bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of laboratory‐scale variability upon batch and column determinations of nonlinearly sorptive behavior in porous media
Authors: Wise William R.
Published: February 2004

Porous media are considered to be composed of spatial distributions of particles, which individually follow Langmuir sorption isotherms (with their own distinct, randomly sampled sorption capacities and selectivity coefficients). Analyses of batch and column methods for determining the sorptive parameters of these porous media reveal that batch‐derived estimates of retardation based upon Langmuir and Freundlich isotherms systematically underestimate and overestimate that observed at low concentrations, respectively, when local equilibrium conditions are met in the columns. These results, derived by stochastically analyzing the sorptive behavior expected during batch and column experiments, follow from the failure of the homogeneous‐based Langmuir and Freundlich models to properly describe sorptive behavior in the ensembles of particles composing the media. As the variability in the underlying sorptive properties increases, the Langmuir isotherm ceases to describe well the behavior of the aggregate of (individually Langmuir) particles both under static (batch) and dynamic (column) conditions. In such composite porous media there tends to be an inherent uncertainty involved with characterizing sorptive behavior at lower concentrations.
A method of estimating optimal catchment model parameters
Authors: Ibrahim Yaacob , Liong Shie‐Yui
Published: February 2004

A review of a calibration method developed earlier (Ibrahim and Liong, 1992) is presented. The method generates optimal values for single events. It entails randomizing the calibration parameters over bounds such that a system response under consideration is bounded. Within the bounds, which are narrow and generated automatically, explicit response surface representation of the response is obtained using experimental design techniques and regression analysis. The optimal values are obtained by searching on the response surface for a point at which the predicted response is equal to the measured response and the value of the joint probability density function at that point in a transformed space is the highest. The method is demonstrated on a catchment in Singapore. The issue of global optimal values is addressed by applying the method on wider bounds. The results indicate that the optimal values arising from the narrow set of bounds are, indeed, global. Improvements which are designed to achieve comparably accurate estimates but with less expense are introduced. A linear response surface model is used. Two approximations of the model are studied. The first is to fit the model using data points generated from simple Monte Carlo simulation; the second is to approximate the model by a Taylor series expansion. Very good results are obtained from both approximations. Two methods of obtaining a single estimate from the individual event's estimates of the parameters are presented. The simulated and measured hydrographs of four verification storms using these estimates compare quite well.
Fractal geometry of individual river channels and its computer simulation
Authors: Nikora Vladimir I. , Sapozhnikov Victor B. , Noever David A.
Published: February 2004

A new method for analyzing the self‐similarity and self‐affinity of single‐thread channels is proposed. It permits the determination of the fractal scaling exponents, of the characteristic scales, and the evaluation of the degree of anisotropy for self‐similar fractal lines. Based upon the application of this method to the Dniester and Pruth rivers we established the self‐similarity of the river pattern on small scales and the self‐affinity on large scales. For these rivers we obtained the fractal scaling exponents, the characteristic scales, and the anisotropy parameters. A computer model has been developed which simulates river patterns whose fractal properties are close to the properties of natural objects. A generalized model of fractal behavior of natural rivers is proposed. On the basis of self‐affinity of natural and simulated rivers on large scales, a hypothesis has been formulated which explains the violation of the dimension principle in the well‐known relation between the river length and the catchment area.
Analytical solution of the one‐dimensional time‐dependent transport equation
Authors: Basha H. A. , El‐Habel F. S.
Published: February 2004

An analytical model which provides an approximate description of scale‐dependent transport is presented. The model is based on the advection‐dispersion equation but with the dispersion coefficient dependent on the travel time of the solute from a single input source. The time dependence of the dispersion coefficient can assume arbitrary functional forms. The governing equation, which includes a time‐varying dispersion coefficient, linear equilibrium adsorption, and first‐order reaction, is reduced to the heat diffusion equation after a series of transformations. Analytical solutions pertaining to a time‐varying mass injection in an infinite medium with arbitrary initial distribution of concentration and functional dependence of the dispersion coefficient can be easily derived from the model. Since the analytical solution is in an integral form, different temporal variation of the dispersion coefficient over different time intervals can also be incorporated. It is shown that the solution reduces to the well‐known result for the case of constant dispersion and mass injection. In this study, particular solutions for various dispersion functions and mass injection scenarios are presented. These include linear, exponential, and asymptotic variation of the dispersion functions and instantaneous as well as continuous mass injection. The analytical results could model the transport of solute in a hydrogeologic system characterized by a dispersion coefficient that varies as a function of travel time from the input source. It could provide a modeling solution to solute transport problems in heterogeneous media and be used as a suitable model for the inversion problem, especially since more than one fitting parameter is available to fit the field tracer data which exhibit a scale effect.
An optimization method for monitoring network design in multilayered groundwater flow systems
Authors: Hudak Paul F. , Loaiciga Hugo A.
Published: February 2004

