bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of a Liquid Phase Geothermal Doublet System at Regina, Saskatchewan, Canada
Authors: Hutchence K. , Weston J. H. , Law A. G. , Vigrass L. W. , Jones F. W.
Published: February 2008

The paper describes a computer‐mathematical model used to analyze the nature of the subsurface temperature disturbance that results from extraction of hot liquid from a geothermal production well with concurrent injection of cooled tailings water in a nearby disposal well. The model was designed specifically to determine, at an early stage of development, an appropriate well spacing for the sedimentary‐basin geothermal project at Regina, Canada. Assumptions include an infinite horizontal confined aquifer with uniform thickness and a finely dispersed pore system. The mathematical model is based on an energy balance equation that combines Darcy's law, Fourier's law, and the change in heat content of an element within the active zone of the aquifer. The numerical model is developed by means of the integrated finite difference technique. Short computer run times are achieved through the use of symmetry, an expanding grid system, and the use of the Theis solution. Investigation of model sensitivity shows the model to be sensitive to such factors as interwell distance, pumping rates, porosity, and aquifer thickness, but quite insensitive to hydraulic conductivity and storativity. Sample results are given for Regin aquifers undergoing both continuous and seasonal pumping. Isotherm maps show that the temperature disturbance evolves with time from a cooled, circular area around the injection well to a strongly noncircular pattern with a protrusion of cooled water extending toward the production well. The model is used to predict time of thermal breakthrough for Regina aquifers using different pumping rates and interwell distances. Temperature histories for continuous pumping show that after thermal breakthrough, the produced water undergoes a slight decline of temperature over a considerable time span. For the withdrawal of equal volumes of fluid, the temperature disturbance around the disposal well is spread over a slightly larger area for the seasonal pumping case compared to continuous pumping. The thermal front is broader for the seasonal case because of the longer period of elapsed time during which thermal conduction occurs. For seasonal operations, thermal breakthrough will occur after less water has been pumped and there is a more gradual decline in the temperature of the production well after thermal breakthrough.
Dual‐gamma attenuation for the determination of porous medium saturation with respect to three fluids
Authors: Ferrand L. A. , Milly P. C. D. , Pinder G. F.
Published: February 2008

A dual‐gamma attenuation technique may be applied to the laboratory determination of the degree of saturation with respect to three immiscible fluids in a porous medium whose bulk density is independent of time. A proposed calibration technique uses samples of the medium containing only two of the fluids at one time and does not require spatial uniformity of porosity or of fluid contents within the sample. Given gamma attenuation data, the system parameters so obtained allow calculation of fluid contents in three‐fluid samples. An experimental application of the technique in which the relative saturations of water, trichloroethylene, and air in a sand were measured demonstrates its potential for use in laboratory studies relevant to the transport of separate phase organic contaminants in groundwater.
The kinetics of ion exchange on natural sediments
Authors: Jackman Alan P. , Ng King T.
Published: February 2008

The influences of external film diffusion and internal pore diffusion in controlling the kinetics of ion‐exchange adsorption on natural streambed sediments are investigated. Natural sediments were segregated according to size into six groups ranging from 0.2–0.50 to 6.3–9.5 mm. Sized sediments were first saturated with calcium ions and then immersed in a reservoir containing a dilute solution of strontium ions under flow conditions similar to those encountered near the surface of a streambed. Reservoir concentration was determined as a function of time until a steady state was achieved. For the smallest sized particles, the strontium ion concentration versus time can be adequately described by a model which assumes that film diffusion controls the adsorption rate. For the largest sized particles, a model which assumes that internal diffusion controls the adsorption rate is adequate. For intermediate sizes, the influence of both film diffusion and internal diffusion must be accounted for to adequately describe the data. A criterion is proposed which is able to predict whether the adsorption process can be adequately described by the simpler film‐diffusion‐limiting or internal‐diffusion‐limiting models or must be described by a model accounting for both processes. Effective diffusivities in the natural sediments were found to be very high due to a large contribution from surface diffusion. Surface diffusivities ranging from 3.6 × 10−8 to 15.9 × 10−8 cm2/s are calculated.
Simulation of contaminant plumes with large dispersive contrast: Evaluation of alternating direction Galerkin Models
Authors: Frind Emil O. , Germain Diane
Published: February 2008

