Testing bedload transport equations with consideration of time scales     

Alain Recking  Frédéric Liébault  Thomas Jolimet 《地球表面变化过程与地形》2012,37(7):774-789

Bedload transport is known to be a highly fluctuating temporal phenomenon, even under constant (mean) flow conditions, as a consequence of stochasticity, bedform migration, grain sorting, hysteresis, or sediment supply limitation. Because bedload transport formulas usually refer to a single mean transport value for a given flow condition, one can expect that prediction accuracy (when compared to measurements) will depend on the amplitude and duration of fluctuations, which in turn depend on the time scale used for observations. This paper aims to identify how the time scale considered can affect bedload prediction. This was done by testing 16 common bedload transport formulas with four data sets corresponding to different measurement period durations: (i) highly fluctuating (quasi‐)instantaneous field measurements; (ii) volumes accumulated at the event scale on two small alpine gravel‐bed rivers, potentially affected by seasonal fluctuations; (iii) volumes accumulated at the interannual scale in a meandering gravel bed river, thought to be weakly subject to fluctuations; (iv) time‐integrated flume measurements with nearly uniform sediments. The tests confirmed that the longer the measurement period, the better the precision of the formula's prediction interval. They also demonstrate several consequential limitations. Most threshold formulas are no longer valid when the flow condition is below two times the threshold condition for the largest elements' motion on the bed surface (considering D₈₄). In such conditions, equations either predict zero transport, or largely overestimate the real transport, especially when D₈₄ is high. There is a need for new sediment data collected with highly reliable techniques such as recording slot bedload samplers to further investigate this topic. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Space- and ground-based measurements of sulphur dioxide emissions from Turrialba Volcano (Costa Rica)   总被引：2，自引：0，他引：2  

Robin Campion  Maria Martinez-Cruz  Thomas Lecocq  Corentin Caudron  Javier Pacheco  Gaia Pinardi  Christian Hermans  Simon Carn  Alain Bernard 《Bulletin of Volcanology》2012,74(7):1757-1770

Remotely sensed measurements of sulphur dioxide (SO₂) emitted by Turrialba Volcano (Costa Rica) are reported for the period September 2009–January 2011. These measurements were obtained using images from Advanced Spaceborne Thermal Emission and Reflexion radiometer, Ozone Monitoring Instrument and a ground-based UV camera. These three very different instruments provide flux measurements in good agreement with each other, which demonstrate that they can be integrated for monitoring SO₂ fluxes. Fluxes from Turrialba increased fourfold in January 2010, following a phreatic explosion that formed a degassing vent in the W crater of Turrialba. Since then, the SO₂ flux has remained high (30–50?kg/s) but seems to be showing a slowly decreasing trend. We interpret this evolution as the start of open vent degassing from a recently intruded magma body. The opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrothermal system.  相似文献   

Global SH-wave propagation using a parallel axisymmetric spherical finite-difference scheme: application to whole mantle scattering     

Gunnar Jahnke  Michael S. Thorne  Alain Cochard †  Heiner Igel 《Geophysical Journal International》2008,173(3):815-826

  相似文献   

Flow dynamics at the origin of thin clayey sand lacustrine turbidites: Examples from Lake Hazar,Turkey          下载免费PDF全文

Sophie Hage  Aurélia Hubert‐Ferrari  Laura Lamair  Ulaş Avşar  Meriam El Ouahabi  Maarten Van Daele  Frédéric Boulvain  Mohamed Ali Bahri  Alain Seret  Alain Plenevaux 《Sedimentology》2017,64(7):1929-1956

Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focused on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X‐ray, thin sections and CT scan imagery combined with grain‐size, geochemical and mineralogical measurements on the cores allow characterization of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence‐dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence‐dominated mechanism despite their high clay content. This divergence may in part relate to input variables, such as water chemistry and clay mineralogy, that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field‐scale basin made of a complex physiography that cannot be tackled by flume experiments.  相似文献   

Critical Review of the Hypervib1 Model to Assess Pile Vibro-Drivability     

Alain Holeyman  Valerie Whenham 《Geotechnical and Geological Engineering》2017,35(5):1933-1951

The vibratory driving technique is used for driving piles, sheet piles, tubes and rods into the ground by imparting to the element a longitudinal periodic motion. The small amplitude vibrations induced by the equipment reduce the ground resistance which allows penetration under the action of a relatively small axial force. The technique offers an alternative to impact driving due to lower installation costs and reduced environmental disturbance (noise, vibration, etc.) especially in sensitive environments, such as industrial and urban sites or offshore wind farm sites. The vibratory technique is also preferred when the maximum stress levels imparted to the driven element are of concern. Despite the advantages of the vibratory driving technique, its application remains however mainly driven by pragmatic aspects. Within that context, the access to experience databases and full-scale field test results is of valuable interest. The aim of this paper is to review the Hypervib1 model developed by (Holeyman 1993) for assessing the vibratory drivability of piles and sheet piles, based on the analysis of such experimental results. New findings and developments brought to the model are discussed. Conclusions in terms of reliability of the method are finally drawn.  相似文献   

Reconstruction of total grain size distribution of the climactic phase of a long-lasting eruption: the example of the 2008–2013 Chaitén eruption     