Multiple migration pathways and the need to consider several potential siting horizons render the problem of groundwater monitoring network design a difficult task for three‐dimensional systems. While the application of quantitative simulation‐based approaches for this problem is often impractical due to computational requirements, qualitative approaches can be ineffective because they are highly subjective and typically lack a set of well‐defined criteria for locating sampling sites. An analytically based methodology developed in this paper integrates the practical implementation aspects of a qualitative approach with a quantitative analysis in deriving groundwater monitoring networks geared toward early detection of migrating contaminant. Monitoring wells are located among sets of candidate nodes in each of several hydrostratigraphic intervals on the basis of contamination susceptibility. Susceptibility is defined by nodal weights, which are derived on the basis of the locations of sites relative to contaminant source boundaries and potential contaminant plumes. As is illustrated from the results of a case study application, derived monitoring network configurations exhibit two key characteristics: (1) clustering of wells around outlets at contaminant source boundaries and (2) coverage of vacant areas in multiple siting horizons that are susceptible to contamination.
Multicomponent cation exchange including alkalinization/acidification following flow through sandy sediment
Authors: Griffioen Jasper
Published: February 2004

Cation exchange associated with displacement of aqueous solutions is a complex physicochemical process. In this study column experiments were combined with numerical modeling to determine the controlling chemical processes for natural systems at near‐neutral pH. The experimental results showed the importance of two processes in addition to exchange between free cations: exchange of monovalent metal‐bicarbonate complexes and proton buffering. The former primarily results from changes in CO2 pressure, whereas the latter results from changes in aqueous pH. Neglecting these two processes had little effect when modeling the cation elution curves. However, the pH and alkalinity breakthrough curves were poorly fit, since nonreactive behavior of these variables was assumed. Inclusion of either specific sorption of Ca and Mg hydroxy complexes or transfer of Al hydroxy species to or from the exchanger sites resulted in a better fit. It is shown theoretically that the two additional processes have a major impact on calcite equilibria when considering calcareous systems.
Permeability measurements on new and equitemperature snow
Authors: Sommerfeld R. A. , Rocchio J. E.
Published: February 2004

Measurements of the air permeability were performed on snow from six horizons within a snowpack at the Glacier Lakes Ecosystems Experiment Site in southeastern Wyoming. The snow was new or equitemperature snow, with densities (ρs) ranging between 0.134 and 0.367 Mg m−3. The specific surface area of ice in each sample was measured stereologically. Intrinsic permeabilities (K0) calculated from these data ranged from 3.0×10−10 to 3.1×10−9 m2. The data fitted the equation K0 = 1.096×10−8e−9.57ρs, with a standard deviation of 2.8× 10−10 m2. A dimensionally correct relationship between permeability and specific surface area did not fit our data as well as a simple density relationship. The small scatter reported is attributed to careful selection of undamaged samples and the prevention of sample sublimation during the measurements.
Variation in aperture estimate ratios from hydraulic and tracer tests in a single fracture
Authors: Cady Candace C. , Silliman Stephen E. , Shaffern Elizabeth
Published: February 2004

Previous theoretical discussion of flow and transport in a single fracture has led to a difference of opinion as to whether the aperture estimated from a tracer test need always be less than (or greater than) the aperture estimated from a concurrent hydraulic test. Interpretation of previously published field results has, to our knowledge, not provided a defensible example where the ratio of these two aperture estimates has varied from less than 1.0 to greater than 1.0 in the same fracture using the same analysis techniques. In the present paper, field experiments involving concurrent hydraulic and tracer tests have been run in two different directions within an isolated fracture. Aperture estimates were derived from both the hydraulic and tracer tests. The ratio of the aperture estimated from the tracer test to the aperture estimated from the hydraulic test is shown to be greater than 1.0 in the first experiment and less than 1.0 in the second experiment. Despite noise in the hydraulic test of the first experiment, it is argued that our interpretation is reasonable. As such, this represents the first set of experimental results known to us in which a defensible interpretation leads to the conclusion that the aperture ratio varies from greater than 1.0 to less than 1.0 within the same fracture.
Operational trade‐offs in reservoir control
Authors: Georgakakos Aris P.
Published: February 2004

Reservoir operation decisions require constant reevaluation in the face of conflicting objectives, varying hydrologic conditions, and frequent operational policy changes. Optimality is a relative concept very much dependent on the circumstances under which a decision is made. More than anything else, reservoir management authorities need the means to assess the impacts of various operational options. It is their responsibility to define what is desirable after a thorough evaluation of the existing circumstances. This article presents a model designed to generate operational trade‐offs common among reservoir systems. The model avoids an all‐encompassing problem formulation and distinguishes three operational modes (levels) corresponding to normal, drought, and flood operations. Each level addresses only relevant system elements and uses a static and a dynamic control module to optimize turbine performance within each planning period and temporally. The model is used for planning the operation of the Savannah River System.
Stream functions in three‐dimensional groundwater flow
Authors: Matanga George B.
Published: February 2004