The evolution of narrow, sharply defined contaminant plumes, corresponding in shape to those often observed in the field, is examined. It is shown that the transverse dispersion mechanism consistent with such shapes can be as low as of the order of molecular diffusion and that dispersivity contrasts of as much as 4 orders of magnitude are possible. Even at the lowest physically realistic values of transverse dispersion parameters, however, transverse mass spreading is capable of significantly retarding the advance of the plume front. The principal direction and alternating direction Galerkin models together are found to be capable of handling all cases of dispersive contrast including those with dispersivity ratio of infinity. The models are formulated in curvilinear coordinates with certain restrictions on the element deformation. A three‐way comparison between principal direction, alternating direction Galerkin, and conventional finite element models is performed with respect to accuracy and efficiency. The effects of longitudinal and transverse numerical dispersion occuring in the various models are examined and related to the discretization. Visual indications of the presence of numerical error are discussed.
Chlorine 36 dating of very old groundwater: 1. The Great Artesian Basin, Australia
Authors: Bentley Harold W. , Phillips Fred M. , Davis Stanley N. , Habermehl M. A. , Airey Peter L. , Calf Graeme E. , Elmore David , Gove Harry E. , Torgersen Thomas
Published: February 2008

Chlorine 36 has many advantages as a dating tool for very old groundwater. These advantages include a suitable half‐life (3.01 × 105 years), simple geochemistry, conservative behavior in groundwater, and a general absence of subsurface sources at levels comparable to the atmospheric input. Recent advances in tandem accelerator mass spectrometry have permitted the analysis of 36Cl at the low abundance expected following residence in the subsurface for 106 years or more. In order to test the suitability of 36Cl for dating very old groundwater, the 36Cl/Cl ratios of 26 groundwater samples from the Great Artesian Basin of Australia have been measured. Groundwater ages calculated from the 36Cl data compare favorably with ages computed independently from hydrodynamic simulations.
A simple model for spatial‐temporal processes
Authors: Stein Michael
Published: February 2008

Suppose a spatial‐temporal process is observed at a fixed network of sites at a number of observation times. The process is modeled as the sum of a random field fixed in time plus a second independent random field that varies both spatially and temporally. We (essentially) assume that values of this second field taken at two different observation times are uncorrelated. Using this model, we obtain a simple expression for the kriging predictor of this process. This model also suggests a method of prediction of the average change in time in the process over a region.
Statistical theory of groundwater flow and transport: Pore to laboratory, laboratory to formation, and formation to regional scale
Authors: Dagan Gedeon
Published: February 2008

The statistical approach has been applied increasingly to groundwater flow problems in the last decade, as is illustrated in Figure 3 by the cumulative number of articles published in this field in Water Resources Reseach. This development has been motivated by the recognition of the fact that porous formations are heterogeneous, i.e., with properties which vary in an irregular manner in space. Flow domains are characterized by the length scale L of their spatial extent and three such scales of a fundamental nature are introduced: the laboratory, the local, and the regional scale. Heterogeneity is characterized by the spatial correlation scale I of the property of interest, the three scales corresponding to the above ones being the pore scale, the log hydraulic conductivity, and the log transmissivity integral scales. The medium properties and related flow variables are regarded as random space functions which satisfy two basic requirements: they enjoy some type of stationarity and I ≪ L. An additional scale D is the measurement or computational scale, characterizing the size of the measurement device of a flow variable or the element over which the variable is averaged for computational purposes. In both cases, the interest resides in the space average of the flow variable over a volume or area of length scale D. The primary aim of the theory of flow and transport through porous media is to determine the statistical moments of the space‐averaged variables, given the statistical structure of the spatially variable property. The main objective of the study is to show that flow and transport problems at the three fundamental scales can be treated by a unified statistical approach, along this line. The specific aspects of each scale are examined separately, and areas of interest for future research are indicated. In the concluding remarks it is submitted that the statistical approach to groundwater flow has become a comprehensive theory, beyond the stage of an ad hoc modeling technique.
Mathematical models of rainstorm events in space and time
Authors: Rodriguez‐Iturbe Ignacio , Eagleson Peter S.
Published: February 2008

The spatial and temporal structure of rainfall from storm events is investigated using point process techniques. Cells are assumed to be distributed in space either independently according to a Poisson process, or with clustering according to a Neyman‐Scott scheme. Cells are born randomly through the storm and their rain is spread in time and space according to functions which may include random parameters. Two processes are studied: the rainfall intensity process which in reality is never measured and the cumulative rainfall process through the life of the storm. The mean, variance, and covariance structure are obtained for both processes under the different assumed models.
Input substitution and demand in the water supply production process
Authors: Kim H. Youn , Clark Robert M.
Published: February 2008

The structure of input demand for U.S. water utilities is analyzed by estimating a translog cost function. An important feature of the model includes the multiproduct specification of the water supply production process. Operating variables are also specified to include capacity utilization and service distance, which are considered important for delivery of water supply. Results show that capital is a substitute for both energy and labor, but that no strong substitution possibilities exist between energy and labor. Energy is an input which requires intensive use in water production. Small utilities are found to enjoy economies of scale. Capacity utilization and service distance are found to have significant effects on input demand.
Groundwater contamination from waste management sites: The interaction between risk‐based engineering design and regulatory policy: 1. Methodology
Authors: Massmann Joel , Freeze R. Allan
Published: February 2008

