Rockfalls into forests: Analysis and simulation of rockfall trajectories ? considerations with respect to mountainous forests in Switzerland

Perret, Simone; Dolf, F.; Kienholz, Hans

doi:10.1007/s10346-004-0014-4

Cited by 76 publications

(44 citation statements)

References 8 publications

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“…The cbA appears to be a good measure of the protective efficacy of forests, as it combines the basal area (which is determined by tree density and tree diameter) with the forested slope length -two parameters which have been promoted as key variables for forest management in previous work (Perret et al, 2004;Berger and Dorren, 2007;Rammer et al, 2015;Fuhr et al, 2015). In a recent study, Dupire et al (2016) showed that the protective effect of forests regarding rockfall frequency and energy can be evaluated only on their basal area, their mean diameter at breast height and the length of the forested slope.…”

Section: Resultsmentioning

confidence: 99%

Quantifying the effect of forests on frequency and intensity of rockfalls

Moos

Dorren

Stoffel

2017

Nat. Hazards Earth Syst. Sci.

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Abstract. Forests serve as a natural means of protection against small rockfalls. Due to their barrier effect, they reduce the intensity and the propagation probability of falling rocks and thus reduce the occurrence frequency of a rockfall event for a given element at risk. However, despite established knowledge on the protective effect of forests, they are generally neglected in quantitative rockfall risk analyses. Their inclusion in quantitative rockfall risk assessment would, however, be necessary to express their efficiency in monetary terms and to allow comparison of forests with other protective measures, such as nets and dams. The goal of this study is to quantify the effect of forests on the occurrence frequency and intensity of rockfalls. We therefore defined an onset frequency of blocks based on a powerlaw magnitude-frequency distribution and determined their propagation probabilities on a virtual slope based on rockfall simulations. Simulations were run for different forest and non-forest scenarios under varying forest stand and terrain conditions. We analysed rockfall frequencies and intensities at five different distances from the release area. Based on two multivariate statistical prediction models, we investigated which of the terrain and forest characteristics predominantly drive the role of forest in reducing rockfall occurrence frequency and intensity and whether they are able to predict the effect of forest on rockfall risk. The rockfall occurrence frequency below forested slopes is reduced between approximately 10 and 90 % compared to non-forested slope conditions; whereas rockfall intensity is reduced by 10 to 70 %. This reduction increases with increasing slope length and decreases with decreasing tree density, tree diameter and increasing rock volume, as well as in cases of clustered or gappy forest structures. The statistical prediction models reveal that the cumulative basal area of trees, block volume and horizontal forest structure represent key variables for the prediction of the protective effect of forests. In order to validate these results, models have to be tested on real slopes with a wide variation of terrain and forest conditions.

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Section: Resultsmentioning

confidence: 99%

Quantifying the effect of forests on frequency and intensity of rockfalls

Moos

Dorren

Stoffel

2017

Nat. Hazards Earth Syst. Sci.

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“…The correct definition of block trajectory (that is to say, the path length, the height, the speed and the kinetic energy of the blocks during the fall) is therefore very important for a correct design. Analytical procedures for the mathematical description of rockfall movement have been developed in the last 20 years (Richards 1988;Pfeiffer and Bowen 1989;Giani 1992;Azzoni et al 1995;Perret et al 2004;Giani et al 2004). When the best position, height and energy to be absorbed is decided on, the correct passive structure can be chosen and designed.…”

Section: Introductionmentioning

confidence: 99%

Ground reinforced embankments for rockfall protection: design and evaluation of full scale tests

2007

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Infrastructures such as roads and railways as well as urbanised areas, in mountainside regions, can frequently be endangered by rockfalls and, therefore, need to be protected against the impact of rolling blocks. Among the various protection works that can be used, ground reinforced embankments can be considered a feasible technique. A set of full-scale tests on embankments made of ground reinforced by geogrids are presented and discussed. The experiments were performed in a specifically designed and constructed test facility, where concrete blocks up to 9,000 kg in weight were thrown onto a geogrid reinforced embankment at a speed of about 30 m/s. Several embankments made of different geogrid types, different soils and construction layouts were tested at different impact energy levels, permitting a quantitative assessment of the resistance impact of these structures. The experimental results were compared with those obtained from a dynamic finite element method numerical model, and a good agreement was obtained.

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“…Several studies have assessed the interaction between rockfall and forest on a local scale, but not on the scale of individual trees (Jahn, 1988;Zinggeler et al, 1991;Mani and Kläy, 1992;Dorren et al, 2004b;Perret et al, 2004;Frehner et al, 2005). In addition, research has mainly focused on short-term observations of contemporary rockfall activity in the field (Luckman, 1976;Douglas, 1980;Gardner, 1983;Matsuoka and Sakai, 1999), or on lichenometric analyses (Luckman and Fiske, 1995;McCarroll et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Spatial and temporal rockfall activity in a forest stand in the Swiss Prealps—A dendrogeomorphological case study

2006

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Rockfall is a major threat to settlements and transportation routes in large parts of the Alps. While protective forest stands in many locations undoubtedly reduce rockfall risk, little is known about the exact frequency and spatial distribution of rockfall activity in a given place or about how these parameters can be assessed. Therefore, the objective of the present study was to reconstruct rockfall events with dendrogeomorphological methods and to analyse the spatial and temporal rockfall activity in a subalpine forest stand. The study site is located in the transit zone of frequently passing, rather small rockfall fragments (mean diameter of 10 to 20 cm). In all, 33 stem discs from previously felled Picea abies trees found at the foot of Schwarzenberg in Diemtigtal (Swiss Prealps) were sampled, and a total number of 301 rockfall events were dated to between A.D. 1724 and 2002.Results showed that the spatial distribution of rockfall changed slightly with time, and that rockfall activity increased considerably over the last century. In contrast, rockfall magnitude presumably remained on a comparable level. The seasonal occurrence of rockfall showed a clear peak during the dormant season of trees, most probably in early spring. Furthermore, on a 10-year moving average basis, rockfall rates were positively correlated with mean annual as well as summer and winter temperatures. This means that higher temperatures resulted in increased rockfall activity. On the other hand, no correlation with annual or seasonal precipitation totals was revealed. Overall, this study provides an appropriate method for the detailed assessment of spatial and temporal variations in rockfall activity in a given place.

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Rockfalls into forests: Analysis and simulation of rockfall trajectories ? considerations with respect to mountainous forests in Switzerland

Cited by 76 publications

References 8 publications

Quantifying the effect of forests on frequency and intensity of rockfalls

Quantifying the effect of forests on frequency and intensity of rockfalls

Ground reinforced embankments for rockfall protection: design and evaluation of full scale tests

Spatial and temporal rockfall activity in a forest stand in the Swiss Prealps—A dendrogeomorphological case study

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