bluuebunny/crossref_metadata_2025 huggingface dataset:
A new insight on pore structure and permeability
Authors: Wise William R.
Published: February 2004

The flow of water through a porous medium is simulated numerically using a cubic network of cylindrical capillary tubes as the conceptual model of the medium. Poiseuille's law is used to relate the viscous dissipation within the fluid to the pressure gradient driving the flow. The pore size distribution is determined from the capillary pressure function of the medium, and the tubes are randomly arranged within the network. A critical pore radius is identified as the limiting pore size which contributes to the permeability structure of the medium. When only tubes from that part of the pore size distribution above this critical radius are used to form the network, the permeability of the network equals the measured permeability of the medium. This parameter, the critical pore radius, links the permeability to the pore size distribution and gives insight into the topological structure of the medium.
Upscaling of hydraulic conductivity in partially saturated heterogeneous porous formation
Authors: Russo David
Published: February 2004

This paper describes a procedure to upscale unsaturated hydraulic conductivity from the scale at which it is measured to a scale more amenable to actual flow simulations in partially saturated heterogeneous porous formations. In the approach adopted here the block conductivity is defined as the ratio of volume‐averaged flux to the volume‐averaged head gradient. The “point” values of the underlying formation properties (characterized by the saturated conductivity Ks and the pore size distribution parameter α) are viewed as realizations of independent random spatial functions. The general approach is applied to a partially saturated, heterogeneous, three‐dimensional statistically anisotropic formation, with statistical isotropy in the horizontal plane and arbitrarily oriented stratification characterized by a finite aspect ratio, for the case where the mean gradient exists only in the vertical direction. The procedure is illustrated by providing a second‐order approximation of the mean (in terms of the components of the block conductivity tensor) and a first‐order approximation of the covariance function of the block conductivity, which depend on the mean capillary pressure head H, the distribution of the “point” values of the underlying log unsaturated conductivity, and the block size. The results of this study allow assessment of the minimal domain size for which the concept of effective properties is appropriate and assessment of the maximal size of conductivity cells which preserve the heterogeneous structure of the porous formation with respect to simulation of flow and transport in the vadose zone. The application of the results to unconditional or conditional simulation of unsaturated flow and transport is straightforward, since knowledge of the mean and the covariance of the block unsaturated conductivity may lead to a relatively simple algorithm for generating its values on a grid at any level of aggregation desired.
Bayesian exchangeability, benefit transfer, and research efficiency
Authors: Atkinson Scott E. , Crocker Thomas D. , Shogren Jason F.
Published: February 2004

We offer an economic model of the policymaker's site‐ or time‐specific benefit estimate extrapolation problem when she must weigh the potential gains from an increase in the accuracy and the precision of her agents' estimates against the costs of conducting their assessments. If Bayesian exchangeability is treated as a maintained hypothesis, we suggest that empirical Bayes estimators offer a powerful way to increase the economic efficiency of extrapolation. Finally, we employ a hedonic study of pollution control benefits to illustrate a Bayesian diagnostic that allows the hypothesis of exchangeability to be tested rather than taken as maintained. The power of the diagnostic arises from its ability to identify those sources of parameter variability most likely to discourage extrapolations.
Water marketing as a reallocative institution in Texas
Authors: Chang Chan , Griffin Ronald C.
Published: February 2004

Policy selection for guiding the allocation of water resources has long been debated among economists and policymakers. Economists have been prone to recommend water marketing on theoretical grounds, but the appraisal of realistic opportunities for employing market institutions requires analysis of actual markets. Twenty years of market activity in the Lower Rio Grande Valley of Texas are reviewed along with the historical development of water law in Texas and procedural requirements for transferring water rights. Developed data indicate active water marketing practices with significant volumes of agricultural water having been sold to municipalities. For transactions involving representative cities, estimated municipal benefits from water marketing are determined to far exceed the agricultural costs of the transfer. Attention to the unique circumstances of this region is required prior to extending results to other areas.
Microtargeting the acquisition of cropping rights to reduce nonpoint source water pollution
Authors: Kozloff Keith , Taff Steven J. , Wang Yingmin
Published: February 2004

Targeting cropland retirement programs to reduce agricultural nonpoint source pollution is accomplished by employing disaggregated information about physical and economic factors that influence the benefits and costs of adopting specific erosion control practices on specific land parcels. The agricultural nonpoint source (AGNPS) model is used in a Minnesota watershed to simulate the relative effectiveness of alternative targeting schemes with respect to budget outlays for annual payments to landowners, reduction in downstream sediment yield and nutrient loss, and reduction in on‐site erosion. Cost‐effectiveness increased with information on economic factors (the opportunity cost of retiring a parcel of land) as well as on physical factors (contribution of a parcel to downstream sediment yield). The marginal cost‐effectiveness of all schemes decreased as the enrolled proportion of watershed land increased.
A perspective on the numerical solution of convection‐dominated transport problems: A price to pay for the easy way out
Authors: Noorishad J. , Tsang C. F. , Perrochet P. , Musy A.
Published: February 2004

