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The quantification of post-disturbance root reinforcement (RR) recovery dynamics is of paramount importance for the optimisation of forest ecosystem services and natural hazards risk management in mountain regions. In this work we analyse the long-term root reinforcement dynamic of spruce forests combining data of the Swiss National Forest Inventory with data on root distribution and root mechanical properties. The results show that root reinforcement recovery depends primarily on stand altitude and slope inclination. The maximum root reinforcement recovery rate is reached at circa 100 years. RR increases continuously with different rates for stand ages over 200 years. These results shows that RR in spruce stands varies considerably depending on the local conditions and that its recovery after disturbances requires decades. The new method applied in this study allowed for the first time to quantify the long term dynamics of RR in spruce stands supporting new quantitative approaches for the analysis of shallow landslides disposition in different disturbance regimes of forests.
Gianluca Flepp; Roger Robyr; Roberto Scotti; Filippo Giadrossich; Marco Conedera; Giorgio Vacchiano; Christoph Fischer; Peter Ammann; Dominik May; Massimiliano Schwarz. Temporal Dynamics of Root Reinforcement in European Spruce Forests. Forests 2021, 12, 815 .
AMA StyleGianluca Flepp, Roger Robyr, Roberto Scotti, Filippo Giadrossich, Marco Conedera, Giorgio Vacchiano, Christoph Fischer, Peter Ammann, Dominik May, Massimiliano Schwarz. Temporal Dynamics of Root Reinforcement in European Spruce Forests. Forests. 2021; 12 (6):815.
Chicago/Turabian StyleGianluca Flepp; Roger Robyr; Roberto Scotti; Filippo Giadrossich; Marco Conedera; Giorgio Vacchiano; Christoph Fischer; Peter Ammann; Dominik May; Massimiliano Schwarz. 2021. "Temporal Dynamics of Root Reinforcement in European Spruce Forests." Forests 12, no. 6: 815.
Worldwide, shallow landslides repeatedly pose a risk to infrastructure and residential areas. To analyse and predict the risk posed by shallow landslides, a wide range of scientific methods and tools to model shallow landslide probability exist for both local and regional scale However, most of these tools do not take the protective effect of vegetation into account. Therefore, we developed SlideforMap (SfM), which is a probabilistic model that allows for a regional assessment of shallow landslide probability while considering the effect of different scenarios of forest cover, forest management and rainfall intensity. SfM uses a probabilistic approach by distributing hypothetical landslides to uniformly randomized coordinates in a 2D space. The surface areas for these hypothetical landslides are derived from a distribution function calibrated from observed events. For each randomly generated landslide, SfM calculates a factor of safety using the limit equilibrium approach. Relevant soil parameters, i.e. angle of internal friction, soil cohesion and soil depth, are assigned to the generated landslides from normal distributions based on mean and standard deviation values representative for the study area. The computation of the degree of soil saturation is implemented using a stationary flow approach and the topographic wetness index. The root reinforcement is computed based on root proximity and root strength derived from single tree detection data. Ultimately, the fraction of unstable landslides to the number of generated landslides, per raster cell, is calculated and used as an index for landslide probability. Inputs for the model are a digital elevation model, a topographic wetness index and a file containing positions and dimensions of trees. We performed a calibration of SfM for three test areas in Switzerland with a reliable landslide inventory, by randomly generating 1000 combinations of model parameters and then maximising the Area Under the Curve (AUC) of the receiver operation curve (ROC). These test areas are located in mountainous areas ranging from 0.5–7.5 km2, with varying mean slope gradients (18–28°). The density of inventoried historical landslides varied from 5–59 slides/km2. AUC values between 0.67 and 0.92 indicated a good model performance. A qualitative sensitivity analysis indicated that the most relevant parameters for accurate modeling of shallow landslide probability are the soil depth, soil cohesion and the root reinforcement. Further, the use of single tree detection in the computation of root reinforcement significantly improved model accuracy compared to the assumption of a single constant value of root reinforcement within a forest stand. In conclusion, our study showed that the approach used in SfM can reproduce observed shallow landslide occurrence at a catchment scale.
Feiko Bernard van Zadelhoff; Adel Albaba; Denis Cohen; Chris Phillips; Bettina Schaefli; Lucas Karel Agnes Dorren; Massimiliano Schwarz. Introducing SlideforMap; a probabilistic finite slope approach for modelling shallow landslide probability in forested situations. 2021, 2021, 1 -33.
AMA StyleFeiko Bernard van Zadelhoff, Adel Albaba, Denis Cohen, Chris Phillips, Bettina Schaefli, Lucas Karel Agnes Dorren, Massimiliano Schwarz. Introducing SlideforMap; a probabilistic finite slope approach for modelling shallow landslide probability in forested situations. . 2021; 2021 ():1-33.
Chicago/Turabian StyleFeiko Bernard van Zadelhoff; Adel Albaba; Denis Cohen; Chris Phillips; Bettina Schaefli; Lucas Karel Agnes Dorren; Massimiliano Schwarz. 2021. "Introducing SlideforMap; a probabilistic finite slope approach for modelling shallow landslide probability in forested situations." 2021, no. : 1-33.
Feiko Bernard van Zadelhoff; Adel Albaba; Denis Cohen; Chris Phillips; Bettina Schaefli; Lucas Karel Agnes Dorren; Massimiliano Schwarz. Supplementary material to "Introducing SlideforMap; a probabilistic finite slope approach for modelling shallow landslide probability in forested situations". 2021, 1 .
AMA StyleFeiko Bernard van Zadelhoff, Adel Albaba, Denis Cohen, Chris Phillips, Bettina Schaefli, Lucas Karel Agnes Dorren, Massimiliano Schwarz. Supplementary material to "Introducing SlideforMap; a probabilistic finite slope approach for modelling shallow landslide probability in forested situations". . 2021; ():1.
