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1.
There are many field techniques used to quantify rates of hyporheic exchange, which can vary in magnitude and direction spatially over distances of only a few metres, both within and between morphological features. We used in‐stream mini‐piezometers and heat transport modelling of stream and streambed temperatures to quantify the rates and directions of water flux across the streambed interface upstream and downstream of three types of in‐stream geomorphic features: a permanent dam, a beaver dam remnant and a stream meander. We derived hyporheic flux estimates at three different depths at six different sites for a month and then paired those flux rates with measurements of gradient to derive hydraulic conductivity (K) of the streambed sediments. Heat transport modelling provided consistent daily flux estimates that were in agreement directionally with hydraulic gradient measurements and also identified vertical heterogeneities in hydraulic conductivity that led to variable hyporheic exchange. Streambed K varied over an order of magnitude (1·9 × 10?6 to 5·7 × 10?5 m/s). Average rates of hyporheic flux ranged from static (q < ±0·02 m/day) to 0·42 m/day. Heat transport modelling results suggest three kinds of flow around the dams and the meander. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
Characteristics of concentrated flow hydraulics for rangeland ecosystems: implications for hydrologic modeling 总被引：1，自引：0，他引：1
Osama Z. Al‐Hamdan F.B. Pierson Jr M.A. Nearing J.J. Stone C.J. Williams C.A. Moffet P.R. Kormos J. Boll M.A. Weltz 《地球表面变化过程与地形》2012,37(2):157-168
Concentrated flow is often the dominant source of water erosion following disturbance on rangelands. Because of the lack of studies that explain the hydraulics of concentrated flow on rangelands, cropland‐based equations have typically been used for rangeland hydrology and erosion modeling, leading to less accurate predictions due to different soil and vegetation cover characteristics. This study investigates the hydraulics of concentrated flow using unconfined field experimental data over diverse rangeland landscapes within the Great Basin Region, United States. The results imply that the overall hydraulics of concentrated flow on rangelands differ significantly from those of cropland rills. Concentrated flow hydraulics on rangelands are largely controlled by the amount of cover or bare soil and hillslope angle. New predictive equations for concentrated flow velocity (R2 = 0·47), hydraulic friction (R2 = 0·52), and width (R2 = 0·4) representing a diverse set of rangeland environments were developed. The resulting equations are applicable across a wide span of ecological sites, soils, slopes, and vegetation and ground cover conditions and can be used by physically‐based rangeland hydrology and erosion models to estimate rangeland concentrated flow hydraulic parameters. Published in 2011. This article is a US Government work and is in the public domain in the USA. 相似文献
3.
Prabhakar S. Naidu 《Pure and Applied Geophysics》1970,79(1):73-84
Summary Steady state heat flow in a weakly random semi-infinite medium is considered from a geophysical point of view. The principal finding of the present investigation is that the variance of thermal gradient (vertical) is several times larger than the variance of thermal conductivity. The variance of the thermal gradient decreases with increasing depth of measurement but approaches a certain constant value, which depends upon the spectral characteristics of thermal conductivity. The variance of heat flow is generally lower ( 10%) than the variance of the thermal gradient, but it behaves similarly. The dip of the medium (assuming it to be randomly layered) significantly affects the variance of the thermal gradient. The variance is miniumum for an intermediate dip. 相似文献
4.
P.C. Schillig J.F. Devlin C.D. McElwee K. Walter B. Gibson 《Ground Water Monitoring & Remediation》2014,34(4):44-50
The concept of equivalent freshwater head was adapted to predict the conditions under which density‐driven flow would adversely impact measured groundwater velocities using point velocity probes (PVPs). Theoretically, vertical flow will result from any density contrast between the PVP tracer and the groundwater. However, laboratory testing of tracers with salinities ranging from 0 to 2000 mg NaCl/L showed that horizontal velocities could be determined with good accuracy with up to 60% of the total flow being vertical due to density effects in a gravel medium. The available data suggest that density effects are less likely to be pronounced in sandy sediments. The relative amount of vertical flow due to tracer density can be estimated from vertical and horizontal velocities measured with PVPs, or from the ratio of vertical to horizontal hydraulic gradients. The equivalent freshwater gradient produced from a given tracer salinity at 10 °C (a typical groundwater temperature at moderate latitudes) can be estimated from 7.80 × 10?7 × (MNaCl), where MNaCl is the mass of NaCl added, in mg, to 1 L of site groundwater in the mixing of the tracer. Equations for other temperatures were also determined. 相似文献
5.
