Evolution of overland flow connectivity in bare agricultural plots          下载免费PDF全文

Andrés Peñuela  Frédéric Darboux  Mathieu Javaux  Charles L. Bielders 《地球表面变化过程与地形》2016,41(11):1595-1613

Soil surface roughness not only delays overland flow generation but also strongly affects the spatial distribution and concentration of overland flow. Previous studies generally aimed at predicting the delay in overland flow generation by means of a single parameter characterizing soil roughness. However, little work has been done to find a link between soil roughness and overland flow dynamics. This is made difficult because soil roughness and hence overland flow characteristics evolve differently depending on whether diffuse or concentrated erosion dominates. The present study examined whether the concept of connectivity can be used to link roughness characteristics to overland flow dynamics. For this purpose, soil roughness of three 30‐m² tilled plots exposed to natural rainfall was monitored for two years. Soil micro‐topography was characterized by means of photogrammetry on a monthly basis. Soil roughness was characterized by the variogram, the surface stream network was characterized by network‐based indices and overland flow connectivity was characterized by Relative Surface Connection function (RSCf) functional connectivity indicator. Overland flow hydrographs were generated by means of a physically‐based overland flow model based on 1‐cm resolution digital elevation models. The development of eroded flow paths at the soil surface not only reduced the delay in overland flow generation but also resulted in a higher continuity of high flow velocity paths, an increase in erosive energy and a higher rate of increase of the overland flow hydrograph. Overland flow dynamics were found to be highly correlated to the RSCf characteristic points. By providing information regarding overland flow dynamics, the RSCf may thus serve as a quantitative link between soil roughness and overland flow generation in order to improve the overland flow hydrograph prediction. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Pressure and shear stress caused by raindrop impact at the soil surface: Scaling laws depending on the water depth          下载免费PDF全文

Amina Nouhou Bako  Frédéric Darboux  François James  Christophe Josserand  Carine Lucas 《地球表面变化过程与地形》2016,41(9):1199-1210

Raindrop impact is an important process in soil erosion. Through its pressure and shear stress, raindrop impact causes a significant detachment of the soil material, making this material available for transport by sheet flow. Thanks to the accurate Navier–Stokes equations solver Gerris, we simulate the impact of a single raindrop of diameter D, at terminal velocity, on water layers of different thickness h: dia:esp3894:esp3894-math-0001" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/6634434f-266b-4506-a134-9ad5b8e6cd68/esp3894-math-0001.png">, dia:esp3894:esp3894-math-0002" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/2fd67660-b61e-4720-905e-d4277ac260f1/esp3894-math-0002.png">, D, 2D, in order to study pressures and shear stresses involved in raindrop erosion. These complex numerical simulations help in understanding precisely the dynamics of the raindrop impact, quantifying in particular the pressure and the shear stress fields. A detailed analysis of these fields is performed and self‐similar structures are identified for the pressure and the shear stress on the soil surface. The evolution of these self‐similar structures are investigated as the aspect ratio h/D varies. We find that the pressure and the shear stress have a specific dependence on the ratio between the drop diameter and the water layer thickness, and that the scaling laws recently proposed in fluid mechanics are also applicable to raindrops, paving the road to obtain effective models of soil erosion by raindrops. In particular, we obtain a scaling law formula for the dependence of the maximum shear stress on the soil on the water depth, a quantity that is crucial for quantifying erosion materials. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river          下载免费PDF全文

Dov Corenblit  Johannes Steiger  Gaspard Charrier  José Darrozes  Virginia Garófano‐Gómez  Alexandre Garreau  Eduardo González  Angela M. Gurnell  Borbála Hortobágyi  Frédéric Julien  Luc Lambs  Sébastien Larrue  Thierry Otto  Erwan Roussel  Franck Vautier  Olivier Voldoire 《地球表面变化过程与地形》2016,41(9):1276-1292

Populations of the riparian pioneer species Populus nigra L. which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms. Dense cohorts of P. nigra have colonized gravel point bars along the channelized River Garonne, France, during the last 20 years and have enhanced the vertical, lateral and longitudinal development of the bars. For this period, the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of P. nigra. Furthermore, P. nigra colonization dynamics were controlled by engineer effects of this same species. This relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010. The development of wooded point bars, which are discrete biogeomorphic units, over the studied period, appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants. We propose a conceptual model of biogeomorphic unit construction for channelized, lateral stable rivers. We consider the resultant biogeomorphic units as functional from an ecological point of view because P. nigra enhances at the cohort scale (i) its own inherent capacity to resist hydrogeomorphic disturbances, and (ii) its resilience capacity as a result of successful colonization, especially downstream of mature poplar stands. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Bulk modulus of Fe-rich olivines corrected for non-hydrostaticity     

