bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory studies on a new laser Doppler Velocimeter System for horizontal groundwater velocity measurements in a borehole
Authors: Momii Kazuro , Jinno Kenji , Hirano Fumiaki
Published: February 2004

This paper introduces a new instrument for measuring groundwater velocity in a borehole using a laser Doppler velocimeter (LDV) technique. The major improvement of the proposed LDV system is that the probe can be inserted into a borehole that has a minimum diameter of 10 cm and that a disk‐type rotating grating is used as a frequency shifter for low velocities in order to determine the velocity sign. The speed of the glass plate passing through the LDV measurement point is calibrated to demonstrate the accuracy of the new LDV system. From a comparison with the true constant speed of the glass plate, we confirm that the new LDV system can measure low speeds in the range from 10−5 to 10−2 cm/s at a measurement error of less than 8%. Laboratory experiments were carried out to investigate the performance of the new LDV system for the horizontal velocity measurement of groundwater in a borehole. The result obtained by the proposed LDV system shows that the horizontal velocity at the center of an unscreened borehole is 3 times larger than the seepage velocity in a confined aquifer. This result agrees with the theoretical solution for groundwater flow in a borehole derived by Sano (1983). The validity of the theoretical solution is experimentally verified in the laboratory using the current LDV system. Although the detectable minimum velocity in a borehole is limited by the velocity fluctuations due to the Brownian motion of scattering particles, results obtained in the experiments using 0.804‐μm polystyrene particles show that the LDV system described in this paper can measure with a sufficient accuracy both the magnitude and the direction of groundwater velocity down to 10−4 cm/s in a borehole.
Some statistics useful in regional frequency analysis
Authors: Hosking J. R. M. , Wallis J. R.
Published: February 2004

Regional frequency analysis uses data from a number of measuring sites. A “region” is a group of sites each of which is assumed to have data drawn from the same frequency distribution. The analysis involves the assignment of sites to regions, testing whether the proposed regions are indeed homogeneous, and choice of suitable distributions to fit to each region's data. This paper describes three statistics useful in regional frequency analysis: a discordancy measure, for identifying unusual sites in a region; a heterogeneity measure, for assessing whether a proposed region is homogeneous; and a goodness‐of‐fit measure, for assessing whether a candidate distribution provides an adequate fit to the data. Tests based on the statistics provide objective backing for the decisions involved in regional frequency analysis. The statistics are based on theLmoments [Hosking, 1990] of the at‐site data.
Effects of irrigation water supply variations on limited resource farming in Conejos County, Colorado
Authors: Eckert Jerry B. , Wang Erda
Published: February 2004

Farms in NE Conejos County, Colorado, are characterized by limited resources, uncertain surface flow irrigation systems, and mixed crop‐livestock enterprise combinations which are dependent on public grazing resources. To model decision making on these farms, a linear program is developed stressing enterprise choices under conditions of multiple resource constraints. Differential access to grazing resources and irrigation water is emphasized in this research. Regarding the water resource, the model reflects farms situated alternatively on high‐, medium‐, and low‐priority irrigation ditches within the Alamosa‐La Jara river system, each with and without supplemental pumping. Differences are found in optimum enterprise mixes, net returns, choice of cropping technology, level of marketings, and other characteristics in response to variations in the availability of irrigation water. Implications are presented for alternative improvement strategies.
Flow path‐composition relationships for groundwater entering an acidic lake
Authors: Schafran Gary C. , Driscoll Charles T.
Published: February 2004

The relationship of groundwater flow paths to the acid/base status and composition of groundwater was examined by directly monitoring groundwater inputs to an acidic Adirondack, New York, lake (Dart's Lake). Groundwater inputs near the shoreline of the lake were acidic throughout the year (pH <5 and alkalinity <0 μeq L−1) and reflected the influence of shallow soil horizons. Groundwater transported within the deep surficial deposits and through sediments farther from shore was characterized by higher alkalinity and higher pH values and was enriched in nitrate (>40 μeq L−1). Elevated concentrations of basic cations and alkalinity as well as lower concentrations of organic anions and sulfate were characteristic of deep groundwater entering the lake at the study site. Spatial variability of groundwater chemistry was found to be substantial over a relatively short distance (<6 m) from the lake shoreline and indicates that inputs to the lake of components dissolved in groundwater are highly flow path dependent.
Analytical solutions for equations describing coupled transport of two solutes and a gaseous product in soil
Authors: Angelakis A. N. , Kadir T. N. , Rolston D. E.
Published: February 2004

