ali.talebi@wur.nl
R. Uijlenhoet
P. A. Troch
Chair of Hydrology and Quantitative Water Management, Wageningen University, Wageningen, The Netherlands
Faculty of Natural Resource, Yazd University, Yazd, P.O. Box 89195-741, Iran
Department of Hydrology and Water Resources, The University of Arizona, Tucson, AZ 85721, USA
Recently, we presented a steady-state analytical hillslope stability model
to study rain-induced shallow landslides. This model is based on kinematic
wave dynamics of saturated subsurface storage and the infinite slope
stability assumption. Here we apply the model to investigate the effect of
neglecting the unsaturated storage on the assessment of slope stability in
the steady-state hydrology. For that purpose we extend the hydrological
model to compute the soil pore pressure distribution over the entire flow
domain. We also apply this model for hillslopes with non-constant soil depth
to compare the stability of different hillslopes and to find the critical
slip surface in hillslopes with different geometric characteristics. In
order to do this, we incorporate more complex approaches to compute slope
stability (Janbu's non-circular method and Bishop's simplified method) in
the steady-state analytical hillslope stability model. We compare the safety
factor (<i>FS</i>) derived from the infinite slope stability method and the more
complex approach for two cases: with and without the soil moisture profile
in the unsaturated zone. We apply this extended hillslope stability model to
nine characteristic hillslope types with three different profile curvatures
(concave, straight, convex) and three different plan shapes (convergent,
parallel, divergent). Overall, we find that unsaturated zone storage does
not play a critical role in determining the factor of safety for shallow and
deep landslides. As a result, the effect of the unsaturated zone storage on
slope stability can be neglected in the steady-state hydrology and one can
assume the same bulk specific weight below and above the water table. We
find that steep slopes with concave profile and convergent plan shape have
the least stability. We also demonstrate that in hillslopes with
non-constant soil depth (possible deep landslides), the ones with convex
profiles and convergent plan shapes have slip surfaces with the minimum
safety factor near the outlet region. In general, when plan shape changes
from divergent to convergent, stability decreases for all length profiles.
Finally, we show that the applied slope stability methods and steady-state
hydrology model based on the relative saturated storage can be used safely
to investigate the relation between hillslope geometry and hillslope
stability.
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