This paper puts in place a risk‐cost‐benefit analysis for waste management facilities that explicitly recognizes the adversarial relationship that exists in a regulated market economy between the owner/operator of a waste management facility and the government regulatory agency under whose terms the facility must be licensed. The risk‐cost‐benefit analysis is set up from the perspective of the owner/operator. It can be used directly by the owner/operator to assess alternative design strategies. It can also be used by the regulatory agency to assess alternative regulatory policy, but only in an indirect manner, by examining the response of an owner/operator to the stimuli of various policies. The objective function is couched in terms of a discounted stream of benefits, costs, and risks over an engineering time horizon. Benefits are in the form of revenues for services provided; costs are those of construction and operation of the facility. Risk is defined as the cost associated with the probability of failure, with failure defined as the occurrence of a groundwater contamination event that violates the licensing requirements established for the facility. Failure requires a breach of the containment structure and contaminant migration through the hydrogeological environment to a compliance surface. The probability of failure can be estimated on the basis of reliability theory for the breach of containment and with a Monte‐Carlo finite‐element simulation for the advective contaminant transport. In the hydrogeological environment the hydraulic conductivity values are defined stochastically. The probability of failure is reduced by the presence of a monitoring network operated by the owner/operator and located between the source and the regulatory compliance surface. The level of reduction in the probability of failure depends on the probability of detection of the monitoring network, which can be calculated from the stochastic contaminant transport simulations. While the framework is quite general, the development in this paper is specifically suited for a landfill in which the primary design feature is one or more synthetic liners in parallel. Contamination is brought about by the release of a single, inorganic nonradioactive species into a saturated, high‐permeability, advective, steady state horizontal flow system which can be analyzed with a two‐dimensional analysis. It is possible to carry out sensitivity analyses for a wide variety of influences on this system, including landfill size, liner design, hydrogeological parameters, amount of exploration, extent of monitoring network, nature of remedial schemes, economic factors, and regulatory policy.
Submicron size distributions of inorganic suspended solids in turbid waters by photon correlation spectroscopy
Authors: Gallegos C. L. , Menzel R. G.
Published: February 2008

Photon correlation Spectroscopy (PCS) is a technique for determining size distributions of submicron‐sized particles. A particle diffusion coefficient, which is dependent on particle diameter, is determined from measurements of the autocorrelation function of the intensity fluctuations of light scattered from a laser beam passing through a suspension of particles. We demonstrate the applicability of the technique to particles likely to be found in runoff or turbid impoundments using soil fractions prepared to have a known size distribution. Mean particle diameters of all soil fractions determined by PCS fell within the expected range. Particle‐size distributions of natural water samples were reproducible when analyzed within minutes of collection. The effects of sample storage and pretreatment varied between water bodies and thus can be a source of uncertainty in the results. Particles from a turbid creek carying storm runoff began to coagulate within 2.5–6 hours, whereas particles from a perennially turbid impoundment remained stable for 10 days. Addition of sodium hexametaphosphate improved the reproducibility of the particle‐size distribution with prolonged storage. Applications of the technique include determination of coagulation rates and critical coagulation concentrations of electrolytes, and calculation of settling velocity distributions of submicron particles in turbid natural waters.
A study of cell models: 3. A pilot study on the calibration of manifold cell models in the time domain and in the Laplace domain
Authors: Diskin M. H. , Pegram G. G. S.
Published: February 2008

The results of the calibration of a hydrologic system model depend, among other factors, on the formulation of the model structure and the procedure adopted for the computations. The variation between different methods is relatively small, but it is possible to gain some side benefits by using one method or another. The paper describes the results obtained with different formulations of two semi‐distributed cells models, a cascade model previously described in the technical literature, and a new manifold model. Two equivalent formulations were used for the definition of the models. One was based on the use of convolution integrals, and the second was based on a discretely coincident autoregressive moving average formulation. In addition, a rarely used approach based on Laplace transforms is also described. Results obtained by this method indicate that it has some merits, such as robustness and convergence, which make it an attractive calibration technique.
A quasi‐solution of Richards' Equation for the downward infiltration of water into soil
Authors: Swartzendruber Dale
Published: February 2008