An analytical solution for transient soil‐gas diffusion coupled to two convective‐dispersive solute transport equations is presented. First‐order kinetic transformations, linear equilibrium distribution coefficient for both solutes, and equilibrium gas solubility for the gaseous product were assumed. The solution was obtained by means of Laplace transforms for zero initial concentrations of all three species, pulse application of both solutes, and semi‐infinite media. Concentration profiles of the soil gas as a function of soil depth and time were computed. An example problem was used to demonstrate the use of the solution and its sensitivity to various parameters. The solution was verified by comparison to a numerical solution using an explicit finite difference scheme. The analytical solution shows that the soil‐gas distributions were highly affected by the gas solubility and by the distribution coefficient and the transformation rate constants of both solutes. However, the gas distributions were not significantly affected by the dispersion coefficient of either solute. The gas distributions are slightly affected by changes in the gas diffusivity over the range expected for different gas species at a single value of air‐filled porosity. Changes in soil‐water content and the corresponding change in air‐filled porosity would result in large changes in the gas concentration profiles.
Pumping tests in nonuniform aquifers: The radially asymmetric case
Authors: Butler James J. , Liu Wenzhi
Published: February 2004

An analytical solution for the case of transient, pumping‐induced drawdown in a nonuniform aquifer is presented. The nonuniform aquifer is conceptualized as a uniform matrix into which a disk of anomalous properties has been placed. The disk can be arbitrarily located with respect to the pumping well. This solution can be used to develop considerable insight concerning the nature of drawdown in nonuniform systems. Changes in drawdown are sensitive to the hydraulic properties of a discrete portion of an aquifer for a time of limited duration. After that time, it is virtually impossible to gain further information about those properties. The volume of the aquifer controlling a given increment of drawdown at an observation well increases greatly as the distance between the pumping and observation well increases. At observation wells located at moderate to large distances from the pumping well, this volume is so large that the effect of spatial variations in flow properties may be negligible. In general, drawdown data from wells located at a distance from the pumping well should nicely fit the ideal models of the well hydraulics literature. When combined with previous work, these results demonstrate that constant rate pumping tests are not an effective tool for characterizing lateral variations in flow properties.
Accuracy of gamma ray computerized tomography in porous media
Authors: Brown Glenn O. , Stone Marvin L. , Gazin Jack E.
Published: February 2004

Computerized tomography (CT) is being increasingly applied to analyzing flow in porous media. Tomography systems being used include both medical X ray units and custom gamma ray machines. Up until now the precision of such systems in porous media work has been ill defined. A systematic analysis of CT performance and errors is presented and applied to a prototype gamma ray system we have recently developed. The prototype system is detailed and its accuracy quantified as a function of scanning beam diameter, ray step size, and photon count.
Surface runoff contamination by chemicals initially incorporated below the soil surface
Authors: Wallach Rony , Shabtai Rina
Published: February 2004

One method of reducing the contamination of overland flow by soil chemicals (e.g., nutrients, pesticides) is to reduce their concentration at the immediate soil surface. This can be done by incorporating the chemicals at lower depths, by either tilling the soil or by irrigating shortly after chemical application. A mathematical model designed to predict the runoff concentration of chemicals initially located at different depths below the soil surface is presented. The model accounts for transient water infiltration and convective‐dispersive solute transport in the soil, and also considers rate‐limited mass transfer through a laminar boundary layer at the soil surface/runoff water interface. Sorption‐desorption interactions between soil and chemicals are assumed to be subject to linear isotherms or to first‐order kinetics. The dissolved chemical concentrations at the soil surface and in the surface runoff were simulated for coarse and fine soils at different antecedent soil moistures and rainfall intensities. The simulation indicated that the initial depth of chemical incorporation below the soil surface is negatively correlated to the dissolved chemical concentration at the soil surface and in runoff water. A basic and characteristic difference between the chemical whose retention by the soil solids is expressed by an equilibrium model and the one whose retention is expressed by a kinetic model is soil surface concentration during water and chemical redistribution following the termination of rainfall and runoff. Contrary to the instantaneous equilibrium‐type chemicals, the dissolved concentration of the kinetic‐type chemicals increases sharply to its final value. For the coarser soil with higher saturated hydraulic conductivity, the relative chemical concentrations in surface runoff are lower than for the finer soil, when similar values of initial pressure head ψ0 and rainfall intensities (three times the saturated hydraulic conductivity of each soil) are used.
Asymptotic calculation of Laplace Inverse in analytical solutions of groundwater problems
Authors: Chen Chia‐Shyun , Stone William D.
Published: February 2004

The Laplace transform with respect to time, t, is normally used in finding analytical solutions for transient groundwater problems. The behavior of a function at large or small t is known to correspond to that of its Laplace transform counterpart at small or large p, respectively; p is the Laplace transform parameter of t. This condition is generally translated as t being inversely related to p and vice versa. By this relationship many asymptotic solutions for large or small t have been determined from the Laplace domain solutions valid only for small or large p. However, an example is given here which shows this kind of asymptotic calculation may fail to yield correct asymptotic solutions. Hence, the asymptotic calculation must be exercised with care. To deal with this possible failure, the Tauberian theorem is offered to evaluate the asymptotic behavior of functions from their Laplace transform counterparts.
A methodology for quantifying and valuing the impacts of flow changes on a fishery
Authors: Harpman David A. , Sparling Edward W. , Waddle Terry J.
Published: February 2004

