Gian Battista Bischetti

Root cohesion of forest species in the Italian Alps

Forests can prevent and/or mitigate hydrogeomorphic hazards in mountainous landscapes. Their effect is particularly relevant in the case of shallow landslides phenomena, where plants decrease the water content of the soil and increase its mechanical strength. Although such an effect is well known, its quantification is a relatively new challenge. The present work estimates the effect of some forest species on hillslope stability in terms of additional root cohesion by means of a model based on the classical Wu and Waldron approach (Wu in Alaska Geotech Rpt No 5 Dpt Civ Eng Ohio State Univ Columbus, USA, 1976; Waldron in Soil Sci Soc Am J 41:843–849, 1977). The model is able to account for root distribution with depth and non-simultaneous root breaking. Samples of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), European larch (Larix decidua Mill.), sweet chestnut (Castanea sativa Mill.) and European hop-hornbeam (Ostrya carpinifolia Scop.), were taken from different locations of Lombardy (Northern Italy) to estimate root tensile strength, the Root Area Ratio and the root cohesion distribution in the soil. The results show that, in spite of its dramatic variability within the same species at the same location and among different locations, root cohesion can be coherently interpreted using the proposed method. The values herein obtained are significant for slope stabilisation, are consistent with the results of direct shear tests and back-analysis data, and can be used for the estimation of the stability of forested hillslopes in the Alps.

IDENTIFICATION AND ANALYSIS OF NATURAL CHANNEL NETWORKS FROM DIGITAL ELEVATION MODELS

The identification and analysis of natural channel networks from digital elevation models are discussed from the point of view of their environmental applications. An interactive, graphical software package that implements some of the most widely used techniques for the automatic recognition of channel networks and for the computation of some useful geomorphologic indices and functions is presented.

An integrated, multisensor system for the continuous monitoring of water dynamics in rice fields under different irrigation regimes

The cultivation of rice, one of the most important staple crops worldwide, has very high water requirements. A variety of irrigation practices are applied, whose pros and cons, both in terms of water productivity and of their effects on the environment, are not completely understood yet. The continuous monitoring of irrigation and rainfall inputs, as well as of soil water dynamics, is a very important factor in the analysis of these practices. At the same time, however, it represents a challenging and costly task because of the complexity of the processes involved, of the difference in nature and magnitude of the driving variables and of the high variety of field conditions. In this paper, we present the prototype of an integrated, multisensor system for the continuous monitoring of water dynamics in rice fields under different irrigation regimes. The system consists of the following: (1) flow measurement devices for the monitoring of irrigation supply and tailwater drainage; (2) piezometers for groundwater level monitoring; (3) level gauges for monitoring the flooding depth; (4) multilevel tensiometers and moisture sensor clusters to monitor soil water status; (5) eddy covariance station for the estimation of evapotranspiration fluxes and (6) wireless transmission devices and software interface for data transfer, storage and control from remote computer. The system is modular and it is replicable in different field conditions. It was successfully applied over a 2-year period in three experimental plots in Northern Italy, each one with a different water management strategy. In the paper, we present information concerning the different instruments selected, their interconnections and their integration in a common remote control scheme. We also provide considerations and figures on the material and labour costs of the installation and management of the system.

On the Origin of Soil Bioengineering

Abstract Soil bioengineering is a discipline dealing with hill slopes, riverbanks, and earth embankment stabilisation, which in recent decades has gained worldwide popularity. Its peculiarity consists in the technical use of vegetation, sometimes coupled with other materials. Owing to aesthetic and environment-friendly characteristics of vegetation, soil bioengineering techniques are frequently adopted to achieve a low environmental impact of protective works within the fields of landscape architecture and environmental restoration. In spite of such success, the origin and the contents of soil bioengineering have not been completely investigated. This paper shows that soil bioengineering is not as old as most of the researchers think; rather, it was developed in a very specific context, the building of highways during the Nazi dictatorship, although it is the result of a longer process. The paper also shows that the contents of soil bioengineering are not related to the mere use of vegetation for stabilising purposes, but they focus on broader environmental concerns.

A proposal for assessing the success of soil bioengineering work by analysing vegetation: results of two case studies in the Italian Alps

The evaluation of the success of soil bioengineering work is an issue still poorly addressed by the scientific community. Nevertheless, soil bioengineering techniques are increasingly used worldwide when mitigating the impact on the environment and the landscape is one, but not the only, goal of intervention. A tool to measure the success of soil bioengineering work, with reference to landslide stabilization, is presented in this paper: the index of ecological success (IES). The IES is based on the phytosociological analysis of vegetation and widens the potential applications of the ecological index of maturity (EIM), recently formulated by Giupponi et al. (Restor Ecol 23:635–644, 2015) to assess the degree of disturbance affecting a plant community. The IES compares the EIM values of the vegetation of an area affected by soil stabilization work with those of the expected vegetation at a precise time after completion of soil stabilization work, providing values ranging between 0 (maximum failure) and 1 (complete success). The IES was applied in two study areas located on two mountain slopes of the Southern Alps (Italy) which, as a result of landslides, were subject to soil bioengineering work aimed at slope stabilization. The results of these first two applications confirm the efficacy of the IES in evaluating the success of soil bioengineering work in mountain areas and bode well as to its future application.