In a brief but fundamental review of the evolution of the conventional numerical techniques used in the solution of convection‐dominated transport problems, we explore the difficulties that have been remedied to various degrees by various workers. In the course of this review we obtain the performance characteristic of the Crank‐Nicolson Galerkin finite element method in the form of a curve in Peclet number and Courant number space. We show that the performance can be altered through a new upwind parameter that can easily be incorporated into many of the existing numerical solution methods. By providing an insight into the limitations of some of these methods we demonstrate, by means of numerical experiments, that the proposed upwinding procedure ensures acceptable solutions throughout the Pe‐Cr space at a reasonable cost of the smearing effect.
Revenue neutral water conservation: Marginal cost pricing with discount coupons
Authors: Collinge Robert A.
Published: February 2004

This paper points out how a system of marketable discount coupons applied to the sale of water by an agency can satisfy both redistributional and revenue constraints without compromise to economic efficiency, in effect creating marketable multipart pricing. This procedure achieves marginal cost pricing for each user while decreasing the average consumer's expenditures on water. Efficiency would obtain both in allocation among users and in overall usage. No information on consumer demand for water is required. A useful by‐product is market revelation of the marginal value of incremental water usage, thereby also shedding light on the value of incremental water projects.
Estimating urban residential water demand: Effects of price structure, conservation, and education
Authors: Nieswiadomy Michael L.
Published: February 2004

Water demand equations are estimated using the most current American Water Works Association (1984) survey of 430 (of 600 largest) U.S. utilities. The data set was augmented by monthly rainfall and temperature data from the National Oceanic and Atmospheric Administration's climatological data. Demographic data were obtained from the U.S. Department of Commerce (1988). Besides the usual endogeneity problems involving block price structures this paper also examines the possible endogeneity of conservation and education programs. Three types of models were used: a marginal price model, an average price model, and Shin's (1985) price perception model. The results generally show that price elasticity is higher in the South and the West. Conservation does not appear to reduce water use, but public education appears to have reduced water usage in the West. The Shin (1985) tests in this study indicate that consumers react more to average than marginal prices in all regions.
Flow resistance under conditions of intense gravel transport
Authors: Pitlick John
Published: February 2004

A study of flow resistance was undertaken in a channelized reach of the North Fork Toutle River, downstream of Mount St. Helens, Washington. Hydraulic and sediment transport data were collected in flows with velocities up to 3 m/s and shear stresses up to 7 times the critical value needed for bed load transport. Details of the flow structure as revealed in vertical velocity profiles indicate that weak bed load transport over a plane gravel bed has little effect on flow resistance. The plane gravel bed persists up to stresses ∼3 times critical, at which point, irregular bed forms appear. Bed forms greatly increase flow resistance and cause velocity profiles to become distorted. The latter arises as an effect of flows becoming depth‐limited as bed form amplitude increases. At very high rates of bed load transport, an upper stage plane bed appeared. Velocity profiles measured in these flows match the law of the wall closely, with the equivalent roughness being well represented by ks = 3D84 of the bed load. The effects noted here will be important in very large floods or in rivers that are not free to widen, such as those cut into bedrock.
Episodic stream acidification caused by atmospheric deposition of sea salts at Acadia National Park, Maine, United States
Authors: Heath Richard H. , Kahl Jeffrey S. , Norton Stephen A. , Fernandez Ivan J.
Published: February 2004

Major episodic acidifications were observed on several occasions in first‐order brooks at Acadia National Park, Mount Desert Island, Maine. Short‐term declines of up to 2 pH units and 130 μeq L−1 acid‐neutralizing capacity were caused by HCl from soil solutions, rather than by H2SO4 or HNO3 from precipitation, because (1) SO4 concentrations were constant or decreased during the pH depression, (2) Cl concentrations were greatest at the time of lowest pH, and (3) Na:Cl ratios decreased from values much greater than those in precipitation (a result of chemical weathering), to values equal to or less than those in precipitation. Dilution, increases in NO3 concentrations, or increased export of organic acidity from soils were insufficient to cause the observed decreases in pH. These data represent surface water acidifications due primarily to an ion exchange “salt effect” of Na+ for H+ in soil solution, and secondarily to dilution, neither of which is a consequence of acidic deposition. The requisite conditions for a major episodic salt effect acidification include acidic soils, and either an especially salt‐laden wet precipitation event, or a period of accumulation of marine salts from dry deposition, followed by wet inputs.
A solute flux approach to transport in heterogeneous formations: 2. Uncertainty analysis
Authors: Cvetkovic V. , Shapiro A. M. , Dagan G.
Published: February 2004