A quasi‐population model for adult brown trout was developed for the Taylor River below the Taylor Park Reservoir in Colorado. This model allows the population to be predicted under alternative flow management regimes. The predicted population effects of two different flow release patterns were compared with the predicted population for the current reservoir operation regime. Changes in angler catch were imputed for these scenarios. The changes in catch were valued using estimates of willingness to pay obtained from anglers fishing at the site. Total angling effort was held constant. For both of the flow scenarios examined the difference in economic use value was limited. The relatively small changes in value predicted were shaped by the small changes in catch predicted and the high number of fish caught under current conditions.
A performance comparison of scalar, vector, and concurrent vector computers including supercomputers for modeling transport of reactive contaminants in groundwater
Authors: Tripathi Vijay S. , Yeh G. T.
Published: February 2004

Sophisticated and highly computation‐intensive models of transport of reactive contaminants in groundwater have been developed in recent years. Application of such models to real‐world contaminant transport problems, e.g., simulation of groundwater transport of 10–15 chemically reactive elements (e.g., toxic metals) and relevant complexes and minerals in two and three dimensions over a distance of several hundred meters, requires high‐performance computers including supercomputers. Although not widely recognized as such, the computational complexity and demand of these models compare with well‐known computation‐intensive applications including weather forecasting and quantum chemical calculations. A survey of the performance of a variety of available hardware, as measured by the run times for a reactive transport model HYDROGEOCHEM, showed that while supercomputers provide the fastest execution times for such problems, relatively low‐cost reduced instruction set computer (RISC) based scalar computers provide the best performance‐to‐price ratio. Because supercomputers like the Cray X‐MP are inherently multiuser resources, often the RISC computers also provide much better turnaround times. Furthermore, RISC‐based workstations provide the best platforms for “visualization” of groundwater flow and contaminant plumes. The most notable result, however, is that current workstations costing less than $10,000 provide performance within a factor of 5 of a Cray X‐MP.
In situ measurement of microbial activity and controls on microbial CO2 production in the unsaturated zone
Authors: Wood Brian D. , Keller C. Kent , Johnstone Donald L.
Published: February 2004

Carbon dioxide concentrations were measured at various depths and times in the unsaturated zones of two hydraulically and geochemically contrasting field sites, one in southeastern Washington state, and the other in south central Saskatchewan. In situ CO2 production rates were calculated from a mass balance that accounted for diffusive fluxes and partitioning of CO2 into an advecting aqueous phase. Production rates were compared with (1) microbial abundance and (2) subsurface temperature to determine whether subsurface CO2 production rates could be expressed as a simple function of these two variables. At the Washington site, subsurface production was successfully expressed as a function of microbial abundance and temperature for a large portion of the year, but not near the end of the growing season. Although subsurface microbes and organic carbon were more abundant at the Saskatchewan site, subsurface CO2 production rates were generally several orders of magnitude lower than at the Washington site, and no correlation could be established between microbial numbers, temperature, and production rate. The cases where production rates could not be expressed as a function of microbial numbers and temperature suggested conditions in which some other factor, such as nutrient limitations, was controlling.
Fish population losses from Adirondack Lakes: The role of surface water acidity and acidification
Authors: Baker Joan P. , Warren‐Hicks William J. , Gallagher James , Christensen Sigurd W.
Published: February 2004

Changes over time in the species composition of fish communities in Adirondack lakes were assessed to determine (1) the approximate numbers offish populations that have been lost and (2) the degree to which fish population losses may have resulted from surface water acidification and acidic deposition. Information on the present‐day status offish communities was obtained by the Adirondack Lakes Survey Corporation, which surveyed 1469 Adirondack lakes in 1984–1987 (53% of the total ponded waters in the Adirondack ecological zone). Two hundred and ninety‐five of these lakes had been surveyed in 1929–1934 during the first statewide biological survey; 720 had been surveyed in one or more years prior to 1970. Sixteen to 19% of the lakes with adequate historical data appeared to have lost one or more fish populations as a result of acidification. Brook trout and acid‐sensitive minnow species had experienced the most widespread effects. Populations of brook trout and acid‐sensitive minnows had been lost apparently as a result of acidification from 11% and 19%, respectively, of the lakes with confirmed historical occurrence of these taxa. By contrast, fish species that tend to occur primarily in lower elevation and larger lakes, such as largemouth and smallmouth bass and brown trout, have experienced little to no documented adverse effects. Lakes that were judged to have lost fish populations as a result of acidification had significantly lower; pH and, in most cases, also had higher estimated concentrations of inorganic aluminum and occurred at higher elevations than did lakes with the fish species still present. No other lake characteristics were consistently associated with fish population losses attributed to acidification. The exact numbers and proportions of fish populations affected could not be determined because of limitations on the quantity and quality of historical data. Lakes for which we had adequate historical data to assess long‐term trends in fish communities were significantly larger and deeper and have higher pH than do Adirondack lakes in general; thus, fish communities adversely affected by acidification and acidic deposition may be underrepresented in this study.
Fuzzy rule‐based models for infiltration
Authors: Bárdossy András , Disse Markus
Published: February 2004

