共查询到20条相似文献，搜索用时 31 毫秒
1.
Assessing flow systems in carbonate aquifers using scale effects in hydraulic conductivity 总被引：4，自引：0，他引：4
C. W. Rovey II 《Environmental Geology》1994,24(4):244-253
Counter to intuition, small-scale measurements of hydraulic conductivity do not average to regional values. Instead, mean hydraulic conductivity increases with measurement scale up to a critical distance termed the range, beyond which a constant regional value prevails. Likewise, variance in log hydraulic conductivity increases with separation distance between measurement points as the spatial correlation decreases. As dissolution proceeds in carbonate aquifers, heterogeneity and the volume necessary for an equivalent homogeneous medium (EHM) both increase. As these variables increase, the range of scale increase in both mean hydraulic conductivity and variance increases proportionately. Consequently, the range in scale effects is a reliable measure of the degree of secondary dissolution. By correlating the numeric value of range with independently measured hydraulic properties, the prevalent type of flow system, diffuse, mixed or conduit can be determined. 相似文献
2.
Hugo A. Loaiciga Roy B. Leipnik Paul F. Hudak Miguel A. Marino 《Mathematical Geology》1996,28(5):563-584
Starting with a stochastic differential equation with random coefficients describing steady-state flow, the effective hydraulic conductivity of 1-, 2-, and 3-dimensional aquifers is derived. The natural logarithm of hydraulic conductivity (lnK) is assumed to be heterogeneous, with a spatial trend, and isotropic. The effective conductivity relates the mean specific discharge in an aquifer to the mean hydraulic gradient, thus its importance in predicting Darcian discharge when field data represent mean or average values of conductivity or hydraulic head. Effective conductivity results are presented in exact form in terms of elementary functions after the introduction of special sets of coordinate transformations in two and three dimensions. It was determined that in one, two, and three dimensions, for the type of aquifer heterogeneity considered, the effective hydraulic conductivity depends on: (i) the angle between the gradient of the trend of lnK and the mean hydraulic gradient (which is zero in the one-dimensional situation); (2) (inversely) on the product of the magnitude of the trend gradient of lnK, b, and the correlation scale of lnK, and (3) (proportionally) on the variance of lnK,
f
2
. The productb plays a central role in the stability of the results for effective hydraulic conductivity. 相似文献
3.
在野外水文地质调查的基础上,采集青岛市大沽河下游咸水入侵区砂样,首先对含水介质的粒度和矿物组成进行了分析,然后通过室内砂槽模拟试验,对咸淡水驱替过程中含水介质的渗透性变化规律进行了研究。结果表明,当咸淡水相互驱替时,含水介质的渗透性会发生显著变化,这种变化主要是由于驱替液盐浓度的变化,使得伊利石、高岭石和绿泥石等非膨胀性粘土矿物经释放、迁移、絮凝和沉积,从而重新分布所引起的。含水介质渗透性的变化具有明显的非均质性,即位于距入水处不同水平距离以及不同高度处的含水介质,其渗透性变化规律有所不同。 相似文献
4.
Effect of hypersaline cooling canals on aquifer salinization 总被引：1，自引：1，他引：0
Joseph D. Hughes Christian D. Langevin Linzy Brakefield-Goswami 《Hydrogeology Journal》2010,18(1):25-38
The combined effect of salinity and temperature on density-driven convection was evaluated in this study for a large (28 km2) cooling canal system (CCS) at a thermoelectric power plant in south Florida, USA. A two-dimensional cross-section model was used to evaluate the effects of hydraulic heterogeneities, cooling canal salinity, heat transport, and cooling canal geometry on aquifer salinization and movement of the freshwater/saltwater interface. Four different hydraulic conductivity configurations, with values ranging over several orders of magnitude, were evaluated with the model. For all of the conditions evaluated, aquifer salinization was initiated by the formation of dense, hypersaline fingers that descended downward to the bottom of the 30-m thick aquifer. Saline fingers reached the aquifer bottom in times ranging from a few days to approximately 5 years for the lowest hydraulic conductivity case. Aquifer salinization continued after saline fingers reached the aquifer bottom and coalesced by lateral movement away from the site. Model results showed that aquifer salinization was most sensitive to aquifer heterogeneity, but was also sensitive to CCS salinity, temperature, and configuration. 相似文献
5.
