An advanced process-based distributed model for the investigation of rainfall-induced landslides: The effect of process representation and boundary conditions

Abstract

Extreme rainfall events are the major driver of shallow landslide occurrences in mountainous and steep terrain regions around the world. Subsurface hydrology has a dominant role on the initiation of rainfall-induced shallow landslides, since changes in the soil water content affect significantly the soil shear strength. Rainfall infiltration produces an increase of soil water potential, which is followed by a rapid drop in apparent cohesion. Especially on steep slopes of shallow soils, this loss of shear strength can lead to failure even in unsaturated conditions before positive water pressures are developed. We present HYDROlisthisis, a process-based model, fully distributed in space with fine time resolution, in order to investigate the interactions between surface and subsurface hydrology and shallow landslides initiation. Fundamental elements of the approach are the dependence of shear strength on the three-dimensional (3-D) field of soil water potential, as well as the temporal evolution of soil water potential during the wetting and drying phases. Specifically, 3-D variably saturated flow conditions, including soil hydraulic hysteresis and preferential flow phenomena, are simulated for the subsurface flow, coupled with a surface runoff routine based on the kinematic wave approximation. The geotechnical component of the model is based on a multidimensional limit equilibrium analysis, which takes into account the basic principles of unsaturated soil mechanics. A series of numerical simulations were carried out with various boundary conditions and using different hydrological and geotechnical components. Boundary conditions in terms of distributed soil depth were generated using both empirical and process-based models. The effect of including preferential flow and soil hydraulic hysteresis was tested together with the replacement of the infinite slope assumption with the multidimensional limit equilibrium analysis. The results show that boundary conditions play a crucial role in the model performance and that the introduced hydrological (preferential flow and soil hydraulic hysteresis) and geotechnical components (multidimensional limit equilibrium analysis) significantly improve predictive capabilities in the presented case study.

A hydroclimatological approach to predicting regional landslide probability using Landlab

“…For both datasets, soil depth is deeper in the valleys and shallower near the ridge tops (Fig. 7c, d), consistent with other studies (Anagnostopoulos et al, 2015;Montgomery and Dietrich, 1994).…”

“…While using transient hydrologic models provided slight improvements in the prediction of landslide locations, overall, statistical comparisons of model outputs between steadystate and transient models revealed fairly similar degrees of success (Gorsevski et al, 2006;Zizioli et al, 2013;Anagnostopoulos et al, 2015;Bordoni et al, 2015;Formetta et al, 2016). In some applications, model complexity increased the accuracy of predicted landslide locations at the expense of overestimating instability on unsaturated hillslopes (e.g., Godt et al, 2008;Bellugi, 2011).…”

“…Data uncertainty due to spatial and temporal variability in parameters continues to be one of the major challenges in predicting landslides over broad regions (Crozier, 1986;Sidle and Ochiai, 2006;van Westen et al, 2006;Baum et al, 2014;Anagnostopoulos et al, 2015). Parameter uncertainties can develop from geological anomalies, inherent spatial heterogeneities in soil and vegetation properties and their changes over time, and sampling limitations (El-Ramly et al, 2002;Cho, 2007;Baum et al, 2014).…”

“…The degree of soil saturation is predicted proportional to the ratio of upslope contributing area to local slope and a ratio of watershed recharge and local soil transmissivity, following TOPMODEL (TOPography based hydrological MODEL) assumptions (Beven and Kirkby, 1979;O'Loughlin, 1986;Pack et al, 1998). More recent efforts have focused on the development of transient flow models in various complexities by coupling vertical infiltration and redistribution processes in the unsaturated zone, using the Richards equation for unsaturated flow (Richards, 1931) or its variants, with lateral flow parameterizations such as kinematic wave in one and two dimensions (Iverson, 2000;Casadei et al, 2003;Baum et al, 2008b;Godt and McKenna, 2008;Raia et al, 2014;Alvioli et al, 2014;Anagnostopoulos et al, 2015).…”

“…Recent processbased numerical models have largely focused on improving the characterization of the space-time dynamics of subsurface flow as a driver of pore-water pressure (e.g., Baum et al, 2008b;Raia et al, 2014;Anagnostopoulos et al, 2015;Montrasio and Valentino, 2016). Distributed hydrology models that use steady-state or transient solutions for subsurface flow depth were coupled with an infinite-slope stability model that solves the ratio of stabilizing to destabilizing forces on a failure plane parallel to the land surface (Montgomery and Dietrich, 1994;Miller, 1995;Wu and Sidle, 1995;Pack et al, 1998;Borga et al, 1998;Casadei et al, 2003;Tarolli and Tarboton, 2006;Baum et al, 2008b).…”