Modeling water movement in the unsaturated zone requires a great number of parameters, such as the initial water content, the saturated moisture content, and the saturated hydraulic conductivity, which can relatively easily be assessed. Other functions such as the suction head and the relative hydraulic conductivity, which are highly nonlinear functions of the actual water content are more difficult to find. Furthermore, infiltration experiments carried out at a few locations can only define these parameters at selected locations, and a reasonable interpolation of these parameters is extremely difficult. In this paper, two fuzzy logic‐based models are presented for the infiltration process. Basic definitions of fuzzy sets are given, and basic operations are explained. Principles of the rule‐based infiltration models are presented. The rules for the first model are based on the moisture content of the adjacent layers and the depth of the wetting front. Using these rules, the flows can be calculated as exact quantities. The rules are derived from a training set which was obtained from several test runs of a Green and Ampt (GA) infiltration model. Separate rules are derived for the flow dynamics in the upper layer (runoff and infiltration), and for water flow between the layers. Examples of the application of the model are given. The model performs with similar accuracy as the GA model, using only 40% of its parameters and running 2 orders of magnitude faster. A training set obtained by numerical solution of the Richards equation was used to create a second fuzzy rule‐based model. Here the rules are based on the moisture content of the adjacent layers. Results obtained by the use of the models are compared with measured values, showing a very accurate reproduction of the values.
On time integration of groundwater flow equations by spectral methods
Authors: Gambolati Giuseppe
Published: February 2004

A study of the computational performance of the recently introduced spectral approach for the time integration of finite element flow equations is performed. Two reduction methods are presented and discussed. One method relies on the classical modal decomposition wherein the leftmost eigenpairs of a generalized symmetric eigenvalue problem are evaluated one at a time by a cost‐effective orthogonal deflation technique. The other uses a set of Lanczos vectors for the coordinate transformation matrix and involves a recursive product between the inverse of the stiffness matrix and a vector. An extensive analysis of the behavior of the two methods is made with a representative sample problem of subsurface flow solved over a regular and an irregular mesh. The results show that the spectral approach cannot be competitive from a computational viewpoint with a more traditional time‐stepping or direct integration scheme (e.g., the Crank‐Nicolson scheme). The eigenvector technique is slow to converge, and a large portion, if not all, of the “flow modes” need to be determined to accurately describe the desired solution. The Lanczos algorithm may converge faster in the Lanczos vector space. However, its actual performance depends to a large extent on the initial guessed vector and is adversely influenced by the requirement to solve an equivalent steady state problem at each iteration. It is concluded that for a robust and efficient finite element code of transient ground water flow, direct integration methods are generally to be preferred.
Habitat suitability for brook trout (Salvelinus fontinalis) reproduction in Adirondack Lakes
Authors: Schofield Carl L.
Published: February 2004

The relationships between habitat characteristics and reproductive status of Adirondack brook trout populations were examined utilizing the Adirondack Lake Survey Corporation data base, which includes physical, chemical, and biological data for 1469 lakes. The only variables strongly related to brook trout natural reproduction were indices of groundwater influence on surface water chemistry, specifically silica and sodium concentrations. This finding supports the hypothesis that lake spawning populations of brook trout are strongly dependent on groundwater seepage for successful reproduction. Spawning habitat in small headwater lakes impounded by beaver activity may be degraded as a result of siltation of nearshore zones and diminished groundwater seepage. Adirondack lakes situated in thick‐till basins receive proportionally greater groundwater input than thin‐till lake types and thick‐till lakes also had the highest proportion of self‐sustaining brook trout populations. Acidification is most pronounced in thin‐till basins, which also exhibited a low frequency of self‐sustaining brook trout populations. Although brook trout fisheries may be maintained in acidic lakes by liming and stocking, the establishment of self‐sustaining brook trout populations is not a likely outcome of these management practices. Additionally, there appears to be limited potential for restoration of lake spawning brook trout populations in currently acidic, fishless lakes should acidic inputs decline as a result of reductions in acid‐forming emissions.
A dual‐porosity model for simulating the preferential movement of water and solutes in structured porous media
Authors: Gerke H. H. , van Genuchten M. T.
Published: February 2004