Development of the partial differential equation of stream function ψ in two‐dimensional groundwater flow is based on the assumption that the curl of hydraulic gradient vector (∇×∇ϕ) is equal to zero. The equation of ψ is expressed in terms of hydraulic conductivity. This equation is valid for steady state groundwater flow only. In this paper, two partial differential equations of stream functions χ and λ in three‐dimensional groundwater flow are developed. In development of these equations, it is assumed that the curl of pseudopotential gradient (∇×∇β) is equal to zero. Pseudopotential gradient is the hydraulic gradient in the direction of flow. The equations of χ and λ are expressed in terms of pseudopotential conductivity. Pseudopotential conductivity is the hydraulic conductivity in the direction of flow. It is a scalar function and can be defined in terms of hydraulic gradient and hydraulic conductivity. Therefore besides being valid for steady state flow, the equations of χ and λ can be applied to evaluate stream functions in anisotropic porous media at a given point in time, provided that the hydraulic gradient field is known at the point in time. Application of the χ and λ equations is demonstrated by considering steady state groundwater flow under the Borden landfill in Ontario, Canada. The two equations will be valuable in visualization of groundwater flow and contaminant transport, design of numerical solution grids for contaminant transport modeling, and design of contaminant remediation well systems.
Correlation model of transport in random fields
Authors: Shvidler Mark I.
Published: February 2004

This paper is an investigation of the correlation model for transport of nonreactive solutes in media with random porosity and permeability. The method of perturbation is used to obtain a second‐order approximate, nonlocal (integrodifferential) equation for mean concentration. An approximate method of localization is used to convert to with the same order of approximation differential equations of transport. Exact averaged equations for one‐dimensional transport are examined, and the question of the consistency and asymptotic behavior for approximate averaged equations is discussed. A detailed investigation of transport in a stratified system has been carried out. The second moment of concentration is examined, the variance of the concentration is computed, and cross‐correlation moments are obtained for fields of porosity and velocity, including solute concentration.
A Fast Fourier transform stochastic analysis of the contaminant transport problem
Authors: Deng F.‐W. , Cushman J. H. , Delleur J. W.
Published: February 2004

A three‐dimensional stochastic analysis of the contaminant transport problem is developed in the spirit of Naff (1990). The new derivation is more general and simpler than previous analysis. The fast Fourier transformation is used extensively to obtain numerical estimates of the mean concentration and various spatial moments. Data from both the Borden and Cape Cod experiments are used to test the methodology. Results are comparable to results obtained by other methods, and to the experiments themselves.
Advection in geologic media
Authors: Moltyaner G. L.
Published: February 2004

In situ sensing technology, used in a series of natural‐gradient tracer tests at the Chalk River Laboratories in Ontario, leads to the introduction of a conceptually new approach to the study of groundwater motion in porous media. As opposed to the conventional approach, based on the consideration of a fictitious fluid continuum with fluid properties distributed over both voids and solids, in the new approach the actual groundwater motion in the void space of a porous medium is considered and described at the local scale by the statistical characterization of the propagation of gamma‐radiation energy associated with the moving water as a tracer. The essential feature of the new approach is that the mean free path of a gamma‐energy photon instead of the porosity is used as a scaling factor in transferring information associated with pore‐scale fluid motion to the local scale. This scaling factor is employed for reintroducing the familiar particle model of fluid motion but at the local scale. It is shown that when the local‐scale dispersion is neglected, the evolution of local‐scale fluid particles making up the tracer plume can be described by the advection equation; its equation of characteristics describes trajectories of local‐scale particles. A simple analytical solution to the advection equation is then used to produce three‐dimensional images of the spatial distribution of local‐scale particles observed in the Twin Lake test. It is also shown that the spatial averaging procedure with regard to the weighting function for a spherical averaging volume of one mean free path radius may be used to introduce the three‐dimensional field of local‐scale concentration. The averaging procedure is then used to illustrate that the concept of the three‐dimensional field of plume‐scale concentration does not make physical sense and only the one‐dimensional plume‐scale concentration field may be introduced in shallow aquifers.
Three‐dimensional analytical solutions to the advection‐dispersion equation in arbitrary Cartesian coordinates
Authors: Ellsworth T. R. , Butters G. L.
Published: February 2004

Analytical solutions for the advection‐dispersion equation (ADE) usually assume that boundary and initial conditions are orthogonal to the principal axes of the dispersion tensor. However, this is not always the case in field studies or modeling scenarios. Using the method of Green's functions, a generalized analytical solution of the three‐dimensional ADE set in an arbitrary Cartesian coordinate system (i.e., not orthogonal to the principal flow direction) is given for the solute resident concentration in a semi‐infinite porous medium with an arbitrary initial condition, surface boundary condition, and sink/source terms. Two particular solutions for a rectangular surface flux boundary condition and a buried parallelopiped, respectively, are derived from the general solution. The corresponding frequency domain solutions are also given which provide a more efficient method of computation for generating two‐and three‐dimensional grids via use of a two‐dimensional fast Fourier transform algorithm (as an alternative to the two‐dimensional numerical integration required to calculate the concentration using the real space solution). When the arbitrary coordinate system is orthogonal to the principal axes, it is shown that these particular solutions are the same as previously published results.
Practical use of analytically derived runoff models based on rainfall point processes
Authors: Puente C. E. , Bierkens M. F. P. , Diaz‐Granados M. A. , Dik P. E. , López M. M.
Published: February 2004