Frédéric Béjina  Misha Bystricky  Nicolas Tercé  Matthew L. Whitaker  Haiyan Chen 《Comptes Rendus Geoscience》2019,351(2-3):86-94

In situ X-ray diffraction was used to measure the isothermal bulk modulus at room conditions (K_T0) of synthetic olivines with different iron contents. The chemical formulae of the olivine samples were ${({\mathrm{Fe}}_x,{\mathrm{Mg}}_{1?x})}_2\mathrm{Si}{\mathrm{O}}_4$ with x = 0.45; 0.64; 0.82; 1, with 1% standard deviation (referenced as Fa45, Fa64, Fa82 and Fa100, respectively). All experiments were performed in the multi-anvil apparatus installed at NSLS beamline X17B2, to pressures up to about 7 GPa. Unit-cell volumes under hydrostatic conditions and differential stresses present in the samples were calculated using the method developed by Singh et al. (1998), and pressures measured using NaCl as a standard were then corrected for these stresses. Using a second-order Birch–Murnaghan equation of state, we obtained the isothermal bulk modulus of each composition: $K_{T0}^{\mathrm{Fa45}}=131.4\pm 2.6$ GPa, $K_{T0}^{\mathrm{Fa64}}=132.1\pm 3.1$ GPa, $K_{T0}^{\mathrm{Fa82}}=136.3\pm 1.7$ GPa and $K_{T0}^{\mathrm{Fa100}}=134.8\pm 1.4$ GPa. These values combined with data available in the literature show that the K_T0 of Fe-rich olivines increases very slowly with the Fe content, but possibly not in a simple linear trend.  相似文献   

Trace element mapping by LA-ICP-MS: assessing geochemical mobility in garnet   总被引：1，自引：0，他引：1  

Tom?RaimondoEmail authorView author&#;s OrcID profile  Justin?Payne  Benjamin?Wade  Pierre?Lanari  Chris?Clark  Martin?Hand 《Contributions to Mineralogy and Petrology》2017,172(4):17

A persistent problem in the study of garnet geochemistry is that the consideration of major elements alone excludes a wealth of information preserved by trace elements, particularly the rare-earth elements (REEs). This is despite the fact that trace elements are generally less vulnerable to diffusive resetting, and are sensitive to a broader spectrum of geochemical interactions involving the entire mineral assemblage, including the growth and/or dissolution of accessory minerals. We outline a technique for the routine acquisition of high-resolution 2D trace element maps by LA-ICP-MS, and introduce an extension of the software package XMapTools for rapid processing of LA-ICP-MS data to visualise and interpret compositional zoning patterns. These methods form the basis for investigating the mechanisms controlling geochemical mobility in garnet, which are argued to be largely dependent on the interplay between element fractionation, mineral reactions and partitioning, and the length scales of intergranular transport. Samples from the Peaked Hill shear zone, Reynolds Range, central Australia, exhibit contrasting trace element distributions that can be linked to a detailed sequence of growth and dissolution events. Trace element mapping is thus employed to place garnet evolution in a specific paragenetic context and derive absolute age information by integration with existing U–Pb monazite and Sm–Nd garnet geochronology. Ultimately, the remarkable preservation of original growth zoning and its subtle modification by subsequent re-equilibration is used to ‘see through’ multiple superimposed events, thereby revealing a previously obscure petrological and temporal record of metamorphism, metasomatism, and deformation.  相似文献   

Sedimentology and depositional environments of the Ordovician Umm Sahm Sandstone Formation in southern Jordan     

Issa Makhlouf  Abdalla Abu Hamad  Basem Moh’d 《Arabian Journal of Geosciences》2017,10(7):178

The Ordovician Umm Sahm Sandstone Formation of Jordan comprises approximately 200-m-thick succession of fluvial quartzarenites with subordinate claystone and siltstone lithologies of shallow marine conditions. The Umm Sahm Formation is characterized by its dark brown color, frequent jointing, and steep scarps. The Umm Sahm Formation is bounded by the marine claystones of Hiswah Formation at the top and the fluvial sandstones of the Disi Formation at the bottom. The Umm Sahm Formation is composed of two main facies: fluvial facies and tidal facies. The fluvial facies constitutes about 93% of the total thickness. The lower few meters of the succession passes upward from the Disi Sandstone Formation into similar massive white sandstone facies exhibiting similar white color, fine- to coarse-grained sandstone, with round-shaped pebbles. Trough and planar cross-bedding show a northwest unidirectional palaeocurrent trend. Light brown colored quartzarenites similar to those of the Cambrian Umm Ishrin Sandstone Formation are most common in the upper part of the succession. The tidal facies occupies three intervals in the middle part of the succession. It is composed of laminated and thin-bedded sandstones, siltstones, and claystones. They are rippled and varicolored with abundant trace fossils (Cruziana, Harlania, ruzophycus). The presence of hummocky cross stratification indicates the earliest short-lived tempestite conditions during the Paleozoic erathem of Jordan. The first appearance of Graptolites in the Ordovician rocks of Jordan was recorded during this study in the tidal facies of the Umm Sahm Formation. The vertical arrangement of both fluvial and tidal facies indicates three successive short-lived transgressions and regressions. These marine incursions indicate the successive shoreline advances of the Tethys Ocean, which was located northward, and inundated the southern braid plain. The three short-lived transgressive events took place, and the Tethys marine margin was displaced southward, giving rise to deposition of tidal facies in an open coast tidal flat. Following the transgressive events, renewed progradation and strandline retreat took place, fed by large amounts of siliciclastics derived from the continent and transported by braided streams across the intertidal zone.  相似文献   

