Design of sediment detention basins: Scaled model experiments and application     

Anita Moldenhauer-Roth  Guillaume Piton  Sebastian Schwindt  Mona Jafarnejad  Anton JSchleiss 《国际泥沙研究》2021,36(1):136-150

Sediment detention basins are implemented on mountain rivers to trap solid material that may aggravate the flooding of downstream settlements.However,retention structures built in the past may unnecessarily retain sediment during non-hazardous flood events,resulting in high maintenance costs and sediment deficit downstream.In addition,the so-called spontaneous self-flushing of previously retained sediment during floods has occasionally been observed.Recent research suggests to design sediment detention basins for controlling sediment passage with a guiding channel across the deposition area upstream of a hybrid barrier.Such barriers consist of a check dam with a slot orifice and an upstream bar screen with a bottom clearance in order to benefit from a combined mechanical-hydraulic retention control.The present paper enhances this pioneering research with the help of new experimental data,including a wide range of sediment mixtures and large wood,as well as variable barrier heights.Improved design criteria are provided regarding the bar screen and the basin storage capacity.The functionality of the enhanced concept for sediment detention is illustrated by a case study on a physical model:the protection of the Villard-Bonnot village(France)against torrential hazards.  相似文献   

Resolution of MRS applied to the characterization of hard-rock aquifers   总被引：4，自引：0，他引：4  

Legchenko A  Descloitres M  Bost A  Ruiz L  Reddy M  Girard JF  Sekhar M  Mohan Kumar MS  Braun JJ 《Ground water》2006,44(4):547-554

The performance of the Magnetic Resonance Sounding (MRS) method applied to the investigation of heterogeneous hard-rock aquifers was studied. It was shown using both numerical modeling and field measurements that MRS could be applied to the investigation of the weathered part of hard-rock aquifers when the product of the free water content multiplied by the thickness of the aquifer is >0.2 (for example, 10-m-thick layer with a 2% water content). Using a currently available one-dimensional MRS system, the method allows the characterization of two-dimensional subsurface structures with acceptable accuracy when the size of the subsurface anomaly is equal to or greater than the MRS loop. However, the fractured part of hard-rock aquifers characterized by low effective porosity (<0.5%) cannot be resolved using currently available MRS equipment. It was found that shallow water in the weathered part of the aquifer may screen MRS signals from deeper water-saturated layers, thus further reducing the possibility of investigating deeper fractured aquifers. A field study using the NUMIS(plus) MRS system developed by IRIS Instruments was carried out on an experimental watershed in southern India. A heterogeneous unconfined aquifer in a gneissic formation was successfully localized, and MRS results were confirmed by drilling shortly after the geophysical study. The top of the aquifer revealed by MRS was found to be in a good agreement with observed static water level measurements in boreholes.  相似文献   

First-principles study of the structural and isotopic properties of Al- and OH-bearing hematite     

Marc Blanchard  Guillaume Morin  Michele Lazzeri  Etienne Balan 《Geochimica et cosmochimica acta》2010,74(14):3948-14056

A series of hematite structures containing various amounts of aluminum and hydroxyl groups was modeled using first-principles methods based on the density functional theory. Evolution of the lattice parameters was quantified as a function of Al and H concentrations. The a and c lattice parameters decrease with the aluminum content and increase with the water content. This allows explaining experimental data reported for synthetic hematites, in particular the observed deviation from the Vegard’s rule. Investigation of several hydroxyl configurations associated with cationic vacancies suggests that the speciation of water also significantly affects the hematite structure. The ⁵⁷Fe and ¹⁸O reduced partition functions (β-factor) were determined. Results show a linear dependence of the iron and oxygen β-factors on the aluminum content. An incorporation of 18 mole % Al₂O₃ in hematite would increase the iron β-factor of about 0.6‰ and the oxygen β-factor of about 5.5‰ at 0 °C. This effect is sufficiently large to be measurable and to affect the interpretation of natural isotopic compositions. On the other hand, the effect of water is found to be negligible for the hydroxyl configuration investigated.  相似文献   

Rapid extraction of discrete magma batches from a large differentiating magma chamber: the Central Plateau Member rhyolites, Yellowstone Caldera, Wyoming   总被引：1，自引：1，他引：0  

Guillaume Girard  John Stix 《Contributions to Mineralogy and Petrology》2010,160(3):441-465

