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151.
RésuméA Madagascar, les morphologies karstiques et leur activité dépendent de l’interaction entre les facteurs climatiques, lithologi-ques et structuraux, en particulier de l’histoire tectonique récente à actuelle. Le rôle des différents facteurs est analysé et quatre cas-types d’activité karstique sont dégagés en fonction de l’importance, variable dans l’espace et dans le temps, des facteurs tectoniques (fracturation et mouvements verticaux) et climatiques (excédent ou déficit pluviométri-que). 相似文献
152.
Résumé Développé sur tableur MS Excel, Calhy est un modèle monodimensionnel d'irrigation à la planche sur calan homogène, pour un sol sur horizon sous-jacent très drainant. De type onde cinétique ou onde diffusante, il adapte le modèle de Green et Ampt et l'équation de Manning-Strickler en tenant compte d'une rétention de surface. Avec cinq paramètres, dont deux mesurés pour décrire l'état d'humectation initial du sol et trois optimisés, le modèle reproduit l'avancement du front ruisselé et le débit de colature observés lors d'irrigations sur prairie dans la plaine semi aride de la Crau (Sud de la France). Les paramètres optimisés sont: la conductivité hydraulique à saturation du sol, constante; le coefficient de Strickler et la rétention de surface, décroissants durant la saison avec l'évolution de la flore et du microrelief. Didactique et convivial, le modèle peut aider à optimiser l'irrigation, dans le but d'obtenir l'infiltration désirée en apportant le moins d'eau possible. Citation Bader, J.-C., Saos, J.-L. & Charron, F. (2010) Modèle de ruissellement, avancement et infiltration pour l'irrigation à la planche sur un sol recouvrant un sous-sol très perméable. Hydrol. Sci. J. 55(2), 177–191. 相似文献
153.
Menno-Jan Kraak Jean-Claude Müller Ferjan Ormeling 《International journal of geographical information science》2013,27(6):637-645
Abstract This paper describes a new joint Dutch research initiative ‘GIS-cartography’, combining the research efforts of the cartographers of Utrecht University, Delft University of Technology and the International Institute for Aerospace Survey and Earth Sciences (ITC) in Enschede. The research initiative focuses on the quantification and visualization of data quality, which will be placed in the context of providing automated visual decision support in specific map use strategies. As these map use strategies can only be performed if the relevant cartographic images can be created, studies of both physical access to the data, user interfaces and the provision of sufficient support to allow the user to understand and to derive sensible conclusions from the data are included in the project. Before modules automatically visualizing data quality can be implemented, data documentation, standardization and integration have to be effected, therefore these issues are also covered. 相似文献
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156.
Johannes Rempfer Thomas F. Stocker Fortunat Joos Jean-Claude Dutay 《Geochimica et cosmochimica acta》2011,75(20):5927-5950
The neodymium (Nd) isotopic composition (?Nd) of seawater is a quasi-conservative tracer of water mass mixing and is assumed to hold great potential for paleoceanographic studies. Here we present a comprehensive approach for the simulation of the two neodymium isotopes 143Nd, and 144Nd using the Bern3D model, a low resolution ocean model. The high computational efficiency of the Bern3D model in conjunction with our comprehensive approach allows us to systematically and extensively explore the sensitivity of Nd concentrations and ?Nd to the parametrisation of sources and sinks. Previous studies have been restricted in doing so either by the chosen approach or by computational costs. Our study thus presents the most comprehensive survey of the marine Nd cycle to date.Our model simulates both Nd concentrations as well as ?Nd in good agreement with observations. ?Nd covaries with salinity, thus underlining its potential as a water mass proxy. Results confirm that the continental margins are required as a Nd source to simulate Nd concentrations and ?Nd consistent with observations. We estimate this source to be slightly smaller than reported in previous studies and find that above a certain magnitude its magnitude affects ?Nd only to a small extent. On the other hand, the parametrisation of the reversible scavenging considerably affects the ability of the model to simulate both, Nd concentrations and ?Nd. Furthermore, despite their small contribution, we find dust and rivers to be important components of the Nd cycle. In additional experiments, we systematically varied the diapycnal diffusivity as well as the Atlantic-to-Pacific freshwater flux to explore the sensitivity of Nd concentrations and its isotopic signature to the strength and geometry of the overturning circulation. These experiments reveal that Nd concentrations and ?Nd are comparatively little affected by variations in diapycnal diffusivity and the Atlantic-to-Pacific freshwater flux. In contrast, an adequate representation of Nd sources and sinks is crucial to simulate Nd concentrations and ?Nd consistent with observations. The good agreement of our results with observations paves the way for the evaluation of the paleoceanographic potential of ?Nd in further model studies. 相似文献
157.