Uncertainty in the mass flux for advection dominated solute movement in heterogeneous porous media is investigated using the Lagrangian framework developed in paper 1 by Dagan et al. (this issue). Expressions for the covariance of the mass flux and cumulative mass flux are derived as functions of the injection volume and sampling area size relative to the scale of heterogeneity. The result is illustrated for solute advection in three types of heterogeneous porous media: stratified formations, two‐ and three‐dimensional porous media; small perturbation approximation is used for the two‐ and three‐dimensional cases. Variances of the mass flux and cumulative mass flux are evaluated as functions of the injection volume (area) scale versus log‐hydraulic conductivity integral scale. The greatest decrease in coefficient of variation (CV) of the mass flux is for the source scale 1–5 times the hydraulic conductivity integral scale; further increase in the source size decreases CV comparatively less. The variance of the cumulative mass flux (or total discharge) indicates that for the source size of 20 hydraulic conductivity integral scales, the transport conditions are almost ergodic. The present results also indicate that the cumulative mass flux is a relatively robust quantity for describing field‐scale solute transport.
Modification of the Kinematic Wave‐Philip Infiltration Overland Flow Model
Authors: Luce Charles H. , Cundy Terrance W.
Published: February 2004

In previous work a solution was developed for the kinematic wave overland flow equation with rainfall excess given by Philip's infiltration equation. Subsequent application of this solution to field data from small plots revealed the need for an improved model. The principal requirement is the incorporation of depression storage into the rising limb calculation. A second requirement is a more precise approximation of the water surface profile at the end of rainfall. This improves the falling limb calculations. This paper shows the solutions obtained by incorporating these improvements and demonstrates their effects on predicted hydrographs and water surface profiles.
Sea breezes and advective effects in southwest James Bay
Authors: McKendry Ian , Roulet Nigel
Published: February 2004

Observations from a transect extending 100 km inland during the Northern Wetlands Study (NOWES) in 1990 show that the sea breeze develops on approximately 25% of days during summer and may penetrate up to 100 km inland on occasions. The sea breeze exhibits a marked diurnal clockwise rotation as a result of the Coriolis effect along the unobstructed coastline. The marine advective effect is shown to depend on gradient wind direction. With northwesterly upper level flow the sea breeze tends to be northeasterly in direction and is associated with decreased temperatures and vapor pressure deficits (VPD). With southwesterly upper level flow the sea breeze tends to have a southeasterly direction and less effect on temperatures and VPD. This is attributed to shorter residence times of air parcels over water. For two cases, Colorado State University mesoscale model simulations show good agreement with surface wind observations and suggest that under northwesterly gradient flow, Bowen ratios are increased in the onshore flow along western James Bay, while during southwesterly gradient flow these effects are negligible. These results have implications for the interpretation of local climate, ecology, and hydrology as well as land‐based and airborne turbulent flux measurements made during NOWES.
Modeling solute advection coupled with sorption kinetics in heterogeneous formations
Authors: Selroos Jan‐Olof , Cvetkovic Vladimir
Published: February 2004

A method for coupling sorption kinetics and solute advection in particle‐tracking models is proposed; this method is efficient for the case where sorption rate coefficients can be assumed constant field scale parameters. A simulation example of reactive solute advection in two‐dimensional heterogeneous porous media is presented. The effect of sorption kinetics on solute advection is investigated. Nonequilibrium effects are exhibited as enhanced tailing in the solute breakthrough. Because high variability in the hydraulic conductivity also yields enhanced tailing, the nonequilibrium effect is more pronounced for the case of low variability. Moreover, it may be difficult to distinguish cases of low variability with nonequilibrium sorption from cases of high variability with equilibrium sorption. A comparison of Monte Carlo ensemble results is made with an analytical model for the mass arrival of kinetically sorbing solute in heterogeneous porous media obtained using first‐order perturbation. The comparison indicates that the analytical model provides reasonable approximations of the expected solute breakthrough if the variance of the natural logarithm of the hydraulic conductivity is smaller than 1.
Use of airborne multispectral video data for water quality evaluation in Sandy Hook, New Jersey
Authors: Bagheri Sima , Stein Matt
Published: February 2004

A local mission of short duration was carried out to investigate the relationship between signals acquired by an airborne multispectral camera (MSC‐02) developed by XYbion Corporation and in situ water sampling. The MSC‐02 was used to produce video images in six spectral bands in the reflective and near‐infrared region of the spectrum from which all below‐surface hydrological signals originate. Images of halon‐coated panels were obtained in all bands to calculate relative radiometric calibration functions. These functions were applied to corresponding spectral images to calculate relative radiances of both panel and estuarine water targets. These values were then input to regression equations to establish a correlation between water constituents (organic/inorganic) and MSC‐02 signals indicating the degree of eutrophication in the estuary. It is hypothesized that if reliable relationships between MSC‐02 data with fine spatial resolution and selected water quality parameters are obtained, then it would be possible to calibrate the concurrently acquired Landsat 5 thematic mapper (TM) data with coarser spatial resolution for monitoring of estuarine water quality.
A model for vertical frazil distribution
Authors: Liou C. P. , Ferrick M. G.
Published: February 2004

