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排序方式: 共有125条查询结果,搜索用时 78 毫秒
1.
Hanne Hendrickx Lars De Sloover Cornelis Stal Reynald Delaloye Jan Nyssen Amaury Frankl 《地球表面变化过程与地形》2020,45(14):3653-3669
Talus slopes are common places for debris storage in high-mountain environments and form an important step in the alpine sediment cascade. To understand slope instabilities and sediment transfers, detailed investigations of talus slope geomorphology are needed. Therefore, this study presents a detailed analysis of a talus slope on Col du Sanetsch (Swiss Alps), which is investigated at multiple time scales using high-resolution topographic (HRT) surveys and historical aerial photographs. HRT surveys were collected during three consecutive summers (2017–2019), using uncrewed aerial vehicle (UAV) and terrestrial laser scanning (TLS) measurements. To date, very few studies exist that use HRT methods on talus slopes, especially to the extent of our study area (2 km2). Data acquisition from ground control and in situ field observations is challenging on a talus slope due to the steep terrain (30–37°) and high surface roughness. This results in a poor spatial distribution of ground control points (GCPs), causing unwanted deformation of up to 2 m in the gathered UAV-derived HRT data. The co-alignment of UAV imagery from different survey dates improved this deformation significantly, as validated by the TLS data. Sediment transfer is dominated by small-scale but widespread snow push processes. Pre-existing debris flow channels are prone to erosion and redeposition of material within the channel. A debris flow event of high magnitude occurred in the summer of 2019, as a result of several convective thunderstorms. While low-magnitude (<5,000 m3) debris flow events are frequent throughout the historical record with a return period of 10–20 years, this 2019 event exceeded all historical debris flow events since 1946 in both extent and volume. Future climate predictions show an increase of such intense precipitation events in the region, potentially altering the frequency of debris flows in the study area and changing the dominant geomorphic process which are active on such talus slopes. © 2020 John Wiley & Sons, Ltd. 相似文献
2.
Cornelis Kasse 《Boreas: An International Journal of Quaternary Research》2014,43(2):403-421
In the present paper the effects of rapid, high‐amplitude base‐level changes during the last glacial‐interglacial transition were studied for the Ain River in eastern France. During the Würm glacial maximum (MIS 2) rapid aggradation by deep‐water Gilbert‐type deltas and shallow‐water fan deltas occurred at the margins of a 20 to 50 m deep proglacial lake. A temporal high‐amplitude lake‐level fall of 60 m resulted in gravel deposition by forced‐regressive deltas, followed by rapid lake‐level rise and fine‐grained glaciolacustrine deposition. During the final deglaciation, a rapid base‐level fall of 40 m resulted in a complex fluvial response. Knickpoint formation and headward incision of the highstand deltas and concomitant deposition of gravel sheets by forced‐regressive deltas and braided systems occurred in several depocentres on the former glacial lake floor. Preservation of highstand and falling‐stage deposits and terrace formation in the incised valley depended on vertical incision and lateral channel migration. Terraces are well developed in the former lake‐floor depressions, whereas vertical incision was dominant in the higher lake‐floor areas. The Ain terrace staircase was likely formed by autogenic processes during a single allogenic base‐level fall. This case study possibly offers an analogue for the preservation of interglacial highstand coastal deltas during sea‐level fall at warm‐to‐cold climate transitions, although the rates of base‐level fall are different. 相似文献
3.
Mojtaba Pakparvar Hossein Hashemi Meisam Rezaei Wim M. Cornelis Gholamali Nekooeian Sayyed Ahang Kowsar 《水文科学杂志》2018,63(8):1183-1202
To assess recharge through floodwater spreading, three wells, approx. 30 m deep, were dug in a 35-year-old basin in southern Iran. Hydraulic parameters of the layers were measured. One well was equipped with pre-calibrated time domain reflectometry (TDR) sensors. The soil moisture was measured continuously before and after events. Rainfall, ponding depth and the duration of the flooding events were also measured. Recharge was assessed by the soil water balance method, and by calibrated (inverse solution) HYDRUS-1D. The results show that the 15 wetting front was interrupted at a layer with fine soil accumulation over a coarse layer at the depth of approx. 4 m. This seemed to occur due to fingering flow. Estimation of recharge by the soil water balance and modelling approaches showed a downward water flux of 55 and 57% of impounded floodwater, respectively. 相似文献
4.
Lapperre Rimbaud E. Bense Victor F. Kasse Cornelis van Balen Ronald T. 《Hydrogeology Journal》2022,30(4):1233-1257
Hydrogeology Journal - Faults in the Roer Valley Rift System (Netherlands, Belgium, and Germany) act as barriers to lateral groundwater flow in unconsolidated sedimentary aquifers. This causes a... 相似文献
5.
6.
Nicole A. Dijkman Henricus T.S. Boschker Lucas J. Stal Jacco C. Kromkamp 《Journal of Sea Research》2010,63(1):62-70
The beaches of the North Sea barrier island Schiermonnikoog (The Netherlands) are covered by microbial mats. Five types of microbial mats were distinguished based on a variety of characteristics, located along a transect perpendicular to the coast. Biomass abundance and composition of the microbial community were analyzed in these mats using pigments and phospholipid-derived fatty acids (PLFA) as biomarkers. Biomass per gram sediment increased more than six-fold from the mats at the low water mark to mats found at the edge of the dunes. Microscopic analysis revealed that the increase in biomass was accompanied by a change in species composition. Pigment- and PLFA composition reflected the changes in species composition. The PLFA data could be used to estimate the relative group abundance using the matrix factorization program CHEMTAX., whereas the pigment data were found not to be suitable for this purpose. 相似文献
7.
Susan Ringrose Cornelis Vanderpost Wilma Matheson 《Applied geography (Sevenoaks, England)》1998,18(4):331-354
The critical need to consider all options in the search for groundwater in semi-arid areas has promoted work on the possible association of near-surface groundwater and vegetation characteristics using a combination of remote-sensing data and geographic information systems (GIS) techniques. Two vegetative criteria (dense woody cover and abundance of deep-rooting species) are identified as being indicative of near-surface groundwater, and their spatial distribution is tested against the location of aquifers in southeast Botswana. Vegetative criteria classes were combined in a GIS environment with the distribution of geomorphic units and bedrock geology to determine the degree of coincidence with assumed or known aquifers. Results indicate that the distribution of dense woody vegetation as mapped from Thematic Mapper imagery has some potential in identifying especially surficial but also bedrock near-surface groundwater sources in mostly naturally vegetated semi-arid areas. Dense woody cover classes tend to select aquifers in topographically higher areas while classes comprising some deep-rooting species tend to select low-lying aquifers such as those occurring in fossil valleys. Deep-rooting species, however, are less successful as a vegetative criterion. Although various technical refinements are suggested, this work shows that vegetative criteria mapping can however be used in conjunction with conventional geological/geophysical techniques to enhance the prospects for groundwater location in relatively undisturbed semi-arid areas. 相似文献
8.
An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility. 相似文献
9.
10.
The contributions of any arbitrary photospheric velocity field to (macroturbulent) line displacement, and to (microturbulent) line broadening can be expressed by the macro- and micro-turbulent filters f
M
(k) and f
t(k), where k is the wavenumber of the energy spectrum in which the line-of-sight component of the velocity field can be decomposed. As a correction to a previous computation of f
M
and f
t
we give in this Note improved values for the filter functions for weak lines in LTE. An example of the way to use the filter functions is given. 相似文献