A. C. LIAKOPOULOS Dr. Eng. 《水文科学杂志》2013,58(3):41-48
Synopsis The dynamic equation of motion that governs the laminar flow of water through soils is the empirical equation of Darcy. According to Darcy's equation the velocity of the flowing water is proportional to the hydraulic gradient under which the water is flowing, with the constant of proportionality being the coefficient of permeability. The interesting question arising is whether or not the coefficient of permeability is a scalar quantity (having only a magnitude) or a vector (having both magnitude and direction). It is proved, in the present paper, that the permeability coefficient is neither a scalar nor a vector but a symmetric tensor of second rank. The fact that the permeability tensor is symmetric gives rise to great simplifications and permits a simple graphical construction of the tensor ellipsoid. Having the tensor ellipsoid, the determination of the direction at which the water will flow under a known imposed hydraulic gradient can be found graphically. In case of isotropic soils (the permeability coefficient has the same value along any direction) the ellipsoid reduces to a sphere and the tensor becomes a scalar. In the general case of anisotropic soils the permeability tensor is an entity with nine elements, six of which are independent representing pure extension or contraction along the three principal coordinate axes, thus transforming the permeability sphere into an ellipsoid and vice versa. It should be noted that in anisotropic soils the only directions along which the flow takes place in the direction of the hydraulic gradient are those of the principal axes of the tensor ellipsoid. Permeability tests were conducted on anisotropic sandstone samples taken at different directions with respect to rectangular coordinates. The permeability coefficient values plotted on a two-dimensional polar coordinate graph paper give rise to an ellipse substantiating therefore the tensor concept of the permeability coefficient. The graphical construction of the tensor ellipse and the use of it in order to obtain the direction of flow by knowing the direction of the hydraulic gradient is also shown. 相似文献
6.
Simulation of heat transport has its applications in geothermal exploitation of aquifers and the analysis of temperature dependent chemical reactions. Under homogeneous conditions and in the absence of a regional hydraulic gradient, groundwater flow and heat transport from or to a well exhibit radial symmetry, and governing equations are reduced by one dimension (1D) which increases computational efficiency importantly. Solute transport codes can simulate heat transport and input parameters may be modified such that the Cartesian geometry can handle radial flow. In this article, SEAWAT is evaluated as simulator for heat transport under radial flow conditions. The 1971, 1D analytical solution of Gelhar and Collins is used to compare axisymmetric transport with retardation (i.e., as a result of thermal equilibrium between fluid and solid) and a large diffusion (conduction). It is shown that an axisymmetric simulation compares well with a fully three dimensional (3D) simulation of an aquifer thermal energy storage systems. The influence of grid discretization, solver parameters, and advection solution is illustrated. Because of the high diffusion to simulate conduction, convergence criterion for heat transport must be set much smaller (10?10) than for solute transport (10?6). Grid discretization should be considered carefully, in particular the subdivision of the screen interval. On the other hand, different methods to calculate the pumping or injection rate distribution over different nodes of a multilayer well lead to small differences only. 相似文献
7.
The palaeomagnetism of a vertical sequence of Deccan traps ranging in elevation from 1750 to 2900 ft. along the eastern margins of the Deccan trap exposures near Jabalpur, has been studied. Eleven different flows were sampled at approximately 100 ft. elevation interval. Nine flows at elevations between 2150 and 2900 ft. showed normal polarization with up dip. The mean direction for these siving unit weight to each flow was,D=343°E andI=28°(up). Two flows at elevations between 1740 and 2000 ft. showed intermediate directions with down dip. It appears that the latter corresponds to a zone of actual field reversal which has been encountered at several locations on the territory of the Deccan traps. The mean directions of the nine upper flows give a reliable estimate of the palaeosecular variation of the geomagnetic field during the period of normal polarity. The mean directions obtained from vertical sequences of traps studied from different localities are compared for estimating the amount of continental drift that might have taken place during the period of main Deccan trap activity. Correlation of magnetic directions of flows from various localities indicates that the geomagnetic field reversal at about 2000 ft. elevation can be traced over a large territory of the traps. 相似文献
8.
