1,721,024 research outputs found
Il contributo della vegetazione riparia alla stabilità delle sponde nei canali agricoli della pianura lombarda
No full textUn approccio probabilistico alla valutazione della stabilità dei versanti forestali=A probabilistic approach to the evaluation of forested hillslopes stability
No full textCome è noto, la vegetazione influenza la stabilità dei versanti attraverso diversi processi di natura idrologica e meccanica, principalmente dovuti all’apparato radicale che rinforza il terreno e ne riduce il contenuto idrico. Il rinforzo esercitato dalle radici è considerato, in termini di coesione aggiuntiva, direttamente proporzionale al numero delle radici che attraversano le superfici di scorrimento del volume di terreno instabile ed alla resistenza mobilizzata dalle singole radici poste in tensione durante lo scivolamento. Nonostante gli studi in tale ambito siano stati numerosi negli ultimi anni, contribuendo ad avere una buona comprensione del processo di rinforzo ed accumulando una notevole mole di dati, il tema della variabilità spaziale del rinforzo e della sua relazione con le caratteristiche dei popolamenti (specie, età, stato di salute, densità, ecc.) è ancora poco chiaro. Per tener conto di ciò è stato sviluppato un modello “process-based” in grado di tener conto e gestire la variabilità spaziale del rinforzo radicale in funzione delle caratteristiche forestali dei versanti. Nella presente memoria vengono presentati i primi risultati della sua applicazione ad un piccolo bacino montano.Vegetation, as well known, can affect slope stability in different ways, mainly by the root system, which mechanically reinforces the soil and reduces soil moisture content. Root reinforcement is generally expressed in terms of additional root cohesion, which is directly related to the number of roots crossing the margin of a sliding soil volume and to the force mobilized by each root element subjected to tension during the sliding phenomenon. Although in the last decades, several studies have been conducted on such topic and a deep comprehension of the process has been reached, however, the spatial variability of the root reinforcement and its dependence from the forest stand characteristics (species, density, DBH, etc.), remains open points. To introduce such points into process-based models of slope stability, we have developed a method able to account for the variability of root reinforcement and its spatial distribution as function of the characteristics of forest stands. In this paper, we present preliminary results of its application to a small headwater catchment
Incorporating the effect of root systems of forest species into spatially distributed models of shallow landslides
No full textIn this paper, the stability model SINMAP was applied to a mountainous study area in order to include soil reinforcement exerted by root systems of forest species. Including root cohesion information in slope stability models, in fact, can lead to a better description of the shallow landsliding process and decrease the requirement for information on past landslides that is needed for model calibration.
The study area is located in northern Italy (Lombardy Region) and was classified in seven forest regions with different species composition. A two-phase procedure was applied: first of all, a standard calibration approach led to a realistic and strongly-related set of parameters for each defined calibration region; secondly, multi-scenario criteria was applied in order to test different hypothetical sliding depths, with particular attention to root distribution profiles obtained from field surveys. A quantitative index (the Weighted Modified Success Rate) was used to test the results obtained by the stability model (both standard calibration and multiple scenario).
The results showed that using forest categories to set up multiple calibration regions is very effective in standard calibration procedure. Moreover, potential sliding depth in each region was effectively identified at the depth where Root Area Ratio values fall below 0.1 % and the maximum available rooted soil cohesion is less than 5 kPa.
