Terracing is one of the oldest means of saving soil and water. The objective of this paper is to ... more Terracing is one of the oldest means of saving soil and water. The objective of this paper is to provide information on the different types of terraces and their functioning, and to describe advantages and disadvantages of terraces regarding their efficacy to stop or reduce soil erosion. Existing literature and information shows that terraces can considerably reduce soil loss due to water erosion if they are well planned, correctly constructed and properly maintained. If not maintained, they can provoke land degradation. Terracing has to be combined with additional soil conservation practices, of which the most important one is the maintenance of a permanent soil cover. There are several disadvantages to terracing, therefore hedgerows and vegetation ridges could be good alternatives for terraces, but eventually they work in the same way. A future challenge is to develop conservation practices that are also productive. The ancient farming techniques such as terracing may provide a go...
The role of trees and forests as mitigation measures is more and more taken into account in natur... more The role of trees and forests as mitigation measures is more and more taken into account in natural hazard engineering. This requires quantification of the capacity of individual trees to dissipate the energy released by dynamic impacts, which has previously only been based on data obtained from static tree-pulling tests or from dynamic impact tests on wood samples. We predicted that these data are not representative of the maximum amount of energy that can be dissipated by living trees during dynamic impacts. To test this prediction, we carried out rockfall experiments on a forested slope in the French Alps. To calculate the rock’s energy before and after impact, rockfalls were filmed digitally. The recordings of nine impacts causing instantaneous breakage of Abies alba Mill. trees were analyzed in detail. An exponential relationship between stem diameter at breast height (DBH) and the maximum amount of energy a tree can dissipate was highly correlated for all of our experimental d...
Forests are multi-functional ecosystems, but a major function is not well taken into account: the... more Forests are multi-functional ecosystems, but a major function is not well taken into account: the protective function against rockfall risks. Its why research institutes (dealing with mountain forest management and risk assessment) and private companies (working in the field of risk prevention) from France, Austria, Spain and Switzerland have decided to initiate a research project on this topic: the ROCKFOR project (http://rockfor.grenoble.cemagref.fr/). The duration of this project is 3 years and the starting date was the first of January 2001. The project aim is to incorporate tree mechanical behaviour in a spatial rockfall model in order to assess the efficiency of forest stands against rockfall and to produce management guidelines for sustainable rockfall hazard mitigation by mountain forests. This article presents the framework used for the tree mechanical behaviour modelling and the rockfall real size experiments methodology. As the data coming from these experiments will be u...
/ Le Guide de Sylviculture de Montagne Alpes du Nord synthetise une demarche d'analyse des pe... more / Le Guide de Sylviculture de Montagne Alpes du Nord synthetise une demarche d'analyse des peuplements forestiers de montagne et etablit des recommandations sylvicoles pour les peuplements forestiers a objectif de protection marquee ou a objectif de production. Il est comporte : - Une partie introductive presentant de la demarche d'analyse et une fiche diagnostique de terrain. - Une partie presentant des cles diagnostiques sur les themes des risques naturels, de l'exploitation, des stations forestieres et de la structure des peuplements. - Une partie presentant des recommandations sylvicoles pour 9 unites dynamiques differentes (une unite dynamique regroupe un certain nombre de stations forestieres comparables en termes de preconisations de gestion). Pour chaque Unite dynamique, les preconisations sont declinees suivant la priorite de gestion (protection contre les risques naturels ou production) et par type de structure de peuplement. - Une partie regroupant des fiches thematiques sur les themes de l'ecologie et la dynamique naturelle des peuplements, sur les risques naturels, sur la sylviculture et l'exploitation, sur la biodiversite et les autres fonctions de la foret. - Des annexes avec les fiches d'analyse de terrain vierges a photocopier. Par rapport aux documents anterieurs, le Guide presente les originalites suivantes : - Une demarche d'analyse de terrain formalisee dans la fiche de terrain combinant a la fois un diagnostic de terrain precis, et une integration de contraintes et objectifs de gestion multiples. - Une analyse precise du role de protection de la foret contre les risques naturels - Une prise en compte explicite de la station forestiere.