为了定量地反映复杂非均匀介质非均匀地质体的尺度大小,本文利用统计学方法建立了能够很好地描述复杂非均匀介质特征的随机介质模型,模型参量自相关长度描述了非均匀介质横向和纵向上非均匀体的平均尺度。基于所建立的随机介质模型通过速度的横向变化和速度标准差分别探讨了自相关长度与非均匀体尺度之间的关系。对速度横向变化的研究表明:随机介质内速度具有一定均值和方差并呈随机扰动特征;随着模型自相关长度的增大,非均匀体尺度也随之增大。通过速度标准差的研究得出自相关长度与非均匀体尺度之间关系的拟合公式,利用此公式可以定量地获取非均匀体尺度的实际大小。 相似文献
9.
Large differences in chemistry between sampling points separated In short vertical intervals are often observed in contaminant plumes in both granular and fractured aquifers. However, most regional models assume that such differences will be reduced by dispersive mixing during transport. At a field site located in a discharge area on the Oak Ridge Reservation, Tennessee, ground water flows along discrete flowpaths, as evidenced by the presence of four distinct water types—Ca-HCO3 , Ca-Na-HCO3 , and Na-Ca-HCO3 , and Na-Ca-HCO3 -S04 —in samples collected from shallow (< 3D in) multilevel wells. The preservation of distinct chemical signatures suggests that ground water must he contained in discrete flow zones during much of its transport time. The chemical composition of the water types can be explained primarily by strata-bound flow over varying flowpath lengths and secondarily by mixing of waters during cross-formational flow in a discharge zone. The hydrochemical facies identified by correlation of water types between the boreholes indicate the general orientation of ground water How paths. These inferred flowpaths are oblique to the orientation of the measured hydraulic gradient and are more closely aligned with bedding and the calculated flow direction. Results of this study indicate that discrete multilevel sampling for analysis of major ions, in addition to information gathered from tracer tests, borehole flow tests. and visual core observations, can provide valuable information on flow directions and preferential flowpaths for contaminant transport. 相似文献
10.
Although it is believed that natural fracture sets predominantly have near‐vertical orientation, oblique stresses and some other mechanisms may tilt fractures away from the vertical. Here, we examine an effective medium produced by a single system of obliquely dipping rotationally invariant fractures embedded in a transversely isotropic with a vertical symmetry axis (VTI) background rock. This model is monoclinic with a vertical symmetry plane that coincides with the dip plane of the fractures. Multicomponent seismic data acquired over such a medium possess several distinct features that make it possible to estimate the fracture orientation. For example, the vertically propagating fast shear wave (and the fast converted PS‐wave) is typically polarized in the direction of the fracture strike. The normal‐moveout (NMO) ellipses of horizontal reflection events are co‐orientated with the dip and strike directions of the fractures, which provides an independent estimate of the fracture azimuth. However, the polarization vector of the slow shear wave at vertical incidence does not lie in the horizontal plane – an unusual phenomenon that can be used to evaluate fracture dip. Also, for oblique fractures the shear‐wave splitting coefficient at vertical incidence becomes dependent on fracture infill (saturation). A complete medium‐characterization procedure includes estimating the fracture compliances and orientation (dip and azimuth), as well as the Thomsen parameters of the VTI background. We demonstrate that both the fracture and background parameters can be obtained from multicomponent wide‐azimuth data using the vertical velocities and NMO ellipses of PP‐waves and two split SS‐waves (or the traveltimes of PS‐waves) reflected from horizontal interfaces. Numerical tests corroborate the accuracy and stability of the inversion algorithm based on the exact expressions for the vertical and NMO velocities. 相似文献
11.
