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11.
K. Wuhrmann Peter Perret Ch. Imboden H. R. Bürgi F. Klötzli Jürg Bloesch R. Koblet H. Bührer R. Koblet 《Aquatic Sciences - Research Across Boundaries》1977,39(1):104-108
Ohne Zusammenfassung 相似文献
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Spatial and temporal rockfall activity in a forest stand in the Swiss Prealps—A dendrogeomorphological case study 总被引：1，自引：4，他引：1
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. 相似文献
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Jacques Wannesson Monique Pelras Bernard Petitperrin Martine Perret Jacques Segoufin 《Marine and Petroleum Geology》1985,2(3):192-200
In 1982, a geophysical survey of the Antarctic margin, including multichannel seismic, gravity, magnetic and bathymetric surveying, was carried out off Adélie Coast-Wilkes Land and in the eastern Ross Sea. Of the 5000 km of lines recorded, 3000 km were in the Adélie Coast area. Lines ATC 101–102, approximately following meridian 138°E, show the first complete transect of the Adélie Coast margin from the Southeast Indian abyssal plain at DSDP Site 269 to the continental shelf. These lines reveal a thick sedimentary series divided into three main acoustic units by two major unconformities considered to be Upper Eocene (42 Ma) and late Oligocene (25 Ma). Oceanic or continental basement can be traced under the whole area, and the ocean-continent boundary clearly lies beneath the lower continental slope. A deep, high-amplitude, low-frequency horizon, extending under the oceanic basement for over 300 km of line, is considered to be the Moho. Our interpretation supports a recent revision be Cande and Mutter proposing an early Upper Cretaceous opening between Australia and East Antarctica. 相似文献
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Bedload transport is a complex phenomenon that is not well understood, especially for poorly sorted sediment and low transport rates, which is what is typically found in alpine gravel-bed rivers. In this paper, the interaction between bedload rate, bed stability and flow is investigated using flume experiments. Significant differences in bedload rates were observed for experiments conducted on beds formed with the same gravel material but presenting diverse arrangements and bedforms. Tests were performed under regimes of low transport rate, which are mainly controlled by gravel-bed roughness. Different scales of roughness were identified using the statistical characteristics of detailed bed elevation measurements: grain, structure and large bedform scales. The role played by these different roughness scales in bedload dynamics was examined. For quasi-flat beds, bed stability was quantified using a combination of bed surface criteria describing grain and structure scales. It was found that bed stability affects the bedload rate directly and not only through its influence on the flow or on the incipient motion. For beds with large bedforms, the analysis of bedload dynamics also showed the importance of accounting for effective bed shear stress distributions. An empirical bedload model for low transport regimes was suggested. Compared with previous formulae developed for alpine rivers, this model accounts for bed stability and distribution of effective bed shear stress. It significantly improves the understanding of gravel dynamics over complex beds such as arranged beds or those with large bedforms. However, further tests are needed to use the model outside the range of conditions of this study. © 2019 John Wiley & Sons, Ltd. 相似文献
15.
M. Cassel H. Piégay G. Fantino J. Lejot L. Bultingaire K. Michel F. Perret 《地球表面变化过程与地形》2020,45(5):1123-1140
Radio frequency identification (RFID) technologies, which allow wireless detection of individual buried or immersed tracers, represent a step forward in sediment tracking, especially passive integrated transponders (PIT tags) that have been widely used. Despite their widespread adoption in the scientific community, they typically have low efficiency when deployed in river systems with active bedload transport or deep wet channels, attributed to their technical specifications. A recent evaluation of active ultra-high frequency transponders (a-UHF tags) assessed their larger detection range and provided a methodology for their geopositioning. In this study, we test five different survey methods (one including an unmanned aerial vehicle [UAV]) in a sediment tracking study, and compare them in terms of recovery rate, field effort, geopositioning error, and efficiency. We then tested the method on a larger reach following a Q5 flood and performed cross-comparisons between active and passive RFIDs. The results confirmed that the a-UHF RFID technology allowed rapid (1.5 h ha−1) survey of a large area (<34 ha) of emerged bars and shallow water channels with recovery of a high percentage of tracers (72%) that had travelled large distances (mean ≈ 1000 m; max ≈ 3400 m). Moreover, the tracers were identified with low geopositioning error (mean ≈ 7.1 m, ≤1% of their travel distance). We also showed that a UAV-based survey was fast (0.38 h ha−1), efficient (recovery rate = 84%), and low error (mean ≈ 4.2 m). Thus, a-UHF RFID technology permits the development of a variety of survey methods, depending on the study objectives and the human and financial resources available. This allows field efforts to be optimized by determining an appropriate balance between the high equipment cost of a-UHF tracers and the resulting reduced survey costs. © 2019 John Wiley & Sons, Ltd. 相似文献
16.
Ch. E. Perret 《Aquatic Sciences - Research Across Boundaries》1924,3(1-2):1-86
Sans résumé
Ce travail a obtenu le Prix Léon Du Pasquier 1924. 相似文献
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H. Ambühl A. Gyr F. Stössel Peter Perret R. Koblet 《Aquatic Sciences - Research Across Boundaries》1980,42(2):332-337
Ohne Zusammenfassung 相似文献
20.
H. R. Bürgi J. Zobrist Peter Perret 《Aquatic Sciences - Research Across Boundaries》1974,36(2):357-359
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