A model is presented for the evolution of frazil over depth and with time in a turbulent flow. The net upward migration due to buoyancy of the frazil is opposed by intermittent mixing induced by large energy‐containing eddies. A surface renewal model is used to describe the effects of large eddy mixing. Parameters that represent an entire water body are obtained by averaging those of discrete water columns using a probability density function. These parameters include the concentration profile, the surface age, and the surface layer thickness. A dimensionless surface renewal frequency characterizes the frazil distribution at equilibrium. The rate of heat loss from the water surface, the surface renewal frequency, and the critical surface layer thickness determine whether the frazil will evolve toward a well‐mixed equilibrium state or a layered state. The model provides a physical basis for understanding the transition between these states, consistent with existing empirical criteria and field data.
Optimal extraction of small‐scale surface water storage in Asia
Authors: Mahendrarajah S. , Warr P. G. , Jakeman A. J.
Published: February 2004

This paper analyzes the optimization of water storage of small‐scale dams (tanks) found in the semiarid regions of Asia. The focus is on monsoonal water storage in small tank systems in Sri Lanka, and in particular on optimal extraction for supplementary irrigation under double cropping, also allowing for nonirrigation uses of storage. The problem of intraseasonal allocation of storage for irrigation is solved by deterministic dynamic programming (DP) using simulated crop response functions. An approach to solving the optimal interseasonal allocation problem is demonstrated by operating in sequence the DP models for the two seasons. An important feature is the generation and use of seasonal water response functions with respect to each cropping season ensuring optimality in both crop area and intraseasonal distribution of irrigation. The determination of the scarcity value of water in this framework is also illustrated. Our results show that in most years both the optimal conservation of storage from the wet season and the optimal area of irrigation in the dry season are much higher than the current practice.
Rapid calculation of catchment boundaries using an automated river network overlay technique
Authors: Sekulin Ann E. , Bullock Andrew , Gustard Alan
Published: February 2004

Techniques for constructing watershed boundaries by combining a river network and raster data bases are described. Data types and archive structure required for application of the river network technique are presented, and the methods and algorithms for watershed boundary construction and catchment characteristic derivation are defined. The river network methodology allows rapid watershed definition that is equivalent in ease to the generation of boundaries from digital elevation or digital terrain models, but without the necessity for large and expensive data bases of elevation data.
Groundwater flow in a compressible unconfined aquifer with uniform circular recharge
Authors: Zlotnik Vitaly , Ledder Glenn
Published: February 2004

The distributions of the hydraulic head and velocity components of the transient groundwater flow in an unconfined compressible aquifer of finite thickness under constant uniform circular recharge are obtained from the linearized mathematical model by the use of integral transforms. The result generalizes Dagan's (1967) solution which was derived by neglecting the compressibility. By treating the compressibility parameter as a small value, the formula for the hydraulic head is analyzed by asymptotic methods, resulting in approximations to the exact solutions for the head and velocities on small and large time scales. The hydraulic head and flow velocities can be accurately approximated by Dagan's formula for large times; for small times, neglecting the compressibility gives a large relative error but small absolute error.
An evaluation of boundary conditions for one‐dimensional solute transport: 1. Mathematical development
Authors: Novakowski Kent S.
Published: February 2004

The Laplace transform method is employed to obtain the solution to several boundary value problems in which mixing occurs in reservoirs attached to a porous medium. Flow is assumed to be uniformly one‐dimensional throughout the porous medium. Solutions are obtained for both continuous and discontinuous concentrations at the reservoir‐medium boundary and for resident and flux‐averaged concentrations. A mass balance conducted on each solution shows that neither continuity condition can be proved generally superior. An evaluation of the parametric sensitivity of the solutions is also conducted and shows that the distinction between the continuity conditions and the flux and resident concentrations is only important at small Peclet numbers. The only exception to this is the distinction between flux‐averaged versus resident continuous concentrations in a finite solution domain. In this case, the flux concentrations were found to be insensitive to the volume of the downstream reservoir and, consequently, the flux and resident concentrations can differ substantially for larger reservoirs. In consideration of the general behavior of the solutions, three conceptual problems were identified which must be investigated by physical modeling: (1) determination of the appropriate solution at small Peclet number, (2) the possibility that dispersive mass flux occurs from the upstream reservoir under conditions of continuous concentration, and (3) the use of the flux transformation for continuous concentration in a finite solution domain. The physical modeling is discussed in a companion paper.
Assessing the economic cost of restrictions on outdoor water use
Authors: Dandy Graeme
Published: February 2004

