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501.
A systematic analysis shows how results from the finite difference code SEAWAT are sensitive to choice of grid dimension, time step, and numerical scheme for unstable flow problems. Guidelines to assist in selecting appropriate combinations of these factors are suggested. While the SEAWAT code has been tested for a wide range of problems, the sensitivity of results to spatial and temporal discretization levels and numerical schemes has not been studied in detail for unstable flow problems. Here, the Elder-Voss-Souza benchmark problem has been used to systematically explore the sensitivity of SEAWAT output to spatio-temporal resolution and numerical solver choice. A grid size of 0.38 and 0.60% of the total domain length and depth respectively is found to be fine enough to deliver results with acceptable accuracy for most of the numerical schemes when Courant number (Cr) is 0.1. All numerical solvers produced similar results for extremely fine meshes; however, some schemes converged faster than others. For instance, the 3rd-order total variation-diminishing method (TVD3) scheme converged at a much coarser mesh than the standard finite difference methods (SFDM) upstream weighting (UW) scheme. The sensitivity of the results to Cr number depends on the numerical scheme as expected. 相似文献
502.
Jan Šafanda Philipp Heidinger Helmut Wilhelm Vladimír Čermák 《Hydrogeology Journal》2007,15(2):423-428
As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10?11 m2. This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region. 相似文献
503.
Numerical simulation of groundwater flowing to horizontal seepage wells under a river 总被引:6,自引:0,他引:6
A horizontal seepage well, consisting of an interconnected vertical well, galleries, chambers and small-diameter radiating
bores, is used to acquire relatively clean water that has been filtered through natural alluvial deposits in a riverbed. It
has wide application, especially in arid and semi-arid areas. The lack of calculation formulae or models for horizontal seepage
wells, up until now, has resulted in several false applications. Based on the analysis of groundwater flow characteristics,
it has been concluded that several flow regimes coexist and hydraulic head loss exists in the horizontal seepage well. To
avoid the difficulty of confirming the flux or head distribution in such a complex system, the model boundary of the whole
horizontal seepage well has been moved to that of just the vertical well, and the well-aquifer system was treated as a heterogeneous
medium, where the horizontal seepage well itself is a highly permeability medium. A mathematical model has been developed,
based on the coupled seepage-pipe flow, by the introduction of equivalent hydraulic conductivity according to different flow
regimes. Then a three-dimensional finite difference numerical model, based on the mathematical model, was developed and applied
to a horizontal seepage well in China. The numerical model verified the groundwater flow characteristics of the horizontal
seepage well.
An erratum to this article can be found at 相似文献
504.
A simple, well-constrained simulation of solute increases in a downgradient direction was used in the shallow unconfined aquifer
of eastern Abu Dhabi Emirate (United Arab Emirates). The simulation indicates that the observed exponential increase in solute
concentrations results from a combination of upward transport of solutes from underlying mudstones and evaporites, and groundwater
losses by evaporation. Groundwater recharge and discharge flux in unconfined regional aquifers in arid regions commonly are
difficult to estimate because there are few constraints on the flux of water lost or gained from the system. Total dissolved
solids (TDS) and deuterium isotopes (δ2H) in groundwater are used to constrain estimated fluxes to the shallow aquifer of eastern Abu Dhabi Emirate. Vertical upward
transport of solutes from underlying mudstones and evaporites accounts for solute increases along approximately the first
80 km of the simulated flow path, but a combination of upward solute transport and evaporation is necessary to explain observed
solute concentrations beyond 80 km. Mobilization and transport of solutes in the unsaturated zone by recharging precipitation
is not a significant factor.