This work reports on the practical usage of the four stochastic rainfall‐runoff models introduced by Bierkens and Puente (1990). These models, which are lumped in space, were analytically derived combining two rainfall point process models with two simple runoff parameterizations. The rainfall models employ rectangular pulses with Poisson (PRP) and Neyman‐Scott (NSRP) arrivals, respectively. The runoff models route individual rainfall pulses via linear reservoirs. One runoff parameterization accounts for surface runoff by using a single linear reservoir (SLR). The other model considers both surface and groundwater runoff employing two linear reservoirs in parallel (PLR). All four representations were tested on two catchments located in the Netherlands and Colombia. Emphasis was placed on the models' ability to (1) give stable parameter values for data sets at alternative averaging (aggregation) lengths (consistency) and (2) preserve historical statistics at alternative averaging lengths when using parameters found from data at other averaging scales (robustness). Results show that the use of alternative rainfall models may have little effect on runoff performance. Specifically, the NSRP model resulted in more robust runoff behavior than the PRP model only when combined to the SLR parameterization. The type of model used to route individual rainfall pulses was found to be important. Runoff representations containing the PLR component were found more robust than those having the SLR model.
Groundwater management using numerical simulation and the outer approximation method for global optimization
Authors: Karatzas George P. , Pinder George F.
Published: February 2004

Groundwater quantity management problems with fixed charges have been formulated in the past as mixed integer and linear programming problems. In this paper a new methodology is presented where the fixed charges are incorporated into the objective function in an exponential form and the problem is solved as a concave minimization problem. The principal difficulty in the minimization of a concave function over a linear or nonlinear set of constraints is that the local minima which are determined by the classical minimization algorithms may not be global. In an effort to circumvent this problem the outer approximation method is introduced. This method is applicable to the global minimization of a concave function over a compact set of constraints. In the present work the outer approximation is applied to concave minimization problems over a convex compact set of constraints. Two applications of the method to groundwater management problems are presented herein, and the results are compared with an existing solution obtained using a different optimization approach.
Transaction risk versus transaction costs in water transfers
Authors: Lund Jay R.
Published: February 2004

Transaction cost has been a frequent topic in theoretical and practical discussions of water transfers. However, the risk or probability that a transfer effort will be unsuccessful should also have a significant effect on the decision by potential water purchasers to seek water transfers in lieu of seeking water by conventional means (source capacity expansion or water conservation). The importance of the uncertainty of transfer completion is examined analytically under a decision theory framework. Some implications of uncertain transaction completion for water transfer policy are discussed. In general, seeking water transfers becomes more attractive to potential water purchasers if the probability of a successful transfer is increased, if more of the transaction costs for water transfers are incurred after a transfer has been approved, and if the costs of delaying implementation of alternative water supplies are small.
Induced infiltration in aquifers with ambient flow
Authors: Wilson John L.
Published: February 2004

Well water quality depends on the relative amounts of water drawn from the pumped aquifer and nearby surface water bodies, such as streams, lakes, and wetlands. Although a surface water body may normally gain water from the aquifer, pumping can reverse gradients, causing it to lose water near the well. Surface water then enters the well by induced infiltration. Two‐dimensional vertically integrated models of induced infiltration are developed for various combinations of aquifer geometry and sources of recharge. The models, which have applications in wellhead protection, aquifer pollution characterization, and aquifer remediation, are presented graphically. They show that the propensity for and rate of induced infiltration are enhanced by higher pumping rates, proximity of the well to the stream, and the presence of nearby barrier boundaries. The propensity and rate are reduced by the presence of other surface water bodies. Ambient groundwater discharge rate to the surface water body also plays a role, but not its source, whether it is from local vertical recharge, lateral inflow, or both. The results are also largely indifferent to whether the aquifer transmissivity is assumed to be a constant, or a function of water table elevation. Finally, if the well is close enough to the surface water body, say, less than 5% of the aquifer width, then the aquifer acts as if it were semi‐infinite.
Stability of the standard Crank‐Nicolson‐Galerkin Scheme applied to the diffusion‐convection equation: Some new insights
Authors: Perrochet Pierre , Bérod Dominique
Published: February 2004

A stability analysis of the classical Crank‐Nicolson‐Galerkin (CNG) scheme applied to the one‐dimensional solute transport equation is proposed on the basis of two fairly different approaches. Using a space‐time eigenvalue analysis, it is shown, at least for subsurface hydrology applications, that the CNG scheme is theoretically stable under the condition PeCr ≤ 2, where Pe and Cr are the mesh Peclet and Courant numbers. Then, to assess the computational stability of the scheme, the amplification matrix is constructed, and its norm is displayed in the (Pe, Cr) space. The results indicate that the norm of the amplification matrix is never smaller than unity and exhibits a hyperbolic nature analogous to the above theoretical condition.
Annual river discharge in southeastern Australia related to El Nino‐Southern Oscillation forecasts of sea surface temperatures
Authors: Simpson H. J , Cane M. A. , Herczeg A. L. , Zebiak S. E. , Simpson J. H.
Published: February 2004