A one‐dimensional dual‐porosity model has been developed for the purpose of studying variably saturated water flow and solute transport in structured soils or fractured rocks. The model involves two overlaying continua at the macroscopic level: a macropore or fracture pore system and a less permeable matrix pore system. Water in both pore systems is assumed to be mobile. Variably saturated water flow in the matrix as well as in the fracture pore system is described with the Richards' equation, and solute transport is described with the convection‐dispersion equation. Transfer of water and solutes between the two pore regions is simulated by means of first‐order rate equations. The mass transfer term for solute transport includes both convective and diffusive components. The formulation leads to two coupled systems of nonlinear partial differential equations which were solved numerically using the Galerkin finite element method. Simulation results demonstrate the complicated nature of solute leaching in structured, unsaturated porous media during transient water flow. Sensitivity studies show the importance of having accurate estimates of the hydraulic conductivity near the surface of soil aggregates or rock matrix blocks. The proposed model is capable of simulating preferential flow situations using parameters which can be related to physical and chemical properties of the medium.
Water balance and hydrologic characteristics of a rain forest catchment in the Central Amazon Basin
Authors: Lesack Lance F. W.
Published: February 2004

The water balance and hydrologic characteristics of streamflow and subsurface outflow were measured for a first‐order catchment draining a 23.4‐ha stand of undisturbed terra firme rain forest in the central Amazon Basin over a 1 year period. Total rainfall during the study period, representing a 1 in 10 wet year, was 2870 mm of which 1650 mm and 42 mm respectively were exported from the catchment as streamflow and subsurface outflow. A hydrograph separation technique applied to the entire streamflow record distinguished 173 storms. The storm flow volume was 88 mm, which represented only 5% of overall streamflow and less than 3% of the rainfall. The 20% of least frequent, large‐volume storms accounted for 75% of the rainfall volume and 80% of the storm flow volume. The fraction of the catchment that could account for the volume of storm flow runoff in a given storm as overland flow never exceeded 4%, even for the largest storms. The change in soil water storage from the previous year was equivalent to about 57 mm of water. Evapotranspiration, estimated as the water balance residual, was equivalent to 1120 mm per year with an uncertainty, estimated by propagating measurement errors, of ±16–21%. Evapotranspiration is significantly less than values previously reported from catchment‐scale water balance studies in the central Amazon, and is slightly lower than recent estimates derived from micrometeorologieal techniques, though differences in the latter case are within measurement error.
Geostatistical analysis of interwell transmissivity in heterogeneous aquifers
Authors: Desbarats A. J.
Published: February 2004

Steady state flow between an injection well and a pumping well in a heterogeneous confined aquifer is investigated using a combined numerical‐empirical approach. Transmis sivity at the measurement or point support scale is modeled as an isotropic, stationary, multivariate lognormal spatial random function. In a recent study (Desbarats, 1992) it was found that the effective transmissivity of a single‐well radial flow system was very well estimated by a spatial geometric average of point transmissivities weighted by their inverse squared distance from the well bore axis. This result provides an approximate solution for steady state drawdown in a heterogeneous medium which can be used with the principle of superposition to derive an expression for the interwell head difference in a dipole well configuration. The interwell transmissivity corresponding to this head difference is shown to be the harmonic mean of transmissivities averaged over circular regions centered at each well. This deterministic averaging law and the geostatistical model for point transmissivities are combined in order to derive expressions for the ensemble mean and variance of interwell transmissivity. Expressions are also obtained for the conditional moments of interwell transmissivity when values at the two wells are available from core measurements. Multiple realizations of the heterogeneous transmissivity field, discretized on a nodal grid, are generated using the turning bands method. Interwell transmissivities obtained by spatial averaging over the grid are compared with corresponding true effective values obtained numerically using a finite difference model of steady state interwell flow. Empirical and numerical values are found to be in excellent agreement for variances of log transmissivity as high as 5. Further numerical experiments show that results of this study are relatively insensitive to moderate departures from the multivariate lognormal transmissivity model.
Willingness to pay for improvements in drinking water quality
Authors: Jordan Jeffrey L. , Elnagheeb Abdelmoneim H.
Published: February 2004

In this paper, data from a 1991 survey of Georgia residents were used to study people's willingness to pay (WTP) for improvements in drinking water quality and people's perceptions of potential groundwater contamination. Results showed that 27% of the respondents served by public water supplies rated drinking water quality as poor, and 23% were uncertain about their drinking water quality. The contingent valuation method was used to estimate WTP using a checklist format. The median estimated WTP was $5.49 per month above their current water bills for people on public systems and $7.38 for those using private wells, after rejecting outliers and using the maximum likelihood method. The aggregate WTP for all of Georgia was estimated to be about $111.5 million per year for public water users and $42.3 million per year for private well owners. This aggregate WTP can serve as an estimate of benefits to consumers from improvements in drinking water quality statewide.
Properties of concentration waves in presence of nonlinear sorption, precipitation/dissolution, and homogeneous reactions: 1. Fundamentals
Authors: Schweich D. , Sardin M. , Jauzein M.
Published: February 2004