Many water authorities use water restrictions as a method for rationing water during a drought. Water restrictions impose an economic cost on the community consisting of a loss of consumer surplus and a loss of producer surplus to the water authority. A general expression is developed for the economic cost of stringent time restrictions on outdoor water use. Particular examples of this are developed for the case of households with linear demand functions and households with demand functions of constant elasticity. It is shown that the economic cost of stringent time restrictions is greater than that for an equivalent price increase. The difference is due to variations in the demand curves between households and variations in the responses of individual households to water restrictions.
Falling head ponded infiltration
Authors: Philip J. R.
Published: February 2004

It is remarkable that the Green‐Ampt (or delta function) solution for falling head ponded infiltration takes precisely the same functional form as that for constant head infiltration: Only the values of the constants change. Falling head infiltration experiments are thus as amenable to Green‐Ampt analysis as more complicated constant head experiments.
Behavior of dense aqueous phase leachate plumes in homogeneous porous media
Authors: Oostrom M. , Hayworth J. S. , Dane J. H. , Güven O.
Published: February 2004

Surface contaminant plumes emanating from waste disposal facilities are often denser than the ambient groundwater. Under certain conditions these dense plumes may become unstable, contaminating larger regions of an aquifer. The behavior of contaminant plumes with different densities was examined in three flow containers packed with homogeneous porous media simulating unconfined aquifers. Glass beads and a medium sand were used as the porous media. A horizontal ambient groundwater stream was established in each flow container using deionized water. The contaminant plumes consisted of NaI or NaBr solutions introduced into each flow container from a line source located on top of the porous medium and extending over the total width of the container. Optical tracers were added to the salt solutions to allow flow visualization. Results show that, for a given porous medium, dense plumes were either stable or unstable depending on the magnitude of the horizontal flow velocity, the contaminant leakage rate, and the density difference between the contaminant solution and the ambient groundwater. When a dense plume becomes unstable, lobe‐shaped gravitational instabilities develop which are unsteady and three dimensional. Our experimental results suggest that the behavior of dense contaminant plumes overlying a less dense groundwater stream in a homogeneous porous medium depends on the magnitude of certain nondimensional parameters. It appears that gravitational instabilities begin to develop when the values of these nondimensional parameters exceed certain critical values.
Data requirements for seasonal discharge programs: An application of a regionalized sensitivity analysis
Authors: Lence Barbara J. , Takyi A. K.
Published: February 2004

The design of seasonal water quality management programs that allow different waste discharge rates during different periods of the year may require reliable long‐term records of stream conditions. A modified regionalized sensitivity analysis (RSA) is applied for assessing the effect of unreliable stream records on the design of such programs. This approach is demonstrated for a seasonal waste discharge program that controls biochemical oxygen demand in a typical river basin. Here the uncertain input parameters include flow and temperature data at different times in the year and at different locations in the stream. An RSA is conducted for waste management scenarios that have different season length combinations and dissolved oxygen goals. Results indicate that the design of a seasonal waste discharge program for this case study is generally more sensitive to uncertainty in summer flow and temperature data than to uncertainty in winter data. Downstream flow data are shown to be more important than upstream data in low‐flow periods, while upstream flows are also important in high‐flow periods. In addition, the degree to which uncertain stream conditions affect the management model outcome depends on the water quality goals of the governing agency and the length of the seasons examined.
Censored‐data correlation and principal component dynamic programming
Authors: Saad Maarouf , Turgeon Andre , Stedinger Jery R.
Published: February 2004

A principal component stochastic dynamic programming algorithm for stochastic multireservoir hydropower system operation optimization was proposed by Saad and Turgeon (1988). The dimension of the state space of the system is reduced by using only the major principal components of the system's state as determined by a principal component analysis of the results of a deterministic optimization. A significant refinement of the procedure is to employ censored‐data principal component analysis. The more sophisticated statistical analysis provides a better model of the full dynamic range of the reservoir system's state, explains more observed variability of the reservoir volumes, and provides more accurate estimates of the statistical description's parameters. In an example presented of a four‐reservoir system, the first component of the censored‐data principal component analysis, for a given month, explained all but 7% of the uncensored system's variability, whereas the standard analysis for the same month left 12% of the observed system's variability unexplained.
Simulation of natural acid sulfate weathering in an Alpine Watershed
Authors: Bassett R. L. , Miller William R. , McHugh John , Catts John G.
Published: February 2004