Annual natural discharge (Q) of the River Murray and its most extensive tributary, the Darling River system, is often inversely related to sea surface temperature (SST) anomalies in the eastern tropical Pacific Ocean. These SST variations are components of a planetary‐scale phenomenon referred to as El Nino‐Southern Oscillation (ENSO). Darling and Murray river historical values of Q indicate that annual surface runoff from regions dominated by subtropical summer monsoon precipitation and annual surface runoff primarily responding to temperate winter storms are both strongly influenced by ENSO cycles. Forecasting, approximately 1 year in advance, of ENSO‐related SST from geophysical model calculations thus provides a mechanism for estimating probabilities of annual river discharge amount. Contingency tables relating annual Q to SST, based on combining observed data for 95 years and forecast SST over a period of 15 years, provide probabilities of expected annual Q as a function of forecast SST. The SST of the eastern tropical Pacific was successfully forecast to be appreciably warmer than long‐term mean conditions for much of the year beginning in mid 1991. Precipitation data through 1991 indicated that annual natural Q for the Darling River was probably substantially below the mean. However, winter precipitation in higher‐runoff portions of the Murray Basin was above average during this El Nino episode, contrary to the trend for most such events over the past Century.
An approximate analytical study of aquifers with pressure‐sensitive formation permeability
Authors: Yeung Kacheong , Chakrabarty Chayan , Zhang Xiling
Published: February 2004

Fluid flow in hydrocarbon reservoirs and groundwater aquifers is traditionally studied by assuming that the formation permeability is constant. Such an assumption can, however, result in significant errors in the estimation of temporal and spatial variation of pressure when the formation permeability is pressure sensitive. In the present study a simple technique is proposed to obtain approximate analytical solutions to the diffusive problem with pressure‐dependent formation permeability. A constant pressure test in an infinitely large system is considered. Solutions to the flow problem in linear, cylindrical, and spherical systems are derived. These solutions are then compared with the corresponding constant permeability solutions and are related to a dimensionless parameter αD which is a measure of the pressure sensitivity of the formation permeability. In the present analysis the parameter αD is used to define a simple relationship between the pressure‐sensitive and constant permeability solutions for all three geometries. It is shown that the constant permeability solutions may underestimate the pressure distribution by approximately 10% or more for a spherical system for αD, = 0.2. Moreover, it is demonstrated that the pressure difference between the two solutions would be most significant within a distance of a few well bore radii around the well bore and at large times. For a cylindrical system the maximum pressure difference is located at the well bore and is approximately 10% for αD = 0.2.
Modeling percolation properties of random media using a domain network
Authors: Ewing Robert P. , Gupta S. C.
Published: February 2004

Many models for calculating hydraulic conductivity assume that the pore size distribution of a medium can be uniquely derived from the water retention curve. We examine this assumption by comparing water retention curves from simulations of drainage and imbibition of a domain network model to curves derived solely from the input pore size distribution. We use domain networks rather than the more usual oil reservoir pore scale networks to account for features of soils not commonly found in oil reservoirs. Simulated drainage and imbibition curves are substantially different from the input curve due to (1) the presence of a threshold in both the simulated drainage and imbibition curves and (2) the presence of entrapped air during imbibition. Differences between the simulated and input curves increase or decrease depending upon the network size, the type of percolation mechanism considered for drainage and imbibition, the aspect ratio of the pores, and the coordination number of the medium.
Comparison of univariate and transfer function models of groundwater fluctuations
Authors: Tankersley Claude D. , Graham Wendy D. , Hatfield Kirk
Published: February 2004

Seasonal autoregressive integrated moving average (SARIMA) univariate models and single input‐single output transfer function (SARIMA with externalities or SARIMAX) models of groundwater head fluctuations are developed for 21 Upper Floridan aquifer observation wells in northeast Florida. These models incorporate empirical relationships between rainfall input and head response based on historical correlations and cross correlations between these two time series. The magnitude of the forecast error terms indicates that the SARIMA and SARIMAX models explain an average of 84–87% of the variation observed in the monthly piezometric head levels for 1‐month lead forecasts. Thus the models account for the dominant processes which affect temporal groundwater fluctuations. Both the SARIMA and SARIMAX models provide unbiased forecasts of piezometric head levels; however, the SARIMAX models produce more accurate forecasts (i.e., smaller forecast probability limits) than the SARIMA models, particularly as lead time increases. Modeling efforts reveal consistent model structures over the study region, with local hydrologic and geologic conditions causing site‐specific variability in the time series model parameters.
Two‐phase flow in smooth and rough fractures: Measurement and correlation by porous‐medium and pipe flow models
Authors: Fourar M. , Bories S. , Lenormand R. , Persoff P.
Published: February 2004