Properties of concentration waves of solutes affected by nonlinear sorption, precipitation/dissolution and homogeneous reactions in the mobile and stationary phases are established when the number of phases is constant. These properties essentially depend on the structure of a stoichiometric matrix which describes the chemical interactions. A reduction procedure of the stoichiometric matrix gives the number of waves or peaks together with their propagation velocities, and the retardation factors of species at trace levels. The location of the peaks and their broadening behavior due to the nonlinear equilibria are estimated. The number of waves and the properties of suitable linear combinations of concentrations provide a method for discriminating among rival interaction mechanisms irrespective of the equilibrium constants. This cannot be done using conventional methods based on the comparison between numerical simulations and experimental curves.
Properties of concentration waves in presence of nonlinear sorption, precipitation/dissolution, and homogeneous reactions: 2. Illustrative examples
Authors: Schweich D. , Sardin M. , Jauzein M.
Published: February 2004

Theoretical properties of breakthrough curves (BTCs) of solutes subject to nonlinear sorption, precipitation/dissolution and homogeneous reactions are compared with numerical simulations. The example treated here involves heterovalent ion exchange on clays, ionization of carbonic acid and water, and dissolution of gaseous carbon dioxide and of solid calcite. Despite the complexity of the solid‐fluid interaction mechanism (13 reacting species and six reactions), the number of waves, the possible existence of an unretarded wave, and the expressions for the concentrations of the stoichiometric tracers are easily derived from the stoichiometric matrix. The location of peaks or waves and their broadening characteristics due to the nonlinear equilibria are estimated exclusively from the compositions of the injected and initial solutions. All of these theoretical properties are confirmed by numerical simulations, even in the presence of dispersion. The number of waves and the stoichiometric tracers are shown to depend on whether or not the pore solution equilibrates with a gas phase. This property illustrates the strong sensitivity of the breakthrough curves to the interaction mechanism. Finally, calculating the BTCs of the stoichiometric tracers from the experimental BTCs of the liquid phase species allows one to discriminate among rival interaction mechanisms without requiring a numerical model and knowledge of the equilibrium constants.
Evaporation from Lake Kinneret: 1. Eddy correlation system measurements and energy budget estimates
Authors: Assouline S. , Mahrer Y.
Published: February 2004

Evaporation rates over Lake Kinneret were directly and continuously measured by means of the eddy correlation system (ECS) for the relatively long periods of 20 and 44 days at the beginning and end of the summer (first and second periods), respectively. Results clearly show that wind speed and stability of thermal stratification over the water surface strongly affect evaporation from the lake. Consequently, large differences in measured daily evaporation rates were apparent during both periods. Evaporation rates, estimated by the energy budget method (EBM) were compared with the corresponding values measured directly by the ECS. Large differences were found between the estimated hourly evaporation rates and the measured ones, in both the values and the timing of maximal rates. In addition, the EBM calculated negative nocturnal evaporation rates, while the ECS measured positive values. Differences between estimated and measured evaporation rates monitored on a daily basis were also noted. The differences were larger for the first period, characterized by sharav events denoting climatic instability. High evaporation rates resulting from strong winds were not depicted by EBM estimates. The distributions of hourly evaporation rates over a 24 hour period or of the daily rates over an entire period as estimated by the EBM were very similar to those of net radiation, while corresponding distributions resulting from ECS measurements were very similar to those of wind speed. The daily average evaporation rate for the first period, calculated by the EBM, was smaller than the corresponding value resulting from ECS measurements. When applied on a hourly basis, the EBM gave a much more similar estimate. For the second period, there were no significant differences between the daily average based on the computed values (for both daily and hourly intervals) and the corresponding average based on the measured ones.
Upscaling of permeability of anisotropic heterogeneous formations: 2. General structure and small perturbation analysis
Authors: Indelman P. , Dagan G.
Published: February 2004