It is still uncertain what a mountain forest should look like to provide optimal protection again... more It is still uncertain what a mountain forest should look like to provide optimal protection against rockfall. Knowledge is limited due to the slow reaction of mountain forests to the rapid environmental and socio-economic changes that have occurred in the Alps over the past 100 years. Fortunately, research has progressed and an enormous amount of experiential knowledge has been gained, providing a basis for finding a balance between maintaining traditional practices and implementing new technology. This paper identifies an approach that could be used as a rough framework for managing and sustaining forests with a protective function in the Alps. Three main points are discussed: 1) evaluating traditional ‘good practices’ and mistakes, 2) evaluating new technologies, especially those in the field of rockfall-protection forests, and 3) merging the best of the two worlds. The evaluation of traditional ways of managing protection forests shows that the 'do nothing approach' and e...
Large woody debris fulfills important ecological functions in river systems, but it also increase... more Large woody debris fulfills important ecological functions in river systems, but it also increases the risk of damage during flood events in populated regions or along traffic routes. The mobilization and recruitment of “fresh” large woody debris has often been documented to be an important component of the total amount of wood transported during flood events in mountainous catchments. Therefore, research interest on recruitment, transport and deposition of large woody debris has arisen during the last decades. Although the main contributing processes are generally acknowledged and several modeling approaches have been proposed, less is known about the precise mechanisms behind recruitment and mobilization in mountainous catchments. Additionally, the role of vegetation in influencing the magnitude and the frequency of these mechanisms is often neglected or not considered in detail. Root reinforcement is particularly recognized to play an important role on bank erosion, bank failure ...
To compensate for the temporary loss of protection due to the reduced forest stand density in the... more To compensate for the temporary loss of protection due to the reduced forest stand density in the felling area, a considerable part of the trees felled in rock fall protection forests are left in place. Although being a widely used technique, there is little objective information on the efficacy of these trees felled transverse to the slope. To quantify the protective function of such structures, full scale rock fall tests on a protective structure made with trees felled transverse to the slope were carried out. The results show significant energy losses when impacting the structure. However, the rock energy significantly increases again after the structure if the rock is not stopped. Consequently, a larger number of transverse tree trunks is required to stop all rocks and, to increase the number of stopped rocks, the structure height has to be determined in relation to the rock size which promotes, in most cases, structures made of stacked trees.
In order to model rockfall on forested slopes, we developed a trajectory rockfall model based on ... more In order to model rockfall on forested slopes, we developed a trajectory rockfall model based on the discrete element method (DEM). This model is able to take the complex mechanical processes at work during an impact into account (large deformations, complex contact conditions) and can explicitly simulate block/soil, block/tree contacts as well as contacts between neighbouring trees. In this paper, we describe the DEM model developed and we use it to assess the protective effect of different types of forest. In addition, we compared it with a more classical rockfall simulation model. The results highlight that forests can significantly reduce rockfall hazard and that the spatial structure of coppice forests has to be taken into account in rockfall simulations in order to avoid overestimating the protective role of these forest structures against rockfall hazard. In addition, the protective role of the forests is mainly influenced by the basal area. Finally, the advantages and limitations of the DEM model were compared with classical rockfall modelling approaches.