Chicago/Turabian StyleFeiko Bernard van Zadelhoff; Adel Albaba; Denis Cohen; Chris Phillips; Bettina Schaefli; Lucas Karel Agnes Dorren; Massimiliano Schwarz. 2021. "Supplementary material to "Introducing SlideforMap; a probabilistic finite slope approach for modelling shallow landslide probability in forested situations"." , no. : 1.
We have recently been made aware by the Forests Editorial Offices of some errors and omissions in the Introduction Section 1
Giampiero Branca; Irene Piredda; Roberto Scotti; Laura Chessa; Ilenia Murgia; Antonio Ganga; Sergio Campus; Raffaella Lovreglio; Enrico Guastini; Massimiliano Schwarz; Filippo Giadrossich. Correction: Branca, G., et al. Forest Protection Unifies, Silviculture Divides: A Sociological Analysis of Local Stakeholders’ Voices after Coppicing in the Marganai Forest (Sardinia, Italy). Forests 2020, 11, 708. Forests 2020, 11, 1353 .
AMA StyleGiampiero Branca, Irene Piredda, Roberto Scotti, Laura Chessa, Ilenia Murgia, Antonio Ganga, Sergio Campus, Raffaella Lovreglio, Enrico Guastini, Massimiliano Schwarz, Filippo Giadrossich. Correction: Branca, G., et al. Forest Protection Unifies, Silviculture Divides: A Sociological Analysis of Local Stakeholders’ Voices after Coppicing in the Marganai Forest (Sardinia, Italy). Forests 2020, 11, 708. Forests. 2020; 11 (12):1353.
Chicago/Turabian StyleGiampiero Branca; Irene Piredda; Roberto Scotti; Laura Chessa; Ilenia Murgia; Antonio Ganga; Sergio Campus; Raffaella Lovreglio; Enrico Guastini; Massimiliano Schwarz; Filippo Giadrossich. 2020. "Correction: Branca, G., et al. Forest Protection Unifies, Silviculture Divides: A Sociological Analysis of Local Stakeholders’ Voices after Coppicing in the Marganai Forest (Sardinia, Italy). Forests 2020, 11, 708." Forests 11, no. 12: 1353.
Today, a forest is also understood as a real social actor with multiple-scale influences, capable of significantly conditioning the social, economic, and cultural system of a whole territory. The aim of this paper is to reconstruct and interpret the population’s perception of the silvicultural activities related to traditional use of forest resources of the southwestern Sardinian Marganai State Forest. The “Marganai case” has brought to the attention of the mass media the role of this forest and its silviculture. The research was carried out via semi-structured interviews with the main stakeholders in the area. The qualitative approach in the collection and analysis of the information gathered has allowed us to reconstruct the historical-cultural and social cohesion function that the forest plays in rural communities. The results highlight that the main risks concern the erosion of the cultural forest heritage due to the abandonment of the rural dimension (mainly by the new generations, but not only), with the consequent spread of deep distortions in the perception, interpretation, and necessity of forestry activities and policy.
Giampiero Branca; Irene Piredda; Roberto Scotti; Laura Chessa; Ilenia Murgia; Antonio Ganga; Sergio Francesco Campus; Raffaella Lovreglio; Enrico Guastini; Massimiliano Schwarz; Filippo Giadrossich; Sergio Campus. Forest Protection Unifies, Silviculture Divides: A Sociological Analysis of Local Stakeholders’ Voices after Coppicing in the Marganai Forest (Sardinia, Italy). Forests 2020, 11, 708 .
AMA StyleGiampiero Branca, Irene Piredda, Roberto Scotti, Laura Chessa, Ilenia Murgia, Antonio Ganga, Sergio Francesco Campus, Raffaella Lovreglio, Enrico Guastini, Massimiliano Schwarz, Filippo Giadrossich, Sergio Campus. Forest Protection Unifies, Silviculture Divides: A Sociological Analysis of Local Stakeholders’ Voices after Coppicing in the Marganai Forest (Sardinia, Italy). Forests. 2020; 11 (6):708.
Chicago/Turabian StyleGiampiero Branca; Irene Piredda; Roberto Scotti; Laura Chessa; Ilenia Murgia; Antonio Ganga; Sergio Francesco Campus; Raffaella Lovreglio; Enrico Guastini; Massimiliano Schwarz; Filippo Giadrossich; Sergio Campus. 2020. "Forest Protection Unifies, Silviculture Divides: A Sociological Analysis of Local Stakeholders’ Voices after Coppicing in the Marganai Forest (Sardinia, Italy)." Forests 11, no. 6: 708.
The influence of vegetation on the hydro-geomorphological response is widely recognized, and root reinforcement mechanisms are an important component of slope stability models. The calculation of this essential information is very complex because of the multiple interactions in the root-soil system, but also because of several mechanical characteristics that influence the tension and compression behaviour of the root itself.
This contribution has two aims. The first one is to show parameters of root reinforcement effects of Robinia pseudoacacia (L.), a tree commonly used for the mitigation of rainfall-induced landslides at small scale. This species is very widespread because it is able to grow on marginal areas, such as abandoned hillside sites, or on infrastructures, such as road and railway scarps, but its characterization represents a gap in knowledge in the literature. Field pullout tests were performed to collect input data for the quantification of root reinforcement using the Root Bundle Model with Weibull survival function (RBMw, Schwarz et al, 2013). Recent studies have shown how the RBMw is a very efficient model for the evaluation of root reinforcement by considering the heterogeneity of both root mechanical characteristics and their distribution in the soil. However, due to the model complexity and the need for information difficult to obtain, other simpler but less accurate approaches, such as the Wu model, have been preferred.