A new equation is presented that expresses depth Z of soil water content θ at time t as an explicit function of θ and t and holds for all t ≥ 0. The new Z(θ, t) includes the classical J. R. Philip (1957b, c) solution for asymptotically large times. At moderate times, the new Z(θ, t) is matched to the classical Philip solution expressed as ϕt½ + χt + ψt⅔ + ω;t2 + …, where ϕ, χ, ϕ, ω,… are different functions of θ alone. The matching process enables the characterizing functions (or parameters) within Z(θ, t) to be evaluated in straightforward fashion from the moderate‐time Philip functions (ϕ, χ, ψ, ω,…). When evaluated for either Philip's data or the Green and Ampt step‐function solution, the new Z(θ, t) in each case describes the water content profiles with excellent accuracy for all times. Also, for all t ≥ 0, the new Z(θ, t) can be directly integrated to provide a new equation for cumulative quantity of water infiltrated or flux, both as explicit functions of time.
Accuracy of sediment deposition estimation
Authors: Bárdossy A. , Bogárdi I. , Duckstein L.
Published: February 2008

A statistical model is developed for the error analysis of surveying sediment deposition in reservoirs. The estimation variance of both the volume and weight of deposition can be calculated from a simple expression. The calculated error is shown to depend on inherent spatial variability, type of measurement, and the number of survey points. Survey networks for six reservoirs were designed by the model in such a way that the total weight of deposition could be measured with a coefficient of variation in the range 0.02–0.06.
A perturbation boundary element code for steady state groundwater flow in heterogeneous aquifers
Authors: Lafe O. E. , Cheng H‐D.
Published: February 2008

A boundary element code is developed for the steady state Darcy's flow in heterogeneous porous media. The solution is based on the expansion of the piezometric head into perturbation series. The governing equation is decomposed into a Laplace equation and a sequence of Poisson equations with known right‐hand sides. Regular boundary element procedure is applied for their solutions. Three numerical examples with moderate hydraulic conductivity variations are provided to demonstrate the applicability of the code. The convergence of the perturbation solution is discussed using a one‐dimensional problem.
Screening tactics in a water management policy analysis for the Netherlands
Authors: Walker Warren E. , Veen Meinaard A.
Published: February 2008

Large policy studies generally involve too many alternative policies to examine each in detail. As a result, such studies often include a step in which policy options (tactics) that are clearly unattractive are screened out. The output from this step is a small list of tactics that deserve a more thorough evaluation. We describe the screening of tactics to change the movement and storage of water in the lakes and waterways of the Netherlands. This analysis was part of a larger study to help the Dutch government develop a new water management policy. The screening process for each tactic involved obtaining an upper bound on the expected annual benefits from the tactic under various assumptions about future water demands (UB) and comparing this upper bound with the tactic's annualized fixed cost (AFC). If the AFC was less than the UB, the tactic was considered promising and was retained for further analysis. If not, the tactic was screened out. Results from the screening analysis informed policy decisions that will avoid investment expenditures of hundreds of millions of dollars and will reduce agricultural damage by about $15 million/year.
Use of weighted integral variables to determine the relation between rainfall intensity and storm flow and peak flow generation
Authors: Bren L. J. , Farrell P. W. , Leitch C. J.
Published: February 2008

Hewlett's (1977) work using his storm flow separation technique has established that peak rainfall intensities have little predictive value in the determination of storm flow depth or storm peak flow from small upland streams emanating from forested catchments. A logical but disconcerting inference is that storm rainfall intensities have little influence on either the volume of storm flow or peak flow. To obtain additional information a variant of the technique was applied to excellent records from two separate, steep, upland catchments in southern Australia. The catchments were regarded as having quite distinct rainfall response characteristics by hydrologists involved in data collection. Antecedent flow, storm rainfall, and measures of maximum rainfall intensity were supplemented by weighted integrals of rainfall intensity with time to test whether they gave additional insight into the influence of rainfall intensity. As expected, regression analysis showed that knowledge of maximum intensities gave little increase in predictive ability over storm rainfall. However, the time integral of rainfall intensity to the power of 1.5 was better correlated with peak flow than any other measure on both catchments. The results suggest that rainfall intensities are more important in the generation of peak flows than indicated by regression analysis using only peak rainfall intensities. Comparison of independent measurements of the variables using separated rain gauges showed that independent measures of the weighted variables were better correlated than measures of storm maximum intensities, indicating that they are also a more precise measure.
Using the method of moments to analyze three‐dimensional diffusion‐limited solute transport from temporal and spatial perspectives
Authors: Goltz Mark N. , Roberts Paul V.
Published: February 2008

