Добірка наукової літератури з теми "Alluvial quifer"

AbstractValley asymmetry reflects differences in landform evolution with aspect; however, few studies assess rates and timing of asymmetric erosion. In south-central Idaho, we combine alluvial fan volume reconstructions with radiocarbon deposit dating to compare the source-catchment normalized fan deposition rates of catchments incised into north (n=5) and south-facing (n=3) valleys, which differ during the late Holocene from 7.7 to 10.1 mm/ka, respectively, but are not significantly different. South-facing catchments produced 1.3× more fan sediment per unit source-area during the late Holocene, whereas over the last 10 Ma they have evolved to be 2.1× larger with 2.8× greater eroded volumes and 7.6° gentler slopes (24.5° versus 32.1°, average). Late Holocene differences in sediment yields with aspect cannot fully explain differences in landforms. Potential bias in sediment deposition and/or remobilization cannot fully explain the similarity of erosion rates during the late Holocene. Valley asymmetry appears to have developed primarily during different conditions. While valley asymmetry development may be quicker during glacial climates, development is likely accelerated early in a valley’s history, such as during initial valley incision, because asymmetric degradation serves as a negative feedback that reduces aspect-related differences in erosion and drives valleys towards steady state.

SummaryTo study the response of three sugarcane genotypes (CO 1148, COJ 64 and CO 1158) to variations in moisture availability in sandy loam soil (entisol), field trials were conductedat Lucknow (26·5° N, 80·5° E, 120 m altitude) during 1984–5 and 1985–6. Three moisture regimes, i.e. wet (irrigation at 75% available soil moisture (ASM)), moist (irrigation at 50% ASM) and dry (irrigation at 25% ASM) were maintained during the pre-monsoon (before June) period in spring-planted (February-March) sugarcane. During the summer months (until June)the variety CO 1148 had a significantly greater sheath moisture percentage than COJ 64 and CO 1158. Under stress conditions, leaf area index was reduced most in COJ 64 and least in CO 1148.Underground shoots and roots grew faster in CO 1148, and the growth of above-ground parts was quicker in COJ 64. Compared with the 75% ASM regime the reduction in cane yield in the 25% regime was more in COJ 64 and CO 1158 (31 t/ha) than in CO 1148 (12 t/ha). The water requirement of COJ 64 was greater than that of the other varieties. Therefore, for higheryields COJ 64 needed frequent irrigation whereas CO 1148 performed well even under moderate irrigation (50% ASM).

The engineering behavior of nonplastic silts is more difficult to characterize than is the behavior of clay or sand. Especially, behavior of silty soils is important in view of the seismicity of several regions of alluvial deposits in the world, such as the United States, China, and Turkey. In several hazards substantial ground deformation, reduced bearing capacity, and liquefaction of silty soils have been attributed to excess pore pressure generation during dynamic loading. In this paper, an experimental study of the pore water pressure generation of silty soils was conducted by cyclic triaxial tests on samples of reconstituted soils by the slurry deposition method. In all tests silty samples which have different clay percentages were studied under different cyclic stress ratios. The results have showed that in soils having clay content equal to and less than 10%, the excess pore pressure ratio buildup was quicker with an increase in different cyclic stress ratios. When fine and clay content increases, excess pore water pressure decreases constant cyclic stress ratio in nonplastic silty soils. In addition, the applicability of the used criteria for the assessment of liquefaction susceptibility of fine grained soils is examined using laboratory test results.