Résumé Une simulation simple et bien contrainte de l’augmentation des solutés dans la direction de l’écoulement a été réalisée sur l’aquifère phréatique et libre de l’Est de l’émirat d’Abu Dhabi (émirats Arabes Unis). La simulation indique que l’augmentation observée de solutés, de forme exponentielle, est le produit de la combinaison du transport ascendant de solutés provenant des mudstones et des évaporites sous-jacents, et de l’évaporation des eaux souterraines. La recharge des eaux souterraines et les flux de vidange dans les aquifères régionaux libres des régions arides sont habituellement difficiles à estimer du fait du peu de contraintes agissant sur la perte ou le gain d’eau dans le système. La charge dissoute totale (TDS, en anglais) et les isotopes deutérium (δ2H) des eaux souterraines sont utilisés pour contraindre l’estimation des flux en direction de l’aquifère phréatique de l’Est de l’émirat d’Abu Dhabi. Le transport vertical ascendant des solutés à partir des mudstones et des évaporites fait parti des processus qui concentrent les solutés approximativement le long des 80 premiers kilomètres du trajet des écoulements simulés, mais une combinaison du transport ascendant des solutés et de l’évaporation est nécessaire pour expliquer les concentrations observées en soluté au delà des 80 km. La mobilisation et le transport des solutés par les précipitations efficaces dans la zone non saturée ne représentent pas des facteurs significatifs.
Resumen Se utilizó una simulación simple y muy restringida, de incrementos de soluto en la dirección del flujo, en el acuífero libre poco profundo del Emirato oriental de Abu Dhabi, (Emiratos árabes Unidos). La simulación indica que el aumento exponencial observado en las concentraciones del soluto, resulta de una combinación de transporte ascendente de solutos desde las evaporitas y lodolitas subyacentes, y por pérdidas del agua subterránea por evaporación. Los flujos de recarga y descarga de agua subterránea, en los acuíferos libres regionales en regiones áridas, normalmente son difíciles estimar, porque hay algunas restricciones en el flujo de agua perdido o ganado por el sistema. Los sólidos disueltos totales (TDS) y los isótopos de deuterio (δ2H) en el agua subterránea, se usan para forzar los flujos estimados hacia el acuífero poco profundo del Emirato oriental de Abu Dhabi. El transporte ascendente vertical de solutos desde las lodolitas y evaporitas subyacentes, involucra los aumentos del soluto a lo largo de aproximadamente los primeros 80 Km. de la dirección de flujo simulada, pero es necesaria una combinación de transporte ascendente del soluto y la evaporación para explicar las concentraciones del soluto observadas más allá de 80 Km. La movilización y transporte de solutos en la zona no saturada, por recarga debida a precipitación, no es un factor significante.相似文献
505.
Installation of a vertical slurry wall around an Italian quarry lake: complications arising and simulation of the effects on groundwater flow 总被引:1,自引:0,他引:1
Slurry walls are non-structural barriers that are constructed underground to impede groundwater flow or manage groundwater
control problems. The study area is in the Piemonte plain (Italy), close to the River Po. Quarrying works carried out below
the piezometric surface created two big quarry lakes. The local groundwater system is characterized by a lower semi-confined
aquifer, which is overlain by a semi-permeable bed of clayey peat (aquitard) and an upper unconfined aquifer. Locally, the
peat fades away and the granulometry of this horizon becomes silty sandy. A planned enlargement of the quarry will increase
the size and depth of the quarry lakes. So the aquitard bed between the two aquifers will be damaged, creating a mixing rate
of groundwater. Such a procedure would not be compatible with the presence of two municipal wells upstream from the quarries.
Consequently, the installation of a vertical diaphragm (slurry wall) is recommended to separate the aquifers and to act as
a filter for the groundwater flowing from the unconfined to the semi-confined aquifer. To predict the consequences caused
by the installation of the vertical diaphragm separating the unconfined aquifer and the semi-confined one, a specifically
adjusted finite-difference model was used. The model showed a maximum rising of the water table equal to 12 cm, just upstream
of the diaphragm and for a distance of about 100 m, and a maximum lowering of 2 cm just downstream of the diaphragm. However,
the slurry wall would not cause any change in the piezometric head in the area where there are municipal wells and, hence,
will not have any negative effect on the functionality of the municipal wells. Moreover, the migration of water from the unconfined
aquifer through the vertical diaphragm will stimulate a series of attenuation and auto-depuration processes of eventual contaminants.
These processes are due to the higher crossing time that the groundwater flow takes to go through the vertical barrier (t
a = 96.5 days, whereas for the horizontal semi-permeable layer t
a = 9.6 days). So, the vertical diaphragm can be a resolutive element, representing a mediation and separation factor between
the unconfined and the semi-confined aquifers along the border of the quarrying areas, and a protective barrier for the water
quality of the quarry lake and the semi-confined aquifer. 相似文献
506.
