Une méthode simple de sous-échantillonnage pour les prélèvements de macroinvertébrés dérivants     

Par Guy Chavanon  Michel Bournaud 《Aquatic Sciences - Research Across Boundaries》1980,42(2):322-330

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Mesures isotopiques du rubidium et du strontium et essais de mesure de l'age de la mineralisation de l'uranium du reacteur naturel fossile d'Oklo     

Robert Hagemann  Monique Lucas  Guy Nief  Etienne Roth 《Earth and Planetary Science Letters》1974,23(2):170-176

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2,4,6-Trinitrotoluene in soil and groundwater under a waste lagoon at the former Explosives Factory Maribyrnong (EFM), Victoria, Australia     

Richard Martel  Timothy James Robertson  Minh Quan Doan  Sonia Thiboutot  Guy Ampleman  Arthur Provatas  Thomas Jenkins 《Environmental Geology》2008,53(6):1249-1259

Energetic materials contamination was investigated at the former Explosives Factory Maribyrnong, Victoria, Australia. Spectrophotometric/high performance liquid chromatography (HPLC) analysis was utilised to delineate a 5 tonne crystalline 2,4,6-trinitrotoluene (TNT) source in a former process waste lagoon that was found to be supplying contaminant leachate to the surficial clay aquitard with a maximum-recorded concentration of 7.0 ppm TNT. Groundwater within underlying sand and gravel aquifers was found to be uncontaminated due to upward hydraulic gradients resulting in slow plume development and propagation. Adsorption and microcosm test results from a parallel study were used as input parameters to simulate aqueous TNT transport in the clay aquitard using ATRANS20 software. The simulated TNT plume was localised within a few metres of the source, and at steady state, though leaching rate calculations suggest that without mitigation or other changes to the system, persistence of the source would be approximately 2,000 years. Remediation strategies may involve removal of the near surface source zone and infilling with an impermeable capping to impede leaching while facilitating ongoing natural attenuation by anaerobic degradation.  相似文献   

Association between Messinian drainage network formation and major tectonic activity in the Marche Apennines (Italy)     

Sonia Scarselli  Guy D. H. Simpson  Philip A. Allen  Giorgio Minelli  Lorenzo Gaudenzi 《地学学报》2007,19(1):74-81

The Marche Apennines (Italy) offer an excellent opportunity to constrain the temporal and spatial relationships between drainage network formation and tectonic activity. Using a combination of field data, seismic lines and boreholes we show that the main deformation phase took place during the Messinian when the area, affected by the Messinian sea level drop, emerged and evolved from marine to continental conditions. The results highlight that during the Messinian emersion a drainage network developed contemporaneously with an increase in tectonic activity that could be related to sea level fall and river erosion. The present‐day river system, which is dominated by transverse rivers that cut straight across the tectonic grain, is located in older Messinian palaeovalleys, even though the region was subsequently covered by water until the late Pliocene–early Pleistocene.  相似文献   

Theoretical analysis of non‐geometric PS‐waves recorded at the water bottom interface          下载免费PDF全文

Guy Drijkoningen 《Geophysical Prospecting》2016,64(3):543-553

When a seismic source is placed in the water at a height less than a wavelength from the water–solid interface, a prominent S‐wave arrival can be observed. It travels kinematically as if it was excited at the projection point of the source on the interface. This non‐geometric S‐wave has been investigated before, mainly for a free‐surface configuration. However, as was shown in a field experiment, the non‐geometric S‐wave can also be excited at a fluid–solid configuration if the S‐wave speed in the solid is less than the sound speed in the water. The amplitude of this wave exponentially decreases when the source is moved away from the interface revealing its evanescent character in the fluid. In the solid, this particular converted mode is propagating as an ordinary S‐wave and can be transmitted and reflected as such. There is a specific region of horizontal slownesses where this non‐geometric wave exists, depending on the ratio of the S‐wave velocity and the sound speed of water. Only for ratios smaller than 1, this wave appears. Lower ratios result in a wider region of appearance. Due to this property, this particular P‐S converted mode can be identified and filtered from other events in the Radon domain.  相似文献   

Spatial and temporal variability of farm size in China in context of rapid urbanization     

TAN Minghong  Guy M ROBINSON  LI Xiubin  XIN Liangjie 《中国地理科学(英文版)》2013,23(5):607-619

During the last 30 years,China has witnessed rapid economic growth and dramatic urbanization,with about 1.2 × 107rural people migrating annually into urban areas.Meanwhile,especially since 1995,the rural population has been declining,which is closely linked to land circulation and the increase in farm size in many villages.Increasing scale of farming operations is often regarded as a key to avoiding the abandonment of farmland and to increasing the income of rural farmers.However,until now,there has been little research on the spatial and temporal variability of farm size at the national level in China.Using data from the national agricultural census and rural household surveys,this study examines the characteristics of land use circulation and the consequent changes in the area of farmland per household.The results show that: 1) 12.2% of rural households were involved in land circulation at the national level.The highest amounts of land circulation have occurred in those provinces where the farmland per capita is more than 0.2 ha or less than 0.1 ha;2) over 80% of households operate less than 0.6 ha of farmland;3) the proportion of mid-sized farms(between 0.2 ha and 0.6 ha per household) has decreased while the smallest and the largest farms have increased.This bears some similarity with the phenomenon known as the ′disappearing middle′,referring to the changes in farm size.This study establishes a framework for interpreting the factors affecting the changes in farm size in China,which include two promoting factors(urbanization and agriculture) and four hindering factors(agricultual land system,household registration,stable clan system,and farmland loss).  相似文献   