Stochastic analysis of the effect of spatial variability of diffusion parameters on radionuclide transport in a low permeability clay layer 总被引：1，自引：0，他引：1
Most studies that incorporate subsurface heterogeneity in groundwater flow and transport models only analyze and simulate the spatial variability of hydraulic conductivity. Heterogeneity of the other flow and transport parameters are usually neglected. This approach is often justified, but there are, however, cases in which disregarding the heterogeneity of the other flow and transport parameters can be questionable. In low permeability media, for instance, diffusion is often the dominant transport mechanism. It therefore seems logical to incorporate the spatial variability of the diffusion parameters in the transport model. This study therefore analyses and simulates the spatial variability of the effective diffusion coefficient and the diffusion accessible porosity with geostatistical techniques and incorporates their heterogeneity in the transport model of a low permeability formation. The formation studied was Boom clay (Belgium), a candidate host rock for the deep geological disposal of high-level radioactive waste. The calculated output radionuclide fluxes of this model are compared with the fluxes calculated with a homogeneous model and a model with a heterogeneous hydraulic conductivity distribution. This analysis shows that the heterogeneity of the diffusion parameters has a much larger effect on the calculated output radionuclide fluxes than the heterogeneity of hydraulic conductivity in the low permeability medium under study. 相似文献
6.
Spatial averaging of hydraulic conductivity in three-dimensional heterogeneous porous media 总被引：4，自引：0，他引：4
A. J. Desbarats 《Mathematical Geology》1992,24(3):249-267
Numerical models of groundwater flow require the assignment of hydraulic conductivities to large grid blocks discretizing the flow domain; however, conductivity data is usually available only at the much smaller scale of core samples. This paper describes a geostatistical model for hydraulic conductivity at both the core or point scale and that of grid blocks. Conductivity at the block scale is obtained empirically as a spatial power-average of point scale values. Assuming a multivariate Gaussian model for point log-conductivity, expressions are derived for the ensemble mean and variance of block conductivity. The expression for the ensemble mean of block scale conductivity is found to be similar to an expression for the ensemble effective conductivity of an infinite field derived analytically by earlier authors. Here, block conductivities obtained by power averaging are compared with effective conductivities obtained from a numerical flow model and are found to be in excellent agreement for a suitably chosen averaging exponent. This agreement deteriorates gradually as the log variance of conductivity increases beyond 2. For arbitrary flow field geometry and anisotropic conductivity covariances, the averaging exponent can be calibrated by recourse to numerical flow experiments. For cubic fields and an isotropic spatial covariance, the averaging exponent is found to be 1/3. In this particular case, it was found that flow field discretization at the block scale through local averaging of point conductivities gave similar results to those obtained directly using a point scale discretization of the flow field. 相似文献
7.
岩体裂隙系统渗流场与应力场耦合模型 总被引：15，自引：0，他引：15
仵彦卿 《地质灾害与环境保护》1996,7(1):31-34
岩体系统具有复杂的结构。一般认为，岩体系统是非均质各向异性不连续的多相介质体系。当岩体以裂隙为主，且其分布较密集时，可将岩体系统看作等效连续多相介质体系。本文运用等效连续介质理论，提出了两种岩体裂隙系统渗流场与应力场耦合模型：一是以渗透水压力与隙变形关系、应力与渗透系统数关系为基础，建立渗透系数张量计算公式，进而建立等效效连续介质渗流为数学模型。以裂隙岩体应变张量分析为基础，建立裂隙岩体效应力张量 相似文献
8.
Slopes composed of stratified and poorly cemented rocks that fail during heavy rainfalls are typical in the outer zone of Taiwan's Western Foothills. This study investigates how hydraulic conductivity anisotropy influences pore water pressure (PWP) distributed in stratified, poorly cemented rock slopes and related slope stability through numerical simulation. The notion of representing thin alternating beds of stratified, poorly cemented rocks as an equivalent anisotropic medium for ground‐water flow analysis in finite slopes was validated. PWP was then derived in a modelled slope comprising an anisotropic medium with suitable boundary conditions. Simulation results indicate the significance of the principal directions of hydraulic conductivity tensor and the anisotropic ratio on PWP estimation for anisotropic finite slopes. For a stratified, poorly cemented rock slope, estimating PWP utilizing a phreatic surface with isotropic and hydrostatic assumptions will yield incorrect results. Stability analysis results demonstrate that hydraulic conductivity anisotropy affects the slope safety factor and slip surface pattern. Consequently, steady‐state groundwater flow analysis is essential for stratified, poorly cemented rock slopes when evaluating PWP distribution and slope stability. This study highlights the importance of hydraulic conductivity anisotropy on the stability of a stratified, poorly cemented rock slope. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
9.