For this reason, the second aim of the work is to present a new tool written in C++, and called RBM++, easy to use that enables anyone, from Universities to private companies, to quantify the effect of roots on slope stability. RBM++ allows the calculation of root reinforcement using two different methods: the first one by entering own data of the mechanical parameters of the roots, estimated beforehand with pullout tests in the field, and the root distribution in the soil; the second one by selecting the tree species and the data related to the spatial root distribution. For the first method, it is necessary to use a pullout machine to obtain the data. Because this instrument is not commonly available the model has the option to use default parameters for nine tree species based on values found in the literature.
Output from RBM++ comes in tabular format and with a plot that shows, via the graphical user interface, the spatial distribution of forces as a function of the distance from the tree trunk and size of the tree.
RBM++ makes it easier to share and exchange knowledge related to root reinforcement. Therefore, it will allow the realization of a database containing standard data on root mechanical behavior of tree species commonly used for shallow landslide mitigation.
Ilenia Murgia; Denis Cohen; Filippo Giadrossich; Gian Franco Capra; Massimiliano Schwarz. A new tool to accurately calculate root reinforcement: the Root Bundle Model software RBM++. 2020, 1 .
AMA StyleIlenia Murgia, Denis Cohen, Filippo Giadrossich, Gian Franco Capra, Massimiliano Schwarz. A new tool to accurately calculate root reinforcement: the Root Bundle Model software RBM++. . 2020; ():1.
Chicago/Turabian StyleIlenia Murgia; Denis Cohen; Filippo Giadrossich; Gian Franco Capra; Massimiliano Schwarz. 2020. "A new tool to accurately calculate root reinforcement: the Root Bundle Model software RBM++." , no. : 1.
Until now, slope stability models include the effects of the vegetation by adding a fixed value of apparent root cohesion as an estimate of root strength. However, some studies have demonstrated that root reinforcement depends on poorly constrained factors such as the heterogeneous distribution of roots in the soil and their tensional and compressional strength behavior.
SOSlope (Self-Organized Slope) is a hydro-mechanical model that computes the factor of safety on a hillslope discretized into a two-dimensional array of blocks connected by bonds to simulate the interactions of root-soil systems (Cohen and Schwarz, 2017). SOSlope estimates slope stability considering the presence of vegetation as a function of parameters such as species, tree density and diameter at breast height. In particular, bonds between adjacent blocks represent mechanical forces acting across the blocks due to roots and soil, in tension or compression, depending on the relative position of blocks. It is a strain-step discrete element model that reproduces the self-organized redistribution of forces on a slope during a rainfall-triggered shallow landslide. The innovative aspect of this model is a complete evaluation of the effects of roots on slope stability calculated using the Root Bundle Model with Weibull survival function (RBMw, Schwarz et al, 2013).
In this case study, SOSlope was used to reconstruct a critical shallow landslide triggering and to observe how the factor of safety changes depending on the presence, or not, of vegetation. The study area is located in the north-eastern part of the Oltrepò Pavese (Pavia, Italy), and is characterized by a high density of past landslides as reported in the database of Italian landslide inventories (IFFI). In the past, the common land use was vineyards, abandoned in the 1980s. Presently, the vegetation consists of grasses and shrubs moving to a thinned forest of young Robinia pseudoacacia L.
On 27 and 28 April 2009 a shallow landslide triggered after an intense and prolonged rainfall event (160 mm accumulated in 62 h with a maximum intensity of 22.6 mm/h). A large number of shallow landslides occurred in the surrounding area with about 29 landslides per km2 (1600 landslides in 240 km2). Five years later, on 28 February - 2 March 2014, 15 meters from a monitoring station and close to the previously affected area, another superficial landslide was triggered after 30 days of rain with a total precipitation of 105.5 mm (68.9 mm in 42 h recorded by the rain gauge of the monitoring station). In addition to the significance of this large landslide, this case study was scientifically important because it wasthe first documented case of a natural shallow landslide induced by rainfall since the 1950s (Bordoni et al, 2015).
The results of SOSlope simulations show good agreement with the real event of 28 February - 2 March 2014, and emphasize the important role of tree roots in the variation of the factor of safety. In this specific case, adding trees results in a reduction of about 39% of the dimensions of the unstable area.
Massimiliano Schwarz; Ilenia Murgia; Filippo Giadrossich; Massimiliano Bordoni; Claudia Meisina; Gian Battista Bischetti; Gian Franco Capra; Denis Cohen. Factor of safety analysis with and without vegetation using the SOSlope model. 2020, 1 .
AMA StyleMassimiliano Schwarz, Ilenia Murgia, Filippo Giadrossich, Massimiliano Bordoni, Claudia Meisina, Gian Battista Bischetti, Gian Franco Capra, Denis Cohen. Factor of safety analysis with and without vegetation using the SOSlope model. . 2020; ():1.
Chicago/Turabian StyleMassimiliano Schwarz; Ilenia Murgia; Filippo Giadrossich; Massimiliano Bordoni; Claudia Meisina; Gian Battista Bischetti; Gian Franco Capra; Denis Cohen. 2020. "Factor of safety analysis with and without vegetation using the SOSlope model." , no. : 1.