A Probabilistic 3-D Slope Stability Analysis for Forest Management

A 3-D physical-based approach to slope stability has been proven to be very promising in order to provide reliable spatially distributed landslides maps. Over large areas, however, such an approach still presents some limitations, mainly related to the variability and the uncertainty of the input parameters. By combining a 3-D physical-based model with a Monte Carlo technique, such constraints can be overcome, improving the performance and the applicability of the method. Whereas uncertainties of geotechnical, morphological and hydrological parameters have been widely investigated, few studies have been focused on the variability of root reinforcement, which plays a crucial role in preventing shallow landslides in forested areas. To contribute to define the effect of different forest management strategies on slope stability, we developed a 3-D model able to properly take into account for the effect of the root systems into the soil. The main objectives of our study are: (i) to define a probability distribution function for the root reinforcement according to the forest stands characteristics (tree density, mean diameter at breast height, minimum distance between trees), (ii) to obtain a probability distribution of the Factor of Safety through the combination between a 3-D slope stability model and a Monte Carlo simulation technique, and (iii) to evaluate the difference between several forest management scenarios in terms of shallow landslide risk. The model has been applied to a small Alpine area, mainly covered by coniferous forest and characterized by steep slopes and a high landslide hazard. Our findings contribute to provide forest managers with useful information for understanding the consequences of different forestry strategies.

Source areas, connectivity, and delivery rate of sediments in mountainous-forested hillslopes: A probabilistic approach

In mountainous-forested landscape, quantifying the materials produced at hillslope scale that effectively reach the channel network with a given probability is currently challenging, due to the uncertainties in modelling the frequency-magnitude distribution of failures and in determining the sediment connectivity between unstable areas and channel network. The purpose of this study is to develop a modular approach to assess the sediment source areas and the probability of mobilization from hillslope, and to estimate the probability of sediment input to the streams proposing a new connectivity index. The first goal was faced adopting a 3D probabilistic slope stability method that includes the spatially distributed characteristics of forest coverage. The second aim was tackled by comparing sediment travel distance and the minimum-topographic distance to reach the nearest stream. A simple deposition model was applied to estimate the percentage of the sediment entering into the stream network. The methodology was tested on three headwater catchments in northern Italian Alps. The outputs were landslide susceptibility maps, which showed robust performances when compared to the available landslide inventories (AUC > 0.726), and maps of the probability that sediment reaches the channel network. In this way, it was possible to identify which areas are the most susceptible to landsliding, how many sediment materials can be mobilised with a given probability, and which is the degree of sediment connectivity with the channel system. Results obtained for the tested catchments, compared with data available from the literature, showed that the proposed methodology is of general validity, especially for those territories characterized by rainfall-triggered landslides and forest coverage. This study, then, provides a robust framework to improve debris-flow risk management and to implement watershed management strategies, such as planning forestry operations or positioning retention structures addressed to increase slope stability and to reduce sediment delivery.

How to renew soil bioengineering for slope stabilization: some proposals

Mountain environments play a crucial role in maintaining biodiversity despite becoming more vulnerable to colluvial processes primarily induced by extreme meteorological events. Soil bioengineering stabilizes mountain slopes and limits impacts on ecosystems and is increasingly used worldwide, yet its effectiveness requires better assessment through post-intervention environmental monitoring. However such studies are only rarely performed even though they are essential to improve future intervention. This study reports soil and vegetation monitoring data of an area in the Italian Alps in which soil bioengineering work was carried out to restore an area hit by landslides. The monitoring involved an analysis of the floristic-vegetational and ecological features of the plant communities of the area of the soil bioengineering intervention (and in adjacent areas), as well as an analysis of the chemical–physical characteristics of the soils (texture, pH, organic matter, nitrogen content, roots depth) where these communities were established. The results of the monitoring, analyzed in the overall framework of the state of the art of the sector, have highlighted some lines of research and action that should be undertaken by technicians, researchers, and politicians to innovate and to make work aimed at the stabilization of landslides more effective. In particular, it would be extremely useful to study the biotechnical characteristics of herbaceous plants that are still “unknown” in soil bioengineering and to evaluate their possible effects on ecosystems in order to produce seed mixtures that, besides being useful for soil stabilization, can accelerate vegetation dynamics, therefore maximizing the success of such works.