基于MIKE3研究扰动底层盐水楔实现抑制咸潮上溯的最优化方案。结果表明,在河道底部喷水扰动盐水楔可以有效减弱底层盐水浓度,且存在最优喷水流量与最优喷水点。当喷水流量小于该值时,咸潮上溯距离随流量的增大而减小,当大于该值时,咸潮上溯距离随流量的增大反而会增大;最优喷水流量从小潮到大潮逐渐增加,且随着径流量的增大而减小,如径流量为500 m/s~3时,小、中、大潮期间的最优喷水流量分别为20 m/s~3、20 m/s~3和25 m/s~3,减少的咸潮上溯距离分别为3.82 km、3.40 km和1.18 km。随着径流量增大,取得最佳抑咸效果的最优喷水点位置逐渐向下游移动。针对珠江河口的特殊径潮环境,盐水楔扰动的抑咸效果在小潮和中潮期间较好,在大潮期间相对较差。 相似文献
10.
Because of their simplicity, assumptions of isotropy and homogeneity are often applied to slug test analyses, determining hydraulic conductivity of heterogeneous and anisotropic formations, in spite of their inherent unfitness. In this study, it was examined how anisotropy and heterogeneity of the formation affect well recovery curves and therefore estimates of hydraulic conductivity in slug tests. Using a finite element method (FEM) slug test model, several hypothetical slug tests in anisotropic and heterogeneous formations with known hydraulic parameters and actual formations of unknown parameters were analyzed. Error factors as a result of the assumptions of isotropy and homogeneity were quantified through sensitivity analyses of well recovery curves. Results of slug tests analyzed in this study indicate that: (1) the well recovery curves in slug tests do not show unique shape or signs reflecting the anisotropy and heterogeneity of the tested formation; (2) the assumption of isotropy does not deviate estimates of hydraulic conductivity significantly when the radial hydraulic conductivity is larger than the vertical one in the formation; (3) the assumption of homogeneity in a layered heterogeneous system has a high potential for errors in hydraulic conductivity estimation, however it can be avoided by placing the screened section apart from the adjacent layers; (4) a low permeability well skin skews the hydraulic conductivity of the original formation, depending on the size and hydraulic conductivity of the skin. 相似文献
11.
基于SEAWAT-2000程序构建室内二维砂箱试验中咸水入侵数值模型,利用该模型分析了针对不同补给井井位、补给井流量、截渗墙位置及贯穿深度等多种情景下的咸淡水界面运移规律。二维砂箱实验模拟结果表明,当注水井位于盐水楔前锋附近,距咸水边界40 cm、砂箱顶部边界5 cm处时,注水井工程措施能达到最佳海水入侵驱退效果,回退系数达21.5%。当截渗墙布设于距咸水边界10 cm处,贯穿深度为35 cm时,截渗墙工程措施能达到最佳海水入侵驱退效果,回退系数达81.1%。在此基础上,结合实际场地条件,构建山东龙口地区滨海含水层中某典型二维剖面的海水入侵数值模型,探讨了不同截渗墙布设情景模式下海水入侵状况。模拟结果表明,当截渗墙布设于距海岸线600 m处,贯穿深度为18 m时,截渗墙工程措施达到最佳海水入侵驱退效果,回退系数达28.4%。研究结果揭示了补给井井位、补给井流量、截渗墙位置及贯穿深度等因素对咸淡水界面运移规律的影响,可为场地条件下滨海含水层海水入侵防治中的工程管理措施优化提供参考依据。 相似文献
12.
林火会造成火烧迹地土壤斥水性增强及渗透性降低,导致降雨期间流域内地表产流率激增。在一定条件下,尤其是地形陡峭的高海拔山区,地表产流激增一般是泥石流灾害发生的重要诱因。然而,对于高海拔山区火烧迹地土壤斥水性和渗透性变化特征的研究相对缺乏。以海拔高程3029~4474 m的四川省雅江县恶古乡火烧迹地为研究对象,通过现场水滴入渗试验和圆盘入渗试验,探究斥水性强度分布及其与土壤入渗参数之间的内在联系。结果显示:土壤斥水性强度分布具备较大的空间异质性,林火对斥水性的影响深度在轻度火烧区为2 cm,在中度和严重火烧区为3 cm;研究区土壤渗透能力与斥水性强度呈反比,饱和导水率和吸渗率与水滴入渗时间之间遵循幂函数分布,其变异系数与火烈度呈正比,且严重火烧区部分土壤由于斥水性被高温破坏造成饱和导水率增大;斥水性土壤相较于亲水性土壤出现明显的入渗延迟现象。研究结果丰富了高海拔山区火烧迹地水文特征的研究,为揭示火烧迹地泥石流坡面物源起动机理提供理论依据。 相似文献
13.