Wald, Steinschlagschutznetz oder beides? Ein risikobasierter Vergleich unter Einbezug von Störung... more Wald, Steinschlagschutznetz oder beides? Ein risikobasierter Vergleich unter Einbezug von Störungen Dank Schutzwäldern können in der Schweiz an vielen Orten die Kosten für technische Schutzmassnahmen reduziert oder vermieden werden. Um finanzielle Mittel im Schutzwald- und Naturgefahrenmanagement möglichst effizient einsetzen zu können, ist eine realistische Quantifizierung der langfristigen Schutzwirkung wichtig. Das Ziel dieser Studie ist es, den Kapitalwert eines Steinschlagschutzwaldes in Mendrisio (TI) zu ermitteln und mit dem Kapitalwert von Steinschlagschutznetzen sowie einer Kombination der beiden Massnahmen zu vergleichen. Dabei soll die zeitliche Variabilität in der Schutzwirkung des Waldes aufgrund von Störungen miteinbezogen werden. Die in der Analyse berücksichtigten Kosten sind Holzerntekosten sowie Investitions- und Unterhaltskosten für die Steinschlagschutznetze. Der angenommene Nutzen setzt sich aus der monetarisierten Risikoreduktion einer Schutzmassnahme sowie aus...
Floods and subsequent bank erosion are recurring hazards that pose threats to people and can caus... more 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 a...
Large woody debris (LWD) exacerbates flood damages near civil structures and in urbanized areas a... more Large woody debris (LWD) exacerbates flood damages near civil structures and in urbanized areas and the awareness of LWD as a risk is becoming more and more relevant. The recruitment of “fresh” large woody debris has been documented to play a significant role of the total amount of wood transported during flood events in mountain catchments. Predominately, LWD recruitment due to hydraulic and geotechnical bank erosion and shallow landslides contribute to high volumes of wood during floods. Quantifying the effects of vegetation on channel and slope processes is extremely complex. This manuscript therefore presents the concepts that are being implemented in a new modelling framework that aims to improve the quantification of vegetation effects on LWD recruitment processes. One of the focuses of the model framework is the implementation of the effect of spatio-temporal distribution of root reinforcement in recruitment processes such as bank erosion and shallow landslides in mountain ca...
... Ces rochers arrêtés par les arbres montrent également que les forêts de montagne peuvent, dan... more ... Ces rochers arrêtés par les arbres montrent également que les forêts de montagne peuvent, dans certains cas, offrir une alter-native, écologique et économique efficace au génie civil, comme l'ont confirmée Jahn (1988) et Dorren et al. (2005). ...
Terracing is one of the oldest means of saving soil and water. The objective of this paper is to ... more Terracing is one of the oldest means of saving soil and water. The objective of this paper is to provide information on the different types of terraces and their functioning, and to describe advantages and disadvantages of terraces regarding their efficacy to stop or reduce soil erosion. Existing literature and information shows that terraces can considerably reduce soil loss due to water erosion if they are well planned, correctly constructed and properly maintained. If not maintained, they can provoke land degradation. Terracing has to be combined with additional soil conservation practices, of which the most important one is the maintenance of a permanent soil cover. There are several disadvantages to terracing, therefore hedgerows and vegetation ridges could be good alternatives for terraces, but eventually they work in the same way. A future challenge is to develop conservation practices that are also productive. The ancient farming techniques such as terracing may provide a go...
The role of trees and forests as mitigation measures is more and more taken into account in natur... more The role of trees and forests as mitigation measures is more and more taken into account in natural hazard engineering. This requires quantification of the capacity of individual trees to dissipate the energy released by dynamic impacts, which has previously only been based on data obtained from static tree-pulling tests or from dynamic impact tests on wood samples. We predicted that these data are not representative of the maximum amount of energy that can be dissipated by living trees during dynamic impacts. To test this prediction, we carried out rockfall experiments on a forested slope in the French Alps. To calculate the rock’s energy before and after impact, rockfalls were filmed digitally. The recordings of nine impacts causing instantaneous breakage of Abies alba Mill. trees were analyzed in detail. An exponential relationship between stem diameter at breast height (DBH) and the maximum amount of energy a tree can dissipate was highly correlated for all of our experimental d...