Streams with acidic sulfate compositions (pH less than 3.5) are naturally generated in the alpine Geneva Creek Basin of the southern Rocky Mountains, an area underlain by Proterozoic metamorphic and igneous rocks that are intruded by Tertiary felsic stocks with associated pyritic alteration. These naturally acidic waters are similar in composition to more familiar man‐made acid mine waters or to surface waters acidified by sulfate precipitation. Detailed study of the stream compositions has revealed the principal reactions driving the weathering process and was used to estimate the relative effects of snowpack ionic input versus the solute contribution from acid attack in soil zones and groundwater. In the Geneva Creek Basin, atmospheric sources of solute represent a minor component to the stream water composition, except for chloride, which can be used to determine the fraction of contribution. The weathering process is a balance between oxidation of sulfides, dissolution of silicates, formation of the clay minerals vermiculite, kaolinite, and smectite, carbonate neutralization, and precipitation of ferric and aluminum oxyhydroxides and aluminum sulfate. The chemical analyses of snow samples, multiple samples of water from Geneva Creek and its tributaries, and the composition of primary and secondary minerals identified in the basin serve as input to a mass balance geochemical model, which facilitates the interpretation of the principal geochemical processes.
A nonlinear disaggregation method with a reduced parameter set for simulation of hydrologic series
Authors: Koutsoyiannis Demetris
Published: February 2004

A multivariate dynamic disaggregation model is developed as a stepwise approach to stochastic disaggregation problems, oriented toward hydrologic applications. The general idea of the approach is the conversion of a sequential stochastic simulation model, such as a seasonal AR(1), into a disaggregation model. Its structure includes two separate parts, a linear step‐by‐step moments determination procedure, based on the associated sequential model, and an independent nonlinear bivariate generation procedure (partition procedure). The model assures the preservation of the additive property of the actual (not transformed) variables. Its modular structure allows for various model configurations. Two different configurations (PAR(1) and PARX(1)), both associated with the sequential Markov model, are studied. Like the sequential Markov model, both configurations utilize the minimum set of second‐order statistics and the marginal means and third moments of the lower‐level variables. All these statistics are approximated by the model with the use of explicit relations. Both configurations perform well with regard to the correlation of consecutive lower‐level variables each located in consecutive higher‐level time steps. The PARX(1) configuration exhibits better behavior with regard to the correlation properties of lower‐level variables with lagged higher‐level variables.
Equivalent porosity estimates for Colonnade Networks
Authors: Khaleel Raziuddin
Published: February 2004

Using a particle‐tracking procedure, numerical simulations are performed to evaluate the asymptotic limits and the length scale requirements for equivalent porosity estimates of discrete colonnade networks. The simulation results are used to determine differences between the scale requirements for equivalent hydraulic conductivities and porosities. The directional dependence of the equivalent porosity is investigated using a polar plot. For a continuous network of hexagonal colonnades with uniform apertures, the asymptotic porosity estimates become directionally dependent; the numerical values compare favorably with those based on theoretical considerations. With uniform apertures, the porosity values drop sharply whenever a fracture set is perpendicular to the applied gradient and thereby becomes nonconductive. With lognormally distributed apertures, the effect of a particular fracture set's being perpendicular to the gradient is overshadowed by the effect of distributed velocities, and the asymptotic limit for the equivalent porosity ellipse approaches that of a circle. For colonnade network models with filled or unfilled apertures, the computed length scale requirements for equivalent porosity approximation are slightly smaller than those for equivalent hydraulic conductivity. The study provides guidance in selecting an acceptable block size for use in a continuum model of ground water flow and transport through colonnade networks.
Cubic approximation of hydraulic properties for simulations of unsaturated flow
Authors: Ross Peter J.
Published: February 2004

An adequate description of soil hydraulic properties is critical to modeling unsaturated flow. However, flexible descriptions based on the functions normally used may increase simulation times. This disadvantage can be overcome by using piecewise cubic approximation of such descriptions based on a table of function and derivative values. A further advantage of this technique is that the Kirchhofif transform variable can be approximated in the same way, even when it cannot be obtained analytically. Results for simulated infiltration into an aggregated soil indicated that hydraulic properties over the entire matric potential range could be approximated using 8–12 points without causing significant errors in simulations, whether the Kirchhoff transform was used or not. Run times using the original van Genuchten functions were 40% or 280% greater, depending on whether an incomplete beta function was used. The cubic approximation method thus allows more flexible use of the popular van Genuchten hydraulic property functions, since these involve incomplete beta functions unless unsatisfactory restrictions are placed on their parameters.
A mathematical model for dispersion with a moving front in groundwater
Authors: Strack Otto D. L.
Published: February 2004