This paper focuses on the analysis and application of an analytical model that incorporates solute diffusion within immobile regions into the three‐dimensional advection/dispersion solute transport equation. The diffusion term of the model is formulated using either a first‐order rate expression or an expression assuming Fickian diffusion into spherical, cylindrical, or rectangular immobile regions. In order to assist in the analysis of solute transport behavior by means of the models, a modified form of Aris's method of moments is developed, which permits the calculation of the spatial and temporal moments of solute distributions simulated using the three‐dimensional diffusion models, without having to invert the Laplace‐ or Fourier‐transformed solutions. By using this method, the moments of the diffusion models are compared with one another, with the moments of a model that assumes equilibrium advective/dispersive transport, and with the moments of a model that assumes that a first‐order rate law governs mass transfer between the mobile and immobile regions. The method of moments also is used to assess the differences in the spatial and temporal moment behavior of each transport model under discussion.
Bacteria in deep coastal plain sediments of Maryland: A possible source of CO2 to groundwater
Authors: Chapelle Francis H. , Zelibor Joseph L. , Grimes D. Jay , Knobel LeRoy L.
Published: February 2008

Nineteen cores of unconsolidated Coastal Plain sediments obtained from depths of 14 to 182 m below land surface near Waldorf, Maryland, were collected and examined for metabolically active bacteria. The age of the sediments cored range from Miocene to Early Cretaceous. Acridine orange direct counts of total (viable and nonviable) bacteria in core subsamples ranged from 108 to 104 bacteria/g of dry sediment. Direct counts of viable bacteria ranged from 106 to 103 bacteria/g of dry sediment. Three cores contained viable methanogenic bacteria, and seven cores contained viable sulfate‐reducing bacteria. The observed presence of bacteria in these sediments suggest that heterotrophic bacterial metabolism, with lignitic organic material as the primary substrate, is a plausible source of CO2 to groundwater. However, the possibility that abiotic processes also produce CO2 cannot be ruled out. Estimated rates of CO2 production in the noncalcareous Magothy/Upper Patapsco and Lower Patapsco aquifers based on mass balance of dissolved inorganic carbon, groundwater flow rates, and flow path segment lengths are in the range 10−3 to 10−5 mmol L−1 yr−1. Isotope balance calculations suggest that aquifer‐generated CO2 is much heavier isotopically (∼—10 to + 5 per mil) than lignite (∼−24 per mil) present in these sediments. This may reflect isotopic fractionation during methanogenesis and possibly other bacterially mediated processes.
Two‐ and three‐dimensional steady quasi‐linear infiltration from buried and surface cavities using boundary element techniques
Authors: Pullan A. J. , Collins I. F.
Published: February 2008

A general numerical method is presented for solving the problem of quasi‐linearized steady infiltration from general two‐dimensional and axisymmetric surface cavities and from a general cavity buried at an arbitrary depth in either a two‐ or three‐dimensional semi‐infinite porous medium. Numerical results are compared with known analytical results for the cases of a shallow circular pond and a circular cylindrical cavity and a spherical cavity buried in an infinite medium. Further results are presented graphically illustrating the effect of an upper surface on the flux from a circular cavity and also the effect on the size of the effective wetted region. Two‐dimensional surface cavities are also investigated, and the dependence of the flux on geometry, gravity, and capillarity is examined.
Laboratory evidence of the scale effect in dispersion of solutes in porous media
Authors: Silliman S. E. , Simpson E. S.
Published: February 2008

Field observations by other authors indicate that dispersivity is dependent on distance from source. In this study, tests were conducted under controlled laboratory conditions to investigate the changes in dispersivity caused by the presence of heterogeneities. The experiments were conducted in a 2.4 × 1.07 × 0.10 m “sandbox” with measurements of tracer concentration taken at various distances from the input. Results for various sand‐packing arrangements were as follows: (1) Breakthrough curves for a uniform coarse sand showed a constant dispersivity of approximately 0.02 m. (2) Breakthrough curves for a three‐layer arrangement of coarse‐fine‐coarse deviated from the homogeneous results only in the late‐time tails. (3) The middepth fine‐sand layer was then replaced by small blocks of fine sand surrounded by coarse sand. Two distinct portions of the breakthrough curves could be identified: one for the coarse‐sand matrix and one for the heterogeneous layer. (4) Small blocks of fine sand were uniformly distributed through the entire coarse‐sand matrix. Results indicated a continuous increase in dispersivity with distance and a change in the shape of the breakthrough curve at each of five measurement sections. These results are in general agreement with several recent theoretical developments regarding transport.
A new method for qualitative simulation of water resources systems: 1. Theory
Authors: Camara A. S. , Pinheiro M. , Antunes M. P. , Seixas M. J.
Published: February 2008

A new dynamic modeling methodology, SLIN (Simulação Linguistica), allowing for the analysis of systems defined by linguistic variables, is presented. SLIN applies a set of logical rules avoiding fuzzy theoretic concepts. To make the transition from qualitative to quantitative modes, logical rules are used as well. Extensions of the methodology to simulation‐optimization applications and multiexpert system modeling are also discussed.
A new method for qualitative simulation of water resources systems: 2. Applications
Authors: Antunes M. P. , Seixas M. J. , Camara A. S. , Pinheiro M.
Published: February 2008