Sébastien Détriché Anne-Sophie SusperreguiEric Feunteun Jean-Claude LefeuvreAlain Jigorel 《Continental Shelf Research》2011,31(6):611-630
This paper provides a detailed study on the sedimentation patterns and the recent morphodynamic evolution affecting the macro-tidal salt marshes located west of the Mont-Saint-Michel (France). Twenty-two stations along three transects on the marshes were seasonally monitored for marsh surface level variations from 1999 to 2005, using a sediment erosion bar. The corresponding erosion/accretion rates were obtained together with data on topography, vegetation cover, and grain size of surface sediment. To examine the mechanisms contributing to the salt marsh sedimentation, the data and their evolution were treated with respect to tides, relative mean regional sea level, and wind speed/frequency variations.From 1999 to 2005, the marsh was globally accreting (from 3.45 to 38.11 mm yr−1 in the low marsh, up to 4.91 mm yr−1 in the middle marsh, and up to 1.35 mm yr−1 in the high marsh), while the study was conducted during a window of decreasing trend in mean regional sea level (−2.45 mm yr−1 according to regional-averaged time series). These sedimentation rates are one of the highest recorded worldwide; however, the sedimentation was not found to be continuous over the period in question. This pattern is illustrated by the strong extension of the marshes from 1999 to 2002, and the relative stability observed from 2003 to 2005. The imported and reworked sediments are trapped and fixed by the dense vegetation (Puccinellia maritima, Halimione portulacoides), inducing the general seaward extension of the marshes. The processes governing sediment budget (accretion/erosion) show annual, seasonal, and spatial variability on the marsh. Spatial variations display contrasted patterns of erosion/sedimentation between the low, middle, and high marsh, and between the different transects. These patterns are a result of distance from sediment sources, strong heterogeneity in vegetation cover (human induced or not), and contrasting topographic and micro-topographic characteristics. The higher accretion rates are observed in distal settings in the low marsh, and strongly decrease toward the middle and high marsh. This evolution results from a decrease in accommodation space/water column thickness, and frequency of inundation coupled with an increase in station elevation, but also from the cumulated effects of vegetation cover and micro-topography. The vegetation cover of the low and middle marsh enhance the settling and fixing of fine sediments imported through tides or dispersed by flood and ebb currents.The seasonal evolution of the marshes is marked by contrasting effects of water storage in the sediment. The overall seasonal sediment budget is controlled by the variation of the frequency of inundation relative to tidal range and marshes topography. Autumns are influenced by the tide (equinoxes), relative mean regional sea level, and variations in wind speed/frequency. Winter wind speed and frequency in relation with tidal variations appear to be the main parameters regulating winter marsh evolution. Summers are predominantly under the influence of local variations in water storage (desiccation) while external parameters generally display a low influence. Although it is not governed by any one parameter, springtime sediment budget seems to result from strong interaction between the above-cited parameters, despite the significant frequency of inundation (equinoxes). 相似文献
158.
