Geomorphological control on variably saturated hillslope hydrology and slope instability

Abstract

In steep topography, the processes governing variably saturated subsurface hydrologic response and the interparticle stresses leading to shallow landslide initiation are physically linked. However, these processes are usually analyzed separately. Here, we take a combined approach, simultaneously analyzing the influence of topography on both hillslope hydrology and the effective stress fields within the hillslope itself. Clearly, runoff and saturated groundwater flow are dominated by gravity and, ultimately, by topography. Less clear is how landscape morphology influences flows in the vadose zone, where transient fluxes are usually taken to be vertical. We aim to assess and quantify the impact of topography on both saturated and unsaturated hillslope hydrology and its effects on shallow slope stability. Three real hillslope morphologies (concave, convex, and planar) are analyzed using a 3-D, physically based, distributed model coupled with a module for computation of the probability of failure, based on the infinite slope assumption. The results of the analyses, which included parameter uncertainty analysis of the results themselves, show that convex and planar slopes are more stable than concave slopes. Specifically, under the same initial, boundary, and infiltration conditions, the percentage of unstable areas ranges from 1.3% for the planar hillslope, 21% for convex, to a maximum value of 33% for the concave morphology. The results are supported by a sensitivity analysis carried out to examine the effect of initial conditions and rainfall intensity.

Geomorfología paraglacial asociada a la inestabilidad de laderas en el Brazo Norte del Lago Argentino, Patagonia, Argentina

“…Este aporte da como resultado, un aumento en el contenido de humedad del suelo. No solo se debe a la filtración por la precipitación, sino también a los flujos saturados del subsuelo que fluyen desde la cresta de la cuenca hacia la salida de la cuenca (Giuseppe et al, 2016).…”

Physically based approaches incorporating evaporation for early warning predictions of rainfall-induced landslides

“…This isothermal approach only takes into account changes in atmospheric temperature through Eq. (5), where it is assumed that T s = T a (an approach called "isothermal model with atmospheric coupling" by Fredlund et al, 2012). The model takes only evaporation into account as a boundary phenomenon, which occurs only at the top boundary, with no possibility of a downward shift of the water-state-change surface.…”

Hydro‐geomorphic behavior of contrasting tropical landscapes and critical zone response to changing climate

“…where c is the combined effect of root cohesion and effective soil cohesion, h s is the thickness of landslide mass (landslide failure depth), ρ s is soil density, α t is the time-varying slope angle, θ t is the average soil moisture in the landslide control volume, θ r and θ s are the residual and saturated volumetric water contents, respectively, ρ w is water density, and φ is the friction angle. The slope stability model explicitly accounts for the spatial heterogeneity of factors that control shallow landslides, including mechanical and hydrological soil properties (Arnone et al, 2014(Arnone et al, , 2016, local topographic characteristics, and the temporal variation of soil moisture in response to precipitation events, which controls the temporal FS dynamics at the watershed scale (Simoni et al, 2008;Arnone et al, 2011;Lepore et al, 2013;Formetta et al, 2016). Possible landslide deposition paths are estimated based on the concept of run-out distance (Bathurst et al, 1997).…”

“…Bedrock weathering processes may lead to the depletion of primary minerals leading to mechanical disaggregation and increasing material susceptibility to erosion, and can be influenced by climate through moisture and temperature controls (White and Brantley, 2003;Dixon and Earls, 2009), and by landscape characteristics (Dietrich et al, 1995;Heimsath et al, 1999;Riebe et al, 2003). Hillslope erosion is controlled by rainfall-triggered landslides, the propensity for which depends on a multitude of non-climatic factors including slope morphology and soil and forest properties (Roering et al, 1999;Simoni et al, 2008;Hales et al, 2009;De Rose, 2013;Formetta et al, 2016;Moos et al, 2016), and on the frequency of extreme hydro-meteorological events (Casadei et al, 2003;Chen et al, 2013;von Ruette et al, 2014;Arnone et al, 2016). Clarifying the relative contribution of climatic vs non-climatic factors to the hillslope erosion rates of diverse landscapes is no trivial task (Riebe et al, 2003;Cook et al, 2015).…”