SLIN (Simulação Linguistica) is a new method for qualitative dynamic simulation. As was presented previously (Camara et al., this issue), SLIN relies upon a categorical representation of variables which are manipulated by logical rules. Two applications to water resources systems are included to illustrate SLIN's potential usefulness: the environmental impact evaluation of a hydropower plant and the assessment of oil dispersion in the sea after a tanker wreck.
A model for hysteretic constitutive relations governing multiphase flow: 1. Saturation‐pressure relations
Authors: Parker J. C. , Lenhard R. J.
Published: February 2008

In these companion papers, a general theoretical model is presented for the description of functional relationships between relative permeability k, fluid saturation S, and pressure P in two‐or three‐phase (e.g., air‐water or air‐oil‐water) porous media systems subject to arbitrary saturation paths. A parametric description of hysteretic S‐P relations is developed in paper 1 which includes effects of air and oil phase occlusion or “entrapment” during imbibition. Entrapped nonwetting fluid saturations at a given point along a saturation path are linearly interpolated between endpoints of primary imbibition scanning curves using maximum trapped saturations estimated by extension of the method of Land (1968). Arbitrary order scanning curves are predicted using an empirical interpolation scheme coupled with a scaling procedure which simplifies computations and minimizes the parametric complexity of the model. All model parameters are defined in terms of measurements which may be obtained from two‐phase systems (air‐water, air‐oil, oil‐water). Extension to three‐phase systems is based on the assumption that fluid entrapment processes in three phase systems are similar to those in two‐phase systems and that wettability decreases in the order: water to oil to air.
Regression models for hydraulic conductivity and field test of the borehole permeameter
Authors: Stephens Daniel B. , Lambert Kevin , Watson David
Published: February 2008

The saturated hydraulic conductivity Ks of sediments in the vadose zone is an important parameter in predicting the seepage rates of water and contaminants. The borehole permeameter is an in situ technique to test a relatively large sample size at any depth. Solutions are presented which account for the effects of unsaturated flow. These solutions are derived from a regression analysis of results of numerical simulations in which unsaturated hydraulic conductivity is represented by one or two parameters. The results of a borehole permeameter test in a uniform sand are compared with field ponding tests and air entry permeameter tests. The regression‐based solutions for the borehole permeameter which account for capillarity provide very good agreement with other permeameter results. Depending upon the approach used to solve the borehole problem Ks values determined by methods which neglected and included capillary effects varied by a factor of only about two for the soil tested.
Forest evaporation and meteorological data: A test of a complementary theory advection‐aridity approach
Authors: Byrne G. F. , Dunin F. X. , Diggle P. J.
Published: February 2008

A relationship between daily forest evaporation and meteorological screen data, based on an extension of a previous complementary theory approach to pasture evaporation, is proposed. The resulting formulation is tested against 800 days of a 5‐year lysimeter record for a eucalypt forest and appears to offer an alternative and plausible formulation of the relationship between the meteorological data and regional evaporation.
A field technique to measure the tortuosity and sorption‐affected porosity for gaseous diffusion of materials in the unsaturated zone with experimental results from near Barnwell, South Carolina
Authors: Kreamer David K. , Weeks Edwin P. , Thompson Glenn M.
Published: February 2008

A tracer experiment was conducted at the commercial low‐level nuclear waste disposal site near Barnwell, South Carolina, to test a new method for determining the tortuosity and sorption‐affected porosity for gaseous diffusion transport of materials in the Unsaturated zone. Two tracers, CBrClF2 and SF6, were released at constant rates of 105 and 3.3 ng/s, respectively, from permeation devices, which were placed in short screened sections in access holes. Soil gas was sampled from 15 piezometers located at various distances from the sources by sequentially pumping 60–160 mL of gas from the piezometers into a dual‐column gas chromatograph located at the test site. The CBrClF2 concentration data obtained from several of the piezometers were analyzed by use of type curves for a continuous point source in an areally extensive medium bounded above and below by planar no‐flow boundaries. The tortuosity of the geologic unit tested, an eolian sand, was determined to be about 0.4, and the sorption‐affected porosity to be 0.22. The tortuosity value is plausible, but the sorption‐affected porosity value is substantially less than that computed from the drained porosity, particularly if adjustments are made for retardation due to solution of the tracer in the liquid phase and sorption on the solid phase. The SF6 data could not be reliably analyzed.
Volume sharing of reservoir water
Authors: Dudley Norman J.
Published: February 2008