In this way the multiple region calibration approach becomes feasible also when data on observed landslides are scarce and it can be used just to calibrate the hydrologic factor range
CALIBRATION OF DISTRIBUTED SHALLOW LANDSLIDE MODELS IN FORESTED LANDSCAPES
Full text linkIn mountainous-forested soil mantled landscapes all around the world, rainfall-induced shallow landslides are one of the most common hydro-geomorphic hazards, which frequently impact the environment and human lives and properties. In order to produce shallow landslide susceptibility maps, several models have been proposed in the last decade, combining simplified steady state topography- based hydrological models with the infinite slope scheme, in a GIS framework. In the present paper, two of the still open issues are investigated: the assessment of the validity of slope stability models and the inclusion of root cohesion values. In such a perspective the “Stability INdex MAPping” has been applied to a small forested pre-Alpine catchment, adopting different calibrating approaches and target indexes. The Single and the Multiple Calibration Regions modality and three quantitative target indexes – the common Success Rate (SR), the Modified Success Rate (MSR), and a Weighted Modified Success Rate (WMSR) herein introduced – are considered. The results obtained show that the target index can 34 003_Bischetti(569)_23 1-12-2010 9:48 Pagina 34 significantly affect the values of a model’s parameters and lead to different proportions of stable/unstable areas, both for the Single and the Multiple Calibration Regions approach. The use of SR as the target index leads to an over-prediction of the unstable areas, whereas the use of MSR and WMSR, seems to allow a better discrimination between stable and unstable areas. The Multiple Calibration Regions approach should be preferred, using information on space distribution of vegetation to define the Regions. The use of field-based estimation of root cohesion and sliding depth allows the implementation of slope stability models (SINMAP in our case) also without the data needed for calibration. To maximize the inclusion of such parameters into SINMAP, however, the assumption of a uniform distribution of probability of the parameters must be overtaken. In small and steep catchments where there is an intrinsic susceptibility to instability phenomena, moreover, an additional class of low probability of instability (0.81)<1.0) has been proposed to better discriminate the areas classified as unstable.</p
(2008) Applicazione dell’Instream Flow Incremental Methodology per l’analisi della disponibilità d’habitat e la riqualificazione dei canali
No full textValutazione a scala locale e regionale del contributo della vegetazione alla stabilità dei versanti
No full textEvaluation of the effects of three European forest types on slope stability by field and probabilistic analyses and their implications for forest management
No full textIt is well known that forests play a crucial role in preventing soil erosion and landslides; however, forests are also subjected to dynamic evolution driven by natural processes and anthropogenic factors. This dynamic evolution affects spruce and chestnut forests in some European regions (e.g., Italian Alps, central and northern Europe), where these species have been forced by management practice to establish over long periods where other species, such as European beech, would be expected to occur as a result of natural processes.Using a large dataset of field and laboratory measurements of root density and root mechanical properties, the performances of Norway spruce, Sweet chestnut and European beech are analyzed from a slope stability perspective by using a model based on the limit equilibrium principle within a probabilistic framework.The results showed differences and similarities between the root systems of the analyzed species, both in terms of root distribution and mechanical properties. However, the probabilistic distribution that better fits the root reinforcement values obtained by the experimental work is, in all cases, a lognormal function.The developed method can be used to estimate the factor of safety for several combinations of geotechnical and hydrological parameters and different root reinforcement probability distributions using Monte Carlo techniques. The obtained values have been evaluated in terms of probability to have a factor of safety of less than 1 for increasing values of slope steepness.Although each single hillslope should be studied individually to account for local stand conditions that strongly affect root system performance, European beech is generally more efficient than Sweet chestnut and Norway spruce in terms of enhancing slope stability.Based on our results, in all cases where the stability of slopes represents a concern and spruce and chestnut communities are perishing, the natural colonization by European beech should be evaluated positively and possibly promoted by forest managers. Moreover, the developed method provides a general framework that could be applied to other species and conditions to define the consequences of different forest management scenarios in terms of slope stability
Root strength and density decay after felling in a Silver Fir-Norway spruce stand in the Italian Alps
No full textAims: Forests induce a mechanical reinforcement of soil, generally quantified in terms of additional root cohesion (cr), which decreases due to root decay after felling. The aim of this work is providing new field data on soil reinforcement by roots after trees cutting. Methods: The present work investigated cr decay in a mixed Silver Fir-Norway Spruce (Abies alba Mill. Picea abies (L.) Karst.) stand in the Italian Alps over a period of 3 years after felling by monitoring the two cr driving variables: root tensile resistance and root density. Results: Results showed that a significant difference in root resistance occurred only 3 years after felling, whereas the decrease in the number of roots was significant in the second year. The degradation process was more rapid in shallower layers and for thinner roots, as a consequence of the pattern of biological activity rate. The reduction of cr after felling was, for a reference profile depth of 70 cm, 55 % in the first 2 years and another 16 % in the third year. Conclusions: The findings of this study, providing new data on the decrease of cr after felling, can be introduced into geotechnical models allowing a better estimation of the stability of forest hillslopes
Comparison of Predicted and Measured Soil Retention Curve in Lombardy Region Northern of Italy
No full text- …