A multi-period capacitated school location problem with modular equipment and closest assignment considerations 总被引:1,自引:0,他引:1
Eric M. Delmelle Jean-Claude Thill Dominique Peeters Isabelle Thomas 《Journal of Geographical Systems》2014,16(3):263-286
In rapidly growing urban areas, it is deemed vital to expand (or contract) an existing network of public facilities to meet anticipated changes in the level of demand. We present a multi-period capacitated median model for school network facility location planning that minimizes transportation costs, while functional costs are subject to a budget constraint. The proposed Vintage Flexible Capacitated Location Problem (ViFCLP) has the flexibility to account for a minimum school-age closing requirement, while the maximum capacity of each school can be adjusted by the addition of modular units. Non-closest assignments are controlled by the introduction of a parameter penalizing excess travel. The applicability of the ViFCLP is illustrated on a large US school system (Charlotte-Mecklenburg, North Carolina) where high school demand is expected to grow faster with distance to the city center. Higher school capacities and greater penalty on travel impedance parameter reduce the number of non-closest assignments. The proposed model is beneficial to policy makers seeking to improve the provision and efficiency of public services over a multi-period planning horizon. 相似文献
159.
Carolina Bernal Frédéric Christophoul José Darrozes Jean-Claude Soula Patrice Baby José Burgos 《International Journal of Earth Sciences》2011,100(7):1759-1782
The geomorphological study by means of remote sensing imagery of the Rio Pastaza Megafan (Ecuador and northern Peru) reveals
the traces of numerous avulsions. One hundred and eight avulsion sites have been defined. The location of these sites, the
available radiocarbon ages as well as historical maps of the seventeenth century, enable us to propose an evolution history
of the migration and avulsions of the Rio Pastaza since the Last Glacial Maximum. The first avulsions of the Río Pastaza occurred
after the LGM in a zone close to and roughly parallel to the sudandean front, where the developed avulsion gave a distributive
pattern to the ancient stream of the Río Pastaza in an area located between the modern Río Morona and Pastaza, where they
caused the Rio Pastaza to develop a fan-like distributary pattern. This is interpreted as a response to thrust-related forelimb
tilt, progressively shifting eastward the Rio Pastaza and the apex of the megafan. This sequence of events ended with the
Great Diversion of the Rio Pastaza towards the modern Rios Corrientes and Tigre. Avulsions occurred in the Tigre-Corrientes
Area between 9200 and 8,500 years Cal BP. Afterwards, the Río Pastaza was diverted to its present-day north–south course.
This last significant avulsion occurred before AD 1691. In the area located between the modern Río Morona and Pastaza, avulsion
frequency—probably overestimated—ranges between 100 and 200 years. In the Ríos Tigre and Corrientes area, avulsion frequency—probably
underestimated—ranges from 300 to 400 years. Regional tectonics is likely to have triggered most of the avulsions in the Morona
Pastaza area but its influence is restricted to this area. The factors controlling the avulsions in the Tigre-Corrientes area
are less clear because the frequently described “hydrologic”-driven avulsion as observed in areas characterized by contrasted
hydrologic cycles are inconsistent with the characteristics of the hydrologic cycles of the Rio Pastaza. 相似文献
160.
Nahon S Pruski AM Duchêne JC Méjanelle L Vétion G Desmalades M Charles F 《Marine environmental research》2011,71(4):266-274
The growth, tentacle development and feeding activity of the benthic polychaete Eupolymnia nebulosa were examined to determine whether UV might affect marine deposit-feeders indirectly through the modification of the nutritional quality of their resources. Since marine invertebrates have higher nutritional requirements during the period following settlement, we tested the effect of UV-altered phytodetritus on freshly settled juveniles of E. nebulosa. Phytodetritus was prepared from cultures of the diatom Skeletonema costatum either grown under or sheltered from UVB radiation. Sterol content of phytodetritus was unmodified by UV radiation. Conversely, phytodetritus was noticeably depleted in polyunsaturated fatty acids. Growth and tentacle development of juveniles fed on altered phytodetritus were reduced by 35% and 15% respectively, suggesting potential deficiencies in essential nutrients. In response to the lower quality of the phytodetritus, juveniles explored a wider area as they search for food, a strategy that could compensate for low food quality. 相似文献