La dispersion à grande échelle en aquifère est principalement dominée par la structure spatiale du champ des perméabilités. L’objectif est ici de caractériser les propriétés dispersives de l’aquifère alluvial du Drac par deux approches basées sur l’utilisation de données expérimentales de traçage. La première approche est classique : des traçages en écoulement naturel sont menés sur un site expérimental comportant 17 puits crépinés sur toute leur hauteur, et permettant une extension maximale de 45m dans l’axe du gradient. La restitution est suivie dans les puits situés en aval, dont la concentration est homogénéisée sur la hauteur. Les paramètres hydrodispersifs sont obtenus par calage de la solution analytique de l’équation de convection-dispersion en 2D sur les courbes expérimentales. La seconde approche consiste à caractériser la variabilité spatiale du champ des perméabilités, pour générer ensuite des champs stochastiques. La distribution verticale des vitesses de Darcy horizontales est mesurée dans les puits par la méthode de dilution ponctuelle, qui est modélisée comme une combinaison de systèmes d’écoulement simples conduisant à une expression analytique. La vitesse de Darcy est alors déduite par calage du modèle sur les courbes expérimentales de dilution, et la perméabilité en découle en supposant un gradient hydraulique moyen sur la parcelle. Ces profils verticaux, menés sur les 17 forages, conduisent à 185 valeurs de perméabilités, moyennées sur 1 mètre. La distribution des perméabilités est supposée suivre une loi de distribution lognormale. La corrélation spatiale est décrite par les variogrammes calculés dans les directions horizontale et verticale. Deux types de modèles de variogrammes sont alors testés : le modèle classique exponentiel, et un autre plus complexe avec ‘effet de trou’ pour simuler la chenalisation. Des champs de perméabilités stochastiques 3D suivant ces deux lois spatiales sont générés à l’aide du logiciel de géostatistique ISATIS, pour être ensuite incorporés dans le code de calcul aux éléments finis CASTEM2000 qui calcule les champs d’écoulement associés. Le transport est modélisé par suivi de particules et technique de Monte-Carlo. Les paramètres hydrodispersifs se déduisent du calcul des moments spatiaux d’ordres 1 et 2 des nuages de particules. Les dispersivités simulées sont alors comparées aux dispersivités déduites des expériences de traçages, et à celles prédites par les théories stochastiques. La dispersivité longitudinale semble avoir atteint une limite asymptotique au terme d’un parcours moyen de l’ordre de la dizaine de longueurs de corrélation horizontale
Dispersion in aquifer at large scale is mainly dominated by the spatial structure of the hydraulic conductivity field. The aim of the study is to characterize the dispersive properties of an alluvial aquifer located near Grenoble through two approaches both based on the use of experimental tracing data. The first approach is the classical one: some field-scale tracer tests are conducted under natural gradient on an experimental site which includes 17 fully-penetrating wells. The maximum extent is about 45 meters along the main flow direction. Fluorescent tracers are injected, and their migration is monitored in the restitution wells by sampling device of the volume-averaged concentration. The hydrodispersive parameters are estimated by fitting the classical 2D analytical solution of the advection-dispersion equation on the experimental breakthrough curves. The second approach is to characterize the spatial variability of hydraulic conductivity, in order to generate stochastic fields. The vertical distribution of the horizontal groundwater flow is measured in boreholes by dilution method. This measurement method is modelled as a combination of simple flow structures, which leads to an analytical expression of the tracer concentration versus time. The flow is estimated from the fit of this analytical model on the experimental dilution curves. Hydraulic conductivity is then deduced from the flow through the Darcy’s equation, supposing an average hydraulic gradient on the site. Such vertical profiles on one-meter averaged hydraulic conductivities are conducted in wells to give 185 values on the entire site. The distribution of hydraulic conductivity draws near to a lognormal one, and is assumed to be so in the later generation of stochastic fields. The spatial correlation of the measured data is described by variograms in horizontal and vertical directions. Two types of model are used to fit these variograms: an exponential one, and a more complex model with ‘hole-effect’ in order to simulate channelling. 3D-stochastic hydraulic conductivity fields following these two spatial laws are generated using the geostatistical software ISATIS. These fields are then incorporated in the finite-elements code CASTEM2000 to lead to the associated flow fields. The transport is modelled by particle-tracking and Monte-Carlo techniques. The determination of the first and second order spatial moments leads to the dispersion coefficients. The simulated dispersivities are then compared to the experimental ones, and to the ones predicted by stochastic theories. The longitudinal dispersivity seems to reach an asymptotic limit after a 10 correlation lengths travel

La dispersion à grande échelle en aquifère est principalement dominée par la structure spatiale du champ des perméabilités. L'objectif ici est de caractériser les propriétés dispersives de l'aquifère alluvial du Drac par deux approches basées sur l'utilisation de données expérimentales de traçage.

This chapter describes the preservation efforts undertaken by the American Research Center in Egypt on the famous murals, preserved in the Cairo Coptic Museum, which were originally excavated in Apa Jeremiah's Saqqara monastery and Apa Apollo's Bawit monastery. These wall paintings have traditionally been considered the principal symbols of Coptic art. The Saqqara niches were excavated between 1906 and 1910. In keeping with Egyptian tradition, all the paintings are painted on plaster a secco. The Saqqara niches were constructed of mud brick lined with a white lime plaster arricio, often quite coarse and uneven, containing siliceous alluvial sand and some occasional plant fibers. The Bawit niches were excavated in 1913. The two niches were painted on mud with only a thin white lime wash applied for the paintings, rendering them considerably more delicate than the Saqqara niches.

If we look at a vineyard, it’s very tempting to assume that what we see at the surface simply continues on downward. Maybe it does, but most soils vary with depth, and the surface can be quite unrepresentative of down where the work is done, of the materials that surround the vine roots. That’s why these days vineyards are peppered with soil pits. Normally, immediately below the surface of the ground is the topsoil, the most fertile part, from which vines get most of their water and nutrients. Below this is increasingly compact, commonly clayey material, subsoil, in which relatively little grows. If we continue downward, sooner or later we hit bedrock, for every vineyard sits on bedrock, at some depth or other. Unlike many plants, vine roots can probe many meters downward into the subsoil and even penetrate fissures in the bedrock, particularly if there’s a need to seek out supplementary water. The way soil varies with depth is called its profile. The variations in physical and chemical properties may be gradual, or in discrete layers, referred to as soil horizons, an arrangement sometimes called a duplex soil. A hypothetical example of a layered soil profile is shown in Figure 10.1, and Figure 10.2 gives an example of how a property can vary with depth. The overall depth of a soil above bedrock is termed its thickness. In vineyards, this can be anywhere from as little as 20 centimeters, such as at Auxey-Duresses in the Côte d’Or, to alluvium on plains such as California’s Central Valley that is measured in hundreds of meters. Even where bedrock has weathered in place to yield the overlying soil, its effects (Figure 10.3) can only be very generalized, because of all the permutations of climate, landform, biology, history, and so on, that influence soil profiles. Granite, with its coarse grains and high content of feldspar and quartz, both of which are fairly stable minerals physically, tends to yield sandy, well-drained soils. They are often pale colored, like the parent rock, though in places with a higher manganese content, such as parts of Barolo and Beaujolais, they can have a bluish tone.