The general methodology developed in part 1 (Indelman and Dagan, this issue) of this study is applied to the detailed analysis of upscaled permeability. First, the structure of the dissipation function for the general conductivity, a tensor of stationary random components, is examined with the aid of dimensional analysis. It is shown that for arbitrary shapes of the numerical elements, the upscaled permeability has also this general structure, and the numbers of unknown parameters and equations match. This result suggests that the upscaling problem has an unique solution. In the particular case of scalar permeability of isotropic covariance of the actual formation, it is shown that a similar upscaled permeability is possible only for spherical (circular) numerical elements. Otherwise, the upscaled permeability has to be a tensor of anisotropic covariance. If the actual formation has a scalar permeability of axisymmetric covariance, upscaling preserves the last property only for axisymmetric partition elements, i.e., for a sphere, cylinder, and ellipsoid. Explicit expressions for the first moments of the upscaled permeability (mean, covariance) are derived at first order in the log permeability variance. The detailed computations for a scalar permeability of axisymmetric covariance and for axisymmetric numerical elements lead to simple results. The upscaled permeability expected values are components of an axisymmetric tensor, whereas the fluctuations are determined by a scalar random space function of anisotropic covariance. The general case of upscaling by a first‐order approximation is examined in Appendix B. These results will be applied to a few particular cases in part 3 (Indelman, this issue).
Upscaling of permeability of anisotropic heterogeneous formations: 3. Applications
Authors: Indelman Peter
Published: February 2004

The general results of Indelman and Dagan (this issue (a), (b)) are applied to some cases of interest in applications. The exact solution of upscaling of stratified formations is used in order to assess the range of applicability of the first‐order analysis. The explicit expressions of the two first moments of the upscaled permeability are derived for media of two‐dimensional isotropic and three‐dimensional axisymmetric actual log permeability of Gaussian covariance and for parallelepipedic (rectangular for two‐dimensional) averaging elements. The effects of the actual log permeability covariance and of the anisotropy of partition elements on the upscaled permeability statistics are analyzed. The asymptotic behavior of the upscaled permeability for large and small blocks is discussed for general heterogeneity. The strong dependence of the small element limit on the properties of actual heterogeneity and on the shape of the elements is illustrated by typical examples. In contrast, the homogenization of the upscaled media by large blocks depends primarily on the volume (area for two dimensions) of the partition element relative to the one based on the correlation scale of the log permeability.
Evaluation of a first‐order water transfer term for variably saturated dual‐porosity flow models
Authors: Gerke H. H. , van Genuchten M. T.
Published: February 2004

Variably saturated water flow in a dual‐porosity medium may be described using two separate flow equations which are coupled by means of a sink source term Γw, to account for the transfer of water between the macropore (or fracture) and soil (or rock) matrix pore systems. In this study we propose a first‐order rate expression for Γw, which assumes that water transfer is proportional to the difference in pressure head between the two pore systems. A general expression for the transfer coefficient αw was derived using Laplace transforms of the linearized horizontal flow equation. The value of αw could be related to the size and shape of the matrix blocks (or soil aggregates) and to the hydraulic conductivity Ka of the matrix at the fracture/matrix interface. The transfer term Γw, was evaluated by comparing simulation results with those obtained with equivalent one‐ and two‐dimensional single‐porosity flow models. Accurate results were obtained when Ka was evaluated using a simple arithmetic average of the interface conductivities associated with the fracture and matrix pressure heads. Results improved when an empirical scaling coefficient γw was included in αw. A single value of 0.4 for γw was found to be applicable, irrespective of the hydraulic properties or the initial pressure head of the simulated system.
Large‐scale dispersion experiments in a sandy aquifer in Denmark: Observed tracer movements and numerical analyses
Authors: Jensen K. Høgh , Bitsch K. , Bjerg P. L.
Published: February 2004

A large‐scale natural gradient dispersion experiment was carried out in a sandy aquifer in the western part of Denmark using tritium and chloride as tracers. For both plumes a marked spreading was observed in the longitudinal direction while the spreading in the transverse horizontal and transverse vertical directions was very small. The horizontal transport parameters of the advection‐dispersion equation were investigated by applying an optimization model to observed breakthrough curves of tritium representing depth averaged concentrations. No clear trend in dispersion parameters with travel distance for distances between 50 and 200 m could be found, suggesting that the asymptotic stage was reached within a short distance from the point of injection. A three‐dimensional numerical model for flow and transport was applied to the aquifer in order to quantify the dispersivity parameters more closely. The following “best fit” dispersivity parameters were identified: longitudinal horizontal, 0.45 m; transverse horizontal, 0.001 m; and transverse vertical, 0.0005 m.
Optimal control for groundwater remediation by differential dynamic programming with Quasi‐Newton Approximations
Authors: Culver Teresa B. , Shoemaker Christine A.
Published: February 2004

Differential dynamic programming with quasi‐Newton approximations (QNDDP) is combined with a finite element groundwater quality simulation model to determine optimal time‐varying pumping policies for reclamation of a contaminated aquifer. The purpose of the QNDDP model is to significantly reduce the large computational effort associated with calculation of optimal time‐varying policies. A Broyden rank‐one quasi‐Newton technique is developed to approximate the second derivatives of the groundwater quality model; these second derivatives are difficult to calculate directly. The performance of the QNDDP algorithm is compared to the successive approximation linear quadratic regulator (SALQR) technique, which sets the complicated second derivatives to 0. QNDDP converged to the optimal pumping policy in approximately half the time that the SALQR technique required. The QNDDP algorithm thus shows great promise for the management of complex, time‐varying systems.
Linear transport models for adsorbing solutes
Authors: Roth K. , Jury W. A.
Published: February 2004