Influence of bedding orientation on the anisotropy of hydraulic conductivity in a well-sorted fluvial sediment 总被引：2，自引：0，他引：2
The paper describes a permeameter test method for determination of the hydraulic conductivity(AT) along multi-directions in fluvial sediments with cross beddings.Unlike existing in-situ permeameter methods that determine hydraulic conductivity for submerged streambeds,our method was intended to measure hydraulic conductivity of exposed streambeds or fluvial sediments.The method was applied to the Wei River,Shaanxi Province,Central China for characterization of the anisotropy of K in a well-sorted fluvial sediment.The results illustrated that even in well-sorted sediments,cross-bedding and sediment fabrication(or texture) can lead to varied K values along different measurement directions.The K value was the largest along the dip direction(or the major direction) that is parallel to the orientation of cross bedding and the smallest in the direction perpendicular to the bedding(or the minor direction). The K value in a given direction between the major and minor direction often fell in the range bounded by the K values in the major and minor directions.The anisotropy ratio of K(the ratio of K value between the major and minor directions) in two trenches for this well-sorted fluvial sediment was up to 1.14 to 1.23,respectively.Our results also demonstrated that even for well-sorted sediments,the K values between two sampling points only about 10 cm apart can differ.It is clear that the K distribution strongly correlates to the bedding orientation. 相似文献
12.
Refracted arrivals are analysed to estimate the near‐surface anisotropy of marine sediments using a vertical‐cable (VC) configuration. In the presence of dip, the horizontal and vertical ray‐slownesses are obtained from the observed apparent slownesses in the up‐ and downdip directions using a sum or difference at each azimuth. The multiple azimuths generated by a VC geometry permit the ray‐slowness distribution of the marine sediments to be determined. An inversion procedure is developed to provide dip and anisotropy parameters for refractive layers from the measured refraction traveltimes in multilayered azimuthally isotropic and anisotropic media. Two sets of transversely isotropic models are used to analyse the azimuthal variations of apparent and ray slownesses. In the first set, we fix the anisotropic parameters of the models but vary the dip (0°, 5° and 10°) to test the effects of the presence of dip. In the second set, we vary the P‐wave anisotropy strength (5.2%, 10.3%, 15.8% and 22.0%) to examine the sensitivity and accuracy of ray‐slowness approximations which are independent of dip. We test this inversion procedure on synthetic P‐wave VC data calculated for six different models by a finite‐difference method. The results of applications to real VC data acquired from the North Sea are also presented. 相似文献
13.
We designed and evaluated a “tube seepage meter” for point measurements of vertical seepage rates (q), collecting groundwater samples, and estimating vertical hydraulic conductivity (K) in streambeds. Laboratory testing in artificial streambeds show that seepage rates from the tube seepage meter agreed well with expected values. Results of field testing of the tube seepage meter in a sandy‐bottom stream with a mean seepage rate of about 0.5 m/day agreed well with Darcian estimates (vertical hydraulic conductivity times head gradient) when averaged over multiple measurements. The uncertainties in q and K were evaluated with a Monte Carlo method and are typically 20% and 60%, respectively, for field data, and depend on the magnitude of the hydraulic gradient and the uncertainty in head measurements. The primary advantages of the tube seepage meter are its small footprint, concurrent and colocated assessments of q and K, and that it can also be configured as a self‐purging groundwater‐sampling device. 相似文献
14.
Wells in aquifers of loose collapsible sediment are cased so that they have a blind wall and gain water only from the bottom. The hydraulic gradient established at the bottom of these wells during pumping brings the aquifer materials in a quicksand state, which may cause abrasion of pipes and pumps and even the destruction of well structure. To examine the quicksand occurrence, an analytical solution for the steady flow to a partially penetrating blind‐wall well in a confined aquifer is developed. The validity of the proposed solution is evaluated numerically. The sensitivity of maximum vertical gradient along the well bottom in response to aquifer and well parameters is examined. The solution is presented in the form of dimensionless‐type curves and equations that can be easily used to design the safe pumping rate and optimum well geometry to protect the well against sand production. The solution incorporates the anisotropy of aquifer materials and can also be used to determine the hydraulic conductivity of the aquifer. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
15.
Geothermal fields and hydrothermal mineral deposits are manifestations of the interaction between heat transfer and fluid
flow in the Earth’s crust. Understanding the factors that drive fluid flow is essential for managing geothermal energy production
and for understanding the genesis of hydrothermal mineral systems. We provide an overview of fluid flow drivers with a focus
on flow driven by heat and hydraulic head. We show how numerical simulations can be used to compare the effect of different
flow drivers on hydrothermal mineralisation. We explore the concepts of laminar flow in porous media (Darcy’s law) and the
non-dimensional Rayleigh number (Ra) for free thermal convection in the context of fluid flow in hydrothermal systems in three dimensions. We compare models
of free thermal convection to hydraulic head driven flow in relation to hydrothermal copper mineralisation at Mount Isa, Australia.