Floods and subsequent bank erosion are recurring hazards that pose threats to people and can cause damage to buildings and infrastructure. While numerous approaches exist on modeling bank erosion, very few consider the stabilizing effects of vegetation (i.e., roots) for hydraulic bank erosion at catchment scale. Taking root reinforcement into account enables the assessment of the efficiency of vegetation to decrease hydraulic bank erosion rates and thus improve risk management strategies along forested channels. A new framework (BankforNET) was developed to model hydraulic bank erosion that considers the mechanical effects of roots and randomness in the Shields entrainment parameter to calculate probabilistic scenario-based erosion events. The one-dimensional, probabilistic model uses the empirical excess shear stress equation where bank erodibility parameters are randomly updated from an empirical distribution based on data found in the literature. The mechanical effects of roots are implemented by considering the root area ratio (RAR) affecting the material dependent critical shear stress. The framework was validated for the Selwyn/Waikirikiri River catchment in New Zealand, the Thur River catchment and the Sulzigraben catchment, both in Switzerland. Modeled bank erosion deviates from the observed bank erosion between 7% and 19%. A sensitivity analysis based on data of vertically stable river reaches also suggests that the mechanical effects of roots can reduce hydraulic bank erosion up to 100% for channels with widths < 15.00 m, longitudinal slopes < 0.05 m m−1 and a RAR of 1% to 2%. The results show that hydraulic bank erosion can be significantly decreased by the presence of roots under certain conditions and its contribution can be quantified considering different conditions of channel geometry, forest structure and discharge scenarios.
Eric Gasser; Paolo Perona; Luuk Dorren; Chris Phillips; Johannes Hübl; Massimiliano Schwarz. A New Framework to Model Hydraulic Bank Erosion Considering the Effects of Roots. Water 2020, 12, 893 .
AMA StyleEric Gasser, Paolo Perona, Luuk Dorren, Chris Phillips, Johannes Hübl, Massimiliano Schwarz. A New Framework to Model Hydraulic Bank Erosion Considering the Effects of Roots. Water. 2020; 12 (3):893.
Chicago/Turabian StyleEric Gasser; Paolo Perona; Luuk Dorren; Chris Phillips; Johannes Hübl; Massimiliano Schwarz. 2020. "A New Framework to Model Hydraulic Bank Erosion Considering the Effects of Roots." Water 12, no. 3: 893.
In view of the important role played by roots against shallow landslides, root tensile force was evaluated for two widespread temperate tree species within the Caspian Hyrcanian Ecoregion, i.e., Fagus orientalis L. and Carpinus betulus L. Fine roots (0.02 to 7.99 mm) were collected from five trees of each species at three different elevations (400, 950, and 1350 m a.s.l.), across three diameter at breast height (DBH) classes (small = 7.5–32.5 cm, medium = 32.6–57.5 cm, and large =57.6–82.5 cm), and at two slope positions relative to the tree stem (up- and down-slope). In the laboratory, maximum tensile force (N) required to break the root was determined for 2016 roots (56 roots per each of two species x three sites x three DBH classes x two slope positions). ANCOVA was used to test the effects of slope position, DBH, and study site on root tensile force. To obtain the power-law regression coefficients, a nonlinear least square method was used. We found that: 1) root tensile force strongly depends on root size, 2) F. orientalis roots are stronger than C. betulus ones in the large DBH class, although they are weaker in the medium and small DBH classes, 3) root mechanical resistance is higher upslope than downslope, 4) roots of the trees with larger DBH were the most resistant roots in tension in compare with roots of the medium or small DBH classes, and 5) the root tensile force for both species is notably different from one site to another site. Overall, our findings provide a fundamental contribution to the quantification of the protective effects of forests in the temperate region.
Azade Deljouei; Ehsan Abdi; Massimiliano Schwarz; Baris Majnounian; Hormoz Sohrabi; R. Kasten Dumroese. Mechanical Characteristics of the Fine Roots of Two Broadleaved Tree Species from the Temperate Caspian Hyrcanian Ecoregion. Forests 2020, 11, 345 .
AMA StyleAzade Deljouei, Ehsan Abdi, Massimiliano Schwarz, Baris Majnounian, Hormoz Sohrabi, R. Kasten Dumroese. Mechanical Characteristics of the Fine Roots of Two Broadleaved Tree Species from the Temperate Caspian Hyrcanian Ecoregion. Forests. 2020; 11 (3):345.
Chicago/Turabian StyleAzade Deljouei; Ehsan Abdi; Massimiliano Schwarz; Baris Majnounian; Hormoz Sohrabi; R. Kasten Dumroese. 2020. "Mechanical Characteristics of the Fine Roots of Two Broadleaved Tree Species from the Temperate Caspian Hyrcanian Ecoregion." Forests 11, no. 3: 345.
In the Alps, shallow landslides repeatedly pose a risk to infrastructure and residential areas. For example, dozens of shallow landslides led to the destruction of several houses, killed one person and led to the evacuation of more than 50 houses, multiple road closure for several days in Austria in Nov. 2019. To analyse and predict the risk posed by shallow landslide, a wide range of scientific methods and tools for modelling disposition and runout exists, both for local and regional scale analyses. Most of these tools, however, do not take the protective effect, i.e. root reinforcement, of vegetation into account. Therefore, we developed SlideforMap (SfM), a probabilistic model that allows for a regional assessment of the disposition of shallow landslides while considering the effect of different scenarios of forest cover and management and of rainfall intensity.
SfM uses a probabilistic approach by attributing landslide surface areas, randomly selected from a gamma shaped distribution published by Malamud (2004), to random coordinates within a given study area. For each generated landslide, SfM calculates a factor of safety using the limit equilibrium infinite slope approach. Thereby, the relevant soil parameters, i.e. angle of internal friction, soil cohesion and soil depth, are defined by normal distributions based on mean and standard deviation values representative for the study area. Hydrology is implemented using a stationary flow approach and the topographical wetness index. Root reinforcement is computed based on root distribution and root strength derived from single tree detection data and the root bundle model of Schwarz et al. (2013). Finally, the fraction of unstable landslides to the number of generated slides per raster cells is calculated and used as an index for landslide onset susceptibility. Inputs for the model are a Digital Terrain Model, a topographical wetness index and a file containing positions and sizes of trees.
