Hydrological modelling of a slope covered with shallow pyroclastic deposits from field monitoring data

Abstract

Abstract.A one-dimensional hydrological model of a slope covered with pyroclastic materials is proposed. The soil cover is constituted by layers of loose volcanic ashes and pumices, with a total thickness between 1.8 m and 2.5 m, lying upon a fractured limestone bedrock. The mean inclination of the slope is around 40 • , slightly larger than the friction angle of the ashes. Thus, the equilibrium of the slope, significantly affected by the cohesive contribution exerted by soil suction in unsaturated conditions, may be altered by rainfall infiltration. The model assumes a single homogeneous soil layer occupying the entire depth of the cover, and takes into account seasonally variable canopy interception of precipitation and root water uptake by vegetation, mainly constituted by deciduous chestnut woods with a dense underbrush growing during late spring and summer. The bottom boundary condition links water potential at the soil-bedrock interface with the fluctuations of the water table of the aquifer located in the fractured limestone, which is conceptually modelled as a linear reservoir. Most of the model parameters have been assigned according to literature indications or from experimental data. Soil suction and water content data measured between 1 January 2011 and 20 July 2011 at a monitoring station installed along the slope allowed the remaining parameters to be identified. The calibrated model, which reproduced very closely the data of the calibration set, has been applied to the simulation of the hydrological response of the slope to the hourly precipitation record of 1999, when a large flow-like landslide was triggered close to the monitored location. The simulation results show that the lowest soil suction ever attained occurred just at the time the landslide was triggered, indicating that the model is capable of predicting slope failure conditions.

Invited perspectives: Hydrological perspectives on precipitation intensity-duration thresholds for landslide initiation: proposing hydro-meteorological thresholds

“…Greco and Bogaard (2016) give an example of the possible inclusion of slope hydrological processes in the definition of landslide initiation thresholds for the case of a slope covered by loose granular volcanoclastic deposits overlying a fractured limestone bedrock. The hydraulic characteristic curves of the volcanic ashes constituting the majority of the soil cover were known (Damiano et al, 2012;Greco et al, 2013), as well as the moisture state of the cover before all 78 observed rainfall events (Comegna et al, 2016). Hence, it was possible to define non-dimensional variables by comparing the meteorological triggers with the infiltration and storage capacity of the soil cover.…”

Analysis of landslide triggering conditions in the Sarno area using a physically based model

“…The role played by the possible interaction of the unsaturated cover with the underlying groundwater, through an impervious soil-bedrock interface, has also been analyzed, by Greco et al (2013), for a slope similar to those in Sarno.…”

Quantification of the influence of preferential flow on slope stability using a numerical modelling approach

“…The limit equilibrium method or infinite slope stability approach is frequently integrated with Richards' equation (Lanni et al, 2013;Ng and Shi, 1998;Godt et al, 2008;Shuin et al, 2012;Wilkinson et al, 2002;Talebi et al, 2008;Greco et al, 2013) or conceptual models (Arnone et al, 2011;Simoni et al, 2008;Qiu et al, 2007) for landslide hazard evaluation. The limit equilibrium method and infinite slope approach assume or search for a potential failure surface.…”