14.
River discharge, tide, wind, topography and other factors all have great impacts on the saltwater intrusion of Modaomen Waterway (MW), a major outlet of the Pearl River Estuary. A coupled 1D–3D numerical model was applied in this study to account for the dynamic characteristics of saltwater intrusion in the MW, and the impacts of tide and river discharge on the length of saltwater intrusion were uncovered. Results are as the followings: (1) River discharge from upstream induces an obvious dilution of salinity along the MW, whereas tide can exert a positive force that pushes salt water landward. The effects of river discharge and tide on the length of saltwater intrusion can be well described by a regression function; (2) the saltwater intrusion along the MW is generally aggravated by increases in tidal range from the South China Sea. The length of saltwater intrusion usually reaches a maximum 2 or 3 days before spring tide, and the hourly length of saltwater intrusion along the MW usually slows the tidal process for approximately 4 h, which can provide important information that the pumping operation along the MW to store freshwater in the backup storages needs to be at least 3 days ahead of the spring tide so as to avoid serious impact from saltwater intrusion; (3) the length of saltwater intrusion generally decreases with increasing river discharge. In 2005, 2009 and 2010, the average river discharge from upstream was 2680, 2630 and 3160 m3/s, respectively, with corresponding average lengths of saltwater intrusion of 32.7, 42.3 and 21.4 km. The inverse correlation between the water flow and the length of saltwater intrusion may provide some guidance for operations to maintain enough upstream flow to dilute the salinity and therefore satisfy the domestic water supply. 相似文献
15.
Stefan Bachu 《Tectonophysics》1991,190(2-4):299-314
Heterogeneity is present in geological sedimentary structures at all scales from pore to basin, and its distribution has an impact on transport processes such as heat and fluid flow. The rock masses at any scale need to be characterized by their effective properties at that scale, based on the individual characteristics of the heterogeneous porous medium. The effective thermal and hydraulic conductivity of sediments characterized by a stochastic distribution of heterogeneity is studied using an inverse approach based on numerical experiments. The simulations, covering a large range of conductivity contrasts, are carried out for actual core-scale cases of shale clasts in a sand matrix, and on a diagrammatic cross-section through a clastic sedimentary group at the basin scale.
The effective conductivity depends primarily on the heterogeneity fraction and on the conductivity contrast between heterogeneities and the embedding matrix, a dependency which can be described by a generalized weighted mean model. This model is better suited to estimate the effective conductivity at any scale than other models like the self-consistent, or any of the arithmetic, geometric or harmonic averages. The effective conductivity has an anisotropic character although the individual components are homogeneous and isotropic. The variation in effective conductivity is significant even for small conductivity contrasts, like in heat flow processes, and exhibits an asymptotic behaviour for large conductivity contrasts characteristic of fluid flow processes. The effective conductivity has a second-order dependence on such heterogeneity characteristics as shape, aspect ratio, orientation, and distribution. Depending on these characteristics, the bounds of effective conductivity values can be narrowed further from the extreme bounds expressed by the arithmetic and harmonic averages. 相似文献
16.
Modeling of subsidence and stress-dependent hydraulic conductivity for intact and fractured porous media 总被引：4，自引：0，他引：4
Summary This study investigates the changes in deformation and stress dependent hydraulic conductivities that occur as a result of underground mining in intact and fractured porous media. The intact porous medium is assumed to be comprised of regularly packed spherical grains of uniform size. The variation in grain size or pore space due to the effect of changing intergranular stresses results in a change in rock hydraulic conductivity. A model is developed to describe the sensitivity of hydraulic conductivity to effective stresses through Hertzian contact of spherical grains. The fractured porous medium is approximated as an equivalent fracture network in which a single fracture is idealized as a planar opening having a constant equivalent thickness or aperture. Changes in fracture aperture as a result of changes in elastic deformation control the variation of hydraulic conductivity. A model is presented to illustrate the coupling between strain and hydraulic conductivity. Subsidence induced deformations that result from mining induced changes in hydraulic conductivity in both intact and fractured media. These changes are examined and compared with results from a mining case study. 相似文献
17.