Uncertainty of moment tensor determination from surface wave analysis for shallow earthquakes     

B. Bukchin  E. Clévédé  Alexander Mostinskiy 《Journal of Seismology》2010,14(3):601-614

We treat the problem of the non-uniqueness of the moment tensor inversion for shallow earthquakes from long period surface wave data. We give an existence condition for double couples radiating the same long period surface waves as the deviatoric moment tensor obtained by such inversion. We describe the family of such double couples and show that they may provide better estimates of double couple mechanisms than the traditional “best double-couple” solution. We demonstrate the results of application to four large shallow earthquakes with different source signatures.  相似文献   

High-resolution modeling of the mean flow and meso-scale eddy variability around the Grand Banks of Newfoundland     

Li Zhai  Youyu Lu  Simon Higginson  Fraser Davidson  Frédéric Dupont  François Roy  Jérôme Chanut  Gregory C. Smith 《Ocean Dynamics》2015,65(6):877-887

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Quantifying the protective function of a forest against rockfall for past,present and future scenarios using two modelling approaches   总被引：2，自引：0，他引：2  

Christophe Bigot  Luuk K. A. Dorren  Frédéric Berger 《Natural Hazards》2009,49(1):99-111

Following a major rockfall event in 1987, two types of protection measures were taken in the village Saint Martin le Vinoux (French Alps). Firstly, technical measures using civil engineering were installed, and secondly, a forest management intervention to increase its protection was carried out. This study aims to assess whether this intervention was successful in the sense that it improved the protective function of the forest. We evaluated the rockfall risk for the situation of 1987 (before the intervention), today and the future, using model simulations with past, present and future vegetation cover scenarios. To increase the meaningfulness of our results, we used two different models, called Rockfor^.NET, which is a rapid one-dimensional rockfall forest evaluation tool, using simple slope and forest characteristics and RockyFor, a process based on three-dimensional rockfall simulation model that takes the barrier effect of individual trees explicitly into account. Both models correctly predicted that the forest was not capable of stopping rocks from the 1987 rockfall event. Further, both models indicate an increase of the number of rocks reaching the base of the slope from 1987 onwards. RockyFor shows an increase from 11% in 1987 to 19% in 2086. Rockfor^.NET shows an increase from 26% in 1987 to 56% in 2086. We conclude that a second attempt to increase the protective function of the forest should aim at restoring a dense coppice stand.  相似文献   

Analysis of hydrodynamic and hydrochemical behaviour of an aquifer using dialysis cells   总被引：1，自引：0，他引：1  

Frédéric Barrez  Jacky Mania 《Hydrogeology Journal》2009,17(4):781-792

Passive multi-level sampling using dialysis membrane diffusion cells is applied to the Chalk aquifer in order to estimate and monitor vertical contaminant distribution. This technique is associated with in situ profiles of field parameters which allow zones of groundwater flow to be established. Through three study cases (confined, semi-confined and unconfined aquifer conditions), the technique shows that vertical chemical heterogeneities are the particular result of flow zonation, or the renewal of water in the upper parts of the aquifer. The aquifer appears stratified or homogeneous according to depth depending on the chemical element being analysed, the sampling period (recharge period or not) and the hydrological situation (unconfined/confined zone). The high vertical resolution of this multi-level sampling also shows the influence of the Chalk lithology on hydrochemical variations, in particular for silica, iron and aluminium, in hardground and marly zones. By using these sampling techniques, the study emphasizes the importance of accurately measuring according to depth certain parameters such as temperature, electrical conductivity and the ratios of the major elements, in particular, Na/K, Mg/Ca and Sr/Ca. Interpretation of these measurements leads to an understanding of the local hydrodynamic and hydrochemical behaviour of an aquifer, and also allows geological heterogeneities to be located.  相似文献