Environmental isotopic and hydrochemical study of water in the karst aquifer and submarine springs of the Syrian coast 总被引:1,自引:0,他引:1
The groundwater of major karst systems and submarine springs in the coastal limestone aquifer of Syria has been investigated using chemical and isotopic techniques. The δ18O values of groundwater range from ?6.8 to ?5.05‰, while those for submarine springs vary from ?6.34 to +1.08‰ (eastern Mediterranean seawater samples have a mean of +1.7‰). Groundwater originates from the direct infiltration of atmospheric water. Stable isotopes show that the elevation of the recharge zones feeding the Banyas area (400–600 m a.s.l.) is higher than that feeding the Amrit area (100–300 m a.s.l.). The 18Oextracted (18O content of the seawater contribution) for the major submarine springs suggests a mean recharge area elevation of 600–700 m a.s.l., and lower than 400 m a.s.l. for the spring close to Amrit. Based on the measured velocity and the percentage of fresh water at the submarine springs outlet, the estimated discharge rate is 350 million m3/year. The tritium concentrations in groundwater (1.6–5.9 TU) are low and very close to the current rainfall values (2.9–5.6 TU). Adopting a model with exponential time distribution, the mean turnover time of groundwater in the Al-sen spring was evaluated to be 60 years. A value of about 3.7 billion m3 was obtained for the maximum groundwater reservoir size. 相似文献
507.
2-D Crustal thermal structure along Thuadara-Sindad DSS profile across Narmada-Son lineament,central India 总被引:1,自引:0,他引:1
Central India is traversed by a WSW-ENE trending Narmada-Son lineament (NSL) which is characterized by the presence of numerous
hot springs, feeder dykes for Deccan Traps and seismicity all along its length. It is divided in two parts by the Barwani-Sukta
Fault (BSF). To the west of this fault a graben exists, whereas to the east the basement is uplifted between Narmada North
Fault (NNF) and Narmada South Fault (NSF). The present work deals with the 2-D thermal modeling to delineate the crustal thermal
structure of the western part of NSL region along the Thuadara-Sindad Deep Seismic Sounding (DSS) profile which runs almost
in the N-S direction across the NSL. Numerical results of the model reveal that the conductive surface heat flow value in
the region under consideration varies between 45 and 47mW/m2. Out of which 23mW/m2 is the contribution from the mantle heat flow and the remaining from within the crust. The Curie depth is found to vary between
46 and 47 km and is in close agreement with the earlier reported Curie depth estimated from the analysis of MAGSAT data. The
Moho temperature varies between 470 and 500°C. This study suggests that this western part of central Indian region is characterized
by low mantle heat flow which in turn makes the lower crust brittle and amenable to the occurrence of deep focused earthquakes
such as Satpura (1938) earthquake. 相似文献
508.
在天然气管道网络系统的工艺设计方案中,对布站的站点选择主要取决于其运营成本的相互比较,但鉴于需求和供应之间的关系,还必须考虑管道的输送能力和站点的容量等问题。对于这样复杂化的问题,利用网络流理论的最大流问题和最小费用的最大流问题,建立了输油管道最大输送问题的网络优化模型,并通过实例说明其有效性和可靠性。为输油管道网系统的构建提供了一种新的优化方法,在天然气管道输送决策管理中具有一定的理论参考价值和现实意义。 相似文献
509.
