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Forests strongly modify the accumulation, metamorphism and melting of snow in mid and high-latitude regions. 17 Recently, snow routines in hydrological and land surface models have been improved to incorporate more accurate 18 representations of forest snow processes, but model inter-comparison projects have identified deficiencies, partly due to incomplete knowledge of the processes controlling snow cover in forests. The Snow Under Forest (SnoUF) project was initiated to enhance knowledge of the complex interactions between snow and vegetation. Two field campaigns, during the winters 2016-17 and 2017-18, were conducted in a coniferous forest bordering the snow study at Col de Porte (1325 m a.s.l, French Alps) to document the snow accumulation and ablation processes. This paper presents the field site, instrumentation, and collection methods. The observations include distributed forest characteristics (tree inventory, LIDAR measurements of forest structure, sub-canopy hemispherical photographs), meteorology (automatic weather station and radiometers array), snow cover and depth (snow poles transect and laser scan), and snow interception by the canopy during precipitation events. The weather station installed under dense canopy during the first campaign has been maintained since then and provides continuous measurements throughout the year since 2018. Data are publicly available from the repository of the Observatoire des Sciences de l'Univers de Grenoble (OSUG) data center at http://dx.doi.org/10.17178/SNOUF.2022 (Sicart et al., 2022). [ABSTRACT FROM AUTHOR]

Seismic monitoring of mass movements can significantly help to mitigate the associated hazards; however, the link between event dynamics and the seismic signals generated is not completely understood. To better understand these relationships, we conducted controlled releases of single blocks within a soft-rock (black marls) gully of the Rioux-Bourdoux torrent (French Alps). A total of 28 blocks, with masses ranging from 76 to 472 kg, were used for the experiment. An instrumentation combining video cameras and seismometers was deployed along the travelled path. The video cameras allow reconstructing the trajectories of the blocks and estimating their velocities at the time of the different impacts with the slope. These data are compared to the recorded seismic signals. As the distance between the falling block and the seismic sensors at the time of each impact is known, we were able to determine the associated seismic signal amplitude corrected for propagation and attenuation effects. We compared the velocity, the potential energy lost, the kinetic energy and the momentum of the block at each impact to the true amplitude and the radiated seismic energy. Our results suggest that the amplitude of the seismic signal is correlated to the momentum of the block at the impact. We also found relationships between the potential energy lost, the kinetic energy and the seismic energy radiated by the impacts. Thanks to these relationships, we were able to retrieve the mass and the velocity before impact of each block directly from the seismic signal. Despite high uncertainties, the values found are close to the true values of the masses and the velocities of the blocks. These relationships allow for gaining a better understanding of the physical processes that control the source of high-frequency seismic signals generated by rockfalls. [ABSTRACT FROM AUTHOR]

Abstract: At the scale of forest stands, there is a lack of quantitative, statistically valid data on the protective effect of forests against rockfall. Therefore, the first objective of this study was to quantify the velocities, rebound heights as well as the residual hazard of rockfall on a forested and a non-forested slope. The second objective was to evaluate existing rockfall protection forest management guidelines, as well as the underlying criteria. We carried out and analysed 100 real size rockfall experiments at a non-forested site (Site 1) and 102 identical experiments at a forested site (Site 2) on the same slope. We compared the obtained results with literature data on rockfall protection forests. At the non-forested site, results show that the mean maximum velocity is 15.4ms−1 compared to 11.7ms−1 at the forested site. The maximum rebound height decreases from 8m (Site 1) to 2m (Site 2) and the number of rocks that surpass the 223.5m slope distance decreases from 95 out of 100 (Site 1) to 35 out of 102 (Site 2). A major effect of rockfall on a forested slope is the development of a treeless rockfall path or couloir, which had evolved after releasing 78 rocks at Site 2. The effect of such a couloir can be mitigated by cutting trees on both sides of the couloir and leaving the trunks on the slope, diagonally to the slope direction. This is a known and effective technique to reduce the effect of gaps in protection forests. During our experiments, none of the rocks attained their maximal velocity within the first 40m. They did, however, attain destructive velocities (11–15ms−1) within that distance. Based on our observations, we propose a maximum gap size in the slope direction of 1.3 times the mean tree height, with a maximum of 40m. Further, we present various findings that have direct implications for the management of rockfall protection forests. Finally, the results proved that forests can provide effective protection against rockfall. [Copyright &y& Elsevier]