Validation of SfM has been done by calculating the AUC (Metz, 1978) for three test areas with a reliable landslide inventory in Switzerland. These test areas are in mountainous areas ranging 0.5 – 7.5 km2 with varying mean slope gradients (18 - 28°). The density of inventoried historical landslides varied from 0.4 – 59 slides/km2. This resulted in AUC values between 0.64 and 0.86. Our study showed that the approach used in SfM can reproduce shallow landslide onset susceptibility on a regional scale observed in reality.
SfM was developed to quantify the stabilizing effect of vegetation at regional scale and localize potential areas where the protective effect of forests can be improved. A first version of the model will be released in 2020 by the ecorisQ association (www.ecorisq.org).
Feiko Van Zadelhoff; Luuk Dorren; Massimiliano Schwarz. SlideforMap – a regional scale probabilistic model for shallow landslide onset analysis and protection forest management. 2020, 1 .
AMA StyleFeiko Van Zadelhoff, Luuk Dorren, Massimiliano Schwarz. SlideforMap – a regional scale probabilistic model for shallow landslide onset analysis and protection forest management. . 2020; ():1.
Chicago/Turabian StyleFeiko Van Zadelhoff; Luuk Dorren; Massimiliano Schwarz. 2020. "SlideforMap – a regional scale probabilistic model for shallow landslide onset analysis and protection forest management." , no. : 1.
The increasing urbanization of mountainous areas increased the risk imposed on residential buildings and infrastructure. In Switzerland, shallow landslides and hillslope debris flows are responsible every year for high infrastructure damage, blocking of important highways, evacuations and deaths. Up till now, the assessment of these processes has been mainly based on the experience of experts, especially in the assessment of their run-out extent and expected damage. In this research we present a new computationally efficient Discrete Element Model (DEM) which has been developed for the aim of simulating the run-out of hillslope debris flows.
YADE-DEM open source code has been extended and an elasto-plastic adhesive contact law have been implemented, which partially account for the presence of the fluid composed of water and find material. This is achieved through the adhesive aspect of the contact law, which would indirectly take the presence of such fluid into account, as this fluid would increase the cohesion of the flowing mass. A parametric study has been carried out to define the most sensitive model parameters, which were found to be the microscopic basal friction angle (Φb) and the ratio between stiffness parameters (loading and unloading) of the flowing particles . Data of full-scale experiments of hillslope debris flows were used to compare the flow kinematics with the model’s prediction. A good agreement between the model and experiments was observed concerning the mean front velocity (average margin of error of 8%) and the maximum applied pressure (average margin of error of 5%), with less agreement of the flow height (average margin of error of 13%). Detailed comparisons of pressure evolution between different selected experiments and simulations revealed the model’s capability of reproducing observed pressure curves, especially during the primary loading phase, leading to maximum pressure.
In order to test the model’s prediction of run-out distance of hillslope debris flow, hundreds of past hillslope debris flow events in the Swiss Alps were analyzed and 30 cases were selected representing different situations (i.e. different release volumes, slopes and forest cover). Due to the discrete nature of results in YADE, a GIS algorithm was developed in order to create envelopes representing the temporal evolution of the simulated propagating processes, which were compared to the those of the historical events. Results of the comparison revealed that, with the calibration of the two sensitive parameters in YADE, a fair to very good agreement was observed between the envelopes of the model and those of historical events for 87% of the tested cases. Difficulties in reproducing the envelopes of the rest of the cases are linked to the uncertainties in the mapping of the envelopes of past events, the role of the forest which is not taken into account in the model, and the lack of direct representation of fluid in the model.
Adel Albaba; Niels Hollard; Christoph Schaller; Massimiliano Schwarz; Luuk Dorren. Comparing a newly developed DEM-based runout model for hillslope debris flows with full-scale experiments and historical events. 2020, 1 .
AMA StyleAdel Albaba, Niels Hollard, Christoph Schaller, Massimiliano Schwarz, Luuk Dorren. Comparing a newly developed DEM-based runout model for hillslope debris flows with full-scale experiments and historical events. . 2020; ():1.
Chicago/Turabian StyleAdel Albaba; Niels Hollard; Christoph Schaller; Massimiliano Schwarz; Luuk Dorren. 2020. "Comparing a newly developed DEM-based runout model for hillslope debris flows with full-scale experiments and historical events." , no. : 1.
This paper presents a discrete-element-based elastoplastic-adhesive model which is adapted and tested for producing hillslope debris flows. The numerical model produces three phases of particle contacts: elastic, plastic and adhesive. A parametric study was conducted investigating the effect of model parameters and inclination angle on flow height, velocity and pressure, in order to define the most sensitive parameters to calibrate. The model capabilities of simulating different types of cohesive granular flows were tested with different ranges of flow velocities and heights. The basic model parameters, the microscopic basal friction (ϕb) and ratio between stiffness parameters k1/k2, were calibrated using field experiments of hillslope debris flows impacting a pressure-measuring sensor. Simulations of 50 m3 of material were carried out on a channelized surface that is 41 m long and 8 m wide. The calibration process was based on measurements of flow height, flow velocity and the pressure applied to a sensor. Results of the numerical model matched those of the field data in terms of pressure and flow velocity well while less agreement was observed for flow height. Those discrepancies in results were due in part to the deposition of material in the field test, which is not reproducible in the model. Results of best-fit model parameters against selected experimental tests suggested that a link might exist between the model parameters ϕb and k1/k2 and the initial conditions of the tested granular material (bulk density and water and fine contents). The good performance of the model against the full-scale field experiments encourages further investigation by conducting lab-scale experiments with detailed variation in water and fine content to better understand their link to the model's parameters.