Forests are multi-functional ecosystems, but a major function is not well taken into account: the... more Forests are multi-functional ecosystems, but a major function is not well taken into account: the protective function against rockfall risks. Its why research institutes (dealing with mountain forest management and risk assessment) and private companies (working in the field of risk prevention) from France, Austria, Spain and Switzerland have decided to initiate a research project on this topic: the ROCKFOR project (http://rockfor.grenoble.cemagref.fr/). The duration of this project is 3 years and the starting date was the first of January 2001. The project aim is to incorporate tree mechanical behaviour in a spatial rockfall model in order to assess the efficiency of forest stands against rockfall and to produce management guidelines for sustainable rockfall hazard mitigation by mountain forests. This article presents the framework used for the tree mechanical behaviour modelling and the rockfall real size experiments methodology. As the data coming from these experiments will be u...
/ Le Guide de Sylviculture de Montagne Alpes du Nord synthetise une demarche d'analyse des pe... more / Le Guide de Sylviculture de Montagne Alpes du Nord synthetise une demarche d'analyse des peuplements forestiers de montagne et etablit des recommandations sylvicoles pour les peuplements forestiers a objectif de protection marquee ou a objectif de production. Il est comporte : - Une partie introductive presentant de la demarche d'analyse et une fiche diagnostique de terrain. - Une partie presentant des cles diagnostiques sur les themes des risques naturels, de l'exploitation, des stations forestieres et de la structure des peuplements. - Une partie presentant des recommandations sylvicoles pour 9 unites dynamiques differentes (une unite dynamique regroupe un certain nombre de stations forestieres comparables en termes de preconisations de gestion). Pour chaque Unite dynamique, les preconisations sont declinees suivant la priorite de gestion (protection contre les risques naturels ou production) et par type de structure de peuplement. - Une partie regroupant des fiches thematiques sur les themes de l'ecologie et la dynamique naturelle des peuplements, sur les risques naturels, sur la sylviculture et l'exploitation, sur la biodiversite et les autres fonctions de la foret. - Des annexes avec les fiches d'analyse de terrain vierges a photocopier. Par rapport aux documents anterieurs, le Guide presente les originalites suivantes : - Une demarche d'analyse de terrain formalisee dans la fiche de terrain combinant a la fois un diagnostic de terrain precis, et une integration de contraintes et objectifs de gestion multiples. - Une analyse precise du role de protection de la foret contre les risques naturels - Une prise en compte explicite de la station forestiere.
It is still uncertain what a mountain forest should look like to provide optimal protection again... more It is still uncertain what a mountain forest should look like to provide optimal protection against rockfall. Knowledge is limited due to the slow reaction of mountain forests to the rapid environmental and socio-economic changes that have occurred in the Alps over the past 100 years. Fortunately, research has progressed and an enormous amount of experiential knowledge has been gained, providing a basis for finding a balance between maintaining traditional practices and implementing new technology. This paper identifies an approach that could be used as a rough framework for managing and sustaining forests with a protective function in the Alps. Three main points are discussed: 1) evaluating traditional ‘good practices’ and mistakes, 2) evaluating new technologies, especially those in the field of rockfall-protection forests, and 3) merging the best of the two worlds. The evaluation of traditional ways of managing protection forests shows that the 'do nothing approach' and e...
Large woody debris fulfills important ecological functions in river systems, but it also increase... more Large woody debris fulfills important ecological functions in river systems, but it also increases the risk of damage during flood events in populated regions or along traffic routes. The mobilization and recruitment of “fresh” large woody debris has often been documented to be an important component of the total amount of wood transported during flood events in mountainous catchments. Therefore, research interest on recruitment, transport and deposition of large woody debris has arisen during the last decades. Although the main contributing processes are generally acknowledged and several modeling approaches have been proposed, less is known about the precise mechanisms behind recruitment and mobilization in mountainous catchments. Additionally, the role of vegetation in influencing the magnitude and the frequency of these mechanisms is often neglected or not considered in detail. Root reinforcement is particularly recognized to play an important role on bank erosion, bank failure ...
