International Journal of Earth Sciences - The Polish Lowlands, located southwest of the Teisseyre–Tornquist Zone, within Trans-European Suture Zone, were affected by bimodal, but dominantly... 相似文献
Upscaling permeability of grid blocks is crucial for groundwater models. A novel upscaling method for three-dimensional fractured porous rocks is presented. The objective of the study was to compare this method with the commonly used Oda upscaling method and the volume averaging method. First, the multiple boundary method and its computational framework were defined for three-dimensional stochastic fracture networks. Then, the different upscaling methods were compared for a set of rotated fractures, for tortuous fractures, and for two discrete fracture networks. The results computed by the multiple boundary method are comparable with those of the other two methods and fit best the analytical solution for a set of rotated fractures. The errors in flow rate of the equivalent fracture model decrease when using the multiple boundary method. Furthermore, the errors of the equivalent fracture models increase from well-connected fracture networks to poorly connected ones. Finally, the diagonal components of the equivalent permeability tensors tend to follow a normal or log-normal distribution for the well-connected fracture network model with infinite fracture size. By contrast, they exhibit a power-law distribution for the poorly connected fracture network with multiple scale fractures. The study demonstrates the accuracy and the flexibility of the multiple boundary upscaling concept. This makes it attractive for being incorporated into any existing flow-based upscaling procedures, which helps in reducing the uncertainty of groundwater models. 相似文献
Like almost all fields of science, hydrology has benefited to a large extent from the tremendous improvements in scientific instruments that are able to collect long-time data series and an increase in available computational power and storage capabilities over the last decades. Many model applications and statistical analyses (e.g., extreme value analysis) are based on these time series. Consequently, the quality and the completeness of these time series are essential. Preprocessing of raw data sets by filling data gaps is thus a necessary procedure. Several interpolation techniques with different complexity are available ranging from rather simple to extremely challenging approaches. In this paper, various imputation methods available to the hydrological researchers are reviewed with regard to their suitability for filling gaps in the context of solving hydrological questions. The methodological approaches include arithmetic mean imputation, principal component analysis, regression-based methods and multiple imputation methods. In particular, autoregressive conditional heteroscedasticity (ARCH) models which originate from finance and econometrics will be discussed regarding their applicability to data series characterized by non-constant volatility and heteroscedasticity in hydrological contexts. The review shows that methodological advances driven by other fields of research bear relevance for a more intensive use of these methods in hydrology. Up to now, the hydrological community has paid little attention to the imputation ability of time series models in general and ARCH models in particular. 相似文献
The three-dimensional high-resolution imaging of rock samples is the basis for pore-scale characterization of reservoirs. Micro X-ray computed tomography (µ-CT) is considered the most direct means of obtaining the three-dimensional inner structure of porous media without deconstruction. The micrometer resolution of µ-CT, however, limits its application in the detection of small structures such as nanochannels, which are critical for fluid transportation. An effective strategy for solving this problem is applying numerical reconstruction methods to improve the resolution of the µ-CT images. In this paper, a convolutional neural network reconstruction method is introduced to reconstruct high-resolution porous structures based on low-resolution µ-CT images and high-resolution scanning electron microscope (SEM) images. The proposed method involves four steps. First, a three-dimensional low-resolution tomographic image of a rock sample is obtained by µ-CT scanning. Next, one or more sections in the rock sample are selected for scanning by SEM to obtain high-resolution two-dimensional images. The high-resolution segmented SEM images and their corresponding low-resolution µ-CT slices are then applied to train a convolutional neural network (CNN) model. Finally, the trained CNN model is used to reconstruct the entire low-resolution three-dimensional µ-CT image. Because the SEM images are segmented and have a higher resolution than the µ-CT image, this algorithm integrates the super-resolution and segmentation processes. The input data are low-resolution µ-CT images, and the output data are high-resolution segmented porous structures. The experimental results show that the proposed method can achieve state-of-the-art performance. 相似文献
Within the Ararat Valley (Armenia), a continuously growing water demand (for irrigation and fish farming) and a simultaneous decline in groundwater recharge (due to climate change) result in increasing stress on the local groundwater resources. This detrimental development is reflected by groundwater-level drops and an associated reduction of the area with artesian conditions in the valley centre. This situation calls for increasing efforts aimed at more sustainable water resources management. The aim of this baseline study was the collection of data that allows for study on the origin and age distribution of the Ararat Valley groundwater based on environmental tracers, namely stable (δ2H, δ18O) and radioactive (35S, 3H) isotopes, as well as physical-chemical indicators. The results show that the Ararat Valley receives modern recharge, despite its (semi-)arid climate. While subannual groundwater residence times could be disproved (35S), the detected 3H pattern suggests groundwater ages of several decades, with the oldest waters being recharged around 60 years ago. The differing groundwater ages are reflected by varying scatter of stable isotope and hydrochemical signatures. The presence of young groundwater (i.e., younger that the 1970s), some containing nitrate, indicates groundwater vulnerability and underscores the importance of increased efforts to achieve sustainable management of this natural resource. Since stable isotope signatures indicate the recharge areas to be located in the mountains surrounding the valley, these efforts must not be limited to the central part of the valley where most of the abstraction wells are located.
