Abstract
Abstract. Recently, D'Odorico and Fagherazzi (2003) proposed "A probabilistic model of rainfall-triggered shallow landslides in hollows" (Water Resour. Res., 39, 2003). Their model describes the long-term evolution of colluvial deposits through a probabilistic soil mass balance at a point. Further building blocks of the model are: an infinite-slope stability analysis; a steady-state kinematic wave model (KW) of hollow groundwater hydrology; and a statistical model relating intensity, duration, and frequency of extreme precipitation. Here we extend the work of D'Odorico and Fagherazzi (2003) by incorporating a more realistic description of hollow hydrology (hillslope storage Boussinesq model, HSB) such that this model can also be applied to more gentle slopes and hollows with different plan shapes. We show that results obtained using the KW and HSB models are significantly different as in the KW model the diffusion term is ignored. We generalize our results by examining the stability of several hollow types with different plan shapes (different convergence degree). For each hollow type, the minimum value of the landslide-triggering saturated depth corresponding to the triggering precipitation (critical recharge rate) is computed for steep and gentle hollows. Long term analysis of shallow landslides by the presented model illustrates that all hollows show a quite different behavior from the stability view point. In hollows with more convergence, landslide occurrence is limited by the supply of deposits (supply limited regime) or rainfall events (event limited regime) while hollows with low convergence degree are unconditionally stable regardless of the soil thickness or rainfall intensity. Overall, our results show that in addition to the effect of slope angle, plan shape (convergence degree) also controls the subsurface flow and this process affects the probability distribution of landslide occurrence in different hollows. Finally, we conclude that incorporating a more realistic description of hollow hydrology (instead of the KW model) in landslide probability models is necessary, especially for hollows with high convergence degree which are more susceptible to landsliding.
Highlights
The relationship between the return period of rainfall and shallow landslides has attracted the interest of numerous researchers (e.g. Dietrich and Dunne, 1978; Montgomery et al, 1998; Iverson, 2000; Borga et al, 2002; D’Odorico et al, 2005; Rosso et al, 2006) because rainfall is the most frequent landslide-triggering factor in many regions in the world
As the purpose of this study is to investigate the effect of hollow geometry and hydrology on landslide probability, we employ the subsurface flow similarity parameter for complex hollows proposed by Berne et al (2005)
As the aim of this paper is to investigate the effect of geometry and hydrology of hollows on www.nat-hazards-earth-syst-sci.net/8/733/2008/
Summary
The relationship between the return period of rainfall and shallow landslides has attracted the interest of numerous researchers (e.g. Dietrich and Dunne, 1978; Montgomery et al, 1998; Iverson, 2000; Borga et al, 2002; D’Odorico et al, 2005; Rosso et al, 2006) because rainfall is the most frequent landslide-triggering factor in many regions in the world. The relationship between the return period of rainfall and shallow landslides has attracted the interest of numerous researchers Dietrich and Dunne, 1978; Montgomery et al, 1998; Iverson, 2000; Borga et al, 2002; D’Odorico et al, 2005; Rosso et al, 2006) because rainfall is the most frequent landslide-triggering factor in many regions in the world. In steep soil-mantled landscapes, landslides tend to occur in topographic hollows due to convergence of water and accumulation of colluvial soils that leads to a cycle of periodic filling and excavation by landsliding (Dietrich and Dunne, 1978). Shallow landsliding is a stochastic process, and understanding what controls the return period is crucial for risk assessment (Sidle et al, 1985; Iida, 1999; D’Odorico and Fagherazzi, 2003). To estimate the long-term susceptibility to shallow landsliding, a combined model of soil depth development and rainstorm occurrence is needed, since both of these factors control the recurrence interval of shallow landsliding (Iida, 2004).
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