Adel Albaba; Massimiliano Schwarz; Corinna Wendeler; Bernard Loup; Luuk Dorren. Numerical modeling using an elastoplastic-adhesive discrete element code for simulating hillslope debris flows and calibration against field experiments. Natural Hazards and Earth System Sciences 2019, 19, 2339 -2358.
AMA StyleAdel Albaba, Massimiliano Schwarz, Corinna Wendeler, Bernard Loup, Luuk Dorren. Numerical modeling using an elastoplastic-adhesive discrete element code for simulating hillslope debris flows and calibration against field experiments. Natural Hazards and Earth System Sciences. 2019; 19 (11):2339-2358.
Chicago/Turabian StyleAdel Albaba; Massimiliano Schwarz; Corinna Wendeler; Bernard Loup; Luuk Dorren. 2019. "Numerical modeling using an elastoplastic-adhesive discrete element code for simulating hillslope debris flows and calibration against field experiments." Natural Hazards and Earth System Sciences 19, no. 11: 2339-2358.
Passive earth resistance plays an important role in slope stability analyses for predicting shallow landslide susceptibility. Three‐dimensional models estimate the contribution of this factor to slope stability using geotechnical theories designed for retaining structures and add it to the resistive forces. Systematic investigations have not been conducted to quantify this resistance in soils experiencing compression during the triggering of shallow landslides. This study presents field‐scale experimental data of passive earth force for cohesive and frictional clayey gravel evaluated at different combinations of soil depths and slopes. The experimental setup included a specialized device composed of a steel structure and a stiff plate that moved toward a mass of soil. In both dynamic and quasi‐static states, force‐displacement curves and maximum compression resistance were determined for several water content conditions induced by a rainfall simulator. The maximum dynamic force ranged from 8.49 kN to 31.67 kN for soil depths ranging between 0.36 m and 0.50 m, whereas the quasi‐static force corresponded to 60% of the dynamic force. Furthermore, rainfall generated an additional decrease of compression resistance compared to that measured in the field. A comparison of measured data with theoretical models of passive earth force indicated that Rankine's solution provided the best estimate, whereas the logarithmic spiral approach significantly overestimated passive earth force by up to 70%. Therefore, the correct choice of geotechnical formulation or the direct use of field measurements to estimate passive earth force may significantly improve the accuracy of 3‐D limit equilibrium models for assessing slope stability over natural landscapes.
Alessio Cislaghi; Denis Cohen; Eric Gasser; Gian Battista Bischetti; Massimiliano Schwarz. Field Measurements of Passive Earth Forces in Steep, Shallow, Landslide‐Prone Areas. Journal of Geophysical Research: Earth Surface 2019, 124, 838 -866.
AMA StyleAlessio Cislaghi, Denis Cohen, Eric Gasser, Gian Battista Bischetti, Massimiliano Schwarz. Field Measurements of Passive Earth Forces in Steep, Shallow, Landslide‐Prone Areas. Journal of Geophysical Research: Earth Surface. 2019; 124 (3):838-866.
Chicago/Turabian StyleAlessio Cislaghi; Denis Cohen; Eric Gasser; Gian Battista Bischetti; Massimiliano Schwarz. 2019. "Field Measurements of Passive Earth Forces in Steep, Shallow, Landslide‐Prone Areas." Journal of Geophysical Research: Earth Surface 124, no. 3: 838-866.
This paper presents a Discrete Element-based elasto-plastic-adhesive model which is adapted and tested for producing hillslope debris flows. The numerical model produces three phases of particle contacts: elastic, plastic and adhesion. The model capabilities of simulating different types of cohesive granular flows were tested with different ranges of flow velocities and heights. The basic model parameters, being the basal friction (ϕb) and normal restitution coefficient (ϵn), were calibrated using field experiments of hillslope debris flows impacting two sensors. Simulations of 50 m3 of material were carried out on a channelized surface that is 41 m long and 8 m wide. The calibration process was based on measurements of flow height, flow velocity and the pressure applied to a sensor. Results of the numerical model matched well those of the field data in terms of pressure and flow velocity while less agreement was observed for flow height. Those discrepancies in results were due in part to the deposition of material in the field test which are not reproducible in the model. A parametric study was conducted to further investigate that effect of model parameters and inclination angle on flow height, velocity and pressure. Results of best-fit model parameters against selected experimental tests suggested that a link might exist between the model parameters ϕb and ϵn and the initial conditions of the tested granular material (bulk density and water and fine contents). The good performance of the model against the full-scale field experiments encourages further investigation by conducting lab-scale experiments with detailed variation of water and fine content to better understand their link to the model's parameters.
Adel Albaba; Massimiliano Schwarz; Corinna Wendeler; Bernard Loup; Luuk Dorren. Elasto-plastic-adhesive DEM model for simulating hillslope debris flows: cross comparison with field experiments. 2018, 1 -30.
AMA StyleAdel Albaba, Massimiliano Schwarz, Corinna Wendeler, Bernard Loup, Luuk Dorren. Elasto-plastic-adhesive DEM model for simulating hillslope debris flows: cross comparison with field experiments. . 2018; ():1-30.
Chicago/Turabian StyleAdel Albaba; Massimiliano Schwarz; Corinna Wendeler; Bernard Loup; Luuk Dorren. 2018. "Elasto-plastic-adhesive DEM model for simulating hillslope debris flows: cross comparison with field experiments." , no. : 1-30.