A discontinuous outcrop of Palaeozoic rhythmic clastites appears in the North Chilean Coastal Cordillera. The Formación El Toco (21°15–22°15S) whose scarce flora points to a presumably Upper Devonian age forms the northernmost part of the outcrop. It is discordantly overlain by Lower Jurassic volcanics (Fm. La Negra), its base, however, is not exposed. Hercynian heteromorphous deformation led to predominantly NW trending folds strongly inclined mostly to the SW. Chevron-like folds of 0.1 to 30 m occur locally and seem to display properties transitional between synsedimentary-gravitational and early tectonic deformation.The series which is at least 2300 m thick consists of proximal, in parts pebbly turbidites with non-turbiditic finegrained intercalations. Incomplete BOUMA-sequences frequently begin with A-beds of grey to green immature, badly sorted coarse sandstones of up to 6 m thickness containing isolated quartz- and pelite-clasts.Measurements of flute casts and f oresets show palaeocurrents which came from NW and NNE. Along with petrographic observations they indicate southward directed transport of detritus from low metamorphic sedimentary and magmatic source areas into an Upper Devonian nonvolcanic basin.
Zusammenfassung Die Formación El Toco ist der nördlichste Aufschluß einer Kette von Vorkommen paläozoischer rhythmischer Klastite in der nordchilenischen Küstenkordillere. Diese Formation (21°15–22°15S), deren spärliche Flora vorbehaltlich dem Oberdevon zuzuordnen ist, wird diskordant von unterjurassischen Vulkaniten (Fm. La Negra) überlagert —das Liegende ist nicht aufgeschlossen. Variszische heteromorphe Deformation führte zu vorherrschend NW-streichender Faltung, die meist starke SW-Vergenz zeigt. Lokal tritt eine scharfe Verfaltung im 0,1 bis 30 m-Bereich hinzu, die sowohl synsedimentär-gravitative als auch frühtektonische Deformationsmerkmale zeigt.Die mindestens 2300 m mächtige Serie ist ein proximaler Flysch mit z. T. kiesführenden Turbiditen, in die nichtturbiditische feinkörnige Partien eingeschaltet sind. Die unvollständigen BOUMA-Sequenzen beginnen häufig mit einer aus grauen bis grünen unreifen und schlechtsortierten Grobsandsteinen bestehenden A-Division von bis zu 6 m Mächtigkeit, die isolierte Quarz- und Pelitklasten enthalten kann.Flute cast- und Foreset-Messungen weisen auf Paläoströmungsrichtungen aus NW und NNO hin. Zusammen mit petrographischen Analysen läßt sich daraus ein südwärts gerichteter Transport von schwachmetamorphsedimentärem und magmatischem Detritus in ein oberdevonisches nicht-vulkanisches Becken ableiten.
Résumén Ritmitas clásticas de edad paleozoica forman afloramientos discontinuos en la Cordillera de la Costa del Norte de Chile. La Formación El Toco (21°15–22°15S), que contiene una flora escasa de probable edad Devónico Superior, constituye la parte más septentrional de estos afloramientos. La base no se conoce, mientras que el techo infrayace discordantemente a volcanitas jurásicas inferiores (Fm. La Negra). Deformaciones hercínicas heteromórficas llevan a la formación de pliegues orientados predominantemente al NW inclinados fuertemente al SW. Localmente aparecen pliegues en forma de chevron de un tamano de 0.1 a 30 m que muestran caracteristicas de deformación transicional entre sinsedimentana-gravitativa y tectónica temprana.La serie que tiene una potencia de por lo menos 2300 m consiste en turbiditas proximales parcialmente con gravas e intercalaciones finas no-turbidíticas. Secuencias incompletas de BOUMA empiezan frecuentemente con capas de la division A (espesor maximo 6 m) los cuales se componen con frecuencia de areniscas gruesas gris-verdes, composicionalmente inmaduras y mal seleccionadas, con clastos aislados de cuarzo y pelita.Medidas de flute casts y foresets muestran paleocorrientes provenientes de NW y NNE. Junto con observaciones petrográficas, las paleocorrientes indican un transporte de material detrítico, originado de áreas con rocas sedimentarias, metamórficas de bajo grado e ígneas, dirigido al sur hacia una cuenca no volcánica de edad Devónico Superior.
During a large nuclear war, the atmosphere would be loaded with huge quantities of pollutants, which are produced by fires in urban and industrial centers, cultivated lands, forests and grasslands. Especially detrimental are the effects of light absorbing airborne particles. An analysis of the amounts of the various types of fuels which could burn in a nuclear war indicates that more than 1014 g of black smoke could be produced by fires started by the nuclear explosions. Due to this, the penetration of sunlight to the earth's surface would be reduced greatly over extended areas of the northern hemisphere, maybe even globally. This could temporarily cause extreme darkness in large areas in midlatitudes and reduce crop growth and biospheric productivity.This situation would last for several weeks and cause very anomalous meteorological conditions. Much solar radiation would be absorbed in the atmosphere instead of at the earth's surface. The land areas and lower atmosphere would, therefore, cool and the overlying atmosphere warm, creating strong vertical thermal stability in a highly polluted atmosphere. For extended periods and in large parts of the world, weather conditions would be abnormal. The resulting cold, probably freezing, temperatures at the ground would interfere severely with crop production during the growing season and cause extreme conditions for large sections of the biosphere. The combination of lack of sunlight, frost and other adverse meteorological conditions would add enormously to the already huge problems of the survivors. 相似文献