Free thermal convection occurs if the permeability of the fault system results in Ra above the critical threshold, whereas a vertical head gradient results in an upward flow field. 相似文献
16.
17.
In this paper, I introduce a new approach based on truncated singular value decomposition (TSVD) analysis for improving implementation of grid-based Euler deconvolution with constraints of quasi 2D magnetic sources. I will show that by using TSVD analysis of the gradient matrix of magnetic field anomaly (reduced to pole) for data points located within a square window centered at the maximum of the analytic signal amplitude, we are able to estimate the strike direction and dip angle of 2D structures from the acquired eigenvectors. It is also shown that implementation of the standard grid-based Euler deconvolution can be considerably improved by solving the Euler's homogeneity equation for source location and structural index, simultaneously, using the TSVD method. The dimensionality of the magnetic anomalies can be indicated from the ratio between the smallest and intermediate eigenvalues acquired from the TSVD analysis of the gradient matrix. For 2D magnetic sources, the uncertainty of the estimated source location and structural index is significantly reduced by truncating the smallest eigenvalue.Application of the method is demonstrated on an aeromagnetic data set from the Åsele area in Sweden. The geology of this area is dominated by several dike swarms. For these dolerite dikes, the introduced method has provided useful information of strike directions and dip angles in addition to the estimated source location and structural index. 相似文献
18.
19.
Vertically Integrated Hydraulic Conductivity: A New Parameter for Groundwater-Surface Water Analysis
Numerical modeling of groundwater-surface water interactions provides vital information necessary for determining the extent of nutrient transport, quantifying water budgets, and delineating zones of ecological support. The hydrologic data that drive these models are often collected at disparate scales and subsequently incorporated into numerical models through upscaling techniques such as piecewise constancy or geostatistical methods. However, these techniques either use basic interpolation methods, which often simplifies the system of interest, or utilize complex statistical methods that are computationally expensive, time consuming, and generate complex subsurface configurations. We propose a bulk parameter termed “vertically integrated hydraulic conductivity” (KV), and defined as the depth-integrated resistance to fluid flow sensed at the groundwater-surface water interface, as an alternative to hydraulic conductivity when investigating vertical fluxes across the groundwater-surface water interface. This bulk parameter replaces complex subsurface configurations in situations dominated by vertical fluxes and where heterogeneity is not of primary importance. To demonstrate the utility of KV, we extracted synthetic temperature time series data from a forward numerical model under a variety of scenarios and used those data to quantify vertical fluxes using the amplitude ratio method. These quantified vertical fluxes and the applied hydraulic head gradient were subsequently input into Darcy's Law and used to quantify KV. This KV was then directly compared to the equivalent hydraulic conductivity (KT) assuming an infinitely extending layer. Vertically integrated hydraulic conductivity allows for more accurate and robust flow modeling across the groundwater-surface water interface in instances where complex heterogeneities are not of primary concern. 相似文献
20.
Internal erosion is one of the most common causes of failure in hydraulic engineering structures, such as embankments and levees. It also plays a vital role in the geohazards (such as landslides and sinkhole developments) and more importantly, the earth landscape evolution, which has a broad environmental and ecosystem impacts. The groundwater seepage is multi-directional, and its multi-dimensional nature could affect the initiation and the progression of internal erosion. With a newly developed apparatus, we carry out nine internal erosion experiments under five different seepage directions. The results reveal that the critical hydraulic gradient increases as the seepage direction varies from the horizontal to the vertical. After a global erosion is triggered, preferential erosion paths distribute randomly from the bottom to the top of the specimen. If the seepage direction is not vertical, small preferential erosion paths merge into a large erosion corridor, in which the loss of fine particles is significant but negligible outside. Results of experiments manifest that the erosion is heterogeneous and three-dimensional, even in the unidirectional seepage flow. The particles are rapidly eroded at the early stage of the erosion, indicating a high erosion rate. With the erosion time increasing, the particle loss slows down and even ceases if the time is long enough. The erosion rate increases if the seepage direction approaches a vertical direction. Overall, the erosion rate approximately decreases with erosion time exponentially. We proposed exponential equations to illustrate the variation of the erosion rate in the erosion process. 相似文献