A unified linear theory for the transport of adsorbing solutes through soils is presented and applied to analyze movement of napropamide through undisturbed soil columns. The transport characteristics of the soil are expressed in terms of the travel time distribution of the mobile phase which is then used to incorporate local interaction processes. This approach permits the analysis of all linear transport processes, not only the small subset for which a differential description is known. From a practical point of view, it allows the direct use of measured concentrations or fluxes of conservative solutes to characterize the mobile phase without first subjecting them to any model. For complicated flow regimes, this may vastly improve the identification of models and estimation of their parameters for the local adsorption processes.
Field experiments in a fractured clay till: 1. Hydraulic conductivity and fracture aperture
Authors: McKay Larry D. , Cherry John A. , Gillham Robert W.
Published: February 2004

Field values of horizontal hydraulic conductivity measured in the upper 1.5–5.5 m of a weathered and fractured clay‐rich till were strongly influenced by smearing around piezometer intakes, which occurs during augering, and by the physical scale of the measuring device. Values measured in conventional augered piezometers were typically 1–2 orders of magnitude lower than those measured in piezometers designed to reduce smearing. Measurements of hydraulic conductivity in small‐scale seepage collectors or piezometers, which typically intersect fewer than 10 fractures, vary over a much greater range, 10−10 to 10−6 m/s, than large‐scale values based on infiltration into 5.5‐m‐deep trenches which intersect thousands of fractures (range 10−7 to 3×10−7 m/s). Values of hydraulic fracture aperture, 1–43 μm, and fracture porosity, 3×10−5 to 2×10−3, were calculated using the cubic law with fracture orientation/distribution measurements and the small‐scale hydraulic conductivity measurements. This paper provides the first reliable determination of the magnitude and spatial distribution of hydraulically derived fracture parameters in a clay deposit. The absence of such data has, until now, severely limited the application of quantitative groundwater flow and contaminant transport models in this type of deposit.
Prediction of suspended bed material transport in flows over silt and very fine sand
Authors: van den Berg Jan H. , van Gelder André
Published: February 2004

Three equilibrium sand transport formulae were tested for prediction of the suspended bed material transport rate in the silt‐laden Huanghe (Yellow River): Ackers and White (1973), Engelund and Hansen (1967), and Van Rijn (1984b). The best results were obtained with the Van Rijn function. However, at low flow stages better results were produced by the Engelund‐Hansen equation. The Ackers‐White formula seriously overpredicted the measured values. Some modifications of the Van Rijn formula were proposed for application in flows over very fine sand and silt. In a verification analysis it was demonstrated that these modifications slightly improve its predictive strength. Also, attention was paid to the effect of turbulence damping by sediment particles at high concentrations.
Effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow
Authors: Bunte Kristin , Poesen Jean
Published: February 2004

Rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion. This makes modeling soil erosion difficult. Systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield. Therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments. High local turbulence was caused by horseshoe vortex erosion around individual rock fragments. For a given discharge and slope, the dimension of the scour was affected by the space between the rock fragments. For low cover percentages the scour can develop undisturbed, and sediment yield increases with percent of rock fragment cover up to about 20%. Sediment yield then declines as percent cover increases above 20%. Beyond a cover threshold value of 20%, the larger opportunity for scour hole development is counteracted by limited inter‐rock fragment space that does not allow scour holes to develop to their full extent. As sediment yield varies nonmonotonically with rock fragment cover percent, sediment yield cannot be predicted by spatially averaged flow hydraulics.
Burgers' Equation: A solution for soil water flow in a finite length
Authors: Hills R. G. , Warrick A. W.
Published: February 2004

Burgers' equation can be considered a special case of the one‐dimensional Richards' equation for vertical flow for which the soil water diffusivity is constant and the unsaturated hydraulic conductivity is proportional to the square of the reduced water content. Here, a Fourier series solution for Burgers' (1948) equation for a finite region is presented. The solution is useful to modelers seeking a simplified representation of vertical water flow through the vadose zone and as an analytical solution for benchmarking which maintains many of the nonlinear characteristics of solutions to Richards' equation. Two example problems are presented. In the first, infiltration into a dry soil is modeled showing that Burgers' equation gives developing wetting front profiles similar to those observed for Richards' equation. In the second example, one‐step outflow from an 8‐cm core is modeled. Comparisons between the analytical and finite difference solutions for Burgers' equation are presented to help verify the analytical solutions.