The role of heterogeneity and uncertainty in hydraulic conductivity on hillslope runoff production was evaluated using the fully integrated hydrologic model ParFlow. Simulations were generated using idealized high-resolution hillslopes configured both with a deep water table and a water table equal to the outlet to isolate surface and subsurface flow, respectively. Heterogeneous, correlated random fields were used to create spatial variability in the hydraulic conductivity. Ensembles, generated by multiple realizations of hydraulic conductivity, were used to evaluate how this uncertainty propagates to runoff. Ensemble averages were used to determine the effective runoff for a given hillslope as a function of rainfall rate and degree of subsurface heterogeneity. Cases where the water table is initialized at the outlet show runoff behavior with little sensitivity to variance in hydraulic conductivity. A technique is presented that explicitly interrogates individual realizations at every simulation timestep to partition overland and subsurface flow contributions. This hydrograph separation technique shows that the degree of heterogeneity can play a role in determining proportions of surface and subsurface flow, even when effective hillslope outflow is seen. This method is also used to evaluate current hydrograph separation techniques and demonstrates that recursive filters can accurately proportion overland and base-flow for certain cases. 相似文献
18.
Ronggao Qin Yanqing Wu Zengguang Xu Derrick Xie Chi Zhang 《Hydrogeology Journal》2013,21(6):1235-1246
The combined influence of dip angle and adsorption heterogeneity on solute transport mechanisms in heterogeneous media can be understood by performing simulations of steady-state flow and transient transport in a heterogeneous aquifer with dipping anisotropy. Reactive and non-reactive contaminant transport in various types of heterogeneous aquifer is studied by simulations. The hydraulic conductivity (K) of the heterogeneous aquifer is generated by HYDRO_GEN with a Gaussian correlation spectrum. By considering the heterogeneity of the adsorption distribution coefficient (K d), a perfect negative correlation between lnK and lnK d is obtained by using the spherical grains model. The generated K and K d are used as input to groundwater flow and transport models to investigate the effects of dipping sedimentary heterogeneity on contaminant plume evolution. Simulation results showed that the magnitude of the dip angle strongly controls the plume evolution in the studied anisotropic and heterogeneous aquifer. The retarded average pore-water velocity (v/R) of the adsorption model significantly controls the horizontal spreading of the plume. The bottom plume is intensively retarded in the zones between the dipping lenses of lower hydraulic conductivity and the no-flow bottom boundary. The implications of these findings are very important for the management of contaminated heterogeneous aquifers. 相似文献
19.
为了探讨在法向应力和剪应力的共同作用下裂隙开度的变化对于耦合的温度场、渗流场和应力场的作用,引入裂隙的渗透系数与开度关系的“立方定律”,建立了裂隙渗透系数演化式。应用开发的遍有节理岩体双重孔隙-裂隙介质热-水-应力耦合二维有限元程序,以一个假定的位于非饱和地层中的高放废物地质处置库为算例,分别在2组裂隙斜交和正交的条件下,针对与裂隙开度3种计算方式对应的6种工况进行了数值分析,考察了围岩中的温度、孔隙和裂隙水压力、裂隙开度、裂隙的渗透系数、地下水流速、应力的变化、分布状态。结果显示,当裂隙开度仅取决于法向应力时,裂隙开度受压应力作用产生的闭合量最大,从而裂隙水压力最高;而当裂隙开度是法向应力和剪切位移的函数时,由于“剪胀”效应,裂隙开度闭合量较前述情况为小,裂隙水压力居中;而当裂隙开度是常数时,裂隙水压力最低 相似文献
20.
This study focuses on coupling geochemistry with geo-hydraulics to enable time-dependent modelling of the remediation of acidic groundwater using an alkaline permeable reactive barrier (PRB). Chemical clogging due to secondary mineral precipitates reduces the porosity and hydraulic conductivity of the reactive medium. The governing equations are incorporated into commercial numerical codes, MODFLOW and RT3D. An original algorithm was developed for RT3D to simulate geochemical reactions occurring in the PRB. The results and the model predictions are in agreement, confirming that the hydraulic conductivity reduction due to mineral precipitation occurs at the start of permeation and continues until halfway through the testing phase. 相似文献