Analysis of radial movement of an unconfined leaky aquifer due to well pumping and injection 总被引:1,自引:0,他引:1
Jiang Li 《Hydrogeology Journal》2007,15(6):1063-1076
Radial movement of an unconfined leaky aquifer was studied with respect to hydraulic forces that are induced by well recharge
and discharge. New analytic solutions in the velocity and displacement fields were found and applied to describe transient
movement in an unconfined leaky aquifer. Linear momentum and mass balance of saturated porous sediments, the Darcy-Gersevanov
law, and the analytic solution of hydraulic drawdown for unsteady flow within the unconfined leaky aquifer were introduced
to find the new solutions. Analytic results indicate that the nonlinear relation between the initial hydraulic head (h0) and the well function has an insignificant effect on the aquifer transient movement when the drawdown s<0.02h
0. When the well function is simplified with different assumptions and pumping conditions, the new solutions correspondingly
reduce to cases that are similar to the Hantush-Jacob, Muskat, and Theis transient movement of a confined leaky aquifer. It
was found that large leakance is important in slowing radial movement and reducing aquifer deformation. Flow velocity in the
aquifer is more responsive to leakance than to cumulative displacement within the aquifer. The zones and boundary with tensile
stress can be located using the same approach applied to a confined aquifer for risk assessment of earth fissuring.
相似文献
Résumé Le mouvement radial dans un aquifère semi-perméable libre a été étudié en considérant les forces hydrauliques induites par la recharge et le prélèvement au niveau d’un puits. De nouvelles solutions analytiques des champs de vitesse et de déplacement ont été trouvées et appliquées pour décrire le mouvement transitoire dans un aquifère semi-perméable libre. Pour trouver les nouvelles solutions, le moment linéaire et le bilan de masse dans les sédiments poreux saturés, la loi de Darcy-Gersevanov, et la solution analytique du rabattement hydraulique pour un écoulement transitoire dans un aquifère semi-perméable libre sont pris en compte. Les résultats analytiques montrent que la relation non-linéaire entre le potentiel hydraulique initial (h0) et la fonction de puits a un effet insignifiant sur le mouvement transitoire de l’aquifère quand le rabattements s <0.02h0. Si la fonction de puits est simplifiée en tenant compte de différentes hypothèses et conditions de pompage, les nouvelles solutions se réduisent en conséquence à des cas similaires au mouvement transitoire dans un aquifère semi-perméable captif selon Hantush-Jacob, Muskat, et Theis. Il s’est avéré qu’une drainance élevée est importante pour le ralentissement du mouvement radial et la réduction de la déformation de l’aquifère. La vitesse d’écoulement dans l’aquifère est plus sensible à la drainance qu’au déplacement cumulé dans l’aquifère. Les zones et la frontière présentant des contraintes de traction peuvent être localisées en utilisant la même approche appliquée à un aquifère captif pour l’évaluation des risques de fissuration du sol.
Resumen Se ha estudiado el movimiento radial en un acuífero no confinado con fuga en relación a las fuerzas hidráulicas que son inducidas por la descarga y recarga del pozo. Se encontraron nuevas soluciones analíticas en los campos de desplazamiento y velocidad, las cuales se aplicaron para describir el movimiento transitorio en un acuífero no confinado con fuga. Se han introducido cálculos de balance de masa y momentum lineal de los sedimentos porosos saturados, la Ley Darcy-Gersevanov, y la solución analítica de descenso hidráulico para flujo sin régimen permanente dentro del acuífero no confinado con goteo para encontrar las nuevas soluciones. Los resultados analíticos indican que la relación no lineal entre la presión hidráulica inicial (h0) y la función del pozo tiene efecto insignificante en el movimiento transitorio del acuífero cuando el descenso s < 0.02h0. Cuando se simplifica la función del pozo en base a diferentes supuestos y condiciones de bombeo se reducen las nuevas soluciones a casos que son similares a el movimiento transitorio Hantush-Jacob, Muskat, y Theis de un acuífero confinado con goteo. Se encontró que las fugas grandes son importantes en la disminución del movimiento radial y en la reducción de la deformación del acuífero. La velocidad de flujo en el acuífero responde más a las fugas que al desplazamiento acumulativo dentro del acuífero. Pueden localizarse zonas y límites con esfuerzos tensionales usando el mismo enfoque aplicado a acuíferos confinados para evaluación de riesgo de generación de fracturas en el terreno.
相似文献
510.
Ian Knowles Michael Teubner Aimin Yan Paul Rasser Jong Wook Lee 《Hydrogeology Journal》2007,15(6):1107-1118
A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate
a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga
Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined
significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater
recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter
values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good
estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved
groundwater resource management.
Supported in part by US National Science Foundation grants, DMS-0107492 and DMS-0079478. 相似文献