The Central Plateau Member rhyolites have been erupted between 173 and 70 ka and are the youngest Yellowstone intracaldera rhyolites. They mostly comprise very voluminous lava flows totaling ~600 km³ in volume. Their eruptive vents define two NNW-trending lineaments which are aligned with regional faults. We present new whole rock, glass, and mineral analyses and propose a petrogenetic and volcano-tectonic model for these rhyolites. At a caldera-wide scale, there is a temporal enrichment in elements such as Nb, Y and HREE, and a depletion in Sr, Ba, and Ce/Yb. Simultaneously, clinopyroxene becomes less magnesian while Ti contents in quartz decrease. By contrast, quartz in all rhyolites is rounded and bears long glass re-entrants, suggesting heating. Based on these data and observations, we propose that the Central Plateau Member rhyolites have been generated as follows. A hydrothermally altered low-δ¹⁸O rhyolitic protolith beneath the Mallard Lake Resurgent Dome in the southwestern part of the caldera started to melt at ~250 ka. Repeated heating pulses caused the melting front to expand radially, and a large crystal mush formed beneath much of the caldera. The mush was able to differentiate but not erupt due to its high crystallinity and viscosity. Further inputs of heat and silicic magma in this mush increased the degree of melting, forming crystal-poor magma batches which erupted a few hundred to a few thousand years later through regional faults to form the Central Plateau Member rhyolites.  相似文献   

Stochastic simulations of fault networks in 3D structural modeling     

Nicolas Cherpeau  Guillaume Caumon  Bruno Lévy 《Comptes Rendus Geoscience》2010,342(9):687-694

3D structural modeling is a major instrument in geosciences, e.g. for the assessment of groundwater and energy resources or nuclear waste underground storage. Fault network modeling is a particularly crucial step during this task, for faults compartmentalize rock units and plays a key role in subsurface flow, whether faults are sealing barriers or drains. Whereas most structural uncertainty modeling techniques only allow for geometrical changes and keep the topology fixed, we propose a new method for creating realistic stochastic fault networks with different topologies. The idea is to combine an implicit representation of geological surfaces which provides new perspectives for handling topological changes with a stochastic binary tree to represent the spatial regions. Each node of the tree is a fault, separating the space in two fault blocks. Changes in this binary tree modify the fault relations and therefore the topology of the model.  相似文献   

Correlated seasonal and climatic variations of trace constituents in the stratosphere     

André Girard  Jean Besson  Renée Giraudet  Louis Gramont 《Pure and Applied Geophysics》1978,117(3):381-394

Summary Spectrometric experiments performed, in November 1976, within the framework of the Latitude Survey Mission on board the NASA Convair 990 from Ames Research Center are briefly deseribed. The results presented concern odd nitrogen molecules, HCl and water vapor. In terms of vertical column density, HNO₃ is predominant over NO+NO₂ at all latitudes higher than 40 degrees. A seasonal variation of NO₂ abundance is observed, with larger values in the summer hemisphere at high latitude. The mean zenith column density of HCl above 11 km is 1.5×10¹⁵ mol.cm^–2, with no evidence for any seasonal or climatic variation. Local number densities as high as 1.4×10¹⁰ mol.cm^–3 for HNO₃ and 5.4×10¹⁴ mol.cm^–3 for water vapor have been measured during the same flight near 11 km.  相似文献   

Thermodynamics of falling precipitation zones     

Claude Girard  Roland List 《Pure and Applied Geophysics》1975,113(1):1035-1053

A number of numerical experiments are performed in order to study the role of thermodynamics during the fall of precipitation zones. Thereby the air motion is handled in a Eulerian fashion, using the approximate equations for deep convection, and the precipitation-size particles are treated by a Lagrangian method. The results indicate that the behavior of a precipitation zone is greatly affected by both atmospheric stability and drop evaporation. Stable air strongly opposes downdraft development. Furthermore, air entrained downward by the zone becomes buoyant leading to a considerable updraft aloft. Evaporation, on the other hand, tends to counter the effect of stability and to cause a cool downdraft near the ground and a gust front. In spite of the many simplifications, particularly in the initial conditions, the results as seen by a surface observer show much realism.  相似文献   