Two‐phase (air‐water) flow experiments were conducted in horizontal artificial fractures. The fractures were between glass plates that were either smooth or artificially roughened by gluing a layer of glass beads to them. One smooth fracture with an aperture of 1 mm and three rough fractures, one with the two surfaces in contact and two without contact, were studied. For both types of fractures, the flow structures are similar to those observed in two‐phase flow in a pipe, with structures (bubbles, fingering bubbles, films, and drops) depending on the gas and liquid flow rates. The pressure gradients measured for different liquid and gas velocities were interpreted by three models. First, using Darcy's law leads to relative permeability curves similar to conventional ones for porous media. However, these curves depend not only on saturation but also on flow rates. This effect is caused by inertial forces which are not included in this approach. Second, the standard approach for two‐phase flow in pipes (Lockhart and Martinelli's equation) agrees with experimental results, at least for small pressure gradients. Finally, the best fit was obtained by treating the two phases as one homogeneous phase. All the properties are averaged, and the pressure drop is deduced from an empirical correlation between the two‐phase Reynolds number and the friction factor.
Long‐term frozen storage of stream water samples for dissolved orthophosphate, nitrate plus nitrite, and ammonia analysis
Authors: Avanzino Ronald J. , Kennedy Vance C.
Published: February 2004

Many researchers have used freezing as an effective, short‐term, water sample preservation method for subsequent nutrient analysis. In this study, filtered samples held at −16±2°C for 4–8 years were reanalyzed for orthophosphate, nitrate plus nitrite, and ammonia. Orthophosphate and ammonia concentrations decreased by 0.2 μg P/L and 5 μg N/L, respectively, at mean concentrations of 69.4 μg P/L and 246 μg N/L. Nitrate plus nitrite increased by 1.1 μg N/L at a mean concentration of 139.1 μg N/L. An anaerobic well sample proved to be unsuitable for freezing because it lost significant amounts of orthophosphate during the freezing process. None of the differences observed over long periods of frozen storage were more than twice the estimated standard deviation of the analytical methods used in the study. The small changes observed demonstrate the effectiveness of frozen storage as a means of nutrient preservation in water samples that are unaffected by the freezing process itself.
Hydrogeology and redox geochemistry of CH4in a Late Wisconsinan Till and Loess Sequence in central Iowa
Authors: Simpkins W. W. , Parkin T. B.
Published: February 2004

The hydrogeology and redox geochemistry of CH4in two hydrogeological settings within a late Wisconsinan till and loess sequence in central Iowa were investigated using CH4, Eh, dissolved O2, NO3‐N, NH4‐N, dissolved Fe, SO4, H2S, dissolved organic carbon (DOC), particulate organic carbon (POC), δ13C‐CH4, δ2H‐CH4, δ13C of dissolved inorganic carbon (DIC), and14C−CH4. Depleted δ13C‐CH4and δ2H‐CH4values, enriched δ13C‐DIC values, and the lack of higher hydrocarbons suggest that the CH4is microbial and is formed by CO2reduction. Carbon 14 dates of CH4indicate that 14,000‐ to 17,000‐year‐old POC and DOC in the 1oess and till compose the substrate for methanogenesis. Production of CH4probably began after deglaciation at about 12,000 years B.P. and has continued to the present. Groundwater recharge, particularly in the upland topographic position at the site, has decreased CH4concentrations in the upper part of the till.
Approximate analysis of falling‐head lined borehole permeameter
Authors: Philip J. R.
Published: February 2004

The falling‐head lined borehole permeameter consists of a snugly fitting tube extending to the base of a vertical borehole in unsaturated soil. Water is suddenly introduced into the tube to standard depth, and the subsequent time course of water depth is observed. Soil‐water data in the Amazon basin has been secured with this instrument. We develop an approximate analysis based on a Green‐Ampt model, with the flow treated as a gravity‐perturbed spherically symmetrical pressure‐capillarity‐driven flow.
On dispersion in fractal porous media
Authors: Cushman J. H. , Ginn T. R.
Published: February 2004

Molecular hydrodynamics and the associated theories of statistical mechanical correlation functions are used to develop a spatially and temporally nonlocal convective‐dispersive equation for transport in fractal porous media. A frequency and wave vector dependent dispersion tensor is developed from statistical mechanical principles. All results reduce to their classical Fickian counterparts under appropriate conditions.
Unsaturated‐saturated flow near a quasi‐linear line source
Authors: Warrick A. W.
Published: February 2004

Soil water flow from a horizontal cylindrical cavity into a surrounding unsaturated soil is analyzed. The steady state saturated bulb is described following the assumption that the conductivity function is Ks exp (αh), where Ks is the saturated hydraulic conductivity (meters per second), α is a constant (meters−1), and h is the pressure head (meters). The approach is similar to that recently presented by Philip (1992) for a point source. When the dimensionless matric flux potential 2πKs/(αq) is larger than 2.5, the corresponding saturated bulb is nearly a cylinder of radius R0 = 4α−l exp [−(2πKs/αq) − 0.5772], where q is the source strength (square meters per second). The center of the saturated cylinder is at a distance πR02Ks/q below the line source singularity.
The maintenance of high salt concentrations in interstitial waters above the New Albany shale of the Illinois Basin
Authors: Ranganathan Vishnu
Published: February 2004