To compensate for the temporary loss of protection due to the reduced forest stand density in the... more To compensate for the temporary loss of protection due to the reduced forest stand density in the felling area, a considerable part of the trees felled in rock fall protection forests are left in place. Although being a widely used technique, there is little objective information on the efficacy of these trees felled transverse to the slope. To quantify the protective function of such structures, full scale rock fall tests on a protective structure made with trees felled transverse to the slope were carried out. The results show significant energy losses when impacting the structure. However, the rock energy significantly increases again after the structure if the rock is not stopped. Consequently, a larger number of transverse tree trunks is required to stop all rocks and, to increase the number of stopped rocks, the structure height has to be determined in relation to the rock size which promotes, in most cases, structures made of stacked trees.
In order to model rockfall on forested slopes, we developed a trajectory rockfall model based on ... more In order to model rockfall on forested slopes, we developed a trajectory rockfall model based on the discrete element method (DEM). This model is able to take the complex mechanical processes at work during an impact into account (large deformations, complex contact conditions) and can explicitly simulate block/soil, block/tree contacts as well as contacts between neighbouring trees. In this paper, we describe the DEM model developed and we use it to assess the protective effect of different types of forest. In addition, we compared it with a more classical rockfall simulation model. The results highlight that forests can significantly reduce rockfall hazard and that the spatial structure of coppice forests has to be taken into account in rockfall simulations in order to avoid overestimating the protective role of these forest structures against rockfall hazard. In addition, the protective role of the forests is mainly influenced by the basal area. Finally, the advantages and limitations of the DEM model were compared with classical rockfall modelling approaches.
Wald, Steinschlagschutznetz oder beides? Ein risikobasierter Vergleich unter Einbezug von Störung... more Wald, Steinschlagschutznetz oder beides? Ein risikobasierter Vergleich unter Einbezug von Störungen Dank Schutzwäldern können in der Schweiz an vielen Orten die Kosten für technische Schutzmassnahmen reduziert oder vermieden werden. Um finanzielle Mittel im Schutzwald- und Naturgefahrenmanagement möglichst effizient einsetzen zu können, ist eine realistische Quantifizierung der langfristigen Schutzwirkung wichtig. Das Ziel dieser Studie ist es, den Kapitalwert eines Steinschlagschutzwaldes in Mendrisio (TI) zu ermitteln und mit dem Kapitalwert von Steinschlagschutznetzen sowie einer Kombination der beiden Massnahmen zu vergleichen. Dabei soll die zeitliche Variabilität in der Schutzwirkung des Waldes aufgrund von Störungen miteinbezogen werden. Die in der Analyse berücksichtigten Kosten sind Holzerntekosten sowie Investitions- und Unterhaltskosten für die Steinschlagschutznetze. Der angenommene Nutzen setzt sich aus der monetarisierten Risikoreduktion einer Schutzmassnahme sowie aus...
Floods and subsequent bank erosion are recurring hazards that pose threats to people and can caus... more 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 a...
Large woody debris (LWD) exacerbates flood damages near civil structures and in urbanized areas a... more Large woody debris (LWD) exacerbates flood damages near civil structures and in urbanized areas and the awareness of LWD as a risk is becoming more and more relevant. The recruitment of “fresh” large woody debris has been documented to play a significant role of the total amount of wood transported during flood events in mountain catchments. Predominately, LWD recruitment due to hydraulic and geotechnical bank erosion and shallow landslides contribute to high volumes of wood during floods. Quantifying the effects of vegetation on channel and slope processes is extremely complex. This manuscript therefore presents the concepts that are being implemented in a new modelling framework that aims to improve the quantification of vegetation effects on LWD recruitment processes. One of the focuses of the model framework is the implementation of the effect of spatio-temporal distribution of root reinforcement in recruitment processes such as bank erosion and shallow landslides in mountain ca...
... Ces rochers arrêtés par les arbres montrent également que les forêts de montagne peuvent, dan... more ... Ces rochers arrêtés par les arbres montrent également que les forêts de montagne peuvent, dans certains cas, offrir une alter-native, écologique et économique efficace au génie civil, comme l'ont confirmée Jahn (1988) et Dorren et al. (2005). ...
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