Previous models optimize short‐, intermediate‐, and long‐run irrigation decision making in a simplified river valley system characterized by highly variable water supplies and demands for a single decision maker controlling both reservoir releases and farm water use. A major problem in relaxing the assumption of one decision maker is communicating the stochastic nature of supplies and demands between reservoir and farm managers. In this paper, an optimizing model is used to develop release rules for reservoir management when all users share equally in releases, and computer simulation is used to generate an historical time sequence of announced releases. These announced releases become a state variable in a farm management model which optimizes farm area‐to‐irrigate decisions through time. Such modeling envisages the use of growing area climatic data by the reservoir authority to gauge water demand and the transfer of water supply data from reservoir to farm managers via computer data files. Alternative model forms, including allocating water on a priority basis, are discussed briefly. Results show lower mean aggregate farm income and lower variance of aggregate farm income than in the single decision‐maker case. This short‐run economic efficiency loss coupled with likely long‐run economic efficiency losses due to the attenuated nature of property rights indicates the need for quite different ways of integrating reservoir and farm management.
A representation of spatial cross correlations in large stochastic seasonal streamflow models
Authors: Oliveira G. C. , Kelman J. , Pereira M. V. F. , Stedinger Jery R.
Published: February 2008

Pereira et al. (1984) present a special disaggregation procedure for generating cross‐correlated monthly flows at many sites while using what are essentially univariate disaggregation models for the flows at each site. This was done by using a nonparametric procedure for constructing residual innovations or noise vectors with cross‐correlated components. This note considers the theoretical underpinnings of that streamflow disaggregation procedure and a proposed variation and their ability to reproduce the observed historical cross correlations among concurrent monthly flows at nine Brazilian stations.
Metering utility services: Evaluation and maintenance
Authors: Lund Jay R.
Published: February 2008

The value of metering customer connections to public utilities is often taken for granted. The paper proposes methods for evaluating customer metering in terms of maximizing economic efficiency, utility profits, and economic equity. Significant improvements are made in methods for assessing the conservation benefits of metering. Methods are illustrated using domestic water supply examples, but are applicable to any utility service. When metering is inefficient, so is marginal cost pricing. The paper also applies Bayesian decision analysis and regeneration theory to the maintenance of water meters. This maintenance scheduling method is relevant for other component maintenance problems in water resource systems.
Application of principal component analysis to long‐term reservoir management
Authors: Saad Maarouf , Turgeon André
Published: February 2008

Determining the optimal long‐term operating policy of a multireservoir power system requires solution of a stochastic nonlinear programing problem. For small systems the solution can be found by dynamic programing, but for large systems, no direct solution method exists yet, so that one must resort to mathematical manipulations to solve the problem. This paper presents a very efficient procedure for the case where high correlation exists between the reservoirs' trajectories and hence between the state variables. The procedure consists of performing principal component analysis (PCA) on the trajectories to find a reduced model of the system. The reduced model is then substituted into the operating problem, and the resulting problem is solved by stochastic dynamic programing. The reservoir trajectories on which the PCA is performed can be obtained by solving the operating problem deterministically for a large number of equally likely flow sequences. The results of applying the manipulation to Quebec's La Grande river, which has five reservoirs, are reported.
Groundwater flow systems in mountainous terrain: 2. Controlling factors
Authors: Forster Craig , Smith Leslie
Published: February 2008

The modeling technique developed in paper l (Forster and Smith, this issue) of this two‐part study provides a quantitative means for assessing the impact of factors controlling groundwater flow systems in mountainous terrain. Conditions to be examined include surface topography (slope profile, relief, three‐dimensional form), geology (permeability and thermal conductivity), climate (available infiltration, presence and extent of alpine glaciers, surface temperature conditions), and regional heat flux. Modeling results indicate that water table elevation is a sensitive indicator of the factors controlling mountain flow systems. Under certain conditions, overestimating the bulk permeability of a mountain massif by a factor of 5 can lead to underestimates of the water table elevation in excess of 1000 m. Under the same conditions, rates of fluid flux may be overestimated by at least 60%. The infiltration rate, regional heat flux, and the presence of glaciers have important, but lesser impacts. High topographic relief amplifies the influence of surface topography and permeable fracture zones on patterns of groundwater flow and on the position of groundwater flow divides. Although computed water table elevations are sensitive to controlling factors, uncertainties inherent in resolving the magnitude of many of the controlling parameters will complicate efforts to constrain simulations using measured water table elevations.
Three‐dimensional radial dispersion in a variable velocity flow field
Authors: Yates S. R.
Published: February 2008

An analytical solution is developed which provides a three‐dimensional solution for the fate and transport of contaminants in a variable velocity and axially symmetric flow field. Due to the axially symmetric nature of the flow field, the equations which describe the transport process can be written in two space dimensions, r and z. The solution allows a first‐order decay process and linear retardation of the contaminant and assumes that the aquifer is homogeneous and isotropic. Two solution techniques are used and approximate early and late time solutions are presented. The analytical solution is illustrated by several examples using three different boundary conditions at the well.
A maximum likelihood criterion for use with data collected at unequal time intervals
Authors: Duan Qingyun , Sorooshian Soroosh , Ibbitt Richard P.
Published: February 2008