Beach morphology and change along the mixed grain-size delta of the dammed Elwha River, Washington     

Jonathan A. Warrick  Douglas A. George  Guy Gelfenbaum  Peter Ruggiero  George M. Kaminsky  Matt Beirne 《Geomorphology》2009,111(3-4):136-148

Sediment supply provides a fundamental control on the morphology of river deltas, and humans have significantly modified these supplies for centuries. Here we examine the effects of almost a century of sediment supply reduction from the damming of the Elwha River in Washington on shoreline position and beach morphology of its wave-dominated delta. The mean rate of shoreline erosion during 1939–2006 is ~ 0.6 m/yr, which is equivalent to ~ 24,000 m³/yr of sediment divergence in the littoral cell, a rate approximately equal to 25–50% of the littoral-grade sediment trapped by the dams. Semi-annual surveys between 2004 and 2007 show that most erosion occurs during the winter with lower rates of change in the summer. Shoreline change and morphology also differ spatially. Negligible shoreline change has occurred updrift (west) of the river mouth, where the beach is mixed sand to cobble, cuspate, and reflective. The beach downdrift (east) of the river mouth has had significant and persistent erosion, but this beach differs in that it has a reflective foreshore with a dissipative low-tide terrace. Downdrift beach erosion results from foreshore retreat, which broadens the low-tide terrace with time, and the rate of this kind of erosion has increased significantly from ~ 0.8 m/yr during 1939–1990 to ~ 1.4 m/yr during 1990–2006. Erosion rates for the downdrift beach derived from the 2004–2007 topographic surveys vary between 0 and 13 m/yr, with an average of 3.8 m/yr. We note that the low-tide terrace is significantly coarser (mean grain size ~ 100 mm) than the foreshore (mean grain size ~ 30 mm), a pattern contrary to the typical observation of fining low-tide terraces in the region and worldwide. Because this cobble low-tide terrace is created by foreshore erosion, has been steady over intervals of at least years, is predicted to have negligible longshore transport compared to the foreshore portion of the beach, and is inconsistent with oral history of abundant shellfish collections from the low-tide beach, we suggest that it is an armored layer of cobble clasts that are not generally competent in the physical setting of the delta. Thus, the cobble low-tide terrace is very likely a geomorphological feature caused by coastal erosion of a coastal plain and delta, which in turn is related to the impacts of the dams on the Elwha River to sediment fluxes to the coast.  相似文献   

Techniques for mode separation in Rayleigh wave testing     

Mourad Karray  Guy Lefebvre 《Soil Dynamics and Earthquake Engineering》2009

The spectral analysis of surface wave (SASW) developed in the early eighties has opened the way to the use of surface waves for the definition of shear wave velocity profiles in soil deposits or pavement structures without the need of any borings or intrusion. The SASW testing procedure was designed to minimize the contribution of higher modes and thus assumes that the Rayleigh waves which propagate at the surface belong only to the fundamental mode. Several studies have however demonstrated that, in some conditions, higher Rayleigh modes can contribute significantly to the dispersion curve. Different tests configurations exist today to deal with Rayleigh mode problem by the use of an array of receivers. In spite of that, the SASW configuration remains attractive due to the limited number of receivers, as well as, the Rayleigh modes contributing in SASW records configuration can be identified by multiple-filter technique and isolated using time-variable filters. The proposed techniques are first validated by simulated records and then applied to SASW records obtained in the field. The study confirms that higher modes can participate and even dominate in SASW records. An important contribution of higher Rayleigh modes can also exist, even if the shear wave velocity increases regularly with depth. The higher Rayleigh modes can significantly affect the accuracy of the shear wave velocity profile if they are not properly identified and separated. A multi-mode inversion process is shown to be important to have an accurate soil characterization.  相似文献   

Weather radar and hydrology     

Guy Delrieu 《Advances in water resources》2009

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Distributed hydrologic and hydraulic modelling with radar rainfall input: Reconstruction of the 8–9 September 2002 catastrophic flood event in the Gard region,France     

Laurent Bonnifait  Guy Delrieu  Matthieu Le Lay  Brice Boudevillain  Arielle Masson  Philippe Belleudy  Eric Gaume  Georges-Marie Saulnier 《Advances in water resources》2009

On 8–9 September 2002, an extreme rainfall event caused by a stationary mesoscale convective system (MCS) occurred in the Gard region, France. Distributed hydrologic and hydraulic modelling has been carried out to assess and compare the various sources of data collected operationally and during the post-event field surveys. Distributed hydrological modelling was performed with n-TOPMODELs and assessed for ungauged basins with the discharge estimates of the post-event surveys. A careful examination of the occurrence in time and space of the flash floods over the head watersheds indicates that flooding was controlled by the trajectory of the convective part of the MCS. Stationarity of the MCS over the Gardon watershed (1858 km² at Remoulins) for 28 h was responsible for the exceptional magnitude of the flood at this scale. The flood dynamics were characterized by an extensive inundation of the Gardonnenque plain upstream of the Gardon Gorges resulting in a significant peak flow reduction downstream. One-dimensional unsteady-flow hydraulic modelling was found to be required to reproduce these dynamics. Hydraulic modelling also proved to be potentially useful for the critical analysis and extrapolation of operational discharge rating curves.  相似文献