Plio-Quaternary extension in the Venezuelan Andes: Mapping from SAR JERS imagery     

Damien Dhont  Guillaume Back  Yves Hervouët 《Tectonophysics》2005,399(1-4):293

The geometry of extensional structures is described for the first time in the active setting of the Venezuelan Andes using remote sensing imagery. We favored the use of a mosaic of Synthetic Aperture Radar (SAR) scenes of the Japanese Earth Resources Satellite-1 (JERS-1) assisted by complementary remote sensing devices (Landsat TM, digital elevation models) and field observations to make a structural analysis at regional scale. Radar images are particularly efficient in the Venezuelan Andes where dense vegetation and frequent cloud covering earlier lent difficulties to remote sensing studies. We focused our analysis in the Valera–Rio Momboy and Bocono faults corner and in the Mucujun area. We show that, in an area where ongoing compression and strike–slip deformations occur, brittle extension can be detected independently from previous knowledge. Extensional structures correspond to elongated tilted blocks with dimension less than 10 km in width. Blocks are bounded by curved faults in plan view, the concavity being turned towards the axial part of the belt. The geometry and kinematics of such structures suggest that syn-orogenic extension started together with initiation of right-lateral strike–slip motion along the Bocono Fault in the Plio-Quaternary.  相似文献   

Using 2D inversion of magnetic resonance soundings to locate a water-filled karst conduit     

M. Boucher  J.-F. Girard  A. Legchenko  J.-M. Baltassat  N. Drfliger  K. Chalikakis 《Journal of Hydrology》2006,330(3-4):413-421

A new methodology for magnetic resonance sounding (MRS) data acquisition and interpretation was developed for locating water-filled karst cavities. This methodology was used to investigate the Ouysse karst system in the Poumeyssens shaft in the Causse de Gramat (France). A new 2D numerical MRS response model was designed for improved accuracy over the previous 1D MRS approach. A special survey performed by cave divers confirmed the accuracy of the MRS results. Field results demonstrated that in favourable conditions (a low EM noise environment and a relatively shallow, large target) the MRS method, used with a coincident transmitter/receiver loop, can be an effective tool for locating a water-filled karst conduit. It was shown numerically that because an a priori orientation of the MRS profile with the karst conduit is used in the inversion scheme (perpendicular for instance), any error in this assumption introduces an additional error in locating the karst. However, the resulting error is within acceptable limits when the deviation is less than 30°. The MRS results were compared with an electrical resistivity tomography (ERT) survey. It was found that in Poumeyssens, ERT is not able to locate the water-filled karst. On the other hand, ERT provides additional information about heterogeneities in the limestone.  相似文献   

Thermal ion measurements on board Interball Auroral Probe by the Hyperboloid experiment     

N. Dubouloz  J.-J. Berthelier  M. Malingre  L. Girard  Y. Galperin  J. Covinhes  D. Chugunin  M. Godefroy  G. Gogly  C. Guérin  J.-M. Illiano  P. Kossa  F. Leblanc  F. Legoff  T. Mularchik  J. Paris  W. Stzepourginski  F. Vivat  L. Zinin 《Annales Geophysicae》1998,16(9):1070-1085

Hyperboloid is a multi-directional mass spectrometer measuring ion distribution functions in the auroral and polar magnetosphere of the Earth in the thermal and suprathermal energy range. The instrument encompasses two analyzers containing a total of 26 entrance windows, and viewing in two almost mutually perpendicular half-planes. The nominal angular resolution is defined by the field of view of individual windows 13° × 12.5°. Energy analysis is performed using spherical electrostatic analyzers providing differential measurements between 1 and 80 eV. An ion beam emitter (RON experiment) and/or a potential bias applied to Hyperboloid entrance surface are used to counteract adverse effects of spacecraft potential and thus enable ion measurements down to very low energies. A magnetic analyzer focuses ions on one of four micro-channel plate (MCP) detectors, depending on their mass/charge ratio. Normal modes of operation enable to measure H⁺, He⁺, O⁺⁺, and O⁺ simultaneously. An automatic MCP gain control software is used to adapt the instrument to the great flux dynamics encountered between spacecraft perigee (700 km) and apogee (20 000 km). Distribution functions in the main analyzer half-plane are obtained after a complete scan of windows and energies with temporal resolution between one and a few seconds. Three-dimensional (3D) distributions are measured in one spacecraft spin period (120 s). The secondary analyzer has a much smaller geometrical factor, but offers partial access to the 3D dependence of the distributions with a few seconds temporal resolution. Preliminary results are presented. Simultaneous, local heating of both H⁺ and O⁺ ions resulting in conical distributions below 80 eV is observed up to 3 Earths radii altitudes. The thermal ion signatures associated with large-scale nightside magnetospheric boundaries are investigated and a new ion outflow feature is identified associated to the polar edge of the auroral oval. Detailed distribution functions of injected magnetosheath ions and ouflowing cleft fountain ions are measured down to a few eVs in the dayside.  相似文献