Much controversy centers on whether groundwater flow velocities in basin‐scale circulation are large (tens of centimeters per year or more) or small (a few millimeters per year or less). Resolution of the controversy is particularly important in sedimentary basins in which salt beds are unknown but interstitial brines are pervasive. An example of one such basin is the Illinois Basin. The total dissolved solids (TDS) content of interstitial waters above the Upper Devonian New Albany Shale in the Illinois Basin increases with depth at an average rate of 15 wt% km−1. Mass transport calculations show that if no salt dissolved above the New Albany, upward diffusion alone should have lowered the salinity gradient over a 200 m.y. time span (i.e., since the Mid‐Triassic) to between 10 and 30% of the present value. The high salinity gradient found today requires either that halite dissolved slowly in rocks above the New Albany Shale over the past 200 m.y. or that the paleosalinity gradient, say, 200 m.y.B.P., was much greater than the value today. The flushing out of brines by meteoric water was simulated in a rectangular cross section of a generic basin 500 km wide and 1.5 km deep with a freshwater head gradient of 0.06% across the top. Simulations were run using the computer code PORFLOW (Runchal, 1987) which models coupled transport of fluid, heat, and dissolved salt. The simulations of brine flushing suggest that if topography‐driven flow occurred for time spans of several million years, then the preservation of brines in rocks above the New Albany shale could only have been possible if macroscopic flow rates (flow rates averaged over large rock volumes) were very small, on the order of 10 −3 m yr−1or less. When the horizontal permeability was 10−13 m2(10−1 darcy) and the vertical permeability 10−14 m2, brines that initially filled the basin were flushed out and replaced by fresh water in less than 5 m.y., despite the fact that the initial concentration gradient assumed was almost twice the present day value. For such high permeabilities, even very high salt dissolution rates equivalent to the removal of 4.7 m of halite column per million years were insufficient to maintain high concentrations. When the permeabilities were lower, 10−15 m2 along the horizontal and 10−16 m2 along the vertical, high dissolved salt concentrations were maintained for longer times. Even so, about half of the dissolved salt initially in the pore waters was removed after 50 m.y.
Forecasting piezometric head levels in the Floridan Aquifer: A Kalman Filtering Approach
Authors: Graham Wendy D. , Tankersley Claude D.
Published: February 2004

A Kalman filtering algorithm is developed to forecast groundwater levels in the Upper Floridan aquifer throughout the St. Johns River Water Management District (SJRWMD) in Florida. The algorithm processes historic and currently available head measurements to make optimal predictions of future head levels over a grid of 554 wells spanning the SJRWMD. Measurements are obtained monthly from a subset of 20 wells and semiannually from the remaining wells. The Kalman filter incorporates an empirical spatiotemporal model of regional groundwater fluctuations derived from long‐term historical data records at the 20 monthly measured wells. The algorithm (1) extrapolates the measurements provided by the 20 monthly measured wells to estimate monthly head levels at all 554 wells in the grid and (2) predicts future head levels at each well in the absence of measurements. The performance of the Kalman filtering algorithm is assessed by examining its ability to forecast piezometric head behavior at the 534 well locations where historic data were not used to estimate either the system model or the spatiotemporal correlation structure of the model residuals.
Effective hydraulic conductivity of fractured clay beds at a hazardous waste landfill, Louisiana Gulf Coast
Authors: Hanor Jeffrey S.
Published: February 2004

Installation of surface levees and subsurface slurry walls around a 1600‐m by 950‐m hazardous waste landfill in southeastern Louisiana has inadvertently converted the site into a large‐scale permeameter. Differences in water levels in wells screened above and below a 15‐m‐thick clay “confining layer” define a vertical hydraulic gradient of +0.1. Basic climatological data permit calculation of a complete water budget for the site, including vertical recharge qz down through the clay. Cumulative precipitation over a 44‐month period was 5.5 m, and recharge was over 1.0 m. The calculated vertical hydraulic conductivity of the clay sequence is approximately 10−5 cm s−1, up to 4 orders of magnitude higher than laboratory values for the same sediment. Intercalated sands and zones of pedogenic secondary porosity and fracturing developed during periods of subaerial weathering are apparently the dominant controls on vertical permeability, not the matrix properties of the clay.
A fractal‐based stochastic interpolation scheme in subsurface hydrology
Authors: Molz Fred J. , Boman Gerald K.
Published: February 2004