Fabrizio Alfano  Costanza Bonadonna  Sebastian Watt  Chuck Connor  Alain Volentik  David M. Pyle 《Bulletin of Volcanology》2016,78(7):46

  相似文献   

The Ereendavaa Range (north-eastern Mongolia): an additional argument for Mesozoic extension throughout eastern Asia   总被引：3，自引：0，他引：3  

Yannick Daoudene  Denis Gapais  Patrick Ledru  Alain Cocherie  Sébastien Hocquet  Tatiana V. Donskaya 《International Journal of Earth Sciences》2009,98(6):1381-1393

Mesozoic rift basins locally bounding metamorphic core complexes have been recognized in Transbaikalia and northern China. Numerous basement outcrops located between these two regions, in eastern Mongolia, are considered as pre-Palaeozoic in age. One of these, the Ereendavaa Range, appears as a gneissic core marked by amphibolite-facies metamorphic conditions. The range is overlain to the NW by the unmetamorphosed Mesozoic Onon Basin. Below the basin, the upper part of the range consists of a gently NW-dipping shear zone associated with top-to-the-NW motion. The structural pattern is consistent with syn-extensional exhumation of the range. Preliminary geochronological data indicate that the shear zone is late Jurassic to early Cretaceous in age, coeval with the Onon Basin. These new data from eastern Mongolia constitute a link between Transbaikalia and northern China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region.  相似文献   

A new mammalian fauna from the earliest Eocene (Ilerdian) of the Corbières (Southern France): palaeobiogeographical implications     

Bernard Marandat  Sylvain Adnet  Laurent Marivaux  Alain Martinez  Monique Vianey-Liaud  Rodolphe Tabuce 《Swiss Journal of Geoscience》2012,105(3):417-434

A new mammal fauna from the earliest Eocene of Le Clot (Corbières, Southern France) is described. Some taxa identified there, such as Corbarimys hottingeri and Paschatherium plaziati, allow a correlation with the previously described Corbières fauna of Fordones. Moreover, the presence at Le Clot of Lessnessina praecipuus, which is defined in Palette (Provence, Southern France) allows correlating both localities. All three of these localities are referred to the MP7 reference level, even if a direct correlation with the type locality of MP7 (Dormaal, Belgium) is not ascertained. A Southern Europe biochronological sequence is proposed for the beginning of the Eocene: Silveirinha, Fordones/Palette/Le Clot, Rians/Fournes. The diagnosis of a new species of a neoplagiaulacid multituberculate (?Ectypodus riansensis nov. sp.) is proposed. From a compilation of data concerning the earliest Eocene faunas from both Northern Europe and Southern Europe, we conclude that two faunas corresponding to two distinct palaeobiogeographical provinces existed in Western Europe. This faunal disparity, probably related to climatic differences, makes correlations particularly difficult between the two provinces.  相似文献   

Links between NAO fluctuations and inter-annual variability of winter-months precipitation in the Seine River watershed (north-western France)     

Nicolas Fritier  Nicolas MasseiBenoit Laignel  Alain DurandBastien Dieppois  Julien Deloffre 《Comptes Rendus Geoscience》2012,344(8):396-405

The inter-annual to multi-decadal winter variability (DJFM) of precipitation on the Seine River watershed (France) was analysed using continuous wavelet transform analysis and compared to the winter North Atlantic Oscillation Index (NAOI). Nine weather stations were used over the 1951 to 2004 period and confirmed the homogeneity of inter-annual fluctuations for all stations but one. Wavelet coherence between SLP over the Icelandic and Azores regions and precipitation highlighted coherence for different scales of variability according to the centre of action considered. Segmentation and wavelet analysis and coherence between precipitation and NAOI over a long period of time (1873–2004) showed: i) increasing variability across the last century at most time scales, especially for NAOI; ii) the existence of change points for the mean and variance of both signals; iii) overall discontinuity of the coherence whatever the scale considered, especially between ∼1910 and ∼1955 for inter-decennial to pluri-decennial scales.  相似文献   

A 3D gravity data interpretation of the Matagami mining camp, Abitibi Subprovince, Superior Province, Québec, Canada: Application to VMS deposit exploration     

Pierre Boszczuk  Li Zhen Cheng  Hanafi Hammouche  Patrice Roy  Sylvain Lacroix  Alain Cheilletz 《Journal of Applied Geophysics》2011,75(1):77-86

Two inversions, unconstrained and constrained, of a gravity survey of the Matagami mining camp (Abitibi Archaean Subprovince, Canada) have been performed in order to identify the downward extension of a rhyolitic horizon hosting VMS-type base metals deposit and the morphologies of the major felsic plutons. A comparative study exhibits the similarities between measured and calculated densities from chemical compositions of the Matagami lithologies. This allows building an initial 3D geodensity model which integrates densities and available structural and geological surface mapping data. This model is integrated during the iteration process of the constrained inversion in the objective function. The resulting true density model and two derived cross-sections upgrade the 3D imaging of this area. Also, the model gives new insight for regional geological interpretation exposing possible shapes of the main geological units at depth and suggests the potential existence of deep fertile geological bodies.  相似文献