Vegetation strongly influences the hydrology of hillslopes through different processes that may be important for the mitigation of flood risks. The complicated interactions of mechanisms that contribute to the formation of runoff at different spatial and temporal scales represent a big challenge for catchment hydrology. However, it is recognized that storage capacity and infiltration are one of the most important processes positively influenced by vegetation. Moreover, numerical studies have discussed the importance of preferential subsurface flow as dominant processes contributing to fast runoff in mountain catchments. While, previous studies have shown the importance of bedrock topography on the connectivity and drainage of shallow soil mantled hillslopes, no studies discussed the role of heterogeneous root distribution on the drainage of hillslope with stagnic soils so far. In this work we present a conceptual model that aims to link modelling approaches of root distribution combined to hydrological modelling of preferential flow, and the quantification of hydrological connectivity of forest hillslopes. We use a spatial distributed root distribution model to calculate the number of fine roots based on the structure of forest cover (tree position and dimension). The results of root distribution are used as input parameter for the quantification of preferential flow patches using a numerical approach. Finally, we use the spatial distributed values of preferential flow to calculate the hydrological connectivity of a vegetated hillslope considering topography and soil profile characteristics. The new proposed framework is calibrated through field experiments at the soil profile scale, and the first results of the numerical simulations considering different combination of parameters are discussed in the context of protection forests mitigation effects against flood risks.
Massimiliano Schwarz; Filippo Giadrossich; Peter Lüscher; Peter F. Germann. Subsurface hydrological connectivity of vegetated slopes: a new modeling approach. Hydrology and Earth System Sciences Discussions 2018, 2018, 1 -32.
AMA StyleMassimiliano Schwarz, Filippo Giadrossich, Peter Lüscher, Peter F. Germann. Subsurface hydrological connectivity of vegetated slopes: a new modeling approach. Hydrology and Earth System Sciences Discussions. 2018; 2018 ():1-32.
Chicago/Turabian StyleMassimiliano Schwarz; Filippo Giadrossich; Peter Lüscher; Peter F. Germann. 2018. "Subsurface hydrological connectivity of vegetated slopes: a new modeling approach." Hydrology and Earth System Sciences Discussions 2018, no. : 1-32.
Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models usually include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the self-organized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. The variation in root stiffness with diameter can, in some cases, invert this relationship. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of this force is comparable to the slope-perpendicular tensile force. In this case, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, a crack parallel to the slope forms near the top of the hillslope. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, intermediate-sized roots (5 to 20 mm in diameter) appear to contribute most to root reinforcement. Our results show more complex behaviors than can be obtained with the traditional slope-uniform, apparent-cohesion approach. A full understanding of the mechanisms of shallow landslide triggering requires a complete re-evaluation of this traditional approach that cannot predict where and how forces are mobilized and distributed in roots and soils, and how these control shallow landslides shape, size, location, and timing.
Denis Cohen; Massimiliano Schwarz. Tree-root control of shallow landslides. Earth Surface Dynamics 2017, 5, 451 -477.
AMA StyleDenis Cohen, Massimiliano Schwarz. Tree-root control of shallow landslides. Earth Surface Dynamics. 2017; 5 (3):451-477.
Chicago/Turabian StyleDenis Cohen; Massimiliano Schwarz. 2017. "Tree-root control of shallow landslides." Earth Surface Dynamics 5, no. 3: 451-477.
Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. These observations contradict the common assumptions used in present models. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the self-organized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. The model is driven by root data of Norway spruce obtained from laboratory and field measurements. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of these forces is comparable to the slope-perpendicular tensile forces. In these cases, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, hillslopes form a crack parallel to the slope near its top. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, large roots, greater than 20 mm, are too few too contribute significantly to root reinforcement. Omitting roots larger than 8 mm predicted a landslide when none should have occurred. Intermediate roots (5 to 20 mm) appear to contribute most to root reinforcement and should be included in calculations. To fully understand the mechanisms of shallow landslide triggering requires a complete re-evaluation of the traditional apparent-cohesion approach that does not reproduce the incremental loading of roots in tension or in compression. Our model shows that it is important to consider the forces held by roots in a way that is entirely different than done thus far. Our work quantifies the contribution of roots in tension and compression which now finally permits to analyze more realistically the role of root reinforcement during the triggering of shallow landslides.
Denis Cohen; Massimiliano Schwarz. Tree-roots control of shallow landslides. 2017, 2017, 1 -43.
AMA StyleDenis Cohen, Massimiliano Schwarz. Tree-roots control of shallow landslides. . 2017; 2017 ():1-43.
Chicago/Turabian StyleDenis Cohen; Massimiliano Schwarz. 2017. "Tree-roots control of shallow landslides." 2017, no. : 1-43.
The control of erosion processes is an important issue worldwide. In New Zealand, previous studies have shown the benefits of reforestation or bioengineering measures to control erosion. The impetus for this work focuses on linking recent research to the needs of practitioners by formulating quantitative guidelines for planning and evaluation of ground bioengineering stabilisation measures. Two root distribution datasets of ‘Veronese’ poplar (Populus deltoides x nigra) were used to calibrate a root distribution model for application on single root systems and to interacting root systems at the hillslope scale. The root distribution model results were then used for slope stability calculations in order to quantitatively evaluate the mechanical stabilisation effects of spaced trees on pastoral hillslopes. This study shows that root distribution data are important inputs for quantifying root reinforcement at the hillslope scale, and that root distribution strongly depends on local environmental conditions and on the tree planting density. The results also show that the combination of soil mechanical properties (soil angle of internal friction and cohesion) and topographic conditions (slope inclination) are the major parameters to define how much root reinforcement is needed to stabilise a specific slope, and thus the spacing of the trees to achieve this. For the worst scenarios, effective root reinforcement (>2 kPa) is reached for tree spacing ranging from 2500 stems per hectare (sph) for 0.1 m stem diameter at breast height (DBH) to 300 sph for 0.3 m stem DBH. In ideal growing conditions, tree spacing less than 100 sph is sufficient for stem DBH greater than 0.15 m. New quantitative information gained from this study can provide a basis for evaluating planting strategies using poplar trees for erosion control on pastoral hill country in New Zealand.