The need for a realistic and rational method for interpolating sparse data sets is widespread. Real porosity and hydraulic conductivity data do not vary smoothly over space, so an interpolation scheme that preserves irregularity is desirable. Such a scheme based on the properties of fractional Brownian motion (fBm) and fractional Gaussian noise (fGn) is presented. Following the methodology of Hewett (1986), the authors test for the presence of fGn in a set of 459 hydraulic conductivity (K) measurements. The use of rescaled‐range analysis strongly indicated the presence of fGn when applied to the natural logs of the K data, and the resulting Hurst coefficient (H) was determined to be 0.82. This H value was then used along with the methodology of successive random additions to generate a fBm K interpolation (realization) in the vertical cross section between two wells. The results appeared realistic, and the overall methodology presented herein may serve as an improved basis for a conditional simulation approach to the study of various transport processes in porous media. It is now known that fGn‐ and fBm‐related processes are among the most common spatial and temporal variations found in nature, although a common physical origin, if any, remains obscure.
Modeling of multiphase transport of multicomponent organic contaminants and heat in the subsurface: Numerical model formulation
Authors: Adenekan A. E. , Patzek T. W. , Pruess K.
Published: February 2004

A numerical compositional simulator (Multiphase Multicomponent Nonisothermal Organics Transport Simulator (M2NOTS)) has been developed for modeling transient, three‐dimensional, nonisothermal, and multiphase transport of multicomponent organic contaminants in the subsurface. The governing equations include (1) advection of all three phases in response to pressure, capillary, and gravity forces; (2) interphase mass transfer that allows every component to partition into each phase present; (3) diffusion; and (4) transport of sensible and latent heat energy. Two other features distinguish M2NOTS from other simulators reported in the groundwater literature: (1) the simulator allows for any number of chemical components and every component is allowed to partition into all fluid phases present, and (2) each phase is allowed to completely disappear from, or appear in, any region of the domain during a simulation. These features are required to model realistic field problems involving transport of mixtures of nonaqueous phase liquid contaminants, and to quantify performance of existing and emerging remediation methods such as vacuum extraction and steam injection.
Evaluation of the evaporative fraction for parameterization of the surface energy balance
Authors: Nichols William E. , Cuenca Richard H.
Published: February 2004

The evaporative fraction is a ratio of latent heat flux to the sum of latent and sensible heat fluxes. It has been used to characterize the energy partition over land surfaces and has potential for inferring daily energy balance information based on midday remote sensing measurements. The HAPEX‐MOBILHY program SAMER system provided surface energy balance data over a range of agricultural crops and soil types. Data from this large‐scale field experiment was analyzed to study the behavior and daylight stability of the evaporative fraction in both ideal and general meteorological conditions. Strong linear relations were found to exist between the midday evaporative fraction and the daylight evaporative fraction. Statistical tests, however, rejected the hypothesis that the two quantities were equal. Relations between the evaporative fraction and surface soil moisture as well as soil moisture over the complete root zone were explored, but no correlation was identified.
Calcitonin gene‐related peptide facilitates serotonin release from guinea‐pig colonic mucosa via myenteric neurons and tachykinin NK2/NK3 receptors
Authors: Kojima Shu‐ichi , Ueda Shuichi , Ikeda Masashi , Kamikawa Yuichiro
Published: February 2004

The ability of calcitonin gene‐related peptide (CGRP), to alter the outflow of 5‐hydroxytryptamine (5‐HT) from the guinea‐pig proximal colon, was evaluated using three different isolated preparations: whole colon, mucosa‐free muscle layer and submucosa/mucosa preparations.

In the presence of the monoamine oxidase A inhibitor, clorgyline, CGRP elicited a concentration‐dependent increase in 5‐HT outflow from the whole colon, but not from mucosa‐free muscle layer preparations. The CGRP‐evoked 5‐HT outflow was sensitive to tetrodotoxin (TTX) or hexamethonium, but was not detectable in submucosa/mucosa preparations. HCGRP8–37 (3 μM) inhibited the submaximal effect of CGRP on the 5‐HT outflow. [Cys(ACM)2,7]hCGRP had a slight stimulant influence on the 5‐HT outflow.

The selective NK2 and NK3 receptor antagonists, SR48968 or SR142801, respectively, prevented the enhancing effect of CGRP. By contrast, a selective NK1 receptor antagonist L703606, failed to block the effect of CGRP.

The enhancing effect of CGRP was mimicked by the NK2 receptor agonist [β‐Ala8]‐neurokinin A (NKA)4–10 and the NK3 receptor agonist senktide. The effect of [β‐Ala8]‐NKA4–10 on the 5‐HT outflow was unaffected by TTX, while the effect of senktide was prevented by TTX, hexamethonium or SR48968. The present data also demonstrated a synergistic action of the NK2 and NK3 receptor agonists on the CGRP‐evoked 5‐HT outflow.

We concluded that CGRP facilitates 5‐HT release from the guinea‐pig colonic mucosa through an action on myenteric neurons and that this effect is mediated by endogenously released tachykinins, acting via tachykinin NK2/NK3 receptors in cascade.

British Journal of Pharmacology (2004) 141, 385–390. doi:10.1038/sj.bjp.0705624