A new maximum likelihood (NMLE) criterion suitable for model calibration using data which are recorded at unequal time intervals and contain autocorrelated errors is derived. Validation of the NMLE criterion has been carried out both on a simple two‐parameter reservoir model using synthetically generated data and on a more complicated hillslope model using real data from the Pukeiti catchment in New Zealand. Comparison between the NMLE criterion and the simple least squares criterion reveals the superiority of the former over the latter. Comparison between the NMLE criterion and the maximum likelihood criterion for the autocorrelated case proposed by Sorooshian (1978) has shown that both criteria would yield results with no practical difference if equal time interval data were used. However, the NMLE criterion can work on variable time interval data, which provide more information than equal time interval data and therefore produce better visual results in hydrologic simulations.
Nonaqueous phase liquid transport and cleanup: 2. Experimental studies
Authors: Hunt James R. , Sitar Nicholas , Udell Kent S.
Published: February 2008

An analysis of the movement of nonaqueous liquids such as organic solvents and gasoline in part 1 (Hunt et al., this issue) showed that separate phase liquids are not completely displaced by groundwater flow under typical pumping conditions and that removal of the compounds by dissolution is mass transfer limited. Steam displacement was proposed as a more efficient cleanup strategy for separate phase organic liquids present in porous media. This paper presents the results of a series of laboratory sand column experiments designed to confirm the theoretical analyses presented in part 1 (Hunt et al., this issue). Experiments with trichloroethylene, a benzene‐toluene mixture, and a commercial gasoline, showed that water flow at rates as high as 15 m d−1 could not displace the separate phase liquids when present in a sand matrix in quantities corresponding to a column average saturation of 2.5%. Steam injection, on the other hand, displaced the contaminants as a separate phase just ahead of the steam front, producing a concentrated, small‐volume waste stream. Analysis of the laboratory data consisting of pressure gradients, temperature profiles, and water flow velocities shows that the laboratory results are consistent with the theoretical predictions. Moreover, computations of energy requirements show that steam displacement of separate phase contaminants is economically attractive.
Sampling strategies and associated errors in estimating epilimnetic chlorophyll in eutrophic lakes
Authors: Stauffer Robert E.
Published: February 2008

The spatial distributions of chlorophyll a were studied in Lake Mendota and Delavan during thermal stratification in 1971 and 1972. Both lakes are calcareous and support large epilimnetic chlorophyll standing crops (CSC) (milligrams per square meters) of planktonic blue‐green algae. The root‐mean‐square (rms) coefficient of variation (CV) between chlorophyll samples l m apart in the epilimnetic profile was 23% during sunny windless interludes following cold fronts. The CV for samples within the profile increased as the two thirds power of their separation distance. During conditions of elevated wind stress the interstrata CV for chlorophyll converged to the pure analytical error (2–3%). For Mendota, the rms CV (CSC) varied as 7 ds or, alternatively, 9.5 ds2/3, where ds represents the interstation separation distance (kilometers). The rate of increase was greater for Delavan (∼13 ds), probably because of increased nutrients, hence the increased incidence of large self‐shaded and buoyancy‐prone chlorophyll standing crops that are readily advected by the wind. Profile sampling near the center of Mendota or Delavan provides an unbiased estimate of pelagic mean CSC with a coefficient of variation of 14%. Lake stations at the margins of the pelagic zone (NE, NW, SW, and SE) are biased for pelagic mean CSC and also have large temporal CV. The station biases reflect the prevailing westerly winds; the large CV reflect the cyclical wind shifts related to cyclonic storms.
Maximum entropy spectral analysis of hydrologic data
Authors: Padmanabhan G. , Rao A. Ramachandra
Published: February 2008

Determination of periodicities is a frequently encountered problem in stochastic analysis of hydrologic time series data. Conventional methods of spectral analysis such as those currently used in the analysis of hydrologic data have some long recognized disadvantages. The maximum entropy spectral analysis (MESA) method was developed as an alternative to conventional spectral analysis and has received considerable attention in exploratory geophysics. Several aspects of application of MESA to hydrologic time series are discussed in this paper. The performance of the MESA method is compared with the commonly used Blackman and Tukey method. MESA can be extended to obtain additional stochastic characteristics such as autocorrelation, partial autocorrelation, inverse autocorrelation, inverse partial autocorrelation, and cross spectra of time series data. Thus spectral analysis and computations related to stochastic model development may be integrated by using MESA. The simple relationship between maximum entropy and maximum likelihood spectra may be used to filter our pseudoperiodicities that occur in maximum entropy spectra estimated by using large filter orders.