Abstract
A physically based mathematical model of the slope of Cervinara (southern Italy), which is characterized by a shallow pyroclastic soil cover laying upon a limestone fractured bedrock, has been developed. Previous and current ongoing monitoring suggested that leakage through the soil–bedrock interface occurred, with leaking water temporarily stored in a perched aquifer located in the upper part of the fractured limestone (epikarst). This aquifer supplied several springs, and recharge to the deeper groundwater circulation occurred. Hence, in the proposed model, the unsaturated water flow taking place within the soil cover is coupled with the saturated water flow in the perched aquifer. The application of the model to the simulation of the slope hydrologic behavior over a period of 11 years, between 2006–2017, provides realistic results in terms of soil storage, epikarst storage, spring discharge, and groundwater recharge. The different response times of soil and epikarst aquifer to precipitation input allow distinguishing the hydrological predisposing causes of potential landsliding (i.e., a few months of persistent rainfall that is capable of filling the epikarst aquifer) from the triggers, which are represented by single intense rainfall events. The application of the model offers a key of interpretation of the hydrological processes leading to the landslide that occurred on 16 December 1999.
Highlights
Rainfall-induced landslides in shallow granular soil covers are among the most hardly predictable landslide types
First, some results from field monitoring are reported, which are at the basis of the development of the mathematical model described in Section 2.2, and which give some insight about the choice of the values of the parameters of the model
The obtained results show that the coupled modeling of the unsaturated flow in the soil cover and the perched aquifer developing in the epikarst allows for a realistic simulation of the water potential regime in the soil cover, which is the result of the superposition of long-term seasonal fluctuations and short variations directly related to the sequence of rainfall events and dry intervals
Summary
Rainfall-induced landslides in shallow granular soil covers are among the most hardly predictable landslide types. The triggering of shallow landslides requires an increased storage of water within the soil cover, leading to pore pressure increase [5]. The hydraulic behavior of the boundaries of the soil cover, through which it exchanges water with the surrounding hydrological systems, needs to be understood [5]. It has often been recognized in shallow soil covers that soil moisture follows a long-term trend e.g., Cascini et al, Comegna et al [9,10], and so the initiation of landslides has been related by many authors to rainfall accumulated over various time intervals
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