A new, non‐Fickian, constitutive equation is presented for the mass flux due to macroscopic dispersion in porous media. This constitutive equation contains the classical term of the diffusive type as well as a new term that may be viewed as an inertia term. Combination of the constitutive equation with the mass balance equation for a conservative contaminant yields a set of four first‐order partial differential equations in terms of the three components of the vector of dispersive mass flux and the concentration. For the case of longitudinal dispersion only, this system is reduced to a set of two first‐order partial differential equations in terms of the convective and dispersive mass fluxes as the two unknown functions. The sets of differential equations are hyperbolic and can be used to simulate and predict the movement of the front of a contaminant plume at finite velocity. An expression of the velocity of the front is presented in terms of the Darcian velocity and the ratio of the two dispersion coefficients that enter into the model. The effect of the non‐Fickian terms decreases for increasing times; the model reduces to the classical one as time increases. An exact solution is presented for the case of one‐dimensional flow and compared with the results of simulated column experiments.
Thermal energy storage in an unconfined aquifer: 2. Model development, validation, and application
Authors: Molson John W. , Frind Emil O. , Palmer Carl D.
Published: February 2004

A fully three‐dimensional numerical model for simulating coupled density‐dependent groundwater flow and thermal energy transport is developed and validated. The transport solution is based on a finite element time integration algorithm which generates a symmetric coefficient matrix while retaining second‐order accuracy in time. The use of a symmetric conjugate gradient solver for both the flow and transport matrices results in a high degree of computational efficiency. Three‐dimensional deformable block elements are used to allow the model to conform to domains with irregular geometry. The thermal transport model is validated against the results of the Borden thermal injection field experiment presented in the companion paper. The model simulations provide an excellent match with the observed temperature distribution over time, with the effects of thermal buoyancy and losses across the ground surface accurately reproduced by the model. The model is shown to be a practical tool for simulating the type of low‐temperature thermal transport problems that arise in connection with seasonal aquifer thermal energy storage and ground source heat extraction systems.
Propagation of uncertainty due to variable meteorological forcing in lake temperature models
Authors: Hondzo Midhat , Stefan Heinz G.
Published: February 2004

Propagation of uncertainty in lake temperature models is studied using a vector state space method. The output uncertainty is defined as the result of deviations of the meteorological variables from their mean values. The analysis is applied to systems with correlated and uncorrelated meteorological variables. Surface water temperatures are strongly affected by uncertain meteorological forcing. Air temperatures and dew point temperature fluctuations have significant effect on lake temperature uncertainty. Ignoring correlation in meteorological variables underestimates uncertainties in lake temperature estimates. Long‐term average water temperature structure in lakes can be estimated by computer model simulation for just 1 year when results from a statistical analysis of meteorological variables are used as input. The analysis presents a useful alternative for the study of long‐term averages and variability of water temperature structures in lakes due to variable meteorological forcing.
Modeling alternatives for basin‐level hydropower development: 1. Optimization methods and applications
Authors: Chang Shoou‐Yuh , Liaw Shu‐Liang , Railsback Steven F. , Sale Michael J.
Published: February 2004

Development of multiple hydroelectric projects at navigation dams on large river systems can result in a number of environmental impacts, including potential reductions in dissolved oxygen (DO) concentrations. This study presents a method for generating hydropower development alternatives for evaluation by planners by quantifying the trade‐offs between water quality and power generation. This method employs a Streeter‐Phelps model to simulate DO and the bounded implicit enumeration algorithm to solve an optimization model formulated to maximize hydroelectric energy production. A portion of the upper Ohio River basin was selected to illustrate the methodology. The results indicate that various alternatives that meet the specified DO constraints can be generated efficiently. These alternatives are nearly optimal solutions with respect to the modeled objectives but are different with respect to decision variables.
Drought management, service interruption, and water pricing: Evidence from Hong Kong
Authors: Woo Chi‐Keung
Published: February 2004

Supply shortage is a common problem faced by an urban water supply system. Nonmarket programs are often used to reduce consumption. Using monthly water consumption data collected for Hong Kong for the period 1973–1984, we estimate the effect of service interruption on per capita consumption. The findings show that this effect is statistically significant but relatively small in size. A price increase of 16–35% could have produced the same amount of consumption reduction.
Optimal time‐varying pumping rates for groundwater remediation: Application of a constrained optimal control algorithm
Authors: Chang Liang‐Cheng , Shoemaker Christine A. , Liu Philip L.‐F.
Published: February 2004

A numerically efficient procedure is presented for computing optimal time‐varying pumping rates for remediation of contaminated groundwater described by two‐dimensional numerical models. The management model combines a pollutant transport model with a constrained optimal control algorithm. The transport model simulates the unsteady fluid flow and transient contaminant dispersion‐advection in a two‐dimensional confined aquifer. A Galerkin's finite element method coupled with a fully implicit time difference scheme is applied to solve the groundwater flow and contaminant transport equations. The constrained optimal control algorithm employs a hyperbolic penalty function. Several sample problems covering 5–15 years of remediation are given to illustrate the capability of the management model to solve a groundwater quality control problem with time‐varying pumping policy and water quality constraints. In our example, the optimal constant pumping rates are 75% more expensive than the optimal time‐varying pumping rates, a result that supports the need to develop numerically efficient optimal control‐finite element algorithms for groundwater remediation.
Time‐space continuum description of fluid/rock interaction in permeable media
Authors: Lichtner Peter C.
Published: February 2004