M. Schwarz; Christopher Phillips; M. Marden; I. R. McIvor; G. B. Douglas; A. Watson. Modelling of root reinforcement and erosion control by ‘Veronese’ poplar on pastoral hill country in New Zealand. New Zealand Journal of Forestry Science 2016, 46, 4 .
AMA StyleM. Schwarz, Christopher Phillips, M. Marden, I. R. McIvor, G. B. Douglas, A. Watson. Modelling of root reinforcement and erosion control by ‘Veronese’ poplar on pastoral hill country in New Zealand. New Zealand Journal of Forestry Science. 2016; 46 (1):4.
Chicago/Turabian StyleM. Schwarz; Christopher Phillips; M. Marden; I. R. McIvor; G. B. Douglas; A. Watson. 2016. "Modelling of root reinforcement and erosion control by ‘Veronese’ poplar on pastoral hill country in New Zealand." New Zealand Journal of Forestry Science 46, no. 1: 4.
It is well recognized that roots reinforce soils and that the distribution of roots within vegetated hillslopes strongly influences the spatial distribution of soil strength. Previous studies have focussed on the contribution of root reinforcement under conditions of tension or shear. However, no systematic investigation into the contribution of root reinforcement to soils experiencing compression, such as the passive Earth forces at the toe of a landslide, is found in the literature. An empirical-analytical model (CoRoS) for the quantification of root reinforcement in soils under compression is presented and tested against experimental data. The CoRoS model describes the force-displacement behavior of compressed, rooted soils and can be used to provide a framework for improving slope stability calculations. Laboratory results showed that the presence of 10 roots with diameters ranging from 6 to 28 mm in a rectangular soil profile 0.72 m by 0.25 m increased the compressive strength of the soil by about 40% (2.5 kN) at a displacement of 0.05 m, while the apparent stiffness of the rooted soil was 38% higher than for root-free soil. The CoRoS model yields good agreement with experimentally determined values of maximum reinforcement force and compression force as a function of displacement. These results indicate that root reinforcement under compression has a major influence on the mechanical behavior of soil and that the force-displacement behavior of roots should be included in analysis of the compressive regimes that commonly are present in the toe of landslides.
Mike Schwarz; A. Rist; Denis Cohen; F. Giadrossich; P. Egorov; D. Büttner; M. Stolz; J.‐J. Thormann. Root reinforcement of soils under compression. Journal of Geophysical Research: Earth Surface 2015, 120, 2103 -2120.
AMA StyleMike Schwarz, A. Rist, Denis Cohen, F. Giadrossich, P. Egorov, D. Büttner, M. Stolz, J.‐J. Thormann. Root reinforcement of soils under compression. Journal of Geophysical Research: Earth Surface. 2015; 120 (10):2103-2120.
Chicago/Turabian StyleMike Schwarz; A. Rist; Denis Cohen; F. Giadrossich; P. Egorov; D. Büttner; M. Stolz; J.‐J. Thormann. 2015. "Root reinforcement of soils under compression." Journal of Geophysical Research: Earth Surface 120, no. 10: 2103-2120.
Root networks contribute to slope stability through complex interactions with soil that include mechanical compression and tension. Due to the spatial heterogeneity of root distribution and the dynamics of root turnover, the quantification of root reinforcement on steep slopes is challenging and consequently the calculation of slope stability also. Although considerable progress has been made, some important aspects of root mechanics remain neglected. In this study we address specifically the role of root-strength variability on the mechanical behavior of a root bundle. Many factors contribute to the variability of root mechanical properties even within a single class of diameter. This work presents a new approach for quantifying root reinforcement that considers the variability of mechanical properties of each root diameter class. Using the data of laboratory tensile tests and field pullout tests, we calibrate the parameters of the Weibull survival function to implement the variability of root strength in a numerical model for the calculation of root reinforcement (RBMw). The results show that, for both laboratory and field data sets, the parameters of the Weibull distribution may be considered constant with the exponent equal to 2 and the normalized failure displacement equal to 1. Moreover, the results show that the variability of root strength in each root diameter class has a major influence on the behavior of a root bundle with important implications when considering different approaches in slope stability calculation. Sensitivity analysis shows that the calibration of the equations of the tensile force, the elasticity of the roots, and the root distribution are the most important steps. The new model allows the characterization of root reinforcement in terms of maximum pullout force, stiffness, and energy. Moreover, it simplifies the implementation of root reinforcement in slope stability models. The realistic quantification of root reinforcement for tensile, shear and compression behavior allows for the consideration of the stabilization effects of root networks on steep slopes and the influence that this has on the triggering of shallow landslides.
M. Schwarz; F. Giadrossich; D. Cohen. Modeling root reinforcement using a root-failure Weibull survival function. Hydrology and Earth System Sciences 2013, 17, 4367 -4377.
AMA StyleM. Schwarz, F. Giadrossich, D. Cohen. Modeling root reinforcement using a root-failure Weibull survival function. Hydrology and Earth System Sciences. 2013; 17 (11):4367-4377.
Chicago/Turabian StyleM. Schwarz; F. Giadrossich; D. Cohen. 2013. "Modeling root reinforcement using a root-failure Weibull survival function." Hydrology and Earth System Sciences 17, no. 11: 4367-4377.