The feasibility of integrating multicomponent mass transport equations over geologic time spans is demonstrated for the case of pure advection in a homogeneous porous medium. The mathematical formulation of the problem is based on the quasi‐stationary state approximation, or multiple reaction path description, in which the time evolution of a geochemical system is represented by a sequence of stationary states or reaction paths. The method is implemented in the computer code MPATH which solves the transport equations in a single spatial dimension taking into account irreversible mineral precipitation/dissolution reactions and local equilibrium of aqueous complexing reactions. An adaptive grid enables the positions of reaction zones, with widths which vary over many orders of magnitude and which move with greatly differing velocities, to be tracked simultaneously over geologic time spans. There appears to be virtually no limitation to the number of chemical species that can be included in the code without rendering the computational effort beyond the bounds of a high‐performance workstation. The numerical accuracy of the solution can be verified through global mass conservation equations and by comparing the asymptotic kinetic solution with the corresponding solution to algebraic equations representing local equilibrium conditions for pure advective transport, if such solutions exist. The code MPATH is applied to several examples including migration of redox fronts, weathering and hydrothermal alteration in a spatially varying temperature field. These examples demonstrate the absolute necessity of solving the governing transport equations for sufficiently long time spans in order to fully characterize the behavior of the system.
Seasonal variations in methane flux andδl3CH4 values for rice paddies in Japan and their implications
Authors: Tyler Stanley C. , Brailsford Gordon W. , Yagi Kazuyuki , Minami Katsuyuki , Cicerone Ralph J.
Published: February 2004

We have made measurements of the methane (CH4) flux and δ13C value in CH4 from rice paddies in Ryugasaki, Japan. This study is the first we are aware of in which a significant change in the δ13C signature of emitted CH4 has been documented over the rice growing season. Nutrient treatments studied were of two kinds: compound mineral fertilizer either with or without rice straw from the previous growing season incorporated into the inorganic fertilizer. The calculated annual emission rates during the 1990 growing season were 43.1 g/m2 (straw) and 40.6 g/m2 (no straw) for the two treatments. In both treatments, CH4 started out relatively enriched in 13C, became lighter in 13C, and then became more enriched again during the latter part of rice growth. The 1991 growing season showed a lower integrated flux in both nutrient treatments than for 1990 but plots of the fluxes versus time had the same general shape as the flux curves in 1990 and a similar although less pronounced trend in δ13CH4 signal. Seasonal changes in δ13C are probably related to changes in CH4 production and oxidation and plant‐mediated transport. The likelihood of each process occurring and its effect on δ13C values is discussed. The range of δ13CH4 values from seasonal effects was ∼12‰ in 1991 for both nutrient treatments. The δ13CH4 range for 1991 was ∼10‰ (straw) and ∼5‰ (no straw). Our data indicate that when using flux‐weighted isotopic signatures to put constraints on the tropospheric CH4 budget, attention should be paid to seasonal changes in isotopic signatures from rice paddy CH4 in a manner similar to that previously suggested from measurements in natural wetlands.
HNO3 profiles obtained during the EASOE Campaign
Authors: Murcray F. J. , Starkey J. R. , Williams W. J. , Matthews W. A. , Schmidt U. , Aimedieu P. , Camy‐Peyret C.
Published: February 2004

A small cryogenically cooled spectrometer system designed to obtain atmospheric emission spectra in the 7.5µm to 13.0µm region was flown piggyback on 9 balloon flights from ESRANGE (67.9° N, 21.1° E) during the EASOE campaign. Initial analysis of the spectra obtained has been concentrated on obtaining HNO3 profiles for the various flights. HNO3 profiles for 17 December 1991, 9 January 1992, 22 January 1992, 5 February 1992 and 14 March 1992 are presented.
Ground‐based FTIR measurements of CLONO2 Vertical column amounts in the Arctic
Authors: Notholt J. , Clarmann T.V. , Adrian G. P. , Schrems O.
Published: February 2004

During the EASOE campaign measurements have been performed in March at Ny‐Ålesund (79°N, 11°E) by high resolution FTIR spectroscopy to derive the vertical column amounts of ClONO2. For the first part of this period the polar vortex was found to be situated above Ny‐Ålesund.

The measurements give ClONO2 zenith column amounts of about 3.9×1015 mol cm−2 outside the polar vortex, much higher than midlatitude values for an undisturbed atmosphere. Inside the vortex strong variabilities with burdens between 2.8 and 6.8×1015 mol cm−2 were observed. These high values might be explained by the reaction of ClO with NO2 and the relatively warm stratosphere ensuring that the ClONO2 so formed remains in the gas phase.